Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single‐Centre and Ziegler–Natta Catalysts for Ethylene Polymerization

The ability of a MgCl₂ support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu₂ with HCl gave high activity with TiCl₄ but low activity with (n‐PrCp)₂ZrCl₂. High polymerization activities with the zirconocene were only obtained with supports of type MgCl₂/AlR_n(OEt)_3−n prepared from the reaction of AlR₃ with MgCl₂ · 1.1EtOH. These supports are characterized by additional peaks in the X‐ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.

     

Surface‐enhanced Raman spectroscopy (SERS) on silver colloids for the identification of ancient textile dyes: Tyrian purple and madder

Surface‐enhanced Raman spectroscopy (SERS) was used for the identification of natural organic dyes belonging to indigoid and anthraquinone classes in archeological samples, and good agreement with the corresponding reference commercial materials was found. Special attention was paid to the well‐known problem of anomalous bands that arise sometimes in the SERS spectra on colloids: as suggested in the literature, this problem could be reduced by the use of poly‐L ‐lysine and ascorbic acid as aggregating agents, but we observed that also the addition first of the analyte and subsequently of suitable electrolytes to the colloid in an inverted order compared to the most widely used method can be of help in limiting the intensity of such spurious bands. This procedure allowed us to obtain, for the first time, the SERS spectra of both modern and ancient Tyrian purple and to solve a specific problem observed in the analysis of archeological wool samples dyed with madder lake, i.e. the competition in the SERS response between the dye and other compounds possibly deriving from the degradation of the peptide chain during the hydrolysis treatment during the extraction of the dye from the wool fiber. Copyright © 2009 John Wiley & Sons, Ltd.     

Salt Modulated Fibrillar Aggregation of the Sweet Protein MNEI in Aqueous Solution

The mechanism of conversion of globular native proteins into amyloid fibrils represents one of the most attractive research topics in biophysics, because of its involvement in the development of severe pathologies and in various biotechnological processes. Aqueous medium properties, such as pH and ionic strength, as well as interactions with other species in solution, play a key role in tuning the fibrillization process. Here, we describe a comparative study of the influence of different ions from the Hofmeister series on the thermal unfolding and aggregation propensity of MNEI, a model protein, selected because of its tendency to form amyloid aggregates at acidic pH, even at temperatures well below its melting temperature. By selecting a temperature at which only negligible amounts of protein are unfolded, we have focused on the effect of ions on fibril formation. ThT fluorescence experiments indicated that all the salts examined increased the rate and the extent of fibrillization. Moreover, we found that anions, particularly sulfate, strongly influence the process, which instead is only marginally affected by different cations. Finally, a specific link to the chloride concentration was detected.     

Binding modes identification through molecular dynamic simulations: A case study with carnosine enantiomers and the Teicoplanin A2‐2‐based chiral stationary phase

In the present study, an in silico methodology able to define the binding modes adopted by carnosine enantiomers in the setting of the chiral recognition process is described. The inter‐ and intramolecular forces involved in the enantioseparation process with the Teicoplanin A2‐2 chiral selector and carnosine as model compound are successfully identified. This approach fully rationalizes, at a molecular level, the (S) < (R) enantiomeric elution order obtained under reversed‐phase conditions. Consistent explanations were achieved by managing molecular dynamics results with advanced techniques of data analysis. As a result, the time‐dependent identification of all the interactions simultaneously occurring in the chiral selector‐enantiomeric analyte binding process was obtained. Accordingly, it was found that only (R)‐carnosine is able to engage a stabilizing charge–charge interaction through its ionized imidazole ring with the carboxylate counter‐part on the chiral selector. Instead, (S)‐carnosine establishes intramolecular contacts between its ionized functional groups, that limit its conformational freedom and impair the association with the chiral selector unit.     

Diamond-like carbon coatings for the protection of metallic artefacts: effect on the aesthetic appearance

Plasma-enhanced chemical vapour deposition (PECVD) is an environmentally friendly process used to deposit a variety of nano-structured coatings for the protection or the surface modification of metallic artefacts like the SiO₂-like films that have been successfully tested on ancient silver, bronze and iron artefacts as barriers against aggressive agents. This paper deals with the preliminary results of a wider investigation aimed to the development of eco-sustainable coatings for the protection of Cu and Ag-based artefacts of archaeological and historic interest. Diamond-like carbon (DLC) coatings have been deposited by PECVD in different experimental conditions, in a capacitively coupled asymmetric plasma reactor, placing the substrates either on electrically powered electrode (cathodic mode) or grounded electrode (anodic mode) with and without hydrogen addition in the gas mixture. The final goal is to develop a coating with good protective effectiveness against aggressive atmospheres and contemporarily with negligible effects on the aesthetic appearance of the artefacts. The evaluation of possible colour changes of the surface patinas, due to coating process, was performed by optical microscopy and colorimetric measurements. Furthermore, to evaluate the reversibility of the thin DLC layer, an etching treatment in oxygen plasma has been successfully carried out and optimized. The chemical-physical characterization of the deposited DLC coatings was performed by means of the combined use of micro-Raman and XPS spectroscopies. The results show that the DLC films obtained in the anodic mode, may be proposed as a viable alternative to polymeric coatings for the protection of metallic ancient objects.     

New Developments and Results for Mathematical Models in Environment Evaluations

A new mathematical model capable to provide a detailed evaluation of the ecological state of an environmental system is here presented. The mathematical model consists in a set of ordinary differential equations. The state variable of the system is the so-called Biological Territorial Capacity. The analysis is performed at the scale of each biotope that is the patch of land cover with homogeneous vegetation. Since the model consists in a very large number of ODE, in order to implement numerical computations with a fast algorithm, an approximated solution procedure is proposed. Finally a study case with comparisons between different designs and plans of the territory under investigation is performed.     

A large‐volume gas cell for high‐energy X‐ray reflectivity investigations of interfaces under pressure

A cell for the investigation of interfaces under pressure is presented. Given the pressure and temperature specifications of the cell, P≤ 100 bar and 253 K ≤T≤ 323 K, respectively, high‐energy X‐rays are required to penetrate the thick Al₂O₃ windows. The CH₄(gas)/H₂O(liquid) interface has been chosen to test the performance of the new device. The measured dynamic range of the high‐energy X‐ray reflectivity data exceeds 10^?8, thereby demonstrating the validity of the entire experimental set‐up.     

The give-up problem for blocked regional lists with multi-winners

The current electoral law for the Italian Parliament prescribes blocked, linearly ordered lists of candidates for each party within each constituency. The peculiarity of the Italian electoral system is that a party can present the same candidate in different constituencies. There are several seats at stake in each constituency; these seats are allocated to the parties proportionally to the total number of votes they get. If the blocked list mechanism-which assigns the seats obtained by a party in a constituency to the first candidates of the corresponding ordered list-causes some candidates to win in more than one constituency, they may retain only one of the seats, giving up all the remaining ones. Thus, the problem arises for a party to find a suitable “schedule of give-ups” that produces the final set of winners for that party. In order to do this, we assume that such decision is centralized and based on some models of global (inter-regional) preferences over the set of candidates. In this paper, we introduce two classes of models to formulate the “give-up problem”, i.e., utility and ordinal models, and we show that for both of them some natural formulations of the problem can be efficiently solved by network flows techniques.     

Synthetic Potential of Fucosyltransferase III for the Synthesis of Fluorescent‐labeled Milk Oligosaccharides

Various fundamental biologic roles of milk oligosaccharides have been recognized; however, their structure‐affinity relationship is still not fully revealed. Herein, we describe the synthesis of the fluorescent‐labeled milk oligosaccharides 3‐(5‐dimethylaminonaphthalene‐1‐sulfonylamino)propyl β‐D‐galactopyranosyl‐(1→3)‐[α‐L‐fucopyranosyl‐(1→4)]‐2‐acetamido‐2‐deoxy‐β‐D‐glucopyranoside (1) and 3‐(5‐dimethylamino‐naphthalene‐1‐sulfonylamino)propyl β‐D‐galactopyranosyl‐(1→3)‐[α‐L‐fucopyranosyl‐(1→4)]‐β‐D-glucopyranoside (2) as useful tools for synthetic, analytic, and biologic applications. For the fucosylation of lactose and lacto‐N‐biose, the chemical and the enzymatic syntheses using fucosyltransferase III were compared.