Oxitranyl-Β-aminovinyl ketones. 2. Synthesis of 3(2H)-furanones

The reaction of oxiranyl--dimethylaminovinyl ketones with secondary amines, hydrochloric, and hydrobromic acids leads to the formation of the corresponding 2-aminomethyl- and 2-halomethyl-3-(2H)-furanones.For Communication 1, see [1].Translated from Khimiii Geterotsiklicheskikh Soedinenii, No. 12, pp. 1600–1603, December, 1988.Original article submitted May 20, 1987.     

Synthesis of alkyl-substituted 2-halo-4-aminomethyl-2-buten-4-olides

The reaction of esters of alkyl-substituted (E)-5-amino-4-hydroxy-2,3,epoxyvaleric acids with some hydrohalic acids gave the corresponding 2-halo-4-amino-methyl-2-buten-4-olides, the hydrochlorides of which have diuretic activity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1471–1474, November, 1985.     

Synthesis of cis-5-aryl-4-aroyl-1,3-dioxolanes

The reaction of trans-3-aryl-2-aroyloxiranes containing electron-acceptor substituents in the aryl group with acetone under acid-catalysis conditions gives the corresponding cis-1,3-dioxolanes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1315–1317, October, 1984.     

Reaction of 2,2-dialkoxy-2,3-dihydrofurans with benzenesulfenyl chloride. Convenient method for obtaining 4-oxo-3-phenylthioalkanoic acid esters

The reaction of 2,2-dimethoxy(ethoxy)-2,3-dihydrofurans with benzenesulfenyl chloride with subsequent treatment with dilute hydrochloric acid leads to the corresponding 4-oxo-3-phenylthioalkanoic acid esters in high yields.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 163–166, February, 1988.     

Reactions of hydrogen atom with hydrogen peroxide

Rate coefficients are calculated using canonical variational transition state theory with multidimensional tunneling (CVT/SCT) for the reactions H + H2O2 --> H2O + OH (1a) and H + H2O2 --> HO2 + H2 (1b). Reaction barrier heights are determined using two theoretical approaches: (i) comparison of parametrized rate coefficient calculations employing CVT/SCT to experiment and (ii) high-level ab initio methods. The evaluated experimental data reveal considerable variations of the barrier height for the first reaction: although the zero-point-exclusive barrier for (1a) derived from the data by Klemm et al. (First Int. Chem. Kinet. Symposium 1975, 61) is 4.6 kcal/mol, other available measurements result in a higher barrier of 6.2 kcal/mol. The empirically derived zero-point-exclusive barrier for (1b) is 10.4 kcal/mol. The electronic structure of the system at transition state geometries in both reactions was found to have "multireference" character; therefore special care was taken when analyzing electronic structure calculations. Transition state geometries are optimized by multireference perturbation theory (MRMP2) with a variety of one-electron basis sets, and by a multireference coupled cluster (MR-AQCCSD) method. A variety of single-reference benchmark-level calculations have also been carried out; included among them are BMC-CCSD, G3SX(MP3), G3SX, G3, G2, MCG3, CBS-APNO, CBS-Q, CBS-QB3, and CCSD(T). Our data obtained at the MRMP2 level are the most complete; the barrier height for (1a) using MRMP2 at the infinite basis set limit is 4.8 kcal/mol. Results are also obtained with midlevel single-reference multicoefficient correlation methods, such as MC3BB, MC3MPW, MC-QCISD/3, and MC-QCISD-MPWB, and with a variety of hybrid density functional methods, which are compared with high-level theory. On the basis of the evaluated experimental values and the benchmark calculations, two possible recommended values are given for the rate coefficients.     

Improved measurement of the positive-muon lifetime and determination of the Fermi constant

The mean life of the positive muon has been measured to a precision of 11 ppm using a low-energy, pulsed muon beam stopped in a ferromagnetic target, which was surrounded by a scintillator detector array. The result, tau(micro)=2.197 013(24) micros, is in excellent agreement with the previous world average. The new world average tau(micro)=2.197 019(21) micros determines the Fermi constant G(F)=1.166 371(6)x10(-5) GeV-2 (5 ppm). Additionally, the precision measurement of the positive-muon lifetime is needed to determine the nucleon pseudoscalar coupling g(P).     

Structure of a Mutant Form of Translation Regulator Hfq with the Extended Loop L4

Crystallography Reports - The bacterial protein Hfq is a member of a large family of Lsm proteins, which are characterized by a conserved tertiary structure and form a stable ring-shaped quaternary...     

Chitinase Chit62J4 Essential for Chitin Processing by Human Microbiome Bacterium Clostridium paraputrificum J4

Commensal bacterium Clostridium paraputrificum J4 produces several extracellular chitinolytic enzymes including a 62 kDa chitinase Chit62J4 active toward 4-nitrophenyl N,N′-diacetyl-β-d-chitobioside (pNGG). We characterized the crude enzyme from bacterial culture fluid, recombinant enzyme rChit62J4, and its catalytic domain rChit62J4cat. This major chitinase, securing nutrition of the bacterium in the human intestinal tract when supplied with chitin, has a pH optimum of 5.5 and processes pNGG with K_m = 0.24 mM and k_cat = 30.0 s⁻¹. Sequence comparison of the amino acid sequence of Chit62J4, determined during bacterial genome sequencing, characterizes the enzyme as a family 18 glycosyl hydrolase with a four-domain structure. The catalytic domain has the typical TIM barrel structure and the accessory domains—2x Fn3/Big3 and a carbohydrate binding module—that likely supports enzyme activity on chitin fibers. The catalytic domain is highly homologous to a single-domain chitinase of Bacillus cereus NCTU2. However, the catalytic profiles significantly differ between the two enzymes despite almost identical catalytic sites. The shift of pI and pH optimum of the commensal enzyme toward acidic values compared to the soil bacterium is the likely environmental adaptation that provides C. paraputrificum J4 a competitive advantage over other commensal bacteria.     

Structural investigation of endoglucanase 2 from the filamentous fungus <Emphasis Type="Italic">Penicillium verruculosum</Emphasis>

Enzyme additives capable of degrading non-starch polysaccharides of cereal cell walls, which are major ingredients used in animal feed, can improve the efficiency of livestock production. Non-starch polysaccharides have antinutritional properties that interfere with efficient digestion and assimilation of nutrients by animals. Therefore, the improvement of the properties and characteristics of enzyme additive is an important issue. The three-dimensional structure of one of the key industrial enzymes involved in the degradation of non-starch polysaccharides — endoglucanase 2 from the filamentous fungus Penicillium verruculosum — was determined (PDB ID: 5I6S). The catalytic site of this enzyme was established. Based on the enzyme structure, it was suggested that the pH optimum of the enzyme activity can be shifted from acidic to neutral or alkaline pH values.     

Incoherent Form Factor in Diffraction and Smith—Purcell Radiations

JETP Letters - Pronounced spectrally extended quadrupole X-ray emission has been theoretically predicted in resonant inelastic scattering of two photons near the ionization threshold energy of the...