Syntheses and structural investigation of some alkali metal ion-mediated LVVO2- (L2- = tridentate ONO ligands) species: DNA binding, photo-induced DNA cleavage and cytotoxic activities

Dalton

Transactions

View Article Online

View Journal | View Issue

PAPER

Syntheses and structural investigation of some

−

alkali metal ion-mediated LV^VO₂(L²⁻= tridentate

Cite this: Dalton Trans., 2014, 43,

10139

ONO ligands) species: DNA binding, photo-

induced DNA cleavage and cytotoxic activities†

Subhashree P. Dash,^aAlok K. Panda,^bSagarika Pasayat,^aRupam Dinda,*^a

Ashis Biswas,^bEdward R. T. Tiekink,^cYogesh P. Patil,^dM. Nethaji,^dWerner Kaminsky,^e

Subhadip Mukhopadhyay^fand Sujit K. Bhutia^f

Eight alkali metal ion-mediated dioxidovanadium(V), [{V^VO₂L¹⁻⁶}A(H₂O)_n]_∝, complexes for A = Li⁺, Na⁺, K⁺

and Cs⁺, containing tridentate aroylhydrazonate ligands coordinating via ONO donor atoms, are

described. All the synthesised ligands and the metal complexes were successfully characterised by

elemental analysis, IR, UV-Vis and NMR spectroscopy. X-ray crystallographic investigation of 3, 5–7 shows

the presence of distorted NO₄coordination geometries for LVO₂⁻in each case, and varying μ-oxido and/

or μ-aqua bridging with interesting variations correlated with the size of the alkali metal ions: with small

Li⁺, no bridging-O is found but four ion aggregates are found with Na⁺, chains for K⁺and ﬁnally, layers for

Cs⁺. Two (5) or three-dimensional (3, 6 and 7) architectures are consolidated by hydrogen bonding. The

dioxidovanadium(^V) complexes were found to exhibit DNA binding activity due to their interaction with

CT-DNA by the groove binding mode, with binding constants ranging from 10³to 10⁴M⁻¹. Complexes

1–8 were also tested for DNA nuclease activity against pUC19 plasmid DNA which showed that 6 and 7

had the best DNA binding and photonuclease activity; these results support their good protein binding

and cleavage activity with binding constants ranging from 10⁴to 10⁵M⁻¹. Finally, the in vitro antiprolifera-

tive activity of all complexes was assayed against the HeLa cell line. Some of the complexes (2, 5, 6 and 7)

show considerable activity compared to commonly used chemotherapeutic drugs. The variation in cyto-

toxicity of the complexes is inﬂuenced by the various functional groups attached to the aroylhydrazone

derivative.

Received 25th March 2014,

Accepted 9th May 2014

DOI: 10.1039/c4dt00883a

www.rsc.org/dalton

considered as potential candidates for use as therapeutic

agents in medicinal applications and for genomic research.^1–6

Introduction

Metal-based anticancer drug discovery is at the forefront of Therefore, attempts are being made to replace the most

pharmaceutical research. Metal complexes which can eﬃcien- successful anti-cancer drug cisplatin with suitable alternatives

tly bind and cleave DNA under physiological conditions are and hence numerous transition metal complexes have been

synthesised and tested for their anti-cancer activities. Among

the transition metals, the coordination chemistry of vanadium

attracts increasing interest because of the use of many

^aDepartment of Chemistry, National Institute of Technology, Rourkela 769008,

Odisha, India. E-mail: rupamdinda@nitrkl.ac.in; Fax: +91 6612462022;

vanadium complexes as models for the biological functions of

vanadium,^7–10such as haloperoxidation,¹¹phosphorylation,¹²

insulin mimicking,^13–17nitrogen fixation,¹⁸tumour growth

inhibition and prophylaxis against carcinogenesis.¹⁹This bio-

element takes part in various DNA maintenance reactions and

thereby prevents genomic instability which otherwise leads to

cancer.^20,21Vanadium complexes could also suppress the

growth and spread of existing tumours by inhibiting tumour

cell proliferation, inducing apoptosis and limiting the invasion

and metastatic potential of neoplastic cells. Moreover, it has

been found that oxidovanadium complexes that eﬃciently

Tel: +91 6612462657

^bSchool of Basic Sciences, Indian Institute of Technology Bhubaneswar, Bhubaneswar

751 013, Odisha, India

^cDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia

^dDepartment of Inorganic and Physical Chemistry, Indian Institute of Science,

Bangalore 560012, India

^eDepartment of Chemistry, University of Washington, Box 351700, Seattle,

WA 98195, USA

^fDepartment of Life Science, National Institute of Technology, Rourkela 769008,

Odisha, India

†Electronic supplementary information (ESI) available: Tables S1 and S2,

Fig. S1–S23. CCDC 991925–991928. For ESI and crystallographic data in CIF or

other electronic format see DOI: 10.1039/c4dt00883a

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10139

View Article Online

Paper

Dalton Transactions

interact with DNA also show antitrypanosomatid activity.^21–23

In previous studies it was found that a change in the substi-

Thus, the DNA-binding, DNA photocleavage and anti-prolifera- tuent in the hydrazone moiety changed the bio-activity.³⁶In

tive activity of oxidometal complexes based on vanadium and connection with that, in the present work the syntheses, struc-

multifunctional ligands have been of recent interest.²⁴

tural investigation and pharmacological activities of some

Additionally, in recent times a new area of research invol- water-soluble alkali metal (Li⁺, Na⁺, K⁺and Cs⁺) ion-mediated

ving the design and synthesis of extended frameworks via dioxidovanadium(^V) hydrazone complexes, with varying substi-

supramolecular interactions has emerged. Hydrogen bonding tution, that show interesting DNA binding, photo-induced

interactions have been particularly explored in the context of DNA cleavage and cytotoxicity profile activities are reported.

molecular recognition and engineering of molecular solids.²⁵The interaction of these complexes with calf-thymus DNA

Many studies have focused on the use of monovalent alkali (CT-DNA) was investigated using UV-Vis absorption titration,

metals as a source of counter ions for the formation of polymeric circular dichroism and thermal denaturation studies. Their

aggregates,²⁶featuring channels or sheets of metal ions which photo-cleavage reactions with pUC19 supercoiled plasmid

may have potential to act as ionic conductors,²⁷charge storage DNA were investigated by gel electrophoresis, and for 6 and 7,

materials as well as biomimetic models.²⁸In most of these cases the protein binding and cleavage activity were also tested. In

water molecules are present as part of aquated A⁺ions (A = alkali addition, the cytotoxicity of the new complexes against the

metal), and play a vital role in holding the components of the HeLa cell line was assessed by the MTT assay.

assembly together through hydrogen bonding networks and

thereby enhancing the stability through charge neutralisation. In

the context of the present study it is relevant to mention that

Experimental section

Materials and methods

although the pharmacological activity of many vanadium–hydra-

zone complexes has been studied^21–23and the syntheses and

structural investigation of alkali metal ion-mediated LV^VO₂

All chemicals were purchased from commercial sources and

−

complexes have been reported previously,^26b,c,h,ithe study of the used without further purification. [VO(acac)₂] was prepared as

pharmacological activity of the latter has yet to be explored.

described in the literature.³⁷MTT (3-[4,5-dimethylthiazol-2-yl]-

Hydrazones, –NH–NvCRR′ (R and R′ = H, alkyl, aryl), are 2,5-diphenyltetrazolium) and DAPI (4′,6-diamidino-2-phenyl-

versatile ligands and have applications in the fields of analyti- indole dihydrochloride) were purchased from Sigma Aldrich

cal²⁹and medicinal chemistry.³⁰Hydrazone moieties are (USA). Minimal essential medium (MEM) was purchased from

important pharmacophoric cores of several anti-cancer, anti- Gibco, India. Reagent grade solvents were dried and distilled

inflammatory, anti-nociceptive and anti-platelet drugs.³¹More- prior to use. The supercoiled (SC) pUC19 DNA was purified

over, the electronic eﬀects of hydrazone complexes are also from E. coli cells with the aid of the GeneJET Plasmid Isolation

important in the design of complexes with better DNA-binding Kit (Thermo Scientific, USA). Calf thymus (CT) DNA was pur-

and cleaving characteristics.³²In addition, the presence of a chased from SRL (India) (biochemistry grade). Agarose (mole-

rigid aromatic system in the Schiﬀ base structure gives rise to cular biology grade) and bovine serum albumin (BSA) were

particular spectroscopic properties, which makes it a potential purchased from Sigma Aldrich (USA). Elemental analyses were

probe for nucleic acids. Recently, reports on vanadium hydra- performed on a Vario ELcube CHNS Elemental analyzer and IR

zone complexes with potential biological properties have spectra were recorded on a Perkin-Elmer Spectrum RXI spec-

1

appeared.³³In this context, the utilisation of the intercalating trophotometer. H and ¹³C NMR spectra were recorded with a

aroylhydrazone moiety when coordinated to vanadium might Bruker Ultrashield 400 MHz spectrometer using SiMe₄as the

accentuate the biochemical activity of the derived hybrid mole- internal standard. Electronic spectra were recorded on a

cules, which may lead to eﬃcient DNA binding and cleavage. Perkin-Elmer Lamda25 spectrophotometer.

As the complexes cause photocleavage of DNA and exhibit

Synthesis of ligands (H₂L^1–6). Schiﬀ base ligands, H₂L^1–6

,

photocytotoxic properties, these are established as important were prepared in good yield by the condensation of acid hydra-

potential chemotherapeutic agents.^23,34In short, the new oxi- zide with the corresponding carbonyl compound in equimolar

dovanadium complexes may prove to be a promising and ratio in ethanol by a standard procedure.³⁸The resulting white

attractive approach in the search for new potential drugs for compounds were filtered, washed with ethanol and dried over

the treatment of cancer.

Over the past few years, we have been studying the chem- IR data for all of these verified their preparation.

fused CaCl₂. Elemental analysis results, NMR (¹H and ¹³C) and

istry of oxido-metal complexes including those of vanadium,

H₂L¹: Yield: 68%. Anal. Calcd for C₁₅H₁₄N₂O₃: C, 66.65; H,

in N,O-donor environments³⁵along with electro-generation of 5.22; N, 10.36; found C, 66.63; H, 5.27; N, 10.38. FTIR (KBr,

mixed-valence divanadium(^IV,V),^35a,band some highly stable cm⁻¹): 3303 (O–H), 3053 (N–H), 1627 (CvO), 1615 (CvN),

nonoxido vanadium(^IV) complexes.³⁶Although many hydra- 1580 (CvC/aromatic). H NMR (400 MHz, DMSO-d₆): δ (ppm)

1

zone complexes exhibit good biological activities, their water- = 13.18 (s, 1H, OH), 12.10 (s, 1H, OH), 11.55 (s, 1H, NH),

solubility is still unsatisfactory, which may restrict their appli- 8.00–6.88 (m, 8H, C₆H₄), 2.42 (s, 3H, CH₃). ¹³C{¹H} NMR

cation. Hence, it seemed of interest to synthesise some new (100 MHz, DMSO-d₆): δ (ppm) = 162.69, 159.04, 157.11, 156.37,

water-soluble dioxido-metal complexes of hydrazones which 134.22, 131.73, 131.02, 128.94, 120.23, 119.67, 119.11, 117.76,

may have significant pharmacological eﬀects.

117.66, 117.36, 13.62.

10140 | Dalton Trans., 2014, 43, 10139–10156

This journal is © The Royal Society of Chemistry 2014

View Article Online

Dalton Transactions

Paper

H₂L²: Yield: 64%. Anal. Calcd for C₁₄H₁₂N₂O₃: C, 65.61; H, 4.42; N, 6.78. FTIR (KBr, cm⁻¹): 3400 (O–H), 1603 (CvN), 1261

4.72; N, 10.93; found C, 65.63; H, 4.74; N, 10.89. FTIR (KBr, (C–O)_enolic, 947, 901 (VvO). UV-Vis (DMF): λ_max, nm (ε, dm³

1

cm⁻¹): 3383 (O–H), 3102 (N–H), 1629 (CvO), 1619 (CvN), mol⁻¹cm⁻¹): 410 (25 410), 365 (33 650), 278 (39 321). H NMR

1

1573 (CvC/aromatic). H NMR (400 MHz, DMSO-d₆): δ (ppm) (400 MHz, DMSO-d₆): δ (ppm) = 12.58 (s, 1H, OH), 7.87–6.83

= 12.05 (s, 1H, OH), 11.79 (s, 1H, OH), 11.22 (s, 1H, NH), 8.68 (m, 8H, C₆H₄), 2.73 (s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz,

(s, 1H, CH), 7.91–6.90 (m, 8H, C₆H₄). ¹³C{¹H} NMR (100 MHz, DMSO-d₆): δ (ppm) = 170.16, 164.98, 161.96, 159.42, 133.23,

DMSO-d₆): δ (ppm) = 164.99, 159.50, 157.99, 149.48, 134.44, 132.79, 130.20, 129.43, 122.36, 120.55, 119.15, 118.00, 116.96,

132.08, 130.55, 129.95, 129.27, 119.85, 117.76, 117.33, 116.92, 116.16, 17.12. ⁵¹V NMR (DMSO-d₆): δ (ppm) = −542.

116.06.

[{VO₂L¹}K(H₂O)₂]_∝(2). Yield: 67%. Anal. Calcd for

H₂L³: Yield: 64%. Anal. Calcd for C₁₅H₁₄N₂O₂: C, 70.85; H, C₁₅H₁₆KN₂O₇V: C, 42.26; H, 3.78; N, 6.57; found C, 42.24; H,

5.54; N, 11.01; found C, 70.82; H, 5.56; N, 11.02. FTIR (KBr, 3.81; N, 6.55. FTIR (KBr, cm⁻¹): 3590 (O–H), 1599 (CvN), 1253

cm⁻¹): 3341 (O–H), 3216 (N–H), 1650 (CvO), 1606 (CvN), (C–O)_enolic, 921, 903 (VvO). UV-Vis (DMF): λ_max, nm (ε, dm³

1

1579 (CvC/aromatic). H NMR (400 MHz, DMSO-d₆): δ (ppm) mol⁻¹cm⁻¹): 408 (23 910), 323 (38 209), 265 (43 120). H NMR

= 13.45 (s, 1H, OH), 11.37 (s, 1H, NH), 7.99–6.91 (m, 9H, (400 MHz, DMSO-d₆): δ (ppm) = 12.58 (s, 1H, OH), 7.83–6.84

C₆H₄), 2.46 (s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz, DMSO-d₆): (m, 8H, C₆H₄), 2.73 (s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz,

δ (ppm) = 164.92, 159.29, 158.62, 133.47, 132.40, 131.72, DMSO-d₆): δ (ppm) = 170.14, 165.04, 161.90, 159.42, 133.18,

128.94, 128.86, 128.58, 119.91, 118.99, 117.80, 14.48.

132.71, 130.18, 129.47, 122.33, 120.61, 119.08, 117.88, 117.66,

H₂L⁴: Yield: 69%. Anal. Calcd for C₁₄H₁₃N₃O₂: C, 65.87; H, 116.19, 17.10. ⁵¹V NMR (DMSO-d₆): δ (ppm) = –540.

[{VO₂L²}Li(H₂O)_{4.5 ∝}

]

(3). Yield: 63%. Anal. Calcd for

5.13; N, 16.46; found C, 65.88; H, 5.11; N, 16.50. FTIR (KBr,

cm⁻¹): 3218 (O–H), 3099 (N–H), 1679 (CvO), 1607 (CvN),

C₂₈H₃₈Li₂N₄O₁₉V₂: C, 39.54; H, 4.50; N, 6.58; found C, 39.51;

H, 4.49; N, 6.60. FTIR (KBr, cm⁻¹): 3457 (O–H), 1606 (CvN),

1228 (C–O)_enolic, 929, 905 (VvO). UV-Vis (DMF): λ_max, nm (ε,

1

1574 (CvC/aromatic). H NMR (400 MHz, DMSO-d₆): δ (ppm)

= 13.32 (s, 1H, OH), 11.72 (s, 1H, NH), 8.20–6.89 (m, 8H,

C₆H₄), 2.42 (s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz, DMSO-d₆):

δ (ppm) = 163.40, 160.01, 159.21, 150.56, 140.84, 132.05,

129.19, 122.84, 122.63, 122.43, 119.68, 119.10, 117.82, 14.78.

H₂L⁵: Yield: 62%. Anal. Calcd for C₁₃H₁₁N₃O₂: C, 64.72; H,

4.59; N, 17.41; found C, 64.68; H, 4.58; N, 17.45. FTIR (KBr,

cm⁻¹): 3167 (O–H), 3002 (N–H), 1683 (CvO), 1612 (CvN),

1

dm³mol⁻¹cm⁻¹): 406 (30 600), 336 (44 480), 265 (46 680). H

NMR (400 MHz, DMSO-d₆): δ (ppm) = 12.21 (s, 1H, OH), 9.09

(s, 1H, CH), 7.83–6.80 (m, 8H, C₆H₄). ¹³C{¹H} NMR (100 MHz,

DMSO-d₆): δ (ppm) = 170.73, 165.19, 159.03, 156.78, 134.20,

133.24, 133.15, 129.46, 120.06, 119.16, 117.52, 116.97, 115.94.

⁵¹V NMR (DMSO-d₆): δ (ppm) = −539.

1

[{VO₂L²}Cs(H₂O)₃]_∝(4). Yield: 69%. Anal. Calcd for

C₁₄H₁₆CsN₂O₈V: C, 32.08; H, 3.07; N, 5.34; found C, 32.04; H,

3.10; N, 5.35. FTIR (KBr, cm⁻¹): 3488 (O–H), 1607 (CvN), 1227

(C–O)_enolic, 920, 899 (VvO). UV-Vis (DMF): λ_max, nm (ε, dm³

1567 (CvC/aromatic). H NMR (400 MHz, DMSO-d₆): δ (ppm)

= 12.33 (s, 1H, OH), 11.14 (s, 1H, NH), 8.69 (s, 1H, CH),

8.80–6.89 (m, 8H, C₆H₄). ¹³C{¹H} NMR (100 MHz, DMSO-d₆): δ

(ppm) = 161.83, 157.96, 150.81, 150.11, 149.56, 140.40, 132.19,

129.76, 123.17, 121.98, 119.88, 119.09, 116.90.

1

mol⁻¹cm⁻¹): 403 (24 160), 337 (33 200), 266 (35 600). H NMR

H₂L⁶: Yield: 63%. Anal. Calcd for C₁₅H₁₅N₃O₂: C 66.90; H,

5.61; N, 15.60; found C, 66.89; H, 5.62; N, 15.63. FTIR (KBr,

cm⁻¹): 3476 (O–H), 3364 (N–H₂)_s, 3207 (N–H₂)_as, 3028 (N–H),

1627 (CvO), 1611 (CvN), 1573 (CvC/aromatic). ¹H NMR

(400 MHz, DMSO-d₆): δ (ppm) = 13.55 (s, 1H, OH), 11.09 (s,

1H, NH), 7.68–6.61 (m, 8H, C₆H₄), 2.48 (s, 3H, CH₃). ¹³C{¹H}

NMR (100 MHz, DMSO-d₆): δ (ppm) = 166.68, 159.23, 157.52,

150.49, 133.10, 131.54, 129.64, 128.78, 119.99, 118.95, 117.77,

116.89, 115.30, 113.61, 14.35.

(400 MHz, DMSO-d₆): δ (ppm) = 12.21 (s, 1H, OH), 9.11 (s, 1H,

CH), 7.85–6.81 (m, 8H, C₆H₄). ¹³C{¹H} NMR (100 MHz, DMSO-

d₆): δ (ppm) = 170.74, 165.12, 159.04, 156.83, 134.23, 133.26,

133.16, 129.50, 120.08, 119.18, 117.61, 116.99, 115.93.

⁵¹V NMR (DMSO-d₆): δ (ppm) = –539.

[{VO₂L³}Cs(H₂O)₂]_∝(5). Yield: 61%. Anal. Calcd for

C₁₅H₁₄CsN₂O₅V: C, 37.06; H, 2.90; N, 5.76; found C, 37.03; H,

2.91; N, 5.79. FTIR (KBr, cm⁻¹): 3562 (O–H), 1599 (CvN), 1243

(C–O)_enolic, 946, 900 (VvO). UV-Vis (DMF): λ_max, nm (ε, dm³

1

mol⁻¹cm⁻¹): 390 (11 240), 317 (16 200), 266 (19 280). H NMR

Synthesis of complexes [{VO₂L^1–6}A(H₂O)_n]_∝(1–8). To the

(1 mmol) sample of ligand H₂L^1–6in 20 mL of ethanol, alkali

metal carbonate (1 mmol) dissolved in 5 mL of water was

added. The white suspension turned yellowish. The mixture

was refluxed for 5 min to give a clear yellow solution. There-

after a sample of [VO(acac)₂] (1 mmol) was added under reflux-

ing conditions. After 1 h, the resulting deep-yellow solution

was filtered and slow evaporation of the filtrate over 4–5 days

produced thin yellow or orange crystals. The crystals were fil-

tered and washed with ethanol. Elemental analysis results,

NMR (¹H, ¹³C, ⁵¹V), UV-Vis and IR data for all of these verified

their preparation.

(400 MHz, DMSO-d₆): δ (ppm) = 8.07–6.81 (m, 9H, C₆H₄), 2.87

(s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz, DMSO-d₆): δ (ppm) =

168.76, 164.27, 162.11, 133.36, 131.82, 130.60, 129.60, 128.30,

128.11, 127.92, 122.48, 120.04, 117.39, 16.26. ⁵¹V NMR (DMSO-

d₆): δ (ppm) = −534.

[{VO₂L⁴}K(H₂O)₂]_∝(6). Yield: 63%. Anal. Calcd for

C₁₄H₁₅KN₃O₆V: C, 40.88; H, 3.67; N, 10.21; found C, 40.85; H,

3.66; N, 10.24. FTIR (KBr, cm⁻¹): 3429 (O–H), 1601 (CvN),

1248 (C–O)_enolic, 943, 907 (VvO). UV-Vis (DMF): λ_max, nm

(ε, dm³mol⁻¹cm⁻¹): 395 (36 920), 322 (45 840), 268 (50 760).

¹H NMR (400 MHz, DMSO-d₆): δ (ppm) = 8.71–6.82 (m, 8H,

C₆H₄), 2.89 (s, 3H, CH₃). ¹³C{¹H} NMR (100 MHz, DMSO-d₆):

δ (ppm) = 167.26, 165.01, 164.25, 150.49, 141.19, 132.60,

[{VO₂L¹}Li(H₂O)₃]_∝(1). Yield: 63%. Anal. Calcd for

C₁₅H₁₈LiN₂O₈V: C, 43.70; H, 4.40; N, 6.79; found: C, 43.67; H,

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10141

View Article Online

Paper

Dalton Transactions

130.19, 122.58, 122.15, 120.58, 117.78, 16.68. ⁵¹V NMR (DMSO- each structure was carried out on F²using full-matrix least-

d₆): δ (ppm) = −533.

squares procedures.⁴⁰Based on hydrogen bonding consider-

ations, the hydroxyl- and water-H atoms in 3 were included in

their idealised positions. The water-H atoms in 5 and 7 were

located from the respective diﬀerence Fourier maps and

refined with the distance restraint O–H = 0.84 0.01 Å. The

water-H atoms in 6 were located in the case of the O1w water

molecule but not for O2w. For the latter, the H atoms were

placed based on stereochemical grounds and all refined with

[{VO₂L⁵}Na(H₂O)₄]_∝(7). Yield: 60%. Anal. Calcd for

C₁₃H₁₇N₃NaO₈V: C, 37.42; H, 4.10; N, 10.07; found C, 37.47; H,

4.13; N, 10.04. FTIR (KBr, cm⁻¹): 3531 (O–H), 1614 (CvN),

1223 (C–O)_enolic, 926, 907 (VvO). UV-Vis (DMF): λ_max, nm

(ε, dm³mol⁻¹cm⁻¹): 410 (65 240), 328 (77 920), 268 (87 560).

¹H NMR (400 MHz, DMSO-d₆): δ (ppm) = 9.05 (s, 1H, CH),

8.69–6.78 (m, 8H, C₆H₄). ¹³C{¹H} NMR (100 MHz, DMSO-d₆):

δ (ppm) = 168.32, 165.44, 157.83, 150.52, 140.59, 134.15, 133.34,

122.02, 120.11, 117.33. ⁵¹V NMR (DMSO-d₆): δ (ppm) = −531.

[{VO₂L⁶}Cs(H₂O)₃]_∝(8). Yield: 65%. Anal. Calcd for

C₁₅H₁₉CsN₃O₇V: C, 33.54; H, 3.56; N, 7.82; found C, 33.56; H,

3.52; N, 7.85. FTIR (KBr, cm⁻¹): 3454 (O–H), 3365 (NH₂)_s, 3237

(NH₂)_as, 1597 (CvN), 1253 (C–O)_enolic, 932, 897 (VvO). UV-Vis

(DMF): λ_max, nm (ε, dm³mol⁻¹cm⁻¹): 398 (15 780), 320

the distance restraint O–H = 0.84

0.01 Å. While the O1w

molecule formed the anticipated hydrogen bonding inter-

actions, the same was not true for the O2w water molecule

which exists in a pocket, forming O⋯O separations in the

range 2.852(4) to 3.364(2) Å with four putative hydrogen bond

acceptors as detailed in ESI Table S1.† Therefore, it was con-

cluded that the O2w-bound hydrogen atoms are disordered

over several positions. Crystal data and refinement details are

given in Table 1. Molecular structure diagrams, showing the

atom labelling schemes, were drawn with 50% (6 and 7) or

70% (3 and 5) displacement ellipsoids using ORTEP-3 for

Windows,⁴¹the overlay diagrams were drawn with QMol⁴²and

the remaining crystallographic figures were drawn with

DIAMOND.⁴³Data manipulation and interpretation were

accomplished using WinGX³and PLATON.⁴⁴

1

(21 718). 258 (28 242). H NMR (400 MHz, DMSO-d₆): δ (ppm)

= 7.83–6.84 (m, 8H, C₆H₄), 2.73 (s, 3H, CH₃). ¹³C{¹H} NMR

(100 MHz, DMSO-d₆): δ (ppm) = 170.76, 164.81, 160.67, 149.45,

132.02, 131.60, 129.87, 122.86, 120.44, 117.56, 116.80, 115.19,

114.99, 113.74, 17.20. ⁵¹V NMR (DMSO-d₆): δ (ppm) = −540.

Crystallography

Intensity data for 3, 5–7 were collected on a Bruker APEXII

diﬀractometer equipped with a CCD area detector and graph-

ite-monochromated Mo Kα radiation (λ = 0.71069 Å). Data

reduction and empirical absorption correction, based on the

DNA binding experiments

(a) Absorption spectral studies. Binding of the dioxido-

multi-scan method, were performed by standard methods.³⁹vanadium(^V) complexes to calf thymus (CT) DNA was studied

The structures were solved by direct methods using in 10 mM Tris-HCl buﬀer (pH 8.0) containing 10% DMF.

SHELXS97²and refinement (anisotropic displacement para- UV-Vis absorption titration experiments were performed with a

meters and C-bound hydrogen atoms in idealised positions) of Perkin-Elmer Lamda35 spectrophotometer using

a fixed

Table 1 Crystal data and reﬁnement details for 3, 5–7

3

5

6

7

Empirical formula

Formula weight

Li₂, 2(C₁₄H₁₀N₂O₅V), 9H₂O

850.38

Cs, C₁₅H₁₂N₂O₄V, H₂O

486.13

K, C₁₄H₁₁N₃O₄V, 2H₂O

411.33

Na, C₁₃H₉N₃O₄V, 4H₂O

417.23

Crystal size (mm)

Crystal morphology, colour

Temperature (K)

0.15 × 0.15 × 0.60

Prism, orange

100(2)

0.04 × 0.07 × 0.30

Prism, yellow

100(2)

0.0 × 0.05 × 0.32

Prism, yellow

293(2)

0.03 × 0.04 × 0.27

Prism, yellow

293(2)

Crystal system

Space group

A (Å)

b (Å)

c (Å)

Triclinic

P1

Monoclinic

P2₁/c

15.430(2)

7.1128(10)

30.505(4)

90

98.682(8)

90

3309.5(8)

8

Orthorhombic

Pbca

11.6880(4)

8.2858(2)

34.9484(11)

90

Triclinic

P1

ˉ

6.8227(2)

15.4441(6)

18.3454(7)

67.969(2)

80.954(2)

89.346(2)

1767.24(11)

2

7.7429(8)

10.3131(10)

12.0373(13)

109.590(6)

104.363(5)

92.983(5)

867.59(15)

2

α (°)

β (°)

γ (°)

90

V (Å³)

Z

3384.56(18)

8

1.614

D_x(g cm⁻³

)

1.598

0.616

1.951

2.795

1.597

0.644

μ (mm⁻¹

)

0.868

θ Range (°)

2.2–28.5

24 488

8797; 0.026

7372

498

0.036

0.054, 0.949

0.102

0.54, −0.50

1.8–28.4

107 431

8117; 0.049

6866

447

0.028

0.019, 5.712

0.059

0.95, −0.92

2.1–30.6

63 472

5179; 0.070

3225

239

0.046

0.040, 1.998

0.109

0.43, −0.48

1.9–30.7

17 852

5283; 0.028

4107

259

0.042

0.057, 0.095

0.111

0.39, −0.27

Reflections measured

Independent reflections; R_int

Reflections with I > 2σ(I)

Number of parameters

R(F) [I > 2σ(I) reflns]

a, b in weighting scheme

wR(F²) (all data)

Δρ_{max, min}(e Å⁻³

)

10142 | Dalton Trans., 2014, 43, 10139–10156

This journal is © The Royal Society of Chemistry 2014

View Article Online

Dalton Transactions

Paper

concentration of the metal complex (25 μM) but variable

(b) Photo-induced DNA cleavage. The eﬀect of complexes

nucleotide concentrations ranging from 0 to 100 μM. After (1–500 µM) on the cleavage of supercoiled (SC) pUC19 DNA

each addition of DNA (10 μM) to the metal complex, the read- (300 ng) was studied by agarose gel electrophoresis in 50 mM

ings were noted. The data were then fit to the following Tris-HCl buﬀer (pH 8.0). DNA photocleavage studies were

45

equation to obtain the binding constant K_b

carried out under illuminated conditions using a UVA source

at 350 nm (Luzchem Photoreactor Model LZC-1, Ontario,

Canada) fitted with 14 UVA (84 W) tubes for 3 h. After photoirra-

diation, each sample was further incubated for 1.0 h at 37 °C

and analyzed for the photo-cleaved products using gel electro-

phoresis. The samples after incubation were added to the

loading buﬀer containing 0.25% bromophenol blue and 30%

glycerol (2 µL) and the solution was finally loaded on 0.8%

agarose gel containing 0.5 µg mL⁻¹ethidium bromide (EB).

Electrophoresis was carried out for 1.0 h at 90 V in TAE (Tris-

acetate EDTA) buﬀer. DNA cleavage was indicated by the

decrease in the supercoiled pUC19 DNA (Form I) and sub-

sequently the formation of nicked circular DNA (Form II) and

linearised DNA (Form III). Bands were visualised with UV light

(302 nm) and photographed. The extent of SC DNA cleavage

was measured from the intensities of the bands using the UVP

(Gel Doc It²) Gel Documentation System. Due corrections were

made for the low level of the nicked circular (NC) form of DNA

present in the original SC DNA sample and for the low aﬃnity

of EB binding to SC compared to NC and linear forms of

DNA.⁴⁷The percentage of net DNA cleavage was calculated by

the following equation:

½DNAꢀ ½DNAꢀ

1

¼

þ

;

ð1Þ

ε_aꢁ ε_fε_bꢁ ε_fK_bðε_bꢁ ε_fÞ

where [DNA] is the concentration of DNA base pairs, ε_a, ε_fand

ε_bcorrespond to the apparent extinction co-eﬃcient for the

complex, i.e. Abs/[complex] in the presence of DNA, in the

absence of DNA and to fully bound DNA, respectively. A plot of

[DNA]/(ε_a− ε_f) vs. [DNA] gave a slope and the intercept

equal to 1/(ε_a− ε_f) and (1/K_b)(ε_b− ε_f), respectively. The

binding constant K_bis calculated from the ratio of the slope to

the intercept. Binding of ligands to CT-DNA was also studied.

In order to find out the binding constant (K_b) of the “ligand–

DNA interaction”, a fixed concentration of ligand [25 μM in

10 mM Tris-HCl buﬀer (pH 8.0) containing 10% DMF] was

titrated with variable DNA concentrations ranging from 0 to

350 μM.

(b) Thermal denaturation studies. Thermal denaturation

studies of CT-DNA (160 μM) in the absence and presence of

complexes (100 μM) were carried out by monitoring the absor-

bance at 260 nm in the temperature range of 30–90 °C with a

ramp rate of 1 °C min⁻¹in 10 mM Tris-HCl buﬀer (pH 8.0).

The experiments were carried out using a Chirascan CD spec-

tropolarimeter (Applied Photophysics, UK) in absorbance

mode equipped with a quantum temperature controller. The

melting of the double stranded DNA to single stranded DNA

was observed with significant hyperchromicity of the absor-

bance at 260 nm. The melting temperature (T_m) was deter-

mined from the derivative plot (dA₂₆₀/dT vs. T) of the melting

profile.⁴⁶

Form IIs þ 2 ꢂ Form IIIs

Net DNA cleavage % ¼

Form Is þ Form IIs þ 2 ꢂ Form IIIs

Form IIc þ 2 ꢂ Form IIIc

ꢁ

Form Ic þ Form IIc þ 2 ꢂ Form IIIc

ð2Þ

The subscripts “s” and “c” refer to the sample and control

respectively.⁴⁸Appropriate DNA controls were taken to calcu-

late the net DNA cleavage percent. The observed error in

measuring the band intensities ranged between 3% and 6%.

The mechanistic studies were performed using diﬀerent addi-

tives (sodium azide, ^L-histidine, KI and D-mannitol, each

0.5 mM) prior to the addition of the complex.

(c) Circular dichroism studies. Circular dichroism (CD)

spectroscopy was studied using a Chirascan CD spectropolari-

meter (Applied Photophysics, UK) at 25 °C. CD spectra of

CT-DNA (160 μM) in the absence and presence of complexes

(300 μM) were obtained in the wavelength range of

240–400 nm in 10 mM Tris-HCl buﬀer (pH 8.0) using a quartz

cell with 2 mm path length.⁴⁶

Protein binding and cleavage experiments

(a) Bovine serum albumin (BSA) interaction studies. The

protein binding study was performed by tryptophan fluo-

rescence quenching experiments using BSA (2 μM) as a sub-

strate in 10 mM Tris-HCl buﬀer (pH 8.0) using a Fluoromax 4P

spectrofluorimeter (Horiba Jobin Mayer, USA). The quenching

of the emission intensity of tryptophan residues of BSA at

344 nm (excitation at 295 nm) was monitored with increasing

complex concentration [0–20 μM in 10 mM Tris-HCl buﬀer (pH

8.0) containing 1% DMF].⁴⁹Stern–Volmer plots were obtained

and Scatchard analysis was performed using corrected fluo-

rescence data taking into account the eﬀect of dilution. Linear

fit of the data using the Stern–Volmer equation,

DNA cleavage experiments

For DNA cleavage experiments, 300 ng supercoiled (SC) pUC19

DNA was used and all experiments were carried out in 50 mM

Tris-HCl buﬀer (pH 8.0) containing 10% DMF. The photo-

induced DNA cleavage experiments were also carried out in

10 mM phosphate buﬀer (pH 7.8) containing 1% DMF or

10 mM Tris-HCl buﬀer (pH 8.0) containing 1% DMF.

(a) Chemical-induced DNA cleavage. For chemical nucle-

ase studies, the reactions were performed in the dark using

hydrogen peroxide (0.5 mM) as the oxidising agent in the

absence and presence of complexes (1–500 µM). The solutions

were incubated at 37 °C for 3 h and analysed for DNA cleaved

products by agarose gel electrophoresis.

F₀

¼ 1 þ K_SV½Qꢀ

ð3Þ

F

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10143

View Article Online

Paper

Dalton Transactions

and the Scatchard equation,

described.⁵¹Briefly, HeLa cells either treated or untreated with

test compounds were smeared on a clean glass slide, cells were

fixed with 3.7% formaldehyde for 15 min, permeabilised with

0.1% Triton X-100 and stained with 1 μg mL⁻¹DAPI for 5 min

at 37 °C. 10% DMF solution which was used to dissolve the

drugs was also used in control group treatment. The cells were

then washed with PBS and examined by fluorescence

microscopy (Olympus IX 71) to ascertain any condensation or

fragmentation of the nuclei indicating cells undergoing

apoptosis.

ꢀ

ꢁ

F₀ꢁ F

log

¼ log K_BSAþ n log ½Qꢀ

ð4Þ

F

where F₀and F are the emission intensity of BSA in the

absence and in the presence of the quencher (complexes) con-

centration [Q], respectively, gave the Stern–Volmer quenching

constant (K_SV), the binding constant (K_BSA) and the number of

binding sites (n).⁴⁵

(b) BSA photo-induced cleavage studies. Freshly prepared

solution of BSA in 10 mM Tris-HCl buﬀer (pH 8.0) was used

for photochemical protein cleavage studies. The BSA (5 μM)

solution in the absence and presence of complexes [1–500 μM

in 10 mM Tris-HCl buﬀer (pH 8.0) containing 1% DMF] was

photo-irradiated using a UVA source at 350 nm (Luzchem

Photoreactor Model LZC-1, Ontario, Canada) fitted with 14

UVA tubes (84 W) for 90 min. The irradiated samples (20 μL)

were dissolved in loading buﬀer (20 μL) containing SDS (7% w/v),

glycerol (4% w/v), Tris-HCl buﬀer (50 mM, pH 6.8), mercapto-

ethanol (2% v/v) and bromophenol blue (0.01% w/v). The

samples were then heat denatured at 100 °C for 5 min and

loaded onto a 12% SDS PAGE separating gel. The gel electro-

phoresis was performed at 60 V until the dye passed into the

separating gel from the stacking (5%) gel, and then the voltage

was increased to 120 V. The gels were run for 2 h, stained with

Coomassie Brilliant Blue R-250 solution (acetic acid: metha-

nol–water = 1 : 5 : 4 v/v) and destained with a water–methanol–

acetic acid mixture (5 : 4 : 1 v/v). The gels after destaining were

photographed using the UVP (Gel Doc It²) Gel Documentation

System. Molecular weight markers were used in each gel to

calibrate the molecular weight of BSA.⁴⁹We also studied the

BSA cleavage activity in the dark as well as in the presence of

UV-A light (84 W) for all the complexes with a molar ratio of

BSA to complex 1 : 20.

Results and discussion

Synthesis

Eight dioxidovanadium(^V) complexes [{V^VO₂L^1–6}A(H₂O)_n]_∝

(1–8) have been prepared (Scheme 1) in the present study by

using six diﬀerent aroyl hydrazones as ligands, with varying

substitution in their hydrazone moieties, in order to observe

their influence on the pharmacological activities of the com-

plexes. Reactions of the selected aroylhydrazones with

VO(acac)₂along with alkali metal carbonate proceed in reflux-

ing ethanol–water aﬀorded yellow or orange products in good

yields. These compounds are highly soluble in protic solvents,

viz. water, ethanol and methanol, as well as in aprotic solvents,

viz. CH₃CN, DMF and DMSO. Alternatively, these complexes

can also be synthesised using acetonitrile–water as a solvent.

Spectral characteristics

The spectral (IR, UV-Vis and NMR) data of all the ligands,

H₂L¹⁻⁶, and their corresponding dioxidovanadium(V) com-

plexes, 1–8, are given in the Experimental section. The infrared

spectra of all the complexes display a broad band in the range

3590–3400 cm⁻¹, due to the O–H stretch of the coordinated

water molecules which form extensive hydrogen bonding inter-

actions. The disappearance of characteristic bands due to –NH

and –CvO in the ligand spectra, and the appearance of new

Cytotoxicity studies

(a) MTT assay. Human cervical cells HeLa were obtained bands in the range 1261–1223 cm⁻¹in the complexes indicate

from the National Centre of Cell Science (NCCS), Pune, India, the enolisation of these two groups forming a –NvC–O bond

and were maintained in minimal essential medium sup- sequence. The strong and sharp peak displayed by the com-

plemented with 10% fetal bovine serum, penicillin–streptomy- plexes in the range 1614–1597 cm⁻¹is likely to be associated

cin solution and incubated at 37 °C in a 5% CO₂and 95% with the –CvN–NvC– moiety.^35a,b,52The presence of two

humidified incubator. HeLa cells were harvested from main- strong bands in the range 947–897 cm⁻¹is assigned to VvO

tenance cultures in the logarithmic phase, after counting in a stretching,^26h,iwhich clearly indicates the dioxido nature of

hemocytometer using trypan blue solution. The cell concen- the complexes.

tration was adjusted to 5 × 10⁴cells mL⁻¹and the cells were

The electronic spectra of the complexes 1–8 were recorded

plated in a 96 well flat bottom culture plate and incubated for in DMF at 25 μM concentration, and are quite similar for all

72 h with various concentrations of the test complexes which eight complexes. The strong absorptions observed in the wave-

were dissolved in a 10% (v/v) DMF solution. The eﬀect of the length range 410–390 nm are assignable to the ligand-to-metal

drugs on the cancer cell viability was studied using the MTT charge transfer transitions whereas the other bands in the

dye reduction assay by measuring the optical density at higher energy region (365–258 nm) are likely to be due to

595 nm using a micro-plate reader spectrophotometer (Perkin- ligand centred transitions.^35a,b

1

Elmer 2030).⁵⁰A 10% (v/v) DMF solution which was used to

dissolve the drugs was used in the control group treatment.

The H and ¹³C NMR data of the free ligands (H₂L^1–6) and

the corresponding dioxidovanadium(^V) complexes (1–8) were

(b) Nuclear staining. Nuclear staining using the DAPI recorded using DMSO-d₆and the data are given in the Experi-

stain was performed according to the method previously mental section. The spectra of all the ligands exhibit reson-

10144 | Dalton Trans., 2014, 43, 10139–10156

This journal is © The Royal Society of Chemistry 2014

View Article Online

Dalton Transactions

Paper

Scheme 1 Schematic diagram of various pathways through which the dioxidovanadium(V) complexes (1–8) were synthesised.

ances in the range δ = 13.55–11.79 ppm due to phenyl–OH and 0.47 (V2), the resulting NO₄donor set defines a geometry inter-

δ = 11.72–11.09 ppm due to –NH, which disappear in the mediate between square pyramidal (ideal value of τ = 0.0) and

spectra of the complexes confirming deprotonation and com- trigonal bipyramidal (τ = 1.0).⁵⁴The five- and six-membered

plexation of the ligands. The presence of resonances in the chelate rings are practically planar with r.m.s. deviations of

range δ = 12.58–12.21 ppm in complexes 1–4 is due to the the atoms comprising these being 0.013 Å (0.008) and 0.031 Å

uncoordinated –OH present in the hydrazide part of the (0.036), respectively; values for the V2-containing anion are

ligand. Complexes 3, 4 and 7 possess a resonance in the range given in parenthesis. Co-planarity between the five-membered

δ = 9.11–9.05 ppm, and complexes 1, 2, 5, 6 and 8 display a ring and the attached hydroxyphenyl ring (dihedral angles =

singlet in the range δ = 2.89–2.73 ppm due to –CH and –CH₃3.48(8) and 1.95(8)°, respectively) is ensured by an intramole-

groups, respectively. All the aromatic protons of the complexes cular O–H⋯N hydrogen bond (see ESI Table S1† for details).

are clearly observed in the expected region,

δ

=

This planarity extends throughout the anion as is seen in the

dihedral angles between the terminal rings of 5.37(9) and

8.71–6.78 ppm.^35a,b

The ⁵¹V NMR spectrum of 1–8 each displays a singlet in 2.69(9)°, respectively. According to a search of the Cambridge

the range δ = −542 to −531 ppm. These chemical shifts are Structural Database (CSD),⁵⁵the specific anion in 3 has been

usual for complexes containing the dioxovanadium(^V) com- characterised as a variety of vanadium salts and adopts very

plexes.⁵³A representative spectrum, of 1, is shown in ESI similar molecular conformations.⁵⁶

Fig. S1.†

The Li⁺cations are bridged by a water molecule and each of

their tetrahedral coordination geometries is completed by

three additional water molecules. The components of the

crystal structure are connected into supramolecular layers in

the ab-plane by an extensive network of O–H⋯O hydrogen

bonds involving all but the hydroxyl-O atoms (ESI Fig. S3a†);

geometric data defining the intermolecular interactions for 3,

5–7 are collated in ESI Table S1.† The Schiﬀ base ligands

project to either side of the layers and associate via significant

C–H⋯O(hydroxyl) hydrogen bonds to consolidate the three-

dimensional crystal packing (ESI Table S1 and Fig. S3b†).

The asymmetric unit of 5 comprises two Cs⁺cations, two

complex anions and two aqua ligands (Fig. 2). In contrast to

the other structures described herein, both the five- and six-

membered rings deviate significantly from planarity, with the

former adopting an envelope conformation with the V1 or V2

atom being the flap atom. The six-membered rings adopt half-

chair conformations with the V1 atom lying 0.566(3) Å above

the plane of the remaining five atoms comprising the chelate

ring (r.m.s. deviation = 0.0461 Å); the corresponding values for

the V2-containing anion are 0.840(3) and 0.0487 Å, respect-

Molecular and supramolecular structures

The crystal and molecular structures of 3, 5–7 have been deter-

mined and reveal a wide variety of structural motifs dependent

in the main on the type of cation and the presence of water

(coordinated or lattice). The common feature of the structures

is the presence of five-coordinate vanadium within NO₄donor

sets which define coordination geometries between the

extremes of square pyramidal and trigonal bipyramidal.

The asymmetric unit of 3 comprises two complex anions,

two Li⁺cations and nine water molecules (Fig. 1); selected geo-

metric parameters are given in the caption. Seven of the water

molecules coordinate to Li⁺cations. The molecular structures

of the anions are quite similar as can be seen from the overlay

diagram (ESI Fig. S2†) and feature five-coordinate vanadium

atoms, being coordinated by a dinegative tridentate ligand and

two oxido-O atoms. The status of the Schiﬀ base ligand as

2-hydroxy-N-(2-oxidobenzylidene)benzenecarbohydrazonate,

i.e. an azo ligand, is confirmed from the CvN bond lengths

(Fig. 1). Based on τ values of 0.51 (V1-containing anion) and

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10145

View Article Online

Paper

Dalton Transactions

Fig. 1 Perspective view of the components of the crystallographic asymmetric unit of 3. Selected geometric parameters: V1–O2 2.0028(12), V1–O3

1.9119(13), V1–O4 1.6330(13), V1–O5 1.6238(13), V1–N2 2.1121(14), N1–N2 1.3994(19), N1–C7 1.302(2), N2–C8 1.298(2), V2–O7 1.9771(12), V2–O8

1.9109(13), V2–O9 1.6284(13), V2–O10 1.6343(13), V2–N4 2.1163(14), N3–N4 1.3975(19), N3–C21 1.301(2), N4–C22 1.297(2) Å; O2–V1–O3 157.54(5),

O7–V2–O8 156.95(5)°.

Fig. 2 Perspective view of the components of the crystallographic asymmetric unit of 5. Selected geometric parameters: V1–O1 1.892(2), V1–O2

1.9656(19), V1–O3 1.6352(19), V1–O4 1.634(2), V1–N1 2.149(2), N1–N2 1.399(3), N1–C7 1.305(4), N2–C9 1.298(4), V2–O5 1.883(2), V2–O6 1.9631

(19), V2–O7 1.6534(19), V2–O8 1.618(2), V2–N3 2.162(2), N3–N4 1.402(3), N3–C22 1.299(3), N4–C24 1.295(4), O3⋯Cs1 2.923(2), O4⋯Cs1ⁱ3.302(2),

O7⋯Cs1 3.019(2), O3⋯Cs2ⁱ3.014(2), O7⋯Cs2 2.9900(19), O8⋯Cs2ⁱ3.292(2) and O8⋯Cs2ⁱⁱ3.473(2) Å. Symmetry operation i: x, 1 + y, z, and ii:

−x, −y, 1 − z.

ively. The two anions adopt distinct conformations (ESI base ligands, in the ammonium salt the five-membered ring is

Fig. S4†) with the diﬀerences best reflected in the dihedral very close to planar and the six-membered ring has a half-

angles between the five-membered and the attached phenyl chair conformation with the phenoxide-O atom lying above the

ring of 8.34(13) and 18.54(13)°, respectively. The values of τ plane of the remaining atoms.⁵⁷

compute to 0.04 and 0.21, consistent with descriptions of the

The Cs1 cation is in a highly distorted eight-coordinate

coordination geometry being based on a square pyramid.⁵⁴environment whereas the Cs2 cation is in a seven-coordinate

The same anion as found in 5 has been described in the litera- geometry resembling closely a square anti-prism but with one

ture as its anhydrous diethylammonium salt.⁵⁷Underscoring site vacant. The μ-O bridging leads to a layer in the ab-plane as

the flexibility of coordination modes exhibited by these Schiﬀ illustrated in ESI Fig. 5a.† The layers are also stabilised by an

10146 | Dalton Trans., 2014, 43, 10139–10156

This journal is © The Royal Society of Chemistry 2014

View Article Online

Dalton Transactions

Paper

extensive network of O–H⋯O hydrogen bonds (ESI Table S1†)

and stack along the c-axis with no specific interactions

between them (ESI Fig. S5b†).

For 6, the asymmetric unit comprises a K⁺cation, a

complex anion and two coordinated water molecules (Fig. 3).

The introduction of a methyl group into the backbone of the

ONO-coordinating tridentate ligand of 3 introduces a change

in the configuration of the six-membered chelate ring. Thus,

while the five-membered ring is planar (r.m.s. deviation =

0.028 Å), the conformation of the six-membered ring is based

on a screw-boat. This has the result that overall the dianion

exhibits a twist as seen in the dihedral angle of 11.12(12)°

between the terminal rings. The value of τ is 0.14, suggesting a

coordination geometry approaching square pyramidal.⁵⁴There

are no V-containing precedents featuring this Schiﬀ base

ligand in the crystallographic literature.⁵⁵

Fig. 4 Crystal packing in 6: zigzag chain along the b-axis mediated by

μ-O bridging. For clarity, only the chelate rings of the anions are

illustrated.

The cation in 6 is coordinated by the two water molecules

comprising the asymmetric unit (Fig. 3) and direct links

between this and the anion are aﬀorded by oxido bridges. The

oxido-O4 and phenoxide-O2 atoms also link symmetry related

cations, which in turn are bridged by two water molecules with

the result that the K⁺cation is eight-coordinate within an O₈

donor set (range of K–O bond lengths: 2.7176(17) to 3.107(3)

Å). The coordination geometry is based on a heavily distorted

square anti-prism with each face defined by two oxido- and

two water-O atoms. The K–O bridging leads to a supramolecu-

lar zigzag chain oriented along the b-axis (Fig. 4). Chains are

linked into a three-dimensional architecture by water-O–H⋯O

(phenoxide), N(pyridyl) hydrogen bonds as well as phenyl-

C–H⋯O(oxido) and methyl-C–H⋯π(arene) interactions, as

illustrated in ESI Fig. S6;† see ESI Table S1† for parameters. In

this scheme, the O2w molecule does not form significant

hydrogen bonding interactions, most likely as the hydrogen

atoms are disordered in a pocket defined by four possible

hydrogen atom acceptors, see the Experimental section and

ESI Table S1.† It is noted that all four oxygen atoms in the

pocket belong to a single supramolecular chain indicating that

any putative hydrogen bonds formed by the O2w molecule

would contribute primarily to the stability of the chain.

The asymmetric unit of 7 comprises a Na⁺cation, a

complex anion, three coordinated water molecules and a water

molecule of hydration (Fig. 5). The anion exhibits similar fea-

tures to those described for 3. The r.m.s. deviations for the

five- and six-membered chelate rings are 0.036 and 0.045 Å,

respectively. A small twist is noted between the five-membered

ring and the attached pyridyl ring, i.e. 9.33(9)°, so that the

ligand is no longer planar; the dihedral angle between the

terminal rings is 8.42(10)°. The value of τ is computed to be

0.41, indicating a coordination geometry intermediate between

square pyramidal and trigonal pyramidal.⁵⁴There is only one

precedent in the crystallographic literature⁵⁵for a vanadium

complex of the Schiﬀ base ligand in 7. In this single molecule

structure, the charge balance is achieved by protonation at the

Fig. 3 Perspective view of the components of the crystallographic

asymmetric unit of 6. Selected geometric parameters: V1–O1 1.9668

(16), V1–O2 1.8926(16), V1–O3 1.6174(17), V1–O4 1.6350(16), V1–N3

2.1552(19), N2–N3 1.409(2), N2–C6 1.291(3), N3–C7 1.306(3), O3⋯

K 2.9383(19), O4⋯K 2.8330(18) and O4ⁱ⋯K 2.7178(17) Å. Symmetry oper-

ation i: 1/2 − x, −1/2 + y, z.

Fig. 5 Perspective view of the components of the crystallographic

asymmetric unit of 7. Selected geometric parameters: V1–O1

1.9884(12), V1–O2 1.9027(13), V1–O3 1.6183(14), V1–O4 1.6263(14), V1–

N3 2.1236(14), N2–N3 1.4067(18), N2–C6 1.291(2), N3–C7 1.293(2),

O4⋯Na 2.3889(16), O3⋯Naⁱ2.7274(19) and O4⋯Naⁱ2.5576(18) Å.

Symmetry operation i: 1 − x, −y, 2 − z.

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10147

View Article Online

Paper

Dalton Transactions

pyridyl-N atom,⁵⁸i.e. the Schiﬀ base ligand is present as a

zwitterion.

The ions in 7 are connected into a centrosymmetric four-

component aggregate via oxido-O bridges whereby the O3

atom connects to one Na cation and the O4 atom bridges two

Na cations (Fig. 6). In this way, the Na cation achieves a coordi-

nation number of six based on an octahedral O₆donor set,

with a range of Na–O bond lengths = 2.2904(18) to 2.7277(19)

Å. A supramolecular layer in the ab-plane is formed by

O–H⋯O hydrogen bonds as well as an O–H⋯N hydrogen bond

involving the non-coordinating azo-N3 atom, ESI Fig. S7a (ESI

Table S1†). Layers are connected along the c-axis by water–

O–H⋯N(pyridyl) hydrogen bonds, ESI Fig. S7b.†

DNA binding studies

(a) Absorption spectroscopic studies. DNA binding is an

important parameter for the chemical- and photo-induced

DNA cleavage activity of the metal complexes, therefore the

binding aﬃnity of the complexes 1–8 to CT-DNA was studied

using various spectral techniques. UV-Vis titration experiments

were carried out to determine the equilibrium binding con-

stant (K_b) of the complexes to CT-DNA (Table 2, Fig. 7, ESI

Fig. S8†). Binding of complexes to DNA through intercalation

generally leads to hypochromism and bathochromism of the

absorption band. This shift is observed due to the strong stack-

ing interaction between the aromatic chromophore of the

ligand and the base pairs of the DNA. Minor groove binding of

the complexes to DNA results in hyperchromism in the absorp-

Fig. 7 Electronic absorption spectra of 6 (a) and 7 (b) (25 μM each)

upon the titration of CT-DNA (0–100 μM) in 10 mM Tris-HCl buﬀer (pH

8.0) containing 10% DMF. The arrow shows the changes in absorbance

with respect to an increase in the CT-DNA concentration. The inset

shows the linear ﬁt of [DNA]/(ε_a− ε_f) vs. [DNA] and the binding constant

(K_b) was calculated using eqn (1).

tion intensity, resulting in the unwinding of the DNA double

helix as well as its unstacking and concomitant exposure of

the bases.⁴⁶Therefore the extent of hypochromism or hyper-

chromism observed provides a measure of the strength of

intercalative binding or minor groove binding of the com-

plexes. The UV-Vis spectra of the complexes in the absence

and presence of CT-DNA (at a constant complex concentration

of 25 μM) exhibited a hypochromic shift around ∼260 nm

(Fig. 7, ESI Fig. S8†), which indicates that there is an inter-

action/binding between the complexes and CT-DNA.

Fig. 6 Crystal packing in 7: centrosymmetric four-ion aggregate

mediated by μ-O bridging.

Table 2 Thermodynamic data for CT-DNA binding with 1–8

Complex

Binding constant (K_b)^a(M⁻¹

)

ΔT_m^b(°C)

In order to quantify the binding aﬃnity of the interaction

between CT-DNA and each of 1–8, the binding constant (K_b)

was calculated using eqn (1) (Experimental section). The K_b

values are reported in Table 2. Complexes 6 and 7 showed

higher K_bvalues among all the complexes, i.e. 3.34 × 10⁴and

6.88 × 10⁴M⁻¹, respectively. The binding propensities of

ligands to CT-DNA were also estimated. All the ligands showed

the DNA binding aﬃnity yielding K_bvalues ∼10³M⁻¹(ESI

Fig. S9 and Table S2†).

1

2

3

4

5

6

7

8

1.23 × 10⁴

5.5 × 10³

0.75

1.30

1.63

1.31

1.15

1.95

2.09

1.03

1.67 × 10⁴

2.41 × 10⁴

7.6 × 10³

3.34 × 10⁴

6.88 × 10⁴

1.11 × 10⁴

^aThe DNA binding constant by the UV-vis spectral method. ^bChange

in the melting temperature of CT-DNA.

10148 | Dalton Trans., 2014, 43, 10139–10156

This journal is © The Royal Society of Chemistry 2014

View Article Online

Dalton Transactions

Paper

(b) Thermal denaturation studies. To understand the

nature of the interaction between CT-DNA and these com-

plexes, thermal denaturation experiments were performed.⁴⁶

The melting temperature of CT-DNA (T_m) increased very

slightly upon interaction with complexes 1–8 (Table 2, ESI

Fig. S10†). The shift of DNA melting temperature (ΔT_m) for the

interaction between CT-DNA and complexes 6 and 7 was

greater among eight synthesised dioxidovanadium complexes,

i.e. ∼2 °C. The low ΔT_mvalues for 1–8 suggest groove binding

of the complexes to CT DNA rather than an intercalative mode

of binding to DNA which usually gives a large positive ΔT_m

value.^59,60

(c) Circular dichroism studies. The conformational

changes in CT-DNA due to the interaction with the complexes

were monitored by circular dichroism (CD) spectroscopy.⁶¹The

B-conformation of CT-DNA shows two conservative CD bands

in the UV region, a positive band at 275 nm due to base stack-

ing and a negative band at 245 nm due to right handed heli-

city.⁶¹Groove binding and electrostatic interaction of small

molecules show less or no perturbation in the base stacking

and helicity bands whereas an intercalation mode can induce

intensity changes of both bands, thus modulating the right

handed B-conformation of DNA.⁶¹The CD spectra of CT-DNA

(160 μM) in the presence of the complexes showed very mar-

ginal changes, with a slight increase in the negative ellipticity

at 245 nm for all the complexes except for 8 which exhibited a

slight decrease in negative ellipticity (Fig. 8, ESI Fig. S11†). The

positive band at 275 nm did not show any significant change

in intensity. The results of CD spectra indicate that there is an

interaction between complexes and CT-DNA.

DNA cleavage studies

Fig. 8 Circular dichroism spectra of CT-DNA (160 μM) in the presence

and absence of 6 (a) and 7 (b) in 10 mM Tris-HCl buﬀer (pH 8.0). The

path length of the cuvette was 2 mm.

(a) Chemical-induced DNA cleavage. The cleavage of

supercoiled (SC) pUC19 DNA (300 ng) by 1–8 (1–500 μM) in the

dark using hydrogen peroxide as the oxidising agent was

studied. The complexes do not show any apparent DNA clea-

vage implying no hydrolytic cleavage activity (data not shown).

The lack of chemical nuclease activity may be due to their

weak interaction and binding with DNA.

(b) Photo-induced DNA cleavage. To investigate whether

the DNA binding properties of the complexes were associated

with the photonuclease activity, a photo-induced nuclease

activity assay was performed. The photo-induced DNA nuclease

activity of 1–8 was studied using supercoiled (SC) pUC19 DNA

in 50 mM Tris-HCl buﬀer (pH 8.0) upon irradiation of UVA

light of 350 nm with the aid of gel electrophoresis in the pres-

ence and absence of the complexes (Fig. 9). The extent of SC

DNA cleavage by the complexes was monitored in a concen-

tration-dependent manner as shown in Fig. 10. All of the com-

plexes (except for 3) exhibited more than 10% enhanced

photo-induced DNA cleavage activity at a complex concen-

tration of 10 μM (Fig. 10, inset). The cleavage activity is satu-

rated for each of the complexes at a concentration of 100 μM

and the highest nuclease activity of 33 and 39%, at 100 μM

complex concentration, was conferred by 6 and 7, respectively,

which correlates well with their DNA binding parameters

(Fig. 10, inset and Table 2). All the complexes exhibited almost

similar cleavage even in solutions having low DMF concen-

trations, i.e. 1% DMF (v/v) (ESI Fig. S12†). Butenko et al.

reported that organic buﬀers such as tris, MOPS, HEPES, etc.

suppressed the nuclease activity of some vanadium com-

plexes.⁶²In the same paper, they demonstrated that these com-

plexes exhibited more nuclease activity in phosphate buﬀer

compared to that in organic buﬀers listed above. Thus, we also

performed the photo-induced DNA cleavage activity of 1–8 in

10 mM phosphate buﬀer (pH 7.8) containing 1% DMF (ESI

Fig. S13†). We found that the buﬀer had no eﬀect on the photo-

nuclease activity of these complexes. They exhibited almost

similar activity even when we used phosphate buﬀer instead of

tris buﬀer (ESI Fig. S12†). Since, we worked with buﬀer solu-

tions having basic pH (>7.5), this may rule out the influence of

tris buﬀer on the photo-nuclease activity of these dioxidovana-

dium complexes. Control experiments suggest that neither DMF

(10%) nor the ligands show any photo-induced DNA cleavage

activity, which implies that the ligands or DMF alone are clea-

vage inactive under similar conditions (ESI Fig. S14†).

This journal is © The Royal Society of Chemistry 2014

Dalton Trans., 2014, 43, 10139–10156 | 10149

View Article Online

Paper

Dalton Transactions

Fig. 9 Gel diagram showing concentration dependent DNA cleavage by 1–8; 300 ng of SC pUC19 DNA at diﬀerent concentrations of the com-

plexes [1–500 µM in 50 mM Tris-HCl buﬀer (pH 8.0) containing 10% DMF] was photo-irradiated with UVA at 350 nm for 3 h. Lanes 1–9: 1, 2.5, 5.0,

7.5, 10, 50, 75, 100 and 500 µM of 1–8.

not inhibit the DNA cleavage activity of any complex (ESI

Fig. S15 and S16†). These results suggest that 6 and 7 exhibit

photo-induced DNA cleavage activity via both singlet oxygen

and hydroxyl radical pathways. Although the other complexes

showed slight inhibition of the DNA cleavage activity in the

presence of various additives, the mechanistic pathway fol-

lowed could not be stated with certainty.

Protein binding and cleavage experiments

(a) Bovine serum albumin (BSA) binding studies. As 6 and

7 revealed good binding propensities towards CT-DNA and

showed better photo-induced DNA cleavage activity, the inves-

tigation of the interaction of these two complexes with bovine

serum albumin (BSA) was undertaken. Qualitative analysis of

Fig. 10 Concentration dependent DNA cleavage by 1–8; 300 ng of

the interaction of the complexes with BSA was studied by

SC pUC19 DNA at diﬀerent concentrations of the complexes [1–500 µM

examining the quenching of tryptophan fluorescence emission

in 50 mM Tris-HCl buﬀer (pH 8.0) containing 10% DMF] was photo-

of BSA in the presence of 6 and 7. The fluorescence of the

irradiated with UVA at 350 nm for 3 h. The net DNA cleavage percent

protein is specifically caused by three amino acid residues

namely tryptophan, tyrosine and phenylalanine. The sequence

analysis of BSA reveals the presence of two tryptophan residues

and exhibits tryptophan fluorescence at an excitation of

295 nm with an emission maximum at 344 nm. The inter-

action with BSA was followed by monitoring the quenching of

tryptophan fluorescence upon the addition of 6 and 7. The

eﬀect of the increasing concentration of 6 and 7 on the fluo-

rescence emission of BSA is shown in Fig. 11. The intrinsic

tryptophan fluorescence intensity of BSA was found to quench

gradually on increasing the complex concentration (Fig. 11).

The Stern–Volmer quenching constant (K_SV) was calculated

using eqn (3) (Experimental section). The quenching constants

for 6 and 7 are 2.60 × 10⁴and 2.86 × 10⁵M⁻¹, respectively,

(Table 3) which reveals that 7 has ∼10-fold greater quenching

ability than 6. The extent of quenching of the fluorescence

intensity confers a measure of association of the complex with

BSA. Small molecules bind independently to a set of sites in a

protein molecule and the equilibrium between the free and

the bound molecule is given by the Scatchard equation⁴⁵(eqn

(4)). The binding constant (K_BSA) and the number of binding

was calculated using eqn (2). The inset shows a bar diagram represen-

tation of the net DNA cleavage of diﬀerent complexes at 10 and 100 µM.

In order to understand the mechanistic pathway involved in

the DNA cleavage reactions, we systematically investigated the

photo-induced DNA cleavage activity in the presence of various

additives. The DNA cleavage reaction involving molecular

oxygen can proceed in two mechanistic pathways, namely, a

type-II process involving singlet oxygen species (¹O₂) and a

photo-redox pathway involving reactive hydroxyl radicals

(OH).⁴⁹For the present mechanistic studies NaN₃and L–histi-

dine were used as singlet oxygen quenchers, and KI and

D-mannitol were employed as hydroxyl radical quenchers. The

addition of singlet oxygen quenchers like NaN₃partially

inhibited the DNA cleavage activity of 6 and 7 among the

series, whereas the other singlet oxygen quencher ^L-histidine

did not inhibit the DNA cleavage activity of any complex. Simi-

larly, the hydroxyl radical scavenger KI showed moderate inhi-

bition of the photo-induced DNA cleavage activity for 6 and 7,

whereas the other hydroxyl radical scavenger, ^D-mannitol, did

10150 | Dalton Trans., 2014, 43, 10139–10156

View Article Online

Dalton Transactions

Paper

gated. The photo-induced BSA cleavage activity of these two

complexes in UVA light of 350 nm was carried out using 5 μM

of BSA in 10 mM Tris-HCl buﬀer (pH 8.0) monitored by

SDS-PAGE gel electrophoresis in the presence and absence of

6 and 7. A 100 μM solution of 6 and 7 showed more than 75%

cleavage of BSA (5 μM) with a photo-irradiation of 90 min

(Fig. 12(a, b), lane 8) which suggests that both the complexes

have similar photo-induced BSA cleavage activity. At this same

molar ratio of BSA to complex, all other complexes also exhibi-

ted similar kind of photo-induced BSA cleavage activity (ESI

Fig. S18a†), whereas all the complexes (1–8) failed to show any

cleavage of BSA in the dark (ESI Fig. S18b†). Moreover, the

densitometry analysis of photo-induced BSA cleavage experi-

ments revealed that ∼33–36% BSA cleavage occurred even at

1 : 1 molar ratio of BSA to complex (Fig. 12(c)).

Cytotoxicity studies

(a) MTT assay. In the present study, the antiproliferative

eﬃcacy of 1–8 was assayed by determining the viability of

HeLa cells using the MTT assay. The ligands, H₂L^1–6and

VO(acac)₂gave high IC₅₀values of >200 μM, whereas 1–8 gave

values in the range 45–17 μM (Table 4). By contrast, cisplatin,

gefitinib, gemcitabine, 5-fluorouracil and vinorelbine, com-

monly used chemotherapeutic drugs, are comparably eﬀective

in HeLa cells with an IC₅₀value of 13, 20, 35, 40 and 48 μM,

respectively, under the same experimental conditions.⁶³The

significant decrease in the inhibitory activity of the ligands as

well as their lower binding aﬃnity to CT-DNA compared to

their metal complexes clearly indicate that incorporation of

vanadium has a marked eﬀect on the cytotoxicity. A possible

explanation is that by coordination, the polarity of the ligand

and the central metal ion is reduced through the charge equili-

bration, which favours permeation of the complexes through

the lipid layer of the cell membrane.^64,65The results of the

DNA binding/cleavage ability for the ligands (ESI Fig. S9 and

S14†) have been considered and are consistent with the obser-

vation that metal complexes can exhibit greater biological

activities than the free ligands.⁶⁶

Fig. 11 Intrinsic tryptophan ﬂuorescence spectra of BSA (2 µM) in the

presence of complex 6 (a) and 7 (b) (0–20 μM in 10 mM Tris-HCl buﬀer

(pH 8.0) containing 1% DMF). Tryptophan ﬂuorescence spectra were

recorded in the range 310–400 nm at 25 °C. The excitation wavelength

was 295 nm. The arrow indicates the eﬀect of increasing concentration

of complexes on the tryptophan ﬂuorescence emission of BSA. The

inset shows the linear ﬁt of the F₀/F vs. [complex] and Stern–Volmer

quenching constant (K_SV) was calculated using eqn (3).

Within the series 1–8, the cytotoxicities of 2, 5, 6 and 7 are

almost similar whereas those of 6 and 7 are greater as reflected

from their IC₅₀values, Table 4, with their dose dependence

illustrated in Fig. 13. The variation in results of cytotoxicity of

the complexes may be aﬀected by the various functional

groups attached to the aroylhydrazone derivative. Very recently,

the antiproliferative activity of some vanadium compounds

reported by Yamaguchi et al.⁶⁷and us³⁶using U937 cells and

HeLa cells, respectively, and the present results are in accord-

ance with the reported values.

(b) Nuclear staining assay. To investigate the apoptotic

potential of test compounds in HeLa cells, DAPI staining was

performed. Chromatin condensation during the process of

apoptosis (type I programmed cell death) is a characterising

marker of nuclear alteration. HeLa cells were treated with 40,

15, 20, 30, 18, 15, 12 and 30 μM of complexes 1–8, respectively.

The cells were incubated for 24 h before DAPI nuclear staining.

Cells were examined under a fluorescent microscope fitted

Table 3 BSA binding parameters of 6 and 7

Stern–Volmer

Binding constant Number of

Complex constant (K_SV) (M⁻¹

)

(K_BSA) (M⁻¹

)

binding sites (n)

6

7

2.52 0.11 × 10⁴

2.72 0.15 × 10⁵

3.12 0.13 × 10⁴

4.12 0.18 × 10⁵

0.81 0.11

1.04 0.07

ꢀ

ꢁ

F₀ꢁ F

sites (n) were obtained from the plot of log

vs. log[Q]

F

(ESI Fig. S17,† Table 3). Both complexes interact with BSA in a

1 : 1 stoichiometry, although the binding aﬃnity of complex 7

towards BSA is greater than for complex 6.

(b) BSA cleavage activity. Since both the complexes exhibi-

ted good binding aﬃnity towards BSA, their protein cleavage

activity by the photo-induced BSA cleavage assay was investi-

Dalton Trans., 2014, 43, 10139–10156 | 10151

View Article Online

Paper

Dalton Transactions

Fig. 12 SDS-PAGE proﬁle of concentration dependent photo-induced cleavage of BSA (5 μM) in UVA light of 350 nm by 6 (a) and 7 (b) in 10 mM

Tris-HCl buﬀer (pH 8.0) containing 1% DMF. Lane 1, molecular marker; lane 2, BSA only; lane 3, BSA + complex (1 μM); lane 4, BSA + complex

(2.5 μM); lane 5, BSA + complex (5 μM); lane 6, BSA + complex (10 μM); lane 7, BSA + complex (50 μM); lane 8, BSA + complex (100 μM); lane 9,

BSA + complex (300 μM); lane 10, BSA + complex (500 μM). (c) Net BSA cleavage percent of concentration dependent photo-induced cleavage of

BSA (5 μM) in UVA light of 350 nm (84 W) by 6 and 7.

Table 4 Cytotoxic scores for 1–8 in HeLa cancer cells

Complex

IC₅₀(µM)

1

2

3

4

5

6

7

8

44.96 3.98

20.56 4.58

24.25 3.74

33.25 2.9

23.18 3.66

18.96 4.09

17.23 3.24

37.45 4.26

with a DAPI filter. Control cells (treated with 10% (v/v) DMF)

hardly showed any sort of condensation in comparison with

the treated cells, as shown in Fig. 14. All images taken in gray-

scale demonstrate the brightly condensed chromatin bodies

and the nuclear blebbings as marked by arrows in Fig. 14.

Besides showing the nuclear change, the treated cells exhibited

a shrinking morphology, which is another important hallmark

of apoptosis.

Fig. 13 Eﬀect of 1–8 on cell viability and growth: HeLa cells were

treated with diﬀerent concentrations of the test compound for 72 h and

then the cell viability was measured by the MTT assay. Data reported as

the mean SD for n = 6 and compared against 10% (v/v) DMF treated

control using a Student’s t-test (*signiﬁcant compared to the control).

10152 | Dalton Trans., 2014, 43, 10139–10156

View Article Online

Dalton Transactions

Paper

Fig. 14 Study of apoptosis by morphological changes in nuclei of HeLa cells: HeLa cells, from control and treated groups, were ﬁxed with 3.7% for-

maldehyde for 15 min, permeabilised with 0.1% Triton X-100 and stained with 1 µg mL⁻¹DAPI for 5 min at 37 °C. The cells were then washed with

PBS and examined by ﬂuorescence microscopy (Olympus IX 71) (200×). HeLa cells were treated with 40, 15, 20, 30, 18, 15, 12 and 30 μM of com-

plexes 1–8, respectively. Arrows showing the morphological changes in nuclei of HeLa cells observed on applying 1–8 in comparison with the

control group treated with 10% (v/v) DMF.

induced cleavage of pUC19 supercoiled plasmid DNA. Among

Conclusion

1–8, complexes 6 and 7 showed the best CT-DNA binding pro-

The following are the salient observations of the present work: perties. Moreover, these two complexes exhibited greater clea-

a series of dioxidovanadium(^V) complexes (1–8) with tridentate vage activity of pUC19 DNA under photolytic conditions

aroylhydrazonates containing a ONO donor atom form poly- probably via both singlet oxygen and hydroxyl radical path-

meric extended structures incorporating various alkali metal ways. Complexes 6 and 7 also exhibit good binding aﬃnity in

ions. The vanadium anions in 3, 5–7 have been shown by X-ray the range of 10⁴–10⁵M⁻¹towards BSA. Both complexes also

crystallography to be five-coordinated within NO₄donor sets showed eﬃcient photo-induced BSA cleavage activity. The

tending towards square pyramidal. The primary influence of results obtained are significant in the context that vanadium

the cations is related to the size so that with small Li⁺, no brid- complexes showing only DNA photo-cleavage activity but no

ging-O is found between the constituent ions but four-ion chemical nuclease activity are sparse. The in vitro antiprolifera-

aggregates are found with Na⁺, chains for K⁺and finally, layers tive activity of complexes 1–8 against the HeLa cell line was

for Cs⁺. Strong electrostatic and hydrogen bonding inter- assayed. Among the complexes, 2, 5, 6 and 7 show consider-

actions play the central role in stabilizing these extended struc- able activity compared to commonly used chemotherapeutic

tures in the solid state.

drugs and the variation of the cytotoxicity of the complexes

Complexes 1–8 demonstrated moderate DNA binding pro- may be aﬀected by the various functional groups attached to

pensity. Their DNA binding activities were investigated using the aroylhydrazone derivative whereby it may be globally stated

UV-Vis absorption titration, circular dichroism and thermal that 6 and 7 are more potent against the HeLa cell line. The

denaturation studies. The experimental results show that the results of DNA binding, photo-induced DNA cleavage and anti-

complexes moderately interact with CT-DNA probably by proliferative activity of the new dioxidovanadium(^V) complexes

groove binding mode, with binding constants ranging from of aroylhydrazones reported in this paper reveal that the

10³to 10⁴M⁻¹. All complexes also show eﬃcient photo- pharmacological activities of these complexes can be fine-

Dalton Trans., 2014, 43, 10139–10156 | 10153

View Article Online

Paper

Dalton Transactions

tuned by changing the substituent on the hydrazone residue. 12 C. R. Cornman, E. P. Zovinka and M. H. Meixner, Inorg.

It is important to mention that the alkali metal ion variation Chem., 1995, 34, 5099.

in 1–8 may have some influence on the results of pharmaco- 13 K. H. Thompson, J. H. McNeill and C. Orvig, Chem. Rev.,

logical activity but their precise role remains unknown. 1999, 99, 2561.

Further work is in progress to identify the reasons. The results 14 K. H. Thompson, B. D. Liboiron, Y. Sun, K. D. D. Bellman,

obtained from the present dioxidovanadium(^V) complexes are

of importance for the development of metal-based agents for

anti-cancer applications. Further work is in progress to better

V. Karunaratne, G. Rawji, J. Wheeler, K. Sutton, S. Bhanot,

S. B. C. Cassidy, J. H. McNeill, V. G. Yuen and C. Orvig,

J. Biol. Inorg. Chem., 2003, 8, 66.

identify the mechanism of action and to prepare more potent 15 H. Yasui, Y. Adachi, A. Katoh and H. Sakurai, J. Biol. Inorg.

related compounds for the treatment of cancer.

Chem., 2007, 12, 843.

16 Y. Shechter, I. Goldwaser, M. Mironchik, M. Fridkin and

D. Gefel, Coord. Chem. Rev., 2003, 237, 3.

17 A. M. B. Bastos, J. G. da Silva, P. I. S. Maia, V. M. Deflon,

A. A. Batista, A. V. M. Ferreira, L. M. Botion, E. Niquet and

H. Beraldo, Polyhedron, 2008, 27, 1787.

Acknowledgements

The authors thank the reviewers for their comments and sug-

gestions, which were helpful in preparing the revised version 18 R. R. Eady, Coord. Chem. Rev., 2003, 237, 23.

of the manuscript. Funding for this research was provided by 19 P. K. Sasmal, A. K. Patra and A. R. Chakravarty, J. Inorg.

the Department of Science and Technology, India [Grant SR/

WOS-A/CS-145/2011 (S.P.D), grant SR/FT/CS-016/2008 (R.D)] 20 I. C. Mendes, L. M. Botion and A. V. M. Ferreira, Inorg.

and the Council of Scientific and Industrial Research, India Chim. Acta, 2009, 362, 414.

[Grant 37(1535)/12/EMR-II) (AB)]. R.D. thanks Prof. S. K. Chat- 21 J. Benítez, L. Guggeri, I. Tomaz, J. C. Pessoa, V. Moreno,

Biochem., 2008, 102, 1463.

topadhyay, Bengal Engineering and Science University,

Shibpur for fruitful discussion. A.K.P. acknowledges the

J. Lorenzo, F. X. Avilés, B. Garat and D. Gambino, J. Inorg.

Biochem., 2009, 103, 1386.

receipt of ICMR, India grant 45/25/2012-Bio/BMS for providing 22 J. Benítez, L. Guggeri, I. Tomaz, G. Arrambide, M. Navarro,

fellowship. Support from the High Impact Research MoE

Grant UM.C/625/1/HIR/MoE/SC/12 from the Ministry of Higher

Education, Malaysia, is also gratefully acknowledged.

J. C. Pessoa, B. Garat and D. Gambino, J. Inorg. Biochem.,

2009, 103, 609.

23 J. Benítez, L. Becco, I. Correia, S. M. Leal, H. Guiset,

J. C. Pessoa, S. Tanco, P. Escobar, V. Moreno, B. Garat and

D. Gambino, J. Inorg. Biochem., 2011, 105, 303.

ˇ

24 (a) L. Andrezalova, H. Gbelcova and Z. Durackova, J. Trace

Notes and references

Elem. Med. Biol., 2013, 27, 21; (b) Z. H. Chohan,

S. H. Sumrra, M. H. Youssoufi and T. B. Hadda, Eur. J. Med.

Chem., 2010, 45, 2739; (c) J. Lu, H. Guo, X. Zeng, Y. Zhang,

P. Zhao, J. Jiang and L. Zang, J. Inorg. Biochem., 2012, 112,

39; (d) T. Yamaguchi, S. Watanabe, Y. Matsumura,

Y. Tokuoka and A. Yokoyama, Bioorg. Med. Chem., 2012, 20,

3058.

1 B. Rosenberg, L. VamCamp, J. E. Trosko and

V. H. Mansour, Nature, 1969, 222, 385.

2 O. Zelenko, J. Gallagher, Y. Xu and D. S. Sigman, Inorg.

Chem., 1998, 37, 2198.

3 Z. Wu, Q. Liu, X. Liang, X. Yang, N. Wang, X. Wang,

H. Sun, Y. Lu and Z. Guo, J. Biol. Inorg. Chem., 2009, 14,

1413.

4 D. S. Raja, N. S. P. Bhuvanesh and K. Natarajan, Dalton

Trans., 2012, 41, 4365.

25 (a) D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev.,

1998, 98, 1375; (b) D. Braga and F. Grepioni, Coord. Chem.

Rev., 1999, 183, 19; (c) D. Braga and F. Grepioni, Acc. Chem.

Res., 2000, 33, 601.

5 X. Qiao, Z. Y. Ma, C. Z. Xie, F. Xue, Y. W. Zhang, J. Y. Xu,

Z. Y. Qiang, J. S. Lou, G. J. Chen and S. P. Yan, J. Biol. Inorg. 26 (a) S. Dutta, P. Basu and A. Chakraborty, Inorg. Chem.,

Chem., 2011, 105, 728.

6 P. J. Bednarski, F. S. Mackay and P. J. Sadler, Anticancer

Agents Med. Chem., 2007, 7, 75.

7 Vanadium and its Role in Life, Metal Ions in Biological

Systems, ed. H. Sigel and A. Sigel, Marcel Dekker, New York,

1995, vol. 31.

8 D. C. Crans, J. J. Smee, E. Gaidamauskas and L. Yang,

Chem. Rev., 2004, 104, 849.

9 A. S. Tracey, G. R. Willsky and E. S. Takeuchi, Vanadium

Chemistry, Biochemistry, Pharmacology and Practical Appli-

cations, CRC Press, Boca Raton, 2007.

10 D. Rehder, Bioinorganic Vanadium Chemistry, John Wiley &

Sons, Chichester, 2008.

1993, 32, 5343; (b) S. K. Dutta, S. Samanta,

S. Mukhopadhyay, P. Burckel, A. Pinkerton and

M. Choudhry, Inorg. Chem., 2002, 41, 2946; (c) S. Samanta,

S. Mukhopadhyay, D. Mandal, R. J. Butcher and

M. Choudhry, Inorg. Chem., 2003, 42, 6284;

(d) D. M. J. Doble, A. J. Blake, W. S. Li and M. Schroder,

Dalton Trans., 2001, 3137; (e) C. Ling Pan, J. Qing Xu,

G. Hua Li, X. Bing Cui, L. Ye and G. Di Yang, Dalton Trans.,

2003, 517; (f) H. Zhu, C. Chen, X. Zhang, Q. Liu, D. Liao

and L. Li, Inorg. Chim. Acta, 2002, 328, 96;

(g) W. Przybylski, R. Gryboś, D. Rehder, M. Ebel,

M. Grzywa, W. Łasocha, K. Lewinski and J. T. Szklarzewicz,

Polyhedron, 2009, 28, 1429; (h) R. Dinda, P. K. Majhi,

P. Sengupta, S. Pasayat and S. Ghosh, Polyhedron, 2010, 29,

11 A. Butler and J. V. Walker, Chem. Rev., 1993, 93, 1937.

10154 | Dalton Trans., 2014, 43, 10139–10156

View Article Online

Dalton Transactions

Paper

248; (i) A. Hazra, S. Gupta, S. Roy, T. N. Mandal, K. Das,

S. Konar, A. Jana, S. Ray, R. J. Butcher and S. K. Kar, Polyhe-

dron, 2011, 30, 187.

2009, 44, 4585; ( j) K. Ghosh, P. Kumar, N. Tyagi,

U. P. Singh, V. Aggarwal and M. C. Baratto, Eur. J. Med.

Chem., 2010, 45, 3770; (k) Z. C. Liu, B. D. Wang, B. Li,

Q. Wang, Z. Y. Yang, T. R. Li and Y. Li, Eur. J. Med. Chem.,

2010, 45, 5353; (l) P. Krishnamoorthy, P. Sathyadevi,

A. H. Cowley, R. R. Butorac and N. Dharmaraj, Eur. J. Med.

Chem., 2011, 46, 3376; (m) B. D. Wang, Z. Y. Yang and

T. R. Li, Bioorg. Med. Chem., 2006, 14, 6012;

(n) P. Krishnamoorthy, P. Sathyadevi, R. R. Butorac,

A. H. Cowley, N. S. P. Bhuvanesh and N. Dharmaraj, Dalton

Trans., 2012, 41, 4423; (o) M. Alagesan, N. S. P. Bhuvanesh

and N. Dharmaraj, Dalton Trans., 2013, 42, 7210.

27 P. G. Bruce, Solid State Electrochemistry, Cambridge Univer-

sity Press, Cambridge, 1993.

28 M. J. Pregel, L. Jullien and J. M. Lehn, Angew. Chem., Int.

Ed. Engl., 1992, 31, 637.

29 L. H. A. Terra, M. C. Areias, I. Gaubeur and M. E. V. Suez-

Iha, Spectrosc. Lett., 1999, 32, 257.

30 (a) M. R. Maurya, S. Agarwal, M. Abid, A. Azam, C. Bader,

M. Ebel and D. Rehder, Dalton Trans., 2006, 937;

(b) L. Savini, L. Chiasserini, V. Travagli, C. Pellerano and

E. Novellino, Eur. J. Med. Chem., 2004, 39, 113; (c) Z. Cui, 33 (a) M. R. Maurya, A. A. Khan, A. Azam, A. Kumar,

X. Yang, Y. Shi, H. Uzawa, J. Cui, H. Dohi and Y. Nishida,

Bioorg. Med. Chem. Lett., 2011, 21, 7193.

S. Ranjan, N. Mondal and J. C. Pessoa, Eur. J. Inorg. Chem.,

2009, 5377; (b) M. R. Maurya, A. A. Khan, A. Azam,

S. Ranjan, N. Mondal, A. Kumar, F. Avecilla and

J. C. Pessoa, Dalton Trans., 2010, 39, 1345; (c) J. Benítez,

A. C. de Queiroz, I. Correia, M. A. Alves, M. S. Alexandre-

Moreira, E. J. Barreiro, L. M. Lima, J. Varela, M. González,

H. Cerecetto, V. Moreno, J. C. Pessoa and D. Gambino,

Eur. J. Med. Chem., 2013, 62, 20.

31 (a) A. C. Cunha, J. M. Figueiredo, J. L. M. Tributino,

A. L. P. Miranda, H. C. Castro, R. B. Zingali, C. A. M. Fraga,

M. C. B. V. Souza, V. F. Ferreira and E. Barreiro, J. Bioorg.

Med. Chem., 2003, 11, 2051; (b) J. Easmon, G. Puerstinger,

K. S. Thies, G. Heinisch and J. Hofmann, J. Med. Chem.,

2006, 49, 6343; (c) T. B. Chaston, R. N. Watts, J. Yuan and

D. R. Richardson, Clin. Cancer Res., 2004, 10, 7365; 34 (a) D. C. Crans, J. J. Smee, E. Gaidamauskas and L. Yang,

(d) G. R. Braslawsky, M. A. Edson, W. Pearce, T. Kaneko and

R. S. Greenfield, Cancer Res., 1990, 50, 6608; (e) G. Darnell

and D. R. Richardson, Blood, 1999, 94, 781; (f) C. D. Fan,

H. Su, J. Zhao, B. X. Zhao, S. L. Zhang and J. Y. Miao,

Eur. J. Med. Chem., 2010, 45, 1438; (g) L. R. Morgan,

B. S. Jursic, C. L. Hooper, D. M. Neumann, K. Thangaraj and

B. LeBlanc, Bioorg. Med. Chem. Lett., 2002, 12, 3407;

(h) P. Dandawate, E. Khan, S. Padhye, H. Gaba, S. Sinha,

J. Deshpande, S. K. Venkateswara, M. Khetmalas, A. Ahmad

and F. H. Sarkar, Bioorg. Med. Chem. Lett., 2012, 22, 3104;

(i) W. Y. Liu, H. Y. Li, B. X. Zhao, D. S. Shin, S. Lian and

J. Y. Miao, Carbohydr. Res., 2009, 344, 1270; ( j) Y. Xia,

Chem. Rev., 2004, 104, 849; (b) G. G. Nunes, A. C. Bonatto,

C. G. de Albuquerque, A. Barison, R. R. Ribeiro, D. F. Back,

A. V. C. Andrade, E. L. de Sá, F. O. de Pedrosa, J. F. Soares

and E. M. de Souza, J. Inorg. Biochem., 2012, 108, 36;

(c) R. Tudor, N. Maria, P. Simona, P. Elena, P. Donald and

G. Aurelian, Eur. J. Med. Chem., 2010, 45, 774;

(d) S. H. Sumrra and Z. H. Chohan, Spectrochim. Acta, Part

A, 2012, 98, 53; (e) D. S. Raja, S. P. Bhuvanesh Nattamai

and K. Natarajan, Inorg. Chim. Acta, 2012, 385, 81;

(f) A. Bishayee, A. Waghray and M. A. Patel, Cancer Lett.,

2010, 294, 1; (g) X. Liao, J. Lu, P. Ying, P. Zhao, Y. Bai, W. Li

and M. Liu, J. Biol. Inorg. Chem., 2013, 18, 975.

C. D. Fan, B. X. Zhao, J. Zhao, D. S. Shin and J. Y. Miao, 35 (a) R. Dinda, P. Sengupta, S. Ghosh and T. C. W. Mak, Inorg.

Eur. J. Med. Chem., 2008, 43, 2347; (k) K. Eﬀenberger,

S. Breyer and R. Schobert, Eur. J. Med. Chem., 2010, 45, 1947;

(l) G. S. Hassan, H. H. Kadry, S. M. Abou-Seri, M. M. Ali and

A. E. Mahmoud, Bioorg. Med. Chem., 2011, 19, 6808;

Chem., 2002, 41, 1684; (b) R. Dinda, P. Sengupta,

M. Sutradhar, T. C. W. Mak and S. Ghosh, Inorg. Chem., 2008,

47, 5634; (c) S. P. Dash, S. Pasayat, S. Bhakat, H. R. Dash,

S. Das, R. J. Butcher and R. Dinda, Polyhedron, 2012, 31, 524.

(m) F. F. Tian, J. H. Li, F. L. Jiang, X. L. Han, C. Xiang, 36 S. P. Dash, S. Pasayat, S. Bhakat, R. Dinda, E. R. T. Tiekink,

Y. S. Ge, L. L. Li and Y. Liu, RSC Adv., 2012, 2, 501;

(n) D. R. Richardson, Antimicrob. Agents Chemother., 1997,

41, 2061.

S. Mukhopadhyay, S. K. Bhutia, M. R. Hardikar, B. N. Joshi,

Y. P. Patil and M. Nethaji, Inorg. Chem., 2013, 52, 14096.

37 R. A. Rowe and M. M. Jones, Inorg. Synth., 1957, 5, 113.

32 (a) D. S. Raja, N. S. P. Bhuvanesh and K. Natarajan, J. Biol. 38 S.

Naskar,

D.

Mishra,

R.

J.

Butcher

and

Inorg. Chem., 2012, 17, 223; (b) T. B. Chaston and

S. K. Chattopadhyay, Polyhedron, 2007, 26, 3703.

D. R. Richardson, J. Biol. Inorg. Chem., 2003, 8, 427; 39 Bruker, APEX2 (version 2.1-4), SAINT (version 7.34A) and

(c) Q. Wang, Z. Y. Yang, G. F. Qi and D. D. Qin, Biometals,

2009, 22, 927; (d) Z. Y. Yang, B. D. Wang and Y. H. Li,

SADABS (version 2007/4), BrukerAXS Inc, Madison, Wiscon-

sin, USA, 2007.

J. Organomet. Chem., 2006, 691, 4159; (e) B. D. Wang, 40 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystal-

Z. Y. Yang, P. Crewdson and D. Q. Wang, J. Inorg. Biochem., logr., 2008, 64, 112.

2007, 101, 1492; (f) T. R. Li, Z. Y. Yang, B. D. Wang and 41 L. J. Farrugia, J. Appl. Crystallogr., 2013, 45, 849.

D. D. Qin, Eur. J. Med. Chem., 2008, 43, 1688; (g) Q. Wang, 42 J. Gans and D. Shalloway, J. Mol. Graphics Model., 2001, 19,

Z. Y. Yang, G. F. Qi and D. D. Qin, Eur. J. Med. Chem., 2009,

557.

44, 2425; (h) Z. C. Liu, B. D. Wang, Z. Y. Yang, Y. Li, 43 DIAMOND, Visual Crystal Structure Information System,

D. D. Qin and T. R. Li, Eur. J. Med. Chem., 2009, 44, 4477;

(i) Y. Li, Z. Y. Yang and M. F. Wang, Eur. J. Med. Chem.,

Version 3.1, CRYSTAL IMPACT, Postfach 1251, D-53002

Bonn, Germany, 2006.

Dalton Trans., 2014, 43, 10139–10156 | 10155

View Article Online

Paper

Dalton Transactions

44 A. L. Spek, Acta Crystallogr., Sect. D: Biol. Crystallogr., 2009, 55 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 380.

65, 148.

56 (a) M. Sutradhar, G. Mukherjee, M. G. B. Drew and

S. Ghosh, Inorg. Chem., 2006, 45, 5150; (b) M. Sutradhar,

T. R. Barman, G. Mukherjee, M. G. B. Drew and S. Ghosh,

Polyhedron, 2012, 34, 92.

45 P. Krishnamoorthy, P. Sathyadevi, A. H. Cowley,

R. R. Butorac and N. Dharmaraj, Eur. J. Med. Chem., 2011,

46, 3376.

46 P. Kumar, S. Gorai, M. K. Santra, B. Mondal and D. Manna, 57 B. Mondal, M. G. B. Drew and T. Ghosh, Inorg. Chim. Acta,

Dalton Trans., 2012, 41, 7573. 2010, 363, 2296.

47 P. K. Sasmal, A. K. Patra and A. R. Chakravarty, J. Inorg. 58 G. H. Shahverdizadeh, S. W. Ng, E. R. T. Tiekink and

Biochem., 2008, 102, 1463.

48 W. M. Dai, K. W. Lai, A. Wu, W. Hamaguchi, M. Y. Lee,

B. Mirtamizdoust, Acta Crystallogr., Sect. E: Struct. Rep.

Online, 2012, 68, m236.

L. Zhou, A. Ishii and S. Nishimoto, J. Med. Chem., 2002, 45, 59 Y. An, S. D. Liu, S. Y. Deng, L. N. Ji and Z. W. Mao, J. Inorg.

758. Biochem., 2006, 100, 1586.

49 P. K. Sasmal, S. Saha, R. Majumdar, S. De, R. R. Dighe and 60 S. Banerjee, A. Hussain, P. Prasad, I. Khan, B. Banik,

A. R. Chakravarty, Dalton Trans., 2010, 39, 2147.

P. Kondaiah and A. R. Chakravarty, Eur. J. Inorg. Chem.,

50 S. K. Bhutia, S. K. Mallick, S. M. Stevens, L. Prokai,

2012, 3899.

J. K. Vishwanatha and T. K. Maiti, Toxicol. In Vitro, 2008, 61 L. Li, Q. Guo, J. Dong, T. Xu and J. Li, J. Photochem. Photo-

22, 344. biol., B, 2013, 125, 56.

51 S. Mukhopadhyay, P. K. Panda, B. Behera, C. K. Das, 62 N. Butenko, A. I. Tomaz, O. Nouri, E. Escribano, V. Moreno,

M. K. Hassan, D. N. Das, N. Sinha, A. Bissoyi, K. Pramanik,

T. K. Maiti and S. K. Bhutia, Food Chem. Toxicol., 2014, 64,

369.

S. Gama, V. Ribeiro, J. P. Telo, J. C. Pesssoa and I. Cavaco,

J. Inorg. Biochem., 2009, 103, 622.

63 M. Ahmed and K. Jamil, Biol. Med., 2011, 3, 60.

52 S. Das, G. P. Muthukumaragopal, S. N. Pal and S. Pal, New 64 A. M. Ramadan, J. Inorg. Biochem., 1997, 65, 183.

J. Chem., 2003, 27, 1102.

65 P. G. Avaji, C. H. V. Kumar, S. A. Patil, K. N. Shivananda

53 (a) M. R. Maurya, A. Kumar, M. Ebel and D. Rehder, Inorg.

and C. Nagaraju, Eur. J. Med. Chem., 2009, 44, 3552.

Chem., 2006, 45, 5924; (b) M. R. Maurya, C. Haldar, 66 T. Rosu, E. Pahontu, S. Pasculescu, R. Georgescu,

A. Kumar, M. L. Kuznetsov, F. Avecilla and J. C. Pessoa,

Dalton Trans., 2013, 42, 11941.

N. Stanica, A. Curaj, A. Popescu and M. Leabu, Eur. J. Med.

Chem., 2010, 45, 1627.

54 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and 67 T. Yamaguchi, S. Watanabe, Y. Matsumura, Y. Tokuoka and

G. C. Verschoor, Dalton Trans., 1984, 1349. A. Yokoyama, Bioorg. Med. Chem., 2012, 20, 3058.

10156 | Dalton Trans., 2014, 43, 10139–10156

Article Doi

Syntheses and structural investigation of some alkali metal ion-mediated LVVO2- (L2- = tridentate ONO ligands) species: DNA binding, photo-induced DNA cleavage and cytotoxic activities

DOI: 10.1039/c4dt00883a

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c4dt00883a

Full text of DOI:10.1039/c4dt00883a

Products guided by the article

R&D Labs maybe for 15533-09-2

Relevant to this article

Hot Product