Using Resonance Raman microspectrometry we identify polyenes as shell pigments in 13 gastropod, 1 cephalopod and 4 bivalve taxa. The pigments are either isolated polyenes or polyenes bound to other molecules. Polyenes are present in coloured parts of the shell of all investigated taxa. Pigments differ between taxa and there is no trivial relationship between colour, pigment and taxon. The same colour in different taxa may be due to different pigments; different colours in the same taxon are due to different pigments; different colour saturation is due to different concentration of the same pigment. The pigment polyenes are unsubstituted chains of 8 -13 conjugated double-bonds (16 -26 carbon atoms) in the chain, with terminals incorporating -CH 3 groups. This is the first demonstration of polyenes as shell pigment in the Mollusca. We also identify a carotenoid as the external, yellow pigment in Cypraea moneta.

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The structure of a series of alcohol-terminated bifunctional long-tail organosilane films with varying numbers of superimposed monolayers (between 1 and 11), prepared on smooth, hydrophilic silicon substrates by the layer-by-layer self-assembly approach, has been investigated with the purpose of elucidating details of the molecular organization and the intra-and interlayer modes of binding in such films. To this end, experimental results obtained by synchrotron X-ray scattering, micro-Raman, and Fourier transform infrared (FTIR) spectroscopic techniques have been combined and compared. A comprehensive analysis of all data demonstrates that the studied multilayer films consist of stacks of uncorrelated discrete monolayers, the inner molecular order of which is preserved with the growing total number of superimposed layers. Similar to self-assembled films of long-tail silanes with terminal -COOH groups, 1 the intermolecular binding in the present films is characterized by partial intra-and interlayer covalent bond formation. The molecular hydrocarbon tails are perpendicularly oriented on the layer planes, forming a densely packed rotator phase like hexagonal lattice with a molecular surface area of ∼20 Å 2 and a lateral correlation length of the order of 16 molecular diameters.

International audienceThe nature of the physical mechanisms related to the gamma-Fe2O3 to alpha-Fe2O3 phase transition under laser irradiation and heat treatment has been investigated using in situ micro-Raman spectroscopy and X-ray powder diffraction (XRPD) analysis. Measurements were carried out on as-prepared gamma-Fe2O3 nanoparticles of about 4 nm in size as a function of laser power and on annealed gamma-Fe2O3 particles. Annealing temperature affects the relative fractions of the gamma-Fe2O3 and alpha-Fe2O3 phases, and at 450 degrees C, the phase transition into alpha-Fe2O3 becomes complete with apparent crystallite size < D > of about 30 nm. The hematite nanoparticles increase then up to more than 180 nm at 1400 degrees C. The excellent agreement between evolution of the wavenumbers and bandwidths confirms that the heat treatment and laser irradiation produces the same effects on nanoparticles. Correlations between structure modifications occurring at the nanometric scale during grain coalescence and the evolution of Raman vibrational spectra were quantitatively examined, and a physical mechanism for the gamma -> alpha-Fe2O3 phase transition was proposed