The adsorption of four naturally occurring a-amino-acids on calcium montmorillonite and sodium and calcium illite has been studied and compared with that of glycine and its di-, tri-and tetra-peptides. Linear isotherms were obtained for adsorption by the calcium clays. These have been treated in terms of a constant partition of solute between the solution and the Stern layer of the adsorbent. Free energies of adsorption were obtained from the selectivity coefficients for the partition reaction. The relative magnitudes of these are related to the molecular weights, dielectric increments and shapes of the adsorbed dipolar ions. Adsorption energies for an illite were similar to those for montmorillonite, but were larger in all instances. Enthalpies and entropies of adsorption were determined for glycine and its peptides on calcium montmorillonite. Only for triglycyl glydne does the entropy term become favourable to the adsorption process, and only for this peptide is there a desorption of water when the peptide is adsorbed.

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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

During an investigation of the infrared spectra of organic sulphonamides and related compounds we made some observations of the spectrum of X-methylmethane sulphonamide in dilute carbon tetrachloride solution. The compound showed absorption bands at 3404 and 3300 cm-l which varied in relative intensity, when the concentration of the solution was changed, in a manner characteristic of a monomer-dimer equilibrium. The broader, lower frequency band that is characteristic of the dimer had a symmetrical contour, indicating that only a single species was involved. This we assume to have the formula (I).The sample of N-methylmethane sulphonamide was prepared in 80% yield by the condensation of methylamine with methane sulphonyl chloride in ether solution at 0 "C (Baxter, Cymerman-Craig, and Willis 1955). It was purified by distillation, b.p. 162 O C , at 15 mm. The hygroscopic substance was stored over phosphorus pentoxide for several weeks and then solutions were made up in spectroscopic grade carbon tetrachloride just before the spectra were recorded.The absorption bands were scanned with a Perkin Elmer 112, single-beam, double-pass, infrared spectrometer, fitted with a calcium fluoride prism, at the rate of 0 ~6 8 cm-l sec-l for the monomer band and 0 ~6 2 cm-l see-l for the dimer band. Allowance for convergence of the beam through the specimen was shown to introduce a correction of about 0.3%. The computed (cm-l) spectral slitwidths were 5 a 7 at 3400 cm-l and 5 a 1 a t 3300 cm-l. The integrated band areas were calculated by the " triangular slit function " method of Ramsay (1952) which assumes that the contour of the absorption band is a Lorentz curve. The measurements are summarized in Table 1.

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