The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by single crystal X-ray diffraction (XRD) experiments at 23 K. Four different structural models fitting an extensive set of XRD data to a resolution of (sinθ/λ)max = 1.143 Å−1 are compared. Two of the models include anharmonic temperature factors, whose inclusion is supported by the Hamilton test at a 99.95% level of confidence. Positive Fourier residuals up to 0.5 eÅ–3 in magnitude were found close to the methyl group and in the region of hydrogen bonds. Residual density analysis (RDA) and molecular dynamics simulations in the solid-state demonstrate that these residuals can be likely attributed to unresolved disorder, possibly dynamical and long–range in nature. Atomic volumes and charges, molecular moments up to hexadecapoles, as well as maps of the molecular electrostatic potential were obtained from distributed multipole analysis of the EDD. The derived electrostatic properties neither depend on the details of the multipole model, nor are significantly affected by the explicit inclusion of anharmonicity in the least–squares model. The distribution of atomic charges in 1-MUR is not affected by the crystal environment in a significant way. The quality of experimental findings is discussed in light of in-crystal and gas-phase quantum simulations.

Anharmonic thermal motion modelling in the experimental xrd charge density determination of 1-methyluracil at t = 23 k / R. Destro, P. Roversi, M. Barzaghi, L. Lo Presti. - In: MOLECULES. - ISSN 1420-3049. - 26:11(2021 May 21), pp. 3075.1-3075.19. [10.3390/molecules26113075]

Anharmonic thermal motion modelling in the experimental xrd charge density determination of 1-methyluracil at t = 23 k

R. Destro
Primo
Conceptualization
;
M. Barzaghi
Penultimo
Software
;
L. Lo Presti
Ultimo
Conceptualization
2021

Abstract

The experimental electron density distribution (EDD) of 1-methyluracil (1-MUR) was obtained by single crystal X-ray diffraction (XRD) experiments at 23 K. Four different structural models fitting an extensive set of XRD data to a resolution of (sinθ/λ)max = 1.143 Å−1 are compared. Two of the models include anharmonic temperature factors, whose inclusion is supported by the Hamilton test at a 99.95% level of confidence. Positive Fourier residuals up to 0.5 eÅ–3 in magnitude were found close to the methyl group and in the region of hydrogen bonds. Residual density analysis (RDA) and molecular dynamics simulations in the solid-state demonstrate that these residuals can be likely attributed to unresolved disorder, possibly dynamical and long–range in nature. Atomic volumes and charges, molecular moments up to hexadecapoles, as well as maps of the molecular electrostatic potential were obtained from distributed multipole analysis of the EDD. The derived electrostatic properties neither depend on the details of the multipole model, nor are significantly affected by the explicit inclusion of anharmonicity in the least–squares model. The distribution of atomic charges in 1-MUR is not affected by the crystal environment in a significant way. The quality of experimental findings is discussed in light of in-crystal and gas-phase quantum simulations.
1-methyluracil; Anharmonicity; Charge density; Crystal chemistry; Electrostatic moments; Molecular dynamics; Quantum chemistry; Quantum theory of atoms in molecules; X-ray diffraction
Settore CHIM/02 - Chimica Fisica
Settore CHIM/06 - Chimica Organica
https://www.mdpi.com/1420-3049/26/11/3075
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/869393
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