Adrian Carpov

Physico-chemical characterization of Ca-alginate microparticles produced with different methods.

In the present paper the physico-chemical characterization of Ca-alginate microparticles produced with different methods is presented. Ca-alginate microparticles were obtained either by emulsification method or by dripping an aqueous alginate solution into a solution of calcium salt. Inverse Size Exclusion Chromatography (ISEC) was used for the determination of dimensions of the pores and porous volume of microparticles having a mean diameter of 220 microm when obtained by emulsification method. The same technique was used to study the variation of the pore size and porous volume with pH. The results were related with the content of calcium and sodium in the microparticles, before and after their treatment with different HCl solutions. For the particles with a mean diameter of 1.2 mm (obtained by dripping method) we adopted an other approach based on the steric exclusion of solute at equilibrium. For a convenient interpretation of the obtained data, determination of water regain, swelling degree, and scanning electron microscopy (SEM) were performed. Finally, a comparison of the characteristics of microparticles produced by ionic and epichlorohydrin crosslinkings was made. The maximum dimensions of the pores of the microparticles obtained by emulsification were found smaller than those obtained by other technics. The variation of the dimensions of the pores and porous volume with pH is not significant. The structure of the chemically crosslinked beads with epichlorohydrin is more elastic and the swelling is reversible; after drying and reswelling process, the dimensions of the pores and porous volume of these microparticles remain unchanged. On the opposite, for the microparticles obtained by emulsification or dripping method in the presence of calcium ions, these characteristics are changed after a first drying process.

Preparation and characterization of Ca-alginate microspheres by a new emulsification method

Abstract The preparation and characterization of Ca-alginate microspheres obtained by a new procedure from alginic acid, treated with an excess of NaOH and subsequently with a very concentrated solution of CaCl 2 are described. The produced particles have a spherical shape with an average diameter of 350 μ m. The particles show a relative dense and homogeneous internal structure in comparison with previously reported alginate microcapsules (the bulk density being 0.47 g/cm 3 ), consequently the particle matrix is characterized by a high density of charged carboxylic groups. Particles produced with a contact time of 1 h showed a degree of crosslinking of 54%. Microspheres have a good stability, and despite of very low degree of swelling, they have a good solvents regain, and an excellent ionic binding capacity of cationic drugs. After preparation the beads were loaded by ionic complexation with an antitumor aromatic tetramidine. In addition, the in vitro release of drug has been studied.

Chemical reactions on polysaccharides: I. Pullulan sulfation

Abstract In this paper, studies on the reaction parameters of sulfation of pullulan with SO3, used as a complex with organic bases are reported. The differences in reactivity of pullulan towards dextran sulfation were attributed both to the differences of structures of two polysaccharides and to the differences of their solubilities in the reaction media. The influence of the reaction conditions on the characteristics of the macromolecular chain was investigated.

Potential drug delivery systems from maleic anhydride copolymers and phenothiazine derivatives

New functionalized derivatives of phenothiazine containing amino or hydroxy groups with potential pharmacological properties were synthesized and characterized. They were reacted with maleic anhydride copolymers in order to obtain conjugates which can be used as controlled-release systems.

Efficient solvent-free microwave phosphorylation of microcrystalline cellulose

Environmentally friendly microwave phosphorylation of microcrystalline cellulose is herein described for the first time. Microwave irradiation is found to offer an efficient solvent-free procedure for cellulose modification without its pre-treatment (swelling in appropriate solvent).

Chemical modification of poly(hydroxyalkanoates). Copolymers bearing pendant sugars

“Petru Poni” Institute of Macromolecular Chemistry, Romanian Academy, RO 6600 Iasi, Romania(Received: October 8, 1998; revised: November 6, 1998)SUMMARY: Copolymers of poly(3-hydroxyoctanoates) (PHAs) containing repeating units with unsaturatedor brominated pendant side chains have been obtained from cultures of Pseudomonas oleovorans grown onmixtures of octanoic acid and undecenoic acid or 11-bromoundecanoic acid as carbon sources. These poly-mers, bearing reactive functionalities, have been used to graft acetylated maltosyl units either by anti-Mar-kovnikov addition to the double bond or S

Review: Analysis and Characterization of Maleic Copolymers

Abstract We review the methods and techniques used for the analysis and characterization of copolymers of maleic anhydride with different vinylic or acrylic monomers. The data are arranged according to four topics, namely: determination of the composition and the distribution of the monomer sequences; determination of molecular weight and molecular weight distribution; thermal properties; physicochemical behavior of maleic acid copolymer aqueous solutions.

Sodium cholate sorption on cationic dextran hydrogel microspheres. 1. Influence of the chemical structure of functional groups

New hydrogel microspheres based on crosslinked dextran, containing pendant quaternary ammonium groups with different chemical structures have been synthesized and tested as possible bile acid sorbents The in vitro sodium cholate sorption by these hydrogels has been followed in the absence or in the presence of competing anions The sorption results have indicated a strong influence of the chemical structure of functional groups on both the affinity and selectivity towards cholate ions. The best sorption performances were obtained with hydrogels having in the structure of functional groups an alkyl substituent with the length higher than C(8).

On the compatibility of polysaccharide/maleic copolymer blends I. Thermal behaviour of dextran containing blends

Abstract The compatibility of dextran (D) with maleic acid–vinyl acetate copolymer (MAc–VA) in the solid state as a thin film has been studied by coupling thermogravimetry and differential scanning calorimetry with infrared spectroscopy. Optical and electron microscopy have been also used to investigate the morphology of the blends. It has been established that blends with a content of dextran higher than 85 wt.% exhibit good compatibility, the morphology of the blends being a homogeneous fine particle dispersion, while blends with a prevalent MAc–VA copolymer content exhibit a tendency to phase separation.

Aminated polysaccharides as bile acid sorbents: in vitro study

Dextran, pullulan, and microcrystalline cellulose were cross-linked with 1-chloro-2,3-epoxypropane and reacted with N-(1-chloroethyl)-N,N-diethylamine or N-glycidyl-N,N,N-trialkylammonium chloride in order to obtain sorbents containing tertiary amino and/or quaternary ammonium groups. In vitro equilibrium sorption of cholic acid on these sorbents was studied in comparison with Cholestyramine, and in vitro dissociation of ionic complexes of cholic acid-sorbents was determined under dynamic conditions. The sorption capacity and the affinity of these sorbents for cholic acid were investigated in relation to the nature of the polymeric support, the swelling porosity of sorbent, the basicity of amino groups, and the nature of the substituents at the nitrogen atom. The maximum sorption capacity increases with the increase in amino group content, their basicity, and the length of alkyl substituents at the nitrogen atom. The affinity for cholic acid of all polysaccharide-based sorbents is higher than that of Cholestyramine. Dextran-based sorbents display the highest sorption affinity. It was found that there exists an optimum swelling porosity for the polysaccharide sorbents to attain the highest affinity for cholic acid. The dissociation rate of ionic complexes depends also on the nature of the polysaccharide and the swelling porosity and its lower for sorbents with higher sorption affinity.