The C-N coupling reaction of pendant naphthyl group of palladium(II) complexes of 1-alkyl-2-(naphthyl-β-azo)imidazoles. Structural characterization, spectral and redox properties, and correlation with DFT computed data

The reaction of Pd(β-NaiR)Cl₂ (2) [β-NaiR (1) = 1-alkyl-2-(naphthyl-β-azo)imidazoles] with ArNH₂ in MeCN has yielded a C-N coupled product chloro[1-alkyl-2-{(7-imidoaryl)naphthyl-β-azo}imidazole-N,N′,N′′]palladium(II), Pd(β-NaiR-N-Ar)Cl (3-5) and coupling takes place at ortho-C-H position of pendant naphthyl group. The structural confirmation has been achieved by single crystal X-ray structure determination of the representative complexes, Pd(β-NaiEt)Cl₂ (2b) and Pd(β-NaiEt-N-C₆H₄-Cl-p)Cl (5b). The electronic spectra of the products, 3-5, exhibit characteristic transition within 600-900 nm those are absent in Pd(β-NaiR)Cl₂ (2). Cyclic voltammogram shows one oxidative response and two ligand reductions. The products are emissive. The excited state decays via radiative and non-radiative biexponential routes. The electronic structure, spectra and redox properties are explained by DFT computation.     

Synthesis, structure, DNA binding and photocleavage activity of a ruthenium(II) complex with 11-(9-acridinyl)dipyrido[3,2-a:2′,3′-c]phenazine ligand

In our search for new DNA intercalating ligands, a novel bifunctional intercalator 11-(9-acridinyl)dipyrido[3,2-a:2′,3′-c]phenazine, acdppz (has two potentially effective intercalators via dipyridophenazine(dppz) and acridine which are linked together via C-C bond) and its corresponding Ru(II) polypyridyl complex [Ru(phen)₂(acdppz)]²⁺ (where phen = 1,10-phenanthroline) have been synthesized and characterized. The electrochemical behaviors of the ligand and its complex have been thoroughly examined. The structure of acdppz and [Ru(phen)₂(acdppz)]²⁺ were determined by X-ray crystallography. From the crystal structure of the complex, we found that the dppz moiety is not coplanar with the acridine ring, having a dihedral angle of 64.79 in the acdppz. The selected bond lengths and angles for the crystal structure of [Ru(phen)₂(acdppz)]²⁺ were compared to the geometry-optimized molecular structure of [Ru(phen)₂(acdppz)]²⁺ derived by Gaussian. The interaction of [Ru(phen)₂(acdppz)]²⁺ with calf-thymus (CT) DNA was investigated by absorption and viscometry titration, thermal denaturation studies. The above measurements indicated that the complex binds less strongly with the CT DNA due to the intercalation by the ruthenium bound acdppz with an intrinsic binding constant of 2.6 × 10⁵ M⁻¹. Molecular-modeling studies also support an intercalative mode of binding of the complex to the model duplex d(CGCAATTGCG)₂ possibly from the major groove with a slight preference for GC rich region. Additionally, the title complex promotes the cleavage of plasmid pBR322 DNA upon irradiation under aerobic conditions.     

Synthesis, structure, DNA binding and cleavage properties of ternary amino acid Schiff base-phen/bipy Cu(II) complexes

Ternary Cu(II) complexes [Cu(II)(saltrp)(B)] (1,2), (saltrp = salicylidene tryptophan, B = 1,10 phenathroline (1) or 2,2′ bipyridine (2)) were synthesized and characterized. Complex 2 was structurally characterized by single crystal X-ray crystallography. The molecular structure shows a distorted square pyramidal coordination geometry (CuN₃O₂) in which the ONO donor Schiff base is bonded to the Cu(II) in the basal plane. The N,N donor heterocyclic base displays an axial-equatorial binding mode. CT-DNA binding studies revealed that the complexes show good binding propensity (Intrinsic binding constant, K_b = 3.32 × 10⁵ M⁻¹ for 1 and K_b = 3.10 × 10⁵ M⁻¹ for 2). The catalytic role of these complexes in the oxidative and hydrolytic cleavage of DNA was studied in detail. Complex 1 binds and cleaves DNA more efficiently as compared to 2. From the kinetic experiments, rate constants for the hydrolysis of phosphodiester bond of DNA backbone were determined as 1.94 h⁻¹ and 1.05 h⁻¹ for 1 and 2 respectively. It amounts to (2.93-5.41) × 10⁷ fold rate enhancement compared to uncatalyzed double stranded DNA, which is impressive as compared to related Cu(II) Schiff base complexes.     

Synthesis and characterization of 5,5′-dibromo-2,2′-dipyridyl disulfide and some of its derivatives: X-ray structure of 5,5′-dibromo-2,2′-dipyridyl disulfide and bis(5-bromopyridine-2-ylthio) methane

Synthesis and characterization of 5,5′-dibromo-2,2′-dipyridyl disulfide and some of its derivatives under mild reaction conditions is described. A series of some novel synthetically important symmetrical/unsymmetrical bromo substituted pyridyl alkyl/aryl sulfur compounds have been easily synthesized from a variety of alkyl halides, using NaBH₄ in moderate to good yields. The important features of this protocol are strong base-free, operational simplicity, short reaction time and high yield. The synthesized compounds are characterized with the help of elemental analysis, IR, ¹H NMR, ¹³C NMR and mass spectral data (in representative cases). X-ray crystal structure analysis of 5,5′-dibromo-2,2′-dipyridyl disulfide (1) and bis(5-bromopyridine-2-ylthio) methane (2a) have been carried out to establish their molecular structure. Compound (1) and (2a) are monoclinic and crystallizes into P2₁/n and C2/c space group, respectively.