Synthesis,Characterization and Surface Properties of Amidosulfobetaine Surfactants Bearing Odd-Number Hydrophobic Tail

Three amidosulfobetaine surfactants were synthesized namely: 3-(N-pentadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2a); 3-(N-heptadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2b), and 3-(N-nonadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2c). These surfactants were prepared by direct amidation of commercially available fatty acids with 3-(dimethylamino)-1-propylamine and subsequent reaction with 1,3-propanesultone to obtain quaternary ammonium salts. The synthesized surfactants were characterized by IR, NMR and mass spectrometry. Thermogravimetric analysis (TGA) results showed that the synthesized surfactants have excellent thermal stability with no major thermal degradation below 300 °C. The critical micelle concentration (CMC) values of the surfactants 2a and 2b were found to be 2.2 × 10^?4 and 1.04 × 10^?4 mol/L, and the corresponding surface tension (γ_CMC) values were 33.14 and 34.89 mN m^?1, respectively. The surfactants exhibit excellent surface properties, which are comparable with conventional surfactants. The intrinsic viscosity of surfactant (2b) was studied at various temperatures and concentrations of multi-component brine solution. The plot of natural logarithm of relative viscosity versus surfactant concentration obtained from Higiro et al. model best fit the surfactant behavior. Due to good salt resistance, excellent surface properties and thermal stability, the synthesized surfactant has potential to be used in various oil field applications such as enhanced oil recovery, fracturing, acid diversion, and well stimulation.     

Suppository formulation of amodiaquine - In vitro release characteristics

In vitro release characteristics of amodiaquine hydrochloride from suppositories were studied. Results showed that water soluble bases (polyethylene glycol and glycero-gelatin) and water miscible synthetic fatty base (Witepsol W45) are superior to natural fatty bases (theobroma oil and shea butter) in terms of their ability to release amodiaquine hydrochloride.

The in vitro availability of amodiaquine from polyethylene glycol suppository (the suppository which gave the highest rate and extent of release) was compared with its in vitro availability from tablets (Camoquin^R) under the same experimental conditions. Polyethylene glycol suppository was found to be superior to the tablet.     

Influence of Drug Loading and Gel Structure on in-Vitro Release Kinetics from Photopolymerized Gels

Precious work has shown that stabls and homogenous poly HEMA gels can be prepared using a visible light sensitive initiator system. Gels were prepared from solutions of water and poly-2-hydroxyethyl methacrylate monomer. At concentrations of water greater than 10% v/v, translucent gel resulted. However, polymerization solvents such as glycerol and tertiary butyl alcohol (T.B.T.A) gave transparent, flexible gels over a wider range of concentrations. Subsequent work showed that changes in polymerization solvent and monomer concentration brought about changes in the mechanical and structural properties of the gels.

In this work, the effects of drug loading and polymerization solvents on in vitro drug release rate from the photopolymerized polyHEMA gels were studied. Polymerization solvents used included glycerol and tertiary butyl alcohol. Results indicated that the release rate in vitro was a diffusion-controlled process except at high drug concentrations in poly HEMA - T.B.T.A. gels when a departure from root-time kinetics occurred. Poly HEMA T.B.T.A. gels presented greater hindeirance to the mobility of the drug than polyHEMA - glycerol gels. Higuch's model for release from incoluble homogenous matrices containing dispersed solute was found to be inappropriate for the analysis of the release of the drug from the gels. A simple equation based on the modelling of desorption in diffusion was found more appropriate. Estimates of drug release rates in vitro may be made from measurements of the physical crosslinking density of the polymer (if matrix-diffusion controlled release is operative). Quantitative drug loading was achieved in the gels as evidenced from variation in crosslinking density and in vitro release rate with drug loading.     

Does concept-oriented reading instruction increase strategy use and conceptual learning from text?

The authors define reading engagement as the mutual support of motivations, strategies, and conceptual knowledge during reading. To increase reading engagement, a collaborative team designed a year-long integration of reading/language arts and science instruction (Concept-Oriented Reading Instruction, CORI). The authors compared students who received this instruction to similar students who received traditionally organized instruction aimed toward the same objectives. A path analysis showed that CORI had a positive effect on strategy use and text comprehension for students at Grades 3 and 5 when accounting for past achievement and prior knowledge. CORI also had a positive, indirect effect on conceptual knowledge mediated by strategy use, and this instruction facilitated conceptual transfer indirectly through several paths simultaneously. The findings are discussed in relation to a growing literature on instructional contexts for motivated strategy use and conceptual learning from text. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aufklärung von Korrosionsprozessen bei der Erdölverarbeitung mittels Mössbauer- und Röntgenuntersuchung – I. Atmosphärische Destillationskolonnen

Study of the corrosion processes at the primary oil refining by Mössbauer and X-ray investigation – I. Atmospheric distillation columns Samples from zones of intensive corrosion in distillation and stabilization columns of atmospheric crude oil distillation were studied by means of Mössbauer spectroscopy and X-ray diffraction. Qualitative and quantitative composition of the surface layers were established. They were found to consist of sulphides, sulphates, oxides and oxihydroxides of iron as well as sulphur. Sulphide, sulphate, and oxygen corrosion dominate. Secondary physicochemical and chemical transformations of the formed products have importance. The probable mechanism of the corrosion processes taking place is discussed.     

Surface finish prediction models for precision grinding of silicon

Conventional grinding of silicon substrates results in poor surface quality unless they are machined in ductile mode on expensive ultra-precision machine tools. However, precision grinding can be used to generate massive ductile surfaces on silicon so that the polishing time can be reduced immensely and surface quality improved. However, precision grinding has to be planned with reliability in advance and the process has to be performed with high rates of reproducibility. Therefore, this work reports the empirical models developed for surface parameters R _a, R _max, and R _t with precision grinding parameters, depths of cut, feed rates, and spindle speeds using conventional numerical control machine tools with Box–Behnken design. Second-order models are developed for the surface parameters in relation to the grinding parameters. Analysis of variance is used to show the parameters as well as their interactions that influence the roughness models. The models are capable of navigating the design space. Also, the results show large amounts of ductile streaks at depth of cut of 20?μm, feed rate of 6.25?mm/min, and spindle speed of 70,000?rpm with a 43-nm R _a. Optimization experiments by desirability function generate 37-nm R _a, 400-nm R _max, and 880-nm R _t with massive ductile surfaces.     

Organic redox-initiated polymerization process for the fabrication of hydrogels for colon-specific drug delivery

Organic-redox initiated polymerization technique based on the co-initiators system comprising benzoyl peroxide and N-phenyldiethanolamine was used at ambient temperature to fabricate pH-responsive hydrogels. The effects of changes in the concentration of the co-initiators system, the ratio in which the co-initiators combined, the type of the polymerization solvent, the pH of the hydrating medium, the concentration of the cross-linking agent based on azo-bond and the pH-sensitive cross-linking agent on the properties of the hydrogels were investigated. Increasing the concentration of the co-initiators system, decreasing the concentration of the two types of cross-linking agents, and replacing DMSO by ethanol as the polymerization solvent resulted in hydrogels with increased equilibrium swelling ratio and increased molecular weight between cross-links at pH 7.4. Increasing the concentration of N-phenyldiethanolamine while keeping the concentration of benzoyl peroxide constant gave hydrogels with increased equilibrium swelling ratios. The equilibrium swelling ratios of the hydrogels at pH 2.0 were not affected by the factors investigated. The polymerization technique may be suitable for the design of drug delivery systems containing thermolabile bioactive agents like peptides and proteins.     

Novel pH-sensitive hydrogels with adjustable swelling kinetics

Novel pH-sensitive hydrogels were synthesized by copolymerization of N,N-dimethylacrylamide, tert.-butylacrylamide, acrylic acid, 4,4'-di(methacryloylamino)azobenzene, and N-alkanoyl, O-methacryloylhydroxylamines. The influence of the length (and consequently hydrophobicity) of the alkanoyl (propionyl, hexanoyl, and lauroyl), and its content in the hydrogel on the kinetics of swelling were investigated. Upon change in the pH from acidic to neutral, N-alkanoyl, O-acylhydroxylamine moieties were hydrolyzed. The rate of side-chain hydrolysis was dependent on the length of the alkyl and the content of the hydrolyzable comonomer in the network structure. Further, chemical control of kinetics of swelling was coupled to biophysical control of kinetics of swelling by synthesizing hydrogels containing two types of cross-linking agents, one hydrolyzable, the other enzymatically degradable. The kinetics of swelling of cross-linked polymers was compared with the kinetics of hydrolysis of N-alkanoyl, O-methacryloylhydroxylaminemoieties incorporated into linear soluble copolymers of similar structures.