Quantum chemistry-based NMR spin Hamiltonian parameters of GABA for quantitation in magnetic resonance spectroscopy

Abstract

Chemical shifts delta and spin-spin coupling constants J have been calculated using quantum chemistry approaches for the gamma-amino butyric acid GABA which is a brain metabolite. Two theoretical methods HF and DFT/B3LYP, two basis sets 6-31G* and 6-311+G(2d,p) and two gauge-invariant methods CSGT and GIAO have been used. From delta and J values, NMR spectra have been obtained from the strongly coupled spin system Hamiltonian using the NMR-SCOPE package. Solvent effects have been considered within the polarisable continuum model. Comparisons between calculated and experimental NMR spectra at 300 MHz show that our best results correspond to the B3LYP/6-311+G(2d,p)-GIAO calculations. They are seen to be in good agreement with experiment. This demonstrates the usefulness of quantum chemistry methods for estimating NMR spin Hamiltonian parameters involved in specific algorithms used for quantitation of metabolites such as GABA.

J‐difference editing of gamma‐aminobutyric acid (GABA): Simulated and experimental multiplet patterns

“…and are given in Table . These values were estimated from high‐resolution NMR data of a GABA sample using PERCH (Kuopio, Finland) automated consistency analysis software and, in comparison with previously published chemical shifts and coupling constants , were shown to produce simulated spectra which best agreed with experimental high‐resolution GABA spectra recorded at high magnetic field strength.…”

Theoretical and experimental NMR studies on muscimol from fly agaric mushroom (Amanita muscaria)

“…1 H and 13 C NMR spectroscopy in DMSO-d6 solution of muscimol was selected as source of experimental information of muscimol molecular structure in solution. The current approach is partly similar to recent theoretical and experimental 1 H NMR studies on GABA 51 , as well as cytosine and 1-methylcytosine in solution 54 . However, in our study the analysis of the observed NMR data was supported by high-level DFT calculations combined with fairly complete basis sets and using both equilibrium and rovibrationally averaged geometry [59][60][61][62] .…”

“…From these studies emerges that in the presence of water GABA could exist as zwitterion [51][52][53] . However, this form is only slightly more stable than the neutral form and the results are strongly method and basis set dependent.…”

“…For example, at B3LYP/6-311++G** level of theory the canonical form of GABA + 5 water molecules was found slightly more stable than the zwitterion one 48 . 1 H NMR parameters of non-ionized and zwitterionic GABA were also calculated theoretically 51 .…”

DFT calculations of 1H chemical shifts, simulated and experimental NMR spectra for sarcosine

“…Being currently involved in calculations of NMR spin Hamiltonian parameters for metabolites [3][4][5], in order to produce reliable values of these parameters from which NMR spectra could be simulated and used further in quantitation procedures, we investigated sarcosine in the present study.…”