NMR spin-relaxation measurements

Bain. A. and Cramer, J.A. (1993) A method for optimizing the study of slow chemical exchange by NMR spin-relaxation measurements. Application to tripodal carbonyl rotation in a metal complex. 

The 3D homology model of the protein structure is validated as much as possible with experimental data, such as mutagenesis data, NMR spin-relaxation measurements (28-30), active site chemical probe studies (31,32), and predictions of CYP substrate- and/or inhibitor-binding and regioselective metabolism and... 

This was verified by NMR spin relaxation measurements, which show that the spin relaxation declines with increasing water content [17]. It was observed in the hydroformylation of 1-heptene using a HRh(CO)(TPPTS)3-SAPC that the TOF increases with a factor as high as 100 when going from 2.9 to 9 wt. % water (table 3). 

High-resolution 13C NMR studies have been conducted on intact cuticles from limes, suberized cell walls from potatoes, and insoluble residues that remain after chemical depolymerization treatments of these materials. Identification and quantitation of the major functional moieties in cutin and suberin have been accomplished with cross-polarization magic-angle spinning as well as direct polarization methods. Evidence for polyester crosslinks and details of the interactions among polyester, wax, and cell-wall components have come from a variety of spin-relaxation measurements. Structural models for these protective plant biopolymers have been evaluated in light of the NMR results. 

In liquid-state NMR, spin relaxation due to cross-correlation of two anisotropic spin interactions can provide useful information about molecular structure and dynamics. These effects are manifest as differential line widths or line intensities in the NMR spectra. Recently, new experiments were developed for the accurate measurement of numerous cross-correlated relaxation rates in scalar coupled multi-spin systems. The recently introduced concept of transverse relaxation optimized spectroscopy (TROSY) is also based on cross-correlated relaxation. Brutscher outlined the basic concepts and experimental techniques necessary for understanding and exploiting cross-correlated relaxation effects in macromolecules. In addition, he presented some examples showing the potential of cross-correlated relaxation for high-resolution NMR studies of proteins and nucleic acids. 

For conjugated (diene)metal complexes, the 7r-molecular orbitals of cyclobutadiene consist of a degenerate eg pair (Figure 3). Because of this orthogonality, there is not a single electronically preferred conformei and barriers for rotation of the cyclobutadiene ligand are generally low . For (cyclobutadiene)Fe(CO)3, in the solid state, NMR spin relaxation data indicate that there are two inequivalent lattice sites. For each of these inequivalent lattice sites, barriers for rotation of the cyclobutadiene have been measured to be 3.63 and... 

A coexistence region in SQA was also evidenced by 13C 2D temperature jump correlation NMR.172 Proton 1H spin lattice and spin-spin relaxation measurement on SQA was performed within 320 460 K.138 In addition to a typical critical behavior manifested at the known temperature of the anti-ferroelectric phase transition near Tc 373 K, both relaxation data also show a second critical behavior around 420 K, which opens the question of a second phase transition for SQA. 

We have also used Nuclear Magnetic Resonance (NMR) based spin-spin relaxation measurements to look at ageing effects as minor changes in the polymer structure, under long term or accelerated ageing conditions, can be monitored using this technique [ 7]. 

Proton, deuteron and carbon spin relaxation measurements of liquid crystals have provided detailed information about the molecular motions of such anisotropic liquids (anisotropic rotation and translation diffusion of individual molecules), and about a peculiar feature of liquid crystalline phases, namely collective molecular reorientations or order fluctuations. Spin relaxation in liquid crystalline mesophases has challenged NMR groups since the early 1970s, shortly after the publication of theoretical predictions that order fluctuations of the director (OFD, OF), i.e. thermal excitations of the long-range orientational molecular alignment (director), may play an important unusual role in nuclear spin relaxation of ordered liquids. Unique to these materials, which are composed of rod-like or disc-like (i.e. strongly anisotropic molecules), it was predicted that such thermal fluctuations of the director should, at the frequencies of these fluctuation modes, produce rather peculiar Ti(p) dispersion profiles. For example in the case of uniaxial nematic... 

T2, spin—spin relaxation. Measures the loss of coherence of the NMR signal during a FID. 

During the past two years, significant advances have been made in the development of NMR methods for studying biomolecular dynamics on the microsecond to millisecond timescale. Thuduppathy and HilP reviewed applications of NMR spin relaxation methods for measuring biological motions. Fernandez and Wider discussed transverse relaxation-optimized spectroscopy (TROSY) that promises to further enhance the determination of solution structures of large biomolecules. 

Muon Spin Relaxation refers to the observation of incoherent motions of the muon spins which result in a loss of polarization with time. This will occur if the magnetic field sensed by the ensemble of implanted muons is broadly distributed. If the local field each muon sees in addition fluctuates randomly during a muon s life we observe what is called dynamic depolarization , but also a stationary distributed field causes depolarization by phase incoherence ( static depolarization ). These two cases must be clearly distinguished. The situation corresponds to the two relaxation times Ty (spin-lattice) and Ti (spin-spin) in NMR. Muon Spin Relaxation measurements can be carried out without observing spin rotation and thus are possible in zero applied field or with a longitudinally applied field (i.e., a field applied parallel to the muon spin direction at the moment of implantation). Longitudinal field measurements are the most appropriate way to obtain a clear distinction between static and dynamic muon spin depolarization. Muon Spin Relaxation hence mostly refers to zero or longitudinal field (iSR. 

Jo et al prepared and characterised Gel polymer electrolytes composed of methy methacrylete-styrene copolymers (PMS) and electrolyte solution (LiT-FSI in EC/DMQ. Depending on the molar composition of the copolymer, these gel polymer electrolytes exhibited different electrochemical and mechanical properties. In order to investigate the physical interactions among organic solvents, polymer, and lithium ions occurred in the gel polymer electrolyte, Raman spectroscopy and solid state Li NMR spin-spin relaxation measurements were performed. 

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