Aromaticity of the Bergman, Myers-Saito, Schmittel, and directly related cyclizations of enediynes

Aromaticity criteria (magnetic susceptibility exaltations, nucleus independent chemical shifts (NICS), and aromatic stabilization energy (ASE) evaluations) for enediyne and enyne-allene cyclizations evaluated at (UBS)-BLYP/6-31G* all agree that the degrees of cyclic electron delocalization of the benzenoid systems formed by the Bergman (3) and Myers-Saito reactions (5) are comparable to benzene. The reaction enthalpy differences between the parent cyclizations and their benzannelated analogues are not entirely due to disparities in gained ASE during the reactions. The alternative formation of fulvene biradicals is not accompanied by favorable aromatic effects.     

Computational studies of aliphatic amine basicity

Computational studies have been used to examine the structural and energetic effects of adding small numbers of water molecules to ammonia, methylamine, dimethylamine, and trimethylamine, and their respective ammoniums ions using the effective fragment potential method. Distinct structural effects with only a few fragment water molecules are revealed. The complexity of structures increases with the number of water fragments with the water fragments forming complex networks. Structural and energetic effects are used to probe the so-called anomalous basicity effect of ammonia and the methylamines on going from the gas phase to aqueous solution.     

Compact two-photon fluorescence microscope based on a single-mode fiber coupler

We present a two-photon fluorescence microscope based on a three-port single-mode optical fiber coupler. It is found that the coupler behaves as a low-pass filter that can deliver an ultrashort-pulsed laser beam of as much as 150 mW of power in the wavelength range from 770 to 870 nm as well as collect a two-photon fluorescence signal in the visible range. As a result of using the fiber coupler, the new two-photon imaging system exhibts a number of advantages, including a compact arrangement, freedom from vibration from lasers and electronic devices, self-alignment, reduction of multiple scattering, and an enhanced optical sectioning effect. The effectiveness of the new instrument is demonstrated with a set of three-dimensional images of biological samples. This instrument may make two-photon fluorescence endoscopy possible for in vivo medical applications.     

A conjecture of Beauville and Catanese revisited

A theorem of Green, Lazarsfeld and Simpson (formerly a conjecture of Beauville and Catanese) states that certain naturally defined subvarieties of the Picard variety of a smooth projective complex variety are unions of translates of abelian subvarieties by torsion points. Their proof uses analytic methods. We refine and give a completely new proof of their result. Our proof combines galois-theoretic methods and algebraic geometry in positive characteristic. When the variety has a model over a function field and its Picard variety has no isotrivial factors, we show how to replace the galois-theoretic results we need by results from model theory (mathematical logic). Furthermore, we prove partial analogs of the conjecture of Beauville and Catanese in positive characteristic.     

The inelastic neutron scattering spectrum of H3B:NH3 and the reproduction of its solid-state features by periodic DFT

The inelastic neutron scattering (INS) and periodic density functional theory (DFT) vibrational spectra of H3B:NH3 are reported to 1600 cm-1. The H3B:NH3 structural and INS features, specifically the reduced solid-state B:N dative bond length and the altered B:N stretching frequency, are reproduced by the periodic DFT calculations, placing the B:N stretching mode at 800 cm-1, in excellent agreement with experiment relative to previous nonperiodic theoretical treatments of this molecule.     

Matlab package for the Schrödinger equation

The paper presents a Matlab package for the linear time-(in)dependent Schr?dinger equation, based on the Hermite spectral method. The matrix form of the discretized problem is suitable for the linear algebra capabilities of Matlab. The high accuracy and efficiency of the algorithm is proved by many examples taken from the literature.      

Palladium‐catalysed P?C bond forming reactions between diphenylphosphine and ortho‐substituted aryl bromides

The use of palladium catalysts derived from 1,1′‐bis‐diisopropylphosphino‐ferrocene and a microwave heating source allows the coupling of a range of ortho‐substituted aryl bromides to diphenylphosphine derivatives to proceed in good yield in under 30 min. Optimization studies reveal that the combination of diphenylphosphine and DABCO is superior to more basic phosphide nucleophiles such as Ph₂PK or Ph₂PMgBr. High yields are only observed when moderately bulky electron rich diphosphines are used as ligands. The differences between P? C coupling and other cross‐coupling reactions are discussed in the light of the reactivity observed. Studies aimed at producing industrially important 1,2‐bis‐phosphino‐benzene ligands are also described. Copyright © 2009 John Wiley & Sons, Ltd.     

Nicotinamide Prevents Ultraviolet Radiation-induced Cellular Energy Loss

UV radiation is carcinogenic by causing mutations in the skin and also by suppressing cutaneous antitumor immunity. We previously found nicotinamide (vitamin B3) to be highly effective at reducing UV-induced immunosuppression in human volunteers, with microarray studies on in vivo irradiated human skin suggesting that nicotinamide normalizes subsets of apoptosis, immune function and energy metabolism-related genes that are downregulated by UV exposure. Using human adult low calcium temperature keratinocytes, we further investigated nicotinamide’s effects on cellular energy metabolism. We found that nicotinamide prevented UV-induced cellular ATP loss and protected against UV-induced glycolytic blockade. To determine whether nicotinamide alters the effects of UV-induced oxidative stress posttranslationally, we also measured UV-induced reactive oxygen species (ROS). Nicotinamide had no effect on ROS formation, and at the low UV doses used in these studies, equivalent to ambient daily sun exposure, there was no evidence of apoptosis. Hence, nicotinamide appears to exert its UV protective effects on the skin via its role in cellular energy pathways.     

Micro-bore titanium housed polymer monoliths for reversed-phase liquid chromatography of small molecules

A new method for the fixation of polymethacrylate monoliths within titanium tubing of up to 0.8 mm I.D. for use as a chromatographic column under elevated temperatures and pressures is described. The preparation of butyl methacrylate–ethylene dimethacrylate-based monolithic stationary phases with desired porous structures was achieved within titanium tubing with pre-oxidised internal walls. The oxidised titanium surface was subsequently silanised with 3-trimethoxysilylpropyl methacrylate resulting in tight bonding of butyl methacrylate porous monolith to the internal walls, providing stationary phase stability at column temperatures up to 110 °C and at operating column pressure drops of >28 MPa. The titanium housed monoliths exhibited a uniform and dense porous structure, which provided peak efficiencies of up to 59,000 theoretical plates per meter when evaluated for the separation of small molecules in reversed-phase mode, under optimal conditions (achieved at 15 μL/min and temperature of 110 °C for naphthalene with a retention factor, k = 0.58). The developed column was applied to the reversed-phase isocratic separation of a text mixture of pesticides.