Low-level otoacoustic emissions may predict susceptibility to noise-induced hearing loss

In a longitudinal study with 338 volunteers, audiometric thresholds and otoacoustic emissions were measured before and after 6 months of noise exposure on an aircraft carrier. While the average amplitudes of the otoacoustic emissions decreased significantly, the average audiometric thresholds did not change. Furthermore, there were no significant correlations between changes in audiometric thresholds and changes in otoacoustic emissions. Changes in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions were moderately correlated. Eighteen ears acquired permanent audiometric threshold shifts. Only one-third of those ears showed significant otoacoustic emission shifts that mirrored their permanent threshold shifts. A Bayesian analysis indicated that permanent threshold shift status following a deployment was predicted by baseline low-level or absent otoacoustic emissions. The best predictor was transient-evoked otoacoustic emission amplitude in the 4-kHz half-octave frequency band, with risk increasing more than sixfold from approximately 3% to 20% as the emission amplitude decreased. It is possible that the otoacoustic emissions indicated noise-induced changes in the inner ear, undetected by audiometric tests. Otoacoustic emissions may therefore be a diagnostic predictor for noise-induced-hearing-loss risk.     

Photodissociation of cyclobutyl bromide at 234 nm studied using velocity map imaging

This study investigates the 234 nm photodissociation dynamics of cyclobutyl bromide using a two-dimensional photofragment velocity imaging technique. The spin-orbit ground- and excited-state Br(2P) atoms are state-selectively detected via [2+1] resonance enhanced multiphoton ionization (REMPI), whereas the cyclobutyl radicals are ionized using 157 nm laser light. The Br(2P(3/2)) and the Br(2P(1/2)) atoms and their c-C4H7 radical cofragments evidence a single-peaked, Gaussian-shaped translational energy distribution ranging from approximately 14 to approximately 39 kcal/mol and angular distributions with significant parallel character. The Br(2P(1/2))/ Br(2P(3/2)) spin-orbit branching ratio is determined to be 0.11 +/- 0.07 by momentum match between the Br(2P) photofragments and the recoiling c-C4H7 fragments, assuming a uniform photoionization probability of the c-C4H7 radicals with an internal energy range of 10-35 kcal/mol. The REMPI line strength ratio for the detection of Br(2P(3/2)) and Br(2P(1/2)) atoms at 233.681 and 234.021 nm, respectively, is therefore derived to be 0.10 +/- 0.07. The measured recoil kinetic energies of the c-C4H7 radicals, and the resulting distribution of internal energies, indicates some of the radicals are formed with total internal energies above the barrier to isomerization and subsequent dissociation, but our analysis indicates they may be stable due to the substantial fraction of the internal energy which is partitioned to rotational energy of the radicals.     

Complementary control by additives of the kinetics of amorphous CaCO3 mineralization at an organic interface: in-situ synchrotron x-ray observations

The kinetics of biomimetic mineralization at a fatty acid monolayer interface have been measured in situ by synchrotron x-ray reflectivity. The formation of biologically relevant amorphous calcium carbonate films is affected by soluble macromolecules, supersaturation rate of change, and Mg cations. We find that these solution conditions influence mineral film formation in a complementary fashion. Poly(sodium acrylate) extends the lifetime of metastable amorphous calcium carbonate, solution saturation controls the mineral film growth rate, and Mg cations create a longer induction time. This is the first quantification of potentially competitive biomineralization mechanisms that addresses nucleation and growth of the amorphous mineral phases, which are important in biomineralization.     

Synthesis,crystal structure and conformational analysis of an unexpected [1,5]dithiocine product of aminopyridine and thiovanillin

The condensation reaction of 2‐mercapto‐3‐methoxybenzaldehyde with 3‐aminopyridine afforded an unexpected N‐alkylated [1,5]dithiocine instead of the N‐salicylideneaniline. The proposed mechanism for this condensation involves a strong intramolecular hydrogen bond between the thiol and the amine groups, leading to a second condensation. The corresponding product, i.e. 4,10‐dimethoxy‐13‐(pyridin‐3‐yl)‐6H,12H‐6,12‐epiminodibenzo[b,f][1,5]dithiocine methanol 0.463‐solvate, C₂₁H₁₈N₂O₂S₂·0.463CH₃OH, was characterized by single‐crystal X‐ray diffraction analysis. The supramolecular structure shows π–π stacking and S…S interactions in the crystal packing. Within the asymmetric unit, two geometries of the N atom are observed. Although a planar geometry should be expected, a pyramidal one is observed due to the crystal packing. The presence of the two geometries was further supported by density functional theory (DFT) calculations that show an electronic energy difference of less than 2 kJ mol^?1 between the two conformers.     

Issues Mapping: A problem structuring method for addressing science and technology conflicts

There are new opportunities for the application of problem structuring methods to address science and technology risk conflicts through stakeholder dialogue. Most previous approaches to addressing risk conflicts have been developed from a traditional risk communication perspective, which tends to construct engagement between stakeholders based on the assumption that scientists evaluate technologies using facts, and lay participants do so based on their values. ‘Understanding the facts’ is generally privileged, so the value framings of experts often remain unexposed, and the perspectives of lay participants are marginalized. When this happens, risk communication methodologies fail to achieve authentic dialogue and can exacerbate conflict. This paper introduces ‘Issues Mapping’, a problem structuring method that enables dialogue by using visual modelling techniques to clarify issues and develop mutual understanding between stakeholders. A case study of the first application of Issues Mapping is presented, which engaged science and community protagonists in the genetic engineering debate in New Zealand. Participant and researcher evaluations suggest that Issues Mapping helped to break down stereotypes of both scientists and environmental activists; increased mutual understanding; reduced conflict; identified common ground; started building trust; and supported the emergence of policy options that all stakeholders in the room could live with. The paper ends with some reflections and priorities for further research.     

Calculation of Gauss-Kronrod quadrature rules

The Jacobi matrix of the -point Gauss-Kronrod quadrature rule for a given measure is calculated efficiently by a five-term recurrence relation. The algorithm uses only rational operations and is therefore also useful for obtaining the Jacobi-Kronrod matrix analytically. The nodes and weights can then be computed directly by standard software for Gaussian quadrature formulas.

     

Effect of the guest size and shape on its binding dynamics with sodium cholate aggregates

The binding dynamics of the guests acenaphthene, phenanthrene, fluorene, and acenaphthenol with sodium cholate aggregates were studied using laser flash photolysis and fluorescence. The location of the guests in the bile salt aggregate is determined by the guest's hydrophobicity, where acenaphthene, phenanthrene, and fluorene bind to the primary aggregates, while acenaphthenol binds to the secondary bile salt aggregates. The residence time of the guests in the primary aggregates and the access of ionic species from the aqueous phase to the guest in the aggregate depend on the size and the shape of the guest. These results show that bile salt aggregates are adaptable supramolecular host systems.     

Analysis of selected carbonyl oxidation products in wine by liquid chromatography with diode array detection

A high performance liquid chromatography (HPLC) method for the detection and quantitation of acetaldehyde, glyceraldehyde, pyruvic acid, 2-ketoglutaric acid, and formaldehyde in wine, based on the formation of the 2,4-dinitrophenylhydrazones, is presented. These carbonyl compounds often result from the chemical oxidation of major wine components, and are known to affect flavor and color stability. Their analysis in wine is complicated due to their instability and their tendency to react reversibly with bisulfite to form α-hydroxysulfonates. Published methods that break down the sulfonates for the quantitation of total carbonyls in wine involve alkaline hydrolysis of sulfite-bound carbonyls, but we show, for the first time, that this alkaline treatment step significantly increases the concentration of carbonyls during analysis. A solution based on oxygen exclusion is described. The technique offers good specificity, reproducibility (%RSD 0.45-10.6), and limits of detection (1.29-7.53 μg L⁻¹). The method was successfully used to monitor concentration changes of these compounds in both white and red wines.     

Spectroscopic and computational investigation of second-sphere contributions to redox tuning in Escherichia coli iron superoxide dismutase

In Fe- and Mn-dependent superoxide dismutases (SODs), second-sphere residues have been implicated in precisely tuning the metal ion reduction potential to maximize catalytic activity (Vance, C. K.; Miller, A.-F. J. Am. Chem. Soc. 1998, 120, 461-467). In the present study, spectroscopic and computational methods were used to characterize three distinct Fe-bound SOD species that possess different second-coordination spheres and, consequently, Fe(3+/2+)reduction potentials that vary by approximately 1 V, namely, FeSOD, Fe-substituted MnSOD (Fe(Mn)SOD), and the Q69E FeSOD mutant. Despite having markedly different metal ion reduction potentials, FeSOD, Fe(Mn)SOD, and Q69E FeSOD exhibit virtually identical electronic absorption, circular dichroism, and magnetic circular dichroism (MCD) spectra in both their oxidized and reduced states. Likewise, variable-temperature, variable-field MCD data obtained for the oxidized and reduced species do not reveal any significant electronic, and thus geometric, variations within the Fe ligand environment. To gain insight into the mechanism of metal ion redox tuning, complete enzyme models for the oxidized and reduced states of all three Fe-bound SOD species were generated using combined quantum mechanics/molecular mechanics (QM/MM) geometry optimizations. Consistent with our spectroscopic data, density functional theory computations performed on the corresponding active-site models predict that the three SOD species share similar active-site electronic structures in both their oxidized and reduced states. By using the QM/MM-optimized active-site models in conjunction with the conductor-like screening model to calculate the proton-coupled Fe(3+/2+) reduction potentials, we found that different hydrogen-bonding interactions with the conserved second-sphere Gln (changed to Glu in Q69E FeSOD) greatly perturb the p K of the Fe-bound solvent ligand and, thus, drastically affect the proton-coupled metal ion reduction potential.     

Azodicarboxylate-Mediated Peptide Cyclisation: Application to Disulfide Bond Formation in Solution and Solid Phase

Cyclic peptides are important molecules, playing key roles in protein architecture, as chemical probes, and increasingly as crucial structural elements of clinically-useful therapeutics. Herein we report methodology using azodicarboxylates as efficient reagents for the facile synthesis of cyclic peptides through a disulfide bridge. The utility of this approach in both solution and solid-phase, and compatibility with common amino acid side chain functionalities is demonstrated, resulting in cyclic peptides in good yield and purity. This approach has significant potential application for synthesis of molecules of biological or therapeutic significance.