RESUMEN
From a theoretical analysis of the resonance Raman spectra of 19 isotopomers of spheroidene reconstituted into the reaction center (RC) of Rhodobacter sphaeroides R26, we conclude that the carotenoid in the RC occurs in two configurations. The normal mode underlying the resonance Raman transition at 1239 cm(-1), characteristic for spheroidene in the RC, has been identified and found to uniquely refer to the cis nature of the 15,15' carbon-carbon double bond. Detailed analysis of the isotope-induced shifts of transitions in the 1500-1550 cm(-1) region proves that, besides the 15,15'-cis configuration, spheroidene in the RC adopts another cis-configuration, most likely the 13,14-cis configuration.
Asunto(s)
Carotenoides/análisis , Carotenoides/química , Proteínas del Complejo del Centro de Reacción Fotosintética/análisis , Rhodobacter sphaeroides/metabolismo , Carbono , Hidrógeno , Proteínas del Complejo del Centro de Reacción Fotosintética/química , Reproducibilidad de los Resultados , Espectrometría Raman/métodos , Estereoisomerismo , Difracción de Rayos XRESUMEN
We have studied ultrathin spin-coated high-density polyethylene films by means of single-molecule spectroscopy and microscopy at 1.8 K. The films have been doped with 2.3,8.9-dibenzanthanthrene (DBATT) molecules, which function as local reporters of their immediate environment. The orientation distributions of single DBATT probe molecules in 100-200 nm thin films of high-density polyethylene differ markedly from those in low-density films. We have found a preferential orientation of dopant molecules along two well-defined, mutually perpendicular directions. These directions are preserved over at least a 2 mm distance. The strong orientation preference of the probe molecules requires the presence of abundant lateral crystal faces and is therefore not consistent with a spherulitic morphology. Instead, a "shish-kebab" crystal structure is invoked to explain our results.