The effect of substrate roughness on the static friction of CuO nanowires

The dependence of static friction on surface roughness was measured for copper oxide nanowires on silicon wafers coated with amorphous silicon. The surface roughness of the substrate was varied to different extent by the chemical etching of the substrates. For friction measurements, the nanowires (NWs) were pushed by an atomic-force microscope (AFM) tip at one end of the NW until complete displacement of the NW was achieved. The elastic bending profile of a NW during this manipulation process was used to calculate the ultimate static friction force. A strong dependence of static friction on surface roughness was demonstrated. The real contact area and interfacial shear strength were estimated using a multiple elastic asperity model, which is based on the Derjaguin–Muller–Toporov (DMT) contact mechanics. The model included vertical elastic flexure of NW rested on high asperities due to van der Waals force.     

Real-time manipulation of gold nanoparticles inside a scanning electron microscope

The forces needed to overcome static friction and move 150 nm diameter Au nanoparticles on an oxidized Si substrate were measured in Normal and Shear oscillation modes inside a scanning electron microscope (SEM) in real time. The experimental setup consisted of a quartz tuning fork (QTF) mounted onto a high-precision 3D nanomanipulator used with a glued silicon or tungsten tip as a force sensor. Static friction was found to range from tens of nN to several hundred nN. Large variations in static friction values were related to differences in particle shape. Kinetic friction tended to be close to the detection limit and in most cases did not exceed several nN. The influence of thermal treatment in reducing the static friction of nanoparticles was considered.     

Nonenzymatic recombination of RNA by means of transesterification

Coupled nonenzymatic cleavage/ligation of oligoribonucleotides catalyzed by magnesium ions afforded longer RNA molecules with a new sequence. The efficiency of formation of ligation products reaches 6%. The possible role of this reaction in the evolution of the RNA world is discussed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2413–2419, December, 2007.     

Molecular Interactions of Oligonucleotides in Organism – A Source of Broad Spectrum of Biological Activities

Abstract

Oligodeoxynucleotides interact with a few proteins at the cell surface and in the bloodstream. These interactions determine cellular uptake, biodistribution and some nonspecific antiviral and immunomodulating effects of oligonucleotides.     

10-23 DNA enzymes for targeting MDR1 mRNA

The properties of the 31-mer 10-23 DNA enzyme and its analog with the terminal 3"-3" internucleotide linkage, which are complementary to an mRNA region of the multi-drug resistance gene MDR1, were investigated. DNA enzymes can selectively cleave RNA with high efficiency in a catalytic mode as exemplified by a synthetic 18-mer fragment of MDR1 mRNA.     

Site-directed cleavage of DNA by an oligonucleotide conjugate with o-bromobenzoic acid in the presence of copper ions

Site-directed cleavage of single- and double-stranded DNAs by an oligonucleotide conjugate with 5-[N-(3-aminopropyl)sulfamoyl]-2-bromobenzoic acid was investigated. When forming duplex complexes with a single-stranded DNA and triplex complexes with a double-stranded DNA, this conjugate cleaves DNA near the binding site in the presence of copper ions and free o-bromobenzoic acid. The efficacy and specificity of DNA cleavage by this conjugate and other oligonucleotide conjugates bearing tetracarboxyphthalocyanine Co^II and bleomycin A5 as reactive groups were compared.     

Cationic lipid-DNA complexes-lipoplexes-for gene transfer and therapy

Cationic lipid-mediated gene transfer and delivery still attract great attention of many gene therapy laboratories. From the point of view of the most important characteristics of lipoplex particles, e.g. its charge and size, we reviewed recent studies available. In general, the paper deals with non-viral systems of gene transfer into eukaryotic cell based on various lipids. Having usually less efficiency in gene transfer, lipid-based gene transfer vehicles (lipoplexes/genosomes) are characterized with certain advantages even over viral ones: they are less toxic and immunogenic, could be targetable and are easy for large-scale production, a size of transferred DNA being quite high. Conditions of DNA condensation during interactions with lipids are described. Results of the studies of mechanism of DNA-lipid complex interactions with the cell membrane and their transport into the nucleus are summarized. Dependence of efficiency of gene transfer on lipoplex structure and physical-chemical properties is reviewed. Advantages and disadvantages of different macromolecule complexes from the point of view of transfection efficiency, possibility of use in vivo, cytotoxicity and targeted gene transfer in certain organs and tissues are also discussed. Results of transfection of different cells using neutral, anion and cation liposomes are reviewed. The conclusion reached was that efficiency and specificity of gene transfer may grow considerably when mixed macromolecule lipid systems including polycations and glycolipids are used.     

Source-size measurements in the e3He(4He) → e′pΛX reaction

We report preliminary data on proton-lambda correlations at small relative momentum q in the e ³He(⁴He) → e′pΛX reaction at E ₀ = 4.7(4.46) GeV using the CLAS detector at Jefferson Lab. The enhancement of the correlation function at small q was found to be in qualitative agreement with theoretical expectations. The size of emission region about 1.5 fm was estimated using Lednicky-Lyuboshitz analytical model. The experimental correlation function is comparable with the P-matrix fit of the hyperon-nucleon data. Small-relative-momentum-proton-lambda correlations both for ³He(⁴He) target and for electroproduction reaction were studied for the first time. (for CLAS Collaboration) The text was submitted by the authors in English.     

Reversion of the multiple-drug resistance phenotype mediated by short interfering RNAs

Repression of MDR1 gene expression and restoration of cancer cell sensitivity to cytostatic agents were studied with the use of synthetic siRNAs directed to different MDR1 mRNA regions. Short interfering RNAs that enhance sensitivity of drug-resistant cells to vinblastine were revealed. The ability of various siRNAs to repress gene expression does not correlate with the efficiency of antisense oligonucleotides complementary to the same mRNA regions. An siRNA sample remained intact in a medium during a period of time sufficient to exhibit biological activity. The results of our study suggest that siRNAs can be considered as a basis for therapeutic drugs for enhancement of the efficiency of antitumor chemotherapy. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1260–1267, May, 2005.     

The dependence of proton correlations on integral characteristics of eA interactions

We report the results of analysis of correlations of the product protons from inelastic eA collisions at smallQ ². The experimental data were measured by the ARGUS detector. The correlation effect at small relative momentaq (interference and final state interaction) is closely associated with the angular correlations due to momentum conservation. The examined correlations in eA collisions also show features similar to correlations in hA collisions.