Biocompatible small molecules that enhance silica solubilization under ambient conditions: chemical profile of such complexes, possible mechanism for enhancement, and their effect on the growth and protection from pests in the rice plant (Oryza sativa L.)

Abstract

Recent studies suggest that the depletion of silicon available to plants may be a major reason for the yield decline observed for rice cultivation. In the present article, a novel strategy is explored to identify small biocompatible molecules (carriers) that would enhance the solubility of sand (SiO ₂. nH ₂ O) (here after named silica) in water under ambient conditions. All considerations, notably biocompatibility, make the 20 proteinous amino acids and their simplified analogs the first choice. Among the proteinous amino acids, notable enhancement of silica solubility was seen at 1000 μ mole.L^-1 : Blank: 1; glutamine: 3.5; histidine: 3; alanine: 2.9. Based on the assumption that the observed enhancement is related to proclivity for hydrogen bond formation with water, a large number of varied biocompatible substrates were examined. Among these, notable enhancement of silica solubilization at 1000 μ mole.L^-1 was seen as exemplified with Blank: 1; imidazole: 5; inositol: 4.5; mannitol: 3.9; 3, 4-dihydroxy phenylalanine (DOPA): 3.5. A complementary gravimetric protocol coupled with thermogravimetric analysis (TGA) enabled the estimation of an approximate empirical formula for few of the carrier-silica complexes. A possible mechanism for the interaction of the carrier at the silica-water interface is suggested. Field experiments (reported separately) with selected carriers, monitored in the stem extract by colorimetry and in the leaf by scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis showed enhanced levels of silica and were significantly beneficial for the growth and protection from predators of the rice plant.