Isomeric differentiation of green tea catechins using gas-phase hydrogen/deuterium exchange reactions.
Hydrogen/deuterium exchange reactions in a quadrupole ion trap mass spectrometer are used to differentiate galloylated catechin stereoisomers (catechin gallate and epicatechin gallate; gallocatechin gallate and epigallocatechin gallate) and the nongalloylated analogs (catechin and epicatechin, gallocatechin and epigallocatechin). Significant differences in the hydrogen/deuterium exchange behavior of the four pairs of deprotonated catechin stereoisomers are observed upon reaction with D(2)O. Interestingly, the nongalloylated catechins undergo H/D exchange to a much greater extent than the galloylated species, incorporating deuterium at both aromatic/allylic and active phenolic sites. Nongalloylated catechin isomers are virtually indistinguishable by their H/D exchange kinetics over a wide range of reaction times (0.05 to 10 s). Our experimental results are explained using high-level ab initio calculations to elucidate the subtle structural variations in the catechin stereoisomers that lead to their differing H/D exchange kinetics.
Niemeyer
Emily D
ED
Department of Chemistry and Biochemistry, Southwestern University, Georgetown, Texas 78626, USA. niemeyee@southwestern.edu
Brodbelt
Jennifer S
JS
D002392:Catechin / Q000737:chemistry*; D003198:Computer Simulation; D041961:Deuterium Exchange Measurement / Q000379:methods*; D005740:Gases / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D010936:Plant Extracts / Q000737:chemistry*; D013237:Stereoisomerism; D013662:Tea / Q000737:chemistry*
D005740:Gases; D010936:Plant Extracts; D013662:Tea; D002392:Catechin
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