Thermal properties and CT-DNA/BSA binding behavior of a binuclear Cu(II) complex with acylhydrazone containing naphthalene ring

Article abstract of DOI:10.1080/00958972.2018.1457145

A novel Cu(II) complex [Cu₂L₂(NO₃)₂] with 2-hydroxy-1-naphthaldehyde-(4’hydroxy)phenylacetyl hydrazone (C₁₉H₁₄N₂O₂·H₂O, HL) was synthesized. The structure o

Full text of DOI:10.1080/00958972.2018.1457145

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Thermal properties and CT-DNA/BSA binding
behavior of a binuclear Cu(II) complex with
acylhydrazone containing naphthalene ring
Ming-Kun Yu, Xiang-Rong Liu, Jin-Wen Ren, Jing-Jing Liu, Zai-Wen Yang &
Shun-Sheng Zhao
To cite this article: Ming-Kun Yu, Xiang-Rong Liu, Jin-Wen Ren, Jing-Jing Liu, Zai-Wen Yang &
Shun-Sheng Zhao (2018): Thermal properties and CT-DNA/BSA binding behavior of a binuclear
Cu(II) complex with acylhydrazone containing naphthalene ring, Journal of Coordination Chemistry,
DOI: 10.1080/00958972.2018.1457145
To link to this article: https://doi.org/10.1080/00958972.2018.1457145
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Publisher: Taylor & Francis
Journal: Journal of Coordination Chemistry
DOI: http://doi.org/10.1080/00958972.2018.1457145
Thermal properties and CT-DNA/BSA binding behavior of a binuclear Cu(II)
complex with acylhydrazone containing naphthalene ring
MING-KUN YU, XIANG-RONG LIU*, JIN-WEN REN, JING-JING LIU, ZAI-WEN YANG and SHUN-
SHENG ZHAO
Chemistry and Chemical Engineering, Xi’an University of Science and Technology Xi’an 710054, PR China
A novel Cu(II) complex [Cu2L2(NO3)2] with 2-hydroxy-1-naphthaldehyde-(4’-
hydroxy)phenylacetyl hydrazone (C19H14N2O2·H2O, HL) was synthesized. The structure of
[Cu2L2(NO3)2] was characterized by X-ray single-crystal diffraction and can be described as a
distorted rectangular pyramid with binuclear coordination. IR, UV-vis and EPR spectra are used
to discuss the structure of Cu(II) complex in different conditions. Magnetic properties were
determined by EPR spectra and magnetic susceptibility studies, showing magnetic exchange
interaction and weak antiferromagnetic exchange between two Cu(II) ions. The apparent
activation energy (Ea) of thermal decomposition of compounds indicated that the thermal
stability of [Cu2L2(NO3)2] is better than HL. The CT-DNA binding behavior of compounds was
determined by UV-vis absorption and viscosity measurements and the results confirmed an
intercalative binding mode with CT-DNA. Kb obtained was 6.24(0.12)×106 M-1 and
3.09(0.006)×106 M-1 for [Cu2L2(NO3)2] and HL, respectively, revealing that the binding ability
of [Cu2L2(NO3)2] with CT-DNA was stronger. The thermogenic curves of compounds interacting
with CT-DNA were monitored by microcalorimetry, showing they were all endothermic
reactions with reaction within 27-42 min; interaction enthalpies (ΔH) of [Cu2L2(NO3)2] and HL
were 30.3 and 4.31 kJ·mol-1. Binding studies with BSA were evaluated by fluorescence
*Corresponding author. Email: liuxiangrongxk@163.com
1

spectroscopy and the same relative interactions were found comparing with the above CT-DNA
experiments.
Keywords: Complex; Thermal stability; DNA-Binding; Microcalorimetry; BSA-Binding
1. Introduction
Recently, acylhydrazone ligands and their metal complexes have drawn considerable attention in
chemistry and biology [1, 2]. The biological properties of acylhydrazone complexes, which are
linked to active groups and metal ions, may be different from those of either the ligand or the
metal ion. We reported the naphthalene-based acylhydrazone compound C19H14N2O2·H2O (HL),
which can serve as drug for antidiabetic [3], anti-arrhythmia [4], antitumor [5], antioxidant [6]
and anti-tubulin [7]. Furthermore, copper is a bioessential trace element that takes part in the
electronic transformation and oxidation-reduction reactions in living beings. There are many
copper complexes that have been investigated for potential activities as anti-tumoral agents [8,
9]. For example, the Ruiz group [10] has designed anti-tumoral Cu(II) compounds (Casiopeinas)
and studied the DNA interactions by fluorimetric methods employing EB (ethidium bromide)
and SG (Syber-Green I); the results show that Cu(II) complexes interact with DNA by different
binding modes. The mode of binding and intensity of these interactions are influenced by ligands
coordinated to Cu(II). Tisato and Santini group [11] has synthesized monocationic hydrophilic
complexes [Cu(thp)4]+ and [Cu(bhpe)2]+; the complexes were tested against a panel of several
human tumor cell lines and Cu(I)-phosphine complex is able to inhibit the growth of tumor cells
via G2/M cell cycle arrest. They have also reported a paper about the advances in copper
complexes as anticancer agents, which could be a useful tool for the research community
involved in copper-based anticancer drug discovery [12].
DNA and proteins are bio-macromolecules with essential physiological functions that are
studied to estimate the bio-activities of compounds. Drugs often exert anti-tumor effects through
binding to DNA [13]. Proteins are involved in transportation of metal ions, which are the
2

catalytic centers for many biological processes and require one or more metal ions to provide
binding sites to the substrates [14, 15]. In vivo, Cu(II), Zn(II) and rare earth ions may have a
synergistic effect with organic compounds so that the bio-activities of metal-organic complexes
is better than organic compounds alone [16-22]. Therefore, investigation of interaction models
between small molecules, especially metal-organic complexes and bio-macromolecules, is
helpful to understand the mechanisms of drug action in the body and can also establish a
relationship between the chemical structure and biological activities.
Based on the above facts, this paper focuses on the preparation of a new Cu(II) complex
with naphthalene-based acylhydrazone, which has been synthesized and characterized by X-ray
single-crystal diffraction. IR and UV-vis methods were used to ensure the structure of Cu(II)
complex. Magnetic properties of Cu(II) complex were studied by EPR spectra and magnetic
susceptibility studies; spectroscopic (UV-vis and fluorescence) and microcalorimetry methods
were assigned to evaluate the interaction of compounds with CT-DNA and BSA.
2. Experimental
2.1. Materials and methods
All reagents and chemicals were purchased from commercial sources and used without
purification. Elemental analyses were performed on a P.E.2400-II instrument. The structures
were determined by a Bruker Smart Apex II CCD diffractometer equipped with graphite
monochromated Mo-Kα radiation (λ = 0.71073 Å), solved by direct methods and refined by full-
matrix least-squares on F2 with the SHELXL program. IR spectra were recorded on a P.E.
GXIV5.0.1 instrument using KBr discs from 400-4000 cm-1. UV-vis spectra were obtained with
a TU-1900 spectrophotometer. EPR spectra were displayed using a Bruker EMX-10/12
spectrophotometer. Magnetic susceptibility experiments for [Cu2L2(NO3)2] were carried out with
a Quantum Design MPMS-XL-7 magnetometer under an applied magnetic field of 1000 Oe.
Thermal gravimetric analyses were investigated by a Mettler-Toledo TG-DSC1 HT instrument.
Viscosity measurements were carried out by a Ubbelohde viscometer. Interaction heat flows
3

between compounds with CT-DNA were measured with a C80 microcalorimeter. BSA binding
behavior of compounds was analyzed by a P.E. Fluorescence Spectrometer LS55 (λex = 280 nm).
2.2. Synthesis
2.2.1. Synthesis of C19H14N2O2·H2O (HL). HL was synthesized according to the previous report
of our laboratory [23]. 2-Hydroxy-1-naphthaldehyde (0.086 g, 0.5 mmol) and 4-hydroxy
phenylacetyl hydrazine (0.083 g, 0.5 mmol) were dissolved in 5 mL and 10 mL ethanolic
solution, respectively. Then the two solutions were mixed, giving a transparent yellow solution
which was refluxed for 4 h with stirring. Then it was cooled to room temperature and, after
3 days, yellow single-crystals were obtained. HL is soluble in MeOH, EtOH, DMSO and DMF
but insoluble in non-polar solvents and water. Anal. Calcd of HL (%): C, 67.45; H, 5.36; N, 8.28.
Found (%): C, 67.13; H, 5.35; N, 8.12, m.p. 250-251 °C. Λm = 1.35 S·cm2·M-1. The synthetic
route for HL is illustrated in scheme 1(a).
2.2.2. Synthesis of [Cu2L2(NO3)2]. HL (0.064 g, 0.2 mmol) was dissolved in 10 mL ethanol and
the pH was adjusted to 8~9 with NaOH solution. Cu(NO3)2·3H2O (0.048 g, 0.2 mmol) was
dissolved in 5 mL ethanol, then it was added dropwise into the solution of HL. The mixture was
refluxed for 4 h with stirring and then was filtered. After a week, brown single crystals of Cu(II)
complex were obtained. The complex is soluble in DMSO and DMF but insoluble in MeOH,
EtOH and water. Anal. Calcd of [Cu2L2(NO3)2] (%): C, 51.29; H, 3.40; N, 9.45. Found (%): C,
51.95; H, 3.17; N, 9.33. Λm = 77.94 S·cm2·M-1. When the m.p. of [Cu2L2(NO3)2] is above
300 °C, its color turns from brown to black. Values of Λm in DMSO (10-3 M) in room
temperature for HL and Cu(II) complex indicate that HL is a nonelectrolyte while Cu(II)
complex is an electrolyte [24]. The synthetic route of [Cu2L2(NO3)2] is shown in scheme 1(b).
4

OHC
HO
H
H
N
H
C
NH2NH2¡¤H2O
N
OCH3
NH2
N
EtOH, 80o , 4h
C
HO
EtOH, 80oC, 4h
O
O
O
HO
HO
HO
(a)
(b)
H
N
N
H
C
O
HO
H
H
C
O
N
Cu
O
N
O
O
N
O
Cu2+
NaOH
EtOH, 80oC, 5h
O
N
+
Cu
O
HO
HO
O
OH
O
O
N
N
C
H
H
Scheme 1. Synthetic routes for (a) HL and (b) [Cu2L2(NO3)2].
2.3. Thermal stability experiment
Thermal gravimetric analyses were investigated under nitrogen at heating rates of 5.00, 10.00
and 15.00 °C·min-1 from room temperature to 800 °C.
2.4. DNA Binding properties
UV-vis spectrophotometer measurements: the CT-DNA solution (0.1 M, pH = 7.9) was prepared
by dissolving CT-DNA in Tris-HCl buffer solution (250 mL) and its purity was checked by the
absorbance ratio A260/A280, of 1.8~1.9. [Cu2L2(NO3)2] (1.0×10-4 M) was dissolved in DMF and
Tris-HCl (5:95, v/v), the CT-DNA solution (50 μL for each time) was dropped into the solution
of [Cu2L2(NO3)2] (3 mL), the mixed solution was scanned.
Viscosity measurements: the viscosity titration experiments were carried out on a
Ubbelohde viscometer in a thermostated water-bath maintained at 250.01 °C. The concentration
of CT-DNA was kept constant (0.1 M), then different concentrations of the tested compounds
(0.005-0.025 M) were gradually added, and then the flowing time of the mixture was recorded.
Microcalorimetry measurements: solution of compound (1 mL) and Tris-HCl buffer
solution (1 mL) were added in the bottom of sample cell and reference cell, respectively, then
CT-DNA solution (2 mL) was added to both sample cell and reference cell; when the baseline
5

was stable, the solutions in upper and bottom cells were mixed, then the heat flows of the
reaction were recorded at 25 °C.
2.5. BSA Binding properties
BSA solution (0.1 M, pH = 7.2) was prepared by dissolving BSA in Tris-HCl-NaCl buffer
solution (50 mL). [Cu2L2(NO3)2] solution (1.0×10-4 M) was prepared by dissolving
[Cu2L2(NO3)2] in DMF and Tris-HCl-NaCl buffer (5:95, v/v). Then the solution of
[Cu2L2(NO3)2] (30 μL for each time) was dropped into the BSA solution (1.0×10-7 M, 3 mL) and
the mixed solution was monitored by a fluorescence spectrometer.
3. Results and discussion
3.1. IR Spectra
IR spectra are displayed in figure S1. Table 1 shows the main IR absorption data of compounds.
IR spectra of HL contain a strong C=O absorption band at 1660 cm-1 and a N-H absorption at
3201 cm-1 and 3489 cm-1; imine C=N absorption band appears at 1602 cm-1 [25]. The
disappearance of C=O and N-H frequencies in the Cu(II) complex is attributed to the enolization
of the keto functionality [26]. The shifting of C=N vibration to 1568 cm-1 proves its chelation
with copper. New M-N and M-O vibration bands are observed in the complex at 474 cm-1 and
646 cm-1, respectively, which are attributed to v(M-O) and v(M-N) for Cu(II) [27, 28]. The band
-1
at 1385 cm-1 is assigned to monodentate of NO3-1 groups comparing with the free NO3
(1380 cm-1) [29].
3.2. UV-Vis Spectra
UV-vis spectra of [Cu2L2(NO3)2] were recorded at room temperature in DMSO and CH3CN (10-
5 M). The significant electronic absorption bands of [Cu2L2(NO3)2] are shown in figures S2 and
S3. Bands at 266 nm (εmax = 132100 M-1cm-1) and 221 nm (εmax = 136100 M-1cm-1) are due to
ππ* transitions in DMSO and CH3CN, respectively. The bands at 331 nm (εmax = 53250 M-
6

1cm-1) in DMSO and 330 nm (εmax = 22350 M-1cm-1) in CH3CN are assigned to nπ*
transitions. Bands at 401-423 nm in DMSO (εmax = 48530 M-1cm-1) and 383-423 nm in CH3CN
(εmax = 13330 M-1cm-1) are associated with the ligand-to-metal charge-transfer (LMCT)
transition [30]. The spectra also show low-intensity broad bands (d-d transitions) at 579 nm (εmax
= 460 M-1cm-1) and 703 nm (εmax = 510 M-1cm-1) in CH3CN and DMSO, respectively. The high
εmax values for d-d bands show that the donor groups (N, O from HL) are coordinated to Cu(II)
-
ion in equatorial plane and NO3 occupy the axial position [31, 32].
3.3. EPR Spectra
The EPR spectra of [Cu2L2(NO3)2] in DMSO solution at 77 K, in solid state at 77 K and 298 K
were determined in the X-band mode using 100 kHz modulation; g factors were quoted relative
to the standard marker TCNE (g = 2.0023). Figure S4 shows the EPR spectra of [Cu2L2(NO3)2]
in solid state at 77 K and 298 K; the values of g|| and g are higher than 2.0023, suggesting that
the unpaired electron is localized in the dx2-y2 orbital of the Cu(II) ion [33]. There is a slight half-
field signal around 1560 G at 77 and 298 K because of the forbidden resonance transition of
Ms=2, showing weak antiferromagentic Cu···Cu interactions [34, 35] and suggesting the
formation of binuclear complex in the solid state [36-39]. Figure S5 shows the frozen EPR
spectrum in DMSO of the Cu(II) complex, which gives g|| = 2.1190, g = 2.0413, A|| = 164 G and
A = 39 G. The gav and Aav values are calculated using the equations: gav = (g||+2g)/3; Aav =
(A||+2A)/3, giving gav = 2.0672 and Aav = 81 G. Typical solution EPR spectrum of binuclear
complex in which two Cu(II) ions are connected via small bridges usually have a hyperfine
structure consisting of 7 lines. But frozen solution EPR spectrum of the Cu(II) complex have 2-
line hyperfine structures corresponding to Ms=1 transition and no half-field signal is observed
due to the forbidden magnetic dipolar transition for the Cu(II) complex, confirming that the
dimeric structure may undergo partial dissociation of Cu-O-Cu bonds with formation of O3-Cu-N
coordination in monomeric complex [40-42].
7

Bonding parameters α2 and β2 are calculated for [Cu2L2(NO3)2]; α2 represents the in-plane
σ-bonding, α2 = 1 indicates complete ionic character, whereas α2 = 0.5 indicates 100% covalent
bonding. The β2 parameter gives an indication of the covalency in-plane π-bonding; the smaller
β2 indicates the larger covalency of the bonding [43]. The value of α2 (= 0.59) is close to 0.5 and
β2 (= 0.43) is smaller, suggesting that the in-plane σ-bonding and in-plane π-bonding are
covalent in the Cu(II) complex.
3.4. Structure description of [Cu2L2(NO3)2]
The molecular structure of [Cu2L2(NO3)2] is illustrated in figure 1. The hydrogen bonds in
[Cu2L2(NO3)2] are shown in figure S6. The packing structure of [Cu2L2(NO3)2] is displayed in
figure 2. Crystal data are given in table 2 and selected bonds lengths and angles are listed in
table 3.
[Cu2L2(NO3)2] crystallized in the triclinic system, space group P1 with Z = 1 in the unit
cell. Each Cu(II) is chelated by a nitrogen and three oxygens from HL and an oxygen from
nitrate. The bond lengths of [Cu-N] and [Cu-O] are in agreement with similar reported data [44-
46], while the length of [Cu-N] is shorter than that of [Cu-O], which means nitrogen has better
coordination ability than the oxygen. Comparing with C-N single bond (1.47 Å) and C=N double
bond (1.273 Å) distances, the bond distance of [C12-N2] is 1.324(6) Å, which is shorter than C-
N single bond but longer than C=N double bond, due to the conjugation between C=O and C=N.
The bond length of [O2-C12] is 1.240(6) Å, between C=O double bond (1.233 Å) and C-O
single bond (1.336 Å); these data indicate that HL adopts enolic coordination with Cu(II) ions.
The environment of each Cu(II) ion can be described as a distorted rectangular pyramid
according to the ligand-metal-ligand angles [O1`-Cu1-O1] (= 79.34(14)°) and [O1-Cu1-O2] (=
171.32(13)°), the torsion angles varying between [N1-Cu1-O1-C1] (= 1.0(4)°) and [O1-Cu1-N1-
N2] (= -177.0(3)°). Each Cu(II) forms a quadrilateral structure by two hydroxyl oxygens in
binuclear coordination; five-membered [N1-N2-C12-O2-Cu1] and six-membered [O1-C1-C10-
C11-N1-Cu1] chelate rings are mainly planar. The crystal structure of [Cu2L2(NO3)2] is
8

stabilized by intermolecular hydrogen bonds N2-H2…O5 and O3-H3…O4 presented in figure
S6 and table 4. The packing structure of [Cu2L2(NO3)2] displays a configuration, which looks
like a canoe on the match.
3.5. Thermal stability analyses
Figure 3 shows TG-DTG curves of the compounds under nitrogen at 5.00 °C·min-1 heating rates.
TG-DTG curves at 10.00 and 15.00 °C·min-1 are similar with that at 5.00 °C·min-1. There are
four steps for thermal decomposition of [Cu2L2(NO3)2] (figure 3). The first step at 280.05 °C
-
with mass loss of 18.81% (calcd. 17.76%) can be assigned to the loss of NO3 and OH-. The
second step at 294.88 °C with mass loss of 18.01% (calcd. 17.08%) is from loss of hydroxy
benzene. The third step at 368.63 °C with mass loss of 5.86% (calcd. 6.29%) can be considered
as the loss of C=O. The fourth step is at 411.36 °C with mass loss of 3.71% (calcd. 3.60%),
indicating the loss of -CH2-.
There are two major steps for thermal decomposition of HL. The first step with 5.83%
weight loss (calcd. 5.33%) corresponds to elimination of one lattice water at 145.02 °C. The
lattice water is involved in the formation of hydrogen bonds, resulting in loss of lattice water at a
higher temperature. The second step is attributed to decomposition of hydroxy-naphthalene ring
at 323.01 °C with mass loss of 74.10% (calcd. 74.68%). Figure S7 shows the DTG curves of
[Cu2L2(NO3)2] and HL at three heating rates.
3.6. Magnetic properties of [Cu2L2(NO3)2]
The variable-temperature (2-300 K) magnetic susceptibility curves are shown in figure 4, where
M is the mole magnetic susceptibility and MT is the magnetic moment per Cu(II) ion. With
decreasing temperature, the M value reaches a maximum at TN = 2 K. The MT value at 300 K is
0.58 cm3mol-1K, which is lower than that of isolated binuclear Cu(II) ions (0.75 cm3mol-1K) and
indicates antiferromagnetic exchange between two Cu(II) ions [47, 48].
9

3.7. DNA Binding studies
Many small molecules bind to DNA through covalent and non-covalent interactions. In covalent
binding, small molecules interact with base pairs of DNA. Non-covalent interactions include
intercalation, electrostatic and groove binding. UV-vis spectroscopy is an effective method to
explore the interaction mode between small molecules and DNA [49].
The UV-vis spectra of compounds interacting with CT-DNA consist of bands at 207 nm
and 275 nm. As shown in figures 5 and 6, these bands show significant hypochromism
accompanied by a small red-shift; it is assigned to the ππ* transition, suggesting that
[Cu2L2(NO3)2] and HL bind to CT-DNA in an intercalative mode [50].
In order to compare the binding strength of [Cu2L2(NO3)2] and HL, the intrinsic binding
constants are calculated by equation (1) [51]:
[DNA]/[(a – f)] = [DNA]/[(b – f)]+1/ Kb[ (b – f)](1)
where [DNA] is the concentration of DNA, a, f and b are the extinction coefficients for the
compound in free solution, fully bound form, respectively. [DNA]/[(a–f)] versus [DNA] gives
the slope and the intercept, which equal to 1/[(a–f)] and (1/Kb)[ (b–f)], respectively; Kb is the
ratio of slope to the intercept. Kb is calculated to be 6.24(0.12)×106 M-1 and
3.09(0.006)×106 M-1 for [Cu2L2(NO3)2] and HL, respectively (figures S8 and S9), which reveals
that [Cu2L2(NO3)2] is more strongly bound to CT-DNA than HL. The Kb values at 106 M-1
comparing to similar binuclear Cu(II) complexes (103-105 M-1) [52, 53] are higher, showing that
the activity for [Cu2L2(NO3)2] interacting with CT-DNA is better than similar complexes.
Relative viscosity of CT-DNA in either the presence or absence of compound was
calculated from the following relation [54]:
η = (t-t0 ) / t0 (2)
where t is the observed flow time of the CT-DNA containing solution and t0 the flow time of the
buffer. Classical intercalation usually reflects an increase in the viscosity of DNA due to the
10

separation base pairs at the intercalation sites [55], whereas the groove-binding or electrostatic
mode causes less positive or negative or no change in the viscosity of DNA [56]. In this
experiment, as illustrated in figure 7, viscosity of CT-DNA increased with the addition of HL
and Cu(II) complex solutions, revealing their intercalative binding mode with CT-DNA.
3.8. Microcalorimetry studies
Microcalorimetry is a high-accuracy tool used to study the thermokinetic properties of
interaction between molecules [57-59].
Figure 8 shows thermogenic curves of compounds interacting with CT-DNA at 25 °C.
The processes are all endothermic. Table 5 lists the results of microcalorimetry of [Cu2L2(NO3)2]
and HL interacting with CT-DNA. The thermogenic curve of [Cu2L2(NO3)2] shows the
interaction occurs at 3.4 min and ends at 44.8 min, an endothermic peak appears at 4.9 min and
the reaction time lasted for 41.4 min, and the enthalpy change is 30.3 kJ·mol-1 (ΔH =
30.3 kJ·mol-1), while the thermogenic curve of HL shows the interaction occurs at 1.7 min and
ends at 28.9 min, an endothermic peak appears at 3.4 min and the reaction time lasted for
31.5 min, and the enthalpy change is 4.31 kJ·mol-1 (ΔH = 4.31 kJ·mol-1). The results indicate that
[Cu2L2(NO3)2] shows stronger interaction with CT-DNA.
3.9. BSA Binding studies
The interaction of compounds with BSA was studied by fluorescence quenching of BSA with
increasing concentration of compounds. The fluorescence of the protein is caused by tryptophan,
tyrosine and phenylalanine residues. The fluorescence intensities can be attenuated by binding a
small molecule. Figures 9 and 10 show the fluorescence intensities of BSA, which decreased
with increasing concentration of compounds. The Stern-Volmer equation [60] can be used to
describe the fluorescence quenching.
I0/I=1+Ksv[Q]=1+kqτ0[Q] (3)
11

where I0 and I are the steady-state fluorescence intensities in the absence and presence of
quencher, respectively, Ksv the Stern-Volmer quenching constant, [Q] the concentration of
quencher, kq the bimolecular quenching constant and τ0 the average lifetime of protein in the
absence of quencher, 10-8 s [61]. Ksv can be obtained by the slope from the plot of I0/I versus [Q].
Fluorescence quenching is usually classified as dynamic quenching or static quenching. The kq
values 1.9(0.3)×1011 M-1s-1 and 7.4(0.5)×1010 M-1s-1 corresponding to [Cu2L2(NO3)2] and HL
are higher than the maximum scatter collision quenching constant of diverse kinds of quenchers
for biopolymer fluorescence 2×1010 M-1s-1, indicating the existence of static quenching
mechanism of compounds interacting with BSA [62]. The Scatchard equation is:
log[(F0-F)/F] = logKq + nlog[Q] (4)
where Kq is the binding constant and n the binding sites. Figures S10 and S11 are plots of
log[(F0-F)/F] versus log[Q] and the binding constant and number of binding sites are listed in
table 6. The values of n indicate partial interaction of compounds with BSA. The biological
activity of interaction with BSA for [Cu2L2(NO3)2] is better than that of HL. However, it is
weaker (102-103 M-1) than other binuclear Cu(II) complexes (105 M-1) [63].
4. Conclusion
[Cu2L2(NO3)2] with a naphthalene ring has been synthesized and characterized. The structure of
[Cu2L2(NO3)2] can be described as a distorted rectangular pyramid in binuclear coordination in
the solid state, but may undergo partial dissociation with formation of monomeric complex in
solution. The apparent activation energy values (Ea) of thermal decomposition show that
[Cu2L2(NO3)2] is more stable than HL. There are magnetic exchange and antiferromagnetic
exchange interactions between two Cu(II) ions studied by EPR spectra and magnetic
susceptibility measurements, respectively. CT-DNA binding of compounds are determined by
UV-vis spectra and viscosity measurements, confirming intercalation. Interaction heat flows of
[Cu2L2(NO3)2] and HL with CT-DNA monitored with a C80 microcalorimeter show that the
12

enthalpy changes (ΔH) are 30.3 and 4.31 kJ·mol-1, respectively. Binding of compounds with
BSA is investigated by fluorescence spectra and the presence of static quenching and the values
of n indicate partial interaction between compounds with BSA. The results reflect that the CT-
DNA/BSA-binding activities of [Cu2L2(NO3)2] are better than HL.
Supplementary material
CCDC 987959 contain the supplementary crystallographic data for [Cu2L2(NO3)2]. The data can
be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/conts/retrieving.html.
Acknowledgements
The authors are grateful to the National Natural Science Foundation of China (Nos. 21073139,
21103135, 21373158 and 21301139) for financial support.
References
[1]
G.N. Ramesh, B. Prathima, Y. Subba Rao, Y.P. Reddy, K.S.R. Pai, A. Varada Reddy.
Arab. J. Chem., 9, S404 (2016).
[2]
[3]
J. Wang. X.R. Liu, Y.J. Sun, L.Y. Yan, S.Y. He. J. Coord. Chem., 64, 1554 (2011).
L. Somsak, K. Czifrak, M. Toth, E. Bokor, E.D. Chrysina, K.M. Alexacou, J.M. Hayes,
C. Tiraidis, E. Lazoura, D.D. Leonidas, S.E. Zographos, N.G. Oikonomakos. Curr. Med.
Chem., 15, 2933 (2008).
[4]
[5]
Q. Cheng, H. Li, D. Zhang. Med. J. Chin., 35, 395 (2010).
W.G. Gutheil, G. Reed, A. Ray, S. Anant, A. Dhar. Curr. Pharm. Biotechnol., 13, 173
(2012).
[6]
V. Magesh, J.P.V. Singh, K. Selvendiran, G. Ekambaram, D. Sakthisekaran. Mol. Cell.
Biochem., 287, 127 (2006).
13

[7]
[8]
[9]
E. Rasolofonjatovo, O. Provot, A. Hamze, J. Rodrigo, J. Bignon, J. Wdzieczak-Bakala,
D. Desravines, J. Dubois, J.D. Brion, M. Alami. Eur. J. Med. Chem., 52, 22 (2012).
S. Anbu, A. Paul, R. Ravishankaran, M.F.C. Guedes da Silva, A.A. Karande, A.J.L.
Pombeiro. Inorg. Chim. Acta, 423, 183 (2014).
M. Ganeshpandian, R. Loganathan, S. Ramakrishnan, A. Riyasdeen, M.A. Akbarsha, M.
Palaniandavar. Polyhedron, 52, 924 (2013).
[10] M.E. Bravo-Gómez, C. Campero-Peredo, D. Garcia-Conde, M.J. Mosqueira-Santillán, J.
Serment-Guerrero, L. Ruiz-Azuara. Polyhedron, 102, 530 (2015).
[11] C. Marzano, V. Gandin, M. Pellei, D. Colavito, G. Papini, G.G. Lobbia, E.D. Giudice, M.
Porchia, F. Tisato, C. Santini. J. Med. Chem., 51, 798 (2008).
[12] C. Santini, M. Pellei, V. Gandin, M. Porchia, F. Tisato, C. Marzano. Chem. Rev., 114,
815 (2014).
[13] M. Mohanraj, G. Ayyannan, G. Raja, C. Jayabalakrishnan. J. Coord. Chem., 69, 3545
(2016).
[14] Y.E. Alexeev, B.I. Kharisov, T.C. Hernández García, A.D. Garnovskii. Coord. Chem.
Rev., 254, 794 (2010).
[15] M.B. Bannwarth, T.E. Eidmann, K. Landfester, D. Crespy. Chem. Mater., 26, 1300
(2014).
[16] K.M. Ibrahim, I.M. Gabr, R.R. Zaky. J. Coord. Chem., 62, 1100 (2009).
[17] C.F. Wang, Z.J. Chen, K.D. Zhao, X.F. Chen, C.Y. Zhang, G.H. Sheng, H.L. Zhu. J.
Coord. Chem., 69, 2656 (2016).
[18] L.D. Xu, M. Hong, Y.G. Yang, J.C. Cui, C.Z. Li. J. Coord. Chem., 69, 2598 (2016).
[19] Y.P. Singh, R.N. Patel, Y. Singh, R.J. Butcher, P.K. Visshakama, R.K.B. Singh.
Polyhedron, 122, 1 (2017).
[20] S. Mondal, B. Pakhira, A.J. Blake, M.G.B. Drew, S.K. Chattopadhya. Polyhedron, 117,
327 (2016).
14

[21] P.R. Inamdar, R. Chauhan, J. Abraham, A. Sheela. Inorg. Chem. Commun., 67, 67
(2016).
[22] I.M. Gabr. J. Coord. Chem., 62, 3206 (2009).
[23] S.S. Zhao, L.L. Li, X.R. Liu, Z.C. Chen, Z.W. Yang. Acta Phys.-Chim. Sin., 33, 356
(2017).
[24] W.J. Geary. Coord. Chem. Rev., 7, 81 (1971).
[25] B. Shaabani, A.A. Khandar, H. Mobaiyen, N. Ramazani, S.S. Balula, L. Cunha-Silva.
Polyhedron, 80, 166 (2014).
[26] W.D. do Pim, T.R.G. Simoes, W.X.C. Oliveira, I.R.A. Fernandes, C.B. Pinheiro, F.
Lloret, M. Julve, H.O. Stumpf, C.L.M. Pereira. Cryst. Growth Des., 14, 5929 (2014).
[27] L.Q. Chai, Y.X. Li, L.C. Chen, J.Y. Zhang, J.J. Huang. Inorg. Chim. Acta, 444, 193
(2016).
[28] S.P. Santoso, A.E. Angkawijaya, Y.H. Ju, F.E. Soetaredjo, S. ismadji, A. Ayucitra.
J. Taiwan Inst. Chem. Eng., 68, 23 (2016).
[29] X.Q. Song, Z.P. Zang, W.S. Liu, Y.J. Zhang. J. Solid State Chem., 182, 841 (2009).
[30] P.B. Sreeja, M.R.P. Kurup, A. Kishore, C. Jasmin. Polyhedron, 26, 1427 (2004).
[31] E. Prenesti, P.G. Daniele, S. Toso. Anal. Chim. Acta, 459, 323 (2002).
[32] E. Prenesti, P.G. Daniele, S. Berto, S. Toso. Polyhedron, 25, 2815 (2006).
[33] R.R. Cheng, Z.L. Wu, Y.L. Hou, J. Dong, J.Z. Cui, B. Zhao. Inorg. Chem. Commun., 51,
95 (2015).
[34] N. Noshiranzadeh, M. Emami, R. Bikas, K. Slepokura. Polyhedron, 133, 155 (2017).
[35] T. Kurc, V.V. Adrabinska, I.T. Tyrk, M. Duczmal, M. Jerzykiewicz. J. Mol. Struct.,
1054-1055, 134 (2013).
[36] O.J. Singh, M. Damayanti, N.R. Singh, R.K.H. Singh, M. Mohapatra, R.M. Kadam.
Polyhedron, 24, 909 (2005).
[37] M. Bose, K. Ohta, Y. Babu, M.D. Sastry. Chem. Phys. Lett., 324, 330 (2000).
[38] A. Sreekanth, M.R.P. Kurup. Polyhedron, 22, 3321 (2003).
15

[39] S.P. Devi, S.M. Devi, N.S. Devi, R.K.H. Singh, M. Mohapatra, R.M. Kadam. Inorg.
Chem. Commun., 11, 1441 (2008).
[40] H.H. Repich, S.I. Orysyk, V.V. Orysyk, Y.L. Zborovskii, A.K. Melnyk, V.V.
Trachevskyi, V.I. Pekhnyo, M.V. Vovk. J. Mol. Struct., 1146, 222 (2017).
[41] L. Tom, N. Aiswarya, S.S. Sreejith, M.R.P. Kurup. Inorg. Chim. Acta (2018),
https://doi.org/10.1016/j.ica.2018.01.005.
[42] T. Hirohama, A. Chiba, M. Chikira, Y.K. Fujii. J. Inorg. Biochem., 98, 371 (2004).
[43] M.M. Bekheit, A.R. El-Shobaky, M.T.G. Allah. Arab. J. Chem., 10, S3064 (2017).
[44] J.W. Ren, X.R. Liu, Z.W. Yang, S.S. Zhao. Thermochim. Acta, 582, 17 (2014).
[45] A.A. Khandar, K. Nejati. Polyhedron, 19, 607 (2000).
[46] J. Jaskova, D. Miklos, M. Korabik. Inorg. Chim. Acta, 360, 2771 (2007).
[47] S.K. Barman, T. Mondal, D. Koley, F. Lloret, R. Mukherjee. Dalton Trans., 46, 4038
(2017).
[48] F.A. El-Saied, T.A. Salem, M.M.E. Shakdofa, A.N. Al-Hakimi, A.S. Radwan. Ben-Suef
Univ. J. Basic Appl. Sci. (2017), https://doi.org/10.1016/j.bjbas.2017.09.002.
[49] Z.H. Xu, F.J. Chen, P.X. Xi, X.H. Liu, Z.Z. Zeng. J. Photochem. Photobiol., A, 196, 80
(2008).
[50] N. Chitrapriya, V. Mahalingam, M. Zeller, K. Natarajan. Inorg. Chim. Acta, 363, 3685
(2010).
[51] C. Gökce, R. Gup. J. Photochem. Photobiol., B, 122, 15 (2013).
[52] L. Andrezalova, J. Plsíkova, J. Janockova, K. Konarikova, I. Zitnanova, M. Kohutova, M.
Kozurkova. J. Organomet. Chem., 827, 67 (2017).
[53] S. Elumalai, K. Muthusamy, V. Babu. Polyhedron, 61, 33 (2013).
[54] H.G. Li, Z.Y. Yang, B.D. Wang, J.C. Wu. J. Organomet. Chem., 695, 415 (2010).
[55] S. Satyanarayana, J.C. Dabrowiak, J.B. Chaires. Biochemistry, 32, 2573 (1993).
[56] S. Satyanarayana, J.C. Dabrowiak, J.B. Chaires. Biochemistry, 31, 9319 (1992).
[57] G. Buckton. Thermochim. Acta, 248, 117 (1995).
16

[58] Y. Feng, Y. Liu, C.L. Xie, S.S. Qu, Z.F. Le, H.Y. Sheng, M.S. Duan, X.C. Zhang.
Thermochim. Acta, 285, 181 (1996).
[59] Y. Liang, C.X. Wang, G.L. Zou, Z.Y. Wang, Y.W. Liu, S.S. Qu. Thermochim. Acta, 351,
21 (2000).
[60] N. Akbay, Z. Seferoglu, E. Gök. J. Fluoresc., 19, 1045 (2009).
[61] J. Wang, L.J. Liu, B. Liu, Y. Guo, Y.Y. Zhang, R. Xu, S.X. Wang, X.D. Zhang.
Spectrochim. Acta, Part A, 75, 366 (2009).
[62] G.W. Zhang, N. Zhao, X. Hu, J. Tian. Spectrochim. Acta, Part A, 76, 410 (2010).
[63] Z. Li, H. Yan, G.L. Chang, M. Hong, J.M. Dou, M.J. Niu. J. Photochem. Photobiol., 163,
403 (2016).
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Table 1. Main IR data of the compounds (cm-1).
-
Compound
HL
ν (N-O)(NO3 )
ν(N-H)
ν(C=N) ν(C=O) ν(M-O) ν(M-N)
-
3201, 3489
3311
1602
1568
1660
1625
-
-
[Cu2L2(NO3)2] 1385
474
646
Table 2. Crystallographic data for the compounds.
[Cu2L2(NO3)2]
HL [23]
Formula weight
889.76
338.35
Monoclinic
C2/c
Crystal system
Triclinic
P1
Space group
a/ Å
7.643(3)
8.627(4)
13.778(6)
72.438(6)
84.667(7)
88.368(7)
862.4(6)
1
29.950(13)
8.208(3)
13.227(6)
90
b/ Å
c/ Å
α/ °
β/ °
92.055(8)
90
γ/ °
Volume/ Å3
3250(2)
8
Z
Density (calculated)/ g·m-3
θ range for data collection
Reflections collected / unique
Goodness-of-fit on F2
R indices (all data)
1.713
1.383
2.48-25.10
1.36-25.10
4293 / 3030 [R(int) = 0.0377] 7672 / 2862 [R(int) = 0.0415]
1.056
1.103
R1 = 0.0726, wR2 = 0.1973
R1 = 0.1087, wR2 = 0.2110
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Table 3. Selected bonds lengths (Å), bond angles (°) and torsion angles (°) of [Cu2L2(NO3)2].
Bond lengths (Å)
Bond angles (°)
N1-Cu1-O1
N1-Cu1-O2
O1-Cu1-O2
O1`-Cu1-O1
O1`-Cu1-O6
N2-N1-Cu1
N1-Cu1-O6
O1-Cu1-O6
O2-Cu1-O6
Torsion angles (°)
O1-Cu1-N1-N2
O2-Cu1-N1-N2
O1`-Cu1-N1-N2
O6-Cu1-N1-N2
O1-Cu1-N1-C11
O2-Cu1-N1-C11
O1`-Cu1-N1-C11
O6-Cu1-N1-C11
Cu1-N1-N2-C12
Cu1-N1
Cu1-O1
Cu1-O2
Cu1-O6
Cu1-O1`
N1-N2
1.914(4)
90.80(14)
80.82(14)
171.32(13)
79.34(14)
80.06(13)
111.8(3)
-177.0(3)
5.3(3)
1.925(3)
1.974(3)
2.282(4)
2.010(3)
1.391(5)
1.324(6)
1.240(6)
118.0(4)
-75.9(3)
6.0(4)
-171.7(4)
-59.0(6)
107.2(4)
-3.4(5)
N2-C12
O2-C12
123.41(15)
98.84(13)
87.73(14)
Table 4. Hydrogen bonding geometry for [Cu2L2(NO3)2] (Å, °).
Compound
D-H…A
d(D-H) (Å) d(H…A) (Å) d(D-A) (Å) ∠DHA (°)
N2-H2…O5i
O3-H3…O4ii
0.86
0.82
2.17
2.04
2.982
2.855
155.84
170.82
[Cu2L2(NO3)2]
Symmetry code: i x+1, y, z; ii 1-x, 1-y, -z
Table 5. The main microcalorimetry data of compounds interacting with CT-DNA.
Compound
[Cu2L2(NO3)2]
HL
Start time (min) End time (min) Reaction time (min) ΔH (kJ mol-1)
3.4
1.7
44.8
28.9
41.4
27.2
30.3
4.31
19

Table 6. The quenching constant, binding constant and number of binding sites for
the interactions of compounds with BSA.
Compound
[Cu2L2(NO3)2]
HL
Ksv (M-1)
kq (M-1s-1)
n
Kq (M-1)
1.9(0.3)×103
7.4(0.5)×102
1.9(0.3)×1011
7.4(0.5)×1010
1.705(0.002)×103
1.21(0.01)×102
0.97
0.73
Figure captions
Figure 1. Molecular structure of Cu(II) complex.
Figure 2. Packing structure of Cu(II) complex.
Figure 3. Thermal curves for Cu(II) complex and HL.
Figure 4. MT vs T plot of Cu(II) complex.
Figure 5. UV-Vis absorption spectra of CT-DNA interaction with Cu(II) complex.
Figure 6. UV-Vis absorption spectra of CT-DNA interaction with HL.
Figure 7. Effect of increasing amount of HL, Cu(II) complex on the relative viscosity of CT-
DNA at 250.01 °C.
Figure 8. Thermogenic curves of Cu(II) complex and HL with CT-DNA.
Figure 9. Fluorescence spectra of interaction between BSA and Cu(II) complex.
Figure 10. Fluorescence spectra of interaction between BSA and HL.
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