Abstract

Natural nanoparticles occur widely in soils derived from volcanic ash like Andisols. The more important constituent of Andisols is allophane, which is an aluminosilicate non-crystalline. These nanoclays have morphology sphereroidal with an outer diameter of 3.5-5.0 nm, the think wall (0.7-1.0 nm) is composed of an outer Al octahedral sheet and an inner Si sheet. Also, defects in the wall structure give rise to perforations of ~ 0.3 nm diameter. These nanoparticles form stable microaggregates, with pores within the nanoscale range with similar physical characteristics to silica nanomaterials which were very important in biocatalysis. Studies have reported that nanomaterials are more promising clays for enzyme immobilization compared to conventional materials. The aims of this study were: characterize natural clay and nanoclay with and without organic matter from an Andisol and ii) evaluate clay and nanoclays as support to immobilize acid phsophatase. An Andisol, Piedras Negras soil from Southern Chile was sampled within 0-20 cm of depth, sieved to 2 mm mesh and air-dried. One part of the soil was treated with 30% hydrogen peroxide to remove the soil organic matter. The separation of particle-size < 2 um fractions was obtained by sedimentation procedures based on Stoke's law. Natural nanoclays were extracted using the methodology described by Liu et al. (2005). The clays and nanoclays were characterized by using energy dispersive X ray (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electronic diffraction (ED). Synthetic complexes were formed by interaction between acid phosphatase and either allophanic clay or nanoclay, and used as model systems to simulate enzymatic reactions occurring in heterogeneous environment. The enzymatic activities of immobilized phosphatase on nanoclay, with or without organic matter, were measured with p-nitrophenylphosphate (pNPP) as substrate. The kinetics parameters (Vmax and Km values) were calculated by a non-linear regression analysis according to the Michaelis-Menten equation. The TEM analysis showed the nanoclay presence (< 50) nm in the samples evaluated. The occurrence of amorphous and crystalline particles were observed by DE analysis in samples the clay and nanoclay. The SEM analysis the immobilized phosphatase showed cavities of different sizes. The enzymatic activity increased in 90 % compared with the free enzyme. Likewise, the kinetic parameters showed that the catalytic efficiency (between 60 and 70 %) and Vmax (between 110 and 130 %) were enhanced.