1,721,185 research outputs found
Reactive Intermediates in Peptide Synthesis: the N-Oxysuccinimide Ester of N-alpha-para-Toluensulfonyl-alpha-Aminoisobutyric Acid
No full textThe preparation, characterization, and molecular and crystal structures of succinimido 2-(tosylamino)isobutyrate, C15H18N2O6S, are described. The succinimido ring is nearly orthogonal to the ester grou
L’occultamento delle violenze sui minori: il caso della Sindrome da Alienazione Parentale.
No full textUncommon, but emerging, alpha-peptide conformations
No full textCompared with the classical secondary structural elements of proteins [a-helix, p-pleated sheets, isolated P-turns, and Poly(Pro)(n) helix] other types of helical conformations [3(10)-helix and p-turn ribbon spiral, gamma-helix, and 2.0(5)-helix] of peptides based on a-amino acids are currently emerging particularly from detailed analyses of appropriately designed model compounds. Their 3D-structural characterizations offer fascinating issues of precise control of probe -probe distances and relative orientations. Therefore, they present real potential to play a significant role as rigid, but easily tunable, spacers and templates in various areas of organic chemistry, supramolecular chemistry, and physical chemistry
The relationship between parents' violence against daughters and violence by other perpetrators - An Italian study
No full text
Tunable E- Z Photoisomerization in α,β-Peptide Foldamers Featuring Multiple (E/ Z)-3-Aminoprop-2-enoic Acid Units
No full textSystems in which an external stimulus elicits a response through some sort of modification at the molecular or supramolecular level bear potential for the development of smart materials and devices. This work describes a versatile synthetic approach suitable for the stepwise incorporation of multiple, even consecutive, units of the simplest Cα,β-unsaturated β-amino acid, (E/Z)-3-aminoprop-2-enoic acid, in peptide-based foldamers. The properties of these, including photoinduced E/Z isomerizations, were investigated
Synthesis and X-Ray Crystal Structure of the First Pure and Air-Stable Salt of Peroxymonosulphuric Acid: (Ph)4PHSO5
No full textIn this paper we describe the synthesis of tetraphenylphosphonium peroxymonosulphate, its crystal structure and packing mode. The asymmetric unit accomodates two independent molecules of the monopersulphate anion, which are held together by hydrogen bonds. In the packing mode, rows of such dimers are surrounded by four rows of tetraphenyl cations. The consequence is that the highly water sensitive HSO5¯ anions are segregated inside hydrophobic channels composed by the lipophilic cations. This circumstance presumably accounts for the exceptional stability of the title compound
A helical, aromatic, peptide nanotube
No full textThe self-assembly in the crystal state of the terminally protected, linear dipeptide Boc-(S,S)c3diPhe-(R,R)c3diPhe-NHiPr (1) through intermolecular hydrogen bonds leads to the formation of a supramolecular helix of large diameter (18 Å), internally decorated with phenyl rings. As a result, a hollow helical channel large enough to accommodate guest molecules is observed. This supramolecular structure differs from previous examples of peptide nanotubes. Compound 1 incorporates a highly restricted cyclopropane phenylalanine analogue (c3diPhe) with remarkable conformational properties
Reactive intermediates in peptide synthesis: First crystal structures and ab initio calculations of 2-alkoxy-5(4H)-oxazolones from urethane-protected amino acids
No full textThe structures of the 2-alkoxy-5(4H)-oxazolones derived from 2,2,6,6-tetramethyl-4-[(benzyloxycarbonyl)amino]-1-oxypiperidine-4-carboxylic acid and 2,2,6,6-tetramethyl-4-[(9'-fluorenylmethycarbonyl)amino]-1-oxycarbonylpiperidine-4-carboxylic acid have been solved by single-crystal X-ray diffraction. The overall geometry of their oxazolone ring compares well with that of 2-alkyl-5(4H)-oxazolones. However, the bond distance from C-2 to the exocyclic O(2) atom is shorter than expected for a (sp(2))C-O single bond, thus Suggesting a significant involvement of a O(2) lone pair in the electron delocalization of the C=N pi-system. These two structures represent the first examples of 2-alkoxy-5(4H)-oxazolones in the crystal state. Ab initio molecular orbital calculations have been performed on (4S)-2-methoxy-4-methyl-5(4H)-oxazolone and (4S)-2,4-dimethyl-5(4H)-oxazolone [as simple models for 2-alkoxy- and 2-alkyl-5(4H)-oxazolones, respectively, derived front the chiral protein amino acid L-Ala] both in the neutral and deprotonated state. The calculated geometries of the 2-alkoxy- and 2-alkyl-5(4H)-oxazolone systems at the MP2/6-31+G(d,p) level agree well with those experimentally determined in the crystal state, The calculated energetics of deprotonation show only modest differences between the two systems, Conversely, a theoretical investigation of the reaction of model oxazolones with ammonia as a nucleophile indicates that for 2-alkoxy-5(4H)oxazolones the activation energy of the rate-determining step is significantly lower and the overall stabilization energy is larger than for 2-alkyl-5 (4H)-oxazolones. The implications of these results with respect to coupling and racemization of urethane-protected amino acids in peptide synthesis are outlined
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