Comparison of Solid-Liquid and Liquid-Liquid Mass Transfer

Mass transfer from solutions of m-acetotoluide, phenacetin and salicylamide into a stationary solvent, water, was studied. A sharp concentration jump was found at the leading solute front for all three liquid-liquid systmes. A comparison was made between the mass transferred in solid-liquid and liquid-liquid systems. The dissolution of m-acetotoluide, phenacetin and salicylamide was compared with mass transfer of solute from solutions with concentrations C_i, 2C_i and C_s into the pure solvent. In all cases, the amount dissolved from the solid was approximated by the C_i or the 2C_i-solvent system with the amount transferred in the C_s-solvent system approximately 100 fold greater than was dissolved from the solid. It was concluded that a concentration much less than saturation exists at the solid-liquid interface and that dissolution of the three compounds studied is controlled by the rate of solvent interaction at the solid surface.     

Influence of Certain Additives on the Diffusion Rate of Aspirin, Salicylamide and Phenacetin Through the Rat's Ileum

The diffusion rate of aspirin, salicylamide and phenacetin through the rat's ileum was found to be concentration dependent. The presence of glucoseamine hydrochloride decreased the amount diffused from each drug. The higher diffusion rate of aspirin was happened in presence of 0.01% w/v Myrj 59, followed by Brij 58 and then cetrimide. While that of salicylamide increased in presence of 0.01% w/v Tween 80. The more convenient increase in the diffusion rate of phenacetin produced in presence of 0.01% w/v Tween 20 and 0.3% w/v sodium lauryl sulfate. The other tested surfactants either reduced the amounts of drugs diffused or produced insignificant effect. With regard to the effect of aliphatic acids-drugs solid dispersions, tartaric acid increased the diffusion rate of aspirin; citric, tar taric and succinic acids as well as PEG 4000 increased the diffusion rate of salicylamide while, succinic acid increased the diffusion rate of phenacetin through the rat's ileum.     

A New Approach for Enhancing the Dissolution Rate of Phenacetin

Abstract

Numerous attempts are conducted so as to develop a rapid dissolution rate for those poorly water-soluble drugs. A new approach for enhancing the intrinsic dissolution rate of phenacetin is ascribed. This technique is based on the concept of the recrystallization of phencetin from different surfactants concentrations. The observed enhancing effect in the dissolution rate of phenacetin, using this technique, may be cue to wetting and/or deaggregation effect. The dissolution rate study was investigated in 0.1 N HC1 at 37°C and 50 r.p.m. The experimental study showed that the dissolution rate, during the first few minutes, is markedly affected by this technique. The relative area under the curve from 0 to 30 minutes (R.A.U.C.) was used as a parameter to 0–30 compare the different dissolution rates of the drug after being recrystallized from 1% w/v of each surfactant solution. The extent, in the dissolution rate enhancing effect, was found to range from 2.66 to 3.25 times of that of the control. This technique is valuable as a preformulation phase of phenacetin in solid dosage forms.     

Mechanochemical synthesis and heating-induced ordering of Ni-Al-Cr-C quaternary solid solutions

Nanocrystalline mixed (substitutional/interstitial) solid solutions have been prepared by milling four-component mixtures with the overall compositions (Ni_2.8AlCr_0.2)C_0.5 and (Ni₃Al_0.8Cr_0.2)C_0.5. Analysis of X-ray diffraction data indicates that the formation of the solid solutions is accompanied by an increase in deformation stacking fault probability, which is directly related to the amount of dissolved carbon. Our results demonstrate that the heating-induced ordering of the solid solutions occurs in several steps. Nucleation of the antiperovskite phase E2₁ occurs through spinodal decomposition of the Ni(Al,Cr,C) solid solution starting at 400°C. Heating to higher temperatures leads to partial Cr precipitation from the ordered phase and the formation of the chromium carbide Cr₃C₂, which reduces the carbon content of the antiperovskite phase.     

Esr Study of C60 N- Anion Radicals in DMSO Solution

Abstract

With the aim to stabilize reduced C₆₀ molecules of solid fulleride as free anion radicals in solution, Na_xC₆₀ (x=l, 10) was dissolved in DMSO. The Na_xC₆₀ was chosen among the other alkali-metal fullerides due to the possibility to increase a number of intercalated Na atoms in a fee. lattice of C₆₀ A sufficiently high concentration of C₆₀ anion radicals of an order of magnitude larger than that usually achieved in solution by an electrochemical reduction was obtained. The sharp resonances with the linewidths of order of 0.1 G and with g=2.0004(6) ?2.0012(8) of the room temperature ESR spectra of fluid solution were assigned from mono- to pentaanions of C₆₀. An appearance of additional sharp peaks at g=2.0016–2.0019 in the spectra of solution of nominal Na₁₀C₆₀, but Na₁C₆₀, tentatively related to C₆₀ ^n- with n>6. The results of this study showed a simple approach in an accomplishment of highly concentrated solutions of free anion radicals C₆₀ ^n-, as well as in stabilization of the anion radicals with increased n. In this way a homogeneity of alkali metal intercalation and characteristics of the solvent will be important.     

Impact of isovalent defect engineering strategies on carbon-related clusters in silicon

In electron-irradiated silicon (Si) the formation of oxygen-vacancy pairs (VO or A-centers) is deleterious and for this reason isovalent defect engineering strategies have been proposed to suppress their concentration. Carbon-related clusters such as C_iO_i and C_iC_s are also important as they are electrically active and their properties need to be determined. The present study has two aims. The first aim is to review the impact of isovalent doping [germanium (Ge), tin (Sn) and lead (Pb)] on the thermal stability of the C_iO_i and C_iC_s pairs in Si by means of infrared (IR) spectroscopy. The second aim is to analyze these results and show that the presence of isovalent dopants in Si reduces the temperature of annealing (T_ann) of the C_iO_i pairs and increases the temperature of annealing of the C_iC_s pairs. The results are discussed in view of recent experimental and theoretical studies. It is suggested that the change in the thermal stability of the C-related defects is due to the local strains induced in the lattice by the oversized isovalent dopants. It is surmised that these strains have an opposite impact on the T_ann of the C_iO_i and C_iC_s pairs as a result of their different structures.     

Utilizing spray drying technique to improve oral bioavailability of apigenin

The aim of this study was to prepare, characterize, and evaluate apigenin in a solid dispersion system to improve the dissolution rate and bioavailability of such poorly soluble drug. Apigenin was dissolved in organic solvent with micelle forming polymer Pluronic F-127 (PL-F127). Solid dispersion of apigenin-PL F-127 was developed using spray drying technique. Physicochemical and in vitro characterization of the produced solid dispersion particles were conducted using scanning electron microscopy, differential scanning calorimetry, Fourier transform infrared spectroscopy, powder X-ray diffractometry and dissolution study. In addition, in vivo study was performed for the spray dried versus pure and marketed apigenin. C_max was found to be around 5 folds higher for spray dried product compared to non spray dried materials. The prepared drug:polymer formulation showed elongated particles and complete lack of crystallinity at 1:4 ratio. The change in the vibrational wave numbers strongly suggested the formation of hydrogen bonding between apigenin and PL F-127. Significant increase in the dissolution rate and bioavailability of the spray dried apigenin showed the potential of solid dispersion system to overcome problem related to BCS II drugs.     

All-cellulose composites by partial dissolution in the ionic liquid 1-butyl-3-methylimidazolium chloride

Fully bio-based and biodegradable all-cellulose composites were prepared in the form of films by partial dissolution of two cellulose sources: a commercially available microfibrillated cellulose (MFC) and filter paper (FP). The solvent selected for this work was the ionic liquid 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl). Both cellulose sources were partially dissolved at 80 °C and consolidated by partial dissolution, resulting in excellent mechanical properties. X-ray diffraction and electron microscopy demonstrated that partial dissolution was a viable path to transform FP into a continuous paracrystalline matrix reinforced with cellulose I crystallites. In contrast, partially dissolved MFC was not as thoroughly dissolved and large amounts of undissolved material were still visible along the centre line of the films after the longest dissolution times. Consequently, partially dissolved MFC retained its initially high crystallinity. The degree of polymerization of the materials after dissolution was significantly reduced.     

[60]Fullerene as a Novel Photoinduced Antibiotic

Abstract

The antibacterial activity of [60]fullerene (C₆₀), dissolved with poly(vinylpyrrolidone) K30 (PVP), was studied. Under photo‐irradiation, C₆₀/PVP aqueous solutions showed antibacterial activity, whereas PVP solution alone or fullerene solutions in the absence of light showed no activity. These results reveal that C₆₀ is a potentially good device as a photoinduced antibacterial agent.     

Electron Capture and Fragmentation at Ar6+–C60 Collisions

Abstract

Mass/charge spectra of recoil ionic fragments formed in collisions of C₆₀ molecules with keV‐energy Ar⁶⁺ projectile ions were studied using registration of the fragments in coincidence with the projectile captured certain number of electrons s at the same single collision. Different channels of the fragmentation accompanied by additional ionization were observed. The degree of fragmentation is caused mainly by electronic excitation transferred predominantly to C₆₀ at the electron capture and increases with s value from 1 to 6.     

Effect of copper addition and heat treatment on segregation behaviour of Al–7Mg–Cu alloys

Abstract

Electron probe microanalysis showed that Al–7Mg–Cu alloys possess serious segregation tendencies. The addition of copper promoted the segregation of magnesium and led to the formation of non-equilibrium eutectic. With an increase in the copper content of the alloys, the severity of the solute segregation increased. Homogenisation reduced the solute segregation significantly. During homogenisation, the non-equilibrium eutectic compound Al_xCu_yMg_z gradually dissolved. Its dissolution behaviour depended on its copper content. Precipitates of Al_xCu_yMg_z with a comparatively low level of copper dissolved, while those with a high level of copper were less soluble and became divided into small blocks. The higher the copper content of the alloys, the larger and the greater in number the remaining Al_xCu_yMg_z particles. In the undissolved Al_xCu_yMg_z, the concentration of copper increased and that of magnesium decreased. Two step homogenisation reduced the solute segregation and dissolved the non-equilibrium eutectic further.

MST/3194     

Synthesis and characterization of vanadium-containing ZrO2 solid solutions pigmenting system from gels

A procedure is reported for the synthesis of vanadium-doped zirconia pigmenting system with different vanadium loadings which permitted their complete formation and further characterization. Monoclinic vanadium-zirconia solid solutions were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate and studied over the range of temperature up to 1300 °C. Succesive steps of the reactions leading to the final monoclinic vanadium-zirconia solid solution phase were investigated by X-ray powder diffraction. It was found that the formation of the monoclinic solid solution took place by a phase transformation from a phase with the structure of tetragonal zirconia. The transformation temperature of metastable tetragonal to monoclinic phase was found to be governed by the nominal vanadium amount. Measurements of lattice parameters of monoclinic vanadium-zirconia solid solutions as a function of the nominal vanadium amount revealed that vanadium was dissolved in the zirconia lattice. Energy dispersive X-ray microanalysis and lattice parameters variation indicates that the maximum amount of vanadium into the monoclinic zirconia lattice was about 5 mol % of vanadium (3.7 wt % as V₂O₅). UV-Vis diffuse reflectance of monoclinic V-ZrO₂ solid solutions indicated that vanadium was dissolved as V⁺⁴ and that the color of vanadium-zirconia yellow pigments was produced by the dissolved vanadium.     

Carbamazepine and Polyethylene Glycol Solid Dispersions: Preparation,in Vitro Dissolution,and Characterization

Abstract

The objective of this study was to prepare solid dispersions of carbamazepine (CBZ) using polyethylene glycol (PEG) 4000 and PEG 6000, measure the dissolution, and characterize using x-ray diffraction, DSC, and IR spectroscopy. Solid dispersions were prepared by either the melt or solvent methods. A comparison of dissolution profiles of the solid dispersions indicated dramatic increases in the rate and extent of CBZ dissolution from solid dispersions. The dissolution of physical mixtures provided evidence of the solubilizing effects of PEGs. Untreated CBZ exhibited 10.09 ± 2.92% dissolution in 10 min (D_l0); whereas, a melt of PEG 6000 and CBZ at a ratio of 6: 1 provided 36.49 ± 1.97% and a melt of PEG 4000 and CBZ at a ratio of 6: 1 gave a D₁₀ of 23.59 ± 1.45%. The rate and extent of dissolution of CBZ were significantly higher when blends of the PEGs were employed to prepare solid dispersion. The melt method provided significantly higher rate and extent of dissolution of CBZ than the solvent method. Also, the rate and extent of dissolution of CBZ were significantly greater when the solid dispersion was cooled at room temperature as opposed to with ice (faster). X-ray diffractometry revealed almost a complete loss of crystallinity of CBZ in solid dispersions. IR spectrometry indicated an increase in amorphocity of the PEGs after melting. IR spectra suggested that no complexation occurred between the PEGs and CBZ. Alterations in the crystallinity of the system were also supported by the DSC thermograms. Decreasing heats of fusion implied decrease in crystallinity, which would be expected to provide greater dissolution rates. Peak melting temperatures obtained from the thermograms ruled out the possibility of the formation of a eutectic mixture. However, the formation of solid solution could also be a possible mechanism for the increase in dissolution.     

Relative concentrations of carbon related defects in silicon

Irradiation induced defects in silicon are technologically important as they impact the electronic properties. Calculations based on density functional theory employing hybrid functionals have been previously used to investigate the structures and relative energies of defect clusters formed between vacancies, self-interstitials, carbon and oxygen atoms in silicon. In this study we employ a model to calculate the relative concentrations of carbon related defects in silicon. It is calculated that the carbon content has a significant impact upon the concentration of carbon-related defects. The C_iC_s defect is the most populous for all the conditions considered followed by the C_iO_iSi_I and the C_iO_i defects. C_iO_iSi_I and the C_iO_i become increasingly important for silicon with high carbon concentrations.     

Mucoadhesive plasticized system of branched poly(lactic-co-glycolic acid) with aciclovir

Commercially available antibacterial semisolid preparations intended for topical application provide only short-term drug release. A sustained kinetics is possible by exploitation of a biodegradable polymer carrier. The purpose of this work is to formulate a mucoadhesive system with aciclovir (ACV) based on a solid molecular dispersion of this drug in poly(lactic-co-glycolic acid) branched on tripenterythritol (PLGA/T). The ACV incorporation into PLGA/T was carried out either by solvent method, or melting method, or plasticization method using various plasticizers. The drug–polymer miscibility, plasticizer efficiency and content of residual solvent were found out employing DSC. Viscosity was measured at the shear rate range from 0.10 to 10.00?s^?1 at three temperatures and data were analyzed by Newtonian model. The mucoadhesive properties were ascertained in the tensile test on a mucin substrate. The amount of ACV released was carried out in a wash-off dissolution test. The DSC results indicate a transformation of crystalline form of ACV into an amorphous dissolved in branched polyester carrier, and absence of methyl formate residuals in formulation. All the tested plasticizers are efficient at T_g depression and viscosity decrease. The non-conventional ethyl pyruvate possessing supportive anti-inflammatory activity was evaluated as the most suitable plasticizer. The ACV release was strongly dependent on the ethyl pyruvate concentration and lasted from 1 to 10 days. The formulated PLGA/T system with ACV exhibits increased adhesion to mucosal hydrophilic surfaces and prolonged ACV release controllable by degradation process and viscosity parameters.     

Kinetic approach to the release of vinyl chloride monomer from polymer films,as related to diffusional theories

Monomer-release kinetics from polyvinyl chloride films, previously saturated by equilibration with monomer solutions in $\text{n}$-hexane, ethylene glycol monomethylether, methanol, and water, were measured by extraction with these model solvents, at 10–50 °C. Solute desorption rate data fitted a linear plot of total amount of solute released $\text{vs}$. the square root of time. Their analysis, in terms of diffusional release theory of a dissolved solute from a polymer matrix with initial solute loading given by the solubility limit, allowed one to obtain diffusivities of vinyl chloride in the polymer as a function of temperature, from which an activation energy of 11.9 ± 0.9 Kcal/mol could be calculated. Release kinetics were practically controlled by the low diffusivities, without any resistance to solute transport due to external mass transfer coefficients. The accelerating influence of solvents, relative to solvent-free experiments reported in the literature, may be compared to a plasticizing penetrant effect, which, however, does not appear to be susceptible, as to its bearing on diffusivities, to the chemical nature of the solvent used.     

Formulation and pharmacokinetics of gelucire solid dispersions of flurbiprofen

Context: Development of solid dispersions is to improve the therapeutic efficacy by increasing the drug solubility, dissolution rate, bioavailability as well as to attain rapid onset of action.

Objective: The present research deals with the development of solid dispersions of flurbiprofen which is poorly water soluble to improve the solubility and dissolution rate using gelucires.

Materials and methods: In this study, solid dispersions were prepared following solvent evaporation method using gelucire 44/14 and gelucire 50/13 as carriers in different ratios. Then the formulations were evaluated for different physical parameters, solubility studies, DSC, FTIR studies and in vitro dissolution studies to select the best formulation that shows rapid dissolution rate and finally subjected to pharmacokinetic studies.

Results and discussion: From the in vitro dissolution study, formulation F3 showed the better improvement in solubility and dissolution rate. From the pharmacokinetic evaluation, the control tablets produced peak plasma concentration (C_max) of 9140.84?±?614.36?ng/ml at 3?h T_max and solid dispersion tablets showed C_max?=?11?445.46?±?149.23?ng/ml at 2?h T_max. The area under the curve for the control and solid dispersion tablets was 31?495.16?±?619.92 and 43?126.52?±?688.89?ng h/ml and the mean resident time was 3.99 and 3.68?h, respectively.

Conclusion: From the above results, it is concluded that the formulation of gelucire 44/14 solid dispersions is able to improve the solubility, dissolution rate as well as the absorption rate of flurbiprofen than pure form of drug.     

Distribution of 3d Activator Ions over C i and C s Isomorphic Positions in Olivine-Structure Crystals

The effect of the olivine structure and properties of 3d activator ions on their distribution over the isomorphic positions C _i and C _s is analyzed. It is shown that the choice of a higher symmetry subgroup among the subgroups of the space group of olivine (Pnma) corresponding to the structures formed by ions in either the C _i or C _s position and Brown's principle lead to a higher probability of incorporation of the activator into position C _i. In terms of the crystal-field potential, this selectivity is due to the deeper potential minimum in position C _i. The angular distribution of electron density in the ground state of 3d ions influences their distribution over positions C _i and C _s in weak crystal fields through the strength of chemical bonding. These conclusions are supported by experimental data for olivine-structure crystals: forsterite and pyroxene activated with iron-group ions and alexandrite.     

Simplified calculation of temperature field in heat treated cylinder using temperature measured at one point

Abstract

The calculation of the temperature field T(r) in a heat treated cylinder requires a knowledge of the heat transfer coefficient h(T_s) which may show a highly non-linear dependence on the surface temperature T_s. Since h(T_s) can very often not be explicitly determined, measurement of a temperature T_i near the surface is employed. As a result the analysis becomes an inverse (‘ill posed’) problem which cannot be handled using standard finite element codes that are applicable only to direct problems. By implementing a procedure for an explicit estimation of the surface temperature T_s the problem can be overcome via two direct calculations. Diagrams are presented for calculation of both the surface temperature T_s and the heat transfer coefficient h(T_s). The method is applied to the investigation of a duplex steel cylinder which is quenched in cold water. The accuracy of the method is discussed and the complex nature of h(T_s) is demonstrated.

MST/1497