Conformational Transformation Exhibited by the Peptide Extracted from Crystalline Region of Bombyx mori Silk Fibroin in Solid and Solution States

The conformational transformation of a 30-residue peptide H（Ala-Gly-Ser-Gly-AIa-Gly）5OH, i.e., （AGSGAG）5, extracted from highly crystalline region of Bombyx mori （B. mori） silk fibroin was described by using the high resolution solid state 13^C NMR, and CD spectroscopies. Based on the conformation-dependent 13^C NMR chemical shifts of the Ala, Gly and Ser residues and the line-shape analysis of the conformation sensitive Ala Cβ resonance, the peptide revealed a strong preference for silk Ⅱ structural form, i,e,, an antiparallel fl-sheet structure （φ= - 140±20°and ψ= 135±20°） in solid state. On the contrary, the CD spectra of this peptide in the two non-native hexafluorinated fibre spinning solvents, hexafluoroisopropanol （HFIP） and hexafluoroacetone （HFA）, exhibited the existence of an unusual tightly-folded conformation resembling 310-helix （φ=- 60±20° and ψ=-30±20°）, as judged from the R ratio of [θ]222/[θ]203 in HFIP solution, whereas a dynamically averaged unordered structure in HFA, Taken together, the information inclined to hypothesis that the primary structure of the highly crystalline regions of B. mori silk fibroin may be easily accessible to the large conformational changes, which in turn may be critical for facilitating the structural transformation from unprocessed silk fibroin （silk I form） to processed silk fiber （silk Ⅱform）.     

多波长线性回归计算光度法同时测定铝合金中铁、铜、镍

2-（5-溴-2-吡啶偶氮）-5-二乙氨基酚（5-Br-PADAP）与金属阳离子（M^n＋）显色体系,最大吸收波长接近,存在明显相互干扰,但因其吸收光谱具有显著差别,可用化学计量学方法加以分离的特点,可通过多波长线性回归同时测定多种金属元素。本文根据多波长线性回归分析原理,以5-Br-PADAP为显色剂,测定铝合金中铁、铜、镍,结果满意。