Search results for "Polyenes"
showing 3 items of 13 documents
Experimental and theoretical studies on corals. I. Toward understanding the origin of color in precious red corals from Raman and IR spectroscopies a…
2010
An attempt to explain the origin of the vivid red color in precious pink and red corals was undertaken. Raman and IR spectroscopies were applied to characterize white, pink and red corals. The position of the Raman signal near 1500 cm−1 of some corals and pearls was associated by several authors with the presence of the mixture of all‐trans‐polyenic pigments, containing 6–16 conjugated CC bonds or β‐carotenoids. This hypothesis was examined theoretically by performing extensive B3LYP‐DFT calculations of vibrational spectra of the model polyenic compounds. The B3LYP/6‐311++G** predicted positions of the dominating Raman mode depend on the number of CC units (Cn parameter) and can be accura…
Modeling red coral (Corallium rubrum) and African snail (Helixia aspersa) shell pigments: Raman spectroscopy versus DFT studies
2016
Pigments from red coral (Corallium rubrum) and African snail (Helixia aspersa) shell were studied non-invasively using Raman spectroscopy with 1064-nm laser beam. The two observed bands because of organic pigments confined in biomineralized CaCO3 matrix at about 1500 and 1100 cm−1 were assigned to ν(C[DOUBLE BOND]C) and ν(C―C), respectively. Both signals originate from polyene(s) of largely unknown structure, containing several conjugated C[DOUBLE BOND]C bonds. The small peak at 1016 cm−1 in the Raman spectrum of coral pigment was assigned to in-plane ―CH3 rocking or structural deformation of polyene chain because of spatial confinement in the mineral matrix. The organic pigments in red cor…
Raman Investigations to Identify Corallium rubrum in Iron Age Jewelry and Ornaments
2016
International audience; During the Central European Iron Age, more specifically between 600 and 100 BC, red precious corals (Corallium rubrum) became very popular in many regions, often associated with the so-called (early) Celts. Red corals are ideally suited to investigate several key questions of Iron Age research, like trade patterns or social and economic structures. While it is fairly easy to distinguish modern C. rubrum from bone, ivory or shells, archaeologists are confronted with ancient, hence altered, artifacts. Due to ageing processes, archaeological corals lose their intensive red color and shiny surface and can easily be confused with these other light colored materials. We pr…