2D correlated spectroscopy

Figure 1.45 Coherence transfer pathways in 2D NMR experiments. (A) Pathways in homonuclear 2D correlation spectroscopy. The first 90° pulse excites singlequantum coherence of order p= . The second mixing pulse of angle /3 converts the coherence into detectable magnetization (p= —1). (Bra) Coherence transfer pathways in NOESY/2D exchange spectroscopy (B b) relayed COSY (B c) doublequantum spectroscopy (B d) 2D COSY with double-quantum filter (t = 0). The pathways shown in (B a,b, and d) involve a fixed mixing interval (t ). (Reprinted from G. Bodenhausen et al, J. Magn. Resonance, 58, 370, copyright 1984, Rights and Permission Department, Academic Press Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887.)...

Another direction of future research is to investigate the relationships between IR and NIR spectra in the form of PLS2 modeling and 2D correlation spectroscopy [6]. A preliminary 2D correlation spectrum is shown in Fig. 8. 

The general experimental approach used in 2D correlation spectroscopy is based on the detection of dynamic variations of spectroscopic signals induced by an external perturbation (Figure 7.43). Various molecular-level excitations may be induced by electrical, thermal, magnetic, chemical, acoustic, or mechanical stimulations. The effect of perturbation-induced changes in the local molecular environment may be manifested by time-dependent fluctuations of various spectra representing the system. Such transient fluctuations of spectra are referred to as dynamic spectra of the system. Apart from time, other physical variables in a generalised 2D correlation analysis may be temperature, pressure, age, composition, or even concentration. 

Two-dimensional spectroscopy is a rather novel concept, and a powerful tool in analysing spectra. The advantages of generalised 2D correlation spectroscopy are ... 

Generalised 2D correlation spectroscopy is powerful in exploring complicated NIR spectra [1016]. Both 2D IR [1017] and 2D NIR correlation spectroscopy [1018] have been reviewed for wD NMR, see refs [1019,1020]. 

Applications The potential use of 2D correlation spectroscopy is very wide [1007], Most multidimensional techniques arise from the correlation of frequency domains in the presence of external perturbations, as in NMR. For applications of multidimensional NMR spectroscopy and NMR diffusion measurements, see Sections 5.4.1 and 5.4.1.1. 

In recent years new NMR techniques offering broad applications in stereochemical analysis have come into use. A prominent example is 2D-NMR (both 2D-resolved and 2D-correlated spectroscopy), which has been extensively applied to biopolymers (149-151). Its use with synthetic polymers has, until now, been limited to but a few cases (152, 153). A further technique, cross-polarization magic-angle spinning spectroscopy (CP-MAS NMR) will be discussed in the section on conformational analysis of solid polymers. 

The concept of two-dimensional (2D) correlation spectroscopy was originally developed by Noda (97) and has been applied to a number of systems to... 

The pulse methods rely on selective irradiation of a particular resonance line with a radio frequency (rf) and observation of the resulting effects in the rest of the spectrum. Among commonly employed methods are 2D correlated spectroscopy (COSY), 2D spin-echo correlated spectroscopy (SECSY), 2D nuclear Overhauser and exchange spectroscopy (NOESY), 2D J-resolved spectroscopy (2D-J), and relayed coherence-transfer spectroscopy (RELAYED-COSY) (Wutrich, 1986). 

C , n-fold axis of symmetry C(A)T, computed (axial) tomography COSY, 2D correlation spectroscopy CSR, chemical shift reagent... 

The results are represented in a 2D correlation spectroscopy diagram (COSY) as is shown for Val-Leu in Figure 7-20. The diagonal of this two dimensional diagram corresponds to the original (one-dimensional) spectrum of the sample. The COSY... 

Although at first glance 2D correlation spectroscopy of C with quadrupolar nuclei seems unfeasible due to relaxation problems, there are two metal nuclei where, owing to the relatively small quadrupolar moment, such a correlation has been performed. Gunther and co-workers were the first... 

Park H S, Choi Y S, Jung Y M, et al. Intermolecular interaction-induced hierarchical transformation in Id nanohybrids Analysis of conformational changes by 2d correlation spectroscopy. J. Am. Chem. Soc. 2008. 130, 845-852. 

Each of these experiments has pros and cons. The SEDOR experiment is easiest to set up but lacks the resolution since it is made on a static sample, and is often limited in the range of accessible dipolar couplings by T2. The REDOR experiment is more elaborate to set up and requires stable spinning, but its increased resolution enables multisite systems to be explored, while the longer T2 enables longer distances to be determined. TEDOR is less sensitive than REDOR as it involves a transfer step with a theoretical maximum efficiency of 50 percent. However, it is not a difference experiment, and is therefore less prone to experimental errors. An important application of TEDOR is its use in 2D-correlation spectroscopy. 

General symmetry principles for rotor-synchronized pulse sequences in MAS solid-state NMR have been presented. The synunetry theory has been extended to the case of generalized Hartmann-Hahn sequences, in which rotor-synchronized r.f. irradiation is applied simultaneously to two isotopic spin species. The symmetry theory has been used to design pulse sequences which implement heteronuclear dipolar recoupling at the same time as decoupling homonuclear spin-spin interactions, and which also suppress CSAs. Experimental demonstrations of heteronuclear 2D correlation spectroscopy, heteronuclear MQ spectroscopy, and the estimation of intemuclear dipolar couplings have been given. 

D Correlation Spectroscopy. A simple, quahtative approach has been described for the determination of membrane protein secondary structure and topology in lipid bilayer membranes." The new approach is based on the observation of wheel-like resonance patterns in the NMR H- N/ N polarization inversion with spin exchange at the magic angle (PISEMA) and H/ N HETCOR spectra of membrane proteins in oriented lipid bilayers. These patterns, named Pisa wheels, have been previously shown to reflect helical wheel projections of residues that are characteristic of a-helices associated with membranes. This study extends the analysis of these patterns to P-strands associated with membranes and demonstrates that, as for the case of a-helices, Pisa wheels are extremely sensitive to the tilt, rotation, and twist of P-strands in the membrane and provide a sensitive, visually accessible, qualitative index of membrane protein secondary structure and topology. 

Most but not all wpllcaUons of 2D correlated spectroscopy to date have Involved and studies. A 2D spec trim In which C chemical shifts and the other chemical... 

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