Electronic and vibrational second-order nonlinear optical properties of protein secondary structural motifs

A perturbation theory approach was developed for predicting the vibrational and electronic second-order nonlinear optical (NLO) polarizabilities of materials and macromolecules comprised of many coupled chromophores, with an emphasis on common protein secondary structural motifs. The polarization-dependent NLO properties of electronic and vibrational transitions in assemblies of amide chromophores comprising the polypeptide backbones of proteins were found to be accurately recovered in quantum chemical calculations by treating the coupling between adjacent oscillators perturbatively. A novel diagrammatic approach was developed to provide an intuitive visual means of interpreting the results of the perturbation theory calculations. Using this approach, the chiral and achiral polarization-dependent electronic SHG, isotropic SFG, and vibrational SFG nonlinear optical activities of protein structures were predicted and interpreted within the context of simple orientational models.     

Computer simulation studies of anisotropic systems. The influence of external fields on the nematic—isotropic transition

The results of Monte Carlo simulations are reported for a model nematogen in the presence of an intense magnetic field. The predictions of a molecular field theory for the system are found to be in reasonable accord with the simulations. It would appear therefore that the critical field for a real nematogen may be unobservably high.     

The first fluorogenic assay for detecting a Baeyer-Villigerase activity in microbial cells

The first fluorogenic assay allowing for detection of microbial enzymes able to perform Baeyer-Villiger oxidation is described. This is based on the use of 4-oxopentyl umbelliferyl ether 1 as a fluorogenic substrate. When Baeyer-Villigerases active against this test ketone are present in the selected whole cells, 1 is transformed into 3-hydroxypropyl umbelliferyl ether 3, which, in a subsequent step, releases the fluorescent product umbelliferone. Different microorganisms, known to be endowed with Baeyer-Villigerase activity, were assayed.     

Reactions of tetracarbonylcobaltate(-I) with chlorosilanes in ether solvents

The reactions of NaCo(CO)₄ with Me_nSiCl_4?n (n = 0–3) in diethylether (Et₂O) and in tetrahydrofuran (THF) have been studied. Three distinct reaction pathways were recognised which depend on the acidity of the chlorosilane and basicity of solvent. Attack at the silicon centre via the Co atom of Co(CO)₄^? leads to formation of a SiCo bond; reaction involving a CO ligand of Co(CO)₄^? gives clusters R₃SiOCCo₃(CO)₉; and chlorosilane induced attack of Co(CO)₄^? on the solvent gives products derived from THF molecules.     

Unusual selectivity of unprotected aziridines in palladium-catalyzed allylic amination enables facile preparation of branched aziridines

Functionalized branched aziridines can be prepared in high yields and with high levels of regioselectivity using unprotected aziridines as nitrogen sources in palladium-catalyzed allylic amination. High levels of enantioselectivity can be achieved with BINAP on palladium. This methodology allows for strategic placement of an aziridine-containing fragment within a complex molecule environment for further elaboration.     

The first structural and spectroscopic characterization of a neptunyl polyoxometalate complex

The reaction between PW9O349- and NpO2+ has yielded the first structurally characterized neptunyl(V) polyoxometalate complex, [Na2(NpO2)2(A-PW9O34)2]14-. This complex is isostructural with the uranyl(VI) analogue, and there is also spectroscopic evidence for its existence in solution. The complex is readily extracted into toluene, and this may have significance in the sequestering and/or separation of the neptunyl ion in terms of nuclear waste management.     

Infrared multiphoton excitation of small molecules

The collisionless infrared excitation by short CO₂ laser pulses of the molecules SO₂, OCS, NO₂, NH₃ and DN₃ is compared with that of larger molecules. The average number of photons absorbed per molecule and the fraction of molecules dissociated depends predominantly on the laser intensity, while for larger molecules with higher densities of vibrational states the excitation is primarily determined by the laser fluence.