Solution NMR

This is due mainly to isotopic factors that relate to the large number of vibrational modes for molecularly-bound H2 or D2, which offset the weakness of the D-D bond relative to the H-H bond. The values of K /Kj, observed thus far are 0.36-0.77 for formation of H2 complexes and 0.47-0.85 for complete splitting of the H-H bond to form hydrides. 

The single most important NMR spectroscopic parameter is the scalar coupling constant, for the HD isotopomer of an H2 complex without the superscript is normally used here to refer to the one-bond coupling). The signal becomes a 1 1 1 triplet (D has spin 1) with much narrower linewidth and is direct proof of the existence of an H2 ligand, since classical hydrides do not show significant Jhd because no residual H-D bond is present. J d for HD gas is 43 Hz, the maximum possible value is 0.74 A). A lower value represents a proportionately shorter dup. 7hp determined in solution correlates well with hh in the solid state via the empirical relationships developed by both Morris [40] and Heine-key [41]  

The fast internal rotation of that causes crystallographic problems can also effect the calculation of from 71 if the rotational rate is faster than molecular tumbling. Although the term spinning H2 is often used, the H2 does not really spin like a propeller but undergoes rapid libration combined with less 

4-fold term is often added as a correction for non-sinusoidal behavior such as wobbling off the plane of rotation. However in some cases, e.g. four identical ligands cis to H2 as in [MH(H2)(diphosphine)2]+ species, a 4-fold component to rotation truly exists (90° rotation) giving very low rotational barriers near 0.5 kcal mol i and a faster spinning H2. 

As established by Zilm and coworkers, solid state H NMR is very effective in accurately determining d H because the measurement is unaffected by rotational or other motion of the bound H2 [55]. Only a small amount of solid in powder form is required to observe the signals using broad-line techniques (Fig. 

how does an irradiation at the proton frequency decouple the protons from the carbon-13 nuclei, for example In a qualitative way, we can see that the irradiation at the Larmor frequency of the proton can induce transitions-between the two allowed proton levels corresponding to the parallel and antiparallel orientations with respect to the static field. If such a transition between the two orientations occurred fast enough, the carbon nucleus will simply see an average field from the protons. Thus, in the presence of a decoupling field the carbon resonance will be a singlet at the average position of the doublet. 

Within the realm of heteronuclear decoupling, we have a choice of irradiating all of the lines in the proton spectrum (in the proton-carbon system we are still considering as an example) or just some of them. In order to irradiate all of the proton lines, we need a scheme for distributing the irradiation over the appropriate chemical shift range. Most commonly, noise decoupling is used wherein the decoupler output is modulated in a random way to make its spectrum 

Irradiating a selected line or a portion of a spectrum yields different information from noise decoupling. It is simpler in that the second irradiation need not be modulated and the total power required is less than noise decoupling. On the other hand, it is not as trivial to set up because a careful adjustment of where to put the coherent decoupling irradiation in the proton spectrum is necessary. In this regard, a most helpful capability for the spectrometer is that of being able to obtain the proton spectrum during the 13C experiment 

Aside from the effect on the line position mentioned in the last paragraph, decoupling irradiation, especially coherent 

Gated decoupling is useful when we want to separate the decoupling effects from NOE effects. For example, we may want a decoupled spectrum without NOE for careful intensity studies. (NOE is usually not uniform across the spectrum.) In this case, we could turn on the decoupler only during the FID acquisition and off at other times as shown. 

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Champmartin D and Rubini P 1996 Determination of the 0-17 quadrupolar coupling constant and of the C-13 chemical shielding tensor anisotropy of the CO groups of pentane-2,4-dione and beta-diketonate complexes in solution. NMR relaxation study/norg. Chem. 35 179-83... 

Tjandra N and Bax A 1997 Solution NMR measurement of amide proton chemical shift anisotropy in N-15-enriched proteins. Correlation with hydrogen bond length J. Am. Chem. Soc. 119 8076-82... 

For the investigation of molecular recognition in micelles, adenine derivatives and positively charged (thyminylalkyl)ammonium salts such as shown in Figure 30 were prepared, which were solubilized in sodium dodecyl sulfate (SDS) solutions. Nmr studies have shown that binding occurs in a 1 1 molar ratio in the interior of the micelles as illustrated in Figure 30 (192). 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

Report 125 Structural Studies of Polymers by Solution NMR, H.N. Cheng, Hercules Incorporated. 

A high-resolution 1 1 solution NMR structure of lmPy-y9-lm-y9-lmPy-y9-Dp elucidated the role of /9-alanine in minor groove recognition (Fig. 3.7 b) [47]. The p residues allow both Im rings in the /9-lm-/9-lm subunit to adapt to the relatively large... 

M(CO)2()] -C5H5. Mei,) vertices in tetrahedral IMsl/xi-tr-RCiRKCOla (t] -CsHs nMen)2l Tripodal Co(CO)3 rotation was sufficiently rapid in MoCoi (/r,rCC02Pr )(C0)(,(L)(i)" -C5R4R )l that it could not be frozen out in solution NMR studies. A similarly rapid turnstile motion was observed at one cobalt atom in WCo2(7t-EtC2Et)(( r-t7 -CEtCEtCEtCEt) CO)8l, but Co(CO)3 rotation at the other cobalt was retarded by adjacent ethyl groups." ... 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

In addition to sample rotation, a particular solid state NMR experiment is further characterized by the pulse sequence used. As in solution NMR, a multitude of such sequences exist for solids many exploit through-space dipolar couplings for either signal enhancement, spectral assignment, interauclear distance determination or full correlation of the spectra of different nuclei. The most commonly applied solid state NMR experiments are concerned with the measurement of spectra in which intensities relate to the numbers of spins in different environments and the resonance frequencies are dominated by isotropic chemical shifts, much like NMR spectra of solutions. Even so, there is considerable room for useful elaboration the observed signal may be obtained by direct excitation, cross polarization from other nuclei or other means, and irradiation may be applied during observation or in echo periods prior to... 

Typical characterization of the thermal conversion process for a given molecular precursor involves the use of thermogravimetric analysis (TGA) to obtain ceramic yields, and solution NMR spectroscopy to identify soluble decomposition products. Analyses of the volatile species given off during solid phase decompositions have also been employed. The thermal conversions of complexes containing M - 0Si(0 Bu)3 and M - 02P(0 Bu)2 moieties invariably proceed via ehmination of isobutylene and the formation of M - O - Si - OH and M - O - P - OH linkages that immediately imdergo condensation processes (via ehmination of H2O), with subsequent formation of insoluble multi-component oxide materials. For example, thermolysis of Zr[OSi(O Bu)3]4 in toluene at 413 K results in ehmination of 12 equiv of isobutylene and formation of a transparent gel [67,68]. 

Thiols are known to be excellent hgands for the stabilization of gold and platinum nanoparticles. In this respect, we did not observe any Iluxional behavior [31,52] in solution NMR experiments for thiols coordinated to the surface of noble metal particles (Fig. 8). However, in the case of rutheniiun, we foimd the slow catalytic formation of alkyl disulfides [31]. After exclud-... 

Lee, S., Mesleh, M. F Opella, S. ). Structure and dynamics of a membrane protein in micelles from three solution NMR experiments./. Biomol. NMR 2003, 26, 327-334. 

The scope of this review is to summarize the recent development of the solution NMR to DD from aqueous phase to lipid bilayer membranes on the basis of our recent NMR work. Relevant physicochemical and computational aspects of the membrane DD are also referred to here. 

Beryllium(II) is the smallest metal ion, r = 27 pm (2), and as a consequence forms predominantly tetrahedral complexes. Solution NMR (nuclear magnetic resonance) (59-61) and x-ray diffraction studies (62) show [Be(H20)4]2+ to be the solvated species in water. In the solid state, x-ray diffraction studies show [Be(H20)4]2+ to be tetrahedral (63), as do neutron diffraction (64), infrared, and Raman scattering spectroscopic studies (65). Beryllium(II) is the only tetrahedral metal ion for which a significant quantity of both solvent-exchange and ligand-substitution data are available, and accordingly it occupies a... 

Principles and Characteristics The qualifying features for the application of solution NMR to extracts of polymeric materials have already been outlined in Section 5.4. For NMR spectroscopy, which is a powerful analytical tool for identification and quantification, extraction of additives from the polymer is not required. Recent NMR developments suggest various possibilities for direct additive analysis ... 

REX-CPHMD simulations have also been applied to understand the mechanism of the formation of protein intermediate states. Recent solution NMR data revealed a sparsely populated intermediate in the villin headpiece domain, in which the N-terminal subdomain is largely random but the C-terminal subdomain adopts a nativelike fold [34], Interestingly, H41 in this intermediate state titrates at a pH value of... 

Thus solid state NMR can be considered as a (potential) bridge between solution NMR and X-ray crystallography. 

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