Tautomerism in neutral histidine.

Change of the tautomeric preference for radical cation of pyruvic acid. DFT studies in the gas phase

Keto-enol tautomerism was investigated for ionized pyruvic acid using the DFT(B3LYP) method and the larger basis sets [6-31++G(d,p), 6-311++G(3df, 3pd) and aug-cc-pVDZ]. Change of the tautomeric preference was observed when going from the neutral to ionized tautomeric mixture. Ionization favors the enolization process (ketoenol) of pyruvic acid, whereas the ketonization (ketoenol) is preferred ...

Secondary Structure Effects on the Acidity of Histidine and Lysine-Based Peptides Model; A Theoretical Study

     In this study, the effect of the secondary structure of the protein on the acid strength of three structures of random (R), alpha helix (α) and beta sheet (b) were investigated theoretically. These structures are related to the cationic amino acids of histidine and lysine in the polypeptide chain of eight-glycine residue. Computational methods at the HF, B3LYP, X3LYP and M05-2X levels in t...

Studies on Prototropic Tautomerism in Neutral and Monoanionic Forms of Pyrimidines by Nuclear Magnetic Resonance Spectroscopy

NMR methods have been applied to evaluation of prototropic tautomerism, N (1)H ^ N (3) H. in several selected pyrimidines, viz. the neutral forms of isocytosine and 2-alkylthiopyrimidone-4, and the monoanionic forms of uracil, 5-fluorouracil and 4-thiouracil. The predominant tautomeric species of the neutral forms could be estimated only qualitatively from chemical shifts. For the monoanionic f...

Tautomeric equilibria for ionized oxamic acid - inhibitor of LDH

Amide-iminol tautomerism was studied for ionized oxamic acid (OA+•) in the gas phase using theDFT method with the UB3LYP functional and various basis sets {6-31++G(d,p), 6-311+G(d,p), and augcc-pVDZ}. Among twenty tautomers-rotamers possible for OA+•, eleven isomers were found to bethermodynamically stable. Similarly as for the neutral molecule, ionization (OA → OA+• + e) favors theamidization ...

Curcumin is soluble in oil and alkali, practically insoluble in water, acidic and neutral pH. In solutions the principal colouring components of curcumin exhibit keto- enol tautomerism and depending on the solvent, up to 95 percent are in the enol