No abstract

High-resolution 13C NMR (75.46 MHz) spectra of silk fibroins in the solid state were recorded by the cross-polarization-magic angle spinning method with emphasis on revealing conformational features of the dimorphic structures, silk I and II, of Bombyx mori fibroin prepared under different conditions. It was found that the 13C chemical shifts of Gly, Ala, and Ser residues of silk II samples from B. mori fibroin by different preparations and of cocoon samples from several silkworms gave identical values with those of corresponding model polypeptides having the /3-sheet conformation. Thus, identification of the silk II type form is easily performed by examining their 13C chemical shift values. The 13C chemical shifts of samples having the silk I form are significantly displaced from those of the silk II form, and can be used for diagnostic purposes. As expected, the 13C chemical shifts of Ala and Gly residues of the silk I samples were identical with those of (Ala-Gly)"II. However, we found that none of the 13C chemical shifts predicted from the crankshaft model [Lotz, B.; Keith, H. D. J. Mol. Biol. 1971, 61, 201-215] in which Ala and Gly residues are close to the /S-sheet and -helix conformations, respectively, was in agreement with the 13C chemical shifts of (Ala-Gly)"II and silk I type form. Instead, we found that predicted 13C chemical shifts from the loose helix proposed by Konishi and Kurokawa [Konishi, T.; Kurokawa, M. Sen'i Gakkaishi 1968, 24, 550-554] on the basis of the calculated 13C contour map of chemical shifts for Ala residue are in good agreement with the displacement of the l3C chemical shifts.

No abstract

ABSTRACT:Various molecular parameters characterizing the solution properties of poly(Nisopropylacrylamide) (in the range of molecular weight from 13.8 to 910 x l

The photocatalytic degradation of bisphenol A (BPA), a representative endocrine disruptor, was carried out in TiO2 aqueous suspension. The main purposes were to confirm the total mineralization of BPA and to evaluate the estrogenic activity in the treated water during the photocatalytic reaction. An initial BPA concentration of 175 microM in water was totally degraded to carbon dioxide by TiO2-photocatalyzed reactions under UV irradiation of 10 mW cm-2 for 20 h. Four HPLC peaks indicating intermediate products appeared in chromatograms monitored at 275 nm, but the heights relative to that of the initial BPA were very low, at most 0.04 in the time period 5-10 h after the start of UV irradiation. All of the peaks finally disappeared after 20 h. For the treated water, the transcriptional estrogenic activity in response to human estrogen receptor in a yeast hybrid assay decreased drastically to less than 1% of the initial BPA's activity within 4 h. On the basis of these results, we conclude that TiO2 photocatalysis could be a useful technology for the purification of water containing BPA without generating any serious secondary pollution.