Examining Trichloroisocyanuric Acid and Oxalyl Chloride in Complementary Approaches to Fluorination of Group 15 Heteroatoms

A mild, oxidative fluorination approach to a variety of fluorinated phosphorus compounds using trichloroisocyanuric acid (TCICA) and KF was developed as a complement to a recent study on deoxygenative fluorination using oxalyl chloride. Herein, the syntheses of several fluorinated organophosphorus compounds are reported, and both TCICA/KF and oxalyl chloride/KF conditions are compared and contrasted throughout. Initial investigations of the method on other group 15 heteroatoms (i. e., As, Sb, and Bi) are also reported, with varied success. This work notably extends the known TCICA/KF reactivity series to another group of elements beyond previously studied chalcogens (S, Se, and Te) and halogens (iodine) and expands the utility of the previously reported oxalyl chloride/KF method.     

Self-induced harmonic generation in a storage-ring free-electron laser

Coherent radiation from a relativistic electron beam is a valuable way to overcome the present limitations of conventional lasers and synchrotron radiation light sources. The typical scheme has electrons, directly from a linac, in a single-pass interaction with a laser pulse in the presence of a static undulator magnetic field. We demonstrate that a storage-ring free-electron laser can also achieve harmonic generation (down to 36.5 nm), presenting both experimental and theoretical results, and offer a reliable interpretation of the peculiar underlying physical processes involved.     

Evidence for radial flow of thermal dileptons in high-energy nuclear collisions

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.     

Radiation torque and force on optically trapped linear nanostructures

We study the optical trapping of highly elongated linear nanostructures in the focal region of a high-numerical aperture lens (optical tweezers). The radiation torque and trapping force on these nanostructures that are modeled as chains of identical spherical scatterers are calculated by means of multipole field expansions in the framework of the transition matrix approach. We investigate both orientational and trapping stability and calculate force constants and trap parameters in order to clarify the role of the linear geometry in the optical trapping mechanism. Furthermore, we calculate optical trapping of nanowires of different materials and compare our theoretical findings with available experimental results.     

Triptycene‐Roofed Quinoxaline Cavitands for the Supramolecular Detection of BTEX in Air

Two novel triptycene quinoxaline cavitands ( DiTriptyQxCav and MonoTriptyQxCav ) have been designed, synthesized, and applied in the supramolecular detection of benzene, toluene, ethylbenzene, and xylenes (BTEX) in air. The complexation properties of the two cavitands towards aromatics in the solid state are strengthened by the presence of the triptycene moieties at the upper rim of the tetraquinoxaline walls, promoting the confinement of the aromatic hydrocarbons within the cavity. The two cavitands were used as fiber coatings for solid‐phase microextraction (SPME) BTEX monitoring in air. The best performances in terms of enrichment factors, selectivity, and LOD (limit of detection) values were obtained by using the DiTriptyQxCav coating. The corresponding SPME fiber was successfully tested under real urban monitoring conditions, outperforming the commercial divinylbenzene–Carboxen–polydimethylsiloxane (DVB–CAR–PDMS) fiber in BTEX adsorption.     

A Deep Eutectic Solvent‐based Amperometric Sensor for the Detection of Low Oxygen Contents in Gaseous Atmospheres

The possibility of adopting deep eutectic solvents (DESs) instead of room temperature ionic liquids (RTILs) in membrane‐free electrochemical gas probes was estimated by first evaluating the performance of ethaline as electrochemical medium. This very easily prepared DES was chosen as prototype since it displays high conductivity and fairly modest viscosity, comparable with those of RTILs usually adopted in electrochemical measurements. Its electrostability window at Au, Pt and GC electrodes was first detected, together with diffusion coefficients displayed in this medium by ferrocene in the range 2.0–26.5 °C, it being adopted as prototype analyte in view of its well known electrochemical behavior and high enough solubility in ethaline. These diffusion coefficients were then used to infer viscosity values of ethaline at all temperatures considered, by exploiting the Stokes‐Einstein equation. Even though ferrocene diffusion coefficients turned out to be remarkably lower than those displayed in usual aprotic solvents, they were fairly higher than those usually found in electrochemical measurements conducted in RTILs, thus pointing out that the use of DESs as solvents adhering to electrode surfaces for assembling electroanalytical gas sensors could be advantageous. On these bases, a conveniently assembled DES‐based probe was tested for the electrochemical detection of low oxygen contents in cooled atmospheres. The quite satisfactory results found indicated that the drawback affecting DESs, consisting in the low values of diffusion coefficients displayed by dissolved analytes, can be overcome by using thin enough DES layers and resorting to a high sensitive detection approach such as amperometry under flow conditions. In fact, good sensitivities were found at all temperatures considered (2.0–26.5 °C), accompanied by a low detection limit (ca. 0.1 % v/v).     

Catalytic ethylene polymerisation in carbon dioxide as a reaction medium with soluble nickel(II) catalysts

A series of neutral Ni(II)-salicylaldiminato complexes substituted with perfluorooctyl- and trifluoromethyl groups, [Ni{kappa(2)-N,O-6-C(H)==NAr-2,4-R'(2)C(6)H(2)O}(Me)(pyridine)] (6 a: Ar=2,6-{4-(F(17)C(8))C(6)H(4)}(2)C(6)H(3), R'=I; 6 b: Ar=2,6-{4-(F(3)C)C(6)H(4)}(2)C(6)H(3), R'=I; 6 c: Ar=2,6-{3,5-(F(3)C)(2)C(6)H(3)}(2)C(6)H(3), R'=3,5-(F(3)C)(2)C(6)H(3); 6 d: Ar=2,6-{4-(F(17)C(8))C(6)H(4)}(2)C(6)H(3), R'=3,5-(F(3)C)(2)C(6)H(3); 6 e: Ar=2,6-{3,5-(F(3)C)(2)C(6)H(3)}(2)C(6)H(3), R'=I) were studied as catalyst precursors for ethylene polymerisation in supercritical CO(2). Catalyst precursors 6 a and 6 c, which are soluble in scCO(2), afford the highest polymer yields, corresponding to 2 x 10(3) turnovers. Semicrystalline polyethylene (M(n) typically 10(4) g mol(-1)) is obtained with variable degrees of branching (11 to 24 branches per 1000 carbon atoms, predominantly Me branches) and crystallinities (54 to 21 %), depending on the substitution pattern of the catalyst.     

Chirality in the Absence of Rigid Stereogenic Elements: The Design of Configurationally Stable C3‐Symmetric Propellers

Residual stereoisomerism is a form of stereoisomerism scarcely considered so far for applicative purposes, though extremely interesting, since the production of stereoisomers does not involve classical rigid stereogenic elements. In three‐bladed propeller‐shaped molecules, a preferred stereomerization mechanism, related to the correlated rotation of the rings, allows the free interconversion of stereoisomers inside separated sets (the residual stereoisomers) that can interconvert through higher energy pathways. In light of possible future applications as chiral ligands for transition metals in stereoselective processes, some C₃‐symmetric phosphorus‐centered propellers, which could exist as residual enantiomers, are synthesized and the possibility of resolving their racemates into residual antipodes is explored. While the tris(aryl)methanes are configurationally stable at room temperature, only selected tris(aryl)phosphane oxides display a configurational stability high enough to allow resolution by HPLC on a chiral stationary phase (CSP HPLC) at a semipreparative level at room temperature. Stability was evaluated through different techniques (circular dichroism (CD) signal decay, dynamic CSP HPLC (CSP DHPLC), dynamic NMR analysis (DNMR)) and the results compared and discussed. Phosphanes were found much less stable than the corresponding phosphane oxides, for which preliminary calculations suggest that the three‐ring‐flip enantiomerization mechanism (M₀) would be easier than phosphorus pyramidal inversion. The parameters affecting the configurational stability of the residual enantiomers of C₃‐symmetric propellers are discussed.     

Hetero‐difunctional dimers as building blocks for the synthesis of poly(amidoamine)s with hetero‐difunctional chain terminals and their derivatives

This article reports on a simple and straightforward preparation method of poly(amidoamine)s (PAAs) with hetero‐difunctional chain ends as well as of several up to now hardly obtainable PAA derivatives of biotechnological interest, such as for instance PAAs of controlled molecular weight and narrow polydispersity mono‐functionalized at one end with an acrylamide group, PAAs with star‐like molecular architecture, graft‐PAA‐protein conjugates, “tadpole‐like” PAA conjugates with hydrophobic moieties able to self assemble into nanoparticles in aqueous media. The key step was to design suitable building blocks consisting of hetero‐difunctional dimers (HDDs). In particular, the HDDs considered were the mono‐addition products of bis‐sec‐amines and bisacrylamides expected to give PAAs of proven biomedical potential and were obtained as hydrochlorides or trifluoroacetates. In this form, they could be indefinitely kept dormant at 0–5 °C in the dry state, whereas at room temperature and in aqueous media, they polymerized at pH > 7.5. The preparation of the above‐cited PAA derivatives did not necessarily involve the preliminary synthesis of hetero‐difunctional PAAs but was directly achieved by one‐pot polymerization of HDDs in the presence of the substrates of interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012