Polyphenols and caffeoylquinic acid (CQA) derivatives (3-CQA, 4-CQA, 5-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) were prepared from Ilex kudingcha C.J. Tseng, and their effects and mechanisms on the activities of α-glucosidase from Saccharomyces cerevisiae were investigated in the present study. As results, the IC50 values for CQA derivatives were 0.16-0.39 mg/mL, and the inhibition mode of CQA derivatives was noncompetitive. On the basis of fluorescence spectroscopy and circular dichroism spectroscopy data, the binding constants and number of binding sites were calculated to be 10(6)-10(8) M(-1) and 1.42-1.87, respectively. CQA derivatives could bind to the enzyme mainly through hydrophobic interaction, altering the microenvironment and molecular conformation of the enzyme, thus decreasing the catalytic activity. To the authors' knowledge, this is the first report on α-glucosidase inhibitory mechanism by CQA derivatives from I. kudingcha, and the findings suggest a potential use of kudingcha as functional foods for the prevention and treatment of diabetes and related symptoms.

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Approaching the 1.53-dB shaping gain limit in mean-squared error (MSE) quantization of R n is important in a number of problems, notably dirty-paper coding. Unlike the traditional method of trellis-coded quantization (TCQ), in this paper we propose quantization codebooks constructed from binary low-density generation-matrix (LDGM) codes and from two such codes combined with Gray mapping. The quantization algorithm is based on belief propagation, and it uses a novel adaptive decimation procedure to do the guessing necessary for convergence. Simulation results show that the proposed code can achieve a shaping gain of 1.477 dB, or 0.056 dB from the limit, which is significantly better than the 1.40 dB previously achieved with TCQ.