QSPR Modeling of the Reactivity Parameters of Monomers in Radical Copolymerizations

For a series of monomers, QSPR test analysis is performed by optimizing the correlation weights of the local invariants of molecular graphs representing monomer structures in order to construct models of the reactivity parameters of monomers Q and e. This approach may be used as a tool in reactivity predictions for monomers for which no experimental data on Q and e are available.Original Russian Text Copyright © 2004 by A. A. Toropov, V. O. Kudyshkin, N. L. Voropaeva, I. N. Ruban, and S. Sh. Rashidova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 994–998, November–December, 2004.     

Second Dissociation Constants of 4-[N-morpholino]butanesulfonic Acid and N-[2-hydroxyethyl]piperazine-N′-4-butanesulfonic Acid from 5 to 55°C

The values of the second dissociation constant, pK ₂, for the dissociation of the NH⁺ charge center of the zwitterionic buffer compounds 4-(N-morpholino)butanesulfonic acid (MOBS), and N-(2-hydroxyethyl)piperazine-N-4-butanesulfonic acid (HEPBS) have been determined from 5 to 55°C, including, 37°C at intervals of 5°C. The electromotive-force (emf) measurements have been made utilizing hydrogen electrodes and silver–silver chloride electrodes. The value of pK ₂ for MOBS was found to be 7.702 ± 0.0005, and 8.284 ± 0.0004 for HEPBS, at 25°C, respectively. The related thermodynamic quantities, G ^o, H ^o, S ^o, and C _p ^o for the dissociation processes of MOBS and HEPBS have been derived from the temperature coefficients of pK ₂. Both the MOBS and HEPBS buffer materials are useful as primary pH standards for the control of pH 7.3 to 8.6 in the region close to that of physiological fluids.     

Thermodynamics of the dissociation of 2-aminopyridinium ion in synthetic seawater and a standard for pH in marine systems

Buffer solutions composed of 2-aminopyridinium chloride and 2-aminopyridine in synthetic seawater are useful as a supplement to buffers of Tris (pH 8.2) and Bis (pH 8.8) in standardizing measurements of hydrogen ion concentration (pm _H or pH(SWS)) in oceanography. The dissociation constant of 2-amino-pyridinium ion over the range of salinities (S) from 30 to 40 has now been determined from the emf of cells without liquid junction at eight temperatures (T) from 278.15 to 313.15 K. The results fit the equation pK=2498.31/T–15.3274+2.4050 lnT+S(0.012928–2.9417×10^–5T) with a standard deviation of 0.0023. Thermodynamic constants for the dissociation process and standard reference values of pm _H and pH(SWS) were derived from the data. The pm _H of the buffer consisting of 2-aminopyridinium chloride and 2-aminopyridine (each 0.04 molal) in synthetic seawater of salinity 35 varies from 7.356 at 278.15 K to 6.601 at 313.15 K.     

Anti-metatype antibodies in immunoassays

In this review anti-metatype antibodies are described invoking new principles in immunoassay development. Anti-metatype antibodies are immunological reagents specific for the conformation of the liganded antibody active site which do not interact with bound ligand or unliganded antibody. Relationships between anti-metatype antibody reactivity and the ligand-induced conformational state of monoclonal antibodies are reviewed with emphasis on the fluorescein hapten as a small molecule model system. One characteristic result of the interaction of anti-metatype antibodies with liganded antibodies is a significant delay in the dissociation rate (k₂) of the ligand bound within the primary immune complex. The latter is an important consideration for assay development. Polyclonal and monoclonal anti-metatype antibody reagents are characterized in terms of their differential effects on the ligand dissociation rate. Anti-metatype antibody reactivity is further discussed in terms of protein-protein specificity patterns and relative interactions with idiotype-family members, structural derivatives, and site-specific mutants. Incorporation of principles inherent in the anti-metatype concept and their application to assay development are summarized.Abbreviations D₂O deuterium oxide - Fab 50 kd antibody fragment containing V_HC_H1 + V_LC_L domains - FITC(I) fluorescein isothiocyanate (isomer I) - Fv 26 kd fragment of the antibody molecule containing the variable domains of the H and L chains - Ig immunoglobulin - IgG immunoglobulin G with a mol. wt. of 150 kd. - IgM immunoglobulin M with a mol. wt. of 10⁶d - Id idiotype - Ka antibody affinity (k₁/k₂) in M^–1 - k₁ second order rate of ligand association in M^–1s^–1 - k₂ first order rate of ligand dissociation in s^–1 - K_D dissociation constant or the reciprocal of the affinity constant (1/Ka) - Mab monoclonal antibody - Met metatype - NMR nuclear magnetic resonance - SCA single chain Fv derivative containing a synthetic linker between the two variable domains - V_H variable domain of the antibody H chain - V_L variable domain of the antibody L chain     

Overproduction of riboflavin by anArthrobacter sp. mutant resistant to 5-fluorouracil

Effects of pH and dissolved oxygen concentration on batchwise riboflavin production by a 5-fluorouracil (5-FU)-resistant mutant ofArthrobacter sp. were investigated. The reaction was carried out in a jar fermentor. The optimal pH of culture medium was around 7.3. Dissolved oxygen concentration was almost constant during fermentation at 600 rpm of agitation rate. Production of riboflavin reached a maximum of 160 mg/L after 70 h fermentation under the agitation rate of 600 rpm, aeration rate of 1.0 L/min, and pH 7.0.     

集成微管路离子选择电极功能块研究

本文对微型管状离子选择电极在流动条件下的电化学特征进行了研究,并设计了新的集成微管路离子选择以电极功能块。用此微型装置测定了土壤、血清、水和药物中的K~+、Na~+、pH、Cl~-、F~-、阿托品、东茛菪碱,并和各种标准方法作了比较,获得满意分析结果。     

Effect of Mobile Phase pH* on Chromatographic Behaviour in Chiral Ligand-Exchange Thin-Layer Chromatography (CLETLC) of Amino Acid Enantiomers

The enantiomers of some amino acids have been separated on commercial chiral TLC plates in reversed-phase mode. The effect of the pH* of the aqueous-organic mobile phase on the retention and mobility of the enantiomers and on selectivity was investigated. It was shown that for most of the amino acids investigated the highest enantioselectivity was obtained at pH* 3–4 or 6–7. The drift and disturbance of the baseline on the chromatograms were also much smaller at pH* 3–4 and 6–7.     

Equations for calculation of the pH of buffer solutions containing sodium or potassium dihydrogen phosphate, sodium hydrogen phosphate, and sodium chloride at 25°C

Published thermodynamic data measured in aqueous mixtures of sodium or potassium dihydrogen phosphate with hydrogen phosphate and chloride at 25°C were used to test recently developed methods for calculation of the pH of phosphate buffer solutions. Equations for ionic activity coefficients are used in these methods. It is shown that all data used in the tests up to an ionic strength of about 0.5 mol-kg^-1 can be accurately predicted by the two methods recommended. In one of these methods, equations of the Hückel type are used for ionic activity coefficients and in the other equations of the Pitzer type. Several sets of phosphate buffer solutions are recommended,e.g., for calibrations of glass electrode cells. In the recommended sets, the pH of the buffer solutions can be calculated either by the Hückel or Pitzer method, and the pH predictions of these methods agree in most cases within 0.005 at least up to ionic strengths of about 0.2 mol-kg^-1. The pH values of the two primary pH standards endorsed by IUPAC based on aqueous mixtures of KH₂PO₄ and Na₂HPO₄,i.e., pH values of 6.865 and 7.413, can also be accurately predicted by the equations recommended in this study.     

Fluorescence ratiometric pH sensor prepared from covalently immobilized porphyrin and benzothioxanthene

A fluorescence ratiometric sensor for pH determination is described in this paper. The sensor incorporated the pH-sensitive dye meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP) as an indicator and a pH-insensitive dye N-(2-methacryloxyethyl)benzo[k,l]thioxanthene-3,4-dicarboximide (MBTD), a benzothioxanthene derivative, as a reference for fluorescence ratiometric measurement. To prevent leakage of the dyes, both were photocopolymerized with acrylamide, hydroxyethyl methacrylate, and triethylene glycol dimethacrylate on the silanized glass surface. The reproducibility and response time of the prepared sensor were sufficient. Most common coexisting inorganic ions and organic compounds did not interfere with pH sensing. In the acidic pH range from 1.5 to 5.0 the fluorescence intensity ratio of the two dyes varied linearly as a function of pH. The sensing membrane was found to have a lifetime of at least one month. The sensor was applied to the analysis of waste water and artificial samples.