On the error in the nucleus-centered multipolar expansion of molecular electron density and its topology: A direct-space computational study.

The convergence of nucleus-centered multipolar expansion of the quantum-chemical electron density (QC-ED), gradient, and Laplacian is investigated in terms of numerical radial functions derived by projecting stockholder atoms onto real spherical harmonics at each center. The partial sums of this exact one-center expansion are compared with the corresponding Hansen-Coppens pseudoatom (HC-PA) formalism [Hansen, N. K.

Computational analysis of thermal-motion effects on the topological properties of the electron density.

The distributions of bond topological properties (BTPs) of the electron density upon thermal vibrations of the nuclei are computationally examined to estimate different statistical figures, especially uncertainties, of these properties. The statistical analysis is based on a large ensemble of BTPs of the electron densities for thermally perturbed nuclear geometries of the formamide molecule. Each bond critical point (BCP) is found to follow a normal distribution whose covariance correlates with the displacement amplitudes of the nuclei involved in the bond.

The IMAGINE instrument: first neutron protein structure and new capabilities for neutron macromolecular crystallography.

The first high-resolution neutron protein structure of perdeuterated rubredoxin from Pyrococcus furiosus (PfRd) determined using the new IMAGINE macromolecular neutron crystallography instrument at the Oak Ridge National Laboratory is reported. Neutron diffraction data extending to 1.65 Å resolution were collected from a relatively small 0.

Experimental charge density studies of disordered N-phenylpyrrole and N-(4-fluorophenyl)pyrrole.

The static electron densities of the title compounds were extracted from high-resolution X-ray diffraction data using the nucleus-centered finite multipole expansion technique. The interpretation of the data collected for the N-phenylpyrrole crystal revealed a static disorder that could be successfully resolved within the aspherical-atom formalism. The local and integrated topological properties of the density obtained via a constrained multipole refinement are in statistical agreement with those calculated at the B3LYP/cc-pVTZ level of theory for the isolated molecule and for those derived from the experimental density of the para-fluorinated derivative N-(4-fluorophenyl)pyrrole.

On the basis-set dependence of local and integrated electron density properties: Application of a new computer program for quantum-chemical density analysis.

A new computer program for post-processing analysis of quantum-chemical electron densities is described. The code can work with Slater- and Gaussian-type basis functions of arbitrary angular momentum. It has been applied to explore the basis-set dependence of the electron density and its Laplacian in terms of local and integrated topological properties.

Bond orders and atomic properties of the highly deformed halogenated fullerenes C60F18 and C60Cl30 derived from their charge densities.

The experimental charge densities of the halogenated C(60) fullerenes C(60)F(18) and C(60)Cl(30) were determined from high-resolution X-ray data sets measured with conventional Mo(Kalpha) radiation at 20 K for C(60)Cl(30) and with synchrotron radiation at 92 K for the fluorine compound. Bond topological and atomic properties were analyzed by using Bader's AIM theory. For the different C--C bonds, which vary in lengths between 1.

Invarioms for improved absolute structure determination of light-atom crystal structures.

The determination of molecular absolute configuration from an X-ray analysis for structures that contain only light elements is challenging owing to the weak anomalous dispersion signal. The achievable precision of the Flack x parameter for such structures is therefore limited, especially when the independent-atom model is employed. Invariom modelling can improve this situation.

The low-temperature study of D- and DL-camphoric anhydride.

The low-temperature crystal stuctures of D- and DL-camphoric anhydride, C(10)H(14)O(3), have been determined by X-ray diffraction methods. Although the two enantiomers crystallize in different space groups, the cell volumes and densities are essentially the same. The six-membered rings deviate significantly from planarity, both exhibiting half-boat conformations.

Charge density and experimental electrostatic potentials of two penicillin derivatives.

Two penicillin derivatives, the active penamecillin and the inactive penamecillin-1beta-sulfoxide, were used to study the relationship between their charge density and their activity. Single crystals of both compounds were measured at the synchrotron beamline F1 at the HASYLAB/DESY, at 100 K and up to resolutions of around 0.4 A.

The weakly coordinating trichloromethanesulfonate anion: NQR comparison of its coordinating abilities via oxygen with those of the chloroacetate ions.

Ionic and covalent derivatives of the chlorine analogue of the nonbasic, weakly coordinating triflate ion, Cl3CSO3(-) or "trichlate" ion, have been prepared and compared with the corresponding more strongly coordinated chloroacetates, Cl(x)CH(3-x)CO(2)M (x = 1-3), using 35Cl NQR (nuclear quadrupole resonance) spectroscopy. The (35)Cl NQR frequencies of all types of derivatives are sensitive to the nature of the metal ion or Lewis acid and are most sensitive in the case of monochloroacetates. In covalent (including zirconocene) derivatives, the average NQR frequencies fall as the Pauling electronegativity of M falls.

Aspherical-atom scattering factors from molecular wave functions. 1. Transferability and conformation dependence of atomic electron densities of peptides within the multipole formalism.

In this study, the feasibility of building a database of theoretical atomic deformation density parameters applicable to the construction of the densities of biomacromolecules and to the interpretation of their X-ray diffraction data is discussed. The procedure described involves generation of valence-only structure factors of tripeptides calculated from theoretical densities at the B3LYP level and the refinement of multipole parameters against these simulated data. Our results so far indicate that the backbone pseudoatoms extracted in such a way are highly transferable and fairly invariant with respect to rotations around single bonds in the peptide framework.

Reproducability and transferability of topological properties; experimental charge density of the hexapeptide cyclo-(D,L-Pro)2-(L-Ala)4 monohydrate.

The charge density of a hexapeptide was determined from high-resolution CCD area-detector experiments at 100 K. Two datasets, one from a rotating anode and a second one from synchrotron radiation, were measured and the results are compared. The data are interpreted in terms of the 'rigid pseudoatom' model.

Intra- and intermolecular topological properties of amino acids: a comparative study of experimental and theoretical results.

The charge densities rho(r) of the six amino acids L-Asn.H(2)O, DL-Glu.H(2)O, DL-Lys.

Electronic Insight into an Antithrombotic Agent by High-Resolution X-Ray Crystallography.

Five instead of 200 days measurement time are sufficient (thanks to area detection rather than conventional scintillation detection) to obtain the accurate charge density distribution of an antithrombotic agent with more than 50 atoms by a high-resolution X-ray diffraction experiment. The preferred sites of intermolecular interactions were identified from various topological properties, such as the reactive surface (zero Laplacian function, see picture) and the electrostatic potential.

Topological properties of the peptide bond in glycyl-L-threonine dihydrate based on a fast synchrotron/CCD-diffraction experiment at 100 K.

The charge density of glycyl-L-threonine dihydrate is extracted from a synchrotron data set of 98405 reflections collected at 100 K with a Bruker CCD area detector up to a resolution of d=0.38 A (sintheta/lambda = 1.32 A 1).

On the errors in molecular dipole moments derived from accurate diffraction data.

The error in the molecular dipole moment as derived from accurate X-ray diffraction data is shown to be origin dependent in the general case. It is independent of the choice of origin if an electroneutrality constraint is introduced, even when additional constraints are applied to the monopole populations. If a constraint is not applied to individual moieties, as is appropriate for multicomponent crystals or crystals containing molecular ions, the geometric center of the entity considered is a suitable choice of origin for the error treatment.

Fast Experiments for Charge-Density Determination: Topological Analysis and Electrostatic Potential of the Amino Acids L-Asn, dl-Glu, dl-Ser, and L-Thr.

Synchrotron radiation and CCD detection give the possibility for fast diffraction experiments, which were employed to deduce the exact charge-density distributions of some amino acids. Their topological analysis (the figure shows the negative Laplacian function of dl-serine in the plane of the carboxylate group) yields not only comparable information about intramolecular but also about weak intermolecular interactions.

Accurate experimental electronic properties of dl-proline monohydrate obtained within 1 Day.

A 1-day x-ray diffraction experiment on dl-proline monohydrate was performed at 100 kelvin with synchrotron radiation and a charge-coupled device area detection technique. The accuracy of the charge density distribution and of the related electronic properties extracted from these data is comparable or even superior to the accuracy obtained from a 6-week experiment on dl-aspartic acid with conventional x-ray diffraction methods. A data acquisition time of 1 day is comparable to the time needed for an ab initio calculation on the isolated molecules.

The Gram-Charlier and multipole expansions in accurate X-ray diffraction studies: can they be distinguished?

The Gram-Charlier temperature factor formalism has been applied to a set of accurate low-temperature data on bis(pyridine)(meso-tetraphenylporphinato)iron(II), and to a theoretical set of static structure factors on the hexaaquairon(II) ion. The refinements are compared with the multipole treatment for atomic asphericity due to chemical bonding. In a treatment of the experimental data in which only the iron atom asphericity is considered, the 'thermal motion' formalism is as efficient as the multipole formalism in accounting for the observations.