Investigation of multiple quantum coherence transfer in two-dimensional NMR spectroscopy

[摘要] The limitations of zero quantum NMR pulse sequences reported in the literature are discussed. Several new pulse sequences which improve and extend the scope of the currently available pulse sequences are described.A modified double quantum filtered proton zero quantum 2D-NMR pulse sequence which employs a potentially more efficient and chemical shift independent excitation scheme is described. Results obtained with the modified experiment are illustrated using the complex alkaloid gelsemine.Two new pulse sequences which provide $Fsb1$ homonuclear decoupling double quantum filtered zero quantum 2D-NMR spectra are introduced. One of the pulse sequences uses a chemical shift dependent excitation scheme while the second uses a chemical shift independent sequence. The effects of composite 180$sbsp{y}{o}$ pulses during the excitation and evolution of zero quantum coherences are explored. The effectiveness of a magnetic field homogeneity spoiling pulses on the signal intensity of zero quantum resonances is investigated as is the effect of the tip angle of the radio frequency conversion pulse, $alpha$.Double quantum filtered, $Fsb1$ proton homodecoupled zero quantum relayed coherence transfer is discussed and a new pulse sequence described. The pulse sequence provides a mechanism for exploring remote proton-proton connectivities. The mapping of the two four spin systems of the helicene derived phenanthro (3$spprime$,4$spprime$:3,4) phenanthro (2,1-b) thiophene is discussed in the context of zero quantum relay. A remote 5-bond ;;W;; connectivity is observed for phenanthro (4,3-a) dibenzothiophene.Heteronuclear $sp{13}$C-$sp{31}$P chemical shift correlation via heteronuclear multiple quantum coherence is described. Enhanced sensitivity is afforded by the inverse detection of $sp{31}$P rather than detection of the much less abundant $sp{13}$C spin. Correlations via $sp1Jsb{CP}$ and $sp{n}Jsb{CP}$ where n = 2, 3, are observed with minor variations in the pulse sequence. A description of the laboratory built probes and X-band decoupler is also presented.

[发布机构] Rice University

[效力级别] chemistry