Jeener experiment

By incrementing the duration of the evolution period systematically and collecting a free induction decay during the detection period for each value of f I, the two-dimensional data matrix is created. In the two-dimensional data set of the Jeener experiment, the amplitude of a coupled resonance is modulated as a function of f,. More specifically (Bax, 1982), the modulation of a transition Pj, in an AX spin system (refer to Fig. 4) by transition Pj—i is given by... 

In Section II the methodology of the homonuclear chemical-shift correlated technique is discussed. Applications of the Jeener experiment are now described, showing how two-dimensional, chemical-shift correlated spectra provide insight into the assignment of complicated P spectra. 

What was so exciting about Jeener s original experiment What is the... 

Jeener s idea was to introduce an incremented time ti into the basic ID NMR pulse sequence and to record a series of experiments at different values of second dimension to NMR spectroscopy. Jeener described a novel experiment in which a coupled spin system is excited by a sequence of two pulses separated by a variable time interval <]. During these variable intervals, the spin system is allowed to evolve to different extents. This variable time is therefore termed the evolution time. The insertion of a variable time period between two pulses represents the prime feature distinguishing 2D NMR experiments from ID NMR experiments. 

Oil and 0)2, and (b) 2D shift-correlation spectra, involving either coherent transfer of magnetization [e.g., COSY (Aue et al, 1976), hetero-COSY (Maudsley and Ernst, 1977), relayed COSY (Eich et al, 1982), TOCSY (Braunschweiler and Ernst, 1983), 2D multiple-quantum spectra (Braun-schweiler et al, 1983), etc.] or incoherent transfer of magnedzation (Kumar et al, 1980 Machura and Ernst, 1980 Bothner-By et al, 1984) [e.g., 2D crossrelaxation experiments, such as NOESY, ROESY, 2D chemical-exchange spectroscopy (EXSY) (Jeener et al, 1979 Meier and Ernst, 1979), and 2D spin-diffusion spectroscopy (Caravatti et al, 1985) ]. 

D-NMR methods are highly useful for structure elucidation. Jeener described the principles of the first 2D-NMR experiment in 1971 [31]. In standard NMR nomenclature, a data set is referred to by one, i.e., less than the total number of actual dimensions, since the intensity dimension is implied. The 2D-data matrix therefore can be described as a plot containing two frequency dimensions. The inherent third dimension is the intensity of the correlations within the data matrix. This is the case in ID NMR data as well. The implied second dimension actually reflects the intensity of the peaks of a certain resonance... 

In 1971, the idea of 2D NMR spectroscopy was proposed by Jeener and later implemented by Aue, Bartholdi and Ernst, who published their work in 1976.47 The first experiments, carried out mostly in the liquid phase, have unambiguously proved that 2D NMR spectra provide more information about a molecule than ID NMR spectroscopy and are especially useful in determining the structure of molecules that are too complicated to work with using ID NMR. With the progress in the methodology and software improvement, three-dimensional (3D) and four-dimensional (4D) NMR experiments were gradually introduced into the laboratory practice. Such strategy, the so-called multi-dimensional (or ND) NMR spectroscopy, has found a number of spectacular applications in the structure analysis of natural products. 

These composite pulses can be used in liquid- and solid-state multi-pulse experiments such as the //V PT experiment (insensitive nuclei enhanced by polarization transfer) and the Jeener-Broekaert echo experiment [Wiml]. 

In the stimulated echo experiment, also shown in Fig. 6.2.3, the second pulse transfers the system into a mixture of Zeeman and double quantum order (alongandpg). Here, the relevant relaxation times are Ti (longitudinal Zeeman) and T q (double quantum), for which the 45 pulses of the Jeener-Broekaert sequence are replaced by 90v pulses. Again, two echos evolve at T] around the third pulse, and are refocussed by the fourth pulse. The two negative echo amplitudes vary as function of T2, with -[exp(-T2/Tiz) + exp(-T2/Ti3Q)], and both Ti and Tqq can be determined as separate values [14]. 

The idea of two-dimensional (2D) NMR spectroscopy was introduced in 1971 by Jeener, and several experimental demonstrations were soon reported by Ernst and co-workers. Since then many new 2D NMR experiments have been designed to give higher resolution of the resonances and information about the spectral parameters, and therefore the structural details, that would be inaccessible or at least more laborious to determine with ID NMR experiments. The improved resolution in 2D NMR experiments has paved the way for general acceptance that NMR spectroscopy is a valid analytical technique in analysis of complex samples. ... 

The concept of two-dimensional NMR spectroscopy was introduced in 1971 by Jeener [15] and its potential was demonstrated by Aue, Bartholdi and Ernst [16]. Jeener suggested a sequence in which an extra time interval and pulse were inserted into the usual pulse H-NMR experiment to give 90 —/1—90 —<2-... 

Pulses which are multiples of n/2 pulses are the easiest to set, but other pulse lengths are occasionally needed, like a 45 degree pulse for Jeener echoes (IV.B.4.), or arbitrary length pulses for variable nutation T experiments (III.D.5.) and the DANTE sequence (II.D.2.). For any submultiple of n/2 pulses, the trick is to repeat the pulse an appropriate number of times so that the combined effect is that of a n/2 pulse or multiples thereof. For example, you could go for 30 degree pulses by having three identical pulses act like a 90 degree pulse. Any odd length pulses must be interpolated after that. 

One of the first steps in a conventional assault on a complex assignment problem in proton NMR is to run a series of homonuclear double resonance experiments. Not only can this establish which multiplets have a mutual J coupling, but it can reveal hidden resonances obscured by overlap, through their couplings to less crowded parts of the spectrum. Since a separate experiment is needed for each multiplet, this approach can be quite time-consuming. Similar information can however be obtained more efficiently by 2D NMR methods indeed, this was the purpose of the first 2D NMR experiment, proposed by Jeener in 1971. 

The full analysis of the Jeener two-pulse experiment was presented in a seminal paper by Aue, Bartholdi and Ernst,3 although the first experimental spectra appeared slightly earlier. 9 Unfortunately, the density matrix methods needed for the analysis rapidly become unwieldy with systems of more than two or three spins. This, together with the need for large data matrices to hold all the information produced by the experiment, has until recently tended to discourage its use. Although very few spectra obtained using the basic Jeener method have been published, a recent modification of the experiment has attracted considerable interest. 

The simplest experiment is to extend the basic Jeener two-pulse sequence to two nuclei ... 

A large number of experimental facts and a series of indirect experiments have led Brachet and Caspersson, independently of each other, to the conclusion that nucleic acids are involved in protein synthesis. The concentration of RNA in the cell is approximately proportional to the growth of Bac. lactic aerogenes, thus leading Caldwell to consider RNA as being the template itself. Jeener has shown for his part that during experimental modifications of the volumes of the nucleus and the cytoplasm of Thermobacterium acidophilus protein synthesis was quantitatively related to the level of RNA. Finally, direct experiments have shown that in various cells or fragments of cells, treatment with ribonuclease suppresses protein synthesis. 

In another work the MAS NMR technique is compared to the static powder quadrupole echo (QE) and Jeener-Brockaert (JB) pulse sequences for a quantitative investigation of molecular dynamics in solids. The line width of individual spinning sidebands of the ID MAS spectra were found to be characteristic of the correlation time from 10 to s so that the dynamic range is increased by approximately three orders of magnitude when compared to the QE experiment. As a consequence, MAS NMR is found to be more sensitive to the presence of an inhomogeneous distribution of correlation times than the QE and JB experiments which rely upon line shape distortions due to anisotropic T2 and Tiq relaxation, respectively. All these results have been demonstrated experimentally and numerically using the two-site flip motion of dimethyl sulfone and of the nitrobenzene guest in the a-p-tert-butylcalix[4]arene-nitrobenzene inclusion compound. 

The COSY experiment was first proposed in 1971 by Prof. Jean Jeener of the Universite Libre de Bmxelles. 

By 1971 NMR was beginning to look like a mature spectroscopy with all the major developments in place. However, in that year Jeener suggested the idea of multidimensional spectroscopy, and in 1973 Lauterbur published his method for imaging of objects by applying magnetic field gradients. These two events stimulated Ernst and his collaborators to develop the first two-dimensional experiments, and a new age of rapid development in NMR began. 

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