Isotope Effects in Exchange, Desorption, and Decomposition of Water Molecules on Ru(0001) at Cryogenic Temperatures

2020 ◽  
Vol 124 (51) ◽  
pp. 28139-28144
Author(s):  
Ryutaro Souda ◽  
Takashi Aizawa ◽  
Masaki Takeguchi
Keyword(s):  
Isotope Effects ◽  
Water Molecules ◽  
Cryogenic Temperatures ◽  
Decomposition Of Water

scholarly journals Electrocatalysis of the HER in acid and alkaline media

2013 ◽  
Vol 78 (12) ◽  
pp. 2007-2015 ◽  
Author(s):  
Nemanja Danilovic ◽  
Ram Subbaraman ◽  
Dusan Strmcnik ◽  
Vojislav Stamenkovic ◽  
Nenad Markovic
Keyword(s):  
Catalytic Decomposition ◽  
Alkaline Media ◽  
Alkaline Solutions ◽  
Water Molecules ◽  
Bifunctional Catalysts ◽  
High Coverage ◽  
Acidic Solutions ◽  
Noble Metal Catalysts ◽  
Alkaline Environments ◽  
Decomposition Of Water

Trends in the HER are studied on selected metals (M= Cu, Ag, Au, Pt, Ru, Ir, Ti) in acid and alkaline environments. We found that with the exception of Pt, Ir and Au, due to high coverage by spectator species on non-noble metal catalysts, experimentally established positions of Cu , Ag, Ru and Ti in the observed volcano relations are still uncertain. We also found that while in acidic solutions the M-Hupd binding energy most likely is controlling the activity trends, the trends in activity in alkaline solutions are controlled by a delicate balance between two descriptors: the M-Had interaction as well as the energetics required to dissociate water molecules. The importance of the second descriptor is confirmed by introducing bifunctional catalysts such as M modified by Ni(OH); e.g. while the latter serves to enhance catalytic decomposition of water, the metal sites are required for collecting and recombining the produced hydrogen intermediates.

A comparison of the mechanisms of hydrolysis of benzimidates, esters, and amides in sulfuric acid media

2005 ◽  
Vol 83 (9) ◽  
pp. 1391-1399 ◽  
Author(s):  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Isotope Effects ◽  
Ester Hydrolysis ◽  
Water Molecules ◽  
Acid Media ◽  
Tetrahedral Intermediate ◽  
Amide Hydrolysis ◽  
Solvent Isotope ◽  
Reaction Media ◽  
Hydrolysis Of

The mechanisms given in textbooks for both ester and amide hydrolysis in acid media are in need of revision. To illustrate this, benzimidates were chosen as model compounds for oxygen protonated benzamides. In aqueous sulfuric acid media they hydrolyze either by a mechanism involving attack of two water molecules at the carbonyl carbon to give a neutral tetrahedral intermediate directly, as in ester hydrolysis, or by an SN2 attack of two water molecules at the alkyl group of the alkoxy oxygen to form the corresponding amide, or by both mechanisms, depending on the structure of the benzimidate. The major line of evidence leading to these conclusions is the behavior of the excess acidity plots resulting from the rate constants obtained for the hydrolyses as functions of acid concentration and temperature. The first of these mechanisms is in fact very similar to one found for the hydrolysis of benzamides, as inferred from: (1) similar excess acidity plot behaviour; and (2) the observed solvent isotope effects for amide hydrolysis, which are fully consistent with the involvement of two water molecules, but not with one or with three (or more). This mechanism starts out as essentially the same one as that found for ester hydrolysis under the same conditions. Differences arise because the neutral tetrahedral intermediate, formed directly as a result of the protonated substrate being attacked by two water molecules (not one), possesses an easily protonated nitrogen in the amide and benzimidate cases, explaining both the lack of 18O exchange observed for amide hydrolysis and the irreversibility of the reaction. Protonated tetrahedral intermediates are too unstable to exist in the reaction media; in fact, protonation of an sp3 hybridized oxygen to put a full positive charge on it is extremely difficult. (This means that individual protonated alcohol or ether species are unlikely to exist in these media either.) Thus, the reaction of the intermediate going to product or exchanged reactant is a general-acid-catalyzed process for esters. For amide hydrolysis, the situation is complicated by the fact that another, different, mechanism takes over in more strongly acidic media, according to the excess acidity plots. Some possibilities for this are given.Key words: esters, amides, benzimidates, hydrolysis, excess acidity, mechanism, acid media.

scholarly journals Capacitive Sensing of Icing under Vacuum and Cryogenic Temperatures

Sensors ◽  
2019 ◽  
Vol 19 (16) ◽  
pp. 3574 ◽  
Author(s):  
Juliana Padilha Leitzke ◽  
Tobias Mitterer ◽  
Hubert Zangl
Keyword(s):  
Capacitive Sensor ◽  
Water Molecules ◽  
Residual Water ◽  
Cryogenic Temperatures ◽  
Term Study ◽  
Long Term Study ◽  
Cryogenic Liquids ◽  
Sensor Configuration ◽  
The Stability

In certain industrial processes, ice aggregations on surfaces can occur under almost vacuum conditions and at very low to cryogenic temperatures due to residual water molecules. This aggregation can affect the performance of the process and it is therefore of interest to monitor such surfaces. In this paper, we present a capacitive ice measurement system capable to operate in vacuum and temperatures of about - 120 ∘ C and below. We present a capacitive sensor setup with a separation of sensor element and sensor electronics, such that the sensor electronics can reside outside the cold environment. It is demonstrated that the permittivity of such ice formations at vacuum and low temperatures is sufficient for measurement using the proposed sensor configuration. Results from a long-term study using a prototype further demonstrate the stability of the system and thus the feasibility of the proposed system for long term condition monitoring of surfaces in vacuum that are e.g., cooled by cryogenic liquids. The developed system uses wireless communication in order to allow for simple retrofitting of existing infrastructure even in remote locations.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 733-737
Author(s):  
Maurice M Kreevoy ◽  
Victor G Young, Jr.
Keyword(s):  
Isotope Effect ◽  
Dihedral Angle ◽  
Room Temperature ◽  
Isotope Effects ◽  
Water Molecules ◽  
Aromatic Rings ◽  
Structural Water ◽  
The Mean ◽  
Increasing Temperature ◽  
Ubbelohde Effect

The crystal structure of sodium hydrogen bis(4-nitrophenoxide) dihydrate, 1, with deuterium replacing hydrogen in the bridge and the structural water molecules, has been determined crystallographically at 113, 173, and 295 K. The structure of 1 had previously been determined at similar temperatures (Kreevoy et al.). The O,O distances are 1.5-1.7 pm greater in the deuterated compound than in the undeuterated, at all three temperatures, providing another example of an Ubbelohde effect in a Speakman-Hadzi compound. The temperature invariance of the Ubbelohde effect at temperatures up to room temperature is evidence against centralization of the hydron within this temperature range. It has previously been suggested (Kreevoy et al.) that simplification of the IR spectrum of 1 with increasing temperature is due to an increase in the rate of the hydron shift between the two basic oxygens. This suggestion is strengthened by the elimination of hydron centralization as an alternative. The O,O distance in 1 also increases with temperature, and the dihedral angle between the mean planes of the two aromatic rings decreases. Similarly, the increase in the O,O distance with isotopic substitution is accompanied by a small decrease in the dihedral angle; another geometric isotope effect. Ubbelohde effects in Speakman-Hadzi compounds make the geometric isotope effects found computationally in the critical complexes for hydron, hydrogen atom, or hydride transfer more credible.Key words: low-barrier hydrogen bond, Speakman-Hadzi compound, geometric isotope effect, Ubbelohde effect.

scholarly journals Preparation and Performance Analysis of Ag/ZnO Humidity Sensor

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 857
Author(s):  
Peng Li ◽  
Shuguo Yu ◽  
Hongyan Zhang
Keyword(s):  
Active Sites ◽  
Humidity Sensor ◽  
Molar Ratio ◽  
Water Molecules ◽  
Humidity Sensors ◽  
Response Recovery ◽  
Highly Sensitive ◽  
Stable Performance ◽  
And Performance ◽  
Decomposition Of Water

Highly sensitive silver (Ag) modified zinc oxide (ZnO) humidity sensors were prepared by hydrothermal synthesis and the mechanism was studied. Experimental results show that Ag-modified ZnO can effectively enhance the performance of a humidity sensor. Large number of oxygen vacancies and many active sites are generated on the surface when molar ratio of Ag+ to Zn2+ is 1:100, which can accelerate the decomposition of water molecules on surface of the material, thereby improving the response of humidity sensor. Moreover, the linearity of ZnO humidity sensor is greatly improved by silver nanoparticles. Compared with previously reported ZnO-based humidity sensors, Ag/ZnO humidity sensors have a better response (151,700%), good linearity, low hysteresis (3%), and short response/recovery time (36/6 s). At the same time, it is found that the light had little effect on the performance of Ag/ZnO. Therefore, this kind of ZnO sensor with stable performance and excellent performance is expected to be used in the detection of relative humidity in conventional environments.

scholarly journals Fast Rotational Diffusion of Water Molecules in a 2D Hydrogen Bond Network at Cryogenic Temperatures

2018 ◽  
Vol 120 (19) ◽  
Author(s):  
T. R. Prisk ◽  
C. Hoffmann ◽  
A. I. Kolesnikov ◽  
E. Mamontov ◽  
A. A. Podlesnyak ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Rotational Diffusion ◽  
Water Molecules ◽  
Cryogenic Temperatures ◽  
Hydrogen Bond Network ◽  
Bond Network

Voltage-Gated Proton Channels and Other Proton Transfer Pathways

2003 ◽  
Vol 83 (2) ◽  
pp. 475-579 ◽  
Author(s):  
Thomas E. Decoursey
Keyword(s):  
Ion Channels ◽  
Nadph Oxidase ◽  
High Selectivity ◽  
Isotope Effects ◽  
Water Molecules ◽  
Amino Acid Residues ◽  
Proton Channels ◽  
Voltage Gated ◽  
Specific Subset ◽  
Nadph Oxidase Complex

Proton channels exist in a wide variety of membrane proteins where they transport protons rapidly and efficiently. Usually the proton pathway is formed mainly by water molecules present in the protein, but its function is regulated by titratable groups on critical amino acid residues in the pathway. All proton channels conduct protons by a hydrogen-bonded chain mechanism in which the proton hops from one water or titratable group to the next. Voltage-gated proton channels represent a specific subset of proton channels that have voltage- and time-dependent gating like other ion channels. However, they differ from most ion channels in their extraordinarily high selectivity, tiny conductance, strong temperature and deuterium isotope effects on conductance and gating kinetics, and insensitivity to block by steric occlusion. Gating of H+channels is regulated tightly by pH and voltage, ensuring that they open only when the electrochemical gradient is outward. Thus they function to extrude acid from cells. H+channels are expressed in many cells. During the respiratory burst in phagocytes, H+current compensates for electron extrusion by NADPH oxidase. Most evidence indicates that the H+channel is not part of the NADPH oxidase complex, but rather is a distinct and as yet unidentified molecule.

scholarly journals Unexpected organic hydrate luminogens in the solid state

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Feng Zhou ◽  
Peiyang Gu ◽  
Zhipu Luo ◽  
Hari Krishna Bisoyi ◽  
Yujin Ji ◽  
...  
Keyword(s):  
Solid State ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Fluorescence Emission ◽  
Structural Rearrangement ◽  
Water Molecules ◽  
Hydrogen Atoms ◽  
Keto Form ◽  
Practical Applications ◽  
Photoluminescent Materials

AbstractDeveloping organic photoluminescent materials with high emission efficiencies in the solid state under a water atmosphere is important for practical applications. Herein, we report the formation of both intra- and intermolecular hydrogen bonds in three tautomerizable Schiff-base molecules which comprise active hydrogen atoms that act as proton donors and acceptors, simultaneously hindering emission properties. The intercalation of water molecules into their crystal lattices leads to structural rearrangement and organic hydrate luminogen formation in the crystalline phase, triggering significantly enhanced fluorescence emission. By suppressing hydrogen atom shuttling between two nitrogen atoms in the benzimidazole ring, water molecules act as hydrogen bond donors to alter the electronic transition of the molecular keto form from nπ* to lower-energy ππ* in the excited state, leading to enhancing emission from the keto form. Furthermore, the keto-state emission can be enhanced using deuterium oxide (D2O) owing to isotope effects, providing a new opportunity for detecting and quantifying D2O.

Isotopieeffekte in den Hydratstrukturen von festem und gelöstem Kupfersulfat / Isotope effects in the hydrated structure of solid and aqueous copper sulphate

1972 ◽  
Vol 27 (5) ◽  
pp. 819-826 ◽  
Author(s):  
B Maiwald ◽  
K Heinzinger
Keyword(s):  
Copper Sulphate ◽  
Isotope Effects ◽  
Copper Ion ◽  
Hydrogen Isotopes ◽  
Bulk Water ◽  
Water Molecules ◽  
Hydrogen Atoms ◽  
Copper Sulphate Solution ◽  
Crystal Water ◽  
Lone Pairs

The fractionation of the oxygen isotopes of the water molecules in CuS04-5 H20 and in aqueous solutions of copper sulphate has been measured at 25 °C. In the total crystal water (G) three kinds of water can be distinguished by their binding: 1) The bisector of the two lone pairs directed to­wards the copper ion (Kj), 2) One of the lone pairs directed towards the copper ion (K2), 3) The two lone pairs directed towards two hydrogen atoms of water molecules coordinated with the cop­per ion (L). The water molecules in the copper sulphate solution are considered either hydration water (HW) or bulk water (FW). Defining a.\-B= (180/160)a/(180/180)b the following results have been obtained:There remains some doubt if the values attributed to ctKi-G and aK2-G have to be interchanged. The elementary cell of CuS04*5 H20 consists of two molecules. Four molecules of Kj-water are coordinated with one copper ion and four molecules of K2-water are coordinated with the second copper ion. The remaining two water molecules are of L-type. It is concluded from the results that on dehydration at temperatures below 50 °C first one copper ion loses it’s water and then the other. There is some doubt as to which group breaks up first. In addition, the results show that the L-type water becomes quantitatively the water of the monohydrate in agreement with the conclusions drawn from the results of the fractionation of the hydrogen isotopes in CuS04-5 H20. It is de­monstrated that, by considering only the overall fractionation of the oxygen or hydrogen isotopes between total crystal water and the saturated solution, wrong conclusions about the crystallization process could be drawn. In the case of CuCl2 solutions, it has been shown that the separation factor aHW-FW is sensi­tive towards changes in the structure of the solution.

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