arXiv subjects

Amir Goldbourt

Publications and source records attributed to Amir Goldbourt.

5 recordsLinked to original sources

arXiv2025

Enhanced 133cs Triple-Quantum Excitation in Solid-State NMR of Cs-Bearing Zeolites

Geopolymers are aluminosilicate materials that exhibit effective immobilization properties for low-level radioactive nuclear waste, and more specifically for the immobilization of radioactive cesium. The identification of the cesium-binding sites and their distribution between the different phases making up the geopolymeric matrix can be obtained using solid-state NMR measurements of the quadrupolar spin 133Cs, which is a surrogate for the radioactive cesium species present in nuclear waste streams. For quadrupolar nuclei, acquiring two-dimensional multiple-quantum experiments allows the acquisition of more dispersed spectra when multiple sites overlap. However, 133Cs has a spin-7/2 and one of the smallest quadrupole moments, making multiple-quantum excitation highly challenging. In this work we present pulse schemes that enhance the excitation efficiency of 133Cs triple quantum coherences by a factor of ~2 with respect to a two-pulse excitation scheme. The improved schemes were developed by using numerical simulation and verified experimentally by applying one and two-dimensional triple-quantum solid-state NMR experiments to a mixture of cesium-exchanged hydrated zeolites A and X, which possess dynamically averaged small quadrupolar coupling constants in the order of 10 kHz.

physics.chem-ph↗

arXiv2025

Prediction of NMR Parameters and geometry in 133Cs-containing compounds using Density Functional Theory

The need to immobilize low-level nuclear waste, in particular 137Cs-bearing waste, has led to a growing interest in geopolymer-based waste matrices, in addition to optimization attempts of cement matrix compositions for this specific application. Although the overall phase composition and structure of these matrices are well characterized, the binding sites of Cs in these materials have not been clearly identified. Recent studies have suggested that combining the sensitivity of solid-state Nuclear Magnetic Resonance (SSNMR) to the local atomic structure with other structural techniques provides insights into the mode of Cs binding and release. Density Functional Theory (DFT) can provide the connection between spectroscopic parameters and geometric properties. However, the reliability of DFT results strongly relies on the choice of a suitable exchange-correlation functional, which for 133Cs, the NMR surrogate for such studies, is not well-established. In this work we benchmark various functionals against their performance in predicting the geometry of various simple Cs compounds, their NMR quadrupolar coupling constants, and their chemical shift values, while prioritizing the ability to incorporate dispersion interactions and maintaining low computational cost. We examined Cs salts, Cs oxides, perovskites, caged materials, a borate glass and a cesium fluoroscandate. While no single functional performs equally well for all parameters, the results show rev-vdW-DF2 and PBEsol+D3 to be leading candidates for these systems, in particular with respect to geometry and chemical shifts, which are of high importance for Cs-immobilization matrices.

physics.chem-ph↗

arXiv2023

XCloud-VIP: Virtual Peak Enables Highly Accelerated NMR Spectroscopy and Faithful Quantitative Measures

Nuclear Magnetic Resonance (NMR) spectroscopy is an important bio-engineering tool to determine the metabolic concentrations, molecule structures and so on. The data acquisition time, however, is very long in multi-dimensional NMR. To accelerate data acquisition, non-uniformly sampling is an effective way but may encounter severe spectral distortions and unfaithful quantitative measures when the acceleration factor is high. By modelling the acquired signal as the superimposed exponentials, we proposed a virtual peak (VIP) approach to selfadapt the prior spectral information, such as the resonance frequency and peak lineshape, and then feed these information into the reconstruction. The proposed method is further implemented with cloud computing to facilitate online, open, and easy access. Results on simulated and experimental data demonstrate that, compared with the low-rank Hankel matrix method, the new approach reconstructs high-fidelity NMR spectra from highly undersampled data and achieves more accurate quantification. The maximum quantitative errors of distances between nuclear pairs and concentrations of metabolites in mixtures have been reduced by 61.1% and 57.7%, respectively.

physics.med-ph↗

arXiv2022

Pulse induced resonance with angular dependent total enhancement of multi-dimensional solid-state NMR correlation spectra

We demonstrate a new resonance condition that obeys the relation $Δδ=nν_{R}/2$, where $Δδ$ is the chemical shift difference between two homonuclear-coupled spins, $ν_{R}$ is the magic-angle spinning speed and $n$ is an integer. This modulation on the rotational resonance recoupling condition is obtained by the application of rotor-synchronous $^{1}$H pulses when at least one proton is dipolar-coupled to one of the homonuclear-coupled spins. We suggest a new experimental scheme entitled "pulse induced resonance with angular dependent total enhancement" (PIRATE) that can enhance proton-driven spin diffusion by the application of a single $^{1}$H pulse every rotor period. Experimental evidence is demonstrated on the two carbon spins of glycine and on the Y21M mutant of fd bacteriophage virus. Numerical simulations reveal the existence of the resonances and report on the important interactions governing this phenomena.

physics.chem-ph↗

arXiv2020

Distance measurements between carbon and bromine using a split-pulse PM-RESPDOR solid-state NMR experiment

Solid-state NMR have been long used to probe atomic distances between nearby nuclear spins by virtue of the dipolar interaction. New technological advances have enabled simultaneous tuning of the radio-frequency resonance circuits to nuclei with close Larmor frequencies, bringing a great promise also to distance measurements between such nuclei, in particular for nuclei with a spin larger than one-half. However, this new possibility has also required modifications of those experiments since the two nuclei cannot be irradiated simultaneously. When measuring distances between a spin S=1/2 and a quadrupolar spin (S > 1/2), this drawback can be overcome by splitting the continuous-wave recoupling pulse applied to the quadrupolar nucleus. We show here that a similar adjustment to a highly-efficient phase-modulated (PM) recoupling pulse enables distance measurements between nuclei with close Larmor frequencies, where the coupled spin experiences a very large coupling. Such an experiment, split phase-modulated RESPDOR, is demonstrated on a 13C-81Br system, where the difference in Larmor frequencies is only 7%, or 11.2 MHz on a 14.1T magnet. The inter-nuclear distances are extracted using an unscaled analytical formula. Since bromine usually experiences particularly high quadrupolar couplings, as in the current case, we suggest that the split-PM-RESPDOR experiment can be highly beneficial for the research of bromo-compounds, including many pharmaceuticals, where carbon-bromine bonds are prevalent, and organo-catalysts utilizing the high reactivity of bromides. We show that for butyl triphenylphosphonium bromide, distances are in agreement with a low-hydration compound rather than a semi-clathrate form. The split-PM-RESPDOR experiment is suitable for distance measurement between any quadrupolar/spin-1/2 pairs, in particular when the quadrupolar spin experiences a significantly large coupling.

physics.chem-ph↗