Multispectroscopic studies on the interaction of a copper(ii) complex of ibuprofen drug with calf thymus DNA

The interaction of copper(II)–ibuprofenato complex with calf thymus DNA (ct-DNA) has been explored following, UV-visible spectrophotometry, fluorescence measurement, dynamic viscosity measurements, and circular dichroism spectroscopy. In spectrophotometric studies of ct-DNA it was found that [Cu(ibp)₂]₂ can form a complex with double-helical DNA. The association constant of [Cu(ibp)₂]₂ with DNA from UV-Vis study was found to be 6.19 × 10⁴ L mol^?1. The values of K_f from fluorescence measurement clearly underscore the high affinity of [Cu(ibp)₂]₂ to DNA. The experimental results showed that the conformational changes in DNA helix induced by [Cu(ibp)₂]₂ are the reason for the fluorescence quenching of the DNA-Hoechst system. In addition, the fluorescence emission spectra of intercalated methylene blue (MB) with increasing concentrations of [Cu(ibp)₂]₂ represented a significant increase of MB intensity as to release MB from MB-DNA system. The results of circular dichroism (CD) suggested that copper(II)–ibuprofenato complex can change the conformation of DNA. In addition, the results of viscosity measurements suggest that copper(II)–ibuprofenato complex may bind with non-classical intercalative mode. From spectroscopic and hydrodynamic studies, it has been found that [Cu(ibp)₂]₂ interacts with DNA by partial intercalation mode which contains intercalation and groove properties.     

The Effects of Grafting of 2-Pyridyl to [Ru(bpy)2(Hpip)]2+ on Acid-Base and DNA-Binding Properties: Experimental and DFT Studies

Abstract

A new Ru(II) complex of [Ru(bpy)₂(Hppip)]²⁺ {bpy = 2,2′-bipyridine; Hppip = 2-(4-(pyridin- 2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} has been synthesized by grafting of 2-pyridyl to parent complex [Ru(bpy)₂(Hpip)]²⁺ {Hppip = 2-(4-phenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline}. The acid-base properties of [Ru(bpy)₂(Hppip)]²⁺ studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)₂(Hppip)]²⁺ that was driven by the protonation/deprotonation of the imidazolyl and the pyridyl moieties. The complex was demonstrated to be a DNA intercalator with an intrinsic DNA binding constant of (5.56 ± 0.2) × 10⁵ M^?1 in buffered 50 mM NaCl, as evidenced by UV-visible and luminescence titrations, reverse salt effect, DNA competitive binding with ethidium bromide, steady-state emission quenching by [Fe(CN)₆]^4-, DNA melting experiments and viscosity measurements. The density functional theory method was also used to calculate geometric/electronic structures of the complex in an effort to understand the DNA binding properties. All the studies indicated that the introduction of 2-pyridyl onto Hpip ligand is more favorable for extension of conjugate plane of the main ligand than that of phenyl, and for greatly enhanced ct-DNA binding affinity accordingly.     

pH effects on optical and DNA binding properties of a thiophene-containing ruthenium(II) complex

A new ruthenium(II) complex, [Ru(bpy)₂(Htip)]Cl₂ {where bpy = 2,2′-bipyridine and Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}, has been synthesized and characterized by ¹H NMR spectroscopy, elemental analysis, and mass spectrometry. The pH effects on UV-Vis absorption and emission spectra of the complex have been studied, and the ground- and excited-state acidity ionization constant values have been derived. The calf thymus (ct) DNA binding properties of the complex have been investigated with UV-Vis absorption and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The molecular structures and electronic properties of [Ru(bpy)₂(Htip)]²⁺ and deprotonated form [Ru(bpy)₂(tip)]⁺ have also been investigated by means of density functional theory calculations in an effort to understand the DNA binding properties. The results suggest that the complex undergo three-step successive protonation/deprotonation reactions with one of which occurring over physiological pH region, and act as a ct-DNA intercalator with an intrinsic DNA binding constant value on 10⁵ M⁻¹ order of magnitude that is insensitive to pH.     

Potential new inorganic antitumour agents from combining the anticancer traditional Chinese medicine (TCM) matrine with Ga(III), Au(III), Sn(IV) ions, and DNA binding studies

Three new compounds of Ga(III), Au(III), Sn(IV) with matrine (MT), [H-MT][GaCl₄] (), [H-MT][AuCl₄] () and [Sn(H-MT)Cl₅] (), have been synthesized and characterized by elemental analysis, IR, ESI-MS and single crystal X-ray diffraction methods. The crystal structural analyses indicate that 1 and 2 are ionic compounds, whereas 3 is a tin(IV) complex formed by the monodentate MT via its carbonyl oxygen atom of MT coordinating to Sn(IV). Their in vitro cytotoxicity towards eight selected tumour cell lines has been evaluated by MTT (3-[4,5-Dimentylthiazole-2-yl]-2,5-diphenpyltetra-zolium bromide) method, and compounds 1 and 2 exhibit enhanced activity, such as 1 to SW480, 2 to HeLa, HepG2 and MCF-7, which exceeds matrine and cisplatin, and display synergistic contribution of their components. The cell cycle analyses show that compounds 1, 3 and MT exhibit cell cycle arrest at the G₂/M phase. Interactions of these compounds with calf thymus DNA (ct-DNA) have been investigated by spectroscopic analyses. The planar extension of the intercalative metal-matrine compounds increases the interaction of the metal-matrine with DNA, indicating that the cationic metal ions and configuration of the intercalated metal-matrine will affect the extent of interaction. Compound 2, [H-MT][AuCl₄], exhibits more intensive binding ability to DNA, which may correlate with intercalation and other action mode. The circular dichroism spectra of the ct-DNA bound with metal-MT compounds also suggest that ct-DNA interacted with 1, 2, 3 does not influence its secondary structure. Furthermore, both compounds 1 and 2 exhibit effective inhibition ability to topoisomerase (TOPO I) at concentration of 50 μM, while matrine and compound 3 do not.     

Hydrogen-halide versus alkyl-halide oxidative addition in dimethyl platinum(II) complexes: Crystal structure of [PtBr2(bpy)]

Dimethyl platinum(II) complexes [PtMe₂(NN)] {NN = bu₂bpy (4,4′-di-tert-butyl-2,2′-bipyridine) (1a), bpy (2,2′-bipyridine) (1b), phen (1,10-phenanthroline) (1c)} reacted with commercial 3-bromo-1-propanol in the presence of 1,3-propylene oxide to afford cis, trans- [PtBrMe₂{(CH₂)₃OH}(NN)] (NN = bu₂bpy (2a), bpy (2b), phen (2c)). On the other hand, [PtMe₂(NN)] (1a)-(1b) reacted with the trace of HBr in commercial 3-bromo-1-propanol to give [PtBr₂(NN)] (NN = bu₂bpy (3a), bpy (3b)). The reaction pathways were monitored by ¹H NMR at various temperatures. Treatment of 1a-1b with a large excess of 3-bromo-1-propanol at −80 °C gave the corresponding methyl(hydrido)platinum(IV) complexes [PtBr(H)Me₂(NN)] (NN = bu₂bpy (4a), bpy (4b)) via the oxidative addition of dimethyl platinum(II) complexes with HBr. The complexes [PtBr(H)Me₂(NN)] decomposed by reductive elimination of methane above −20 °C for bu₂bpy and from −20 to 0 °C for bpy analogue to give methane and platinum(II) complexes [PtBrMe(NN)] (5a)-(5b) and then decomposed at about 0 °C to yield [PtBr₂(NN)] and methane. When the reactions were performed at a molar ratio of Pt:RX/1:10, the corresponding complexes [PtBrMe(NN)] (5a)-(5b) were also obtained. The crystal structure of the complex 3b shows that platinum adopts square planar geometry with a twofold axis through the platinum atom. The Pt…Pt distance (5.164 Å) is considerably larger than the interplanar spacing (3.400 Å) and there is no platinum-platinum interaction.     

Oxidative addition of mercury(II) halides and carboxylates to platinum(II): formation of Pt-Hg covalent and donor-acceptor bonds

The complex [PtMe₂(bu₂bpy)], 1, bu₂bpy = 4,4′-di-t-butyl-2,2′-bipyridine reacts with mercury(II) halides HgX₂ (X = Cl, Br, O₂CCF₃, O₂CMe) to give the corresponding complexes [PtMe₂X(HgX)(bu₂bpy)], 2, by trans oxidative addition followed, when X = O₂CCF₃, O₂CMe only, by easy isomerization to the cis isomers 3. The complexes 2 or 3 react with complex 1 to give the corresponding adducts [PtMe₂X(bu₂bpy)(μ-HgX)PtMe₂X(bu₂bpy)], 4, which are shown to contain both covalent and donor-acceptor Pt-Hg bonds in the solid state, and which exhibit very easy fluxionality in solution.     

Binding analysis of ytterbium(III) complex containing 1,10-phenanthroline with DNA and its antimicrobial activity

To evaluate the biological preference of [Yb(phen)₂(OH₂)Cl₃](H₂O)₂ (phen is 1,10-phenanthroline) for DNA, interaction of Yb(III) complex with DNA in Tris–HCl buffer is studied by various biophysical and spectroscopic techniques which reveal that the complex binds to DNA. The results of fluorescence titration reveal that [Yb(phen)₂(OH₂)Cl₃](H₂O)₂ has strongly quenched in the presence of DNA. The binding site number n, apparent binding constant K _b, and the Stern–Volmer quenching constant K _SV are determined. ΔH ⁰, ΔS ⁰, and ΔG ⁰ are obtained based on the quenching constants and thermodynamic theory (ΔH ⁰?>?0, ΔS ⁰?>?0, and ΔG ⁰?<?0). The experimental results show that the Yb(III) complex binds to DNA by non-intercalative mode. Groove binding is the preferred mode of interaction for [Yb(phen)₂(OH₂)Cl₃](H₂O)₂ to DNA. The DNA cleavage results show that in the absence of any reducing agent, Yb(III) complex can cleave DNA. The antimicrobial screening tests are also recorded and give good results in the presence of Yb(III) complex.     

Intercalation of manganese-mefenamic acid complex into double stranded of calf thymus DNA

Abstract

The interaction of the [Mn(mef)₂(phen)H₂O] complex in which mef is mefenamic acid drug and phen is 1,10 phenanthrolin ligand with calf thymus DNA (ct-DNA) was studied by using different spectroscopic methods, molecular docking and viscometery. The competitive fluorescence and UV–Vis absorption spectroscopy indicated that the complex interacted with ctDNA via intercalating binding mode with the binding constant of 1.16?×?10⁴ Lmol^?1. The thermodynamic studies showed that the reaction between the complex and ctDNA is exothermic. Furthermore, the complex induced changes in DNA viscosity. Circular dichroism spectroscopy (CD) was employed to measure the conformational changes of ctDNA in the presence of the complex and verified intercalation binding mode. The molecular modeling results illustrated that the complex interacted via intercalation by relative binding energy of ?28.45?kJ mol^?1.     

Anticancer activity of organotin compounds. 2. Interaction of diorganotin dihalides with nucleic acid bases and nucleosides; the synthesis of adenine,adenosine and 9-methyladenine adducts

The syntheses of the complexes formulated as SnMe₂Cl₂(Ad)₂ (I), SnMe₂Cl₂(Ado)₂ (II), SnMe₂Cl₂- (9-MeAd)₂ (III) [Ad = adenine, Ado = adenosine, 9-MeAd = 9-methyladenine] as well as the more unexpected SnPhCl₂(OH)(Ad)₂·3H₂O (IV) and SnPhCl₃(Ado)₂ (V) by reaction of SnMe₂Cl₂ or SnPh₂Cl₂ with the appropriate bases in methanol is described. ¹H NMR studies suggest that coordination is through the N-7 position of the adenine base.     

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

A novel Ru(II) complex, [Ru(bpy)₂(btppz)]Cl₂, where bpy = 2,2′-bipyridine and btppz = benzo[h]tripyrido[3,2-a:2′,3′-c:2″,3″-j]phenazine, has been synthesized and characterized. The pH effects on UV-visible (UV-vis) absorption and emission spectra of the complex have been studied and ground- and excited-state ionization constants of the complex have been derived. The calf thymus DNA (ct-DNA) binding properties of the complex were investigated with UV-vis absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, reverse salt titrations and viscosity measurements. The complex was demonstrated to act as dual molecular switches: pH-induced “on-off” emission switch with an on-off intensity ratio of ∼54 which is favorably compared with those reported for structurally analogous Ru(II) complexes, and a DNA molecular light switch with a luminescence enhancement factor of 22 as it intercalatively bound to the DNA.     

Intercalation of a Zn(II) complex containing ciprofloxacin drug between DNA base pairs

In this study, an attempt has been made to study the interaction of a Zn(II) complex containing an antibiotic drug, ciprofloxacin, with calf thymus DNA using spectroscopic methods. It was found that Zn(II) complex could bind with DNA via intercalation mode as evidenced by: hyperchromism in UV–Vis spectrum; these spectral characteristics suggest that the Zn(II) complex interacts with DNA most likely through a mode that involves a stacking interaction between the aromatic chromophore and the base pairs of DNA. DNA binding constant (K_b = 1.4 × 10⁴ M^?1) from spectrophotometric studies of the interaction of Zn(II) complex with DNA is comparable to those of some DNA intercalative polypyridyl Ru(II) complexes 1.0 ?4.8 × 10⁴ M^?1. CD study showed stabilization of the right-handed B form of DNA in the presence of Zn(II) complex as observed for the classical intercalator methylene blue. Thermodynamic parameters (ΔH < 0 and ΔS < 0) indicated that hydrogen bond and Van der Waals play main roles in this binding prose. Competitive fluorimetric studies with methylene blue (MB) dye have shown that Zn(II) complex exhibits the ability of this complex to displace with DNA-MB, indicating that it binds to DNA in strong competition with MB for the intercalation.     

DNA binding and bending by dinuclear complexes comprising ruthenium polypyridyl centres linked by a bis(pyridylimine) ligand

The interaction of enantiomerically pure dinuclear complexes of the form [Ru₂(L-L)₄L¹]⁴⁺ (where L-L = 2,2^′-bipyridine (bpy) or 1,10-phenanthroline (phen) and L¹ = bis(pyridylimine) ligand ((C₅H₄N)CN(C₆H₄))₂CH₂)) with ct-DNA have been investigated by absorbance, circular dichroism, fluorescence displacement assays, thermal analysis, linear dichroism and gel electrophoresis. The complexes all bind more strongly to DNA than ethidium bromide, stabilise DNA and have a significant bending effect on DNA. The data for Δ,Δ-[Ru₂(bpy)₄L¹]⁴⁺ are consistent with it binding to DNA outside the grooves wrapping the DNA about it. By way of contrast the other complexes are groove-binders. The phen complexes provide a chemically and enantiomerically stable alternative to the DNA-coiling di-iron triple-helical cylinder previously studied. In contrast to the di-iron helicates, the phen complexes show DNA sequence effects with Δ,Δ-[Ru₂(phen)₄L¹]⁴⁺ binding preferentially to GC and Λ,Λ-[Ru₂(phen)₄L¹]⁴⁺ to AT.     

The dichotomy in the DNA-binding behaviour of ruthenium(II) complexes bearing benzoxazole and benzothiazole groups

The substituted tris(bipyridine)ruthenium(II) complexes {[Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) [where bpy=2,2'-bipyridine and bbob=bis(benzoxazol-2-yl)-2,2'-bipyridine] have been prepared and compared to the previously studied complex [Ru(bpy)(2)(4,4'-bbtb)](2+) [where bbtb=bis(benzothiazol-2-yl)-2,2'-bipyridine]. From the UV/VIS titration studies, Delta-[Ru(bpy)(2)(4,4'-bbob)](2+) displays a stronger association than the Lambda-isomer with calf-thymus DNA (ct-DNA). For [Ru(bpy)(2)(5,5'-bbob)](2+), there appears to be minimal interaction with ct-DNA. The results of fluorescence titration studies suggest that [Ru(bpy)(2)(4,4'-bbob)](2+) gives an increase in emission intensity with increasing ct-DNA concentrations, with an enantiopreference for the Delta isomer, confirmed by membrane dialysis studies. The fluorescent intercalation displacement studies revealed that [Ru(bpy)(2)(4,4'-bbob)](2+) and [Ru(bpy)(2)(5,5'-bbob)](2+) display a preference for more open DNA structures such as bulge and hairpin sequences. While Lambda-[Ru(bpy)(2)(4,4'-bbtb)](2+) has shown the most significant affinity for all the oligonucleotides sequences screened in previous studies, it is the Delta isomer of the comparable benzoxazole ruthenium(II) complex (Delta-[Ru(bpy)(2)(4,4'-bbob)](2+)) that preferentially binds to DNA.     

Synthesis and DNA threading properties of quaternary ammonium [Ru(phen)2(dppz)] derivatives

Ruthenium complexes with one dipyrido[3,2-a:2′-3′-c]phenazine (dppz) ligand, e.g. [Ru(phen)₂(dppz)]²⁺ (phen = phenanthroline), shows strong binding to double helical DNA and are well-known DNA “light-switch” molecules. We have here investigated four new [Ru(phen)₂(dppz)]²⁺ derivatives with different bulky quaternary ammonium substituents on the dppz ligand to find relationships between molecular structure and intercalation kinetics, which is considered to be of importance for antitumor applicability. Linear dichroism spectroscopy shows that the enantiomers of the new complexes exhibit very similar binding geometries (intercalation of dppz moiety between adjacent DNA base pairs) as the enantiomers of the parent [Ru(phen)₂(dppz)]²⁺ complex. Absorption spectra and luminescence properties provide further evidence for a final intercalative binding mode which has to be reached by threading of a bulky moiety between the strands of the DNA. Δ-enantiomers of all the new complexes show much slower association and dissociation kinetics than that of a reference complex without a cationic substituent. Kinetics were not very different whether the bulky quaternary group was derived from hexamethylene tetramine or 1,4-diazabicyclo-(2,2,2)octane (DABCO) or whether it had one or two positive charges. However, a complex in which the hexamethylene tetramine substituent is attached via a phenyl group showed a lowered association rate, in addition to an improved quantum yield of luminescence. A second positive charge on the DABCO substituent resulted in a much slower dissociation rate, suggesting that the distance from the Ru-centre and the amount of charge are both important for threading intercalation kinetics.     

Organotin(IV) derivatives containing bis(diphenylphosphine)- and bis(diphenylphosphineoxo)alkanes

Di-organotin(IV)halides R₂SnCl₂ (R=Me or Ph) react with bis(diphenylphosphine)methane (DPPM) and bis(diphenylphosphine)ethane (DPPE) in ethanol in aerobic conditions yielding 1:1 adducts [R₂SnCl₂(DPPM–O₂)] and [R₂SnCl₂(DPPE–O₂)], respectively, containing the bis(diphenylphosphine) in oxidized form. The 1:1 adduct [SnMe₂Cl₂(DPPM–O₂)] is composed of separate molecules containing six-coordinate tin, with the ligands coordinated in the bidentate O₂-fashion, whereas [SnMe₂Cl₂(DPPE–O₂)] is polymeric, with octahedral and centrosymmetric (all trans) tin atoms. In inert atmosphere, the interaction between R₂SnCl₂ and DPPM or DPPE does not take place. Mono-organotin halides RSnCl₃ (R=Me, Buⁿ or Ph) react with DPPM and DPPE yielding 1:1 adducts [RSnCl₃(DPPM)] (R=Me, Buⁿ or Ph) and [RSnCl₃(DPPE)] (R=Buⁿ or Ph).     

Electrochemical behaviour and reactivity of [Os(bpy)2(CO)(OTf)] in halogenated solvents

The dimethylaminopyridine (DMAP) promoted reaction between [Os(bpy)₂(CO)(OTf)]OTf (where ) and methylene chloride is reported. C-Cl bond breaking of a solvent molecule leads to the formation of the [Os(bpy)₂(CO)(Cl)]OTf complex. The reactivity and redox properties of [Os(bpy)₂(CO)(OTf)]OTf were investigated by means of room- and low-temperature electrochemical experiments. In CH₂Cl₂, at low temperature, the complex undergoes two 1e electrochemical and chemical reversible reductions (E_rE_r mechanism), but at room temperature a more complex electrochemical mechanism is observed, leading to the electro-synthesis of [Os(bpy)₂(CO)(Cl)]OTf via electrochemical reversible and chemical irreversible reduction processes (E_rC_i mechanism). The DMAP nucleophilicity was used to produce the new [Os(bpy)₂(CO)(Br)]OTf and [Os(bpy)₂(CO)(I)]OTf complexes which have been fully characterized.     

Synthesis,structure, and biological active evaluation of a new cyclic tetranuclear copper(II) complex bridged both by oxamido and carboxylate groups

A new tetracopper(II) complex bridged both by oxamido and carboxylato groups, namely [Cu₄(dmaepox)₂(bpy)₂](NO₃)₂·2H₂O, where H₃dmaepox and bpy represent N‐benzoato‐N′‐ (3‐methylaminopropyl)oxamide and 2,2′‐bipyridine, was synthesized, and its structure reveals the presence of a centrosymmetric cyclic tetracopper(II) cation assembled by a pair of cis‐dmaepox^3–‐ bridged dicopper(II) units through the carboxylato groups, in which the endo‐ and exo‐copper(II) ions bridged by the oxamido group have a square‐planar and a square‐pyramidal coordination geometries, respectively. The aromatic packing interactions assemble the complex molecules to a two‐dimensional supramolecular structure. The reactivity toward DNA and protein bovine serum albumin (BSA) indicates that the complex can interact with herring sperm DNA through the intercalation mode and the binding affinity is dominated by the hydrophobicity and chelate ring arrangement around copper(II) ions and quenches the intrinsic fluorescence of BSA via a static process. The cytotoxicity of the complex shows selective cancer cell antiproliferative activity.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Synthesis, characterization, structures and DNA-binding properties of complexes [Ru(bpy)2(L)] (L = ptdb, ptda and ptdp) with asymmetric intercalative ligands

A series of Ru(II) polypyridyl complexes [Ru(bpy)₂(ptdb)](ClO₄)₂ (1), [Ru(bpy)₂(ptda)](ClO₄)₂ (2) and [Ru(bpy)₂(ptdp)](ClO₄)₂ (3) with asymmetric intercalative ligands have been synthesized and characterized by EA, mass spectra, ¹H NMR and cyclic voltammetry. The crystal structure of complex 1 has been determined. The DNA-binding properties of the complexes were investigated by absorption titration, luminescence spectroscopy and viscosity measurements. The experimental results suggest that all these complexes bind to DNA in an intercalation mode. The results also show that the order of DNA-binding affinities (A) of this series of complexes is A(1) < A(2) < A(3). It is further confirmed that a ligand planarity of the complexes is a very important factor in affecting the DNA-binding behaviors of such complexes. Theoretical studies for these complexes were also carried out with the density functional theory (DFT) method. The trend in the DNA-binding affinities of this series of complexes can be reasonably explained by the synthetical considerations of the calculated planarity of intercalative ligands, some frontier molecular orbital energies of the complexes and the planarity area (S) of the intercalative ligands.     

Adducts of tin(IV) and organotin(IV) derivatives with 2,2′-azopyridine II. Crystal and molecular structure of SnMe2Br2AZP and further mössbauer and photoelectronic spectroscopic studies

A series of adducts of tin(IV) derivatives with 2,2′-azopyridine, AZP, has been studied by Mössbauer and X-ray photoelectronic spectroscopies and the crystal and molecular structure of SnMe₂Br₂- AZP has been determined. The linear correlation of the Mössbauer parameter isomer shift with partial atomic charge on tin suggests the occurrence of a single homologous series of isostructural adducts. The correlation of the Mössbauer parameter quadrupole splitting and C-Sn-C bond angle permits their calculation in SnMe₂X₂AZP adducts (X = Cl, Br). The N_1s binding energies, obtained by XPS data, pointed out two slightly different values for both pyridinic and azo-group nitrogens. The crystallographic study of the SnMe₂Br₂AZP adduct shows a new structure in which the Sn atom is seven-coordinated.