Chemical reasonableness in Rietveld analysis; organics

2007 ◽  
Vol 22 (1) ◽  
pp. 74-82 ◽  
Author(s):  
James A. Kaduk
Keyword(s):  
Rietveld Refinement ◽  
Normal Values ◽  
Solution Process ◽  
Molecular Geometry ◽  
Rietveld Analysis ◽  
Rigid Bodies ◽  
Torsion Angles ◽  
Structure Solution ◽  
Calcium Tartrate

We know a lot about normal values of bond distances, bond angles, torsion angles, and other molecular parameters. This knowledge can be incorporated into the structure solution process and into Rietveld refinement through the use of restraints and rigid bodies. An important measure of the quality of the refined model is the chemical reasonableness of molecular geometry. Refinement of the structures of calcium tartrate tetrahydrate and guaifenesin is used to illustrate the importance of chemical reasonableness in determining the quality of a Rietveld refinement.

Chemical reasonableness in Rietveld analysis: Inorganics

2007 ◽  
Vol 22 (3) ◽  
pp. 268-278 ◽  
Author(s):  
James A. Kaduk
Keyword(s):  
Hydrogen Bonding ◽  
Rietveld Refinement ◽  
Rietveld Analysis ◽  
Structural Features ◽  
Rigid Bodies ◽  
Approximate Symmetry ◽  
Hydrogen Bonding Pattern ◽  
Normal Ranges ◽  
Chemical Knowledge

Besides statistical and graphical measures, many structural features can be used to assess the quality of a Rietveld refinement. These include the metric symmetry of the lattice (which can assist in determining the true symmetry and in identifying isostructural compounds), bond distances and angles (which should fall within normal ranges), displacement coefficients, refined stoichiometry, the absolute values of the standard uncertainties of the fractional coordinates, the hydrogen bonding pattern, the presence of approximate symmetry, the presence of unindexed peaks in the pattern, and whether the refinement converges at all. Chemical knowledge can be built into a Rietveld refinement though the use of restraints and rigid bodies. A knowledge of chemical reasonableness proved important in refining the correct structures of [Fe(H2O)6](BF4)2, (Ba1.5Sr0.5)TiO4, and (Ba1.25Sr0.75)TiO4.

Automatic structure determination from powder data withEXPO2004

2004 ◽  
Vol 37 (6) ◽  
pp. 1025-1028 ◽  
Author(s):  
Angela Altomare ◽  
Rocco Caliandro ◽  
Mercedes Camalli ◽  
Corrado Cuocci ◽  
Carmelo Giacovazzo ◽  
...  
Keyword(s):  
Structure Factor ◽  
Solution Process ◽  
Direct Methods ◽  
Molecular Geometry ◽  
Supplementary Information ◽  
Structure Model ◽  
Graphical Interface ◽  
Automatic Structure ◽  
Structure Solution

EXPO2004is the updated version of theEXPOprogram [Altomareet al.(1999).J. Appl. Cryst.32, 339–340]. The traditional steps of theab initiopowder solution process are performed automatically: indexing, space-group determination, decomposition of the pattern for extracting the observed structure-factor moduli, structure solution by direct methods, model refinement by Rietveld technique. Special strategies may be applied to improve both the estimates of the extracted structure-factor moduli and the quality of the structure model. In addition, the use of special procedures exploiting available supplementary information on molecular geometry can be successfully adopted. The graphical interface has also been improved.

EXPO: a program for full powder pattern decomposition and crystal structure solution

1999 ◽  
Vol 32 (2) ◽  
pp. 339-340 ◽  
Author(s):  
Angela Altomare ◽  
Maria Cristina Burla ◽  
Mercedes Camalli ◽  
Benedetta Carrozzini ◽  
Giovanni Luca Cascarano ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Crystal Structures ◽  
Rietveld Refinement ◽  
Prior Information ◽  
Solution Process ◽  
Powder Pattern ◽  
Pattern Decomposition ◽  
Structure Solution

EXPOis the integration of two programs,EXTRAandSIRPOW.92, the first devoted to full powder pattern decomposition and the second to the solution and refinement of crystal structures. The program is able to exploit the prior information obtained during the crystal structure solution process for improving the classical decomposition.EXPOalso allows preliminary cycles of Rietveld refinement.

scholarly journals The Rietveld Refinement in the EXPO Software: A Powerful Tool at the End of the Elaborate Crystal Structure Solution Pathway

Crystals ◽  
2018 ◽  
Vol 8 (5) ◽  
pp. 203 ◽  
Author(s):  
Angela Altomare ◽  
Francesco Capitelli ◽  
Nicola Corriero ◽  
Corrado Cuocci ◽  
Aurelia Falcicchio ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Rietveld Refinement ◽  
Structure Solution

scholarly journals In situ proteolysis of an N-terminal His tag with thrombin improves the diffraction quality of human aldo-keto reductase 1C3 crystals

2018 ◽  
Vol 74 (5) ◽  
pp. 300-306 ◽  
Author(s):  
Jovana J. Plavša ◽  
Pavlína Řezáčová ◽  
Michael Kugler ◽  
Petr Pachl ◽  
Jiří Brynda ◽  
...  
Keyword(s):  
High Resolution ◽  
Enzyme Inhibitor ◽  
Structural Studies ◽  
Potential Therapeutic Target ◽  
Thrombin Cleavage ◽  
His Tag ◽  
Structure Solution ◽  
Biotransformation Of Xenobiotics

Human aldo-keto reductase 1C3 (AKR1C3) stereospecifically reduces steroids and prostaglandins and is involved in the biotransformation of xenobiotics. Its role in various cancers makes it a potential therapeutic target for the development of inhibitors. Recombinant AKR1C3 with a thrombin-cleavable N-terminal His6 tag was expressed from a pET-28(+) vector for structural studies of enzyme–inhibitor complexes. A modified in situ proteolysis approach was applied to specifically remove the His tag by thrombin cleavage during crystallization screening trials. This improved the morphology and diffraction quality of the crystals and allowed the acquisition of high-resolution diffraction data and structure solution. This approach may be generally applicable to other proteins expressed using the pET-28(+) vector.

scholarly journals Improving the Performance of Metaheuristics: An Approach Combining Response Surface Methodology and Racing Algorithms

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Eduardo Batista de Moraes Barbosa ◽  
Edson Luiz França Senne ◽  
Messias Borges Silva
Keyword(s):  
Optimization Problems ◽  
Great Influence ◽  
Solution Process ◽  
Fine Tuning ◽  
Quality Of Results ◽  
Process Understanding ◽  
Tuning Process ◽  
Research Challenge ◽  
Best Fit

The setup of heuristics and metaheuristics, that is, the fine-tuning of their parameters, exercises a great influence in both the solution process, and in the quality of results of optimization problems. The search for the best fit of these algorithms is an important task and a major research challenge in the field of metaheuristics. The fine-tuning process requires a robust statistical approach, in order to aid in the process understanding and also in the effective settings, as well as an efficient algorithm which can summarize the search process. This paper aims to present an approach combining design of experiments (DOE) techniques and racing algorithms to improve the performance of different algorithms to solve classical optimization problems. The results comparison considering the default metaheuristics and ones using the settings suggested by the fine-tuning procedure will be presented. Broadly, the statistical results suggest that the fine-tuning process improves the quality of solutions for different instances of the studied problems. Therefore, by means of this study it can be concluded that the use of DOE techniques combined with racing algorithms may be a promising and powerful tool to assist in the investigation, and in the fine-tuning of different algorithms. However, additional studies must be conducted to verify the effectiveness of the proposed methodology.

scholarly journals The Hygienic Quality of Raw Romanian Goat Milk Depending on the Milking Season

2018 ◽  
Vol 75 (1) ◽  
pp. 50
Author(s):  
Zorica VOŞGAN ◽  
Lucia MIHALESCU ◽  
Stela JELEA ◽  
Anca DUMUŢA ◽  
Flavia POP
Keyword(s):  
Normal Values ◽  
Bacterial Load ◽  
Goat Milk ◽  
Microbiological Analysis ◽  
Lactation Period ◽  
Milk Samples ◽  
Goat Farm ◽  
Number Of Microorganisms ◽  
Production Period

The milk samples were yielded by manual milking from a goat farm that was maintained in extensive system, at monthly intervals during the production period (spring, summer, autumn). Goat milk from a traditional stall in the Maramures County, depending on the lactation period and the season has been analyzed in this study. The milk samples were collected aseptically and transported in laboratory for microbiological analysis. During springtime, when milking is done three times a day, and the amount of milk is higher, the total number of germs is 77.8×103 CFU/ml. A smaller number compared to the number of microorganisms recorded in the summer (97.3×103 CFU/ml) when milking is done twice a day and there are higher temperatures. During autumn, in the conditions of low milk production, at the end of the lactation period and when the samples are harvested only once a day, the number of microorganisms was 81.5×103 CFU /ml. Somatic cells from milk indicating an excess of the normal values especially towards the end of the lactation period. Particular attention should be paid to hygiene conditions when handling milk, to improve its quality. Thus, goat milk has a higher bacterial load (SPC) during summer, and SCC exceeds the recommended limits, especially in the autumn.

Well-controlled silver nanowire/graphene hybrid from full solution process

2016 ◽  
Vol 51 (8) ◽  
pp. 1149-1154 ◽  
Author(s):  
Jeong Eon Park ◽  
Dong Hack Suh
Keyword(s):  
Mass Production ◽  
Silver Nanowires ◽  
Solution Process ◽  
Silver Nanowire ◽  
Ultrasonic Power ◽  
Two Dimensional ◽  
One Dimensional ◽  
Conductive Materials ◽  
Full Solution

The surface of a one-dimensional silver nanowire was covered with amphiphilic materials, N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide, and patched with two-dimensional graphene to form individually controlled hybrid. Graphene was prepared from ultrasonic in o-dichlorobenzene without any additives. As N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide between silver nanowires and graphene tightly held each other, silver nanowire was individually covered with graphene without introducing ultrasonic power, the necessary process to evenly mix silver nanowires and graphene but lead to damage and oxidize silver nanowires. Although the quality of graphene was inferior, the properties of hybrid were superior compared with pristine silver nanowire/graphene except introducing N-(2-aminoethyl)-3a-hydroxy-5b-cholan-24-amide. All processes to form the hybrid were carried out in solution. Therefore, this makes the processes less expensive and more useful and opens up opportunities for the mass production for conductive materials.

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