Formation Of AB Research Articles

Synthesis of branched polymers by means of living anionic polymerization. 10. Synthesis of well-defined heteroarm star-branched polymers by coupling reaction of chain-functionalized polystyrenes with benzyl halide moieties with living anionic polymers of tert-butyl methacrylate

The synthesis of well-defined heteroarm star-branched polymers having poly( t BMA) arms by the coupling reactions of living anionic polymers of tert-butyl methacrylate ( t BMA) with chain-functionalized polymers with a definite number of benzyl halide moieties was described. The reaction of living anionic poly( t BMA) bearing potassium countercation with benzyl bromide-functionalized polystyrenes proceeded readily and quantitatively in THF at −40 °C for 1 h and −78 °C for 5 h, respectively. Similarly heteroarm star-branched polymers of AB 2, AB 3, AB 4, A 2B 4, and ABC 4 types with well-defined architectures were successfully synthesized. On the other hand, the same living poly( t BMA) was sluggish to react with benzyl chloride-functionalized polystyrenes, requiring 168 h to achieve quantitative formation of AB 4 star polymer. Moreover, no reaction occurred between living poly( t BMA) bearing lithium countercation in the presence of LiCl and benzyl chloride-functionalized polystyrene in THF at −78 °C for 168 h.

Hydrogen storage properties of the mechanically alloyed LaNi 5-based materials

Mechanical alloying has been used to synthesize LaNi 5-based hydrogen storage alloys. Mechanical milling of the La and Ni powder blend results in the direct formation of nanocrystalline AB 5 phase. Hydrogen storage measurements show that this as-milled LaNi 5 compound does not absorb much hydrogen reversibly. Annealing leads to grain growth, release of microstrain, and to an increase of storage capacity. Substitution of La or Ni by a third element can easily be achieved by mechanical alloying. The structure and hydrogen storage properties of these LaNi 5-based alloys prepared by mechanical alloying and annealing show no big difference with those of melt casting alloys.

Effect on parasite eradication of Pneumocystis carinii-specific antibodies produced in the presence or absence of CD4(+) alphabeta T lymphocytes.

The contribution of specific antibodies (Ab) to successful clearance of Pneumocystis carinii from host pulmonary tissues has received increasing attention. Sera collected from diseased recombinase-activating gene (RAG)-1(-/-), TCRbetaxdelta(-/-), TCRbeta(-/-) and Abeta(-/-) mutants as well as from aerogenic parasite-exposed (aero) and intranasally (i. n.) infected C57BL/6 mice were transferred to RAG-1(-/-) mutants inoculated with freshly isolated parasites. All sera, except for RAG-1(-/-) serum, contained P. carinii-specific Ab of varying isotype concentrations. Four weeks after serum treatment pulmonary parasite numbers were reduced slightly by Abeta(-/-) and C57BL/6-aero sera, and markedly by TCRbeta(-/-) and C57BL/6-i.n. sera. Our data reveal: (1) T cells are essential, and CD4(+) T cells are important for formation of protective Ab; (2) at least in the absence of alpha beta T cells, gamma delta T cells provide help for protective Ab. In vitro treatment of bronchoalveolar lavage cells with the different sera largely led to comparable results. Opsonizing Ab impeding parasite attachment to host cells, as well as Ab possibly neutralizing parasite-secreted products were implicated. Furthermore, serum components other than Abappear to participate in resistance to fungal manifestation.

Pyrazole bioisosteres of leflunomide as B-cell immunosuppressants for xenotransplantation and chronic rejection: scope and limitations.

T-cell immunosuppressant-based therapies efficiently control early graft rejection in allotransplantation settings. They fail, however, to prevent those rejection events which are mediated by transplant-induced antibody (Ab) responses such as those involved in xenograft and chronic allograft rejection. This is mainly due to their inability to block T-cell-independent Ab production against the transplanted organs. The bioactive metabolite 2(Z) of leflunomide (1) inhibits the formation of such Ab, but the drug has pharmacokinetic properties and a therapeutic window incompatible with transplantation indications. Pyrazole 3, a constrained analogue of 2(Z), was designed and shown to be conformationally and biologically similar to 2(Z). Further investigations with derivatives of 3 demonstrated that the pyrazoles had very tight structure-activity relationships, the only equipotent compound being 3o. However, in contrast to 2(Z), both 3 and 3o were inactive in vivo due to short half-life and drug concentrations lower than the in vitro obtained IC50 values. Compound 3o inhibits T-cell-independent Ab production by a different biochemical mechanism from that of 2(Z) and 3 and may therefore represent a valuable tool for the identification of new targets for B-cell inhibition.

Transformation of “living” carbocationic and other polymerizations to controlled/“living” radical polymerization

AbstractTransformation of “living” carbocationic polymerization of styrene and isobutene to controlled atom transfer radical polymerization (ATRP) is described and formation of the corresponding AB and ABA block copolymers with styrene (St), methyl methacrylate (MMA, methyl acrylate (MA) and isobornyl acrylate (IBA) was demonstrated. A similar approach was applied to the cationic ring opening polymerization of tetrahydrofuran leading to the AB and ABA block copolymers with St, MMA and MA using ATRP. Site transformation approach was also used for the ring opening metathesis polymerization of norbornene and polycondensation systems using polysulfone as an example. In both cases, AB and ABA block copolymers were efficiently formed with styrene and acrylates.

Strong hydrogen bonds in Ca(HSeO 3) 2·H 2O. Crystal structure and temperature induced formation of ABC bands

Ca(HSeO 3) 2·H 2O is a model compound for the formation of AB and ABC multi band systems in the OH stretching mode region of oxo acids, acid oxo salts or other compounds with strong hydrogen bonds. It was obtained from aqueous solutions of Ca(HSeO 3) 2 and has been investigated by means of single crystal X-ray diffraction measurements at ambient temperature and temperature dependent powder X-ray diffraction and IR measurements. From the single crystal X-ray measurements, the H-bond scheme of Ca(HSeO 3) 2·H 2O including a hexacyclic H-bond system was determined. The temperature dependent IR and X-ray data mainly result in (i) a reversible phase transition between or at T 1 ≈ 200 and T 2 ≈ 305 K, (ii) a strong reversible contraction of the hexacyclic H-bond system, and (iii) a correlated, reversible formation of a γ(OH) and a C band in the out-of-plane bending and OH stretching mode region of the SeOH group, respectively. These findings are discussed with respect to the AB/ABC band transition in the vibrational spectra of Ca(HSeO 3) 2·H 2O and the formation of ABC multi band systems of the other compounds mentioned above.

Kinetics of Rapid Heterogeneous Reactions on the Nanometer Scale

Steady-state kinetics of catalytic reactions, occurring on supported catalyst particles of the nanometer size, are analyzed by employing two schemes taking into account respectively (i) the interplay of reactions on different facets of the catalyst particle and (ii) the possibility of adsorption of reactants on the support followed by diffusion to the catalyst. A chosen model reaction, 2 A + B 2 → 2 AB, is assumed to involve monomolecular A adsorption, dissociative B 2 adsorption, and the Langmuir-Hinshelwood step resulting in the formation of AB. This reaction mimics such practically important catalytic processes as CO oxidation on Pt, Rh, or Pd, and its kinetics for the infinite surface have been explored in detail during the past decade. The results obtained in the present study demonstrate that the kinetics on the nanometer-size catalyst particles can be remarkably different from those corresponding to the infinite surface. This conclusion is drawn on the basis of Monte Carlo simulations with realistic ratio between the rates of reaction and reactant diffusion [scheme (i)] and self-consistent equations explicitly describing A diffusion on the support and the reaction steps on the catalyst [scheme (ii)].

Analysis of antigen binding and idiotypic expression by antibodies with polyglycine-replaced complementarity-determining regions.

We investigated the feasibility and usefulness, for structure-function studies, of removing the side chains of entire complementarity-determining regions (CDRs) of Abs by replacement with polyglycine. The CDRs of a murine Ab specific for p-azophenylarsonate (Ars) were replaced with polyglycine, one CDR at a time and in combinations, by oligonucleotide-directed mutagenesis of the V region genes. Mutant Abs were expressed in transfected hybridoma cells and analyzed for Ars binding and for idiotypic expression. The results suggest that, except for the longest CDRs, polyglycine replacement does not alter the general structure of the Ab molecule. However, for analysis of functional contributions of a CDR, the polyglycine replacement method appears to be most useful for CDRs with extended structures whose replacement by polyglycine does not affect the structure of other parts of the variable regions. In the current studies, such CDRs were CDR1 of the heavy chain (H1) and CDR2 of the light chain (L2). The polyglycine replacement of L2, which does not contain an Ag-contacting residue, allowed the formation of an Ars binding Ab. Furthermore, this mutant Ab revealed previously uncharacterized contributions of L2 to idiotypic expression. Polyglycine replacement of H1 abolished Ars binding as expected, because H1 contains an Ag-contacting residue. However, introduction of the contacting residue (Asn) on the polyglycine-replaced H1 background restored the ability of the Ab to bind Ars. The results suggest that polyglycine replacement of CDRs can provide structural information that complements and extends the information obtained by other methods.

Excess properties and vapor-liquid equilibrium data for the chloroform + tetrahydrofuran binary system at 30�C

Excess molar volume, excess viscosity, excess molar enthalpy, and excess molar Gibbs free energy were calculated from the experimental density, viscosity, heat of mixing and vapor-liquid equilbrium data, respectively, for the chloroform + tetrahydrofuran system at 30°C over the complete molar fraction range. The results have been satisfactorily interpreted by assuming the existence of three species A, AB, and B in mutual equilibrium and that these species mix ideally. Values are given for the equilibrium constant and heat of formation of AB.

Recognition of oxidized DNA bases by sera of patients with inflammatory diseases

Chronic inflammatory conditions result from or contribute to many diseases. Prominent among them is systemic lupus erythematosus (SLE). Sera of SLE patients contain an array of various auto-antibodies (Ab), including antinuclear Ab of unknown etiologies. The most puzzling is formation of Ab directed against autologous DNA. Our hypothesis was that increased oxidant production causes oxidation of DNA bases, which provide antigenic determinants that elicit antioxidized DNA Ab. To test this hypothesis, we used oxidized DNA nucleoside (5-hydroxymethyl-2′-deoxyuridine [HMdU]) conjugated to bovine serum albumin (HMdU-BSA) as the antigen. The results of the enzyme-linked immunosorbent assay showed that these Abs are sensitively detectable in SLE sera and sera of various other inflammatory autoimmune diseases. The titers of anti-HMdU Ab were significantly higher ( p < .01) than those present in the control sera. Anti-HMdU Ab were predominantly of the IgM isotype, with low levels of IgG and no IgA. Anti-HMdU Ab bound to the HMdU-BSA-coated wells in a concentration- and time-dependent manner. That binding was inhibited by HMdU-BSA and to a lesser extent by thymidine-BSA, a normal nucleoside conjugate. The specific binding appears to be inversely related to the age of the patients, but no significant differences were observed between the sexes of the same age.

Internal Solid State Reactions of the Type A + B = AB: Diffusion‐Controlled Formation of AB from A and B Dissolved in a Crystalline Host Matrix

AbstractA and B diffuse from opposite sides into a finite slice of solid C. After a certain diffusion time the solubility product of a product phase, AB, may be reached and AB precipitates. The location of the first nuclei formation is calculated as a function of the solubilities and the diffusion coefficients of A and B in the matrix C, and of the solubility product. Chemical diffusion coefficients of A and B, which are either constant or proportional to their own concentration, or proportional to the concentration of the other diffusing species are considered. For some sets of typical system parameters the diffusion profiles are calculated and the time and coordinate for first precipitation are shown.—Further growth of small nuclei is given by further diffusion of A and B into the matrix C and to the precipitate, which constitutes a sink for A and B. The precipitate grows in the diffusion field with a preference for certain directions. These directions and the initial growth rate of the precipitate depend on the transport properties of both the matrix and the precipitate, as well as on the thermodynamic conditions of phase coexistence of precipitate and matrix. Limiting cases of an infinitely fast or negligible material transport inside the precipitated phase are considered and the initial growth of a single precipitate in the diffusion field and its shape evolution during growth are calculated.—The global morphology of the assembly of AB precipitates for long diffusion times is discussed by considering the morphological evolution of an intermediate AB layer.

Residues involved in the antigenic sites of transmissible gastroenteritis coronavirus S glycoprotein

The S glycoprotein of transmissible gastroenteritis virus (TGEV) has been shown to contain four major antigenic sites (A, B, C, and D). Site A is the main inducer of neutralizing antibodies and has been previously subdivided into the three subsites Aa, Ab, and Ac. The residues that contribute to these sites were localized by sequence analysis of 21 mutants that escaped neutralization or binding by TGEV-specific monoclonal antibodies (MAbs), and by epitope scanning (PEPSCAN). Site A contains the residues 538, 591, and 543, which are essential in the formation of subsites Aa, Ab, and Ac, respectively. In addition, mar mutant 1B.H6 with residue 586 changed had partially altered both subsite Aa and Ab, indicating that these subsites overlap in residue 586; i.e. this residue also is part of site A. The peptide 537-MKSGYGQPIA-547 represents, at least partially, subsite Ac which is highly conserved among coronaviruses. This site is relevant for diagnosis and could be of interest for protection. Other residues contribute to site B (residues 97 and 144), site C (residues 50 and 51), and site D (residue 385). The location of site D is in agreement with PEPSCAN results. Site C can be represented by the peptide 48-P-P/S-N-S-D/E-52 but is not exposed on the surface of native virus. Its accessibility can be modulated by treatment at pH >11 (at 4°) and temperatures >45°. Sites A and B are fully dependent on glycosylation for proper folding, while sites C and D are fully or partially independent of glycosylation, respectively. Once the S glycoprotein has been assembled into the virion, the carbohydrate moiety is not essential for the antigenic sites.

Thermodynamics of molecular interactions in ethyl iodide+toluene mixtures

The excess Gibb's free energy of mixing, GE, for ethyl iodide+toluene at 25°C have been obtained from the measured vapor pressuure data. The HE and GE values for ethyl iodide+toluene are positive throughout the ethyl iodide concentration range and GE>HE. The results have been analyzed in terms of Flory and ideal associated model theory of nonelectrolyte solutions. It has been observed that the ideal associated model approach which assumes the presence of AN and A2B molecular species describes well (within±10 J-mol−1 in the worst case) the general dependence of HE on XA (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide+toluene mixtures. The equilibrium constants for A+A⇆ AB and 2A+B⇆A2B reactions along with the enthalpies of formation of AB and A2B molecular species have been calculated.

Output grating couplers on planar optical waveguides as direct immunosensors

We demonstrated the feasibility of using integrated optical output grating couplers in direct immunosensing. We monitored as functions of time, first the adsorption of an antigen (Ag) on the waveguide's surface, and subsequently, the binding of the corresponding antibody (Ab), i.e. the formation of the immuno-complex AgAb. The Ag was human immunoglobulin G (h-IgG), and the Ab was rabbit anti-h-IgG. We also studied the adsorption of avidin. The refractive indices n F′, thicknesses d F′, and surface coverages Γ of the adsorbed adlayers and of the immuno-complex AgAb, respectively, were determined.

Thermodynamics of ethyl iodide + benzene mixtures

The values of the excess Gibbs free energy of mixing G E for ethyl iodide + benzene and ethyl iodide + cyclohexane at 298.15 K have been obtained from the measured vapour pressure data. Heats of mixing H E of ethyl iodide + cyclohexane at 298.15 K have been measured over the entire composition range. The H E and G E values for ethyl iodide + benzene are positive throughout the ethyl iodide concentration range, and H E > G E. The results have been analysed in terms of the Flory, Sanchez and Lacombe and the ideal associated solution model theory of non-electrolyte solutions. It has been observed that the ideal associated model approach, which assumes the presence of AB and A 2B molecular species, describes well (within ±10 J mol −1 at the worst) the general dependence of H E on X A (mole fraction of ethyl iodide) over the whole composition range for ethyl iodide + benzene mixtures. The equilibrium constants for A + B ⇌ AB and 2A + B ⇌ A 2B reactions, along with the enthalpies of formation of AB and A 2B molecular species, have also been calculated.

Thermal and volumetric properties of chloroform + dimethylsulfoxide: Thermodynamic analysis using the ideal associated solution model

We have made new measurements of partial molar enthalpies of solution, excess heat capacities, and excess volumes of mixtures of chloroform and dimethylsulfoxide. In combination with published vapor pressures and excess enthalpies the results of these measurements have been analyzed within the context of the ideal associated solution model to yield ΔC p ϑ and ΔVϑ for the formation of AB and A2B complexes. It is shown that the ideal associated solution model is consistent with all of the available thermodynamic data for this system, indicating that nearly all of the deviations of this system from ideal solution behavior can be accounted for in terms of chemical interactions of the two components.

Thermodynamics of complex formation in chloroform + 1,4-dioxane

We have made new measurements of excess heat capacities and excess volumes of mixtures of chloroform and dioxane. In combination with published vapor pressures and excess enthalpies the results have been analyzed using the ideal associated solution model to yield K, ΔHθ, ΔCpθ, and ΔVθ for the formation of AB and A2B complexes. It is demonstrated that the ideal associated solution model is consistent with all of the available thermodynamic data for this system, indicating that chemical interactions of the two components can account for nearly all of the deviations from ideal solution behavior. The results of our thermodynamic analysis are discussed in relation to the results of similar analyses of other systems in which there are strong chemical interactions of chloroform with electron-donor molecules. Keywords: complex formation, hydrogen bonding, ideal associated solution model, chloroform, 1,4-dioxane.

Effect of immunoglobulin preparations on the aggregation of human erythrocytes

The aggregation of human erythrocytes induced by four kinds of immunoglobulin preparations was examined by a low shear rheoscope. After removing anti-A+ and anti-B+ activities contaminated in all preparations by incubating with erythrocytes of different blood groups, the facilitating effect on the rouleau formation of erythrocytes was compared: (i) The effect of polyethyleneglycol-treated preparation was the same in A+-, B+-, AB+- and O+-erythrocytes. (ii) Sulfonation did not affect the velocity of rouleau formation. (iii) Some of pepsin-treated preparations showed the strongest facilitation for A+-, B+- and AB+-erythrocytes, but the facilitation was much weaker for O+-erythrocytes. The others showed the weak facilitation for all types of erythrocytes (especially O+-erythrocytes). (iv) Plasmin treatment markedly decreased the velocity of rouleau formation of AB+- and O+-erythrocytes, but was not of A+- and B+-erythrocytes.

Cell cycle-dependent intervention by benzamide of carcinogen-induced neoplastic transformation and in vitro poly(ADP-ribosyl)ation of nuclear proteins in human fibroblasts.

Human fibroblasts were subjected to nutritionally induced G1 block, followed by release and subsequent entry into S phase, and exposed to nontoxic concentrations of carcinogens in early S phase. Cell transformation occurred as determined by early morphologic cell alterations, anchorage-independent colony formation, cell invasiveness, and augmentation of Ab 376 human malignancy-specific cell-surface antigenic determinant. Methylazoxymethanol acetate was the most potent transforming agent at doses that were negative in toxicity tests. Benzamide (10 microM intracellular concentration), a specific inhibitor of poly(ADP-ribose) polymerase, prevented transformation in a cell cycle-specific manner, maximal prevention coinciding with early S phase, also characteristic of maximal susceptibility to transformation. Neither an interference of carcinogen deoxyguanosine nucleoside adduct formation nor a chemical reaction between benzamide and carcinogens was detected. Methylazoxymethanol acetate at transforming but nontoxic dose partially inhibited poly(ADP-ribosyl)ation to about the same extent as benzamide. However, simultaneous exposure of cells to both agents in early S phase, resulting in the prevention of transformation, augmented poly(ADP-ribosyl)ation above the controls. Enzymatic activities ran parallel with the formation of DNA-associating polymer-nonhistone protein adducts that are assumed to regulate the physiological function of chromatin at the structural level.

Laser photolysis studies of spiropyran-merocyanine aggregate formation in solution

The photoinduced processes leading to formation of J-aggregate stacks of 1-(β-methacryloxyethyl)-3,3-dimethyl-6′- nitrospiro-(indoline-2,2′-[2H-[2H-1] benzopyran) d its associated ring opened merocyanine form B have been determined by N 2-laser transient spectroscopy. Detailed mechanisms for formation of complexes AB, A 2B, and J-aggregate stacks (A 2B) n in aliphatic and aromatic solvents are presented.