Deuterium lock

What physical changes would you expect in the shape of the NMR signal if the deuterium lock is not applied during data acquisition  

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The deuterium line of the deuterated solvent is used for this purpose, and, as stated earlier, the intensity of this lock signal is also employed to monitor the shimming process. The deuterium lock prevents any change in the static field or radiofrequency by maintaining a constant ratio between the two. This is achieved via a lock feedback loop (Fig. 1.10), which keeps a constant frequency of the deuterium signal. The deuterium line has a dispersion-mode shape i.e., its amplitude is zero at resonance (at its center), but it is positive and negative on either side (Fig. 1.11). If the receiver reference phase is adjusted correcdy, then the signal will be exactly on resonance. If, however, the field drifts in either direction, the detector will... 

Figure 1.10 (a) The dispersion mode line should have zero amplitude at resonance, (b) The deuterium lock keeps a constant ratio between the static magnetic field and the radiofrequency. This is achieved by a lock feedback loop, which keeps the frequency of the deuterium signal of the solvent unchanged throughout the experiment. 

The deuterium lock prevents changes in the static field (Bq) and radiofrequency (B,) by maintaining a constant ratio between the two. It therefore ensures long-term stability of the magnetic field. If the lock is not applied, a drastic deterioration in the shape of the NMR lines is expected, due to magnetic and radioffequency inhomogeneities, (a) With deuterium lock... 

The NMR spectrum of calcitriol, recorded on a Varian XL-100/Nicolet TT-100 pulsed Fourier Transform NMR spectrometer, with internal deuterium lock, is shown in Figure 2 (2). The spectrum was recorded using a solution of 0.84 mg of sample dissolved in 50 microliters of CD OD (100%D) containing 1% v/v tetramethylsilane in a 1.7 mm capillary tube. The spectral assignments are given in Table I. 

The proton noise-decoupled 13c-nmr spectra were obtained on a Bruker WH-90 Fourier transform spectrometer operating at 22.63 MHz. The other spectrometer systems used were a Bruker Model HFX-90 and a Varian XL-100. Tetramethylsilane (TMS) was used as internal reference, and all chemical shifts are reported downfield from TMS. Field-frequency stabilization was maintained by deuterium lock on external or internal perdeuterated nitromethane. Quantitative spectral intensities were obtained by gated decoupling and a pulse delay of 10 seconds. Accumulation of 1000 pulses with phase alternating pulse sequence was generally used. For "relative" spectral intensities no pulse delay was used, and accumulation of 200 pulses was found to give adequate signal-to-noise ratios for quantitative data collection. 

Bruker Smart Magnet control System (BSMS) including the digital deuterium lock system and the BOSSl shim system... 

Spectra. P-31 and H-l NMR spectra were obtained with a Bruker HX90 Fourier transform spectrometer using spinning 10-mm tubes, a deuterium lock from the deuterated solvent, and external 85% H3P04 as the reference. IR spectra were obtained using a Perkin-Elmer Model 337 grating spectrometer that covered the range from 4000 cm-1 to 400 cm-1. 

These types of experiments call for efficient doubly tuned coils, ideally with a separate deuterium lock channel. For more complex molecules, such as proteins, considerably more intricate NMR pulse sequences, such as (HNCO) [32,33], require the probe to operate at three or four distinct frequencies. High efficiency is demanded from the proton observe channel. Ideally, the additional circuitry allowing multiple tuning should not interfere with the proton efficiency when compared to a singly tuned proton coil. In practice, some reduction is tolerated. The two most important design criteria for such... 

C-NMR spectra were recorded with a Jeol FX-—loo spectrometer at 25.o5 MHz. The sample of ketotifen base was dissolved in both CDC1, and DMSO-dg, and hydrogen fumarate only in DHSO-d (5). The samples were measured in 5 mm tubes with TMS as internal standard and using internal deuterium lock. 

When solubility dictates use of different deuteriated solvents for reference and measured samples, the chemical shift (5corr measured against the external reference and corrected for susceptibility difference must be also corrected for the difference in the chemical shifts of the lock signals, A. With a deuterium lock this difference is just the difference in 2H NMR chemical shifts of the two deuteriated solvents, which equals the difference in XH shifts of their pro tic isotopomers (equation 4) ... 

For selectively deuterated compounds, an interesting opportunity is offered by polarization transfer from 2H as demonstrated for 13C INEPT and DEPT142 among the advantages of the method is that all probes have the needed deuterium lock coil. Of course, the last-mentioned experiment can enhance the silicon signal only due to rapid deuterium relaxation but can be useful for line assignment through selective deuteration. 

THE DEUTERIUM LOCK FEEDBACK LOOP 3.3.1 The Lock Channel... 

Before we acquired the spectrum to the right, the field homogeneity was carefully adjusted by maximizing the deuterium lock signal but the methyl singlets are split into distorted doublets. In fact, every line in the spectrum is identically split. What is producing this effect ... 

To the right is part of the spectrum from a single transient obtained without the use of the deuterium lock. All the signals in the spectrum show the same pattern. What is the source of the distortion ... 

Shim the NMR magnet using a deuterium lock or free induction decay, (FID), signal. 

C NMR Measurements. The NMR spectra were observed with a Varian XL-100 spectrometer modified for pulse Fourier transform spectroscopy and interfaced with a Nicolet model 1080 computer. The protons were decoupled from the carbon nuclei using a random noise decoupling field. Free induction decays were stored in 8K computer locations using a dwell time of 200 / sec, i.e., a spectral window of 2500 Hz. The pulse width was 23/xsec (for a 90° pulse), and the pulse interval was 3.0 sec. Hexamethyldisiloxane was used as an internal reference (2.0 ppm vs. TMS), and the internal deuterium lock signal was... 

Physical Measurements. For the electrolyses, a Wenking potentiostat model 70TS1 and a Koslow Scientific coulometer model 541 were used. Voltammetry with wax-impregnated graphite and rotating platinum electrodes was performed as described elsewhere (7, 8). IR and electronic spectra were measured on Perkin-Elmer 225 and Cary 14 instruments. X-band ESR spectra were recorded at room temperature on a JEOL MES-3X spectrometer. Phosphorus-31 NMR spectra were recorded in the pulse mode on a Varian XL-100 instrument at 40.5 MHz using a deuterium lock, or on a Bruker HFX-90 instrument at 36.43 MHz using a fluorine lock. 

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