New Quaternary Ammonium Derivatives Based on Citrus Pectin.

New citrus pectin derivatives carrying pendant ,-dimethyl--alkyl--(2-hydroxy propyl) ammonium chloride groups were achieved via polysaccharide derivatization with a mixture of ,-dimethyl--alkyl amine (alkyl = ethyl, butyl, benzyl, octyl, dodecyl) and epichlorohydrin in aqueous solution. The structural characteristics of the polymers were examined via elemental analysis, conductometric titration, Fourier Transform Infrared spectroscopy (FTIR) and 1D (H and C) nuclear magnetic resonance (NMR). Capillary viscosity measurements allowed for the study of viscometric behavior as well as the determination of viscosity-average molar mass for pristine polysaccharide and intrinsic viscosity ([η]) values for pectin and its derivatives.

Bile Acid Sequestrants Based on Natural and Synthetic Gels.

Bile acid sequestrants (BASs) are non-systemic therapeutic agents used for the management of hypercholesterolemia. They are generally safe and not associated with serious systemic adverse effects. Usually, BASs are cationic polymeric gels that have the ability to bind bile salts in the small intestine and eliminate them by excretion of the non-absorbable polymer-bile salt complex.

Role of Hydrophobic Associations in Self-Healing Hydrogels Based on Amphiphilic Polysaccharides.

Self-healing hydrogels have the ability to recover their original properties after the action of an external stress, due to presence in their structure of reversible chemical or physical cross-links. The physical cross-links lead to supramolecular hydrogels stabilized by hydrogen bonds, hydrophobic associations, electrostatic interactions, or host-guest interactions. Hydrophobic associations of amphiphilic polymers can provide self-healing hydrogels with good mechanical properties, and can also add more functionalities to these hydrogels by creating hydrophobic microdomains inside the hydrogels.

Bile salts adsorption on dextran-based hydrogels.

Dextran-based gels bearing two types of pendant N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride groups with different alkyl chain length substituents (C and C/C, respectively) at the quaternary nitrogen were synthesized and structural characteristics of the compounds were studied by elemental analysis, potentiometric titration, FTIR and NMR spectroscopy. The morphology and size of polymeric microspheres were examined by SEM and their swelling behavior in water was also investigated. The hydrogels were evaluated as sorbents for sodium cholate (NaCA) and sodium deoxycholate (NaDCA) in water and 10 mM NaCl solutions.

Self-assembly of dextran - b - deoxycholic acid polyester copolymers: Copolymer composition and self-assembly procedure tune the aggregate size and morphology.

Self-assembly potential of new amphiphilic block copolymers containing dextran (M 4500, 8000, 15,000) and a semi-rigid deoxycholic acid-oligoethyleneglycol polyester (M 2500-8800, 2 or 4 ethyleneglycol units), was evaluated as a function of copolymer composition and self-assembly procedure, using dynamic light scattering and transmission electron microscopy. Addition of copolymer solution to water provided small star-like micelles (∼ 100 nm), while addition of water to copolymer solution led to various morphologies and sizes (60-600 nm), depending on polymer composition. Worm-like micelles were obtained from a copolymer containing dextran with M 4500 and 66 wt% polyester, and vesicles were formed by copolymers prepared from dextran with M 8000 and containing 46 wt% polyester.

Novel amphiphilic dextran esters with antimicrobial activity.

New amphiphilic dextran esters were obtained by polysaccharide functionalization with different substituted 1,2,3-triazoles-4-carboxylic acid via in situ activation with N, N'-carbonyldiimidazole. Nitrogen-containing heterocyclic derivatives were achieved by copper(I)-catalyzed cycloaddition reaction between organic azides and ethyl propiolate. Structural characteristics of the compounds were studied by elemental analysis, Fourier transform infrared and nuclear magnetic resonance spectroscopy (H and C-NMR).

Block copolymers containing dextran and deoxycholic acid polyesters. Synthesis, self-assembly and hydrophobic drug encapsulation.

New biocompatible amphiphilic block copolymers were prepared using two natural compounds as starting materials, a polysaccharide (dextran) and a bile acid (deoxycholic acid). The copolymers were synthesized by dipolar 1,3-cycloaddition reaction between dextran with azide end groups and deoxycholic acid - oligo(ethylene glycol)s polyester with propargyl end groups. Different copolymer composition were obtained by variation of molecular weights of dextran (M 4.

Influence of dextran hydrogel characteristics on adsorption capacity for anionic dyes.

A series of cationic amphiphilic dextran hydrogels with pendent N, N-dimethyl-N-alkyl-N-(2-hydroxypropyl) ammonium chloride pendent groups was obtained with various molar ratios hydrophilic (alkyl = C)/hydrophobic groups (alkyl = C or C), total content in amino groups (50-68 mol%) and water swelling capacity (3-15 g water/g dry gel). Adsorption capacity for anionic dyes (Methyl Orange and Rose Bengal) was studied as a function of hydrogel characteristics. Adsorption kinetics was mainly influenced by swelling porosity and dye molecular weight.

Dextran derivatives application as flocculants.

A large variety of hydrophilic and amphiphilic polyelectrolytes based on dextran have been previously tested as coagulating and flocculating agents in model wastewater treatment and the results are presented in this review article. The dextran derivatives are either cationic, bearing (i) pendent quaternary ammonium groups, N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride and (ii)1-(2-hydroxypropyl)-3-methyl imidazolium chloride, randomly distributed along the polymer backbone or anionic, (i) dextran monobasic phosphate with HP(O)(OH) groups and (ii) dextran derivatives with carboxylic groups namely, dextran-g-poly(acrylamide-co-sodium acrylates). This paper will give an overview of the main results obtained in the separation of suspensions and emulsions containing either inorganic (clay, titanium dioxide, zirconium silicate (kreutzonit), zinc oxide and ferric oxide (hematite)) or organic (pesticides: Fastac 10EC, Decis, Dithane M45) contaminants.

Antimicrobial activity of chemically modified dextran derivatives.

Cationic amphiphilic dextran derivatives with a long alkyl group attached to the reductive end of the polysaccharide chain and quaternary ammonium groups attached as pendent groups to the main dextran backbone were synthesized and tested for their antimicrobial properties against several bacteria and fungi strains. Dependence of antimicrobial activity on both polymer chemical composition (dextran molar mass, length of end alkyl group and chemical structure of ammonium groups) and type of microbes was highlighted by disc-diffusion method (diameter of inhibition zone) and broth microdilution method (minimum inhibitory concentrations). Polymers had antimicrobial activity for all strains studied, except for Pseudomonas aeruginosa ATCC 27853.

Cationic gemini surfactant as a dual linker for a cholic acid-modified polysaccharide in aqueous solution: thermodynamics of interaction and phase behavior.

Understanding the thermodynamics of formation of biocompatible aggregates is a key factor in the bottom up approach to the development of novel types of drug carriers and their structural tuning using small amphiphilic molecules. We chose an anionic amphiphilic and biocompatible polymer that consists of a dextran and grafted cholic acid pendants, randomly distributed along the dextran backbone, with a degree of substitution (DS) of 15 mol% (designated Dex-15CACOONa). The thermodynamics of interaction and phase behavior of mixtures of this polyelectrolyte and a cationic gemini surfactant hexanediyl-α,ω-bis(dodecyldimethylammonium bromide) (CCCBr) or its monomer surfactant dodecyltrimethylammonium bromide (DTAB) in aqueous solution were characterized by isothermal titration calorimetry (ITC) and turbidity, together with cryogenic transmission electron microscopy (Cryo-TEM).

Dextran based Polymeric Micelles as Carriers for Delivery of Hydrophobic Drugs.

Background: The improvement of drugs bioavailability, especially of the hydrophobic ones, by using various nanoparticles is a very exciting field of the modern research.

Objective: The applicability of nano-sized shell crosslinked micelles based on dextran as supports for controlled release of several hydrophobic drugs (nystatin, rifampicin, resveratrol, and curcumin) was investigated by in vitro drug loading/release experiments.

Methods: The synthesized crosslinked micelles were loaded with drugs of various hydrophobicities and their retention/release behavior was followed by dialysis procedure.

Ionic dextran derivatives for removal of Fastac 10 EC from its aqueous emulsions.

Separation studies of Fastac 10 EC from model emulsions by cationic polysaccharides were followed by UV-vis spectroscopy and zeta potential measurements. Floc size measurements at the optimum polycation dose were also carried out using laser diffraction technology. The investigated polyelectrolytes contained various amounts of quaternary ammonium salt groups, N-ethyl(octyl)-N,N-dimethyl-2-hydroxypropyl ammonium chloride, attached to a dextran backbone.

New shell crosslinked micelles from dextran with hydrophobic end groups and their interaction with bioactive molecules.

Micelles formed in aqueous solution by dextran with hydrophobic (alkyl) end-groups were stabilized through divinyl sulfone crosslinking of the dextran shell. The efficacy of the crosslinking reaction was influenced by the divinyl sulfone amount, the pH and micelle concentration. Crosslinked micelles with a moderate crosslinking degree were further functionalized by attachment of 10 and 17 moles% N-(2-hydroxypropyl)-N,N-dimethyl-N-benzylammonium chloride groups along the dextran chain.

Micelle-like association of polysaccharides with hydrophobic end groups.

New dextran derivatives with hydrophobic end groups were synthesized by reductive amination of dextran chain ends, followed by chemical modification of the dextran main chain by attachment of cationic groups and/or by crosslinking. Properties of the aggregates formed by hydrophobic association of the end groups were studied by fluorescence, dynamic light scattering, atomic force microscopy and transmission electron microscopy and depended on the length of the dextran chain (6, 10, 25 kDa) and the hydrophobicity of the end group (alkyl, dialkyl, bile acid). All neutral derivatives were able to form micelle-like aggregates above a critical aggregation concentration (0.

Cationic amphiphilic dextran hydrogels with potential biomedical applications.

Dextran microparticles were chemically modified for the attachment of quaternary ammonium groups carrying substituents with different hydrophobicity, in order to obtain amphiphilic cationic hydrogels with different hydrophilic/lipophilic balance. These hydrogels retain various amounts of dyes: Rose Bengal, Brilliant Blue and Vitamin B12, used as models for hydrophobic, amphiphilic and hydrophilic drugs, as a function of their hydrophilic/hydrophobic properties. Bovine serum albumin (BSA) retention by hydrogels occurs in higher amounts at pH 6.

Critical role of the degree of substitution in the interaction of biocompatible cholic acid-modified dextrans with phosphatidylcholine liposomes.

The interaction between biocompatible cholic acid-modified dextrans with different pendent cholic acid groups' content and phosphatidylcholine liposomes was studied by a variety of techniques including isothermal titration calorimetry (ITC), differential scanning calorimetry (DSC), turbidity measurements, microscopy imaging (transmission electron microscopy (TEM), and cryo-scanning electron microscopy (cryo-SEM)). The variation of the interaction enthalpy with polymer concentration, as obtained by ITC, highlighted the formation of different aggregates. Complete phase modification, from vesicles covered with a few polymer chains to vesicle disintegration, was observed by turbidity measurements.

Separation of TiO2 particles from water and water/methanol mixtures by cationic dextran derivatives.

Cationic polysaccharides with N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride pendent groups attached to a dextran backbone were used to flocculate titanium dioxide (TiO2) particles suspended in water as well in water/methanol mixtures (90:10 and 50:50 v/v %). The investigations were performed with respect to the polycation dose, the suspension medium composition and the length of alkyl substituent at the quaternary nitrogen (alkyl=ethyl, octyl, dodecyl). The supernatant residual turbidity values were much lower for TiO2 particles dispersed in solvent mixtures than in water.

Intrinsic viscosities of polyelectrolytes in the absence and in the presence of extra salt: Consequences of the stepwise conversion of dextran into a polycation.

Viscosities of dilute polymer solutions were measured in capillary viscometers for samples varying in their fraction f of charged units from 0.00 to 0.90.

Cationic polyelectrolytes as drug delivery vectors: calorimetric and fluorescence study of Rutin partitioning.

The interaction between hydrophobically modified cationic polysaccharides based on dextran and a flavonoid drug (Rutin) was studied by isothermal titration calorimetry (ITC) and fluorescence spectroscopy, in order to assess the factors responsible for the interaction and characterize its energetics, as well as for evaluating their encapsulation capacity, for possible applicability of these polymers as drug delivery vectors. To address the importance of the hydrophobic pendant groups in the solution behavior of these polymer/drug systems, we also studied the interaction of Rutin with a cationic surfactant, cetyltrimethylammonium chloride (CTAC). The interaction enthalpies and drug binding constants for D40R30/Rutin systems were derived from ITC through a simple binding model.

Novel biodegradable flocculanting agents based on cationic amphiphilic polysaccharides.

Flocculation properties of a series of cationic polysaccharides, with N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl)ammonium chloride pendent groups attached to a dextran backbone, were evaluated in clay dispersions with respect to length of the alkyl substituent, molar mass, the charge density, and polycation dose. According to turbidimetric results, the alkyl chain length greatly influenced the optimum polymer dose as well as the width of the flocculation window since both increased from an ethyl to a butyl group and decreased for when octyl or dodecyl group was present. The residual turbidity values also varied with the charge density but no dramatic effect was observed with the molar masses investigated.

Ionic polymers based on dextran: hydrodynamic properties in aqueous solution and solvent mixtures.

Hydrodynamic properties of a series of ionic polysaccharides with different charge density but the same molecular weight have been evaluated in salt-free aqueous solution and aqueous/organic solvent mixtures by means of capillary viscometry. The polyelectrolytes investigated contain quaternary ammonium salt groups, N-ethyl-N,N-dimethyl-2-hydroxypropylammonium chloride, attached to a dextran backbone. The experimental viscometric data have been plotted in terms of the Wolf method.

Characterization of aggregates formed by hydrophobically modified cationic dextran and sodium alkyl sulfates in salt-free aqueous solutions.

The interaction between polyelectrolytes based on dextran with pendant N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl) ammonium chloride groups, where n = 2, 4, 8, 12, or 16, and sodium alkyl sulfates, SCnS, with n = 8, 10, 12, 14, and 16, has been studied by conductometry and fluorescence techniques. Comparison of cumulative specific conductivities of the mixtures of polymer-surfactant over a large surfactant concentration range, with those of pure surfactant and NaCl, has clearly shown that the surfactants start to bind to polymer at very low concentrations (10(-6) M), forming mixed aggregates. The steady-state emission fluorescence measured in the presence of pyrene, 1,3,6-diphenylhexatriene (DPH), and 1-pyrenylbutyric acid sodium salt demonstrated the existence of a critical surfactant concentration (CACs) at which the previously formed mixed aggregates are interconnected due to self-association of surfactant molecules included in different mixed polymer/surfactant aggregates.

Microcalorimetric evidence of hydrophobic interactions between hydrophobically modified cationic polysaccharides and surfactants of the same charge.

We synthesized and characterized a series of new polymers-hydrophobically modified cationic polysaccharides-based on dextran having pendant N-(2-hydroxypropyl)-N,N-dimethyl-N-alkylammonium chloride groups randomly distributed along the polymer backbone. These polymers are good candidates for studying the hydrophobic effect on polymer/surfactant association. In previous papers we reported their interactions with oppositely charged surfactants.

Transport properties of some cationic polysaccharides 2. Charge density effect.

The charge density effect on the behavior of some cationic polysaccharides in aqueous and nonaqueous (methanol) solutions was studied by viscometric and conductometric measurements. The polyelectrolytes investigated contain quaternary ammonium salt groups, N-alkyl-N,N-dimethyl-2-hydroxypropylene ammonium chloride, attached to a dextran backbone. This new class of polyelectrolytes has various linear charge density parameters, xi, located below and above the critical threshold value of counterions condensation, xi(c)=1(xi=0.