1,721,001 research outputs found
Covalently Linked Purine-Pyrimidine Analogs. The Structure o 7-(4,6-dioxo-5-pyrimidinyl)-theophylline Dihydrate, C11H10N6O4 ∑ 2H2O
No full textOxyfunctionalization of CalixareneQuinone Rings
No full textThe epoxidation of quinone rings of calixquinones represents a valid route for the introduction of oxygenated functionalities into the de-tert-butylated calixarene walls originating cis-diepoxy-p-dione moieties. Carbonyl reduction of these systems leads to hybrid calixarenes containing dianhydroinositol moieties (calixinositols) belonging to the calixcyclitols family. The regio- and stereochemistry of these derivatives was determined by 2D NMR studies, in conjunction with MM3 calculations and X-ray crystallography
Covalently Linked Purine-Pyrimidine Analogs. The Structure of 7-(5-hydroxy-3-oxo-2,3-dihydro-4-pyrazolyl)-theophylline Monohydrate, C10H10N6O4∑H2O
No full textSOLID STATE STRUCTURE AND MICELLAR MODELS OF THE BILE ACIDS
No full textPUBBLICATO SULLA RIVISTA: MATERIAL STRUCTURE IN CHEMISTRY, BIOLOGY,PHYSICS AND TECHNOLOGY, VOL.5,P.88. Relazione su invit
Exploring the interest of 1,2-Dithiolane ring system in peptide chemistry. Synthesis of a chemotactic tripeptide and x-ray crystal structure of a 4-amino-1,2-dithiolane-4-carboxylic acid derivative
No full textDue to their relevant biological functions and specific chemical reactivity 1,2-dithiolanes (five-membered cyclic disulfides) represent an emerging class of heterocyclic compounds. However, despite the extensive research centered on lipoic acid and its analogues, only very few data are at the present available on peptides containing this ring system. We report here synthesis, conformation and bioactivity of a fMLF-OMe analogue, namely For-Met-Adt-Phe-OMe (7), in which the residue of the 4-amino-1,2-dithiolane-4-carboxylic acid (Adt) (4) replaces the central L-leucine. The crystal conformation of the synthetic intermediate Boc-Adt-OMe (5) is also described and compared to that of lipoic acid (R-1,2-dithiolane-3-pentanoic acid) (3) and asparagusic acid (1,2-dithiolane-4-carboxylic acid) (2)
Calcium Ion Binding to Bile Salts
No full textThe nature of the interactions between calcium ions and bile salt anions and the effect of the competition between calcium and sodium ions for possible formation of micellar aggregates are investigated. The crystal structures of calcium deoxycholate (CaDC) and glycodeaxycholate (CaGDC) and quasi-elastic lightscattering measurements, carried out on sodium deoxycholate (NaDC) and glycodeoxycholate (NaGDC) aqueous solutions containing CaCl2, are discussed. The calcium ions are coordinated to oxygen atoms of carboxylate groups and water molecules by means of ion-ion and ion-dipole interactions. The hydroxyl groups of the bile salt anions are not involved. The Ca2+-bile salt complexes fulfill both a 1:1 (CaDC) and a 1:2 (CaGDC) stoichiometry. An assembly of wedge-shaped bilayers, cemented with CaDC anions, or an assembly of irregular trimeric units, each one containing three anions, can be recognized in the crystal packing of CaDC. Ca2+ and Cl- ions and water molecules are located in liquid-like regions. The crystal packing of CaGDC is characterized by 2(1) helices and units with a 2-fold rotation axis. The quasi-elastic light-scattering measurements show that NaDC and NaGDC aqueous solutions with low concentrations of Ca2+ ions have micellar aggregates with apparent hydrodynamic radii remarkably greater than those of the solutions containing only Na+ ions. The Ca2+ ions seem to have a greater affinity for the deoxycholate and glycodeoxycholate anions than the Na+ ions, and the micellar aggregates with Na+ and Ca2+ ions seem to be more stable than those containing only Na+ ions. It is proposed that the Ca2+ ions act as aggregation centers of the sodium micellar aggregates
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