Hybridization of DNA at the surface of phospholipid monolayers. Effect of orientation of oligonucleotide chains

We studied the properties of lipid monolayers formed at the air-water interface composed of dioleoylphosphatidylcholine (DOPC) with incorporated short (19-mer) oligonucleotides. These oligonucleotides were modified by oleylamine at both (3' and 5') terminals or only at one (3') terminal. Interaction of single-stranded (19-mer) oligonucleotides without oleylamine with DOPC monolayers resulted only in slight increase of surface pressure and the area per phospholipid molecule, while more substantial and significant increase of these values were observed following incorporation of oligonucelotides modified by oleylamine. This influence is similar for both types of oligonucleotide modifications. However, considerable differences in changes of monolayer properties took place after hybridization with complementary oligonucleotides. The hybridization of oligonucleotides with the DNA modified by oleic acid at both 3' and 5' terminals at the surface of lipid monolayer resulted in further increase of surface pressure and in the increase of the area per phospholipid molecule, while decrease of both the surface pressure and the area per phospholipid molecules were observed for hybridization with DNA modified by oleic acid at 3' terminal. It is possible that in latter case, the hybridization caused the loss of hybridized molecules from monolayers. Interaction of noncomplementary chains with DOPC monolayers with incorporated oleyl acid-modified DNA also influenced the properties of monolayers, but the effect was weaker in comparison with that observed for complementary chains.     

The determination of small amounts of vanadium in the presence of large amounts of uranium

To eliminate the color interference of large amounts of uranium in the determination of vanadium by the Hamner method, the vanadium was separated prior to titration by the extraction of vanadium cupferrate with chloroform. The chloroform extract was evaporated with sulfuric acid and the excess cupferron removed by oxidation with nitric acid and perchloric acid. The vanadium was reduced with ferrous ammonium, sulfate solution, the excess ferrous ion oxidized with ammonium persulfate, and the vanadium (IV) titrated with 0.02 N potassium permanganate. As little as 1.02 mg of vanadium in the presence of 5 g of uranium oxide was determined accurately by this method.     

Synthesis of Isomeric Aminomethyl Derivatives of Furylmethanephosphonates

By chloromethylation of diethyl 2- and 3-furylmethanephosphonates 5-chloromethylfur-2(3)-ylmethanephosphonates were synthesized. The other four isomers of chloromethyl derivatives of furylmethanephosphonates were prepared by substitution of hydroxy groups in the corresponding phosphorylated furylmethanols via the reaction with thionyl chloride in the presence of pyridine. Thermal stability of these chlorides was sufficiently high, and they were involved in nucleophilic substitution of chlorine with azido group by treating with sodium azide in boiling acetonitrile in the presence of potassium iodide. No decomposition of substrates was observed. The azides obtained were reduced to amines with triphenylphosphine in ethanol.     

Heats of Mixing of Mixed Solvent Solutions of Alkali Metal Salts of Substituted Benzenesulfonic Acids

The enthalpy change on mixing solutions of methyl-substituted benzenesulfonic acids and their salts, with salts having a common cation or anion, at constant ionic strength in mixtures of 1,4-dioxane with water, were measured at 25°C. The heat effects of mixing solutions having a common anion increase almost linearly with the reciprocal value of the dielectric constant of the solvent. The heat effects of mixing solutions having a common cation, which are all negative in water-rich solutions, become endothermic after a certain value of the dielectric constant is passed. The results are discussed in terms of the solute-solvent structural properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of some ethyleneimine derivatives of pyrimidine

It has been shown that 2, 6-dichloto-4-methylpyrimidine reacts with ethyleneimine in benzene solution in the presence of triethylamine or in an aqueous alkaline medium with the formation of 6-chloro-2-ethyleneimino-4-methylpyrimidine. The condensation of 2, 6-di-chloro-4-methyl-5-nitropyrimidine with an excess of ethyleneimine and in benzene solution in the presence of triethylamine has given 2, 6-diethyleneimino-4-methyl-5-nitropyrimidine.     

A collaborative study of four methods of assay of benzylpenicillin

The assay of benzylpenicillin by iodimetric titration, spectrophotometry with a mercury(II) chloride—imidazole reagent, titration with mercury(II) nitrate in acetate buffer solution, and titration with mercury(II) perchlorate in aqueous pyridine solution, was examined in four laboratories. The first two methods were applied to two samples (the third one being the reference sample), the mercury(II) nitrate titration to three, and the mercury(II) perchlorate method to two samples. The four methods gave very similar results, but the purity obtained with the mercury(II) perchlorate method was slightly lower, and this procedure is less desirable because pyridine is used as solvent. There were no great differences in the relative standard deviations of the four methods. The titration with mercury(II) nitrate is preferred because it is an absolute method.     

Evaluation of the uncertainty of environmental measurements of radioactivity

Results obtained by measurement of radioactivity have traditionally been associated with an expression of their uncertainty, based on the so-called counting statistics. This is calculated together with the actual result on the assumption that the number of counts observed has a Poisson distribution with equal mean and variance. Most of the nuclear scientific community has, therefore, assumed that it already complied with the latest ISO 17025 requirements. Counting statistics, however, express only the variability observed among repeated measurements of the same sample under the same counting conditions, which is equivalent to the term repeatability used in quantitative analysis. Many other sources of uncertainty need to be taken into account before a statement of the uncertainty of the actual result can be made. As the first link in the traceability chain calibration is always an important uncertainty component in any kind of measurement. For radioactivity measurements in particular we find that counting geometry assumes the greatest importance, because it is often not possible to measure a standard and a control sample under exactly the same conditions. In the case of large samples we have additional uncertainty components associated with sample heterogeneity and its influence on self-absorption and counting efficiency. In this paper we prepared an uncertainty budget for existing data for ¹³⁷Cs in Danish soil, which is shown to account adequately for all sources of uncertainty. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanism of radiothermoluminescence of crystalline tetracosane

Radiothermoluminescence (RTL) of tetracosane irradiated in liquid nitrogen with γ-rays is due to trapped charges. At doses below 2 kGy, all processes leading to RTL are localized in tetracosane intracrystalline areas in traps with a depth of 0.1–2.0 eV that were present in tetracosane before irradiation. With increasing the dose, radiation-induced traps with a depth of 3 eV or higher appear in addition. At the same time, part of the charges reach the surface and become available for interaction with an electron acceptor. The presence of shallow traps (less than 0.15 eV) leads to a decrease in the RTL intensity over the entire temperature range from 100 to 300 K during storage of irradiated samples in liquid nitrogen.     

氨基酸从水到尿素水溶液中的迁移焓研究

用微量量热法测定甘氨酸、L-丙氨酸、L-丝氨酸在水和尿素水溶液中的溶解焓, 计算得到氨基酸从水到尿素水溶液的迁移焓, 并根据水合结构相互作用模型予以讨论. 结果表明, 氨基酸两性离子与尿素分子的静电作用以及两性离子头部与尿素分子的结构相互作用对氨基酸迁移焓有负贡献, 氨基酸侧链与尿素分子的结构相互作用依其亲水性或疏水性分别对迁移焓有负贡献或正贡献. 在实验浓度范围(0～13 mol/kg)内, 三种氨基酸的迁移焓总体上随尿素浓度的增加而下降, 其大小依次为L-丝氨酸＜甘氨酸＜L-丙氨酸, 氨基酸迁移焓的差异反映了溶质-溶剂结构相互作用的变化.     

Dependence of the viscosity coefficients of magnetic fluids on parameters of state

Dependences of the viscosity coefficients of magnetic fluids on parameters of state were investigated numerically using previously derived dynamic equations. It was shown that the volume viscosity and shear viscosity coefficients of a magnetic fluid based on kerosene increase with increasing density and concentration and decrease with increasing temperature; the coefficients increase with an increase in the magnetic field gradient. The results obtained are in satisfactory agreement with the experimental data.     

Assignment of dielectric loss of K-L zeolite

Dielectric spectra of zeolite L (LTL) with potassium ions were measured to investigate movements of potassium ion in it. K,TMA-L was prepared through an ion-exchange of K9-L with tetramethylammonium (TMA) ion, and changed to K,H-L by gentle calcination in air. Since the TMA ion in K,TMA-L was expected to exclusively occupy site D, the hydrogen ion in K,H-L was considered to be located around site D. K9-xHx-L with 0相似文献   

Monte Carlo simulations of systems of rodlike molecules with semiflexible terminal groups

The results of Monte Carlo simulations of systems of rodlike molecules with semiflexible terminal groups are compared with those of systems with terminal groups at a fixed angle τ with respect to the rigid core and with those of a system containing the rigid cores alone in the same total volume. The nematic/isotropic transition temperature decreases with increasing flexibility or with increasing τ. For semiflexible groups, the transition is coupled with a conformational change favouring more extended conformations in the nematic phase. The results of the simulations are discussed in connection with those obtained for similar models in the recent literature and with the predictions of the Maier‐Saupe and Flory‐Ronca‐Irvine theories.     

环糊精与新型表面活性剂的主客体相互作用

在298.15 K下用微量热法结合核磁共振法研究了α-环糊精, β-环糊精与十二烷基多氧乙烯磺酸钠C12EnS(n=1, 3)在水溶液中的包结作用. 实验结果表明, β-环糊精与客体的包合是焓、熵共驱的过程, α-环糊精与客体的包合则是焓驱动过程. β-环糊精与两种客体包合的化学计量比随客体中氧乙烯链的不同而不同, 而α-环糊精与两种客体包合的化学计量比则无差别. 1H NMR数据表明, C12EnS的存在使两种环糊精上各质子的化学位移向高场移动, 从微观上证明了包结作用的发生.     

Regioselectivity of the methanolysis of polychlorinated biphenyls

Regioselectivity of the methanolysis of lower polychlorinated biphenyls with sodium methoxide in a mixture of methanol and DMSO at 100–130°С was studied. It was found that 2,4,4'-tricholobiphenyl is much more reactive than 2,4-dichlorobiphenyl. This results in different mechanisms of substitution. 2,4-Dichlorobiphenyl reacts with sodium methoxide by the elimination–addition mechanism to form four monosubstitution products in comparable quantities. 2,4,4'-Trichlorobiphenyl reacts with the methodixe ion by the classical SNAr mechanism, with preferential substitution of the 2-chlorine atom.     

Enthalpy of formation of thiophene derivatives

The enthalpy of formation in the gas phase has been calculated for 21 carbonyl compounds of the thiophene series with the aid of the PM3, MINDO, AM1, and MNDO semiempirical quantum-chemical methods. Comparison of them with experimental data showed that the best linear correlation was achieved with the PM3 method. The latter in conjunction with a developed linear regression equation has been used to predict the enthalpy of formation of 22 carboxylic acids and ketones of the thiophene series.     

活性炭表面性质对氧气扩散电极电催化性能的影响

 分别采用硝酸和空气氧化处理制得具有不同表面性质的粉末活性炭,并以此为催化层材料制成炭基氧气扩散电极,测定了不同电极的极化曲线和电化学阻抗谱. N2物理吸附和He程序升温脱附(He-TPD)研究表明,硝酸处理对活性炭孔结构的影响较小,但可使其表面含氧基团明显增加; 而空气氧化处理则会导致活性炭的中孔面积和孔容显著增大,但对表面含氧基团的影响较小. 极化曲线和电化学阻抗谱研究发现,当活性炭的孔结构相近时,电极的催化性能随着表面含氧基团的增多而急剧下降; 当活性炭表面含氧基团的量相近时,中孔孔容增大将导致电极催化性能的恶化. 与活性炭表面含氧基团相比,孔结构对氧气扩散电极的电化学性能具有更显著的影响.     

Kinetics of J-aggregation of cyanine dyes in the presence of gelatin

The kinetics of formation of J-aggregates for 3,3'-bis[sulfopropyl]-R-4',5'-dibenzo-9-ethylthiacarbocyanines (R=5-methoxy; R=4,5-dibenzo) and 3,3'-bis[sulfopropyl]-5,5'-diphenyl-9-ethyloxacarbocyanine were studied in aqueous solution in the presence of gelatin at different pH values and at room and elevated temperatures. Addition of gelatin at concentrations of 0.0005-0.05 wt % to solutions of dyes results in the production of J-aggregates in the tens of seconds to tens of minutes range. The rate of J-aggregate formation increases with increasing concentrations of dye and gelatin, correlates with the rate of decay of dimers, and is also dependent on the dye structure, temperature, and pH. The rate of J-aggregation is increased for and decreased for with an increase in temperature. For and, the rate increases with increasing [H+] and reaches the maximum value at pH 3.3-4.3 for 3. The interaction of with gelatin is considered to be a cooperative binding process, and J-aggregation is characterized by the time-dependent rate constant. Sigmoidal- and nonsigmoidal-type kinetic curves of both formation of J-aggregates and decay of the dimers are best fitted with a stretched exponential function.     

Thermodynamics of interactions of vancomycin and synthetic surrogates of bacterial cell wall

Glycopeptide antibiotics, including vancomycin, form complexes via a set of five hydrogen bonds with the acyl-l-Lys-d-Ala-d-Ala portion of the peptidyl stems of the bacterial cell wall peptidoglycan. This complexation deprives the organism from the ability to cross-link peptidyl stems of the peptidoglycan, leading to bacterial cell death. Four synthetic fragments as surrogates of the components of the bacterial cell wall have been prepared in our lab in multistep syntheses. These synthetic samples were used in investigations of the thermodynamics properties (DeltaG degrees , DeltaH degrees , and TDeltaS degrees ) for the complexation with vancomycin by isothermal titration calorimetry (ITC). Complexation with the glycopeptide analogues is largely enthalpy-driven (formation of five hydrogen bonds), and in the analogues with a single peptidyl stem, the complexation is 1:1. The complexation is more complicated with an approximately 2 kDa cell wall surrogate (compound 4), which possesses two peptidyl stems. The data were suggestive of interactions between the two vancomycin molecules, with an entropic penalty attributable to restriction of molecular movements within the complex due to restriction of motion of the highly mobile acyl-d-Ala-d-Ala moiety of the peptidyl stems. These data were reconciled with the recently determined NMR solution structure for the peptidoglycan fragment 4 and its implications for the larger cell wall.     

Thermodynamic parameters of solvation of nonelectrolytes in aqueous solutions of amides of carboxylic acids

Interaction and reorganization contributions to solvation enthalpies of nonelectrolytes in aqueous solutions of amides of carboxylic acids with different degree of N-substitution and N-methylpyrrolidone are calculated. The data are discussed using structurally thermodynamic characteristics of water-amide systems obtained by us previously. It is found that the type of concentration dependence of the solvation enthalpy of nonelectrolytes in all solutions investigated is determined by the type of reorganization component. It is shown that the highest solvation exothermicity of nonelectrolytes in water is due to the lowest value of the reorganization contribution in spite of that nonelectrolytes interact weaker with water than with non aqueous components.     

Comparison of fast scan voltammetry with microelectrode voltammetry of reduction of 1,4-benzoquinone

The reduction of 1,4-benzoquinone (BQ) in acetonitrile was blocked in steady-state microelectrode voltammetry although it has been believed to be a sluggish electron transfer reaction. Ferrocene was added to the BQ solution with equi-concentration in order to confirm the diffusion-control step and to evaluate accurately the kinetic effect from potential differences. Fast scan voltammograms showed the negative potential shifts both of the cathodic and the anodic peaks with an increase in the scan rate. In contrast, microelectrode voltammetry showed that the ratio of the steady-state limiting current for BQ to that for ferrocene decreased with a decrease in the electrode radii. The halfwave potential of the reduction of BQ did not vary with the radii within error. These features are largely deviated from the Butler–Volmer kinetic behavior. The electrode surface after the long term electro-reduction was coated with a precipitate. The proposed reaction mechanism is formation of films by follow-up chemical reactions of BQ associated with slight potential shift. The film blocks diffusion of BQ. This model was theoretically formulated and elucidated the experimental results.