Boris M. Sergeev

Cryosynthesis and properties of metal-organic nanomaterials

Abstract Materials containing metal nanoparticles have been obtained by co-deposition of metal and organic compound vapors onto a surface at 77 K. A new method to encapsulate the metal nanoparticles and mesogenic cyanobiphenyls in a polymer matrix has been developed. Co-condensates of metal vapors (Ag, Mg, Cd, Zn, Pb, Sm, Mn, Sn) with the p-xylylene monomers lead to the polymers at low temperatures. Globular metal particles of 5–8 nm in size encapsulation polymer films have been obtained. The particles size was estimated by means of transmission electron microscopy (TEM). UV-vis, IR and NMR spectroscopy were used to control the processes of nanomaterial preparation. Bimetallic Ag/Pb cryoorganodispersions with particle size of about 5 nm have been obtained. Properties of bimetallic mixed clusters have been computed by ab initio quantum chemistry techniques.

β-Polymorph of phenazepam: a powder study.

The title compound [systematic name: 7-bromo-5-(2-chlorophenyl)-1H-1,4-benzodiazepin-2(3H)-one] (β-polymorph), C15H10BrClN2O, has been obtained via cryomodification of the known α-polymorph of phenazepam [Karapetyan et al. (1979 ▶). Bioorg. Khim. 5, 1684–1690]. In both polymorphs, the molecules, which differ only in the dihedral angles between the aromatic rings [75.4 (2)° and 86.2 (3)° in the α- and β-polymorphs, respectively], are linked into centrosymmetric dimers via N—H⋯O hydrogen bonds. In the crystal structure of the β-polymorph, weak intermolecular C—H⋯O hydrogen bonds further link these dimers into layers parallel to bc plane.

Low-temperature synthesis and properties of silver nanoparticles stabilised by acrylic polymers

Abstract A cryochemical synthesis of silver nanoparticles stablised by poly(2-dimethylaminoethyl methacrylate) has been performed. It has been shown that precursors which do not possess optical properties of colloidal silver are present in the freshly prepared organodispersion of silver in 2-(dimethylamino)ethyl methacrylate (DMAEMA) on the early stages of nanoparticle growth. Sols prepared with cryochemically synthesised silver nanoparticles in water, acetone, and toluene were found to be sterically stabilised by macromolecular poly-DMAEMA layers formed at the surface of the nanoparticles. Dynamic light scattering data show that the thickness of these layers depends on the nature of the solvent.

Visible light-induced reduction of Ag+ cations in silver hydrosols

It is shown that, in silver hydrosols that are produced by the reduction of metal cations under the action of borohydride and do not contain electron-donor additives, the photoinduced reduction of Ag+ ions and photoinduced oxidation of nanoparticles occur at pH 9.0 and 4.0, respectively. The effect of ionic composition of sols on the direction of the photoinduced process makes it possible to assume that OH− anions reduce silver cations on the surface of nanosized nuclei.

Photoreduction of Ag+ ions and coalescence of silver nanoparticles in aqueous polyacrylate solutions

It is shown that changes in the spectral composition of irradiating light makes it possible to realize the competing photoreduction of Ag+ ions by polyacrylate anions in the bulk of an aqueous solution and on the surface of silver nanoparticles, which is accompanied by their coalescence.

Reactivity of Organic Compounds in Frozen Aqueous Dispersed Systems

Abstract The hydrolysis of p-nitrophenylacetate in aqueous solutions of inorganic salts, gelatin and silica gel suspensions at temperatures under 273 K is used as a model to ascertain the relation between the kinetic regularities of chemical reactions in frozen aqueous disperse systems and their phase state as well as conditions under which the samples are formed.

Nanosize metal particles in novel dielectric metal-polymer materials

Three synthetic methods have been developed for embedding nanosize metal particles into polymers: (i) in situ synthesis of colloidal silver in cross-linked poly(acrylamide) gels, (ii) implantation of cryochemically produced silver nanoparticles into poly(acrylamide) gels, and (iii) encapsulation of metal nanoparticles in poly(p-xylylene) films. All methods allow one to produce 3-20 nm stable clusters embedded into bulk materials, thin films or fine metal-polymer particles dispersed in organic solvents. Some physical properties of the metal-polymer systems are discussed.