Triple resonance 3D NMR

One-dimensional 119Sn NMR spectroscopy in solution was used to characterise soluble polymer-supported organotin compounds181,199. To get a more detailed understanding of the microstructure of tin-containing polymers, 1H/13C/119Sn triple resonance 3D NMR... 

FIGURE 12.16 Pulse sequence for the triple resonance 3D NMR experiment HNCO. H and N denote H and 15N, C denotes 13C=0, and K denotes 13C . Pulses at times 1, 2, and 3 constitute an INEPT sequence that transfers coherence from H to. V, where it precesses during q. Pulses at times 6, 7, and 8 represent an HMQC sequence that creates multiple quantum coherence in C (where it precesses during and transfers coherence back to N. Pulses 10 and 11 are an inverse INEPT sequence that transfers coherence back to H for detection during f3.The other 180° pulses refocus heteronuclear spin couplings. Note that coherence is not transferred to spin K. 

Triple resonance 3D-NMR has been used to study polymers containing three NMR active nuclei, and parallel methods for studying hydrocarbon-based polymers are now being used. H- C-X (X = E, Si, and NMR correlation experiments help to simplify and unambiguously assign both main chain and chain-end resonances in a variety of fluoropolymers, polyorga-nosilanes, and phosphorus-containing polystyrenes. 

The interpretation of one- and two-dimensional spectra of large biomolecules such as proteins and nucleic acids is usually impossible due to the large number of highly degenerated peaks. Hence, even for the medium-sized molecules, it is necessary to use isotopic enrichment with and nuclei, and to perform triple-resonance 3D NMR experiments for resonance assignment and extraction of structural constraints. However, as we pointed out above, the resolution of conventionally acquired 3D spectra, is limited by sampling requirements. Therefore, it is rarely possible to obtain line widths close to the natural ones in a reasonable time, even for very fast-relaxing molecules. The conventional 4D spectra, such as or... 

Figure 7. Pulse sequence diagram for an HXY triple resonance 3D-NMR, open rectangles represent 180°pulses and solid rectangles represent 90°...

Li et al. (10) used HCF triple resonance 3D NMR to assign the H, and " F resonances of poly(l-chloro-l-fluoroethylene) (PCFE). Figure 8 shows the ID NMR spectra of this polymer. The H spectrum contains very little useful information and the C spectrum shows essentially two clusters of resonances firom C-F and CHa groups. The F spectrum contains three groups of resonances in ca. 1 2 1 ratio, fi om mm, nor/rm and rr triad stereosequences. Application of HCF triple resonance 3D-NMR is particularly usefiil in this case, since has a natural abundance of 100% and an enormous chemical shift dispersion. The sensitivity of this erqreriment is comparable to that of a simple double resonance H C -HMQC experiment. 

Figure 9. Slices corresponding to flJ3 planes (a-c) from the HCF triple resonance 3D-NMR spectrum (d) of poly(1-chloro-l-fluoroethylene) (PCFE) at the shifts of the three F resonances. (Reproducedfrom reference 10. Copyright 1997 American Chemical Society.)...

Similarly, H/ C/ Si triple resonance 3D-NMR was used to study the structure of poly(l-phenyl-l-silabutane) (PPSB).f72 In this polymer, stereogenic centers are present at the Si atoms. While the H ID NMR spectrum only revealed two sets of resonances fix)m protons a and 3 to Si (Figure 10a), the ID Si NMR spectrum exhibited three peaks from mm, mr/rm and rr stereosequences (Figure 10c). As with PCFE, a H- C- Si chemical shift correlated 3D-NMR spectrum (Figure 11) permitted assignment of the resonances from the three triad steieosequences. 

H/ C/ Si Triple Resonance 3D NMR Study of Poly(dimethyisiloxane) MDjM ... 

NMR has been a powerful technique for structural analyses of macromolecules. However, ID NMR spectra of PDMS are usually complicated due to signal overly. Their complete characterization often requires combinations of several techniques. Multidimensional NMR techniques, especially inversely detected 3D heteronuclear shift correlation experiments, offer the opportunity to obtain the complete structural characterization by using NMR experiments alone. Biological 3D-NMR experiments are usually performed in conjunction with uniform and isotopic labeling. In polymer chemistry, when isotopic labeling is possible, it is often very difficult and expensive. By modifying the 3D-pulse sequence used for biopolymers, triple resonance 3D-NMR techniques have been adapted for sbufying the structures of polymers, which involve H- C- P, H- C- Si spin... 

Triple resonance 3D-NMR experiments can be useful for studying polymeric structures without resorting to isotopic labeling, even when the nuclei involved are present in low natural abundance. This study of MD3M shows that the considerable spectral dispersion obtained in the Si NMR spectra of siloxanes, compared with the narrow H and C chemical shift ranges, permits detailed examination of the structure of PDMS by the 3D H/ C/ Si NMR correlation experiment. These techniques can also be usefiil for characterizing star-branched polymers which contain NMR active nuclei, polymers with low concentrations of heteroatoms (e.g. at the chain end or at low occurrence branch points) and many organometallic compounds. 

Ordinarily, it is possible to distinguish between mm/rr and mr/rm triad stereosequences using standard NMR experiments, but distinction between the resonances of mm and rr triads can be made only if a spectrum from a stereoregular polymer of known relative configuration is available. Triple resonance 3D-NMR techniques combined with isotopic labelling have provided powerful tools for biomolecular structure determination which have tremendous potential applications in polymer chemistry [63-66]. 

Triple resonance 3D-NMR techniques combined with isotopic labelling have provided powerful tools for biomolecular structure determination [63-65] which have tremendous potential applications in polymer chemistry. 

In most cases, structural characterization of carbosilane dendrimers is accomplished by multinuclear one-dimensional NMR spectroscopy (1H, 13C and 29Si). However, as larger dendrimers are characterized standard spectroscopic methods become less useful due to the overlap of signals. This problem has been elegantly circumvented as described in a recent paper by Tessier, Rinaldi and coworkers56. In this paper the researchers described the use of 1 H/13C/29Si triple resonance, 3D and pulse field gradient NMR techniques to... 

Zhou Donghua H, Shea John J, Nieuwkoop Andrew J et al (2007) Solid-state protein-structure determination with proton-detected triple-resonance 3D magic-angle-spinning NMR spectroscopy. Angew Chem IntEd 46 8380-8383... 

Many different types of 3D and 4D experiments can be devised. We described briefly one class, in which two different kinds of 2D experiments are joined, primarily to use the third dimension to clarify the presentation of spectral data. With the ability of most modern NMR spectrometers to provide precise frequency and phase control for several radio frequencies simultaneously and to apply them efficiently in the probe, a class of 3D and 4D triple resonance experiments has become feasible. These experiments usually use two HSQC and/or HMQC sequences to transfer magnetization in the path I— S— T— S— I. I is almost always H 5 and T are 13C and 15N in proteins, the type of molecule in which these experiments are most often utilized. In addition,31P may be involved in nucleic acids, another frequent subject for these methods, and many other nuclides can be used in other applications. 

For non-deuterated complexes, NMR experiments were performed on either Vaiian Unity600 or Varian Unity+500 spectrometers. The 600 MHz instrument was equipped with a triple resonance probe and a PTS synthesizer as a pseudo fourth channel. The 500 MHz spectrometer was a four channel instrument with a triple resonance probe with an actively shielded pulsed field gradient coil. All experiments were performed at 37 C. The heteronuclear experiments shown in Figure 1 were performed as described in Zhang et al (11) and Revington et al (24). For all 3D ex riments 32 transients were required for sufficient signal to noise. This necessitated the use of fewer increments and the use of linear prediction (25)... 

The concept of chemical shift-coding monitors chemical shifts in multi-dimensional NMR experiments without additional polarization transfer elements and evolution periods. The chemical shifts are coded in the line-shape of the crosspeak through an apparent scalar coupling dependent upon the chemical shift. This concept has been applied to the 3D triple-resonance experiment HNCA adding the information of C(beta) or C chemical shifts. On average, the... 

Three-dimensional (3D) NMR is an upcoming area that holds a lot of promise. Peter Rinaldi, who is an acknowledged leader in 2D and 3D NMR, has written a timely and authoritative review in a special Invited Paper (48). In addition, he and his coworkers have used 3D NMR and triple resonance methods to study poly(dimethylsiloxanes) (50), and fluoropolymers (49). 

In this work the applications of three dimensional (3D) solution NMR techniques for characterizing the structures of synthetic polymers and dendrimers are illustrated, including the characterization of polymer chain-end structure, monomer sequence, stereosequence, and branching. The utility of triple resonance and pulsed field gradient NMR techniques in these research endeavors are discussed. 

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