Dipole moment and mobility of molecules in nematic liquid crystals of the 4-n-butyl ester of [4′-n-hexyloxyphenyl] benzoic acid in the absence of external orienting fields

Dielectric polarization was studied in a nematic liquid crystal of the 4-n-butyl ester of [4′-n-hexyloxyphenyl] benzoic acid (BE[HOP]BA) in the absence of external orienting fields in the isotropic and mesophase states in a frequency range of 10³–10⁷ Hz. In the isotropic melt, three regions of dielectric absorption of a relaxation origin were revealed. It is shown that two of them are related to a reorientation motion of individual molecules about the longitudinal axes (process I) and about the short axes (process II). Processes I and II have relaxation times τ ～ 10^?9 and 10^?8 s and activation energies ΔU ～ 16 and 23 kcal/mol, respectively; the energy of activation of process II in the liquid-crystal phase increases to ΔU ～ 38 kcal/mol. In the isotropic melt, in addition to processes I and II, process III occurs in the low-frequency range, which is characterized by greater relaxation times τ ～ 10^?7 s and an activation energy ΔU ～ 28 kcal/mol. In order to establish the nature of process III, temperature dependences of the dipole moments and Kirkwood correlation factor g were studied in both BE[HOP]BA phases. The magnitude of the Kirkwood factor in the isotropic phase of the BE[HOP]BA near the transition temperature from the mesomorphic state (g ～ 0.88) indicates the retention of the orientational ordering of molecules of the low-molecular liquid crystal and the compensation of their dipole moments intrinsic to the liquid-crystal state. This circumstance suggests that the third process of the relaxation of dipole polarization is due to a cooperative mode of motion of molecules in mesophase nuclei in the isotropic melt.     

Primitive connected and additive theories of polygons

We study into monoids S the class of all S-polygons over which is primitive normal, primitive connected, or additive, that is, the monoids S the theory of any S-polygon over which is primitive normal, primitive connected, or additive. It is proved that the class of all S-polygons is primitive normal iff S is a linearly ordered monoid, and that it is primitive connected iff S is a group. It is pointed out that there exists no monoid S with an additive class of all S-polygons. __________ Translated from Algebra i Logika, Vol. 45, No. 3, pp. 300–313, May–June, 2006.     

Asymptotic Behavior of the Far Stress Field in the Problem of Crack Growth in a Damaged Medium under Creep Conditions

An asymptotic analysis of stress fields, creep-strain rates, and continuity in the vicinity of the tip of a crack that grows under creep conditions is performed with allowance for accumulation of dissipated damages. The configuration of a region of a fully damaged material adjacent to the crack edges and its tip is determined and studied. It is shown that the Hutchinson-Rice-Rosengren solution cannot be used as the boundary condition at an infinite point, and a new asymptotic representation of the far stress field, governing the geometry of the region of the fully damaged material, is obtained.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 4, pp. 133–145, July– August, 2005.     

Ways To Improve the Specific Power of Alkaline Batteries

Principles of designing of ultrahigh-power batteries and their electrodes are formulated on the basis of a theoretical analysis of phenomena limiting the rate of battery discharge. Experimental evidence in favor of the possible practical implementation of the principles proposed is presented.     

Manufacture of Hydraulic Oil by Solvent Extraction Refining of 225-290°C Fraction of Low-Paraffinicity Oil

A raffinate meeting the requirements for the hydraulic oil body was obtained from the 225-290°C fraction of low-paraffinicity oil by extraction refining with aqueous methyl Cellosolve in the presence of pentane.     

Spectrophotometric study of dehalogenation of benzyl halides with nickel in aprotic dipolar solvents in the presence of oxygen

Oxidative dissolution of nickel in the benzyl halogenide – dipolar aprotic solvent system in the presence of air oxygen proceeds with the formation of benzaldehyde, benzyl alcohol, 1,2-diphenylethane, and trace amounts of 4,4'-ditolyl. Spectrophotometry studies have revealed that the oxidation products are formed in the solution rather than at the nickel surface. It has been shown that the oxygen adsorbed at the nickel surface practically does not pass into the solution.     

The thermodynamic parameters of sorption and enantioselectivity of the chiral smectic liquid crystal 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid

The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and optical isomers of camphene and butanediol-2,3 by a chiral smectic liquid crystal, 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid, from the gas phase were studied over the temperature range including the S*_C and S*_A mesophases and isotropic phase. The standard and excess thermodynamic functions of sorption were determined for 26 sorbates of the classes of substances specified. The S*_C and S*_A mesophases exhibited selectivity with respect to the separation of para and meta xylenes (α _p/m = 1.06–1.07, 90–108°C) and pronounced enantioselectivity (α_R/S = 1.05–1.09, 87–108°C). The helically twisted structure of the smectic liquid crystal was shown to play an important role in the mechanism of the chiral recognition of optical isomers of polar and low-polarity compounds under gas-liquid chromatography conditions.     

Phase behavior of amphiphilic lipid molecules at air-water interfaces: an off-lattice self-consistent-field modeling

We introduce an extended application of the off-lattice self-consistent-field theory (SCFT) to model lipid monolayers at air-water interfaces. The off-lattice SCFT is used without a priori symmetry assumptions on equilibrium morphologies. This enables us to capture asymmetric lipid membranes at air-water interfaces which are otherwise unattainable with a conventional SCF model. Equilibrium morphologies in systems containing lipid molecules, fractions of air, and water are studied as a function of the relative amount of lipid molecules. The corresponding Langmuir isotherms are analyzed to reveal possible phase transitions. We consider both saturated and unsaturated lipid molecules with a branched structure. For saturated lipids, we find two distinct morphological phases, i.e., micellar and lamellar, showing a pronounced first-order phase transition with a well-defined region of phase coexistence. This region is sensitive to the hydrophilicity of lipid molecules and the miscibility of air with water molecules. The phase coexistence is also influenced by the size of hydrophilic and hydrophobic parts of lipid molecules. In contrast, membranes of unsaturated lipids have developed a continuous range of smooth structural transformations from a circular to an ellipsoidal micellar morphology and eventually to a lamellar structure. The shape of the lamella changes from a slightly undulated to a vigorously curved. Unlike saturated lipid membranes, there is no apparent first-order phase transition or a region of phase coexistence for unsaturated lipid membranes. We interpret this as a result of a higher flexibility of unsaturated lipid membranes which enables them to adopt a wider range of conformations in comparison with saturated lipid membranes.     

The <Emphasis Type="Italic">Mycobacterium tuberculosis</Emphasis> Rv2540c DNA sequence encodes a bifunctional chorismate synthase

Background

The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product.

Results

In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (Mt CS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant Mt CS. The bifunctionality of Mt CS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMN_ox and Mt CS. FMN_ox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting.

Conclusion

This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C₄-proS hydrogen is being transferred during the reduction of FMN_ox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMN_ox. The results on enzyme kinetics described here provide evidence for the mode of action of Mt CS and should thus pave the way for the rational design of antitubercular agents.

     

Algebraic study of chiral anomalies?

The algebraic structure of chiral anomalies ismade globally valid on non-trivial bundles by the introduction of a fixed background connection. Some of the techniques used in the study of the anomaly are improved or generalized, including a systematic way of generating towers of ??descent equations??.