The interaction of biological molecules with clay minerals: A scanning force microscopy study

Summary: We have used the technique of scanning forcemicroscopy (SFM) to investigate the reaction of both aminoacids and activated nucleotides in the presence of the claymineral Cu(II)-exchanged hectorite. Using simulated pre-biotic heating and wetting cycles, we have shown that theclay mineral acts to adsorb, concentrate, and subsequentlycatalyze the polymerization of these biological monomersinto short peptides and oligonucleotides. The presence ofthe Cu(II) cations within the clay intergallery regions, andat surface step edges and cracks, is crucial for the observedreactions to occur. Clay minerals such as hectorite mayhave thus played an important role in the evolution of bio-logically viable molecules on the prebiotic earth. Key words : scanning force microscopy, prebiotic, nucleo-tide, amino acid PACS : 82.65.J; 87.14 Introduction The solid-phase synthesis of peptides and oligonu-cleotides on the prebiotic earth was proposed as early as1951 (Bernal 1951). In this paper, Bernal postulated thatnaturally occurring clay minerals could act as substrates toadsorb and concentrate biological molecules such as aminoacids and nucleotides. It was further conjectured that someaspect of the clay minerals might even act to catalyze thereactions that would form the first peptides or oligonu-cleotides needed for the emergence of life. In this study, wereview the interaction of the amino acid glycine with theclay mineral Cu(II)-exchanged hectorite and investigate thereactions of the biological molecule phosphorimidazolideof adenosine (ImpA) with the same clay mineral hectorite.Many types of clays are abundant in soils, sediments, andsedimentary rocks. These clays are also active chemicallyin the environment. Most of the clay minerals found in theearth’s crust are illites (mica and mica type minerals),smectites, and kaolinites (Weaver and Pollard 1973). Thekaolinites are 1:1 layer silicates (one Si-O sheet in eachlayer) while the illites and smectites are 2:1 layer silicates(two Si-O sheets in each layer). Hectorite (a smectite clay)is known to adsorb, react, and in some cases catalyze reac-tions with organics. In hectorite, individual layers areformed by sandwiching a sheet of octahedrally coordi-nated metal ions (Mg