Sulle varietà abeliane

Alla memoria di Guido Castelnuovo, nel primo centenario della nascita.     

Catalysis on gold-nanoparticle-passivating monolayers

Clusters of gold atoms in the range 1–100 nm of diameter are unstable and tend to aggregate to form insoluble materials but become very stable once passivated with a monolayer of organic molecules typically anchored on the surface via an Au–S bond. The properties of this monolayer as a reaction loci constitute the topic of this overview of the recent literature. In analyzing the examples reported with functionalized monolayers we show how efficient catalysts these systems may become. Several data point out the occurrence of unusual reaction pathways and significant cooperativity between functional groups not observed not only in monomeric equivalent catalysts but also in other aggregation colloids like micelle and vesicles. The picture that emerges is that of a unique environment mimicking several features of enzymatic processes.     

Polypeptide grafted hyaluronan: A self-assembling comb-branched polymer constructed from biological components

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(l-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(l-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.     

Ruthenium molecular wires with conjugated bridging ligands: onset of band formation in linear inorganic conjugated oligomers

We have prepared and characterized a series of multimetallic oligomers of Ru using the pi-conjugated bridging ligand tetra-2-pyridyl-1,4-pyrazine (tppz), as well as mixed-ligand complexes with terpyridine end caps, and analyzed their electrochemical and spectroscopic properties, comparing them with modern computational electronic structure methods. The results suggest that the high degree of metal-metal interunit communication in these linear oligomers yields low HOMO-LUMO gaps, high delocalization, and the onset of "quasi-band" features, all indicative that these compounds should be excellent molecular wire materials. Recent spectroscopic and excited-state analyses of these and related compounds focus on optically accessible states, which ignore optically silent frontier electronic states more relevant to nanoelectronic applications.     

Metal chelate formation using a task-specific ionic liquid

An imidazolium-based task-specific ionic liquid containing an ethylaminediacetic acid moiety readily results in the formation of 2:1 octahedral chelate complexes with aqueous Co2+, Ni2+, and Cu2+.     

Using modulated DSC to investigate the origin of multiple thermal transitions in frozen 10% sucrose solutions

Modulated differential scanning calorimetry (MDSC) was used to investigate the effect of annealing on multiple thermal transitions in frozen aqueous sucrose solutions. Two thermal transitions were detected from the reversing heat flow. Here, to maintain consistency with terminology used in the practice of freeze-drying [1], the higher temperature is denoted, T^′g, and the lower transition is given the symbol, T^″g. The transition at low temperature is usually believed to be a true glass transition. However, the origin of the transition at high temperature is still highly controversial. Based upon a study of 10% sucrose solutions with different cooling histories and annealing conditions, we suggest that the transition at high temperature is also a glass transition. We conclude that the lower transition is a glass transition of a phase plasticized by a higher than equilibrium amount of unfrozen water, and the higher transition, T^′g, corresponds to a glass transition in a maximally freeze-concentrated solute phase.