Evaluation of the physico-chemical properties of chitosan as a potential carrier for rifampicin, using voltammetric and spectrophotometric techniques

Rifampicin is an antibiotic which, on a carbon paste electrode, shows an oxidation response of 0.492 V (vs. Ag/AgCl) at pH 7.0, due to the electroactivity of the hydroquinone group. Interaction of rifampicin with chitosan is strongly dependent on pH, species concentrations and contact time between the latter. Compared to the carbon paste electrode, electrodes modified with chitosan showed greater sensitivity, with optimum voltammetric profile obtained at pH 8.0. Spectrophotometric measurements indicate that rifampicin is strongly absorbed by chitosan at pH less than the pKa of the pharmaceutical, such behaviour being favourable for the use of chitosan as a carrier for the controlled release of rifampicin in the intestinal tract.     

Nanocomposites of genipin-crosslinked chitosan/silver nanoparticles--structural reinforcement and antimicrobial properties

This study investigates the feasibility of a novel nanocomposite (GC/Ag) of a genipin-crosslinked chitosan (GC) film in which was embedded various amounts of Ag nanoparticles for wound-dressing applications. In situ UV-vis results revealed that adding chitosan solution did not affect the characteristics of Ag nanoparticles. The water uptake ratios and surface hydrophilicity of the GC/Ag nanocomposite were better and the degradation rates slightly lower than those of the pure GC film. The presence of Ag nanoparticles enhanced L929 cell attachment and growth. Its function as an anti-microbial agent in a GC/Ag nanocomposite was assessed for Ag contents of over 100 ppm. In conclusion, silver ions had dual functions--structural reinforcement and provision of antimicrobial properties to a biocompatible polymer.     

Evaluation of physico-chemical properties of electron beam-irradiated polycarbonate film

In this work, polycarbonate (PC) film samples were irradiated with 10 MeV electrons at different doses ranging from 25 to 250 kGy. Characterization techniques viz. thermogravimetric analysis (TGA), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction analysis (XRD) and electron paramagnetic resonance (EPR) were exploited to understand the induced changes in the physico-chemical properties of the polymer. An increase in the decomposition temperature with increasing dose was observed, while the crystallinity remained unchanged as a result of the formation of cross-link bond. EPR technique characterized the stability of the free radicals in the irradiated PC. The result showed that cross-linking process occurs at low absorbed doses, whereas polymer degradation happens at higher doses.     

Evaluation of gamma irradiation effect on physico-chemical properties of a mixed beverage based in soy milk and grape juice

The effects of the main operation variables on the electrochemical oxidation of simulated tributyl phosphate (TBP) waste by a boron-doped diamond anode are individually studied. The optimum operating conditions are obtained as follows: 4 g L^?1 initial TBP concentration, 180 min degradation time, 40 mA cm^?2 current density, 0.5 mol L^?1 Na₂SO₄ as the supporting electrolyte, and unadjusted pH of the aqueous phase. Under such conditions, a chemical oxygen demand (COD) removal ratio of 82.3% is achieved, and the energy consumption is 26.16 kWh m^?3. A degradation mechanism of TBP is tentatively proposed.     

Looking for a synergic effect between NHCs and chiral P-ligands

The issue of the added value of NHCs in asymmetric catalysis with respect to trusted chiral P-ligands was addressed: considering a prototypical asymmetric allylic alkylation reaction as a model, the association of a priori inhibiting and achiral NHCs with modular P-ligand resulted in enhancement of er up to 508% and increased rates.     

Plasma-assisted regenerable chitosan antimicrobial finishing for cotton

In this study, nitrogen-plasma treatment was used to enhance the coating of chitosan onto cotton fabric and chlorine was introduced into nitrogen-containing groups on the chitosan coated fabric in order to make it antimicrobial by chlorination with sodium hypochlorite. The antimicrobial property and its rechargeability were investigated. FTIR, UV and scanning electron microscope were used to evaluate the surface properties, including the existence of chitosan on cotton fabric, the content of chitosan on cotton fabric and the surface topography of cotton fabric after modification. The results showed that nitrogen-plasma introduces nitrogen-containing groups into cotton fabric, the coating of chitosan on fabric was improved with nitrogen plasma treatment and chlorine was introduced into the chitosan coated fabric successfully which inhibits bacteria effectively and it is rechargeable. Thus, the antimicrobial property of cotton fabric coated with chitosan with the aid of nitrogen-plasma treatment after chlorination achieved good effects.     

Precipitation and physico-chemical properties of a drug substance

The useful!ness of thermoanalytical techniques in early preformulation studies of drug substances is demonstrated with a substituted benzamide derivative precipitated from solvents containing various amounts of water. Slow ageing of the crystalline products registered as changes in the bonding of water could be registered with TA-techniques only.     

Polyhydroxyl-based surfactants and their physico-chemical properties and applications

This contribution deals with the physical-chemical properties of surfactants carrying hydroxyl groups in the polar part. Topics discussed include surface and colloid properties, micelles (both single and multi-component), general phase behaviour and microemulsions. A general conclusion is that our understanding of polyhydroxy surfactants is increasing, but that further work is needed to unravel certain aspects of this important class of surfactants. Examples of such aspects are the origin of the liquid-liquid phase separation and the adsorption to solid surfaces of polyhydroxy surfactants.     

Synthesis,physico-chemical characterization,antimicrobial activity and toxicological features of AgZnO nanoparticles

Silver-zinc oxide nanoparticles (AgZnO NPs) were chemically synthesized by the deposition of Ag NPs on the surface of ZnO NPs using silver nitrate, three types of anionic polyelectrolytes and citric acid as reagents. The Wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometry of AgZnO NPs revealed 0.41–0.69 wt% Ag, and balance ZnO. The existence of Ag NPs on the surface of ZnO NPs with hexagonal wurtzite structure was highlighted by X-ray Diffraction (XRD) analysis, scanning electron microscopy (SEM), and Ultraviolet–Visible (UV–Vis) spectroscopy. The diffuse reflectance absorption of AgZnO NPs in the visible light region increased with the increase of Ag NPs content. The Fourier Transform Infrared (FTIR) spectrometry revealed no chemical bonding between Ag NPs and ZnO NPs and confirmed the presence of functional groups characteristic to ZnO and carboxylic acid salts. The newly synthesized AgZnO NPs displayed antimicrobial activity against all the tested medically relevant pathogens, with minimal (biofilm) inhibitory concentrations ranging from 1.875 mg/mL to 7.5 mg/mL. Although the in vitro genotoxicity assay revealed a relatively high micronuclei index, the in vivo micronucleus (MN) test revealed a low MN frequency in animals treated with AgZnO NPs. The histopathological analysis revealed non-significant structural changes of the hepatic parenchyma, renal cortex and intestinal mucosa and minimal inflammatory reactions. The AgZnO NPs administration induced TUNEL positive nuclei of Kupffer cells in the liver parenchyma. The present study shows that the newly synthesized AgZnO NPs are active against planktonic and adherent microorganisms and could be exploited to develop novel antimicrobial strategies for the biotechnology and biomedical fields. Easy scalability of the developed chemical synthesis is a major advantage in producing large batches of AgZnO NPs with reproducible properties.     

Emulsification properties of chitosan

 The chitosans use as an emulsifier in food emulsions was explored. The properties of chitosan (air/solution surface activity, electrical conductivity, HLB) were studied. The obtained emulsions were stable multiple w/o/w emulsions, whose characteristics were explained on the basis of the emulsifier structure and solution properties. The reaction with an anionic surfactant, sodium dodecylsulfate, was also studied, giving a water-insoluble complex at a given surfactant/chitosan ratio. Received: 24 March 1998 Accepted: 13 July 1998     

Combinatorial properties of graphs and groups of physico-chemical interest

Combinatorial properties of graphs and groups of physico-chemical interest are described. A type of mathematical modeling is applied which involves "translating" algebraic expressions into graphs. The idea is applied to both graph theory and group theory. The former topic includes objects of importance in physics and chemistry such as trees, polyomino graphs, king boards, etc. Our study along these lines emphasizes nonadjacency relations, graph-generation, quasicrystals, continued fractions, fractals, and general ordering schemes of graphs. The second part of the paper considers certain colored graphs as models of several group-theoretical concepts including coset representations of groups, subduction of groups, character tables, and mark tables which are essential to the understanding of recent developments of combinatorial enumeration in chemistry.     

价电子组态参数Ve与镧系元素理化性质的相关性研究

由元素的价电子组态构建的三个矩阵A、B、C及原子序数Z定义了价电子组态参数：Ve=ZABC与镧系元素的12种物理化学性质（P）按数学模型P^m=bVe^d a(m,d,b,a为常数）进行关联。结果表明，Ve不仅与镧系元素的12种理化性质呈现更令人满意的相关性及对所有元素达到唯一性表征，而且在表达各元素的结构特征上较其他文献更清晰、方法更简单。     

一种细菌糖脂的化学结构和物化性能

从土壤中分离得到一支假单孢菌, 当它生长在正烷烃或植物油中时分离得到两个具有表面活性的体外糖脂, 用柱层析及制备薄层层析得以纯化, 样品经负离子化学电离质谱、快原子轰击质谱以及^1H和^1^3C核磁共振谱鉴定其结构为鼠李糖脂1和2; 它们都具有降低表面张力、水与十六烷之间的界面张力, 以及良好的乳化性、发泡性及增溶性.     

Synthesis,characterization and antimicrobial activity of maltol functionalized chitosan derivatives

Chitin was isolated from prawn shell powder through demineralization and deproteinization process. Chitosan was synthesized from isolated chitin by deacetylation process and characterized by Fourier Transform Infrared (FTIR) spectra which showed close agreement with commercial chitosan. Physicochemical features such as moisture content, ash content, degree of deacetylation and molecular weight has been measured. The prepared chitosan was found to have comparatively higher molecular weight than the commercial chitosan. Functionalization of NH₂ group of chitosan with C?=?O group of maltol and ethyl maltol by refluxing equimolar quantities of respective ketones was performed. These synthesized derivatives of chitosan were characterized by their FTIR, ¹³C-Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, X-Ray Diffraction (XRD), Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA) instrumental techniques. Antibacterial screening results of the synthesized chitosan and its derivatives indicate that these compounds are active against Escherichia coli bacteria.     

Lanthanide-mediated triangular cationic assemblies: structural and physico-chemical properties

This contribution investigates Ln(III) complexes formed with a small ditopic ligand, L1, and their structural, thermodynamic and photophysical properties. The spectrophotometric and NMR titrations evidence the triangular assemblies [Ln(3)(L1-H)(3)](6+) at stoichiometric conditions and their properties are discussed in relation to L2-containing analogues. In addition, the dinuclear species, [Ln(2)(L1-H)](5+), is observed with an excess of metal.     

Transport properties of chitosan films

Effect of the history of chitosan films on their transport characteristics in relation to elimination of drugs from the body is studied.     

Thermodynamic properties of chitosan dodecahydro-closo-dodecaborate

Combustion enthalpies of chitosan dodecahydro-closo-dodecaborate corresponding to ?13194 kJ/mol are measured via combustion in an AKS-3M automatic calorimeter. The standard enthalpy of formation corresponding to ?5223 kJ/mol is calculated from the resulting experimental data.     

The effect of heat-treatment on the physico-chemical properties of silica aerogel prepared by sub-critical drying technique

Synthesis of transparent and crack-free monoliths of silica aerogel by sub-critical drying technique is reported in the present article. Silane ageing with 50% tetraethylorthosilicate:ethanol followed by solvent exchange using ethanol was adopted. The effect of heat-treatment on the textural and physical characteristics of silica aerogel was evaluated. The chosen composition resulted in a high surface area silica aerogel of 1,000 m² g⁻¹ and a pore volume of 1.4 cm³ g⁻¹ at room temperature. The aerogel heat-treated at 900 °C possessed a surface area of 450 m² g⁻¹ with a pore volume of 0.4 cm³ g⁻¹. The decrease in surface area and pore volume was associated with the sintering process. The present technique seems advantageous in preserving the high surface area of the material at high temperatures. The XRD studies showed that the amorphous nature of aerogel matrix was retained till 1,400 °C, beyond which it crystallized to phase pure crystoballite.     

New physico-chemical properties of extremely diluted aqueous solutions

The 'extremely diluted solutions', anomalous solutions prepared through the iteration of a process of dilution and succussion, have been studied with the aim of obtaining information about the influence of the preparation method on the water structure of the solutions. We measured the heats of mixing of basic solutions with such 'extremely diluted solutions', and their electrical conductivity, comparing with the analogous heats of mixing, electrical conductivity of the solvent. We found some relevant exothermic excess heats of mixing, and higher conductivity than those of the untreated solvent. The heats of mixing and electrical conductivity show a good correlation, underlining a single cause for the behaviour of the extremely diluted solutions. This revised version was published online in July 2006 with corrections to the Cover Date.