The Experts below are selected from a list of 54939 Experts worldwide ranked by ideXlab platform
P. Kumar - One of the best experts on this subject based on the ideXlab platform.
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Excitation of multiple quantum Coherences by a single nonselective radiofrequency pulse due to the breakdown of the high-field approximation
Chemical Physics Letters, 1996Co-Authors: P. KumarAbstract:Multiple quantum Coherences are created by a single nonselective pulse from the equilibrium density matrix when the high-field approximation breaks down. In this situation the equilibrium density matrix also contains bilinear spin operators. In the case of a two spin system having scalar as well as dipolar coupling, both double and zero quantum Coherences are excited whereas in the presence of scalar coupling alone, only the zero quantum Coherence is created, with no double quantum Coherence. Flip angle dependence of the multiple quantum Coherences is discussed.
Peter B Kingsley - One of the best experts on this subject based on the ideXlab platform.
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scalar coupling and zero quantum Coherence relaxation in steam implications for spectral editing of lactate
Magnetic Resonance in Medicine, 1994Co-Authors: Peter B KingsleyAbstract:Accurate values were obtained for the lactate Zero-Quantum Coherence frequency, omega ZQ identical to omega 1-omega s = CH3 - CH chemical shift difference, and scalar coupling constant, J, by using the methyl signal's amplitude modulation during the TM period of a STEAM sequence, 90 degrees - TE/2 - 90 degrees - TM - 90 degrees - TE/2 - Acquire. Although most previous work has used J = 7.35 Hz, or 1/J = 136 ms, the actual value is J = 6.93 +/- 0.05 Hz or 1/J = 144.3 +/- 1 ms. In addition, the CH3 - CH chemical shift difference = 2.7956 +/- 0.0005 ppm, and the relaxation time for Zero-Quantum Coherence, TZQ, was much shorter than either T2 or T1 for the methyl resonance. A small component of the signal with TE = 144 ms, which was not modulated at the Zero-Quantum Coherence frequency or by scalar coupling, was assigned to longitudinal two-spin order magnetization (IzSz) created by imperfect radio frequency pulse profiles. This information will allow improved editing of the lactate signal and more accurate quantitation of lactate concentrations.
Kurt Wuthrich - One of the best experts on this subject based on the ideXlab platform.
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Determination of h2J(NN) and h1J(HN) coupling constants across Watson-Crick base pairs in the Antennapedia homeodomain-DNA complex using TROSY.
Journal of Biomolecular NMR, 2000Co-Authors: Konstantin Pervushin, Masatsune Kainosho, César Fernández, Roland Riek, Kurt WuthrichAbstract:This paper describes NMR measurements of 15N–15N and 1H–15N scalar couplings across hydrogen bonds in Watson–Crick base pairs, h2JNN and h1JHN, in a 17 kDa Antennapedia homeodomain–DNA complex. A new NMR experiment is introduced which relies on Zero-Quantum Coherence-based transverse relaxation-optimized spectroscopy (ZQ-TROSY) and enables measurements of h1JHN couplings in larger molecules. The h2JNN and h1JHN couplings open a new avenue for comparative studies of DNA duplexes and other forms of nucleic acids free in solution and in complexes with proteins, drugs or possibly other classes of compounds.
Michael R Wasielewski - One of the best experts on this subject based on the ideXlab platform.
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fast photo driven electron spin Coherence transfer the effect of electron nuclear hyperfine coupling on Coherence dephasing
Journal of Materials Chemistry C, 2015Co-Authors: Matthew D Krzyaniak, Lukas Kobr, Brandon K Rugg, Brian T Phelan, Eric A Margulies, Jordan N Nelson, Ryan M Young, Michael R WasielewskiAbstract:Selective photoexcitation of the donor in an electron donor–acceptor1–acceptor2 (D–A1–A2) molecule, in which D = perylene and both A1 and A2 = naphthalene-1,8:4,5-bis(dicarboximide), results in sub-nanosecond formation of a spin-correlated singlet radical pair 1(D+˙–A1−˙–A2) having a large electron spin–spin exchange interaction, 2J, which precludes its observation by transient EPR spectroscopy. Subsequent selective photoexcitation of A1−˙ rapidly produces 1(D+˙–A1–A2−˙), resulting in a dramatic decrease in 2J, which allows coherent spin evolution to mix the singlet (S) radical pair state 1(D+˙–A1–A2−˙) with the T0 triplet sublevel of 3(D+˙–A1–A2−˙) in an applied magnetic field, where B ≫ 2J. A spin-polarized transient EPR spectrum characteristic of the spin-correlated radical pair D+˙–A1–A2−˙ is then observed. The time delay between the two laser pulses was incremented to measure the rate of deCoherence in 1(D+˙–A1−˙–A2) in toluene at 295 K, which was found to be 8.1 × 107 s−1. Deuteration of the perylene donor or the toluene solvent decreases the deCoherence rate constant of 1(D+˙–A1−˙–A2) to 4.3 × 107 s−1 and 4.6 × 107 s−1, respectively, while deuteration of both the perylene donor and the toluene solvent reduced the deCoherence rate constant by more than half to 3.4 × 107 s−1. The data show that decreasing electron-nuclear hyperfine interactions significantly increases the zero quantum Coherence lifetime of the spin-correlated radical pair.
James Keeler - One of the best experts on this subject based on the ideXlab platform.
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elimination of zero quantum interference in two dimensional nmr spectra
Angewandte Chemie, 2003Co-Authors: Michael J Thrippleton, James KeelerAbstract:High-resolution NMR experiments often contain periods during which the magnetization is placed along the z-axis. For example, the magnetization must be along the z-axis during the mixing time in a NOESY experiment so that crossrelaxation can take place. Either phase cycling or field gradient pulses are used to ensure that only the wanted zmagnetization ends up contributing to the spectrum. However, neither of these methods can distinguish between zmagnetization and homonuclear Zero-Quantum Coherence, which is invariably present. The Zero-Quantum Coherence gives rise to anti-phase dispersive components in the spectra, thereby reducing the effective resolution, introducing misleading correlations, and obscuring wanted features. Over the years a number of methods have been devised to suppress these Zero-Quantum contributions, but it is fair to say that none of these methods have proved entirely satisfactory. Herein we present a new method for suppressing zeroquantum Coherence; the method is widely applicable, does not extend the duration of the experiment significantly, and can be implemented easily on any modern spectrometer. Our new method of Zero-Quantum suppression involves applying simultaneously a swept-frequency 1808 pulse and a gradient. Figure 1a shows how this combination can be introduced into the NOESY pulse sequence. The way in which this swept-pulse/gradient pair works can be envisaged in the following way. The application of the gradient (along the z-axis) results in the Larmor frequency becoming a function of position in the NMR tube. The swept-frequency 1808 pulse will therefore flip the spins at different positions in the sample at different times. Thus, the top of the sample might experience the 1808 pulse at the start of the sweep, the middle of the sample at time tf/2, and the bottom at time tf, where tf is the duration of the sweep. In general, the 1808 pulse occurs at time atf, where a is 0 at the top of the sample and 1 at the bottom. The 1808 pulse forms a spin echo which refocuses the evolution of the Zero-Quantum Coherence over a time 2atf ; however, for the remainder of the time, (1–2a)tf, the zeroquantum continues to evolve. The result is that in different parts of the sample the Zero-Quantum has evolved for different times, and so has acquired a different phase. If the range of these phases across the sample is large enough, the net result will be cancelation of the Zero-Quantum Coherence. A simple calculation (see Supporting Information) shows that the degree of attenuation A of the Zero-Quantum depends on both its frequency, WZQ (in rad s ), and the length of the swept-pulse/gradient pair, tf, [Eq. (1)]:
