Structure ofSi(OH)4 stabilized by two chloride anions.
Typically orthosilicic acid is assumed to be a product of the hydrolysis of its esters,Si(OR)4, where R stands fororganyl group, as is practiced insol-gel syntheses.[2] These conditions are however too vigorous to allow isolation of the parent acid.
Silicon has been explored as a nutrient for plant growth, with silica constituting up to 10% of plant weight on a dry matter basis.[6] Orthosilicic acid is of particular interest as it is thought to be the form in which plants acquire silicon from the soil,[7][8] before being deposited as phytoliths throughout the plant, leading to research in the application of orthosilicic acid through foliar sprays to supplement plant growth.[9] Studies have demonstrated that foliar application of stabilized orthosilicic acid can alleviate abiotic stressors such as drought,[10][11] heavy metal toxicity,[12][13] and salinity,[14] resulting in increased yields.[15] Additionally, applications of orthosilicic acid have been demonstrated to reduce fungal infections and disease in plants,[16] suggesting the possibility of using stabilized orthosilicic acid as an alternative or complement to existing disease control measures. The mechanisms by which orthosilicic acid alleviates abiotic stress and controls diseases is not well understood; current theories advanced include the activation of plant defense reactions[17] and the precipitation of silica in the apoplast of the plant.[18]
Dissolved silica (DSi) is a term used in the field of oceanography to describe the form of water-solublesilica, which is assumed to beSi(OH)4 (orthosilicic acid) or itsconjugate bases (orthosilicate anions) such as−O−Si(OH)3 and(−O−)2Si(OH)2. Theoretical computations indicate that the dissolution of silica in water proceeds through the formation of aSiO2·2H2O complex and then orthosilicic acid.[20]Thebiogeochemical cycle ofsilica is regulated by thealgae known as thediatoms.[21][22] These algaepolymerise the silicic acid to so-calledbiogenic silica, used to construct theircell walls (calledfrustules).[23]
In the uppermost water column the surfaceocean is undersaturated with respect to dissolved silica, except for theAntarctic Circumpolar Current south of 55°S.
The dissolved silica concentration increases with increasing water depth, and along the conveyor belt from the Atlantic over the Indian into the Pacific Ocean.[24][25]
^Souri, Zahra; Khanna, Kanika; Karimi, Naser; Ahmad, Parvaiz (14 Jun 2020). "Silicon and Plants: Current Knowledge and Future Prospects".Journal of Plant Growth Regulation.40 (3). Springer Science and Business Media LLC:906–925.doi:10.1007/s00344-020-10172-7.ISSN0721-7595.S2CID253843062.
^Goyal, Vinod; Baliyan, Vaibhav; Avtar, Ram; Mehrotra, Shweta (20 Aug 2022). "Alleviating Drought Stress in Brassica juncea (L.) Czern & Coss. by Foliar Application of Biostimulants—Orthosilicic Acid and Seaweed Extract".Applied Biochemistry and Biotechnology.195 (1). Springer Science and Business Media LLC:693–721.doi:10.1007/s12010-022-04085-2.ISSN0273-2289.PMID35986841.S2CID251672735.
^Dwivedi, Sanjay; Kumar, Amit; Mishra, Seema; Sharma, Pragya; Sinam, Geetgovind; Bahadur, Lal; Goyal, Vinod; Jain, Neeru; Tripathi, Rudra Deo (17 Apr 2020). "Orthosilicic acid (OSA) reduced grain arsenic accumulation and enhanced yield by modulating the level of trace element, antioxidants, and thiols in rice".Environmental Science and Pollution Research.27 (19). Springer Science and Business Media LLC:24025–24038.Bibcode:2020ESPR...2724025D.doi:10.1007/s11356-020-08663-x.ISSN0944-1344.PMID32301095.S2CID215793851.
^Bhaskar Mondal, Deepanwita Ghosh, and Abhijit K. Das (2009): "Thermochemistry for silicic acid formation reaction: Prediction of new reaction pathway".Chemical Physics Letters, volume 478, issues 4–6, pages 115-119.doi:10.1016/j.cplett.2009.07.063
^Siever, R. (1991). Silica in the oceans: biological-geological interplay. In: Schneider, S. H., Boston, P. H. (eds.),Scientists On Gaia, The MIT Press, Cambridge MA, USA, pp. 287-295.
^The figures here have been drawn using the interactive web site which feeds on annual DSi values fromLEVITUS94:World Ocean Atlas 1994, an atlas of objectively analyzed fields of major ocean parameters at the annual, seasonal, and monthly time scales. Superseded by WOA98. Edited by Syd Levitus.
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