Biomimetic Model of Coenzyme B₁₂: Aquabis(ethane‐1,2‐diamine‐κN,κN′)ethylcobalt(III) – Its Kinetic and Binding Studies with Imidazoles and Amino Acids and Interactions with CT DNA

Abstract

Pseudo-first-order reaction kinetics and binding studies of trans-[Co(en) 2 (Et)H 2 O] complex with 1H-imidazole, substituted 1H-imidazoles, histidine, histamine, glycine and glycine ethyl ester were investigated by means of spectrophotometric techniques. Equilibrium constants were determined as a function of pH at 258. Binding and kinetic studies were correlated to basicity and steric hindrance. From the equilibrium data, it was found that the entering nucleophile is participating in the transition state, an I d mechanism is proposed. The effect of the incoming ligands on the complex was studied by molecular mechanics. The interaction of trans-[Co(en) 2 (Et)H 2 O] with CT DNA was studied spectrophotometrically.Introduction. -To understand the mechanistic aspect of coenzyme B 12 , which actively carries many enzymatic reactions, model complexes of the coenzyme are widely studied. Much of the study with model complexes reveals that the active part of the coenzyme is the CoÀC bond cleavage, which initiates the enzymatic reaction. The pentammine(methyl)cobalt(III) complex is the simplest model for coenzyme B 12 [1], where four ammine ligands are bound to the Co-center in equatorial positions and one ammine and the methyl ligand are in axial positions trans to each other. Later, cobalamins and cobaloximes were extensively studied.The carbanion ligand coordinated to the Co III center is influenced by the presence of other ligands in cis or trans position with respect to the carbanion ligand. A cis and trans effect on the CoÀC bond was reported for naturally occurring methylcobalamin [2] and various synthetic complexes such as those with tetrapyrrole, imine, oxime, mixed imine-oxime or ammine ligands [3 -7]. The data for the trans-[Co(DH) 2 (Me)L] (DH ¼ dmg ¼ dimethylglyoximato) revealed that the 13 C-NMR chemical shift, the

Interaction of cobalt(III) polypyridyl complexes containing asymmetric ligands with DNA

“…The synthesis of 1,10-phenanthroline-5, 6-dione was according to Yamada and Tanaka [20]. Interactions of the complexes with DNA were studied was in BPE buffer (5 mM Tris-HCl, 50 mM NaCl, pH 7.0).…”

“…Polypyridyl ruthenium(II) complexes with such ligands exhibit concentration dependent binding to DNA [11][12][13], as well as altered spectral properties [14][15][16]. Recently, several mixed complexes of ruthenium(II) and cobalt(III) have been reported [17][18][19]. In this paper, we describe the interaction of mixed ligand cobalt(III) complexes 1-4 ( Fig.…”

Synthesis, DNA interaction and photocleavage studies of ruthenium(II) complexes with 2-(pyrrole) imidazo[4,5-f]-1,10-phenanthroline as an intercalative ligand

“…(HBT = 11H,13H-4,5,9,10,12,14-hexaaza-benzo-[b]-triphenylene). Recently, our group has reported [21][22][23][24][25] binding and photocleavage studies of several mixed ligand complexes of ruthenium(II) and cobalt(III). We chose to concentrate our work on ruthenium(II) complexes of polypyridyls, which have interesting DNA-binding properties.…”

DNA interactions of ruthenium(II) complexes with a polypyridyl ligand: 2-(2, 5-dimethoxyphenyl)-1H-imidazo[4,5-f]1,10-phenanthroline

“…The intercalating mode and DNA-binding affinity of these complexes is greatly influenced by electronic effects from their ligand substituents. Recently, our group has reported [20][21][22][23][24] binding and photocleavage studies of several mixed ligand complexes of ruthenium(II) and cobalt(III). Herein, we report the synthesis and characterization of 2-(2, 5-dimethoxyphenyl)-1H-imidazo [4,5- (2) and [Ru(phen) 2 DMPIP] 2?…”