Singlet nuclear magnetic resonance of nearly-equivalent spins (original) (raw)
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Weak nuclear spin singlet relaxation mechanisms revealed by experiment and computation
2021
Nuclear spin singlet states are often found to allow long lived storage of nuclear magnetization, which can form the basis of novel applications in spectroscopy, imaging, and in studies of dynamic processes. Precisely how long such polarization remains intact, and which factors affect its lifetime is often difficult to determine and predict. We present a combined experimental/computational study to demonstrate that molecular dynamics simulations and ab initio calculations can be used to fully account for the experimentally observed singlet lifetimes in an organic molecule in solution. %Intermolecular interactions with Cl nuclei of the chloroform solvent are shown to contribute significantly to the relaxation. Paramagnetic relaxation due to dissolved oxygen is taken into account in a self-consistent manner. The correspondence between experiment and simulations is achieved without adjustable parameters. These studies highlight the importance of considering unusual and difficult-to-con...
Constant-adiabaticity radiofrequency pulses for generating long-lived singlet spin states in NMR
The Journal of Chemical Physics, 2019
A method is implemented to perform “fast” adiabatic variation of the spin Hamiltonian by imposing the constant adiabaticity condition. The method is applied to improve the performance of singlet-state Nuclear Magnetic Resonance (NMR) experiments, specifically, for efficient generation and readout of the singlet spin order in coupled spin pairs by applying adiabatically ramped RF-fields. Test experiments have been performed on a specially designed molecule having two strongly coupled 13C spins and on selectively isotopically labelled glycerol having two pairs of coupled protons. Optimized RF-ramps show improved performance in comparison, for example, to linear ramps. We expect that the methods described here are useful not only for singlet-state NMR experiments but also for other experiments in magnetic resonance, which utilize adiabatic variation of the spin Hamiltonian.
Singlet-filtered NMR spectroscopy
Science Advances
Selectively studying parts of proteins and metabolites in tissue with nuclear magnetic resonance promises new insights into molecular structures or diagnostic approaches. Nuclear spin singlet states allow the selection of signals from chemical moieties of interest in proteins or metabolites while suppressing background signal. This selection process is based on the electron-mediated coupling between two nuclear spins and their difference in resonance frequency. We introduce a generalized and versatile pulsed NMR experiment that allows populating singlet states on a broad scale of coupling patterns. This approach allowed us to filter signals from proton pairs in the Alzheimer’s disease–related b-amyloid 40 peptide and in metabolites in brain matter. In particular, for glutamine/glutamate, we have discovered a long-lived state in tissue without the typically required singlet sustaining by radiofrequency irradiation. We believe that these findings will open up new opportunities to stud...
Longitudinal relaxation in a homonuclear coupled two-spin system. The case of (13C, 2H) glycine
Journal of Magnetic Resonance (1969), 1981
The longitudinal relaxation of the two carbon-13 nuclei of doubly enriched glycine (i3C and *H) has been investigated by the conventional nonselective [180"-r-W] pulse sequence. Some approximations are proposed which lead to a straightforward interpretation of the experimental results, a refined analysis being carried out by means of a general computer program previously described. These results together with those of other isotopomers (normal glycine NH&H,COOH and NH2**CH,i3COOD) allow the determination of random field rates at the two carbons and of the spectral densities relative to the carbon-carbon and methylene carbon-proton dipolar interactions. These spectral densities yield the following correlation times: 7cc = 17 + 4 psec and rc,, = 5.5 2 0.3 psec. In addition, the effect of a dipolar chemical shift anisotropy interference term has been observed by applying the sequence [1800r-30"]. Its sign is in agreement with a positive carbon-carbon indirect coupling and a positive carbonyl chemical shift anisotropy.
arXiv (Cornell University), 2021
Dissolution dynamical nuclear polarization has been applied in various fields, including chemistry, biology, and medical science. To expand the scope of these applications, the nuclear singlet state, which is decoherence-free against dipolar relaxation between spin pairs, has been studied experimentally, theoretically, and numerically. The singlet state composed of proton spins is used in several applications, such as enhanced polarization preservation, molecular tag to probe slow dynamic processes, and detection of ligand--protein complexes. In this study, we predict the lifetimes of the nuclear spin states composed of proton spin pairs using the molecular dynamics method and quantum chemistry simulations. We consider intramolecular and intermolecular dipolar, chemical shift anisotropy, and spin--rotation interactions. In particular, the relaxation rate of intermolecular dipolar interactions is calculated using the molecular dynamics method for various solvents. The calculated values and the experimental values are of the same order of magnitude. Our program would provide insight into the molecular design of several NMR applications and would be helpful in predicting the nuclear spin relaxation time of synthetic molecules in advance.
Constant-adiabaticity RF-pulses for generating long-lived singlet spin states in NMR
2018
A method is implemented to perform "fast" adiabatic variation of the spin Hamiltonian by imposing the constant adiabaticity condition. The method is applied to improve the performance of singlet-state Nuclear Magnetic Resonance (NMR) experiments, specifically, for efficient generation and readout of the singlet spin order in coupled spin pairs by applying adiabatically ramped RF-fields. Test experiments have been performed on a specially designed molecule having two strongly coupled C-13 spins and on selectively isotopically labelled glycerol having two pairs of coupled protons. Optimized RF-ramps show improved performance in comparison, for example, to linear ramps. We expect that the methods described here are useful, not only for singlet-state NMR experiments, but also for other experiments in magnetic resonance, which utilize adiabatic variation of the spin Hamiltonian.
Nuclear Spin Singlet Order Selection by Adiabatically Ramped RF Fields
The journal of physical chemistry. B, 2016
We describe an NMR method to generate singlet order in spin pairs from longitudinal spin magnetization and suppress residual background signals. This method can also be used for generating and observing long-lived spin states. A singlet order selection (SOS) filter is proposed, which allows us to find signals of the spin pair of interest buried in a crowded NMR spectrum. Likewise, SOS filtering enables proton NMR measurements in H2O without pulse sequences for solvent suppression. We demonstrate that the method works perfectly for both weakly and strongly coupled spin pairs. Furthermore, it can be combined with standard NMR pulse sequences: in this way, T1- and T2-relaxation times for spin pairs of interest can be measured. The power of the SOS-filter is demonstrated by relaxation studies in biomolecules.