No abstract

No abstract

The effect of palladium-and ruthenium-based clusters on nanocrystalline tin dioxide interaction with oxygen was studied by temperature-programmed oxygen isotopic exchange with mass-spectrometry detection. The modification of aqueous sol−gel prepared SnO 2 by palladium and, to a larger extent, by ruthenium, increases surface oxygen concentration on the materials. The revealed effects on oxygen exchangelowering the threshold temperature, separation of surface oxygen contribution to the process, increase of heteroexchange rate and oxygen diffusion coefficient, decrease of activation energies of exchange and diffusionwere more intensive for Ru-modified SnO 2 than in the case of SnO 2 /Pd. The superior promoting activity of ruthenium on tin dioxide interaction with oxygen was interpreted by favoring the dissociative O 2 adsorption and increasing the oxygen mobility, taking into account the structure and chemical composition of the modifier clusters.

The synthesis of cholesterol based cationic lipids in which the hydrophobic steroidal fragment is linked to a spermine residue as the hydrophilic domain by ester or carbamate linkage is described.In gene therapy, any curative action is achieved through introduction, into the organism, of DNA, mRNA, or oli gonucleotides that reach the cells by special transport sys tems. 1 Cationic lipids and liposomes based on them are attractive systems for the delivery owing to their biode gradability and low probability of eliciting immune and inflammatory reactions. 2-5 A cationic lipid molecule is a combination of two structural domains, hydrophobic and hydrophilic ones, which are connected by linkers. Long chain hydrocarbons, steroids, and diglycerides are used as the hydrophobic domains. The hydrophilic domain can contain one (monocationic lipids) or more (polycationic lipids) positively charged groups. Monocationic lipids are most often tertiary or quaternary derivatives of aliphatic or heterocyclic nitrogen bases. In polycationic lipids, natural or synthetic polyamines or amino acids are used as the hydrophilic domains. 3,6,7 The type of linking of the hy drophobic and hydrophilic domains determines the stabil ity and toxicity of cationic amphiphiles in biological sys tems. 3,8 Stable lipids with ether linkage are more toxic to cells than acyl lipids, which are readily hydrolyzed in the cell by endogenous esterases. A carbamoyl linkage pro vides a more favorable compromise between the am phiphile stability and toxicity.Natural polyamines, spermine and spermidine, play an important role in the vital activity of cells. 9 Polyamines can pack DNA to toroidal and rod like structures 10 and the methylene fragments separating the nitrogen atoms play an important role in the interaction of polyamine with the DNA double helix. 11,12 The structure functional studies have shown that lipophilic derivatives of poly amines condense DNA more efficiently than natural polyamines 13,14 and can be used as non viral systems for the delivery of genetic material. Among lipophilic poly amines, spermine derivatives bind and condense DNA most efficiently 15,16 and, therefore, they better transport it to the cells. However, some researchers note that am phiphiles based on synthetic polyamines can deliver DNA to eukaryotic cells more efficiently than lipophilic deriva tives of spermine. 17,18 On the basis of spermine, commer cial products for transfection were developed. 19-22A number of approaches to the preparation of polyca tionic amphiphiles whose hydrophobic parts are bound to the polyamine by spacers of different length have been reported. Most of the methods include initial in troduction of the spacer group to the polyamine ma trix and subsequent linking of the obtained fragment to the activated hydrophobic component. 17,23-26 However, the overall yields of the target compounds in these syn theses are 14-25% (see Refs 17,23,27). A solid state method was proposed 15,27 for the synthesis of choles terol polycationic amphiphiles, which increas...