Total Silica Concentration Research Articles

In Vitro Evaluation of a Peptide-Mesoporous Silica Nanoparticle Drug Release System against HIV-1

It has been shown that the optimized VIR-576 derivative of the natural HIV-1 entry inhibitor targeting the viral gp41 fusion peptide is safe and effective in infected individuals. However, high doses of this peptide were required, and stability, as well as delivery, must be improved for clinical application. Here, we examined the loading and release of VIR-576 into/from mesoporous silica nanoparticles (MSNs) in vitro. We found that a moderately high peptide loading of 11.5 wt % could be achieved by adsorption from PBS buffer (pH 7.2), i.e., under mild, fully peptide-compatible conditions. The release rate of peptide into the same buffer was slow and the equilibrium concentration as indicated by the adsorption isotherm could not be reached even within 50 h at the particle concentrations studied. However, a faster release was observed at lower particle concentrations, indicating that partial particle dissolution had a positive influence on peptide release. To determine the antiviral activity of VIR-576-loaded MSNs, TZM-bl indicator cells were exposed to HIV-1 and the infection rates were followed as a function of time and VIR-576 concentration. The inhibitory activity observed for VIR-576 released from the MSNs was virtually identical to that of free VIR-576 at the 48 h time point, indicating that (a) VIR-576 was released in an active form from the MSNs, and (b) the release rate in the presence of serum proteins was clearly higher than that observed under protein-free conditions. These observations are discussed based on competitive peptide/protein adsorption, as well as potential influences of serum proteins on the dissolution-reprecipitation of silica under conditions where the total silica concentration is above the saturation level for dissolved silica. Our results highlight the need for studying drug release kinetics in the presence of serum proteins, in order to allow for a better extrapolation of in vitro data to in vivo conditions. Furthermore, due to the high peptide loadings that can be achieved using MSNs as carriers, such a formulation appears promising for local release applications. For systemic administration, however, peptides with a higher potency would be needed, due to their high molar masses limiting the drug loading in terms of moles per gram carrier.

Europium silicate complexation at 25 °C and 0.7 molar ionic strength

Abstract Previous determinations of rare earth element (REE) complexation by silicate have been confined to observations of Eu(SiO(OH) 3 ) 2 + formation. Critical assessment of these observations reveals order-of-magnitude ambiguities in the stability constants derived from a variety of experimental designs. A salient feature of prior Eu(SiO(OH) 3 ) 2 + stability constant assessments is that the largest silicate stability constants were obtained in the presence of substantial silica polymerization. In the present work, Eu(SiO(OH) 3 ) 2 + formation is described under conditions where polymerization should be negligible. Stability constants were obtained via observations of the following equilibrium: Eu 3 + + Si(OH) 4 0 ⇌ Eu(SiO(OH) 3 ) 2 + + H + with total silicon concentrations on the order of 0.5 mM or less. The formation constant for this equilibrium at 25 °C and 0.7 M ionic strength is log β Si ∗ 1 = Eu OSi OH 3 2 + H + Eu 3 + Si OH 4 0 = − 3.27 ± 0.18 This stability constant coupled with the first ionization constant of Si(OH) 4 0 yields log Si β 1 = 6.18 ± 0.18 for the equilibrium Eu 3 + + OSi(OH) 3 − ⇌ Eu(SiO(OH) 3 ) 2 + . Both of these constants are more than an order of magnitude smaller than results obtained under conditions conducive to silica polymerization (i.e., total silica concentrations between 2 and 20 mM). These new stability constants indicate that Eu(SiO(OH) 3 ) 2 + is a significant fraction of the total dissolved europium in deep waters of the Atlantic and Pacific but a very minor species in surface waters. In contrast to predictions obtained via the recent speciation model of Akagi (2013), concentrations of REE–silicate complexes throughout the oceans are much smaller than those of REE–carbonate complexes.

Experimental study of the ultrafiltration for bi-disperse silica systems

Abstract The filtration rate in monodisperse colloidal systems has previously been predicted by taking into account the interactions between particles, interpreted in the form of an osmotic pressure. However, most membrane filtration applications deal with multi-component feeds, consisting of particles of different sizes. These polydisperse ultrafiltrations are poorly understood, largely due to the lack of adequate experimental data and the complexity of the system. These systems are also more difficult to interpret when compared to the single component feed systems. This work investigates the ultrafiltration of bi-disperse feed solutions of colloidal silica. Experimental studies were carried out on two different sized silica particles: X30 and W30. Feed solutions with a total silica concentration of 4 g l−1 were prepared. These solutions consisted of a 0.03M NaCl electrolyte with the following mixing ratio of X30:W30 by weight: (i) 100% X30, (ii) 100% W30, (iii) 20%:80% (iv) 40%:60%, (v) 60%:40% and (vi) 80%:20%. The solutions were filtered at an applied pressure of 200 kPa, through a 4 kDa molecular weight cut-off membrane. The permeate flux versus time data was recorded at pH’s 4, 6 and 9. At each pH, the variation of the permeate flux was observed and compared to the two monodisperse systems.

Seawater RO treatment of RO concentrate to extreme silica concentrations

Severe restrictions exist in the disposal of the concentrate from the 15 mgd (2370 m3/h) reverse osmosis (RO) plant in El Paso, Texas (i.e., 15 mgd blended to 27.5 mgd). The current permit for the disposal by deep well injection limits the total dissolved solids in the brine to 10,000 mg/l. This limits water recovery in the plant and drives up the cost of sending a large volume of the concentrate a long distance for discharge. We have continued to work on developing a concentrate treatment process aimed at zero liquid discharge or a greatly reduced concentrate volume suitable for evaporation ponds. This is an interim report documenting an exciting demonstration of the feasibility of using a seawater RO system and synergistic antiscalant and low pH inhibition of reactive silica polymerization to concentrate the primary brackish water RO concentrate to total silica concentrations exceeding 1000 mg/l. This approach makes possible the use of tandem brackish RO followed immediately by a seawater RO (SWRO) to a...

Release of Colloids from Injection Grout Silica Sol

AbstractNon-cementitious grouts have been tested in Olkiluoto for the sealing of fractures with the small hydraulic aperture. A promising non-cementitious inorganic grout material for sealing the fractures of the apertures less than 0.05 mm is commercial colloidal silica called silica sol. The use of colloidal material has to be considered in the long-term safety assessment of a spent nuclear fuel repository. Objective of this work was to determine colloid release from the silica sol gel and stability of silica colloids in different groundwater conditions. To use silica sol as a grout, the injected colloids have to aggregate and form a gel within a predictable time by using a saline solution as an accelerator. Silica sol gel samples were stored in contact with medium salinity and low salinity groundwater simulates. Release of silica colloids and colloid stability was followed by analyzing the colloid concentration, particle size distribution, concentration of reactive silicon, solution pH and zeta potential after one month, half a year and one year. Malvern Zetasizer Nano ZS equipment was used to determine colloidal particle size distributions applying the dynamic light scattering method and zeta potential based on dynamic electrophoretic mobility. The colloidal particle concentration was estimated from Zetasizer measurements applying a standard series. Dissolved reactive silica concentration was determined using the molybdate blue method and total silica concentrations were determined using ICP–MS. The release and stability of silica colloids were found to be dependent significantly on groundwater salinity. Zeta potential values near zero and the increase in particle size at first and then the disappearance of large particles indicated particle flocculation or coagulation and instable colloidal dispersion in a saline groundwater simulate. In low salinity ground water simulate high negative zeta potential values, small particle size and constant size distribution indicate the existence of stable silica colloids. The concentrations of the released colloids were slightly higher than determined in natural granitic ground waters. Under prevailing saline groundwater conditions in Olkiluoto no significant release of colloids from silica sol is expected but the possible influence of low salinity glacial melt waters has to be considered.

Effects of light on sediment nutrient flux and water column nutrient stoichiometry in a shallow lake

The effects of light and temperature on nutrient cycling (silica (Si), nitrogen (N) and phosphorus (P)) between sediments and water in a shallow eutrophic lake (Loch Leven, Scotland), and consequent effects on water column nutrient stoichiometry, were assessed using a series of intact sediment core incubation experiments. Estimates of actual seasonal dark and light P-fluxes were assessed using 24-h incubations. Sediment-P uptake was observed in spring (7 °C) and release in autumn (12 °C) and summer (17 °C), with the highest release rates (∼17 mg PO 4-P m −2 sediment surface area d −1) occurring in summer. In a longer (21-day) experiment in which the effects of light (light ( n=6) and dark ( n=6)) and temperature (five 4-day cycles to represent: 7 °C⇒13 °C⇒23 °C⇒13 °C⇒7 °C) on water column nutrient concentrations were assessed, PO 4--P, total P (TP), SiO 2 and total silica (TSi) concentrations in the water column were all significantly higher under dark conditions (ANOVA, α=0.05). NH 4-N (ammonium N) water column concentrations were observed to be higher under dark conditions at low temperatures and higher under light conditions following a high-temperature (23 °C) treatment. No significant light effects were observed for water column total N (TN) concentration. Flux estimates for all nutrients measured are given. In terms of water column nutrient stoichiometry, TN:TP ratio was significantly higher under light conditions, TSi:TN was significantly lower under light conditions, and TSi:TP did not vary significantly between the dark and light treatments. The main processes acting to regulate diffusive nutrient release appeared to be photosynthetic elevation of bottom water pH and dissolved oxygen concentration (both significantly higher under light conditions) and direct microalgal sequestration. Thus, a feedback mechanism exists in recovering shallow lakes where benthic microalgae can affect the stoichiometry (to favour P/Si limitation) of the plankton, and also of the main source of nutrients back to the sediments via the disproportionate regulation of sediment P, Si and N release.

Modeling of nucleation of orthosilicic acid in geothermal brine

On the basis of a mathematical model, a program is developed for numerical modeling of orthosilicic acid nucleation in geothermal brine with the formation of colloidal silica particles. Data on the dependence of the process parameters on the properties of brine (temperature, pH, and total silica concentration) are obtained. These data can be used to design technological systems of silica removal from the geothermal heat-transfer medium.

Complexation of Cm(III)/Eu(III) with silicates in basic solutions

Summary The complexation of Cm(III) and Eu(III) with dissolved silica was studied by solubility measurement and time resolved laser fluorescence spectroscopy (TRLFS) in basic solutions over a range of total silica concentrations and ionic strengths (NaNO3). In initial experiments on the solubility of Eu(OH)3 in silicate containing solutions we observed a rapid increase in the soluble Eu(III) concentration under basic conditions. The Eu(III)/Cm(III) silicate complexes that formed caused a significant increase of the hypersensitive 5 D 0 → 2 F 2 band around 615 nm relative to the non-hypersensitive 5 D 0 → 7 F 1 band at 592 nm for Eu(III). Further studies of Eu(III) and Cm(III) containing solutions showed a shift of the fluorescence spectral maximum from 594 nm to up to 607 nm for Cm(III) along with a significant increase of fluorescence intensities. The fluorescence lifetimes for Eu(III) species increased from 115 μs to 1.8 ms in 3.0 M and 5.0 M NaNO3, corresponding to full coordination, and from 68 μs to 202 μs for Cm(III) in 0.1 M NaNO3, consistent with the removal of 6–7 water molecules upon silicate complexation. The variations of the fluorescence intensity and the concentrations of the monomeric and polymeric silicates suggested that in basic silicate solutions, Eu(III)/Cm(III) mainly complexes with polysilicates.

Silica recovery from Sumikawa and Ohnuma geothermal brines (Japan) by addition of CaO and cationic precipitants in a newly developed seed circulation device

With the objective of preventing silica scaling, several types of chemical compounds such as silica gels, clay minerals, chlorides of Ca, Mg, Al and Fe, and calcium compounds were first examined to remove the excess silica in the Ohnuma geothermal brines. The total silica concentrations of silica in the brines after reaction by addition of these chemicals were observed to decrease linearly with an increase in the reagent concentration. Quicklime (CaO), added at dosages of 0.5 and 1.0 g/l, can remove excess and most silica at 90 °C, respectively. These results indicate that the silica concentration of Ohnuma brines (520 mg/l initial concentration) can be controlled by the amount of quicklime added, and that low-temperature resources can be used without scaling. Continuous flow tests were then performed at Ohnuma and Sumikawa fields by addition of CaO or cationic precipitants in a newly developed seed circulation device (flow rate of 10 l brine/min). At Ohnuma, the total silica concentrations of brines after reaction with CaO showed almost constant values: 10, 200 and 300 mg/l for additions of 1.0, 0.65 and 0.50 g CaO/l, respectively. At Sumikawa, 11 experiments were run, adding cationic precipitants. The total silica concentrations decrease with the increase in reagent concentrations (25–100 mg/l) and with an increase in the retaining time (15–120 min). With the addition of CaO (2 g/l) to Sumikawa geothermal brines with a retaining time of 120 min at 90 °C, the total silica concentration was almost non-detectable after 10 h from the start of the reaction. After reaction for 118 h, addition of CaO was suspended and only silica deposits were reused through the circulation pipe to desilicate brine. After this treatment, the total silica concentration quickly increased to 400 mg/l and remained constant for 210 h before increasing to 650 mg/l after 265 h. There are good correlations between the zeta potentials, a measure of colloidal stability, and the Si/Ca atomic ratios of the silica deposits and amounts of silica removed from brines at Ohnuma and Sumikawa. The CaO addition and circulation method (SACS method) is a very useful way of removing excess silica in brines for silica scale prevention.

Silica removal from Mokai, New Zealand, geothermal brine by treatment with lime and a cationic precipitant

Preliminary experiments using two chemicals (CaO, a quicklime, and a cationic nitrogen-bearing precipitant, EC-004) to remove silica from geothermal brine were undertaken at the Mokai geothermal plant, New Zealand. The brine was mixed with the reagent (CaO or EC-004). The reaction was studied from the start of the experiment (NRT, 0 min, no retaining time) and after 15 min (15RT) at 90 °C. The concentration of silica in the brine was initially 954 mg/l, and decreased linearly with increasing reagent concentration. When CaO is added, the silica concentration at 15RT was 200 mg/l lower than at NRT and became almost zero on addition of 1.5 g/l. In contrast, when EC-004 is added, the total silica concentration nearly reaches the solubility of amorphous silica at 90 °C. In order to prevent silica scaling in Mokai brines cooled to 90 °C, the CaO and EC-004 added should be individually adjusted to 0.5 g/l and 80 mg/l, respectively.

Zeolite Growth by Addition of Subcolloidal Particles: Modeling and Experimental Validation

Seeded growth of tetrapropylammonium (TPA)-silicalite-1 is studied using simulations and dynamic light scattering, atomic force microscopy, and transmission electron microscopy experiments. The effects of the total silica concentration, temperature, and total seed concentration are examined. When the composition of silica in solution is above a critical value, growth is observed. In such a case, the size of the seeds increases linearly with time, with a growth rate that is not significantly affected by the total silica concentration. Growth appears to be activated with an activation energy of 90 kJ/mol for a range of seed concentrations. Transmission electron microscopy and dynamic light scattering indicate the presence of subcolloidal particles. Simulations of the growth of a static particle in a suspension of subcolloidal particles are carried out. Good agreement with experimental results regarding the growth rate and the apparent activation energy is possible by considering DerjaguinLandau-Verwey-Overbeek (DLVO) interactions with electrostatic repulsion described with a constant surface charge model. The type of interaction was also verified with atomic force microscopy force measurements between a silicalite surface and a glass sphere. By use of these types of interactions, it is also possible to explain the stability of the seeded suspension and show that only a relatively narrow size distribution of growth precursors participate in the growth of the seeds. Our results support the possibility that under the conditions studied, growth of silicalite seeds proceeds by a mechanism with the rate-limiting step being the addition of subcolloidal particles.

Diffusion- and reaction-limited aggregation of aqueous silicate solutions

Two different aggregation processes (diffusion- and reaction-limited cluster aggregation) are observed in aqueous silicate solutions which are acidified. The type of aggregation depends on total silica concentration of the starting silicate water glass and the presence of oligomeric silicate anions in the starting silicate solution. If Q 4 3-silicate anions are present in solution and the water glass is low in concentration (≈ 0.2 wt%), fast, diffusion-limited cluster-cluster aggregation (DL-CCA) is observed, whereas if no oligomers are present, slow, reaction limited cluster-cluster aggregation (RL-CCA) is observed. Diffusion-limited cluster-cluster aggregation is induced by fast reaction of reactive oligomers with monomers and other oligomers. The low silica concentration induces diffusion to become rate determining in the aggregation process. The fractal dimensionality of gels formed by RL-CCA does not depend on total silica concentration, whereas the size of the aggregates strongly depends on total silica concentration.

Influence of sodium silicate addition on the adsorption of oleic acid by fluorite, calcite and barite

A study has been made of the adsorption of sodium silicate by calcite, fluorite and barite and the effect that this adsorption has on the flotation of these minerals with oleic acid. The results show that sodium silicate depresses these minerals by preventing oleate species from reacting with surface sites. This effect is independent of the total silica concentration. Aged sodium silicate solutions do not produce markedly different results to those obtained with fresh solutions. The concentration of the sodium silicate solutions was generally such that the total silica concentration was below that in equilibrium with amorphous silica. Under these conditions the solutions contained no polymeric silica species and the mechanism of silica adsorption can be generally attributed to interactions of monosilicate ion and monosilicic acid with surface sites.

The effect of volatile anaesthetics on rat hippocampal CA1 neurons in vitro

With the objective of preventing silica scaling, several types of chemical compounds such as silica gels, clay minerals, chlorides of Ca, Mg, Al and Fe, and calcium compounds were first examined to remove the excess silica in the Ohnuma geothermal brines. The total silica concentrations of silica in the brines after reaction by addition of these chemicals were observed to decrease linearly with an increase in the reagent concentration. Quicklime (CaO), added at dosages of 0.5 and 1.0 g/l, can remove excess and most silica at 90 °C, respectively. These results indicate that the silica concentration of Ohnuma brines (520 mg/l initial concentration) can be controlled by the amount of quicklime added, and that low-temperature resources can be used without scaling. Continuous flow tests were then performed at Ohnuma and Sumikawa fields by addition of CaO or cationic precipitants in a newly developed seed circulation device (flow rate of 10 l brine/min). At Ohnuma, the total silica concentrations of brines after reaction with CaO showed almost constant values: 10, 200 and 300 mg/l for additions of 1.0, 0.65 and 0.50 g CaO/l, respectively. At Sumikawa, 11 experiments were run, adding cationic precipitants. The total silica concentrations decrease with the increase in reagent concentrations (25–100 mg/l) and with an increase in the retaining time (15–120 min). With the addition of CaO (2 g/l) to Sumikawa geothermal brines with a retaining time of 120 min at 90 °C, the total silica concentration was almost non-detectable after 10 h from the start of the reaction. After reaction for 118 h, addition of CaO was suspended and only silica deposits were reused through the circulation pipe to desilicate brine. After this treatment, the total silica concentration quickly increased to 400 mg/l and remained constant for 210 h before increasing to 650 mg/l after 265 h. There are good correlations between the zeta potentials, a measure of colloidal stability, and the Si/Ca atomic ratios of the silica deposits and amounts of silica removed from brines at Ohnuma and Sumikawa. The CaO addition and circulation method (SACS method) is a very useful way of removing excess silica in brines for silica scale prevention.

Kinetics of silica polymerization and deposition from dilute solutions between 5 and 180°C

Between 5 and 90°C the maximum rate of silica polymerization in dilute neutral solutions at constant supersaturation, increases only slowly (formal Energy of Activation = 3 kcal/mole). From 90 to 180°C the maximum rate decreases to below the rate at 5°C. The reactions show induction periods, whose lengths increase with temperature and decrease with supersaturation. The maximum reaction rates after the period of induction obey approximate 4th order kinetics. As the reaction temperature increases from 5 to 180°C, the average molecular weight of the polymers formed increases from approximately 10 5 to 10 9. A model is proposed, which is consistent with these kinetics. It assumes a slow bimolecular reaction between monomers; as polymers are formed, active sites on them react rapidly with further monomer. Because fewer, but larger, polymers are formed at higher temperatures, the reaction rate is little affected by temperature. Between 5 and 90°C the total silica concentration remains constant throughout the polymerization reaction. Above 90°C, the total silica concentration progressively decreases with rising temperature, as formation of larger polymers leads to silica deposition. Deposition is accelerated by rocking the reaction vessel. At 180°C, in an Incoloy-lined vessel, the total silica concentration falls to below the quartz solubility; possibly some iron or nickel silicates are formed. At 180°C in a gold reaction vessel, the total silica concentration falls to the quartz solubility; the deposit consists of amorphous silica, cristobalite, and a trace of quartz. It is suggested that at elevated temperatures, especially in iron pipes, aerated geothermal waters could deposit silica scales, even though the silica concentration of the water is near, or even below, the amorphous silica solubility at that temperature.