Synthesis of thiazol‐2‐imines from the reduction of single enantiomer 2‐imino‐thiazolidin‐4‐ones followed by a spontaneous water elimination

Chirality ◽  
2020 ◽  
Vol 32 (6) ◽  
pp. 866-875 ◽  
Author(s):  
Senel Teke Tuncel ◽  
Ilknur Dogan
Keyword(s):  
Water Elimination

Characterizing Peritumoral Tissue Using DTI-Based Free Water Elimination

2019 ◽  
pp. 123-131 ◽  
Author(s):  
Abdol Aziz Ould Ismail ◽  
Drew Parker ◽  
Moises Hernandez-Fernandez ◽  
Steven Brem ◽  
Simon Alexander ◽  
...  
Keyword(s):  
Free Water ◽  
Water Elimination ◽  
Peritumoral Tissue

Phenylalanine: Its ˙OH and SO4˙⁻-Induced Oxidation and Decarboxylation. A Pulse Radiolysis and Product Analysis Study

1993 ◽  
Vol 48 (6) ◽  
pp. 761-770 ◽  
Author(s):  
Degui Wang ◽  
Heinz-Peter Schuchmann ◽  
Clemens von Sonntag
Keyword(s):  
Radical Cation ◽  
Pulse Radiolysis ◽  
Side Reactions ◽  
Intramolecular Electron Transfer ◽  
Oh Radical ◽  
Product Analysis ◽  
Water Elimination ◽  
Deprotonation Reaction ◽  
Type Radical ◽  
Radical Yield

Phenylamine has been oxidized by radiolytically generated hydroxyl and sulfate radicals, the ensuing intermediates and their reactions have been studied by pulse radiolysis and product analysis in the absence and presence of oxidants such as Fe(CN)63- and O2. Upon OH radical attack, hydroxycyclohexadienyl-type radicals are mainly formed while Η-abstraction reactions can be neglected. In the presence of Fe(CN)63- these radicals are for the most part oxidized to the corresponding tyrosines (80%), except for the ipso-OH-adduct radicals (≈ 20%). It is concluded that ˙OH-addition is almost random, but with a slight avoidance of the metaposition relative to the ortho-, para- and ipso-positions. Oxygen adds reversibly to the OH-adduct radicals (kf = 1.8 × 108 dm3 mol-1 s-1, kr = 5.4 × 104 s-1). In this case, tyrosine formation occurs by HO2˙-elimination. However, due to side reactions, tyrosine formation only reaches 52% of the OH radical yield. The tyrosine yield drops to 10% in the absence of an oxidant.Upon SO4˙⁻-attack, decarboxylation becomes a major process (33% of SO4˙⁻) alongside the production of tyrosines (43%). Here, with Fe(CN)63- as the oxidant the formation of p-Tyr (18.5%) and m-Tyr (16.5%) is preferred over o-Tyr formation (8.5%). It is believed that in analogy to other systems a radical cation is formed immediately upon SO4˙⁻-attack which either reacts with water under the formation of hydroxycyclohexadienyl-type (“OH-adduct”) radicals, or decarboxylates after intramolecular electron transfer. The radical cation can also arise indirectly through H+-catalysed water elimination from the ˙OH-adduct radicals. At pH 2 and a dose rate of 0.0046 Gy s-1 CO2 formation matches the OH radical yield when ˙OH is the attacking radical. Below pH 2, G(CO2) decreases with falling pH. This indicates the occurrence of another, unimolecular, pathway under these conditions competing effectively with decarboxylation. This appears to be a relatively slow deprotonation reaction of the carboxylprotonated phenylalanine radical cation which gives rise to the benzyl-type radical.

Catalysis with a Skip: Dynamically Coupled Addition, Proton Transfer, and Elimination During Au- and Pd-Catalyzed Diol Cyclization

2021 ◽  
Author(s):  
Matthew Teynor ◽  
Windsor Scott ◽  
Daniel Ess
Keyword(s):  
Potential Energy ◽  
Proton Transfer ◽  
Energy Landscape ◽  
Cyclization Reactions ◽  
Potential Energy Landscape ◽  
Water Elimination ◽  
Catalytic Intermediates ◽  
Pd Complexes ◽  
Dynamics Simulations ◽  
Step Mechanism

Au and Pd complexes have emerged as highly effective π-bond cyclization catalysts to construct heterocycles. These cyclization reactions are generally proposed to proceed through multi-step addition-elimination mechanisms involving Au- or Pd-alkyl intermediates. For Au- and Pd-catalyzed allylic diol cyclization, while the DFT potential energy surface landscapes show a stepwise sequence of alkoxylation π-addition, proton transfer, and water elimination, quasiclassical direct dynamics simulations reveal new dynamical mechanisms that depend on the metal center. For Au, trajectories reveal that after π-addition the Au-alkyl intermediate is always skipped because addition is dynamically coupled with proton transfer and water elimination. In contrast, for Pd catalysis, due to differences in the potential-energy landscape shape, only about half of trajectories show Pd-alkyl intermediate skipping. The other half of the trajectories show the traditional two-step mechanism with the intervening Pd-alkyl intermediate. Overall, this work reveals that interpretation of a DFT potential-energy landscape can be insufficient to understand catalytic intermediates and mechanisms and that atomic momenta through dynamics simulations is needed to determine if an intermediate is genuinely part of a catalytic cycle.<br>

scholarly journals Effects of Drugs and Excipients on Hydration Status

Nutrients ◽  
2019 ◽  
Vol 11 (3) ◽  
pp. 669 ◽  
Author(s):  
Ana Puga ◽  
Sara Lopez-Oliva ◽  
Carmen Trives ◽  
Teresa Partearroyo ◽  
Gregorio Varela-Moreiras
Keyword(s):  
Gastrointestinal Tract ◽  
Water Balance ◽  
Gastrointestinal Transit ◽  
The Other ◽  
Hydration Status ◽  
Gastrointestinal Transit Time ◽  
Input And Output ◽  
Water Elimination ◽  
Essential Nutrient ◽  
The Difference

Despite being the most essential nutrient, water is commonly forgotten in the fields of pharmacy and nutrition. Hydration status is determined by water balance (the difference between water input and output). Hypohydration or negative water balance is affected by numerous factors, either internal (i.e., a lack of thirst sensation) or external (e.g., polypharmacy or chronic consumption of certain drugs). However, to date, research on the interaction between hydration status and drugs/excipients has been scarce. Drugs may trigger the appearance of hypohydration by means of the increase of water elimination through either diarrhea, urine or sweat; a decrease in thirst sensation or appetite; or the alteration of central thermoregulation. On the other hand, pharmaceutical excipients induce alterations in hydration status by decreasing the gastrointestinal transit time or increasing the gastrointestinal tract rate or intestinal permeability. In the present review, we evaluate studies that focus on the effects of drugs/excipients on hydration status. These studies support the aim of monitoring the hydration status in patients, mainly in those population segments with a higher risk, to avoid complications and associated pathologies, which are key axes in both pharmaceutical care and the field of nutrition.

scholarly journals Dedicated diffusion phantoms for the investigation of free water elimination and mapping: insights into the influence of T 2 relaxation properties

2020 ◽  
Vol 33 (4) ◽  
Author(s):  
Ezequiel Farrher ◽  
Farida Grinberg ◽  
Li‐Wei Kuo ◽  
Kuan‐Hung Cho ◽  
Richard P. Buschbeck ◽  
...  
Keyword(s):  
Free Water ◽  
Relaxation Properties ◽  
Water Elimination

Changes in specific airway resistance during prolonged breathing of moist air

1970 ◽  
Vol 48 (9) ◽  
pp. 592-597 ◽  
Author(s):  
G. Norris Melville ◽  
W. T. Josenhans ◽  
W. T. Ulmer
Keyword(s):  
Relative Humidity ◽  
Water Content ◽  
Water Loss ◽  
Healthy Subjects ◽  
Airway Resistance ◽  
Tap Water ◽  
Distilled Water ◽  
Moist Air ◽  
Specific Airway Resistance ◽  
Water Elimination

Effects of increased water content of inspired air at 21–38 °C on specific airway resistance (sRaw) in 107 healthy subjects were measured with a body plethysmograph. Mean sRaw increased insignificantly at 23 °C with 92% relative humidity (water content, 20.7 g∙m−3) for up to 71 h but became significant at 6 h with water content 25 g∙m−3. Increases were greater when evaporated tap water was inhaled than when distilled water was used. It is postulated that the increase in sRaw is due to mucosal swelling and to contaminants in tap water. A theory of respiratory "water elimination" is proposed to replace the concept of respiratory water loss.

scholarly journals Diffusion kurtosis imaging with free water elimination: A bayesian estimation approach

2018 ◽  
Vol 80 (2) ◽  
pp. 802-813 ◽  
Author(s):  
Quinten Collier ◽  
Jelle Veraart ◽  
Ben Jeurissen ◽  
Floris Vanhevel ◽  
Pim Pullens ◽  
...  
Keyword(s):  
Bayesian Estimation ◽  
Free Water ◽  
Diffusion Kurtosis Imaging ◽  
Water Elimination ◽  
Diffusion Kurtosis

scholarly journals A diffusion model‐free framework with echo time dependence for free‐water elimination and brain tissue microstructure characterization

2018 ◽  
Vol 80 (5) ◽  
pp. 2155-2172 ◽  
Author(s):  
Miguel Molina‐Romero ◽  
Pedro A. Gómez ◽  
Jonathan I. Sperl ◽  
Michael Czisch ◽  
Philipp G. Sämann ◽  
...  
Keyword(s):  
Time Dependence ◽  
Brain Tissue ◽  
Diffusion Model ◽  
Free Water ◽  
Microstructure Characterization ◽  
Tissue Microstructure ◽  
Model Free ◽  
Water Elimination ◽  
Echo Time

Self-regulation of water elimination in an H2-O2 fuel cell

1971 ◽  
Vol 21 (4) ◽  
pp. 1242-1245
Author(s):  
V. S. Bagotskii ◽  
M. S. Beletskii ◽  
Yu. M. Vol'fkovich ◽  
É. I. Grigorov ◽  
I. G. Gurevich ◽  
...  
Keyword(s):  
Fuel Cell ◽  
Self Regulation ◽  
Water Elimination

scholarly journals A Model Study on the Dynamics of the Amino Acid Content in Micrometeoroids during Atmospheric Entry

Chemistry ◽  
2020 ◽  
Vol 2 (4) ◽  
pp. 918-936
Author(s):  
Carlo Canepa
Keyword(s):  
Amino Acid ◽  
Acid Content ◽  
Amino Acid Content ◽  
Organic Content ◽  
Gravitational Energy ◽  
Chemical Degradation ◽  
Rate Coefficients ◽  
Atmospheric Entry ◽  
Exponential Factor ◽  
Water Elimination

A model for the survival of the amino acid content in micrometeorites and its possible transformations upon atmospheric entry is described. Since any organic species released in the atmosphere at high altitudes would exhibit a limited lifetime with respect to the typical timescale for atmospheric mixing (due to the substantial radiation field of the early Sun), only the organic content inside the meteorites could have contributed to prebiotic chemistry. It is thus important to determine both the amino acid loss from meteorites, due to both degassing and chemical degradation, and the extent of the chemical transformation of amino acids subjected to the increased temperature due to friction with the atmosphere. According to the interplay between the potential energy barrier and the pre-exponential factor in rate coefficients, either diffusion or chemical processing might be the dominant process following the rising temperature upon atmospheric entry. The possibility of the elimination of water from glycine to form aminoketene, or CO2 to form methylamine, ultimately driven by gravitational energy, was examined along with the more conventional formation of a peptide bond between two glycine units to afford Gly–Gly. While retention, degassing, and decarboxylation are the fastest processes, each dominating in different ranges of the initial velocity and radius, the formation of either Gly–Gly from bimolecular water elimination or aminoketene from unimolecular water elimination appears to be negligible.

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