A Bis(Diphosphanyl N‐Heterocyclic Carbene) Gold Complex: A Synthon for Luminescent Rigid AuAg2 Arrays and Au5 and Cu6 Double Arrays

A mononuclear bis(NHC)/Au^I (NHC=N‐heterocyclic carbene) cationic complex with a rigid bis(phosphane)‐functionalized NHC ligand (PC_NHCP) was used to construct linear Au₃ and Ag₂Au arrays, a Au₅ cluster with two intersecting crosslike Au₃ arrays, and an unprecedented Cu₆ complex with two parallel Cu₃ arrays. The impact of metallophilic interactions on photoluminescence was studied experimentally.     

Synthesis, solution thermodynamics, and X-ray study of CuII [12]metallacrown-4 with GABA hydroxamic acid: an unprecedented crystal structure of a [12]MC-4 with a gamma-aminohydroxamate

The solution equilibria of gamma-aminobutanehydroxamic acid (GABAha) with H+ and Cu2+ were investigated by potentiometry, titration calorimetry, spectrophotometry, NMR spectroscopy, and ESI-MS. The thermodynamic parameters of the CuII [12]metallacrown-4 obtained for GABAha were compared with those of the corresponding complexes of (S)-alpha-Alaha and beta-Alaha. The stability (-DeltaG0) sequence was beta-Alaha>alpha-Alaha>GABAha, whereas the order of formation enthalpies (-DeltaH0) was beta-Alaha>GABAha>alpha-Alaha. These data were interpreted on the basis of the dimensions of the chelate rings and the planarity of the metallamacrocycles. The CuII [12]metallacrown-4 ([12]MC-4) complex of GABAha was isolated and its crystal structure, which is the first reported for a [12]MC-4 of a gamma-aminohydroxamic acid, fully supports the structural features interpreted from the thermodynamic data.     

The role of fluorine in the stereoselective tandem aza-Michael addition to acrylamide acceptors: an experimental and theoretical mechanistic study

Aza-Michael additions of alpha-amino esters to fluorinated acceptors take place in a highly stereoselective manner, to give partially modified Psi[NHCH2]retropeptides incorporating a hydrolytically stable trifluoroalanine mimic. The reaction mechanism has been investigated experimentally and theoretically, in order to explain the effect of the trifluoromethyl group on the reactivity and the origins of the experimentally observed stereocontrol. The reaction is a two-step process, involving a tandem aza-Michael addition followed by a stereoselective hydrogen transfer. Both steps are base-catalyzed. The high level of stereocontrol is the result of a combination of electrostatic interactions and steric effects.     

Dissipation-Dependent Thermal Escape from a Potential Well

Langevin simulations are conducted to investigate the Josephson escape statistics over a large set of parameter values for damping and temperature. The results are compared to both Kramers and Büttiker–Harris–Landauer (BHL) models, and good agreement is found with the Kramers model for high to moderate damping, while the BHL model provides further good agreement down to lower damping values. However, for extremely low damping, even the BHL model fails to reproduce the progression of the escape statistics. In order to explain this discrepancy, we develop a new model which shows that the bias sweep effectively cools the system below the thermodynamic value as the potential well broadens due to the increasing bias. A simple expression for the temperature is derived, and the model is validated against direct Langevin simulations for extremely low damping values.     

Quantum Probes for the Characterization of Nonlinear Media

Active optical media leading to interaction Hamiltonians of the form H=λ˜(a+a†)ζ represent a crucial resource for quantum optical technology. In this paper, we address the characterization of those nonlinear media using quantum probes, as opposed to semiclassical ones. In particular, we investigate how squeezed probes may improve individual and joint estimation of the nonlinear coupling λ˜ and of the nonlinearity order ζ. Upon using tools from quantum estimation, we show that: (i) the two parameters are compatible, i.e., the may be jointly estimated without additional quantum noise; (ii) the use of squeezed probes improves precision at fixed overall energy of the probe; (iii) for low energy probes, squeezed vacuum represent the most convenient choice, whereas for increasing energy an optimal squeezing fraction may be determined; (iv) using optimized quantum probes, the scaling of the corresponding precision with energy improves, both for individual and joint estimation of the two parameters, compared to semiclassical coherent probes. We conclude that quantum probes represent a resource to enhance precision in the characterization of nonlinear media, and foresee potential applications with current technology.     

Amphiphilic pentablock copolymers and their blends with PDMS for antibiofouling coatings

Well‐defined amphiphilic pentablock copolymers Siy‐(EGx‐FAz)₂ composed of polysiloxane (Si), polyethylene glycol (EG), and perfluorohexylethyl polyacrylate (FA) blocks are synthesized by ATRP of FA monomer starting from a difunctional bromo‐terminated macroinitiator. Diblock copolymers EGx‐FAz are also synthesized as model systems. The block copolymers are used, either alone or blended with a PDMS matrix in varied loadings, to prepare antibiofouling coatings. Angle‐resolved XPS and contact angle measurements show that the coating surface is highly enriched in fluorine content but undergoes reconstruction after contact with water. Protein adsorption experiments with human serum albumin and calf serum highlight that diblock copolymers resist protein adhesion better than do pentablock copolymers. Blending of the pentablock copolymer with PDMS results in increased protein adsorption. By contrast, the PDMS‐matrix coatings show high removal percentages of sporelings of the green fouling alga Ulva linza. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015 , 53, 1213–1225