摘要:

AbstractPart I of this paper describes an on‐resonance, rotating‐frame relaxation method and proposes a procedure for the accurate evaluation of the contribution of chemical exchange to rotating‐frame spin‐lattice relaxation (T1p). Dynamic information, such as exchange lifetimes and chemical shift differences between exchange sites, can be extracted from the exchange contribution. The procedure extends the T1pmethod to medium‐sized and large molecules. Part II presents a verification of the T1pmethod and an analysis of experimental results. The accuracy of these dynamic parameters has been examined using simple, well‐characterized conformational exchange systems. The examination shows that T1pis convenient for studying molecular dynamics on the microsecond time scale. The application of the method to peptides and to right‐ and left‐handed DNA oligomers gives unique dynamic information on the conformational exchange processes in

ISSN:1043-7347    

DOI:10.1002/cmr.1820050102

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractA general review of applications of selective excitation techniques is provided. The different methods for suppression of solvent signal are summarized. The theoretical basis of selective population inversion and selective polarization transfer is considered and applications are treated. Direct observation of chemical‐exchange processes is discussed for both the two‐site and the multi‐site system. Finally, the potential of selective excitation techniques for extracting structural and dynamic information from single‐ and double‐selective relaxation rates is addressed, with particular emphasis given to NMR studies of small ligands bound to macro

ISSN:1043-7347    

DOI:10.1002/cmr.1820050103

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractChemical shift imaging techniques are magnetic resonance imaging methods that separately map the spatial distribution of individual peaks or components in a complex NMR spectrum. A range of chemical shift imaging techniques based around the commonly employed spin‐echo Fourier imaging sequences is classified and described. The performance of the methods with regard to field dependence, chemical shift selectivity, signal‐to‐noise ratio, and imaging times is compared as a guide to selecting the most appropriate technique for a particular applic

ISSN:1043-7347    

DOI:10.1002/cmr.1820050104

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe basic electrical properties of transmission lines are reviewed, and it is shown how these properties determine the characteristic impedance of the line. For resonant lines, the formation of standing waves is explained. The variation of the impedance of the line as a function of its length is shown to be caused by the standing waves of voltage and current. Various equations for the standing‐wave ratio and the concomitant power losses are derived for systems that are impedance mismatched. Applications in NMR spectroscopy include the use of transmission lines as filters, as impedance‐matching devices, and for directing pulses toward the probe and away from the preamplifier. Finally, a simple laboratory experiment demonstrates the properties of open and shorted quarter‐ and half‐wavelength

ISSN:1043-7347    

DOI:10.1002/cmr.1820050105

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050106

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050107

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050108

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050109

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050110

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY

ISSN:1043-7347    

DOI:10.1002/cmr.1820050101

出版商:John Wiley&Sons, Inc.    

年代:1993

数据来源: WILEY