Solution-state NMR

The paramagnetic contributions to the chemical shielding of octahedral low spin d Co(III) complexes have commonly been interpreted through the strong-field approximation of the Ramsey shielding model  

I ( Aig I Lz I Tig) 1 are collectively known as the covalency or the nephe-lauxetic factor. The classical Freeman-Murray-Richards (FMR) approach emphasizes the dependence of shielding on excitation energies, whereas the independent investigations by Juranic and Bramley demonstrated the importance of the nephelauxetic effect in Co shielding variation. On the one hand, Taura convincingly showed that the solvent dependence of the Co chemical shift for K3Co(CN)6 arises mainly from the solvent shift of the Tig transition. The Co chemical shifts of a wealth of Werner-type complexes were successfully rationalized in terms of empirical 

Indeed, the graphs of isotropic chemical shifts versus the quotients of nephelauxetic factors and the d-d transition energies show a better correlation than the conventional FMR plot for Co(III) pentaamine and Co(III) pentacyano complexes.  

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Sachleben J R ef a/1998 Solution-state NMR studies of the surface structure and dynamics of semiconductor nanocrystals J. Phys. Chem. B 102 10 117... 

Molecular Packing and Ring Interconversion by Solid State and Solution State NMR Spectra of Cyclododecane and Octamethyl-tetrasiloxane... 

Lu, F. Ralph, J. Non-degradative dissolution and acetylation of ball-milled plant cell walls high-resolution solution-state NMR. Plant J. 2003, 35, 535-544. 

Many components of food are in the solid state and possess very short T2. The linewidths from solid components are generally too wide to be observed directly by solution state NMR methods. However, these components can be detected by the special techniques of solid state NMR. These techniques involve the use of cross polarization excitation (from 3H to 13C), high power 3H decoupling (to inhibit... 

UB and UB H solution-state NMR spectra (see Fig. la) clearly show the different boron environments within the m-carborane unit. The eight peaks in the -10 to 0 ppm range are indicative of the different boron environments in the w-carborane cage, including B—B, B—C, and B—H bonds. The spectrum also contains... 

Figure 1 Solution-state NMR spectra of the CD2C12 soluble fraction of phenyl modified poly (7 -carboranyl-si Ioxane ) rubber, (a) nB and 11 B 1111 NMR (b) 111 and 1H[11B] NMR. 

One of the issues in using solution state NMR for PET analysis is that, due to the high crystallinity content of the polymer, it is fairly difficult to dissolve. Harsh... 

Marcotte I, Auger M (2005) Bicelles as model membranes for solid- and solution-state NMR studies of membrane peptides and proteins. Concept Magn Reson A 24A 17-37... 

Ab initio computations, particularly at MP2 and (the computationally less intensive) B3LYP levels of theory, have been largely responsible for the rapid progress in carborane structural research, permitting the determination of the molecular geometry of a novel carborane from solution-state NMR data where X-ray diffraction could not be used (such as those in trace amounts or for which suitable crystals could not be obtained). Earlier... 

Although the same nuclear spin interactions are present in solid-state as in solution-state NMR, the manifestations of these effects are different because, in the solid, the anisotropic contribution to the spin interactions contributes large time-independent terms to the Hamiltonian that are absent in the liquid phase. Therefore, the experimental methods employed in solids differ from the ones in the liquid state. The spin Hamiltonian for organic or biological solids can be described in the usual rotating frame as the sum of the following interactions ... 

The dipolar-coupling Hamiltonian (TTy) describes the through-space coupling between two nuclear spins l and Ij. The dipolar coupling has an rk- dependence, and is key to the determination of internuclear distances in both solid-state and solution-state NMR. The high-field truncated form of the dipolar Hamiltonian is given by... 

Composite-pulse decoupling schemes like WALTZ [36, 37], DIPSI [38], or GARP [39], which are used in solution-state NMR, have failed to offer any significant improvements in the solid state compared to CW decoupling. The residual line width in CW-decoupled spectra is dominated by a cross term between the chemical-shielding tensor of the protons and the heteronuclear dipolar-coupling tensor [40, 41]. 

CH3CN (8 -85.1) and 32 CH3CN (8 -84.8) by the solid-state NMR experiments. Furthermore, the solution-state NMR data of 31 and 32 differ significantly from all the other 29Si chemical shifts listed in Table IV. These results are indicative of special structural features of the zwitterions 31 and... 

Some of the zwitterionic A557-silicates described in this chapter were studied for their chemical properties. As shown for 32,44, and 45 in Scheme 7, compounds of this particular formula type undergo an intermolecular exchange of their benzene-1,2-diolato(2-) ligands in solution at room temperature.38 Solution-state NMR studies ([D6]DMSO XH, 13C, 29Si) and FD MS experiments provided evidence for the equilibrium 32 + 44 2 45. 

Attempts to characterize compounds 77a 0.7CH3CN, 78 CH3CN, 78, and 79 by solution-state NMR experiments (XH, 13C, 29Si) in [D6]DMSO gave unsatisfactory results the NMR data obtained were not in accordance with the existence of the respective zwitterions as the only species in solution. However, NMR studies of 79 in CDC13 unequivocally demonstrated that this particular zwitterion exists in solution (because of their poor solubility, 77a and 78 could not be studied in CDC13). 

Solution-state NMR studies (XH, 13C, 19F, 29Si) at room temperature have shown that the zwitterions 94-104 are also present in solution. The 29Si chemical shifts were found to be very similar to the isotropic 29Si chemical... 

The underlying physical principles of NMR have been established and are well understood.8 Applications of both solid- and solution-state NMR spectroscopy can be found in many different disciplines. It is routinely used in structural elucidation of organic and inorganic compounds, polymers, and biomolecules (e.g., proteins, nucleic acids, and carbohydrates). Additionally, NMR can be used to study molecular interactions (e.g., protein-protein and protein-ligand), molecular dynamics, and chemical reactions. It has also been used extensively in medical research and imaging (magnetic resonance imaging). 

Measurement of cross-correlated relaxation has been described for homo-nuclear cases [10,11], and is widely used in soUd-state NMR [12-14]. It is the availability of isotopically labelled biomolecules and its appHcation to solution-state NMR that makes the method so interesting. The first application of CCR in solution-state NMR with a N, C labelled protein, was the determination of the torsion angle in the small protein rhodniin [7]. This torsion angle is difficult to obtain by traditional methods. 

To further extend the utility of structural methods, researchers compare solid state X-ray crystallographic and solution-state NMR structures to define important differences. For instance, the Bertini group has studied the enzyme matrix metalloproteinase 12 (MMP12), in the presence of its inhibitors. Matrix metalloproteinases (MMPs) are involved in extracellular matrix degradation, a fundamental step in tissue remodeling and repair. There are a great variety of enzymes of this type, the one studied here is one of many found in humans. Most MMPs have three domains (1) a prodomain that is removed... 

Solution-state NMR studies suggest that the catalysts containing l- and D-Pro adopt p-turns and p-hairpins in solution,respectively. Reactions exhibit first-order dependence on catalyst 24, consistent with a monomeric catalyst in the ratedetermining step of the reaction. These catalysts exhibit enantiospecific rate acceleration, in comparison to the reaction rate when NMI is employed as catalyst. An isosteric replacement of an alkene for a backbone amide in a tetrapeptide catalyst (catalysts 32 and 33, Fig. 4) has lent credence to a proposed mechanism of rate acceleration [31). While catalyst 32 exhibits a fcrei=28 with substrate 27, alkene-containing catalyst 33 is not selective in this kinetic resolution and also affords a reduced reaction rate. This suggests that the prolyl amide is kinetically significant in the stereochemistry-determining step of the reaction. 

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