Aqueous Suspending Medium Research Articles

Size control of self-assembled nanoparticles by an emulsion/solvent evaporation method

A novel and simple method for size control of self-assembled nanoparticles is suggested in this paper. Polymeric nanoparticles were prepared from amphiphilic chitosan derivatives fluorescein isothiocyanate (FITC)-conjugated glycol chitosans (FGCs). The attachment of hydrophobic FITC onto hydrophilic glycol chitosan induced the amphiphilic conjugate to form self-assembled nanoparticles in aqueous media, depending on degree of substitution. The size of self-assembled nanoparticles was controlled by a novel emulsion/solvent evaporation method. Adding a small amount of an immiscible solvent with water (chloroform) to FGC nanoparticle suspensions in aqueous media followed by ultrasonification and solvent evaporation led to partial dissociation and subsequent reformation of nanoparticles. The evaporation of chloroform facilitated the hydrophobic association, which resulted in more dense and hardened hydrophobic cores. The size of nanoparticles was closely related with the FGC concentration in the emulsion. The mean diameters of self-assembled nanoparticles were 150–500 nm at the FGC concentrations of 0.3–2.5 mg/ml. Higher FGC concentration resulted in larger particles. The polydispersity factors (μ 2/Γ 2) of the reformed nanoparticles were fairly low (0.001–0.094), indicating narrow size distribution. The FGC nanoparticles were stable in phosphate-buffered saline at 37°C up to 20 days. Lactose was a good excipient for maintaining the structural integrity of nanoparticles during freeze-drying. Without lactose, the freeze-dried nanoparticles were not homogeneously redispersed in aqueous media. However, the freeze-dried nanoparticles with lactose were spontaneously redispersed in aqueous milieu with their own sizes.

Dispersion of barium titanate in aqueous media

Four kinds of dispersants including poly(acrylic acid-co-maleic acid), poly- dl-aspartic acid, polyacrylic acid and ammonium citrate were chosen from more than seventy kinds of dispersants by screening experiments concerning their dispersing abilities for barium titanate (BT) suspension in aqueous media. Sediment experiments, rheology characterization and particle distribution measurements were conducted through orthogonal experiments. The optimum concentrations of dispersants, pH value and ball-milling time have been obtained. Judging from the results of both rheological behavior and particle distribution curves, we can conclude that the best effective dispersant for BT particles in aqueous media is poly(acrylic acid-co-maleic acid), while the least effective one is ammonium citrated among these four kinds of dispersants.

Effectiveness of disinfectants used in the food industry on microorganisms of sanitary interest

The effectiveness of five commercial disinfectants used in the food industry was evaluated against different strains isolated from foodborne outbreaks (E. coli O157:H7, Salmonella spp. and L. monocytogenes) and a collection strain (S. aureus) in an aqueous suspension medium. The disinfectants evaluated included quaternary ammonium compounds, aldehydes, hydrogen peroxide and peracetic acid, clorhexidine and a tertiary alkylamine. In the absence of organic matter, all the disinfectants tested were effective with an exposure time of 10 min at the lowest concentration recommended by the manufacturer. However, in the presence of organic matter their effectiveness decreased. The most effective disinfectant against pathogenic bacteria tested was a quaternary ammonium compound based disinfectant combined with non-ionic surfactants, polyphosphates and alkaline salts. The least effective ones were disinfectants containing tertiary alkylamine, peracetic acid and hydrogen peroxide.

Influence of the electrokinetic behaviors of abrasive ceria particles and the deposited plasma-enhanced tetraethylorthosilicate and chemically vapor deposited Si3N4 films in an aqueous medium on chemical mechanical planarization for shallow trench isolation

The effects of the electrokinetic behavior of abrasive ceria particles suspended in an aqueous medium and the deposited plasma-enhanced tetraethylorthosilicate (PETEOS) and chemical vapor deposition (CVD) Si3N4 films on chemical mechanical planarization (CMP) for shallow trench isolation were investigated. The colloidal characteristics of ceria slurries, such as their stability and surface potential, in acidic, neutral, and alkaline suspensions were examined to determine the correlation between the colloidal properties of ceria slurry and CMP performance. The surface potentials of the ceria particles and the PETEOS and CVD Si3N4 films in an aqueous suspending medium were dependent on the pH of the suspending medium. The differences in surface charges of ceria particles and the PETEOS and CVD Si3N4 films have a profound effect on the removal rate and oxide-to-nitride selectivity of CMP performance.

Membrane self‐assembly processes: Steps toward the first cellular life

This review addresses the question of the origin of life, with emphasis on plausible boundary structures that may have initially provided cellular compartmentation. Some form of compartmentation is a necessary prerequisite for maintaining the integrity of interdependent molecular systems that are associated with metabolism, and for permitting variations required for speciation. The fact that lipid-bilayer membranes define boundaries of all contemporary living cells suggests that protocellular compartments were likely to have required similar, self-assembled boundaries. Amphiphiles such as short-chain fatty acids, which were presumably available on the early Earth, can self-assemble into stable vesicles that encapsulate hydrophilic solutes with catalytic activity. Their suspensions in aqueous media have therefore been used to investigate nutrient uptake across simple membranes and encapsulated catalyzed reactions, both of which would be essential processes in protocellular life forms.

Temperature induced forming of zirconia from aqueous slurries: mechanism and rheology

Abstract Several near-net shape-forming techniques via colloidal process were received a great attention for manufacturing low cost and reliable advanced ceramics. Temperature induced forming is known as a suitable procedure that allows the solidification of aqueous suspension, which produce green parts, with interesting economics and environmental benefits. In the present work, well-dispersed zirconia suspensions in aqueous media were prepared using tri-ammonium citrate (TAC) as dispersant agent. Results of electrokinetics phenomena and rheological properties of the investigated system were used to optimize the content of TAC and to maximize the solid loading. Krieger–Dougherty's model was applied to describe the relation between relative viscosity of the dispersion and volume fraction of the solids in this system. Consolidation mechanism of the 40-vol.% zirconia suspensions in aqueous media was studied using temperature induced forming technique. The consolidation conditions were evaluated via measuring of viscoelastic functions of the sample, storage modulus (G′) and loss modulus (G″) as a function of temperature at frequency of 10 s −1 . To confirm the gel formation, the heights of the moulded samples were measured at different temperatures after keeping the mold in the oven for 14 h at the desired temperature. The obtained green body by this technique was characterized in terms of density and microstructure.

Preparation of Si3N4 ceramics with high strength and high reliability via a processing strategy

Abstract In this study, the preparation of Si 3 N 4 ceramics with high mechanical reliability is investigated. The influences of several processing steps on the bending strength and the Weibull modulus are reported including: (i) coating of the Si 3 N 4 powder with its sintering aids, (ii) oxidation of the coated powder, (iii) cold isostatic pressing, (iv) gelcasting of the green bodies and (v) gas pressure sintering. It was found that all the aforementioned steps contribute to improvements of strength and reliability of Si 3 N 4 ceramics. Via an optimised processing strategy, Si 3 N 4 ceramics with a bending strength and a Weibull modulus as high as 944.7±29.5 MPa and 33.9, respectively, could be prepared. Additionally, it was also found that surface modifications, i.e. coating and oxidation of Si 3 N 4 powder, increased the rheological properties of the powder suspension in aqueous media, which is favourable for in situ colloidal forming such as gelcasting.

Controlled-release liquid suspensions based on ion-exchange particles entrapped within acrylic microcapsules

Eudragit® RS/RL polymers were used to prepare microcapsules containing terbutaline-loaded ion-exchange resins, with the final aim of formulating this anti-asthmatic drug in a controlled-release liquid form. Oil-in-oil (o/o) and oil-in-water (o/w) solvent evaporation procedures were conveniently modified in order to encapsulate the resin cores. The microcapsules were then suspended in a hydroxypropylmethylcellulose solution of adequate viscosity and palatability, and stored at 20°C and ambient humidity conditions for a 6-month period. Stability studies of the dispersed microparticles were performed in order to evaluate the changes occurred in the diffusion of the drug to the suspending medium and in the dissolution behaviour during storage. The morphological alterations of the stored microcapsules were followed throughout the duration of the study by scanning electron microscopy. The polymer coatings of microcapsules prepared by the o/o method broke up on the first day of storage, while those made by the aqueous procedure remained intact during all the storage period. This agreed with the modification observed in the controlled-release profiles of terbutaline in the case of microcapsules prepared by the o/o method, which completely changed after the first week of storage. On the contrary, the microcapsules prepared by the aqueous method showed identical controlled-release profiles for all the stability study. The different behaviour of both types of microcapsules was attributed to the swelling suffered by the resin particles in contact with the aqueous suspending medium, which was higher in the microcapsules prepared by the o/o technique. In fact, in the anhydrous procedure, the microencapsulation was carried out on the shrunken resin particles, whereas in the o/w method, the presence of water during the microencapsulation process allowed the coating of the swollen particles, thus avoiding the further problem of rupture of the polymer coating.

Useful Methods in Enzymatic Synthesis of Peptides: A Comparative Study Focussing on Kinetically Controlled Synthesis of Ac-Phe-Ala-NH2 Catalyzed by α-Chymotrypsin

The usefulness of different reaction systems for enzymatic peptide synthesis was evaluated by studying the formation of a dipeptide from equimolar amounts of acyl-donor and acyl-acceptor. α-Chymotrypsin (EC 3.4.21.1.), dissolved or deposited on celite, was used for the synthesis of Ac-Phe-Ala-NH2 from Ac-Phe-OEt and H-Ala-NH2. Reactions were carried out at room temperature (≈25°C), if not otherwise stated, in aqueous solutions (<21% yield), frozen solutions at -30°C (<60% yield), suspensions in aqueous media with and without 0.5% (v/v) of Triton X-100 (<82% yield), suspensions in hydrophobic organic media with Na2CO3 10H2O as water source (<90% yield), eutectic mixtures at 37°C (<97% yield), arid acetonitrile containing 1-5% (v/v) of aqueous buffer (<99% yield). Initial rates of synthesis were in the range of 5.9 × 10-2- 7.1 × 10-2μmol min-1 (mg of enzyme)-1. The lowest one was obtained with dissolved reactants in acetonitrile containing 1 % (v/v) of aqueous buffer, and the highest one was obtained with suspended acyl-donor in aqueous medium containing 0.5% (v/v) of Triton X-100.

High energy electron beam inactivation of lactate dehydrogenase suspended in different aqueous media

The direct and indirect effects of 5 MeV electron beam irradiation in the range (0–400 Gy) at 20°C, 0°C, −3°C and −196°, as well as the influence of the aqueous suspending medium (ultrapure water and heavy water) on the total enzymatic activity of lactate dehydrogenase (LDH) have been studied. Our results showed an exponential decrease on the enzymatic activity of irradiated LDH, at all irradiation temperatures, independently of the direct or indirect action of radiation. The temperature gradient used to lower the temperature of the samples to −196°C drastically influences the results. Freeze-thawing in two steps down to −196°C protects LDH to radiation, in the dose range used. The data obtained here inform on the high energy electrons effects on the enzymatic activity loss during irradiation and during thawing, when the subsequent growth of the water crystals [5] influences the three dimensional structure of the enzyme. A 99.98% concentration of D2O in the suspending medium of the enzyme decreases the global enzymatic activity, but reduces the rate of radiation inactivation of the enzyme. The rate of radiation inactivation of the enzyme suspended in ultrapture water is reduced when compared to the enzyme suspended in bidistilled water, but compared to the D2O suspended enzyme is lightly increased.

Interaction of barium titanate powders with an aqueous suspending medium

Characterisation by SEM, TEM and XPS of BaTiO 3 powders that have been exposed to water provides an assessment of the extension of their interaction with the suspending medium. Ba 2+ ions are released into the aqueous solution when powder suspensions are prepared, as detected by atomic absorption spectroscopy, but it appears that their presence in the aqueous medium is due to dissolution of BaCO 3 present in the powders as an impurity. No changes in morphology of the powders or composition of the surface were observed, a part from precipitation of BaCl 2 on the surface of the particles when the pH was lowered with HCl. However, a ∼20 nm layer depleted in Ba 2+ develops at the surface of undoped sintered materials after exposure to water, as a result of the partial hydrolysis of the BaTiO 3, which affect in less extent to Nb-doped sintered material.

Supramolecular structure of gel-forming systems of pectins of different origin

Two pectin preparations (citrus ‘Copenhagen Pectin’ and that derived from pumpkin) that formed opalescing suspensions in aqueous media were investigated. The values of concentration and mean size of supramolecular particles determined by a spectroturbidimetric method were used as indicators of the structural heterogeneity of the preparations. According to these criteria, the pumpkin pectin preparation had a higher degree of structural heterogeneity than that of the citrus pectin. The process of gel formation in the systems studied did not cause any significant turbidimetric effects that could have pointed to the formation of particles of a new phase. Resuspended fractions of the supramolecular particles, which were obtained from the pumpkin preparations by centrifugation, formed gels in acid solutions of sucrose. In this case, the temperature of gel formation was close to that recorded for the initial preparations. However, it was about 10°C below the temperature of gel formation registered for the supernatants of pumpkin pectin preparations that remained after removal of the supramolecular particles by centrifugation.

Production and characterization of poly(ethylene glycol dimethacrylate-styrene-glycidyl methacrylate) microbeads

Nonswellable and swellable poly(ethyleneglycol dimethacrylate)-based microbeads that could react directly with the biological molecules were produced by a suspension polymerization procedure. For this purpose, ethyleneglycol dimethacrylate (EGDMA) was copolymerized with glycidyl methacrylate (GMA) in an aqueous suspension medium. Benzoyl peroxide and poly(vinyl alcohol) were used as the initiator and the stabilizer, respectively. The copolymerization provided nonswellable, tranparent, and spherical copolymer microbeads in the size range of 100–300 μm. On the other hand, swellable copolymer microbeads in the aqueous medium were obtained by using toluene as a diluent in the same copolymerization recipe. In a separate group of polymerizations, styrene (St) monomer was also included within the monomer phase to regulate the hydrophobicity of resulting microbeads. Nonswellable and swellable poly-(EGDMA-St-GMA) microbeads were obtained by changing the type and concentration of the ingredients within the monomer phase. The effects of glycidyl methacrylate, styrene, and toluene concentrations on the microbead yield, the average size, and the swellability of microbeads were investigated. In the second part of the study, the interaction of produced microbeads with a selected enzyme (i.e., chymotrypsin) was investigated. The most stable chymotrypsin immobilization was achieved with the swellable poly(EGDMA)-based microbeads including styrene. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1319–1334, 1998

Short chain fatty acid esters synthesis by commercial lipases in low-water systems and by resting microbial cells in aqueous medium

Thirteen commercial lipases in hexane and seventeen bacterial cell suspensions in aqueous media were screened for the production of ethyl valerate and ethyl butyrate. The highest esterifying activity was obtained with commercial Pancrealipase (Biozymes Inc.) and Candida rugosa lipase (Amano Enzyme Ltd) and with bacterial cell suspension from Pseudomonas fragi CRDA 446. Commercial enzymes gave molar conversion yield of 68% over 24 h as compared to 17% with whole cells in aqueous medium. However, a comparison of both sources of biocatalyst i.e. whole microbial cells and commercial lipases, based on the amount of ester produced per g of protein for a complete reaction, indicated similar activities. © Rapid Science Ltd. 1998

The Interaction of Barium Titanate with an Aqueous Suspending Medium

The Interaction of Barium Titanate with an Aqueous Suspending Medium

Preparation of SrTiO&lt;sub&gt;3&lt;/sub&gt; Ceramic Foam from Alkoxide-Derived Oxide Green Sheets Containing Polymer Micrspheres via Polymer Extraction

Preparation of SrTiO3 ceramic foam from alkoxide-derived oxide green sheets containing polymer microspheres via polymer extraction has been studied. SrTiO3 suspension in aqueous media was prepared by hydrolysis of Sr(OC3H7i)2 and Ti(OC3H7i)4. Polystyrene microspheres and PVA (poly (vinyl alcohol)) were added to this suspension (weight ratio: SrTiO3/polystyrene/PVA=100/60/8), and then precursor green sheets were produced. Polystyrene microspheres were incorporated in the SrTiO3 matrix phase in this green sheets. The polystyrene microspheres were extracted with organic solvent from the green sheets before the heat treatment. The dimension of the green sheets was not changed by the extraction of the polystyrene microspheres. Ceramic foam with spherical pores could be obtained by the heat treatment of the green sheets after extracting the polystyrene microspheres. Linear shrinkage of the sheets observed in the heat treatment was 20%.

Adsorption of amphiphilic mixtures and stabilization of suspensions of hydrophobic solids in water

The adsorption at the water/air and graphon/water interface of mixtures of an anionic surfactant (sodium decyl sulphate) and a non-ionic polymer (polyvinylpyrrolidone) has been studied by investigating the stabilization of hydrophobic solid suspensions in aqueous media. ESCA, viscosity, surface tension, zeta potential and adsorption kinetics measurements converge in demonstrating the presence of an associate in solution and on the solid surface. The maximum stability of the aqueous suspensions of carbons is reached for the adsorption from mixtures having a composition corresponding to that typical of the associate in solution.

A Novel Series of Amphiphilic Imidazolinium Compounds for in Vitro and in Vivo Gene Delivery

We have developed three catioinic amphiphiles based on the structure 1-[2-(acyloxy)ethyl]-2-alkyl(alkenyl)-3-(2-hydroxyethyl)imidazolinium chloride. Although these three compounds differ only in the structure of the hydrophobic acyl chains, they differ greatly in their ability to mediate in vivo and in vitro gene delivery. Moreover, in vitro efficiency is not predictive of in vivo efficiency. The myristoyl form is the most effective compound in vitro, and the oleoyl form is the most effective compound in vivo. The compounds readily form suspensions in aqueous media, both in the pure form and as mixtures with either cholesterol or dioleoylphosphatidylethanolamine. These suspensions can be sonicated to produce smaller particles. Particle size, electron microscopy, and the ability to capture glucose suggest that these lipids form liposomes on suspension in aqueous media. When mixed with plasmid DNA, the lipid particles appear to fuse and form larger particles. Fusion is maximal at the critical DNA:lipid ratio where extensive aggregation and precipitation are observed. Therefore, these compounds behave similarly to other cationic liposome-forming lipids upon interaction with DNA.

A Novel Method of Isolating Taxanes from Cell Suspension Cultures of Yew (TaxusSpp.)

Abstract A method is described to isolate a mixture of taxanes from cell suspension cultures of Taxus species. The aqueous suspension medium is pre-filtered and centrifuged to remove cellular debris, and then passed through either nylon or PVDF membranes. Contaminants are washed from the membranes and the taxanes are eluted with appropriate solvents. This method provides a rapid, efficient, and inexpensive means of extracting taxanes from cell suspension medium, as well as a significant reduction in the total volume of solvents used.

Chemical modification of crosslinked phenyl acrylate copolymers with monoethanolamine

AbstractCopolymerisation of phenyl methacrylate, 4‐chlorophenyl acrylate, 4‐nitrophenyl acrylate and 2,4,6‐tribromophenyl acrylate with divinyl benzene was carried out in aqueous suspension medium at 80°C using benzoyl peroxide as radical initiator. The resulting beaded copolymers were characterised by FTIR. optical and scanning electron microscopy. Polymer analogue reactions of these particulate copolymers with monoethanolamine were carried out at 60.80 and 100°C in dimethyl sulphoxide as solvent. The progress of the reactions was followed by observing the disappearance of phenyl ester carbonyl absorption at 1750 cm−1 and the appearance of 1650cm−1 vibration corresponding to the characteristic amide carbonyl. The percentage conversions were calculated, and the effect of polar substituents in the phenyl acrylates as well as temperature on the reaction are discussed.