Exchange-transferred experiments

Highly interesting for most pharmaceutical applications is the conformahon of a ligand bound to its receptor. In Section 9.3, exchange-transferred experiments... 

Fig. 9.11 The difference in the strength of relaxation processes (A) or the difference in alignment (B) can be used to detect interactions (eg. NOE or RDCs, respectively) of the ligand-receptor complex in exchange-transferred experiments.

All these methods have in common that the receptor is not detected so that no size limit applies. Relaxation-based exchange-transferred experiments actually show best performance for longest correlation times, i.e. very large receptors. 

An important aspect of all exchange-transferred experiments is the occurrence of nonspecific binding which contributes equally to the NMR interactions in the bound state and carmot easily be distinguished. Nonspecific interaction is best... 

Peralkylated tetracarba-mdo-hexaboranes(6) 56 [72] are extremely stable, and almost inert in air and stable towards H20, in contrast with the parent carbaborane [73], nB/nB magnetization transfer experiments performed at 140 °C for the per-ethyl derivative show that exchange reactions between boron atoms in positions 1 and 6 are very slow. 

Proton-hydride exchanges similar to those in Scheme 10.9 are manifested in the H NMR spectra as broadenings and coalescences of the hydride and HX resonances upon heating and can be characterized quantitatively with the help of line-shape analysis or saturation transfer experiments. As in the case of proton... 

Fig. 13.8 Overall perspective view of the charge exchange apparatus. A thermal Na beam is laser excited in the interaction region to produce a target for Rydberg-to-Rydberg charge transfer experiments. The number of target Rydberg atoms is determined by pulsed field ionization between the parallel plates and by collection of the resultant ions in the electron...

Modern NMR techniques such as quantitative analysis of multisite exchange using either ID magnetization transfer experiments (JOS) or the 2D exchange spectroscopy (EXSY) method (104,105) promise to be of great help in unraveling the complex stereochemical exchange networks involved in cluster fluxionality. The usefulness of EXSY in the context of this article is illustrated by the phase-sensitive 13C 1H EXSY spectrum (255 K, tm = 0.5 sec)... 

Fig. 5.40. (A) H NMR spectra at 298 K of oxidized spinach plastocyanin at 800 MHz (adapted from [117]). (B) Far downfield region of the H NMR spectra of oxidized (i) P. aeruginosa azurin, (ii) spinach plastocyanin and (iii) cucumber stellacyanin containing signals not observable in direct detection (adapted from [198]). The positions and line widths of the signals were obtained using saturation transfer experiments by plotting the intensity of the respective exchange connectivities with the reduced species as a function of the decoupler irradiation frequency.

Figure 10 (a) Rising-droplet apparatus and (b) Venturi tube for droplet mass transfer experiments. (1—feed storage, 2—metering pump, 3—double-flow valve, 4, 5—pumps, 6—heat exchanger, 7—collecting funnel, 8—stream to analysis, 9—valve). 

In a typical free NOESY experiment of a molecule in the absence of any interacting protein, cross-peak volumes are interpreted in terms of a set of interproton distances r that can be used as distance restraints in structure determination procedures, like restrained simulated annealing protocols [44], In a tr-NOESY, i.e. a NOESY measured under exchange-transferred conditions in the presence of a protein - i.e., an excess of soluble ligand is in fast exchange equilibrium with a smaller amount of protein-bound ligand -, these r reflect the interproton distances of the ligand in the bound... 

NMR has the capability, using magnetization transfer techniques, to measure very rapid metabolic fluxes in vivo, of the order of 1(F3 M s-1. A magnetization transfer experiment, in which exchange between ATP and Pj was measured in yeast... 

Figure 11 shows the contour plots of the 2D 51V EXSY spectrum of a two-site system (40 mM total vanadate at pH 10.9) in which V exchanges with V2. Quantification of the EXSY spectrum and calculation of the error propagated to the rate constants from the integration precision gives a 25% error on the rate constant. The results (both the rate constants and the errors) correspond nicely to the results obtained from a ID magnetization transfer experiment on the same sample (27). The EXSY spectrum of a sample containing 12.5 mM total vanadate at 1.0... 

Fig.3. 800-MHz NMR spectra of oxidized (A) Pseudomonas aeruginosa azurin, (B) spinach plastocyanin, and (C) cucumber stellacyanin recorded in D2O solution. The letters identify the resonance of the equivalent proton in the three proteins. In the insets the far-downheld regions containing signals not observable in direct detection are shown (Bertini et al., 2000). The positions and the linewidths of the signals of the oxidized species were obtained using saturation transfer experiments over the far-downheld region by measuring the intensity of the exchange connectivity with the corresponding signal in the reduced species (Bertini et al., 1999, 2000).

The cyanide-bound and cyanide-free forms of SOD are in slow exchange on the NMR timescale. On addition of increasing amounts of anion, a new set of resonances appears to be due to the CN-bound form. The assignment of the NMR spectrum was achieved through saturation transfer experiments (Paci et at., 1988), which also show that binding of this anion produces structural rearrangements similar to those observed for the other anions. 

The best evidence for metal fluxionality in Cd7-MT was provided by " Cd NMR saturation transfer experiments, which established the presence of inter- and/or intramolecular metal exchange within the 3-metal cluster of the /3-domain with a half-hfe of the order of 0.5 s. The confirmation of similar processes taking place within the 4-metal cluster, but with a half-hfe of about 16 min, was afforded by metal exchange studies using the radioactive Cd isotope. In this context, it should be noted that the intersite cadmium exchange measured in the 3-metal cluster of MT-1 was found to be much faster than that in MT-2. This finding was in line with the enhanced backbone flexibility recognized in the NMR studies of the former isoform. ... 

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