Characterization of cephalexin loaded nonionic microemulsions

Water/propylene glycol/sucrose laurate/ethoxylated mono-di-glyceride/isopropyl myristate/peppermint oil U-type microemulsions were used to solubilize cephalexin. Microemulsion dilution and interfacial factors contributing to the cephalexin solubilization were evaluated. Cephalexin solubilization capacity increases with the increase in the aqueous phase volume fraction (φ) up to 0.4 then decreases. Electrical conductivity of drug loaded and drug free microemulsions increases with φ. The hydrodynamic radius measured by dynamic light scattering of the oil-in-water loaded microemulsions decreases with temperature. The microemulsions were characterized by the volumetric parameters, density, excess volume, ultrasonic velocity and isentropic compressibility. The microemulsion densities increase with φ up to 0.8 then decrease. The excess volume decreases with φ up to 0.8 then stabilizes. Ultrasonic velocities increase with the increase in φ while isentropic compressibility decreases. Analysis of the volumetric parameters enabled the characterization of structural transition along the microemulsion phase region. The presence of water-in-oil, bicontinuous and oil-in-water microemulsions, at aqueous phase volume fractions below 0.2, between 0.3 and 0.7 and above 0.8, respectively were found. Interfacial properties and dynamic structure of the monolayer for drug loaded and drug free microemulsions, were studied by electron paramagnetic resonance spectroscopy employing the nitroxide spin probe 5-doxylstearic acid. The rigidity of the interface was affected by the water content and also the presence of cephalexin.     

Fourier Transform and Multi Dimensional EPR Spectroscopy for the Characterization of Hydroxyapatite Gels

Calcium hydroxyapatite powder was prepared by the sol-gel method, using calcium acetate and PO(OC₂H₅)₃ as initialcompounds, and alcohol(methyl, ethyl, and propyl-alcohol) as solvent. Homogenous solutions andgels were prepared, using a molar ratio of Ca / P = 1.67. Theevolution of the structure was followed by XRD (X-ray diffraction), IR(Infrared), and FT-n(= 1, 2, 3)D-EPR (Fourier transform Electron Paramagnetic Resonance) spectroscopy. The dried gel exhibits a signalcharacterized by a central line and two satellites. The 2D spectrum(Electron Spin Echo Envelop Modulation ESEEM vs. field sweep) showed thesame modulation for the central line. The FT-EPR spectrum vs. field sweep2D-spectrum indicated that the satellites are due to an hfs splitting withwater. The central region of this 2D spectrum is influenced by P and H in a concentration ratio of[H] / [P] = 2.5. TheESEEM spectrum was simulated, assuming the equation for two spin systems S = 1/2 andI = 1/2. This simulation gave, for m and n, the values of 2 and5, respectively. This finding suggests a–P–O–P–O–P– linear evolution of thestructure. It appears that one ethyl group does not hydrolyze in thegelation process. This result was confirmed by IRspectroscopy.     

Platinum-dihalide complexes with N-alkyl O-ethylthiocarbamates

Summary The thiocarbamic esters (L)ETC(EtOSCNHEt) and PTC (EtOSCNHPr) act as sulphur donors towards platinum halides, yielding the cis-[Pt(L)₂Cl₂], trans-[Pt(L)₂Br₂], [Pt(L)₃X]X (X = Cl or Br) and [Pt(L)₄]X₂ (X = Cl, Br or I) complexes. By addition of n-hexane to platinum chloride solutions in pure ligands the 16 adducts [Pt(L)₄]-Cl₂·2L have been isolated. The non-bonded ligand molecules are easily released to give the corresponding 14 complexes. The compounds have been characterized by elemental analysis and spectroscopy. The 14 and 16 complexes decompose in benzene to form the 13 species, except for [Pt(ETC)₄]I₂, which releases two ligand molecules to give trans-[Pt(ETC)₂I₂]. The 12 and 13 complexes have been tested for in vitro cytostatic activity against KB cells.     

Computational Kinetic Study for the Unimolecular Decomposition of Cyclopentanone

Among various categories of potential biofuel molecules, ketones are of significant interest. Cyclopentanone is a cyclic ketone that can be produced from biomass, and its combustion is still unknown. Moreover, its cyclic configuration makes it an interesting feedstock for the further production of high‐density fuels such as bi(cyclopentane). This study reports the first computational kinetic investigation of the unimolecular decomposition pathways of cyclopentanone by using the compound G3B3 method. The rate constants were calculated using Rice–Ramsperger–Kassel–Marcus theory in the temperature range of 800–2000 K. The results presented here can be used in a future kinetic combustion mechanism.     

Biocompatible microemulsions based on limonene: formulation, structure, and applications

The preparation of biocompatible (w/o) microemulsions based on R-(+)-limonene, water, and a mixture of lecithin and either 1-propanol or 1,2-propanediol as emulsifiers was considered. The choice of the compositions of the microemulsions used was based on the pseudo-ternary phase diagrams of the four-component system determined at 30 degrees C for different weight ratios of the components. When 1-propanol was considered as co-surfactant, the area of the microemulsion zone was remarkably increased. Interfacial properties and the dynamic structure of the emulsifier's monolayer were studied by electron paramagnetic resonance (EPR) spectroscopy using the spin-labeling technique. The rigidity and polarity of the interface were affected by the nature of the alcohol used as co-surfactant. When 1-propanol was used, the emulsifier's interface was much more flexible, indicating a less tight packing of lecithin molecules than in the case of 1,2-propanediol. In addition, the membrane's polarity was decreased when the diol was added as co-surfactant in the microemulsion system. To evaluate the size of the dispersed aqueous domains as a function of water content and other additives concentration, dynamic light scattering (DLS) measurements were carried out. Radii in the range from 60 to 180 nm were observed when 1-propanol was used as co-surfactant, and the water content varied from 0 to 12% w/w. Electrical conductivity measurements of R-(+)-limonene/lecithin/1-propanol/water microemulsions with increasing weight fractions of water indicated the appearance of a percolation threshold at water content above 4% w/w. Lipase from Rhizomucor miehei was solubilized in the aqueous domains of the biocompatible microemulsions, and the esterification of octanoic, dodecanoic, and hexadecanoic acids with the short-chained alcohols used as co-surfactants for the formulation of microemulsions was studied. The enzyme efficiency was affected by the chain length of the carboxylic acids and the nature of the alcohol. In the case of 1-propanol, a preference for the long-chain carboxylic acids was observed. On the contrary, when 1,2-propanediol was used formulation of the corresponding esters was not observed. This behavior could be possibly attributed to either the specificity of the lipase toward the alcohol employed for the esterification of the acids or the structural changes induced in the system when 1-propanol was replaced by 1,2-propanediol.     

Calorimetric study of dissolution kinetics of phosphorite in diluted acetic acid

In this report, we present a thermodynamic and kinetic study of the selective dissolution of calcite from low-grade phosphate ores (Epirus area, Greece) by dilute acetic acid at isothermal conditions. A twin calorimeter with two identical membrane vessels, for the acid dissolution process, and for the reference was used. The curves of rate vs. time of the phosphorite dissolution for various temperatures show that the maximum (.q _max) was increased, whereas the time (t _peak) to achieve the corresponding .q _max values was decreased, as the experimental temperature was increased. The dissolution enthalpy was increased from 13.1 to 16.7 kJ mol⁻¹, as the experimental temperature was increased from 10.0 to 28.0°C. The chemical analysis of the supernatant solutions shows that the main process was the calcite dissolution. The reaction model with general form, ln(1/(1-X))=kt ^m, was found to fitted the experimental data regardless of the experimental temperature. These results were assigned in the presence of two different kinds of particles in the phosphorite. The activation energy of the dissolution process was found 69.7 kJ mol⁻¹. The SEM micrographs of acid dissolution samples showed two different textures after acid dissolution.     

Thermal behavior of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> mesoporous gels

Summary Titania-based photocatalytic materials were prepared by sol-gel method using Fe³⁺ and polyethyleneglycol (PEG₆₀₀) as additives. Thermogravimetry (TG), differential thermal analysis (DTA) and evolved gas analysis (EGA) with MS detection were used to elucidate processes that take place during heating of Fe³⁺ containing titania gels. The microstructure development of the Fe₂O₃/TiO₂ gel samples with and without PEG₆₀₀ admixtures was characterized by emanation thermal analysis (ETA) under in situ heating in air. A mathematical model was used for the evaluation of ETA results. Surface area and porosity measurements of the samples dried at 120&deg;C and the samples preheated for 1 h to 300 and 500&deg;C were compared. From the XRD measurements it was confirmed that the crystallization of anatase took place after thermal heating up to 600&deg;C.     

Sol-Gel Route and Characterization of Supported Perovskites for Membrane Application

In the last decades the sol-gel method has registered an intensive development in new fields of applications as membrane technologies, solid-state chemical sensors, SOFCs, etc. The aim of the present work is to make a bibliographic overview on the problem discussed and to develop supported perovskites for membranes application via sol-gel route and to study them. In this context a preparation procedure has been accomplished for deposition of mixed conducting La_0.8Sr_0.2Co_0.8Fe_0.2O_{3 –} thin layers on porous ceramic supports. Characterization techniques, as ESR control of Fe(III) ions into the precursor solutions, SEM surface morphology study, La- Sr- Co- and Fe-element distribution, as well as XPS partial spectra of La3d- Sr3d- Co2p- Fe2p and O1s- for a single coating surface have been applied. Adequate interpretation and conclusions regarding membranes investigated are presented as well.     

Colloidal structures in natural oils

Natural oils are in general mixtures of triglycerides of various fatty acids containing also small quantities of a multitude of other molecules, the minor components. Their composition depends on the type of their sources, either vegetable or animal, and on agronomic and climatic conditions. Extraction process highly influences the final composition of the natural oils. The bulk triglyceride phase presents some structural order due to the internal polarity of these molecules. The presence of the minor components, which are either amphiphilic or even hydrophilic together with some remaining moisture, induces colloidal association within the lipophilic triglyceride phase. These local organizates host proteins and antioxidants that preserve their activity influencing the quality and stability of the edible oils. Of specific interest is the case of the veiled virgin olive oil, the untreated juice of the olives. Veiled virgin olive oil is unique among vegetable oils that is consumed without any refining process and consequently possesses colloidal structure. It is remarkable that this unfiltered oil presents higher resistance to oxidation than the filtered ones, indicating the significance of internal structure to the final quality of the product.     

Electrical conductivity and photoconductivity studies of TiO2 sol–gel thin films and the effect of N-doping

Several sol–gel TiO₂ thin films, N-doped and undoped, were prepared using the dip-coating technique. Dark conductivity in vacuum and in air gives information on the role of the adsorbed oxygen or water and the influence of nitrogen. Transient photoconductivity in vacuum and in air was studied with illumination time for various light intensities and found to be very sensitive to the environment. The rise and decay are much faster in air than in vacuum, suggesting the predominant mechanism of conduction in each case. The role of the presence of nitrogen is also discussed.