Coupled-cluster calculations of vibrational Raman optical activity spectra

We present the first calculations of Raman optical activity spectra at the coupled-cluster level of theory. Calculations are presented for (S)-methyloxirane and compared to recent experimental gas-phase measurements as well as the results obtained at the Hartree-Fock and density functional level of theory using the popular B3LYP functional. For the experimentally relevant frequency region of 400-1600 cm(-1), the Hartree-Fock, B3LYP and coupled-cluster spectra are very similar when the same force field is used, and the results also agree well with experiment. For high-frequency vibrational modes, differences in the ROA difference parameters are observed and are analyzed. The new coupled-cluster ROA code will allow for critical benchmarking of the accuracy of modern exchange-correlation functionals in the calculation of ROA spectra.     

Role of long-range intermolecular forces in the formation of inorganic nanoparticle clusters

An understanding of the role played by intermolecular forces in terms of the electron density distribution is fundamental to the understanding of the self-assembly of molecules in the formation of a molecular crystal. Using ab initio methods capable of describing both short-range intramolecular interactions and long-range London dispersion interactions arising from electron correlation, analyses of inorganic dimers of As(4)S(4) and As(4)O(6) molecules cut from the structures of realgar and arsenolite, respectively, reveal that the molecules adopt a configuration that closely matches that observed for the crystal. Decomposition of the interaction energies using symmetry-adapted perturbation theory reveals that both model dimers feature significant stabilization from electrostatic forces as anticipated by a Lewis acid/Lewis base picture of the interaction. London dispersion forces also contribute significantly to the interaction, although they play a greater role in the realgar structure near equilibrium than in arsenolite.     

Bacterial symbionts and natural products

The study of bacterial symbionts of eukaryotic hosts has become a powerful discovery engine for chemistry. This highlight looks at four case studies that exemplify the range of chemistry and biology involved in these symbioses: a bacterial symbiont of a fungus and a marine invertebrate that produce compounds with significant anticancer activity, and bacterial symbionts of insects and nematodes that produce compounds that regulate multilateral symbioses.     

New Convenient Methods for the Preparation of Pendant Chain Cyclobutadiene Tricarbonyliron Complexes

Simple, economical, and more practical procedures have been developed for the synthesis of precursors to pendant chain cyclobutadiene metal complexes. Facile reduction of the mono and disubstituted 1,2-cyclobutenediones gave cyclobutenediols which were converted to their corresponding trans dibromides with PBr₃. Reduction and complexation using Fe₂(CO)₉ formed the pendant chain cyclobutadiene tricarbonyliron complexes in good yields.     

Synthesis and Characterization of Diethyl Fumarate‐1,4‐Cyclohexanedimethanol Polyesters for Use in Bioresorbable Bone Cement Composites

Unsaturated polyesters are prepared by transesterification polymerization of diethyl fumarate and 1,4‐cyclohexanedimethanol. The structure of the polyesters was characterized by FT‐IR and ¹H‐ and ¹³C‐NMR spectroscopy. Semicrystalline morphology of the polymers is suggested by DSC analysis with T_g at 21°C and melting at 140°C. The thermogravimetric analysis indicated that the onset of degradation takes place at 300°C. The polyester's structure has significant impact on the properties of the composites prepared by crosslinking the fumarate double bonds with N‐vinyl pyrrolidone in the presence of an inorganic filler, calcium sulfate dihydrate, with the addition of a radical initiator, benzoyl peroxide, at ambient temperatures. The compressive strength and hydrolytic stability of the cement compositions was correlated with structure of the polyesters.     

Energetic salts of the binary 5-cyanotetrazolate anion ([C2N5]-) with nitrogen-rich cations

The reaction of cyanogen (NC-CN) with MN(3) (M=Na, K) in liquid SO(2) leads to the formation of the 5-cyanotetrazolate anion as the monohemihydrate sodium (1·1.5 H(2)O) and potassium (2) salts, respectively. Both 1·1.5 H(2)O and 2 were used as starting materials for the synthesis of a new family of nitrogen-rich salts containing the 5-cyanotetrazolate anion and nitrogen-rich cations, namely ammonium (3), hydrazinium (4), semicarbazidium (5), guanidinium (6), aminoguanidinium (7), diaminoguanidinium (8), and triaminoguanidinium (9). Compounds 1-9 were synthesised in good yields and characterised by using analytical and spectroscopic methods. In addition, the crystal structures of 1·1.5 H(2)O, 2, 3, 5, 6, and 9·H(2)O were determined by using low-temperature single-crystal X-ray diffraction. An insight into the hydrogen bonding in the solid state is described in terms of graph-set analysis. Differential scanning calorimetry and sensitivity tests were used to assess the thermal stability and sensitivity against impact and friction of the materials, respectively. For the assessment of the energetic character of the nitrogen-rich salts 3-9, quantum chemical methods were used to determine the constant volume energies of combustion, and these values were used to calculate the detonation velocity and pressure of the salts using the EXPLO5 computer code. Additionally, the performances of formulations of the new compounds with ammonium nitrate and ammonium dinitramide were also predicted. Lastly, the ICT code was used to determine the gases and heats of explosion released upon decomposition of the 5-cyanotetrazolate salts.     

Laser drilling of high aspect ratio holes in copper with femtosecond,picosecond and nanosecond pulses

Deep laser holes were drilled in copper sheets using various pulse lengths and environments. By recording the intensity on a photodiode placed under the sample while drilling the holes, we obtained the number of pulses to drill through the sheet as a function of pulse length and energy. The entrance diameter of the holes was successfully predicted using a Gaussian approximation and a material removal fluence threshold of 0.39 J/cm² for a pulse length of 150 fs. From cross sections of the holes, the morphology of the inside walls was observed and shows an increase in the amount of molten material with pulse length. A transition pulse length is defined as the point at which the laser affected material goes from being mainly vaporized to mainly melted. This transition occurs near ∼10 ps, which corresponds approximately to the electron–phonon relaxation time for copper. PACS 62.20.Mk; 62.25.+g; 79.20.Ds     

Staleya guttiformis attachment on poly(tert-butylmethacrylate) polymeric surfaces

The attachment behaviour of Staleya guttiformis DSM 11458^T on poly(tert-butyl methacrylate) (P(tBMA)) polymeric surfaces has been studied. The electrostatic charge of the S. guttiformis cell surface (measured as zeta potential via microelectrophoresis) was −43.18 mV. S. guttiformis cells appeared weakly hydrophilic as the water contact angle measured on lawns of bacterial cells was found to be 55 ± 4.9°. It was found that while attaching on P(tBMA) surfaces, S. guttiformis cells produced extracellular polymeric substances (EPS) as observed from atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis. The AFM high resolution imaging revealed the nano-topography of the ‘free’ (the EPS that is produced by the bacterial cells, but no longer directly attached to the cells) EPS associated on the cell surface and also found on P(tBMA) surface. The ‘free’ EPS exhibited granular structure with lateral dimensions of 30–50 nm and a vertical nano-roughness of 7–10 nm. Another type of the EPS secreted by S. guttiformis cells appeared as a hydogel substance, presumably polysaccharide that formed a biopolymer network that facilitated bacterial attachment.     

Stereoselective Synthesis of Sialyl Lewisa Antigen and the Effective Anticancer Activity of Its Bacteriophage Qβ Conjugate as an Anticancer Vaccine

Sialyl Lewis^a (sLe^a), also known as cancer antigen 19-9 (CA19-9), is a tumor-associated carbohydrate antigen. The overexpression of sLe^a on the surface of a variety of cancer cells makes it an attractive target for anticancer immunotherapy. However, sLe^a-based anticancer vaccines have been under-explored. To develop a new vaccine, efficient stereoselective synthesis of sLe^a with an amine-bearing linker was achieved, which was subsequently conjugated with a powerful carrier bacteriophage, Qβ. Mouse immunization with the Qβ-sLe^a conjugate generated strong and long-lasting anti-sLe^a IgG antibody responses, which were superior to those induced by the corresponding conjugate of sLe^a with the benchmark carrier keyhole limpet hemocyanin. Antibodies elicited by Qβ-sLe^a were highly selective toward the sLe^a structure, could bind strongly with sLe^a-expressing cancer cells and human pancreatic cancer tissues, and kill tumor cells through complement-mediated cytotoxicity. Furthermore, vaccination with Qβ-sLe^a significantly reduced tumor development in a metastatic cancer model in mice, demonstrating tumor protection for the first time by a sLe^a-based vaccine, thus highlighting the significant potential of sLe^a as a promising cancer antigen.     

ChemInform Abstract: Boron Cluster Cations: Transition from Planar to Cylindrical Structures.

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