Hyperfine interaction studies and magnetic properties of FeCoAlN nanocomposite films

Nanogranular magnetic films were produced by specially designed UHV plasma-jet system with DC hollow-cathode discharge. We investigated the properties of these ferromagnetic FeCoAlN-based films. The analyses of the samples were additionally complemented by the study of nuclear magnetic resonance (NMR), Mössbauer spectroscopy, magnetic measurements, and X-ray diffraction.     

Big,Strong, Neutral,Twisted, and Chiral π Acids

General synthetic access to expanded π‐acidic surfaces of variable size, topology, chirality, and π acidity is reported. The availability of π surfaces with these characteristics is essential to develop the functional relevance of anion–π interactions with regard to molecular recognition, translocation, and transformation. The problem is that, with expanded π surfaces, the impact of electron‐withdrawing substituents decreases and the high π acidity needed for strong anion–π interactions can be more difficult to obtain. To overcome this problem, it is herein proposed to build large surfaces from smaller fragments and connect these fragments with bridges that are composed only of single atoms. Two central surfaces for powerful anion–π interactions, namely, perfluoroarenes and naphthalenediimides (NDIs), were selected as fragments and coupled with through sulfide bridges. Their oxidation to sulfoxides and sulfones, as well as fluorine substitution in the peripheral rings, provides access to the full chemical space of relevant π acidities. According to cyclic voltammetry, LUMO levels range from ?3.96 to ?4.72 eV. With sulfoxide bridges, stereogenic centers are introduced to further enrich the intrinsic planar chirality of the expanded surfaces. The stereoisomers were separated by chiral HPLC and characterized by X‐ray crystallography. Their topologies range from chairs to π boats, and the latter are reminiscent of the cation–π boxes in operational neuronal receptors. With pentafluorophenyl acceptors, the π acidity of NDIs with two sulfoxide groups in the core reaches ?4.45 eV, whereas two sulfone moieties give a value of ?4.72 eV, which is as low as with four ethyl sulfone groups, that is, a π superacid near the limit of existence. Beyond anion–π interactions, these conceptually innovative π‐acidic surfaces are also of interest as electron transporters in conductive materials.     

Comparative metabolite profiling of carboxylic acids in rat urine by CE‐ESI MS/MS through positively pre‐charged and 2H‐coded derivatization

A new approach to the selective comparative metabolite profiling of carboxylic acids in rat urine was established using CE‐MS and a method for positively pre‐charged and ²H‐coded derivatization. Novel derivatizing reagents, N‐alkyl‐4‐aminomethyl‐pyridinum iodide (alkyl=butyl, butyl‐d9 or hexyl), containing quaternary amine and stable‐isotope atoms (deuterium), were introduced for the derivatization of carboxylic acids. CE separation in positive polarity showed high reproducibility (0.99–1.32% RSD of migration time) and eliminated problems with capillary coating known in CE‐MS anion analyses. Essentially complete ionization and increased hydrophobicity after the derivatization also enhanced MS detection sensitivity (e.g. formic acid was detected at 0.5 pg). Simultaneous derivatization of one sample using two structurally similar reagents, N‐butyl‐4‐aminomethyl‐pyridinum iodide (BAMP) and N‐hexyl‐4‐aminomethyl‐pyridinum iodide, provided additional information for recognizing a carboxylic acid in an unknown sample. Moreover, characteristic fragmentation acquired by online CE‐MS/MS allowed for identification and categorization of carboxylic acids. Applying this method on rat urine, we found 59 ions matching the characteristic patterns of carboxylic acids. From these 59, 32 ions were positively identified and confirmed with standards. For comparative analysis, 24 standard carboxylic acids were derivatized by chemically identical but isotopically distinct BAMP and N‐butyl‐d9‐4‐aminomethyl‐pyridinium iodide, and their derivatization limits and linearity ranges were determined. Comparative analysis was also performed on two individual urine samples derivatized with BAMP and N‐butyl‐d9‐4‐aminomethyl‐pyridinium iodide. The metabolite profiling variation between these two samples was clearly visualized.     

Two-dimensional lanthanide coordination polymers with bis(diphenylphosphino)hexane dioxide. The determination of the polymeric structure from twinned crystals

Lanthanide nitrates and bis(diphenylphosphino)hexane dioxide (dpphO₂) formed under solvothermal conditions a series of coordination polymers [Ln(dpphO₂)₂(NO₃)₂](NO₃) (Ln = Pr (1), Nd (2), Sm (3), Dy (4), Lu (5)), featuring two-dimensional network structure of the (4, 4) topology. The compounds [Ln(dpphO₂)₂Cl₂]Cl (Ln = Pr (6), Nd (7), Gd (8)) were obtained from corresponding chlorides. Coordination polymer 7 formed regular single crystals of the orthorhombic Pna₂₁$\mathit{Pna}{2}_1$ space group. The nitrate complexes crystallized in the orthorhombic Aea2 space group, however, the crystals were pseudo-merohedral twins simulating a tetragonal diffraction pattern. Unlike our previously characterized neutral polymers with bis(diphenylphosphino)ethane dioxide, all present coordination networks are cationic, with anions located between or within the two-dimensional layers.     

Screening of pi-basic naphthalene and anthracene amplifiers for pi-acidic synthetic pore sensors

Synthetic ion channels and pores attract current attention as multicomponent sensors in complex matrixes. This application requires the availability of reactive signal amplifiers that covalently capture analytes and drag them into the pore. pi-Basic 1,5-dialkoxynaphthalenes (1,5-DAN) are attractive amplifiers because aromatic electron donor-acceptor (AEDA) interactions account for their recognition within pi-acidic naphthalenediimide (NDI) rich synthetic pores. Focusing on amplifier design, we report here the synthesis of a complete collection of DAN and dialkoxyanthracene amplifiers, determine their oxidation potentials by cyclic voltammetry, and calculate their quadrupole moments. Blockage experiments reveal that subtle structural changes in regioisomeric DAN amplifiers can be registered within NDI pores. Frontier orbital overlap in AEDA complexes, oxidation potentials, and, to a lesser extent, quadrupole moments are shown to contribute to isomer recognition by synthetic pores. Particularly important with regard to practical applications of synthetic pores as multianalyte sensors, we further demonstrate that application of the lessons learned with DAN regioisomers to the expansion to dialkoxyanthracenes provides access to privileged amplifiers with submicromolar activity.     

Rheological properties of asphalt/SBS/clay blends

The effect of the addition of clay as a third component in polymer modified asphalts has been investigated. After a preliminary investigation on the binary asphalt/clay and polymer/clay blends, the tertiary blends were prepared by adding the clay and polymer to the asphalt, either separately or in the form of a premixed master batch. Intercalated nanocomposites with comparable interlayer distances and glass transition temperatures were obtained in both cases. However, the results show that the mixing procedure significantly affected the final rheological properties. The master curves built in the linear viscoelastic range and represented in both the frequency and the temperature domains help to visualize and evaluate such differences.     

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic C_A* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.     

Hyperfine interactions in nanocrystallized NANOPERM-type metallic glass containing Mo

NANOPERM-type alloy with chemical composition Fe₇₆Mo₈CuB₁₅ was studied by combination of ⁵⁷Fe Mössbauer spectroscopy and ⁵⁷Fe(¹⁰B, ¹¹B) nuclear magnetic resonance in order to determine distribution of hyperfine magnetic fields and evolution of relative concentration of Fe-containing crystalline phases within the surface layer and the volume of the nanocrystallized ribbons with annealing temperature. Differential scanning calorimetry revealed two crystallization stages at T_x1 ～ 510 ^°C and T_x2 ～ 640 ^°C, connected to precipitation of α-Fe and Fe(Mo,B) nanocrystals, respectively. The amorphous and partially crystalline state was obtained by annealing at several temperatures in the range 510-650 ^°C. The combination of conversion electron (CEMS) and transmission Mössbauer spectrometry (TMS) showed that annealing induces crystallization starting from both surfaces of the ribbons. For the as-quenched sample, scanning electron microscopy (SEM) and CEMS revealed significant differences in the “air” and “wheel” sides of the ribbons, crystallites were preferentially formed at the latter. While SEM micrographs of annealed samples showed various mean diameters of the crystals at opposite sides of the ribbons, the amounts of crystalline volume derived from the CEMS spectra approximately equaled. Mössbauer spectra of annealed samples contained narrow sextet ascribed to crystalline α-Fe phase, three sextets with distribution of hyperfine field assigned to the interface regions of the nanocrystals and the contribution of the amorphous phases. In-field TMS performed at 4.2 K with magnetic moments aligned by external magnetic field enabled to properly determine in particular the contribution of the amorphous phases in the samples. Resulting distributions of the hyperfine fields were compared with ⁵⁷Fe(¹⁰B, ¹¹B) nuclear magnetic resonance (NMR) spectra.     

Impact of silica environment on hyperfine interactions in 𝜖-Fe2O3 nanoparticles

Magnetic nanoparticles have found broad applications in medicine, especially for cell targeting and transport, and as contrast agents in MRI. Our samples of ??-Fe₂O₃ nanoparticles were prepared by annealing in silica matrix, which was leached off and the bare particles were then coated with amorphous silica layers of various thicknesses. The distribution of particle sizes was determined from the TEM pictures giving the average size ～20 nm and the thickness of silica coating ～5; 8; 12; 19 nm. The particles were further characterized by the XRPD and DC magnetic measurements. The nanoparticles consisted mainly of ??-Fe₂O₃ with admixtures of ～1 % of the α phase and less than 1 % of the γ phase. The hysteresis loops displayed coercivities of ～2 T at room temperature. The parameters of hyperfine interactions were derived from transmission Mössbauer spectra. Observed differences of hyperfine fields for nanoparticles in the matrix and the bare ones are ascribed to strains produced during cooling of the composite. This interpretation is supported by slight changes of their lattice parameters and increase of the elementary cell volume deduced from XRD. The temperature dependence of the magnetization indicated a two-step magnetic transition of the ??-Fe₂O₃ nanoparticles spread between ～85 K and ～150 K, which is slightly modified by remanent tensile stresses in the case of nanoparticles in the matrix. The subsequent coating of the bare particles by silica produced no further change in hyperfine parameters, which indicates that this procedure does not modify magnetic properties of nanoparticles.     

Enolate Stabilization by Anion–π Interactions: Deuterium Exchange in Malonate Dilactones on π‐Acidic Surfaces

Of central importance in chemistry and biology, enolate chemistry is an attractive topic to elaborate on possible contributions of anion–π interactions to catalysis. To demonstrate the existence of such contributions, experimental evidence for the stabilization of not only anions but also anionic intermediates and transition states on π‐acidic aromatic surfaces is decisive. To tackle this challenge for enolate chemistry with maximal precision and minimal uncertainty, malonate dilactones are covalently positioned on the π‐acidic surface of naphthalenediimides (NDIs). Their presence is directly visible in the upfield shifts of the α‐protons in the ¹H NMR spectra. The reactivity of these protons on π‐acidic surfaces is measured by hydrogen–deuterium (H–D) exchange for 11 different examples, excluding controls. The velocity of H–D exchange increases with π acidity (NDI core substituents: SO₂R>SOR>H>OR>OR/NR₂>SR>NR₂). The H–D exchange kinetics vary with the structure of the enolate (malonates>methylmalonates, dilactones>dithiolactones). Moreover, they depend on the distance to the π surface (bridge length: 11–13 atoms). Most importantly, H–D exchange depends strongly on the chirality of the π surface (chiral sulfoxides as core substituents; the crystal structure of the enantiopure (R,R,P)‐macrocycle is reported). For maximal π acidity, transition‐state stabilizations up to ?18.8 kJ mol^?1 are obtained for H–D exchange. The Brønsted acidity of the enols increases strongly with π acidity of the aromatic surface, the lowest measured pK_a=10.9 calculates to a ΔpK_a=?5.5. Corresponding to the deprotonation of arginine residues in neutral water, considered as “impossible” in biology, the found enolate–π interactions are very important. The strong dependence of enolate stabilization on the unprecedented seven‐component π‐acidity gradient over almost 1 eV demonstrates quantitatively that such important anion–π activities can be expected only from strong enough π acids.