Helix macrodipole control of beta 3 peptide 14-helix stability in water

beta-Peptides have attracted considerable attention by virtue of their ability to populate helical secondary structures in methanol, even in the absence of stabilizing tertiary interactions. Recent efforts in beta-peptide design have produced few beta3-peptides that form stable 14-helices in water; those that do require stabilizing intramolecular salt bridges on two of three helical faces and therefore possess limited utility as tools in biological research. Here we show that favorable interactions with the 14-helix macrodipole significantly stabilize the 14-helix in water, alleviating the need for multiple salt bridges on two of three helical faces. We also report the previously unrecognized stabilization of 14-helix structure by gamma-branched beta3-amino acids. The most structured molecules we describe are highly heterogeneous at the primary sequence level, containing seven different beta3-amino acids within an 11-residue sequence. These results represent the essential first step toward the design of well-folded 14-helices that explore the interactions between beta3-peptides and biological macromolecules in vitro and in vivo.     

Anion sensing using colorimetric amidourea based receptors incorporated into a 1,3-disubstituted calix[4]arene

The synthesis of amidourea-based colorimetric anion sensors 1 and 2 and the evaluation of these sensors using anions such as acetate , fluoride (F⁻), hydrogen phosphate and hydrogenpyrophosphate (pyr) in DMSO is described. While 1 has a single amidourea moiety, 2 has two such receptors incorporated into a lower-rim 1,3-disubstituted calix[4]arene scaffold. Whilst both sensors gave rise to red shifts in their absorption spectra upon anion recognition, the sensing of F⁻ and pyr gave rise to large changes with concomitant colour changes from yellow to purple, which were visible to the naked eye.     

Partially fluorinated heterocycles. Part 25[1]. The formation of fused-ring 3 -azepine derivatives: 6,7,8,9-Tetrafluoro-2,4-diphenyl-3 -1-benzazepine and 6,7,8,9,10,11-hexafluoro-2,4-diphenyl-3 -naphth[2,1-b] azepine

Pentafluoroaniline(1) and 1,3,4,5,6,7,8-heptafluoro-2-naphthylamine(2) react with acetophenone in tetralin at reflux temperature in the presence of anhydrous zinc chloride to give the 3 -azepine derivatives 6,7,8,9-tetrafluoro-2,4,-diphenyl-3 -1-benzazepine (5) and 6,7,8,9,10,11-hexafluoro-2,4,-diphenyl-3 -napth[2,1-b]azepine (6) respectively, in addition to the Schiff bases (3) and (4), found previously. The self-condensation product of acetophenone, β-benzoyl-α-methylstyrene (“dypnone”), is an intermediate in the ring-forming reactions. The heterocycles (5) and (6) exhibit fluxional behaviour which at 297K is fast for (5) but slow for (6) on the NMR time-scale.     

Intramolecular ditryptophan crosslinks enforce two types of antiparallel beta structures.

BACKGROUND: Two types of biaryl crosslinks can be formed with natural protein sidechains: ditryptophan and dityrosine. Biaryl crosslinks have the same topology as disulfide crosslinks, yet little is known about their effect on local peptide structure. RESULTS: Three ditryptophan-linked peptide dimers based on the sequence Ac-Leu-Trp-Ala-COX were prepared. The tripeptide dimer with -CONH(2) termini was too insoluble to study, but the tripeptide dimer with -COOMe termini crystallized from methanol/chloroform as an antiparallel beta-sheet. The tripeptide dimer with a -CONMe(2) termini adopted a slipped antiparallel beta structure in methanol/chloroform. CONCLUSIONS: These results suggest that intermolecular ditryptophan crosslinks that join the middle of peptide chains can confer a preference for antiparallel beta-sheet structure. The effect is most dramatic when both the inside and outside edges of the dimer can form hydrogen bonds as in the crystal structure of dimer 3b.     

The quantification of total lead in lipstick specimens by total reflection X‐ray fluorescence spectrometry

Lipstick is known to contain lead, and this has been a general area of concern. Methods of quantifying lead in lipstick currently require the use of rather harsh digestion procedures given that lipstick specimens are high in their lipid content and contain many refractory materials. A simple method of performing lead analysis in lipstick specimens based on total reflection X‐ray fluorescence spectrometry (TXRF) is presented here. Samples were prepared by melting lipstick specimens along with a non‐ionic surfactant and an yttrium internal standard followed by homogenization. Solid prepared samples were then finely streaked directly onto a quartz reflector, and TXRF measurements made for 900‐s live time. The method was found to produce a mean limit of detection for lead of 0.04μg/g. Precisions were found to be on the order of 11–38% relative standard deviation (RSD) and apparent recoveries for lead between 92% and 106% (n = 8). Although the spreading technique may result in thickness variations that may contribute to the higher than expected variances about the determined lead concentrations, the method presented in this work does show promise as a means of performing routine lead analysis in lipstick specimens without the need for harsh digestion procedures. Copyright © 2015 John Wiley & Sons, Ltd.     

Measurement of relative cerebral blood volume using BOLD contrast and mild hypoxic hypoxia

Relative cerebral blood volume (CBV) was estimated using a mild hypoxic challenge in humans, combined with BOLD contrast gradient-echo imaging at 3 T. Subjects breathed 16% inspired oxygen, eliciting mild arterial desaturation. The fractional BOLD signal change induced by mild hypoxia is expected to be proportional to CBV under conditions in which there are negligible changes in cerebral perfusion. By comparing the regional BOLD signal changes arising with the transition between normoxia and mild hypoxia, we calculated CBV ratios of 1.5±0.2 (mean±S.D.) for cortical gray matter to white matter and 1.0±0.3 for cortical gray matter to deep gray matter.     

Decay of pure quantum turbulence in superfluid 3He-B

We describe measurements of the decay of pure superfluid turbulence in superfluid 3He-B, in the low temperature regime where the normal fluid density is negligible. We follow the decay of the turbulence generated by a vibrating grid as detected by vibrating wire resonators. Despite the absence of any classical normal fluid dissipation processes, the decay is consistent with turbulence having the classical Kolmogorov energy spectrum and is remarkably similar to that measured in superfluid 4He at relatively high temperatures. Further, our results strongly suggest that the decay is governed by the superfluid circulation quantum rather than kinematic viscosity.