Interfacial polymerisation of anilinium at Langmuir monolayers

Anilinium is strongly adsorbed at monolayers of the phospholipid L-alpha-dimyristoylphosphatidic acid (DMPA) and hexadecanesulfonic acid (HDSA) at the air-water interface, and undergoes chemical polymerisation under conditions where bulk polymerisation does not occur.     

Aza-Claisen Rearrangement: Synthesis of 5′-branched 5′-aminothymidines

The syntheses of both diastereoisomers of 5′-ethyl-substituted thymidine dimers, the (5′R)- and (5′S)-configurated 33a and 33b respectively, in which the natural phosphodiester linkage is replaced by an amide group (C(3′)-CH₂CONH-CH(5′)(Et)), arc described. Their fully protected derivatives 35a and 35b , respectively, are suitable for incorporation into antisense oligonucleotides. Unexpectedly, an attempted Pd^II-catalysed aza-Claisen rearrangement of trichloroacetimidate 7 provided the diastereoisomerically pure cyclopropane derivative 17 , whose structure was confirmed by X-ray analysis.     

Waiting Time Variability in some Single-Server Queueing Systems

This paper considers the range of values of the coefficient of variation of waiting time in some general single-server queueing systems. It is shown that in M/G/1 systems with given ρ, the square of this coefficient increases linearly with m₁m₃/m²₂, where m_i is the ith moment of the service distribution. This implies always a lower bound, and for some widely used distributions an upper bound as well. A few ranges are illustrated and compared to those implied in two GI/M/1 systems. The usefulness of knowing such ranges for modelling purposes is explained.     

Incorporation of pseudoproline derivatives allows the facile synthesis of human IAPP, a highly amyloidogenic and aggregation-prone polypeptide

The efficient Fmoc solid-phase peptide synthesis of the 37-residue human Amylin and its amyloidogenic 8-37 fragment was achieved using pseudoproline (oxazolidine) dipeptide derivatives. Syntheses of hAmylin(8-37) using Fmoc amino acids produced only traces of the desired peptide. Incorporation of pseudoproline dipeptides produced the desired product with high yield and allowed for the synthesis of the full length peptide. The crude material was pure enough to allow formation of the Cys-2 to Cys-7 disulfide by air oxidation. [Structure: see text]     

Non-aqueous capillary electrophoresis of the positional isomers of a sulfated monosaccharide

A non-aqueous capillary electrophoresis (NACE) method coupled to indirect absorbance detection has been developed for the separation of the three positional isomers of monosulfated fucose. The optimized electrolyte was composed of 12 mM ethanolamine, 2 mM trimesic acid buffer in a methanol-ethanol (1:1, v/v) mixture. As the retained electrolyte entails no separating agent other than the pH buffer, the NACE separation of the positional isomers has been ascribed mainly to selective ion-pairing with the electrolyte counter-ion and the possibility of a selective solvation effect in the alcohol mixture. In the absence of pure isomeric standards, peak identification was completed by MS and NMR spectroscopy and selective enzymatic desulfation. This method should be of interest for the structure elucidation of monosulfated fucose-based polysaccharides and for the screening of sulfoesterase of unknown activity.     

Avalanches and self-organized criticality in simulations of particle piles

Simulations are carried out for an athermal pile of particles in the presence of a gravity-like force. As the force increases, the pile structure rearranges through discrete avalanche events. The sizes of the avalanche events are characterized by the change in energy, and it is found that the avalanche size follows a power-law probability distribution with a power-law exponent of −0.96. These results suggest that the particle pile is in a self-organized critical state.     

Capture-ROMP-release: application to the synthesis of amines and alkyl hydrazines

Application of a capture-ROMP-release strategy for the chromatography-free purification of Mitsunobu reaction products is described. Norbornenyl-tagged reagents are utilized for standard solution phase Mitsunobu chemistry. Post-reaction phase-switching is accomplished via in situ ring-opening metathesis polymerization (ROMP) followed by precipitation of the polymer with methanol. Release of the product from the polymer affords amines and alkyl hydrazine derivatives with good yields and purities.     

Bromination of sydnones. III. Bromination of 3-(2-substituted-phenyl)sydnones and subsequent side chain modification

Bromination of the sydnone ring of several ortho-substituted N-arylsydnones is reported. Subsequent side-chain modification generally can be achieved without concomitant removal of the 4-bromo protective group.     

A tris(mu-hydroxy)tricopper(II) complex as a model of the native intermediate in laccase and its relationship to a binuclear analogue

The reaction of a copper(I) complex with a sterically demanding secondary diamine ligand and O2 yields a tris(mu-hydroxy)tricopper(II) complex. This complex is a structural model of the proposed native intermediate in multicopper oxidases, with interesting structural, magnetic, and solution properties.     

Effective interactions in the colloidal suspensions from hypernetted-chain theory

The hypernetted-chain (HNC) Ornstein-Zernike integral equations are used to determine the properties of simple models of colloidal solutions where the colloids and ions are immersed in a solvent considered as a dielectric continuum and have a size ratio equal to 80 and a charge ratio varying between 1 and 4000. At an infinite dilution of colloids, the effective interactions between colloids and ions are determined for ionic concentrations ranging from 0.001 to 0.1 mol/l and compared to those derived from the Poisson-Boltzmann theory. At finite concentrations, we discuss on the basis of the HNC results the possibility of an unambiguous definition of the effective interactions between the colloidal molecules.