Molecular acrobatics: self-assembly of calixarene-porphyrin cages

Calix[4]arenes equipped with two and four zinc porphyrins have been prepared, and they show remarkable flexibility in their self-assembly properties with the bidentate ligand DABCO. The calix-bisporphyrin forms a 2:2 complex with DABCO, generating a large cavity that has the potential to act as a supramolecular host. The calix-tetraporphyrin, on the other hand, forms four different complexes with DABCO depending on the stoichiometry and concentration. During the course of a titration, all four complexes are populated, leading to large conformational changes and the formation of both intramolecular and intermolecular calix-tetraporphyrin-DABCO sandwich complexes. The system was fully characterized using a combination of UV-visible and (1)H NMR spectroscopy to identify the complexes. At a calix-tetraporphyrin:DABCO ratio of 2:4, the major species is dimeric cage assembly that features a large internal cavity for guest complexation.     

Chemistry at surfaces: from ab initio structures to quantum dynamics

Recent years have witnessed an ever growing interest in theoretically studying chemical processes at surfaces. Apart from the interest in catalysis, electrochemistry, hydrogen economy, green chemistry, atmospheric and interstellar chemistry, theoretical understanding of the molecule–surface chemical bonding and of the microscopic dynamics of adsorption and reaction of adsorbates are of fundamental importance for modeling known processes, understanding new experimental data, predicting new phenomena, controlling reaction pathways. In this work, we review the efforts we have made in the last few years in this exciting field. We first consider the energetics and the structural properties of some adsorbates on metal surfaces, as deduced by converged, first-principles, plane-wave calculations within the slab-supercell approach. These studies comprise water adsorption on Ru(0001), a subject of very intense debate in the past few years, and oxygen adsorption on aluminum, the prototypical example of metal passivation. Next, we address dynamical processes at surfaces with classical and quantum methods. Here the main interest is in hydrogen dynamics on metallic and semi-metallic surfaces, because of its importance for hydrogen storage and interstellar chemistry. Hydrogen sticking is studied with classical and quasi-classical means, with particular emphasis on the relaxation of hot–atoms following dissociative chemisorption. Hot atoms dynamics on metal surfaces is investigated in the reverse, hydrogen recombination process and compared to Eley–Rideal dynamics. Finally, Eley–Rideal, collision-induced desorption, and adsorbate-induced trapping are studied quantum mechanically on a graphite surface, and unexpected quantum effects are observed.     

Projective surfaces withk-very ample line bundles of genus ≤3k+1

Let be the set of surfaces,S, polarized by a k-very ample line bundle,L, with genus≤3k+1. All the elements (S, L) of are listed. The classification of surfaces polarized by ak-very ample line bundle of degree ≤4k+4 is completed by proving that this class of surfaces is a subset of .     

Analytical prediction and experimental validation for longitudinal control of cable oscillations

The paper summarizes the knowledge acquired from the analytical studies and the experimental implementation of a longitudinal non-collocated control strategy for the reduction of cable oscillations. The control is introduced by imposing a longitudinal action at one support based on the knowledge of transverse displacements and velocities of a few selected points. A spatially one-dimensional continuous model of a suspended cable has been used to describe the main features of the non-collocated longitudinal active control strategy. A discrete modal representation has permitted the introduction of suitable non-linear state-feedback controllers. The results have been used to derive an implementable strategy, based on direct output feedback, which preserves the main previous control features. A physical model of an actively controlled cable has been used to demonstrate the control effectiveness of the proposed strategy through a large campaign of experiments, conducted in various frequency ranges and amplitude levels including meaningful external resonance conditions. The responses predicted by the analytical model and the experimental results show good qualitative agreement with one another, in both the uncontrolled and controlled experienced cable dynamics.     

Stability and phase transformations of the mesomorphic form of isotactic polypropylene in stereodefective polypropylene

A study of the thermodynamic stability and the related polymorphic transformations induced by thermal treatments of the mesomorphic form that crystallizes in stereodefective metallocene isotactic polypropylene (iPP) is presented. We show that the mesomorphic form of the more isotactic samples is stable at room temperature, whereas the mesomorphic form crystallizing in the more stereoirregular sample is unstable and crystallizes at room temperature in the crystalline α form. In any case, the mesomorphic form transforms during heating or by annealing at temperatures higher than 60–80 °C always in the α form, regardless of the stereoregularity, even in the case of stereoirregular samples generally crystallizing from the melt in the γ form. These data confirm the proposed model of structure of the mesomorphic form as small aggregates of chains in three-fold helical conformation packed with lateral correlations similar to the α form of iPP.     

The synthesis of a series of 7-amino-1-cyclopropyl-8-fluoro-1,4-dihydro-4-oxo-1,6-naphthyridine-3-carboxylic acids as potential antibacterial agents

A series of 7-amino-1-cyclopropyl-1,4-dihydro-8-fluoro-4-oxo-1,6-naphthyridine-3-carboxylic acids has been prepared and evaluated for antibacterial activity. These compounds were prepared by the displacement of the chloro substituent from 7-chloro-1-cyclopropyl-1,4-dihydro-8-fluoro-4-oxo-1,6-naphthyridine-3-carboxylic acid employing the requisite nitrogen nucleophile to produce the title compounds. The naphthyridine acid was synthesized in ten steps from ethyl 2,4-dihydroxy-3-nitro-5-pyridinecarboxylate. The key step in the sequence was a Schiemann reaction carried out using the hexafluorophosphate salt of the diazonium ion derived from ethyl 3-amino-2,4-dichloro-5-pyridinecarboxylate.     

Effects of mutational (Lys to Ala) surface charge changes on the redox properties of electrode-immobilized cytochrome c

Untrimethylated yeast iso-1-cytochrome c (cytc) and its single and multiple Lys to Ala variants at the surface lysines 72, 73, and 79 were adsorbed on carboxyalkanethiol self-assembled monolayers (SAMs) on gold, and the thermodynamics and kinetics of the heterogeneous protein-electrode electron-transfer (ET) reaction were determined by voltammetry. The reaction thermodynamics were also measured for the same species freely diffusing in solution. The selected lysine residues surround the heme group and contribute to the positively charged domain of cytc involved in the binding to redox partners and to carboxyl-terminated SAM-coated surfaces. The E degrees' (standard reduction potential) values for the proteins immobilized on SAMs made of 11-mercapto-1-undecanoic acid and 11-mercapto-1-undecanol on gold were found to be lower than those for the corresponding diffusing species owing to the stabilization of the ferric state by the negatively charged SAM. For the immobilized proteins, Lys to Ala substitution(s) do not affect the surface coverage, but induce significant changes in the E degrees' values, which do not simply follow the Coulomb law. The results suggest that the species-dependent orientation of the protein (and thereby of the heme group) toward the negatively charged SAM influences the electrostatic interaction and the resulting E degree' change. Moreover, these charge suppressions moderately affect the kinetics of the heterogeneous ET acting on the reorganization energy and the donor-acceptor distance. The kinetic data suggest that none of the studied lysines belong to the interfacial ET pathway.