Effect of glycyrrhizinate on dissolution behavior and rectal absorption of amphotericin B in rabbits.

The effects of dipotassium glycyrrhizinate (GLYK) on the dissolution behavior and bioavailability of amphotericin B (AMB) were investigated. The mixtures of AMB and GLYK were prepared at different molar ratios by lyophilization. Lyophilization resulted in amorphous AMB either alone or in the mixture. Dissolution rates of AMB of the mixtures were markedly faster than that of lyophilized AMB alone, which was followed by a decrease of dissolution. The initially-enhanced dissolution rate was likely to be due to the improvement of surface wettability of drug particles with GLYK rather than the amorphous state of AMB. A phase solubility study of AMB with GLYK indicated that the increasing solubility was caused by micellar solubilization. The in vitro release rate of AMB from suppositories containing the lyophilized mixtures was significantly accelerated by increasing the amount of GLYK. The rectal absorption of AMB from suppositories containing either the drug alone, a physical mixture or a lyophilized mixture was studied using rabbits. The absorption of the mixture (AMB/GLYK = 1/9) was about 35 times greater in the area under the serum concentration-time curve (0-24 h) than that of lyophilized AMB alone. These results suggest that GLYK is useful for improving the dissolution property of AMB and the bioavailability of the drug incorporated in suppositories.     

Formulation study for lansoprazole fast-disintegrating tablet. I. Effect of compression on dissolution behavior

Lansoprazole fast-disintegrating tablet (LFDT) is a new patient-friendly formulation of lansoprazole. Since lansoprazole is an antiulcer agent and is unstable under acidic conditions, we have developed LFDT as an orally disintegrating tablet containing enteric-coated microgranules. The effect of compression on dissolution behavior was investigated, as compression affected cleavage and crushing of the enteric layer. To decrease cleavage and crushing of the enteric layer, the effects of the combined ratio of methacrylic acid copolymer dispersion to ethyl acrylate-methyl methacrylate copolymer dispersion and the concentration of triethyl citrate on the dissolution in the acid stage and the dissolution in the buffer stage were evaluated. By adjusting the ratio of methacrylic acid copolymer dispersion to ethyl acrylate-methyl methacrylate copolymer dispersion to 9 : 1 and adding a 20% triethyl citrate concentration, sufficient flexibility of the enteric layer and sufficient stability against compression forces were achieved. Agglomeration of enteric-coated microgranules during the coating process was decreased at the optimized concentration of triethyl citrate and glyceryl monostearate. We compared the absorption properties of LFDT and lansoprazole capsules in dogs. The absorption profiles of LFDT were similar to those of lansoprazole capsules.     

Effect of absorbed hydrogen on the iron dissolution

The rate of the anodic dissolution of iron in acid sulfate electrolytes is reduced by hydrogen absorbed in the metal. The dependence of the degree of retardation of the anodic process on the concentration of hydrogen atoms in the near-surface layer of the metal is obtained. The difference in the effect the adsorbed and absorbed forms of hydrogen exert on the iron dissolution rate is noted. At a certain content of absorbed hydrogen, the current efficiency for dissolved iron exceeds 100%, and the weight loss of the hydrogen-charged metal is maximum under the conditions of its anodic polarization. Dedicated to the ninetieth anniversary of Ya.M. Kolotyrkin’s birth.     

Effects of dehydration temperatures on moisture absorption and dissolution behavior of theophylline.

Anhydrous theophylline was prepared by heating theophylline monohydrate at temperatures between 60 degrees C and 140 degrees C. The effects of dehydration temperatures on the moisture absorption and dissolution behavior of anhydrous theophylline were investigated in this study. The hydration rate of anhydrous theophylline at 95% relative humidity and 25 degrees C decreased with increasing dehydration temperatures. From the fitting analysis of solid-state reaction models, the hydration reaction was found to be governed by the phase boundary reaction model for samples prepared at lower dehydration temperatures (<100 degrees C) but the reaction obeyed the growth of nuclei reaction model when samples were dehydrated at higher temperatures. The dissolution rates of various anhydrous theophylline samples were measured by the rotating disk method. The calculated solubility of anhydrous theophylline prepared by heating was about 2.5 times higher than that of theophylline monohydrate. The phase transformation rate from the anhydrous form to the monohydrate during dissolution tests decreased with higher dehydration temperatures. It was found that the anhydrous theophylline prepared at different dehydration temperatures transformed to the monohydrate by way of different growth of hydrate nuclei mechanism.     

Influence of the dissolution rate on the collapse and shedding behavior of monostearin/monopalmitin-rich coated microbubbles

A low cost food grade emulsifier (a mixture of monoglycerides, diglycerides, and sodium stearoyl lactylate) in combination with polyethylene glycol-40 stearate (PEG-40S) was used as an alternative to pure saturated phospholipids to form the thin shell of a microbubble. To investigate the stability of these microbubbles in a water system over time, their dissolution behavior was studied at various degas factors and at two percentages of PEG-40S. It was found that the favored shell collapse/shedding mechanism switched, as the dissolution rate increased (degas factor decreased), from folding with a smooth surface contour to buckling accompanied by surface folding/expulsion with a cyclic buckled-smooth surface contour. The compositional change that we made played a more minor role, mainly controlling the resistance to mass transfer of the microbubble shell and again modifying the mechanism-determinant dissolution rate. The shell resistance behavior for these microbubbles varied from that of previous lipid/PEG-40S-coated microbubbles by the presence of a maximum in shell resistance during dissolution. We hypothesize that the dominance of one collapse mechanism over another for these compositions is related to the time scales of two competing processes, fold nucleation and area compression. For these mixtures at room temperature, we estimate that the maximum area compression rate for folding as the major collapse mechanism is approximately 0.2 s (-1), a rate unattainable in a traditional Langmuir trough but achievable by the use of a dissolving microbubble.     

Effect of anions on the dissolution of Al in acid solutions

The effect of Cl^?, Br^?, I^?, ClO₄^?, NO₃^?, HSO₄^?, HCrO₄^? and H₂PO₄^? on the of Al in 2 M HCl is studied by the thermometric method. Three sets of experiments are carried out, which allow the variation of the concentration of the various species in a programmed manner. Dissolution promotion is noted in solutions to which HCl, HBr and H₂CrO₄ are added. The way of action of each of these anions is discussed. Additions of HI, HClO₄, H₂SO₄ and H₃PO₄, on the other hand, first retard and later enhance the dissolution of Al in 2 M HCl, as their concentration in solution is increased. This is related to anion adsorption, which is counterbalanced by increase in acidity. HNO₃ differs from the other tested acids in causing only dissolution retardation. Experiments in which LaCl₃ is added to the test solution indicate that the NO₃^? is adsorbed as such on Al₂O₃. The ability of the various anions to retard the dissolution of Al in 2 M HCl decreases in the succession: NO₃^? (strong)>I^?>HSO₄^?>H₂PO₄^?>Br^?, ClO₄^? (weak)     

Effect of the temperature of polyurethane dissolution on the mechanism of wet-casting membrane formation

An analysis of data from scanning electron microscopy (SEM), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) for two series of polyurethane membranes is presented. Membranes were prepared by direct immersion of the casting solution of polyurethane, dissolved in dimethyl formamide at different temperatures, into either water or 1-octanol bath at 25 °C. Depending on the temperature of polyurethane dissolution, a gradual variety in the membrane structure was observed by SEM. As the temperature of polymer dissolution was increased, the membrane structure changed from dense to cellular or particulate morphologies. On the basis of the GPC and DSC results, polyurethane molecular weight decreased but the degree of microphase separation caused by clustering of some of the soft and hard segments into separate domains in the membrane increased with increasing the temperature of polymer dissolution. It is thus proposed that the change in membrane structure is due to the variation of molecular weight of polyurethane, which in turn can change polymer chain mobility during membrane formation. In addition, the extent of microphase separation was described and related to the particulate morphology when 1-octanol was used as the nonsolvent.     

Anomalous dissolution behavior of the diazepam — γ-cyclodextrin complex in polymer solutions

The dissolution process of the diazepam — -cyclodextrin complex in aqueous polymer solutions has been studied. Hydroxypropyl cellulose and polyvinylpyrrolidone stabilize the supersaturated state of the complex, maintaining the higher drug level for a longer period. Polyethyleneglycol and dextran accelerated the dissociation of the complex, and caused a rapid decrease in drug concentration. These anomalous dissolution behaviors are discussed on the basis of viscosity changes of the polymer solutions along with the competitive interaction of polymers for the inclusion complex.     

Effect of methanol on the dissolution of neodymium oxide in hydrochloric acid solutions

The effect of methanol on the solubility of Nd₂O₃ in HCl medium in the temperature range of 25–55°C were studied. HCl-CH₃OH was observed to be a better solvent than HCl-CH₃OH-H₂O and hydrochloric acid for the dissolution of Nd₂O₃ mainly due to prevention of neodymium hydroxide and dissolution increased with increase of HCl concentration even at high HCl concentrations. Presence of methanol in the medium was determined to cause corresponding decreases in conductivity, E_SCE, pH values with corresponding increase in E_R values. Neodymium compounds formed in HCl-CH₃OH medium at 25°C were isolated and identified using X-ray diffraction, thermal and chemical analysis methods and their thermal behaviour were investigated between 25–1100°C. NdCl₃ × x ₁CH₃OH and NdCl₃ × x ₂CH₃OH × 4.14H₂O (x ₁ + x ₂ = 2.8) were formed in non-aqueous medium and these compounds were converted into NdCl₃, NdCl_2.37 and NdCl₃ × 0.47CH₃OH with complete and partial loss of water and methanol around 240°C respectively. Methanol was completely removed around 390°C with formation of NdCl_2.37 (77.5%) and NdOCl (22.5%) and NdOCl was detected as the major stable phase above 700°C.     

Effects of water content on the dissolution behavior of wool keratin using 1-ethyl-3-methylimidazolium dimethylphosphate

Ionic liquids(ILs) are eco-friend and recyclable solvents for dissolution of wool keratin, and water is often used as antisolvent to regenerate keratin from IL solution. To recycle the ILs, removing water is the necessary step. However, complete removal of the water is energy-intensive and costly. The water in ionic liquids would change the physicochemical properties and cluster structures of the IL and further affect its dissolution behavior on keratin. Here, 1-ethyl-3-methylimidazolium dimethylphosphate([Emim]DMP) was used for experiments due to its good performance on dissolving keratin. The experimental and simulation results showed that the dissolving capability of [Emim]DMP was decreased and the interactions between cation and anion became weaker with water concentration increasing. Furthermore, the dissolution time of wool keratin in [Emim]DMP increased with water content rising. At the same time, the effect of water in ILs on the secondary structure distribution and thermal stability of regenerated keratin was not obvious. In this work, by taking the structures of [Emim]DMP, keratin dissolution time and properties of the regenerated keratin into consideration, a balanced range of water content in [Emim]DMP was determined, which could not only reduce recycling cost but also not affect the dissolution behavior of the IL.     

Effect of deprotection extent on swelling and dissolution regimes of thin polymer films

The response of unentangled polymer thin films to aqueous hydroxide solutions is measured as a function of increasing weakly acidic methacrylic acid comonomer content produced by an in situ reaction-diffusion process. Quartz crystal microbalance with energy dissipation and Fourier transform infrared spectroscopy measurements are used to identify four regimes: (I) nonswelling, (II) quasiequilibrium swelling, (III) swelling coupled with partial film dissolution, and (IV) film dissolution. These regimes result from chemical heterogeneity in local composition of the polymer film. The acid-catalyzed deprotection of a hydrophobic group to the methacrylic acid tends to increase the hydrophilic domain size within the film. This nanoscale structure swells in aqueous base by ionization of the methacrylic acid groups. The swollen film stability, however, is determined by the hydrophobic matrix that can act as physical cross-links to prevent dissolution of the polyelectrolyte chains. These observations challenge current models of photoresist film dissolution that do not include the effects of swelling and partial film dissolution on image quality.     

Effect of Cl substituent in the aromatic tetracycline ring on its reactivity with solvated electrons

Decomposition yields of tetracycline hydrochloride /TC.HCl/ and chlorotetracycline hydrochloride /ClTC?HCl/ in methanol solution saturated with Ar or N₂O were determined. Rate constants of the reaction e_s with some antibiotics were obtained: $$\begin{gathered} k/e_s^ - + ClTC \cdot HCl/ = 2 \cdot 49 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} ; \hfill \\ k/e_s^ - + TC \cdot HCl/ = 2 \cdot 86 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} \cdot \hfill \\ \end{gathered} $$ On the basis of the diffence between decomposition yields: ΔG=G_?TC.HCl^?G?ClTC.HCl′ 7-C?Cl group decomposition yield and the rate constant $$k/e_s^ - + Cl - C - 7/ = 7 \cdot 94 \times 10^8 dm^3 \cdot mole^{ - 1} \cdot s^{ - 1} $$ were determined. It was demonstrated by¹H NMR that the radical formed by degradation of 7-C?Cl group is recombined with the H atoms leading to ClTC.HCl being converted into tetracycline hydrochloride /TC.HCl/.