De la déliquescence au mottage des poudres cristallines (cas du chlorue de sodium)

Le mottage ou l agglomération non désirée des cristaux déliquescents est un phénomène récurrent dans l industrie, notamment au cours du transport et du stockage. Les variations des conditions environnantes sont fréquemment responsables de la dégradation de ce type de poudres. En particulier, les fluctuations de l humidité ambiante conduisent à la formation d une solution saturée par déliquescence du solide puis à la formation de ponts solides par évaporation de l eau. Dans cette étude, on se concentre sur le chlorure de sodium. L équilibre avec la vapeur d eau et les cinétiques de prise et perte en eau sont analysés et reliés au comportement mécanique macroscopique des cristaux. Le contact avec des cristaux de différente nature tels que le sucrose met en évidence le phénomène de déliquescence mutuelle. Le modèle des solutions régulières appliqué aux systèmes ternaires comportant du NaCl, du sucrose et de l eau permet de mieux comprendre la chute de déliquescence. La présence des molécules d eau à la surface des cristaux et la condensation capillaire à faible humidité relative provoque la déliquescence de NaCl et du sucrose simultanément. L évaporation de l eau et la recristallisation des cristaux à partir de la solution ainsi formée sont inhibées, en particulier à la composition solide du point eutonique. Le comportement singulier à cette composition qui s apparente à celui d un corps pur montre une recristallisation partielle du mélange "eutonique" associée à la formation d une phase amorphe dans les conditions de l expérimentation. Afin d éviter le renforcement au mottage, l étude de différents agents anti-mottants révèle l efficacité du stéarate de magnésium.Caking or undesired agglomeration of deliquescent crystals is a recurrent phenomenon in industry, especially during transportation and storage. The variation of environmental conditions is often pointed out as a cause of the degradation of this kind of powders. More precisely, the fluctuations of ambient humidity lead to the formation of a saturated solution by deliquescence followed by the formation of solid bridges when water evaporates. Sodium chloride is chosen as a model substance in this study. The equilibrium with water vapor and the kinetics of water uptake and loss are analyzed and related to the mechanical macroscopic behavior of crystals. The contact with crystals of different nature such as sucrose highlights the phenomenon of mutual deliquescence. The model of regular solutions applied to ternary systems containing NaCl, sucrose and water allows a better understanding of deliquescence lowering. The presence of water molecules and capillary condensation at low relative humidity lead to the deliquescence of NaCl and sucrose simultaneously. Water evaporation and recrystallization of solid from such solution is compromised, especially at the solid composition of the eutonic point . The singular behavior at this composition which resembles to the one of a pure substance shows a partial recrystallization of the eutonic mixture and the formation of an amorphous phase under the experimental conditions applied. In order to avoid caking reinforcement, the study of differentanti-caking agents reveals the efficiency of magnesium stearate.COMPIEGNE-BU (601592101) / SudocSudocFranceF

Phosphocholine-binding antibody activities are hierarchically encoded in the sequence of the heavy-chain variable region: dominance of self-association activity in the T15 idiotype

A physical and mathematical model identifies similarities between phosphocholine-binding antibodies.A methodology based on the representation of each amino acid of a protein sequence by the electron-ion interaction potential and subsequent analysis by signal processing was used to determine the characteristic or common frequency (in Hz) that reflects the biological activity shared among phosphocholine (PC)-binding antibodies. The common frequency for the variable portion of the heavy chain (VH) of the PC-specific antibodies is found to be at f 0.37 Hz. The VH sequences of the PC-binding antibodies exhibit three subsites for the PC moiety where hypervariable region 2 (CDR2) plays a role in the interaction with the phosphate group. Mutations in this VH region have an impact on the ability of mutant variants to bind PC and its carrier molecule, as well as on the characteristic frequency shift toward f 0.12 Hz for mutants failing to bind both hapten and carrier. The VH sequence of mutants that retain the ability to bind PC still shows f 0.37 Hz, suggesting that this frequency determines PC binding. However, this statement was not confirmed as mutation in another PC subsite impairs PC binding but retains both the phosphate-group recognition and the frequency at f 0.37 Hz. Herein, this finding is discussed to promote the idea that the VH sequence of the PC-binding antibodies encodes the subsite for phosphate-group binding as a dominant functional activity and that only CDR2 of the T15-idiotype antibodies together with FR3 region form an autonomous self-association function represented by the T15VH5073 peptide with f 0.370.05 Hz. Thus, these data confirmed that T15VH50-73 peptide might be used in superantibody technology

Naturally occurring V region connected antibodies inhibit anti-dsDNA antibody reactivity with dsDNA

The production of autoantibodies against a vast array of self antigens, most notably double stranded (ds) DNA, characterized systemic lupus erythematosus (SLE). The purpose of this work is to study specific Ig fractions isolated from normal human serum (NHS) and their effect on the binding of anti-double-stranded deoxyribonucleic acid (dsDNA) antibodies (Abs) to dsDNA. A fraction named immunoglobulin G (IgG)-reactive IgG was purified from total NHS IgG by absorption onto (CNBr)-activated Sepharose 4B linked to intact IgG molecules (IgG-Sepharose column). IgG-reactive IgG was co-incubated with systemic lupus erythematosus (SLE) patients serum and binding of the anti-dsDNA Abs to dsDNA was measured by enzyme-linked immunosorbent assay (ELISA). Co-incubation of SLE patients serum with IgG-reactive IgG resulted in a dose-dependent reduction in binding of anti-dsDNA Abs to dsDNA. A reduction greater than 70% was observed at a concentration of 300 mu g of IgG-reactive IgG per mL of a 400-fold diluted SLE patients serum whereas total NHS IgG, at the same concentration, resulted in a 10% reduction in binding. The purification process used to isolate IgG-reactive IgG was based on interactions between intact Ig rather than on interactions between F(ab)(2) portions. IgG(2) is the predominant immunoglobulin (Ig) subclass in IgG-reactive IgG. Thus, IgG(2) might have an important role in the connectivity characteristics of NHS IgG. The capacity of IgG-reactive IgG to inhibit anti-DNA Ab binding to dsDNA may have potential application in the treatment of SLE. This targeted biological approach may provide an alternative strategy to immunosuppressants. (C) 2011 Elsevier GmbH. All rights reserved

Design of peptide mimetics of HIV-1 gp120 for prevention and therapy of HIV disease

It has been reported that the C-terminus of the second conserved region (C2) of the envelope glycoprotein gp120, encompassing peptide RSANFTDNAKTIIVQLNESVEIN (NTM), is important for infectivity and neutralization of the human immunodeficiency virus type 1 (HIV-1). It was also demonstrated that human natural anti-vasoactive intestinal peptide (VIP) antibodies reactive with this gp120 region play an important role in control of HIV disease progression. The bioinformatic analysis based on the time-frequency signal processing revealed non-obvious similarities between NTM and VIP. When tested against a battery of sera from 46 AIDS patients, these peptides, in spite of a significant difference in their primary structures, showed a similar reactivity profiles (r = 0.83). Presented results point out that similarity in the periodical pattern of some physicochemical properties in primary structures of peptides plays a significant role in determination of their immunological crossreactivity. Based on these findings, we propose this bioinformatic criterion be used for design of VIP/NTM peptide mimetics for prevention and treatment of HIV disease