Concentration Of Monosilicic Acid Research Articles

Silicon-mediated regulation of cadmium transport and activation of antioxidant defense system enhances Pennisetum glaucum resistance to cadmium stress

Pennisetum glaucum is an important forage grass for livestock. However, the large accumulation of cadmium (Cd) in plant tissues increases the risk of heavy metals entering the food chain in Cd-contaminated soils. Silicon (Si) can inhibit cadmium (Cd) uptake and enhance tolerance of plant to Cd toxicity, but whether and how Si alleviates Cd toxicity in grass and the underlying mechanisms are unclear. The present study explored the differential mechanisms of silicon-induced Cd transport in apoplast and symplast, Cd distribution in root tissue and antioxidant defense system in P. glaucum under Cd stress through hydroponic and pot experiments. The present results showed that exogenous Si supply significantly reduced Cd concentrations in apoplast and symplast; Si treatment increased monosilicic acid concentration in apoplast and symplast of the roots and shoots under Cd stress. Elemental analysis of root microdomains showed that Si treatment increased the distribution of Cd and Si in the endodermis by 42.6% and 14.0%, respectively. Si alleviated the adverse influences of Cd on plant growth, which were manifested in root morphological traits and root activity. In addition, Si addition significantly increased the activities of catalase and superoxide dismutase by 37.0% and 72.7%, and improved the efficiency of the ascorbate-glutathione cycle in Cd-stress shoots. Furthermore, Si significantly reduced the contents of hydrogen peroxide and superoxide anion in Cd-stressed shoots by 16.6% and 48.7%, respectively. These findings demonstrate that Si enhances the resistance of P. glaucum to Cd stress through regulating Cd transport pathways and activating antioxidant defense systems.

Growth of Bacillus amyloliquefaciens as influence by Si nutrition.

The aim of study was to determine the influence of soluble and solid forms of Si on the growth of B. amyloliquefaciens. The experiment was conducted at two regimes: under sterile conditions (without B. amyloliquefaciens) and infected conditions (with B. amyloliquefaciens). New formed silica gel, diatomite and monosilicic acid at 1mM Si and 2mM Si were used as source of Si. The concentration of monosilicic acid in the solution was measured on second and tenth days of experiment. The total carbon in the solution before and after centrifugation was determined on day 10 of the experiment. The experiment has demonstrated a significant positive effect (by 4.7-41.2%) on B. amyloliquefaciens growth in water system. The presence of B. amyloliquefaciens in Si-rich solution reduced the concentration of monosilicic acid in the solution up to 16.2%. About 13.5-30.7% of B. amyloliquefaciens can be attached to the Si-rich surface without formation of cell clusters. Si can be classified as a beneficial nutrient for B. amyloliquefaciens. The tested strain of Bacillus can form channels in silica gel. The presence of monosilicic acid resulted in the formation of an aligned positioning of cells in water-based solution. This study is the first to demonstrate the direct influence of active Si forms on bacteria growth. The research showed that monosilicic acid or Si-rich solid substances with high solubility on Si can be recommended to increase B. amyloliquefaciens growth in soil, water or reactors.

An Overview on the Potential of Silicon in Promoting Defence Against Biotic and Abiotic Stresses in Sugarcane

Although silicon (Si) is ubiquitous in the earth’s crust, its essentiality for growth of higher plants is still under discussion. By recognising the overwhelming potential of Si in alleviating a wide range of biotic and abiotic stresses, the Association of American Plant Food Control Officials and the International Plant Nutrition Institute, Georgia, USA, have designated Si as a plant ‘beneficial substance’ in 2014 and 2015, respectively. Sugarcane is a Si-accumulating crop which strongly responds to Si fertilisation especially in Si-deficient soil. Due to intensive weathering prevailing in humid and sub-humid regions, most of the soil-available Si, taken up by plants in the form of monosilicic acid (H4SiO4), is lost through leaching. If the concentration of monosilicic acid is being maintained at a fixed level by soil reserves, the highly weathered soils of humid and sub-humid regions tend to become depleted in Si if continuously cultivated with sugarcane. Hence, leaching of Si from the soil coupled with plant uptake is an important factor in determining Si concentrations in soil. Consequently, it can be said that the intensive cultivation of sugarcane depletes the existing low available Si content in soil, resulting in necessity for Si fertilisation. Moreover, the uptake of Si by sugarcane (500–700 kg Si ha−1) sometimes surpasses those of the macronutrients (especially N, P and K). At the same time, due to change in global climate and monoculture system followed in sugarcane, it is affected by a wide range of biotic and abiotic stresses in field condition which calls for external Si supplementation to achieve sustainable growth and yield of sugarcane. The beneficial effects of Si in sugarcane include improvement of photosynthesis and lodging, enhancement of growth and development, regulation of reactive oxygen species, protection from soil salinity, reduction in metal toxicity, alleviation of freeze damage, mitigation of water stress and suppression of diseases and pests. In this review, we made an effort to compile the existing literature describing the potential of Si in promoting defence against various biotic and abiotic stresses in sugarcane and suggested possible future research perspectives.

Silicon increases chlorophyll and photosynthesis and improves height and NDVI of cotton (Gossypium hirsutum L. r. latifolium Hutch)

Silicon (Si) it is a beneficial element that relieves biotic and abiotic stresses in plants. However, cotton plants are not considered Si accumulators, with low potential for uptake the element by roots. The objective of this study was to evaluate the effect of combinations of Si rates applied by leaf spray and soil on the physiology, growth and yield of cotton (Gossypium hirsutum L. r. latifolium Hutch). The experimental design was a randomized complete block in a 3 x 4 factorial scheme with four replications. Leaf spraying consisted of three Si concentrations (0, 500, and 1000 mL ha-1) corresponding to 0, 100, and 200 ml ha-1 of monosilicic acid, with spraying split into three applications at stages V4, V6 and V8. Soil-based fertilization consisted of four Si rates in (0, 2.5, 5.0, and 10.0 kg ha-1) corresponding to 0, 0.5, 1.0, and 2.0 kg ha-1 of SiO2. At flowering, photosynthesis, green color index (GCI), plant height, and NDVI were evaluated. The application of Si in the planting furrow near the rhizosphere increased the green color index, reflecting a gain in photosynthesis and plant height, which positively increased NDVI. The use of high solubility Si in the planting furrow can increase the concentration of monosilicic acid in the area with the highest root distribution, enhancing the effect of this element in a non-accumulator crop such as cotton, by improving the green color index, photosynthesis and hence reflecting on gains in plant height and plant leaf area demonstrated by NDVI.

In situ observations of silica nanoparticle growth in geothermal brine at the Sumikawa geothermal station, Japan, by dynamic light scattering

Silica nanoparticle growth in geothermal brine was examined during the polymerization of silicic acid by observation with dynamic light scattering (DLS) at the Sumikawa geothermal station, examining raw (pH 6.6), pH adjusted (pH 8), and diluted brines (100 to 60%). The monosilicic acid concentration rapidly decreased over time in the raw brine but was almost constant in the samples with lower silicic acid concentrations. The average polysilicic acid particle diameter in the raw brine rapidly increased, from 1 to 6 nm, within 5 min (stage I) and then was almost constant at 7 nm for the subsequent 30 min (stage II).

Cadmium and arsenic adsorption in aqueous systems in the presence of monosilicic acid

The effect of different concentrations of monosilicic acid on the sorption capacity of quartz sand, diatomite, zeolite, and brown coal with respect to cadmium and arsenic has been studied in laboratory conditions. The applicability of different adsorption models, including exponential, semilogarithmic, and linear dependences, as well as the Langmuir and Freundlich equations, has been compared. An increase in monosilicic acid concentration from 0 to 2 mM increased the sorption capacity of all materials. It has been suggested that either the interaction of monosilicic acid with a pollutant takes place directly in the solution followed by sorption of the reaction products on the surface or in the pores of the sorbent, or first adsorption of the monosilicic acid by the sorbent occurs followed by interaction of the sorbed silicic acid with cadmium and arsenic; it is also possible that both process proceed in parallel.

As and Cd Sorption on Selected Si-Rich Substances

The processes of pollutant sorption by soil components control their mobility, migration, and transformation in the soil-plant system and depend on numerous properties, among which the elemental composition and surface area are dominant. In a laboratory experiment, the sorption of As and Cd by Si-rich substances differing in surface area, solubility of Si, and mineralogical composition was studied. The adsorption data were fitted to the linear, logarithmic, exponential, Langmuir, and Freundlich equations. Both size of the particles and mineral solubility of Si affected the As and Cd sorption. In the systems with lower initial concentrations of As and Cd, size of the particles had more pronounced effect on the sorption capacity. In the systems with high initial concentrations of As and Cd, the concentration of monosilicic acid was more significant than the surface area.

Accelerating effect of salicylate and phthalate anions on silica particle formation

To study the effects of organic compounds on the formation of silica, the polymerization of silicic acid in sodium silicate solutions in the presence and absence of sodium salicylate and disodium phthalate was investigated. The monosilicic acid concentration showed minor differences among the three different solutions. However, the concentration of polysilicic acid particles larger than 0.45 μm varied significantly among the three solutions, suggesting that the two organic compounds accelerate the growth of polysilicic acid. In particular, the concentration of polysilicic acid particles larger than 0.45 μm increased sharply in accordance with phthalate concentration, which is further evidence that phthalate accelerates the growth of silica. SEM images and size distribution measurements revealed that phthalate accelerates the aggregate of small silica particles to form larger silica pieces. FT-IR spectra of the silica formed during the polymerization of silicic acid showed the presence/or adsorption of salicylate and phthalate in the silica particles/or on the silica surfaces. The bidentate adsorption of salicylate or phthalate to two different polysilicic acid particles may accelerate the P–P reaction to aggregate the individual silica particles and rapidly form large size of silica.

Monosilicic acid potential in phytoremediation of the contaminated areas

The contamination of agricultural areas by heavy metals has a negative influence on food quality and human health. Various remediation techniques have been developed for the removal and/or immobilization of heavy metals (HM) in contaminated soils. Phytoremediation is innovative technology, which has advantages (low cost, easy monitoring, high selectivity) and limitations, including long time for procedure and negative impact of contaminants on used plants. Greenhouse investigations have shown that monosilicic acid can be used for regulation of the HM (Cd, Cr, Pb and Zn) mobility in the soil-plant system. If the concentration of monosilicic acid in soil was increased from 0 to 20 mg L−1 of Si in soil solution, the HM bioavailability was increased by 30–150%. However, the negative influence on the barley by HM was reduced under monosilicic acid application. If the concentration of monosilicic acid was increased more than 20 mg L−1, the HM mobility in the soil was decreased by 40–300% and heavy metal uptake by plants was reduced 2–3 times. The using of the monosilicic acid may increase the phytoremediation efficiency. However the technique adaptation will be necessary for phytoremediation on certain areas.

INFLUENCE OF PLANT ASSOCIATIONS ON THE SILICON CYCLE IN THE SOIL-PLANT ECOSYSTEM

Soluble Si compounds such as monosilicic and polysilicic acids affect chemicals and physical properties of the soil. The main aim of this study is to evaluate Si cycle in the various soil-plant s ystems via the determination of mobile Si forms in the soi l and of the total content of Si in the plant assoc iations. The concentrations of monosilicic acid, polysilicic acids and acid-extractable Si in unmowed meadow, mowed meadow, birch-aspen forest, spruce wood and agricultural land soil-plant systems, were tested at the soil depths of 0-10, 20-30 and 50-60 cm in a Ru ssian region, south of Moscow. The annual content o f Si within the investigated soil-plant systems was c alculated. Forty to 80 kg ha -1 of Si is annually removed from Grey Forest Soil (Luvisol). The concentration of monosilicic acid in the upper soil horizon depended on the type of plant association and on th e total content of adsorbed Si. The removal of plan t remains from the ecosystems resulted in decreased monosilicilic acid concentration in the upper soil horizon. The ecosystems which utilize annual plant remains increased the content of monosilicilic acid of the surface soil horizon. The concentration of mono silicic acid in the upper soil layer can be used as indicator of the stability of plant association. Th e unmowed meadow and the birch-aspen forest were characterized as ecosystems with accumulative type of Si cycle. The agricultural land, the mowed

Quantification of initial steps of nucleation and growth of silica nanoparticles: An in-situ SAXS and DLS study

The initial steps of silica polymerization and silica nanoparticle formation have been studied in-situ and in real-time. The experiments were carried out in near neutral pH (7–8) solutions with initial silica concentrations of 640 and 1600 ppm ([SiO 2]) and ionic strengths (IS) of 0.02, 0.05, 0.11 and 0.22 M. The polymerization reactions were induced by neutralizing a high pH silica solution (from pH 12 to 7) and monitored by the time-dependent depletion in monosilicic acid concentration over time. The accompanied nucleation and growth of silica nanoparticles (i.e., change in particle size over time) was followed in-situ using time-resolved synchrotron-based Small Angle X-ray Scattering (SAXS) and conventional Dynamic Light Scattering (DLS) combined with scanning and (cryo)-transmission electron microscopy (SEM/cryo-TEM). The critical nucleus diameter was quantified (1.4–2 nm) and results from SAXS and DLS showed that over 3 h the particle diameter increased to a final size of ∼8 nm. SEM and TEM photomicrographs verified the SAXS and DLS data and confirmed the spherical and hydrous structure of the forming silica nanoparticles. Furthermore, fractal analysis (i.e., fractal dimension, D m ∼ 2.2) indicated that the formed particles consisted of open, polymeric, low-density structures. For the nucleation and growth of silica nanoparticles a 3-stage growth process is proposed: (1) homogeneous and instantaneous nucleation of silica nanoparticles, (2) 3-D, surface-controlled particle growth following 1st order reaction kinetics and (3) Ostwald ripening and particle aggregation.

Silicate adsorption by goethite at elevated temperatures

Batch adsorption experiments with relatively low silica concentrations between 10 µM and 100 µM were conducted at three different ionic strength (0.01 − 0.1 M), and four different temperatures between 10 °C and 75 °C, yielding in a total of 550 experimental data points. The residual concentration of monosilicic acid is controlled by an adsorption equilibrium which is dependent on pH. The % Si adsorbed vs. − log[H +] curves reveal an upward bend with a maximum at about a pH of 9. With acidification below pH 9 the residual Si concentration in the suspensions steadily increases, as well as in the increasingly alkaline pH range. The slope of the latter is becoming steeper with increasing temperature. A basic Stern layer and charge distribution approach was used for modelling surface charge. The − log[H +]-dependent Si adsorption at the goethite surface was modelled involving a single-site approach for both neutral and hydrolyzed silicate inner-sphere surface complexes. For both a binuclear bidentate 2C complex was chosen according to spectroscopic information. Experimental data at all ionic strengths and temperatures are matched equally well by the adsorption model. The model output suggests a decrease in the pH where hydrolysis of the Si surface complex starts, and therefore an increasing importance of the hydrolyzed surface species with increasing temperature. The equilibrium adsorption constants could be well represented by a linear Van't Hoff log K T vs. 1/ T plot, from which thermodynamic Δ r H 298 and Δ r G 298 values of the adsorption reactions were derived. Adsorption of the silicate on the goethite surface is exothermic (Δ r H 298 = − 43.7 kJ mol − 1 for the dominating surface complex), and becomes therefore weaker with increasing temperature.

Identification of the Silicon Form in Xylem Sap of Rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a typical silicon (Si)-accumulating plant, but the mechanism responsible for the translocation from the root to the shoot is poorly understood. In this study, the form of Si in xylem sap was identified by (29)Si-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv. Oochikara) cultured in a monosilicic acid solution containing 0.5 mM Si, the Si concentration in the xylem reached 6 mM within 30 min. In the (29)Si-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. A (1)H-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the components of the xylem sap were not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.

Kinetics of silica oligomerization and nanocolloid formation as a function of pH and ionic strength at 25°C

Rate laws reported for the oligomerization of silica in natural environments are often contradictory, and the kinetics of monosilicic acid condensation are poorly understood. Here we present rate expressions that systematically describe the initial oligomerization of silica in terms of concentration of initial silica, ionic strength, and pH for a natural brine solution. The oligomerization of silica in dilute aqueous solutions was examined in solutions with ionic strengths of 0.01 and 0.24 molal, from pH 3 to 11, and with initial silica concentrations of 4.2, 12.5, and 20.8 millimolal (250, 750, and 1250 ppm SiO 2 respectively). The decrease in concentration of molybdate-reactive silica was monitored over time to determine the extent of oligomerization. This decrease in concentration of molybdate-reactive silica is accompanied by the appearance of a transient population of nanocolloidal particles with diameter ∼3 nm, as determined by atomic force microscopy (AFM). The oligomerization rate increases as pH approaches near neutral and as ionic strength increases. Early in the reaction where the concentration of molybdate-reactive silica, [SiO 2] n≤3 , is assumed to equal the concentration of monosilicic acid, [H 4SiO 4], the rate of change of monosilicic acid as a function of time, R, shows a fourth-order dependence: R = k 4 [ H 4 S i O 4 ] 4 Furthermore, the log of the rate constant ( k 4 , millimolal −3 s −1) varies linearly with pH according to log k 4 = m pH + log k o , where k o is the rate constant at pH 0 and m is an empiric constant. The value of m is positive below pH 7 and negative above pH 7. The observed fourth-order rate dependence with respect to [H 4SiO 4] is consistent with formation of a critical nucleus with four silica groups during the oligomerization of silica into metastable nanocolloidal silica. The sensitivity of the reaction rate constant, k 4 , to ionic strength and to silica concentration as a function of pH suggests that the critical species (in our model, a cyclic tetramer) chemically behaves as a bulk surface. In the brine solution employed in this study at 25°C, nanocolloids are relatively stable at low pH and at low ionic strength, and thus such colloids would be expected to occur in natural solutions even as they approach steady-state equilibrium with amorphous silica. The form of the log rate (oligomerization) vs. pH curve is roughly the inverse of the form of the log rate (dissolution)-pH curve for feldspar dissolution, and therefore may also be indicative of the importance of silica condensation reactions during feldspar dissolution.

Interaction of uranium(VI) with silicic acid in aqueous solutions studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS)

We investigated for the first time the complex formation in the uranyl–silicate system by fluorescence spectroscopy. The interaction between soluble species of uranium(VI) with silicic acid was studied in 0.3 M NaClO 4 solution using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Tetramethylorthosilicate (TMOS) was used as source of silicic acid in order to minimize the formation of polymeric silicon species. Fluorescence lifetimes were obtained for (a) the free uranyl cation of 1.7±0.3 μs, and (b) the 1:1 silicato–uranyl complex of 19.0±4 μs. The main fluorescence bands of the complex UO 2OSi(OH) 3 + are centered at 500, 521, 544 and 570 nm. The stability constant of the complex UO 2OSi(OH) 3 + was determined at pH 3.9, as log β°=−(1.67±0.20) using an uranyl concentration of 2.3×10 −5 M, and a monosilicic acid concentration up to 5.4×10 −3 M.

Effect of aluminium on the polymerization silicic acid in aqueous solution and the deposition of silica of silica

The effect of aluminium on the polymerization of silicic acid was studied at pH 7, 8 and 9 in the aluminium concentration range of 0–26 ppm (Al) by spectrophotometry, gel chromatography and 27Al NMR. Retarding and accelerating effects of aluminium on the growth of polysilicic acid particles and on the reaction between monosilicic acid and polysilicic acid were observed by changing the pH. It is suggested that the accelerating effect on the reaction between polysilicic acid particles is due to the formation of aluminium hydroxide on the surface of polysilicic acid. The rate of decrease in the monosilicic acid concentration in the presence of aluminium was faster than that in the absence of aluminium at pH 9, because monosilicic acid could be adsorbed rapidly on the aluminium hydroxide. From the results it was presumed that the formation of aluminium hydroxide on the solid surface may accelerate the deposition of silicic acid from geothermal water.

Liposomes in silicosis investigations.

The effects of quartz and sodium metasilicate on liposomes were studied in order to understand the mechanism of silicosis. 8-Hydroxyquinoline-5-sulfonic acid was tested for its in situ silicosis-prevention capacity. Two types of liposomes--(A) those incorporating cholesterol and (B) those without cholesterol--were used. The tests consisted of measuring permeability changes caused by the above-mentioned chemicals. Permeabilities were found to depend on membrane composition. Tests on quartz action led us to the conclusion that liposomes of this composition did not simulate the erythrocytes very well. It was also observed that absence or presence of cholesterol and the mode of contact altered the effect of quartz. Silicate destabilized type A liposomes, but this was less than that caused by quartz. This was explained by the concentration of monosilicic acid that dissolves out from quartz and silicate. When quartz was pretreated with the preventive, the type A liposomes were stabilized, but a slight destabilizing effect was observed on type B. 8-Hydroxyquinoline-5-sulfonic acid augmented the destabilizing effect of silicate, whereas it decreased the hemolytic activity of uncoated quartz, indicating a preventive potential in in vivo.

Study of the polymerization of silicic acid in aqueous solution by trimethylsilylation—gas chromatography

The effects of pH, concentration of monosilicic acid and temperature on the formation of low-molecular-weight silicic acid species in the early stages of polymerization were studied by trimethylsilylation—gas chromatography (TMS—GC). The change with time in the distribution of silicic acid species up to the hexamer was measured. The results obtained by TMS—GC are compared with those obtained by colorimetry. In solutions of initial monosilicic acid concentration of 600 ppm SiO 2 at pH 1.8, 20°C and at pH 8.5, 90°C, it was found that a temporary equilibrium is set up among ▪, ▪ and ▪ during the induction period. On the other hand, for 2500 and 5000 ppm SiO 2 solutions at pH 1.8, 20°C, higher-molecular-weight silicic acid species than ▪ were formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period, and the distribution of these species changed with time. All of the silicic acid species formed during the induction period were determined by colorimetry.

Dissolution and deposition of monosilicic acid in suspensions of ground Quartz

Ground quartz, pretreated with HF, was shaken with buffer of pH 7·7 at 25°C. Suspensions, with and without added monosilicic acid, gave the same steady monosilicic acid concentration viz. 18–20 ppm SiO 2. Quartz samples which were contaminated with Al generally failed to establish steady concentrations of monosilicic acid.

Uptake of silica byTrifolium incarnatum in relation to the concentration in the external solution and to transpiration

The uptake of monosilicic acid by crimson clover (Trifolium incarnatum L.) was investigated using solution cultures in which the level ranged from 0.4 to 60 ppm SiO2, and soils in which the level in solution ranged from 7 to 67 ppm SiO2. With increasing levels of silica in the external solution there were systematic increases in uptake, but the quantities of silica in the tops were always less than those which were theoretically carried to the roots in the mass flow of water. The silica content of the roots was higher than in the corresponding tops and seemed to be largely associated with the epidermis. These findings and the observation that the concentration of monosilicic acid in the xylem sap is lower than that in the external solution, are regarded as evidence that the plant excludes a proportion of the monosilicic acid from the transpiration stream. This exclusion is attributed to a barrier in the root through which monosilicic acid passes at a slower rate than water.