Isomer-Selective Adsorption of Amino Acids by Components of Natural Sediments

• Published in: Environmental science & technology 2005-04, Vol.39 (7), p.2115-2119
• Main Authors: Wedyan, M, Preston, M. R
• Format: Article
• Language: English
• Subjects: Adsorption; Amino acids; Amino Acids - chemistry; Bentonite - chemistry; Brackish; Chromatography, High Pressure Liquid; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; Geologic Sediments - chemistry; Hydrogen-Ion Concentration; Isomerism; Kaolin - chemistry; Marine and continental quaternary; Sediments; Soil and rock geochemistry; Sorption; Surficial geology
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es040474o

We present evidence that under circumstances of low pH and organic-free surfaces an ordinary estuarine sediment can exhibit strong optical isomer selectivity in its absorption of a number of amino acids. This selectivity can also be seen to a lesser degree in the minerals quartz, montmorillonite, and kaolin. Adsorption reactions were performed with racemic amino acid mixtures, and after equilibrium, deviations from a d/l ratio of 1 were measured and in many cases were found to be significant. This was particularly pronounced at pH 4.0, where selective removal of the l isomers by adsorption onto sediment fractions was almost total. Changes in both the nature and degree of selectivity were also observable in different sediment size fractions. While we are at this stage unable to identify the mode of primary selectivity, adsorption experiments with these candidate sediment components, quartz, kaolin, and montmorillonite do exhibit some selective behavior. We believe that the existence of natural chirally selective components in sediment may indicate a new approach to the development of chiral catalysis and synthesis.