title: Mild synthesis of a family of planar triazinium cations via proton-assisted cyclization of pyridyl containing azo compounds and studies on DNA intercalation.
abstract: 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.
authors.affiliation: Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Kolkata 700 032, India.
authors.forename: M
authors.initials: M
authors.lastname: Sinan
authors.forename: M
authors.initials: M
authors.lastname: Panda
authors.forename: A
authors.initials: A
authors.lastname: Ghosh
authors.forename: K
authors.initials: K
authors.lastname: Dhara
authors.forename: P E
authors.initials: PE
authors.lastname: Fanwick
authors.forename: D J
authors.initials: DJ
authors.lastname: Chattopadhyay
authors.forename: S
authors.initials: S
authors.lastname: Goswami
mesh_terms: D000818:Animals; D001391:Azo Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000633:toxicity; D002412:Cations / Q000737:chemistry; D002417:Cattle; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D002522:Chlorocebus aethiops; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D003500:Cyclization; D004247:DNA / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D013053:Spectrophotometry; D014783:Viscosity
chemical_list: D001391:Azo Compounds; D002412:Cations; D011725:Pyridines; D004247:DNA; C427203:calf thymus DNA; C023666:pyridine