A folded,secondary structure in step-growth oligomers from covalently linked,crowded aromatics

This study delineates general methods to create a new class of folded oligomers by covalently attaching overcrowded aromatics to each other. Crucial to observing the secondary structure in these oligomers was the employment of C-shaped linkers. These linkers preorganize the strands to form intramolecular hydrogen bonds. In solution, one- and two-dimensional (1)H NMR data show well-defined columnar conformations. The side chains in these oligomers are critical for the secondary structure to emerge in solution. Using tris(dodecyloxy)phenethyl side chains in combination with tert-butyl side chains in the terminal subunit provides a soluble trimer and prevents intermolecular association above millimolar concentrations. This new folding motif, formed through a synergy between hydrogen bonds and pi-stacking, is so robust that even dimers have secondary structure in solution.     

The organization and assembly of a beta-sheet formed by a prion peptide in solution: an isotope-edited FTIR study

Insight into the details of protein misfolding diseases requires a detailed understanding of the conformation and dynamics of multistrand beta-sheet aggregates. Here, we report an isotope-edited FTIR study of a model peptide directed at the elucidation of residue-level details of the structure and mechanism of a beta-sheet aggregate. A series of specifically isotope-labeled derivatives of a short peptide (H1) derived from residues 109 through 122 of the prion protein PrPC have been synthesized and characterized by FTIR. On the basis of the analysis of variable temperature FTIR spectra of these peptides in solution, the organization of strands within the beta-sheets has been determined; at equilibrium, the strands form a beta-sheet in which the hydrophobic core (112-122) participates in the sheet structure, resulting in the alignment of residue 117 in all of the strands. The peptides initially form a kinetically trapped intermediate beta-sheet, with a distribution of strand alignments, which can be rearranged into the stable equilibrium conformation by an annealing cycle. These observations are discussed in terms of the biological significance of residue 117 of the prion protein and the mechanism of beta-aggregate nucleation in prion proteins.     

Nuclear relaxation of H2 and H2@C60 in organic solvents

The 1H nuclear spin-lattice relaxation time (T1) of H2 and H2@C60 in organic solvents varies with solvent, and it varies proportionally for H2 and for H2@C60. Since intermolecular magnetic interactions are ruled out, the solvent must influence the modulating processes of the relaxation mechanisms of H2 both in the solvent cage and inside C60. The temperature dependence of T1 also is very similar for H2 and H2@C60, T1 going through a maximum by varying the temperature in solvents which allow a wide range of temperatures to be explored. This behavior is attributed to the presence of dipolar and spin-rotation mechanisms which have an opposite dependence on temperature.     

Experimental evidence for the reorganization of beta-strands within aggregates of the Abeta(16-22) peptide

Amyloidogenic deposits that accumulate in brain tissue with the progression of Alzheimer's disease contain large amounts of the amyloid beta-peptide. A small fragment of this peptide, comprising residues 16-22 (Abeta(16-22)), forms beta-sheets in isolation, which then aggregate into amyloid fibrils. Here, using isotope edited infrared spectroscopy to probe the secondary structure of the peptide with residue level specificity, we are able to show conclusively that the beta-sheets formed are antiparallel and, following an anneal cycle or prolonged incubation, are in register with the central residue (Phe19) in alignment across all strands. The alignment of strands proceeds via a rapid interchange from one sheet to another. This realignment of the peptide strands into a more favorable registry may have important implications for therapeutics since previous work has shown that well aligned beta-sheets form more stable amyloid fibrils.