Stability, lability, spectral parameters and structure of complexes and stereoselective effects in the nickel(II) – l/d/dl-histidine – l/d/dl-methionine systems

Speciation study involving mononuclear binary transition metal (CoII, NiII and CuII) complexes of L-methionine in non-ionic micellar medium

The present work aims to evaluate the binding capacities of binary complexes of L-Methionine with transition metal ions Co^II, Ni^II and Cu^II in Triton X 100-water mixtures, a non-ionic micellar media of different compositions (0.0–2.5% (v/v)), investigated under the experimental conditions of 0.16 mol/dm³ ionic strength using NaNO₃ at a temperature of 303.0 ± 0.1 K Potentiometrically. The potentiometric data was assessed by Irving-Rossotti pH metric technique with the least-squares method of MINIQUAD75, a computer program. The selectivity of the best fit model obtained by continuous exhaustive chemical modelling studies and the accuracy of the results is assessed based on statistical parameters. MLH, ML and ML₂ are the identified species for the three M(Co^II, Ni^II and Cu^II) - Met systems. The shift in the equilibrium of binary metal-methionine complexes with variation in composition (0.0–2.5%) of the solvent can be explained by electrostatic together with non-electrostatic forces contributed by the interaction of solute with solvent.

The kinetics and mechanisms of reactions in the flow systems glycine-sodium trimetaphosphate-imidazoles: the crucial role of imidazoles in prebiotic peptide syntheses

The kinetics of oligopeptides formation in the flow systems glycine-sodium trimetaphosphate-imidazole/N-methylimidazole at thermocyclic regime has been investigated by HPLC and ³¹P NMR methods in the ranges of temperature from 45 to 90 °C and pH from 8.5 to 11.5. Detailed reaction mechanisms have been proposed and justified by quantum chemical calculations using DFT method at the CAM-B3LYP/TZVP level with accounting solvent effect by the C-PCM model. A new imidazole catalysis mechanism by which imidazole reacts with cyclic N,O-phosphoryl glycine giving N-imidazolyl-O-glycyl phosphate as a key intermediate was proposed and validated. It is emphasized that while in the absence of imidazoles, prebiotic activation of amino acids occurs at the N-terminus, in the presence of imidazoles it shifts to the O-terminus. This means that in the peptide elongation N-imidazolyl-O-aminoacyl phosphates play in prebiotic systems the outstanding role similar to that of aminoacyl adenylates formed at the ATP and aminoacyl-tRNA synthetases presence in biosystems. The new crucial role of imidazoles in prebiotic evolution has been noticed. The systems used and modes of their conversion can be good models for prebiotic peptide syntheses in a flow thermocyclic regime.