No abstract

The polycondensation of amino acids to oligopeptides is an important step in the origins of life, and known to be effective on several mineral surfaces. The data available on clay mineral surfaces are heterogeneous and sometimes contradictory, however. The objective of the present work is to investigate the adsorption of a selected amino acid, alanine, in expanding and non-expanding clays and then study the possible peptide condensation by thermal activation. A multi-technique approach was used, including macroscopic measurements of the adsorption process (adsorption isotherms and pHmetry), and in situ molecular-level characterization of the solids obtained (X-ray diffraction, thermogravimetric analysis and infrared spectroscopy). The results indicate that only weak interaction is established between alanine molecule and kaolinite surfaces, most of the deposited molecules being only physically retained. Thermal activation of alanine/kaolinite only led to desorption. In contrast, higher-energy adsorption mechanisms were at play in hectorite, including cation exchange and coordinative adsorption to the interlayer ions, and alanine species adsorbed in this way were observed to form cyclic dimers upon activation between 160 and 270 °C.

In this work, hectorite/alizarin pigments were prepared at pH 9 and 12.Hectorite was initially modified with cetyltrimethylammonium and pectine to produce organo-hectorites. The influence of organo-hectorite on the stabilization of alizarin was evaluated. X-ray diffraction suggested the formation of exfoliated/delaminated structures after organofunctionalization of the hectorite. For raw hectorite and their derivatives with pectin, the formation of hybrid pigments was confirmed by infrared spectroscopy. Thermogravimetry curves confirm the hectorite organofunctionalization and that the alizarin loading was higher at pH 12. The hybrids prepared at pH 12 show more photostability than ones prepared at pH 9. This behavior was probably due to the total deprotonation of dye molecules, which promoted better interactions between the hosts and the guests.

fields that encompass the applications of clays are mainly in civil engineering, paper industry, effluent treatment, photocatalysis, tissue engineering, cosmetics, controlled drug release and others. These materials can be used in manipulations for drug encapsulation both for dermatological application and for oral administration, thus being important material to be exploited in various technological processes, specifically in the pharmaceutical industry [2,[4][5][6][7][8][9][10][11][12][13][14][15]. The objective of this works a bibliographical and technological prospection regarding clays and clay minerals, including their characteristics and modifications, with emphasis on their use as biomaterials, controlled release of drugs.