Spin-State Selective Experiments

Spin-state selective experiments have been an integral part in both the history and development of NMR spectroscopy. Experiments vary from the early simple double-... 

Most spin-state selective experiments have been used to measure coupling constants [5.228]. RNA research has often used chemical synthesized nucleosides as model compounds labelling the nucleosides with and investigating the IR and spin system to extract scalar and dipolar coupling constants, and correlation experiments have been a popular approach. Check it 5.9.2.3 illustrates a IR and correlation experiment ... 

Bouguet-Bonnet S, Mutzenhardt P, Canet D (2004) Measurement of 15 N csa/dipolar crosscorrelation rates by means of spin state selective experiments. J Biomol NMR 30 133-142... 

P. Permi, A spin-state-selective experiment for measuring heteronuclear one-bond and homonuclear two-bond couplings from an HSQC-type spectrum, J. Biomol. 

Nolls, P., Espinosa, J. F., Parella, T. Optimum spin-state selection for all multiplicities in the acquisition dimension of the HSQC experiment. 

Andersson P, Annila A, Otting G, An alpha/beta-HSQC-alpha/beta experiment for spin-state selective editing of IS cross peaks, J. Magn. Resort., 133 364-367, 1998. 

Heteronuclear coupling constants (1,b7c,h) are most commonly measured from heteronuclear 2D experiments. The 3/c H couplings can be easily extracted from /-resolved spectra as well as from f or F2 proton coupled HSQC spectra. The undesired evolution of "/CH during q can be eliminated with use of an appropriate bilinear rotation decoupling (BIRD) pulse, such as BIRDd,x in. /-resolved spectroscopy35 and 111RD in Fi-coupled HSQC.36 Spin-state selective excitation techniques, S3E and S3CT37 38 (spin-state-selective coherence transfer), can also be used for the measurement of... 

Isotope edited experiments 3D HCCH-COSY 3D HCCH-TOCSY ID spin-state selective HMQC and HSQC-based 3D MUSIC CBCANH 3D MUSIC CBCA(CO)NH 2D Pro-HSQC... 

In Check it 5.9.2.1, the S ED element in a spin-state selective HSQC experiment is used to verify by changing the values in a simple phase cycling sequence, it is possible to select a specific spin-state combination. 

Load the file ch5921.cfg. Using the file tppi.temp as a template, write a spin-state-selective a-HSQC-a experiment. Run a simulation using the current spin system and experiment parameters. Modify the phase program as shown on the right hand side in the figure above, to obtain the other correlation peaks in the spin system. Alternatively use the file ch5921x.cfg. 

Implementation of spin-state selection into 2D [ X, IH] HSQC experiments - The TROSY-HSQC... 

The name TROSY [5.226, 5.227] has now became an pseudonym for relaxation optimized pulse sequences and as such, nearly all triple resonance experiments are now available with a TROSY variant allowing the selection of the slowest relaxing component in a multiplet. Consequently, large bio-molecules can now be studied using triple resonance experiments. Check it 5.9.2.2 simulates a 2D [l N, IH] TROSY-HSQC experiment, the original experiment used to illustrate spin-state selection for fast relaxing spin systems. 

In direct detection experiments, several approaches were used to achieve virtual decoupling (to remove homonuclear one-bond carbon-carbon couplings) such as IPAP schemes (in-phase anti-phase) [150-152], in which two FIDs for each increment are recorded and stored separately, one for in-phase and another for antiphase, the two components being combined to remove the splitting. An alternative is S E schemes [152, 153] (spin-state selective excitation), in which two different experiments are performed with one being absorptive and another dispersive. One or more of these building blocks (IPAP and S E) can be implemented in any experiments based on direct detection. A set of based experiments, which can be used for the assignment of backbone and side-chains of labeled... 

Meissner A, Duus JO, S0rensen OW (1997) Integration of spin-state-selective excitation into 2D NMR correlation experiments with the heteronuclear ZQ/2Q pi rotations for Jxh resolved E.COSY-type measurements of heteronuclear coupling constants in proteins. J Biomol NMR 10 89-94... 

Today there are many variants of the basic sequences. The most important modifications are the transverse relaxation optimized experiments suitable for perdeut-erated proteins, the sensitivity enhanced versions and the constant time (CT) implementations for improved resolution. Furthermore there are many experiments based on the basic sequences designed to measure scalar and residual dipolar couplings, often also implemented with spin-state selection as exemplified in Fig. 14.54. 

Spin-state selection in solid state NMR has been demonstrated, using pulse sequences similar to those used in solution NMR. Different transitions of all three carbon resonances in fully C-labelled L-alanine were separated in different spectra. By selecting spin-states, the contribution of the J-couphng to the linewidth was removed, leading to a considerable enhancement in resolution. The spin-state selective technique was demonstrated for MAS frequencies from 6 to 35 kHz. Other experimental conditions affecting the sensitivity of the experiments were also discussed. Sensitivity losses due to the introduction of the spin-state selective filter were shown to be acceptable. In addition, spin-state selection was used to experimentally confirm the differential broadening expected for the two transitions of the CH3 resonance. 

The principal values and even the orientation of the principal axes of the Na hyperfine coupling tensor with respect to axes of the g tensor could be determined from Mims and Davies pulsed ENDOR spectra, refer to Section 2.3.3 in Chapter 2. The values Axx( Na) = Ayy( Na) = 6.3 and Azz( Na) = 10.9 MHz were obtained by simulation taking angular selection into account. The so-called hyperfine enhancement of ENDOR intensities due to the interaction between the radio frequency field and the electron spin could lead to pronounced differences in the ENDOR intensities between signals from different rris electron spin states in experiments at conventional MW frequencies such as in X-band, but also at the W-band. The Na (I = 3/2) nuclear quadrupole tensor is almost coaxial to the A tensor, 2zz = 0.48 MHz, Qyy = -0.07 MHz, and Qxx = -0.41 MHz. Simulation of orientation-selective ENDOR spectra as described in [26, 33] serves to refine the principal values of the hyperfine coupling tensors estimated from experiment. In... 

R. Linser, U. Fink, B. Reif, Assignment of dynamic regions in biological soKds enabled by spin-state selective NMR experiments,. Am. Chem. Soc. 132 (2010) 8891-8893. 

With the aim of quantitatively predicting the orientational order of rigid solutes of small dimensions dissolved in the nematic liquid crystal solvent, 4-n-pentyl-4 cyanobiphenyl (5CB), an atomistic molecular dynamics (MD) computer simulation has been applied. It is found that for the cases examined the alignment mechanism is dominated by steric and van der Waals dispersive forces. A computer simulation of the deuterium NMR spectra of molecules in a thin nematic cell has been carried out and the director distribution in the cell has been studied. An experiment for the direct estimation of an element of the order matrix from H NMR spectra of strongly dipolar coupled spins that is based on the multiple quantum spin state selected detection of single quantum transitions has been proposed. The experiment also enables obtaining nearly accurate starting dipolar... 

A new 3D spin-state-selective coherence transfer experiment has been intro-... 

Cross-Correlated Relaxation Experiments. - Cross-correlated relaxation is usually evaluated from the comparison between a spectrum collected when the cross-correlated relaxation is active, and the reference spectrum with the suppressed cross-correlated relaxation. This approach relies heavily on the effective suppression of the cross-correlated relaxation, which is often difficult to assess. Two independent publications " suggested to use spin-state selection to monitor the relaxation of the individual doublet components and to derive the cross-correlated relaxation contribution from their difference. In such scheme artefacts from the incomplete suppression of one of the components appear in the separate spectrum region and do not interfere with the result. In addition, the number of the cross-peaks remains the same as in the corresponding HSQC spectrum, not creating additional overlap. Vasos et alP used S E element prior the transverse relaxation measurement period, while Bouguet-Bonnet et al opted for the S ED sequence. In addition, the later publication presents a version of the experiment that allows to measure both transverse and longitudinal relaxation rates. 

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