Equilibrium polymerization in a solvent: Solution on the Bethe lattice

The lattice model for equilibrium polymerization in a solvent proposed by Wheeler and Pfeuty is solved exactly on a Bethe lattice (core of a Caylay tree) with general coordination numberq. Earlier mean-field results are reobtained in the limitq, but the phase diagrams show deviations from them for finiteq. Whenq=2, our results turn into the solution of the one-dimensional problem. Although the model is solved directly, without the use of the correspondence between the equilibrium polymerization model and the diluten0 model, we verified that the latter model may also be solved on the Bethe lattice, its solution being identical to the direct solution in all parameter space. As observed in earlier studies of the puren0 vector model, the free energy is not always convex. We obtain the region of negative susceptibility for our solution and compare this result with mean field and renormalization group (-expansion) calculations.     

Mixing properties of mim diodes in the infrared

Point contact MIM diodes of different materials have been tested as harmonic mixers at 29 THz and 88 THz. From the analysis of the I-V static characteristic quantitative informations have been obtained about the effectiveness of the diodes as high order mixers.     

Synthesis of thieno[3.2-<Emphasis Type="Italic">b</Emphasis>]pyrrolenine derivatives under the Fischer reaction conditions

The reaction of alkyl 4-(2-acetylhydrazino)-2-methyl-3-thiophenecarboxylates with 3-methylbutan-2-one was carried out under the Fischer reaction conditions. The influence of Lewis acids and solvents on the process was studied. A convenient method for the synthesis of thieno [3.2-b]pyrrolenine derivatives was proposed.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 725–729, March, 2005.     

Chiral separation of 1,1'-bi-2-naphthol and its analogue on molecular imprinting monolithic columns by HPLC

Two molecular imprinting polymer (MIP) monolithic columns with (S)-(-)-1,1'-bi-2-naphthol and (R)-(+)-5,5',6,6',7,7',8,8'-octahydro-1,1'-bi-2-naphthol as the templating molecules, respectively, have been prepared by in situ polymerization using 4-vinylpyridine and ethylene dimethacrylate as functional monomer and cross-linker, respectively. The columns with good flow-through properties were obtained by changing the molar ratio of the functional monomer and the template molecule. The effects of mobile-phase composition on separation of enantiomers were systematically investigated. The results indicate that hydrophobic interaction in aqueous solution and hydrogen-bonding interaction in ACN between the enantiomers and polymers could play important roles in the retention and resolution. The effects of chromatographic conditions, such as flow rate, column temperature, sample loading, on the enantioseparation were also studied. Further, these two MIP columns show a cross-reactivity.     

高效液相色谱检测Zn（Ⅱ）、Cd（Ⅱ）、Co（Ⅱ）、Pb（Ⅱ）、Ni（Ⅱ）、Cu（Ⅱ）、Hg（Ⅱ）

用双-(2-羟乙基)二硫代甲酸铵(HEDC)在反相液相色谱中作检测某些金属离子的衍生化试剂，HEDC的金属螯合物微溶于水，可直接水样注射于C18柱中进行检测，范围为0．006～10mg／L相对偏差1％～2％，检测波长254nm，金属汞的整合物在HPLC分析前进行浓缩富集检测限可低至0．06～25μg／L，相对偏差小于2％。     

The transformations of fluoroalkyl-containing 2-arylhydrazono-1,3-dicarbonyl compounds with methylamine

Fluoroalkylated 1,2,3-triketone 2-arylhydrazones and 2-arylhydrazono-3-oxo esters react variously with methylamine depending on the structure of the fluorinated substituent. 2-Arylhydrazono-1,3-dicarbonyl compounds having “short” fluoroalkyl substituents condense with methylamine at the carbonyl group attached to the non-fluorinated substituent whereas ones containing a lengthy polyfluoroalkyl substituent undergo haloformic cleavage as a result of the amine addition at the carbonyl group bearing such a substituent. The resulting 2-arylazo-3-(N-methyl)amino-1-polyfluoroket-2-en-1-ones and 1-(N-methyl)amino-2-arylhydrazono-3-fluoroalkyl-3-oxopropanamides have complexing properties, and they can bind to nickel(II) and copper(II) ions. Nickel chelates can be obtained by a three-component condensation of 2-arylhydrazono-1,3-dicarbonyl compounds and methylamine in the presence of nickel(II) cations.     

Preparation of Y2Ba4Cu7O15-δ Superconductor without High Oxygen Pressure

The synthesis of bulk Y₂Ba₄Cu₇O_15-δ superconductor at atmospheric oxygen pressure via solid state sintering is reported. Temperature ranging from 860 to 890 °C as well as time interval over 2 to 15 days were used to investigate the formation of the Y₂Ba₄Cu₇O_15-δ phase. A time-temperature profile characterizing the conditions for the preparation of Y₂Ba₄Cu₇O_15-δ phase suggests the optimal condition to be sintering at 890 °C for over 10 days. Detailed results of X-ray diffraction, electrical resistivity, iodometric titration and magnetization measurements are described.     

Purine Nucleoside Analogs. 12. Synthesis of Novel 8,9-Disubstituted Guanine Derivatives by S-Alkylation of 2-Acetamido-9-(2-acetoxyethoxymethyl)-6-oxo-8-thioxopurine

S-Alkylation of 2-acetamido-9-(2-acetoxyethoxymethyl)-6-oxo-8-thioxopurine was used to synthesize its novel S- and N₍₇₎-substituted derivatives. We have established the effect of the structure of the alkylating agent on the reaction conditions and its regioselectivity. We have shown that the synthesized guanine derivatives can be modified further.     

Trifluoroacetic acid: a more effective and efficient reagent for the synthesis of 3-arylmethylene-3,4-dihydro-1H-quinolin-2-ones and 3-arylmethyl-2-amino-quinolines from Baylis-Hillman derivatives via Claisen rearrangement

Trifluoroacetic acid has been discovered to be a highly effective and efficient reagent for the tandem Claisen rearrangement and cyclization reaction to yield 3-arylmethylene-3,4-dihydro-1H-quinolin-2-ones from compounds obtained from the S_N2 reaction between anilines and acetyl derivatives of Baylis-Hillman adducts of acrylates in the presence of DABCO. In contrast, similar compounds obtained from the acetyl derivatives of Baylis-Hillman adduct of acrylonitrile on treatment with trifluoroacetic acid directly furnish 3-arylmethyl-2-amino-quinoline via tandem Claisen rearrangement, cyclization and isomerization.     

The Substituent Effects of tert-Butyl Radical Addition to 2-Substituted Allyl Chlorides

The relative rates for the addition reactions of tert-butyl radical to 2-substituted ally chlorides I have een determined. The correlation of log k/k₀, vs. σ_m gives a ρ mvalue of 3.59 with correlation coefficient of 0.930. When the substituent CH₂Cl is excluded, correlation coefficient raises to 0.990 and ρ value becomes 3.39. The large p value and the deviation of relative rate of substituent CH₂C1 are discussed.