Browsing by Author "Gorostidi, GRE"

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    Determination of the rates of formation and hydrolysis of the Schiff bases formed by pyridoxal 5'-phosphate with L-tryptophan and its methyl and n-butyl esters
    (2002) Gorostidi, GRE; Santos, JG; Basagoitia, A; Blanco, FG
    The apparent rate constants of the formation (k(1)) and hydrolysis (k(2)) of the Schiff bases formed by pyridoxal 5'-phosphate with L-tryptophan and their methyl and n-butyl esters at a variable pH, 25 degreesC, and an ionic strength of 0.1 M were determined, along with the equilibrium constant (K-pH). The individual rate constants of formation and hydrolysis of the Schiff bases of systems corresponding to different chemical species present in the medium as a function of its acidity were also determined, as were the pK values for the Schiff bases. The influence of the a-carboxyl group on the formation and hydrolysis constants of the Schiff bases, and also on their pK values, is demonstrated.
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    Kinetic study of the reaction of pyridoxal 5 '-phosphate with hydrazine
    (ELSEVIER SCIENCE BV, 1998) Gorostidi, GRE; Basagoitia, A; Blanco, JGS; Blanco, FG
    The kinetics of the reaction between pyridoxal 5'-phosphate (PLP) and hydrazine in aqueous solution at a variable pH and a constant strength of 0.1 M was studied spectrophotometrically. The rate constants of formation and hydrolysis of the resulting Schiff base and its stability were also determined in a wide range of pH. A comparison of the formation rate constants with those for the models of PLP with n-hexylamine and with poly-L-lysine revealed that hydrazine formed Schiff base more quickly than lysine below pH 7 and than n-hexylamine below pH 8. The reactivity shows the sequence poly-L-lysine > n-hexylamine > hydrazine in whole studied range of pH. Schiff bases formed by hydrazine with PLP are more stable than the ones formed by n-hexylamine in the pH range studied and more stable than the formed by poly-L-lysine at pH < 7.0. (C) 1998 Elsevier Science B.V.
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    On the L-DOPA and carbidopa reactivity against pyridoxal 5′-phosphate.: A kinetic study
    (2002) Gorostidi, GRE; Santos, JG; Figueroa, J; Blanco, FG
    The apparent rate constants of the formation (k(1))) and hydrolysis (k(2)) of Schiff bases formed by pyridoxal 5'-phosphate (PLP) with L-3,4-dihydroxyphenylalanine (L-DOPA) at a variable pH, 25 degreesC and an ionic strength of 0. 1 M was determined. The individual rate constants for the formation and hydrolysis of Schiff bases corresponding to the different chemical species present in the medium as a function of its acidity were also determined, as were the pK(a) values for the Schiff bases. The formation and hydrolysis rate constants of the Schiff bases were compared with those of the reaction of PLP with carbidopa (CD), showing that the reactivity Of L-DOPA and carbidopa on PLP are the same over the whole pH range studied, and that the hydrolysis rate is somewhat greater for the Schiff bases between PLP and CD than those between PLP and L-DOPA.
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    Schiff bases of poly-L-lysine and some compounds of the vitamin B-6 group. Influence of polypeptidic structure
    (ELSEVIER SCIENCE BV, 1997) delVado, MAG; Gorostidi, GRE; Blanco, JGS; Blanco, FG
    The apparent rate constants of formation (k(1)) and hydrolysis (k(2)) of the Schiff bases formed between pyridoxal and poly-L-lysine has been fitted to a kinetic scheme that involves the different protonated species in the reaction medium and the individual rate constants of formation (k(1)(i)) and hydrolysis (k(2)(i)). A Bronsted plot with alpha = 0.67 is in accord with an acid catalytic intramolecular process. The effects of hydrophobic medium due to the presence of the macromolecule on the formation and hydrolysis of Schiff bases from FL, DPL and PLP with poly-L-lysine is discussed.
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    Schiff bases of pyridoxal and polyallylamine. The formation rate determining step
    (JOHN WILEY & SONS INC, 1998) del Vado, MAG; Gorostidi, GRE; Basagoitia, A; Blanco, JGS; Blanco, FG
    The apparent rate constants of formation (k(1)) and hydrolysis (k(2)) of the Schiff bases formed between pyridoxal and polyallylamine has been fitted to a kinetic scheme that involve the different protonated species in the reaction medium and the individual rate constants of formation (k(1)(i)) and hydrolysis (k(2)(i)). The (k(1)(i)) values precludes an acid catalyzed intramolecular process. The effects of hydrophobic medium due to the presence of the macromolecule on the reaction is also discussed. (C) 1998 John Wiley & Sons, Inc.
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    Schiff's bases formed between pyridoxal 5′-phosphate and 4-aminobutanoic acid.: Kinetic and thermodynamic study
    (2003) Gorostidi, GRE; Castellanos, MG; Pérez, PM; Santos, JG; Blanco, FG
    The overall and individual kinetic constants of formation (k(1) and k(1)(i)) and hydrolysis (k(2), k(OH) and k(2)(i)) of the Schiff's bases formed between pyridoxal 5'-phosphate (PLP) and 4-aminobutanoic acid (GABA) at 10, 20, 25, 30, and 37degreesC, a variable pH and a constant ionic strength of 0.1 M (1 M=1 mol dm(-3)) were determined. The formation of a Schiff's base is an intramolecular acid-catalyzed process. The activation and thermodynamic parameters for the formation and hydrolysis of the Schiff's bases were also determined. DeltaH and DeltaS for the individual processes were all found to be negative.