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Langmuir 1998, 14, 1822-1828
Potentiometric and Laser-Acoustic Study of Aminecarboxylate Interaction of Amino Acid Molecules Dmitri Muraviev,*,† Natalya V. Drozdova,† Nina B. Dolgina,† and Aleksandr A. Karabutov‡ Department of Physical Chemistry, Chemical Faculty, Lomonosov Moscow State University, 119899 Moscow, Russia, and Department of General Physics and Wave Processes, Physical Faculty, Lomonosov Moscow State University, 119899 Moscow, Russia Received October 20, 1997. In Final Form: January 8, 1998 This paper reports the results of studying aminecarboxylate interaction of amino acid molecules in suspensions of solvent-impregnated sulfonate ion exchangers (SISIEs) with widely variable capacities obtained by modification of the macroporous PS-DVB polymers Amberlite XAD-2 and XAD-4 with toluene solutions of dinonylnaphthalenesulfonic acid. Variation of SISIE capacities leads to modulation of their surface electrochemical properties, such as surface charge density, surface potential, and so forth, which can be easily evaluated by measuring suspension effects (∆pH) in, for example, SISIE-HCl systems and interpretation of the results obtained within the Gouy-Chapman model of the electric double layer (EDL). The results of measuring ∆pH in SISIE-zwitterlyte systems including solutions of β-alanine and -aminohexanoic acid in a wide range of amino acid concentrations have shown that the behavior of SISIE suspensions in amino acid solutions differs dramatically from that of simple electrolyte (HCl) systems. Unlike SISIE-HCl systems, SISIE-zwitterlyte suspensions are characterized by the absence of the concentration compression of the diffuse part of the EDL, which can be interpreted within the framework of the aminecarboxylate interaction of amino acid molecules mechanism as the structuring of the diffuse part of EDL due to formation of amino acid chains surrounding SISIE beads. The results obtained by determination of the sound absorption coefficient in SISIE-electrolyte and SISIE-zwitterlyte systems by wide-band laser-acoustic spectroscopy are in good agreement with those obtained by a potentiometric technique.
Introduction Application of ion-exchange and allied techniques for recovery, separation, and purification of biologically active zwitterlytes such as amino acids, peptides, proteins, and so forth is progressively growing.1-4 However, the detailed mechanisms of interaction of zwitterlytes with ion exchangers of different types are still practically unavailable. A deeper understanding of the nature of the ion-exchange behavior of zwitterlytes may help, on one hand, to improve the efficiency of ion-exchange methods applied for separation and purification of these substances. On the other hand, this information is also useful for the following tasks: (1) for interpretation of mass-transfer processes involving amino acids, peptides, and proteins proceeding in biological systems;5 (2) for further development and wider application of biosorbents;6 and (3) for some other * Author for correspondence. Present address: Department of Analytical Chemistry, Autonomous University of Barcelona, E-08193 Bellaterra (Barcelona), Spain. † Department of Physical Chemistry, Chemical Faculty, Lomonosov Moscow State University. ‡ Department of General Physics and Wave Processes, Physical Faculty, Lomonosov Moscow State University. (1) Samsonov, G. V.; Trostyanskaya, E. V.; Elkin, G. E. Ion Exchange. Sorption of Organic Substances; Nauka: Leningrad, 1969 (Russian). (2) Samsonov, G. V.; Elkin, G. E. In Ion Exchange and Solvent Extraction; Marinsky, J., Marcus, Y., Eds.; Marcel Dekker: New York, 1987; Vol. 9, Chapter 4. (3) Dechow, F. J. In Ion Exchangers; Dorfner, K., Ed.; Walter de Gruyter: Berlin, 1991; Chapter 3.2. (4) Cherkasov, A. N.; Pasechnik, V. A. Membranes and Sorbents in Biotechnology; Khimia: Leningrad, 1991 (Russian). (5) Nakagaki, M. Physical Chemistry of Membranes, Russian ed.; Mir: Moscow, 1991; p 55 (Russian). (6) Creedy, J. H. In Progress in Ion Exchange. Advances and Applications; Dyer, A., Hudson, M. J., Williams, P. A., Eds.; Royal Society of Chemistry: Cambridge, 1997; p 219.
purposes. For this reason the features of ion-exchange processes in systems involving amino acids and other zwitterlytes continue to be the subject of intensive investigations.7-11 The ion-exchange reactions between zwitterlytes and ion exchangers are under certain conditions accompanied by a number of additional effects such as, for example, aminecarboxylate interactions, which are not observed in ion-exchange systems including simple electrolytes. The mechanism of aminecarboxylate interactions of amino acid molecules was introduced for the first time by Muraviev12 to explain two effects observed in ion-exchange systems involving amino acids, namely the ion-exchange isothermal supersaturation (IXISS) and the superequivalent sorption of zwitterlytes (SESZ). The IXISS phenomenon, discovered by Muraviev,12 is observed for a number of ion-exchange systems, where frontal separation is accompanied by the formation of extremely stable supersaturated solutions of low-solubility amino acids such as glutamic acid,12 aspartic acid,13 tyrosine,8,14 and some others15 in the interstitial space of ion-exchange columns. The IXISS of amino acids has been successfully (7) Selemenev, V. F.; Oros, G. Yu.; Ogneva, L. A.; Trubetskih, G. V.; Chikin, G. A. Zh. Fiz. Khim. 1984, 58, 2525 (Russian). (8) Selemenev, V. F.; Zagorodny, A. A.; Polupanov, N. A.; Ogneva, L. A. Zh. Fiz. Khim. 1986, 60, 1461 (Russian). (9) Selemenev, V. F.; Kotova, D. L.; Amelin, A. N.; Zagorodny, A. A. Zh. Fiz. Khim. 1991, 65, 996 (Russian). (10) Zhang Baolin; Seng Fenling; Tao Zuyi. Chem. J. Chin. Univ. 1992, 13, 840. (11) Tao Zuyi. In Ion Exchange and Solvent Extraction; Marinsky, J., Marcus, Y., Eds.; Marcel Dekker: New York, 1995; Vol. 12, Chapter 8. (12) Muraviev, D. Zh. Fiz. Khim. 1979, 53, 438 (Russian). (13) Muraviev, D.; Saurin, A. D. Zh. Fiz. Khim. 1980, 54, 1271 (Russian). (14) Selemenev, V. F.; Zagorodny, A. A.; Uglyanskaya, V. A.; Zavialova, T. A.; Chikin, G. A. Zh. Fiz. Khim. 1994, 66, 1555 (Russian).
S0743-7463(97)01145-1 CCC: $15.00 © 1998 American Chemical Society Published on Web 02/25/1998
Aminecarboxylate Interaction of Amino Acid Molecules
applied by Muraviev et al. for purification of these substances from mineral salt16 and racemate admixtures.17 The SESZ on ion exchangers of different types was reported by many authors. Nys et al.18 observed superequivalent sorption of glycine on a sulfonate cation exchanger in the H-form. Greenland et al.19 observed a SESZ effect for glycine and its peptides on montmorillonite in the H-form. The sorption of glutamic acid on microdisperse anion exchangers in the Cl-form was reported by Vorobjeva et al.20 to be also accompanied by the superequivalent sorption, which significantly exceeded the ion-exchange capacity of the resin toward simple electrolytes. Muraviev and Obrezkov21 observed a SESZ effect when studying the sorption of β-alanine and γ-aminobutiric acid on a strong acid cation exchanger in the H-form. Identification of zwitterlytes manifesting a SESZ effect and determination of the system parameters influencing the sorption capacity of ion exchangers toward target substances may help to increase the efficiency of ionexchange separation and purification of amino acids, peptides, and so forth. In this context the study of aminecarboxylate interaction of amino acid molecules can give useful information for interpretation and tailored application of both IXISS and SESZ effects. On the other hand, the search for adequate models and the development of experimental techniques applicable for studying the processes which proceed at the ion exchanger-solution interface are of general scientific interest. The aim of the present study was to investigate aminecarboxylate interactions of β-alanine and -aminohexanoic acid molecules in systems involving aqueous amino acid solutions of different concentrations and granulated solvent-impregnated sulfonate ion exchangers (SISIEs) with widely variable capacity by potentiometric and wide-band laser-acoustic techniques. Experimental Section Materials, Ion Exchangers, and Analytical Methods. Hydrochloric acid, β-alanine, and -aminohexanoic acid of p.a. grade were purchased from Reanal (Hungary) and used as received. The ammonium salt of dinonylnaphthalenesulfonic acid (HDNNS) was obtained from King Industries (Norwalk, CT) and purified by following the procedure described elsewhere.22,23 Suitably purified samples of Amberlite XAD-2 and Amberlite XAD-4 macroporous polymers of PS-DVB type (Rohm & Haas) were used as polymeric supports for the preparation of SISIEs with different capacities using the “wet” impregnation technique as reported elsewhere.22,24 The capacities of the SISIE sample were determined under dynamic conditions in columns by converting all samples to the H-form, followed by displacement of H+ from the resin phase by 0.2 M KCl and titrating H+ in the eluate obtained with alkali. The concentration of H+ was determined by potentiometric titration using a Radiometer pHmeter with a combined glass electrode. The concentration of (15) Muraviev, D.; Fesenko, S. A.; Gorshkov, V. I. Zh. Fiz. Khim. 1982, 56, 1567 (Russian). (16) Muraviev, D.; Gorshkov, V. I.; Medvedev, G. A.; Ferapontov, N. B.; Kovalenko, Ju. A. Zh. Prikl. Khim. 1979, 52, 1183 (Russian). (17) Muraviev, D.; Gorshkov, V. I. Zh. Fiz. Khim. 1982, 56, 1560 (Russian). (18) Nys, P. S.; Savitskaja, E. M.; Bruns, B. P. In Theory of Ion Exchange and Chromatography; Chmutov, K. V., Ed.; Nauka: Moscow, 1968; p 90 (Russian). (19) Greenland, D. J.; Laby, R. H.; Quirk, J. P. Trans. Faraday Soc. 1965, 61, 2013, 2024. (20) Vorobieva, V. Ja.; Naumova, L. V.; Samsonov, G. V. Zh. Fiz. Khim. 1981, 55, 1679 (Russian). (21) Muraviev, D.; Obrezkov, O. N. Zh. Fiz. Khim. 1986, 60, 396 (Russian). (22) Muraviev, D. Chem. Scr. 1989, 29, 9. (23) Ignatenko, S. P.; Pokrovskaya, A. I.; Soldatov, V. S. Vestn. Akad. Nauk BSSR, Ser. Khim. Nauk 1978, 5, 40 (Russian). (24) Muraviev, D.; Hogfeldt, E. React. Polym. 1988, 8, 97.
Langmuir, Vol. 14, No. 7, 1998 1823 amino acids was determined by potentiometric titration using the formaldehyde method. Procedure and Apparatus. The potentiometric study of aminecarboxylate interaction of amino acid molecules was carried out by measuring the “suspension effects” (∆pH) in systems involving SISIE samples with different capacities in the respective amino acid form equilibrated with amino acid solutions of given concentration. The suspension effect is the difference between the pH of the suspension of ion exchanger and the pH of the equilibrium solution.25-33 The ∆pH measurements in the SISIE-amino acid systems were preceded by the experimental determination of ∆pH values in systems including the same SISIE samples (in the H-form) equilibrated with 0.001 and 0.01 M HCl to compare the results obtained in zwitterlyte-SISIE systems with those obtained in systems involving a simple electrolyte and to check the validity of the Gouy-Chapman model for interpretation of the data obtained. The relative uncertainty of the ∆pH determination was in all cases
