Molecular electric moments from x-ray diffraction data

Spackman, Mark A.

doi:10.1021/cr00016a005

Cited by 183 publications

(148 citation statements)

References 49 publications

Supporting

Mentioning

129

Contrasting

Unclassified

Order By: Relevance

“…For the cytosine base together with the C 1' substituent, the dipole moment from the full multipole model is 11 (2) Debye. For cytosine from cytosine monohydrate, the new full multipole refinement gives a dipole moment of 8.2 (15) Debye, in agreement with the previously reported value [8.0(14) Debye; Spackman, Weber & Craven, 1988] and with theoretical values (Spackman, 1992). The presently (e) 1-fl-D-Arabinosylcytosine.…”

Section: Molecular Dipole Momentssupporting

confidence: 88%

Electrostatic properties of β-cytidine and cytosine monohydrate from Bragg diffraction

Chen¹,

Craven²

1995

Acta Crystallogr Sect B

View full text Add to dashboard Cite

1081electrostatic potential in the expected N lone-pair position as XN is increased incrementally from 0 to 48.5 ° . These calculations are consistent with the crystallographic evidence that all N...H contacts within the sum of van der Waals radii (2.75 A) that have XN > 35° and PH > 130° may be classified as hydrogen bonds. These N...H contacts are closely aligned with the assumed N lone-pair vector and such evidence is normally taken to infer an interaction between H(8+) and the lone-pair density. However, by analogy with the perpendicular approach of truly 'non-bonded' H to planar Nsp 2 systems (XIV), the lone-pair direction is also the approach direction of minimal steric hindrance to sp 3 hybridized N atoms (XV). Despite this analogy, we feel that the crystallographic results presented here provide tentative evidence that the incoming donor H atom tracks the changing direction of the N lone-pair vector as XN increases from 35 ° to --,60 ° during the latter phases of the Nsp2--+ Nsp 3 transition.We are indebted to Professor G. Gilli AbstractThe charge-density distribution in the crystal structure of the nucleoside fl-cytidine at 123 K has been determined * Author for correspondence.© 1995 International Union of Crystallography Printed in Great Britain -all rights reserved from X-ray diffraction data (Ag Kot, 2 = 0.5608 J~) using all 7233 reflections with sin0/2 < 1.14,~ -1. Maps of electrostatic potential for the cytosine base in cytidine are similar to those derived from previous charge-density studies of cytosine monohydrate and 1-fl-D-arabinosylcytosine, after taking chemical differences into account.

show abstract

Section: Molecular Dipole Momentssupporting

confidence: 88%

Electrostatic properties of β-cytidine and cytosine monohydrate from Bragg diffraction

Chen¹,

Craven²

1995

Acta Crystallogr Sect B

View full text Add to dashboard Cite

show abstract

“…The only contributions to the out-of-plane molecular moments are atomic second moments derived from the monopole and quadrupole functions; in contrast, the in-plane molecular moments depend upon these as well as net atomic charges (multiplied by the square of their distance from the centre-of-mass origin) and net atomic dipole moments (multiplied by their distance from the origin). In a sense the out-of-plane moments are less susceptible to variations in the parameters in the multipole model and this is entirely in accord with results of analyses of experimental data for urea, benzene and p-dicyanotetrafluorobenzene (Spackman, 1992), where agreement between experiment and theory was also observed to be much better for outof-plane than for in-plane moments.…”

Section: Second Momentssupporting

confidence: 82%

“…Accumulated evidence suggests that high-quality X-ray diffraction data is capable of providing estimates of the electrostatic properties of molecules in crystals, in particular, electric moments (Spackman, 1992), energies of molecular interactions (Spackman, Weber & Craven, 1988) and electric field gradients (EFG's), especially at protons (Brown & Spackman, 1994). However, few charge density analyses involve determination of these properties, partly because of the present limitations of experimental data and partly because of some skepticism that the numbers derived are meaningful.…”

Section: Introductionmentioning

confidence: 99%

Molecular electric moments and electric field gradients from X-ray diffraction data: model studies

Spackman¹,

Byrom²

1996

Acta Crystallogr Sect B

Self Cite

View full text Add to dashboard Cite

Model X-ray data sets, with and without the inclusion of experimental thermal motion parameters, have been computed via Fourier transformation of ab initio molecular electron densities for 12 different molecular crystals. These datasets were then analysed with three different multipole models of varying sophistication and, from the multipole functions, molecular dipole and second moments, as well as electric field gradients (EFG's), at each nuclear site were computed and compared with results obtained from the original ab initio wavefunctions. The results provide valuable insight into the reliability of these properties, extracted in the same way from experimental X-ray data. Not all molecular systems display identical trends, but a general pattern is discernible. Specifically, dipole moments are typically underestimated by a small but significant amount (~ 10-15%), the trace of the second moment tensor is well determined but overestimated by a few per cent and electric field gradients at protons are confirmed to be well within reach of a careful charge density analysis of X-ray diffraction data.

show abstract

“…An optimization that would produce unrealistic values of the electrostatic properties would obviously not be an acceptable procedure. (Spackman, 1992). "…”

Section: The Molecular Dipole Moment As a Test Of The Mem Proceduresmentioning

confidence: 99%

The Two-Channel Maximum-Entropy Method Applied to the Charge Density of a Molecular Crystal: α-Glycine

Papoular¹,

Vekhter²,

Coppens³

1996

Acta Cryst Sect A

View full text Add to dashboard Cite

A two-channel maximum-entropy method (MEM), first used to enhance magnetization densities from phased polarized neutron data by Papoular & Gillon [(1990). Europhys. Lett. 13,[429][430][431][432][433][434], has been applied to the electron deformation density. The resulting entropic densities are compared with standard deformation densities and with dynamic and static deformation maps obtained from multipole ref'mements. The procedure is illustrated with simulated and real single-crystal X-ray data sets on the molecular crystal of ot-glycine. Both a uniform prior and a prior equal to the MEMenhanced dynamic model deformation density are used in the MEM procedure, the result of which does not depend on the starting density. The method is judged by the appearance of the resulting maps and the values of the molecular dipole moment before and after the MEM. Compared with the conventional deformation density, the MEM procedure sharpens the peaks in the bond but flattens the weaker features, especially when a uniform prior is used. The dipole-moment criterion shows the non-uniform prior to be preferable to the uniform prior in reproducing electrostatic properties. The usefulness of the MEM in charge-density analysis remains open to discussion.

show abstract

Molecular electric moments from x-ray diffraction data

Cited by 183 publications

References 49 publications

Electrostatic properties of β-cytidine and cytosine monohydrate from Bragg diffraction

Electrostatic properties of β-cytidine and cytosine monohydrate from Bragg diffraction

Molecular electric moments and electric field gradients from X-ray diffraction data: model studies

The Two-Channel Maximum-Entropy Method Applied to the Charge Density of a Molecular Crystal: α-Glycine

Contact Info

Product

Resources

About