Marine elasmobranchs maintain their body fluid isoosmotic or slightly hyperosmotic to the external medium by the retention of large urea concentrations. This review focuses on the strategies adopted by these fishes to maintain a large outwardly direct concentration gradient of this osmolyte minimizing the loss across the main interfaces between body fluid and the external medium such as the gil...

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative hydrogen-bonding array between the urea moiety and the hydroxyl group of the allyl alcohol,...

In the title compound, [Na(2)(N(3))(2)(C(21)H(34)N(2)O(6))(2)]·2CHCl(3), the sodium cation is hepta-coordinated by five O atoms of the crown ether unit of the 1-hexyl-3-(2,3,5,6,8,9,11,12-octa-hydro-1,4,7,10,13-benzopenta-oxacyclo-penta-decin-15-yl)urea (L) ligand, the O atom of the urea group of the second, symmetry-related L ligand, and one N atom of the azide anion. The experimentally determ...

Refluxing a mixture of 1,10-phenanthroline, (4-fluoro-phen-yl)thio-urea and cadmium(II) chloride did not produce the expected mixed-ligand complex but formed a co-crystal of the two ligands, C12H8N2·C7H7FN2S. The asymmetric unit consists of two pairs of the co-crystal mol-ecules. In each (4-fluoro-phen-yl)thio-urea mol-ecule, the planes of the N2CS thio-urea units are almost perpendicular to th...

The cytosolic malic enzyme from the pigeon liver is sensitive to chemical denaturant urea. When monitored by protein intrinsic fluorescence or circular dichroism spectral changes, an unfolding of the enzyme in urea at 25 degrees C and pH 7.4 revealed a biphasic phenomenon with an intermediate state detected at 4-5 m urea. The enzyme activity was activated by urea up to 1 m but was completely lo...

Cowpeas grown in nutrient solutions, from which Ni had been removed by a ligand exchange technique, accumulated urea in most tissues. Urea levels were highest (up to 3.1 percent dry weight) in necrotic leaf tips. Urea accumulation in Ni-deficient cowpea tissues amounted to about 1 percent of the total N. The accumulation of urea was presumably associated with the catabolism of N compounds in ol...

Understanding how an amino acid sequence folds into a functional, three-dimensional structure has proved to be a formidable challenge in biological research, especially for transmembrane proteins with multiple alpha helical domains. Mechanistic folding studies on helical membrane proteins have been limited to unusually stable, single domain proteins such as bacteriorhodopsin. Here, we extend su...

BACKGROUND Phosphotyrosine binding (PTB) domains are critically involved in cellular signaling and diseases. PTB domains are categorized into three distinct structural classes namely IRS-like, Shc-like and Dab-like. All PTB domains consist of a core pleckstrin homology (PH) domain with additional structural elements in Shc and Dab groups. The core PH fold of the PTB domain contains a seven stra...