Stereoselective synthesis and optical resolution of chiral calix[4]arenes with mixed ligating functionalities

Exhaustive alkylation of syn-proximal bis[(2-pyridylmethyl)oxy]calix[4]arene 1 with t-butyl bromoacetate or 2-(chloromethyl)quinoline hydrochloride in the presence of Cs₂CO₃ affords selectively a new type of inherently chiral calix[4]arenes 2a,b in the partial cone conformation. (±) 2b has been resolved into its optical antipodes by an HPLC method.     

The projective rank of a Hermitian symmetric space: a geometric approach and consequences

The “Projective Rank” of a compact connected irreducible Hermitian symmetric space M has been defined as the maximal complex dimension of the compact totally geodesic complex submanifolds having positive holomorphic bisectional curvature with the induced K?hler metric. We present a geometric way to compute this invariant for the space M based on ideas developed in [1], [13] and [14]. As a consequence we obtain the following inequality relating the Projective Rank, Pr(M), the usual rank,rk(M), and the 2-number # (which is known to be equal to the Euler-Poincare characteristic in these spaces). Received: 6 June 2000 / Published online: 1 February 2002     

Synthesis,Complexation and Photophysics of 1,3-alternate Calix[4]arene-crowns-6 Bearing Fluorophoric Units on the Bridge

Abstract

Three new calix[4]arene-crown-6 derivatives bearing a fluorophoric unit on the ether bridge were synthesized. All these compounds complex alkali metal picrates in chloroform, and the naphthocrown (2) shows the highest efficiency for cesium ion binding among the calix-crown-6 known so far. Cesium over sodium selectivity is remarkably higher in acetonitrile than in chloroform solution. ¹H NMR studies, carried out in CDCl₃ on the cesium picrate complex of ligand 2, show that the anion is involved in a π-π stacking with the naphthyl unit The lariat calix[4]-crown-6 (4) does not show any relevant change in absorption and fluorescence spectra upon cesium binding, thus indicating that the dansyl unit is not perturbed by metal ion complexation. On the contrary, for ligands 2 and 3 a luminescence intensity decrease is observed upon cation binding, which allows an easy detection of cesium even at very low concentrations (10^?7M).     

Combined cup loading, bis(2-hydroxyethyl) disulfide, and protein precipitation protocols to improve the alkaline proteome of Lactobacillus hilgardii

Despite the large number of papers dealing with bacterial proteomes, very few include information about proteins with alkaline pI's, because of the limits inherent in 2-DE technology. Nonetheless, analyses of in silico proteomes of many prokaryotes show a bimodal distribution of their proteins based on their pI's; the most crowded areas lying between pI 4-7 and 9-11. The aim of the present research was to set up a general, simple, and standardizable 2-DE protocol suitable for studying the alkaline proteome of Lactobacillus hilgardii, a Gram-positive bacillus isolated from wine. The method has also been tested on a Gram-negative bacterium able to degrade aromatic pollutants, Acinetobacter radioresistens S13. Optimization of the method was mainly focused on improving protein extraction and IEF (pI 6-11) separation protocols. Concerning IEF, different methods for sample loading (in-gel rehydration and cup loading), and different reducing agents (DTT and bis(2-hydroxyethyl) disulfide (HED)) were tested and compared. The proposed protocol was found to resolve efficiently alkaline proteins from both of our Lactobacillus and Acinetobacter strains, in spite of their different external layers, thus, enabling a more comprehensive study of their proteomes.     

Nanoparticles for dewetting suppression of thin polymer films used in chemical sensors

Addition of fullerenes (C₆₀ or buckyballs) to a linear polymer has been found to eliminate dewetting when a thin (∼50 nm) film is exposed to solvent vapor. Based on neutron reflectivity measurements, it is found that the fullerenes form a coherent layer approximately 2 nm thick at the substrate – polymer film interface during the spin-coating process. The thickness and relative fullerene concentration (∼29 vol%) is not altered during solvent vapor annealing and it is thought this layer forms a solid-like buffer shielding the adverse van der Waals forces promoted by the underlying substrate. Several polymer films produced by spin- or spray-coating were tested on both silicon wafers and live surface acoustic wave sensors demonstrating fullerenes stabilize many different polymer types, prepared by different procedures and on various surfaces. Further, the fullerenes drastically improve sensor performance since dewetted films produce a sensor that is effectively inoperable.     

More on the weeks method for the numerical inversion of the Laplace transform

Summary Most of the numerical methods for the inversion of the Laplace Transform require the values of several incidental parameters. Generally, these parameters are related to the properties of the algorithm and to the analytical properties of the Laplace Transform functionF(s).One of the most promising inversion methods, the Weeks methods, computes the inverse functionf(t) as a series expansion of Laguerre functions involving two parameters, usually denoted by andb. In this paper we characterize the optimal choiceb _opt ofb, which maximizes the rate of convergence of the series, in terms of the location of the singularities ofF(s).     

Mercury in fish products: what’s the best for consumers between bluefin tuna and yellowfin tuna?

A total of 205 bluefin and yellowfin tuna samples were examined for mercury detection in order to verify possible differences and have a detailed risk assessment of the two tuna species. The results showed significant higher mercury concentration in muscle tissue of bluefin tuna respect yellowfin tuna (p < 0.001) with mean concentration of 0.84 mg/kg and maximum value of 1.94 mg/kg. These differences can be due the different biological and ecological aspects of the two tuna species and to different oceanographic aspects between Atlantic Ocean and Mediterranean sea. The results obtained in this study suggest an advisable containment of the sources of pollution and further studies on the closed-loop farming of bluefin tuna, in order to ensure the product safety.     

Superradiance and ferromagnetic behaviour

Summary The ferromagnetic behaviour is analysed in terms of a new physical mechanism based on superradiance. We show that if thed-electrons’ plasma is in a superradiant state, then ferromagnetism arises in transition metals such as Fe, Co and Ni. Satisfactory agreement with experimental information on several important quantities is obtained.