Electrostatic and Hydrophobic Interactions Involved in CNT Biofunctionalization with Short ss-DNA

This work is aimed at studying the adsorption mechanism of short chain 20-mer pyrimidinic homoss-DNA (oligodeoxyribonucleotide, ODN: polyC(20) and polyT(20)) onto CNT by reflectometry. To analyze the experimental data, the effective-medium theory using the Bruggemann approximation represents a Suitable optical model to account for the surface properties (roughness, thickness, and optical constants) and the size of the adsorbate. Systematic information about the involved interactions is obtained by changing the physicochemical properties of the system. Hydrophobic and electrostatic interactions are evaluated by comparing the adsorption oil hydrophobic CNT and oil hydrophilic silica and by Modulating the ionic Strength With and without Mg(2+). The ODN adsorption process oil CNT is driven by hydrophobic interactions only when the electrostatic repulsion is Suppressed. The adsorption mode results in ODN molecules in a side-on orientation with the bases (nonpolar region) toward the surface. This unfavorable orientation is partially reverse by adding Mg(2+). On the other hand, the adsorption oil silica is dominated by the strong repulsive electrostatic interaction that is screened at high ionic strength or mediated by Mg(2+). The cation-mediated process induces the interaction of the phosphate backbone (polar region) with the surface, leaving the bases free for hybridization. Although the general adsorption behavior of the pyrimidine bases is the same, polyC(20) presents higher affinity for the CNT Surface due to its acid-base properties.

Genomic organization and transcription analysis of the 195-bp satellite DNA in Trypanosoma cruzi

The 195-bp satellite DNA is the most abundant Trypanosoma cruzi repetitive sequence. Here we show by RNA blotting and RT-PCR that 195 SAT is intensely transcribed. We observed a positive correlation between the level of satellite RNA and the abundance of the satellite copies in the genome of T cruzi strains and that the satellite expression is not developmentally regulated. By analyzing CL Brener individual reads, we estimated that 195 SAT corresponds to approximately 5% of the CL Brener genome. 195 SAT elements were found in only 37 annotated contigs, indicating that a large number of satellite copies were not incorporated into the assembled data. The assembled satellite units are distributed in non-syntenic regions with Trypanosoma brucei and Leishmania major genomes, enriched with surface proteins, retroelements, RHS and hypothetical proteins. Satellite repeats were not observed in annotated subtelomeric regions. We report that 12 satellite sequences are truncated by the retroelement VIPER. (C) 2008 Elsevier B.V. All rights reserved.