Interfacial interactions of nanoscale zero-valent iron particles with clay minerals in the aquatic environments: Experimental and theoretical calculation study.

The environmental transport and fate of nanoscale zero-valent iron particles (nZVI) in soil and groundwater can be altered by their hetero-aggregation with clay mineral particles (CMP). This study examines the interactions between bare or carboxymethyl cellulose (CMC)-coated nZVI with typical CMP, specifically kaolinite and montmorillonite. Methods include co-settling experiments, aggregation kinetic studies, electron microscopy, Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (EDLVO) energy analysis, and density functional theory calculations, focusing on the pH dependency of these interactions. The EDLVO theory effectively described the interactions between nZVI and CMP in aquatic environments. Under acidic conditions (pH 3.5), the interfacial interaction between bare nZVI and kaolinite is regulated by van der Waals forces, while complexation, van der Waals forces, and electrostatic attraction govern the interaction of bare nZVI with montmorillonite, primarily depositing on the SiO face. In contrast, the positively charged AlO face and edge of CMP are the main deposition sites for CMC-coated nZVI through hydrogen bonding, van der Waals forces, and electrostatic attraction. At neutral (pH 6.5) and alkaline (pH 9.5) conditions, both bare and CMC-coated nZVI predominantly attach to the AlO face and edge, facilitated by complexation or hydrogen bonding, alongside van der Waals forces. The attachment of CMC-coated nZVI to CMP surfaces shows reversible aggregation or deposition due to the steric repulsion from the CMC coating. These findings hold significant implications for the environmental applications and risk of nZVI.

Lewis-base ligand-reshaped interfacial hydrogen-bond network boosts CO2 electrolysis.

Both the catalyst and electrolyte strongly impact the performance of CO2 electrolysis. Despite substantial progress in catalysts, it remains highly challenging to tailor electrolyte compositions and understand their functions at the catalyst interface. Here, we report that the ethylenediaminetetraacetic acid (EDTA) and its analogs, featuring strong Lewis acid-base interaction with metal cations, are selected as electrolyte additives to reshape the catalyst-electrolyte interface for promoting CO2 electrolysis. Mechanistic studies reveal that EDTA molecules are dynamically assembled toward interface regions in response to bias potential due to strong Lewis acid-base interaction of EDTA4--K+. As a result, the original hydrogen-bond network among interfacial H2O is disrupted, and a hydrogen-bond gap layer at the electrified interface is established. The EDTA-reshaped K+ solvation structure promotes the protonation of *CO2 to *COOH and suppressing *H2O dissociation to *H, thereby boosting the co-electrolysis of CO2 and H2O toward carbon-based products. In particular, when 5 mM of EDTA is added into the electrolytes, the Faradaic efficiency of CO on the commercial Ag nanoparticle catalyst is increased from 57.0% to 90.0% at an industry-relevant current density of 500 mA cm-2. More importantly, the Lewis-base ligand-reshaped interface allows a range of catalysts (Ag, Zn, Pd, Bi, Sn, and Cu) to deliver substantially increased selectivity of carbon-based products in both H-type and flow-type electrolysis cells.

Heteroatom doped biochar-aluminosilicate composite as a green alternative for the removal of hazardous dyes: Functional characterization and modeling studies.

In this work, a novel nitrogen-doped biochar bentonite composite was synthesized by a single-pot co-pyrolysis method. Batch studies were conducted to evaluate the performance of the developed composite in eliminating synthetic dyes from the aqueous matrix. Energy dispersive X-ray spectroscopy analysis and field emission scanning electron microscopy imaging confirmed the N doping and bentonite impregnation into biochar. X-ray photoelectron spectroscopy analysis revealed that the N atoms were doped interstitially into the carbon matrix of biochar in the form of pyridinic and pyrrolic nitrogen. Simultaneous heteroatom doping and bentonite impregnation reduced the specific surface area to 41.721 m2 g-1 but improved the adsorption capacity of biochar for dye adsorption. Further experimental studies depicted that simultaneous bentonite impregnation and N doping into the biochar matrix is beneficial for direct blue-6 (DB-6) and methylene blue (MB) removal and maximum adsorption capacities of 53.17 mg. g-1 and 41.33 mg. g-1 were obtained for MB and DB-6, respectively, at varying conditions. Adsorption energetics of the dyes with the developed composite portrayed the spontaneity of the process through negative ΔG values. The Langmuir and Freundlich isotherm models fitted the best for MB and DB-6 adsorption. The monolayer adsorption capacity and favourability factor for MB and DB-6 adsorption were calculated to be 54.15 mg. g-1 and 0.217, respectively from the best-fitted isotherms. Based on density functional theory calculations and spectroscopic studies, major interactions governing the adsorption were predicted to be charge-based interactions, π-π interactions, H-bonding, and Lewis acid-base interactions.

Introduction of an electrospun nanofibrous membrane incorporated by metal-organic framework-199 (MOF-199) with Lewis acid property for efficient extraction of sulfonamides in on-chip electromembrane extraction.

In this study, a new supporting polymeric membrane having Lewis acid nature was introduced for immobilizing organic solvent in on-chip electromembrane extraction (on-chip EME). For this aim, a polymeric nanofibrous membrane incorporated by a copper based metal-organic framework (MOF-199), with coordinatively unsaturated metal sites and Lewis acid property, was prepared by electrospinning a mixture of polycaprolactone (PCL) and MOF-199. Based on the field emission scanning electron microscopy images, the obtained polymeric membrane consisted of intertwined nanofibers having empty space between the fibers which could provide a suitable place for immobilizing the organic solvent. To demonstrate remarkable extractability of the proposed membrane (PCL/MOF-199 nanofibers) via executing Lewis acid-base interactions, three sulfonamide drugs was selected as anionic polar analytes with Lewis base feature. The parameters affecting the extraction efficiency of the method were optimized through the experimental design method using the orthogonal and rotatable central composite design (CCD). Under optimum conditions, the extraction recoveries ranging from 35.5 to 71.2 %, the relative standard deviations (RSD%) less than 6.45 %, and the detection limits in the range of 0.2-0.5 µg L-1 were achieved. The comparison of the extraction efficiency of the on-chip EME method using the electrospun PCL/MOF-199 nanofibers and PCL nanofibers membranes indicated that the proposed membrane was more efficient for extraction of sulfonamides because of the significant Lewis acid-base interactions of sulfonamides with copper uncoordinated open sites in MOF-199. Finally, the performance of the proposed method for extraction and determination of sulfonamides in three real samples was assayed.

On the Disproportionate Contribution of Membrane Electron Donor Functionality in Membrane Biofouling.

This study set out to uncover which interfacial properties have the greatest impact on membrane organic fouling, biofouling, and fouling resistance. A relatively simple manipulation of the basic equations used in determining Lifshitz-van der Waals (LW) and Lewis acid-base (AB) surface tensions for solid materials reveals that the high electron accepticity of water makes the electron donicity of membrane and biofouling materials the key component governing their interfacial free energy of adhesion (ΔG132), which defines the favorability (or unfavorability) of one material (1) adhering to another (2) when immersed in a liquid (3). Various biofoulant and membrane LW and AB surface tensions were systematically characterized. Static bacterial adhesion, alginic acid filtration, and wastewater filtration tests were conducted to determine the fouling propensities of three different polymeric membrane materials. Experimental results of microbial adhesion, alginate fouling, and biofouling tests all correlated well with membrane electron density, where higher electron density produced less organic fouling or biofouling. These combined theoretical and experimental results confirm the importance of surface electron donicity in determining the fouling propensity of polymeric membranes.

Non-Covalent Interaction-Controlled Site-Selective C-H Transformations.

Site-selective C-H transformations are important to obtain desired compounds as single products in a highly efficient manner. However, it is generally difficult to achieve such transformations because organic substrates contain many C-H bonds with similar reactivities. Therefore, the development of practical and efficient methods for controlling site selectivity is highly desirable. The most frequently used strategy is "directing group method". Although this method is highly effective and promotes site-selective reactions, it has several limitations. Our group recently reported other methods to achieve site-selective C-H transformations using non-covalent interactions between a substrate and a reagent or a catalyst and a substrate (non-covalent method). In this personal account, the background of site-selective C-H transformations, our reaction design to achieve site-selective C-H transformations, and recently reported reactions are explained.

Polysulfide Regulation by Hypervalent Iodine Compounds for Durable and Sustainable Lithium-Sulfur Battery.

Herein, a type of hypervalent iodine compound-iodosobenzene (PhIO)-is proposed to regulate the LiPSs electrochemistry and enhance the performance of Li-S battery. PhIO owns the practical advantages of low-cost, commercial availability, environmental friendliness and chemical stability. The lone pair electrons of oxygen atoms in PhIO play a critical role in forming a strong Lewis acid-base interaction with terminal Li in LiPSs. Moreover, the commercial PhIO can be easily converted to nanoparticles (≈20 nm) and uniformly loaded on a carbon nanotube (CNT) scaffold, ensuring sufficient chemisorption for LiPSs. The integrated functional PhIO@CNT interlayer affords a LiPSs-concentrated shield that not only strongly obstructs the LiPSs penetration but also significantly enhances the electrolyte wettability and Li+ conduction. The PhIO@CNT interlayer also serves as a "vice current collector" to accommodate various LiPSs and render smooth LiPSs transformation, which suppresses insulating Li2 S2 /Li2 S layer formation and facilitates Li+ diffusion. The Li-S battery based on PhIO@CNT interlayer (6 wt% PhIO) exhibits stable cycling over 1000 cycles (0.033% capacity decay per cycle) and excellent rate performance (686.6 mAh g-1 at 3 C). This work demonstrates the great potential of PhIO in regulating LiPSs and provides a new avenue towards the low-cost and sustainable application of Li-S batteries.

Development of FDM 3D-printed tablets with rapid drug release, high drug-polymer miscibility and reduced printing temperature by applying the acid-base supersolubilization (ABS) principle.

Some of the major issues with the development of FDM 3D printed tablets are slow drug release, lack of drug-polymer miscibility, high processing temperature, and poor printability. In this investigation, these issues were addressed by using a novel physicochemical principle called acid-base supersolubilization (ABS) previously developed in our laboratory. The aqueous solubility of a basic drug, haloperidol, was increased to ~300 mg/g of solution by adding glutaric acid, and, upon drying, the concentrated solutions produced amorphous materials. Similar amorphous systems could also be produced by heating haloperidol-glutaric acid mixtures. Filaments for 3D printing were prepared by melt extrusion of formulations containing 15% w/w haloperidol and 10.5% glutaric acid (1:2 M ratio) along with 74.5% polymers, such as Kollidon® VA64 alone or its mixtures with Affinisol™ 15cP. Filaments could be extruded and printed at low temperatures of 115 and 120 °C, respectively. Haloperidol was fully miscible in the formulations because of the acid-base interaction and formed amorphous systems even at higher drug loads. Although filaments of haloperidol-Kollidon® VA64 mixtures by themselves cannot be printed, the printability of formulation improved such that those containing glutaric acid were printable. Drug release rates from the formulations at pH 2 and 6.8 were rapid and complete.

Oxidative Three-Component Carboamination of Vinylarenes with Alkylboronic Acids.

Three-component carboamination of alkenes is of significant interest due to the ease by which functionalized amines can be produced from readily available chemical building blocks. Previously, a variety of carbon-centered radical precursors have been studied as the carbon components for this reaction, however, the use of general alkyl sources has remained as an unsolved challenge. Herein we present our efforts to develop an oxidative carboamination protocol that utilizes alkylboronic acids as carbon-centered radical precursors. The presented work demonstrates 34 examples, ranging from 17 to 88% yields, with a broad scope in vinylarenes, amines, and alkylboronic acids. Preliminary mechanistic studies suggest that a single-electron oxidation of the alkylboronic acid generates a carbon-centered radical intermediate that adds across the olefin followed by C-N bond formation via Cu-mediated inner-sphere or carbocation-mediated pathways.

Acid-Base Interaction Enhancing Oxygen Tolerance in Electrocatalytic Carbon Dioxide Reduction.

Hybrid electrodes with improved O2 tolerance and capability of CO2 conversion into liquid products in the presence of O2 are presented. Aniline molecules are introduced into the pore structure of a polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO2 molecule and the basic amino group of aniline renders enhanced CO2 separation from O2 . Loaded with a cobalt phthalocyanine-based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O2 in the CO2 feed gas. The electrode can still produce CO at an O2 /CO2 ratio as high as 9:1. Switching to a Sn-based catalyst, for the first time O2 -tolerant CO2 electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm-2 in the presence of 5 % O2 .

Insights into the cooperativity between multiple interactions of dimethyl sulfoxide with carbon dioxide and water.

Interactions of dimethyl sulfoxide with carbon dioxide and water molecules which induce 18 significantly stable complexes are thoroughly investigated. An addition of CO2 or H2 O molecules into the DMSO⋯1CO2 and DMSO⋯1H2 O systems leads to an increase in the stability of the resulting complexes, in which it is larger for a H2 O addition than a CO2 . The overall stabilization energy of the DMSO⋯1,2CO2 is mainly contributed by the S=O⋯C Lewis acid-base interaction, whereas the O - H⋯O hydrogen bond plays a significant role in stabilizing complexes of DMSO⋯1,2H2 O and DMSO⋯1CO2 ⋯1H2 O. Remarkably, the complexes of DMSO⋯2H2 O are found to be more stable than DMSO⋯1CO2 ⋯1H2 O and DMSO⋯2CO2 . The level of the cooperativity of multiple interactions in ternary complexes tends to decrease in going from DMSO⋯2H2 O to DMSO⋯1CO2 ⋯1H2 O and finally to DMSO⋯2CO2 . It is generally found that the red shift of the O - H bond involved in an O - H⋯O hydrogen bond increases while the blue shift of a C - H bond in a C - H⋯O hydrogen bond decreases when a cooperative effect occurs in ternary complexes as compared to those of the corresponding binary complexes. © 2018 Wiley Periodicals, Inc.

Highly efficient and selective removal of N-heterocyclic aromatic contaminants from liquid fuels in a Ag(I) functionalized metal-organic framework: Contribution of multiple interaction sites.

An adsorbent with multiple interaction sites for the adsorption of nitrogen-containing compounds (NCCs) has been realized in a silver ion functionalized Cr3+ based metal-organic framework (Cr)-MIL-101-SO3Ag. The adsorptive denitrogenation performance of (Cr)-MIL-101-SO3Ag was evaluated in a batch adsorption system in terms of both its adsorption capacity and selectivity, of which, quinoline and indole were selected as representative organonitrogen contaminants in liquid fuels. (Cr)-MIL-101-SO3Ag could interact with NCCs through multiple ways simultaneously, which exhibited about 50% higher adsorption capacity compared to (Cr)-MIL-101-SO3H, and a still high level of adsorption amount could be remained even in a model fuel where toluene (15% v) was added as a co-solvent and benzothiophene (BT) was added as a competitive adsorbate. The highly efficient and selective denitrogenation performance, we speculated was a combined results of these multiple interaction sites. The immobilized Ag(I) sites could strongly interact with NCCs through π-complexation, which was thought to be responsible for its high adsorption capacity, meanwhile, the hard lewis acid site (Cr3+), which could preferentially interact with the hard nitrogen bases and the acid-base interaction between nitrogen bases and remaining -SO3H groups endowed (Cr)-MIL-101-SO3Ag with high selectivity over BT and other aromatic compounds. Futhermore, the enhanced interaction of (Cr)-MIL-101-SO3Ag with NCCs was also confirmed from the IR spectra with the significantly enhanced absorbance peak at 806 or 745 cm-1 observed for QUI and IND, respectively when compared to BT. After five successive adsorption-desorption cycles, the adsorption capacity of (Cr)-MIL-101-SO3Ag was almost unchanged, and the structural stability was well maintained, making it a potential adsorbent for deep denitrogenation of liquid fuels.

Active MgO-SiO2 hybrid material for organic dye removal: A mechanism and interaction study of the adsorption of C.I. Acid Blue 29 and C.I. Basic Blue 9.

A comparative analysis was performed concerning the removal of two different organic dyes from model aqueous solution using an inorganic oxide adsorbent. The key element of the study concerns evaluation of the influence of the dyes' structure and their acid-base character on the efficiency of the adsorption process. The selection of sorbent material for this research - an MgO-SiO2 oxide system synthesized via a modified sol-gel route - is also not without significance. The relatively high porous structure parameters of this material (ABET = 642 m2/g, Vp = 1.11 mL and Sp = 9.8 nm) are a result of the proposed methodology for its synthesis. Both organic dyes (C.I. Acid Blue 29 and C.I. Basic Blue 9) were subjected to typical batch adsorption tests, including investigation of such process parameters as time, initial adsorbate concentration, adsorbent dose, pH and temperature. An attempt was also made to estimate the sorption capacity of the oxide material with respect to the analyzed organic dyes. To achieve the objectives of the research - determine the efficiency of adsorption - it was important to perform a thorough physicochemical analysis of the adsorbents (e.g. FTIR, elemental analysis and porous structure parameters). The results confirmed the significantly higher affinity of the basic dye to the oxide adsorbents compared with the acidic dye. The regeneration tests, which indirectly determine the nature of the adsorbent/adsorbate interactions, provide further evidence for this finding. On this basis, a probable mechanism of dyes adsorption on the MgO-SiO2 oxide adsorbent was proposed.

Critical evaluation of dipolar, acid-base and charge interactions I. Electron displacement within and between molecules, liquids and semiconductors.

Specific dipolar, acid-base and charge interactions involve electron displacements. For atoms, single bonds and molecules electron displacement is characterized by electronic potential, absolute hardness, electronegativity and electron gap. In addition, dissociation, bonding, atomization, formation, ionization, affinity and lattice enthalpies are required to quantify the electron displacement in solids. Semiconductors are characterized by valence and conduction band energies, electron gaps and average Fermi energies which in turn determine Galvani potentials of the bulk, space charge layer and surface states. Electron displacement due to interaction between (probe) molecules, liquids and solids are characterized by parameters such as Hamaker constant, solubility parameter, exchange energy density, surface tension, work of adhesion and immersion. They are determined from permittivity, refractive index, enthalpy of vaporization, molar volume, surface pressure and contact angle. Moreover, acidic and basic probes may form adducts which are adsorbed on target substrates in order to establish an indirect measure of polarity, acidity, basicity or hydrogen bonding. Acidic acceptor numbers (AN), basic donor numbers (DN), acidic and basic "electrostatic" (E) and "covalent" (C) parameters determined by enthalpy of adduct formation are considered as general acid-base scales. However, the formal grounds for assignments as dispersive, Lifshitz-van der Waals, polar, acid, base and hydrogen bond interactions are inconsistent. Although correlations are found no of the parameters are mutually fully compatible and moreover the enthalpies of acid-base interaction do not correspond to free energies. In this review the foundations of different acid-base parameters relating to electron displacement within and between (probe) molecules, liquids and (semiconducting) solids are thoroughly investigated and their mutual relationships are evaluated.

Prussian Blue Nanocubes with an Open Framework Structure Coated with PEDOT as High-Capacity Cathodes for Lithium-Sulfur Batteries.

It is shown that Prussian blue analogues (PBAs) can be a very competitive sulfur host for lithium-sulfur (Li-S) batteries. Sulfur stored in the large interstitial sites of a PBA host can take advantage of reversible and efficient insertion/extraction of both Li+ and electrons, due to the well-trapped mobile dielectron redox centers in the well-defined host. It is demonstrated that Na2 Fe[Fe(CN)6 ] has a large open framework, and as a cathode, it both stores sulfur and acts as a polysulfide diffusion inhibitor based on the Lewis acid-base bonding effect. The electrochemical testing shows that the S@Na2 Fe[Fe(CN)6 ]@poly(3,4-ethylenedioxythiophene) composite achieves excellent reversibility, good stability, and fast kinetics. Its outstanding electrochemical properties should be ascribed to the internal transport of Li+/e- , maximizing the utilization of sulfur. Moreover, the open metal centers serve as the Lewis acid sites with high affinity to the negatively charged polysulfide anions, reducing the diffusion of polysulfides out of the cathode and minimizing the shuttling effect. The fundamental basis of these exceptional performance characteristics is explored through a detailed analysis of the structural and electrochemical behavior of the material. It is believed that the PBAs will have a useful role in ensuring more effective and stable Li-S batteries.

Stability of pharmaceutical salts in solid oral dosage forms.

Using pharmaceutical salts in solid dosage forms can raise stability concerns, especially salt dissociation which can adversely affect the product performance. Therefore, a thorough understanding of the salt instability encountered in solid-state formulations is imperative to ensure the product quality. The present article uses the fundamental theory of acid base, ionic equilibrium, relationship of pH and solubility as a starting point to illustrate and interpret the salt formation and salt disproportionation in pharmaceutical systems. The criteria of selecting the optimal salt form and the underlying theory of salt formation and disproportionation are reviewed in detail. Factors influencing salt stability in solid dosage forms are scrutinized and discussed with the case studies. In addition, both commonly used and innovative strategies for preventing salt dissociations in formulation, on storage and during manufacturing will be suggested herein. This article will provide formulation scientists and manufacturing engineers an insight into the mechanisms of salt disproportionation and salt formation, which can help them to avoid and solve the instability issues of pharmaceutical salts in the product design.

Crystalline solid dispersion-a strategy to slowdown salt disproportionation in solid state formulations during storage and wet granulation.

Salt disproportionation (a conversion from the ionized to the neutral state) in solid formulations is a potential concern during manufacturing or storage of products containing a salt of the active pharmaceutical ingredient (API) due to the negative ramifications on product performance. However, it is challenging to find an effective approach to prevent or mitigate this undesirable reaction in formulations. Hence, the overall objective of this study is to explore novel formulation strategies to reduce the risk of salt disproportionation in pharmaceutical products. Crystals of pioglitazone hydrochloride salt were dispersed into polymeric matrices as a means of preventing the pharmaceutical salt from direct contact with problematic excipients. It was found that the level of salt disproportionation could be successfully reduced during storage or wet granulation by embedding a crystalline salt into a polymeric carrier. Furthermore, the impact of different polymers on the disproportionation process of a salt of a weakly basic API was investigated herein. Disproportionation of pioglitazone hydrochloride salt was found to be significantly affected by the physicochemical properties of different polymers including hygroscopicity and acidity of substituents. These findings provide an improved understanding of the role of polymeric carriers on the stability of a salt in solid formulations. Moreover, we also found that introducing acidifiers into granulation fluid can bring additional benefits to retard the disproportionation of pioglitazone HCl during the wet granulation process. These interesting discoveries offer new approaches to mitigate disproportionation of API salt during storage or processing, which allow pharmaceutical scientists to develop appropriate formulations with improved drug stability.

Influences of acid-base property of membrane on interfacial interactions related with membrane fouling in a membrane bioreactor based on thermodynamic assessment.

Failure of membrane hydrophobicity in predicting membrane fouling requires a more reliable indicator. In this study, influences of membrane acid base (AB) property on interfacial interactions in two different interaction scenarios in a submerged membrane bioreactor (MBR) were studied according to thermodynamic approaches. It was found that both the polyvinylidene fluoride (PVDF) membrane and foulant samples in the MBR had relatively high electron donor (γ(-)) component and low electron acceptor (γ(+)) component. For both of interaction scenarios, AB interaction was the major component of the total interaction. The results showed that, the total interaction monotonically decreased with membrane γ(-), while was marginally affected by membrane γ(+), suggesting that γ(-) could act as a reliable indicator for membrane fouling prediction. This study suggested that membrane modification for fouling mitigation should orient to improving membrane surface γ(-) component rather than hydrophilicity.

Characterization of Solid Dispersion of Itraconazole Prepared by Solubilization in Concentrated Aqueous Solutions of Weak Organic Acids and Drying.

PURPOSE: The purpose of this study was to develop an amorphous solid dispersion (SD) of an extremely water-insoluble and very weakly basic drug, itraconazole (ITZ), by interaction with weak organic acids and then drying that would enhance dissolution rate of drug and physical stability of formulation. METHODS: Aqueous solubility of ITZ in concentrated solutions of weak organic acids, such as glutaric, tartaric, malic and citric acid, was determined. Solutions with high drug solubility were dried using vacuum oven and the resulting SDs having 2 to 20% drug load were characterized by differential scanning calorimetry (DSC), powder X-ray diffractometry (PXRD) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The dissolution of SDs was initially studied in 250 mL of 0.1 N HCl (pH 1.1), and any undissolved solids were collected and analyzed by PXRD. The pH of the dissolution medium was then changed from 1.1 to 5.5, particle size of precipitates were measured, and drug concentrations in solution were determined by filtration through membrane filters of varying pore sizes. RESULTS: The aqueous solubility of ITZ was greatly enhanced in presence of weak acids. While the solubility of ITZ in water was ~4 ng/ mL, it increased to 25-40 mg per g of solution at 25°C and 200 mg per g of solution at 65°C at a high acid concentration leading to extremely high solubilization. PXRD of SDs indicated that ITZ was present in the amorphous form, wherein the acid formed a partially crystalline matrix. ATR-FTIR results showed possible weak interactions, such as hydrogen bonding, between drug and acid but there was no salt formation. SDs formed highly supersaturated solutions at pH 1.1 and had superior dissolution rate as compared to amorphous drug and physical mixtures of drug and acids. Following the change in pH from 1.1 to 5.5, ITZ precipitated as mostly nanoparticles, providing high surface area for relatively rapid redissolution. CONCLUSIONS: A method of highly solubilizing an extremely water-insoluble drug, ITZ, in aqueous media and converting it into an amorphous form in a physically stable SD was successfully investigated. The dissolution rate and the extent of supersaturation of the drug in dissolution media improved greatly, and any precipitate formed at high pH had very small particle size.

The role of acid-base effects on particle charging in apolar media.

The creation and stabilization of electric charge in apolar environments (dielectric constant≈2) have been an area of interest dating back to when an explanation was sought for the occurrence of what are now known as electrokinetic explosions during the pumping of fuels. More recently attention has focused on the charging of suspended particles in such media, underlying such applications as electrophoretic displays (e.g., the Amazon Kindle® reader) and new printing devices (e.g., the HP Indigo® Digital Press). The endeavor has been challenging owing to the complexity of the systems involved and the large number of factors that appear to be important. A number of different, and sometimes conflicting, theories for particle surface charging have been advanced, but most observations obtained in the authors' laboratory, as well as others, appear to be explainable in terms of an acid-base mechanism. Adducts formed between chemical functional groups on the particle surface and monomers of reverse micelle-forming surfactants dissociate, leaving charged groups on the surface, while the counter-charges formed are sequestered in the reverse micelles. For a series of mineral oxides in a given medium with a given surfactant, surface charging (as quantified by the maximum electrophoretic mobility or zeta potential obtained as surfactant concentration is varied) was found to scale linearly with the aqueous PZC (or IEP) values of the oxides. Different surfactants, with the same oxide series, yielded similar behavior, but with different PZC crossover points between negative and positive particle charging, and different slopes of charge vs. PZC. Thus the oxide series could be used as a yardstick to characterize the acid-base properties of the surfactants. This has led directly to the study of other materials, including surface-modified oxides, carbon blacks, pigments (charge transfer complexes), and polymer latices. This review focuses on the acid-base mechanism of particle charging in the context of the many other factors that are important to the phenomenon, including the presence of water, of other components (e.g., synergists and contaminants), and of electric field effects. The goal is the construction of a road map describing the anticipated particle charging behavior in a wide variety of systems, assisting in the choice or development of materials for specific applications.