Issue 31, 2021

Identification of beryllium fluoride complexes in mechanically distorted gels using quadrupolar split 9Be NMR spectra resolved with solution-state selective cross-polarization

Abstract

The uniformly anisotropic media afforded by hydrogels are being increasingly exploited in analytical (structure elucidation) nuclear magnetic resonance (NMR) spectroscopy, and in studies of mechanosensitive biophysical and biochemical properties of living cells. The 9Be NMR parameters of beryllium fluoride complexes formed in aqueous solutions are sensitive markers of the anisotropic molecular environments produced by gelatin gels. The electric quadrupole moment of the 9Be nucleus (spin I = 3/2) interacts with the electric field gradient tensor in a stretched (or compressed) gel, giving rise to the splitting of peaks in 9Be NMR spectra. These are in addition to those produced by scalar coupling to the 19F nuclei. Thus, an equilibrium mixture of beryllofluoride complexes (BeF2, BeF3, and BeF42−) in mechanically distorted gels generates an envelope of overlapping 9Be NMR multiplets. In the present work, the multiplets were dissected apart by using selective excitation of 9Be–19F cross-polarization; and the spectral components were quantified with multi-parameter line-shape decomposition, coupled with SpinDynamica simulations. The effects of gel density and Bloom number (a measure of gelatin-gel rigidity under standard conditions of sample preparation) on residual quadrupolar splittings were examined. Cross-polarization experiments revealed a bimodal distribution of  residual quadrupolar coupling constants (RQC) of the BeF3 complexes. The average RQC of the dominant BeF3 population was ∼3 times larger than that of BeF42−. The secondary BeF3 population existed in a tetrahedral configuration. It was attributed to BeF3 complexes associated with negatively charged –COO groups of the denatured collagen matrix.

Graphical abstract: Identification of beryllium fluoride complexes in mechanically distorted gels using quadrupolar split 9Be NMR spectra resolved with solution-state selective cross-polarization

Supplementary files

Article information

Article type
Paper
Submitted
05 Jun 2021
Accepted
16 Jul 2021
First published
17 Jul 2021

Phys. Chem. Chem. Phys., 2021,23, 16932-16941

Identification of beryllium fluoride complexes in mechanically distorted gels using quadrupolar split 9Be NMR spectra resolved with solution-state selective cross-polarization

K. Romanenko, S. J. Elliott, A. A. Shubin and P. W. Kuchel, Phys. Chem. Chem. Phys., 2021, 23, 16932 DOI: 10.1039/D1CP02515E

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