Interactions between proteins and clays perturb biological activity in ecosystems, particularly soil extracellular enzyme activity. The pH dependence of hydrophobic, hydrophilic, and electrostatic interactions on the adsorption of bovine serum albumin (BSA) is studied. BSA secondary structures and hydration are revealed from computation of the Amide I and II FTIR absorption profiles. The influence of ionization of Asp, Glu, and His side chains on the adsorption processes is deduced from correlation between p 2 H dependent carboxylic/carboxylate ratio and Amide band profiles. We quantify p 2 H dependent internal and external structural unfolding for BSA adsorbed on montmorillonite, which is an electronegative phyllosilicate. Adsorption on talc, a hydrophobic surface, is less denaturing. The results emphasize the importance of electrostatic interactions in both adsorption processes. In the first case, charged side chains directly influence BSA adsorption that generate the structural transition. In the second case, the forces that attract hydrophobic side chains toward the protein-clay interface are large enough to distort peripheral amphiphilic helical domains. The resulting local unfolding displaces enough internal ionized side chains to prevent them from establishing salt bridges as for BSA native structure in solution. On montmorillonite, a particular feature is a higher protonation of the Asp and Glu side chains of the adsorbed BSA than in solution, which decreases coulombic repulsion. C 2000 Academic Press

Soils have a large solid surface area and high adsorptive capacities. To determine if structural and solvation changes induced by adsorption on clays are related to changes in enzyme activity, alpha-chymotrypsin adsorbed on a phyllosilicate with an electronegative surface (montmorillonite) has been studied by transmission FTIR spectroscopy. A comparison of the pH-dependent structural changes for the solution and adsorbed states probes the electrostatic origin of the adsorption. In the pD range 4.5-10, adsorption only perturbs some peripheral domains of the protein compared to the solution. Secondary structure unfolding affects about 15-20 peptide units. Parts of these domains become hydrated and others entail some self-association. However, the inactivation of the catalytic activity of the adsorbed enzyme in the 5-7 pD range is due less to these structural changes than to steric hindrance when three essential imino/amino functions, located close to the entrance of the catalytic cavity (His-40 and -57 residues and Ala-149 end chain residue), are oriented toward the negatively charged mineral surface. When these functions lose their positive charge, the orientation of the adsorbed enzyme is changed and an activity similar to that in solution at equivalent pH is recovered. This result is of fundamental interest in all fields of research where enzymatic activity is monitored using reversible adsorption procedures. Copyright 1999 Academic Press.

After pressurization to 30 GPA, in a diamond anvil cell, benzene transforms, at room temperature, to a white solid which is stable at ambient pressure. We report here the infrared spectroscopy analysis performed under pressure and at ambient conditions. These preliminary results show that the transformation involves an opening of the benzene rings leading to a highly cross-linked polymer.

This study was done to better understand how lipases are activated at an interface. We investigated the conformational and solvation changes occurring during the adsorption of Humicola lanuginosa lipase (HLL) onto a hydrophobic surface using Fourier transform infrared-attenuated total reflection spectroscopy. The hydrophobic surfaces were obtained by coating silicon attenuated total reflection crystal with octadecyltrichlorosilane. Analysis of vibrational spectra was used to compare the conformation of HLL adsorbed at the aqueous-solid interface with its conformation in solution. X-ray crystallography has shown that HLL exists in two conformations, the closed and open forms. The conformational changes in HLL caused by adsorption onto the surface were compared with those occurring in three reference proteins, bovine serum albumin, lysozyme, and alpha-chymotrypsin. Adsorbed protein layers were prepared using proteins solutions of 0.005 to 0.5 mg/mL. The adsorptions of bovine serum albumin, lysozyme, and alpha-chymotrypsin to the hydrophobic support were accompanied by large unfoldings of ordered structures. In contrast, HLL underwent no secondary structure changes at first stage of adsorption, but there was a slight folding of beta-structures as the lipase monolayer became complete. Solvation studies using deuterated buffer showed an unusual hydrogen/deuterium exchange of the peptide CONH groups of the adsorbed HLL molecules. This exchange is consistent with the lipase being in the native open conformation at the water/hydrophobic interface.

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Blue pigments used by a 19th century French artist were analysed by Raman microspecbometry. The results are discllssed in relation to the painting materials available at that time. This study is connected with an artistic study of the drawings, and allows the artistic and technical aspects of the work of this painter to be compared.