Analytical applications of membrane extraction in chromatography and electrophoresis

An overview of the analytical applications of membrane-based systems for sample enrichment in chromatography and capillary electrophoresis is presented. A brief introduction to the different types of membranes and the main forces related to the transport through them is also given.     

3-methylthiophene self-assembled monolayers on planar and nanoparticle Au surfaces

In this article the adsorption of 3-methylthiophene on planar and nanoparticle Au surfaces is investigated. The resulting systems are compared with a benchmark system based on 1-decanethiol. The characterization data collected evidence the formation of a packed 3-methylthiophene SAM on the planar surface. In particular, spectroscopic investigations suggest that 3-methylthiophene aromatic system is not adsorbed on the surface through the pi-electron system but rather through the S atom alone. On the other hand, the behavior of 3-methylthiophene on nanoparticle surfaces is notably different from that of the alkanethiol. Only a limited fraction of the surface of Au nanoparticles results to be actually coated after purification; this notwithstanding, the nanoparticle growth seems to be strongly influenced by the presence of such a labile encapsulating agent.     

Diffusion-controlled solid-state reactions of spherical particles, a general model for multiphase binary systems

The formal treatment of the diffusion-controlled growth of n binary compounds with narrow homogeneity range during the reaction of a sphere of reactant A immersed in reactant B is presented and discussed. Both constituents are assumed to be mobile. The reaction products are assumed to grow simultaneously as uniform and compact concentric layers with ideal contact at the interfaces as well as at the external surface of the sphere. The kinetic equations follow from the coupling between chemical reactions and partitioning of the diffusion flux at phase boundaries. The results for the formation of two and three compounds are presented. The influence of the initial radius of the sphere, of the relative magnitude of the kinetic constants, and of the volume variation is discussed in detail.     

Localization Operators and Exponential Weights for Modulation Spaces

We study localization operators within the framework of ultradistributions. More precisely, given a symbol a and two windows φ₁, φ₂, we investigate the multilinear mapping from to the localization operator Results are formulated in terms of modulation spaces with weights which may have exponential growth. We give sufficient and necessary conditions for a to be bounded or to belong to a Schatten class. As an application, we study symbols defined by ultra-distributions with compact support, that give trace class localization operators.     

How the First Partial Transpose was Written

We tell the tale of the first writing of a partial transpose, without guaranteeing historical authenticity. Dedicated to Prof. Asher Peres, Haifa, on the occasion of his 70th birthday.     

Folding and unfolding of an elastinlike oligopeptide: "inverse temperature transition," reentrance, and hydrogen-bond dynamics

The temperature-dependent behavior of a solvated oligopeptide, GVG(VPGVG), is investigated. Spectroscopic measurements, thermodynamic measurements, and molecular dynamics simulations find that this elastinlike octapeptide behaves as a two-state system that undergoes an "inverse temperature" folding transition and reentrant unfolding close to the boiling point of water. A molecular picture of these processes is presented, emphasizing changes in the dynamics of hydrogen bonding at the protein/water interface and peptide backbone librational entropy.     

Electronic control of chiral quaternary center creation in the intramolecular asymmetric heck reaction

The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems.     

A simple geometrical model for emulsifier free polymer colloid formation

In this paper we propose a simple model for the formation of monodisperse polymer colloids, which provides a convenient set of synthetic parameters for given bead diameters. We provide experimental data in support of this model.     

Models for biological trinuclear copper clusters. Characterization and enantioselective catalytic oxidation of catechols by the copper(II) complexes of a chiral ligand derived from (S)-(-)-1,1'-binaphthyl-2,2'-diamine

The dinuclear and trinuclear Cu(II) complexes of an octadentate ligand derived from (S)-1,1'-binaphthyl-2,2'-diamine have been prepared and characterized by UV/Vis, CD, EPR and NMR spectroscopy. The ligand contains two tridentate aminobis(benzimidazole) donor arms connected to a central bidentate diaminobinaphthyl linker, which hosts the chiral unit. In the dinuclear Cu complex the ligation occurs essentially within the tridentate arms of the ligand. The two Cu centers are EPR nonequivalent and noninteracting. The EPR data suggests that one of the Cu ions additionally interacts with one of the tertiary aminonaphthyl donors. In the trinuclear complex the two aminonaphthyl donors bind the third Cu ion. The EPR spectrum of this complex shows the signal for a mononuclear Cu(II) center bound to a tridentate arm, while the remaining two Cu(II) centers are coupled through hydroxo groups. The CD spectrum shows that in the free ligand a severe reduction of the dihedral angle between the naphthyl groups from the strain free range occurs. This conformation is stabilized by ring stacking interactions with the benzimidazole groups. On complex formation this interaction is removed because the benzimidazole groups are involved in metal binding. In the dinuclear Cu complex the conformation of the binaphthyl chromophore probably approaches the strain free range, while in the trinuclear Cu complex a marked flattening of the dihedral angle between the two naphthyl rings occurs. Both complexes are active catalysts in the oxidation of L-/D-Dopa derivatives to quinones. High enantioselectivity is observed in the oxidation of L-/D-Dopa methyl ester catalyzed by the dinuclear Cu complex, which exhibits strong preference for the d enantiomer. The enantioselectivity is largely lost for the trinuclear Cu complex.