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The Benchmark of 31P NMR parameters in Phosphate; the Case Study on Structurally Constrained and Flexible Phosphate

Abstract

The benchmark for structural interpretation of the 31P NMR shift and the 2JP,C NMR spin-spin coupling in the phosphate group was obtained by means of the theoretical calculations and the NMR measurements in diethylphosphate (DEP) and 5,5-dimethyl-2-hydroxy-1,3,2-dioxaphosphinane 2-oxide (cDEP). The NMR parameters were calculated employing the B3LYP, BP86, BPW91, M06-2X, PBE0, KT2, KT3, MP2, and HF method, the 6-31+G(d), Iglo-n (n = II, III), cc-pVnZ (n = D, T, Q, 5), aug-cc-pVnZ (n = D, T and Q), and pcS-n and pcJ-n (n = 1, 2, 3, 4) bases including the solvent effects described with explicit water molecules and/or implicit Polarizable Continuum Model (PCM). The effect of molecular dynamic (MD) on NMR parameters was MD-calculated using the GAFF force field inclusive explicit hydration with the TIP3P water molecules. Both the optimal geometries and the dynamical behaviors of the DEP and cDEP phosphates differed notably, which allowed reliable theoretical benchmark of the 31P NMR parameters for highly flexible and structurally constraint phosphate in one-to-one relationship with the experiment. The calculated 31P NMR shifts were referenced employing three different NMR reference schemes to highlight the effect of 31P NMR reference on accuracy of calculated 31P NMR shift. The relative δ(31P) NMR shift calculated employing the MD/B3LYP/Iglo-III/PCM method differed from the experiment by 0.16 ppm while the NMR shifts referenced to H3PO4 and/or PH3 deviated from the experiment notably more, which illustrated superior applicability of the relative NMR reference scheme. The 2JP,C coupling in DEP and cDEP calculated employing the MD/B3LYP/Iglo-III(DSO,PSO,SD)/cc-PV5Z(FC)/PCM method inclusive correction due to explicit hydration differed from the experiment by 0.32 Hz and 0.15 Hz, respectively. The NMR calculations demonstrated that reliable structural interpretation of the 31P NMR parameters in phosphate must involve both the structural and the dynamical component.

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Publication details

The article was accepted on 13 Nov 2017 and first published on 13 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06969C
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    The Benchmark of 31P NMR parameters in Phosphate; the Case Study on Structurally Constrained and Flexible Phosphate

    J. Fukal, O. Páv, M. Budesinsky, J. Šebera and V. Sychrovsky, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP06969C

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