Allen-Fahey and related experiments support the predominance of cochlear slow-wave otoacoustic emissions

Originally proposed as a method for measuring the power gain of the cochlear amplifier, Allen-Fahey experiments compare intracochlear distortion products and ear-canal otoacoustic emissions (OAEs) under tightly controlled conditions. In this paper Allen-Fahey experiments are shown to place significant constraints on the dominant mode of reverse energy propagation within the cochlea. Existing Allen-Fahey experiments are reviewed and shown to contradict the predictions of compression-wave OAE models recently proposed in the literature. In compression-wave models, distortion products propagate from their site of generation to the stapes via longitudinal compression waves in the cochlear fluids (fast waves); in transverse traveling-wave models, by contrast, distortion products propagate primarily via pressure-difference waves whose velocity and other characteristics depend on the mechanical properties of the cochlear partition (slow waves). Compression-wave models predict that the distortion-product OAEs (DPOAEs) measured in the Allen-Fahey paradigm increase at close primary-frequency ratios (or remain constant in the hypothetical absence of tuned suppression). The behavior observed experimentally is just the opposite-a pronounced decrease in DPOAE amplitude at close ratios. Since neither compression-wave nor simple conceptual "hybrid-wave" models can account for the experimental results--whereas slow-wave models can, via systematic changes in distortion-source directionality arising from wave-interference effects--Allen-Fahey and related experiments provide compelling evidence against the predominance of compression-wave OAEs in mammalian cochlear mechanics.     

Infrared spectroscopy and structure of photochemically protonated biomolecules in the gas phase: a noradrenaline analogue, lysine and alanyl alanine

A novel photochemical technique combined with mass spectrometry and resonant infrared multiphoton dissociation spectroscopy (R-IRMPD) has been used to record infrared vibrational spectra of the free protonated noradrenaline analogue, 2-amino-1-phenylethanol (APE-H(+)), the amino acid, lysine (Lys-H(+)), and the dipeptide, alanyl alanine (Ala-Ala-H(+)) in the gas phase. Coupling their spectra, obtained in the OH, NH and CH stretch regions, with ab initio calculations has allowed assignment of their preferred protonation sites and conformations. This simple technique will have wide applicability in future investigations of protonated biomolecular structure and conformation.     

Dynamic multi-coil shimming of the human brain at 7 T

High quality magnetic field homogenization of the human brain (i.e. shimming) for MR imaging and spectroscopy is a demanding task. The susceptibility differences between air and tissue are a longstanding problem as they induce complex field distortions in the prefrontal cortex and the temporal lobes. To date, the theoretical gains of high field MR have only been realized partially in the human brain due to limited magnetic field homogeneity.A novel shimming technique for the human brain is presented that is based on the combination of non-orthogonal basis fields from 48 individual, circular coils. Custom-built amplifier electronics enabled the dynamic application of the multi-coil shim fields in a slice-specific fashion. Dynamic multi-coil (DMC) shimming is shown to eliminate most of the magnetic field inhomogeneity apparent in the human brain at 7 T and provided improved performance compared to state-of-the-art dynamic shim updating with zero through third order spherical harmonic functions. The novel technique paves the way for high field MR applications of the human brain for which excellent magnetic field homogeneity is a prerequisite.     

Identification strategy for unknown pollutants using high-resolution mass spectrometry: Androgen-disrupting compounds identified through effect-directed analysis

Effect-directed analysis has been applied to a river sediment sample of concern to identify the compounds responsible for the observed effects in an in vitro (anti-)androgenicity assay. For identification after non-target analysis performed on a high-resolution LTQ-Orbitrap, we developed a de novo identification strategy including physico-chemical parameters derived from the effect-directed analysis approach. With this identification strategy, we were able to handle the immense amount of data produced by non-target accurate mass analysis. The effect-directed analysis approach, together with the identification strategy, led to the successful identification of eight androgen-disrupting compounds belonging to very diverse compound classes: an oxygenated polyaromatic hydrocarbon, organophosphates, musks, and steroids. This is one of the first studies in the field of environmental analysis dealing with the difficult task of handling the large amount of data produced from non-target analysis. The combination of bioassay activity assessment, accurate mass measurement, and the identification and confirmation strategy is a promising approach for future identification of environmental key toxicants that are not included as priority pollutants in monitoring programs.     

Carbon nanoparticles in lateral flow methods to detect genes encoding virulence factors of Shiga toxin-producing <Emphasis Type="Italic">Escherichia coli</Emphasis>

The use of carbon nanoparticles is shown for the detection and identification of different Shiga toxin-producing Escherichia coli virulence factors (vt1, vt2, eae and ehxA) and a 16S control (specific for E. coli) based on the use of lateral flow strips (nucleic acid lateral flow immunoassay, NALFIA). Prior to the detection with NALFIA, a rapid amplification method with tagged primers was applied. In the evaluation of the optimised NALFIA strips, no cross-reactivity was found for any of the antibodies used. The limit of detection was higher than for quantitative PCR (q-PCR), in most cases between 10⁴ and 10⁵ colony forming units/mL or 0.1–0.9 ng/μL DNA. NALFIA strips were applied to 48 isolates from cattle faeces, and results were compared to those achieved by q-PCR. E. coli virulence factors identified by NALFIA were in very good agreement with those observed in q-PCR, showing in most cases sensitivity and specificity values of 1.0 and an almost perfect agreement between both methods (kappa coefficient larger than 0.9). The results demonstrate that the screening method developed is reliable, cost-effective and user-friendly, and that the procedure is fast as the total time required is <1 h, which includes amplification.     

1,5,2,4,6,8-Dithiatetrazocine. Synthesis, computation, crystallography and voltammetry of the parent heterocycle

The prototypal 1,5,2,4,6,8-dithiatetrazocine has been synthesized for the first time by two routes: reaction of 1,2,3,5-dithiadiazolium chloride with N,N,N'-tris(trimethylsilyl)formamidine in acetonitrile and reaction of 1,2,3,5-dithiadiazolyl radical with dioxygen in solution. Yields are low but single crystals could be obtained for an X-ray crystal structure determination which shows it to have the planar delocalized structure predicted by B3LYP/6-311+G(2d,p) hybrid DFT calculations. The crystal structure is strongly reminiscent of that of benzene in the same Pbca space group. Aromaticity is demonstrated by a (1)H NMR chemical shift of +9.70 ppm indicative of diamagnetic ring shielding and an intense low-energy optical absorption with λ(max) = 349 nm (MeOH). The voltammetric behaviour of the title compound is compared with that of 1,3λ(4)δ(2),5,2,4-trithiadiazepine; both resist electrochemical oxidation and reduction over a wide potential range as is typical for aromatic heterocycles.     

Screening of lipophilic marine toxins in shellfish and algae: development of a library using liquid chromatography coupled to orbitrap mass spectrometry

Most liquid chromatography (LC) mass spectrometric (MS) methods used for routine monitoring of lipophilic marine toxins focus on the analysis of the 13 toxins that are stated in European Union legislation. However, to date over 200 lipophilic marine toxins have been described in the literature. To fill this gap, a screening method using LC coupled to high resolution (HR) orbitrap MS (resolution 100 000) for marine lipophilic toxins has been developed. The method can detect a wide variety of okadaic acid (OA), yessotoxin (YTX), azaspiracid (AZA) and pectenotoxin (PTX) group toxins. To build a library of toxins, shellfish and algae samples with various toxin profiles were obtained from Norway, Ireland, United Kingdom, Portugal and Italy. Each sample extract was analyzed with and without collision induced dissociation fragmentation. Based on their mass and specific fragmentation pattern, 85 different toxins were identified comprising 33 OA, 26 YTX, 18 AZA and 8 PTX group toxins. A major complication of full scan HRMS is the huge amount of data generated (file size), which restricts the possibility of a fast search. A software program called metAlign was used to reduce the orbitrap MS data files. The 200-fold reduced data files were screened using an additional software tool for metAlign: ‘Search_LCMS’. A search library was constructed for the 85 identified toxins. The library contains information about compound name, accurate mass, mass deviation (<5 ppm), retention time (min) and retention time deviation (<0.2 min). An important feature is that the library can easily be exchanged with other instruments as the generated metAlign files are not brand-specific. The developed screening procedure was tested by analyzing a set of known positive and blank samples, processing them with metAlign and searching with Search_LCMS. A toxin profile was determined for each of the contaminated samples. No toxins were found in the blank sample, which is in line with the results obtained for this sample in the routine monitoring program (rat bioassay and tandem LC–MS).     

Application of dried blood spot sampling combined with LC-MS/MS for genotyping and phenotyping of CYP450 enzymes in healthy volunteers

An early clinical development study (phase I) was conducted to determine the usefulness of dried blood spot (DBS) sampling as an alternative to venous sampling for phenotyping and genotyping of CYP450 enzymes in healthy volunteers. Midazolam (MDZ) was used as a substrate for phenotyping CYP3A4 activity; the concentrations of MDZ and its main metabolite 1'-hydroxymidazolam (1-OH MDZ) were compared between the DBS method from finger punctures, plasma and whole blood (WB), drawn by venipuncture, whereby several methodological parameters were studied (i.e. punch width, amount of dots analyzed and storage time stability). Genotyping between DBS and venous WB samples was compared for CYP2D6 (*3, *4, *6), CYP2C19 (*2, *3), CYP3A4 (*1B) and CYP3A5 (*3C). In addition, the subject's and phlebotomist's satisfaction with venous blood sampling compared with the DBS method was evaluated using a standardized questionnaire. An LC-MS/MS method for the quantification of the MDZ and 1-OH MDZ concentrations in DBS samples was developed and validated in the range of 0.100-100 ng/mL. No compromises were made for the limits of quantification of the DBS-LC-MS/MS method vs the authentic plasma and WB methods.     

On a possible node in the Sivers and Qiu-Sterman functions

The possibility of a node in the x dependence of the Sivers and Qiu-Sterman functions is discussed in light of its importance for the experimental check of the overall sign change of the Sivers effect between semi-inclusive DIS and the Drell-Yan process. An x-dependent version of the Ehrnsperger-Schäfer-Greiner-Mankiewicz relation between the Qiu-Sterman function and a twist-3 part of g₂ is presented, which naturally suggests a node in the Qiu-Sterman function. This relation could be checked experimentally as well and could provide qualitative information on the gluonic field strength inside the proton. Satisfying the Burkardt sum rule by means of a node is briefly discussed and the importance of modelling the Sivers function including its full Wilson line is pointed out.