Quadrature detection States method

Figure 13 Pulse sequence for the solid-state 31P—1H frequency-switched Lee-Goldburg (FSLG) experiment. Proton-proton homonuclear decoupling was performed by using the FSLG decoupling sequence. Quadrature detection in Wi was achieved by using the TPPI method. During the acquisition period, TPPM heteronuclear decoupling was applied.

NMR samples contained 0.6 ml receptor (0.5-2.0 mM) dissolved in refolding buffer (vide supra) with 10% DjO. One-dimensional F NMR spectra were obtained at 470 mHz on a General Electric GN 500 spectrometer fitted with a 5 mm F probe. Parameters included 16K data points, 3.0 second relaxation delay and 25 Hz linebroadening for processing spectra. T, relaxation times were measured by the inversion recovery method. The two-dimensional F NOESY NMR spectrum was obtained on a Varian Unity Plus 500 using the standard Varian pulse sequence. A total of 128 experiments with a mixing time of 0.3 seconds were performed with collection of 1024 data points. Quadrature detection in the second dimension was obtained through the method of States and Haberkom. C ( H NMR spectra were obtained on a Varian 500 Unity Plus fitted with a 10 mm broadband probe. 

The spectra were acquired with 2048 t2 complex data points and 256 ri increments in the phase sensitive mode with quadrature detection using the method described by States et al. (25). Water resonance was supressed during the 1.5s relaxation period used in the NOESY, DQF-COSY and TOCSY experiments and the mixing period of the NOESY experiments by irradiating continuously at its resonance frequency. The amide exchange experiments were carried out by... 

Figure 5.17. The States method of fi quadrature detection requires two data sets to be acquired per increment to generate separate sine and cosine modulated data sets.

Howevei on modern spectrometers, the COSY experiment is now carried out in phase-sensitive mode through the use of one of two modifications introduced to achieve quadrature detection in the ti axis, as well as in 2 which is done conventionally. These two approaches are called the States-Haberkorn method and time proportional phase incrementation readers are referred to the Fmrher Reading section for details. 

To obtain true quadrature detection two sets of data with real and imaginary components in must be obtained. In the States method, two set of 2D FIDs are collected and saved. Both sets of data might contain 256 FIDs (2 X 256) and the delays in the corresponding FIDs in the two data sets are identical. Their only difference is that the second set of FIDs is collected with the phase of the 90° pulse immediately after the period shifted by 90° compared with the phase of the same pulse in the first set of FIDs. The first set of FIDs contains the frequency... 

---