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Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization.

ABSTRACT: A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di- or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me₃ES), diethoxydimethylsilane (Me₂DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules.

SUBMITTER: Sandor M

PROVIDER: S-EPMC5456519 | biostudies-other | 2016 Jan

REPOSITORIES: biostudies-other

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Project description:We report the results of a structure-activity relationship study that was undertaken to identify humic substance chemistries that drive the plant biostimulant response. The effects of seven extensively chemically characterized, ore-derived humic acids (HA) on corn seedling biomass and root and shoot morphological parameters were investigated. Chemometric analyses were then conducted to identify correlations between HA chemical features and plant biomass and morphological characteristics. The primary chemical driver of plant biomass and morphology was the ratio between HA electron accepting capacity (EAC) and electron donating capacity (EDC). The HA electron accepting capacity is found in quinones and semiquinone free radicals, while the HA electron donating capacity is found in polyphenolics and glycosylated polyphenolics. Based on our results, we propose a mechanism of action for ore-derived HA plant biostimulation that involves the interplay of pro-oxidants, in the form of quinones and semiquinone radicals, and antioxidants, in the form of polyphenols and possibly glycones and carbohydrates. The quinones/semiquinones initiate an oxidative stress response via the stimulation of transmembrane electron flow that results in both reactive oxygen species (ROS) production (i.e., an oxidative burst) and membrane depolarization, the latter of which allows Ca2+ flux from the apoplast into the cytoplasm. Based on the magnitude of depolarization, a specific cytoplasmic Ca2+ signature is produced. As a secondary messenger Ca2+, via binding to Ca2+- sensor proteins, transmits the signature signal, resulting in specific intracellular responses that include changes to plant morphology. The greater the EAC, the greater the ROS production and magnitude of plasma membrane depolarization and resulting stress response. The HA antioxidants are able to scavenge and quench the ROS and thus modulate the intensity and extent of the stress response to greater or lesser degrees, based on their concentrations and radical scavenging efficiencies, and thus modify the Ca2+ signature and ultimately the intracellular molecular responses.

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Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization.

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