Preparation of Neutral Ionophores for Alkali and Alkaline Earth Metal Cations and their application in ion selective membrane electrodes

The preparation of a series of non-cyclic, uncharged ligands able to selectively complex alkali and alkaline earth metal cations is described. These molecules are designed to be used as carriers for cations through membranes. Some of the compounds show high Ca²⁺ and Na⁺ selectivity, respectively, in liquid membrane electrodes.     

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.     

A facile retro-ene reaction of 5-(methoxyamino)-3-aryl-1,3,4-oxadiazol-2(3H)-ones

5-(N-Methoxy-N-methyl)amino-3-aryl-1,3,4-oxadiazol-2(3H)-ones 3 undergo a heteroretro-ene reaction in refluxing methanol in which the leaving enophile is formaldehyde. The resulting 5-(methylimino)-3-aryl-1,3,4-oxadiazolidin-2-one 4 may be viewed as a kinetic product which tautomerizes to the more stable 5-(methylamino)-3-aryl-1,3,4-oxadiazol-2(3H)-one 5 as the thermodynamic product. Comparison of calculated reaction energies reveals that the presence of the heterocyclic ring facilitates the retro-ene reaction, but the expulsion of formaldehyde is predicted to be highly exothermic even in its absence.     

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.     

The solvation of Li and Na in acetonitrile from ab initio-derived many-body ion–solvent potentials

Several Li⁺- and Na⁺-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN)_n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Böhm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li⁺(MeCN) and Na⁺(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li⁺ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na⁺ is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.     

Model complexes for metallated polythiophenes: gold(I) and palladium(II) complexes of bis(diphenylphosphino)oligothiophenes

The preparations of two new phosphinothiophene ligands, 3,3'-bis(diphenylphosphino)-2,2'-bithiophene (dppbt; 1) and 3,3' "-dihexyl-3',3' '-bis(diphenylphosphino)-2,5':2',2' ':5' ',2' "-quaterthiophene (hdppqt; 2) are reported. Oxidation of 1 gives 3,3'-bis(diphenylphosphine oxide)-2,2'-bithiophene (3), and the crystal structure of this compound was determined. Pd(II) and Au(I) complexes of these ligands have been synthesized and characterized. Crystal structures of [(dppbt)PdCl(2)] (1-Pd), [(hdppqt)PdCl(2)] (2-Pd), [(dppbt)(AuCl)(2)] (1-Au), and [(hdppqt)(AuCl)(2)] (2-Au) were obtained. [(dppbt)(AuCl)(2)] crystallized in two solid-state forms; crystals grown from CH(2)Cl(2)/Et(2)O show a gold-gold interaction of 3.3221(4) A, but from CH(2)Cl(2)/toluene, the molecule crystallizes as a toluene adduct (1-Au-tol) and does not show any gold-gold interaction. All the complexes were characterized via UV-vis spectroscopy and cyclic voltammetry, and the effect of the metal on the energy of the pi-pi transition and oxidation potential was determined. These data are correlated to the interannular torsion angles in the oligothienyl groups from the crystal structure studies.     

Reaction of hydroxylamine with 5-aminooxazoles. A new route to isoxazoles

The nucleophilic attack of hydroxylamine at the 5 position of 2-aryl-4-trifluoroacetyl-5-amino-oxazoles leads to a mixture of stereoisomeric isoxazolines. Dehydration of these isomeric isoxazolines in the presence of trifluoroacetic anhydride gives 3-amino-4-acylamino-5-trifluoromethylisoxazoles. The structures and spectroscopic data of these compounds are discussed.