Thermodynamic aspects of the host-guest chemistry of pyrogallol[4]arenes and peralkylated ammonium cations

The stability constants (K), standard free energy (ΔG^o), enthalpy (ΔH^o), and entropy changes (ΔS^o) for the complexation of pyrogallol[4]arenes with ammonium cations of different size and shape have been determined in ethanol at 298 K by isothermal titration calorimetry. The trends observed in the thermodynamic parameters for 1:1 and/or 1:2 host-guest complexation correspond to the systematic structural changes of the guest molecules. On the basis of the results obtained we compare the complexation properties with two other resorcin[4]arenes and discuss the thermodynamic aspects of this supramolecular host-guest interactions.     

Total Internal Reflection Ellipsometry under SPR Conditions: In-Situ Monitoring of the Growth of Poly(N-isopropylacrylamide) (PNIPAAm) Brushes

Total internal reflection ellipsometry (TIRE) under surface plasmon resonance (SPR) conditions represents a powerful characterization technique combining the conveniences of spectroscopic ellipsometry with SPR. Besides the very high sensitivity to small changes in the optical constants (up to 10 times more sensitive than conventional ellipsometry), the possibility to investigate media of different optical densities or even opaque media makes this analytical method very convenient for different sensing applications. This article presents an example of application of TIRE under SPR conditions for the continuously in-situ monitoring of the growth of covalently tethered poly(N-isopropylacrylamide) (PNIPAAm) chains on a gold surface.     

Perpendicular magnetic anisotropy induced by tetragonal distortion of FeCo alloy films grown on Pd(001)

We grew tetragonally distorted FexCo1-x alloy films on Pd(001). Theoretical first-principles calculations for such films predicted a high saturation magnetization and a high uniaxial magnetic anisotropy energy for specific values of the lattice distortion c/a and the alloy composition x. The magnetic anisotropy was investigated using the magneto-optical Kerr effect. An out-of-plane easy axis of magnetization was observed for Fe0.5Co0.5 films in the thickness range of 4 to 14 monolayers. The magnetic anisotropy energy induced by the tetragonal distortion is estimated to be almost 2 orders of magnitude larger than the value for bulk FeCo alloys. Using LEED Kikuchi patterns, a change of the easy axis of magnetization can be related to a decrease of the tetragonal distortion with thickness.     

Passively mode-locked Raman fiber laser with 100 GHz repetition rate

We experimentally demonstrate the operation of a passively mode-locked Raman fiber ring laser with an ultrahigh repetition rate of 100 GHz and up to 430 mW of average output power. This laser constitutes a simple wavelength versatile pulsed optical source. Stable mode locking is based on dissipative four-wave mixing with a single fiber Bragg grating acting as the mode-locking element.     

Medium modification of hadrons

I discuss pertinent aspects of the phase structure of strongly-interacting matter and their relation to the medium modifications of mesons. Special attention is paid to the critical endpoint in the phase diagram and the electromagnetic response in its vicinity.     

Expanded Prussian Blue Analogue Based on Octahedral {Nb<Subscript>6</Subscript>} Clusters and {K<Subscript>2</Subscript>} Dimers as Nodes

Abstract  The preparation, structures, and characterization of two new compounds containing octahedral niobium cyanochloride clusters as building units and (Et₄N)⁺ as cation are reported. The reaction between Nb₆Cl₁₄ · 8H₂O, KCN and (Et₄N)Cl led to the formation of (Et₄N)₄[Nb₆Cl₁₂(CN)₆] · 2.67H₂O (1) which crystallizes in triclinic P-1 space group (No. 2) with a = 12.552(2), b = 12.818(2), c = 12.919(2) ?, α = 105.157(3)°, β = 104.188(3)°, γ = 117.390(2)°, V = 1611.7(5) ?³ and Z = 1. 1 has a 2D hydrogen-bonded layer structure based on [Nb₆Cl₁₂(CN)₆]⁴⁻ units connected through hydrogen bonding between cyanide ligands and solvent water molecules. In the presence of large excess of K⁺ ions, similar reaction leads to formation of K₂(Et₄N)₂[Nb₆Cl₁₂(CN)₆] (2) which crystallizes in the tetragonal I4/m space group (No. 87) with a = b = 10.9597(3), c = 19.178(1) ?, V = 2303.6(2) ?³ and Z = 2. Its 3D structure is based on [Nb₆Cl₁₂]²⁺ and [K₂]²⁺ nodes bridged by cyanide ligands to form an expanded Prussian blue type framework with (Et₄N)⁺ acting as charge compensating ions. Index Abstract  An expanded Prussian blue type 3D framework based on hexanuclear {Nb₆} and dinuclear {K₂} units which are bridged by cyanide linker was synthesized and characterized. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.