Conformations of proline analogues having double bonds in the ring

The intrinsic conformational preferences of proline analogues having double bonds between carbon atoms in their rings have been investigated using quantum mechanical calculations at the B3LYP/6-31+G(d,p) level. For this purpose, the potential energy surface of the N-acety-N'-methylamide derivatives of three dehydroprolines (proline analogues unsaturated at alpha,beta; beta,gamma; and gamma,delta) and pyrrole (proline analogue with unsaturations at both alpha,beta and gamma,delta) have been explored, and the results are compared with those obtained for the derivative of the nonmodified proline. We found that the double bonds affect the ring puckering and the geometric internal parameters, even though the backbone conformation was influenced the most. Results indicate that the formation of double bonds between carbon atoms in the pyrrolidine ring should be considered as an effective procedure to restrict the conformational flexibility of prolines. Interestingly, we also found that the N-acetyl-N'-methylamide derivative of pyrrole shows a high probability of having a cis peptide bond preceding the proline analogue.     

Coarse-graining the self-assembly of beta-helical protein building blocks

Nanotubular structures constructed using self-assembled beta-helical protein building blocks one atop the other have been coarsened to develop a mesoscopic potential that reproduces the intermolecular interaction energies provided by atomistic force-fields. The resulting potential consists of an analytical expression that depends exclusively on the distance and the relative orientation between the two interacting entities. In spite of its complexity, this coarse-grained potential reproduces satisfactorily the energetic properties of two interacting building blocks. The coarse-grained potential has been used to predict that the interaction between building blocks formed by residues 131-165 of E. coli galactoside acteyltransferase becomes repulsive when the size of the nanotube is larger than a threshold, that is, about 45 self-assembled building blocks.     

Infrared spectroscopy of acetic acid and formic acid aerosols: pure and compound acid/ice particles

Acetic acid aerosol particles, formic acid aerosol particles and mixed acid/ice particles were generated in a collisional cooling cell at a temperature of 78 K and investigated using in situ rapid scan Fourier transform infrared spectroscopy. The infrared spectra reveal that the internal structure of the particles critically depends on the particle formation conditions and, especially for the mixed particles, on the composition. The acetic acid particles are likely to have only a partially crystalline structure whereas the formic acid particles are likely to have an overall crystalline structure. The existence of acid in the mixed acid/ice particles prevents the ice from crystallization even at low acid concentrations (less than 10%). Mid-infrared refractive index data were derived from the different particle spectra, which can be helpful for remote sensing of such systems.     

Speech intelligibility in free field: spatial unmasking in preschool children

This study introduces a new test (CRISP-Jr.) for measuring speech intelligibility and spatial release from masking (SRM) in young children ages 2.5-4 years. Study 1 examined whether thresholds, masking, and SRM obtained with a test designed for older children (CRISP) and CRISP-Jr. are comparable in 4 to 5-year-old children. Thresholds were measured for target speech in front, in quiet, and with a different-sex masker either in front or on the right. CRISP-Jr. yielded higher speech reception thresholds (SRTs) than CRISP, but the amount of masking and SRM did not differ across the tests. In study 2, CRISP-Jr. was extended to a group of 3-year-old children. Results showed that while SRTs were higher in the younger group, there were no age differences in masking and SRM. These findings indicate that children as young as 3 years old are able to use spatial cues in sound source segregation, which suggests that some of the auditory mechanisms that mediate this ability develop early in life. In addition, the findings suggest that measures of SRM in young children are not limited to a particular set of stimuli. These tests have potentially useful applications in clinical settings, where bilateral fittings of amplification devices are evaluated.     

Novel use of glow discharge optical emission spectroscopy (GDOES) to study corrosion of AA2024‐T3 in the presence and absence of inhibitors

Recent interest in environmentally friendly alternatives to chromate‐based corrosion inhibitors has led to the development of a range of novel coating formulations. The work described herein is aimed at developing a novel methodology to contribute to investigation of the self‐healing and active corrosion protection of the new coatings. An experimental procedure has been developed to model a defect in the coating by fixing coated specimens in close proximity to the uncoated AA2024‐T3, each separated by a narrow gap containing sodium chloride solution. After exposure to the corrosive environment, elemental depth profiles of the uncoated specimens were acquired by glow discharge optical emission spectroscopy (GDOES). The depth profiles of selected elements (notably aluminium, oxygen and copper) were shown to have characteristics which can be correlated with bulk surface roughening/intensity of corrosion, the thickness of the corroded layer and de‐alloying/re‐distribution of copper. An unanticipated inhibitory effect was noted in the case of a coating doped with γ‐Al₂O₃ (γ‐alumina or AluOx). Copyright © 2015 John Wiley & Sons, Ltd.     

LED‐Illuminated NMR Studies of Flavin‐Catalyzed Photooxidations Reveal Solvent Control of the Electron‐Transfer Mechanism

Mechanistic insights into chemical photocatalysis are mainly the domain of UV/Vis spectroscopy, because NMR spectroscopy has been limited by the type of illumination so far. An improved LED‐based illumination device can be used to obtain NMR reaction profiles of photocatalytic reactions under synthetic conditions and perform both photo‐CIDNP and intermediate studies. Flavin‐catalyzed photooxidations of alcohols show the potential of this setup. After identical initial photoreaction steps the stabilization of a downstream intermediate is the key to the further reaction mechanism and the reactivity. As a chemical photocatalyst flavin can act either as a one‐ or a two‐electron mediator when the stability of the zwitterionic radical pair is moldulated in different solvents. This demonstrates the importance of downstream intermediates and NMR‐accessible complementary information in photocatalytic reactions and suggests the control of photoorganic reactions by solvent effects.     

Analysis of Solid-State Luminescence Emission Amplification at Substituted Anthracenes by Host–Guest Complex Formation

Small robust organic molecules showing solid-state luminescence are promising candidates for optoelectronic materials. Herein, we investigate a series of diphenylphosphanyl anthracenes [9-PPh₂-10-R-(C₁₄H₈)] and their sulfur oxidised analogues. The oxidation causes drastic changes in the molecular structure as the new orientation of the bulky (S)PPh₂ substituent induces a strong butterfly bent structure of the anthracene core, which triggers a strong bathochromic shift resulting in a green solid-state fluorescence. As the emission properties change only slightly upon aggregation the origin of the emission is attributed to a typical monomer fluorescence. The host–guest complexes of [9-(S)PPh₂-10-Ethyl-(C₁₄H₈)] with four basic arenes reveal an emission enhancement up to five-times higher quantum yields compared to the pure host. Less interchromophoric interactions and a restriction of intramolecular motion within the host molecules due to fixation by weak C−H⋅⋅⋅π interactions with the co-crystallised arene are responsible for that emission enhancement.     

On the Reactivity of NHCtBuAuCl towards Rb6Cs6Si17: The First Gold-Silicon Cluster [(NHCtBuAu)6(η2-Si4)]Cl2·7NH3 and an Imide Capped Gold Triangle (NHCtBuAu)3NHCl

Crystals of the two new compounds (NHC^tBuAu)₃NHCl and [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ could be isolated from the reaction of Rb₆Cs₆Si₁₇ with NHC^tBuAuCl in the presence of [2.2.2]-cryptand in liquid ammonia. Both compounds were characterized by single-crystal X-ray diffraction and crystallize trigonally without any alkali metals or chelating ligands. Additionally, the crystal of [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ was further interpreted by means of ELF and NBO calculations. In the case of (NHC^tBuAu)₃NHCl, NMR experiments provided an exceptional insight into the reaction processes in solution and allowed for the detection of sequential precursors. In the class of capped gold triangles (NHC^tBuAu)₃NHCl impresses with its unique characteristics of being capped by an imide and bound to N-heterocyclic carbenes as ligands instead of the ubiquitously employed phosphines. The gold capped silicon tetrahedron [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ represents the first known silicide-gold compound, as well as the first known functionalized Zintl anion, crystallized with a cationic central moiety.     

Antibody purification by affinity chromatography based on small molecule affinity ligands identified by SPR-based screening of chemical microarrays

Libraries of small molecules were searched for Fc-fragment selective binders to a recombinant human antibody ("MDJ8″, IgG(1)-subtype, κ-light chain) via SPR-based screening of chemical microarrays. Identified hit structures were immobilised on NHS-activated Sepharose for the determination of MDJ8 binding and selectivity versus typical proteineous impurities represented by the spend cell culture supernatant. Columns were packed and the most promising ligands further characterized in terms of binding constants, binding kinetics, as well as dynamic and equilibrium binding capacities. The performance of the best ligand, 2A10, was compared to standard Protein A chromatography. Using ligand 2A10 antibody capture from unprocessed cell culture supernatants was possible at similar recovery yield (>90%), purity (>80%), and eluting concentration (approximately 1 g/L) as with Protein A. Affinity constants (K(d)) of 2A10 were an order of magnitude higher than for the Protein A material, but still in the nM-range, while maximum binding capacities and binding kinetics were in the same order of magnitude. Ligand 2A10 was also able to capture a murine monoclonal antibody, again with similar efficiency as Protein A, as well as a number of humanised therapeutic antibodies. Antibody elution from the 2A10 column was possible using the Protein A standard protocol, i.e. 100mM glycine HCl pH 3.0, but also at near physiological pH, when some organic solvent or modifiers were present. Ligand 2A10 thus constitutes a cheaper, more robust alternative to Protein A as possible generic antibody binder. Moreover, the outlined approach to ligand selection could in principle by used to create suitable affinity ligands for other high value biotech products.