Reaction of organosilicon hydrides with solid surfaces: an example of surface-catalyzed self-assembly

The solution-phase reactions of octadecylsilane (C(18)H(37)SiH(3)) with 10 high surface area metal oxides (groups II-VIII) were investigated. C(18)H(37)SiH(3) reacted with most metal oxides at room temperature and produced supported monolayers (self-assembled monolayers, SAMs) with a high grafting density of C(18), approximately 4.5-5 groups/nm(2). According to the FTIR and (29)Si NMR spectra, molecules in the SAMs demonstrated "horizontal" cross-linking (Si-O-Si and Si-OH.HO-Si bonds) and little or no "vertical" bonds with the metal oxide forming an amorphous, yet ordered film. Also, approximately 3 mol of H(2) was formed per each mole of grafted C(18), indicating complete hydrolysis of C(18)H(37)SiH(3) during the reaction. On the basis of the activity of different metal oxides, we concluded that the hydrolysis of C(18)H(37)SiH(3), the key step in the reaction mechanism, is catalyzed by water adsorbed on acidic and basic centers (Lewis and Br?nsted) of the surface of metal oxide. Metal oxides and solids with weak acidic and basic properties, like silica, carbon, and organic polymers, do not react with C(18)H(37)SiH(3). Increasing the temperature of the reaction or doping neutral surfaces with acids or bases greatly increases their activity in the reaction with RSiH(3).     

Elution behavior of polyethylene in polar mobile phases on a non-polar sorbent

Linear polyethylene standards in the range of 1-500 kg/mol, dissolved in 1,2,4-trichlorobenzene, were injected into a column packed with oligo(dimethylsiloxane) modified silica gel. Fifteen polar solvents (cyclohexanone, cyclohexylacetate, cyclohexanol, nonylalcohol, dimethylformamide, dimethyl sulfoxide, ethylene- and diethylene glycol monobutyl ether, benzylalcohol, hexylacetate, bis(2-ethyl-hexyl)phthalate, N,N-dimethylacetamide, propylene carbonate, dipropylene glycol and N-methyl-pyrrolidone) were evaluated as mobile phases. Depending on the type of mobile phase evaluated, different elution behaviors are observed for polyethylene: (1) polyethylene was eluted in the size exclusion mode, (2) polyethylene was eluted together with the sample solvent peak at constant elution volume, (3) polyethylene was partially or fully retained on the column. The retained polymer was easily removed from the column by injecting a small volume of trichlorobenzene. The use of ethylene glycol monobutyl ether as the mobile phase enabled separation of the polyethylene from polypropylene. In this case polypropylene is eluted in the size exclusion mode, while polyethylene is eluted at a constant elution volume or remains in the column.     

Synthesis, structure, and molecular dynamics of gallium complexes of schizokinen and the amphiphilic siderophore acinetoferrin

A new general synthesis of the citrate-based siderophores acinetoferrin (Af) and schizokinen (Sz) and their analogues is described. The molecular structure of gallium schizokinen, GaSz, was determined by combined (1)H NMR, Hartree-Fock ab initio calculations, DFT, and empirical modeling of vicinal proton NMR spin-spin couplings. The metal-coordination geometry of GaSz was determined from NOE contacts to be cis-cis with respect to the two chelating hydroxamates. One diaminopropane adopts a single chairlike conformation while another is a mixture of two ring pucker arrangements. Both amide hydrogens are internally hydrogen bonded to metal-ligating oxygen atoms. The acyl methyl groups are directed away from each other with an average planar angle of ca. 130 degrees. The kinetics of GaSz racemization were followed by selective, double spin-echo inversion-recovery (1)H NMR spectroscopy over the temperature range of 10-45 degrees C. The racemization proceeds by a multistep mechanism that is proton independent between pD 5 and 12 (k(0) = 1.47 (0.15 s(-1))) and acid catalyzed below pD 4 (k(1) = 2.25 (0.15) x 10(4) M(-1) s(-1)). The activation parameters found for the two sequential steps of the proton independent pathway were DeltaH(++) = 25 +/- 3 kcal M(-1), DeltaS(++) = 25 +/- 7 cal M(-1) K(-1) and DeltaH(++) = 17.1 +/- 0.2 kcal M(-1), DeltaS(++) = 0.3 +/- 2.7 cal M(-1) K(-1). The first step of the proton-independent mechanism was assigned to the dissociation of the carboxyl group. The second step was assigned to complex racemization. The proton-assisted step was assigned to a complete dissociation of the alpha-hydroxy carboxyl group at pD < 4. The ab initio modeling of gallium acinetoferrin, GaAf, and analogues derived from the structure of GaSz has shown that the pendant trans-octenoyl fragments are oriented in opposite directions with the average planar angle of ca. 130 degrees. This arrangement prevents GaAf from adopting a phospholipid-like structural motif. Significantly, iron siderophore complex FeAf was found to be disruptive to phospholipid vesicles and is considerably more hydrophilic than Af, with an eight-fold smaller partition coefficient.     

Evolution of mechanisms of plastic deformation in porous metals

An experimental study was made of the structure of deformed porous iron with a porosity P ranging from 4 to 40% within the range of strains up to fracture. Measurements are made of grain-boundary slip and rotations of structural elements and their individual contributions to the total strain as a function of P and . It is established that there is a change in the dominant mechanisms of plastic deformation with an increase in porosity, this change being connected with a change in the topological characteristics of the system and corresponding to the transition from intergranular slip to a group of mechanisms that ensures movement of the grains as a whole. The established laws are analyzed on the basis of the concept of structural levels of deformation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 101–105, January, 1996.     

Structural and Thermoelectric Properties of Optically Transparent Thin Films Based on Single-Walled Carbon Nanotubes

Physics of the Solid State - Thin films have been produced via a spray method from commercially available single-walled carbon nanotubes (SWCNTs). A SWCNT film thickness has ranged from ~10 to ~80...     

Atomic Layer Deposition of Thin Films onto 3D Nanostructures: The Effect of Wall Tilt Angle and Aspect Ratio of Trenches

Technical Physics - A theoretical model predicting the spatial profile of a film grown on walls by atomic layer deposition (ALD) is developed. The possible initial nonverticality of trench walls...     

Martensitic Phase Transition in Magnetic Thin Films Based on Inverse Mn2FeSi Heusler Alloys

Journal of Experimental and Theoretical Physics - Magnetic Heusler alloys X2BZ (where X and B are 3d elements and Z belongs to the sp group) exhibit diverse magnetic and structural properties,...     

Analysis of autooscillations during co oxidation on a non-uniform surface consisting of two types of sites coupled by coads diffusion

Areas of occurrence and character of autooscillations during CO oxidation on a non-uniform surface consisting of different sites M₁ and M₂, the reaction on which is kinetically connected by the diffusion of adsorbed CO (CO_ads), has been analyzed using numerical integration of an independent system and search of stationary solutions by the homotopy method.     

Synthesis and structures of complexes ofN-2-nitroxyethylpicolinamide and 2-(2-pyridyl)-2-oxazoline with PdCl2

The reaction ofN,N′-bis(2-nitroxyethyl)pyridine-2,6-dicarboxamide with PdCl₂ afforded previously unknowncis-(N-2-nitroxyethylpicolinamide-N,N′)dichloropalladium(II) andcis-[2-(2-pyridyl)-2-oxazoline-N,N′]dichloropalladium(II), which were isolated as a cocrystallizate of the molecular compounds. Its structure was established by X-ray diffraction analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1604–1606, August, 1999.     

Single-stage synthesis of heterocyclic alkaloid-like compounds from (+)-camphoric acid and their antiviral activity

Molecular Diversity - An effective technique for one-stage synthesis of new polycyclic nitrogen-containing compounds has been developed. The procedure involves refluxing mixtures of camphoric acid...