Search results for "Urea"
showing 10 items of 888 documents
Two guaianolides from Centaurea collina
1987
Abstract Two guaianolides isolated from the aerial parts of Centaurea collina were identified as 3β-hydroxy-8α-epoxymethylacriloiloxy-4(15),10(14),11(13 and its 11β,13-dihydro derivative by spectroscopic methods.
Heterodimeric capsules formed by tetratosyl and tetratolyl urea calix[4]arenes
2008
Predictions made by MD simulations for size, shape and guest inclusion of a heterodimer formed by a tetratosyl and a tetratolyl urea calix[4]arene and for its hydrogen bonding system have been entirely confirmed by a single crystal X-ray structure.
Sesquiterpene lactones, flavonoids and coumarins from Centaurea collina
1989
Abstract The isolation and characterization of two coumarins, five flavonoids and four sesquiterpene lactones from the aerial parts of Centaurea collina are reported. The 13 C NMR data are included.
A coupled cluster calculation of the spectrum of urea
2001
Several coupled cluster methods have been used to compute the vertical excitation energies and oscillator strengths of the lowest singlet states of urea. Except for one excitation, the results are in good agreement with experiment, but previously non-detected transitions have been found.
A macrocyclic diurea derived from diphenylether
2010
Abstract A new 16-membered cyclic diurea was synthesized and tested as potential receptor for fluoride. 1 H and 19 F NMR spectroscopy revealed an unexpected deprotonation of both urea groups after initial 1:1 binding. A single crystal X-ray structure shows bifurcated hydrogen bonds to two DMSO molecules.
Die Beeinflussung der Harnstoffsynthese in der Leber durch lokale Gewebssch�den beim Kaninchen
1961
Es wird uber in-vitro-Bestimmungen der Harnstoffsynthese der Lebern von Kaninchen mit einer Crotonolentzundung und einer bakteriellen Entzundung des Kniegelenks und einer mechanischen Kniegelenksentzundung berichtet. Es findet sich eine deutliche Zunahme der Harnstoffbildung gegenuber den bei den Kontrolltieren festgestellten Werten. Die Ergebnisse werden hinsichtlich inrer Bedeutung fur die Pathogenese extrarenaler Azotamien diskutiert.
Fluorescent chemosensors based on cyclohexane: selective sensing of succinate and malonate versus their longer or shorter homologues
2008
The sensing properties towards aliphatic α,ω-dicarboxylates of five cyclohexane-based ligands are described. The studied ligands have been designed following the binding site-signalling unit approach and they all possess thiourea groups as recognition moieties. Ligands 1 and 3 containing naphthalene units can be used as fluorescent sensors as they form intra- or intermolecular excimers in the presence of appropriate dicarboxylates. Selective sensing of succinate and malonate versus their longer or shorter homologues has been observed.
Nanocomposite, an innovative route to large structure and infrastructure protection. A case of study: CNT-doped polyurea
2010
<p>In this work we focus on experimental studies of polymer-nanocomposites intended for passive protection of civil structures. The material consists of a polyurea-matrix enhanced by different quantities of multiwalled carbon nanotubes. Several tensile and cyclic tests are performed to evaluate and characterize the mechanical behaviour of this new material. Furthermore, we subject the material to accelerated thermal aging and study its performance deterioration which is fairly unknown. The results on the unaged specimens are intuitive and indicate that an arbitrary amount of CNTs may result in suboptimal performance. More specifically, 1% in weight of CNTs yields the best mechanical p…
H2-Antihistaminica, 1. Mitt.: 2-Substituierte 4-[[2-(N′-Methyl-thioureido)-äthylmercapto]-methyl]-imidazole
1976
Es wird die Synthese der 2-substituierten 4-[[2-(N′-Methylthioureido)-athylmercapto]-methyl]-imidazole 5a–f als potentielle H2-Antihistaminica beschrieben. Ausgehend von den Imidazol-4-carbinolen 3a–f lassen sich die 2-substituierten 4-[(2-Amino-athylmercapto)-methyl]-imidazole 4a–f durch saurekatalysierte Reaktion mit Cysteamin darstellen und mit Methylisothiocyanat in die entsprechenden Thioharnstoffderivate 5 uberfuhren. 2-Substituted 4-[[2-(N′-Methyl-thioureido)-ethylmercapto]-methyl]-imidazoles The synthesis of 2-substituted 4-[[2-(Ns′-methyl-thioureido)-ethylmercapto]-methyl]-imidazoles 5a–f, as potential H2-antihistaminics, is described. The acid catalyzed reaction of the imidazole-4…
Regioselective Synthesis of 2-Imino-1,3-thiazolidin-4-ones by Treatment ofN-(Anthracen-9-yl)-N′-ethylthiourea with Bromoacetic Acid Derivatives
2002
The reaction between N-(anthracen-9-yl)-N′-ethylthiourea (1) and methyl bromoacetate yielded mainly 2-[(anthracen-9-yl)imino]-3-ethyl-1,3-thiazolidin-4-one (2), together with some of the regioisomeric 3-(anthracen-9-yl)-2-ethylimino-1,3-thiazolidin-4-one (3). The structures of the products were elucidated by NMR techniques and, for 3, X-ray crystallographic analysis. Treatment of 1 with bromoacetyl bromide again yielded 2 and 3, but with a reversed product distribution ratio, thus providing an interesting and unexpected regioselectivity, depending on the electrophile selected. The underlying cause of the observed regioselectivity is a result of different reaction pathways taken by the two e…