Environmental conditions play an important role in conceptual studies of prebiotically relevant chem. reactions that could have led to functional biomols. The necessary source compds. are likely to have been present in dil. soln., raising the question of how to achieve selective concn. and to reach activation. With the assumption of an initial \"RNA World\", the questions of prodn., concn., and interaction of aldehydes and aldehyde phosphates, potential precursors of sugar phosphates, come into the foreground. As a possible concn. process for simple, uncharged aldehydes, we investigated their adduct formation with sulfite ion bound in the interlayer of pos. changed expanding-sheet-structure double-layer hydroxide minerals. Minerals of this type, initially with chloride as interlayer counter anion, have previously been shown to induce concn. and subsequent aldolization of aldehyde phosphates to form tetrose, pentose, and hexose phosphates. The reversible uptake of the simple aldehydes formaldehyde, glycolaldehyde, and glyceraldehyde by adduct formation with the immobilized sulfite ions is characterized by equil. consts. of K = 1.5, 9, and 11, resp. This translates into an observable uptake at concns. exceeding 50 mM. [on SciFinder (R)]