A structural study of phosphate-methylated d(CpG)n and d(GpC)n DNA oligomers : implications of phosphate shielding for the isomerization of B-DNA into Z-DNA

It is shown that the phosphate-methylated DNA miniduplex d(CpG)2 adopts a left-handed Z-type structure, whereas the phosphate-methylated miniduplex d(GpC)2 is right-handed. Furthermore, it is shown that elongation of the systems to the tetramer level results in right-handed duplexes with rather low stability. The phosphate-methylated hexamer d(CpGpCpGpCpG) is present in the single-strand form. It is suggested that these results are of interest in the understanding of the exact role of salt cations in stabilizing the Z-DNA structure of natural duplexes d(CpG…CpG)2 in high salt solution, since the methylated phosphate groups in fact mimic the situation of complete phosphate-charge shielding. Therefore, it is concluded that exclusive cation-phosphate complexation in the d(CpG)2 segments stabilizes the Z structure. 31P-NMR experiments on the natural duplex d(CpGpCpGpCpG)2 at different concentrations of Mg2+ provided independent proof for the proposed model

Click chemistry as a means to functionalize macroporous PolyHIPE

The surface functionalization of macroporous polyHIPE (pHIPE) was achieved by Huisgen-type 'click' chemistry. In the first step a 600-800 nm thick layer of poly(glycidyl methacrylate) (pGMA) was grafted from the pHIPE surface by atom transfer radical polymerization (ATRP). Near quantitative azidation of the pGMA layer was achieved by the ring-opening reaction of the epoxide groups with sodium azide. The influence of the reaction conditions on the uniformity of the 'click' reaction on the three-dimensional macroporous materials was shown in model reactions with propargyl alcohol. Under optimized conditions, azide conversions of around 80% were estimated from IR-spectra. Visualization of the homogeneous functionalization was achieved by the attachment of a fluorescent molecule. Moreover, the first proof of the versatility for biofunctionalization of pHIPE by this method was provided by the attachment of several protected amino acids. The hydrolytic stability of the triazole ring allows for the successful deprotection of the amino acids on the pHIPE. © 2009 The Royal Society of Chemistry