Transitions transverse relaxation

Transition dipole moment 88 Transverse relaxation time 31, 32, 33, 44 Twinning 126 Two-phase model 129 Two-term models 149 ----unfolding model 183,185... 

Richardson, S.J. 1989. Contribution of proton exchange to the oxygen-17 nuclear magnetic resonance transverse relaxation rate in water and starch-water systems. Cereal Chem. 66, 244-246. Richardson, M.J. and Saville, N.G. 1975. Derivation of accurate glass transition temperatures by differential scanning calorimetry. Polymer 16, 753-757. 

On the basic of relaxation theory the concept of TROSY is described. We consider a system of two scalar coupled spins A, I and S, with a scalar coupling constant JIS, which is located in a protein molecule. Usually, I represents H and S represents 15N in a 15N-1H moiety. Transverse relaxation of this spin system is dominated by the DD coupling between I and S and by CSA of each individual spin. An additional relaxation mechanism is the DD coupling with a small number of remote protons, / <. The relaxation rates of the individual multiplet components in a single quantum spectrum may then be widely different (Fig. 10.3) [2, 9]. They can be described using the single-transition basis opera-... 

In the following we will discuss the transverse relaxation of the different single transitions on the basis of Eq. (5). The two brackets multiplied by /(0) in Eq. (5) are the terms of interest. The dominant relaxation mechanisms of spin I and S are the DD coupling and the CSA which are listed in the first bracket The relaxation due to DD coupling... 

Fig. 3 Temperature dependence of the transverse relaxation time Ti for D-RADP-20 as obtained from a bi-exponential fit to the Rb spin echo decay. The fact that T2 changes discontinuously at the phase transition clearly indicates the first order character of the transition...

Nuclear magnetic resonance (NMR) has been used to study segmental motions in block copolymer solutions. The mobility of protons in polymer chains in dilute solutions has been probed using high-resolution H NMR. Association of chains into micelles leads to a reduction in mobility in the core, which leads to a broadening of the respective NMR lines that has been studied for a number of systems, as described by Tuzar and Kratochvil (1993). The sol-gel transition in concentrated solutions has been located via ]H transverse relaxation time experiments, as outlined in Chapter 4. 

The water exchange mechanism can be assessed by determining the activation volume, AV, from variable pressure 170 transverse relaxation measurements [31]. The activation volume, defined as the difference between the partial molar volume of the transition state and the reactants, is related to the pressure dependence of the exchange rate constant through Eq. (22) ... 

To simplify the interpretation of STMAS spectra, it is desirable to remove the CT—>CT correlation signal, particularly when studying nuclei subjected to distribution of local environments or weak quadrupole interactions. Several methods are available to remove the CT CT peak. In the first method, the CT transition is presaturated by a soft pulse, prior to the STMAS sequence (Fig. 12a) [38]. A sequence consisting of a selective soft pulse followed by a delay and a short excitation pulse maybe used for optimising the presaturation pulse. Unfortunately, this simple method only works when aU species present in the sample have very similar transverse relaxation times and quadrupole couphng constants. 

---