Ion-specific channels in artificial membranes have been formed by the addition of gramicidin A, alamethicin, polyene antibiotics and some proteins to the solution surrounding the bilayer lipid membrane. Until now there have been no reports of single-ion channels in unmodified lipid membranes. We have now studied the electrical conductance of planar lipid bilayers membranes made of synthetic distearoylphosphorylcholine (DSPC). Current fluctuations of amplitude approximately 1pA and duration approximately 1 s have been discovered at phase transition temperature, which shows that the appearance of ionic channels may be the result of lipid domain interactions. This would explain the dramatic increase in ion permeability observed in liposomes during phase transition. We suggest that these channels could conduct the transmembrane ionic current in biological membranes without the involvement of peptides and proteins.

Binding of the internal ribosome entry site (IRES) of the hepatitis C virus (HCV) RNA to the eIF-free 40S ribosomal subunit is the first step of initiation of translation of the viral RNA. Hairpins IIId and IIIe comprising 253–302 nt of the IRES are known to be essential for binding to the 40S subunit. Here we have examined the molecular environment of the HCV IRES in its binary complex with the human 40S ribosomal subunit. For this purpose, two RNA derivatives were used that bore a photoactivatable perfluorophenyl azide cross-linker. In one derivative the cross-linker was at the nucleotide A296 in hairpin IIIe, and in the other at G87 in domain II. Site-specific introduction of the cross-linker was performed using alkylating derivatives of oligodeoxyribonucleotides complementary to the target RNA sequences. No cross-links with the rRNA were detected with either RNA derivative. The RNA with the photoactivatable group at A296 cross-linked to proteins identified as S5 and S16 (major) and p40 and S3a (minor), while no cross-links with proteins were detected with RNA modified at G87. The results obtained indicate that hairpin IIIe is located on the solvent side of the 40S subunit head on a site opposite the beak.

The geometric and electronic properties of supported Pt particles have been altered by modifying the ionicity (acid base properties) of the Al 2 O 3 support via the sol-gel method. The Si modifier resulted in the most acidic and Cs in the most basic Al 2 O 3 support. Application of the new Delta XANES technique shows that, above 373K in vacuum, the Pt surface is covered with hydrogen chemisorbed in an atop site for Pt particles dispersed on an acidic Cl-Al 2 O 3 and mostly in the n-fold sites on Pt particles dispersed on a basic Rb-Al 2 O 3 . Further, FTIR data shows a significant bridged CO coverage in the Rb-Al 2 O 3 case but not in the Cl-Al 2 O 3 . At low temperatures, when the coverage of both CO and H should be nearly complete, the Delta XANES results show that the coverage of H on Pt/Cl-Al 2 O 3 is about twice that of Pt/Rb-Al 2 O 3 , consistent with the FTIR data which shows a similar reduction of linear CO adsorption on Pt/Rb-Al 2 O 3 . This is attributed to the different dispersions of the particles. EXAFS analysis makes clear that this difference in dispersion is mostly due to different particle morphologies, almost flat (for Pt/Cl-Al 2 O 3 ) versus (hemi)spherical (for Pt/ Rb-Al 2 O 3 ), although the sizes are also different. The observed changes in CO and H 2 chemisorption properties at high temperature and in Pt particle morphology are due to a shift of the Pt valence band to higher binding energy with decreasing ionicity (increasing acidity) of the support, as indicated by the atomic XAFS results. These atomic XAFS results can be directly correlated, assuming the oxygen Madelung potential model, with the XPS shift of the O 1s BE of about 2 eV, showing a decrease of the net electron charge on the support oxygen atoms with decreasing ionicity of the support. The hydrogen Delta XANES results are combined with a three-site (atop, 2-or 3-fold, and ontop H, in order of decreasing bond strength) Langmuir adsorption model for hydrogen chemisorption. This combination accounts for the variation in hydrogen coverage with change in T, P, and support ionicity as described above. The consequences of these results for Pt-catalyzed CO oxidation and hydrogenolysis/hydrogenation reactions are discussed.