Helix formation, solvents causing

To avoid any complications caused by the intermolecular association, Goodman (78) reinvestigated the optical rotation of the peptides in dimethyl formamide, since in this medium the specific rotation is independent of concentration. From the latter study it was concluded that at 25° C the spontaneous helix formation of poly-y-methyl-L-glutamate in dimethyl formamide is occurring at the critical range of 7—9 units. Extension of these studies (73 b, 79) led to a better understanding of temperature and solvent effects upon the helix-coil transition of oligomeric polypeptides. 

Experimentally, the wild-type Ell peptide adopts a-helical structure under various solvent conditions, but it will also quite readily form fibrils composed of P sheets in aqueous solution (Gasset et al., 1992 Zhang et al, 1995 Nguyen et al, 1995). The wild-type HI sequence maintains a stable helical structure over a 2 ns simulation, as well (Fig. 3, and see Kazmirski et al, 1995). Addition of a valine mutation at residue 117, which is a human-disease-causing mutation (Doh-ura et al, 1989 Hsiao et al, 1991), destabilized the helix and formed extended structure at the C-terminus and may have implications for scrapie formation. Other... 

Abstract The optical inversion of poly(propylene oxide) by solvent is not due to a helix-coil transition or any other conformational change. The inversion was observed also in the monomer or the ether of propylene glycol. The variation of rotivity of solvent seems to be caused by change of the polarizability of methyl or methylene group of polypropylene oxide due to the formation of a contact complex with aromatic solvent. 

The products 41 and 42 were insoluble in any solvents, e.g., aqueous acetic acid and DMSO, which were good solvents for chitosan and amylose, respectively. The XRD patterns of these materials showed typical A-type crystalline structures due to amyloses. Such crystalline structures are generally attributed to the formation of a double helix of amylose [33]. Therefore, we assume that one of the reasons for the insolubility of these materials is probably caused by molecular aggregation as a result of this crystalline structure. The aggregation in the material would contribute its conversion into film and hydrogel forms. For example, the hydrogel of 41 could be formed by drying the reaction mixture slowly in the vessel at 40-50 C. 

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