Adsorption of amino-acids and peptides by montmorillonite and illite. Part 1.—Cation exchange and proton transfer

Abstract

Adsorption isotherms are presented for a range of naturally occurring neutral and acid aminoacids on hydrogen montmorillonite and of basic amino-acid and peptide cations on sodium and calcium montmorillonite and illite. Differences in the isotherms show that the electrostatic bonding which results from proton transfer and cation exchange respectively is supplemented by physical adsorption forces. The magnitude of the physical adsorption forces is determined by the molecular weight and by the shape of the adsorbed molecules. X-ray diffraction analyses of the wet complexes showed that with the exception of lysine, the intercalation of the basic amino-acid cations by montmorillonite led to a decrease in the basal spacing. There was a corresponding reduction in the ease of desorption of the amino-acids in aqueous KCl solutions.When glycine and its di-, tri-and tetra-peptides are adsorbed by hydrogen montmorillonite the dominant adsorption mechanism is a proton transfer reaction.1-3 However, other forces, which increase with the molecular weight of the adsorbed species, act in addition to proton transfer. These additional forces include polar and van der der Waals interactions. In the present paper, an attempt is made to distinguish the contributions of each to the adsorption process. The adsorption of a range of naturally occurring neutral and acid amino-acid dipolar ions by hydrogen montmorillonite, and of basic amino-acid cations by sodium and calcium montmorillonite, has been examined, as well as the adsorption of these compounds by another clay mineral, illite. EXPERIMENTAL MATERIALSThe montmorillonite used was described previously.3 The illite sample came from County Grundy, Illinois, and was obtained from the Illinois Clay Products Co., Joliet, Illinois. After preliminary saturation of the clay with sodium ions, the less than 2 p equivalent spherical diameter (e.s.d.) fraction was separated by mechanical dispersion in distilled water, followed by repeated sedimentation and decantation. X-ray powder photographs of the clay obtained from these suspensions showed that illite and approximately 3 % of quartz were present. The asymmetry of the 10 8, basal reflection suggested that the clay might be interlayered with an expanding lattice mineral.4 The extent of interstratification was shown to be small by comparison of the external surface area of 106 rn2/g, obtained by nitrogen adsorption, with the total surface area 150 m2/g, determined

Adsorption of aspartic acid on kaolinite

“…Adsorption was ascribed mainly to cation-exchange reactions, but with a significant contribution also from hydrophobic interactions. X-ray diffraction data [11] suggested that acidic and neutral amino acids can intercalate into the interlayer spaces of montmorillonite.…”

“…In previous studies of clay systems the sorption of a range of amino acids from salt-free aqueous solutions [7,11] or from seawater [8] to kaolinite [7,8], montmorillonite [7,8,11], or illite [11] was measured at discrete pH values, depending on the particular amino acid solutions and clay suspensions under study. The effect on sorption of varying the pH was not investigated.…”

Antimicrobial Coatings Obtained by Sol–Gel Method

“…Effective antimicrobial coatings on textile substrates with such clay materials can be achieved by using a mixture of the precursors glycidoxypropyltriethoxysilane and tetraethylorthosilicate. After complete hydrolysis of the silane precursors, the exchanged clay material (mixture of illite and calcite) can be Hang and Brindley (1970) 1.87 13.9 95 Greenland et al (1965) 29.3 88 Busenberg and Clemency (1973) 3 added to the sol to yield the final coating agent, which can be applied by a pad-drycure process. It should be noted that the maximum clay concentration in the sol-gel coating agent is limited.…”

Humic substances. Part III. sorptive interactions with environmental chemicals†

“…It is noteworthy to mention that van der Waals forces are also involved in the adsorption of organic cations. The importance of the shape of the cations in determining the extent of van der Waals interaction has been demonstrated by Greenland et al (1965) on the adsorption of some amino acids and peptides by montmorillonite. Since van der Waals forces are known to decay rapidly with distance, their contribution to the adsorption energy would be greatest for those ions which are in closest contact with the surface, or enable close contact to be maintained with the adjacent adsorbed ions.…”