Figure 1.  Chemical structures and molecular weights (MW) of the green tea catechins used in this study.

Figure 2.  Mass spectra of the deprotonated catechin molecular ion, (M − H)^–, before H/D exchange (a) and after 10,000 ms reaction time with D₂O (b).

Figure 3.  Kinetic plot of the H/D exchange reaction of deprotonated catechin with D₂O. Individual points represent experimentally-determined values and lines are determined by KinFit [55]. D(0) represents the initial parent ion and D(x) represents ions incorporating from one to x deuteriums.

Figure 4.  H/D exchange reaction of catechin gallate (a) and epicatechin gallate (b) with D₂O after 10,000 ms reaction time.

Figure 5.  Lowest energy conformations of catechin gallate (a) and epicatechin gallate (b) deprotonated at the 3′-OH position; catechin gallate (c) and epicatechin gallate (d) deprotonated at the 3″-OH position; catechin gallate (e) and epicatechin gallate (f) deprotonated at the 4″-OH position; catechin gallate (g) and epicatechin gallate (h) deprotonated at the 5″-OH position.

Scheme 1. Proposed scrambling mechanism allowing deuterium incorporation at nonlabile sites on a flavonoid such as catechin or epicatechin. Adapted from Reed and Kass [11].

Average rate constants and standard deviations^a for H/D exchange of deprotonated non-galloylated catechin stereoisomers reacting with D₂O. The number of labile hydrogens after deprotonation is shown in parentheses for each stereoisomer^b

Average rate constants and standard deviations^a for H/D exchange of deprotonated galloylated catechin stereoisomers reacting with D₂O. The number of labile hydrogens after deprotonation is shown in parentheses for each stereoisomer^b

Calculated gas-phase absolute and relative acidities for catechin, epicatechin, gallocatechin (GC), and epigallocatechin (EGC)

Calculated gas-phase absolute and relative acidities for catechin gallate (CG) and epicatechin gallate (ECG)