Zum selektiven NMR-Spinecho-Verhalten bei Systemen mit I = 1 im Festkörper am Beispiel des Kaliumoxalatmonohydrats

Investigation of the Selective N.M.R. Spin Echo Response of I = 1 Systems in Solids Demonstrated on Potassium Oxalate Monohydrate The theory of the nonselective spin echo response in solids for dipolar-coupled spins I = 1 with quadrupole interaction by BODEN et al. [5] is modified for the case of selective irradiation to only one line of the n.m.r. spectrum. The theoretical results are compared with ¹H-n.m.r. experiments on dipolar-coupled protonpairs of a (KCOO)₂ · H₂O single crystal. This is possible because in this material the interpair dipolar interaction is substantially smaller than the intrapair dipolar interaction. An echo response results which has some similarities to the behaviour of spin systems with heteronuclear coupling.     

Laser flash photolysis studies on excited singlet states of benzene,toluene, p-xylene,polystyrene, and poly-α-methylstyrene

Optical absorption spectra obtained in cyclohexane solutions of benzene, toluene, and p-xylene contain bands at 620 to 640 nm, assigned to S_n← S₁ monomer transitions. With concentrated solutions, excimer absorption spectra nave been found. With the two polymers, absorption of (intramolecular) excimers has been detected only.     

Experimental investigation of criteria for continuous variable entanglement

We generate a pair of entangled beams from the interference of two amplitude squeezed beams. The entanglement is quantified in terms of EPR paradox and inseparability criteria, with both results clearly beating the standard quantum limit. We experimentally analyze the effect of decoherence on each criterion and demonstrate qualitative differences. We also characterize the number of required and excess photons present in the entangled beams and provide contour plots of the efficacy of quantum information protocols in terms of these variables.     

Photochemical conversion of poly-2,3-diphenylbutadiene to poly-9,10-dimethylenephenanthrene

Poly-2,3-diphenylbutadiene dissolved in CH₂Cl₂ has been subjected to continuous irradiation at 313 nm and to flash photolysis at 266 nm at room temperature. Cyclization of pendant phenyl groups to dihydrophenanthrene groups dominates over isomerization, indicating impeded flexibility of polymer chain segments. In the case of 2,3-diphenylbutene-2, isomerization dominates over cyclization. In the presence of O₂, dihydrophenanthrene groups are converted to phenanthrene groups. Flash photolysis experiments in oxygenated solution revealed that phenanthrene groups are formed in the polymer according to two processes, viz. a fast spontaneous dehydrogenation and a slower oxidation.     

Two-state folding, folding through intermediates, and metastability in a minimalistic hydrophobic-polar model for proteins

Within the frame of an effective, coarse-grained hydrophobic-polar protein model, we employ multicanonical Monte Carlo simulations to investigate free-energy landscapes and folding channels of exemplified heteropolymer sequences, which are permutations of each other. Despite the simplicity of the model, the knowledge of the free-energy landscape in dependence of a suitable system order parameter enables us to reveal complex folding characteristics known from real bioproteins and synthetic peptides, such as two-state folding, folding through weakly stable intermediates, and glassy metastability.     

Galactic-cosmic-ray-produced 3He in a ferromanganese crust: any supernova 60Fe excess on earth?

An excess of 60Fe in 2.4-3.2 x 10(6) year old ferromanganese crust (237 KD) from the deep Pacific Ocean has been considered as evidence for the delivery of debris from a nearby supernova explosion to Earth. Extremely high ;{3}He/;{4}He (up to 6.12 x 10(-3)) and 3He concentrations (up to 8 x 10(9) atoms/g) measured in 237 KD cannot be supernova-derived. The helium is produced by galactic cosmic rays (GCR) and delivered in micrometeorites that have survived atmospheric entry to be trapped by the crust. 60Fe is produced by GCR reactions on Ni in extraterrestrial material. The maximum (3)He/(60)Fe of 237 KD (80-850) is comparable to the GCR (3)He/(60)Fe production ratio (400-500) predicted for Ni-bearing minerals in iron meteorites. The excess 60Fe can be plausibly explained by the presence of micrometeorites trapped by the crust, rather than injection from a supernova source.     

Identification of characteristic protein folding channels in a coarse-grained hydrophobic-polar peptide model

Folding channels and free-energy landscapes of hydrophobic-polar heteropolymers are discussed on the basis of a minimalistic off-lattice coarse-grained model. We investigate how rearrangements of hydrophobic and polar monomers in a heteropolymer sequence lead to completely different folding behaviors. Studying three exemplified sequences with the same content of hydrophobic and polar residues, we can reproduce within this simple model two-state folding, folding through intermediates, as well as metastability.     

Differences in solution behavior among four semiconductor-binding peptides

Recent experiments have identified peptides that adhere to GaAs and Si surfaces. Here, we use all-atom Monte Carlo simulations with implicit solvent to investigate the behavior in aqueous solution of four such peptides, all with 12 residues. At room temperature, we find that all four peptides are largely unstructured, which is consistent with experimental data. At the same time, we find that one of the peptides is structurally different and more flexible, as compared to the others. This finding points at structural differences as a possible explanation for differences in adhesion properties among these peptides. By also analyzing designed mutants of two of the peptides, an experimental test of this hypothesis is proposed.     

Inverse metal-stripe polarizers

Received: 18 May 1998/Revised version: 17 August 1998