Topotactic Synthesis of Phosphabenzene‐Functionalized Porous Organic Polymers: Efficient Ligands in CO2 Conversion

Progress toward the preparation of porous organic polymers (POPs) with task‐specific functionalities has been exceedingly slow—especially where polymers containing low‐oxidation phosphorus in the structure are concerned. A two‐step topotactic pathway for the preparation of phosphabenzene‐based POPs (Phos‐POPs) under metal‐free conditions is reported, without the use of unstable phosphorus‐based monomers. The synthetic route allows additional functionalities to be introduced into the porous polymer framework with ease. As an example, partially fluorinated Phos‐POPs (F‐Phos‐POPs) were obtained with a surface area of up to 591 m² g^?1. After coordination with Ru species, a Ru/F‐Phos‐POPs catalyst exhibited high catalytic efficiency in the formylation of amines (turnover frequency up to 204 h^?1) using a CO₂/H₂ mixture, in comparison with the non‐fluorinated analogue (43 h^?1) and a Au/TiO₂ heterogeneous catalysts reported previously (<44 h^?1). This work describes a practical method for synthesis of porous organic phosphorus‐based polymers with applications in transition‐metal‐based heterogeneous catalysis.     

Non-interferometric transient quantitative phase microscopy for ultrafast engineering

Lead-free piezoelectric ceramics Bi_0.5(Na_1-x-yK_xAg_y)_0.5TiO₃ [BNKAT(x/y)] have been synthesized by the mixed oxide method. The effects of the amount of K⁺ and Ag⁺ on the electrical properties were examined. X-ray diffraction patterns indicate that K⁺ and Ag⁺ ions partially substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃ and form a solid solution during sintering. At room temperature, the ceramics exhibit good performances with piezoelectric constant d₃₃=189 pC/N, electromechanical coupling factor k_p=35.0%, remanent polarization P_r=39.5 μC/cm², and coercive field E_c=3.3 kV/mm, respectively. The curves of the dielectric constant ε_r and loss tangent tan δ versus temperature show that the transition temperature from ferroelectric to anti-ferroelectric phase decreases with increasing the K⁺ content for the compositions researched. The dependencies of k_p and polarization versus electric (P–E) hysteresis loops on temperature reveal that the depolarization temperature T_d of BNKAT(0.15/0.015) ceramics, which have good piezoelectric properties (d₃₃=134 pC/N, k_p=32.5%) and strong ferroelectricity (P_r=39.5 μC/cm², E_c=4.1 kV/mm) at room temperature, is above 160 °C. PACS 77.22.-d; 77.65.Bn; 77.80.Bh; 77.80.Dj; 77.84.Dy     

Solubility in supercritical carbon dioxide: importance of the Poynting correction and entrainer effects

Gibbs ensemble Monte Carlo simulations were used to investigate the effect of pressure and of entrainers on the solubility of low-volatility species in CO 2. Two entrainers were examined, n-octane and methanol, as well as two solutes, hexamethylbenzene and benzoic acid. For the three pressures studied (12, 20, and 28 MPa), the simulations demonstrate that the increase in the solubility with increasing pressure is mostly due to an increase in the solute's chemical potential (as expressed by the Poynting correction) and not due to an increase in the solvent strength of supercritical CO 2. The presence of an entrainer enhances solubility, particularly when the solute and entrainer can form hydrogen bonds. The solubility of benzoic acid is enhanced by an order of magnitude upon addition of methanol entrainer, whereas the enhancements are less than 2 for the other systems.     

Structure and speciation in hydrous silica melts. 1. Temperature and composition effects

Monte Carlo simulations were used to investigate the phase behavior of hydrated liquid silica as a function of temperature and overall water mole fraction, x w. Simulations using the Feuston-Garofalini potential were performed in the isobaric-isothermal ensemble at p = 1 GPa for 15 temperatures (2000 < or = T < or = 9000 K) and 25 compositions (0.0 < or = x w < or = 0.4). The unusual volume minimum exhibited by tetrahedrally coordinated liquid silica is found to persist up to x w approximately 0.267, although the temperature of the volume minimum decreases with increasing water content. Structural properties of the pure and hydrated systems are compared and the addition of water to liquid silica disrupts the silica network more dramatically than temperature alone. The simulations yield very low concentrations of molecular water, e.g. only about 1.2% of the oxygen atoms are bound to exactly two hydrogen atoms at x w = 0.4 and T = 3000 K.     

Internal structure of a thin film of mixed polymeric micelles on a solid/liquid interface

The adsorption of mixed micelles of poly(4-(2-amino hydrochloride-ethylthio)-butylene)- block-poly(ethylene oxide), PAETB 49- b-PEO 212 and poly(4-(2-sodium carboxylate-ethylthio)-butylene)- block-poly(ethylene oxide), PCETB 47- b-PEO 212 on solid/liquid interfaces has been studied with light, X-ray, and neutron reflectometry. The structure of the adsorbed layer can be described with a two-layer model consisting of an inner layer formed by the coacervate of the polyelectrolyte blocks PAETB 49 and PCETB 47 ( approximately 1 nm) and an outer layer of PEO 212 blocks ( approximately 6 nm). The micelles unfold upon adsorption forming a rather homogeneous flat layer that exposes its polyethylene oxide chains into the solution, thus rendering the surface antifouling after modification with the micelles.     

Probing of lipase activity at air/water interface by sum-frequency generation spectroscopy

The infrared-visible sum-frequency generation (SFG) vibrational spectroscopy was used to probe enzymatic activity of Thermomyces lanuginosus lipase (TLL) at air/water interface. A monolayer of amphiphilic O-palmitoyl-2,3-dicyanohydroquinone (PDCHQ), containing target ester group and two CN groups serving as vibrational markers, was utilized as an enzyme substrate. SFG data revealed the detailed molecular scale structure and properties of the PDCHQ layer at the interface. In particular, we demonstrate that hydrophilic headgroup of PDCHQ is mainly in the form of an oxyanion, and the enzyme-induced cleavage of the ester bond could be spectroscopically monitored by the disappearance of the intense C tripple bond N resonance at 2224 cm(-1). The enzymatic nature of the ester bond cleavage was confirmed by the control experiments with deactivated S146A mutant variant of TLL. By comparing action of wild type (WT) TLL and its inactive S146A mutant, it was shown that two effects take place at the interface: disordering of the lipid monolayer due to the adsorption of enzyme and enzymatic cleavage of the ester bond. The concentration of enzyme as low as 10 nM could be easily sensed by the SFG spectroscopy. We present spectroscopic evidence that upon hydrolysis one of the products, 2,3-dicyanohydroquinone, leaves the surface, while the other, palmitic acid, remains at air/water interface in predominantly undissociated form with the mono-hydrogen-bonded carbonyl group. Strong amide I (1662 cm(-1)) and amide A (3320 cm(-1)) SFG signals from TLL suggest that enzyme molecules position themselves at air/water interface in an orderly fashion. Presented work demonstrates the potential of SFG spectroscopy for in situ real-time monitoring of enzymatic processes at air/water interface.     

Characterization of a sCMOS‐based high‐resolution imaging system

The detection system is a key part of any imaging station. Here the performance of the novel sCMOS‐based detection system installed at the ID17 biomedical beamline of the European Synchrotron Radiation Facility and dedicated to high‐resolution computed‐tomography imaging is analysed. The system consists of an X‐ray–visible‐light converter, a visible‐light optics and a PCO.Edge5.5 sCMOS detector. Measurements of the optical characteristics, the linearity of the system, the detection lag, the modulation transfer function, the normalized power spectrum, the detective quantum efficiency and the photon transfer curve are presented and discussed. The study was carried out at two different X‐ray energies (35 and 50 keV) using both 2× and 1× optical magnification systems. The final pixel size resulted in 3.1 and 6.2 µm, respectively. The measured characteristic parameters of the PCO.Edge5.5 are in good agreement with the manufacturer specifications. Fast imaging can be achieved using this detection system, but at the price of unavoidable losses in terms of image quality. The way in which the X‐ray beam inhomogeneity limited some of the performances of the system is also discussed.     

Retention in gas-liquid chromatography with a polyethylene oxide stationary phase: molecular simulation and experiment

Configurational-bias Monte Carlo simulations in the isobaric-isothermal Gibbs ensemble were carried out to investigate the partitioning of normal alkanes, primary and secondary alcohols, symmetric alkyl ethers and arenes between a helium vapor phase and a polyethylene oxide stationary phase (M(W)=382 g mol(-1)). The united-atom version of the transferable potentials for phase equilibria force field was used to model all solutes, polyethylene oxide and helium. The Gibbs free energies of transfer and Kovats retention indices of the solutes were calculated directly from the partition constants at two different temperatures, 353 and 393 K. Chromatographic experiments on a Carbowax 20M retentive phase were performed for the same set of solutes and temperatures ranging from 333 to 413 K. The predicted retention indices for alcohols, ethers and arenes are overestimated by about 120, 70 and 20 retention index units, respectively, pointing to an overestimation of the first-order electrostatic interactions in the model system. Molecular-level analysis shows that hydrogen-bonding and dipole-dipole interactions lead to orientational ordering for the alcohol and ether analytes, whereas the weaker dipole-quadrupole interactions for the arene solutes are not sufficient to induce orientational ordering. The retention indices of alcohols and ethers decrease with increasing temperature because of the large entropic cost of hydrogen-bonding and orientational ordering. In contrast, the retention indices for arenes increase with increasing temperature because the entropic cost of cavity formation is smaller for arenes than for comparable alkanes.     

Leptoquark mechanism of neutrino masses within the grand unification framework

We demonstrate the viability of the one-loop neutrino mass mechanism within the framework of grand unification when the loop particles comprise scalar leptoquarks (LQs) and quarks of the matching electric charge. This mechanism can be implemented in both supersymmetric and non-supersymmetric models and requires the presence of at least one LQ pair. The appropriate pairs for the neutrino mass generation via the up-type and down-type quark loops are \(S_3\)–\(R_2\) and \(S_{1,\,3}\)–\(\tilde{R}_2\), respectively. We consider two distinct regimes for the LQ masses in our analysis. The first regime calls for very heavy LQs in the loop. It can be naturally realized with the \(S_{1,\,3}\)–\(\tilde{R}_2\) scenarios when the LQ masses are roughly between \(10^{12}\) and \(5 \times 10^{13}\) GeV. These lower and upper bounds originate from experimental limits on partial proton decay lifetimes and perturbativity constraints, respectively. Second regime corresponds to the collider accessible LQs in the neutrino mass loop. That option is viable for the \(S_3\)–\(\tilde{R}_2\) scenario in the models of unification that we discuss. If one furthermore assumes the presence of the type II see-saw mechanism there is an additional contribution from the \(S_3\)–\(R_2\) scenario that needs to be taken into account beside the type II see-saw contribution itself. We provide a complete list of renormalizable operators that yield necessary mixing of all aforementioned LQ pairs using the language of SU(5). We furthermore discuss several possible embeddings of this mechanism in SU(5) and SO(10) gauge groups.