Ron de Beer

14N and 15N coupling constants of the oxidized primary donor P-860 of bacterial photosynthesis obtained by electron spin echo envelope modulation spectroscopy

Abstract An electron spin echo modulation frequency analysis of P+-860 is performed in 14N chromatophores of Rhodospirillum rubrum, and in 15N substituted reaction centers from Rhodopseudomonas sphaeroides 2.4.1. For the 14N material two sets of nuclear quadrupole parameters are obtained. From the frequencies found for 15N reaction centers the perpendicular, parallel and isotropic hyperfine coupling constants of three of the four bacteriochlorophyll nitrogen nuclei are inferred.

Electron spin echo envelope modulation (ESEEM) spectroscopy of the triplet state of the primary donor of 14N and 15N bacterial photosynthetic reaction centers and of 14N and 15N bacteriochlorophyll a

Abstract An electron spin echo envelope modulation frequency analysis is performed on the triplet state of the primary electron donor (P-860) in 14 N reaction centers of the photosynthetic bacterium Rhodopseudomonas sphaeroides R26 and 15 N-enriched reaction centers of Rhodopseudomonas sphaeroides 2.4.1, and of the triplet state of 14 N or 15 N bacteriochlorophyll a in vitro. The hyperfine coupling constants for 15 N 3 P-860 are 1.42, 1.74 and 2.04 MHz. The triplet state of the primary donor in bacterial photosynthesis is, on a timescale of a few MHz, delocalized over the two bacteriochlorophyll a molecules making up P-860.

Evaluation of five protocols for quantification of two-dimensional MR spectroscopic images

Five protocols were tested for quantification onin vivo two-dimensional spectroscopic imaging datasets. The datasets are duplo measurements from three individuals. The peaks forN-acetyl aspartate, creatines, and cholines were quantified. The first of the protocols is conventional integration of a selected interval around the peak. The others are various implementations of a Gauss-Newton-based least-squares time-domain fitting algorithm. Fitting a half-echo (free-induction decay curve, FID) to a full echo was compared; this was combined with or without filtering out the water signal using the Lanczos-Hankel singular-value decomposition (LHSVD). It appears that conventional integration yields consistent and accurate results in comparison to the fitting methods. The combination of LHSVD and echo fitting performs equally well; advantages and disadvantages are discussed. The protocols using FID fitting perform poorly with these experimental datasets.