Development of chewing gum model system from phytocompounds of black jamun (Syzygium cumini) pulp and study of its dissolution kinetics

Black jamun is a rich source of polyphenol and anthocyanin that provides major potential as a natural pigment. The different concentrations of encapsulated jamun pulp phytocompounds (0, 0.5, 1, 3 and 5 g 100 g-1) were incorporated with chewing gum for the development of functional food production. The study showed among variants, 5 g 100 g-1 encapsulates of black jamun pulp extract-based chewing gum (BJE-CG) showed better color stability and texture properties caused by the availability of alginate and guar gum in the encapsulates. The results revealed the dissolution behaviour of 5 g 100 g-1 based BJE-CG has a greater (P < 0.05) dissolution of total anthocyanin (TAC) and phenolic content (TPC). The dissolution kinetics model including the Korsmeyer-Peppas model, Higuchi model and Gunes model were statistically tested the dissolution rate of TAC and TPC. The Korsmeyer-Peppas model for TAC and Gunes model for TPC were found the best suitable through R2 (0.995 and 0.991) and the lowest χ2 (0.0098 and 0.0361). The dissolution kinetics study indicated the 5 g 100 g-1 based BJE-CG has the most suitable fitting in dissolution kinetics via simulated salivary fluid at 10 min. The application of the encapsulated phytocompounds shows a better solution for food and pharma industries to deliver decent plant-based pigment and phytocompounds in the food product.

Graphical abstract

A novel theoretical strategy for predicting dissolution kinetics and mechanisms of pharmaceuticals in complex biorelevant media

The influence mechanism of biorelevant media on the dissolution of active pharmaceutical ingredients (APIs) is the key to their formulation design. The dissolution kinetics of naproxen (NAP) and indomethacin (IND) in biorelevant media was systematically investigated. The dissolution mechanism was analyzed by chemical potential gradient model to explore the influence of surfactant type, pH and ionic strength. Hexadecyl trimethyl ammonium bromide (CTAB) is superior to sodium dodecyl sulfate (SDS) in promoting the dissolution of NAP and IND by increasing the solubility and accelerating the surface reaction processes. The electrostatic repulsion between SDS and NAP and IND with the same negative charge facilitates the diffusion of API, while the mutual attraction between CTAB and NAP and IND is not conducive to diffusion. High pH was favorable for the dissolution of acidic NAP and IND, as the simultaneous increase in solubility, surface reaction constant, and diffusion constant. High ionic strength was beneficial for the surface reaction of NAP and IND, but hindered their diffusion. It was shown that the modeling results were in conformity with the in vitro experimental data. These results are expected to provide theoretical supports for the design of biorelevant media and pharmaceutical formulations in the pharmaceutical development.

Formulation and Scale-Up of Fast-Dissolving Lumefantrine Nanoparticles for Oral Malaria Therapy

Lumefantrine (LMN) is one of the first-line drugs in the treatment of malaria due to its long circulation half-life, which results in enhanced effectiveness against drug-resistant strains of malaria. However, LMN's therapeutic efficacy is diminished due to its low bioavailability when dosed as a crystalline solid. The goal of this work was to produce low-cost, highly bioavailable, stable LMN powders for oral delivery that would be suitable for global health applications. We report the development of a LMN nanoparticle formulation and the translation of that formulation from laboratory to industrial scale. We applied Flash NanoPrecipitation (FNP) to develop nanoparticles with 90% LMN loading and sizes of 200-260 nm. The integrated process involves nanoparticle formation, concentration by tangential flow ultrafiltration, and then spray drying to obtain a dry powder. The final powders are readily redispersible and stable over accelerated aging conditions (50°C, 75% RH, open vial) for at least 4 weeks and give equivalent and fast drug release kinetics in both simulated fed and fasted state intestinal fluids, making them suitable for pediatric administration. The nanoparticle-based formulations increase the bioavailability of LMN 4.8-fold in vivo when compared to the control crystalline LMN. We describe the translation of the laboratory-scale process at Princeton University to the clinical manufacturing scale at WuXi AppTec.

Dissolution characteristics of uranium and lead in simulated lung fluid using fly ash samples from coal-fired power plants in the Czech Republic

Samples of fly ash, slag and boiler scale containing elevated amounts of uranium or lead (210Pb) from several coal-fired power stations in the Czech Republic were collected for an assessment of their dissolution parameters - the dissolution rates and their respective fractions in vitro. The dissolution data were fitted either by a biexponential model or by a triexponential model. The uranium 234U and 238U in the fly ash sample are classified as M-type. Similarly, type M could be attributed for most of the materials containing 210Pb. A complementary measurement of the activity concentrations of 210Pb in relation to the grain size confirmed that the radionuclide is deposited mainly in fine particles (<25 μm).

Amorphous silica dissolution kinetics in freshwater environments: Effects of Fe2+ and other solution compositional controls

The availability of dissolved silicon (DSi) exerts an important control on phytoplankton communities in freshwater environments: DSi limitation can shift species dominance to non-siliceous algae and increase the likelihood of harmful algal blooms. The availability of DSi in the water column in turn depends on the dissolution kinetics of amorphous silica (ASi), including diatoms frustules and phytoliths. Here, batch dissolution experiments conducted with diatom frustules from three diatom species and synthetic Aerosil OX 50 confirmed the previously reported non-linear dependence of ASi dissolution rate on the degree of undersaturation of the aqueous solution. At least two first-order dissolution rate constants are therefore required to describe the dissolution kinetics at high (typically, ≥0.55) and low (typically, <0.55) degrees of undersaturation. Our results further showed aqueous ferrous ion (Fe²⁺), which is ubiquitous in anoxic waters, strongly inhibited ASi dissolution. The inhibition is attributed to the preferential binding of Fe²⁺ to Q₂ groups (i.e., surface silicate groups bonded to the silica lattice via two bridging oxygen) which stabilizes the silica surface. However, further increasing the aqueous Fe²⁺ concentration likely catalyzes the detachment of Q₃ groups (i.e., silicate groups bonded to the silica lattice via three bridging oxygen) from the surface. Overall, our study illustrates the manyfold effects the aqueous solution composition, notably the inhibition effect of Fe²⁺ under anoxic conditions, has on ASi dissolution. The results help to explain the controversial redox dependence of DSi internal loading from sediments, which is vital to quantitatively understanding silicon (Si) cycling in freshwater systems.

Dissolution of titanium dioxide nanoparticles in synthetic biological and environmental media to predict their biodurability and persistence

Investigating the biodurability and persistence of titanium dioxide nanoparticles (TiO₂ NPs) is of paramount importance because these parameters influence the particles' impact on human health and the environment. Contrary to most research conducted so far, the present study elucidates the dissolution kinetics, namely the dissolution rates, rate constants, order of reaction and half-times of TiO₂ NPs in five different simulated biological fluids and two synthetic environmental media to predict their behaviour in real life situations. Results have shown that the dissolution of TiO₂ NPs in all simulated fluids was limited. Of all the simulated biological media tested, acidic media such as phagolysosomal and gastric fluid produced the highest dissolution of TiO₂ NPs compared to alkaline media such as blood plasma, Gamble's fluid, and intestinal fluid. Furthermore, when the particles were exposed to simulated environmental conditions, the dissolution was higher in high ionic strength seawater compared to freshwater. The dissolution kinetics of titanium dioxide nanoparticles followed first order reaction kinetics and were generally characterized by low dissolution rates and long half-times. These findings indicate that TiO₂ NPs are very insoluble and will remain unchanged in the body and environment over long periods of time. Therefore, these particles are most likely to cause both short and long-term health effects and will remain persistent following release into the environment.

Dissolution kinetics and solubility of copper oxide nanoparticles as affected by soil properties and aging time

Nano copper oxide (CuO NP) was added to eight soils to study the effect of aging time of copper on the concentration of diethylenetriaminepentaacetic acid (DTPA)-extracted copper (DTPA-Cu), with bulk copper oxide (CuO BP) and copper nitrate [Cu(NO₃)₂] used for comparison. Moreover, the effect of soil properties on the dissolution of CuO NP was studied. A dissolution model was used to quantitatively describe the dissolution kinetics of CuO NPs in different soils. The results showed that the concentration of DTPA-Cu decreased with increasing aging time in soils spiked with Cu(NO₃)₂, while the concentration increased to varying degrees in soils spiked with CuO NPs or CuO BPs. In acidic soils, the equilibrium concentrations of DTPA-Cu were 93.3-98.7 mg·kg^-1 for CuO NP treatments, 65.5-94.3 mg·kg^-1 for CuO BP treatments, and 81.4-90.0 mg·kg^-1 for Cu(NO₃)₂ treatments, which were greater than those in alkaline soils (43.4-56.9 mg·kg^-1, 6.26-8.61 mg·kg^-1, and 73.9-80.0 mg·kg^-1, respectively). In acidic soils, DTPA-Cu equilibrium concentration ranked the different forms of copper treatments as CuO NPs > Cu(NO₃)₂ > CuO BPs, while in alkaline soils, the order was Cu(NO₃)₂ > CuO NPs > CuO BPs. The dissolution rate constants and solubility of CuO NPs were 0.33-6.42 and 37.1-100.1 mg·kg^-1, respectively. Pearson correlation analysis indicated that the dissolution parameters of CuO NPs were negatively correlated with soil pH and positively correlated with the contents of organic matter, clay, iron oxides, and aluminum oxides. Further, the dissolution rate constant and solubility of CuO NPs could be well predicted by soil pH and the content of free or amorphous aluminum. Our study identified the main factors controlling the dissolution of CuO NPs in farmland soils and highlighted the higher availability of CuO NPs in acidic soils.

Drug loading to mesoporous silica carriers by solvent evaporation: A comparative study of amorphization capacity and release kinetics

The sorption of poorly aqueous soluble active pharmaceutical ingredients (API) to mesoporous silica carriers is an increasingly common formulation strategy for dissolution rate enhancement for this challenging group of substances. However, the success of this approach for a particular API depends on an array of factors including the properties of the porous carrier, the loading method, or the attempted mass fraction of the API. At present, there is no established methodology for the rational selection of these parameters. In the present work, we report a systematic comparison of four well-characterised silica carriers and seven APIs loaded by the same solvent evaporation method. In each case, we find the maximum amorphization capacity by x-ray powder diffraction analysis and measure the in vitro drug release kinetics. For a selected case, we also demonstrate the potential for bioavailability enhancement by a permeation essay.

Intracellular uptake of nanocrystals: Probing with aggregation-induced emission of fluorescence and kinetic modeling

Nanocrystal formulations have been explored to deliver poorly water-soluble drug molecules. Despite various studies of nanocrystal formulation and delivery, much more understanding needs to be gained into absorption mechanisms and kinetics of drug nanocrystals at various levels, ranging from cells to tissues and to the whole body. In this study, nanocrystals of tetrakis (4-hydroxyphenyl) ethylene (THPE) with an aggregation-induced emission (AIE) property was used as a model to explore intracellular absorption mechanism and dissolution kinetics of nanocrystals. Cellular uptake studies were conducted with KB cells and characterized by confocal microscopy, flow cytometry, and quantitative analyses. The results suggested that THPE nanocrystals could be taken up by KB cells directly, as well as in the form of dissolved molecules. The cellular uptake was found to be concentration- and time-dependent. In addition, the intracellular THPE also could be exocytosed from cells in forms of dissolved molecules and nanocrystals. Kinetic modeling was conducted to further understand the cellular mechanism of THPE nanocrystals based on first-order ordinary differential equations (ODEs). By fitting the kinetic model against experimental measurements, it was found that the initial nanocrystal concentration had a great influence on the dynamic process of dissolution, cellular uptake, and exocytosis of THPE nanocrystals. As the nanocrystal concentration increased in the culture media, dissolution of endocytosed nanocrystals became enhanced, subsequently driving the efflux of THPE molecules from cells.

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Nanocrystals of Tetrakis(4-hydroxyphenyl) ethylene (THPE), an aggregation-induced emission (AIE) probe was used as a model.

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THPE nanocrystals could be taken up in forms of dissolved molecules and nanocrystals.

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The dynamic process of dissolution, cellular uptake, and exocytosis of THPE nanocrystals was concentration-dependent.

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Exocytosis of intracellular THPE-NCs bore different kinetics and/or mechanisms compared with endocytosis.

Dissolution reaction kinetics and mass transfer during aqueous choline chloride pre-treatment of oak wood

Lignocellulosic biomass processing employing ionic liquids is of recent research interest for the biorefinery industry. The data on biomass dissolution kinetics in ionic liquids is important for designing scale-up pre-treatment reactor design. In this study, the reaction mechanism and kinetics of oak wood dissolution in aqueous choline chloride was investigated. In an extended effort, a correlation of dimensionless numbers was developed for the estimation the mass transfer coefficient. The analyses suggested that oak wood dissolution in choline chloride occurred in two stages. The diffusion of ionic liquid through the product layer was the dominating rate-controlling step in the first stage of dissolution followed by the surface chemical reaction in the second stage. The diffusivity of choline chloride into the oak wood matrix was ranging between 2.96E-14 and 2.84E-13 m²/s. The activation energy of the diffusion controlled stage and surface chemical reaction controlled stage was approximately 24.2 and 40.3 kJ mol^-1, respectively. The proposed mathematical correlation for mass transfer coefficient fitted well with the experimental mass transfer coefficient values.

Lead-contaminated soils with contrasting texture remediated with phosphate: chemical fractionation and chloropyromorphite stability

Pb can be stabilized in soil as Pb-P mineral. The aims of this study were to access the distribution of Pb in organic and mineral fractions of contrasting texture of soil Pb-contaminated and remediated with P and Cl and to evaluate the stability of chloropyromorphite in these soils. A clay loam Oxisol (sandstone) and a clayey Ultisol (basalt) were used in a factorial experiment, with three replications: two soils, two Pb contamination levels, two soil pH values, and four P doses. The Pb concentrations were determined in seven soil phases. Release kinetics of Pb were performed with 0.1 mol L^-1 pH 2.5 citric acid. The transfer of soil Pb to chloropyromorphite was dependent on the level of contamination in the clay loam Oxisol. In the lowest P dose (molar ratios P:Pb 3:5), the main source was the Pb complexed in the organic matter and in the highest P dose (molar ratios P:Pb 12:5) was the Pb adsorbed by inner sphere in gibbsite and kaolinite. The release of Pb in the citric acid was dependent on the texture and mineralogy of the soils. Pb recovery applied to the clay loam Oxisol was around 100% (biphasic kinetic), while for the clayey Ultisol, the recovery ranged from 43 to 52% (single-phase kinetic). Remediation of Pb-contaminated soils with P and Cl is more efficient in clayey and oxidic soils since chloropyromorphite formation is faster and its solubilization is slower, an important combination in environmental terms.

Water chemistry influences on long-term dissolution kinetics of CdSe/ZnS quantum dots

Widespread usage of engineered metallic quantum dots (QDs) within consumer products has evoked a need to assess their fate within environmental systems. QDs are mixed-metal nanocrystals that often include Cd²⁺ which poses a health risk as a nanocrystal or when leached into water. The goal of this work is to study the long-term metal cation leaching behavior and the factors affecting the dissolution processes of mercaptopropionic acid (MPA) capped CdSe/ZnS QDs in aphotic conditions. QD suspensions were prepared in different water conditions, and release of Zn²⁺ and Cd²⁺ cations were monitored over time by size exclusion chromatography-inductively coupled plasma-mass spectrometry. In most conditions with dissolved O₂ present, the ZnS shell degraded fairly rapidly over ~1 week, while some of the CdSe core remained up to 80 days. Additional MPA, Zn²⁺, and Cd²⁺ temporarily delayed dissolution, indicating a moderate role for capping agent detachment and mineral solubility. The presence of H₂O₂ and the ligand ethylenediaminetetraacetate accelerated dissolution, while NOM had no kinetic effect. No dissolution of CdSe core was observed when O₂ was absent or when QDs formed aggregates at higher concentrations with O₂ present. The shrinking particle model with product layer diffusion control best describes Zn²⁺ and Cd²⁺ dissolution kinetics. The longevity of QDs in their nanocrystal form appears to be partly controlled by environmental conditions, with anoxic, aphotic environments preserving the core mineral phase, and oxidants or complexing ligands promoting shell and core mineral dissolution.

Understanding the mobility of potential nutrients in rock mining by-products: An opportunity for more sustainable agriculture and mining

The increase in demand for highly soluble fertilizers brings a global sustainability concern. Alternative sources for traditional fertilization are therefore needed. Rock powder use has been proposed as an alternative approach to soil remineralization. However, research on the agricultural potential of minerals and rocks as alternative sources of nutrients is limited to changes in soil chemical attributes or effects on crop yield. In this work, we report an experimental study addressing the dissolution of two silicate rock-derived powders (andesite and dacite) that were produced during mining activities in Southern Brazil. The rock powders were exposed to Milli-Q water at pH (7.4-8.8) range, in solutions of 0.1 mol L^-1 citric acid at pH range 2.1-3.3, and Milli-Q water acidified with 0.5 mol l^-1 acetic acid (pH 5-5.8), in a continuous mechanical rotatory shaker at room temperature. Dissolution kinetics were determined as a function of reaction times at 24 to 5760 h, and solution pH. Based on this kinetics, dissolution rates were determined for the individual powders and compared to expected values for aluminosilicates. Based on this comparison, it was shown that the application of andesite and dacite rock-derived powder to replace high soluble fertilizers is feasible due to high dissolution rates of their minerals. The average andesite dissolution rates in Milli-Q water, in citric acid solution, and in Milli-Q water acidified with acetic acid were 2.1 × 10^-5, 1.92 × 10^-1 and 6.3 × 10^-4 mmol cm^-2 s^-1, respectively for Ca, being 183%, 22.6%, and 69.2% higher than for the dacite rock. This make andesite rock a potential substitute for carbonate-based liming. In contrast, the average dacite dissolution rates in Milli-Q water, in citric acid solution, and in Milli-Q water acidified with acetic acid were 1.05 × 10-5, 7.22 × 10^-5, and 3.72 × 10^-5 mmol cm^-2 s^-1, respectively for K, being 72.0%, 61.4%, and 73.6% higher than the andesite rock. This highlights its potential use as a K source for agriculture to replace highly soluble K-fertilizers.

Comparative analysis of ZVI materials for reductive separation of 99Tc(VII) from aqueous waste streams

Technetium-99 (Tc) is a long-lived radioactive contaminant present in legacy nuclear waste streams and contaminated plumes of the nuclear waste storage sites worldwide that poses risks for human health and the environment. Pertechnetate (TcO₄^-), the most common chemical form of Tc under oxidative conditions, is of particular concern due to its high aqueous solubility and mobility in the subsurface. One approach to treatment and remediation of TcO₄^- is reduction of Tc⁷⁺ to less soluble and mobile Tc⁴⁺ and its removal from the contaminated streams such as liquid secondary waste generated during vitrification of the Hanford low activity tank waste. Zero valent iron (ZVI) is a common reactive agent for reductive treatment of environmental contaminants, including reducible heavy metal ions, which can offer a potential solution to this challenge. Here, we present a comparative study of eleven commercial ZVI materials manufactured by different methods that were evaluated for the reductive removal of TcO₄^- from an aqueous 80 mM NaCl solution at near neutral pH representing low activity waste off-gas condensate. Performance of ZVI materials was analyzed in relation to time-dependent Fe²⁺ dissolution as well as pH and ORP profiles of the contact solution. Large variability in the efficiency and kinetics of Tc⁷⁺ reduction by different ZVI materials was contingent on their origin. ZVI materials manufactured by electrolytic method exhibited superior performance, and the kinetics of the Tc⁷⁺ reduction correlated to particle size. ZVI materials manufactured by iron pentacarbonyl reduction with hydrogen were ineffective for Tc⁷⁺ reduction. In general, our results highlight the need for thorough performance analysis of commercial ZVI materials for any contaminant of interest.

Effect of pH on phosphorus (P) dissolution and recovery from polyaluminum chlorides (PAC) sludge

Phosphorus (P) dissolution from polyaluminum chlorides (PAC) sludge was investigated for sustainable P recovery. P dissolution followed 1st order kinetics with the rate constants of 3.8 × 10^-2, 0.8 × 10^-2, 1.3 × 10^-2 and 1.9 × 10^-2 min^-1 at pH 1, 2.5, 10.5 and 12, respectively. Strong acidic and alkaline conditions dissolved about 82 (pH 1) and 88% (pH 12) of the total P by adding 0.214 g HCl and 0.357 g NaOH per gram P dissolved, respectively. Chemical P fractionation showed that more than 96% of the total P of the PAC sludge was AlP and it was reduced to 11.3 (pH 12) and 12.6% (pH 1.0) after the acid and alkali treatment. ATR-FTIR showed that AlPO₄ in the PAC sludge was transformed to Mg₃(PO₄)₂∙4H₂O and CaHPO₄∙2H₂O after alkali treatment and H₃PO₄ and Na/MgP after acid treatment. Dissolved P can be recovered by precipitation with Ca and Mg.

Quantification of kinetic rate law parameters for the dissolution of natural autunite in the presence of aqueous bicarbonate ions at high concentrations

Uranium is a key contaminant of concern in the groundwater at U.S. Department of Energy (DOE) facilities within the United States and is a potential source of groundwater contamination and a risk to human health and the environment through discharges to surface water. Dissolved inorganic carbon (bicarbonate/carbonate) has a high affinity for complexing with uranium that is present as sorbed or unique uranium-bearing mineral phases within the sedimentary matrix. This process can result in the formation of soluble uranyl carbonate aqueous species, which are mobile under circumneutral pH conditions. This study was conducted to quantify the rate of release of uranium from the autunite mineral, (Ca[(UO₂)(PO₄)]₂•3H₂O), that was formed during polyphosphate injection to remediate uranium; the dissolution of uranium was studied as a function of the aqueous bicarbonate concentration, ranging from 25 to 100 mM. Experiments were carried out in the pH range from 7 to 11 in the temperature range of 23-90 °C via single-pass flow-through testing. Consistent with the results of previous studies (Gudavalli et al., 2013a, 2013b), the rate of uranium release from autunite exhibited minimal dependency on temperature, but was strongly dependent on pH and increasing concentrations of bicarbonate in the solution. Data obtained during these experiments were compared with results of previous experiments conducted using a low-concentration range of bicarbonate solutions (0.5-3.0 mM). An 8- to 30-fold increase in the rate of uranium release was observed in the presence of high bicarbonate concentrations at pH 7-8 compared to low bicarbonate values, while at pH 9-11, there was only a 5-fold increase in uranium rate of release with an increase in bicarbonate concentrations. The rate of uranium release was calculated to be between 5.18 × 10^-8 and 1.69 × 10^-7 mol m^-2 s^-1. The activation energy values at high and low bicarbonate concentrations were similar, with ratio values in the range of 0.6-1.0.

Prolonged drug release properties for orodispersible films by combining hot-melt extrusion and solvent casting methods

Orodispersible films (ODFs) are an advantageous dosage form to accomplish patient convenience and compliance in oral drug delivery. They provide a number of special application features, such as the ease of administration without water and suitability for patients with swallowing problems. However, this promising dosage form has been limited to immediate release formulations so far. The aim of this study was to develop a thin film produced by solvent casting, which is rapidly disintegrating when placed in the mouth, but which provides prolonged drug release characteristics by incorporating drug-loaded matrix particles (MPs). MPs were produced by hot-melt extrusion and subsequent milling, using theophylline anhydrous as model drug and Eudragit^® RS as matrix-forming agent enabling prolonged drug release. ODFs were manufactured using hypromellose as film former. Dissolution studies were performed to investigate the kinetics and the duration of drug release. Additionally, disintegration time was determined using the PharmaTest^® disintegration tester equipped with a specific sample holder for ODFs. All produced ODFs containing theophylline-loaded MPs show fast disintegration while the drug release was prolonged. The degree of release prolongation increases with increasing sizes of incorporated MPs. Matrix-controlled release kinetics were found for ODFs containing MPs with at least 315 µm in size. In summary, the production of fast disintegrating ODFs with prolonged release properties was feasible. Furthermore, freely adjustable dissolution profiles could be realized for ODFs by incorporating MPs of various particle sizes.

Hydroxypropyl methylcellulose-based controlled release dosage by melt extrusion and 3D printing: Structure and drug release correlation

The objective of this study was to develop a new approach for fabrication of zero order release of active pharmaceutical ingredients (APIs) using hot-melt extrusion (HME) and 3D printing technology to generate tablets with specific 3D structures. By correlating the geometry of the 3D printed tablets with their dissolution and drug release rates, mathematical models that have been developed to describe drug release mechanisms were also studied. Acetaminophen was used as a model drug, and Benecel™ hydroxypropyl methylcellulose (HPMC) E5 and Soluplus® were used to formulate nine fuse depositional 3D-printed tablets with different inner core fill densities and outside shell thicknesses. This work reports the successful fabrication of solid-dispersion filaments with an API dispersed in HPMC based matrix via HME technology, and the production of zero order controlled release tablets with different 3D structures (tablets #3, 5, 6, and 9) using a 3D printer.

Solubility and transport of Cr(III) in a historically contaminated soil - Evidence of a rapidly reacting dimeric Cr(III) organic matter complex

Chromium is a common soil contaminant and, although it has been studied widely, questions about its speciation and dissolutions kinetics remain unanswered. We combined information from an irrigation experiment performed with intact soil columns with data from batch experiments to evaluate solubility and mobilization mechanisms of Cr(III) in a historically contaminated soil (>65 years). Particulate and colloidal Cr(III) forms dominated transport in this soil, but their concentrations were independent of irrigation intensity (2-20 mm h^-1). Extended X-ray absorption fine structure (EXAFS) measurements indicated that Cr(III) associated with colloids and particles, and with the solid phase, mainly existed as dimeric hydrolyzed Cr(III) bound to natural organic matter. Dissolution kinetics of this species were fast (≤1 day) at low pH (<3) and slightly slower (≤5 days) at neutral pH. Furthermore, it proved possible to describe the solubility of the dimeric Cr(III) organic matter complex with a geochemical equilibrium model using only generic binding parameters, opening the way for use of geochemical models in risk assessments of Cr(III)-contaminated sites.

Calcite dissolution rate spectra measured by in situ digital holographic microscopy

Digital holographic microscopy in reflection mode is used to track in situ, real-time nanoscale topography evolution of cleaved (104) calcite surfaces exposed to flowing or static deionized water. The method captures full-field holograms of the surface at frame rates of up to 12.5 s-1. Numerical reconstruction provides 3D surface topography with vertical resolution of a few nanometers and enables measurement of time-dependent local dissolution fluxes. A statistical distribution, or spectrum, of dissolution rates is generated by sampling multiple area domains on multiple crystals. The data show, as has been demonstrated by Fischer et al. (2012), that dissolution is most fully described by a rate spectrum, although the modal dissolution rate agrees well with published mean dissolution rates (e.g., 0.1 µmol m-2 s-1 to 0.3 µmol m-2 s-1). Rhombohedral etch pits and other morphological features resulting from rapid local dissolution appear at different times and are heterogeneously distributed across the surface and through the depth. This makes the distribution in rates measured on a single crystal dependent both on the sample observation field size and on time, even at nominally constant undersaturation. Statistical analysis of the inherent noise in the DHM measurements indicates that the technique is robust and that it likely can be applied to quantify and interpret rate spectra for the dissolution or growth of other minerals.

Impacts of hydrologic variations on chemical weathering and solute sources in the Min River basin, Himalayan-Tibetan region

Feedback between hydrologic variations and chemical weathering is thought to play a crucial role in modulating global carbon cycling. The mechanisms associated with the impacts of hydrologic variations on solute sources and chemical weathering were evaluated by examining the relationships between river discharge and hydrochemistry based on high-frequency sampling of the Min River, which originates in the Himalayan-Tibetan region. Fluid transit times and flow pathways vary with changes in discharge, thereby affecting various biogeochemical processes. Although shorter transit times occur during the high-flow season than during the low-flow season, concentrations of chemical weathering products exhibit chemostatic behaviour (less variation than changes in discharge) in response to increasing discharge due to hydrologic flushing of minerals, which increases the amount of reactive mineral surface area. The contributions of various sources to dissolved loads in the Min River were estimated using a forward model. The calculated annual carbonate and silicate weathering fluxes are 24.1 and 9.6 t/km² year, respectively. Atmospheric contributions increase with increasing discharge, whereas the contributions of silicate weathering decrease with increasing discharge. Both the carbonate weathering flux (F_Carb) and silicate weathering flux (F_Sil) are positively correlated with the discharge, indicating that temporal variations in chemical weathering fluxes in the Min River are highly affected by hydrologic variations. The slope of the relationship between F_Carb and discharge is much greater than that between F_Sil and discharge due to the rapid dissolution of carbonate minerals, suggesting that carbonate weathering is more sensitive than silicate weathering to hydrologic variations. This study demonstrates that high-frequency sampling is necessary when investigating solute sources and chemical weathering processes in river basins influenced by a monsoon climate.

In situ nanoscale observations of gypsum dissolution by digital holographic microscopy

Recent topography measurements of gypsum dissolution have not reported the absolute dissolution rates, but instead focus on the rates of formation and growth of etch pits. In this study, the in situ absolute retreat rates of gypsum (010) cleavage surfaces at etch pits, at cleavage steps, and at apparently defect-free portions of the surface are measured in flowing water by reflection digital holographic microscopy. Observations made on randomly sampled fields of view on seven different cleavage surfaces reveal a range of local dissolution rates, the local rate being determined by the topographical features at which material is removed. Four characteristic types of topographical activity are observed: 1) smooth regions, free of etch pits or other noticeable defects, where dissolution rates are relatively low; 2) shallow, wide etch pits bounded by faceted walls which grow gradually at rates somewhat greater than in smooth regions; 3) narrow, deep etch pits which form and grow throughout the observation period at rates that exceed those at the shallow etch pits; and 4) relatively few, submicrometer cleavage steps which move in a wave-like manner and yield local dissolution fluxes that are about five times greater than at etch pits. Molar dissolution rates at all topographical features except submicrometer steps can be aggregated into a continuous, mildly bimodal distribution with a mean of 3.0 µmolm-2 s-1 and a standard deviation of 0.7 µmolm-2 s-1.

Interfacial kinetics in a model emulsion polymerisation system using microelectrochemical measurements at expanding droplets (MEMED) and time lapse microscopy

Physicochemical processes that take place at the oil-water interface of an epoxy-amine emulsion polymerisation system influence the properties and structural morphology of the polymeric microparticles formed. Investigating these processes, such as the transport of monomers across the liquid/liquid interface brings new understanding which can be used to tune polymeric morphology. Two different approaches are used to provide new insights on these processes. Microelectrochemical measurements at expanding droplets (MEMED) is used to measure the transfer of amine from an organic phase comprised of epoxide and amine into an aqueous receptor phase. The rate of amine transfer across the liquid/liquid interface is characterised using MEMED and finite element method modelling and kinetic values are reported. Time lapse microscopy of epoxide droplets held in deionised water or an aqueous amine solution heated to different temperatures is further used to characterise epoxide dissolution into the aqueous phase. Mass-transport of epoxide into the aqueous phase is shown to be temperature-dependent. Epoxide homopolymerisation at the droplet-water interface is found to influence the rate of epoxide droplet dissolution. The rate of the epoxy-amine cure reaction is shown to be faster than the rate of the epoxide homopolymerisation reaction. The combination of methods used here is not limited to emulsion polymerisation and should find application in a myriad of processes at liquid/liquid interfaces.

Assessment of solvents for cellulose dissolution

A necessary step in the processing of biomass is the pretreatment and dissolution of cellulose. A good solvent for cellulose involves high diffusivity, aggressiveness in decrystallization, and capability of disassociating the cellulose chains. However, it is not clear which of these factors and under what conditions should be improved in order to obtain a more effective solvent. To this end, a newly-developed phenomenological model has been applied to assess the controlling mechanism of cellulose dissolution. Among the findings, the cellulose fibers remain crystalline almost to the end of the dissolution process for decrystallization-controlled kinetics. In such solvents, decreasing the fiber crystallinity, e.g., via pretreatment, would result in a considerable increase in the dissolution rate. Such insights improve the understanding of cellulose dissolution and facilitate the selection of more efficient solvents and processing conditions for biomass. Specific examples of solvents are provided where dissolution is limited due to decrystallization or disentanglement.

Combinatorial localized dissolution analysis: Application to acid-induced dissolution of dental enamel and the effect of surface treatments

A combination of scanning electrochemical cell microscopy (SECCM) and atomic force microscopy (AFM) is used to quantitatively study the acid-induced dissolution of dental enamel. A micron-scale liquid meniscus formed at the end of a dual barrelled pipette, which constitutes the SECCM probe, is brought into contact with the enamel surface for a defined period. Dissolution occurs at the interface of the meniscus and the enamel surface, under conditions of well-defined mass transport, creating etch pits that are then analysed via AFM. This technique is applied to bovine dental enamel, and the effect of various treatments of the enamel surface on acid dissolution (1mM HNO3) is studied. The treatments investigated are zinc ions, fluoride ions and the two combined. A finite element method (FEM) simulation of SECCM mass transport and interfacial reactivity, allows the intrinsic rate constant for acid-induced dissolution to be quantitatively determined. The dissolution of enamel, in terms of Ca(2+) flux ( [Formula: see text] ), is first order with respect to the interfacial proton concentration and given by the following rate law: [Formula: see text] , with k0=0.099±0.008cms(-1). Treating the enamel with either fluoride or zinc ions slows the dissolution rate, although in this model system the partly protective barrier only extends around 10-20nm into the enamel surface, so that after a period of a few seconds dissolution of modified surfaces tends towards that of native enamel. A combination of both treatments exhibits the greatest protection to the enamel surface, but the effect is again transient.

Determination of nanosilver dissolution kinetics and toxicity in an environmentally relevant aqueous medium

Assessing the dissolution of silver nanoparticles (AgNPs) in laboratory test media and in the aquatic environment is critical for determining toxicity. In the present study, the ion-release kinetics for 20-nm, 50-nm, and 80-nm AgNPs in environmentally relevant freshwaters with different electrical conductivity values (30 µS/cm, 150 µS/cm) were examined and related to the associated impact on Daphnia magna. The acute toxicity of the AgNP suspensions to D. magna was assessed after 0 d and 7 d of interaction time between the particles and test media. When 48-h lethal median concentrations were expressed as total silver, D. magna was more sensitive to AgNPs suspended in low ionic strength media relative to higher ionic strength media, with the exception of 50-nm AgNPs suspended in the 150-µS/cm medium. A 3.3-fold increase in hydrodynamic diameter measured by dynamic light scattering and field flow fractionation was observed over time for 20-nm particles in the 150-µS/cm medium, but only a small increase in aggregation size for 50-nm and 80-nm particles (1.4-fold and 1.2-fold increase, respectively) was observed. At a lower conductivity of 30 µS/cm, a 1.7-fold, 1.0-fold, and 1.2-fold increase in aggregation size was observed in the 20-nm, 50-nm, and 80-nm particles, respectively. Thus, the impact of higher conductivity test media on increased aggregation and decreased toxicity (after 7 d) was relatively greater for the smaller (20-nm) AgNP higher compared to the 50-80 nm AgNPs.

Mesoporous carbon with spherical pores as a carrier for celecoxib with needle-like crystallinity: improve dissolution rate and bioavailability

The purposes of this investigation are to design mesoporous carbon (MC) with spherical pore channels and incorporate CEL to it for changing its needlelike crystal form and improving its dissolution and bioavailability. A series of solid-state characterization methods, such as SEM, TEM, DSC and XRD, were employed to systematically investigate the existing status of celecoxib (CEL) within the pore channels of MC. The pore size, pore volume and surface area of samples were characterized by nitrogen physical absorption. Gastric mucosa irritation test was carried out to evaluate the safety of mesoporous carbon as a drug carrier. Dissolution tests and in vivo pharmacokinetic studies were conducted to confirm the improvement in drug dissolution kinetics and oral bioavailability. Uptake experiments were conducted to investigate the mechanism of the improved oral bioavailability. The results of solid state characterization showed that MC was prepared successfully and CEL was incorporated into the mesoporous channels of the MC. The crystallinity of CEL in MC was affected by different loading methods, which involve evaporation method and melting method. The dissolution rate of CEL from MC was found to be significantly higher than that of pure CEL, which attributed to reduced crystallinity of CEL. The gastric mucosa irritation test indicated that the MC caused no harm to the stomach and produced a protective effect on the gastric mucosa. Uptake experiments indicated that MC enhanced the amount of CEL absorbed by Caco-2 cells. Moreover, oral bioavailability of CEL loaded within the MC was approximately 1.59-fold greater than that of commercial CEL. In conclusion, MC was a safe carrier to load water insoluble drug by controlling the crystallinity or crystal form with improvement in drug dissolution kinetics and oral bioavailability.

Nano-cellulosic materials: the impact of water on their dissolution in DMAc/LiCl

The dissolution behaviour of disassociated cellulosic materials in N,N-dimethylacetamide/lithium chloride (DMAc/LiCl) was investigated. The parameters monitored were chromatographic elution profiles and recovered mass by means of gel permeation chromatography (GPC) with RI detection. In order to elucidate the impact of the disassembly on cellulosic fibres, comparative studies were performed with the non-disassociated cellulose counterparts. The importance of the presence of water was addressed by Karl Fischer titration and solvent exchange experiments. Morphological changes during the dissolution process were studied by scanning electron microscopy (SEM). Dissolution of fibrillated cellulosic materials is impeded compared to the non-fibrillated material. This is a consequence of the high-surface-area fibrils prone to retain high amounts of water. Dissolution behaviour of nano-crystalline cellulosic materials appeared to be source-dependent. Due to the absence of entangled networks, these materials retain only water bound at the surface of the nano-crystallites, indicative of both the exposed surface area and solubility. The small cellulose nano-particles extracted from dissolving pulp show lower solubility compared to the large NCC particles from cotton.