Molecular Dynamics of Hydration Shells of Adsorbates in Entropy-Driven Adsorption (Hydrophobic Bonding) to Activated Carbon Surfaces.

Hydrophobic bonding is a phenomenon wherein the adsorption of solutes from aqueous solutions is driven largely by the desire of solvent molecules to interact with each other, thus squeezing out solute molecules onto the adsorbent surface. A novel computational analysis of hydration shell water dynamics was used to study the driving force for the hydrophobic bonding of five small drug molecules to activated carbon. It was demonstrated that the solvation of these drug molecules produced hydration shells of lower density and molecular mobility than bulk water, up to 10.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption II: Effect of pH and pH Buffers on Phenobarbital Adsorption to Activated Carbon.

The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies.

Disagreements Between Calorimetric and Van't Hoff Enthalpies of Adsorption: A New Langmuir-like Model to Account for the Effect of Solvent Displacement Stoichiometry.

The reported inconsistencies between calorimetry and the van't Hoff equation hinder the utility of thermodynamics in pharmaceutical research. In ligand binding or adsorption assays, it is believed that the van't Hoff equation falls short because of the lack of stoichiometric treatment in the equilibrium constant. A new modified Langmuir-Like equation that accounts for the stoichiometry of solute adsorption and solvent displacement is proposed in this work.

A study of Kollicoat® MAE100P film's structure and properties.

Generally, an organic-solvent-based film is denser and tougher than a corresponding aqueous-dispersion-based film. However, Kollicoat® MAE100P films prepared from aqueous dispersions had greater tensile strengths compared to the films cast from organic solutions. It was proposed that MAE100P polymer particles in aqueous media had a core-shell structure with a hydrophilic shell and a hydrophobic core.

Solubilization of organics I: H NMR chemical shift perturbations, diffusometry, and NOESY indicate biphenyls internalize in micelles formed by cetyltrimethylammonium bromide.

Polychlorinated biphenyls are a class of persistent environmental contaminants, and micellar solubilization can be applied to remediate them. The intermolecular aggregates of biphenyl (BP) analogs and cetyltrimethyl ammonium bromide (CTAB) were studied by chemical shift perturbation, nuclear magnetic resonance (NMR) diffusometry, quantitative proton NMR, and nuclear Overhauser effect (NOE) spectroscopy to understand the structural determinants of their solubilization. The micelles of CTAB solubilized BPs readily, but its capacity depended strongly on the nature of the functional group (BPCH OH > > BPCHO > BPCOOH ≈ BPCl ≈ BP).

The Effects of Curing and Casting Methods on the Physicochemical Properties of Polymer Films.

Most film coatings in the pharmaceutical industry are prepared using organic solvents or aqueous solvents. Due to different film-formation mechanisms, their properties are significantly different from each other. Curing can alter the microstructure of films by improving the coalescence of polymer particles for aqueous dispersion-based films or accelerating macromolecule relaxation for organic solvent-based films.

Thermodynamic Evaluation of the Interaction Driven by Hydrophobic Bonding in the Aqueous Phase.

In the present study, the interaction between phenobarbital and activated carbons which is driven by hydrophobic bonding was evaluated. The Two-Mechanism Langmuir-Like Equation was proposed to describe the isotherms for phenobarbital adsorbing to activated carbons. The parameters in the Two-Mechanism Langmuir-Like Equation obtained from the nonlinear fitting of isotherms were used in the calculations of the differential Gibbs free energy for the hydrophobic bonding-driven interaction.

Thermodynamic Estimate of the Number of Solvent Molecules Displaced by a Solute Molecule for Enthalpy-Driven Adsorption: Phenobarbital and Activated Carbons as the Model System.

A Modified Crisp Equation, describing the differential Gibbs free energy of the adsorption process, is being proposed, which considers multiple sites available on the surface for adsorption and their relative fractions. The differential Gibbs free energy can be calculated by the van't Hoff Equation, which depends on the affinity constant in the Langmuir-like equation. To consider the number of solvent molecules displaced by a solute molecule in the adsorption process, a new derivative of the Langmuir-like equation is being proposed as well.

Quantitative Structure-Activity Relationship Analysis of the Effect of Metoclopramide and Related Compounds on the Surface Ionization of Fumed Silica.

Potentiometric titration curves were generated for fumed silica with various concentrations of dissolved metoclopramide. The effects of various benzamide analogs of metoclopramide, which are positively charged in the titration medium and differ solely by their aromatic substituents, as well as lidocaine, which is also structurally analogous but is mainly in the unionized form, were also studied. At sufficiently high pH, pH 7.

The influence of the adsorption of metoclopramide on the surface ionization of fumed silica.

The effect of adsorbed metoclopramide on the surface ionization of fumed silica was studied using potentiometric titration. Adsorption isotherms of metoclopramide to unionized and negatively-charged silica surfaces were generated and compared to the titration data. The adsorption of metoclopramide caused the silica surface charge to become more negative with increasing pH that was independent of ionic strength which suggested that specific adsorbate-surface interactions were occurring.

Characterizing compaction-induced thermodynamic changes in a common pharmaceutical excipient.

Work, heat, and internal energy change values were measured during compression of a common pharmaceutical tablet excipient, anhydrous lactose, using a compression calorimeter. Heat of solution measurements were used independently to measure the energy change caused by compaction. Both the compression calorimeter and the heat of solution measurements showed an increase in anhydrous lactose's energy state as a result of the net compression and decompression process.

Spontaneous crystalline-to-amorphous phase transformation of organic or medicinal compounds in the presence of porous media, part 3: effect of moisture.

Purpose: Amorphization of crystalline compounds using mesoporous media is a promising technique to improve the solubility and drug release of poorly-soluble compounds. The objective of this paper is to understand the effect of moisture on the capacity and performance of vapor-phase mediated amorphization.

Methods: Mesoporous silicon dioxide (SiO(2)) and crystalline naphthalene were used as the model system.

Quantitative mineralogical properties (morphology-chemistry-structure) of pharmaceutical grade kaolinites and recommendations to regulatory agencies.

The physical and chemical characteristics of kaolinite (kaolin) may be variable, and minor amounts of other clay minerals, nonclay minerals, and other impurities may affect the properties of kaolinites. Thus specific technical properties of pharmaceutical grade kaolinites become very important because these clays are used in medical applications, e.g.

Specific and non-specific interactions of procaine with activated carbon surfaces.

The adsorption of procaine on eight activated carbon surfaces from simulated intestinal fluid (SIF) was evaluated using a rotating bottle method and isoperibol calorimetry. The adsorption data were fit using the modified Langmuir-like equation to calculate the non-specific and specific adsorption capacities. The surface atomic compositions were determined by X-ray photoelectron spectroscopy (XPS).

Influence of the polymer-micelle interaction on micelle-substrate binding.

In an attempt to investigate how a nonionic polymer, hydroxypropyl methylcellulose (HPMC), interacts with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), a dialysis method was employed for directly measuring the HPMC-CTAB interaction. The result showed that an interaction existed between CTAB and HPMC, and the higher the HPMC concentration the greater the fraction of CTAB bound. The shift in the UV spectra represents the change in the microenvironment.

Interpreting deformation behavior in pharmaceutical materials using multiple consolidation models and compaction energetics.

Tableting behavior is often characterized using qualitative analyses of compactibility and compressibility measurements. More quantitative methods use consolidation models to estimate parameters indicative of the predominating deformation mechanism exhibited by a material. It will be shown that a concerted approach, using multiple consolidation models and mechanical energy analysis, presents a more reliable way of evaluating the relative plasticity of pharmaceutical materials and identifying complicating behaviors.

Using compression calorimetry to characterize powder compaction behavior of pharmaceutical materials.

The process by which pharmaceutical powders are compressed into cohesive compacts or tablets has been studied using a compression calorimeter. Relating the various thermodynamic results to relevant physical processes has been emphasized. Work, heat, and internal energy change values have been determined with the compression calorimeter for common pharmaceutical materials.

Aerosol OT microemulsions as carriers for transdermal delivery of hydrophobic and hydrophilic local anesthetics.

The skin permeation enhancement of many kinds of drugs and cosmetic substances by microemulsions has been widely known; however, the correlations between microemulsion microstructures and the efficiency of skin permeation are not fully elucidated. Therefore, the aim of our study was to investigate the influence of microemulsion types on in vitro skin permeation of model hydrophobic drugs and their hydrophilic salts. The microemulsion systems were composed of isopropyl palmitate (IPP), water, a 2:1 w/w mixture of Aerosol OT (AOT) and 1-butanol, and a model drug.

Investigation of the drug release and surface morphological properties of film-coated pellets, and physical, thermal and mechanical properties of free films as a function of various curing conditions.

The purpose of the present investigation was to elucidate the influence of curing on different physical properties of Eudragit NE and RS coating systems. Increased curing times resulted in decreased drug release rates from Eudragit NE-coated beads. However, an increase in drug release rates was noticed at longer curing times and higher temperatures for the Eudragit RS coating system.

The effect of binary mixture composition and magnesium stearate concentration on the Hiestand Tableting Indices and other related mechanical properties.

Maltodextrins were chosen as model excipients because maltodextrins possess a series of molecular weights that showed systematically changing consolidation mechanisms. As maltodextrin molecular weight increases, the plasticity of the material increases. Three commercial grades of Maltrin (M040, M100, and M150) were used to prepare binary powder mixtures (M040-M150 and M040-M100).

Effect of curing on water diffusivities in acrylate free films as measured via a sorption technique.

Studies were performed to investigate the effect of curing on the diffusion coefficients of water, as measured via the sorption technique, in acrylate polymeric films. The mathematical model selected for obtaining diffusion constants from the vapor-phase sorption studies was derived from the long-time Fourier equation used for diffusion into a planar sheet. For Eudragit NE films, the diffusion coefficients of water decreased continuously until a constant minimum value was reached.

Determination of the hydrolysis kinetics of alpha-naphthyl acetate in micellar systems and the effect of HPMC (catalyst present).

The change in the hexadecyltrimethylammonium bromide (CTAB) critical aggregation concentration (CAC) was studied in the presence of various concentrations and grades of hydroxypropylmethyl cellulose (HPMC) using surface tension measurement (duNoüy ring and Wilhelmy plate) and oil red O solubilization. According to the surface tension methods, the CAC was higher than the CTAB critical micelle concentration (CMC). CAC and CMC were not different when the solubilization method was used.