Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

Synthesis,characterization and nucleic acid binding studies of mononuclear copper(II) complexes derived from azo containing O,O donor ligands

Abstract

Azo linked salicyldehyde and a new 2-hydroxy acetophenone based ligands (HL¹ and HL²) with their copper(II) complexes [Cu(L¹)₂] (1) and [Cu(L²)₂] (2) were synthesized and characterized by spectroscopic methods such as ¹H, 13C NMR, UV–Vis spectroscopy and elemental analyses. Calculation based on Density Functional Theory (DFT), have been performed to obtain optimized structures. Binding studies of these copper (II) complexes with calf thymus DNA (ct-DNA) and torula yeast RNA (t-RNA) were analyzed by absorption spectra, emission spectra and Viscosity studies and Molecular Docking techniques. The absorption spectral study indicated that the copper(II) complexes of 1 and 2 had intrinsic binding constants with DNA or RNA in the range of 7.6?±?0.2?×?10³?M^?1 or 6.5?±?0.3?×?10³M^?1 and 5.7?±?0.4?×?10⁴ M^?1 or 1.8?±?0.5?×?10³ M^?1 respectively. The synthesized compounds and nucleic acids were simulated by molecular docking to explore more details mode of interaction of the complexes and their orientations in the active site of the receptor.     

Evolution of 1, 3, 5-trisubstituted bipyrazole scaffold based platinum(II) complexes as a biological active agent

Abstract

Square planar mononuclear platinum(II) complexes having general formula [Pt(Lⁿ)Cl₂], (where, Lⁿ?=?L^1–4) were synthesized with neutral bidentate heterocyclic 1,3,5-trisubstituted bipyrazole based ligands. The synthesized compounds were characterized by physicochemical method such as TGA, molar conductance, micro-elemental analysis and magnetic moment, and spectroscopic method such as, FT-IR, UV–vis, ¹H NMR, ¹³C NMR and mass spectrometry. Biological applications of the compounds were carried out using in vitro brine shrimp lethality bioassay, in vitro antimicrobial study against five different pathogens, and cellular level cytotoxicity against Schizosaccharomyces pombe (S. Pombe) cells. Pt(II) complexes were tested for DNA interaction activities using electronic absorption titration, viscosity measurements study, fluorescence quenching technique and molecular docking assay. Binding constants (K_b) of ligands and complexes were observed in the range of 0.23–1.07?×?10⁵?M^?1 and 0.51–3.13?×?10⁵?M^?1, respectively. Pt(II) complexes (I–IV) display an excellent binding tendency to biomolecule (DNA) and possess comparatively high binding constant (K_b) values than the ligands. The DNA binding study indicate partial intercalative mode of binding in complex-DNA. The gel electrophoresis activity was carried out to examine DNA nuclease property of pUC19 plasmid DNA.     

Synthesis,DNA Binding,and Photonuclease Activity of New Tetraaza Macrocyclic Constrained Isoxazole Rings as Subunit in Metal Complexes

The DNA-binding and photonuclease activity of newly synthesized tetra-azamacrocyclic ligand L (C₃₂H₃₂N₈O₄) and its complexes of type [MLCl₂] and [ML]Cl₂ (where M = Co(II), Fe(II) and Cu(II); L = N,N′-[3-(4-{5-[(2-amino-ethylamino)-methyl]-isoxazol-3yl}-phenyl)-isoxazol-5-yl methyl-ethane-1,2-diamine] are specified. An octahedral geometry has been proposed for Fe(II) and Co(II) complexes, while the Cu(II) complex has a square planar environment. The absorption spectral results indicate that the complexes bind with the base pairs of DNA, with an intrinsic binding constant K_b of Fe(II), Co(II), and Cu(II) complexes found to be 3.2 × 10⁴ M^?1, 5.3 × 10⁴ M^?1, and 4.2 × 10⁴ M^?1, respectively, in 5 mM Tris-HCl/50 mM NaCl buffer at pH 7.2. The large enhancement in the relative viscosity of DNA on binding to the complexes supports the proposed DNA binding modes. The viscosity and thermal denaturation studies sustain the effective intercalation with DNA. The DNA photocleavage studies demonstrated that compounds exhibit significant photonuclease activity by a concentration dependent on singlet oxygen mediated mechanism.     

DNA binding,prominent photonuclease activity and antibacterial PDT of cobalt(II) complexes of phenanthroline based photosensitizers

Abstract

The chemistry of Co(II) complexes showing efficient light induced DNA cleavage activity, binding propensity to calf thymus DNA and antibacterial PDT is summarized in this article. Complexes of formulation [Co(mqt)(B)₂]ClO₄ 1–3 where mqt is 4-methylquinoline-2-thiol and B is N,N-donor heterocyclic base, viz. 1,10-phenanthroline (phen 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz 3) have been prepared and characterized. The DNA-binding behaviors of these three complexes were explored by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes 1, 2 and 3 were determined to be 1.6?×?10³?M^?1, 1.1?×?10⁴?M^?1 and 6.4?×?10⁴?M^?1 respectively. The experimental results suggest that these complexes interact with DNA through groove binding mode. The complexes show significant photocleavage of supercoiled (SC) DNA proceeds via a type-II process forming singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against E. coli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.     

Macrocyclic complexes: synthesis,characterization, antitumor and DNA binding studies

Abstract

The present paper deals with the synthesis of novel macrocyclic complexes of the type [MLX]X, where [(M?=?Co(II) (1), and Ni(II) (2) X?=?(Cl₂)]. The complexes are synthesized by the reaction of ligand(L)diquinolineno[1,3,7,9]tetraazacyclododecine-7,15-ethane(14H,16H)-benzene with the corresponding metal salts. The synthesized complexes are thoroughly characterized by elemental analysis, FT-IR, ¹H-NMR, Mass and electronic spectra. The complexes (1) and (2) were evaluated for in vitro cytotoxicity against human breast adenocarcinoma cell (MCF-7). MTT cytotoxicity studies shows both the complexes are most effective. The binding properties of these complexes with calf thymus-DNA were studied by absorption, emission spectra, viscosity measurements, and thermal denaturation studies. On binding to CT-DNA, the absorption spectrum undergoes bathochromic and hypochromic shifts. The absorption spectral results indicate that the intrinsic binding constant (K_b) are 4.8?×?10⁵?M^?1 for (1) and 3.9?×?10⁵?M^?1 for (2) respectively, suggesting that complex (1) binds more strongly to CT-DNA than complex (2). The viscosity measurement results revealed the viscosity of sonicated rod like DNA fragments increased when the complex was added to the solution of CT-DNA. The synthesized ligand and its metal complexes are screened for antibacterial and antifungal activities.     

Nickel(II) and copper(II) complexes of Schiff base ligands containing N4O2 and N4S2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H₂L^m (m = 1−4), [1H-pyrrol-2-ylmethylene]{2-[2-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H₂L¹), [1H-pyrrol-2-ylmethylene]{2-[4-(2-{[1H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H₂L²), [1H-pyrrol-2-ylmethylene][2-({2-[(2-{[1H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H₂L³) and [1H-pyrrol-2-ylmethylene][2-({4-[(2-{[1H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H₂L⁴) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML^m (m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL³ and CuL², which have been determined by single crystal X-ray diffraction, indicate that the NiL³ complex has a distorted octahedral coordination environment around the metal while the CuL² complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL² complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.     

Studies on synthesis, characterization, and G-quadruplex binding of Ru(II) complexes containing two dppz ligands

In this work, the interaction between the guanine-rich single-strand oligomer AG₃(T₂AG₃)₃ quadruplex and two Ru(II) complexes, [Ru(L¹)(dppz)₂](PF₆)₄ (1) and [Ru(L²)(dppz)₂](PF₆)₄ (2) (L¹ = 5,5′-di(1-(trimethylammonio)methyl)-2,2′-dipyridyl cation, L² = 5,5′-di(1-(triethylammonio)methyl)-2,2′-dipyridyl cation, dppz = dipyrido[3,2-a:2′,3′-c] phenazine), has been studied by UV-Visible, fluorescence, DNA melting, and circular dichroism in K⁺ buffer. The two complexes after binding to G-quadruplex have shown different DNA stability and fluorescence enhancement. The results show that both complexes can induce the stabilization of quadruplex DNA. ΔT_m values of complexes 1 and 2 at [Ru]/[DNA] ratio of 1:1 were 9.4 and 7.0, respectively. Binding stoichiometry along with the quadruplex was investigated through a luminescence-based Job plot. The major inflection points for complexes 1 and 2 were 0.49 and 0.46, respectively. The data were consistent with the binding mode at a [quadruplex]/[complex] ratio of 1:1. In addition, the conformation of G-quadruplex was not changed by the complexes at the high ionic strength of K⁺ buffer.     

Design,synthesis, MTT assay,DNA interaction studies of platinum(II) complexes

The square planar Pt(II) complexes of the type [Pt(Lⁿ)(Cl₂)] (where Lⁿ = L^1?3 = thiophene-2-carboxamide derivatives and L^4?6 = thiophene-2-carbothioamide derivatives) have been synthesized and characterized by physicochemical and various spectroscopic studies. MIC method was employed to inference the antibacterial potency of complexes in reference to free ligands and metal salt. Characteristic binding constant (K_b) and binding mode of complexes with calf thymus DNA (CT-DNA) were determined using absorption titration (0.76–1.61 × 10⁵ M^?1), hydrodynamic chain length assay and fluorescence quenching analysis, deducing the partial intercalative mode of binding. Molecular docking calculation displayed free energy of binding in the range of –260.06 to –219.63 kJmol^?1. The nuclease profile of complexes towards pUC19 DNA shows that the complexes cleave DNA more efficiently compared to their respective metal salt. Cytotoxicity profile of the complexes on the brine shrimp shows that all the complex exhibit noteworthy cytotoxic activity with LC₅₀ values ranging from 7.87 to 15.94 μg/mL. The complexes have been evaluated for cell proliferation potential in human colon carcinoma cells (HCT 116) and IC₅₀ value of complexes by MTT assay (IC₅₀ = 125–1000 μg/mL).     

DNA groove-binding and acid-base properties of a Ru(II) complex containing anthryl moieties

Abstract

DNA groove binders have been poorly studied as compared to the intercalators. A novel Ru(II) complex of [Ru(aeip)₂(Haip)](PF₆)₂ {Haip?=?2-(9-anthryl)-1H-imidazo[4,5-f][1,10]phenanthroline and aeip = 2-(anthracen-9-yl)-1-ethyl-imidazo[4,5-f][1, 10]phenanthroline} is synthesized and characterized by elemental analysis, ¹H NMR spectroscopy and mass spectrometry. The complex is evidenced to be a calf-thymus DNA groove binder with a large intrinsic binding constant of 10⁶ M^?1 order of magnitude as supported by UV–visible absorption spectral titrations, salt effects, DNA competitive binding with ethidium bromide, DNA melting experiment, DNA viscosity measurements and density functional theory calculations. The acid-base properties of the complex studied by UV–Vis spectrophotometric titrations are reported as well.     

Synthesis,Characterization, Cellular Uptake,Apoptosis, Cytotoxicity,Dna-Binding,and Antioxidant Activity Studies of Ruthenium(II) Complexes

Two new ruthenium(II) polypyridyl complexes [Ru(dmb)₂(HECIP)](ClO₄)₂ (1) (HECIP = N-ethyl-4-[(1,10)-phenanthroline(5,6-f)imidazol-2-yl]carbazole, dmb = 4,4’-dimethyl-2,2’-bipyridine) and [Ru(dmp)₂(HECIP)](ClO₄)₂ (2) (dmp = 2,9-dimethyl-1,10-phenanthroline) have been synthesized and characterized. The DNA-binding behaviors of the two complexes were investigated by absorption spectra, viscosity measurements, and photoactivated cleavage. The DNA-binding constants for complexes 1 and 2 were determined to be 8.03 (± 0.12) × 10⁴ M^?1 (s = 1.62) and 2.97 (± 0.15) × 10⁴ M^?1 (s = 1.82), respectively. The results suggest that these complexes interact with DNA through intercalative mode. The photocleavage of pBR322 DNA by Ru(II) complexes was investigated. The cytotoxicity of complexes 1 and 2 has been evaluated by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide)] method. Complex 1 shows higher anticancer potency than 2 against the four tumor cell lines. Apoptosis and cellular uptake were investigated. The antioxidant activities of the ligand and these complexes were also performed.     

Structure-activity relationship on DNA binding and anticancer activities of a family of mixed-ligand oxidovanadium(V) hydrazone complexes

The title family of mixed-ligand oxidovanadium(V) hydrazone complexes are [V^VO(HL¹)(hq)] (1) and [V^VO(HL²)(hq)] (2), where (HL¹)^2? and (HL²)^2? are the dinegative form of 2-hydroxybenzoylhydrazone of acetylacetone (H₃L¹) and benzoylacetone (H₃L²), respectively, and hq^? is the mononegative form of 8-hydroxyquinoline (Hhq). Complexes were used to determine their binding constant with CT DNA using various spectroscopic techniques namely, electronic absorption, fluorescence and circular dichroism spectroscopy. The binding constant values suggest the intercalative mode of binding with the CT DNA and follow the order: 2 > 1. The bulky size as well as electron withdrawing property of the phenyl group (which is present in the β-diketone part of the hydrazone moiety in complex 2 in place of a CH₃ group in complex 1) is responsible for the higher activity of 2 than 1. Complexes were screened for cytotoxic activity on cervical cancer cells and were found to be potentially active (IC₅₀ value for 1 and 2 is 33 and 29 μM, respectively), even better than the widely used cis-platin (IC₅₀ = 63.5 μM) and carboplatin (IC₅₀ = > 200 μM) which is evident from the respective IC₅₀ value. Nuclear staining experiment suggests that these complexes kill the SiHa cancer cells through apoptotic mode. The molecular docking study also suggested the intercalative mode of binding of these complexes with CT DNA and HPV 18 DNA.     

Synthesis,characterization, redox behavior,DNA and protein binding and antibacterial activity studies of ruthenium(II) complexes of bidentate schiff bases

Two new ruthenium(II) complexes of Schiff base ligands (L) derived from cinnamaldehyde and ethylenediamine formulated as [Ru(L)(bpy)₂](ClO₄)₂, where L¹ = N,N’-bis(4-nitrocinnamald-ehyde)ethylenediamine and L² = N,N’-bis(2-nitrocinnamaldehyde)-ethylenediamine for complex 1 and 2, respectively, were isolated in pure form. The complexes were characterized by physicochemical and spectroscopic methods. The electrochemical behavior of the complexes showed the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of the complexes with calf thymus DNA (CT-DNA) using absorption, emission spectral studies and electrochemical techniques have been used to determine the binding constant, K_b and the linear Stern–Volmer quenching constant, K_SV. The results indicate that the ruthenium(II) complexes interact with CT-DNA strongly in a groove binding mode. The interactions of bovine serum albumin (BSA) with the complexes were also investigated with the help of absorption and fluorescence spectroscopy tools. Absorption spectroscopy proved the formation of a ground state BSA-[Ru(L)(bpy)₂](ClO₄)₂ complex. The antibacterial study showed that the Ru(II) complexes (1 and 2) have better activity than the standard antibiotics but weak activity than the ligands.     

Studies on the reactions of ruthenium(II) substrates with tridentate (N,N,O) azo ligands

Reactions of 1-{[2-(arylazo)phenyl]iminomethyl}-2-phenol, HL_sal, 1, [where H represents the dissociable protons upon complexation and aryl groups of HL_sal are phenyl for HL¹_sal, p-methylphenyl for HL²_sal, and p-chlorophenyl for HL³_sal], ligands with Ru(H)(CO)(Cl)(PPh₃)₃ afforded complexes of composition [(L_sal)Ru(CO)(Cl)(PPh₃)] and (L_sal)₂Ru where the N,N,O donor tridentate (L_sal)⁻ ligands coordinated the metal centre facially and meridionally, respectively. Stepwise formation of [(L_sal)₂Ru] has been ascertained. Reaction of 1-{[2-(arylazo)phenyl]iminomethyl}-2-napthol, HL_nap, 2, [where H represents the dissociable protons upon complexation and aryl groups of HL_nap are phenyl for HL¹_nap, p-methylphenyl for HL²_nap, and p-chlorophenyl for HL³_nap], ligands with Ru(H)(CO)(Cl)(PPh₃)₃ afforded exclusively the complexes of composition [(L_nap)Ru(CO)(Cl)(PPh₃)], where N,N,O donor tridentate (L_nap)⁻ was facially coordinated. The ligand 1-{[2-(phenylazo)phenyl]aminomethyl}-2-phenol, HL, 3, was prepared by reducing the aldimine function of HL¹_sal. Reaction of HL with Ru(PPh₃)₃Cl₂ afforded new azosalen complex of Ru(III) in concert with regiospecific oxygenation of phenyl ring of HL. All the new ligands were characterized by analytical and spectroscopic techniques. The complexes were characterized by analytical and spectroscopic techniques and subsequently confirmed by the determination of X-ray structures of selected complexes.     

Synthesis,Characterization, and Biological Evaluation of Cu(II) Complexes Containing Triflupromazine with Glycine and Histidine

Two novel copper (II) complexes [Cu(TFP)(Gly)Cl] ⋅ 2H₂O complex ( 1 ) and [Cu(TFP)(His)Cl] ⋅ 2H₂O complex ( 2 ) are synthesized, where TFP stands for trifluropromazine, Gly. represents glycine, and His. is histidine. Chemical composition, IR, mass spectra, and magnetic susceptibility tests are performed. Complex binding with macromolecules was investigated using UV-vis, viscosity, gel electrophoresis, and fluorescence quenching. Fluorescence spectroscopy revealed that each complex could replace ethidium bromide (EB). These complexes exhibit grooved, non-covalent, and electrostatic interactions with CT-DNA. Spectroscopy analysis of the BSA interaction showed that complexes bind to protein (K_b values for ( 1 ) is 5.89×10³ M⁻¹ and for ( 2 ) is 9.08×10³ M⁻¹) more strongly than CT-DNA (K_b values for ( 1 ) is 5.43×10³ M⁻¹ and for ( 2 ) is 7.17×10³ M⁻¹). Molecular docking analysis and spectral absorption measurements showed high agreement. Antimicrobial, antioxidant, and anti-inflammatory properties were tested in vitro. The druggability of complex ( 2 ) should be tested in vivo as it is more biologically active.     

Kinetic study of DNA binding of cisplatin and of a bicycloalkyl-substituted (ethylenediamine)dichloroplatinum(II) complex

 Salmon sperm DNA platination has been conducted under strictly pseudo-first-order conditions with cisplatin (1) and rac-{(1S,2S,4S)-exo-2-(aminomethyl)-2-amino-7-bicyclo[2.2.1]heptane}dichloroplatinum(II) (2). An aquation step first occurs for both complexes, with the rate constants k ₁ = 1.12(0.02)×10^–4 s^–1 and 1.47(0.02)×10^–4 s^–1 respectively for 1 and 2 at 37  °C, values in agreement with those previously reported. It is followed by the actual platination step whose second-order rate constant has been determined for the first time by physicochemical techniques. The values for 1 and 2 respectively are: k ₂ = 2.08(0.07) M^–1 s^–1 and 3.9(0.4) M^–1 s^–1. These kinetic data are discussed in the context of a comparison of several biological properties of the two complexes. Received: 15 May 1998 / Accepted: 26 June 1998     

Synthesis, characterization and X-ray crystal structures of copper(II) and nickel(II) complexes with potentially hexadentate Schiff base ligands

Copper(II) and nickel(II) complexes of potentially N₂O₄ Schiff base ligands 2-({[2-(2-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}ethoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L¹) and 2-({[2-(4-{2-[(1-{2-hydroxy-5-[2-phenyl-1-diazenyl]phenyl}methylidene)amino] phenoxy}butoxy) phenyl]imino}methyl)4-[2-phenyl-1-diazenyl]phenol (H₂L²) prepared of 5-phenylazo salicylaldehyde (1) and two various diamines 2-[2-(2-aminophenoxy)ethoxy]aniline (2) and 2-[4-(2-aminophenoxy)butoxy]aniline (3) were synthesized and characterized by a variety of physico-chemical techniques. The single-crystal X-ray diffractions are reported for CuL¹ and NiL². The CuL¹ complex contains copper(II) in a near square-planar environment of N₂O₂ donors. The NiL² complex contains nickel(II) in a distorted octahedral geometry coordination of N₂O₄ donors. In all complexes, H₂L¹ behaves as a tetradentate and H₂L² acts as a hexadentate ligand. Cyclic voltammetry of copper(II) complexes indicate a quasi-reversible redox wave in the negative potential range.     

The structures and magnetism of trinuclear Ni(II), Co(II) and Mn(II) complexes derived from unsymmetrical compartmental ligands

Trinuclear Ni(II), Co(II) and Mn(II) complexes have been prepared from the asymmetric compartmental proligands 2-alkyliminomethyl-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol(alkyl=ethyl, n-propyl and n-butyl) and 2-[(2-methoxy-ethylimino)-methyl]-4-methyl-6-{[methyl-(2-pyridin-2-yl-ethyl)-amino]-methyl}-phenol, which provide adjacent tridentate N₂O and bidentate NO donor sets. The crystal structures of [Ni₃(L⁶)₂(OAc)₂(NCS)₂] · CH₃OH · H₂O, [Co₃(L⁴)₂(OAc)₂(NCS)₂], and [Mn₃(L⁷)₂(OAc)₂(NCS)₂] · CH₃OH · H₂O were determined and show that the metals provide an isosceles triangle with M¹-M²=M¹-M³ ≈ 3.2 Å and M²-M³ ≈ 5.0 Å. The cryomagnetic properties of the complexes have been studied and indicate a weak antiferromagnetic interaction between the adjacent, M¹M² and M¹M³ ions with little magnetic interaction between the terminal M²M³ ions.     

The relationship between the structures of periphery ligands and the DNA binding mode of [Ru(II)(1,10-phenanthroline)(L1L2)dipyrido[3,2-a:2',3'-c]phenazine](n+) (L1=Cl or pyridine and L2=pyridine, n=1,2)

The binding modes of the [Ru(II)(1,10-phenanthroline)(L₁L₂) dipyrido[3,2-a:2′,3′-c]phenazine]²⁺ {[Ru(phen)(py) Cl dppz]⁺ (L₁ = Cl, L₂ = pyridine) and ([Ru(phen)(py)₂dppz]²⁺ (L₁ = L₂ = pyridine)} to native DNA is compared to that of the [Ru(II)(1,10-phenanthroline)₂dipyrido[3,2-a:2′,3′-c]phenazine]²⁺ complex ([Ru(phen)₂dppz]²⁺) by various spectroscopic and hydrodynamic methods including electric absorption, linear dichroism (LD), fluorescence spectroscopy, and viscometric titration. All measured properties, including red-shift and hypochromism in the dppz absorption band, nearly perpendicular molecular plane of the dppz ligand with respect to the local DNA helix axis, prohibition of the ethidium binding, the light switch effect and binding stoichiometry, increase in the viscosity upon binding to DNA, increase in the melting temperature are in agreement with classical intercalation of dppz ligand of the [Ru(phen)₂dppz]²⁺ complex, in which both phenanthroline ligand anchored to the DNA phosphate groups by electrostatic interaction. [Ru(phen)(py)₂ dppz]²⁺ and [Ru(phen)(py) Cl dppz]⁺ complexes had one of the phenanthroline ligand replaced by either two pyridine ligands or one pyridine plus a chlorine ion. They exhibited similar protection from water molecules, interaction with DNA bases, and occupying site that is common with ethidium. The dppz ligand of these two Ru(II) complex were greatly tilted relative to the DNA helix axis, suggesting that the dppz ligand resides inside the DNA and is not perpendicular relative to the DNA helix axis. These observation suggest that anchoring the [Ru(phen)₂dppz]²⁺complex by both phenanthroline is essential for the dppz ligand to be classically intercalated between DNA base-pairs.