The metastable state silk I structures of Bombyx mori silk fibroin in the solid state were studied on the basis of 15N‐ and 13C‐nmr chemical shifts of Ala, Ser, and Gly residues. The 15N cross‐polarization magic angle spinning (CP/MAS) nmr spectra of the precipitated fraction after chymotrypsin hydrolysis of B. mori silk fibroin with the silk I and silk II forms were measured to determine the 15N chemical shifts of Gly, Ala, and Ser residues. For comparison, 15N CP/MAS nmr chemical shifts of Ala were measured for [15N] Ala Philosamia cynthia ricini silk fibroin with antiparallel β‐sheet and α‐helix forms. The 13C CP/MAS nmr chemical shifts of Ala, Ser, and Gly residues of B. mori silk fibroin with the silk I and silk II forms, as well as 13C CP/MAS nmr chemical shifts of Ala residue of P. c. ricini silk fibroin with β‐sheet and α‐helix forms, are used for the examination of the silk I structure. Both silk I and α‐helix peaks are shifted to a lower field than silk II (β‐sheet) for the Cα carbons of the Ala residues, while both Cβ carbon peaks are shifted to higher field. However, the silk I peak of the 15N nucleus of the Ala residue is shifted to lower field than the silk II peak, but the α‐helix peak is shifted to high field. Thus, the difference in the structure between the silk I and α‐helix is reflected in a different manner between the 13C and 15N chemical shifts. The Cα and Cβ chemical shift contour plots for Ala and Ser residues, and the Cα plot for the Gly residue, were prepared from the Protein Data Bank data obtained for 12 proteins and used for discussing the silk I structure quantitatively from the conformation‐dependent chemical shifts. The plots reported by Le and Oldfield for 15N chemical shifts were also used for the purpose. All these chemical shift data support Fossey's model (Ala: ϕ = −80°, φ = 150°, Gly: ϕ = −150°, φ = 80°) and do not support Lotz and Keith's model (Ala: ϕ = −104.6°, φ = 112.2°, Gly: ϕ = 79.8°, φ = 49.7° or Ala: ϕ = −124.5°, φ = 88.2°, Gly: ϕ = −49.8°, φ = −76.1°) as the silk I structure. © 1997 John Wiley & Sons, Inc.
Solifluction lobes and rock glaciers show similar geometry with a wide range of sizes. Morphometric analysis classifies these lobate landforms in the eastern Swiss Alps into five subgroups. A bouldery rock glacier has an active layer composed of matrix‐free boulders, whereas a pebbly rock glacier consists of matrix‐supported debris derived from less resistant rocks. Both move by permafrost creep at 5–30 m depth, but the former tends to have a longer tread. A high solifluction lobe, having a riser 0.2–3 m high, originates mainly from annual gelifluction operating within the top 0.5 m of sediment, and its variation, a mudflow‐affected high solifluction lobe, occurs where prolonged snowmelt triggers a rapid flow of the thawed surficial layer. A low solifluction lobe has a riser up to 0.2 m high and occurs where thin fine‐grained debris responds mainly to diurnal frost creep. These lobes show, on the whole, positive relations between the tread length (L), width (W ) and the riser height (H ). However, a regression analysis separates the rock glaciers from the solifluction lobes by a distinct gap at W (or L)=30 m and H=3 m and provides different regression lines for the two populations. The morphometry primarily determined by the transport process is H, which approximates or slightly exceeds the maximum depth of movement. The depth of movement also affects the horizontal extent of a moving mass, which defines W. A lobe appears where horizontal homogeneity exceeds 3H, and advances with time until reaching a maximum L controlled by climatic or dynamic conditions. Lobe morphometry can be used as an environmental indicator. Copyright © 2005 John Wiley & Sons, Ltd.
ABSTRACT:The high resolution solid state 13 C NMR spectra were observed for highly syndiotactic polypropylene samples with three kinds of crystalline forms, forms I, II, and III. The forms I and II are the most stable helical conformation, (-TTGG-), and all trans planar zigzag conformation, respectively. The sample with the third new crystalline form, form Ill, was prepared by soaking the sample with form II in toluene at room temperature for two days. The conformation was proposed to be (-T 6 G2 T2 G2-). This is based on the comparison of the observed spectrum with the calculated ones with 13 C NMR y-effect for the candidates of the conformation. There are form I (23%) and amorphous component (I 1 %) other than form III (66%) in the sample at 20°C. From the variable temperature NMR experiments of these three samples with predominantly forms I, II, and III, respectively, the transitions among different crystalline forms and amorphous component were discussed.KEY WORDS Highly Syndiotactic Polypropylene/ High Resolution Solid State 13 C NM R Spectroscopy/ 13 C y Shielding Effect/ Crystalline and Amorphous Components/ (-T6 G2 T 2 G2-) Form of Syndiotactic Polypropylene / Contrary to isotactic polypropylene (i-PP), syndiotactic polypropylene (s-PP) has recieved very little attention. This is due to the poor syndiospecificity of the earlier catalysts. However, in the last few years, new metallocene catalysts have been developed, which allow very high syndiospecificity. 1 • 2 Thus, a detailed structural study of such a highly stereoregular s-PP will be necessary.Two different crystalline forms 3 -7 of the chains have been reported for s-PP obtained by changing the preparations of s-PP samples. One form is called form I which consists of chains with (-TTGG-)i conformation, and another is form II with planar zigzag conformation. Form I is the most stable structure in s-PP, while form II undergoes a transition to form I above 50°C with increasing temperature. 6 The structures of form I and of the sample after drawing have already been studied by Bunn et al. 7 and Sozzani et al. 8 • 9 by using solid-state 13 C NMR. These NMR spectra were interpreted in terms of preferred conformations and the y-effect on the 13 C NMR chemical shift. 10 • 11 In this study, a sample with predominantly new crystalline form, form III, was obtained by special sample preparation. The 13 C CP/MAS NMR spectrum was significantly different from those of other forms, forms I and II. The differences in the spectra among three forms, I, II, and III were interpreted by taking into account of the preferred conformations and the 13 C NMR y-effect. Then the conformation of the new crystalline form, form III, was proposed. Moreover, the transition among three crystalline forms and amorphous component was examined from the temperaturedependent 13 C CP/MAS NMR spectra of three samples and then the determination of the fraction of each form t To whom correspondence should be addressed. tt Present address: Plastic Laboratory, Tokuyama Co., 1-1 Harumicho, To...
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