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

2007 ◽  
Vol 62 (5) ◽  
pp. 696-704 ◽  
Author(s):  
Diana Förster ◽  
Armin Wagner ◽  
Christian B. Hübschle ◽  
Carsten Paulmann ◽  
Peter Luger
Keyword(s):  
Synchrotron Radiation ◽  
Low Temperature ◽  
Charge Density ◽  
Data Sets ◽  
Data Set ◽  
X Ray ◽  
Atomic Properties ◽  
Multipole Refinement ◽  
Refinement Strategy ◽  
Experimental Charge Density

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 (MoKα 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.

scholarly journals Electron density of a new EGFR Tyrokinase-inhibitor at 100 K, consideration of different models

2008 ◽  
Vol 223 (8) ◽  
Author(s):  
Stefan Mebs ◽  
Anja Lüth ◽  
Wolfgang Löwe ◽  
Carsten Paulmann ◽  
Peter Luger
Keyword(s):  
High Resolution ◽  
Synchrotron Radiation ◽  
Electron Density ◽  
Electron Shell ◽  
Cancer Drug ◽  
Outer Electron ◽  
Data Set ◽  
X Ray ◽  
Atomic Properties ◽  
Anti Cancer

AbstractThe electron density (ED) of a substituted 4-(indol-3-yl)-quinazoline, a newly developed anti-cancer drug, was determined from a high resolution X-ray data set measured at 100 K using synchrotron radiation. Because the structure contains a chlorine atom, which has a diffuse outer electron shell and is therefore beyond standard modeling, the influence of the model on the bond topological and atomic properties was studied following Bader's approach of ‘Atoms In Molecules’ (AIM). The expansion/contraction parameters

Towards extracting the charge density from normal-resolution data

2009 ◽  
Vol 42 (6) ◽  
pp. 1110-1121 ◽  
Author(s):  
B. Dittrich ◽  
C. B. Hübschle ◽  
J. J. Holstein ◽  
F. P. A. Fabbiani
Keyword(s):  
Charge Density ◽  
Dipole Moments ◽  
Atomic Displacement ◽  
Limiting Factor ◽  
Data Sets ◽  
Data Set ◽  
Redundant Data ◽  
Multipole Refinement ◽  
Atomic Displacement Parameters ◽  
Resolution Data

The limiting factor for charge-density studies is crystal quality. Although area detection and low temperatures enable redundant data collection, only compounds that form well diffracting single crystals without disorder are amenable to these studies. If thermal motion and electron density ρ(r) were de-convoluted, multipole parameters could also be refined with lower-resolution data, such as those commonly collected for macromolecules. Using the invariom database for first refining conventional parameters (x,y,zand atomic displacement parameters), de-convolution can be achieved. In a subsequent least-squares refinement of multipole parameters only, information on the charge density becomes accessible also for data not fulfilling charge-density requirements. A critical aspect of this procedure is the missing information on the correlation between refined and non-refined parameters. This correlation is investigated in detail by comparing a full multipole refinement on high-resolution and a blocked refinement on `normal-resolution' data sets of ciprofloxacin hexahydrate. Topological properties and dipole moments are shown to be in excellent agreement for the two refinements. A `normal-resolution' data set of ciprofloxacin hydrochloride 1.4-hydrate is also evaluated in this manner.

scholarly journals Validation of experimental charge-density refinement strategies: when do we overfit?

IUCrJ ◽  
2017 ◽  
Vol 4 (4) ◽  
pp. 420-430 ◽  
Author(s):  
Lennard Krause ◽  
Benedikt Niepötter ◽  
Christian J. Schürmann ◽  
Dietmar Stalke ◽  
Regine Herbst-Irmer
Keyword(s):  
Standard Deviation ◽  
Charge Density ◽  
Cross Validation ◽  
Data Sets ◽  
Topological Parameters ◽  
Visualization Tools ◽  
Multipole Refinement ◽  
The Given ◽  
Experimental Charge Density ◽  
Parameter Distributions

A cross-validation method is supplied to judge between various strategies in multipole refinement procedures. Its application enables straightforward detection of whether the refinement of additional parameters leads to an improvement in the model or an overfitting of the given data. For all tested data sets it was possible to prove that the multipole parameters of atoms in comparable chemical environments should be constrained to be identical. In an automated approach, this method additionally delivers parameter distributions ofkdifferent refinements. These distributions can be used for further error diagnostics,e.g.to detect erroneously defined parameters or incorrectly determined reflections. Visualization tools show the variation in the parameters. These different refinements also provide rough estimates for the standard deviation of topological parameters.

scholarly journals Experimental charge density studies: Discard valid data and overfit?

2014 ◽  
Vol 70 (a1) ◽  
pp. C282-C282 ◽  
Author(s):  
Regine Herbst-Irmer
Keyword(s):  
Charge Density ◽  
Data Sets ◽  
Resolution Limit ◽  
Quality Of Data ◽  
Refinement Method ◽  
Scaling Methods ◽  
First Results ◽  
Refinement Process ◽  
Refinement Strategy ◽  
Experimental Charge Density

In experimental charge density investigation it is indispensable to use the highest possible quality of data. Therefore the multiplicity should be as high as possible, but poor data should be omitted. To decide about resolution limit and discarding outlier data often limits for Rint or I/σ(I) are used. A better approach is the `paired refinement method' [1] comparing two data sets by the fit of the models derived by the same refinement protocol to both data sets. For macromolecular data sets it could be shown that a higher resolution should be used than normally derived from the above mentioned criteria. First results for charge density data seem to show the same tendency but of course on a different level. The paired refinement strategy can also be used to investigate the influence of different scaling methods. In a recent version of SADABS [2] a new error model and a 3λ correction is implemented. With the paired refinement strategy the improvement in data quality gets obvious. A further concern in charge density investigation is the question of overfitting. In macromolecular refinement this is answered by the Rfree concept [3]. Here a refinement protocol is developed by refining against a work set of reflections, e.g. 90 % of the data. The remaining reflections are untouched in the whole refinement process but an Rfree value is calculated using only this test set of reflections. An overfitting can clearly be identified by a decrease in Rwork but an increase in Rfree. This refinement protocol is then used for a final refinement against all data. It will be discussed how this method could support charge density studies.

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

2007 ◽  
Vol 63 (5) ◽  
pp. 753-767 ◽  
Author(s):  
Roman Kalinowski ◽  
Birger Dittrich ◽  
Christian B. Hübschle ◽  
Carsten Paulmann ◽  
Peter Luger
Keyword(s):  
Chem Phys ◽  
Atoms In Molecules ◽  
Aim Analysis ◽  
Acta Cryst ◽  
X Ray ◽  
Atomic Properties ◽  
Multipole Refinement ◽  
Resolution Dataset ◽  
Experimental Charge Density

A high-resolution dataset of the tripeptide L-alanyl-L-prolyl-L-alanine hydrate was measured at 100 K using synchrotron radiation and CCD area detection. Electron densities were obtained from a full multipole refinement of the X-ray experimental data, from an invariom transfer and from a theoretical calculation. Topological and atomic properties were derived via an AIM analysis [Atoms in Molecules; see Bader (1990). Atoms in Molecules: A Quantum Theory, No. 22 in International Series of Monographs on Chemistry, 1st ed. Oxford: Clarendon Press] of these densities and compared with each other, as well as with results from the literature of other oligopeptides and amino acids. By application of the invariom formalism to a dataset of limited resolution, its performance was compared with a conventional spherical refinement, highlighting the possibility of aspherically modelling routine structure-determination experiments. The hydrogen-bonding scheme was subject to a detailed analysis according to the criteria of Koch & Popelier [(1995), J. Phys. Chem. 99, 9747–9754] as well as to the characterization of Espinosa et al. [(1998), Chem. Phys. Lett. 285, 170–173; (1999), Acta Cryst. B55, 563–572; (2002), J. Chem. Phys. 117, 5529–5542] using the results from the refined and invariom multipole densities as well as the spherical-density model, which are critically compared.

Experimental charge density of an L-phenylalanine formic acid complex with a short hydrogen bond determined at 25 K

2006 ◽  
Vol 221 (9) ◽  
Author(s):  
Stefan Mebs ◽  
Marc Messerschmidt ◽  
Peter Luger
Keyword(s):  
Hydrogen Bond ◽  
High Resolution ◽  
Formic Acid ◽  
Charge Density ◽  
Topological Properties ◽  
Acid Complex ◽  
Data Set ◽  
X Ray ◽  
Short Hydrogen Bond ◽  
Experimental Charge Density

AbstractThe experimental charge density and related atomic and bond topological properties of an L-phenylalanine formic acid complex were derived from a high resolution X-ray data set (sin θ/λ = 1.18 Å

A batch-wise non-linear fitting and analysis tool for treating large X-ray diffraction data sets

2006 ◽  
Vol 39 (2) ◽  
pp. 262-266 ◽  
Author(s):  
R. J. Davies
Keyword(s):  
Diffraction Data ◽  
Operation Mode ◽  
Large Data ◽  
Scattering Data ◽  
Data Sets ◽  
Analysis Tool ◽  
Data Set ◽  
X Ray ◽  
Linear Fitting ◽  
Non Linear

Synchrotron sources offer high-brilliance X-ray beams which are ideal for spatially and time-resolved studies. Large amounts of wide- and small-angle X-ray scattering data can now be generated rapidly, for example, during routine scanning experiments. Consequently, the analysis of the large data sets produced has become a complex and pressing issue. Even relatively simple analyses become difficult when a single data set can contain many thousands of individual diffraction patterns. This article reports on a new software application for the automated analysis of scattering intensity profiles. It is capable of batch-processing thousands of individual data files without user intervention. Diffraction data can be fitted using a combination of background functions and non-linear peak functions. To compliment the batch-wise operation mode, the software includes several specialist algorithms to ensure that the results obtained are reliable. These include peak-tracking, artefact removal, function elimination and spread-estimate fitting. Furthermore, as well as non-linear fitting, the software can calculate integrated intensities and selected orientation parameters.

scholarly journals Expression, purification, crystallization and preliminary X-ray analysis of tannase fromLactobacillus plantarum

2013 ◽  
Vol 69 (4) ◽  
pp. 456-459 ◽  
Author(s):  
Mingbo Wu ◽  
Xiaohong Peng ◽  
Hua Wen ◽  
Qin Wang ◽  
Qianming Chen ◽  
...  
Keyword(s):  
Synchrotron Radiation ◽  
Gallic Acid ◽  
Diffusion Method ◽  
Ester Bond ◽  
Asymmetric Unit ◽  
Data Set ◽  
X Ray ◽  
Vapour Diffusion ◽  
Serine Esterases ◽  
Hydrolysis Of

Tannase catalyses the hydrolysis of the galloyl ester bond of tannins to release gallic acid. It belongs to the serine esterases and has wide applications in the food, feed, beverage, pharmaceutical and chemical industries. The tannase fromLactobacillus plantarumwas cloned, expressed and purified. The protein was crystallized by the sitting-drop vapour-diffusion method with microseeding. The crystals belonged to space groupP1, with unit-cell paramtersa= 46.5,b= 62.8,c= 83.8 Å, α = 70.4, β = 86.0, γ = 79.4°. Although the enzyme exists mainly as a monomer in solution, it forms a dimer in the asymmetric unit of the crystal. The crystals diffracted to beyond 1.60 Å resolution using synchrotron radiation and a complete data set was collected to 1.65 Å resolution.

A Ccomparison of sedigraph and pipette methods for soil particle-size analysis

Soil Research ◽  
1993 ◽  
Vol 31 (4) ◽  
pp. 407 ◽  
Author(s):  
GD Buchan ◽  
KS Grewal ◽  
JJ Claydon ◽  
RJ Mcpherson
Keyword(s):  
Particle Size ◽  
New Zealand ◽  
Particle Size Analysis ◽  
Size Analysis ◽  
Data Sets ◽  
Regression Equations ◽  
Total Iron Content ◽  
Data Set ◽  
X Ray ◽  
The Difference

The X-ray attenuation (Sedigraph) method for particle-size analysis is known to consistently estimate a finer size distribution than the pipette method. The objectives of this study were to compare the two methods, and to explore the reasons for their divergence. The methods are compared using two data sets from measurements made independently in two New Zealand laboratories, on two different sets of New Zealand soils, covering a range of textures and parent materials. The Sedigraph method gave systematically greater mass percentages at the four measurement diameters (20, 10, 5 and 2 �m). For one data set, the difference between clay (<2 �m) percentages from the two methods is shown to be positively correlated (R2 = 0.625) with total iron content of the sample, for all but one of the soils. This supports a novel hypothesis that the typically greater concentration of Fe (a strong X-ray absorber) in smaller size fractions is the major factor causing the difference. Regression equations are presented for converting the Sedigraph data to their pipette equivalents.

Comparative study of X-ray charge-density data on CoSb3

2013 ◽  
Vol 69 (6) ◽  
pp. 570-582 ◽  
Author(s):  
Mette Stokkebro Schmøkel ◽  
Lasse Bjerg ◽  
Finn Krebs Larsen ◽  
Jacob Overgaard ◽  
Simone Cenedese ◽  
...  
Keyword(s):  
Charge Density ◽  
High Performance ◽  
Theoretical Data ◽  
High Energy ◽  
Data Sets ◽  
High Symmetry ◽  
X Ray ◽  
Structure Factors ◽  
Small Crystals ◽  
Density Analysis

CoSb3is an example of a highly challenging case for experimental charge-density analysis due to the heavy elements (suitability factor of ∼0.01), the perfect crystallinity and the high symmetry of the compound. It is part of a family of host–guest structures that are potential candidates for use as high-performance thermoelectric materials. Obtaining and analysing accurate charge densities of the undoped host structure potentially can improve the understanding of the thermoelectric properties of this family of materials. In a previous study, analysis of the electron density gave a picture of covalent Co–Sb and Sb–Sb interactions together with relatively low atomic charges based on state-of-the-art experimental and theoretical data. In the current study, several experimental X-ray diffraction data sets collected on the empty CoSb3framework are compared in order to probe the experimental requirements for obtaining data of high enough quality for charge-density analysis even in the case of very unsuitable crystals. Furthermore, the quality of the experimental structure factors is tested by comparison with theoretical structure factors obtained from periodic DFT calculations. The results clearly show that, in the current study, the data collected on high-intensity, high-energy synchrotron sources and very small crystals are superior to data collected at conventional sources, and in fact necessary for a meaningful charge-density study, primarily due to greatly diminished effects of extinction and absorption which are difficult to correct for with sufficient accuracy.

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