New Trends and Future Opportunities in the Enzymatic Formation of C-C, C-N, and C-O bonds

Organic chemistry provides society with fundamental products we use daily. Concerns about the impact that the chemical industry has over the environment is propelling major changes in the way we manufacture chemicals. Biocatalysis offers an alternative to other synthetic approaches as it employs enzymes, Nature''s catalysts, to carry out chemical transformations. Enzymes are biodegradable, come from renewable sources, operate under mild reaction conditions, and display high selectivities in the processes they catalyse. As a highly multidisciplinary field, biocatalysis benefits from advances in different areas, and developments in the fields of molecular biology, bioinformatics, and chemical engineering have accelerated the extension of the range of available transformations (E. L. Bell et al., Nat. Rev. Meth. Prim. 2021, 1, 1–21). Recently, we surveyed advances in the expansion of the scope of biocatalysis via enzyme discovery and protein engineering (J. R. Marshall et al., Tetrahedron 2021, 82, 131926). Herein, we focus on novel enzymes currently available to the broad synthetic community for the construction of new C-C, C-N and C-O bonds, with the purpose of providing the non-specialist with new and alternative tools for chiral and sustainable chemical synthesis. © 2021 The Authors. ChemBioChem published by Wiley-VCH GmbH

Optimization of the design of OMNIS, the observatory of multiflavor neutrinos from supernovae

A Monte Carlo code has been developed to simulate the operation of the planned detectors in OMNIS, a supernova neutrino observatory. OMNIS will detect neutrinos originating from a core collapse supernova by the detection of spalled neutrons from Pb- or Fe-nuclei. This might be accomplished using Gd-loaded liquid scintillator. Results for the optimum configuration for such modules with respect to both neutron detection efficiency and cost efficiency are presented. Careful consideration has been given to the expected levels of radioactive backgrounds and their effects. The results show that the amount of data to be processed by a software trigger can be reduced to the <10kHz region and a neutron, once produced in the detector, can be detected and identified with an efficiency of >30%.Comment: Elsevier preprint; 29 pages, 23 figure

Status of experiments leading to a small recirculator

A heavy ion linear induction accelerator is considered to be the leading driver candidate for an Inertial Fusion Energy reactor. To deliver a space-charge-dominated beam at the appropriate energy (several GeV), such an accelerator would be several kilometers in length. Since total length has a strong influence on accelerator cost, we are considering the potential advantages and practical implementation of a recirculating induction accelerator. To address the critical scientific and technical challenges of a recirculating space-charge-dominated heavy ion beam, we have begun to develop the elements of a scaled ``small recirculator``. An operating recirculator must demonstrate full beam control including multi-lap operation, beam insertion/extraction, acceleration and pulse compression. At present, experiments have been conducted using a 2mA, 80keV K{sup +} beam transported through a 45{degree} bend; experiments on a 90{degree} bend with five induction modulators will begin soon. This paper briefly summarizes the recirculator specifications and operational features and reports the latest experimental data as well as the developmental status of beam diagnostics

The calibration of the strength of the localized vibrational modes of silicon impurities in epitaxial GaAs revealed by infrared absorption and raman scattering.

N-type silicon-doped epitaxial layers of gallium arsenide grown by molecular-beam epitaxy (MBE) or metal-organo chemical vapor deposition (MOCVD) have been investigated by measurements of the Hall effect and the strengths of the localized vibrational modes (LVM) of silicon impurities using both Fourier transform absorption spectroscopy and Raman scattering at an excitation energy of 3 eV close to the E sub 1 band gap. Lines from Si(Ga) donors, Si(As) acceptors, Si(Ga)-Si(As) pairs, and Si-X, a complex of silicon with a native defect, were detected and correlated for the two techniques. The maximum carrier concentration (n) found for samples grown under standard conditions was 5.5 x 10 high 18 cm high minus 3. At higher doping levels Si-X becomes dominant and acts as an acceptor, so reducing (n). An integrated absorption of 1 cm high minus 2 in the Si(Ga) LVM line corresponds to 5.0 plus minus 4 x 10 high 16 atoms cm high minus 3: a similar calibration applies to the Si(As) line, but fo r Si-X, an absorption of 1 cm high minus 2 corresponds to only 2.7 plus minus 1.0 x 10 high 16 defects cm high minus 3. Possible structures for Si-X are discussed but a definitive model cannot yet be proposed. MBE samples grown at 400 degree C had values of (n) close to 10 high 19 cm high minus 3, and a negligible concentration of Si-X. On annealing, (n) decreased and Si-X defects were produced together with site switching of Si(Ga) to Si(As). These results are important to the understanding of the mechanism of silicon diffusion at low temperatures. The infrared absorption and Raman measurements are complementary. Absorption measurements made at a resolution of 0.1 cm high minus 1 require layers greater than or equal to 1 mym in thickness doped to a level of 3 x 10 high 17 cm high minus 3 but require the prior elimination of free-carrier absorption. Raman measurements can be made on as-grown layers only 10 nm in thickness doped to a level of 2 x 10 high 18 cm high minus 3, but with a

Percutaneous endoscopic gastrostomy in elderly patients.

Percutaneous endoscopic gastrostomy (PEG) was performed on 28 elderly patients (mean age 82 years) who were dysphagic and intolerant of naso-gastric feeding. Twenty-six patients were recovering from a stroke; the interval between the onset of stroke and PEG averaged 63 days. The procedure was successful and well tolerated by all patients. Nineteen (68%) still had a functioning PEG a median of 14 weeks after placement. One patient whose swallowing recovered had the tube removed 6 months after its insertion. Seven patients (25%) subsequently died from their underlying disease, a mean of 92 days following PEG. There was one procedure-related death from peritonitis. PEG is a useful alternative to surgical gastrostomy in selected elderly patients with dysphagia who are intolerant of naso-gastric feeding