Pulse angle various

Re-evaluation of pulse delay times used to record fullerene 13C NMR spectra revealed that a 16 s pulse delay, twice the value for a standard detection, allowed the observation of a weak resonance in the sp3 region at 90.4 ppm in the 13C NMR spectrum of the unlabeled heterofullerene 114. Attempts were made to optimize the NMR experimental parameters for a long 7 i, i.e. the variation of delay times and pulse angles. Various conditions were tried on the labeled material without success. This is probably due to the mixture of the labeled and unlabeled 114 which give too low S/N for signal detection. Table 49 summarizes the NMR results obtained and illustrates a distinct pattern of the azafullerenes. 

The pulse duration controls the extent to which the magnetization vectors are bent. A misalignment of the pulse would lead to various artifact signals. Including 180° spin-echo pulses can, to some extent, compensate for setting pulses incorrectly. But in certain experiments (e.g., inverse NMR experiments), it is extremely important for the success of the experiment that the proper pulse angles be determined and employed. 

In this section, we review the derivation of the scattering signal from a pulsed X-ray field on a time-dependent molecular system. The key quantity of interest is the differential signal strength dS/dQ, which we define as the total number of scattered photons arriving at the detector per solid angle. Various derivations of dS/dQ exist in the literature based on perturbation or response theory [14, 15, 19]. In the... 

Many HPLC methods for phospholipids have been developed, but chromatographic resolution and dynamics of detection are not always satisfactory. For each source of phospholipids, special standards are needed due to the different distribution of fatty acids. These standards are expensive and in some cases are not available. Another problem is represented by the analysis of phospholipids in complex matrices. In many cases, separation is impossible or very difficult, not least due to the surface activity, which is desired in the application of phospholipids, but which complicates the analysis of these compounds. Therefore, a method is needed which is selective in the detection of phospholipids in order to avoid a separation from the matrix. The P NMR spectroscopy of phospholipids meets these requirements. The I.L.P.S. (Internationa Lecithin and Phospholipid Society) has chosen the P NMR method as the reference method [62],[63],[64]. It has been tested world-wide by round robin tests in comparison to various HPLC and TLC methods. With triphenylphosphate as internal standard, a pulse angle of 15°, 10-s relaxation delay, and 32-256 accumulations, the method has a precision of <0,5%. 

Fig. 3 Solid state 31P NMR spectra of fosinopril sodium acquired under single pulse, high-power proton decoupling and various conditions of magic-angle spinning (A) static, (B) 2.5 kHz, (C) 4.0 kHz, (D) 5.0 kHz, and (E) 6.0 kHz. The isotropic chemical shift is designated by an asterisk. (From Ref. 15.)...

In the above experiments in which an electrode surface is examined, the electrode potential is fixed as the electrode surface is rotated and the SH anisotropy recorded. In a useful variation of this procedure, one can fix the angle of rotation and measure the SH response as a function of potential. Since the absolute orientation of the crystal is known, information can be derived about the various tensor elements describing the nonlinear polarizability from these crystalline surfaces. By fixing the angle and applying a transient potential pulse, one can perform time resolved measurements and watch the evolution of various adsorption and deposition processes along specific crystal axes. 

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