Two heteronuclear

The PAR experiment may be described by considering two heteronuclear dipolar coupling interactions with one proton (7) in common, i.e., a Hamiltonian of the type... 

The scheme is illustrated in Fig. 20. In addition to chiral molecules, one can apply this method to two asymmetric quantum wells, to two heteronuclear molecules aligned in an external DC electric field [97]. In the setup of Fig. 20 (lower plot), we consider operating on states i) and their mirror images 1)m by three pulses in a counterintuitive order [92,93], i.e., two pump pulses with Rabi frequencies fl12(0 and fli3(r), which follow a dump pulse H23(0. The Rabi frequencies are defined as, fiy(r) = dtj ij(t)lh — ilij(t) e1 = 0 (0, where dtJ and y(r) are, respectively, the transition dipoles and the envelopes of electric fields, of carrier frequencies a)ij, operating between states i j (i, j = 1,2, 3). If we symmetrically detune the pulse center frequencies, as shown in Fig. 20,... 

For the practical implementation of Hartmann-Hahn experiments, the type of multiple-pulse sequence can be important (see Section III). Continuous wave (CW) irradiation represents the simplest homonuclear Hartmann-Hahn mixing sequence (Bax and Davis, 1985a). Simultaneous CW irradiation at the resonance frequencies of two heteronuclear spins is the simplest heteronuclear Hartmann-Hahn mixing sequence (Hartmann and Hahn, 1962). 

Fig. 35. Experimental HCCH-COSY spectra of the fully C-labeled protein rhodniin with two heteronuclear Hartmann-Hahn transfer steps. The spectra were acquired at a spectrometer frequency of 600 MHz employing DIPST2 with = 4.8 kHz (A) and MGS-2 with = 3.78 kHz (B). In the experiments the heteronuclear Hartmann-Hahn mixing periods had a duration of 6 ms. The same plot levels were used for both spectra. (Adapted from Schwendinger et al., 1994, courtesy of Academic Press.)...

Homonuclear and heteronuclear coupling constants can be determined from the mixing-time dependence of Hartmann-Hahn transfer (see Sections II and VI). For example, for two heteronuclear spins 1 /2, the ideal polarization-transfer frequency under planar Hartmann-Hahn mbdng is 7,5/2 (see Section VI). Heteronuclear H- Si coupling constants have been determined in IS, I2S, and I S spin systems by Fourier analysis of the cross-polarization intensity as a function of the mbdng time (Bertrand et al., 1978a) and by an iterative fitting procedure (Murphy et al., 1979). 

Are there other theoretical or experimental considerations to distinguish these two heteronuclear correlation experiments More bluntly, should we prefer one or the other experiments First, there are different hardware requirements for the two-experiments some instruments are incapable of running the inverse de-... 

Logan TM, Olejniczak ET, Xu RX, Fesik SW (1992) Side chain and backbone assignments in isotopically labeled proteins from two heteronuclear triple resonance experiments. FEES Lett 314 413 18... 

CP enhancement in isolated spin pairs exhibits an oscillatory signal as a function of contact time due to magnetisation transfer back and forth between the two heteronuclear spins Double resonance... 

FIGURE 10.7 Set of coordinates for the four-body problem with two heteronuclear molecules. 

To be exhaustive about ID double resonance NMR experiments, we have to mention the TEDOR (transferred echo double resonance) experiment, which involves transferring magnetization between two heteronuclear spins [45]. Nevertheless, this experiment has been applied only once to Al-based fluoride, on AIPO4-CJ2, a microporous... 

A second 2D NMR method called HETCOR (heteronuclear chemical shift correlation) is a type of COSY in which the two frequency axes are the chemical shifts for different nuclei usually H and With HETCOR it is possible to relate a peak m a C spectrum to the H signal of the protons attached to that carbon As we did with COSY we 11 use 2 hexanone to illustrate the technique... 

For atoms, electronic states may be classified and selection rules specified entirely by use of the quantum numbers L, S and J. In diatomic molecules the quantum numbers A, S and Q are not quite sufficient. We must also use one (for heteronuclear) or two (for homonuclear) symmetry properties of the electronic wave function ij/. ... 

ColEl Regulation by RNA Hairpins. Rephcation of the E. coli plasmid ColEl is regulated by two short RNA molecules and a protein in a system that provides an example of the unique stmcmral elements accessible to RNA molecules. Multidimensional heteronuclear nmr spectroscopy has been used to characterize the complex formed between the two RNAs (25). Each of the RNA molecules fold back on the other to form a pair of hairpin... 

Two-dimensional C//correlations such as C//COSY or HC HMQC and HSQC provide the Jqh connectivities, and thereby apply only to those C atoms which are linked to H and not to non-protonated C atoms. Modifications of these techniques, also applicable to quaternary C atoms, are those which are adjusted to the smaller Jqh and Jqh couplings (2-25 Hz, Tables 2.8 and 2.9) Experiments that probe these couplings include the CH COLOC (correlation via long range couplings) with carbon-13 detection (Fig. 2.16) and HC HMBC (heteronuclear multiple bond coherence) with the much more sensitive proton detection (Fig. 2.17)... 

COSY Correlated spectroscopy, two-dimensional shift correlations via spin-spin coupling, homonuclear (e.g. HH) or heteronuclear (e.g. CH)... 

In studying the most familiar electrolytes, we have to deal with various molecular ions as well as atomic ions. The simplest molecular solute particle is a diatomic molecule that has roughly the same size and shape as two solvent particles in contact, and which goes into solution by occupying any two adjacent places that, in the pure solvent, are occupied by two adjacent solvent particles. This solution is formed by a process of substitution, but not by simple one-for-one substitution. There are two cases to discuss either the solute molecule is homonuclear, of-the type Bi, or it is heteronuclear, of the type BC. In either case let the number of solute molecules be denoted by nB, the number of solvent particles being nt. In the substitution process, each position occupied by a solvent particle is a possible position for one half of a solute molecule, and it is convenient to speak of each such position as a site, although in a liquid this site is, of course, not located at a fixed point in space. 

In the pure solvent let each particle have z nearest neighbors in contact with it. Let us ask how, removing two adjacent solvent particles from the interior, we may insert a solvent molecule. When a particular site is to be occupied by the B-half of the molecule BC, there are clearly z choices for the position of its C-half. This is true for each of the nB solute particles, provided that the solution is so dilute that they do not compete for the available sites to an appreciable extent. From the independent oiientations of nB solute particles, the quantity Wc/ receives the factor z if the molecules are heteronuclear and receives the factor (z/2)n if the molecules are homonuclear. 

N.M.D.R. experiments can be broadly subdivided into two categories (8, 9). The first is homonuclear in which the two nuclei involved are of the same nuclear species—e.g. XH — H, in this formulation the nuclear species being observed is indicated first, while the species (X) being irradiated is indicated X. The second is heteronuclear, in... 

The bond in a heteronuclear diatomic molecule, a diatomic molecule built from atoms of two different elements, is polar, with the electrons shared unequally by the two atoms. We therefore rewrite Eq. I as... 

FIGURE 3.33 A typical d molecular orbital energy-level diagram for a heteronuclear diatomic molecule AB the relative contributions of the atomic orbitals to the molecular orbitals are represented by the relative sizes of the spheres and the horizontal position of the boxes. In this case, A is the more electronegative of the two elements. 

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