244 research outputs found
Comparative experimental electron density and electron localization function study of thymidine based on 20 K X-ray diffraction data
No full textFrom a high-resolution X-ray data set (sin theta/lambda = 1.1 A(-1)) measured at 20 K the electron-density distribution of the nucleoside thymidine was derived by a classical multipole refinement and by application of the invariom formalism. Owing to the presence of the heteroaromatic thymine ring system two invariom models were compared which considered the nearest and next-nearest neighbors for the invariom assignments. Differences between the two invariom models were small for the bond topological and atomic properties - about five times smaller than differences with the classical multipole refinement. Even the latter differences are in the uncertainty ranges which are commonly observed in experimental charge-density work and were found in molecular regions involved in intermolecular contacts. The application of the constrained wavefunction-fitting approach allowed the electron localization function (ELF) to be obtained from the experimental X-ray data, which was graphically represented and topologically analyzed. ELF basin populations were derived from experiment for the first time. The electron populations in the disynaptic valence basins were related quantitatively to bond orders
The Salience of Hegemonic Masculinity
No full textThis article argues that the concept of “hegemonic masculinity” remains highly salient to critical masculinities studies. The author outlines Raewyn Connell\u27s initial formulation of the concept, how that initial model of hegemonic masculinity has been historically misinterpreted, the reformulation of the concept by Connell and Messerschmidt, and the recent scholarly amplification of the concept. The author concludes that Connell’s original emphasis on the legitimation of unequal gender relations remains essential to both the concept and to the field of critical masculinities studies
Charge Density Analysis of Opioids: A Comparative Study
No full textThe electron densities of five morphine related molecules (codeine, diprenorphine, naltrexone in the neutral and protonated states, and dextromethorphan) were determined from high-resolution X-ray diffraction experiments (Mo K alpha and synchrotron primary radiation) at low temperature and CCD area detection techniques. Bond topological analyses were applied, and a partitioning of the molecules into atomic regions making use of Bader's zero flux surfaces yielded atomic volumes and charges. The obtained atom and bonding properties were compared to the results of a previous experimental study of morphine and to theoretical calculations. Experimental and theoretical properties for all chemically equivalent bonds agree within an uncertainty range as is otherwise seen for different theoretical calculations. Hence, the transferability of chemically equivalent submolecular properties, being a key issue of the atoms in molecules (AIM) theory, has been verified experimentally in this class of chemically related molecules. On the other hand, topological differences could clearly be verified in regions with different chemical environments. Electron density differences between the two forms of naltrexone were examined and made visible in an extendend region around the nitrogen atom which is once in a neutral state and once in a positively charged state
Charge-density study on cyclosporine A
No full textTwo single-crystal X-ray diffraction data sets of cyclosporine A were measured to high resolution using synchrotron radiation at temperatures of 5 and 90 K. They allowed an accurate determination of its molecular and electronic structure. Three electron-density models based on pseudo-atom scattering factors were compared in terms of derived bond topological properties and in terms of electron-density differences on a grid. In one model multipole parameters were freely refined, whereas in the other two models the density was built up from fixed database parameters from the invariom database and University at Buffalo Databank. The data quality not only allowed benchmarking of the quality of both databases with the refined density, but also judgement of the feasibility of a multipole refinement of a larger oligopeptide structure such as cyclosporine A. Both databases performed equally well and reproduced the experimentally determined charge density satisfactorily.Deutsche Forschungsgemeinschaft DFG [921/3-1]; Commonwealth of Australi
Binding and Reduction of Sulfite by Cytochrome c Nitrite Reductase
No full textPentaheme cytochrome c nitrite reductase (ccNiR) catalyzes the six-electron reduction of nitrite to ammonia as the final step in the dissimilatory pathway of nitrate ammonification. It has also been shown to reduce sulfite to sulfide, thus forming the only known link between the biogeochemical cycles of nitrogen and of sulfur. We have found the sulfite reductase activity of ccNiR from Wolinella succinogenes to be significantly smaller than its nitrite reductase activity but still several times higher than the one described for dissimilatory, siroheme-containing sulfite reductases. To compare the sulfite reductase activity of ccNiR with our previous data on nitrite reduction, we determined the binding mode of sulfite to the catalytic heme center of ccNiR from W. succinogenes at a resolution of 1.7 A. Sulfite and nitrite both provide a pair of electrons to form the coordinative bond to the Fe(III) active site of the enzyme, and the oxygen atoms of sulfite are found to interact with the three active site protein residues conserved within the enzyme family. Furthermore, we have characterized the active site variant Y218F of ccNiR that exhibited an almost complete loss of nitrite reductase activity, while sulfite reduction remained unaffected. These data provide a first direct insight into the role of the first sphere of protein ligands at the active site in ccNiR catalysis
BIOPHYSICAL CONTROLS OF MARSH SOIL SHEAR STRENGTH ALONG AN ESTUARINE SALINITY GRADIENT
No full text© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gillen, M. N., Messerschmidt, T. C., & Kirwan, M. L. Biophysical controls of marsh soil shear strength along an estuarine salinity gradient. Earth Surface Dynamics, 9(3),(2021): 413-421, https://doi.org/10.5194/esurf-9-413-2021.Sea-level rise, saltwater intrusion, and wave erosion threaten coastal marshes, but the influence of salinity on marsh erodibility remains poorly understood. We measured the shear strength of marsh soils along a salinity and biodiversity gradient in the York River estuary in Virginia to assess the direct and indirect impacts of salinity on potential marsh erodibility. We found that soil shear strength was higher in monospecific salt marshes (5–36 kPa) than in biodiverse freshwater marshes (4–8 kPa), likely driven by differences in belowground biomass. However, we also found that shear strength at the marsh edge was controlled by sediment characteristics, rather than vegetation or salinity, suggesting that inherent relationships may be obscured in more dynamic environments. Our results indicate that York River freshwater marsh soils are weaker than salt marsh soils, and suggest that salinization of these freshwater marshes may lead to simultaneous losses in biodiversity and erodibility.This research has been supported by the US National Science Foundation (grant nos. 1654374, 1426981, 1529245, and 1832221)
The relationship between parental alcoholism and the emotional coping of their adult children, 1990
No full textThe overall objective of this study was to examine the relationship between alcoholic parents and the emotional coping of their adult children. To attain this objective, theoretical perspectives were addressed in reference to: (a) alcoholism and the dynamics of the alcoholic family, (b) the family roles and rules, (c) characteristics of children reared in an alcoholic family, (d) the implications of these characteristics, and (e) clinical observations of the characteristics of adult children of alcoholics (ACOA's). A correlational research design was used. A descriptive questionnaire, adapted from Woititz (1983) and found to be reliable and valid in identifying personality characteristics among ACOA's, was administered to thirty-two individuals who were identified as ACOA's. The sample was selected from two adult children of alcoholics support groups in Atlanta, Georgia. The study hypothesized that there is no statistical significant relationship between parental alcoholism and the emotional coping of their adult children. With reference to those (84.7%) who identified their father as alcoholic and their emotional coping in adulthood, the contingency table. 2 analysis showed: x = .01678, d.f = 1, and P .05. The null hypothesis was accepted. This study has ramifications for social work professionals to further ascertain the impact that alcoholism has on the family system. Social work literature is limited, especially related to adult children of alcoholics. This study will therefore present as a resource in enhancing the social work literature
Segmented flow generator for serial crystallography at the European X-ray free electron laser
No full textAbstract Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFELs) allows structure determination of membrane proteins and time-resolved crystallography. Common liquid sample delivery continuously jets the protein crystal suspension into the path of the XFEL, wasting a vast amount of sample due to the pulsed nature of all current XFEL sources. The European XFEL (EuXFEL) delivers femtosecond (fs) X-ray pulses in trains spaced 100 ms apart whereas pulses within trains are currently separated by 889 ns. Therefore, continuous sample delivery via fast jets wastes >99% of sample. Here, we introduce a microfluidic device delivering crystal laden droplets segmented with an immiscible oil reducing sample waste and demonstrate droplet injection at the EuXFEL compatible with high pressure liquid delivery of an SFX experiment. While achieving ~60% reduction in sample waste, we determine the structure of the enzyme 3-deoxy-D- manno -octulosonate-8-phosphate synthase from microcrystals delivered in droplets revealing distinct structural features not previously reported.National Science Foundation https://doi.org/10.13039/100000001U.S. Department of Health & Human Services | National Institutes of Health https://doi.org/10.13039/100000002Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Results of experimental electron density determinations of Strychnine, a [1.1.1]-Propellane-Derivative, Adenosinemonophosphate and a Zinc-Dithiolate
No full textTitel und Inhalt
IGrundlagen1
1 Einleitung und Aufgabenstellung 3
2 Röntgenstrukturanalyse 5
2.1Deformationselektronendichte 8
2.2Multipolmodell 9
3 Quantenchemische Rechnungen 11
3.1Berechnungen für isolierte Moleküle 11
3.2Berechnungen für periodische Systeme 13
4 Interpretation der Gesamtelektronendichte 15
4.1Topologische Analyse der Elektronendichte 15
4.2Gradientenvektorfeld 16
4.3Kritische Punkte 17
4.4Laplacefunktion 18
4.5Bindungselliptizität 18
4.6Darstellungsmöglichkeiten 19
IIExperimenteller Aufbau 21
5 Motivation 23
6 Tieftemperaturmeßplatz 25
6.1Aufbau 25
6.2Kryostat mit neu entwickeltem Kaptonzylinder 25
6.3Meßstrategien und erreichbare Auflösung 28
IIIExperimentelle Elektronendichtebestimmungen 31
7 Strychnin - Ein Vergleich von vier Datensätzen 33
7.1Multipolverfeinerung 36
7.2Restdichte 37
7.3Deformationsdichte 38
7.4Laplacefunktion von Strychnin 38
7.5Topologische Eigenschaften 40
7.6Elektrostatisches Potential 42
7.7Diskussion 44
8 Ein [1.1.1]-Propellan-Derivat 45
8.1Kristallstruktur 46
8.2Multipolverfeinerung und Restdichte 47
8.3Theoretische Rechnungen 48
8.4Deformationsdichte und Laplacefunktion 48
8.5Topologische und atomare Eigenschaften 50
8.6Diskussion 50
9 Adenosinmonophosphat 51
9.1Kristallstruktur 51
9.2Multipolmodell 53
9.3Theoretische Rechnungen 55
9.4Deformationsdichte 55
9.5Topologische Analyse 56
9.6Diskussion 59
10. Ein zweikerniger Zink-Dithiolat-Komplex 61
10.1Kristallstruktur 62
10.2Multipolverfeinerung und Deformationsdichte 65
10.3Theoretische Rechnungen 67
10.4Topologische Eigenschaften 68
10.5Diskussion 69
Zusammenfassung 71
Summary 73
Literaturverzeichnis 75
Publikationen 78
LebenslaufEs wurde ein bestehender Tieftemperaturmeßplatz durch einen CCD-
Flächendetektor erweitert. Damit sind nun Elektronendichtebestimmungen bei
Temperaturen bis zu 20K innerhalb von einer Woche möglich, wobei hervorragende
Kristallqualität Voraussetzung ist. Es wurde ein Huber 4-Kreis Goniometer mit
einem geschlossenen Helium Kryostaten der Firma APD verwendet. Der Ausbau mit
einem Bruker-Apex Detektor war mit Mitteln der DFG möglich. Damit verbunden
war auch eine neue Steuerung des Goniometers, die nun komplett über die
Bruker-Software möglich ist. Mit dem vorher verwendeten Beryllium Zylinder war
die erreichbare Datenqualität nicht zufriedenstellen, da dieser stark
strukturierte Streustrahlung erzeugt. Um die für die
Elektronendichtebestimmung nötige Datenqualität zu erreichen, wurde am Beginn
des Umbaus ein Kapton-Vakuumzylinder neu entwickelt. Dieser Zylinder besteht
nur aus 0.125 mm dicker Kaptonfolie. Damit war eine deutliche Reduzierung des
Untergrundes möglich. Vor allem ist die Streustrahlung von Kapton-Folie kaum
strukturiert. Bisher wurde der Meßplatz ausschließlich mit Mo-Kα-Strahlung für
Elektronendichtebestimmungen benutzt. Prinzipiell wäre auch eine Verwendung
von Ag-Strahlung möglich, was aber aufgrund der geringeren Intensität
problematisch ist. Es wird ein Graphit Monochromator verwendet. Zur Steigerung
der Primärstrahlintensität wurde vor kurzem ein fokussierender Kollimator der
Firma XOS installiert. Im Rahmen der vorliegenden Arbeit wurden die
Elektronendichten von Strychnin, einem [1.1.1]-Propellan-Derivat,
Adenosinmonophosphat und einem Dithiolat-Zink-Kom-plex experimentell bestimmt.
Die vergleichende Studie an Strychnin zeigt, daß mit vier verschiedenen
Messungen an unterschiedlichen Geräten sehr gut reproduzierbare
Elektronendichten erhalten werden können. Ein Vergleich zeigt eine geringe
Abweichung zwischen Experiment und theoretischen Rechnungen. An einem [1.1.1
]-Propellan-Derivat konnte die experimentelle Elektronendichte nur mit Hilfe
von Synchrotronstrahlung bei 100 K bestimmt werden. Es konnten alle Bindungen
dieses hochgespannten Systems charakterisiert werden. Zwischen den
Brückenkopftatomen wurde eine Bindung gefunden, was die Formulierung eines
invertierten Kohlenstoffatoms rechtfertig. Diese Bindung wurde schon länger
durch theoretische Rechnungen vorhergesagt, konnte hier aber erstmals
experimentell näher charakterisiert werden. Die Elektronendichtebestimmung an
Adenosinmonophosphat zeigt Probleme des Multipolmodells für Phosphoratome auf.
Im Vergleich mit einer 100 K Messung scheint hier eine niedrigere Temperatur
um 25 K für änderungen am Modell von großem Vorteil zu sein. Es konnte nur für
die Messung bei 25 K und bei Verwendung eines modifizierten Modells eine
brauchbare übereinstimmung mit theoretischen Rechnungen erreicht werden. Die
Modellierung von Phosphoratomen ist aber weiterhin problematisch und weitere
Verbesserungen wären hilfreich. In der Verfeinerung des Dithiolat-Zink-
Komplexes konnten erfolgreich von Dr. Kloosters aus einem Neutronenexperiment
erhaltene Wasserstoffparameter verwendet werden. Das Zinkatom zeigt eine
bemerkenswerte Deformation der 3d und 4s Schale, die nicht in einfacher Weise
mit der Koordinationsgeometrie zu erklären ist. Außerdem wurde eine
Strukturierung der Deformation beobachtet, die über die Möglichkeiten des
vorhandenen Multipolmodells hinausgeht. In den vergangenen zwei Jahren wurden
Messungen zur experimentellen Elektronendichtebestimmung mit dem neu
entwickeltem Meßplatz von zahlreichen Substanzen durchgeführt. Dabei wurden
mehrere Aminosäure-Formiate, Tripeptide, Opiode, sowie Strychnin, Thymidin,
Adenosinmonophosphat und ein Metallkomplex bei Temperaturen um 20 K gemessen.
Außerdem wurden für DL-Serin hochaufgelöste Messungen bei drei verschiedenen
Temperaturen (298, 100 und 25 K) durchgeführt.An existing low temperature diffractometer was extended with a CCD area
detector. This enables electron density determinations at 20 K within one
weak, if crystals with excellent quality are available. A Huber 4-circle
goniometer equipped with a closed cycle cryostat (APD) was used. The extension
with a Bruker-Apex detector was possible through DFG funding. This required a
new goniometer control, that is now completely included in the Bruker
software. The obtainable data quality was not sufficient with former used
Beryllium cylinder, because of its highly structured scattering. To obtain the
required data quality for electron density determinations, a Kapton vacuum
cylinder was constructed at the beginning of reconstruction. This cylinder is
built by 0.125 mm Kapton film only. This result in strongly reduced
background. In addition Kapton film produces nearly unstructured scattering.
Till now only Mo-Kα radiation was used for electron density determinations. Ag
radiation would also be possible, but is problematic because of the lower
intensity. Graphite is used in the monochromator. To enhance the primary
intensity a focusing collimator from XOS was installed short ago. In scope of
this work the electron densities of Strychnine, a [1.1.1]-Propellane-derivate,
Adenosinmonophosphat and a Dithiolate-Zink-complex were experimentally
evaluated. The comparative study on Strychnine shows, that four different
measurements with different instruments can give well reproducible electron
densities. These measurements show a small deviation to theoretical
calculations. The experimental electron density determination of a [1.1.1
]-Propellane-derivate was only possible at 100 K using synchrotron. All bonds
of this highly strained system could be characterised. A bond between the
bridgehead atoms was located, what justifies the description as an inverted
carbon atom. This bond was predicted by theoretical calculations since a
while, but is characterised in detail experimentally first. The electron
density determination of Adenosinmonophosphat shows problems in the multipol
model for phosphorus atoms. In comparison to a 100 K measurement the lower
temperature of 25 K seems to be of great advantage for changing of the model.
Only the 25 K measurement together with modified models to roughly compares
with theoretical calculations. The modelling of phosphorus atom remains
problematic an further improvement would be helpful. Hydrogen parameters
obtained by a neutron diffraction experiment from Dr. Kloosters could be used
in the refinement of the Dithiolat-Zink-complex. The Zink atom shows a
remarkable deformation of the 3d and 4s shell, that could not be deducted
easily by the coordination geometry. In addition the deformation is structured
in a too complicated way for the available multipolar model. Measurements of
numerous substances were performed in the last two years to determine their
experimental electron densities with the new developed instrument. This
includes some amino acid formiates, Tripeptides, Opiods, as well as
Strychnine, Thymidine, Adenosinmonophosphate and one metal complex at
temperatures around 20 K. In addition DL-Serin was measured at three different
temperatures (298, 100 and 25K)
Produktie van propeen uit 2-buteen en etheen via disproportionering
No full textDocument(en) uit de collectie Chemische Procestechnologie.DelftChemTechApplied Science
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