[Azorhodan preparations].

To extend the analytical capabilities of the pyrolysis-gas chromatograph-mass spectrometry system that has been successfully utilized in the past as an integrated reaction, separation, and identification system to study label incorporation patterns in Maillard reaction products, a novel methodology was developed to analyze the composition of nonvolatile residues of the initial reaction products. This was achieved through a postpyrolytic in-situ derivatization technique using trimethylsilyldiethylamine. Application of this technique to the investigation of the nonvolatile products formed during pyrolysis of glucose alone and in the presence of glycine has indicated the formation of several redox-active hydroxylated benzene derivatives such as 1,2,3-trihydroxybenzene (pyrogallol), 1,4-dihydroxybenzene (hydroquinone), 1,2-dihydroxybenzene (catechol), and 2,5-dihydroxypyrazine. Labeling studies have indicated that the intact glucose carbon backbone was involved in the construction of the benzene ring of the hydroxylated benzene derivatives and that dimerization of glycine alone can lead to the formation of 2,5-dihydroxypyrazine.

Benzene↗

PubMed2005

Intrinsic isotope effects on benzylic hydroxylation by the aromatic amino acid hydroxylases: evidence for hydrogen tunneling, coupled motion, and similar reactivities.

Deuterium kinetic isotope effects for hydroxylation of the methyl group of 4-methylphenylalanine have been used as a probe of the relative reactivities of the hydroxylating intermediates in the aromatic amino acid hydroxylases phenylalanine, tyrosine, and tryptophan hydroxylase. When there are three deuterium atoms in the methyl group, all three enzymes exhibit an intrinsic isotope effect of about 13. The temperature dependence of the isotope effect is consistent with moderate tunneling, with the extent of tunneling identical for all three enzymes. In the case of phenylalanine hydroxylase, the presence of the regulatory domain has no effect on the values. The intrinsic primary and secondary isotope effects were determined using 4-methylphenylalanine containing one or two deuterium atoms in the methyl group. With one deuterium atom, the intrinsic primary and secondary effects have average values of 10 and 1.1, respectively. With two deuterium atoms, the primary effects decrease to 7.4 and the secondary effect increases to 1.3, consistent with coupled motion of the primary and secondary hydrogens. The results with all three enzymes are consistent with a hydrogen abstraction mechanism. The similarities of the isotope effects and extent of tunneling establish that the reactivities of the hydroxylating intermediates in the three enzymes are essentially identical.

Benzene↗