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Magnetic Resonance Data (magnetic + resonance_data)
Selected AbstractsMixture modelling of medical magnetic resonance dataJOURNAL OF CHEMOMETRICS, Issue 6 2002Ron Wehrens Abstract In clinical decision making, (semi-)automatic unsupervised classification of data for diagnostic purposes is becoming more and more important. This paper describes the application of mixture modelling, a clustering where multivariate Gaussians are used to describe clusters in the data, to in vivo nuclear magnetic resonance data of patients with brain tumours. Images as well as localized spectra are analysed. The method is able to automatically generate meaningful classifications. Moreover, the results of clustering both the image and spectral data are in close agreement. Copyright © 2002 John Wiley & Sons, Ltd. [source] Multinuclear magnetic resonance study of the structure and tautomerism of azide and iminophosphorane derivatives of chloropyridazinesMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2002Piotr Cmoch Abstract Some azido- and iminophosphorane derivatives of 3,6-dichloro- and 3,4,5,6-tetrachloropyridazine were synthesized and studied by means of NMR measurements. Based on multinuclear data (chemical shifts, coupling constants) for compounds containing the azide group, no potentially possible tetrazole,azide equilibrium can be observed, even under acidic conditions. An unusual substitution of a chlorine atom (in position 4) of tetrachloropyridazine in the reaction with hydrazine was demonstrated by NMR measurements of two newly synthesized compounds containing azido- and iminophosphorane groups. Using multinuclear magnetic resonance data, the sites of ethylation and protonation of azido- and iminophosphorane derivatives of chloropyridazines were established. In the case of the tetrazolopyridazines, ethylation occurs at the N1, and N2, atoms, whereas for monocyclic compounds it takes place at the N1 and/or N2 atoms of the pyridazine ring. Preferred sites of protonation are the N1, atom of the tetrazole ring and the N1 atom of the pyridazine ring. Moreover, the structures of potassium salts of 6-(3-cyano-1-triazeno)tetrazolo[1,5- b] pyridazine and its amido derivative were established using NMR data, especially 15N NMR chemical shifts. Copyright © 2002 John Wiley & Sons, Ltd. [source] Drug resistance in HIV-1 protease: Flexibility-assisted mechanism of compensatory mutationsPROTEIN SCIENCE, Issue 10 2002Stefano Piana Abstract The emergence of drug-resistant variants is a serious side effect associated with acquired immune deficiency syndrome therapies based on inhibition of human immunodeficiency virus type 1 protease (HIV-1 PR). In these variants, compensatory mutations, usually located far from the active site, are able to affect the enzymatic activity via molecular mechanisms that have been related to differences in the conformational flexibility, although the detailed mechanistic aspects have not been clarified so far. Here, we perform multinanosecond molecular dynamics simulations on L63P HIV-1 PR, corresponding to the wild type, and one of its most frequently occurring compensatory mutations, M46I, complexed with the substrate and an enzymatic intermediate. The quality of the calculations is established by comparison with the available nuclear magnetic resonance data. Our calculations indicate that the dynamical fluctuations of the mutated enzyme differ from those in the wild type. These differences in the dynamic properties of the adducts with the substrate and with the gem-diol intermediate might be directly related to variations in the enzymatic activity and therefore offer an explanation of the observed changes in catalytic rate between wild type and mutated enzyme. We anticipate that this "flexibility-assisted" mechanism might be effective in the vast majority of compensatory mutations, which do not change the electrostatic properties of the enzyme. [source] | ||||||||||