Resonance assignment multiplicities

Nuclear coupling between 13C nuclei and directly bonded protons (a relatively strong interaction) causes the multiplicity of lines - sometimes a helpful effect in making resonance assignments. 

A ID NMR experiment provides information on the chemical shift and spin-spin coupling fine structure of the individual resonances in the spectrum. Double or multiple pulse irradiation experiments provide additional data on through bond scalar connectivities or through space dipolar connectivities, which relate to resonance assignments, conformational state and dynamics of the molecules under investigation. 

Application of the LIS method to study the structure of biologically important macromolecules is fraught with some difficulties which are not usually encountered for small molecules. Poor spectral resolution, lack of resonance assignments and the availability of multiple lanthanide binding sites are some of the difficulties in probing the structures of macromolecules. Some LIS studies [101] have been reported for t-RNA. But most of the studies involve low molecular weight proteins which contain one or more lanthanide binding sites. Lanthanide ions bind in normal Ca(II) sites on proteins, such as amylases, ther-... 

Fig. 9 Expansion of the HMBC spectrum of dutasteride in DMSO- e showing multiple bond correlations used to assign quaternary carbon resonances. Highlighted are correlations used to assign Cio, C13, and the carbonyl resonance C20, which is folded over in the dimension. Other correlations in the spectrum serve to confirm resonance assignments made based on results from the other experiments. (See Fig. 10 for structure and numbering scheme.)...

Figure 13(b) shows a JH—15N HSQC spectrum acquired from 0.5 mmol l-1 sample of a 41-residue peptide toxin from the spider Agelena orientalis. The toxin was produced recombinantly and uniformly labeled with 15N. This HSQC spectrum was collected in 30 min, compared with the 12 h required to acquire a natural abundance spectrum from an unlabeled sample of equivalent concentration (see Figure 11). The HSQC, together with the related heteronuclear multiple quantum coherence (HMQC)54 experiment, forms the cornerstone of a wide range of 2D, 3D, and 4D experiments that are designed to facilitate sequence-specific resonance assignment and determination of protein structure. Note that the HSQC technique is the technique of choice for correlation of H and 15N shifts due to generally narrower linewidths in the 15N dimension.55,56 Furthermore, because these and most of the other heteronuclear experiments described below are designed to observe amide protons, the sample must be in H20 (rather than D20). Consequently, a means of suppressing the H20 resonance is required (for details see Section 9.09.2.6).

The T resonances in the 73-74 ppm region have multiple-bond correlations in the HSQC-TOCSY spectmm to proton resonances of S and/or S , methylenes. Therefore, they are attributed to Xm groups such as those found in stmcture 20. Analysis of these data provided resonance assignments for all the S and T type carbons for the stmctures in Scheme 1. Detailed analysis of expansions of the peak-containing regions of the 2D-NMR data provided complete resonance assignments for all monomer sequences up to the tetrad level in poly(EV). 

Proton magnetic resonance (chloroform-d) S (multiplicity, number of protons, assignment) 3.30 (singlet, 12, OC/fg), 6.10 (singlet, 4, ring protons.)... 

C NMR spectra 14 were recorded of cw-l,2-dimethylcyclohexane at the temperatures given the DEPT experiment at 223 K was also recorded in order to distinguish the CH multiplicities (CH and CHs positive, C// negative). Which assignments of resonances and what thermodynamic data can be deduced from these spectra ... 

Assignment of the signals is completed in Table 30.2. The criteria for assignment are the shift values (resonance effects on the electron density on C and N), multiplicities and coupling constants. Because the difference between them is so small, the assignment of N-8 and N-9 is interchangeable. 

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