Synthesis of fluorine-containing betulin esters

28-O-Fluoroacylbetulins were synthesized via acylation of betulin by fluorocarboxylic (perfluorobutyric, perfluorooctanoic, 3-fluorobenzoic, perfluorobenzoic) acid chlorides in CHCl₃ in the presence of Py. 3,28-Di-O-fluoroacylbetulins were prepared by treatment of betulin with fluorocarboxylic (trifluoroacetic, pentafluoropropionic) acid anhydrides in Py in the presence of 4-dimethylaminopyridine. 3,28-Di-O- (3-fluorobenzoyl)betulin was obtained from acylation of betulin by 3-fluorobenzoic acid in CH₂Cl₂ in the presence of N,N′-dicyclohexylcarbodiimide and 4-dimethylaminopyridine whereas acylation by perfluorobutyric acid under the same conditions gave 28-O-perfluorobutanoylbetulin.     

Synthesis and antibacterial activity of betulin esters

Betulin isonicotinate, 6-chloronicotinate, 2-chlorocinnamate, and benzoates were synthesized by the reaction of betulin and the acid chlorides. It was shown that the 3,4-difluorobenzoate exhibited antibacterial activity against Ochrobactrum anthropi, Stenotrophomonas maltophilia, and S. nitritireducens whereas the 3,5-dinitrobenzoate was active against the last two microorganisms.     

Macromolecular systems and nanocomposites based on N-succinylchitosan and silver nanoparticles

Russian Chemical Bulletin - A water-soluble chitosan derivative, namely, N-succinylchitosan (NS-Chit), was used as a matrix for the formation of silver nanoparticles (AgNP) by metal ion re duction...     

Novel nanocomposites based on silver nanoparticles and mixed epoxyamine networks

A procedure has been proposed for the direct synthesis (without the use of reductants) of silver nanoparticles in an epoxy polymer matrix with the formation of novel nanocomposites. The average size of the formed nanoparticles has been shown to be about 18 nm. The polymer cross linking leads to the formation of chain aggregates of the nanoparticles. Nanocomposites containing isolated (individual) silver nanoparticles can also be obtained.     

基于纳米银/碳纳米纤维复合材料的增强效应电化学测定多贝斯

将银纳米粒子(AgNPs)电沉积在碳纳米纤维(CNFs)修饰玻碳电极表面制备纳米银/碳纳米纤维修饰玻碳电极(AgNPs/CNFs/GCE).采用扫描电镜考察其表面形态,在K3[Fe(CN)6]-K4[Fe(CN)6]体系中用循环伏安法和电化学阻抗法研究AgNPs/CNFs/GCE的电化学行为.采用循环伏安法和方波伏安法...     

New composites of betulin esters with arabinogalactan as highly potent anti-cancer agents

Betulin and its esters are the natural compounds with high in vitro cytotoxicity toward many cancer cells. However, the poor water solubility of these compounds has limited their applications. We prepared new composites of betulin esters using two methods, namely ball-milling of the mixtures of betulin esters with arabinogalactan and preparation of thin films of these mixtures by evaporating the aqueous solutions. These composites revealed higher water solubility as compared with the initial substances without losing the structural integrity and functionality. As a result, the new composites have shown much higher inhibitory effects against different cancer cell lines such as Ehrlich ascites carcinoma cells and lung carcinoma cells (A549) in comparison with the initial substances. The cell viability studies based on Annexin V and Propidium iodide probes have confirmed the high proapoptotic effect of betulin ester derivatives against cancer cells.     

The contribution of various network knots during the deformation of ethylene copolymers and nanocomposites based on them

An analysis of the deformation mechanism and changes in mechanical parameters of low-crystallinity ethylene–octene copolymers of various densities and modified with detonation nanodiamonds is performed through the use of models based on the statistical theory of rubber-like elasticity. Experimental data were processed in terms of the Haward model with allowance for the non-Gaussian statistics of macromolecules at high strain and limited extensibility and the so-called “slip-link” model, which considers the density of labile knots and permanent entanglements. Despite obvious simplifications, both models attribute the discovered extrema of the concentration dependences of mechanical properties at low concentrations of nanodiamonds to the change in the number of segments between network knots and the following change in elastic modulus (Haward model) or to the number of labile and permanent knots (“slip-link” model), a circumstance that verifies the nucleating effect of nanodiamonds. It was found that the relative increase in density of each type of knot significantly depends on the degree of crystallinity of the matrix and the concentration of the modifier. Deformation calorimetry showed that tensile and cyclic loading of the investigated systems are followed by changes in internal energy. The roles of its intramolecular and intermolecular components at the various stages of deformation and the causes of their changes were estimated. The correlation between energy effects and the transformation of the structuring and parameters of the used models was determined.     

Conductive elastomeric nanocomposites based on oxidation of aniline with silver nitrate via inverse emulsion polymerization

The present investigation describes a facile and rapid approach of conductive nanocomposites production and assesses the opportunity of their use as electro‐mechanical sensors. Hybrid materials containing silver and polyaniline nanoparticles reinforcing a thermoplastic elastomeric matrix were studied. The approach developed includes ultrasonically assisted in situ inverse emulsion polymerization of aniline oxidized by a weak oxidant and silver nitrate, and supported with a strong oxidant, ammonia peroxydisulfate. Aniline was doped with dodecylbenzene sulfonic acid in the presence of dissolved styrene–isoprene–styrene thermoplastic elastomer. While conventional polymerization of aniline with silver nitrate takes 2 weeks, by utilization of inverse emulsion polymerization, the reaction time reduces to 5 days. The assistance of a strong oxidant dramatically shortens the reaction time to 30 min. The technique developed results in uniform distribution of polyaniline/silver (PANI/Ag) conductive nanoparticles in the elastomeric matrix. The morphological studies of the films reveal spherically shaped 45 nm Ag particles. The presence of PANI/Ag in the styrene–isoprene–styrene elastomeric matrix enhances the electrical, thermal, and mechanical properties of the nanocomposites. The approach described provides an opportunity of the development of tunable structures and a remarkably distinctive architecture. A rapid electrical resistance response to an applied strain makes the nanocomposites developed useful as sensitive strain sensors. Copyright © 2014 John Wiley & Sons, Ltd.     

Micro- and nanocomposites of Keggin heteropolymetalates in cellulose esters

Composites of Keggin heteropolymetalates have been prepared and characterized by SEM, XPS, ³¹P-magic angle spinning/nuclear magnetic resonance and differential scanning calorimetry. The phosphotungstic acid and phosphomolybdic acid form nanocomposites where the oxocluster structure is preserved and is highly dispersed over the material, probably inserted between the polymeric chains. Phosphovanadotungstic clusters suffer partial decomposition during composite formation, resulting in a biphasic microcomposite. The decomposition product, phosphotungstic acid presents surface segregation as shown by comparison of XPS and nuclear magnetic resonance results. Copyright © 2002 John Wiley & Sons, Ltd.     

Synthesis and characterization of UV-irradiated silver/montmorillonite nanocomposites

We have successfully developed a simple method for preparing silver nanoparticles (Ag NPs) using UV irradiation of AgNO₃ in the interlamellar space of a montmorillonite (MMT) without any reducing agent or heat treatment. The properties of Ag/MMT nanocomposites were studied as a function of the UV irradiation period. UV irradiation disintegrated the Ag NPs into smaller size until a relatively stable size and size distribution were achieved. The results from UV–vis spectroscopy show that particles size of Ag NPs decrease with the increase of irradiation period. The crystalline structure of Ag NPs was determined by powder X-ray diffraction (PXRD).     

Influence of polysaccharide matrices of silver nanocomposites on their optical properties

Russian Chemical Bulletin - The specific features of the optical characteristics of spherical silver nanoparticles stabilized by polysaccharide matrices of galactomannan and carrageenan with a...     

Preparation and properties of conductive silver/photosensitive polyimide nanocomposites

A new electrically conductive photoresist has been developed. It is based on the dispersion of silver nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 2‐Mercaptopropionic acid was used as the surfactant to modify the silver nanoflake surface for the dispersion of silver nanoflakes in the polymer. The silver/PSPI nanocomposites showed electrical conductivity at a low silver content of 10 wt %. The electrical conductivity of the silver/PSPI nanocomposites ranged from 10 to 10⁴ S/cm, which was dependent on the silver weight fraction in the resist formulation. Patterns with a resolution of 30 μm were obtained from the silver/PSPI nanocomposites. The silver/PSPI nanocomposites had excellent thermal properties. Their glass transition temperatures were above 360 °C and thermal decomposition temperatures were over 420 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1575–1583, 2009     

Evaluating the antimicrobial activity and cytotoxicity of polydopamine capped silver and silver/polydopamine core-shell nanocomposites

Fabrication of bioactive nanomaterials with improved stability and low toxicity towards healthy mammalian cells have recently been a topic of interest. Bioactive metal nanomaterials such as silver nanoparticles (AgNPs) tend to lose their stability with time and become toxic to some extent, limiting their biological applications. AgNPs were separately encapsulated and loaded on the surface of a biocompatible polydopamine (PDA) to produce Ag-PDA and Ag@PDA nanocomposites to unravel the issue of agglomeration. PDA was coated through the self-polymerization of dopamine on the surface of AgNPs to produce Ag-PDA core-shells nanocomposites. For Ag@PDA, PDA spheres were first designed through self-polymerization of dopamine followed by in situ reduction of silver nitrate (AgNO3) without any reductant. AgNPs sizes were controlled by varying the concentration of AgNO₃. The TEM micrograms showed monodispersed PDA spheres with an average diameter of 238 nm for Ag-PDA and Ag@PDA nanocomposites. Compared to Ag@PDA, Ag-PDA nanocomposites have shown insignificant toxicity towards human embryonic kidney (HEK-293T) and human dermal fibroblasts (HDF) cells with cell viability of over 95% at concentration of 250 µg/mL. A excellent antimicrobial activity of the nanocomposites was observed; with Ag@PDA possessing bactericidal effect at concentration as low as 12.5 µg/mL. Ag-PDA on the other hand were only found to be bacteriostatic against gram-positive and gram-negative bacteria was also observed.     

Structure and dielectric relaxations of antibacterial sulfonated polystyrene and silver nanocomposites

Structure and dielectric relaxations of antibacterial sulfonated polystyrene (SPS) and silver nanocomposites (SPS/Ag) were investigated via broadband dielectric spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, and wide‐angle X‐ray diffraction. SPS/Ag nanocomposites were prepared from SPS containing 2, 4, and 7 mol% of acid contents, followed by ion exchange and a reduction process. Silver nanoparticles were formed in the structural cavities of SPS films. The single glass transition temperature of the SPS copolymers was observed and increased with increasing acid contents and more enhanced with embedded silver nanoparticles because of the restriction of the polymer chain movement. The particle size of embedded silver nanoparticles was about 10 nm and well dispersed in SPS matrices. Four dielectric relaxations were observed above the glass transition temperature, and they were attributed to the fast segmental relaxation, the slow‐hindered segmental relaxation, relaxations associated with Maxwell–Wagner–Sillars interfacial polarization and electrode polarization. Weak local relaxations were observed due to the motion of sulfonated phenyl groups. Copyright © 2014 John Wiley & Sons, Ltd.     

Cationic release behaviour of antimicrobial cellulose/silver nanocomposites

Silver nanoparticles (NPs) have received great attention, mainly due to their application as antimicrobial agents in diverse products, including textile- and paper-based materials. In this context, straightforward methodologies to monitor their cationic silver release capacity in diverse environments are required due to the rise of manufactured products containing silver NPs. Here, we describe the application of a potentiometric method based on a silver-selective electrode to monitor the kinetics of cationic release from cellulose/silver nanocomposites. We designed a set of experiments to apply this method to nanocomposites with several distinct types of cellulose matrices: vegetable, bacterial and nanofibrillated. The morphological features of the cellulose had a great influence on the distribution of silver NPs within the matrix as well as on the Ag⁺ release profiles. The cationic release profiles were interpreted based on common models, showing that, for the vegetal and bacterial cellulose nanocomposites, the kinetics is pseudo-first order, while for the nanofibrillated cellulose materials a model based on Fick’s power law provided the best fit.     

Redox reactions of arabinogalactan with silver ions and formation of nanocomposites

Formation of silver nanoparticles in the course of chemical reduction of AgNO₃ with arabinogalactan in aqueous alkaline solution was studied by electronic absorption spectroscopy and X-ray diffraction analysis. The pH of the solution was found to be the major factor affecting the degree of reduction of Ag⁺ ions. The probable reaction mechanism was discussed. Composites containing up to 58% Ag, with the metal particle size of 7–16 nm, were prepared. The nanoparticle size can be controlled by varying the reactant ratio AgNO₃: arabinogalactan. Chemical modification of arabinogalactan was confirmed by IR and ¹³C NMR spectroscopy and by TLC.     

Effect of the metal nature on hemostatic activity of water-soluble gold and silver nanocomposites

The hemostatic activity of polymeric gold and silver nanocomposites depends on their kinetic stability caused by the interaction of the ligand with nanoparticles. The properties of the nanoparticles are determined by the metal nature.     

Fluorine-containing lepidines and cyanine dyes based on them

6-F-, 6-CF₃-, 6-CF₃S-, and 6-CF₃SO₂ derivatives of lepidine, their ethotosylates, and a number of carbocyanines, merocyanines, and styryl dyes were synthesized. The effect of the indicated substituents on the basicity of the heterocyclic ring and on the position of the absorption maxima of the cyanine dyes was ascertained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 2, pp. 235–238, February, 1973.     

Multicomponent nanocatalysts and fuel cells based on them

We consider the results of original research on design and study of multicomponent catalytic nanostructures for the major current-generating reactions in fuel cells. The activity and selectivity level of the synthesized catalysts (nanoalloys) determines the efficiency of conversion of chemical energy to electrical energy in the present stage of development of electrochemical power generation.