Temperature decoupling

Figure 9 75.5 MHz variable-temperature/decoupling CP/MAS of (Me3Sn)2C03 only methyl region is shown. >ecoupling field stren hs (a) o) -4.5x 10 rad s (b) o i = 1.96 X 10 rad s". (Reproduced with permission from ref. [20J...

This is most readily studied with cyclohexane- /n in which 11 of the 12 protons are replaced with deuterium. The spectrum of cyclohexane- /n resembles the behavior shown in Fig. 4-8 at about — 100°C (the slow exchange regime) two sharp lines are seen these broaden as the temperature is increased, reaching coalescence at — 61.4°C, and becoming a single sharp line at higher temperatures. (The deuterium nuclei must be decoupled by rf irradiation.) Rate constants t for the conversion were measured over the temperature range — 116.7°C to — 24.0°C by Anet and Bourne. It is probable that the chair-chair inversion takes place via a boat intermediate. 

The reason for this decoupling between climate and water temperature in the reservoir is explained in Fig. 3. Moreno-Ostos et al. [37] demonstrated that the degree of stratification and the location of the thermocline both depended on... 

The 140-residue protein AS is able to form amyloid fibrils and as such is the main component of protein inclusions involved in Parkinson s disease. Full-length 13C/15N-labelled AS fibrils and AS reverse-labelled for two of the most abundant amino acids, K and V, were examined by homonuclear and heteronuclear 2D and 3D NMR.147 Two different types of fibrils display chemical shift differences of up to 13 ppm in the l5N dimension and up to 5 ppm for the backbone and side-chain 13C chemical shifts. Selection of regions with different mobility indicates the existence of monomers in the sample and allows the identification of mobile segments of the protein within the fibril in the presence of monomeric protein. At least 35 C-terminal residues are mobile and lack a defined secondary structure, whereas the N terminus is rigid starting from residue 22. In addition, temperature-dependent sensitivity enhancement is also noted for the AS fibrils due to both the CP efficiency and motional interference with proton decoupling.148... 

The 15N spectral peaks of fully hydrated [15N]Gly-bR, obtained via cross-polarization, are suppressed at 293 K due to interference with the proton decoupling frequency, and also because of short values of T2 in the loops.208 The motion of the TM a-helices in bR is strongly affected by the freezing of excess water at low temperatures. It is shown that motions in the 10-j-is correlation regime may be functionally important for the photocycle of bR, and protein-lipid interactions are motionally coupled in this dynamic regime. 

In the early days of carbon-13 spectroscopy, high power decoupling was used and NOE measurements had to be carried out in such a way that temperature was identical for both experiments (interleaved experiments with shift of the proton frequency). With modem spectrometers, such... 

Interestingly, this compound was known for some years [38, 39] before MCE research came back into vogue. Here, the maximum — ASM for a decoupled system is 42 J kg-1 K-1 and is almost met for AH = 0 - 7 T and 1.8 K. So, we have a reasonably high metal content, with a small, though ferromagnetic, interaction, with the appropriate high spin metals. Heat capacity data allow the adiabatic temperature change to be calculated here, this was found to be 12.7 K below 2 K, one of the best by this measure until recently. 

When a model for a CUORICINO detector (see Section 15.3.2) was formulated and the pulses simulated by the model were compared with those detected by the front-end electronics, it was evident that a large difference of about a factor 3 in the pulse rise time existed. This discrepancy was mainly attributed to the uncertainty in the values of carrier-phonon decoupling parameter. For the thermistor heat capacity, a linear dependence on temperature was assumed down to the lowest temperatures. As we shall see, this assumption was wrong. 

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