Synopsis

Synthesis, spectral, structural, electrochemical and metallonuclease activities of copper(II) and nickel(II) complexes with N/O containing ligands

SYNOPSIS SUBMITTED TO ALAGAPPA UNIVERSITY IN PARTIALFULFILMENT FOR THE AWARD OF THE DEGREE OF

DOCTOR OF PHILOSOPHYINCHEMISTRY

ByA. Jayamani(Reg. No: 0321)

Dr. N. Sengottuvelan, M.Sc., B.Ed., Ph.D., Research Supervisor

Department of Industrial ChemistrySchool of Chemical SciencesAlagappa University(Re-accredited with A Grade by NAAC)Karaikudi - 630 003Tamil NaduIndia

May 2015 Synopsis

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Synthesis, spectral, structural, electrochemical and metallonuclease activities of copper(II) and nickel(II) complexes with N/O containing ligandsArtificial metallonucleases are in high demand as cellular regulators of DNA for therapeutic or biochemical purposes [1]. Metal complexes containing site-specific substructures and multiple reactive sites constitute a group of promising candidates for nucleases because of their electronic and structural advantages [2]. Moreover, these complexes generate highly cationic species that favor the electrostatic attraction to anionic phosphate backbone of DNA. Incorporation of a DNA-targeting moiety into the ligands can improve the selectivity of metallonucleases [3]. Chemical nucleases are redox active coordination complexes that cleave DNA by an oxidative pathway. Direct scission of DNA by oxidizing or hydrolytic agents is the subject matter for several current researches in bioinorganic chemistry. Redox-active transition metal complexes in the presence of oxidants have been extensively used for DNA cleavage reactions. Among the transition metal based cleaving reagents, copper and nickel were essential elements which can be estimated by the wide range of Cu/Ni proteins and enzymes playing different roles in biological systems [4]. There is an exigency to identify effective metal-based therapeutics, particularly those that overcome both inherent and acquired resistance to drug therapy which show improved therapeutic properties, stimulating the ongoing investigations of alternative molecular targeted metal-based drugs [5]. Medicinal inorganic chemistry is a thriving interdisciplinary research area [69] which offers exciting possibilities for the design of novel metal-based therapeutic /diagnostic agents with unique mechanisms of action [10].This Ph. D work mainly focuses on the synthesis, spectral, structural, electrochemical and metallonuclease activities of copper(II) and nickel(II) complexes with bidentate ligands containing N2/ O2/N2O2 donors or tetra-dentate acyclic Schiffs base ligands containing N4 coordinating atoms. The protein binding, DNA binding, molecular docking and antimicrobial properties of these complexes were also studied.Chapter IIntroductionThis chapter deals with general introduction to medicinal application of transition metal complexes, especially copper and nickel. It also describes the types of ligands, enzymatic activity of copper and nickel complexes, geometry and electrochemical properties of complexes, bimolecules and their interactions with metal complexes, metallonuclease activity of copper and nickel complexes, and antimicrobial properties. It also critically reviews the reported copper and nickel complexes related to their N/O chelating ligand and their properties pertaining to bidendate and Schiffs base complexes. Literature reports show that spectral, structural, metalonuclease properties and medicinal applicability of the complexes are influenced by the nature of coordination geometry of the complexes and substituent in the ligand framework. This chapter ends with list of references of this part.Chapter IIAim and scopeThe second chapter of the thesis explains the scope of the present work. The reactivity of metal complexes towards DNA and protein BSA is important in understanding the mechanism of binding and in the rational design of metallo-drugs. Metal complexes containing planar heterocyclic aromatic ligands, such as 2, 2-bipyridine and 2, 2-biimidazole or simple aromatic salicylaldehyde derivatives or bulky aromatic naphthaldehyde derivative, have been at the forefront of these investigations owing to their unusual electronic properties and diverse chemical reactivity. Several metal complexes of Schiffs bases derived from salicylaldehyde and amines were also reported and some of them have been proven to be efficient metallonuclease and as novel tumour chemotherapeutic agents. In order to expand the knowledge in this field, we synthesized, characterized the copper(II) and nickel(II) complexes with potential bidendate ligands, mixed ligand and Schiffs base ligands. The spectral, electrochemical, biomolecular interactions, metallonuclease activity and antimicrobial properties of the complexes were studied by using various analytical tools.Chapter IIIExperimental detailsThe third chapter deals with the experimental details and synthetic methodology of copper(II) and nickel(II) complexes with potential bidendate ligands which forms N4, O4, N2O2 type of coordinations and four Schiffs base ligands with four N-donor atoms of bappz and free phenlolic hydroxyl group of hydroxy aldehyde compounds. This chapter also describes the various instrumental methods used during the course of study.The electronic spectra were recorded on a Shimadzu UV3101PC spectrophotometer. The IR spectra were recorded in 4000400 cm1 region using KBr pellets on a Bruker EQUINOX-55 spectrometer. Fluorescence spectra were recorded on Elico SL-174 spectrofluorometer. The circular dichroism (CD) spectra were recorded on Jasco J-810 spectropolarimeter. Elemental analyses were carried out on an Elementar vario MACRO cube elemental analyzer. The Electron Paramagnetic Resonance (EPR) spectra were recorded at liquid nitrogen temperature with Varian E-112 X-band spectrometer operating at 910 GHz (SAIF, IIT Bombay, India). The DNA cleavage studies were visualized and photographed on BIO RAD Gel DOC XR+ with image lab-3.0 software. A Biologic CHI604D electrochemical analyzer was used for studying the electrochemical behavior of complexes using a three-electrode cell in which a glassy carbon electrode was the working electrode, a saturated Ag/AgCl electrode was the reference electrode and a platinum wire was used as an auxiliary electrode in nitrogen atmosphere. The concentration of complexes was 103 M in dimethylformamide (DMF) and tetra(n-butyl)ammonium perchlorate (TBAP) (101 M) was used as the supporting electrolyte. Safety note: Perchlorate salts of metal complexes are potentially explosive and should be handled with care. The rigid molecular docking studies were performed by using HEX 8.0 software.Chapter IVResults and discussionsThe detailed results obtained from spectral, structural, electrochemical, BSA/DNA binding, DNA cleavage activity and antimicrobial studies of all the synthesized complexes are well discussed in this chapter.Synthesis of copper(II) and nickel(II) complexes with heterocyclic bidentate ligands containing N2 chelating donor setThe synthesis of Copper(II) complexes (15) of bipyridine was carried out using a common procedure by the reaction of stoichiometric amount of chloride, perchlorate, acetate salts of copper, bipyridine and sodium perchlorate in methanol (Scheme 1).

The synthesis of Cu(II) and Ni(II) complexes (6 and 7, respectively) of biimidazole were carried out using a common procedure by the reaction of stoichiometric amounts of copper(II) perchlorate hexahydrate, nickel(II) perchlorate hexahydrate with biimidazole in methanol (Scheme 2).

Synthesis of copper(II) and nickel(II) complexes with O2 donor set ligands The synthesis of copper(II) and nickel(II) complexes of 5-methyl salicylaldehyde, 5-bromosalicylaldehyde, 5-nitrosalicylaldehyde and 2-hydroxy-1-napthaldehyde was carried out using a common procedure by the reaction of stoichiometric amounts of copper(II)/ nickel(II) perchlorate salts with respective ligands in ethanol (Scheme 3).

Synthesis of copper(II) complexes with mixed bidentate (N2O2 chelating) ligands The synthesis of the dimeric copper(II) complexes were carried out using a common procedure by reaction of stoichiometric amounts of copper(II) perchlorate salt and respective ligands in methanol. The analytical data obtained for complexes 1623 are consistent with the formation of dimeric copper(II) complexes (Scheme 4 and 5).

Synthesis of acyclic Schiffs base ligands L1 - L4The Schiffs base ligands L1 [N,N-bis(2-hydroxy-5-methylbenzyl)-1,4-bis(3-iminopropyl)piperazine], L2 [N,N-bis(2-hydroxy-5-bromobenzyl)-1,4-bis(3-iminopropyl) piperazine], L3 [N,N-bis(2-hydroxy-5-nitrobenzyl)-1,4-bis(3-iminopropyl) piperazine] and L4 [N,N-bis(2-hydroxy-1-naphthyl)-1,4-bis(3-iminopropyl)piperazine] have been synthesized as given in scheme 6.

Synthesis of mononuclear copper(II) and nickel(II) complexes with Schiffs base ligandsThe mononuclear copper(II) complexes [CuL14](ClO4)2 were synthesized from ligand (L1-4) with copper(II) perchlorate hexahydrate in 1:1 molar ratio. (Scheme 7) and nickel(II) complexes [Ni(bappz)](ClO4)2, [NiL1-4](ClO4)2 were synthesized from ligand bappz, (L1-4), respectively, with nickel(II) perchlorate hexahydrate in 1:1 molar ratio. (Scheme 8)

Crystal structureThe single crystals of Schiffs base ligands (L1, L2 and L4), copper(II) complexes 1-6 and 16-19, nickel(II) complexes 7, 12, 13 and 28 were obtained and the structures were solved by X-ray crystal structure analysis.i) The Schiffs base ligands L1 and L2 crystallize in monoclinc P21/c space group but ligand L4 crystallize in monoclinic P21/c space group as a dimeric ligand.ii) In the crystal structure of copper(II) complexes, the geometry of Cu(II) ion in 1, 5 and 6 were distorted square pyramidal with N4O coordination; in 2 and 3 were distorted trigonal bipyramidal with N4O coordination; in 4, 16, 18 and 19 were distorted octahedral with N2O4 coordination; and in 17 was distorted square planar geometry with N2O2 coordination. iii) In the crystal structure of nickel(II) complexes, the geometry of Ni(II) ion in 7 was distorted octahedral with N4O2 coordination; in 12 and 13 were square planar with O4 coordination; and in 28 was distorted square planar with N4 coordination. Spectral characterizationsThe ESI mass spectral data of the copper(II) and nickel(II) complexes and ESR spectra for all copper(II) complexes were obtained and showed good agreement with the proposed structure of the complexes.The 1H NMR and 13C NMR spectra of the ligands were analyzed to confirm the formation of Schiffs base ligands. The IR spectra of complexes 15 show band near 16001639 cm1 for (C=N) group of bipyridine, at 3650 and 3625 cm1 to the bridging OH group (4 and 5), at 3189 cm1 for N-H stretching and a band at 1315 cm1 for N-H bending vibrations (6 and 7). The IR spectra of complexes 811 has bands near 3095-3070 cm1 and 2895-2876 cm1for aromatic and aldehyde CH stretching and the band at 461-568 cm1 for metal-oxygen (MO). The IR spectra of complexes 1623 a band near 1690 cm1 for C=O (aldehyde), 1620-1650 cm1 for (C=N) group, 1530-1560 cm1 for the phenoxide bridging with the metal ions. The IR spectrum of complexes 2432 show band in the region of 1620-1650 cm1 for (C=N), 1000-1100 cm1 and 625 cm1 for antisymmetric stretch and antisymmetric bend of the perchlorate ions, respectively. The electronic spectra for all complexes were obtained in DMF solution. In the UV region of all complexes the peaks near 240290 nm due to * transition and peaks near 300 - 450 nm due to n */ligandmetal charge transfer/metalligand charge transfer transitions. The copper(II) complexes of bidendate N2 donar ligands show d-d bands around 518 - 636 nm, characteristic of distorted square pyramidal/trigonal bipyramidal geometry (1-3, 5 and 6) and 662 nm of distorted octahedral geometry (4). The copper(II) complexes of O2 donar ligands show d-d bands around 520-560 nm characteristic of square planar geometry (811). The mixed ligand copper(II) complexes show d-d bands around 504-708 nm characteristic of distorted square planar/octahedral geometry (1619). The Schiffs base copper(II) complexes show d-d bands around 568-594 nm which may be distorted square planar geometry (2427). The nickel(II) complexes of biimidazole show d-d bands at 1013, 960 and 593 nm which is characteristic of distorted octahedral geometry (7). The nickel(II) complexes of O2 donar ligands (1215), tetradentate bappz (28) and tetradentate acyclic Schiffs base ligands (2932) show d-d bands around 518-594 nm characteristic of square planar geometry.Hirshfeld surface calculationsThe 2D full and resolved HH, NH and OH fingerprint plots of the copper(II) and nickel(II) complexes of N2 donar ligands conveys that the complex formation of ligands with metal ions destroy the stacking interactions in bipyridine/biimidazole, and perchlorate and hydroxyl group cause a larger influence than other co-ligands. Electrochemical studies(i) At cathodic potentialThe mononuclear copper(II) complexes of bidendate N2 donar ligands exhibit one electron quasi-reversible redox wave at cathodic potential in the region Epc = 0.63 to 0.76 V and the binuclear copper(II) complexes exhibit two one electron quasi-reversible redox waves in the region of E1pc = 0.72 to 0.73 V & E2pc = 1.24 to 1.45 V.The mononuclear copper(II) complexes of bidendate O2 donar ligands exhibit one electron quasi-reversible redox wave at cathodic potential in the region at E1pc = 0.74 to 0.77 V. The mixed ligand copper(II) complexes exhibit one electron quasi-reversible redox wave at cathodic potential in the region at E1pc = 0.74 to 0.90 V. The copper(II) complexes of Schiffs base ligands shows one electron quasi-reversible redox wave at cathodic potential in the region at E1pc = 0.71 to 0.85 V.The mononuclear nickel(II) complexes exhibit one electron quasi-reversible redox wave at cathodic potential in the region at Epc = 0.61 to 0.80 V. The nickel(II) complexes of Schiffs base ligands and bappz shows one electron quasi-reversible redox wave at cathodic potential in the region at Epc = 0.69 to 1.65 V.(ii) At anodic potentialAll the mononuclear nickel(II) complexes show quasireversible one electron transfer at anodic potential (Epa = 1.28 V for biimidazole complex, Epa = 1.08 to 1.44 V for bidendate ligands with O2 donar set complexes and Epa = 0.88 to 1.21 V for Schiffs base complexes).pH-controlled molecular ion motionThe copper(II) and nickel(II) complexes of Schiffs base ligands were analysed for molecular motions by absorption spectroscopy. Titration of the complexes with base induces colour change of the solution and also results in the considerable change in absorption spectrum. The increase in d-d band of the complexes indicates that the colour and spectral changes associated to the deprotonation process. The change of the position of copper/nickel atom from N4 compartment to N2O2 compartment was achieved by varying the pH of the complex solution.BSA binding studiesThe BSA binding studies of the complexes copper(II) and nickel(II) complexes were carried out using fluorescence spectroscopy and binding constant values were determined. The association binding constant for copper(II) and nickel(II) complexes of N2 donar ligands were in the range of 1.65 104 to 3.59 104 M-1, for copper(II) and nickel(II) complexes of O2 donar ligands were in the range of 7.05 104 to 4.68 105 M-1 and for Schiffs base copper(II) and nickel(II) complexes were in the range of 1.27 104 to 1.58 105 M-1. The binding constant values were comparitively higher for complexes with bidentate O2 donar ligands than that of other complexes due to the difference in planarity of the complexes. DNA binding studies(i) Absorption spectroscopy The DNA binding ability of the complexes were investigated using absorption spectroscopy and binding constant values were determined. The Kb values for bidendate copper(II) and nickel(II) complexes of N2 donar ligands were found to be in the range of 2.75 103 to 1.03 105 M-1 and of O2 donar ligands were in the range of 1.16 104 to 6.72 104 M-1. For mixed ligand copper(II) complexes the Kb values were in the range of 2.56 103 to 5.10 104 M-1 and for Schiffs base copper(II) and nickel(II) complexes the Kb values were in the range of 1.63 103 to 6.20 104 M-1.(ii) Fluorescence spectroscopyThe DNA binding ability of the complexes were investigated using fluorescence spectroscopy and linear SternVolmer quenching constant (Ksv) values were determined. The Ksv values for bidendate copper(II) and nickel(II) complexes of N2 donar ligands were found to be in the range of 3.93 104 M1 to 7.86 105 M1 and of O2 donar ligands were in the range of 1.88 103 M1 to 1.41104 M1. For mixed ligand copper(II) complexes the Ksv values were in the range of 2.89 103 M1 to 2.60 104 M1 and for Schiffs base copper(II) and nickel(II) complexes the Ksv values were in the range of 2.33 103 M-1 to 1.51 105 M-1.

(iii) Circular dichroism spectroscopyAll the complexes have shown moderate shift in the positive CD signal at 272-276 nm with slight decrease/increase in intensity for both the negative ellipticity band near 245 nm and the positive ellipticity band near 275 nm. The binding of complexes with ctDNA was found to be in groove and electroststic binding for copper(II) and nickel(II) bidendate N2 / O2 chelating ligands but in the case of mixed ligand copper(II) complexes and Schiffs base copper(II)/ nickel(II) complexes the mode of binding vary from groove binding to itercalation depending on the planarity, hetero atoms and aromaticity of the ligand molecules.Molecular docking studiesAll the complexes were docked within the DNA duplex of sequence d(CGCGAATTCGCG)2 dodecamer (PDB ID: 1BNA) in order to predict the chosen binding site along with preferred orientation of the ligand and the relative binding energies were calculated. DNA cleavage ability of complexesThe DNA cleavage was carried out for all the complexes and their mechanistic pathway was also studied. All the complexes show no cleavage without the addition reactive agents (H2O2/MPA), the cleavage process was concentration dependent and all complexes cleave efficiently at 200 M concentration. All the copper(II) complexes cleaves pBR322 DNA in the presence of 3-mercaptopropionic acid and for the cleavage process to occur the singlet oxygen plays a vital role for formation of involvement of copper-oxo intermediate. All the nickel(II) complexes cleaves pBR322 DNA in the presence of hydrogen peroxide and cleavage process preferentially proceeded by a hydroxyl radical mechanism with OH formation. Oxidative cleavage of plasmid DNA species may lead to the formation of hydrogen peroxide (H2O2), and/or hydroxyl radical (HO) species, which cause damage to the sugar and/or base.Antimicrobial studiesAll the complexes were screened for antimicrobial analysis with four pathogenic bacteria species and two fungal species and the obtained results as zone of inhibiton have also been compared with those of the standard drugs, amikacin and ketokonazole for bacteria and fungi, respectively. Chapter VSummary and conclusionsThe summary of the present work is presented in this chapter. The brief idea about the future course of the task is also offered.The thesis finally ends with list of references that is cited in chapter 3 and 4 of this thesis.

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List of papers published from this work1. A. Jayamani, N. Sengottuvelan, S. K. Kang, Y-I. Kim, Studies on nucleic acid/protein interaction, molecular docking and antimicrobial properties of mononuclear nickel(II) complexes of piperazine based Schiffs base, Inorganic Chemistry Communications, 48 (2014) 147152.2. A. Jayamani, N. Sengottuvelan, G. Chakkaravarthi, Synthesis, structural, electrochemical, DNA interaction, antimicrobial and molecular docking studies on dimeric copper(II) complexes involving some potential bidentate ligands, Polyhedron, 81 (2014) 764776.3. A. Jayamani, V. Thamilarasan, V. Ganesan, N. Sengottuvelan, P. Manisankar, S. K. Kang, Y-I. Kim, Synthesis of mononuclear copper(II) complexes of acyclic Schiffs base ligands: Spectral, structural, electrochemical, antibacterial, DNA binding and cleavage activity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 122 (2014) 365374. 4. B. Saravanan, A. Jayamani, N. Sengottuvelan, G. Chakkaravarthi, V. Manivannan, Di--hydroxido-4O:O-di--perchlorato-4O:O-bis[(2,2-bipyridine-2N,N)-copper(II)], Acta Crystallographica E, 69 (2013) m600.5. A. Jayamani, V. Thamilarasan, V. Ganesan, N. Sengottuvelan, Structural, electrochemical, DNA binding and cleavage properties of nickel(II) complex [Ni(H2biim)2(H2O)2]2+ of 2,2'-biimidazole, Bull. Korean Chem. Soc., 24 (2013) 1-8.