Collaborative Research: A Multi-Disciplinary Study of Selective Adsorption of Chiral Molecules on Mineral Surfaces

George Washington University, Washington DC

Investigators

Abstract

ABSTRACT Selective adsorption of aqueous solutes onto mineral surfaces represents an important mechanism for the concentration, sequestration and organization of organic molecules. Such mineral-organic interactions play key roles in processes as diverse as aquifer purification, biofilm formation and the origin of life. In this regard, the selective adsorption of chiral (left-handed versus right-handed) molecules is of special interest. Strong chiral preference for amino acids, sugars and other essential biomolecules is a defining characteristic of biological systems. Abiotic processes that select left-handed versus right-handed molecules are thus central to geochemical models of life's origin. Chiral recognition and separation of molecules, furthermore, is vital to pharmacological activity of many drugs, biodegradation of packaging materials, development of improved polymers, and many other applications in science and industry. Previous work described selective adsorption of D- and L-aspartic acid, a biological amino acid, on chiral crystal growth faces of calcite. Such chiral selectivity on surfaces of a centric mineral had been predicted by theory, but had not been demonstrated experimentally. This proposal seeks to document further this behavior and to investigate structural mechanisms by which chiral organic molecules adsorb selectively on mineral surfaces. A multi-disciplinary, collaborative, two-part research program includes: I. Phenomenology of Chiral Adsorption on Minerals: Research will expand on previous studies, which demonstrated chiral selectivity on mineral surfaces, by establishing the range and extent of chiral adsorption on mineral surfaces. Proposed experiments include: 1. Investigation of the adsorption of other chiral amino acids, both biological and non-biological, onto calcite crystal growth surfaces. 2. Investigation of the adsorption of chiral amino acid derivatives, sugars, nucleotides and other chiral species onto calcite crystal growth surfaces. 3. Investigation of chiral adsorption onto crystal growth surfaces of gypsum and quartz, both of which are geochemically important minerals that display chiral crystal growth surfaces. II. Adsorption Mechanisms - Experimental Approaches: Structural mechanisms that underlie chiral adsorption of organic molecules on these mineral surfaces will be investigated. Proposed experiments include: 1. Liquid-immersion atomic force microscopy imaging of calcite crystal growth surfaces: Observations will be made of both surface growth and dissolution in the presence and absence of chiral adsorbates. 2. Use of site-specific fluorescent tags: Calcite surfaces with an adsorbed layer of amino acids will be exposed to a variety of fluorescent tags to determine the orientation and distribution of adsorbed molecules. These proposed studies, in concert with ongoing theoretical models of the adsorption process, will lead to an understanding of structural mechanisms of chiral selection. This work, furthermore, will lay the groundwork for future investigations that adapt microarray technology to the combinatorial study numerous of mineral surfaces and adsorbed organic species in a single experiment.