Phosphorescence has been observed at 1.2 K both for C60 dissolved in a decaline/cyclohexane glass and for single crystals of C60. The phosphorescence spectrum of C60 in the glass reveals a weak... Show morePhosphorescence has been observed at 1.2 K both for C60 dissolved in a decaline/cyclohexane glass and for single crystals of C60. The phosphorescence spectrum of C60 in the glass reveals a weak origin at 798.1 +/- 0.5 nm, while most of the intensity shows up in vibronic transitions. The phosphorescence of crystalline C60 consists of two parts. One of these, with the origin of its phosphorescence spectrum at 826 nm, derives probably from a shallow C60 X-trap although an excitonic origin cannot be excluded. The other, with the origin of its phosphorescence spectrum at 862 nm, originates from triplet states previously recognized by magnetic resonance experiments. These concern excitations delocalized over pairs of C60 molecules, so-called mini-excitons that are deep X-traps in the C60 crystal. Show less
Andrew, C.R.; Yeom, H.; Valentine, J.S.; Karlsson, B.G.; Pouderoyen, G. van; Canters, G.W.; ... ; Bonander, N. 1994
A series of metalloprotein mutants with novel copper cysteinate coordination environments has been probed by resonance Raman (RR) spectroscopy. These include H117G, M121E, and M121K mutants of... Show moreA series of metalloprotein mutants with novel copper cysteinate coordination environments has been probed by resonance Raman (RR) spectroscopy. These include H117G, M121E, and M121K mutants of Pseudomonas aeruginosa azurin and H46C, H80C, and H120C mutants of yeast CuZn-superoxide dismutase. In each case, excitation within a (Cys)S --> Cu charge transfer band leads to the enhancement of multiple vibrational modes of the copper cysteinate moiety. The predominant Cu-S stretching vibration, v(Cu-S), located in the 300-450 cm(-1) region, can be identified by (i) its large S- and Cu-isotope shifts, (ii) its high RR intensity, and (iii) its role as the generator of combination bands. The v(Cu-S) frequency appears to be a sensitive indicator of Cu-S(Cys) bond strength and, hence, copper coordination geometry. In the case of type 1 (T1) sites, the increased influence of the weak axial ligand upon moving from a trigonal planar (axial EPR) toward a more tetrahedral (rhombic EPR) geometry is associated with a decrease in v(Cu-S) from similar to 420 to similar to 350 cm(-1). In the case of type 2 (T2) sites with four strong ligands, v(Cu-S) undergoes further decreases from similar to 350 to similar to 310 cm(-1) as the geometry becomes more tetragonal. The Cu-S bond is successively weakened by trans ligand effects as the geometry approaches square planar. The decreased strength of the Cu-S(Cys) bond is further reflected in the increased strength of the adjacent S-C bond whose stretching frequency varies from similar to 750 cm(-1) for axial T1 sites to similar to 765 cm(-1) for T2 sites. The similar to 100-cm(-1) range in v(Cu-S) corresponds to a change in Cu-S(Cys) bond distance from similar to 2.13 Angstrom for an axial T1 site to similar to 2.29 Angstrom, for a tetragonal T2 site. The overlap of T1 and T2 v(Cu-S) frequencies near 350 cm(-1) shows that both types of Cu site can have similar Cu-S(Cys) bond strengths, despite their different EPR and optical characteristics, and points to a continuum of geometries linked through a tetrahedral structure which we describe as a T1.5 intermediate Cu site. Show less
Pancreatic islet transplantation by a new method is introduced here : the isolation of islets in an organ preservation solution, the University of Wisconsin solution. A new concept allowing for the... Show morePancreatic islet transplantation by a new method is introduced here : the isolation of islets in an organ preservation solution, the University of Wisconsin solution. A new concept allowing for the first time large-scale isolation and transplantation of consistently near 100% pure islets of Langerhans in a preclinical dog model with fasting normoglycemia up to 3 years posttransplant. Detailed metabolic studies demonstrated normal insulin levels after meals with preservation of gut hormone action stimulating insulin secretion at the mild hyperglycemia after meals. The introduction of the University of Wisconsin solution organ preservation solution for islet isolation at the start of these studies in 1989 is a new concept … and has been shown by now in 2022 , world-wide , to make the future of islet isolation and transplantation methods for insulin-dependent diabetes mellitus (IDDM). Show less
The relation between quinone (QA) binding and electron transport in reaction centers (RCs) of photosynthetic purple bacteria is investigated, using electron spin polarization (ESP) X-band (9 GHz)... Show moreThe relation between quinone (QA) binding and electron transport in reaction centers (RCs) of photosynthetic purple bacteria is investigated, using electron spin polarization (ESP) X-band (9 GHz) EPR as a tool to probe for structural changes resulting from charge separation and stabilization and from replacing the native QA molecule with other quinones. We present a study of possible changes in Q(A)-binding that might be responsible for the remarkably prolonged Lifetime of the charge-separated state at cryogenic temperatures for RCs of Rhodobacter sphaeroides R26 cooled under illumination [Kleinfeld, D., et al. (1984) Biochemistry 23, 5780-5786]. It is shown that this effect is not caused by a major reorientation of the chromophores. Furthermore, we studied the effects of structurally different quinones functioning as primary electron acceptor in different purple bacteria. With simulations of ESP X-band spectra of the spin-polarized secondary radical pair P.(+)Q(A)(.-) in menaquinone-reconstituted, Zn2+-substituted RCs of Rb. sphaeroides R26, we show that quinone reconstitution is highly selective for site and orientation. Furthermore, we find that a very small exchange interaction between P-.+ and Q(A)(.-) (\J(PQ)\ similar to 1 mu T) is needed to account accurately for the observed relative line intensities at X-band, without affecting the accuracy of the simulations of reported ESP K-band spectra [Fuchsle, G., et al. (1993) Biochim. Biophys. Acta 1142, 23-35; Van der Est, A., et al. (1993) Chem. Phys. Lett. 212, 561-568]. This pronounced influence of small values for J(PQ) On the X-band ESP line shape results from cancellation effects of absorptive and emissive contributions to the spectrum, such that small shifts can be observed. The exchange interaction has opposite sign for the native, ubiquinone-containing RC [viz. J(P.UQ) (-0 8 +/- 0.2) mu T] and the menaquinone-substituted RC [J(P.MK) (+0.3 +/- 0.2)mu T]. The implications of these observations for electron-transport theory are discussed. Show less
Ehrenfeucht, A.; Hoogeboom, H.J.; Rozenberg, G. 1994
In het onderwijsmemorandum van oktober konden de studenten een stuk lezen over de activiteiten die de studentleden in het vakgroepsbestuur hebben opgezet om iets te doen aan de eindeloze stroom... Show moreIn het onderwijsmemorandum van oktober konden de studenten een stuk lezen over de activiteiten die de studentleden in het vakgroepsbestuur hebben opgezet om iets te doen aan de eindeloze stroom organisatorische fouten binnen het onderwijsprogramma. Inmiddels zijn er verdere ontwikkelingen, waar diezelfde leden de studenten op de hoogte van willen houden. Een verslag. Show less
"Meer mensen aan het werk: dat is de sleutel voor de oplossing van veel sociale problemen die ons land kent. Centrale opgave voor samenleving en regering is dan ook langs een veelheid van... Show more"Meer mensen aan het werk: dat is de sleutel voor de oplossing van veel sociale problemen die ons land kent. Centrale opgave voor samenleving en regering is dan ook langs een veelheid van wegen werkgelegenheid te creëren." Deze passage uit de Regeringsverklaring van het kabinet Kok heeft betrekking op de Nederlandse situatie. Hetzelfde kan echter gezegd worden voor de Indiase deelstaat Maharashtra. Ook daar kan werkgelegenheid een oplossing bieden voor veel van de sociale problemen, die de deelstaat kent. De deelstaatregering speelt een belangrijke rol bij het scheppen van die werkgelegenheid. Show less
