Ekaterina R. Gasilova

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.

Development of drug delivery systems for taxanes using ionic gelation of carboxyacyl derivatives of chitosan

Nanoparticles of two chitosan derivatives - N-succinyl-chitosan (SC) and N-glutaryl-chitosan (GC) - were developed as passive transport systems for taxanes (paclitaxel and docetaxel) using an ionic gelation technique with sodium tripolyphosphate. These nanoparticles had an apparent hydrodynamic diameter of 300-350nm, a ζ-potential of 25-31mV, an encapsulation efficiency of 21-26%, and a drug loading efficiency of 6-13%. DLS and SLS analysis shows that the nanoparticles have a unimodal size distribution and spherical form. Drug release kinetics of the taxane-loaded nanoparticles demonstrates that more than 50% of the loaded taxane could be released upon the degradation of the nanoparticles after targeted delivery. The drug-loaded SC and GC nanoparticles exhibit high cytotoxicity towards AGS cancer cell lines and their antitumor activity is consequently enhanced when compared with free taxanes.

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.

O,N-(2-sulfoethyl)chitosan: Synthesis and properties of solutions and films

A series of water-soluble sulfoethylated chitosans (SEC) with degrees of substitution (DS) up to 130% were obtained using a heterogeneous reaction of chitosan with sodium 2-chloroethanesulfonate in 85% isopropanol in the presence of NaOH. NMR and FTIR spectroscopy confirmed that sulfoethylation of chitosan preferentially happens at hydroxyl groups and to some extent at amino groups, giving mixed substituted O,N-SEC. Chitosan shows positive birefringence, whereas SEC shows negative values, indicating self-organization in dilute solution. Dynamic light scattering studies revealed the presence of aggregates in dilute solutions of chitosan and SEC. The sizes of the SEC aggregates are sensitive to the DS and the nature of the solvent. X-ray diffraction of SEC films revealed that the introduction of sulfoethyl groups into chitosan leads to amorphization, which is more pronounced at higher DS. During the storage of SEC films, the samples loose solubility due to the formation of ionic crosslinks upon dehydration.

Self-assembly in the solutions of poly(methyl methacrylates) end-capped with fluorophenyl groups

Abstract Self-assembly of poly(methyl methacrylates) end-capped with -Ge(C6F5)3 groups (PMMA-F) has been studied in a selective solvent (acetone) by means of photon correlation spectroscopy and static light scattering. PMMA-F’s of different molecular weights (MW), were obtained by radical polymerization in the presence of a chain transfer agent, HGe(C6F5)3. At MW>130 000 conformational and hydrodynamic properties of PMMA-F’s is shown to be the same as of PMMA. At MW less than130 000 an aggregation starts: additional fraction of large scatterers appears in PCS. Large aggregates of Rh=200 - 300 nm are likely to be formed by bridged micellar clusters. Presence of large aggregates indicates a super strong segregation limit predicted in the work of Semenov et al.

Dilute solutions of compositionally heterogeneous κ-carrageenan studied by combined dynamic and static light scattering

ABSTRACT Dilute water–salt solutions of compositionally heterogeneous κ-carrageenan (κ-CG) containing 3% of ι-CG units are studied by combined static and dynamic (DLS) light scattering in 0.1M NaCl at 25°C. The structure-sensitive ratio Rg/Rh = 2.2 of the fast DLS mode corresponds to the coils of κ-CG homopolymer. The irreversible core–shell aggregates (Rg/Rh = 0.4) give rise to a slow mode. The optical rotation reveals that the aggregates originate from helical fragments of contaminating multi-block κ/ι-copolymers. Comparison with capillary viscometry shows that the weight fraction of aggregates is as small as the fraction of contaminating κ/ι-hybrids.

Chiroplasmonic magnetic gold nanocomposites produced by one-step aqueous method using κ-carrageenan

Novel water-soluble chiroplasmonic nanobiocomposites with directly varied gold content were synthesized by a one-step redox method in water using a biocompatible polysaccharide κ-carrageenan (industrial product from algae) as both reducing and stabilizing matrix. The influence of the reactants ratio, temperature, and pH on the reaction was studied and the optimal reaction parameters were found. The structure and the properties of composite nanomaterials were examined in solid state and aqueous solutions by using complementary physical-chemical methods X-ray diffraction analysis, transmission electron microscopy, spectroscopy of electron paramagnetic resonance, atomic absorption and optical spectroscopy, polarimetry including optical rotatory dispersion with registration of interphase-crossbred Cotton effect of a chiral polysaccharide matrix on plasmonic chromophore of gold nanoparticles, dynamic and static light scattering. The new perspective multi-purpose nanocomposites demonstrate a complex of chiroplasmonic and magnetic properties, imparted by both nanoparticles and radicals enriched chiral polysaccharide matrix.

Conformations of Alternating Partially Fluorinated Copolymers in Dilute Ethanol Solutions

Equimolar copolymers of N-vinyl pyrrolidone with 1,1,1-3,3,3-hexafluoroisopropyl-α-fluoroacrylate were obtained by reversible addition-fragmentation chain transfer radical (RAFT) polymerization and by conventional radical polymerization (RAD). The copolymer conformation and compositional heterogeneity were analyzed by dynamic and static light scattering. RAFT copolymers of 41,000 ≤ M w ≤ 68,000 g/mol were shown to adopt cylindrical all-trans conformation. RAD copolymer of higher molecular mass (Mw = 390,000 g/mol) exhibited less extended conformation, thus indicating that the statistical Kuhn segment is less than RAD copolymer length.

CONFORMATIONS OF POLY(METHYL METHACRYLATES) END-CAPPED WITH PENTAFLUOROPHENYL GROUPS

The current work deals with the influence of thermodynamic incompatibility of the fluorocarbon end groups and the hydrocarbon main chain on macromolecular conformations of end-capped polymers in solution. Dilute non-aggregated acetone solutions of a set of poly(methyl methacrylates), modified with −GeH(C6F5)2 and −Ge(C6F5)3 end groups, were studied with static and dynamic light scattering and viscometry. It was shown that in spite of their flexibility, these macromolecules exhibit elongated conformations. The conformations of the end-capped poly(methyl methacrylates) tended to those of unmodified ones with the increase of molecular weight.

Preparation of N-succinyl-chitin nanoparticles and their applications in otoneurological pathology

Succinyl-chitin (SCH) nanoparticles were obtained by acylation of partially deacetylated chitin (DCH) nanofibers. Introduction of the succinyl moiety induced a partial amorphization of DCH, as viewed by X-ray diffraction, and increased the fractal dimension of the colloids from df = 1.2 (DCH) to 1.5-1.7 (SCH), as revealed by light scattering. The spherically symmetric form of the colloids remained almost unchanged, as indicated by the range of structure-sensitive ratios 1.0 < Rg/Rh < 1.2; the hydrodynamic diameter ranged from 200 to 300 nm. The cytoprotective activity of the SCH nanoparticles was evaluated in vivo in an acute hearing pathology model (220-250 g male Wistar rats, n = 90) following prophylactic and therapeutic administrations. Ototropic action was estimated using the amplitude of otoacoustic emissions at the frequency of the distortion product otoacoustic emissions in the range of 4-6.4 kHz before acoustic stimulation, as well as at 1 h, 24 h, and 7 days after acoustic stimulation. A dispersion of 0.3% SCH nanoparticles demonstrated prolonged ototropic action and earlier regeneration of hearing functions when compared to a meglumine sodium succinate solution. Thus, intravenous administration of the SCH nanoparticles increases the cycling time of exogenous succinate and improves biodistribution in tissues possessing a hemato-labyrinth barrier.