Gradient correlation spectroscopy

Hadden, C.E., Martin, G.E., and Krishnamurthy, V.V., Constant time inverse-detection gradient accordion rescaled heteronuclear multiple bond correlation spectroscopy CIGAR-HMBC, Magn. Reson. Chem., 38, 143, 2000. 

Reports on the application of pulsed field gradient (PFG) assisted pulse schemes for two-dimensional X/Y correlation spectroscopy focused mainly on the adaptation of HSQC sequences which seemed to perform better than HMQC experiments under these conditions.21 Although the generalisation of standard pulse sequences for / C correlation spectroscopy should in principle be straightforward, large spectral ranges and short relaxation... 

Fig. 1. Pulse sequence for the X/Y H PFG-HSQC experiment as employed for 19F/13C correlation spectroscopy in Ref. 21. 90° and 180° hard pulses are denoted by solid and open bars, respectively groups of two solid and one open bars denote 90° 0 — 180° +9o — 90° pulse sandwiches that serve as composite 180° pulses. 2 are delays of length 1 /(2 Jx,v), and r is a short delay of the same length as the gradient pulse (typically 1 ms). Phase cycles are as in the standard HSQC experiment, and the ratio of gradient pulse strengths is set to G2/G1 = Yy/Yx- Decoupling is employed using WALTZ-16 ( H) and GARP (Y) pulse trains.

Lead, J. R., Wilkinson, K. J., Balnois, E., Cutak, B. J., Larive, C. K., Assemi, S., and Beckett, R. (2000). Diffusion coefficients and polydispersities of the Suwannee River Fulvic Acid Comparison of fluorescence correlation spectroscopy, pulsed-field gradient nuclear magnetic resonance, and flow field-flow fractionation. Environ. Sci. Technol. 34(16), 3508-3513. 

The methods described in this book are primarily concerned with the measurement of the microstructure of complex fluids subject to the application of external, orienting fields. In the case of flow, it is also of interest to measure the kinematics of the fluid motion. This chapter describes two experimental techniques that can be used for this purpose laser Doppler velocimetry for the measurement of fluid velocities, and dynamic light scattering (or photon correlation spectroscopy) for the determination of velocity gradients. 

J. J. Wang, D. Yavich, and L. G. Leal, Time-resolved measurement of velocity gradient tensor in linear flow by photon correlation spectroscopy, Phys. Fluids A, submitted (1995). 

H, C, and NMR chemical shifts of 10 substituted pyrazolo[l,5- ]pyrimidines 40 were assigned based on double quantum filtering (DQF) H, H correlation spectroscopy (COSY), pulsed field gradient (PFG) H, C... 

Various new techniques suitable for estimating D are now available fluorescence correlation spectroscopy (FCS) [5], fluorescence recovery after photobleaching (FRAP) [6], pulsed field gradient nuclear magnetic resonance (PFG-NMR) [7], diffusion ordered NMR spectroscopy (DOSY) [8], and others. Among these, FCS and FRAP are popular in biological studies because they are often installed on a commercial LSM system and conveniently coupled with it. 

The pulse sequence for J-resolved spectroscopy is (90) — fj — (180). The FID is observed as an echo, so there needs to be an additional delay ty before the detection period ti, and the complete sequence is (90) — tj — (180) — tj — f2, as shown in Figure 26. For COSY the basic pulse sequence is (90) — ty— (90) — tj and for NOESY it is (90) — ty— (90) — D — (90) — 2, with a pulsed field gradient applied during the delay, D. A large number of other pulse sequences has been designed both to improve detection and to permit other forms of correlation spectroscopy. 

Kay, L. E., Keifer, R, and Saarinen, T. (1992) Pnre absorption gradient enhanced het-eronnclear single qnantum correlation spectroscopy with improved sensitivity. J. Am. Chem. Soc. 114(26), 10663-10665. 

WiUker, W., Leibfritz, D., Kerssebaum, R., and Bermel, W. (1992) Gradient selection in inverse heteronuclear correlation spectroscopy. Magn. Reson. Chem. 31, 287-292. 

In the early days of heteronuclear correlation spectroscopy, a gradient free version of the double low-pass filter was proposed [5.212, 5.213], but the necessity to suppress unwanted coherences, particularly in INADEQUATE experiments, has forced the design of a gradient version [5.214]. The application of this filter is not just restricted to INADEQUATE experiments it has also become the element of choice in ACCORD-HMBC and ACCORD-CIGAR-HMBC experiments to reduce residual one-bond correlations. These experiments are very sensitive to the suppression of one-bond... 

NMR has become a standard tool for structure determination and, in particular, for these of Strychnos alkaloids. The last general article in this field was authored by J. Sapi and G. Massiot in 1994 [65] and described the advances in spectroscopic methods applied to these molecules. More recently, strychnine (1) has even been used to illustrate newly introduced experiments [66]. We comment, here, on their advantages and sum up the principles of usual 2D experiments in Fig. (1) and Fig. (2) (COSY Correlation SpectroscopY, TOCSY TOtal Correlation SpectroscopY, NOESY Nuclear Overhauser Enhancement SpectroscopY, ROESY Rotating frame Overhauser Enhancement SpectroscopY, HMQC Heteronuclear Multiple Quantum Coherrence, HMBC Heteronuclear Multiple Bond Correlation). This section updates two areas of research in the field new H and 13C NMR experiments with gradient selection or/and selective pulses, 15N NMR, and microspectroscopy. To take these data into account, another section comments on the structure elucidation of new compounds isolated from Strychnos. It covers the literature from 1994 to early 2000. 

In Chapter 1, Fyfe, Mueller, and Kokotailo describe the applications of solid-state NMR to the study of zeolite molecular sieve catalysts and related systems. Zeolites provide an apt arena in which to demonstrate the capabilities of modern techniques such as sample spinning, cross-polarization, and multidimensional correlation spectroscopy. In Chapter 2, Karger, and Pfeifer consider the question of molecular diffusion in catalyst systems. Applications of NMR techniques such as imaging, lineshape analysis, relaxation, pulsed field gradient echo spectroscopy, and NMR tracer exchange are described and compared with other, more traditional techniques such as radioactive tracing. In Chapter 3, Haw discusses the use of NMR to probe catalytic processes, showing how the combination of temperature control with novel NMR probes makes it possible to elucidate reaction mechanisms in situ. 

FIGURE 3.9 The first of three plots of the same region of a H- H 2-D gradient-selected correlation spectroscopy (gCOSY) spectrum showing the effect of plot threshold variation. In this plot, the plot threshold Is set too high (too little Information appears In the 2-D plot). 

The homonudear 2-D NMR experiments that use I-coupling indude the correlation spectroscopy (COSY, and variants induding gradient-selected COSY or gCOSY, double-quantum filtered COSY or DQF-COSY) experiment, the total correlation spectroscopy (TOCSY) experiment, and the incredible natural abimdance double quantum transfer experiment (INADEQUATE) [3]. 

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