Enzymic Baeyer–Villiger Oxidations by Flavin-Dependent Monooxygenases

There has recently been a revival of interest in microbial biochemistry. Part of this resurgence is due to the increased presence of man-made organic compounds in the biosphere and the resultant interest in microorganisms which can degrade these xenobiotic molecules. Also, advances in genetic engineering have raised the possibility of utilizing the chemical machinery of bacteria for commercial profit and social benefit. The Baeyer-Villiger reaction is a useful transformation in organic synthesis which provides chemists with a gentle means of converting ketones into esters or lactones. The reaction, however, suffers from the problems of low yield and the need, in some cases, to utilize harsh conditions. There exist bacteria, capable of growth on aliphatic molecules, that contain enzymes which can catalyze Baeyer-Villiger reactions. These enzymes, known as monooxygenases, are involved in the breakdown of acyclic and alicyclic ketones to provide simpler carbon units for further catabolism. The gamut of reactions catalyzed by some of these enzymes is remarkable. This diversity, plus their availability in pure form in quantity by genetic engineering raises the possibility that these biocatalysts can be useful as reagents in organic synthesis.     

The formation of C3H3 (propynyl) radicals in the reaction of CH2(1A1) with acetylene

Results obtained from the photolysis of ketene with acetylene strongly support the formation of C₃H₃ radicals in the title reaction. Stationary state studies are interpreted in terms of the reaction with a rate constant (10^9.8 s^?1) which is compared to RRKM predictions. In pulsed laser induced decomposition experiments, recombination products involving C₃H₃ have been detected (some for the first time) and their formation modeled using step (3) with the same rate constant.     

Cosmic strings and domains in unified theories

Unified theories predict that the Universe passes through a sequence of phase transitions as it cools after the big bang. Topological structures (domain walls, strings and monopoles) may be created in these transitions. The production of domains of different zero-temperature vacua (separately by massive walls) excludes some popular scenarios for the breaking of SU(5) and SO(10).Massive strings appear in other schemes. They may be open strings or closed loops. We exhibit an SO(10) example with string formation. SO(8) supergravity may deliver an effective SU(5)× SU(2) unified theory below the Planck mass scale. This can also lead to string production. We present the rather restrictive conditions under which string producing theories are harmless to conventional cosmology. Even then, strings do not seem to provide the initial density perturbations that evolved into galaxies.     

Lessons on e+e− annihilation from simple chain emission models

The dearth of solvable models for e⁺e^? annihilation often reduces one to excessively qualitative considerations, leaving obvious dynamical questions open. We discuss here various aspects of chain-emission models that can be cast into solvable form. In such models the virtual photon decays into a link (a pion, for example) and some state (e.g., an off-shell vector meson) which decays by sequentially shedding further links.Topics include the scaling behavior in such models (including how it is broken near ω = 0), neutral/charged distributions, the effect of internal quantum numbers, and, in a particularly simple version of the model, the two-particle distributions. In particular, we show how a large neutral to charged energy ratio can arise. Finally, we discuss variants on such models arising from possible variety in the links of the chain, (i.e., multichannel effects and the nonlinear effects arising from the branching of a chain into chains.     

Spotting glueballs in collinear gluon jets

We suggest looking for pure gluon hadronic states (glueballs) in ?→ 3g → low spherically final state (collinear gluon jets). In these events one gluon has the maximum energy, $\text{M?}\text{2}$, favouring fragmentation into a glueball. The signature for a true C = G + glueball is its prominence at the ? resonance in e⁺e^? →? → (glueball → four charged pions) + … and its absence in q$\text{q}$ jets off (we do not expect significant quark fragmentation into glueballs).     

The application of cathodic sputtering to the production of atomic vapours in atomic fluorescence spectroscopy

Cathodic sputtering is used as a source of atomic vapour for the chemical analysis of metals and alloys by atomic fluorescence spectroscopy. The sputtered vapour is produced in a Pyrex glow-discharge chamber which is suitable for the rapid interchange of flat, metallic samples. The discharge operates with a water-cooled cathode specimen and a flow-through gas control system. Linear calibration curves are obtained for the determination of nickel, chromium, copper, manganese and silicon in some iron-base alloy standards. For nickel, chromium and copper, detection limits are of the order of 20 ppm in the iron, and for manganese and silicon about 70 and 400 ppm respectively. The reproducibility of the fluorescence measurements is about ±1%. The system can be readily adapted to provide simultaneous multi-element analysis.