A set-up to study photochemically induced dynamic nuclear polarization in photosynthetic reaction centres by solid-state NMR.

Recently, solid-state NMR spectroscopy became a viable method to investigate photosynthetic reaction centres (RCs) on the atomic level. To study the electronic structure of the radical cation state of the RC, occurring after the electron emission, solid-state NMR using an illumination set-up can be exploited. This paper describes the illumination set-up we designed for a standard Bruker wide-bore MAS NMR probe. In addition we demonstrate its application to get information from the active site in photosynthetic reaction centres of Rhodobacter sphaeroides R-26 by photochemically induced dynamic nuclear polarization (photo-CIDNP). Solid-state NMR spectra of natural abundance 13C in detergent solubilized quinone depleted photosynthetic reaction centres under continuous illumination showed exceptionally strong nuclear spin polarization in NMR lines. Both enhanced-absorptive and emissive polarization were seen in the carbon spectrum which could be assigned to a bacteriochlorophyll a (BChl a) cofactor, presumably the special pair BChl a. The sign and intensities of the 13C NMR signals provide information about the electron spin density distribution of the transiently formed radical P.+ on the atomic level.

Actividad del virus de la encefalitis equina venezolana en el norte de Colombia, abril y mayo de 1983 / Venezuelan equine encephalitis virus activity in northern Colombia during April and May 1983

Venezuelan equine encephaltis (VEE) virus was isolated from sentinel hamsters exposed in the Rio de Oro region of Colombia, in the Lake Maracaibo drainage área near the border with Venezuela, in 1983-13 years after the first strain was isolated from the region near Tibu. Hydroxylapatite elution profiles of three isolates from the Rio de Oro region were typical of enzootic strains. Relative abundance data and past isolations suggest that culex (Melanoconion) pedroi is a probable enxootic vector at this focus. The virus was no isolated from forests near Santa Marta and Magangue in the Rio Magdalena drainage área in 1983-9 and 16 years, respectively, after the last previous isolations in those áreas. However, equine animals 2 to 10 years of age and humans 25 to 67 years of age living near the Magangue field study área were positive for VEE virus-specific neutralizing antibodies