Effects of Cyclodextrin Inclusions on the Oxidation Rate of NADH Model Compounds Catalyzed by 1, 4-Naphthoquinones

Abstract

The thermal and photochemical oxidations of 1-benzyl- or 1-alkyl-1, 4-dihydronicotinamides (BNAH, RNAHs, respectively) were kinetically examined in the presence of unmodified cyclodextrins (CyDs) or modified CyDs with one or two 3-chloro-1, 4-dioxo-2-naphthylamino groups (hereafter, naphthoquinone moiety: Q) on the primary or secondary side (QCyDs). The α- and β-CyDs formed an inert binary host-guest complex with either of a BNAH or the CyD-free naphthoquinone (NQ), but yCyD afforded a ternary complex exhibiting a weak reactivity only in lower concentrations of γ-CyD than BNAH. The reactivity of QCyDs toward BNAH (k_obs/10^-4 s^-1) decreased in the order: 6-QβCyD (4.1)>3-QβCyD (3.5)>6-QβCyD (2.5)>6-QγCyD (2.2)>3-QαCyD (1.9) at [BNAH]/[QCyDs] 1. The sequence was independent of the nature of the 1-alkyl substituents. Meanwhile, 1-ethyl-1, 4-dihydronicotinamide with a benzyl group at the 3-carbamoyl nitrogen (EBNAH) showed a different rate sequence: 6-QβCyD (3.9)>6-QγCyD (2.7)> 6-QβCyD (2.3)>3-QβCyD (1.7)>3-QαCyD (1.1). Thus, the RNAH (BNAH) and EBNAH molecules seem most suitable for the β-CyD and γ-CyD cavities, respectively.