A novel porphyrin derivative and its metal complexes: Electrochemical, photoluminescence, thermal, DNA-binding and superoxide dismutase activity studies

Article abstract of DOI:10.1016/j.molstruc.2015.10.013

In this study, a new porphyrin-Schiff base ligand (L) and its metal complexes (Cu(II), Fe(III), Mn(III), Pt(II) and Zn(II)) were synthesized. The starting material 4-ethyl-2,6-bis(hydroxymethyl)phenol (A) was synthesized from 4-ethylphenol and formaldehyd

Full text of DOI:10.1016/j.molstruc.2015.10.013

Accepted Manuscript
A novel porphyrin derivative and its metal complexes: Electrochemical,
photoluminescence, thermal, DNA-binding and superoxide dismutase activity studies
Savaş Purtaş, Muhammet Köse, Ferhan Tümer, Mehmet Tümer, Ayşegül Gölcü,
Gökhan Ceyhan
PII:
S0022-2860(15)30313-6
10.1016/j.molstruc.2015.10.013
MOLSTR 21858
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 19 August 2015
Revised Date: 8 October 2015
Accepted Date: 19 October 2015
Please cite this article as: S. Purtaş, M. Köse, F. Tümer, M. Tümer, A. Gölcü, G. Ceyhan, A novel
porphyrin derivative and its metal complexes: Electrochemical, photoluminescence, thermal, DNA-
binding and superoxide dismutase activity studies, Journal of Molecular Structure (2015), doi: 10.1016/
j.molstruc.2015.10.013.
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ACCEPTED MANUSCRIPT
In this study, in order to synthesize the novel porphyrin Schiff base ligand, we prepared both
4-ethyl-2,6-bis(hydroxymethyl)phenol and 4-ethyl-2,6-diformylphenol compounds. The
porphyrin Schiff base ligand is a novel compound. The compounds (A) and (B) were
characterized by the analytical and spectroscopic methods. Single crystals of these
compounds were obtained from the CHCl3-EtOH solution by the slow evaporation and their
structural characterizations were, first time, done by X-ray crystallography technique.

ACCEPTED MANUSCRIPT
A novel porphyrin derivative and its metal complexes: Electrochemical,
photoluminescence, thermal, DNA-binding and superoxide dismutase
activity studies
Savaş Purtaş, Muhammet Köse, Ferhan Tümer, Mehmet Tümer, Ayşegül Gölcü,
Gökhan Ceyhan
Chemistry Department, K.Maras Sütcü Imam University, 46100, K.Maras, Turkey
Abstract
In this study, a new porphyrin-Schiff base ligand (L) and its metal complexes (Cu(II), Fe(III),
Mn(III), Pt(II) and Zn(II)) were synthesized. The starting material 4-ethyl-2,6-
bis(hydroxymethyl)phenol (A) was synthesized from 4-ethylphenol and formaldehyde in the
alkaline media. The compound (A) was then oxidized to the 4-ethyl-2,6-diformylphenol (B).
The starting compounds (A) and (B) were obtained as single crystals. Structures of the
compounds (A) and (B) were determined by the X-ray crytallography technique. The
porphyrin ligand (L) and its metal complexes were characterized by the analytical and
spectroscopic methods. Electronic, electrochemical and thermal properties of the synthesised
compounds were investigated. Superoxide dismutase activities (SOD) of the porphyrin Schiff
base complexes were investigated and results were discussed. Additionally,the DNA (fish
sperm FSdsDNA) binding studies of the complexes were performed using UV-vis
spectroscopy. Competitive studies with ethidium bromide (EB) show that the compounds
interact efficiently with DNA through an intercalating way.
Keywords: Porphyrin-Schiff base, X-ray, superoxide dismutase activity, DNA-binding
Corresponding author: Mehmet Tümer
Tel.: +90 344 280 14 44, Fax: +90 344 280 13 52,
E-mail address: mtumer@ksu.edu.tr
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1. Introduction
Porphyrin compounds are the heterocyclic organic molecules and composed of four
modified pyrrole subunits inter-connected at their α-carbon atoms via methine bridges
(=CH−). Porphyrins are probably the most significant and common class of natural pigments
[1-3]. With their considerable chromophore structure and molecular symmetry metal
porphyrins have a noteable interest in their own right to physicists and chemists [4].
Tetraphenyl porphyrins have assumed a privilege role in various areas of disciplines, ranging
from molecular semiconductors [5] to non-linear optics [6]: in particular several features, such
as chemical and thermal stability, make porphyrins selectable as encouraging materials for gas
sensing applications. Unsymmetrical porphyrin, particularly tetraphenyl porphyrin derivatives
substituted having an expanded π-conjugated system at the meso-position, are very interesting
compopunds. There are some reports about porphyrin-Schiff base ligands and their metal
complexes [7,8].
DNA intercalators are generally small planar molecules including coherent aromatic
rings [9]. Nevertheless, the porphyrins are also known to bind and intercalate within DNA
[10]. The porphyrin ring system is larger and more complex than that of other known
intercalators and poses some fascinating questions for DNA-ligand interactions [11-14].
Mn(III), Fe(III) and Zr(III) complexes bind only by a non-intercalative mechanism to AT-rich
regions of DNA, however the metal-free ligand and its Cu(II) and Ni(II) complexes bind
intercalatively to GC-rich sequences and with less choice at TA sequences.
Copper and zinc containing Cu/ZnSOD enzyme is the maximum influential catalytic
diversity found in the mammalian cell plasma and extracellular spaces. This SOD enzym
-
catalyzes the dismutation of superoxide radical (O2 ) into molecular oxygen and hydrogen
peroxide via one electron redox cycle. With respect to normal cells, cancer cells have been
considered to cause large amount of O2• − production in the cell [15] and the SOD activity in
cancer cell was found to be lower than the normal cell [16-17]. Thus, synthetic SOD mimics
can be taken account of as an excellent device in mediating apoptosis by mentioning oxidative
stress caused by OH• radical.
In this work, a novel porphyrin-Schiff base ligand 4-ethyl-2,6-bis[5-(4-iminophenyl)-
10,15,20-triphenylporphyrin]phenol (L) and its Cu(II), Fe(III), Mn(III), Pt(II) and Zn(II)
complexes were synthesized (Scheme) and characterized by the elemental analyses, MALDI-
1
TOF mass, H(13C)NMR spectra, FT-IR and UV-vis spectra. Single crystals of both 4-ethyl-
2,6-bis(hydroxymethyl)phenol and 4-ethyl-2,6-diformylphenol compounds were obtained.
Their molecular structures were, first time, characterized by single crystal X-ray diffraction
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technique. Electrochemical, photoluminescence and thermal properties of the porphyrin Schiff
base ligand (L) and its metal complexes were investigated. SOD activities and DNA binding
properties of the porphyrin Schiff base ligand and its metal complexes were investigated.
2. Experimental
2.1. Materials and measurements
All reagents and solvents were of reagent-grade quality and obtained from commercial
suppliers (Aldrich or Merck). Elemental analyses (C,H,N) were performed using a LECO
CHNS 932. Infrared spectra were obtained using KBr disc (4000-400 cm-1) on a Perkin Elmer
Spectrum 100 FT-IR. The electronic spectra in the 200–900 nm range were obtained on a
1
Perkin Elmer Lambda 45 spectrophotometer. H and 13C NMR spectra were recorded on a
Bruker 400 MHz instrument and TMS was used as an internal standard and CDCl3 as solvent.
The thermal studies of the compounds were performed on a Perkin Elmer STA 6000
simultaneous Thermal Analyzer under nitrogen atmosphere at a heating rate of 10 °C/min.
The mass spectra of complexes were obtained in dihydroxybenzoic acid as MALDI Matrix
using nitrogen laser accumulating 50 laser shots using Bruker Microflex LT MALDI TOF
mass spectrometer.
The single-photon fluorescence spectra of the porphyrin-Schiff base compound (H2L)
and its metal complexes were collected on a Perkin Elmer LS55 luminescence spectrometer.
All samples were prepared in spectrophotometric grade solvents and analysed in a 1 cm
optical path quartz cuvette.
Cyclic voltammograms were recorded on a Iviumstat Electrochemical workstation
equipped with a low current module (BAS PA–1) recorder. The electrochemical cell was
equipped with a BAS glassy carbon working electrode (area 4.6 mm2), a platinum coil
auxiliary electrode and a Ag+/AgCl reference electrode filled with tetrabutylammonium
tetrafloroborate (0.1 M) in DMF and CH3CN solution and adjusted to 0.00 V vs SCE. Cyclic
voltammetric measurements were performed at room temperature in an undivided cell (BAS
model C–3 cell stand) with a platinum counter electrode and an Ag+/AgCl reference electrode
(BAS). All potentials are reported with respect to Ag+/AgCl. The solutions were
deoxygenated by passing dry nitrogen through the solution for 30 min prior to the
experiments, and during the experiments the flow was maintained over the solution. Digital
simulations were performed using DigiSim 3.0 for windows (BAS, Inc.). Experimental cyclic
voltammograms used for the fitting process had the background subtracted and were corrected
electronically for ohmic drop. Mettler Toledo MP 220 pH meters was used for the pH
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measurements using a combined electrode (glass electrode reference electrode) with an
accuracy of ±0.05 pH.
Data collection for X-ray crystallography was completed using a Bruker APEX2 CCD
diffractometer and data reduction was performed using Bruker SAINT [18]. SHELXS97 and
SHELXL2014/6 were used to solve and refine structures, respectively [19].
2.2. Preparation of the 4-ethyl-2,6-bis(hydroxymethyl)phenol (A)
4-Ethylphenol (25.0 g, 0.17 mol) was added to a stirred warm (70 °C) solution of
NaOH (10.60 g, 0.27 mol) in THF (200 mL). To the stirring mixture p-formaldehyde (45.0 g,
0.61 mol) was added and the mixture was stirred for 48 h at room temperature. THF was
removed on a rotary evaporator. The resulting solid was dissolved in distilled water (100 mL),
acidified with HCI (0.5 M) and extracted with diethylether. The diethylether solution was
dried over Na2SO4 and the solvent was removed on a rotary evaporator. The white crystalline
product was collected and dried in vacuo. (29.50 g, 67%). 1HNMR (CDCl3, TMS): δ 6.90 (s,
2H, Ar-H), 4.80 (s, 4H, -CH2OH), 2.60-2.55 (q, 2H, -CH2-), 1.19-1.23 (t, 3H, CH3). 13CNMR
(CDCl3, TMS): δ 125.94-152.60 (Ar-C), 63.70 (-CH2O), 27.94 (-CH2), 15.80 (-CH3).
FTIR(KBr)/cm-1: 3407 (CH2OH), 3325 (Ph-OH), 2973 (aryl CH), 1635, 1506 (aryl C-C).
2.2. Preparation of the 4-ethyl-2,6-diformylphenol (B)
Activated MnO2 (40 g) was added to CHCl3 (200 mL) in a 500 mL round bottom flask
equipped with an overhead stirrer and a water-cooled condenser. The mixture was heated to
reflux with stirring about 15 min, then the powder of the 4-ethyl-2,6-
bis(hydroxymethyl)phenol (5 g) was added. After being kept refluxing for 24 h, the reaction
was cooled to room temperature and filtered. The solid was washed by CHCl3 (40 mL x 5)
thoroughly until the filtrate was colorless. Then the filtrate was concentrated on a rotary
evaporator yielding a yellow solid. (2.62 g, 53%)
1HNMR (CDCl3, TMS): δ 9.10 (s, 2H, carbonyl-H), 7.70 (s, 2H, Ar-H), 2.57-2.58 (q, 2H, -
CH2-), 1.20-1.23 (t, 3H, CH3). 13CNMR (CDCl3, TMS): δ 190.45 (carbonyl-C), 125.30-
151.55 (Ar-C), 27.92 (-CH2), 15.83 (-CH3). FTIR(KBr)/cm-1: 3345 (Ph-OH), 2965 (aryl CH),
1660 (C=O), 1603, 1596 (aryl C-C).
2.3. Preparation of the 5,10,15,20-tetraphenylporphyrin (TPP)
TPP was synthesized by the known methods [20]. Melting point: > 200 °C. δH
(CDCl3)/ppm: 8.85 (s, 8H, pyr-CH), 8.29 (m, 8H, 4 x C6H5), 7.77 (m, 12H, 4 x C6H5), -2.71
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(s, 2H, pyrrole internal NH). FTIR (KBr, ν, cm–1): 3311 (NH), 3021 (aryl C-H), 1594
(CH=N)porphyrin, 1553 ( C-C)aryl, 1347 (C=C). UV-Vis [Toluene, λmax(nm), εmax (M-1cm-1)]:
416 nm ( 4.30 x 105), 515 ( 1.30 x 104), 550 ( 4.23 x 104), 592 ( 1.71 x 104), 648 ( 0.55 x 104).
2.4. Preparation of the 5-(4-Nitrophenyl)-10,15,20-triphenylporphyrin (TPP-NO2)
TPP-NO2 was obtained by the reaction of TPP and sodium nitrite in trifluoroacetic
1
acid according to the known method [21]. Melting: point > 200 °C. H-NMR: δH
(CDCl3)/ppm: 8.87 (m, 6H, pyr-CH), 8.77 (d, 2H, pyr-CH), 8.69 (m, 2H, C6H4), 8.40 (m,
2H, C6H4), 8.24 (m, 6H, 3 x C6H5), 7.75 (m, 9H, 3 x C6H5), -2.72 (s, 2H, pyrrole internal
NH). FTIR (KBr, ν, cm–1): 3315 (NH), 2988 (C-H), 1594 (CH=N)porphyrin, 1557 (C-C)aryl,
1515, 1344 (NO2), 1344 (C=C). UV-Vis [Toluene, λmax(nm), εmax (M-1cm-1)]: 418 (4.10 x
105), 514 (3.11 x 104), 549 ( 0.95 x 104), 589 ( 0.88 x 104), 646 ( 0.75 x 104).
2.5. Synthesis of 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2)
TPP-NH2 was obtained by the reduction of TPP-NO2 using SnCl2.2H2O as a reducing
agent in concentrated hydrochloric acid [22]. 1HNMR (CDCl3) δ: 8.93 (d, 2H, β-pyrrole), 8.86 (d,
2H, β-pyrrole), 8.85 (s, 4H, β-pyrrole), 8.20 (m, 6H, o-triphenyl), 8.01 (d, 2H, 4-
aminophenyl), 7.76 (m, 9H, m-/p-triphenyl), 7.09 (d, 2H, 4-aminophenyl), 4.04 (s, 2H,
amino), -2.72 (s, 2H, pyrrole internal NH). FTIR (KBr, ν, cm–1): 3318 (NH), 2973 ( C-H),
1615 (CH=N)pyrrole, 1506 (C-C)aryl, 1349 (C=C).
2.6. Preparation of 4-ethyl-2,6-bis[5-(4-iminophenyl)-10,15,20-triphenylporphyrin]phenol (L)
The porphyrin Schiff base ligand was synthesized as follows: TPP-NH2 (0.2 mmol,
126 mg) and the 4-ethyl-2,6-diformylphenol aldehyde compound (0.1 mmol, 178 mg) was
dissolved in 100 ml of dry toluene containing 4 Ǻ molecular sieves. The resulting solution
was refluxed until the disappearance of the TPP-NH2, monitored by TLC (30 h). The solvent
was removed under reduced pressure and the crude product was dissolved in CH2Cl2 and
filtered. Evaporation of the solvent gave purple solid. The obtained product was purified from
CHCl3-hexane (v/v, 1/3) solvent mixture. C98H68N10O, yield: 68%, Melting: point > 200 °C.
Color: purple. Elemental analyses: Found (calcd.)%: C, 84.02 (83.98), H, 4.85 (4.89), 10.95
(9.99). 1HNMR (CDCl3) δ (ppm): 8.93 (d, 2H, β-pyrrole), 8.88 (s, 4H, β-pyrrole), 8.71 (d, 2H,
β-pyrrole), 8.68 (s, H, CH=N (imine)), 8.45 (m, 6H, o-triphenyl-H), 8.02-7.80 (m, 9H+2H,
(m-phenyl-H) + (p-phenyl-H) + aminophenyl), 7.65 (s, 2H, diformyl-H), 2.61-2.59 (q, 2H, -
CH2-part of ethyl group), 1.25-1.22 (t, 3H, CH3-part of ethyl group), -2.70 (s, 2H, pyrrole
5

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internal NH). 13C-NMR (CDCl3) δ (ppm): 15.80, 27.88, 107.55, 110.30, 117.14, 119.65,
121.92, 126.85, 128.06, 134.54, 135.10, 141.65, 146.25, 150.26, 154.27, 164.90. FTIR (KBr,
ν, cm–1): 3324 (NH), 2973 (CH)aliphatic, 1617 (CH=N), 1575 (C-C)aryl, 1492 (CH=N)pyrrole
,
1349 (C=C). MALDI-TOF-MS, (m/z): Calculated: 1401.65; Found: 1402 [C98H68N10O]+.
2.7. Preparation of the Cu(II), Fe(III), Mn(III), Pt(II) and Zn(II) metal complexes of the 4-
ethyl-2,6-bis[5-(4-iminophenyl)-10,15,20-triphenylporphyrin]phenol (L)
The porphyrin Schiff base ligand (0.5 mmol, 0.700 g) was dissolved in CH2Cl2 (20
mL) solution and followed by addition metal salts [2 mmol, 0.273 g for ZnCl2; 0.342 for
CuCl2.2H2O; 0.542 for FeCl3.6H2O; 0.830 g for K2[Pt(Cl)4]; 0.464 g for Mn(AcO)3] in
CH3OH (20 mL). The reaction solution was refluxed for about 1 h. The extent of the reaction
was monitored by measuring the UV–Vis spectrum of the reaction solution every 10 min.
After cooling to room temperature, 200 mL distilled water was added to the reaction mixture
and extracted three times. Purity of the complexes were checked by t.l.c. studies.
LCu4Cl3: Yield: 87.6%, green solid. M.p. > 300 °C. Anal. Calcd. For [C98H63N10OCl3Cu4]:
C, 66.99; H, 3.61; N, 7.97 %; found: C, 67.06; H, 3.67; N, 7.92 %. FTIR (KBr, ν, cm–1): 3021
(C-H)aromatic, 2922, 2840 (C–H)aliphatic, 1619 (CH=N)imine, 1530 (C-C)aromatic, 1281 (C–O)phenolic
,
1002 (Cu-N)porphyrin,565 (M-O), 462 (M-N). MALDI-TOF-MS, (m/z): Calculated: 1757.15;
Found: 1757.15 [C98H63N10OCl3Cu4]+.
LPt4Cl3: Yield: 83.2 %, purple red solid. M.p. > 300 °C; Anal. Calcd. For
[C98H63N10OCl3Pt4]: C, 51.55; H, 2.78; N, 6.13 %; found: C, 51.60; H, 2.84; N, 6.17. FTIR
(KBr, ν, cm–1): 3015 (C-H)aromatic, 2918, 2850 (C–H)aliphatic, 1610 (CH=N)imine, 1518 (C-
C)aromatic, 1250 (C–O)phenolic, 1007 (Pt-N)porphyrin, 558 (M-O), 450 (M-N). MALDI-TOF-MS,
(m/z): Calculated: 2283.31; Found: 2284.57 [C98H63N10OCl3Pt4]+.
LZn4Cl3: Yield: 65.4%, purple red solid. M.p. > 300 °C. Anal. Calcd. For
[C98H63N10OCl3Zn4]: C, 66.70; H, 3.60; N, 7.94 %; found: C, 66.75; H, 3.55; N, 7.88 %.
FTIR (KBr, ν, cm–1): 3021 (C-H)aromatic, 2935, 2844 (C–H)aliphatic, 1621 (CH=N)imine, 1520 (C-
C)aromatic, 1227 (C–O)phenolic, 1005 (Zn-N)porphyrin, 580 (M-O), 456 (M-N). MALDI-TOF-MS,
(m/z): Calculated: 1764.61; Found: 1765.08 [C98H63N10OCl3Zn4]+.
LFe3Cl4(H2O): Yield: 81.3%, purple red solid. M.p. > 300 °C. Anal. Calcd. For
[C98H65N10O2Cl4Fe3]: C, 68.28; H, 3.80; N, 8.12 %; found: C, 68.34; H, 3.86; N, 8.17 %.
FTIR (KBr, ν, cm–1): 3023 (C-H)aromatic, 2930, 2845 (C–H)aliphatic, 1615 (CH=N)imine, 1544 (C-
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C)aromatic, 1230 (C–O)phenolic, 1002 (Fe-N)porphyrin, 530 (M-O), 450 (M-N). MALDI-TOF-MS,
(m/z): Calculated: 1723.97; Found: 1724.54 [C98H65N10O2Cl4Fe3]+.
LMn3(AcO)4(H2O): Yield: 80.1%, purple black solid. M.p. > 300 °C. Anal. Calcd. for
[C106H77N10O10Mn3]: C, 70.12; H, 4.27; N, 7.71 %; Found: C, 70.18, H, 4.32; N, 7.77 %.
FTIR (KBr, ν, cm–1): 3024 (C-H)aromatic, 2925, 2850 (C–H)aliphatic, 1680 (C=O)acetic acid, 1610
(CH=N)imine, 1547 (C-C)aromatic, 1240 (C–O)phenolic, 1011 (Mn-N)porphyrin, 570 (M-O), 460 (M-
N). MALDI-TOF-MS, (m/z): Calculated: 1815.62; Found: 1625.5 [C106H77N10O10Mn3-
Mn(AcO)2(H2O)]+.
2.8. X-ray Structural Determination
The structural properties of the starting compounds (A) and (B) were determined by
X-ray diffraction technique. Data for the starting compounds (A) and (B) were collected at
150(2)K° on a Bruker ApexII CCD diffractometer using Mo-Kα radiation (λ= 0.71073Å).
The structures were solved by direct methods and refined on F2 using all the reflections [19].
All the non-hydrogen atoms were refined using anisotropic atomic displacement parameters
and hydrogen atoms bonded to the carbon atoms were inserted at calculated positions using a
riding model. Hydrogen atom bonded to oxygen atoms were located from difference maps
and allowed to refine with temperature factors. Details of the crystal data and refinement are
given in Table 1. All the bond lengths and angles are within the normal ranges. All bond
lengths and angles in the phenyl ring have normal Csp2- Csp2 values with small distortions.
Bond lengths and angles for the starting compounds (A) and (B) are given in the
supplementary file.
2.9. Superoxide dismutase (SOD) activity studies of the transition metal complexes
SOD assay kit-WST was used to evaluate SOD activities of the complexes. In this
.-
method, xanthine oxidase aerobically oxidases xanthine to urate, producing O2 in the
process. 2-(4-Iodophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt (WST-1)
.-
scavenges the O2 formed in the reaction, which causes the reduction of the colourless WST-1
to the yellow WST-1 formazan. WST-1 formazan has a characteristic absorbance peak at
.-
440 nm, therefore, quantitative reduction of WST-1 to WST-1 formazan by O2 was
monitored spectrophotometrically at pH 7.8 on a UV-160A UV–Vis. Spectrophotometer,
Shimadzu (Japan) at 440 nm and 25 ºC for 20 min. In the presence of the complex being
tested, the absorbance values (at 440 nm) of the WST-1 formazan decrease. This is due to the
.-
complex competes with the WST-1 to scavenge the O2 . The rate of absorption changes was
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determined and the percent inhibition (IC50) of WST reduction to WST-1 formazan was
calculated. The WST-1 assay is an indirect method of analysis because the extent of the
reduction of the appearance of the yellow WST-1 formazan in the presence of a SOD mimic
is taken as a measure of SOD activity [23]. All reagents were obtained from Sigma–Aldrich
Chemical Co. Ltd. and assays were run in 1 mL of solution.
2.10. DNA binding studies of the ligand and its metal complexes
Double-strand FSdsDNA (Sigma) was used as received. The stock solution of DNA was
prepared by dissolving appropriate amount of DNA in Tris-HCl buffer (20 mM Tris–HCl, 20
mM NaCl, pH 7.0) by gentle stirring at room temperature and stored at 4 ºC for no longer
than a week. The ratio of the UV absorbance at 260 and 280 nm (A260/A280) was checked to be
ca. 1.86, indicating that the DNA is sufficiently free from protein contamination. The DNA
concentration per nucleotide phosphate [NP] was determined by the UV absorbance [24] at
260 nm after 1:20 dilutions using the known ε value of 6600 M−1cm−1.
3. Results and Discussion
3.1 Characterization of starting materials
In this study, in order to obtain a novel porphyrin Schiff base ligand (L), the 4-ethyl-
2,6-bis(hydroxymethyl)phenol (A) and 4-ethyl-2,6-diformylphenol (B) compounds were
synthesized and characterized by the analytical and spectroscopic methods. Single crystals of
these compounds were obtained from the CHCl3-EtOH solution by slow evaporation and their
structural characterizations were, first time, determined by X-ray crystallography technique.
Analytical and spectroscopic data of the compounds (A) and (B) are given in the experimental
1
section. In the H NMR spectrum of the starting compound (A), the signal at the 6.90 ppm
may be assigned to the two protons of the aromatic ring. The methylene protons of the -CH2O
groups are shown at the 4.80 ppm. The CH3 and CH2 protons of the ethyl group on the
aromatic ring were shown as multiplets in the 1.19-1.23 and 2.55-2.60 ppm range,
13
respectively. In the C NMR spectrum, the signals in the 125.94-152.60 ppm range can be
attributed to the aromatic ring carbon atoms. The signals at the 63.70, 27.94 and 15.80 ppm
may be assigned to the carbon atoms of the CH2O, -CH2 and -CH3 groups, respectively. In the
FTIR spectrum of the (A), the OH vibrations of the aliphatic CH2OH and phenolic Ph-OH
1
groups were shown at the 3407 and 3325 cm-1, respectively. In the H NMR spectrum of the
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dicarbonyl compound (B), the signal at 9.10 ppm may be assigned to the protons of the
carbonyl groups. The aromatic ring protons were shown at the 7.70 ppm. The CH3 and CH2
protons were shown as multiplets in the 1.20-1.23 and 2.57-2.58 ppm range, respectively. In
13
the C NMR spectrum, the carbon atoms of the carbonyl groups were shown at the 190.45
ppm. The signals in the 125.30-151.55 ppm range can be attributed to the aromatic carbon
atoms. The aliphatic carbon atoms were shown at the 27.92 (-CH2) and 15.83 ppm (-CH3). In
the FTIR spectrum of the compound (B), the vibration band at the 3345 cm-1 can be attributed
to the phenolic OH group. The vibration of the carbonyl group were shown at the 1660 cm-1.
3.2 X-ray structures of 4-ethyl-2,6-bis(hydroxymethyl)phenol(A) and 4-ethyl-2,6-
diformylphenol (B)
The structure of the (A) was solved in monoclinic crystal system, P2(1)/c space
group with Rfinal value of 0.0408. Molecular structure of the compound (B) is shown in Fig. 1.
The asymmetric unit contains two independent molecules differing in the conformation of
alcohol arms and hydrogen bonding interactions within the structure. The C−O bond distances
in the structure are in well agreement with similar structures with different substitute groups
on the p- position [25-27]. The molecules form centrosymmetric dimers held together by two
complementary hydrogen bonds (Fig. 2). The structure is stabilised by intermolecular O−
H····O hydrogen bonds resulting in a 2D hydrogen bond network and the compound does not
show intra-molecular hydrogen bonding within the structure. There are also π-π stacking
interactions between the two adjacent aromatic rings with a centroid–centroid separation of
4.100 A°. Packing diagram of the starting compound (B) are shown in Fig. 2.
Perspective view of the compound (A) is shown in Fig. 3. The compound (A)
crystallizes in triclinic crystal system, P 1 space group with unit cell parameters a=
7.6563(6), b= 7.8598(7), c= 8.4085(7) Å, α= 73.2310(10), β= 71.0790(10), γ= 66.6050(10)°,
V=431.81(6) Å3 and Z=2. The aldehyde (C1=O1 and C10=O3) distances are 1.211(14) and
1.2253(14) Å respectively, which are in the range of C=O double bond character and in good
agreement with literature values of similar compounds [28,29]. The phenolic group (Ph-OH)
involves in intra-molecular hydrogen bonding with one of the aldehyde groups (O2····O3=
2.6508(12) Å) forming a S(6) hydrogen bonding motif. Two aldehyde molecules are linked by
two inter-molecular complementary hydrogen bonds O2−H2····O3 [−x+1,−y,−z+2] resulting
2
in a D2 (4) hydrogen bonding motif (Fig. 3). Weaker hydrogen bond type CH····O
interactions were also observed in the structure. Hydrogen bonded dimers are linked by π-π
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interactions within the structure. Crystal packing of the compound is determined by π-π
interactions (Fig. 4).
3.3 Characterization of the porphyrin-Schiff base ligand (L) and its complexes
5-(4-Aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2) was prepepared by the
reduction of nitro analogue 5-(4-nitrophenyl)-10,15,20-triphenylporphyrin (TPP-NO2). TPP-
NH2 was then used to prepare the porphyrin Schiff base ligand 4-ethyl-2,6-bis[5-(4-
iminophenyl)-10,15,20-triphenylporphyrin]phenol (L). Although the TPP-NH2 compound has
the assymmetric nature, synthesized porphyrin Schiff base ligand (L) has the symmetric
structure. Purification of the porphyrin based compounds is considerably hard and therefore,
the yields of these compounds are very low. Crystallization technique is not suitable in the
purification of TPP, TPP-NO2 and TPP-NH2 because these compounds are soluble in same
solvents. Therefore, the column chromatography method was used for this purpose. The
ligand (L) is soluble in THF, DMF, DMSO, toluene, CH2Cl2, etc. The ligand and its metal
complexes are very stable compounds at room temperature without decomposing. There are a
few reports about porphyrin Schiff base ligand and its metal complexes obtained from the 5-
(4-aminophenyl)-10,15,20-tris(4-nitrophenyl)porphyrin and 4-formylphenol derivative [30].
These compounds are called as “Push-Pull Porphyrins”.
All porphyrine derivatives were characterized by the analytical and spectroscopic
methods. Proposed structures of the porphyrin Schiff base ligand and its complexes were
given in Scheme. In order to determine the structure of the porphyrin Schiff base ligand (L),
1H(13C) NMR spectra have been carried out and obtained data are given in the experimental
section. 1H NMR spectrum of the ligand was measured in deuterated chloroform (CDCl3) as a
solvent. In the spectrum of the porphyrin Schiff base ligand, the eight protons of β-pyrrole
separated into two groups, which exhibited the two β-pyrrolic protons near C=N groups were
in a different chemical environment to the another six protons. The signals at 8.93, 8.88 and
8.71 ppm can be attributed to the β-pyrrole protons. This signal is located at a very low field
as the delocalization of electron on the pyrrole ring. The unsymmetrical chemical
environment of these protons exhibited the influence of the extended π structure or the strong
electron donating effect of the ethoxy and hydroxy groups. A singlet at 8.68 ppm may be
assigned to the proton of the CH=N group of the porphyrin Schiff base ligand (L). The
protons of the phenyl rings bonded on the porphyrin ring were shown as multiplet in the 8.45-
7.80 ppm range. The protons of the diformyl ring were shown as a singlet signal at 7.65 ppm.
The signals in the 2.61-2.59 ppm range can be attributed to the protons of the –CH2- group.
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The triplets in the 1.25-1.22 ppm range may be assigned to -CH3 protons. The singlet of the
NH peak (due to rapid exchange of N-H protons) is found to be very high field (-2.70 ppm),
since they are located within the shielded core of the porphyrin ring.
13C NMR spectrum of the ligand (L) shows six sharp signals (121.92 (Cmeso), 126.85
(Cm,m'), 128.06 (Cp), 134.54 (Cβ), 135.10 (Co,o'), 141.65 (Cp') ppm) and a very broad signal
(146.25 ppm) for α-carbon atoms. The carbon atom of the azomethine group was shown at
164.90 ppm. The signals at 15.80 and 27.88 ppm can be attributed to the carbon atoms of the
ethyl group on the diformyl ring.
In order to investigate the mass spectral properties of the ligand and its metal
complexes, MALDI-TOF-MS studies were performed. The MALDI-TOF spectrum of the
ligand (L) is shown in Fig. 5 and obtained data are given in the experimental section. The
spectra of the Cu(II) and Mn(III) complexes are given in the supplemantary material. As seen
from the obtained data, the MALDI-MS spectra results confirm the proposed structures for
the compounds. In the spectrum of the porphyrin Schiff base ligand (L), the molecular ion
peak [M+H]+ was shown at m/z= 1402.66 as a main peak. On the other hand, the Cu(II),
Fe(III) and Zn(II) complexes show the molecular ion peaks at m/z= 1757.15, 1724.54 and
1765.08, respectively. In the MALDI-MS spectrum of the Pt(II) complex, the peak at m/z=
2284.57 may be assigned to the molecular ion [M+H]+. In the spectrum of the Mn(III)
complex, the molecular ion peak was not obsrved, instead, the peak at m/z= 1625.5 can be
attributed to the [C102H70Mn2N10O5]+ ion. In the course of formation of this ion, the
[Mn(AcO)2(H2O] group from the main complex was seperated. The main peak at m/z=
1398.42 can be attributed to the free ligand [M]+ ion.
Infrared spectral data of the TPP, TPP-NO2, TPP-NH2, L and transition metal
complexes are given in the experimental section. As shown also from the spectral data, the
FTIR absorption frequencies were different from free porphyrin Schiff base ligand and its
metal complexes. It was found that the N-H bond stretching and bending frequencies of the
TPP, TPP-NO2, TPP-NH2 and L located in the 3324-3311 cm-1 range and at ~964 cm-1. In the
spectra of the TPP, TPP-NO2 and TPP-NH2 compounds, the bands in the 2988-3021 cm-1 may
be assigned to the C-H bond of the benzene and pyrrole rings. The bands in the 1494-1480
and 1344-1349 cm-1 range can be attributed to the C=C stretching mode and the C=N
stretching vibration, respectively. In the spectrum of the free porphyrin Schiff base ligand, the
stretching band at 1618 cm-1 can be attributed to the azomethine group. In the spectra of the
complexes, the CH=N vibration were shown in the 1621-1610 cm-1 range and this situation
shows that the nitrogen atom of the azomethine group coordinated to the metal ions. When the
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metal ions were inserted into the porphyrin ring, the N-H bond vibration frequency (Fig. 6) of
free base porphyrins disappeared and the characteristic Fe-N bond formed in the range of
1011-1002 cm-1, which indicated the formation of iron porphyrin compounds [31]. The M-O
and M-N band vibrations were shown in the 580-530 and 462-450 cm-1 range. The FAR
characterization of M-Cl bond vibration (M: Cu(II), Fe(III), Pt(II) and Zn(II)) located at 357-
374 cm-1.
3.4 UV-Vis spectral properties
In order to determine the solvent effect, the electronic properties of the synthesized
porphyrin based compounds were investigated in the DMSO, DMF, CH2Cl2 and toluene
solutions. Obtained Uv-vis absorption spectral data of the TPP and TPP-NO2 compounds are
given in the experimental section. The electronic absorption spectral data and the molar
extinction coefficients of the TPP-NH2, porphyrin Schiff base ligand (L) and its transition
metal complexes are given in Table 2. The UV-vis spectra of the TPP-NH2, porphyrin Schiff
base ligand and its transition metal complexes in the DMF solution are given in Fig. 7. As
shown also from obtained data, the UV–vis spectra of TPP and TPP-NO2 compounds showed
the bands centered at 416, 418 nm (Soret band), and four Q bands absorptions in the 515- 648
and 514-646 nm range, respectively. It could also be observed that the absorption band in the
UV-vis region of free porphyrin compound with –NO2 group at 418 nm, which revealed the
red shift compared to free TPP compound (2 nm). The reason might be that the strong
electron-withdrawing –NO2 group decreased the electronic density of the porphyrin ring.
Thus, the energy levels of π1 and π2 orbits were increased and the energy gap between HOMO
and LUMO of the porphyrin ring became smaller. The π-π* electron excitation of the
porphyrin ring required absorbing the light of smaller energy (longer wavelength),
accordingly the absorption band (Soret band) occurred red shift and located in the long
wavelength region. In the spectra of the TPP-NH2 compound in different solutions, the Soret
band were highly red shifted to 480 nm ( 60 nm). Q bands of this compound are four pieces
and these bands were observed in the 517-652 nm range. In the spectrum of the porphyrin
Schiff base ligand, one Soret band and four weak Q bands were observed. The ligand, aside
from Soret and Q bands, a new absorption band at 379 nm appeared can be attributed to the π-
π* transitions of the azomethine group. The absorption spectra of the porphyrins do not show
n- π* transitions owing to the symmetry of the n-orbitals and asymmetry of the π-orbitals in
point of the plane of the porphyrin compound.
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Soret bands shifted to the lower wavenumbers in the 478-483 nm range in DMSO,
DMF, CH2Cl2 and toluene solutions. This red shift is owing to the hyperconjugation on the
porphyrin Schiff base molecule by the π electron delocalization. On the other hand, Q bands
were shown in the 514-649 nm range. The relative intensities of Q bands are in order of IV >
III > II > I. This situation is consistent with the literature data [32].
The interference of Cu(II), Fe(III), Mn(III), Pt(II) and Zn(II) metal ions into the
porphyrin ring caused blue- or red-shift of 3-5 nm of the related Soret band as well as a
decreasing number of Q bands in their UV–vis spectra. This is because when the hydrogen
ions of N-H was replaced by the metal ions, the symmetry of the porphyrin ring increases. In
the UV-vis spectra of the LCu4Cl3 complex in the different solvents, Q band at 516 nm
disappeared and other three bands at 539, 540 and 541 nm shifted to shorter wavelenghts
compared to the ligand (L). Soret bands of the complexes shifted to the shorter wavenumbers
(413-483 nm range). Q bands of the complexes were shown in the 503-684 nm range.
Quantity of the Q bands were determined as two, three or four in the transition metal
complexes and this situation is agreed with the literature data [33-36].
3.5 Photoluminescence properties
The photoluminescence properties of the ligand (L) and its metal complexes were
investigated in DMF solution and different concentrations (1.0x10-5-1.0x10-7 M) at room
temperature. The obtained data are given in Table 3a,b. The emission and excitation spectra of
the compounds L and LCu4Cl3 were shown in Fig. 8. The excitation spectrum of the free
ligand (L) shows one peak at 383 nm. Depending upon decreasing of the concentration, the
intensity of the excitation peak decreases and shifts to the lower wavelenghts. The emission of
the free porphyrin Schiff base ligand shows one strong peak at 659 nm, seems to be free
porphyrin compound in different solvents [37]. One of them is S2 (B band) and the other is S1
(Q band). The fluorescence emission of the B (Soret) band is attributed to the transition from
the second excited singlet state S2 to the ground state S0, S2 → S0. The Soret emission band
was about two orders of magnitude weaker than the S1 → S0 transition of the Q band
emission.
In the excitation spectra of the transition metal complexes, the Cu(II) and Fe(III)
complexes showed one band at 356 nm in 1.0x10-3 M concentration. Against to the lower
concentrations, the band at 356 nm shifted to the longer wavenumbers at 376 and 372 nm,
respectively [38]. The Zn(II) complex indicates the excitation band. The band at 350 nm in
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1.0x10-3 M concentration shifted to 366 nm in the lower concentrations. In the excitation
spectra of the Mn(III) and Pt(II) complexes, only one band at 352 and 397 nm was observed,
respectively. In the lower concentrations, the band shifted to lower wavenumbers.
Concentration differences have effect on the excitation spectra of the porphyrin Schiff base
ligand and its transition metal complexes. On the other hand, ethyl group on the benzenoid
ring has the electron donating property to the aromatic ring by the mesomeric and inductive
effects. Electron-donating effect falled the energy difference between HOMO and LUMO,
and cause λ shift to red direction.
In the emission spectrum of the Pt(II) complex, in 1.0x10-3 M solution, the a band with
the high intensity at 641 nm was shown, and this band shifted to the lower wavenumber (650
nm) in the 1.0x10-7 M solution. While the Mn(III) complex showed the emission band at 673
nm in 1.0x10-3 M concentration, the Cu(II), Zn(II) and Fe(III) complexes indicated the bands
at 704, 667 and 617 nm, respectively. The emission band of the Cu(II) complex shifted to
lower wavelenght than the other complexes. Other emission bands show blue shift to 617 nm.
On the other hand, the emission band of the Fe(III) complex also shifted to the blue region.
3.6 Thermal properties
Thermal stabilities of the ligand and its metal complexes were studied in the 20-1000
°C temperature range under N2 atmosphere. The Cu(II) complex begins to decompose at 90
°C, and this mass loss may be attributed to the adsorbed water molecules. About 3.93% of the
mass has been lost. In the first decomposition process, the Fe(III) and Mn(III) complexes
showed the mass lost at about 120 °C and this can be attributed to the coordinated water
molecules. In the 200-300 °C temperature range, coordinated chloride ions, except the
Mn(III) complex, move away from the structures [39]. In this step, about 8.50% of the mass
of the complexes was lost. In the Mn(III) complex, coordinated acetate ions were removed at
about 280 °C temperature. At this temperature, the mass loss of the complex corresponds to
13.76% of total mass. The subsequent decomposition of the Pt(II), Fe(III) and Mn(III)
complexes start at about 405 °C, and continue up to 850 °C. On the other hand, the last
decomposition of the Cu(II) and Zn(II) complexes begins at 470 °C and continues up to 1000
°C. After the organic moiety (L) of the complexes decomposed, the metal oxides (CuO, ZnO,
Fe2O3, PtO and Mn2O3) formed at higher temperatures. The Cu(II) and Zn(II) complexes have
the higher thermal stability than the other complexes. Order of thermal stability is
Cu(II) > Zn(II) > Pt(II) > Fe(III) > Mn(III).
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3.7 Electrochemical properties
Electrochemical properties of the porphyrin Schiff base ligand and its metal complexes
were investigated in DMF-0.1 M Bu4NBF4 as supporting electrolyte at 293 K. All potentials
quoted refer to measurements run at a scan rates in the 100–1000 mVs-1 range and against an
internal ferrocene–ferrocenium standard, unless otherwise stated. The electrochemical studies
were studied in the 1 x 10-3 and 1 x 10-4 M DMF solutions and obtained data are given in
supplementray file. The cyclic voltammograms of the ligand L (a) and its Pt(II) (b) complex
are shown in Fig. 9. The voltammograms were recorded in the range from -2.0 to 2.0 V vs
Ag+/AgCl. In 1x10-3 M DMF solution, the free porphyrin Schiff base ligand (L) has the two
anodic peak potentials in the -0.74-0.54 V range at 100-1000 mV/s scan rates. In addition, the
ligand has one anodic peak in the -0.11-(-0.15) V range. On the other hand, in 1x10-4 M DMF
solution, the ligand has two anodic and cathodic peaks in the -054-0.39 V and -1.24-(-0.29) V
range, respectively, at all scan rates. In these concentrations, all redox processes are
irreversible for free ligand. In 1x10-3 M DMF solution, the Cu(II) complex shows the
reversible redox processes at 0.27/0.28 V, 0.28/0.29 V, 0.29/0.30 V, 0.30/0.31 V and
0.31/0.32 V couples, respectively. But, in 1.0x10-4 M DMF solution, the complex has two
anodic and cathodic peaks in the -0.54-0.39 and -1.24-(-0.29) V, respectively, and these redox
processes are irreversible. In 1x10-3 M DMF solution, the Pt(II) complex has quasi-reversible
redox processes in the 0.55-0.74 V (Epa-Epc) range. In 1x10-4 M DMF solution, the Pt(II)
complex has irreversible redox processes in the 0.10-0.79 V range. The Zn(II) complex shows
irreversible redox processes in the 1.0x10-3 M solution, however these redox processes
became reversible in the 1.0x10-4 M solution at all scan rates. The Fe(III) and Mn(III)
complexes indicate one or two anodic and cathodic peak potentials in the -0.60-0.67 and -
1.04-0.79 V, respectively and these processes are irreversible. By the increasing of the scan
rate, while the cathodic peak potentials shifted to the negative regions, the anodic peaks were
shifted to the more possitive regions. When the concentration of the solution of the ligands
decreases to 1x10-4 M, the anodic and cathodic peak potentials data were both reduced and
increased.
3.8 SOD Activity studies
.-
Measuring SOD activity is rather difficult, since the O2 free radical has a short half-
life in neutral aqueous solution. There are many direct and indirect methods reported for
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measuring the SOD activity. The direct measurement of SOD activity falls into two
categories: stopped-flow kinetic analysis and pulse radiolysis [40]. Cyctochrome c and
nitrobluetetrazolium (NBT) are the most commonly used redox indicators due to their
convenience and ease of use [41,42]. In these methods, xanthine/xanthine oxidase generates
steady-state low levels of superoxide. On the other hand, NBT has some disadvantages such
as poor water solubility of the formazan dye and the interaction with the reduced form of
xanthine oxidase.
The SOD activity of porphyrine Schiff base metal complexes were evaluated by a
modified indirect chemical method [43]. The results of our complexes and some literature
data are shown in Table 4. The SOD test results indicated that these compounds could be
considered as good SOD-mimics, as compared with native bovine Cu, Zn-SOD and some
related complexes listed in Table 4. The SOD activity of the Mn3+, Fe3+, Zn2+ and Pt2+ are
similar IC50 values and slightly higher than that of Cu2+ complex. The dismutation of
superoxide to molecular oxygen and hydrogen peroxide by the complexes is shown in the
equation below.
Direct comparisons of SOD activity of complexes with other related complexes are
somewhat complicated due to diverse methodology used for the formation of superoxide.
Acoording to IC50 values, the complexes exhibit lower activity than Cu/ZnSOD (native
bovine) [43] and manganese porphyrine complex [MnTM-4-PyP]Cl5 [44]. However, the
manganese salen complex (EUK-8) [45,46] shows similar IC50 value to the complexes tested
in this study.
3.9 DNA binding properties
The porphyrins and their metal complexes are known to bind to DNA via both
covalent and/or non-covalent interactions [47]. In covalent binding, the labile porphyrin part
of the complexes is replaced by a nitrogen base of DNA such as guanine N7. Moreover, the
non-covalent DNA interactions include intercalative, electrostatic and groove (surface)
binding of compounds along outside of DNA helix, along major or minor groove. It has been
reported that FSdsDNA can provide three distinctive binding sites for all compounds; namely,
groove binding, electrostatic binding to phosphate group and intercalation [48]. This behavior
is of great importance with regard to the relevant biological role of porphyrins and metallo
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porphyrins in the body. The interaction can be studied with UV spectroscopy in order to
investigate the possible binding modes to FSdsDNA. The changes observed in the UV spectra
upon titration may give the evidence of the existing interaction mode, since a hypochromism,
due to π-π* stacking interactions, may appear in the case of the intercalative binding mode,
while red-shift may be observed when the DNA duplex is stabilized. In UV titration
experiments, the spectra of FSdsDNA in the presence of each compounds have been recorded
for a constant compounds concentration in diverse [ligand or complex]/[FSDSDNA] mixing
ratios (r). Fig. 10 shows the spectral changes occurred in 1x10-6 M methanolic solution of the
ligand (L) upon addition of increasing amounts of FSdsDNA. Even though no appreciable
change in the position of the intraligand band of the ligand (L) and its metal complexes are
observed by addition of different initial concentration of FSdsDNA (0.4 ppm for L, 0.5 ppm
for LCu4Cl3 and LZn4Cl3 and 1 ppm for LPt4Cl3). The intensity of the band centred at 415.7
nm for the ligand (L) (from 415.7 to 421.6 for L (Amax, from 0.63 to 0.24), from 413.2 to
419.9 for LCu4Cl3 (Amax, from 1.29 to 0.52), from 432.05 to 434.1 for LZn4Cl3 (Amax, from
0.3 to 0.25) and from 416.1 to 422.5 for LPt4Cl3 (Λmax, from 0.43 to 0.19) decreased in the
presence of DNA. Upon increasing DNA concentration, the absortion intensity is increased
for the ligand (L) over again. In general, the hyperchromism and hypochromism shifts are the
spectral features of DNA concerning changes of its double helix structure. The
hyperchromism means the breakage of the secondary structure of DNA. The hypochromism
shows that binding of complex to DNA can be due electrostatic effect or intercalation which
may stabilize the DNA duplex. Additionally, the existence of a red-shift is indicative of
stabilization of DNA duplex [48]. On the other hand, addition of FSdSDNA to the ligand (L)
results in slight hypochromism of the band at λmax= 415.7 nm, which is accompanied by a
red-shift of 5.9 nm (up to 421.6 nm). These spectral changes may be evidence of a possible
intercalation, which could subsequently stabilize the DNA duplex [49]. For all complexes, the
band centered at 413.2, 432.05 and 416.1 nm exhibits a less pronounced chromism of 40.31 %
for copper complex, 83.33 % for zinc complex and 44.20% for the platinium complex upon
addition of FSdsDNA accompanied with a red-shift (Fig. 11). The binding strength of the
ligand (L) and its complexes with FSdsDNA is mirrored in the intrinsic binding constant Kb,
which represents the binding constant per DNA base pair and can be obtained by monitoring
the changes in the absorbance at different wavelenghts (for all compounds) with increasing
concentrations of FSdsDNA, according to the following equation (Eq. 1) [50,51]:
[DNA] / (εa -εf) = [DNA] / (εb -εf) + 1 / Kb(εa -εf)
(Eq. 1)
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where εa = Aobs / [Complex], εa = extinction coefficient for the free complex and εb =
extinction coefficient for compound in the fully bound form, respectively. In plots [DNA] / (εb
-εf) versus [DNA], Kb is given by the ratio of slope to the y intercept (insets in Figs. 10&11).
The determined Kb values for the ligand (L) and its metal complexes are given in Table 5. The
high value of Kb obtained for LPt4Cl3, LCu4Cl3 or ligand (L), and LZn4Cl3 suggest a strong
binding of complexes to FSdsDNA. Indeed, it is much higher than Kb calculated for the ligand
(L), indicating that the coordination of porphyrin ligand (L) to M(II) ion enhance significantly
the ability to bind to FSdsDNA. This is an important point. The Kb values of the porphyrin
Schiff base ligand (L) and its metal complexes are higher than the EB binding affinity for
DNA (Kb = 1.23 ± 0.07 x 105). For the reason that, the intercalative interaction may affect EB
displacement [52,53]. In addition, a distinct isosbestic point appears at about 425.1 nm upon
addition of FSdsDNA. The behavior of complexes upon addition of FSdsDNA is quite
similar.
Conclusion
In this study, a new symmetric porphyrine-Schiff base ligand and its transition metal
complexes were synthesized and chracterized by spectroscopic and analytical methods.
Starting compounds 4-ethyl-2,6-bis(hydroxymethyl)phenol and 4-ethyl-2,6-diformylphenol
were obtained as single crystals and their structures were identified by X-ray crystallography
method. Uv-Vis, emission, excitation, electrochemical and thermal properties of the ligand
and its metal complexes were investigated in detail. Superoxide dismutase activities of the
porphyrin Schiff base metal complexes were investigated. In addition, the study of the
porphyrin and metalloporphyrin interaction with FSdsDNA has been performed with UV
spectroscopy and it reveals that the complexes can bind to DNA. The UV spectroscopic
titrations were used in order to calculate the binding strength of the complexes with
FSdsDNA which is mirrored in the intrinsic binding constant Kb. The LPt4Cl3 complex
exhibits much higher intrinsic binding constant to FSdsDNA than the other complexes,
porphyrin ligand and EB.
Supplementary Information
CCDC numbers 1038663 and 1038664 contain the supplementary crystallographic data for
(A) and (B), respectively. Bond lenghts and angles of the compounds were given in
Supplementary Information. These data can be obtained free of charge via
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www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre 12 Union Road Cambridge CB2
1EZ, UK Fax: +44(0)1223-336033.
Acknowledgments
We are grateful to The Scientific & Technological Research Council of Turkey (TUBITAK)
(Project number: 113Z907) for the support of this research. The authors are also grateful to
the Department of Chemistry, Loughborough University for X-ray data collection.
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Table 1
Crystallographic data for the starting materials A and B.
Identification code
Empirical formula
Formula weight
Crystal size (mm3)
Crystal color
A
B
C10H14O3
182.21
C10H10O3
178.18
0.41 x 0.36 x 0.08
colourless
Monoclinic
P2(1)/c
0.31 × 0.23 × 0.10
Yellow
Crystal system
Space group
Triclinic
P 1
Unit cell
a (Å)
16.3457(16)
13.3873(13)
8.3694(8)
90
7.6563(6)
7.8598(7)
8.4085(7)
73.2310(10)
71.0790(10)
66.6050(10)
431.81(6)
2
b (Å)
c (Å)
α (°)
β (°)
γ (°)
94.5084(15)
90
3
1825.8(3)
8
Volume (Å )
Z
Abs. coeff. (mm-1)
0.097
0.101
Refl. Collected
18678
5837
100%
99.6%
Completeness to θ = 28.10°
Ind. Refl. [Rint]
4535 [0.0330]
0.0408, 0.0981
0.0534, 0.1076
1038663
2105 [0.0201]
0.0383, 0.1059
0.0468, 0.1127
1038664
R1, wR2 [I>2σ (I)]
R1, wR2 (all data)
CCDC number
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Table 2
Hydrogen-bond geometry (Å, °) for the starting compound (A).
D—H···A
D—H
H···A
D···A
D—H···A
O2—H1A···O3 0.878 (19) 1.878 (19) 2.6508 (12) 145.8 (16)
O2—H1A···O3i 0.878 (19) 2.400 (18) 2.9764 (12) 123.5 (15)
C7—H7···O1ii
C10—H10···O1ii 0.95
0.95
2.65
2.60
3.5230 (14) 153.0
3.4834 (15) 154.5
Symmetry codes: (i) −x+1, −y, −z+2; (ii) x+1, y−1, z.
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Table 3
Hydrogen bonds for the starting compound (B) [Å and °].
D—H···A
D—H
H···A
D···A
D—H···A
171.5(17)
160.9(16)
177.6(17)
156.4(18)
165.0(17)
168.4(17)
O(1)-H(1)...O(3)i
O(2)-H(2)...O(1)ii
O(3)-H(3A)...O(2)iii
O(4)-H(4)...O(5)iv
O(5)-H(5)...O(6)v
O(6)-H(6)...O(4)vi
0.824(18) 2.000(19)
0.831(18) 1.905(18)
0.836(19) 2.025(19)
2.8179(14)
2.7043(13)
2.8610(14)
2.7609(14)
2.6277(14)
2.6907(14)
0.90(2)
1.92(2)
0.901(19) 1.747(19)
0.882(19) 1.821(19)
Symmetry codes: (i) -x+1,-y+2,-z (ii) -x+1,-y+2,-z+1 (iii) x,-y+3/2,z-1/2 (iv) -x,-y+1,-z+1 (v) x,-y+1/2,z+1/2 (vi) -x,-y+1,-z
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Table 4
UV-vis absorption spectral data of ATTP-NH2, the porphyrin Schiff base ligand (L) and its
metal complexes in the different solvents (λmax (nm) (εmax, M-1cm-1)).
Compounds
ATTP-NH2
DMSO
DMF
Toluene
CH2Cl2
479(1.28x104), 481(0.47x104), 425(3.34x104), 481(0.58x104),
558(0.89x104), 518(1.29x104), 524(0.40x104), 517(1.75x104),
592(1.01x104), 557(0.93x104), 560(0.30x104), 554(1.01x104),
591(0.52x104), 592(0.50x104), 587(0.20x104), 591(0.57x104),
652(0.50x104)
651(0.51x104)
650(0.10x104)
649(0.58x104)
L
478(0.90x104), 379(0.50x104), 483(0.77x104), 482(0.84x104),
517(2.90x104), 483(0.76x104), 515(3.03x104), 516(3.14x104),
546(1.89x104), 514(2.28x104), 553(1.71x104), 552(1.76x104),
571(1.20x104), 552(1.36x104), 593(0.93x104), 592(0.99x104),
641(1.03x104)
592(0.74x104), 649(0.76x104)
648(0.70x104)
645(0.86x104)
543(2.08x104), 540(2.03x104), 541(2.04x104), 539(1.90x104),
585(0.69x104), 585(0.50x104), 580(0.37x104), 578(0.43x104),
LCu4Cl3
587(0.68x104), 700(0.18x104)
659(0.12x104)
650(0.15x104), 676(0.22x104)
LFe3Cl4(H2O)
521(1.95x104), 516(2.17x104), 516(1.42x104), 503(3.02x104),
547(1.46x104), 554(1.28x104), 551(0.88x104), 684(2.52x104)
588(0.72x104)
653(0.65x104)
590(0.67x104)
LMn3(ACO)4(H2O) 516(2.42x104), 463(3.22x104), 475(3.52x104), 476(3.30x104),
556(1.62x104), 516(1.94x104), 516(1.94x104), 516(1.80x104),
592(1.19x104)
554(1.12x104), 552(1.19x104), 552(1.11x104),
590(0.80x104) 592(0.85x104) 592(0.81x104)
LPt4Cl3
LZn4Cl3
516(2.42x104), 463(3.22x104), 475(3.52x104), 476(3.30x104),
556(1.62x104), 516(1.94x104), 516(1.94x104), 516(1.80x104),
592(1.19x104)
554(1.12x104), 552(1.19x104), 552(1.11x104),
590(0.80x104) 592(0.85x104) 592(0.81x104)
518(1.85x104), 478(1.71x104), 484(0.52x104), 549(1.92x104),
561(2.68x104), 516(1.83x104), 516(1.70x104), 589(0.69x104),
602(1.61x104)
559(2.68x104), 556(2.07x104), 680(0.78x104)
600(1.52x104)
602(1.13x104)
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Tables 5a,b.
Excitation (a) and emission (b) spectral data of the porphyrin Schiff base ligand and its transition metal complexes in the different concentrations.
Excitation
1x10-4 (M)
381
a)
λmax (nm)
1x10-3 (M)
383
Compounds
L
1x10-5 (M)
380
1x10-6 (M)
379
1x10-7 (M)
377
LCu4Cl3
LZn4Cl3
356
360
367
373
376
350
353
357
360
366
LPt4Cl3
397
390
384
377
371
LMn3(AcO)4(H2O)
LFe3Cl4(H2O)
352
350
347
343
340
356
362
365
369
372
Emission
b)
λmax (nm)
1x10-3 (M)
659
Compounds
L
1x10-4 (M)
1x10-5 (M)
648
1x10-6 (M)
642
1x10-7 (M)
638
655
LCu4Cl3
LZn4Cl3
704
698
693
695
698
667
665
663
661
659
LPt4Cl3
641
643
646
648
650
LMn3(AcO)4(H2O)
LFe3Cl4(H2O)
673
670
665
661
657
617
613
611
605
602
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Fig. 1. Crystal structure of the starting compound (A) (left) and hydrogen bonded dimer
(right).
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Fig. 2. Unit cell packing of the compound, π...π interactions shown as dashed lines, hydrogen
atoms are omitted for clarity.
23