Topic
Urea
About: Urea is a research topic. Over the lifetime, 21394 publications have been published within this topic receiving 382444 citations. The topic is also known as: carbamide & carbonic acid diamide.
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TL;DR: The pairwise interactions of the constituent components of the choline chloride-urea DES are examined and it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples.
Abstract: Deep eutectic solvents (DESs) are exemplars of systems with the ability to form neutral, ionic and doubly ionic H-bonds. Herein, the pairwise interactions of the constituent components of the choline chloride-urea DES are examined. Evidence is found for a tripodal CHCl doubly ionic H-bond motif. Moreover it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples. In contrast to many traditional solvents, an "alphabet soup" of many different types of H-bond (OHO[double bond, length as m-dash]C, NHO[double bond, length as m-dash]C, OHCl, NHCl, OHNH, CHCl, CHO[double bond, length as m-dash]C, NHOH and NHNH) can form. These H-bonds exhibit substantial flexibility in terms of number and strength. It is anticipated that H-bonding will have a significant impact on the entropy of the system and thus could play an important role in the formation of the eutectic. The 2 : 1 urea : choline-chloride eutectic point of this DES is often associated with the formation of a [Cl(urea)2](-) complexed anion. However, urea is found to form a H-bonded urea[choline](+) complexed cation that is energetically competitive with [Cl(urea)2](-). The negative charge on [Cl(urea)2](-) is found to remain localised on the chloride, moreover, the urea[choline](+) complexed cation forms the strongest H-bond studied here. Thus, there is potential to consider a urea[choline](+)·urea[Cl](-) interaction.
253 citations
TL;DR: In this paper, the electrochemical oxidation mechanism of urea on a Ni(OH)2 catalyst in alkaline medium was investigated using in situ surface enhanced Raman spectroscopy.
252 citations
Journal Article•
TL;DR: Relatively large doses of the salts and urea removed much more water than that which was administered, whereas such doses ofThe xanthine diuretics, Bi tartrate and of salyrgan not only failed to produce an increase in diuretic action, but in most instances produced a decrease.
Abstract: 1. A method using white rats has been devised for the bioassay of diuretics. It has been tested experimentally and statistically and applied to the study of various substances. Urea with an activity of 1 was taken as the standard diuretic. 2. The dose-action curves (log dose in millimols per kilogram body weight, plotted against log diuretic action) of urea, various salts, and salyrgan were found to be straight lines of similar slopes within a suitable range of doses. From these the diuretic activities of the substances were calculated. The doseaction curves of the xanthine derivatives were found to be complex, seemingly limited by a physiological factor. 3. Biuret, a urea derivative, assayed in this way, showed a diuretic activity of 1.4. 4. The following diuretic activities were determined from the dose-action curves: salyrgan, 400; bismuth potassium tartrate, 219; theophylline, 115; caffeine, 32; theobromine, 7.2; potassium nitrate, 3.9; sodium nitrate, 2.9; potassium acetate, 3.4; sodium acetate, 2.0; ammonium chloride, 2.7; and urea, 1.0. 5. Relatively large doses of the salts and urea removed much more water than that which was administered, whereas such doses of the xanthine diuretics, Bi tartrate and of salyrgan not only failed to produce an increase in diuretic action, but in most instances produced a decrease.
251 citations
250 citations
TL;DR: In this paper, the vibrational spectrum of urea was interpreted by measuring the solid state infrared spectra of eight isotopomers of Urea at room temperature and at −196 °C.
Abstract: Although a lot of work has been done on the vibrational analysis of urea, there still remain some contradictions and uncertainties, mainly due to interpretation of the vibrational spectrum of crystalline urea based on force field calculations on isolated urea instead of on urea in its crystal phase. We have shown that this approach is not allowed in the case of urea. The vibrational spectrum of urea was interpreted by measuring the solid state infrared spectra of eight isotopomers of urea at room temperature and at −196 °C, and Raman spectra at room temperature and at −120 °C, and of a urea−water solution. Force field calculations from our recently published article on isolated urea and on urea in its crystal structure, at the Hartree−Fock level with a 6-31++G** basis set, were also used. We have also shown that high-pressure measurements using a “diamond anvil cell” are not useful by performing a vibrational analysis.
250 citations