The combination of micro-Raman spectroscopy and an advanced universal fibre tester (UFT) made it possible to probe at the nanoscale (through monitoring the modification of chemical bonds) the change in conformation (a-helix, b-sheet, etc.), macromolecular fibroin chain orientation and coupling during the application of stress, quantitatively. Different single fibres of silkworms (Bombyx mori, Gonometa rufobrunea, Gonometa postica) and a spider (Nephila madagascariensis) were tested in a dry environment and compared with the behaviour of keratin fibre. As observed previously for single keratin fibres, a direct relationship is observed between nano-and micro-mechanical tensile behaviour. The phase transition plateau, well defined for some pristine B. mori fibres, disappears in degummed fibres, which indicates a structural modification and increasing disorder with chemical treatments. Stress-controlled micro-Raman analysis shows that a few modes involving CH 2 and/or amide groups of b-conformation chains undergo a wavenumber softening during the elastic behaviour (∼0-3%), although most of the modes are not affected. A different behaviour is observed for modes associated with 'ordered' and 'disordered' b-sheets and helical chains. Larger softening is observed for lattice modes with increasing stress/strain, as expected. Structural changes and relationships with mechanical behaviour are discussed.
Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by'H and "C n.m.r. and compared with similar data obtained for benzene and pyridine. Takbg into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered Pyrimidines. This study enabled us to assign the "C nmr. spectra of some trisubstituted pyrimidines.Les effets de substituant des groupes mCthyle et amino sur les denlacements chimiques de la pyrimidine ont CtC CtudiCs par RMN du proton et du carbone-13 et cornparts h ceux observes pour le benzkne et la pyridine. Compte-tenu des interactions mutuelles des substituants, les dkplacements chimiques calculCs B l'aide d'un schCma d'additivitb sont en trbs bon accord avec les dkplacements chimiques observCs, sauf dans quelques cas concernant des pyrimidines encombrbes. Cette Ctude des effets de substituant a permis l'attribution sans equivoque des spectres du carbone-13 de pyrimidines trisubstitukes.
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