Total correlation spectroscopy defined

The first step in the assigmnent scheme would be to determine the chemical shifts of the protons contained in each residue. This collection of intra-residue chemical shifts is called a spin system. Spin systems are usually defined using a TOCSY experiment (total correlation spectroscopy) (Bax and Davis, 1985). In the TOCSY experiment magnetization is passed from one spin to another by scalar coupling in much the same way a baton is passed in a relay race (see Figure 3.8, top). While the magnetization exists on a spin it is possible to record the chemical shift of that particular spin. Under favorable conditions, the chemical shifts of all of the spins in an amino acid can be obtained. 

Two conformations of EpoA in complex with tubulin have been proposed on the basis of EC [26] and NMR [76, 96] data, respectively (Fig. 11). The tubulin-bound conformation of EpoA was determined by solution NMR spectroscopy [96] before the EC structure of EpoA bound to tubulin was available. The observation that, in a 100 1 mixture with tubulin, NOE cross-peaks of EpoA have negative sign, indicated that there is a fast exchange equilibrium in solution. This offered the opportunity to measure transferred NMR experiments, that report on the bound conformation of the ligand. A total of 46 interproton distances were derived from cross-peak volumes in tr-NOE spectra. However, these distance restraints did not suffice to define a unique conformation, as several distinct structures were consistent with them. Transferred cross-correlated relaxation (Sect. 2.2.1.3) provided the additional dihedral restraints that were crucial to define the bound conformation [96, 97], One requirement to measure CH-CH dipolar and CH-CO dipolar-CSA CCR rates is that the carbon atoms involved in the interaction are labeled with 13C. The availability of a 13C-labeled sample of EpoA offered the opportunity to derive seven of these dihedral angle restraints from tr-CCR measurements (Fig. 12). 

Several spectroscopic techniques have been used to study different aspects of conventional W/O/S microemulsion structures and properties. The absorption and steady-state emission spectroscopy of probe molecules solubilized in a microemulsion system can find the polarity of the microemulsion at their solvation location [34]. Time-resolved emission spectroscopy also provides information on the dynamics and rotation relaxation of solvent in both classical W/O/S and IL microemulsions [34-36]. Water content, which is defined as the molar ratio of water to total surfactant ([water]/[surfactant]), is one of the key factors in a microemulsion [37]. The ionization degree of bioactivator in IL microemulsion was correlated with the water content (cOj,) using UV-Vis absorption spectra, as shown in Rgure 18.2. 

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