scholarly journals Cycloadditions in mixed aqueous solvents: the role of the water concentration

2005 ◽  
Vol 18 (8) ◽  
pp. 725-736 ◽  
Author(s):  
Theo Rispens ◽  
Jan B. F. N. Engberts
Keyword(s):  
Water Concentration ◽  
Mixed Aqueous Solvents

scholarly journals Enhanced heterogenous hydration of SO 2 through immobilization of pyridinic-N on carbon materials

2020 ◽  
Vol 7 (8) ◽  
pp. 192248
Author(s):  
Longhua Zou ◽  
Ping Yan ◽  
Peng Lu ◽  
Dongyao Chen ◽  
Wei Chu ◽  
...  
Keyword(s):  
Gas Phase ◽  
Energy Barrier ◽  
Carbon Materials ◽  
Water Concentration ◽  
Flue Gases ◽  
Doped Graphene ◽  
Molecular Dynamics Results ◽  
Pyridinic N ◽  
Pyridinic Nitrogen

Carbon materials doped with nitrogen have long been used for SO 2 removal from flue gases for the benefits of the environment. The role of water is generally regarded as hydration of SO 3 which is formed through the oxidization of SO 2 . However, the hydration of SO 2 , especially on the surface of N-doped carbon materials, was almost ignored. In this study, the hydration of SO 2 was investigated in detail on the pyridinic nitrogen (PyN)-doped graphene (GP) surfaces. It is found that, compared with the homogeneous hydration of SO 2 assisted with NH 3 in gas phase, the heterogeneous hydration is much more thermodynamically and kinetically favourable. Specifically, when a single H 2 O molecule is involved, the energy barrier for SO 2 hydration is as low as 0.15 eV, with 0.59 eV released, indicating the hydration of SO 2 can occur at rather low water concentration and temperature. Thermodynamic integration molecular dynamics results show the feasibility of the hydrogenated substrate recovery and the immobilized N acting as a catalytic site for SO 2 hydration. Our findings show that the heterogeneous hydration of SO 2 should be universal and potentially uncover the puzzling reaction mechanism for SO 2 catalytic oxidation at low temperature by N-doped carbon materials.

Ammonia diffusion through Nalophan™ bags

2013 ◽  
Vol 69 (3) ◽  
pp. 486-494 ◽  
Author(s):  
Selena Sironi ◽  
Lidia Eusebio ◽  
Licinia Dentoni ◽  
Laura Capelli ◽  
Renato Del Rosso
Keyword(s):  
Concentration Gradient ◽  
Diffusion Rate ◽  
Water Concentration ◽  
Ammonia Concentration ◽  
Polymeric Film ◽  
Concentration Gradients ◽  
Storage Times ◽  
Film Interface ◽  
Over Time

The aim of the work is to verify the diffusion rate of ammonia through the Nalophan™ film that constitutes the sampling bag, considering storage times ranging from 1 to 26 h. The ammonia decay over time was evaluated using gas-chromatography for the quantification of ammonia concentration inside the bag. The research assesses the roles of both of ammonia and water concentration gradients at the polymeric film interface on the diffusion process. The results show that both the ammonia concentration gradient and, in a less pronounced way, the water concentration gradient are the main ‘engines’ of ammonia diffusion. Double bags seem to represent a simple solution for preventing ammonia losses during storage. Another interesting result concerns the role of the bag surface on the ammonia diffusion rate: the higher the surface/volume (S/V) ratio, the higher the ammonia diffusion rate through the polymeric film.

scholarly journals Decoding natural astrocyte rhythms: dynamic actin waves result from environmental sensing by primary rodent astrocytes

2021 ◽  
Author(s):  
Kate M. O’Neill ◽  
Emanuela Saracino ◽  
Barbara Barile ◽  
Nicholas J. Mennona ◽  
Maria Grazia Mola ◽  
...  
Keyword(s):  
Water Concentration ◽  
Cell Boundary ◽  
Actin Dynamics ◽  
Substrate Topography ◽  
Actin Cortex ◽  
Extraction Algorithm ◽  
Cytoskeletal Dynamics ◽  
Actin Structure ◽  
Actin Waves

AbstractAstrocytes are key regulators of brain homeostasis, which is essential for proper cognitive function. The role of cytoskeletal dynamics in this critical regulatory process is unknown. Here we find that actin is dynamic in certain subcellular regions, especially near the cell boundary. Our results further indicate that actin dynamics concentrates into “hotspot” regions that selectively respond to certain chemophysical stimuli, specifically the homeostatic challenges of ion or water concentration increases. Substrate topography makes actin dynamics more frequent yet weaker, and it also alters actin network structure. Superresolution images analyzed with a filament extraction algorithm demonstrate that surface topography is associated with a predominant perpendicular alignment of actin filaments near the cell boundary whereas flat substrates result in an actin cortex mainly parallel to the cell boundary. Thus, actin structure and dynamics together integrate information from different aspects of the environment that might steer the operation of neural cell networks.TeaserAstrocytes display dynamic actin that is modulated by combinations of chemophysical stimuli and environmental topographies.

scholarly journals Probing the role of water in protein conformation and function

2004 ◽  
Vol 359 (1448) ◽  
pp. 1277-1285 ◽  
Author(s):  
R. P. Rand
Keyword(s):  
Osmotic Stress ◽  
Small Molecules ◽  
Conformational Change ◽  
Protein Conformation ◽  
Water Concentration ◽  
Molecular Function ◽  
Conceptual Distinction ◽  
Cellular Water ◽  
And Function

Life began in a bath of water and has never escaped it. Cellular function has forced the evolution of many mechanisms ensuring that cellular water concentration has never changed significantly. To free oneself of any conceptual distinction among all small molecules, solutes and solvents, means that experiments to probe water's specific role in molecular function can be designed like any classical chemical reaction. Such an ‘osmotic stress’ strategy will be described in general and for an enzyme, hexokinase. Water behaves like a reactant that competes with glucose in binding to hexokinase, and modulates its conformational change and activity. This ‘osmotic stress’ strategy, now applied to many very different systems, shows that water plays a significant role, energetically, in most macromolecular reactions. It can be required to fill obligatory space, it dominates nearest non–specific interactions between large surfaces, it can be a reactant modulating conformational change; all this in addition to its more commonly perceived static role as an integral part of stereospecific intramolecular structure.

scholarly journals Role of grain boundary diffusion in H-D exchange in mantle xenoliths

2020 ◽  
Author(s):  
Konstantinos Thomaidis ◽  
Jannick Ingrin
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Hydrogen Exchange ◽  
Boundary Diffusion ◽  
Water Concentration ◽  
Grain Boundary Diffusion ◽  
Mantle Xenoliths ◽  
Host Magma ◽  
Oxidation Reduction

<p>Water concentration in pyroxenes from mantle xenoliths is frequently used to trace water content in the lithospheric mantle. We do not understand yet how these pyroxenes can preserve a memory of their deep equilibrium during their transport to the surface. In an attempt to evaluate the role of grain boundaries in the exchange of hydrogen between the pyroxenes of the xenoliths and the host magma, we have launched a program of experiments of H exchange in blocks of mantle xenoliths of centimetre size. The blocks, all from the same xenolith, contain clinopyroxenes, orthopyroxenes and olivine of mm to sub-millimetre size. We present here the results of a series of H-D exchange performed at 600, 700 and 900 <sup>o</sup>C at room pressure in a deuterium enriched gas. OH-OD profiles recorded by micro-infrared spectroscopy in pyroxenes at the edge of the block are only slightly different from the ones recorded in pyroxenes at the centre of the block. These results show that the diffusion/solubility of hydrogen in grain boundaries is fast enough to equilibrate rapidly the grains at the center of the xenoliths. It proves that in nature the δD signature of xenoliths is very likely controlled by the equilibrium with the host magma even in the case of xenoliths with large grain size.</p><p>We will also present preliminary results on the role of grain boundary diffusion in the control of hydrogen exchange involving reactions activated at a higher temperature such as the oxidation-reduction of iron (1/2H<sub>2</sub> + Fe<sup>3+</sup>  =  H<sub>i</sub><sup>+</sup> + Fe<sup>2+</sup>) and the formation/destruction of cation vacancies.</p>

scholarly journals The Contrasting Role of Water and Acid Within Organic Phase Amphiphile Aggregation

2021 ◽  
Author(s):  
Biswajit Sadhu ◽  
Aurora E. Clark
Keyword(s):  
Self Assembly ◽  
Metal Ion ◽  
Water Clusters ◽  
Preferential Solvation ◽  
Water Concentration ◽  
The Self ◽  
Acid Extraction ◽  
Large Water ◽  
The Individual

The self-assembly of amphiphiles is often modified by the presence of co-solutes and significant study has examined this behavior in aqueous systems. Much less is known about the role of polar co-solutes upon amphiphile aggregation within non-polar media, however such conditions are relevant to a variety of industrial processes - not the least of which are separations systems like those found in liquid-liquid extraction (LLE). Therein, surface active amphiphiles extract water, acid, and other solutes of interest. Intriguing increases to amphiphile aggregates have been experimentally observed upon water and acid extraction, however a myriad of competitive intermolecular interactions have thus far prevented a fundamental understanding of the individual and dual role of these solutes upon amphiphile self-assembly. Toward this end, this work employs classical molecular dynamics and graph theory analyses to deconstruct the individual affects of water and nitric acid upon the self-assembly of N,N,N',N'-tetraoctyl-3-oxapentanediamide (TODGA), a prevalent amphiphile extractant used in metal ion separations. In the absence of acid, and at low water concentration, H2O is found to promote local dimer and trimer formation of TODGA, however as [H2O]org increases, the preferential solvation of water with itself causes the formation of large water clusters that serve to link large TODGA clusters on the periphery (causing extended aggregation). Addition of HNO3 to the humid solutions disrupts the water hydrogen bond network and inhibits the formation of large water clusters - thus preventing extended aggregation behavior. We rationalize the prior experimental observations as being attributed primarily to the role of water in the self-assembly of TODGA rather than co-extracted HNO3, thus providing valuable new insight into the means by which extractant aggregation can be tuned within LLE processes. In addition, this work differentiates the role of polar solutes upon amphiphile self-assembly via their individual hydrogen bonding capabilities and competitive interactions that disrupt preferred solvation environments.

The role of hydrogen bond donor and water content on the electrochemical reduction of Ni2+ from solvents – an experimental and modelling study

2020 ◽  
Vol 22 (28) ◽  
pp. 16125-16135 ◽  
Author(s):  
Monika Lukaczynska-Anderson ◽  
Mesfin Haile Mamme ◽  
Andrea Ceglia ◽  
Krista Van den Bergh ◽  
Joost De Strycker ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Water Content ◽  
Electrochemical Reduction ◽  
Water Concentration ◽  
Deep Eutectic Solvents ◽  
Hydrogen Bond Donor ◽  
Modelling Study

Water concentration and hydrogen bond donor have both a big influence in the coordination of Ni cations in deep eutectic solvents, and will therefore affect their electroreduction.

scholarly journals Reactivity of a Carene-Derived Hydroxynitrate in Mixed Organic/Aqueous Matrices: Applying Synthetic Chemistry to Product Identification and Mechanistic Implications

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1617
Author(s):  
Addison B. McAlister ◽  
James I. Vesto ◽  
Aaron Huang ◽  
Kathryn A. Wright ◽  
Emily J. McLaughlin Sta. Maria ◽  
...  
Keyword(s):  
Water Concentration ◽  
Organic Aerosol ◽  
Organic Media ◽  
Product Yields ◽  
Major Class ◽  
Product Identification ◽  
Influence Of Water ◽  
Condensed Phase Reactions ◽  
Carbocation Rearrangement

β-hydroxynitrates (HN) are a major class of products formed during OH and NO3 initiated oxidation of terpenes. Their production contributes significantly to secondary organic aerosol (SOA) formation and NOx sequestration. However, studying the condensed phase reactions of this important class of molecules has been hindered by the lack of commercially available authentic standards. The goal of this work was to examine the influence of water concentration and solvent identity on product yields of a tertiary HN derived from 3-carene prepared in house. To assess the role of water on conversion chemistry, bulk-phase reactions were conducted in DMSO-d6, a non-nucleophilic solvent, with a gradient of water concentrations, and analyzed with 1H NMR. Product identifications were made by comparison with authentic standards prepared in house. Four major products were identified, including an unexpected diol produced from carbocation rearrangement, diol diastereomers, and trans-3-carene oxide, with varying yields as a function of water concentration. Product yields were also measured in two protic, nucleophilic solvents, MeOD-d4 and EtOD-d6. Finally, reactions with added chloride formed alkyl chloride products in yields approaching 30%. These results are among the first to highlight the complexities of nucleophilic reactions of hydroxynitrates in bulk, mixed aqueous/organic media and to identify new, unexpected products.

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