Liquid-liquid equilibrium in the-<Emphasis Type="Italic">n</Emphasis>-heptane-<Emphasis Type="Italic">n</Emphasis>-perfluorohexane system

The shape of the liquid-liquid coexistence curve in the C₇H₁₆-C₆F₁₄ system in the molar concentration-temperature coordinates close to the critical solution point was studied by narrow-beam gamma-raying of two-phase samples. The molar volumes of the coexisting liquid phases and critical point coordinates (critical temperature T _c = 316.266 ± 0.03 K and critical concentration x _c = 39.0 ± 0.4 mol % C₆F₁₄) were determined. The critical index β of the coexistence curve was found to be 0.322 ± 0.005. The diameter of the coexistence curve did not obey the classic “rectilinear diameter rule.”     

The smallest Hosoya index in (<Emphasis Type="Italic">n</Emphasis>, <Emphasis Type="Italic">n</Emphasis> + 1)-graphs

A (n, n + 1)-graph G is a connected simple graph with n vertices and n + 1 edges. In this paper, we determine the lower bound for the Hosoya index in (n, n + 1)-graphs in terms of the order n, and characterize the (n, n + 1)-graph with the smallest Hosoya index.     

Isothermal solubility of individual light fullerenes in the homologous series of <Emphasis Type="Italic">n</Emphasis>-alkanes, <Emphasis Type="Italic">n</Emphasis>-alkanols, <Emphasis Type="Italic">n</Emphasis>-alkylcarboxylic acids,and arenes

Available published data on isothermal solubility (at 20°C) of individual light fullerenes in a homologous series of n-alkanes, n-alkanols, n-alkylcarboxylic acids, and arenas were systematized. A correlation between the parameter of Hildebrand’s cohesion and the logarithm of the mole fraction of the fullerene in the saturated solution was revealed.     

Speciation studies of nitric acid and U(VI) third phases in <Emphasis Type="Italic">n</Emphasis>,<Emphasis Type="Italic">n</Emphasis>-dialkyl amides/<Emphasis Type="Italic">n</Emphasis>-dodecane systems

Conventionally composition of the actinide-extractant solvate is assumed to be the same in the unpartitioned organic phase and the formed third phase. For example, if a m:n solvate has formed during extraction, the solvate is expected to be in the same state even during the third phase condition. However contemporary analysis, based on the spectroscopy measurements and empirical observations, has indicated the presence of an extended solvate. In this article, the proposed speciation in nitric acid and U(VI) third phase formation in n–n dialkyl amide/dodecane-nitric acid systems has been modeled with empirical correlations.     

Calculation of the viscosity of <Emphasis Type="Italic">n</Emphasis>-heptane-methanol solutions at low <Emphasis Type="Italic">n</Emphasis>-heptane concentrations

The molar heat capacity C _p of the methanol-n-heptane system was measured at low concentrations of n-heptane and 298.15 K. The dynamic viscosity η of the system at 298.15 K was calculated from data on the molar heat capacity of methanol-n-heptane solutions within the framework of the Flory theory and the theory of free volume with regard to the molecular association. Based on the experimental data and calculation results, it was concluded that the viscosity of the methanol-n-heptane system exhibits an anomalous behavior.     

Synthesis and properties of maleopimaric <Emphasis Type="Italic">N</Emphasis>-(<Emphasis Type="Italic">n</Emphasis>-alkyl)imides

Method of synthesis of maleopimaric N-(n-alkyl)imides by the reaction of maleopimaric acid with primary aliphatic amines in melt was developed. On the basis of the obtained compounds allyl esters were synthesized. Thermal stability of the synthesized compounds was evaluated by the method of derivatography.     

Calculation of the anisotropy of molecular polarizability of liquid <Emphasis Type="Italic">n</Emphasis>-alkanes and <Emphasis Type="Italic">n</Emphasis>-alcohols

Light scattering from liquid n-alkanes and n-alcohols in a strong electric field is measured by a photoelectric colorimeter at various wavelengths. The anisotropy of molecular polarizability of the substances is calculated by the Rayleigh formula.     

Radiothermoluminescence of <Emphasis Type="Italic">n</Emphasis>-eicosane mixtures with <Emphasis Type="Italic">n</Emphasis>-tetracosane: Effect of mixture composition

Radiothermoluminescence (RTL) curves of mixtures of C20 and C24 n-alkanes have been deconvoluted into the curves of crystalline and disordered regions, and their change depending on the mixture composition has been analyzed. The shape of the total RTL curve of the mixture regardless of the its composition is fundamentally different from that shape of the sum of the curves of the individual components taken in the relevant ratios. The difference becomes noticeable at as low a C20 amount in the mixture as 2% and is manifested in the disappearance of the intense RTL peaks of the individual components and appearance of new intense peaks in temperature intervals other than those of the RTL peaks of the components. It has been shown that these changes correlate with changes of the crystalline structure of the mixture: a new crystalline structure other than the structure of any of the individual components emerges and the mixture becomes amorphous. High selectivity of charge trapping in disordered regions of the mixture has been revealed: the contribution of RTL of the disordered regions to the total curve is many times higher than their volume fraction in the mixture. This selectivity might be due to an increase in concentration of defects in the unordered regions of the mixture in comparison with their concentration in the pure alkanes. These defects are traps for electrons that are accessible to acceptors introduced into the mixture.     

Molecular properties of the copolymers of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride and maleic acid

The hydrodynamic and conformational properties of molecules of poly(N,N-diallyl-N,N-dimethylammonium chloride) and N,N-diallyl-N,N-dimethylammonium chloride-maleic acid copolymers of different compositions in solutions with various ionic-strength and pH values, as well as of the polyelectrolyte complex based on the copolymer with dodecyl sulfate anions in chloroform, are studied. For poly(N,N-diallyl-N,N-dimethylammonium chloride) molecules in a 1 M NaCl solution, the Kuhn segment length and the hydrodynamic diameter of the chain are estimated as A = 3.9 nm and d = 0.48 nm, respectively. In acidic solutions with pH 3.5, the copolymers demonstrate behavior typical for polyelectrolytes. In an alkaline solution with pH 13, when 1 M NaCl is added to the solution of the copolymer containing 29 mol % maleic acid units, there is an antipolyelectrolyte effect that manifests itself as an increase in the intrinsic viscosity of the copolymer and in the hydrodynamic radius of its molecules. It is found that an increase in the fraction of maleic acid units in the copolymer from 12 to 42 mol % brings about a reduction in the equilibrium rigidity of its macromolecules from 4.1 to 2.2 nm. The equilibrium rigidity of polyelectrolyte-complex molecules is higher than that of initial copolymer molecules owing to steric interactions arising between the aliphatic chains of dodecyl sulfate anions. In an electric field, the molecules of the complex are oriented owing to the induced dipole moment resulting from the displacement of dodecyl sulfate anions along the chain contour.     

<Emphasis Type="Italic">Z</Emphasis>-and <Emphasis Type="Italic">E</Emphasis>-conformers of <Emphasis Type="Italic">N</Emphasis>-chloroacetylcytisine

N-Chloroacetylcytisine was synthesized by acylation of (–)-cytisine. Stable Z- and E-conformers with respect to rotational isomerism around the N-12–CO bond were found in PMR spectra at room temperature. The point at which PMR resonances of the Z- and E-conformers coalesced upon heating was measured. The transition barrier between the conformers was estimated.     

Quantum-chemical investigation of structure and stability of [<Emphasis Type="Italic">n</Emphasis>]-prismanes and [<Emphasis Type="Italic">n</Emphasis>]-asteranes

The study by DFT [B3LYP/6-311G(2df,p)] method of structural and energy characteristics peculiar to [n]-prismanes and [n]-asteranes demonstrated that prismanes of n = 3–10 and asteranes of n = 3–7 possessed a stable structure of D_nh-symmetry; the D_nh-geometry was distorted in the subsequent terms of the series.     

Conformations and properties of <Emphasis Type="Italic">O</Emphasis>-Alkyl-<Emphasis Type="Italic">S</Emphasis>-(2-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dialkylamino)-ethylmethylthiophosphonates

Conformers of the biologically active compounds CH₃P(O)(OR)(SCH₂CH₂NR ₂ ^′ ), where (I) R = i-C₄H₉, R′ = C₂H₅ and (II) R = C₂H₅, R′ = i-C₃H₇, are calculated within the AM1 level of theory. The elongated and twisted forms with maximum and minimum distances between a nitrogen atom and those of a phosphorus tetrahedron, respectively, and bearing a syn and anti oriented alkoxy group relative to a phosphoryl oxygen, are studied. It is found that the differences between the energy, electronic, and geometric parameters of these forms are apparent in differences between their properties, e.g., the ability to participate in complexation and protonation, reactions that to some extent simulate the interaction between a substance and a biological object.     

A new stilbene glycoside from the <Emphasis Type="Italic">n</Emphasis>-butanol fraction of <Emphasis Type="Italic">Veratrum dahuricum</Emphasis>

A new stilbene glycoside, 5-methylresveratrol-3,4′-O-β-D-diglucopyranoside (1), was isolated from the n-butanol fraction of the rhizomes of Veratrum dahuricum, together with five known stilbenoids: resveratrol-3-O-β-D-glycoside (2), 4′-methylresveratrol-3-O-β-D-glycoside (3), oxyresveratrol-4′-O-β-D-glycoside (4), oxyresveratrol-3-O-β-D-glycoside (5), and oxyresveratrol-3,4′-O-β-D-diglycoside (6), and found for the first time in the investigated plant. The structures of six isolates were identified on the basis of 1D and 2D NMR data. Compounds 1–6 showed platelet aggregation inhibition, and compound 1 had an IC₅₀ value of 383.6 μM against platelet aggregation induced by AA. Published in Khimiya Prirodnykh Soedinenii, No. 3, pp. 279–282, May–June, 2009.     

Structures and magnetic properties of Ni<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> (<Emphasis Type="Italic">n</Emphasis> = 36-40) clusters from first-principles calculations

A genetic algorithm (GA) coupled with a tight-binding (TB) interatomic potential is used to search for the low-energy structures of medium-sized Ni _n (n = 36-40) clusters. Structural candidates obtained from our GA search are further optimized with first-principles calculations. The medium-sized nickel clusters ranging from 36 to 40 atoms are found to favor the double-icosahedron-based structures with a Ni₇ core (a pentagonal bipyramidal structure) except Ni₃₈ cluster. The lowest-energy structure of Ni₃₈ can be considered to be a magic cluster, which is a typical face-centered cubic structure with large stability and magnetic moment.     

Excess enthalpies of binary mixtures of <Emphasis Type="Italic">ortho</Emphasis>-, <Emphasis Type="Italic">meta</Emphasis>-, and <Emphasis Type="Italic">para</Emphasis>-structural isomers

The excess molar enthalpies of 8 binary mixtures for the o-, m-, and p-isomers of fluoroiodobenzene, fluoromethoxybenzene, bromofluorobenzene, chlorofluoro-benzene, difluorobenzene, fluoromethylbenzene, fluoronitrobenzene, and aminofluoro-benzene were measured at 298.15 K. The changes of the measured enthalpies were very small. The experimental results revealed that the isomers containing two electron-acceptor groups showed the most positive excess enthalpy change, while isomers containing both one electron donor and one electron acceptor group, such as aminofluorobenzene, showed more stable and always the most negative results.     

Phase equilibria and critical phenomena in the potassium perchlorate-water-<Emphasis Type="Italic">n</Emphasis>-butoxyethanol ternary system

Phase equilibria and critical phenomena in the potassium perchlorate-water-n-butoxyethanol ternary system, where the boundary liquid binary system is characterized by the presence of a closed stratification region, were studied by the visual-polythermal method over the temperature range 40–150°C. The temperature of the formation of the critical monotectic equilibrium tie line (141.0°C) and temperature dependences of the compositions of mixtures corresponding to the critical solubility points of the stratification region over the temperature ranges 47.7–130.3 and 141.0–150.0°C were determined. The isotherms of phase states constructed at 10 temperatures were used to reveal the topological transformation of the phase diagram of the ternary system depending on temperature. At low concentrations (up to 5.8 wt %), potassium perchlorate had a salting in action on heterogeneous water-n-butoxyethanol mixtures. The solubility of the salt increased as the temperature grew, and, above 141.0°C, potassium perchlorate had a salting out action. The salting out of n-butoxyethanol from aqueous solutions by potassium perchlorate grew stronger as the temperature increased.     

The solubility of fullerenes in <Emphasis Type="Italic">n</Emphasis>-alkanols-1

The isothermal and polythermal solubility of C₆₀ and fullerene mixture (60% C₆₀, 39% C₇₀, and 1% C_76–90) in unbranched saturated alcohols C₁–C₁₁ was studied over the temperature range 20–80°C. The isotherms and polytherms of solubility are presented and characterized.     

Analysis of <Emphasis Type="Italic">Escherichia coli</Emphasis> nicotinate mononucleotide adenylyltransferase mutants <Emphasis Type="Italic">in vivo</Emphasis> and <Emphasis Type="Italic">in vitro</Emphasis>

Background  

Adenylation of nicotinate mononucleotide to nicotinate adenine dinucleotide is the penultimate step in NAD⁺ synthesis. In Escherichia coli, the enzyme nicotinate mononucleotide adenylyltransferase is encoded by the nadD gene. We have earlier made an initial characterization in vivo of two mutant enzymes, NadD72 and NadD74. Strains with either mutation have decreased intracellular levels of NAD⁺, especially for one of the alleles, nadD72.     

Copolymer of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-diallyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylammonium chloride with maleic acid as drug carrier

A copolymer of N,N-diallyl-N,N-dimethylammonium chloride with maleic acid of constant composition was prepared under the conditions of radical initiation. The possibility of the functionalization of the copolymer with drugs containing amino groups by polymer-analogous transformations was examined. Conditions were found for preparing conjugates of the copolymer with isoniazid. The structures and the quantitative compositions of the conjugates were determined by ¹³С NMR spectroscopy, and the possibility of preparing conjugates with controlled drug content was demonstrated.