Effect of cross-linker density of P(NIPAM-co-AAc) microgels at solid surfaces on the swelling/shrinking behaviour and the Young��s modulus

The effect of the amount of cross-linker in poly(N-isopropylacrylamide-co-acrylic acid) microgel particles on the swelling behaviour and their elasticity is studied. The distribution of the stiffness through the particle is also investigated. Therefore, the swelling ratio obtained from dynamic light scattering measurements in aqueous solutions is compared with the one after adsorption at polycation-coated silicon wafers. The studies of the swelling behaviour at the surface are carried out with scanning force microscopy (SFM) against liquid. The Young??s modulus is determined by indentation experiments with an SFM. With increasing amount of cross-linker, the ability to shrink as well as the shift in the lower critical solution temperature and in particle size (hysteresis) during the heating and cooling processes decreases. In addition, the particles at the surface preserve their height/width ratio at high amount of cross-linker, while at low amounts the shrinking and swelling mainly takes place with respect to changes in height. The particles show their highest Young??s modulus in the centre of the particles and become stiffer with increasing the amount of cross-linker and the temperature.     

Population trapping and inversion in ultracold Fermi gases by excitation of the optical lattice: non-equilibrium Floquet–Keldysh description

A gas of ultracold interacting quantum degenerate Fermions is considered in a three-dimensional optical lattice which is externally modulated in the frequency and the amplitude. This theoretical study utilizes the Keldysh formalism to account for the system being out of thermodynamical equilibrium. A dynamical mean field theory, extended to non-equilibrium, is presented to calculate characteristic quantities such as the local density of states and the non-equilibrium distribution function. A dynamic Franz–Keldysh splitting is found which accounts for the non-equilibrium modification of the underlying bandstructure. The found characteristic Floquet-fan like bandstructure accounts for the quantized nature of the effect over all frequency space.     

Phase transition and structures of the twinned low‐temperature phases of (Et4N)[ReS4]

The title compound, tetraethylammonium tetrathiorhenate, [(C₂H₅)₄N][ReS₄], has, at room temperature, a disordered structure in the space group P6₃mc (Z = 2, α‐phase). A phase transition to the monoclinic space group P2₁ (Z = 2, γ‐phase) at 285 K leads to a pseudo‐merohedral twin. The high deviation from the hexagonal metric causes split reflections. However, the different orientations could not be separated, but were integrated using a large integration box. Rapid cooling to 110–170 K produces a metastable β‐phase (P6₃, Z = 18) in addition to the γ‐phase. All crystals of the β‐phase are contaminated with the γ‐phase. Additionally, the crystals of the β‐phase are merohedrally twinned. In contrast to the α‐phase, the β‐ and γ‐phases do not show disorder.     

New Insights into the Catalytic Activity of Cobalt Orthophosphate Co3(PO4)2 from Charge Density Analysis

An extensive characterization of Co₃(PO₄)₂ was performed by topological analysis according to Bader‘s Quantum Theory of Atoms in Molecules from the experimentally and theoretically determined electron density. This study sheds light on the reactivity of cobalt orthophosphate as a solid-state heterogeneous oxidative-dehydration and -dehydrogenation catalyst. Various faces of the bulk catalyst were identified as possible reactive sites given their topological properties. The charge accumulations and depletions around the two independent five- and sixfold-coordinated cobalt atoms, found in the topological analysis, are correlated to the orientation and population of the d-orbitals. It is shown that the (011) face has the best structural features for catalysis. Fivefold-coordinated ions in close proximity to advantageously oriented vacant coordination sites and electron depletions suit the oxygen lone pairs of the reactant, mainly for chemisorption. This is confirmed both from the multipole refinement as well as from density functional theory calculations. Nearby basic phosphate ions are readily available for C−H activation.     

Selective uptake of different proteins by annealed and quenched cationic spherical polyelectrolyte brushes

The selective uptake of bovine serum albumin (BSA) and β-glucosidase (β-G) by annealed and quenched cationic spherical polyelectrolyte brushes (SPB) was systematically studied by combining turbidimetric titration, dynamic light scattering and small angle X-ray scattering (SAXS). These two kinds of SPB consist of a same polystyrene core and a dense shell of poly (2-aminoethyl methacrylate hydrochloride) (PAEMH) and poly [2-(methacryloyloxy) ethyl] trimethylammonium chloride (PMAETA), respectively. Results reveal that the adsorption/desorption of proteins on SPB can be easily controlled by changing external conditions (pH and ionic strength). For a particular annealed or quenched SPB, there is a significant difference of the interaction pH regions between the brush and the two proteins, and this difference can be tuned by ionic strength. At low ionic strength, quenched brushes were more suitable for selective adsorption of BSA and β-G, while annealed brushes performed better at high ionic strength. SAXS analysis demonstrated that volume exclusion effect played a remarkable role in protein uptake by both SPB, and larger proteins were more likely to be adsorbed on the outer layer of the brush. The unique core-shell structure and controllable chain types make SPB an excellent candidate in selective adsorption/separation of proteins of different sizes.     

Surviving structure in colloidal suspensions squeezed from 3D to 2D

Combining colloidal-probe experiments and computer simulations, we analyze the solvation forces F of charged silica colloids confined in films of various thicknesses h. We show that the oscillations characterizing F(h), for sufficiently large h, are determined by the dominant wavelength of the bulk radial distribution function. As a consequence, both quantities display the same power-law density dependence. This is the first direct evidence, in a system treatable both by experiment and by simulation, that the structural wavelength in bulk and confinement coincide, in agreement with predictions from density functional theory. Moreover, theoretical and experimental data are in excellent quantitative agreement.     

Liquid chromatography with triple-quadrupole and quadrupole-time-of-flight mass spectrometry for the determination of micro-constituents – a comparison

The potential of liquid chromatography with triple-quadrupole mass spectrometry (LC-QqQ MS) was compared to that of quadrupole time-of-flight mass spectrometry (LC-Q-ToF MS) for the determination of microconstituents. Three applications were studied: (1) the ng/l quantification of five human drugs in surface water and waste-water effluents; (2) the quantification and confirmation of three corticosteroids in bovine urine at concentrations of 1–100 g/l, and; (3) the confirmation of nicotine in rat plasma. In all cases, the criteria of the EU Commission Decision 2002/657/EC were followed (for confirmation analysis two MS/MS ions were monitored, and the ratio of their abundances were calculated and compared with those of standards). With both techniques fully satisfactory results were obtained in almost all instances. That is, unequivocal confirmation according to the most stringent EU criteria, those for illegal compounds, was possible.One main advantage of LC-Q-ToF MS is that for identification and confirmation purposes, full MS/MS spectra are available after a single injection: no second injection, as required with QqQ MS, is needed. As well as the increased efficiency, the enhanced selectivity due to the impressive mass selectivity of LC-Q-ToF MS must be emphasized, which allows accurate masses of fragment ions to be calculated. Method characteristics such as linear dynamic range and repeatability were found to be essentially the same for both techniques, but LC-QqQ MS has the advantage that its detection limits are somewhat lower.     

Alkali Metal Based Triimidosulfite Cages as Versatile Precursors for Single-Molecule Magnets

Based on the potassium [{S(tBuN)₂(tBuNH)}₂K₃(tmeda)-K₃{(HNtBu)(NtBu)₂S}₂] ( 1 ) and sodium precursors [S(tBuN)₃(thf)₃-Na₃SNa₃(thf)₃(NtBu)₃S] ( 2 ), [S(tBuN)₃(thf)₃Na₃{(HNtBu)(NtBu)₂S}] ( 3 ) and [(tmeda)₃S-{Na₃(NtBu)₃S}₂] ( 4 ) the syntheses and magnetic properties of three mixed metal triimidosulfite based alkali-lanthanide-metal-cages [(tBuNH)Dy{K(0.5tmeda)}₂{(NtBu)₃S}₂]_n ( 5 ) and [ClLn{Na(thf)}₂{(NtBu)₃S}₂] with Ln=Dy ( 6 ), Er ( 7 ) are reported. The corresponding potassium ( 1 ) and sodium ( 2 – 4 ) based cages are characterized through XRD and NMR experiments. Preventing lithium chloride co-complexation led to a significant increase of SMM performance to previously reported sulfur-nitrogen ligands. The subsequent Dy^III-complexes 5 and 6 display slow relaxation of magnetization at zero field, with relaxation barriers U=77.0 cm⁻¹ for 5 , 512.9 and 316.3 cm⁻¹ for 6 , respectively. Significantly, the latter complex 6 also exhibits a butterfly-shaped hysteresis up to 7 K.     

A Stable Dimer of SiS2 Arranged between Two Carbene Molecules

The Me‐cAAC:‐stabilized dimer of silicon disulfide (SiS₂) has been isolated in the molecular form as (Me‐cAAC:)₂Si₂S₄ ( 2 ) at room temperature [Me‐cAAC:=cyclic alkyl(amino) carbene]. Compound 2 has been synthesized from the reaction of (Me‐cAAC:)₂Si₂ with elemental sulfur in a 1:4 molar ratio under oxidative addition. This is the smallest molecular unit of silicon disulfide characterized by X‐ray crystallography, electron ionization mass spectrometry, and NMR spectroscopy. Structures with three sulfur atoms arranged around a silicon atom are known; however, 2 is the first structurally characterized silicon–sulfur compound containing one terminal and two bridging sulfur atoms at each silicon atom. Compound 2 shows no decomposition after storing for three months in an inert atmosphere at ambient temperature. The bonding of 2 has been further studied by theoretical calculations.