Rhenium(V)-catalyzed synthesis of 2-deoxy-alpha-glycosides

A mild method for the synthesis of 2-deoxysugars from the coupling of glycals with a range of nucleophiles is described. The method employs 1 mol % of an air- and moisture-tolerant rhenium-oxo complex [ReOCl3(SMe2)(Ph3PO)] as a catalyst for the formation of O-, N-, and S-alpha-glycosides. The catalytic system tolerates a number of commonly employed protecting groups, including isopropylidene acetals, alkyl and silyl ethers, acetates, and benzoates. Furthermore, the high-oxidation-state complex selectively catalyzes the coupling with the glycal acceptor in preference to oxidation of the glycals, alcohols, and even thiols.     

Attaching organic semiconductors to gate oxides: in situ assembly of monolayer field effect transistors

This study unveils a new tetracene derivative that forms dense, upright monolayers on the surface of aluminum oxide. These monolayers spontaneously self-organize into the active layer in nanoscale field-effect transistor devices when aluminum oxide is used as the dielectric layer. This method gives high yields of working devices that have source-drain distances that are less than 60 nm, thereby providing a method to electrically probe the monolayer assemblies formed from approximately 10 zeptomoles of material (approximately 104 molecules). Moreover, this study delineates a new avenue for research in thin-film organic transistors where the active molecules are linked to the dielectric surface to form a monolayer transistor.     

Rotational spectrum of the dimethyl ether-acetylene complex: evidence for an effective C2v geometry

The rotational spectra for five isotopomers of the 1:1 weakly bound complex formed between dimethyl ether (DME) and acetylene (HCCH) have been measured by Fourier transform microwave spectroscopy. The experimental rotational constants, planar moments, and dipole moment components are consistent with a floppy complex possessing an effective C2v structure in which the hydrogen atom of acetylene is hydrogen bonded to the oxygen atom of dimethyl ether with an intermolecular H...O separation of 2.08(3) A. Experimental rotational constants for the normal isotopic species are A = 10382.5(17) MHz, B = 1535.7187(18) MHz, and C = 1328.3990(17) MHz and the dipole moment components are mua= mutotal = 1.91(10) D. Ab initio calculations at the MP2/6-311++G(2d,2p) level indicate that the energy barrier for motion of the HCCH subunit between the lone pairs of the DME, via a C2v intermediate structure, is very low (approximately 0.29 kJ mol(-1)). Inclusion of basis set superposition error and zero point energy corrections to the energies of four stationary points located on the potential energy surface shows that the relative stabilities are particularly sensitive to these corrections. The ab initio optimizations give rotational constants for the C2v structure of A = 10066 MHz, B = 1496 MHz, and C = 1324 MHz, and a dipole moment of mua= mu(total) = 2.12 D, in reasonable agreement with the experimentally determined values. The structural parameters and energetics of the DME-HCCH complex will be discussed and compared to similar complexes such as H2O-HCCH.     

Molecular structure and the twist-bend nematic phase: the role of terminal chains

ABSTRACT

The synthesis and characterisation of two homologous series of non-symmetric dimers are reported, the 1-(4-methoxybiphenyl-4?-yl)-6-(4-alkylanilinebenzylidene-4?-oxy)hexanes (MeOB6O.m, m = 1–10) and 1-(4-methoxybiphenyl-4?-yl)-6-(4-alkyloxyanilinebenzylidene-4?-oxy)hexanes (MeOB6O.Om, m = 1–9). All 10 members of the MeOB6O.m series exhibit the conventional nematic phase. At lower temperatures, the members with m = 1–7 formed the twist-bend nematic phase, N_TB, whereas for m = 8–10 smectic behaviour replaced the N_TB phase. All nine members of the MeOB6O.Om series also show the conventional nematic phase and for m = 1–3, a strongly monotropic N_TB phase is also observed. The alkyloxy terminated dimers show the higher values of T_NI and T_{NTB N} . For both series, the values of T_NI and T_{NTB N} show a modest alternation and in the same sense as m is increased. These observations suggest that the spatial uniformity of molecular curvature is important in driving the formation of the N_TB phase. The observation of smectic behaviour is attributed to the molecular inhomogeneity arising from the long terminal alkyl chain driving microphase separation. The transitional behaviour of these series is compared to those of the corresponding cyanobiphenyl-based series and overarching observations discussed.     

THE EFFECTS OF ULTRAVIOLET RADIATION EXPOSURE OF ADJACENT CELLS ON PLAQUE FORMATION WITH Herpes simplex VIRUS TYPE I

African green monkey kidney cells (CV-1P) were exposed to low fluences of 254 nm germicidal radiation and then infected with Herpes simplex virus, type I. The result of this treatment was an increase in viral plaque development rate, the large plaque effect (LPE). A measurement of the kinetics of plaque development suggested that a large portion of the effect could be due to events occurring in those cells that are adjacent to the initially infected cell. An infectious center assay was employed in order to isolate the effects of ultraviolet radiation (UV) on the initially infected cells from those effects on the adjacent cells that became infected as the plaque spread radially outward. Plaque development began earlier in UV irradiated cells and progressed at a uniformly accelerated rate compared to untreated cells. Results indicate that although the initially infected cell contributes to the LPE, the major effect is due to events that occur in the adjacent cells. Each round of viral replication appears to contribute equally to the LPE. The virally induced rate of fusion of the initially infected cell with its immediate neighbors is not affected by UV.     

Near-Infrared Raman Spectroscopy for In Vitro Detection of Cervical Precancers

Abstract— In this study, we investigate the potential of near-infrared Raman spectroscopy to differentiate cervical precancers from normal tissues, inflammation and metaplasia and to differentially diagnose low-grade and high-grade precancers. Near infrared Raman spectra were measured from 36 biopsies from 18 patients in vitro. Detection algorithms were developed and evaluated relative to histopathologic examination. Algorithms based on empirically selected peak intensities, ratios of peak intensities and a combination of principal component analysis for data reduction and Fisher discriminant analysis for classification were investigated. Spectral peaks were tentatively identified from measured spectra of potential chromophores. Empirically selected normalized intensities can differentiate precancers from other tissues with an average sensitivity and specificity of 88 ± 4% and 92 ± 4%. Ratios of un-normalized intensities can differentiate precancers from other tissues with a sensitivity and specificity of 82% and 88% and high-grade from low-grade lesions with a sensitivity and specificity of 100%. Using multivariate methods, intensities at eight frequencies can be used to differentiate precancers from all other tissues with a sensitivity and specificity of 82% and 92% in an unbiased test. Raman algorithms can potentially separate benign abnormalities such as inflammation and metaplasia from precancers. Comparison of tissue spectra to published and measured chromophore spectra indicate that the most likely primary contributors to the tissue spectra are collagen, nucleic acids, phospholipids and glucose 1-phos-phate. These results suggest that near-infrared Raman spectroscopy can be used for cervical precancer diagnosis and may be able to accurately separate samples with inflammation and metaplasia from precancer.     

Patterned growth of large oriented organic semiconductor single crystals on self-assembled monolayer templates

This work demonstrates a method for inducing site-specific nucleation and subsequent growth of large oriented organic semiconductor single crystals using micropatterned self-assembled monolayers (SAMs). We demonstrate growth of oriented, patterned, and large organic semiconductor single crystals for potential use in organic electronic devices. The control over multiple parameters in a single system has not yet been reported. The ability to control various aspects of crystal growth in one system provides a powerful technique for the bottom-up fabrication of organic single-crystal semiconductor devices.     

Trajectory study of supercollision relaxation in highly vibrationally excited pyrazine and CO2

Classical trajectory calculations were performed to simulate state-resolved energy transfer experiments of highly vibrationally excited pyrazine (E(vib) = 37,900 cm(-1)) and CO(2), which were conducted using a high-resolution transient infrared absorption spectrometer. The goal here is to use classical trajectories to simulate the supercollision energy transfer pathway wherein large amounts of energy are transferred in single collisions in order to compare with experimental results. In the trajectory calculations, Newton's laws of motion are used for the molecular motion, isolated molecules are treated as collections of harmonic oscillators, and intermolecular potentials are formed by pairwise Lennard-Jones potentials. The calculations qualitatively reproduce the observed energy partitioning in the scattered CO(2) molecules and show that the relative partitioning between bath rotation and translation is dependent on the moment of inertia of the bath molecule. The simulations show that the low-frequency modes of the vibrationally excited pyrazine contribute most to the strong collisions. The majority of collisions lead to small DeltaE values and primarily involve single encounters between the energy donor and acceptor. The large DeltaE exchanges result from both single impulsive encounters and chattering collisions that involve multiple encounters.     

A carbon-13 Nmr assignment study of 3,5-diarylisoxazoles

The assignment of the carbon-13 nmr resonances of 3-(aryl)-5-phenylisoxazoles (I) and 3-phenyl-5-(aryl)-isoxazoles (II) in dimethylsulfoxide-d₆ has been made. The assignments were made by using model compounds, chemical shift arguments, coupling with fluorine substituents, and shifts resulting from quaternization of the isoxazole ring. A carbon-13 nmr method for distinguishing between I and II which can be produced simultaneously by certain synthetic methods is presented.     

Visible and near-infrared chemical imaging methods for the analysis of selected forensic samples

This study investigated various chemical imaging methods for the forensic analysis of paints, tapes and adhesives, inks and firearm propellants (absorption and photoluminescence in the UV-vis-NIR regions). Results obtained using chemical imaging technology were compared with those obtained using traditional techniques. The results show that chemical imaging offers significant advantages in the forensic context, for example the ability to display visual and spectral results side by side and to reduce sample preparation, hence minimizing the risk of contamination. Chemical imaging produced a greater discriminating power than traditional techniques for most evidence types. Chemical imaging also eliminated different brands of ammunition based on the fluorescence characteristics of the propellant grains preserving the evidence for further analysis. It is expected that this technology will find broader forensic applications in the future.