Effects of cyclodextrin inclusions on the oxidation rate of NADH model compounds catalyzed by 1,4-naphthoquinones

The thermal and photochemical oxidations of 1-benzyl- or 1-alkyl-1,4-dihydr onicotinamides (BNAH, RNAHs, respectively) were kinetically examined in the presence of unmodified cyclodextrins (CyDs) or modified CyDs with one or t wo 5-chloro-1,4-dioxo-2-naphthylamino groups (hereafter, naphthoquinone moi ety: Q) on the primary or secondary side (QCyDs). The alpha- and beta-CyDs formed an inert binary host-guest complex with either of a BNAH or the CyD- free naphthoquinone (NQ), but gamma-CyD afforded a ternary complex exhibiti ng a weak reactivity only in lower concentrations of gamma-CyD than BNAH. T he reactivity of QCyDs toward BNAH(k(obs)/10(-4) s(-1)) decreased in the or der: 6-Q beta CyD(4.1) >3-Q beta CyD (3.5) >6-Q beta CyD (2.5) >6-Q gamma C yD(2.2) >3-Q alpha CyD (1.9) at [BNAH]/[QCyDs] = 1. The sequence was indepe ndent of the nature of the 1-alkyl substituents. Meanwhile, 1-ethyl-1,4-dih ydronicotinamide with a benzyl group at the 3-carbamoyl nitrogen (EBNAH) sh owed a different rate sequence: 6-Q beta CyD (3.9) >6-Q gamma CyD (2.7) >6- Q beta CyD (2.3) >3-Q beta CyD (1.7) >3-Q alpha CyD (1.1). Thus, the RNAH ( BNAH) and EBNAH molecules seem most suitable for the beta-CyD and gamma-CyD cavities, respectively.