Decoration of au and ag nanoparticles on self-assembling pseudopeptide-based nanofiber by using a short peptide as capping agent for metal nanoparticles

The surface of a nanofiber that is formed from a self-assembling pseudopeptide has been decorated by gold and silver nanoparticles that are stabilized by a dipeptide. Transmission electron microscopic images make the decoration visible. In this paper, a new strategy of mineralizing a pseudopeptide based nanofiber by gold and silver nanoparticles with use of a two-component nanografting method is described.

The first preparation of beta-lactones by radical cyclization

beta-Lactones have, for the first time, been prepared by 4-exo-trig radical cyclization. Thus, alpha-ethenoyloxy radicals react in the presence of tributylstannane in a photothermal process to give beta-lactones. Highest yields were obtained when groups capable of stabilizing a carboncentered radical were present at the 3-position of the alkenoate acceptor.

A general synthesis of macrocyclic pi-electron-acceptor systems

Cyclocondensations of aromatic diamines with 1,1'-bis(2,4-dinitrophenyl)-4,4'-bipyridinium salts afford doubly or quadruply charged, macrocyclic, N,N'-diarylbipyridinium cations. These are tolerant of a wide range of acids, bases, and nucleophiles, although they appear to undergo reversible, one-electron reduction by tertiary amines. Single-crystal X-ray analysis demonstrates the presence of a macrocycle conformation in which the 4,4'-bipyridinium and 4,4'-biphenylenedisulfonyl residues are suitably spaced and aligned for complexation with pi-donor arenes, and NMR studies in solution indeed confirm binding to 1,5-bis[hydroxy(ethoxy)ethoxy]naphthalene.

Extreme complementarity in a macrocycle-tweezer complex

Interaction of a novel pyrene-based tweezer molecule with a macrocyclic ether-imide-sulfone results in formation of a strongly bound complex (K-a = 24 000 M-1) in which binding results not only from pi-pi stacking interactions involving pyrene units as donors and macrocyclic naphthalene-tetracarboximide and biphenylenedisulfone groups as acceptors but also from N-(HO)-O-... and C-(HO)-O-... hydrogen bonds and from "reverse" pi-stacking of the electron-poor isophthaloyl residue of the tweezer with an electron-rich 3-aminophenoxy residue of the macrocyclic imide.

Stereoselective entry to beta-linked C-disaccharides using a carbon-Ferrier reaction

[GRAPHICS] The synthesis of unsaturated beta-linked C-disaccharides by the Lewis acid-mediated reaction of 3-O-acetylated glycals with monosaccharide-derived alkenes is described. Deprotection and selective hydrogenation of an exocyclic carbon-carbon double, in the presence of an endocyclic double bond, for representative targets is also illustrated.

Stereodivergent approach to the asymmetric synthesis of bacillariolides: A formal synthesis of ent-bacillariolide II

Asymmetric synthesis of densely functionalized bicyclic frameworks for entry into bacillariolides I/III and ent-bacillariolide II is reported. The key features are ring-closing metathesis of a pair of diastereomerically related dienes obtained through a stereodivergent route from a R-(+)-glyceraldehyde derivative, transformation of a nonstereoselective cyclopentene ester enolate alkylation process to a completely stereoselective one through alkylation of a bulky ester enolate with a bulky electrophile, and a remote silyloxymethyl group directed epoxidation.

A new molecular scaffold for the formation of supramolecular peptide double helices: the crystallographic insight

A series of water-soluble synthetic dipeptides (1-3) with an N-terminally located beta-alanine residue, beta-alanyl-L-valine (1), beta-alanyl-L-isoleucine (2), and beta-alanyl-L-phenylalanine (3, form hydrogen-bonded supramolecular double helices with a pitch length of 1 nm, whereas the C-terminally positioned beta-alanine containing dipeptide (4), L-phenylalanyl-beta-alanine, does not form a supramolecular double helical structure. beta-Ala-Xaa (Xaa = Val/Ile/Phe) can be regarded as a new motif for the formation of supramolecular double helical structures in the solid state.

A novel trinuclear nickel(II) complex of an unsymmetrical tetradentate ligand involving bridging oxime and acetylacetone functions

A novel trinuclear nickel(II) complex, [Ni-3(L)(2)(H2O)(2)](ClO4)(2), where L is a bridging unsymmetrical tetradentate ligand, involving o-phenylenediamine, diacetyl monoxime and acetylacetone (H2L = 4-[2-(3-hydroxy-1-methyl-but-2-enylideneamino)-phenylimino]-pentan-2- one oxime) has been synthesized and characterized structurally. In the complex, an octahedral Ni( II) centre is held in the middle by two square planar units with the aid of oxime and ketonic bridges. (c) 2007 Elsevier B. V. All rights reserved.

Water-soluble tripeptide A beta(9-11) forms amyloid-like fibrils and exhibits neurotoxicity

A water-soluble, hydrophilic tripeptide GYE, having sequence identity with the N-terminal segment of amyloid peptides A,beta(9-11), upon self-association exhibits amyloid-like fibrils and significant neurotoxicity towards the Neuro2A cell line. However, the tripeptides GFE and GWE, in which the centrally located tyrosine residue has been replaced by phenylalanine or tryptophan, fail to show amyloidogenic behavior and exhibit little or no neurotoxicity.

Development of tyrosinase labile protecting groups for amines

The development of two novel protecting groups for amines is described. Thus, a range of amines have been converted to ureas, and the deprotection of these upon exposure to mushroom tyrosinase (E.C. 1.14.18.1) has been demonstrated.

A new motif in the formation of peptide nanotubes: the crystallographic signature

Terminally protected acyclic tripeptides Boc-Tyr(1)-Val(2)-Tyr(3)-OMe 1 and Boc-Tyr(1)-lle(2)-Tyr(3)-OMe 2 self-assemble into nanotubes in crystals through various noncovalent interactions with an average internal diameter of 5 Angstrom (0.5 nm), and the tubular ensemble is developed through the hydrogen-bonded side chains of tyrosine residues. The inside of the hollow nanotubular structures is hydrophilic; however, no solvent molecules have been crystallographically detected.

A new class of ammonium ylid for [2,3]-sigmatropic rearrangement reactions: ene-endo-spiro ylids

The first examples of sigmatropic rearrangements of ene-endo-spirocyclic, tetrahydropyridine-derived ammonium ylids are reported. Thus, spiro[6.7]-ylids rearrange primarily by a [2,3]-pathway, whereas the analogous [6.6]-ylids rearrange by [1,2]- and [2,3]-mechanisms in roughly equal proportions. This method serves as a rapid entry to the core of a range of alkaloids bearing a pyrrolo[1,2-a]azepine or octahydroindolizidine nucleus.

First efficient and general copper-catalyzed [2,3]-rearrangement of tetrahydropyridinium ylids

The factors affecting the copper-catalyzed rearrangement of ammonium ylids derived from tetrahydropyriclines and diazoesters; have been examined,and the first examples of high-yielding metal-catalyzed [2,3]-sigmatropic rearrangements of a wide range of such ylids are reported. The nature of the alpha-substituent in the diazo component of the reaction has a dramatic effect upon the yields of the reaction, with electron-withdrawing substituents enhancing the yield of the reaction.

Ultra-thin porous silica coated silver-platinum alloy nano-particle as a new catalyst precursor

Templated sol-gel encapsulation of surfactant-stabilised micelles containing metal precursor(s) with ultra-thin porous silica coating allows solvent extraction of organic based stabiliser from the composites in colloidal state hence a new method of preparing supported alloy catalysts using the inorganic silica-stabilised nano-sized, homogenously mixed, silver - platinum (Ag-Pt) colloidal particles is reported.