Slow Dissolution Rate Research Articles

Crystallization and morphology of mordenite zeolite influenced by various parameters in organic-free synthesis

A series of mordenite zeolites with different morphologies were synthesized via a facile organic-free hydrothermal route, and characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectrometer and N 2 adsorption–desorption techniques. Influences of synthetic parameters, including seed crystal, silicon precursor, SiO 2/Al 2O 3, Na 2O/SiO 2 and H 2O/SiO 2, on mordenite crystallization were investigated systematically. It was found that mordenite zeolites with various morphologies, such as fiber-like, rod-like, prism-like and needle-like ones could be synthesized in control. Especially, novel nano fiber-like MOR crystals with high c/ b aspect ratio were prepared from low silica concentration system, which was manipulated by using small initial SiO 2/Al 2O 3 ratio, large H 2O/SiO 2 and silicon source with slow dissolution rate. Moreover, mordenite samples with various morphologies exhibited different mesopore property and thermal stability.

Physicochemical Characterization and Dissolution Study of Solid Dispersions of Ketoconazole with Nicotinamide

The aim of the present study was to improve the solubility and dissolution rate of a poorly water-soluble drug ketoconazole using solid dispersion technique. Solid dispersions of ketoconazole were prepared in ratios of 90 : 10, 70 : 30, 50 : 50, 30 : 70 and 10 : 90 by the melting method using nicotinamide as carrier. These solid dispersions were characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy to ascertain if there were any physicochemical interactions between drug and carrier that could affect dissolution. Solubility and dissolution studies were conducted with pure ketoconazole, physical mixtures and solid dispersions. Solubility studies indicated that nicotinamide increased significantly the solubility of ketoconazole in water. The Gibbs free energy (ΔG°(tr)) values were negative indicating the spontaneous nature of ketoconazole solubilization, and it decreased with increase in concentration of the carrier, demonstrating that the reaction became more favorable as the concentration of the carrier increased. The cumulative release of ketoconazole within 120 min from solid dispersion at a drug-to-nicotinamide ratio of 10 : 90 (w/w) was 6 times higher than the pure drug in phosphate buffer of pH 6.8. Solid state characterization indicated that there is no interaction between ketoconazole and nicotinamide in the solid state. In contrast to the very slow dissolution rate of pure ketoconazole, the dispersion of the drug in nicotinamide considerably enhanced the dissolution rate. The drug dissolution rate was highest at a drug-to-nicotinamide ratio of 10 : 90 (w/w).

Mechanism of enargite pressure leaching in the presence of pyrite

Hydrometallurgy is a promising alternative to treat copper concentrates that contain large amounts of enargite (Cu 3AsS 4). However, leaching of enargite is difficult due to its slow dissolution rate in acidic solutions. The pressure leaching of an enargite concentrate containing about 40% pyrite was carried out in sulfuric acid/oxygen at temperatures in the range of 160 to 200 °C and oxygen partial pressure of 345 to 1034 kPa. The results showed that the dissolution of enargite in the presence of pyrite was considerably faster than the dissolution of pure enargite. By leaching an enargite–pyrite concentrate sample of particle size −75 + 53 μm at 200 °C and 689 kPa O 2, all the copper was extracted in 15 min. It was also found that temperature, oxygen partial pressure and particle size had a significant influence on the rate of enargite dissolution from the enargite–pyrite concentrate, while the sulfuric acid concentration had little effect. Ferric ions produced in the leaching were responsible for the enhanced dissolution of enargite in the presence of pyrite and pure enargite leaching was similarly enhanced by the addition of ferrous ions. Analysis of the data for the enargite–pyrite concentrate showed linear kinetics for the dissolution of pyrite, whilst the rate of dissolution of enargite increased substantially with time as ferric ions build up in solution.

Dissolution Modeling of Bead Formulations and Predictions of Bioequivalence for a Highly Soluble, Highly Permeable Drug

The objective of this study was to assess the impact of observed in vitro dissolution rate differences on in vivo pharmacokinetics for two enteric-coated bead formulations of a highly soluble, highly permeable drug. A new bead dissolution model was developed to quantitatively simulate the dissolution profiles of the two formulations. The model is based on the boundary layer diffusion model and can be used to simulate dissolution profiles for bead formulations using physicochemical properties of the formulation. The model was applied to show that the observed differences in dissolution profiles can be attributed completely to the difference in surface area of the beads for the two formulations. An absorption/pharmacokinetic model (GastroPlus) was used to predict the in vivo plasma concentration time profiles for the formulations using their respective in vitro dissolution profiles as input. The simulation results showed that the plasma concentration-time profiles were not significantly impacted by slower dissolution rates. Additionally, a sensitivity analysis was performed with a range of dissolution rate profiles. The fastest dissolution rate reached 80% dissolved in 41 min, while the slowest reached 80% in 114 min. Over this range, the predicted C(max) decreased by 9% and the AUC decreased by 1%. An in vivo bioequivalence study on the two experimental formulations demonstrated the formulations were bioequivalent, consistent with predictions. The lack of sensitivity is attributable to the high permeability and long elimination half-life of the drug. The work presented in this article demonstrates the use of a bead dissolution model and an absorption/PK model to predict in vivo formulation performance.

Dissolution enhancement of drugs. part i: technologies and effect of carriers

For complete absorption and good bioavailability of orally administered drug, the drug must be dissolved in gastric fluids. Dissolution of drug is the rate-controlling step which determines the rate and degree of absorption. Drugs with slow dissolution rates generally show erratic and incomplete absorption leading to low bioavailability when administered orally. Since aqueous solubility and slow dissolution rate of BCS class II and class IV drugs is a major challenge in the drug development and delivery processes, improving aqueous solubility and slow dissolution of BCS Class II and Class IV drugs have been investigated extensively. Various techniques have been used in attempt to improve solubility and dissolution rates of poorly water soluble drugs which include solid dispersion, micronization, lipid based formulations, melt granulation, direct compaction, solvent evaporation, coprecipitation, adsorption, ordered mixing, liquisolid compacts, solvent deposition inclusion complexation and steam aided granulation. In these techniques carrier plays an important role in improving solubility and dissolution rate. Polymers, superdisintegrants, surfactants are extensively studied in recent years for dissolution enhancement in drugs. This part of this review discusses technological overview and effect of polymers, superdisintegrants and surfactants on dissolution enhancement of drugs while Part II [Int J Health Res, Sept 2009; 2(3)] describes the role and applications of cyclodextrins, carbohydrates, hydrotropes, polyglocolized glycerides, dendrimers, acids and miscellaneous carriers in enhancing dissolution of drugs. Keywords: Dissolution enhancement; aqueous solubility, water soluble carriers; BCS class II, excipients.

Geochemistry, dissolved elemental flux rates, and dissolution kinetics of lithologies of Alaknanda and Bhagirathi rivers in Himalayas, India

Alaknanda and Bhagirathi (AB) river basins in the Himalayan region in India expose lithologies comprising mainly of granites, low–high-grade metamorphics, shales and carbonates which, in conjunction with the monsoon rains and glacial melt, control water chemistry and dissolved elemental flux rates. In the present study, we monitored two locations: (a) Srinagar on the Alaknanda river and (b) Maneri on the Bhagirathi river for daily variations in total suspended sediments, major ions and dissolved silica over one complete year (July 2004–June 2005). Based on long-term discharge data, discharge-weighted composition and dissolved elemental flux rates (with respect to Ca, Mg, HCO3, Si) of the river were estimated. The information thus obtained has substantially added up to the existing chemical data of these rivers and has refined the flux rates. Our high-frequency samples provide informations such as (a) water chemical compositions that show a large temporal and spatial variation and (b) carbonate lithology that controls water chemistry predominantly. The dissolution kinetics of various lithologies namely leucogranite, gneiss, quartzite, phyllite and shale of the AB river basins were studied through batch experiments at controlled temperature (25 and 5°C) and pH (8.4) condition. In laboratory, these lithologies undergo slow rates of dissolution (10−13 to 10−15 mol/m2 s), while field weathering rates based on dissolved elemental flux rates in the AB rivers are much higher (10−8 to 10−9 mol/m2 s). Extremely high physical weathering rates in AB rivers, which enhance chemical weathering significantly, mainly attribute this wide discrepancy in laboratory-derived rates of representative basin rocks and dissolved elemental fluxes in the field. However, laboratory-simulated experiments facilitate to quantify elemental release rates, understand the kinetics of the dissolution reactions, and compare their roles at individual level.

Formulation and in-vivo evaluation of l-cysteine chewing gums for binding carcinogenic acetaldehyde in the saliva during smoking

Cigarette smoke contains toxic amounts of acetaldehyde that dissolves in saliva, posing a significant risk of developing oral, laryngeal and pharyngeal carcinomas. L-cysteine, a non-essential amino acid, can react covalently with carcinogenic acetaldehyde to form a stable, non-toxic 2-methylthiazolidine-4-carboxylic acid. The main aim of this study was to find out whether it is possible to develop a chewing gum formulation that would contain cysteine in amounts sufficient to bind all the acetaldehyde dissolved in saliva during the smoking of one cigarette. The main variables in the development process were: (1) chemical form of cysteine (L-cysteine or L-cysteine hydrochloride), (2) the amount of the active ingredient in a gum and (3) manufacturing procedure (traditional or novel compression method). Saliva samples were taken over 2.5 minutes before smoking and since smoking was started for 2.5 minutes periods for 10 minutes. During a five minutes smoking period with a placebo chewing gum, acetaldehyde levels increased from 0 to 150-185 microM. Once smoking was stopped, the acetaldehyde levels quickly fell to levels clearly below the in-vitro mutagenic level of 50 microM. All chewing gums containing cysteine could bind almost the whole of the acetaldehyde in the saliva during smoking. However, elimination of saliva acetaldehyde during smoking does not make smoking completely harmless. Cysteine as a free base would be somewhat better than cysteine hydrochloride due to its slower dissolution rate. Both traditional and direct compression methods to prepare chewing gums can be utilized and the dose of L-cysteine required is very low (5 mg).

Rapid dissolution of shells of weakly calcified Antarctic benthic macroorganisms indicates high vulnerability to ocean acidification

AbstractAntarctic calcified macroorganisms are particularly vulnerable to ocean acidification because many are weakly calcified, the dissolution rates of calcium carbonate are inversely related to temperature, and high latitude seas are predicted to become undersaturated in aragonite by the year 2100. We examined the post-mortem dissolution rates of aragonitic and calcitic shells from four species of Antarctic benthic marine invertebrates (two bivalves, one limpet, one brachiopod) and the thallus of a limpet shell-encrusting coralline alga exposed to acidified pH (7.4) or non-acidified pH (8.2) seawater at a constant temperature of 4°C. Within a period of only 14–35 days, shells of all four species held in pH 7.4 seawater had suffered significant dissolution. Despite calcite being 35% less soluble in seawater than aragonite, there was surprisingly, no consistent pattern of calcitic shells having slower dissolution rates than aragonitic shells. Outer surfaces of shells held in pH 7.4 seawater exhibited deterioration by day 35, and by day 56 there was exposure of aragonitic or calcitic prisms within the shell architecture of three of the macroinvertebrate species. Dissolution of coralline algae was confirmed by differences in weight loss in limpet shells with and without coralline algae. By day 56, thalli of the coralline alga held in pH 7.4 displayed a loss of definition of the conceptacle pores and cracking was evident at the zone of interface with limpet shells. Experimental studies are needed to evaluate whether there are adequate compensatory mechanisms in these and other calcified Antarctic benthic macroorganisms to cope with anticipated ocean acidification. In their absence, these organisms, and the communities they comprise, are likely to be among the first to experience the cascading impacts of ocean acidification.

Dissolution Factors of Ta, Th, and U Oxides Present in Pyrochlore

Air pollution can be a problem in industrial processes, but monitoring and controling the aerosols in the work place is not enough to estimate the occupational risk due to dust particle inhalation. The solubility in lung fluid is considered to estimate this risk. The aim of this study is to determine in vitro specific dissolution parameters for thorium (Th), uranium (U), and tantalum (Ta) associated to crystal lattice of a niobium mineral (pyrochlore). Th, U, and Ta dissolution factors in vitro were obtained using the Gamble solution (simulant lung fluid, SLF), particle induced X-ray emission, and alpha spectrometry as analytical techniques. Ta, Th, and U are present in the pyrochlore crystal lattice as oxide; however, they have shown different dissolution parameters. The rapid dissolution fraction (f r), rapid dissolution rate (λ r), slow dissolution rate (f s), and slow dissolution fraction (λ s) measured for tantalum oxide were equal to 0.1 and 0.45 and 0.00007 day−1, respectively. For uranium oxide, f r was equal to 0.05, λ r was equal to 1.1 day−1, and λ s was equal to 0.000068 day−1. For thorium oxide, f r was 0.025, λ r was 1.5 day−1, and λ s was 0.000065 day−1. These results show that chemical behavior of these three compounds in the SLF could not be represented by the same parameter. The ratio of uranium concentration in urine and feces samples from workers exposed to pyrochlore dust particle was determined. These values agree with the theoretical values of estimated uranium concentration using specific parameters for uranium oxide present in pyrochlore.

Physicochemical Properties of Solid Dispersions of Gliclazide in Polyvinylpyrrolidone K90

INTRODUCTIONGliclazide is a second generation hypoglycemic sulfonyl-urea which is useful in the treatment of type 2 diabetesmellitus (1). Following oral administration, however, glicla-zide exhibits slow rate of absorption and interindividualvariation in bioavailability. Statedproblemsofgliclazidemightbe due to its poor water solubility and slow dissolution rate (2–4). But gliclazide exhibits good tolerability, low incidence ofhypoglycemiceffect, low rate ofsecondary failure,and low rateof progression of diabetic retinopathy (2,5). Hence, gliclazideappearstobeadrugofchoiceinlong-termsulfonylureatherapyfor treatment of type 2 diabetes mellitus. Few attempts havebeen made for improvement of solubility and bioavailability ofgliclazide including complexation with cyclodextrin (6,7)orcyclodextrin–hydroxypropylmethylcellulose (8) and using PEG400 (9) as per present literature. The authors investigated thephysicochemical characteristics and dissolution behaviors ofgliclazide in physical mixtures as well as solid dispersions withpolyethylene glycol 6000 in a previous study (10).The main objective of this work was to investigate thephysicochemical characteristics of gliclazide in physical mix-tures (PMs) and solid dispersions (SDs) prepared by usingpolyvinylpyrrolidone K90 (PVP K90). The possible interac-tions between gliclazide and PVP K90 in both solid and liquidstates were investigated. Interaction in solid state was investi-gated by Fourier-transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, and differential scanningcalorimetry (DSC). Interaction in solution was studied byphase solubility analysis and dissolution experiments.MATERIALS AND METHODSMaterialsA gift sample of gliclazide was received from AristoPharmaceuticals Ltd. (Mumbai, India). PVP K90 was re-ceived from BASF (Germany). Double-distilled water wasused throughout the study and all the other chemicals usedwere of analytical grade.Preparation of SDsThe SDs of gliclazide with PVP K90 containing threedifferent weight ratios (1:1, 1:2, 1:5; gliclazide/PVP K90) anddenoted as SD 1/1, SD 1/2, and SD 1/5, respectively, wereprepared by solvent evaporation method. In the solventevaporation method, to a solution of gliclazide in chloroform,an appropriate amount of PVP K90 in solution was added.The solvent was evaporated under reduced pressure at 40°Cby using a rotary evaporator and the resulting residue wasdried under vacuum for 3 h. The mixture was storedovernight in a desiccator. The hardened mixture was pow-dered in a mortar, sieved through a 100-mesh screen, andstored in a screw-cap vial at room temperature until furtheruse (11,12).The PMs having the same weight ratio as SDs wereprepared by thoroughly mixing the required amount ofgliclazide and PVP K90 for 10 min in a mortar. The resultingmixtures were sieved through a 100-mesh sieve and denotedas PM 1/1, PM 1/2, and PM 1/5, respectively. The mixtureswere stored in a screw-cap vial at room temperature untiluse.Phase Solubility of GliclazideSolubility determinations were performed in triplicateaccording to the method of Higuchi and Connors (13). Inbrief, an excess amount of gliclazide was taken into a screw-capped glass vial to which 20 ml of aqueous solutioncontaining various concentrations of PVP K90 was added.Then, the samples were shaken at 37±0.5°C for 72 h in awater bath (Remi Pvt Ltd, Mumbai). After 72 h, sampleswere filtered through a 0.45-μm membrane filter. The filtratewas suitably diluted and analyzed spectrophotometrically at thewavelength of 227 nm using a UV–VIS spectrophotometer(Shimadzu 1700, Pharm Spec, Japan).329

Preparation and characterization of spironolactone nanoparticles by antisolvent precipitation

Due to low aqueous solubility and slow dissolution rate, spironolactone, a synthetic steroid diuretic, has a low and variable oral bioavailability. Nanoparticles were thus prepared by antisolvent precipitation in this work for accelerating dissolution of this kind of poorly water-soluble drugs. Effects of surfactant type/concentration and feed drug concentration on the precipitated particle size were evaluated. It was found that introduction of spironolactone solution in N-methyl-2-pyrrolidone (NMP) to the antisolvent water can produce the particles in the submicron range with hydroxypropyl methylcellulose (HPMC) as the stabilizer. The particle size decreased with the increase of HPMC concentration from 0 to 0.125% (w/v), further increase of which did not affect the size significantly. Increasing feed drug concentration from 10 to 100 mg/ml resulted in the particle size decrease. In comparison with raw drug, the chemical structure of nanosized spironolactone was not changed but the crystallinity was reduced. Dissolution of spironolactone nanoparticles in 0.1 M HCl was 2.59 times faster than raw drugs in 60 min.

Toward an Increased Understanding of the Barriers to Colonic Drug Absorption in Humans: Implications for Early Controlled Release Candidate Assessment

The purpose of this study was to increase the understanding of in vivo colonic drug absorption in humans by summarizing and evaluating all regional in vivo human absorption data with focus on the interpretation of the colonic absorption data in relation to intestinal permeability and solubility. In addition, the usefulness of the Biopharmaceutics Classification System (BCS) in early assessment of the in vivo colonic absorption potential of controlled release drug candidates was investigated. Clinical regional absorption data (Cmax, Tmax, and AUC) of 42 drugs were collected from journal articles, abstracts, and internal reports, and the relative bioavailability in the colon (Frel(colon)) was obtained directly or calculated. Bioavailability, fraction dose absorbed, and information if the compounds were substrates for P-glycoprotein (P-gp) or cytochrome P450 3A (CYP3A) were also obtained. The BCS I drugs were well absorbed in the colon (Frel(colon) > 70%), although some drugs had lower values due to bacterial degradation in the colon. The low permeability drugs (BCS III/IV) had a lower degree of absorption in the colon (Frel(colon) < 50%). There was a clear correlation between in vitro Caco-2 permeability and Frel(colon), and atenolol and metoprolol may function as permeability markers for low and high colonic absorption, respectively. No obvious effect of P-gp on the colonic absorption of the drugs in this study was detected. There was insufficient data available to fully assess the impact of low solubility and slow dissolution rate. The estimated in vivo fractions dissolved of the only two compounds administered to the colon as both a solution and as solid particles were 55% and 92%, respectively. In conclusion, permeability and solubility are important barriers to colonic absorption in humans, and in vitro testing of these properties is recommended in early assessment of colonic absorption potential.

Enhancing process kinetics for mineral carbon sequestration

Abstract The current low-cost process for mineral carbonation involves the direct carbonation of a slurry of magnesium or calcium silicate mineral with supercritical CO 2 . The process is currently limited by the slow reaction kinetics of the carbonation reactions, and in particular the slow dissolution rates of the silicates in weakly acidic conditions. Enhancing the dissolution rate in weakly acidic conditions has been identified as one of the main opportunities for lowering the costs of a direct mineral carbonation process. Serpentine has been identified by its reactivity and abundance as a potential mineral for use in a mineral carbonation process. In this paper we discuss the results of dissolution experiments in which ground serpentine was reacted in weakly acidic aqueous systems containing NH4Cl, NaCl,, sodium citrate, sodium EDTA, sodium oxalate, and sodium acetate. All experiments are carried out at 120 ∘ C and under 20 bars of CO 2 in a batch autoclave. It was found that the sodium salts of citrate, oxalate, and EDTA significantly enhance the dissolution of serpentine under weakly acidic conditions.

Quantification of individual phosphorus species in sediment: a sequential conversion and extraction method

Common sequential phosphorus (P) extraction methods are not specific to particular chemical species and have several limitations. This work presents the first chemical method for quantification of individual mineral and sorbed P species. It was developed by combining a conversion technique with a sequential extraction procedure. Mangrove sediments with different characteristics were incubated in pH-adjusted 0.01 M CaCl 2 with and without reference material additions of octacalcium phosphate (Ca 8 H 2 (PO 4 ) 6 .5H 2 O; OCP), hydroxyapatite (Ca 5 (PO 4 ) 3 OH), strengite (FePO 4 .2H 2 O) or variscite (AIPO 4 .2H 2 O). The changes in soluble phosphate concentration were measured in the supernatant solution, while pH-induced variations in P composition were determined by subsequent sequential extraction of the sediments. Dissolved phosphate concentration was controlled by adsorption below pH 7.8. Above this pH, soluble phosphate concentration was governed by OCP, which was qualitatively determined by plotting the experimental values of pH + pH 2 PO 4 and pH - 0.5 pCa on a solubility diagram including the isotherms of known crystalline phosphate compounds. In contrast to the often-predicted slow dissolution rate of crystalline phosphates in soils or sediments, drastic changes in P composition by dissolution, precipitation and adsorption processes were detected after 7 days. These were mainly not observed indirectly by changes in dissolved phosphate through adsorption effects, but were determined quantitatively by subsequent sequential extraction, thus enabling the quantification of individual species. Evaluation of the method was performed by standard addition experiments. Besides P species quantification, the method provides the means for other applications, such as the determination of P mineral dissolution kinetics in soils and sediments, the prediction of P composition in changing environmental settings and the refinement of theoretical models of phosphate solubility in soil and sedimentary environments.

UNCERTAINTY ANALYSIS OF DOSES FROM INHALATION OF DEPLETED URANIUM

Measurements of uranium excreted in urine have been widely used to monitor possible exposures to depleted uranium (DU). This paper describes a comprehensive probabilistic uncertainty analysis of doses determined retrospectively from measurements of DU in urine. Parametric uncertainties in the International Commission on Radiological Protection (ICRP) Human Respiratory Tract Model (HRTM) and ICRP systemic model for uranium were considered in the analysis, together with uncertainties in an alternative model for particle removal from the lungs. Probability distributions were assigned to HRTM parameters based on uncertainties documented in ICRP Publication 66 and elsewhere, including the Capstone study of aerosols produced after DU penetrator impacts. Uncertainties in the uranium systemic model were restricted to transfer rates having the greatest effect on urinary excretion, and hence retrospective dose assessments, over the measurement times considered (10-10(4) d). The overall uncertainty on dose (the ratio of the upper and lower quantiles, q0.975/q0.025) was estimated to be about a factor of 50 at 10 days after intake and about a factor of 10 at 10(3)-10(4) d. The dose to the lung dominated the committed effective dose, with the lung absorption parameters, particularly the slow dissolution rate, ss, dominating the overall uncertainty. The median dose determined from a measurement of 1 ng DU, collected in urine in a 24-h period, varied from 0.1 microSv at 10 d to about 1 mSv at 10(4) d. Despite the large uncertainties, the upper q0.975 quantile for the assessed dose was below 1 mSv up to 5,000 d.

Surface Morphological Changes Accompanying Dissolution of Bioactive Glass: Effect of Residual Stress

We report our observations concerning the time evolution of surface morphology occurring during the in vitro immersion of bioactive glass surfaces in contact with phosphate buffer solution. We compare regions under intentionally produced residual stresses via micro-indentation to those where no indentation was performed. The sign of the residual stress is shown to be important for predicting dissolution behaviour; compression retards dissolution, whereas tension enhances dissolution. We analyze our results with a simple model for the work of bond dissociation. We report that a highly constrained residual compressive stress state, such as in an indent, leads to a work deficit in comparison to tension, which accounts for the slower dissolution rate of compressed bioactive glass. Such a mechanochemical effect suggests that the presence of residual stresses from the manufacture of biomedical implants and devices could lead to accelerated or delayed dissolution and that careful control of residual stresses should be sought for predictable performance in dissolvable materials.

Phosphates and Nuclear Waste Storage

Research Article| April 01, 2008 Phosphates and Nuclear Waste Storage Eric H. Oelkers; Eric H. Oelkers LMTG-Université de Toulouse-CNRS-IRD-OMP 14 rue Édouard Belin, 31400 Toulouse, France E-mail: oelkers@lmtg.obs-mip.fr Search for other works by this author on: GSW Google Scholar Jean-Marc Montel Jean-Marc Montel LMTG-Université de Toulouse-CNRS-IRD-OMP 14 rue Édouard Belin, 31400 Toulouse, France E-mail: montel@lmtg.obs-mip.fr Search for other works by this author on: GSW Google Scholar Elements (2008) 4 (2): 113–116. https://doi.org/10.2113/GSELEMENTS.4.2.113 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Eric H. Oelkers, Jean-Marc Montel; Phosphates and Nuclear Waste Storage. Elements 2008;; 4 (2): 113–116. doi: https://doi.org/10.2113/GSELEMENTS.4.2.113 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyElements Search Advanced Search Abstract A significant effort has been made by the scientific community to evaluate the potential of phosphate minerals and glasses as nuclear waste storage hosts. Radioactive waste-bearing phosphates, including monazites, apatites, and glasses, can be readily synthesized in the laboratory. Because of their low solubilities and slow dissolution rates, these phosphates are more resistant to corrosion by geological fluids than many other potential nuclear waste storage hosts, including borosilicate glass. Phosphates are, however, not currently being used for nuclear waste storage, in part because their synthesis at the industrial scale is relatively labor intensive, often requiring the separation of the waste into distinct fractions of elements. Such limitations may be overcome by adding phosphate amendments to backfill material, which could provoke the precipitation of stable radiactive waste-bearing phosphate minerals in situ. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The interplay between yam ( Dioscorea sp.) starch botanical source, micromeritics and functionality in paracetamol granules for reconstitution

A comparative investigation of the interplay between starch botanical source, micromeritics and their functionality in formulated paediatric paracetamol granules for reconstitution was conducted using starches extracted from five local yam ( Dioscorea spp. ) species. Significant differences were observed in the physicochemical properties of the different starches studied ( p < 0.05). The observed differences in paracetamol dissolution correlated well with the physicochemical properties of the starches. Granules formulated with Chinese yam and Bitter yam starches showed the fastest rate of paracetamol dissolution with T 80 of 2.2 and 2.6 min, respectively, at 2.5%w/w, and 3.75 and 4.00 min, respectively, at 10% w/w binder concentrations. Those formulated with Round leaf yellow yam starch had the slowest dissolution rate with T 80 of 4.5 and 8.75 min, respectively, at 2.5% and 10% binder concentrations. The results generally indicate a significant dependence of the rate of paracetamol dissolution from granules on starch surface tension, viscosity, swelling power and water binding capacity, particle size distribution, specific surface and porosity. These, in turn, were found to be starch botanic source-dependent suggesting careful consideration of botanic source when substituting one starch product for another in granule formulation.

Study of Solubilizing Capacity of Anionic Surfactants (AOS and SLS) in Spray-Dried Pesticide Formulation

The slow dissolution rate exhibited by sparingly water‐soluble pesticide is a major challenge in the pesticide development process. The aim of this study was to improve the dissolution rate of a sparingly water soluble model pesticide, Atrazine. Microparticles containing the model pesticide (atrazine) were produced by spray‐drying technique in the absence and presence of an anionic surfactant. Alpha olefin sulfonate (AOS) and Sodium lauryl sulfate (SLS) were chosen as the surfactants to improve the particle wetting and the dissolution rate. The spray dried particles were characterized by SEM and particle size analyzer and dissolution studies were carried out by USP XXIII paddle method. Also the effect of spray drying on atrazine was studied by DSC. The results obtained showed that the dissolution rate of the spray dried atrazine‐surfactant particles were significantly increased compared to the active. This proves that the better wetting characteristics conferred by the hydrophilic surfactant were responsible for the enhanced dissolution rate of the model pesticide. 50% water dispersible granules (WDG) of atrazine were also prepared by spray‐drying technique. The resulting granules had a unique combination of good flow ability and a good degree of dispersion.

Dissolution enhancement of gliclazide by preparation of inclusion complexes with β-cyclodextrin

Gliclazide is an oral hypoglycemic agent used in the treatment of non-insulin-dependent diabetes mellitus. The drug is practically insoluble in water and exhibits an exceedingly slow intrinsic dissolution rate and poor bioavailability. The present study has emphasized on improving the solubility and dissolution rate of the drug by forming inclusion complex with β-cyclodextrin. Phase solubility studies indicated the formation of 1:2 M complex in solution. The value of apparent stability constant Kc was found to be 691.45 M–1. The inclusion complexes were prepared by physical mixture and kneading method. Prepared complexes were characterized by infrared (IR) spectroscopy and differential scanning calorimetry (DSC) studies, which indicated formation of 1:2 M complex. The gliclazide:β-CD (1:2 M) complex prepared by kneading method exhibited higher dissolution rate and dissolution efficiency values in 0.1-N HCl. A 20.31-fold increase in dissolution rate and 16.50-fold increase in dissolution efficiency values were observed in the kneading method. Key words: β-cyclodextrin, gliclazide, kneading method, physical mixture