Chemical shift changes

Figure B2.4.1 shows the lineshape for intennediate chemical exchange between two equally populated sites without scalar coupling. For more complicated spin systems, the lineshapes are more complicated as well, since a spin may retain its coupling infonnation even though its chemical shift changes in the exchange.

FIGURE 4.17 A plot of chemical shifts versus pH for the carbons of lysine. Changes in chemical shift are most pronounced for atoms near the titrating groups. Note the correspondence between the p. values and the particular chemical shift changes. All chemical shifts are defined relative to tetramethylsilane (TMS). (From Suprcnant, H., ct at., 1980. 

In principle, any type of NMR spectroscopy may be used to detect the chemical shift changes upon ligand binding. For very small proteins, 1D-NMR might even... 

P]0 is the total molar concentration of the protein and [L]0 is the total molar concentration of ligand. X is the molar concentration of the bound species determined according to the chemical shift change ... 

Table 6.1H-NMR chemical shift changes of the cyclic hexamer of 6,8-dioxabicyclo[ 3.2.1 J-octan-7-one upon interaction with thiocyanate salts in deuterkjchloroforma...

The chemistry of [Rh(OEP)h in benzene is dominated by Rh—Rh bond homolysis to give the reactive Rh(Il) radical Rh(OEP)-. This contrasts with the reactivity of fRh(OEP)] in pyridine, which promotes disproportionation via the formation of the thermodynamically favorable Rh(IlI). ct complex [RhjOEPKpy) ] together with the Rh(l) anion, Rh(OEP)J The hydride complex Rh(OEP)H shows NMR chemical shift changes in pyridine consistent with coordination of pyridine, forming Rh(OEP)H(py). Overall, solutions of Rh(OEP)l in pyridine behave as an equimolar mixture of [Rh(OEP)(py ) and (Rh(OEP). For example, reaction... 

In order to evaluate the DD site semiquantitatively, we have analyzed the chemical shift change A.S of the ring proton signals of PrBe and BzOH on the delivery from water to... 

FIG. 10 Chemical shift change of the NMR signals of EPC induced by the injection of DBC H and PRC H with a molar ratio of 1/1. Negative value means an upheld shift. 

The DD site can be ensured by the chemical shift changes of the BPA signals. The chemical shift differences of the ring proton signals of BPA on the delivery from water to bilayer phases are —0.04 and —0.11 ppm for the ortho and meta sites, respectively. Negative values mean upfield shifts recall the HCS rule. It is concluded that both benzene rings of BPA are trapped in the bilayer from the water phase and the meta site penetrates more deeply into the hydrophobic interior. 

FIG. 13 Chemical shift change of the EPC H NMR signals induced by the ring current effect of BPA. Negative value means upheld shift. (From Ref. 47. Copyright 1999 American Chemical Society.)... 

TABLE 9 Chemical Shift Changes of the EPC C NMR Signals Induced by the Delivery of BPA ... 

Chemical shift change (ppm) induced by the BPA delivery. Positive and negative values mean downfield and upheld shifts, respectively. 

More than 2,000 potential replacements for the bromophenyl or pyridyl groups were then screened using the NMR-screening technique. Several fragments were identified which caused chemical shift changes in the desired binding site of the protein, amongst them indole (7) and 2-phenylimidazole... 

Fig. 1.14 Fragments found to cause chemical shift changes in binding site.

Fig. 2 Chemical shift perturbation and chemical shift mapping, (a) Portions of the [15N, 1H]-HSQC spectra of Bcf-xL recorded in absence (black) and in presence of each of the four molecules (in colors). Resonance assignments for amino acid residues that exhibit large shifts are reported, (b) Structure of Bc1-Xl in complex with the BH3 peptide from Bak (PDB code 1BXL) showing the chemical shift changes in Bcl-xL upon ligand binding (blue, large shits yellow, no shifts the Bak peptide is reported in cyan). Adapted from [48]...

The feasibility of identifying these edges of water base pairs has been supported by our studies of mitomycin C interacting with the model system for AT base pairs 29). Interactions of either component with mitomycin C are not observed but a complex is formed when all three components are present. Chemical shift changes observed in the NMR spectra support the structure 47 for the termolecular complex. The broader implication is that mitomycin C will likewise recognize the minor groove side of a G-C pair (it is known to alkylate the guanidine on this side)31 ... 

Figure 5 (A) Chemical structures of tetranactin and nonactin, (B) The effect of hindered CH3 rotation by short contact with other groups to the prolonged methyl T,c and chemical shift changes.

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