Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

Abstract

The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH 3 þ , where n ¼ 3-16 and 18, and then measuring d (001) , interlayer spacing of the resulting montmorillonite-alkyl ammoniummontmorillonite complex by X-ray diffractometry (XRD).Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units.The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

Modeling the early stages of self-assembly in nanophase materials. II. Role of symmetry and dimensionality

“…II. This generalization opens up the possibility of considering specific reactions, such as the conversion of terminal olefins to internal olefins and branched chain olefins into alumina pillared montmorillionite, studied by Giannelis et al 19 Such reactions are of evident commercial importance, 18 but also speak to a suggestion made independently by Bernal in 1949 23 and Goldschmidt in 1952 24 that monmorillonite clays, formed by the weathering of the volcanic rock and recently detected in martian soils, 25 may have played a central role in the evolution of life. In particular, montmorillonite, a member of the phyllosilicate group of minerals, catalyzes the condensation of activated monomers to form RNA-like oligomers by providing templates for prebiotic synthesis starting from simple precursors like HCN, CO, H 2 S, HCHO, and (possibly) NH 3 ; 26 the first two molecules are linear, the third is a bent trimer, and formaldehyde has the structure termed "bent symmetric-2" in Sec.…”

Shielding biomolecules from effects of radiation by Mars analogue minerals and soils

“…The extent of smectites’ ability to serve as catalyst for the formation of RNA-like oligomers widely varies with their charge density (Ertem et al 2010). Our research designed to test the protective effect of smectite with varying charge densities against radiation will demonstrate the correlation, if any, between the charge density and the protective effect (that is, whether the protective effect of three-sheet smectites varies with the charge density of the mineral).…”

Preparation and characterization of novel clay/PLA nanocomposites

“…The characteristics of surfactant absorption are complex and multi-faceted (Theng et al, 1967;Lagaly and Weiss, 1971;Pan et al, 1997;Chen et al, 1998). The orientation of the adsorbed alkylammonium is a function of the layer composition and charge density of the clay (Lagaly and Weiss, 1971;Ertem et al, 2010), and these aspects tend to differ amongst bentonitic montmorillonites (Jonas and Roberson, 1966). Thus, the orientation of the alkylammonium in m-BRN can best be interpreted as most consistent with that of the bilayer model, based on the extent of the expansion of the basal spacing from 1.35 nm to 1.87 nm (Lagaly et al, 1976;Lagaly, 1981).…”

“…There exists the possibility that the clay layers were well-dispersed in the polymer matrix, resulting in either an increase of the interlayer distance past 4.8 nm or a complete dispersion of the clay layers such that they no longer retained regular periodicity (Wu and Wu, 2006). However, the clay content of the m-BRN-based nanocomposites may be below that of the threshold of detection by XRD (5%) (Eberhart, 1989;Rhouta et al, 2008), and consequently may be absent regardless of the morphology of the clay. Thus, to achieve an accurate depiction of the state of exfoliation and/or intercalation of the nanocomposites, visual evidence via microscopy is necessary.…”