Suppression of strong coupling artefacts in J-spectra

A major problem in J-resolved spectroscopy and many other experiments is the appearance of "artefacts" due to strong coupling. The signals giving rise to these artefacts follow the same coherence transfer pathways as the required signals, making it impossible to suppress them using phase cycling or pulsed field gradients. We present new methods for suppressing these artefacts, applicable to any experiment containing a J-resolved pulse sequence element, as well as to constant-time experiments.     

DYNGA: a general purpose QM-MM-MD program. I. Application to water

We present a general purpose QM-MM-MD engine (DYNGA) designed to test alternative hybrid Hamiltonians geared towards the treatment of problems of interest in structural biology including the use of experimental data constraints. In this first presentation we use DYNGA to explore the behaviour of a traditional QM-MM approach in the treatment of the water—water interaction. We find the potential energy hypersurface for the water dimer computed with the HF 4–31G*/TIP3P hybrid Hamiltonian tends to be too flat. We also explore the effect of using traditional QM-MM techniques on proton wires and conclude there is a need for improvement, possibly addressed by using polarizable force fields.     

PAST AND FUTURE MANAGEMENT OF A COLLAPSED FISHERY: THE BAY OF BISCAY ANCHOVY

Abstract We analyze the efficiency of the international management of the Bay of Biscay anchovy. While a sharing agreement between France and Spain has been in place since 1992, the fish stock collapsed in 2005 and the fishery closed from 2005 to spring 2010. We consider differences in production technologies between both countries and calibrate our model using data from 1987 to 2009. Our results suggest two sources of rent dissipation under the existing sharing agreement: inefficient quota allocation and production inefficiencies due to inflexible national regulations. We discuss several alternatives to improve management.     

ConFlo III - an interface for high precision delta(13)C and delta(15)N analysis with an extended dynamic range

A newly developed interface coupling a CHN combustion device (elemental analyser 'EA') to an isotope ratio mass spectrometer is described and evaluated. The purpose of the device is to extend the dynamic range of delta(13)C and delta(15)N analysis from less than 2 orders of magnitude to more than 3 orders of magnitude. Carbon isotope ratio measurements of atropine as a model compound have been performed analysing between 1 μg to 5 mg C with acceptable to excellent precision (0.6 to 0.06 per thousand, delta-notation). The correction due to the blank signal is critical for sample amounts smaller than 4 μg C. The maximum sample weight is determined by the combustion capacity of the EA. Larger sample amounts are measured using dilution of a small part of the EA effluent with helium. The dilution mechanism works virtually free of isotope fractionation. Copyright 1999 John Wiley & Sons, Ltd.     

Development of a method for the measurement of long-range 13C-1H coupling constants from HMBC spectra

This paper describes a number of improvements to a method, developed in this laboratory and described in J. Magn. Reson. 85 (1989) 111-113, which makes it possible to determine values of long-range 13C-1H coupling constants from heteronuclear multiple bond correlation (HMBC) spectra. First, it is shown how pulsed-field gradients can be introduced into the HMBC experiment without perturbing the form of the cross-peak multiplets; a one-dimensional version of the experiment is also described which permits the rapid measurement of a small number of couplings. Second, the experiment is modified so that one-bond and long-range cross-peaks can be separated, and so that the one-bond cross-peaks have more reliable intensities. Finally, it is shown how these one-bond cross-peaks can be used to advantage in the fitting procedure.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.