Zucker

Ohne Zusammenfassung     

Single-frequency operation of a broad-area laser diode by injection locking of a complex spatial mode via a double phase conjugate mirror

We demonstrate what is believed to be the first phase-coherent locking of a high-power broad-area diode to a single-frequency master laser. We use photorefractive double phase conjugation to lock the diode in a self-optimized complex spatial mode while the photorefractive crystal diffracts that complex mode in a near-diffraction-limited beam.     

Conserved core substructures in the overlay of protein-ligand complexes

The method of conserved core substructure matching (CSM) for the overlay of protein-ligand complexes is described. The method relies upon distance geometry to align structurally similar substructures without regard to sequence similarity onto substructures from a reference protein empirically selected to include key determinants of binding site location and geometry. The error in ligand position is reduced in reoriented ensembles generated with CSM when compared to other overlay methods. Since CSM can only succeed when the selected core substructure is geometrically conserved, misalignments only rarely occur. The method may be applied to reliably overlay large numbers of protein-ligand complexes in a way that optimizes ligand position at a specific binding site or subsite or to align structures from large and diverse protein families where the conserved binding site is localized to only a small portion of either protein. Core substructures may be complex and must be chosen with care. We have created a database of empirically selected core substructures to demonstrate the utility of CSM alignment of ligand binding sites in important drug targets. A Web-based interface can be used to apply CSM to align large collections of protein-ligand complexes for use in drug design using these substructures or to evaluate the use of alternative core substructures that may then be shared with the larger user community. Examples show the benefit of CSM in the practice of structure-based drug design.     

Temperature dependence of the lifetime of pyrene triplet excimer emission

The stabilisation enthalpies of two different kinds of triplet excimers of pyrene are calculated from the temperature dependence of the triplet lifetime. They are found to be 800 cm⁻¹ and 2000 cm⁻¹.     

Anomalous shifts of solvent proton lines of solutions containing aromatic negative ions

A down field contribution to the NMR shifts of solvent proton lines is found for ethereal solutions containing phenanthrene, triphenylene and coronene anions. These exceptional down-field shifts are shown to be correlated with ionic association between the positive and negative ions.     

The relative S*1 emission yield of 3,4-benzpyrene in the vapour phase

The relatives S^*₁ emission yield as a function of excitation energy can be interpreted as arising from an ensemble in which the excess energy is randomly distributed over the vibrational modes.     

Flash photolysis of solutions of sodium in ethers

Flash photolysis of ethereal solutions of sodium results in the almost complete disappearance of the original absorption band at 15000 cm⁻¹ and in the formation of solvated electrons. After the flash an intermediate with an absorption maximum at 12000 cm⁻¹ is formed. This absorption is assigned to a species which has the stoichiometric composition of a sodium atom. Although it may be described as a metal “monomer” we propose as an alternative model the concept of an “ion pair” of a solvated electron and a sodium cation. In analogy to the 12000 cm⁻¹ transient we propose that the blue species can be described as an associate of a sodium cation with two solvated electrons.     

Hydrocarbon ions with triplet ground states

The N.M.R. spectra of meta dichloro and meta dibromo benzenes are analysed in the nematic phase of 4-methoxy benzylidene-4-amino-α-methyl cinnamic acid-n-propyl ester at room temperature.

The direct couplings are found to be of negative sign. The molecules orient preferentially with the aromatic plane along the direction of the magnetic field and the C ₂-symmetry axis perpendicular to it.

The relations between the various direct couplings and the inter-proton distances are reported. The ratio of the distance between the meta protons along the axis perpendicular to the C ₂ symmetry and the ortho protons is determined precisely. The other ratios could not be determined to any reasonable precision. The reasons are discussed.

The angles between the C-H bonds of the equivalent protons and the C-C bonds in both the molecules are determined on the assumption of the C-H bond lengths and the ring geometry of benzene.     

SPECTRAL PROPERTIES OF (ISO)ALLOXAZINES IN THE VAPOUR PHASE

Abstract— Spectral properties of alloxazine and isoalloxazine derivatives were determined at high temperatures in the vapour phase. In comparison with spectra observed in solution, vapour phase spectrometry gives primary photophysical properties of the isolated chromophore. Fluorescence lifetimes in the vapour phase range from <0.5 to 18 ns. There is some indication that an intramolecular complex can exist between the isoalloxazine moiety and its aliphatic side chain carrying a polar (hydroxyl) group. Direct photodissociation of the molecule in its first electronically excited singlet state is not very probable.