Use of homogeneous competition for OH radicals in electrochemical studies of H abstraction from organic molecules

The influence on the N₂O photocurrent of homogeneous competition for OH radicals between two organic solutes which form (as the result of hydrogen abstraction) radicals, one of which is reduced by the electrode, the other being oxidised, is considered theoretically. Such competition can be employed to investigate the kinetics of hydrogen abstraction in a case in which uncompetitive homogeneous destruction of OH radicals by a solute has no effect on the photocurrent. The influence of incomplete oxidation of alcohol radicals when a light pulse of short duration is employed is discussed, together with complications caused by adsorption of the organic solute. Competition for OH radicals between phenol and methanol points to a rate constant for H abstraction from phenol of ca. 2.8 × 10⁹ l mol^?1 s^?1 and to rapid heterogeneous reduction of most of the C₆H₄OH radicals throughout the accessible potential range.     

An efficient synthesis of 3-alkyl-1,5,3-dioxazepanes and their use as electrophiles in double-Mannich reactions

An efficient synthesis of 3-alkyl 1,5,3-dioxazepanes was developed for subsequent use in double-Mannich reactions with a variety of carbon-based nucleophiles. It was found that addition of methyltrichlorosilane to the dioxazepane led to a long-lasting reactive species that reacted rapidly with acid-sensitive ketones and β-ketoesters to afford azabicyclo[3.3.1]nonanes in good yield.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Evaluation of aortic stenosis severity using 4D flow jet shear layer detection for the measurement of valve effective orifice area

Aims

The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method.

Methods and Results

An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOA_JSLD-2D and EOA_JSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOA_CE) with the 2D PC-MRI velocity field and compared to the EOA_JSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA = 0.78 cm²) and experimental measurement (EOA_JSLD-4D = 0.78 ± 0.01 cm²) for peak velocities ranging from 0.9 to 3.7 m/s. In-vivo results showed good correlation and agreement between EOA_JSLD-2D and EOA_CE (r = 0.91, p < 0.001; bias: − 0.01 ± 0.38 cm²; agreement limits: 0.75 to − 0.77 cm²), and between EOA_JSLD-4D and EOA_CE (r = 0.95, p < 0.001; bias: − 0.09 ± 0.26 cm²; limits: 0.43 to − 0.62 cm²).

Conclusion

This study demonstrates the feasibility of measuring EOA_JSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOA_CE measurement variability.     

Advances in coupling a commercial total organic carbon analyser with an isotope ratio mass spectrometer to determine the isotopic signal of the total dissolved nitrogen pool

A new method has been developed to analyse 15N of the total dissolved nitrogen (TDN) pool. The method operates on a commercial total organic carbon (TOC) analyser coupled to an elemental analyser/isotope ratio mass spectrometer (EA-IRMS). Nitrogen compounds are combusted to nitric oxide (NO) and nitrogen dioxide (NO2) by high-temperature catalytic oxidation (HTCO), after which the NOx gas is transferred to an EA-IRMS for isotopic nitrogen analysis. The system is described, including five modifications of the system in order to overcome analytical problems. First, flow paths were modified to run both systems on helium as carrier gas, while complete sample oxidation was maintained. Secondly, the catalyst structure was adapted to allow high injection volumes at the given backpressures delivered by the EA system. Thirdly, we installed a Permapure dehumidification system as the standard Peltier element did not satisfy dehumidification requirements. Finally, we prevented the inflow of atmospheric nitrogen into the system. In a final stage, we are planning to automate the coupled system in order to run a continuous batch of up to 60 samples. We have obtained satisfactory results on the accuracy and precision of 180+/-1 per thousand potassium nitrate samples (IAEA, USGS-32). Running a batch of five samples resulted in a mean isotopic value of 178.8 per thousand with a standard deviation of 2.8 per thousand. Some important issues could not yet be addressed here, and will have to be evaluated once the system is running on a continuous base. However, the results appear promising and this system has the potential to become a method for TD15N analysis. An appropriate TD15N analysis method might open new challenges in aquatic and terrestrial ecosystem nitrogen studies, including a more comprehensive study of the dissolved organic nitrogen pool.     

Protein family classification and functional annotation

With the accelerated accumulation of genomic sequence data, there is a pressing need to develop computational methods and advanced bioinformatics infrastructure for reliable and large-scale protein annotation and biological knowledge discovery. The Protein Information Resource (PIR) provides an integrated public resource of protein informatics to support genomic and proteomic research. PIR produces the Protein Sequence Database of functionally annotated protein sequences. The annotation problems are addressed by a classification-driven and rule-based method with evidence attribution, coupled with an integrated knowledge base system being developed. The approach allows sensitive identification, consistent and rich annotation, and systematic detection of annotation errors, as well as distinction of experimentally verified and computationally predicted features. The knowledge base consists of two new databases, sequence analysis tools, and graphical interfaces. PIR-NREF, a non-redundant reference database, provides a timely and comprehensive collection of all protein sequences, totaling more than 1,000,000 entries. iProClass, an integrated database of protein family, function, and structure information, provides extensive value-added features for about 830,000 proteins with rich links to over 50 molecular databases. This paper describes our approach to protein functional annotation with case studies and examines common identification errors. It also illustrates that data integration in PIR supports exploration of protein relationships and may reveal protein functional associations beyond sequence homology.