G. P. Aleksandrova

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.

Light scattering from aqueous solutions of colloid metal nanoparticles stabilized by natural polysaccharide arabinogalactan.

Colloids of metal nanoparticles (NPs) of Au, Ag, Pd, and Pt protected by natural polymer arabinogalactan (ARB) extracted from Larix sibirica were studied. The nanocomposites were prepared by reduction of metal salts in the water solutions of ARB. We carried out dynamic (DLS) and static light scattering resonantly enhanced by the NP plasmons. The translational diffusion was examined via DLS and a polarized interferometer. The virgin ARB was shown to form aggregates in dilute aqueous solutions. The introduction of NPs reduced the size of the virgin ARB aggregates. The aggregate forms as viewed by the scanning electron microscopy support the light scattering results.

Formation kinetics of gold nanoparticles in the galactomannan polysaccharide matrix

282 Gold nanoparticles and nanocomposites based on them are finding more and more extensive use as highly effective catalysts of various chemical processes [1], optical sensors of biospecific interactions [2], agents for the targeted drug delivery [2] and photo thermolysis of cancer cells [3], inhibitors of autoim mune diseases [4], etc. However, the problem of ther modynamic instability of nanoparticles caused by excess of their surface energy has not still been ulti mately solved [5, 6]. This problem is addressed using stabilizing polymeric matrices of synthetic and natural origin, in particular, polysaccharides, which impart a specific set of additional physicochemical and biolog ical properties to nanoparticles [7, 8]. Galactomannan is a natural water soluble polysac charide widely used in food and pharmaceutical industries [9]. Previously, it was used to prepare bio logically active nanocomposites containing silver metal nanoparticles [10]. Here we report on the results of synthesis of bio compatible aggregation stable nanocomposites con sisting of zerovalent gold nanoparticles stabilized by galactomannan macromolecules. The macromolecule of this polysaccharide (MM 1300 kDa) consists of 1,4 β polymannopyranoside chain with single α galactopyranose side branches. The Man : Gal ratio determined by quantitative 13C NMR spectroscopy is 1.6 [10].

Synthesis of silver-containing nanocomposites based on humic substances of brown coal and their antioxidant activity

72 Silver nanoparticles and nanomaterials based on them exhibit a broad spectrum of biological properties and are multipurpose means for biomedicine [1, 2]. Indeed, the antimicrobial activity of silver nanoparti cles with respect to living cells may be determined by their size, shape, ligand environment, and particular preparation method [3, 4]. One of the most conve nient and environmentally safe methods for the syn thesis of metallic nanoparticles is reduction of a metal containing precursor in water in the presence of a sta bilizer for the formed nanoparticles (these may be polyhydric alcohols [5, 6], polysaccharides [7, 8], polyphenols [9, 10], and the like).

Colloidal aggregates of Pd nanoparticles supported by larch arabinogalactan.

Palladium nanoparticles (PdNPs) are used in catalysis, hydrogen storage, biomedicine, and so on. Arranging the self-assembly of PdNPs within colloidal aggregates is desirable for improving their consumer properties. Stable widely dispersed colloidal aggregates of larch arabinogalactan (LARB) containing nanosized (5-nm) PdNPs were obtained by reducing Pd ions in alkaline solutions of LARB. Centrifugation resulted in a set of LARB-PdNP colloids ranging from 60 to 240 nm. The colloids were studied by static light scattering (SLS) and dynamic light scattering (DLS). The SLS data presented as Kratki plots correspond to a particle scattering factor of linear rather than branched chains. The fractal dimension of the LARB-PdNP colloids was found by SLS to be d = 1.96, which is between the values for diffusion- and reaction-limited aggregation. This result is ascribed to the aggregates internal motion, which is evident from the power-law exponent of the dependence of the DLS relaxation rate on the scattering vector, ~ q(α) with α = 2.24. The structure-sensitive ratio of the radius of gyration to the hydrodynamic radius was found to vary within the interval of 0.8 ≤ R(g)/R(h) ≤ 1.2 corresponding, to the spherical form of LARB-PdNP colloids. A spiderweblike PdNP distribution pattern was observed by transmission electron microscopy. Insertion of PdNPs did not affect the fractal dimension, the power-law exponent α, or the architecture of the pristine LARB aggregates in water. The red shift of the surface plasmon extinction observed with increasing LARB-PdNP colloidal size indicates the collective optical response of the PdNP ensemble in the colloid.

Molecular-weight characteristics of galactomannan and carrageenan

It was established that the action of [H+] at concentration 1.96∙10–2 M at 90°C for 5–20 min decreased sharply the molecular weight of galactomannan and carrageenan and increased their overall reductive capability. The action of [OH–] at concentrations 2.6∙10–2 and 26∙10–2 under the same conditions was characterized by a slow decrease of the molecular weight and retention of the functionality of the polysaccharides. It was shown that modified galactomannan and κ-carrageenan exhibited increased watersolubility while retaining the structure and gel-forming and stabilizing capabilities and degree of sulfation (for carrageenan).

Effect of silver nanoparticles on the thermal characteristics of nanocomposites of galactose-containing polysaccharides

187 Considerable recent attention has focused on design of nanostructured drugs [1–3]. Enhanced interest in them stems from their improved pharmaco logical properties as compared with known materials [3–6]. We have designed silver containing nanocom posites based on natural biopolymers arabinogalactan, galactomannan, and carrageenan [7–9]. The nano composites synergistically combine the properties of the polysaccharide matrix—solubility in water, non toxicity, and biocompartibility—with the antimicro bial and optical properties of silver nanoparticles [7, 9–11]. For biomedical and technical application of the synthesized silver containing nanobiocomposites, of crucial importance is the extent of their stability to heating in the course of sterilization in medicine or on exposure to laser light in plasmon technologies. Inas much as polysaccharides are thermoactive substances, it is necessary to study the behavior of composite materials based on them at elevated temperatures.

Features of gold nanoparticle formation in matrices of humic substances of different origin

One of environmentally friendly methods of prep aration of biocompatible metal nanoparticles consists in the reduction of their precursors in aqueous medium in the presence of a reagent that simulta neously behaves as both a reducing agent and a stabi lizer for resultant nanoparticles [3–6]. Such promising materials for the synthesis of metal nanoparticles are humic substances (HSs), which are a set of com pounds of polyaromatic, polysaccharide, and other biopolymer nature [7].

Estimation of the antioxidant activity of humic substances from various natural sources of Mongolia

Humic substances are a set of polyaromatic and carbohydrate organic compounds. They are formed in soils and bottom sediments upon microbiological decomposition of plant and animal organisms. The functional composition of humic substances com� prises characteristic polar functional groups COOH, OH, CO, and NH2 , and long alkyl side chains of fatty acids [1, 2]. This polyfunctional character of humic macromolecules, apart from the highly conjugated structure of the polyaromatic moieties, gives rise to valuable biological properties of these macromole� cules, in particular, antioxidant activity. The elemental and functional composition, the structure, and prop� erties of humic substances vary depending on their source. This paper reports on the first results of a compar� ative study of the antioxidant activities of humic sub� stances isolated from various natural sources of Mon� golia. The humic substances isolated from the therapeu� tic mud of the Mongolian lake Gurvan Nuur, brown coal from the Baga Nuur deposit, and shales from the Shine Hudag deposit are black crystalline powders with the total ash content of 20–22 wt %. The degree of oxidation (O/C) varies from 0.65 to 0.86, the high� est value being typical of humic substances from the lake. The H/C ratio varies in the range from 0.067 to

Stabilized Silver Nanoparticles and Nanoclusters Ag n in Humic-Based Bioactive Nanocomposites

Silver-containing nanocomposites synthesized from the compounds of a humic series have been studied using modern physical–chemical methods (EPR, TEM, IR and XRD, etc.). It is shown that the humic substances with different functional groups and isolated from different sources have also different ability of stabilizing the silver nanoparticles. Long-term stable nanoparticles and silver clusters have been found. A multiplet, observed in the EPR spectra of silver-containing nanocomposites, which are obtained from humic substances isolated from therapeutic muds and shales, is assigned to the formed Agn nanoclusters. Formation of the silver molecular clusters depends on the kind of humic substances and depth of their decomposition.