Synthesis, Characterization and DNA Interaction

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Synthesis, Characterization and DNA Interaction Study of a New Oxovanadium (IV) Complex Containing Acetylacetone and Dicyandiamide as Ligands a

a

R. K. Bindiya Devi , S. Pramodini Devi & R. K. Hemakumar Singh a

a

Department of Chemistry, Manipur University, Canchipur, Manipur, India

Available online: 17 Feb 2012

To cite this article: R. K. Bindiya Devi, S. Pramodini Devi & R. K. Hemakumar Singh (2012): Synthesis, Characterization and DNA Interaction Study of a New Oxovanadium (IV) Complex Containing Acetylacetone and Dicyandiamide as Ligands, Spectroscopy Letters: An International Journal for Rapid Communication, 45:2, 93-103 To link to this article: http://dx.doi.org/10.1080/00387010.2011.603791

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Spectroscopy Letters, 45:93–103, 2012 Copyright # Taylor & Francis Group, LLC ISSN: 0038-7010 print=1532-2289 online DOI: 10.1080/00387010.2011.603791

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Synthesis, Characterization and DNA Interaction Study of a New Oxovanadium (IV) Complex Containing Acetylacetone and Dicyandiamide as Ligands R. K. Bindiya Devi, S. Pramodini Devi, and R. K. Hemakumar Singh Department of Chemistry, Manipur University, Canchipur, Manipur, India

ABSTRACT A new oxovanadium (IV) complex [VO(acac)2DCDA]H2O (where acac ¼ acetylacetonate; DCDA ¼ dicyandiamide) was synthesized and characterized by elemental analysis, IR, UV, ESR, TG-DTA analysis and powdered XRD. The electronic and ESR spectral studies indicate the monomeric nature of the complex having distorted octahedral structure. The complex shows prominent emission peak at 485 nm and excitation peak at 355 nm. The cyclic voltammetry study shows irreversible process. DNA binding study of the complex with CT-DNA indicates nonintercalative mode with binding constant 2.063 102 M1. KEYWORDS calf thymus DNA (CT-DNA), cyclic voltammetry, distorted octahedral, nonintercalative, photoluminescence

INTRODUCTION

Received 2 May 2011; accepted 5 July 2011. Address correspondence to R. K. Hemakumar Singh, Department of Chemistry, Manipur University, Canchipur, Manipur, India. E-mail: [email protected]

The investigation of DNA interactions with ions and molecules is an important fundamental issue on life science that is of great importance to understanding the action mechanisms of some antitumor, antiviral, and antibiotic drugs.[1,2] It can also provide guidance for the rational design of drugs and for understanding how proteins recognize and bind to specific DNA sequences.[3,4] Among the transition metals, the chemistry of vanadium has received considerable attention due to the significant role of vanadium in a variety of chemical and biological systems.[5,6] The coordination chemistry and the reactivity of vanadium has continued to play a significant role not only because of the physiological relevance of this metal but also for its activity in various industrial processes. Biologically, vanadium is known for its exceptional ability to interact with biomolecules in both cationic and anionic forms and its numerous oxidation states. Several therapeutic effects have been described for vanadium including hormonal, cardiovascular, and anticarcinogenic.[7,8,9] Vanadium complexes have potential applications in catalysis,[10] biological modeling,[11] and design of molecular magnets.[12] It is also well known that 93


vanadium complexes have the potential to take part in nitrogen fixation[13] and haloperoxidation,[14] as insulin mimetic,[15] antitumor[16] and antiamoebic agent.[17] Bis(acetylacetonato)oxovanadium(IV) [VO(acac)2] is also used as a new class of cancerspecific MRI contrast agents that are nontoxic and highly sensitive to cancer metabolism.[18] Novel vanadyl complexes, [VIVO(L2-2H)(L1)], including a bidentate polypyridyl (L1) and a tridentate salicylaldehyde semicarbazone derivative(L2) could interact with DNA, and their potential as antiprotozoa agents was also reported.[19] Oxovanadium complexes [VO(Satsc)(bipy)] and [VO(3,5-dibrsatsc) (bipy)] have been synthesized and studied for their DNA binding and cleavage activities and reported as intercalative mode of binding.[20] A few oxovanadium complexes bearing salicylidine dithiosemicarbazone, [VO(Salmdtc)phen], [VO(Salmdtc)(dpq)] and [VO(Salmdtc)(dppz)] were synthesized and tested for bioactivity as potential insulin-mimetic agents.[21] The DNA cleavage activity of VO(acac)2 and its derivatives: VO(hd)2, VO(acac-NH2)2, VO(acac-NMe2)2 was also evaluated by Nataliya Butenko and et al.[22] However, only few studies have been reported for the interaction of vanadium complexes with DNA and generally, they have been restricted to cases when vanadium is in its highest oxidation state.[23,24,25] On the other hand, dicyandiamide is being employed in a wide variety of applications and utilized as an intermediate for a number of resins and organic nitrogen compounds, biguanides and guanidine. Recently, binuclear copper(II) complexes of dicyandiamide[26,27] and phenyldicyandiamide[28–30] prepared in different alcohols have been reported and some of the complexes are reported to exhibit fungicidal and bactericidal activities.[30,31] Thus, considering the importance of vanadium complexes and dicyandiamide as well as its DNA interaction, we report here a new oxovanadium (IV) complex [VO(acac)2 DCDA]H2O using acetylacetonate(acac) and dicyandiamide(DCDA) as ligands. The synthesized complex has been characterized by elemental analysis, IR, UV, ESR, TGA-DTA, luminescence, cyclic voltammetry, and powdered XRD analysis. The interaction of this complex with CT-DNA (calf thymus DNA) was investigated using UV-vis absorption titration, cyclic-voltammetry and thermal denaturation and reported in this paper. R. K. Bindiya Devi et al.

MATERIALS AND METHODS Materials All chemicals are of reagent grade and used without purification. VOIV(acac)2, where acac ¼ acetylacetonate was prepared using a previously reported procedure.[32] CT-DNA and Tris-HCl molecular biological grade were obtained from Merck (India). Deionized, sonicated triple-distilled H2O was used throughout the experiment (Milli–Q Integral System, Millipore, Billerica, MA, USA).

Physical Measurements Microanalyses (C, H, N) were carried out on a Perkin–Elmer 2400 model elemental analyzer. The metal content of the complex was estimated by gravimetrically as V2O5.[33] IR spectra were recorded on KBr disks on a Shimadzu FT-IR-8400S. Electronic spectra were recorded on a Perkin Elmer UV-Vis Lamda 35 spectrophotometer. The ESR spectra of the complex were recorded on a Varian E-112 spectrometer at the SAIF, IIT, Bombay, India. The room temperature magnetic moment (meff) was measured using Sherwood Scientific susceptibility balance (MSB). Molar conductance of 2 103 M in DMSO was measured at room temperature on Eutech instruments Con 510 conductivity. The thermogram was recorded on a Perkin Elmer STA 6000 machine. Powdered XRD spectra were carried out in PANalytical powder diffractometer (X’ Pert PRO) using CuKa(1.540 A˚) radiation fitted with Ni filter. Emission spectra were recorded on a Perkin Elmer LS55 fluorescence spectrophotometer. Cyclic voltammetry was performed on CH602C electrochemical analyzer.

Preparation of [VO(acac)2DCDA]H2O Complex VO(acac)2 (0.265 g,1 mM) dissolved in acetonitrile (20 ml) was added drop-wise to dicyandiamide ligand (0.08408 g, 1 mM) in acetonitrile (20 ml) and stirred on a hot plate for 30 hr at about 65 C until the color changed from bluish green to dark blue. The resulting solution was filtered and kept at room temperature for slow evaporation. After 2–3 days, a violet crystalline product was obtained. This crystalline product was washed with methanol and air-dried. Yield: 0.2209 g (60%). Anal. Calc. for 94


½DNA=ðea ef Þ ¼ ½DNA=ðeb ef Þ þ ½Kb ðeb ef Þ1 ð1Þ

SCHEME 1 Preparation of [VO(acac)2DCDA]H2O.

VC12O6H20N4 : V,13.88; C, 39.24; H, 5.45; N, 15.26. Found: V,13.21; C, 38.78; H,4.99; N,15.56%. Synthetic route of the complex is shown in Scheme 1

DNA-Binding Studies The Tris buffer containing 5 mM Tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) and 50 mM NaCl (pH ¼ 7.4) was used for absorption titration, thermal denaturation, and cyclic voltammetric study. The stock solution of calf thymus-DNA was prepared by directly dissolving the solid DNA in Tris buffer. The absorbance ratio A260=A280 of CT-DNA was in the range of 1.8–1.9 indicating that the DNA sufficiently free from protein.[34] The concentration of DNA was determined at 260 nm taking the value of molar absorptivity coefficient as 6600 M1 cm1.[35] The absorption titrations of oxovanadium complex in tris buffer were performed by increasing the calf thymus DNA concentration from 0 to 81 mM and keeping the complex concentration constant at 100 mM. The spectra were recorded after equilibration of 5 min. All measurements were performed at 25 C under air saturated condition. From the absorption data, the intrinsic binding constant, Kb was determined from a plot of [DNA]=(ea ef) versus [DNA] using the Eq. (1) 95

where [DNA] is the concentration of CT-DNA in base pairs; the apparent absorption coefficients ef, ea, and eb correspond to the extinction coefficient of the free oxovanadium complex, the extinction coefficient for each addition of DNA to the complex, and the extinction coefficient for the oxovanadium complex in the fully bound form, respectively;[36] and Kb is the ratio of the slope to the intercept. Thermal denaturation studies were studied with a Perkin Elmer UV-Vis Lamda 35 spectrophotometer equipped with a Peltier temperature controlling programmer (PTP6). The melting curves were obtained by measuring the absorbance at 260 nm for solutions of CT-DNA (72 mM) in the absence and presence of varying concentrations of the oxovanadium complex as a function of the temperature. The temperature was scanned from 25 to 98 C at a speed of 120 nm per min. The electrochemical studies were performed by cyclic voltammetry (CV) in the potential range of 1.0 to 2.0 V in tris buffer (pH ¼ 7.4) (using glassy carbonworking electrode), Pt wire as counter electrode and Ag=AgCl as reference electrode. TBAB (0.1 M) is used as supporting electrolyte. The experiments were carried out in 0.005 M complex solution in the absence and the presence of CT-DNA.

RESULTS AND DISCUSSION Synthesis and General Aspects The synthesized oxovanadium (IV) complex, [VO(acac)2DCDA]H2O has been characterized by analytical and spectral techniques. The complex is air-stable and soluble in most of the organic solvents. The complex is crystalline solid having decomposition point around 165 C. The elemental analysis data for the metal complex agree well with the calculated value showing VO(acac)2 and dicyandiamide in the 1:1 molar ratio. The low molar conductance value (3 ohm1 cm2 mol1) of the complex in DMSO (2 103 M) at room temperature is consistent with nonelectrolytic nature of the complex. The room temperature magnetic moment of the complex is found to be 1.63 BM., which was expected for oxovanadium (IV) complex with one unpaired electron, d1, system (1.6–1.8 BM). Study of a New Oxovanadium (IV) Complex


IR Spectra

Electronic Spectra

The IR spectrum of pure dicyandiamide ligand (Appendix, Fig. A1) shows a doublet strong nitrile t(CN) band at 2208 cm1 and 2165 cm1 and a band at 1662 cm1 for the azomethine t(C=N) group. (The Appendix comprises IR spectrum of the Dicyandiamide, TG-DTA curve of the complex, and ESR spectrum of the complex in solid state at 25 C.) The broad bands in the ranges 3427–3332 cm1 and 3186–3155 cm1 are due to NH2 asymmetric and symmetric stetch.[37] In the IR spectra of the complex (Fig. 1), the free nitrile band is observed in higher wave numbers at 2217 cm1 and 2171 cm1 respectively. The t(C=N) stretch of the ligand appearing at 1662 cm1 is shifted to lower wave number at 1650 cm1 in the complex, indicating the binding of the azomethine nitrogen with the metal. NH2 asymmetric and symmetric stretch are observed in the range of 3450–3355 cm1 and 3255–3136 cm1 respectively after the complex formation. Band observed at 3548 cm1 is due to the presence of t(O-H)stretching of lattice water molecule[38] in the complex. When the complex is heated at 110 C, the band is completely lost in the spectra (Fig. 1 inset). In addition, the bands belonging to t(V=O), t(V-O) and t(V-N) could be assigned to 950 cm1, 460 cm1, and 526 cm1 respectively.[39,40]

Electronic spectra of the complex were recorded in the solid state and in DMF and DMSO in the 200–900 nm range (Fig. 2). The spectra of the complex in both solvents exhibit two low intensity transitions: one in the 585–588 nm range and another in the 782–788 nm range and one high intensity band at ca. 404 nm, these transitions are consistent with distorted octahedral geometry commonly associated with spectra of vanadyl ion and its complexes, which can be assigned (from lowest to the highest energy) as the 2 B2 ! 2 Eðdxy ! dxz ; dyz Þ, 2 B2 ! 2 B1 ðdxy ! dx2 y2 Þ 2 B2 ! 2 A1 ðdxy ! d2z Þ transitions according to Ballhausen and Gray molecular orbital scheme.[41] Based on similarity of the electronic spectra both in organic solvents and solid state, it may be assumed that there is no change in structure of the complex in these solvents.

FIGURE 1 IR spectrum of [VO(acac)2DCDA]H2O and inset shows the heated complex at 110 C in the range 3690–2830 cm1.

FIGURE 2 Electronic spectra of the [VO(acac)2DCDA]H2O in DMF,DMSO and solid state.

R. K. Bindiya Devi et al.

TG-DTA Thermal Analysis The thermal decomposition behavior of the synthesized complex was studied by means of thermogravimetric analysis. The thermogravimetric analysis for the synthesized oxovanadium complex was carried out with a temperature ranging from 40

96

to 900 C in N2 atmosphere at a heating rate of 10 C min1. The TG curve of the complex (Appendix, Fig. A2) shows that the complex exhibits weight loss of 5.17% between 100 and 120 C with a weak endothermic peak corresponding to one lattice water molecule (calc. mass loss for one lattice water molecule of the complex is 4.91%). The complex shows another weight loss of 74.70% (calc. mass loss 76.85%) in the interval from 130–650 C with an exothermic peak around 500 C corresponding to liberation of two acetylacetonate molecules and one dicyandiamide molecule.


ESR Spectroscopy The X band ESR spectra of the complex were recorded both in polycrystalline state and DMSO solution at room temperature (25 C) and as a frozen glassy state at 140 C (Fig. 3). The room temperature spectrum in DMSO exhibits eight line patterns typical of vanadium (IV), which indicates that a single vanadium is present in the molecule, that is, the

monomeric structure of the complex. In frozen DMSO the complex displayed well resolved axial anisotropy characterized by two sets of eight lines which result from the interaction of the unpaired 3d1 electron with the spin of the 51V (I ¼ 7=2) nucleus. The spectrum of the complex in solid at room temperature (25 C) is broad and not well resolved enough to extract the ESR Hamiltonian parameters. This may be due to the dipolar interactions between the neighboring molecules and is shown in the Appendix, Fig. A3. In order to get clear ESR parameters, we have recorded ESR spectra of the complex in solution at 25 C and 140 C. The frozen DMSO solution gave the ESR parameters with g? ¼ 1.983 > gII ¼ 1.953; AII ¼ 168.62G > A? ¼ 60.78 G; Aiso ¼ 96.72; giso ¼ 1.973. These values fit well with those of the reported values of VO2þ which have slightly distorted octahedral coordination.[42,43,44]

Photoluminescence Study Photoluminescence study of the complex is carried out in the solid sample. The complex shows two prominent excitation peaks at 270 nm and 355 nm (Fig. 4a). When the complex is excited at these two excitation wavelengths it give an intense emission peak at 485 nm (blue) and some smaller emission peaks at 423 nm, 443 nm, and 526 nm (Fig. 4b). It is found that the excitation and emission energies of the complex are very similar to the starting material VO(acac)2. The emission peak of the complex observed may be due to the charge transfer from the ligand to the vanadium ion.

Powder XRD Study

FIGURE 3 ESR spectra of [VO(acac)2DCDA]H2O in DMSO solution at (a) 25 C; (b) 140 C. 97

Since single crystal of the compound could not be obtained up to date, the exact crystal structure could not be determined. To give a typical idea about the single phasic nature of the compound, we have carried out powder XRD studies. Figure 5 shows the X-ray powder diffraction pattern of the complex, dicyandiamide and VO(acac)2. The observed diffraction data for the complex is given in Table A1. The mononuclear oxovanadium complex crystallizes in triclinic system with unit cell dimensions a ¼ 8.3518 A˚, b ¼ 12.7285 A˚, c ¼ 6.3934 A˚, a ¼ 98.910 , b ¼ 101.321 , c ¼ 90.808 and cell volume ¼ Study of a New Oxovanadium (IV) Complex


FIGURE 5 Powder XRD patterns of [VO(acac)2DCDA]H2O, VO(acac)2 and Dicyandiamide (DCDA) ligand.

Electrochemical Study

FIGURE 4 (a) Excitation and (b) Emission spectra of [VO(acac)2 DCDA]H2O. (color figure available online.)

657.69 A˚3. The computed cell parameters are obtained by using the program P-index. It was also reported that VO(acac)2 is a triclinic system according to Fedorova et al.[45] Hence, the complex has the same pattern of crystal structure with VO(acac)2. To evaluate the crystallite size of the synthesized complex, D is determined using Debye-Scherer formula[46,47] given by

D¼

0:94k b cos h

Where b is the full width at half maximum of the predominant peak and h is the diffraction angle and k is the wavelength of light. The size of the crystallite of the oxovanadium complex is found to be 97 nm. R. K. Bindiya Devi et al.

The electrochemical behavior of the complex is studied by cyclic voltammetry in the potential range of 1.0–2.0 V in DMSO (using Pt working electrode) and tris buffer (using glassy carbon working electrode), Pt wire as counter electrode, and Ag=AgCl as reference electrode. TBAB (0.1 M) is used as supporting electrolyte. In the cyclic voltammogram of the complex (Fig. 6a), the cathodic (forward) scan reduction peaks at 0.23, 0.64 and 1.8 V and in the anodic scan oxidation peaks at 0.48, 0.39 and 0.52 V are exhibited. The first two reduction peaks and the oxidation peak at 0.48 V are observed from the solvent and supporting electrolyte solution. Further, the voltammogram of switching potential 1.1 V does not give oxidation peak in the anodic scan. The oxidation peak of the complex starts to appear when the cathodic scan reaches 1.6 V. The maximum reduction peak at 1.8 V and the oxidation peak at 0.52 V observed are corresponded to the reduction and oxidation of the [VO(acac)2dcda]H2O complex. As reported elsewhere,[48,49] vanadium(IV)acetylacetonate complex also shows two reduction potential at 1.85 and 1.95 V. Thus, the reduction peak at 1.8 V and oxidation peak at 0.52 V can be ascribed to the VIII=VIVO oxidation 98

solution of tris-buffer. Presence of equilibrium species are also reported in the various earlier work.[48–51]

DNA Interaction Study


Electronic Absorption Titration

FIGURE 6 Cyclic voltammogram of [VO(acac)2DCDA]H2O in (a) DMSO at different switching potentials, (b) Tris-buffer at 1.7 V, 1.4 V, 2 V switching potentials. (color figure available online.)

and reduction couples with an irreversible one-electron transfer process. Small oxidation peak at 0.36 V appeared in the higher negative scan is due to the oxidation of acac- ligands. The irreversible process can also be confirmed from the wide separation of the peaks as well as ipa=ipc (¼0.02), which is less than unity. However, the cyclic voltammogram of the complex in Tris-buffer (pH-7.4) (Fig. 6b) shows reduction peak at 1.52 V. In the anodic scan two oxidation peaks at 0.52 V and 0.78 V are observed which are assigned to VIVO and VVO respectively. The oxidation peak at 0.52 V appeared from 1.4 V switching potential and both these oxidation peaks start appearing from switching potential at 1.7 V. This suggests that when the cathodic scan moves to more negative potential the complex further oxidized to VVO. The ligands may have dissociated and hydroxyl species is form in the 99

The absorption titration measurements were carried out to explore the interaction between the complex and CT-DNA (Fig. 7). The hyperchromic and hypochromic effects are the spectral features of DNA, hypochromism results from the contraction of DNA in the helix as well as from the change in DNA conformation, while hyperchromism results from the structural damage of DNA.[52] In general, the absorption spectra of metal complexes bound to DNA exhibit hypochromism with bathochromic shift due to intercalative mode involving strong p-p stacking interactions between the aromatic chromophore ligand of the metal complex and the base pairs of DNA.[53] It is well known that the hypochromic effect, in the case of DNA-interaction of a metal complex, is due to the coupling of the ligand of the metal complex p orbital with the p orbital of DNA base pairs.[54] In fact, the transition probability decreases because the empty p orbital is partially filled by electrons due to overlapping with the p orbital of the DNA base pairs and this leads to hypochromism. Also, the presence of an isosbestic point is indicative of the existence

FIGURE 7 Absorption spectra of the complex in Tris-buffer upon increasing amounts of CT-DNA; [complex] = 100 lM, [DNA] = 0–81 lM. Arrow shows the absorbance changes upon the increase in DNA concentration. Inset: Plots of [DNA]=(ea ef) versus [DNA] for CT-DNA with oxovanadium complex. (color figure available online.) Study of a New Oxovanadium (IV) Complex


of equilibrium between two species in a solution, which are ligand metal complex free and bound to DNA. In this work, the electronic spectra of the oxovanadium complex were recorded in the absence and presence of increasing amount of CT-DNA. The spectra show significant hyperchromic effects at 214 and 279 nm and the hypochromic shifts at 306 nm respectively. A quite small blue shift of 1–2 nm is observed in the band of 304–306 nm and a significant blue shift can be observed in the band 279–261 nm. Isosbestic point of the complex was noted at 290 nm. Thus, binding of the oxovanadium complex with DNA is a homogeneous equilibria reaction each involving two species in solution. In order to further elucidate the binding strengths of the complex, the intrinsic binding constant Kb was calculated with Eq. (1) by monitoring the changes in absorbance of the charge transfer bands with increasing concentration of CT-DNA (Fig. 7 inset), and its value was found to be 2.063 102 M1, which is lower than that of the classical intercalator.[55] These observations indicate that the complex undergo weak interaction with the phosphate backbone of DNA by nonintercalative mode.

Thermal Denaturation Studies Binding of the complex to CT-DNA was also studied from thermal denaturation measurements. It is known that when the temperature is raised, the double-stranded DNA gradually dissociates into single strands. The DNA melting temperature Tm, which is defined as the temperature where half of the total base pairs are unbound,[56] is determined by plotting the absorbance at 260 nm as a function of temperature According to the literature,[57] the intercalation of the natural or synthesized complexes into DNA base pairs causes stabilization of base stacking and hence raises the melting temperature of the doublestranded DNA. The melting curves of the CT-DNA in the absence and presence of complex are illustrated in Fig. 8. The Tm of CT-DNA in the absence of the complex is 75 C and it reaches to ca. 76 C in the presence of the complex. The small increase in Tm (DTm 1 C) in the presence of the complex is suggested that the complex possibly interact with DNA by electrostatic or groove binding.[58,30]

FIGURE 8 Thermal denaturation curves of CT-DNA (72 lM) alone and in the presence of varying amounts (5 lM, 20 lM, 50 lM) of [VO(acac)2DCDA]H2O. (color figure available online.)

buffer (Fig. 9). With increasing concentration of the Calf thymus DNA the peak currents, both the ipc and ipa decrease. The ipc values for 1.7 mM and 6.9 mM concentration of DNA are 0.0792 mA and 0.0746 mA respectively while ipa values are 0.1092 mA and 0.0850 mA respectively. The Epa value was shifted to more negative potentials with increasing concentration of CT-DNA and is shown in (Fig. 9 inset). This phenomenon implied forming a new association complex. These results clearly suggest

Cyclic Voltammetry Study

FIGURE 9 Cyclic voltammogram of 1 103 M [VO(acac)2DC-

The cyclic voltammograms of the complex in different concentrations of CT- DNA was studied in tris

DA]H2O in Tris-HCl=NaCl buffer solution (pH 7.4) with incremental addition of CT-DNA; inset shows the enlarged voltammogram. (color figure available online.)


100

that oxovanadium complex binds to CT-DNA through electrostatic binding.[59]


CONCLUSION A new oxovanadium(IV) complex [VO(acac)2DCDA]H2O was synthesized and characterized. The IR spectrum suggested that the ligand dicyandiamide bound to the complex through azomethine nitrogen. From the magnetic moment value, molar conductance, elemental analysis data, ESR, and electronic spectra, the oxovanadium complex was found to have a distorted octahedral geometry around the central metal ion. The synthesized complex shows irreversible redox chemistry as determined by cyclic voltammetry. The interaction of this complex with CT-DNA indicates weak binding propensity to CT-DNA with binding constant of 2.063 102 M1 through nonintercalative mode.

ACKNOWLEDGMENTS The authors thank IIT Bombay, Mumbai, India, for recording ESR spectra.

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Appendix

FIGURE A1 IR spectrum of Dicyandiamide (DCDA). 102


FIGURE A2 The TG- DTA curve of [VO(acac)2DCDA]H2O. (color figure available online.) FIGURE A3 EPR spectrum of [VO(acac)2DCDA]H2O in solid state at 25 C.

TABLE A1 Crystallographic Data for [VO(acac)2DCDA]H2O Complex 2h values Peak number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

d(obs)(A˚)

d(cal)(A˚)

Observed

calculated

D2h

h

k

l

8.132 7.039 6.707 6.284 6.197 5.927 5.273 5.078 4.821 4.465 4.192 4.072 3.915 3.807 3.751

8.181 7.003 6.715 6.281 6.187 5.942 5.254 5.096 4.811 4.458 4.187 4.069 3.923 3.798 3.759

10.870 12.564 13.189 14.080 14.279 14.934 16.799 17.448 18.387 19.868 21.172 21.806 22.691 23.346 23.698

10.806 12.629 13.173 14.089 14.303 14.897 16.859 17.387 18.425 19.898 21.202 21.820 22.645 23.399 23.645

0.064 –0.065 0.016 –0.009 –0.024 0.037 –0.060 0.061 –0.038 –0.030 –0.030 –0.014 0.046 –0.053 0.053

1 1 1 0 0 0 1 1 0 1 0 1 1 1 0

0 1 1 2 0 1 1 2 2 1 3 1 2 3 3

0 0 0 0 1 1 1 0 1 1 0 1 1 0 1

Chemical formula ¼ VC12O6H20N4. F.W. ¼ 366.94. Triclinic. a ¼ 8.3518 A˚, b ¼ 12.7285 A˚, c ¼ 6.3934 A˚. a ¼ 98.910, b ¼ 101.321, c ¼ 90.808, V ¼ 657.69 A˚3.

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Study of a New Oxovanadium (IV) Complex