scholarly journals Structural Characterization and Comparison of Monovalent Cation-Exchanged Zeolite-W

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3684
Author(s):  
Donghoon Seoung ◽  
Hyeonsu Kim ◽  
Pyosang Kim ◽  
Chihyun Song ◽  
Suhyeong Lee ◽  
...  
Keyword(s):  
Volume Expansion ◽  
Structural Changes ◽  
Monovalent Cation ◽  
Water Molecules ◽  
Channel Opening ◽  
Group A ◽  
Framework Species ◽  
Cation Size ◽  
Cell Volumes ◽  
Channel Unit

We report comparative structural changes of potassium-contained zeolite-W (K-MER, structural analogue of natural zeolite merlinoite) and monovalent extra-framework cation (EFC)-exchanged M-MERs (M = Li+, Na+, Ag+, and Rb+). High-resolution synchrotron X-ray powder diffraction study precisely determines that crystal symmetry of MERs is tetragonal (I4/mmm). Rietveld refinement results reveal that frameworks of all MERs are geometrically composed of disordered Al/Si tetrahedra, bridged by linkage oxygen atoms. We observe a structural relationship between a group of Li-, Na-, and Ag-MER and the group of K- and Rb-MER by EFC radius and position of M(1) site inside double 8-membered ring unit (d8r). In the former group, a-axes decrease reciprocally, c-axes gradually extend by EFC size, and M(1) cations are located at the middle of the d8r. In the latter group, a- and c-axes lengths become longer and shorter, respectively, than axes of the former group, and these axial changes come from middle-to-edge migration of M(1) cations inside the d8r channel. Unit cell volumes of the Na-, Ag-, and K-MER are ca. 2005 Å3, and the volume expansion in the MER series is limited by EFC size, the number of water molecules, and the distribution of extra-framework species inside the MER channel. EFC sites of M(1) and M(2) show disordered and ordered distribution in the former group, and all EFC sites change to disordered distribution after migration of the M(1) site in the latter group. The amount of water molecules and porosities are inversely proportional to EFC size due to the limitation of volume expansion of MERs. The channel opening area of a pau composite building unit and the amount of water molecules are universally related as a function of cation size because water molecules are mainly distributed inside a pau channel.

Application of stereological analysis of cell volume to isolated myocytes in culture with and without adrenergic innervation

1990 ◽  
Vol 48 (3) ◽  
pp. 416-417
Author(s):  
Jane K. Rosenthal ◽  
Dianne L. Atkins ◽  
William J. Marvin ◽  
Penny A. Krumm
Keyword(s):  
Cardiac Myocytes ◽  
Structural Changes ◽  
Three Dimensional ◽  
Adrenergic Innervation ◽  
Culture Cell ◽  
Serial Sections ◽  
Newborn Rats ◽  
Primary Culture Cell ◽  
Biological Studies ◽  
Cell Volumes

To comprehend structural changes in cardiac myocytes accompanying adrenergic innervation, it is essential that a three dimensional analysis be performed. To date, biological studies which utilize stereological methods have been limited to cells in tissue and in organs. Our laboratory has utilized current stereological techniques for measuring absolute volumes of individual myocytes in primary culture. Cell volumes are calculated for two distinct groups of cells at 96 hours in culture: isolated myocytes and myocytes innervated with adrenergic neurons (Figure 1).Cardiac myocytes are cultured from the ventricular apices of newborn rats. Cells are plated directly onto tissue culture dishes with or without preplated explants from the paravertebral thoracolumbar sympathetic chain. On day four cultures are photographed and marked for one-to-one cell location. Following conventional fixation and embeddment in eponate-12, the cells are relocated and mounted for microtomy. The cells are completely sectioned at 120nm in their parallel orientation to the surface of the dish (Figure 2). Serial sections are collected on formvar coated slotted grids and are recorded in sequence.

An ensemble view of thrombin allostery

2012 ◽  
Vol 393 (9) ◽  
pp. 889-898 ◽  
Author(s):  
Bernhard C. Lechtenberg ◽  
Stefan M.V. Freund ◽  
James A. Huntington
Keyword(s):  
Structural Changes ◽  
Allosteric Regulation ◽  
Monovalent Cation ◽  
Coagulation Cascade ◽  
General View ◽  
Multiple Substrates ◽  
Dynamic View ◽  
Static View ◽  
Two State Model ◽  
The Continuum

Abstract Thrombin is the central protease of the coagulation cascade. Its activity is tightly regulated to ensure rapid blood clotting while preventing uncontrolled thrombosis. Thrombin interacts with multiple substrates and cofactors and is critically involved in both pro- and anticoagulant pathways of the coagulation network. Its allosteric regulation, especially by the monovalent cation Na+, has been the focus of research for more than 30 years. It is believed that thrombin can adopt an anticoagulant (‘slow’) conformation and, after Na+ binding, a structurally distinct procoagulant (‘fast’) state. In the past few years, however, the general view of allostery has evolved from one of rigid structural changes towards thermodynamic ensembles of conformational states. With this background, the view of the allosteric regulation of thrombin has also changed. The static view of the two-state model has been dismissed in favor of a more dynamic view of thrombin allostery. Herein, we review recent data that demonstrate that apo-thrombin is zymogen-like and exists as an ensemble of conformations. Furthermore, we describe how ligand binding to thrombin allosterically stabilizes conformations on the continuum from zymogen to protease.

scholarly journals The Water Management Regime in Western Iran: A Retrospective Analysis through a Hybrid Transitions Framework

2021 ◽  
Vol 13 (6) ◽  
pp. 3323
Author(s):  
Nishtman Karimi ◽  
Hossein Azadi ◽  
Kobe Boussauw
Keyword(s):  
Water Management ◽  
Retrospective Analysis ◽  
Structural Changes ◽  
Institutional Arrangements ◽  
Surface Water Management ◽  
Management Regime ◽  
Transition Pathways ◽  
Single Transition ◽  
Group A

Continuously changing conditions of sociotechnical systems are the basis of structural changes in communities. Relationships between transition contexts and regime transformation processes and their driving factors in sociotechnical regimes are poorly understood. Moreover, not all changes in multilevel governance regimes are geared towards sustainability, as demonstrated by the case of the water management regime in Sanandaj county in the west of Iran between 1962 and 2018. The current study shows how the management regime of water resources in the case study has changed over time and identifies the institutional arrangements through a retrospective analysis. The analysis is based on three stages of data collection which included a discussion group, a Delphi survey, and a focus group survey among various types of stakeholders. The “Hybrid Transitions” framework is introduced in order to denote processes of regime change that take place in a range of different transition contexts. The findings do not identify a single transition pathway but show that a number of parallel transition pathways have occurred in the context of groundwater and surface water management and their respective institutional arrangements. The study provides a better understanding of the complexity of transition pathways that were devised at the management regime level.

scholarly journals Origin of the enhanced structural and reorientational relaxation rates in the presence of relatively weak dc electric fields

2004 ◽  
Vol 76 (1) ◽  
pp. 215-221 ◽  
Author(s):  
A. Vegiri
Keyword(s):  
Molecular Dynamics ◽  
Electric Field ◽  
Electric Fields ◽  
Structural Relaxation ◽  
Structural Changes ◽  
Common Mechanism ◽  
Weak Electric Field ◽  
Water Molecules ◽  
Relaxation Rates ◽  
Dynamics Simulations

The origin of the dramatic increase of the reorientational and structural relaxation rates of single water molecules in clusters of size N = 16, 32, and 64 at T = 200 K, under the influence of an external, relatively weak electric field (~0.5 107 V/cm) is examined through molecular dynamics simulations. The observed effect is attributed not to any profound structural changes, but to the increase of the size of the molecular cage. The response of water to an electric field in this range shows many similarities with the dynamics of water under low pressure. By referring to simulations and experiments from the literature, we show that in both cases the observed effects are dictated by a common mechanism.

Fractionation of Hydrogen Isotopes in Aqueous Lithium Chloride Solutions

1988 ◽  
Vol 43 (5) ◽  
pp. 449-453 ◽  
Author(s):  
Masahisa Kakiuchi
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effect ◽  
Lithium Chloride ◽  
Structural Changes ◽  
Platinum Catalyst ◽  
Pure Water ◽  
Free Water ◽  
Hydrogen Gas ◽  
Water Molecules ◽  
Chloride Solutions

The D/H ratio of hydrogen gas in equilibrium with water vapor over aqueous lithium chloride solutions was measured at 25 °C, using a hydrophobic platinum catalyst. Experimental details are described. The hydrogen isotope effect between the solution and pure water depends linearly on the LiCl concentration up to ca. 12 m, and at higher concentrations a marked deviation from linearity takes place, as was also observed for the oxygen isotope effect measured by Bopp et al. On the basis of these hydrogen and oxygen isotope effects it is concluded that H218O is enriched in the water molecules coordinated to Li+ ions and HD16O is enriched in the free water molecules of the solution. The observed deviation from linearity for concentrations higher than ca. 12m is interpreted in terms of structural changes in the hydration sphere of the Li+ ions.

Expression of Cytokeratins 7 and 20 in Helicobacter pylori-associated Chronic Gastritis in Children

2004 ◽  
Vol 7 (2) ◽  
pp. 180-186 ◽  
Author(s):  
M. Cohen ◽  
E. Cueto Rúa ◽  
N. Balcarce ◽  
R. Drut
Keyword(s):  
Helicobacter Pylori ◽  
Chronic Gastritis ◽  
Structural Changes ◽  
Periodic Acid ◽  
Gastric Epithelium ◽  
Surface Epithelium ◽  
Ki 67 ◽  
Periodic Acid Schiff ◽  
Group A ◽  
H Pylori

Helicobacter pylori gastric infection induces structural changes in the gastric epithelium. Among them, variations in the expression of cytokeratins have been reported in adult patients. In the present study, we describe the expression of CK7 and CK20 in gastric samples taken from the antrum in three groups of pediatric patients: (A) Helicobacter pylori-associated chronic gastritis (mean age: 11.4 years); (B) previous H. pylori chronic gastritis patients (mean age: 9.4 years); and (C) controls (mean age: 8.8 years). In all, the presence of sulfomucins was assessed with Alcian blue-periodic acid-Schiff pH 1.0. Immunoreactivity was graded as absent (0), weak (1 +), moderate (2+), or intense (3+), in accordance with the intensity of the staining, and its distribution as focal or diffuse. CK7 reactivity was 2 + either focal or diffuse in all group A biopsies. The reactivity was more evident in the cells at the neck of the glands, in the areas with more inflammatory infiltrates, decorating long vertical segments of epithelium. In groups B and C, CK7 reactivity was also focal and 1 + at the cells of the necks of the glands. However, group B presented longer vertical segments of positive cells as compared to group C, and shorter than those of group A. The deeper glandular structures were focally 1 + in both groups. CK20 expression was comparable in all three groups, depicting a 2+ diffuse reactivity at the surface epithelium and interposed pits with absence or focal reactivity at the neck and coiled gland areas. Ki-67 immunostaining paralleled that of the CK7. Staining for sulfated mucosubstances was positive in two of five cases of groups A and B, and in none of the cases of group C. We conclude that: (1) the long segments of CK7-positive glandular necks in H. pylori cases most probably indicate intense regenerative activity during active inflammation; (2) eradication of H. pylori does not warrant ad integrum restitution since long segments of Ki-67+, CK7+ cells at the germinative compartment of the glands (as well as cells with sulfomucins) were still recognizable in ex- H. pylori patients; (3) finally, differing from what happens in adults, children somehow manage to maintain fully differentiated CK20+ superficial epithelium while the H. pylori is in action.

Monovalent Cation Size and DNA Conformational Stability

Biochemistry ◽  
2011 ◽  
Vol 50 (15) ◽  
pp. 3084-3094 ◽  
Author(s):  
Earle Stellwagen ◽  
Joseph M. Muse ◽  
Nancy C. Stellwagen
Keyword(s):  
Conformational Stability ◽  
Monovalent Cation ◽  
Cation Size

scholarly journals Hydrogen bonding changes of internal water molecules in rhodopsin during metarhodopsin I and metarhodopsin II formation

1998 ◽  
Vol 329 (3) ◽  
pp. 713-717 ◽  
Author(s):  
Parshuram RATH ◽  
Frank DELANGE ◽  
J. Willem DEGRIP ◽  
J. Kenneth ROTHSCHILD
Keyword(s):  
Hydrogen Bonding ◽  
Conformational Changes ◽  
Structural Changes ◽  
Integral Membrane Protein ◽  
Water Molecules ◽  
Rod Outer Segments ◽  
Oh Groups ◽  
Protein Conformational Changes ◽  
Hydrogen Deuterium ◽  
Fourier Transform Ir

Rhodopsin is a 7-helix, integral membrane protein found in the rod outer segments, which serves as the light receptor in vision. Light absorption by the retinylidene chromophore of rhodopsin triggers an 11-cis → all-trans isomerization, followed by a series of protein conformational changes, which culminate in the binding and activation of the G-protein transducin by the metarhodopsin II (Meta II) intermediate. Fourier transform IR difference spectroscopy has been used to investigate the structural changes that water, as well as other OH- and NH-containing groups, undergo during the formation of the metarhodopsin I (Meta I) and Meta II intermediates. Bands associated with the OH stretch modes of water are identified by characteristic downshifts upon substitution of H218O for H2O. Compared with earlier work, several negative bands associated with water molecules in unphotolysed rhodopsin were detected, which shift to lower frequencies upon formation of the Meta I and Meta II intermediates. These data indicate that at least one water molecule undergoes an increase in hydrogen bonding upon formation of the Meta I intermediate, while at least one other increases its hydrogen bonding during Meta II formation. Amino acid residue Asp-83, which undergoes a change in its hydrogen bonding during Meta II formation, does not appear to interact with any of the structurally active water molecules. Several NH and/or OH groups, which are inaccessible to hydrogen/deuterium exchange, also undergo alterations during Meta I and Meta II formation.

Structural changes of water molecules during photoelectrochemical water oxidation on TiO2 thin film electrodes

2018 ◽  
Vol 20 (5) ◽  
pp. 3388-3394 ◽  
Author(s):  
Chandana Sampath Kumara Ranasinghe ◽  
Akira Yamakata
Keyword(s):  
Thin Film ◽  
Hydrogen Bonding ◽  
Water Oxidation ◽  
Structural Changes ◽  
Tio2 Thin Film ◽  
Water Molecules ◽  
Hydrogen Bonding Networks ◽  
Thin Film Electrodes ◽  
Photoelectrochemical Water Oxidation

Hydrogen bonding networks at the water/TiO2 interface were heavily disrupted and an isolated OH band appeared during photoelectrochemical water oxidation.

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