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Raman shifts due to variations in backbone planarity in a group of polydiacetylenes (1998)

Campbell, Alasdair J. ; Davies, Craig K. L. ; Batchelder, David N.

Weinheim : Wiley-Blackwell

Macromolecular Chemistry and Physics 199 (1998), S. 109-112

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ISSN: 1022-1352

Schlagwort(e): Chemistry ; Polymer and Materials Science

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie , Physik

Notizen: Polydiacetylene xBCMU and 9PA crystals, solutions and solution-cast films vary in colour due to differences in backbone order and planarity. Associated with the colour changes are increases in the Raman frequencies of the triple and double backbone bond vibrational modes from those values found in the highly ordered single crystals. These increases are strongly correlated and the ratio of the change in the frequency of the triple bond mode to that of the double bond mode is found to be 1.6 (±0.1) over a wide variation in order. This ratio is compared with the values of 0.3 found under uniform strain and 1.1 predicted by a model of acetylenic to butatrienic delocalisation. The relationship between the Raman frequencies of the yellow solutions and melts and those of the crystal phases suggests that in the former the backbone has a continuous and smoothly curving ‘worm-like’ conformation. Models involving the break-up of the conjugated system by large-angle bond rotations appear to be incorrect for polydiacetylenes. These results have important consequences for theoretical models that predict the dependence of electron delocalisation on backbone order and planarity in polydiacetylenes.

Zusätzliches Material: 3 Ill.

Materialart: Digitale Medien

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Digitale Medien

Avian scale development. Absence of an “epidermal placode” in reticulate scale morphogenesisAided by Biology Department, University of South Carolina, Columbia, South Carolina. (1977)

Sawyer, R. H. ; Craig, K. F.

New York, NY : Wiley-Blackwell

Journal of Morphology 154 (1977), S. 83-93

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ISSN: 0362-2525

Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Biologie , Medizin

Notizen: Timed-sequence studies have shown that reticulate scales on the ventral footpads of birds do not undergo “epidermal placode” formation during their morphogenesis, but arise as symmetrical evaluations similar to the scales of snakes and lizards. Unlike the scutellate scales on the dorsal surface of the foot, in which the formation of an “epidermal placode” and its subsequent morphogenesis result in distinct outer and inner epidermal surfaces, the reticulate scales elaborate only one type of epidermal surface.

Zusätzliches Material: 4 Ill.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1002/jmor.1051540106

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