Charge Density of L-Alanyl-glycyl-L-alanine Based on X-Ray Data Collection Periods from 4 to 130 Hours

Abstract

The charge density of the tripeptide L-alanyl-glycyl-L-alanine was determined from three X-ray data sets measured at different experimental setups and under different conditions. Two of the data sets were measured with synchrotron radiation (beamline F1 of Hasylab/DESY, Germany and beamline X10SA of SLS, Paul-Scherer-Institute, Switzerland) at temperatures around 100 K while a third data set was measured under home laboratory conditions (MoK α radiation) at a low temperature of 20 K. The multipole refinement strategy to derive the experimental charge density was the same in all cases, so that the obtained charge density properties could directly be compared. While the general analysis of the three data sets suggested a small preference for one of the synchrotron data sets (Hasylab F1), a comparison of topological and atomic properties gave in no case an indication for a preference of any of the three data sets. It follows that even the 4 h data set measured at the SLS performed equally well compared to the data sets of substantially longer exposure time.

Experimental charge density of L-alanyl-L-prolyl-L-alanine hydrate: classical multipole and invariom approach, analysis of intra- and intermolecular topological properties

“…It was also shown (Messerschmidt et al, 2005;Fö rster et al, 2007) that even for a single molecule, measured under different conditions, such deviations may occur. For example, three datasets of the tripeptide l-alanyl-glycyl-l-alanine, treated by the same multipole model, give a mean standard deviation for the topological descriptors as high as 0.07 e Å À3 in and 3.4 e Å À5 in r 2 .…”

“…For comparative charge density studies we therefore directed our interest to the electronic structures of tripeptides of the type l-alanyl-Xxx-l-alanine, where Xxx is one of the 20 naturally encoded amino acids. So far we have completed charge density studies on tripeptides of the above mentioned type, with Xxx = l-alanine (A;Rö del et al, 2006), l-tyrosine (Y; Chę chiń ska, Mebs, Hü bschle, Fö rster, Morgenroth & Luger, 2006) and glycine Fö rster et al, 2007). We compared the transferability of bond topological properties, atomic volumes and charges in the peptide bond region.…”

Transferability and reproducibility in electron-density studies – bond-topological and atomic properties of tripeptides of the type L-alanyl-X-L-alanine

“…The same color indicates equality in the nearest-neighbor approximation. Values from eight tripeptides AHA (this study), AFA (this study), two independent molecules in the asymmetric unit of AAA (Rö del et al, 2006), two modifications of AYA (Cheçiń ska et al, 2006), APA (Kalinowski et al, 2007) and AGA (Fö rster et al, 2006) derived from wavefunction calculations at the B3LYP/6-311++G(2d,2p) level of theory at experimental geometries. approximation (NNA).…”

“…In recent years, we have entered into a systematic study on the class of tripeptides l-alanyl-X-l-alanine (AXA). Measurements of six different AXA tripeptides with X being l-alanyl (Rö del et al, 2006), l-tyrosyl (Cheçiń ska et al, 2006), glycyl (Fö rster et al, 2006), l-prolyl (Kalinowski et al, 2007), l-histidinyl (this study) and l-phenylalanyl (this study), have been performed. The measurements were carried out using different synchrotron beamlines at HASYLAB/ DESY in Hamburg and at the Swiss Light Source (PSI, Villigen) as well as using the in-house diffractometer (Mo K radiation, 2 kW Criterion for observed reflections sealed tube) at temperatures ranging from 100 to 9 K. Different integration and data reduction software routines had to be employed, but the multipole modeling strategy of the main chain was identical.…”

Validation of X‐ray Wavefunction Refinement

“…The multipolar model (MM) based on the Hansen & Coppens formalism [26] is the most commonly used technique for the reconstruction of the experimental ED. For small organic compounds various important properties have been derived from the MM ED, such as: interaction energies, [33,34,35,36] topological properties of the molecular ED, [37,38,39,40,41,35,42,43,36] topological properties and energetics of hydrogen bonds in molecular crystals, [44,45,46,47,48,49] inuence of intermolecular interactions on molecular properties, [50] molecular dipole moments [51,52,53,54,36] and electrostatic potentials [55,36] . These studies have been extended to biological systems, e.g.…”