The synthesis of two novel pyrimidine bicyclonucleosides (bc(ox)-nucleosides) has been accomplished. These bicyclonucleosides each carry a lipophilic benzyloxime substituent on the carbocyclic ring ...and show improved conformational similarity to 2'-deoxyribonucleosides as shown by their X-ray structures. The thymine-containing bc(ox)-nucleoside was converted into the corresponding phosphoramidite building block and incorporated into oligodeoxyribonucleotides by standard phosphoramidite chemistry. T(m) data with complementary RNA and DNA were measured and compared to corresponding cases of natural and unfunctionalized bc-DNA. It was found that single incorporations of bc(ox) residues destabilize duplexes by roughly 5 degrees C per modification. The destabilization was found to be due to the oxime substituent and not to the bicyclic scaffold itself. No significant alteration of the base-pairing selectivity as a function of the modification was observed. With RNA (but not with DNA) as a complement the relative thermal destabilization of bc(ox)-oligothymidylates was gradually reduced and converted into a stabilizing interaction with increasing numbers of consecutive modifications. While no cellular uptake of bc(ox)-oligonucleotides into HeLa cells occurred without transfecting agents, a significant increase in the transfection rate relative to unmodified DNA was observed in complexation with lipofectamine.
The synthesis of two novel pyrimidine bicyclonucleosides (bcox-nucleosides) has been accomplished. These bicyclonucleosides each carry a lipophilic benzyloxime substituent on the carbocyclic ring and ...show improved conformational similarity to 2'-deoxyribonucleosides as shown by their X-ray structures. The thymine-containing bcox-nucleoside was converted into the corresponding phosphoramidite building block and incorporated into oligodeoxyribonucleotides by standard phosphoramidite chemistry. Tm data with complementary RNA and DNA were measured and compared to corresponding cases of natural and unfunctionalized bc-DNA. It was found that single incorporations of bcox residues destabilize duplexes by roughly 5 °C per modification. The destabilization was found to be due to the oxime substituent and not to the bicyclic scaffold itself. No significant alteration of the base-pairing selectivity as a function of the modification was observed. With RNA (but not with DNA) as a complement the relative thermal destabilization of bcox-oligothymidylates was gradually reduced and converted into a stabilizing interaction with increasing numbers of consecutive modifications. While no cellular uptake of bcox-oligonucleotides into HeLa cells occurred without transfecting agents, a significant increase in the transfection rate relative to unmodified DNA was observed in complexation with lipofectamine.
The development of a reactive pultrusion process is presented by considering the advantages of an in situ polymerisation of thermoplastic lauryllactam monomers. The specifics of the reaction ...injection unit, of the fibre-drying oven and of different pultrusion dies are given. Models were developed for the optimisation of the pultrusion process and for each processing step, namely: impregnation, polymerisation and cooling. Their individual influence on the overall pultrusion line speed was established. Heat transfer equations were solved in association with polymerisation kinetics and rheology results. Temperature profiles, conversion degrees, and viscosity changes were predicted versus composite part thickness and versus the position along the pultrusion line. Optimal mould lengths can thus be determined for optimum impregnation, polymerisation and cooling. A processing window has been defined in terms of pultrusion line speed and mould temperature. These results demonstrated with the production of profiles that reaction injection pultrusion of PA12 composites can be envisaged at larger scale.
During their acquisition, magnetic resonance (MR) images are affected by random noise, causing the observed magnitude image samples to be Rician distributed. In order to reduce the noise level while ...preserving the relevant image features, we develop an optimized Non-Local Means (NLM) denoising algorithm. The most sensitive parameters of the proposed NLM estimator are optimized on the squared-magnitude image, which follows a non-central chi-square distribution on two degrees of freedom. This minimum MSE optimization is performed via the minimization of the so-called chi-square unbiased risk estimate (CURE). Taking advantage of some acceleration techniques involving convolutions and parallel computation, we show that the proposed CURE-optimized NLM outperforms some state-of-the-art NLM algorithms with no increase in computation time.
Small interfering RNAs (siRNAs) can be exploited for the selective silencing of disease-related genes via the RNA interference (RNAi) machinery and therefore raise hope for future therapeutic ...applications. Especially chemically modifed siRNAs are of interest as they are expected to convert lead siRNA sequences into effective drugs. To study the potential of tricyclo-DNA (tc-DNA) in this context we systematically incorporated tc-DNA units at various positions in a siRNA duplex targeted to the EGFP gene that was expressed in HeLa cells. Silencing activity was measured by FACS, mRNA levels were determined by RT-PCR and the biostability of the modifed siRNAs was determined in human serum. We found that modifications in the 3'-overhangs in both the sense and antisense strands were compatible with the RNAi machinery leading to similar activities compared to wild type (wt) siRNA. Additional modifications at the 3'-end, the 5'-end and in the center of the sense (passenger) strand were also well tolerated and did not compromise activity. Extensive modifications of the 3'- and the 5'-end in the antisense (guide) strand, however, abolished RNAi activity. Interestingly, modifications in the center of the duplex on both strands, corresponding to the position of the cleavage site by AGO2, increased efficacy relative to wt by a factor of 4 at the lowest concentrations (2nM) investigated. In all cases, reduction of EGFP fluorescence was accompanied with a reduction of the EGFP mRNA level. Serum stability analysis further showed that 3'-overhang modifications only moderately increased stability while more extensive substitution by tc-DNA residues significantly enhanced biostability.
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