Magnetochemistry, Volume 4, Issue 1 (March 2018) – 18 articles

In this paper, authors investigate homogeneous-heterogeneous chemical reaction and heat absorption effects on a two-dimensional steady hydromagnetic Newtonian nanoliquid flow along a continuously stretching sheet. The flow field is subjected to a uniform magnetic field acting in a direction perpendicular to the direction of nanoliquid flow. A mathematical model of the physical problem is presented involving nonlinear partial differential equations with appropriate boundary conditions. These equations are then transformed into nonlinear ordinary differential equations using a suitable similarity transformation. Finally, approximate solutions of the transformed equations are obtained using the spectral quasi-linearization method. Results of fluid velocity, fluid temperature, and species concentration are depicted graphically, while the values of skin friction and Nusselt number are presented in tabular form. Fluid flow models of this kind find applications in catalytic reactors involving chemical reactions, insulation systems, and in heat exchangers. The applied magnetic field has a retarding influence on the nanofluid velocity and species concentration, while it does not have any significant effect on the nanofluid temperature. The homogeneous and heterogeneous reactions tend to decrease the species concentration. Full article

This work reports numerical investigation of lateral migration of a paramagnetic microparticle of an elliptic shape in a plane Poiseuille flow of a Newtonian fluid under a uniform magnetic field by direct numerical simulation (DNS). A finite element method (FEM) based on the arbitrary Lagrangian–Eulerian (ALE) approach is used to study the effects of strength and direction of the magnetic field, particle–wall separation distance and particle shape on the lateral migration. The particle is shown to exhibit negligible lateral migration in the absence of a magnetic field. When the magnetic field is applied, the particle migrates laterally. The migration direction depends on the direction of the external magnetic field, which controls the symmetry property of the particle rotational velocity. The magnitude of net lateral migration velocity over a $\pi$ cycle is increased with the magnetic field strength when the particle is able to execute complete rotations, expect for $\alpha$ = 45° and 135°. By investigating a wide range of parameters, our direct numerical simulations yield a comprehensive understanding of the particle migration mechanism. Based on the numerical data, an empirical scaling relationship is proposed to relate the lateral migration distance to the asymmetry of the rotational velocity and lateral oscillation amplitude. The scaling relationship provides useful guidelines on design of devices to manipulate nonspherical micro-particles, which have important applications in lab-on-a-chip technology, biology and biomedical engineering. Full article

Detailed Nuclear Magnetic Resonance (NMR) spectroscopy investigations on a novel naphthalene-substituted 1,2,3-triazole-based fluorescence sensor provided evidence for the “turn-on” detection of anions. The one-step, facile synthesis of the sensors was implemented using the “Click chemistry” approach in good yield. When investigated for selectivity and sensitivity against a series of anions (F⁻, Cl⁻, Br⁻, I⁻, H₂PO₄⁻, ClO₄⁻, OAc⁻, and BF₄⁻), the sensor displayed the strongest fluorometric response for the fluoride anion. NMR and fluorescence spectroscopic studies validate a 1:1 binding stoichiometry between the sensor and the fluoride anion. Single crystal X-ray diffraction evidence revealed the structure of the sensor in the solid state. Full article

A method is proposed to extend the zero-temperature Hall-Klemm microscopic theory of the Knight shift K in an anisotropic and correlated, multi-band metal to calculate $K\left(T\right)$ at finite temperatures T both above and into its superconducting state. The transverse part of the magnetic induction $\mathbf{B}\left(t\right)={\mathbf{B}}_0+{\mathbf{B}}_1\left(t\right)$ causes adiabatic changes suitable for treatment with the Keldysh contour formalism and analytic continuation onto the real axis. We propose that the Keldysh-modified version of the Gor’kov method can be used to evaluate $K\left(T\right)$ at high ${\mathbf{B}}_0$ both in the normal state, and by quantizing the conduction electrons or holes with Landau orbits arising from ${\mathbf{B}}_0$ , also in the entire superconducting regime for an anisotropic, multiband Type-II BCS superconductor. Although the details have not yet been calculated in detail, it appears that this approach could lead to the simple result $K_S\left(T\right)\approx a\left({\mathbf{B}}_0\right)-b\left({\mathbf{B}}_0\right){|\Delta ({\mathbf{B}}_0,T)|}^2$ , where $2|\Delta ({\mathbf{B}}_0,T\left)\right|$ is the effective superconducting gap. More generally, this approach can lead to analytic expressions for $K_S\left(T\right)$ for anisotropic, multiband Type-II superconductors of various orbital symmetries that could aid in the interpretation of experimental data on unconventional superconductors. Full article

Structural characterization of complexes is crucial for a better understanding of biological processes and structure-based drug design. However, many protein–ligand structures are not solvable by X-ray crystallography, for example those with low affinity binders or dynamic binding sites. Such complexes are usually targeted by solution-state NMR spectroscopy. Unfortunately, structure calculation by NMR is very time consuming since all atoms in the complex need to be assigned to their respective chemical shifts. To circumvent this problem, we recently developed the Nuclear Magnetic Resonance Molecular Replacement (NMR²) method. NMR² very quickly provides the complex structure of a binding pocket as measured by solution-state NMR. NMR² circumvents the assignment of the protein by using previously determined structures and therefore speeds up the whole process from a couple of months to a couple of days. Here, we recall the main aspects of the method, show how to apply it, discuss its advantages over other methods and outline its limitations and future directions. Full article

We report the analysis of comb-like polymers by solid-state NMR. The polymers were previously evaluated as solid-polymer-electrolytes (SPE) for lithium-polymer-metal batteries that have suitable ionic conductivity at 60 °C. We propose to develop a correlation between ¹³C solid-state NMR measurements and phase segregation. ¹³C solid-state NMR is a perfect tool for differentiating polymer phases with fast or slow motions. ⁷Li was used to monitor the motion of lithium ions in the polymer, and activation energies were calculated. Full article

In this paper five case studies illustrating applications of NMR (Nuclear Magnetic Resonance) in the field of cultural heritage, are reported. Different issues were afforded, namely the investigation of advanced cleaning systems, the quantitative mapping of moisture in historic walls, the investigation and evaluation of restoration treatments on porous stones, the stratigraphy of wall paintings, and the detection of CO₂ in lapis lazuli. Four of these case studies deal with the use of portable NMR sensors which allow non-destructive and non-invasive investigation in situ. The diversity among cases reported demonstrates that NMR can be extensively applied in the field of cultural heritage. Full article

LiCl and LiNO₃ water solutions in the presence of small amounts of 3-helium have been investigated by means of multinuclear resonance spectroscopy. The resulting concentration dependences of the ³He, ^6,7Li⁺, ¹⁴NO₃⁻ and ³⁵Cl⁻ resonance radiofrequencies are reported in the infinite limit. This data along with new theoretical corrections of shielding lithium ions was analyzed by a known NMR relationship method. Consequently, the nuclear magnetic moments of ⁶Li and ⁷Li were established against that of the helium-3 dipole moment: μ(⁶Li) = +0.8220457(50)μ_N and μ(⁷Li) = +3.256418(20)μ_N. The new results were shown to be very close to the previously obtained values of the (ABMR) atomic beam magnetic resonance method. This experiment proves that our helium method is well suited for establishing dipole moments from NMR measurements performed in water solutions. This technique is especially valuable when gaseous substances of the needed element are not available. All shielding constants of species present in water solutions are consistent with new nuclear magnetic moments and these taken as a reference. Both techniques—NMR and ABMR—give practically the same results provided that all shielding corrections are properly made. Full article

The UV-driven photocuring of coatings results in a crosslinked polymeric network. The degree of crosslinking in these coatings is typically assessed via optical spectroscopy; unfortunately, optical methods are typically limited in their maximum depth access. Alternatively, single-sided nuclear magnetic resonance (NMR) can be used to probe the crosslinking of UV-curable coatings in a spatially sensitive manner. Relaxation measurements, which correlate with crosslinking, can be done with a spatial resolution on the order of microns throughout the depth dimension of the coating, regardless of optical transparency of the material. These results can be visualized via a relaxation cross-section that shows the depth at which a particular relaxation value is observed. These measurements are used to probe the effect of a scavenger molecule that is added to the coating mixture, allowing for efficient crosslinking despite the presence of atmospheric oxygen. This method may find purchase in evaluating systems whose crosslinking properties are intentionally varied throughout its thickness; using NMR, these systems, up to approximately one hundred microns thick, can be measured without repositioning or rastering. Full article

Microvalves play an important role in fluid control in micro total analysis systems (µTAS). Previous studies have reported complex fabrication processes for making microvalve elements in a channel. Hence, there is a need for a simpler microvalve fabrication method for achieving throughput improvement and cost reduction in µTAS. In this study, we propose a simple fabrication method for a magnetically driven microvalve array using a photosensitive composite. The composite was prepared by mixing a photoresist and magnetic particles of pure iron. The simple fabrication process was performed by using a laminating layer composed of a sacrificial part and the composite in a channel. The microvalve elements were fabricated by one-step photolithography using the processability of the sacrificial layer and composite. Further, we demonstrated the magnetic driving property of the fabricated microvalve array device. Compared to devices containing non-driving microvalves, the flow rate was decreased by 50%, and the pressure difference between the inlet and outlet increased by up to 4 kPa with increase in driving microvalve elements. These results imply that our proposed device could be useful for practical µTAS applications. Full article

Five new anilato-based, Ln(III)-containing, layered compounds have been prepared with the asymmetric ligand chlorocyananilato (C₆O₄(CN)Cl)²⁻; different Ln(III) ions Ce(III), Pr(III), Yb(III), and Dy(III); and the three different solvents H₂O, dimethylsolfoxide (DMSO), and dimethylformamide (DMF). Compounds [Ce₂(C₆O₄(CN)Cl)₃(DMF)₆]·2H₂O (1), [Pr₂(C₆O₄(CN)Cl)₃(DMF)₆] (2), [Pr₂(C₆O₄(CN)Cl)₃(DMSO)₆] (3), [Yb₂(C₆O₄(CN)Cl)₃(DMSO)₄]·2H₂O (4) and [H₃O][Dy(C₆O₄(CN)Cl)₂(H₂O)]·4H₂O (5) show the important role that the Ln(III) size, as well as the size and shape of the solvent may play in the crystal structure of each compound. Compounds 1–4 present (6,3)-2D hexagonal lattices, with important differences in the coordination number and geometry of the Ln(III) ion, as well as in the distortion of the hexagonal cavities, depending on the Ln(III) and solvent size. Compound 5 (the only one prepared with water) presents a (4,4)-2D square lattice, where the Dy(III) ions are surrounded by four chelating anilato ligands. Compounds 2–4 are essentially paramagnetic, confirming the presence of weak (if any) magnetic coupling mediated by the anilato ligands when connecting Ln(III) ions. Compounds 2–4 showed a red shift and a broadening of the emission band of the ligand. Compound 4 also showed a strong emission band attributed to the Yb(III), suggesting an antenna effect of the ligand. An energy transfer diagram is proposed to explain these luminescent properties. Full article

Switching magnetic properties have attracted a wide interest from inorganic chemist for the objectives of information storage and quantum computing at the molecular level. This review is focused on magnetic switches based on a mechanical motion, which is an innovative approach. Three main strategies to control magnetic properties by a mechanical motion have been developed in the literature and will be described. The first one (ligand-induced spin change) consists in modulating the ligand field strength by a configuration change of the ligand in spin-crossover complexes. The second one (coordination-induced spin-state switching) is based on a change in the coordination number of a metallic center that is triggered by the motion of one ligand. The third one uses the modulation of the exchange interaction between two spin-centers by a mechanical motion. Full article

We have previously investigated the diverse levels of disruption caused by Zn(II)BLMs with different C-termini to DNA hairpins containing 5′-GC-3′ and 5′-GT-3′ binding sites. The results of this investigation indicated that both the DNA-binding site and the bleomycin C-termini have an impact on the final conformation of the aforementioned hairpins in the drug-target complexes, as suggested by the different sets of intramolecular NOEs displayed by both oligonucleotides when bound to each Zn(II)BLM. The NMR signals elicited by ¹H nuclei in the oligonucleotide bases and sugar moieties were also affected differently (shifted upfield or downfield in various patterns) depending on the BLM C-termini and the binding site in the oligonucleotides. The overall conclusion derived from the precedent research is that the spatial conformation of target DNA segments in DNA-Zn(II)BLM complexes could be forged by interactions between drug and DNA that are guided by the DNA binding site and the BLM C-termini. The present study focuses on the structural alterations exhibited by Zn(II)bleomycin-A₂, -B₂, -A₅ and Zn(II)peplomycin molecules upon binding to the previously studied hairpins. Our main goal is to determine if different spatial conformations of the drugs in their DNA-bound forms are found in drug-DNA complexes that differ in the oligonucleotide binding site and BLM C-termini. Evidence that suggest that each Zn(II)bleomycin is structurally affected depending these two factors, as indicated by different sets of intramolecular NOE connectivities between drug protons and diverse patterns of shifting of their ¹H-NMR signals, is provided. Full article

The combinational use of one-dimensional (1D) NMR-based screening techniques with ¹H and ¹⁹F detections were applied to a human serum albumin–diflunisal complex. Since most NMR screening methods observe ¹H spectra, the overlapped ¹H signals were unavailable in the binding epitope mapping. However, the NMR experiments with ¹⁹F detection can be used as an effective complementary method. For the purpose of identifying the ¹H and ¹⁹F binding epitopes of diflunisal, this paper carries out a combinatorial analysis using ¹H{¹H} and ¹⁹F{¹H} saturation transfer difference experiments. The differences of the ¹H-inversion recovery rates with and without target irradiation are also analyzed for a comprehensive interpretation of binding epitope mapping. Full article

In recent years, there has been a growing interest in fast acquisition and analysis of nuclear magnetic resonance (NMR) spectroscopy data for high throughput protein structure determination. Towards this end, rapid data collection techniques and methods to simplify the NMR spectrum such as amino acid selective unlabeling have been proposed recently. Combining these two approaches can speed up further the structure determination process. Based on this idea, we present three new two-dimensional (2D) NMR experiments, which together provide ¹⁵N, ¹HN, ¹³C^α, ¹³C^β, ¹³C′ chemical shifts for amino acid residues which are immediate C-terminal neighbors (i + 1) of residues that are selectively unlabeled. These experiments have high sensitivity and can be acquired rapidly using the methodology of G-matrix Fourier transform (GFT) NMR spectroscopy combined with non-uniform sampling (NUS). This is a first study involving the application of fast NMR methods to proteins samples prepared using a specific labeling scheme. Taken together, this opens up new avenues to using the method of selective unlabeling for rapid resonance assignment of proteins. Full article

Myosin binding protein C (MyBP-C) is a multi-domain protein that participates in the regulation of muscle contraction through dynamic interactions with actin and myosin. Three primary isoforms of MyBP-C exist: cardiac (cMyBP-C), fast skeletal (fsMyBP-C), and slow skeletal (ssMyBP-C). The N-terminal region of cMyBP-C contains the M-motif, a three-helix bundle that binds Ca²⁺-loaded calmodulin (CaM), but less is known about N-terminal ssMyBP-C and fsMyBP-C. Here, we characterized the conformation of a recombinant N-terminal fragment of ssMyBP-C (ssC1C2) using differential scanning fluorimetry, nuclear magnetic resonance, and molecular modeling. Our studies revealed that ssC1C2 has altered thermal stability in the presence and absence of CaM. We observed that site-specific interaction between CaM and the M-motif of ssC1C2 occurs in a Ca²⁺-dependent manner. Molecular modeling supported that the M-motif of ssC1C2 likely adopts a three-helix bundle fold comparable to cMyBP-C. Our study provides evidence that ssMyBP-C has overlapping structural determinants, in common with the cardiac isoform, which are important in controlling protein–protein interactions. We shed light on the differential molecular regulation of contractility that exists between skeletal and cardiac muscle. Full article