Refocusing similar

X-rays are collected and analy2ed in ema in one of two ways. In wds, x-rays are dispersed by Bragg diffraction at a crystal and refocused onto a detector sitting on a Rowland circle. This arrangement is similar to the production of monochromati2ed x-rays for xps described above. In the other approach, edx, x-rays are all collected at the same time in a detector whose output scales with the energy of the x-ray (and hence, Z of the material which produces the x-ray.) Detectors used for ema today are almost exclusively Li-drifted Si soHd-state detectors. 

The DEPT experiment (Doddrell elal, 1982) involves a similar polarization transfer as the INEPT experiment, except it has the advantage that all the C signals are in phase at the start of acquisition so there is no need for an extra refocusing delay as in the refocused INEPT experiment. Coupled DEPT spectra, if recorded, would therefore retain the familiar phasing and multiplet structures (1 1 for doublets, 1 2 1 for triplets, etc.). Moreover, DEPT experiments do not require as accurate a setting of delays between pulses as do INEPT experiments. 

Nuclei resonating at different chemical shifts will also experience similar refocusing effects. This is illustrated by the accompanying diagram of a two-vector system (acetone and water), the nuclei of which have different chemical shifts but are refocused together by the spin-echo pulse (M, = magnetization vector of acetone methyl protons, M(v = magnetization vector of water protons). 

Both experiments are based on polarization transfer from sensitive nuclei to insensitive nuclei, and therefore the mjyor portions of their pulse sequences are common. The INEPT experiment, without refocusing and decoupling, however, yields spectra with distorted" multiplets. For instance, the two lines of a doublet appear in antiphase with respect one another. Similarly, the central line of a triplet may be too small to be visible, while the outer two lines of the triplet will be antiphase to one another. Introducing a variable refocusing delay A and broadband decoupling in the INEPT sequence can convert this experiment into a more useful one. 

In 2006 Wimperis et al. proposed a method called satellite transitions acquired in real time by MAS (STARTMAS) [142, 202], which allows for the real-time acquisition of high-resolution NMR spectra of spin-3/2 nuclei under MAS. This method combines a train of pulses, similar to CPMG [109, 110], with sample rotation at the magic angle to refocus the quadrupolar broadening in a series of echoes, while allowing the isotropic quadrupolar shift and chemical shift to evolve. 

The UV spectrum [/Imax 245, 296, 341, 352 (sh), and 368 nm] of TAN-999 (296) was very similar to that of (+)-staurosporine (295), indicating the presence of a similar indolo[2,3-fl]carbazole framework with a lactam function. This was also discernible from its IR spectrum with the presence of an NH band at v ax 3430 cm and an amide band at 1680 cm . The H-NMR spectrum of TAN-999 was also very similar to that of (+)-staurosporine, except for the presence of an additional methoxy group at S 3.95, resulting in the presence of a 1,2,4-trisubstituted aromatic ring instead of a 1,2-disubstituted aromatic ring. The location of this additional methoxy group was assigned to C-10, based on COSY, COSY, refocused INEPT, and... 

Non-refocused INEPT spectra can be used to determine both 29Si—XH and 1II—1II couplings (but not their signs) in a manner similar to that described earlier for SPT spectra. The INEPT spectra are measured with several r values chosen almost arbitrarily and then a simulation program119 is used to determine the exact values of the coupling constants120,121. 

In addition to the difficulty of finding the optimal r, the JCP experiment also suffers from extreme sensitivity to the HaHa match. Moreover, the original experiment required both rf fields (Si and H) to be highly homogenous, preferably created by the same transmitter coil, to keep the same ratio of the two fields within the whole active volume of the sample147. To reduce the sensitivity of the enhancement to the HaHa condition and cross-relaxation time, a modified, refocused JCP experiment (RJCP) was suggested151. In this experiment the spin-lock field on the silicon resonance is interrupted at r = j for a duration corresponding to a conventional 90° pulse, and later (r = /) the spin-lock field on protons is similarly interrupted both fields then remain on until r = 2//. 

The width of the final1H pulse in the DEPT sequence ( ) affects the intensity and phase (positive or negative) of the 13C peaks in a way very similar to the length of the refocusing delay A in refocused INEPT, according to the relation = nJA. The intensities are shown below for the three types of carbon in DEPT ... 

Because of the three evolution periods, this pathway is best handled in a manner similar to that in Table 12.1. Using / and S for the proton spins and T for 13C and taking into account the refocusing effect of the 180° pulses, the initial portion (up to time 5) is ... 

Figure 8 ReMims (Doan) ENDOR pulse sequence. The upper level indicates the microwave pulses and immediately below delay times are indicated. The lowest level indicates the rf pulse. SE is the stimulated echo that is not detected, RSE is the refocused stimulated echo that can be detected (for T2 > ti as shown here), and RME is the refocused Mims echo that is normally detected (at time T2 + ti). HE is the Hahn echo that is not detected and normally eliminated by microwave phase cycling. Typical times are given based on an X-band ( 9.6 GHz) spectrometer, but are also applicable at 35 GHz. The timing of both delay times ti and T2 are adjusted to optimize spectral appearance as desired. Other aspects are similar to standard Mims ENDOR...

---