Search results for "Polyene"
showing 7 items of 17 documents
DFT studies on the structural and vibrational properties of polyenes
2015
Detailed density functional theory (DFT) calculations on the structure and harmonic frequencies of model all-trans and all-cis polyenes were undertaken. For the first time, we report on the convergence of selected B3LYP/6-311++G** and BLYP/6-311++G** calculated structural parameters resulting from a systematic increase in polyene size (chains containing 2 to 14 C = C units). The limiting values of the structural parameters for very long chains were estimated using simple three-parameter empirical formulae. BLYP/6-311++G** calculated ν(C = C) and ν(C–C) frequencies for all-trans and all-cis polyenes containing up to 14 carbon–carbon double bonds were used to estimate these values for very lo…
Filipin labelling and intramembrane particles on the membranes of early and later autophagic vacuoles in Ehrlich ascites cells
1987
Cholesterol and intramembrane particle distribution on autophagic vacuole membranes was studied in Ehrlich ascites cells using filipin labelling and freeze-fracture electron microscopy. Unsaturated fatty acids were stained using imidazole-buffered osmium tetroxide. Autophagocytosis was induced with vinblastine, and early autophagic vacuoles were accumulated by lowering the ATP level in the cells with iodoacetate. Filipin labelling was observed in the limiting membranes of later, apparently hydrolase-containing autophagic vacuoles, whereas the most newly-formed, doublemembrane limited vacuoles were not labelled. The limiting membranes of late, residual body-type vacuoles either showed patchy…
Transition Dipole Orientation of Linear Polyenes: Semiempirical Models and Extrapolation to the Infinite Chain Limit
1999
Linear conjugated polyenes have an electronic transition dipole moment for the strongly allowed 1Ag to 1Bu electronic excitation that is not oriented along the major axis of the polyene chain. In this paper, the experimental values of this off-axis angle are compared to semiempirical and ab initio theoretical predictions. The semiempirical computations are shown to be reliable and are extended to long chains (n = 20). The results are then extrapolated to the infinite chain limit. A nonzero value of 6°−11° for the infinite polyene is suggested by this extrapolation but state of the art ab initio results for a series of small polyenes yield a zero asymptotic value.
Synthesis and characterization of polyene chromophores with hydroxyl functionalization
2008
Abstract Eight hydroxyl functionalized donor–acceptor polyene chromophores 3–10 were synthesized and characterized. Knoevenagel condensation reaction of aromatic polyenals with 2-cyanoacetamide derivatives was utilized to synthesize chromophores with all-E configuration. Chromophores of this kind can be attached covalently to polymers or functionalized with dendrons in order to tune the properties. The structures of the molecules were verified by 1H NMR, 13C NMR, ESI-TOF mass spectrometry and UV–vis measurements. Reduced bond-length alternation of the molecules in DMSO-d6 solution were observed by calculating the average difference of the vicinal coupling constants between adjacent CH CH an…
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…