Jet-fluid string formation and decay in high-energy heavy-ion collisions

We propose a new hadronization mechanism, jet-fluid string (JFS) formation and decay, to understand observables in intermediate to high-$p_{T}$ regions comprehensively. In the JFS model, hard partons produced in jet lose their energy in traversing the QGP fluid, which is described by fully three-dimensional hydrodynamic simulations. When a jet parton escapes from the QGP fluid, it picks up a partner parton from a fluid and forms a color singlet string, then it decays to hadrons. We find that high-$p_T$ $v_2$ values in JFS are about two times larger than in the independent fragmentation model.Comment: 6 pages, 2 figures; Proceeding for poster sessions at Quark Matter 2006, Shanghai, China, 14-20 November 2006; to appear in Int. J. of Mod. Phys.

Search for a Ridge Structure Origin with Shower Broadening and Jet Quenching

We investigate the role of jet and shower parton broadening by the strong colour field in the $\Delta\eta$-$\Delta\phi$ correlation of high $p_T$ particles. When anisotropic momentum broadening ($\Delta p_z > \Delta p_T$) is given to jet and shower partons in the initial stage, a ridge-like structure is found to appear in the two hadron correlation. The ratio of the peak to the pedestal yield is overestimated.Comment: Talk given at 20th Int. Conf. on Ultra-Relativistic Nucleus-Nucleus Collisions, Jaipur, India, Feb.4-10, 200

Re-Hardening of Hadron Transverse Mass Spectra in Relativistic Heavy-Ion Collisions

We analyze the spectra of pions and protons in heavy-ion collisions at relativistic energies from 2 A GeV to 65+65 A GeV by using a jet-implemented hadron-string cascade model. In this energy region, hadron transverse mass spectra first show softening until SPS energies, and re-hardening may emerge at RHIC energies. Since hadronic matter is expected to show only softening at higher energy densities, this re-hardening of spectra can be interpreted as a good signature of the quark-gluon plasma formation.Comment: 10 pages, 3 figures, 1 table, Poster presentation at QM2001, Revised to correct latex error in citation on April 6, 200

Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies

We investigate the relativistic equation of state of hadronic matter and quark-gluon plasma at finite temperature and baryon density in the framework of the non-extensive statistical mechanics, characterized by power-law quantum distributions. We impose the Gibbs conditions on the global conservation of baryon number, electric charge and strangeness number. For the hadronic phase, we study an extended relativistic mean-field theoretical model with the inclusion of strange particles (hyperons and mesons). For the quark sector, we employ an extended MIT-Bag model. In this context we focus on the relevance of non-extensive effects in the presence of strange matter.Comment: 12 pages, 5 figure

"Egg of Columbus": single-step complete removal of chloride impurities from ionic liquids by AgCl deposition on silver electrode

Chloride impurities in ionic liquids (ILs), which can be present even in huge amounts depending on the IL synthetic route, are particularly critical for electrochemical processes; thus, their abatement is often mandatory. However, while their analytical quantification has been the subject of many studies involving a variety of techniques, the so far available processes for their abatement are still unsatisfactory, having low efficiency, and/or involving multiple steps, and/or being far from mild and easily scalable. In this context, like an "egg of Columbus", a quite simple and safe process for chloride abatement in ILs is proposed, practically coinciding with the electrolytic preparation of a Ag|AgCl electrode. It proceeds in a single step, at room temperature, at very low potentials, with nearly ideal current efficiencies, and with negligible side effects on the electrolyzed IL. The chloride impurities are quantitatively captured and accumulated on the silver wire and eliminated by simply removing the resulting Ag|AgCl electrode from the solution, with no need of subsequent treatments

Particlization in hybrid models

In hybrid models, which combine hydrodynamical and transport approaches to describe different stages of heavy-ion collisions, conversion of fluid to individual particles, particlization, is a non-trivial technical problem. We describe in detail how to find the particlization hypersurface in a 3+1 dimensional model, and how to sample the particle distributions evaluated using the Cooper-Frye procedure to create an ensemble of particles as an initial state for the transport stage. We also discuss the role and magnitude of the negative contributions in the Cooper-Frye procedure.Comment: 18 pages, 28 figures, EPJA: Topical issue on "Relativistic Hydro- and Thermodynamics"; version accepted for publication, typos and error in Eq.(1) corrected, the purpose of sampling and change from UrQMD to fluid clarified, added discussion why attempts to cancel negative contributions of Cooper-Frye are not applicable her

When ring makes the difference: coordination properties of Cu2+/Cu+ complexes with sulfur-pendant polyazamacrocycles for radiopharmaceutical applications

Three polyazamacrocyclic ligands, i.e. 1,5,9-tris[2-(methylsulfanyl)ethyl]-1,5,9-triazacyclododecane (TACD3S), 1,4,7,10-tetrakis[2-(methylsulfanyl)ethyl]-1,4,7,10-tetrazacyclotridecane (TRI4S) and 1,4,8,11-tetrakis[2-(methylsulfanyl)ethyl]-1,4,8,11-tetrazacyclotetradecane (TE4S), were considered as potential chelators for the medically relevant copper radioisotopes. The ligands have been synthesized through facile, single-step reactions, and their acidity constants have been measured in aqueous solution at 25 degrees C. The kinetic, thermodynamic, electrochemical and structural properties of their Cu2+ and Cu+ complexes were investigated in aqueous solution at 25 degrees C using spectroscopic (UV-Visible, EPR, NMR) and electrochemical techniques (pH-potentiometric titrations, cyclic voltammetry and electrolysis). TACD3S was demonstrated to be unable to stabilize Cu2+, whereas for TRI4S and TE4S the formation of stable monocupric (CuL2+) and monocuprous (CuL+) complexes was detected. TRI4S coordinates Cu(2+)via a [4N] and a [4N]S array of donor atoms while with TE4S only the latter geometry exists. The thermodynamic stability and the kinetic inertness of the copper complexes formed by TACD3S, TRI4S and TE4S were compared with those previously reported for 1,4,7,10-tetrakis-[2-(methylsulfanyl)ethyl]-1,4,7,10-tetrazacyclododecane (DO4S) to unravel the influence of the ring size and the nitrogen donor array on the copper chelation properties of these sulfur-rich macrocycles. The copresence of four nitrogen atoms is an essential feature to allow effective copper coordination when a 12-member ring is employed, as the Cu2+-DO4S complexes were far more stable than those of Cu2+-TACD3S. Furthermore, the larger ring size of TRI4S and TE4S, when compared to DO4S, progressively increases the rate of the Cu2+ complexation reactions but decreases the thermodynamic stability of the Cu2+ complexes. Despite this, the ability of TRI4S and TE4S to stably accommodate both copper oxidation states makes them very attractive for application in nuclear medicine as they could avoid the demetallation after the biologically triggered Cu2+/Cu+ reduction

Electrocatalytic Reduction of Bromothiophenes on Gold and Silver Electrodes: an Example of Synergism in Electrocatalysis

The reductive cleavage of C\u2013Br bonds on silver electrodes can be regarded as an ideal model of dissociative electron transfer (DET) in electrocatalytic conditions, modulated by many factors, among which the molecular structure is of particular relevance. A detailed mechanistic study based on a large set of compounds with different molecular structures allowed us a full rationalization of the process for the case of aryl bromides in acetonitrile. [1] Now we are extending this research to heteroaromatic halides, in which the heteroatom not only makes the aromatic ring asymmetric from the perspective of the electron density but also can have its own specific interactions with the electrode surface, in addition to those of the halide ions. [2] As a first approach, we have selected the mono-, di-, tri- and tetra-bromothiophene series, plus a series of substituted bromothiophenes together with the corresponding bromobenzenes as benchmarks, investigating (by CV, supported by EIS in selected cases) the electrochemical reduction of the whole family: (i) on glassy carbon, GC, assumed as a non-catalytic reference electrode accounting for intrinsic reactivity; (ii) on the highly catalytic silver electrode; (iii) on gold electrode, showing in former halide cases lower catalytic effects than silver but having the highest affinity for the sulphur atom in the thiophene ring. While the results on GC and on Ag are fully consistent with the formerly studied aryl bromide case on the same two electrodes [1] the catalytic effects of Au appear to be neatly modulated by the relative position of the Br leaving group with respect to the sulphur atom. This feature is quite evident and reproducible in the whole series (including polysubstituted cases provided by our organic partner group), and points to the S atom acting as an asymmetrically anchoring group for the molecule on the Au surface. [1] S. Arnaboldi, A. Gennaro, A.A. Isse, P.R. Mussini (2015) Electrochimica Acta, 158, 427-436 [2] S. Arnaboldi, A. Bonetti, E. Giussani, P.R. Mussini, T. Benincori, S. Rizzo, A.A. Isse, A. Gennaro (2014) Electrochemistry Communications, 38, 100-10

Chiral electrochemistry : introducing the inherent chirality Concept in ionic liquids

The typical design of chiral electroactive materials involves attaching chiral pendants to an electroactive polyconjugated backbone and generally results in modest chirality manifestations. In this frame we have proposed our innovative approach based on the concept of "inherent chirality" implying a stereogenic element not external to, but coinciding with, the whole electroactive backbone, derived from a tailored torsion originating in the molecule by the insertion of atropisomeric scaffolds. Therefore both chirality and electroactivity are strictly connected, deriving from the same element, which constitutes the main part of the molecule. Such property is fully transmitted from inherently chiral monomers to the oligomers obtained by their electrooxidation. Thus, the inherent chirality concept has turned out to afford molecular materials endowed with powerful chirality manifestations plus an unprecedented pool of other outstanding properties [1,2,3]. Besides extending such exciting study, we are now trying to apply the same "inherent chirality" approach to the development of inherently chiral ionic liquids (ICILs), hopefully endowed with high enantioselectivity. The new molecules are based on cations including different atropisomeric bis-benzimidazolium and bis-collidinium groups acting as the stereogenic element, responsible for both the molecular chirality and the IL properties of the material, modulated by number, position and length of alkyl chain substituents. An overview will be given of the first structures obtained and of their electrochemical properties compared with those of the corresponding scaffolds. Results emerging from the comparison of the cyclic voltammetry patterns of each scaffold family are here summarized. 1,1’-bis-benzimidazoles [4] display a racemization barrier of ~40 kcal mol-1. First reduction and first oxidation peaks are close to the boundaries of the available potential windows, consistent with very low effective conjugation deriving from the high energy barrier. The effect of alkyl chain length is very slight. 2,2’-bis-benzimidazoles exhibit the narrowest potential window of all scaffold families: both first reduction and first oxidation peaks are significantly shifted to less extreme potentials, pointing to higher effective conjugation between the two equal scaffold moieties, which is in accordance with the much lower computed racemization barriers. Actually the scaffolds are in this case nearly planar, and their reduction CV pattern, featuring two reversible monoelectronic peaks, is consistent with two reciprocally interacting equivalent redox centers. It is worthwhile noticing that bridging alkyl substituents result in a different reduction mechanism with respect to simple alkyl chains and appear to destabilize the first ET product, which reacts much more rapidly. Moreover, the 3-term bridge results in a significantly lower Egap with respect to the 4-term one, consistently with its lower calculated racemization barrier. 3,3’-bis-collidines have the highest computed racemization barrier (42.5 kcal mol-1) and yield the largest potential window in CV experiments (Egap ~4.8 eV). First reduction and oxidation are in this case barely perceivable as background shoulders, coherently with very low effective conjugation. These inherently chiral scaffolds can be employed, even without salification, as chirality inductors in stereoselective processes, either dissolved in achiral commercial ionic liquid media or, together with a supporting electrolyte, in traditional solvents. When mono- or di-alkylation occurs the quaternarization of the imidazole and pyridine rings results in a huge positive shift of the first reduction potentials. The 1,1’-bis-benzimidazolium di- (or mono-) alkyl salt family [4] shows a very high racemization barrier; thus enantiomers can be separated by preparative HPLC, stored and characterized. Unfortunately such salts are solid or wax-like at room temperature, since so far double alkylation has succeeded only when either R or R’ chains were short. However, they could be used as chiral supporting electrolytes or even, at lower concentration, as chirality inductors (see below). The 2,2’-bis-benzimidazolium mono-alkyl salt family are waxes or oils at room temperature. Unfortunately, however, in this case the low barrier and easy rotation between the two equal halves, which results in high effective conjugation, also makes it impossibile to separate stable enantiomers. The 3,3’-bis-collidinium di- (or mono-) alkyl salt family is the most promising one displaying the highest racemization barrier in the three families as the corresponding scaffold; moreover, alkylation with long chains has been successfully achieved, finally affording, with proper counteranion choice, low melting points. Products are synthesized from inexpensive starting reagents; the scaffold enantiomers can be separated by fractional crystallization of diastereomeric salts with o,o-dibenzoyltartaric acids, and also the mono- and dialkylated salts can be isolated by a convenient protocol; thus low-cost synthesis is possible, avoiding the necessity of preparative chiral HPLC. In view of testing the new ICILs as media for electrooligomerizations a first proof was carried out using a 3,3’-bis-collidinium salt as supporting electrolyte evidencing the powerful influence of the anion choice in the oligomerization process. The anion choice is also very important for obtaining the desired melting points. Finally, very promising appear the preliminary enantioselectivity tests (figure below) using 1,1'-bibenzimidazolium enantiopure salts as additives, even in small amount, in the electrooligomerization of our inherently chiral monomer [4]. We are now looking forward to testing as supporting electrolytes and/or ionic liquids the newly achieved low-melting 3,3'-bis-collidinium salts, which look the most promising family, being low-cost, having the highest racemization barriers, the largest potential windows, as well as reaching low melting points. Figure. Electrooligomerization tests of racemic (left) or enantiopure (right) inherently chiral monomer (parent BT2T4) in the absence (red) or in the presence of 2:1 enantiopure (R)- (blue) or (S)- (green)1,1’-bis-benzimidazolium based salt. Acknowledgements With the contribution of Fondazione Cariplo, grant no. 2011-1851 (inherently chiral ionic liquids) References [1] F. Sannicolò, S. Arnaboldi, T. Benincori, V. Bonometti, R. Cirilli, L. Dunsch, W. Kutner, G. Longhi, P.R. Mussini, M. Panigati, M. Pierini, S. Rizzo Potential-driven chirality manifestations and impressive enantioselectivity by inherently chiral electroactive organic films Angew. Chem. Int. Ed., 53 (2014), p. 2623 [2] F. Sannicolò, P.R. Mussini, T. Benincori, R. Cirilli, S. Abbate, S. Arnaboldi, S. Casolo, E. Castiglioni, G. Longhi, R. Martinazzo, M. Panigati, M. Pappini, E. Quartapelle Procopio, S. Rizzo Inherently chiral macrocyclic oligothiophenes: easily accessible electrosensitive cavities with outstanding enantioselection performances Chem. Eur. J., 20 (2014), p. 15298 [3] S. Arnaboldi, T. Benincori, R. Cirilli, W. Kutner, M. Magni, P.R. Mussini, K. Noworyta, F. Sannicolò Inherently chiral electrodes: the tool for chiral voltammetry Chem. Sci., 6 (2015), p. 1706 [4] S. Arnaboldi, R. Cirilli, A. Forni, A. Gennaro, A. A. Isse, V. Mihali, P. R. Mussini, M. Pierini, S. Rizzo, F. Sannicolò Electrochemistry and Chirality in bis-Benzimidazole Systems Electrochim. Acta, (2015), doi:10.1016/j.electacta.2015.03.17