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Steric and electrostatic interactions govern nanofiltration of amino acids
Author(s) -
Shim Yongki,
Chellam Shankararaman
Publication year - 2007
Publication title -
biotechnology and bioengineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.136
H-Index - 189
eISSN - 1097-0290
pISSN - 0006-3592
DOI - 10.1002/bit.21395
Subject(s) - chemistry , amino acid , isoelectric point , steric effects , membrane , nanofiltration , ionic bonding , chromatography , ionic strength , ion , stereochemistry , organic chemistry , biochemistry , aqueous solution , enzyme
Crossflow nanofiltration experiments were performed to investigate the factors influencing the removal of amino acids by a commercially available polymeric thin‐film composite membrane. The removals of five monoprotic (Ala, Val, Leu, Gly, and Thr), one diprotic (Asp), and one dibasic (Arg) amino acids in a range of permeate fluxes, feed pH values, and ionic strengths were analyzed using a phenomenological model of membrane transport. At any given pH and ionic strength, reflection coefficients (rejection at asymptotically infinite flux) of monoprotic amino acids increased with molar radius demonstrating the role of steric interactions on their removal. Additionally, consistent with Donnan exclusion, higher reflection coefficients were obtained when the membrane and the amino acids both carried the same nature of charge (positive or negative). In other words, both co‐ion repulsion and molecular size determined amino acids removal. Importantly, the removal of effectively neutral amino acids were significantly higher than neutral sugars and alcohols of similar size demonstrating that even near their isoelectric point, zwitterionic characteristics preclude them from being considered as strictly neutral. Biotechnol. Bioeng. 2007;98; 451–461. © 2007 Wiley Periodicals, Inc.