Magnetochemistry, Volume 4, Issue 3 (September 2018) – 13 articles

A three-dimensional cyanide-bridged coordination polymer based on Fe^II (S = 2) and Nb^IV (S = 1/2) {[Fe^II(H₂O)₂]₂[Nb^IV(CN)₈]·4H₂O}_n (Fe₂Nb) was modified at the self-assembly stage by inserting an additional formate HCOO⁻ bridge into its cyanide framework. The resulting mixed-bridged {(NH₄)[(H₂O)Fe^II-(μ-HCOO)-Fe^II(H₂O)][Nb^IV(CN)₈]·3H₂O}_n (Fe₂NbHCOO) exhibited additional Fe^II-HCOO-Fe^II structural motifs connecting each of the two Fe^II centers. The insertion of HCOO⁻ was possible due to the substitution of some of the aqua ligands and crystallization water molecules in the parent framework by formate anions and ammonium cations. The formate molecular bridge not only shortened the distance between Fe^II ions in Fe₂NbHCOO from 6.609 Å to 6.141 Å, but also created additional magnetic interaction pathways between the magnetic centers, resulting in an increase in the long range magnetic ordering temperature from 43 K for Fe₂Nb to 58 K. The mixed-bridged Fe₂NbHCOO also showed a much broader magnetic hysteresis loop of 0.102 T, compared to 0.013 T for Fe₂Nb. Full article

Magnetoelectrolysis (electrolysis in magnetic fields) has potential to produce chiral surfaces on metal films. The Lorentz force causes two types of magnetohydrodynamic (MHD) flows; a vertical MHD flow and micro-MHD vortices, and the combination of these MHD flows has been considered to produce chiral surfaces. This paper shows the effects of vertical MHD flow on the chiral surface formation in magnetoelectrodeposition (MED) and magnetoelectrochemical etching (MEE) of copper films. To control the vertical MHD flows the working electrode was embedded in a tube wall with various heights of 2–12 mm, and the vertical MHD flows were expected to penetrate into the tubes with damping. In both MED and MEE experiments, the surface chirality diminished considerably at the wall height of 12 mm. When the penetrating MHD flow could not reach the electrode surface in the sufficiently tall wall, such an MHD flow could not affect the micro-MHD vortices. These results demonstrate that the vertical MHD flow plays a significant role in symmetry breaking of micro-MHD vortices. Full article

The complexes [Ln₂(hfac)₆(L)]·nC₆H₁₄ (Ln = Dy (1) n = 0, Yb (2) n = 1) with the L chiral 3,14-di-(2-pyridyl)-4,13-diaza[6]helicene ligand (hfac⁻ = 1,1,1,5,5,5-hexafluoroacetylacetonate) have been synthesized in their racemic form and structurally and magnetically characterized. Both complexes behave as field-induced single molecule magnets in the crystalline phase. These magnetic properties were rationalized by ab initio calculations. Full article

The synthesis, crystal structure and magnetic properties of the coordination polymers of formula [EDAP{Li₆(H₂O)₈[(Cu₂(μ-mpba)₂)₂(H₂O)₂]}]_n (1) and [(EDAP)₂{K(H₂O)₄[Cu₂(μ-mpba)₂(H₂O)₂]}Cl·2H₂O]_n (2), in which mpba = N,N′-1,3-phenylenebis(oxamate) and EDAP²⁺ = 1,1′-ethylenebis(4-aminopyridinium) are described. Both compounds have in common the presence of the [Cu₂(mpba)₂]⁴⁻ tetraanionic unit which is a [3,3] metallacyclophane motif in which the copper(II) ions are five-coordinate in a distorted square pyramidal surrounding. The complex anion in 1 is dimerized through double out-of-plane copper to outer carboxylate-oxygen atoms resulting in the centrosymmetric tetracopper(II) fragment [Cu₄(μ-mpba)₄(H₂O)₂]⁸⁻ which act as a ligand toward six hydrated lithium(I) cations leading to anionic ladder-like double chains whose charge is neutralized by the EDAP²⁺ cations. In the case of 2, each dicopper(II) entity acts as a ligand towards tetraquapotassium(I) units to afford anionic zig zag single chains of formula {K(H₂O)₄[Cu₂(μ-mpba)₂(H₂O)₂]}_n³ⁿ⁻ plus EDAP²⁺ cations and non-coordinate chloride anions. Cryomagnetic measurements on polycrystalline samples 1 and 2 show the occurrence of ferromagnetic interactions between the copper(II) ions across the –N_amidate–(C–C–C)_phenyl–N_amidate– exchange pathway [J = +10.6 (1) and +8.22 cm⁻¹ (2)] and antiferromagnetic ones through the double out-of-plane carboxylate-oxygen atoms [j = −0.68 cm⁻¹ (1), the spin Hamiltonian being defined as $\mathit{H}=-J\left({\mathit{S}}_{Cu1}·{\mathit{S}}_{Cu2}+{\mathit{S}}_{Cu{2}^i}·{\mathit{S}}_{Cu{1}^i}\right)-j\left({\mathit{S}}_{Cu2}·{\mathit{S}}_{Cu{2}^i}\right)$ ]. Full article

This study describes the first example of a hybrid material comprising corrole- and silica-coated magnetite nanoparticles. Firstly, cuboid and spheroid magnetite nanoparticles were prepared using a simple hydrothermal route, followed by a silica coating. The hybrid nanoparticles were obtained by promoting a covalent link between a gallium (III)(pyridine) complex of 5,10,15-tris(pentafluorophenyl)corrole (GaPFC) and the surface of magnetite–silica core/shell nanoparticles (Fe₃O₄@SiO₂), shaped both as cuboids and spheroids. The hybrids were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), ultraviolet-visible spectrophotometry (UV-Vis) and transmission electron microscopy (TEM). Preliminary studies on the capacity of singlet oxygen generation of the hybrid nanoparticles showed that these have lower efficiency values when compared to the pure corrole compound. Full article

Magneto-electrochemistry (MEC) is a unique paradigm in science, where electrochemical experiments are carried out as a function of an applied magnetic field, creating a new horizon of potential scientific interest and technological applications. Over time, detailed understanding of this research domain was developed to identify and rationalize the possible effects exerted by a magnetic field on the various microscopic processes occurring in an electrochemical system. Notably, until a few years ago, the role of spin was not taken into account in the field of magneto-electrochemistry. Remarkably, recent experimental studies reveal that electron transmission through chiral molecules is spin selective and this effect has been referred to as the chiral-induced spin selectivity (CISS) effect. Spin-dependent electrochemistry originates from the implementation of the CISS effect in electrochemistry, where the magnetic field is used to obtain spin-polarized currents (using ferromagnetic electrodes) or, conversely, a magnetic field is obtained as the result of spin accumulation. Full article

Magneto-optic surface plasmon resonance (MOSPR)-based sensors are highly attractive as next-generation biosensors. However, these sensors suffer from oxidation leading to degradation of performance, reproducibility of the sensor surface, because of the difficulty of removing adsorbed materials, and degradation of the sensor surface during surface cleaning and these limit their applications. In this paper, I propose MOSPR-based biosensors with 0 to 15 nm thick inert polycarbonate laminate plastic as a protective layer and theoretically demonstrate the practicability of my approach in water-medium for three different probing samples: ethanol, propanol, and pentanol. I also investigate microstructure and magnetic properties. The chemical composition and layered information of the sensor are investigated using X-ray reflectivity and X-ray diffraction analyses and these show distinct face-centered-cubic (fcc)-Au (111) phases, as dominated by the higher density of conduction electrons in Au as compared to Co. The magnetic characterization measured with the in-plane magnetic field to the sensor surface for both the as-deposited and annealed multilayers showed isotropic easy axis magnetization parallel to the multilayer interface at a saturating magnetic field of <100 Oersted (Oe). The sensor showed a maximum sensitivity of 5.5 × 10⁴%/RIU (refractive index unit) for water–ethanol media and the highest detection level of 2.5 × 10⁻⁶ for water-pentanol media as the protective layer is increased from 0 to 15 nm. Full article

The synthesis, structures and magnetic properties of a new trinuclear spin crossover complex [Fe^II₃(pyrtrz)₆(TsO)₆]·10H₂O·2CH₃OH (C2) and its analogue binuclear [Fe^II₂(pyrtrz)₅(SCN)₄]·7H₂O (C1), are reported here. These two compounds are synthesized based on the pyrrolyl functionalized Schiff base 1,2,4-triazole ligand 4-((1H-pyrrol-2-yl)methylene-amino)-4H-1,2,4-triazole (pyrtrz), which represent rare discrete multi-nuclear species, with µ₂-N1,N2-triazole bridges linking the Fe^II centers. DC magnetic susceptibility measurements revealed an abrupt single-step spin crossover (SCO) behavior for compound 2 on the central Fe^II site and single-crystal X-ray diffraction (173 K) showed that this compound crystallizes in the monoclinic space group (P21/c), and multiple intramolecular interactions were found responsible for the abrupt transition. Compound 1 is a binuclear complex with thiocyanate as terminal ligands. This compound stays in high spin state over the whole temperature range and displays weak antiferromagnetic exchange coupling. Full article

Nuclear magnetic resonance relaxation dispersion (rd) experiments provide kinetics and thermodynamics information of molecules undergoing conformational exchange. Rd experiments often use a Carr-Purcell-Meiboom-Gill (CPMG) pulse train equally separated by a spin-state selective inversion element (U-element). Even with measurement parameters carefully set, however, parts of ¹H–¹⁵N correlations sometimes exhibit large artifacts that may hamper the subsequent analyses. We analyzed such artifacts with a combination of NMR measurements and simulation. We found that particularly the lowest CPMG frequency (ν_cpmg) can also introduce large artifacts into amide ¹H–¹⁵N and aromatic ¹H–¹³C correlations whose ¹⁵N/¹³C resonances are very close to the carrier frequencies. The simulation showed that the off-resonance effects and miscalibration of the CPMG π pulses generate artifact maxima at resonance offsets of even and odd multiples of ν_cpmg, respectively. We demonstrate that a method once introduced into the rd experiments for molecules having residual dipolar coupling significantly reduces artifacts. In the method the ¹⁵N/¹³C π pulse phase in the U-element is chosen between x and y. We show that the correctly adjusted sequence is tolerant to miscalibration of the CPMG π pulse power as large as ±10% for most amide ¹⁵N and aromatic ¹³C resonances of proteins. Full article

17β-Hydroxysteroid dehydrogenase type 10 (17β-HSD10) is a steroidogenesis enzyme known for its potential role in Alzheimer’s disease. For comparison purposes between steroidal and nonsteroidal 17β-HSD10 inhibitors 1 and 2, respectively, we attempted the chemical synthesis of benzothiazole phosphonate derivative 2. Instead of a one-pot synthesis, we report a two-step synthesis with characterization of both imine intermediate 5 and final compound 2. Furthermore, complete assignation of ¹H and ¹³C nuclear magnetic resonance (NMR) signals of 2 is provided, as we observed a divergence of NMR data with those published previously. Finally, biological assays showed that 1 and 2 inhibited the oxidation of estradiol (E2) into estrone (E1) by the 17β-HSD10 recombinant protein. However, in human embryonic kidney (HEK)-293 intact cells transfected with 17β-HSD10, only the steroidal inhibitor 1 induced a dose-dependent inhibition of E2 to E1 transformation. Full article

Machine learning is gaining popularity in the commercial world, but its benefits are yet to be well-utilised by many in the microfluidics community. There is immense potential in bridging the gap between applied engineering and artificial intelligence as well as statistics. We illustrate this by a case study investigating the sorting of sperm cells for assisted reproduction. Slender body theory (SBT) is applied to compute the behavior of sperm subjected to magnetophoresis, with due consideration given to statistical variations. By performing computations on a small subset of the generated data, we train an ensemble of four supervised learning algorithms and use it to make predictions on the velocity of each sperm. Our results suggest that magnetophoresis can magnify the difference between normal and abnormal cells, such that a sorted sample has over twice the proportion of desirable cells. In addition, we demonstrated that the predictions from machine learning gave comparable results with significantly lower computational costs. Full article

Solid-state nuclear magnetic resonance (NMR) spectroscopy provides significant structural information regarding the conformation and dynamics of a variety of solid samples. In this study, we recorded the ¹³C and ¹⁵N solid-state NMR spectra of a self-assembled isoleucine-phenylalanine (Ile–Phe–OH) dipeptide. Immediately after the addition of hexane to a solution of concentrated peptide in ethyl acetate, the peptide visually aggregated into a nanofiber. Then, we obtained well-resolved ¹³C and ¹⁵N NMR signals of the natural, isotopic-abundant Ile–Phe–OH peptide in the nanofiber. Furthermore, we calculated the chemical shift values of the reported crystal structure of the Ile–Phe dipeptide via the density functional theory (DFT) calculation and compared these results with the experimental values. Notably, the two sets of values were in good agreement with each other, which indicated that the self-assembled structure closely reflected the crystal structure. Therefore, herein, we demonstrated that solid-state NMR characterization combined with DFT calculations is a powerful method for the investigation of molecular structures in self-assembled short peptides. Full article

Two isostructural lanthanide amino-phosphonate complexes [Ln₁₀(μ₃-OH)₃(µ-OH)(CO₃)₂(O₂C^tBu)₁₅(O₃PC₆H₁₀NH₂)₃(O₃PC₆H₁₀NH₃)₂(H₂O)₂][Et₂NH₂] (Ln = Gd(III), 1 and Tb(III), 2) have been obtained through reflux reactions of lanthanide pivalates with, a functionalized phosphonate, (1-amino-1-cyclohexyl)phosphonic acid and diethylamine (Et₂NH) in acetonitrile (MeCN) at 90 °C. Both compounds have been characterized with elemental analysis, single-crystal X-ray diffraction methods, and magnetic measurements. The molecular structure of compounds 1 and 2 reveal two highly unsymmetrical complexes comprising ten lanthanide metal centers, where the lanthanide metal ion centers in the cages are linked through pivalate units and further interconnected by CPO₃ tetrahedra to build the crystal structure. The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K, the magnetic measurements for compound 1 suggests antiferromagnetic interactions between the Gd(III) metal ion centers at low temperatures. The large number of isotropic Gd(III) ions comprising 1 makes it a candidate for magnetocaloric applications, thus the magnetocaloric properties of this molecular cage were investigated indirectly through isothermal magnetisation curves. The magnetic entropy change was found to be 34.5 J kg⁻¹K⁻¹, making 1 a plausible candidate in magnetic cooling applications. Full article