Influence Of Preparation Parameters Research Articles

Preparation of vancomycin microparticles: Importance of preparation parameters

The aim of the present work was to prepare microparticles containing vancomycin for intraocular injection. The primary objective was to guarantee continuous release and keep an intracameral drug concentration above the minimal inhibitory limit for at least 24 h, needed in endophthalmitis prophylaxis after cataract surgery. Poly(lactide-co-glycolide) microparticles were prepared using the double emulsion (water-in-oil-in-water) solvent extraction/evaporation method. The influence of preparation parameters on the final microparticles properties was explored in an attempt to control particle sizes, stability, encapsulation rate and vancomycin release profile. Satisfying release profile and stability were obtained, independently of the process. Sizes and encapsulation rate were controlled using an experimental design. Final obtained properties demonstrated that the fabricated particles are suitable for the prophylactic intraocular use in cataract surgery. Further in vitro and in vivo experiments will be conducted to assess efficiency of the entrapped antibacterial and then validate its potential usefulness in prophylaxis.

Oxidation State of Vanadium Introduced in Dealuminated β Zeolite by Impregnation with VIVOSO4 Solution: Influence of Preparation Parameters

Vanadium was introduced in dealuminated beta zeolite by impregnation with a VIVOSO4 aqueous solution at 353 K in air or argon (to prevent oxidation of VIV), leading to VSibeta and VSibeta-Ar zeolites, respectively. The samples were characterized by spectroscopy, XRD, and N2-physisorption. The oxidation state and environment of V in Sibeta zeolite depend on the preparation parameters (i.e., on the way the solid is recovered after impregnation and on the drying temperature). In solids recovered by centrifugation, washed with distilled water, and then dried overnight at 298 K in argon, vanadium is found as extra-lattice octahedral VIV ions as evidenced by EPR. In contrast, in solids not washed but directly dried overnight at 353 K in air or argon, vanadium is found in both cases as lattice tetrahedral VV ions. These ions are incorporated into vacant T sites associated with SiOH, SiO-, oxygen vacancies (OVs) or nonbridging oxygen (NBOs) defects as shown by diffuse reflectance UV-visible, 51V MAS NMR, FT-IR, and photoluminescence. The oxidation to VV ions is suggested to be due to an electron transfer from VO2+ to trigonal identical with Si+ defect sites followed by reaction of the resulting VO2+ ions with particular defects of vacant T sites. These processes occur already upon drying of V-impregnated Sibeta at 353 K. 51V MAS NMR allows detection of one kind of lattice tetrahedral V ions in VSibeta and two kinds in VSibeta-Ar. The formation of different kinds of tetrahedral V species is related to the presence in vacant T sites of Sibeta zeolite of different types of defect sites such as trigonal identical with Si+ defect or SiOH and SiO- groups.

Adaptation and optimization of the emulsification-diffusion technique to prepare lipidic nanospheres

In this study, the emulsification-diffusion method traditionally used to prepare polymeric nanoparticles was adapted to obtain lipidic nanospheres (LN) using four model lipids. The method consists of dissolving the lipid in a partially water-miscible solvent (previously saturated with water) at room temperature or at controlled temperature depending on lipid solubility. This organic phase is emulsified in an aqueous solution of a stabilizing agent (saturated with solvent) by conventional stirring at the same temperature used to dissolve the lipid. This oil-in-water emulsion is then diluted with an excess of water at controlled temperature in order to provoke the diffusion from the internal phase into the external phase thereby causing lipid aggregation in the form of LN. This new approach for the preparation of LN has clear advantages over the existing methods, namely: (i) it is efficient and versatile; (ii) easy implementation and scaling up (with no need of high energy sources); (iii) high reproducibility and narrow size distribution; (iv) less physical stress (i.e., long exposure to high temperatures and to mechanical dispersion); (v) it is not necessary to dissolve the drug in the melted lipid. The selection of the water-miscible solvent and the stabilizers are critical parameters to obtain lipidic particles in the nanometric range. In general, solvents with high water miscibility and stabilizers able to form stable emulsions are preferred. The results demonstrated that it was possible to reduce the particle size by increasing the process temperature, the stirring rate, the amount of stabilizer, and by lowering the amount of lipid. Control of the preparative variables allowed to obtain LN with diameters under 100 nm. It was found that the influence of preparative parameters was associated with a mechanism based on a physicochemical instability. In this sense, it is suggested that the rapid solvent diffusion produces regions of local supersaturation near the interface, and LN are formed due to the ensuing interfacial phase transformations and lipid aggregation that occur in these interfacial domains. In terms of stability, only poly(vinyl alcohol) (PVAL) was able to preserve the physical stability of the dispersion for long periods after preparation. This effect was attributed to the ability of PVAL chains to form a strongly attached layer on the nanoparticle surface with an excellent repulsion effect.

Radical Crosslinked Albumin Microspheres as Potential Drug Delivery Systems: Preparation and In Vitro Studies

This article reports on the preparation of acryloylated bovine serum albumin microspheres and the evaluation of their employment in drug delivery areas. The influence of preparation parameters on albumin microspheres and the chemicophysical properties of loaded drugs were investigated. In particular, we focussed on acylation albumin degree and the amount of acryloylated albumin against comonomer in the polymerization step. Finally the release profile took into consideration the interaction drug-matrix, the fuctionalization degree of albumin, and the water affinity of matrix.

Radical Cross-Linked Albumin Microspheres as Potential Drug Delivery Systems: Preparation and In Vitro Studies

The aim of this research is the preparation of acryloylated bovine serum albumin microspheres and the evaluation of their employment in drug delivery. The influence of preparation parameters on albumin microspheres and the chemicophysical properties of loaded drugs were investigated. In particular, we focused our attention on acylation albumin degree, amount of acryloylated albumin against comonomer in the polymerization step, and finally the release profile. We considered on the interaction drug-matrix, the fuctionalization degree of albumin, and the water affinity of matrix.

Preparation of Mullite Whiskers from Kaolinite Using CuSO<sub>4</sub> as Fluxing Agent

Mullite whiskers were produced by firing of kaolin at 1400o-1550oC. CuSO4 was used as fluxing agent. Before firing, spray drying and baking with flour and leaven were employed to give free space to the powders. The influence of preparation parameters and firing temperature on the crystalline structure and phase transformations during the entire process was determined. The results showed that there was a beneficial effect of both the incorporation of CuSO4 and the given free space on the formation of mullite whiskers. There was no evidence for the effect of firing temperature on the aspect ratio and morphology of the whiskers within the investigated range.

Influence of Preparation Parameters and Storage Conditions on Rheological Behaviour of Faience Casting Slips Used in Tableware Industry

Influence of Preparation Parameters and Storage Conditions on Rheological Behaviour of Faience Casting Slips Used in Tableware Industry

Two series of triple- and single-domain reconstructions induced by europium on vicinal Si(1 1 1) [ [formula omitted]]-miscut surface

The growth and properties of Eu-induced one-dimensional reconstructions on vicinal Si(1 1 1) surface miscut in the [ 1 ̄ 1 ̄ 2 ] direction have been studied by low energy electron diffraction and scanning tunneling microscope in the submonolayer range. The focus has been attended to the formation of single-domain structures and the influence of preparation parameters on the domain orientation. We have found the critical conditions for the preparation of a variety of Eu-induced single-domain ( n×2) and ( n×1) structures. In addition, a new intermediate phase showing the 9×1 periodicity between 3×2 and 2×1 phases is detected.

Influence of preparation parameters on physical properties of Bi 2S 3 films prepared by the spray pyrolysis method

Polycrystalline Bi 2S 3 thin films of orthorhombic phase were prepared by a spray pyrolysis technique on an amorphous substrate. The influence of substrate temperature, T s, in the range of 180–500°C and solution molarity (0.05–0.4 mol) on the structural, electrical and optical properties were studied in detail. The crystal structure and orientation of the prepared films were investigated by X-ray diffraction pattern. The grain size of Bi 2S 3 was changed between 7.4 and 11.6 nm as the film thickness increased from 50 to 300 nm. Surface roughness, grain size and cross-section analysis were measured by the atomic force microscopy. A decrease in film thickness improves the transmission. This improvement can be attributed to the perfection and stoichiometry of the films. The optical band gap of the films decreased from 2.22 to 1.58 eV due to increasing the solution molarity (film thickness) from 50 to 300 nm.

Influence of preparation parameters on characteristics of zirconia-pillared clay using ultrasonic technique and its catalytic performance in phenol hydroxylation reaction

Ultrasonication method was employed for preparation of zirconia-pillared montmorillonite (Zr-PILC) by using polyhydroxy zirconium cation. The influences of various preparation parameters such as pH, concentration of pillaring agent, aging period on physico-chemical properties of Zr-PILCs are reported. The characterization was done by using different characterizing tools such as powder X-ray diffraction (XRD), thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), X-ray photo-electron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF) and surface area measurements. Effective pillaring was obtained in the pH range 2.0–2.8 at reduced preparation time by using ultrasonication. Ultrasonication, especially at higher pH and concentration of pillaring agent with no aging after ultrasonic agitation of the clay slurry was found to increase zirconium content and specific BET surface area leaving no scope for remarkable increase in d001 spacing. The presence of -OH groups attached to Zr has been revealed by pyridine-adsorbed FITR, TG/DTA and XPS techniques. The acidic character, ease of accessibility and good dispersion of active sites in Zr-PILC were found to be controlling factors for the challenging activity in hydroxylation reaction of phenol. Probably, this first report on the use of Zr-PILC in hydroxylation of phenol and its preparation by employing ultrasonication technique may attract great attention in the catalysis area of academic and industrial importance.

Influences of preparation parameters on the structural and catalytic performance of zirconia in isosynthesis

The influences of precipitation pH, zirconium salt precursors and the calcination temperatures on the crystal structure and catalytic performance of zirconia in isosynthesis have been studied. The results indicated that the catalytic performance of zirconia in isosynthesis was strongly influenced by the pH of precipitating solution, zirconium salt precursors and the calcination temperatures, However, the crystal phase of zirconia was not so sensitively dependent on the pH. Monoclinic was always the main crystal phase when the value of pH was changed in the range of 6–14. Zirconia prepared from Zr(NO 3) 4, ZrCl 4, ZrOCl 2 were monoclinic/tetragonal, but monoclinic was the dominant phase. Zirconia prepared from Zr(SO 4) 2 was a mixture of tetragonal/amorphous. Even trace of SO 4 2− involved in the gel, the crystallization of zirconia was delayed, the phase transformation from tetragonal to monoclinic being inhibited.

Copper- and Silver–Zirconia Aerogels: Preparation, Structural Properties and Catalytic Behavior in Methanol Synthesis from Carbon Dioxide

Copper- and silver-zirconia aerogels containing 10 at% IB metal were prepared from tetra-n-butoxy zirconium(IV) and IB metal acetates using the solution sol-gel method and ensuing high-temperature (HT) and low-temperature (LT) supercritical drying, respectively. The influence of preparation parameters and calcination on the structural and catalytic properties of the aerogels for the synthesis of methanol from carbon dioxide and hydrogen was investigated. After calcination in air at 573 K, the catalysts had BET surface areas in the range of 100–143 m2·g−1(Cu/ZrO2) and 77–125 m2·g−1(Ag/ZrO2), respectively. Due to the reductive alcoholic atmosphere during high-temperature supercritical drying, metallic copper and silver existed in all raw HT-aerogels. The mean size of the copper crystallites was 30 nm. The silver crystallite size for the HT-aerogel prepared with nitric acid was 10 nm, whereas for samples prepared with acetic acid it was 5–7 nm. Calcination in air at 573 K led to the formation of highly dispersed amorphous copper oxide and silver. Comparing the catalytic behavior of the calcined copper–zirconia aerogels with corresponding xerogels prepared by coprecipitation revealed highest activity for the LT-aerogel, whereas the HT-aerogels were least active. In contrast, similar catalytic behavior was observed for the differently dried silver-zirconia samples. Generally, CO2-conversion of the copper–zirconia aerogels was markedly higher than that of the corresponding silver–zirconia aerogels, whereas methanol selectivity was similar.

Influence of the preparative conditions on the precursor phases formed during the synthesis of beta-alumina by the wet chemical gel to crystallite conversions

Hydrated alumina gel, Al 2O 3 · yH 2O (80 < y < 120) reacts with sodium hydroxide in water-rniscible organic solvents yielding crystallites of either Na x AlO x (OH)3 − x (0.17 < x < 0.23), having the gibbsite structure with inserted sodium ions, or Na x AlO 1 + x OH 1 − x (0.17 < x < 0.23) of boehmite structure. On calcination at elevated temperatures these precursors yield phase-pure β″- (Na) alumina. A detailed investigation has been undertaken regarding the influence of preparative parameters on the precursor phases formed. It is observed that the non-aqueous solvents destabilise the gel irreversibly in the presence of alkali hydroxide by decreasing the effective ionic pressure within the gel cavities, and at the same time prevent the back diffusion of alkali ions inserted within the precursor lattice. In the presence of strongly desiccative (water attracting) solvents, dehydroxylation of (Na) gibbsite takes place under wet chemical conditions to yield pseudoboehmite. On calcination, both these phases give rise to intermediate alumina which, in turn, converts to β′'-alumina through a continuous solid state process.

Enhanced selectivity and sensitivity of first‐generation enzyme electrodes based on the coupling of rhodinized carbon paste transducers and permselective poly(o‐phenylenediamine) coatings

AbstractHighly specific oxidase‐based amperometric biosensors, based on the coupling of anti‐interference layers with selective metal‐dispersed carbon transducers are described. In particular, the efficient and preferential electrocatalytic action of rhodinized carbon pastes towards the peroxide product is combined with the discriminative properties of poly(o‐phenylenediamine) (PPD) films. Such focus on both the transducer and recognition layer offers freedom from interferences, while resulting in higher sensitivity towards the substrate. The influence of preparation parameters is explored, and the surface microstructures are discussed. Similar improvements are reported for the electrodeposition of rhodium, PPD and glucose oxidase onto glassy carbon transducers.

Influence of preparation parameters on the particle size of nanosized silicon

The influence of preparation parameters on the particle size of nanosized silicon (n-Si) produced by laser-induced chemical vapour deposition (LICVD) was studied. The optimum parameters for synthesizing the right sized n-Si have been obtained, and they are as follows. The power density of CO 2 laser is 1500 W/cm 2. The silane (SiH 4) concentration is 10 vol%. The dilution gas is argon of high purity. The flow rate of reactant gases is 100 sccm. And the pressure of the reaction chamber is 200 Torr. The particle size of n-Si prepared by LICVD can be varied in the range from 10 to 100 nm depending on the selection of preparation parameters.

Titania-Silica Mixed Oxides: I. Influence of Sol-Gel and Drying Conditions on Structural Properties

Mesoporous titania-silica aerogels with highly dispersed titanium have been prepared by an alkoxide-sol-gel process with ensuing semicontinuous extraction using supercritical CO 2. An acidic hydrolysant was added to a solution of tetraisopropoxytitanium(IV) modified by acetylacetonate and tetramethoxysilicon(IV) in isopropanol. The resulting titania-silica gels were dried by different methods, including conventional drying, high-temperature supercritical drying, and extraction with supercritical CO 2 (low-temperature aerogel). The influence of preparation parameters (the hydrolysis route, Ti-content, drying method, and calcination temperature) on the structural and chemical properties of the aero- and xerogels was studied by means of N 2-physisorption, X-ray diffraction, thermal analysis, and vibrational spectroscopy (FTIR, FTRaman). Prehydrolysis of the silicon alkoxide generally led to lower porosity, but did not influence the Si-O-Ti connectivity up to a calcination temperature of 1073 K. The conventionally dried xerogels contained titanium well-dispersed in the silica matrix and were predominantly microporous. High-temperature supercritical drying afforded meso- to macroporous aerogels with negligible microporosity, but undesired segregation of anatase. With the low-temperature aerogels, an increase of the nominal TiO 2 content from 2 to 20 wt% resulted in lower microporosity, higher BET surface area (up to ca. 700 m 2/g), and a rise in the contribution of Si-O-Ti species. Concomitantly the Ti-O-Ti connectivity increased without any indication of long-range ordering from X-ray analysis. The low-temperature aerogel with 20 wt% TiO 2 combined mesoporosity with high Ti dispersion and structural stability up to 873 K in air, properties desirable for epoxidation of olefins.

Fibre reinforced glasses

A new method of preparing fibre reinforced glasses is put forward, which is based on further developments of the known slurry method and the sol-gel technique. This method combines the advantages of the two procedures. The prepregs are hot-pressed and the influence of preparation parameters on the bending strength are investigated. The pressure, temperature, time of pressing, granulation of the glass powder, the type of sol-gel solution and the gas atmosphere during the hot-pressing were all studied.

The influence of preparation parameters on the deposition rate, density and optical properties of thin hydrogenated amorphous silicon films prepared by r.f. glow discharge

The computerization of the method by which the transmission data of thin hydrogenated amorphous silicon films on transparent substrates are calculated has made the manipulation of a large number of transmission spectra a practical possibility. A comparative study was carried out which demonstrates the effect of pressure, r.f. power and gas flow rate on the density ϱ, the refractive index n(λ), the dielectric constant ε r, the optical absorption α(λ) and the optical gap E 0 of these films which were deposited from pure silane in a glow discharge system. The density of the films was determined by means of the well-known flotation technique using a ZnCl 2 solution as the flotation medium.

Ion plating of copper layers on titanium: Influence of preparation parameters and deformation on the residual stresses

The microstructure of ion-plated copper layers on titanium was studied using scanning electron microscopy and X-ray diffractometry for residual stress analysis. The influence of the processing gas and the deposition rate on the properties of the layers was examined. Finally, the usefulness of these layers for cold impact extrusion was demonstrated.

Absorption spectra of Na and Na 2 in inert-gas matrices

The absorption spectrum of matrix-isolated sodium has been remeasured in the region between 4000 and 6600 Å. Improved evaporation techniques facilitated the preparation of nearly pure Na/X and, for the first time, Na 2/X matrices, where X is an inert gas. The structure observed in Na/Xe agrees with that found by other authors; two triplets at 5300 ⩽ λ ⩽ 6200 Å and a broad structure at 4960 Å. However, the influence of preparation parameters was found to be at variance with effects reported by others. For example, we find that the form of the spectra does not depend on the Na/Xe ratio but on the time rates of inert gas and sodium deposition. By such means, it is shown that the 4960 Å feature is in all probability not inherently Na 2 in nature.