Amit K. Ghosh

Mild Synthesis of a Family of Planar Triazinium Cations via Proton-Assisted Cyclization of Pyridyl Containing Azo Compounds and Studies on DNA Intercalation

An efficient synthesis of a family of heteroaromatic triazinium compounds, [2a]X-[2g]X (X = Cl, ClO4, NO3, and HSO4), from 2-(arylazo)pyridines via proton-catalyzed heterocyclization is described. Characterization of the compounds is made by different spectroscopic, electrochemical techniques, as well as single-crystal structure determination of the triflate salt of a representative compound, [2a]CF3SO3. The bond parameters indicate that the tricyclo compound, 2a(+), is planar and aromatic with a N-N bond length of 1.275(6) A. These exhibited fluorescence with an emission maximum in the range of 540-535 nm with moderate quantum yields. The triazinium salts can be reduced in two successive one-electron steps as probed by cyclic voltammetry and coulometry. The paramagnetic radical intermediate 2a(*) is distinguished by a sharp and intense EPR spectrum. Fluorescence spectroscopy, circular dichroism, cyclic voltammetry, viscosity measurements, together with DNA melting studies have been used to characterize the binding of 2a(+) with calf thymus DNA. The emission quenching of the compound by [Fe(CN)6](4-) decreased when bound to DNA. As determined by a MTT assay, 2a(+) exhibited significant cytotoxicity at a higher concentration range of 1 mg/mL to 1 microg/mL; however, the % survival ratio increased with dilution. Cellular uptake studies of the referenced compound were followed by FACS analysis.

Ruthenium complexes of quinone related N-aryl-1,2-diimines. Metal mediated synthesis, X-ray structure and chemical reaction

A family of ruthenium N-aryl-1,2-diiminoarene chelate complexes, [RuCl2(bpy)(diim)], 1 (bpy=2,2′-bipyridine, diim=N-aryl-1,2-diiminoarene) were isolated from the reaction of [RuCl3(bpy)] and a primary aromatic amine (ArNH2) in the presence of aerial oxygen. The diim ligand was formed in situ due to oxidative dimerisation of ArNH2. The metal complex, in this reaction, acts as a mediator. The dichloro complexes were characterized based on their physicochemical data. The X-ray structure of one member of the family was determined and the results used to authenticate the formation of the product from an unusual oxidative fusion of aromatic monoamines. The X-ray structure of 1c (substituent R on the aromatic ring=Cl) revealed a cis geometry with respect to two coordinated chlorides. The bond length trends within the chelate as well as the aromatic rings are consistent with a diimine oxidation state of the ligand bound to ruthenium in its bivalent oxidation state. These complexes showed multiple transitions in the near-IR and visible regions. The highly intense transition at around 540 nm has been assigned to a transition involving two heavily mixed metal–ligand orbitals. The ruthenium(III)/ruthenium(II) couple for the dihalo complexes appeared at a high anodic potential (range 0.50 to 0.90 V), which for differently substituted compounds depend on the Hammett ∑σp parameters of the substitution on the diim ligand. The syntheses and characterization of a few heteroleptic tris-chelates, [Ru(bpy)(diim)L](ClO4)2·nH2O (L=a bidentate N,N-donor), involving the reaction of 1 with two moles of the silver reagent, [AgL2](ClO4), are reported. The tris-chelates showed intense charge transfer in their electronic spectra and multiple cathodic voltammetric responses, which have been assigned as reductions of coordinated ligands.