Spin Probe Technique Research Articles

Orientational Ordering of Graphene Oxide Membranes by a Spin Probe Technique and SEM Image Analysis

Orientational Ordering of Graphene Oxide Membranes by a Spin Probe Technique and SEM Image Analysis

Electron Spin Resonance Spin Probe Technique for Investigating Non‐TEMPO Radicals Dispersed in Nanospaces of a Crystalline Zn Complex

An ESR spin probe technique with non‐TEMPO radicals, such as nitronyl nitroxide (NN), benzonitronyl nitroxide (BzNN), and iminonitroxide (IN) radicals, was used for a porous metal‐organic framework (MOF), [(ZnI2)3(TPT)2] (ZnTPT; TPT = tris(4‐pyridyl)‐1,3,5‐triazine), at room temperature. The principal values of g and hyperfine coupling (A) tensors estimated from spectral reproduction were different from those for organic matrices for some of these radicals. These results indicate that host‐guest interactions occur between the ZnTPT matrix and guest radicals. Thus, when using NN, BzNN, and IN radicals as spin probes for a porous MOF, the interaction between the metal atoms or organic ligands in host materials and guest radicals should be considered. The experimental ESR spectra for the derivatives of NN or BzNN radicals were reproduced only by the rigid‐limit component in the ESR time scale. However, those for the derivatives of IN radicals were approximately reproduced only by rotational diffusion around the z‐axis perpendicular to the plane in the IN group. Interestingly, this reproduction was not around the y‐axis of the principal axes of the g tensors, parallel to the molecular long axis, as previously observed in a few organic matrices. The IN radicals dispersed in the ZnTPT matrix are expected to be accommodated in cylindrical or pseudocylindrical nanospaces sandwiched by the pyridyl or triazine rings of TPT in ZnTPT. These findings show that the ESR spin probe technique using non‐TEMPO radicals can be used to investigate the chemical and biological structures of nanosized materials.

Liquid-like and solid-like acetonitrile intercalated into graphite oxide as studied by the spin probe technique.

The molecular mobility of acetonitrile intercalated into the inter-plane space of graphite oxide was studied using the spin probe technique. It was revealed that two types of intercalated substance - liquid-like and solid-like - are simultaneously present in between the oxidized graphene planes, and their ratio depends on temperature. The micro-viscosity of liquid-like intercalated acetonitrile was found to be higher than that of bulk acetonitrile and depends on the amount of intercalated liquid.

Orientation Distribution of Molecules in a Smectic Liquid Crystal with a Distorted Director Geometry.

Quantitative determination of the molecular orientation distribution function in samples of liquid crystals with a complex director geometry was performed using the numerical simulation of electron paramagnetic resonance (EPR) spectra of the spin probes in a liquid-crystalline medium. To achieve the quantitative agreement of experimental and simulated EPR spectra, the hierarchy of the orientation order was explicitly taken into account, namely, the local ordering of liquid crystal molecules by the mean-field potential of surrounding molecules, and the partial disordering of local directors within the sample. The samples under study are planar and twist LC cells with liquid crystal 8CB cooled from the nematic into the smectic A phase in the magnetic field. The presence of the magnetic field perpendicular to the cell director leads to distortion of the orientation of the liquid crystal in the cell. The spin probe technique was successfully employed for the reliable measurement of orientation distribution functions of the low nonorthorhombic symmetry. Orientation order parameters up to 12th rank were measured, including nonaxial and nonorthorhombic order parameters. It is shown that the presence of several contradicting aligning forces leads to the tilt of the preferential director toward the direction, which is a compromise between the orienting forces.

Quantitative determination of the orientational ordering of graphene oxide membranes by the spin probe technique.

The orientational alignment of graphene oxide membranes was determined quantitatively using the spin probe technique; the values of the orientational order parameters up to the 6th rank were obtained. It was shown that nitroxide probes as well as Cu(II) complexes adequately reflect the alignment of the membranes. It was estimated that the orientational alignment of the membranes prepared by vacuum filtration using the same material can be significantly different. The membrane prepared by drying the graphite oxide suspension has a very poor orientational alignment in comparison with the membranes prepared by vacuum filtration.

Synthesis and biological and physico-chemical characterization of glycodendrimers and oligopeptides for the treatment of systemic lupus erythematosus.

Anti-(ds)-DNA antibodies are the serological hallmark of Systemic Lupus Erythematosus (SLE). They assemble in the bloodstream with (ds)-DNA, forming immunocomplexes, which spread all over the body causing, among the other symptoms, lupic glomerulonephritis. Pathological manifestations of the disease may be reduced by destabilizing or inhibiting the formation of the immunocomplexes. In this respect, glycodendrimers showed peculiar interacting abilities towards this kind of biomolecule. Various generations of open-shell maltose-decorated poly(amidoamine) (PAMAM) and poly(propyleneimine) (PPI) dendrimers and two oligopeptides with different polyethylene glycol units were synthesized and characterized, and then tested for their anti-SLE activity. The activity of glycodendrimers and oligopeptides was evaluated in human plasma from patients with SLE, compared to healthy plasma, by means of an enzyme-linked immunosorbent assay (ELISA), and electron paramagnetic resonance (EPR) characterization using spin-label and spin-probe techniques. Different strategies for the immunocomplex formation were tested. The results show that both kinds of glycodendrimers and oligopeptides inhibited the formation of immunocomplexes. Also, a partial breakdown of preformed immunocomplexes was observed. Both ELISA and EPR analyses indicated a better activity of glycodendrimers compared to oligopeptides, the 3rd generation PPI dendrimer being the most promising against SLE. This study highlights the possibility to develop a new class of dendritic therapeutics for the treatment of Lupus in pre-clinical studies.

Investigation of Various Organic Radicals Dispersed in Polymethylmethacrylate Matrices Using the Electron Spin Resonance Spectroscopy Technique.

The electron spin resonance (ESR) spectroscopy technique was used to study various organic radicals, such as 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO), 4-hydroxy-TEMPO (TEMPOL), 2-X-nitronylnitroxide (2-X-NN, X = Ph, NO2Ph, or cyclohexyl), 4-Y-benzonitronylnitroxide (4-Y-PhBzNN, Y = Ph or NO2Ph), and 2-Z-iminonitroxide (2-Z-IN, Z = Ph or NO2Ph) dispersed in a polymethylmethacrylate (PMMA) matrix. The experiments were conducted at room temperature. The complex nature of the recorded ESR spectra could be attributed to the superposition of the rotational diffusion component of TEMPO (or TEMPOL) in the nanospace of the PMMA matrix with the rigid-limit component. A single component of the rigid-limit was observed for 2-X-NN and 4-Y-PhBzNN radicals dispersed in the PMMA matrix. The isotropic components of g and hyperfine (A) tensor, estimated by analyzing the solution spectra, were used to determine the g and A components of 4-Y-PhBzNN. Only the rotational diffusion component was observed for the 2-Z-IN radical. These results demonstrated that the PMMA matrix contains cylindrical nanospaces. Various radicals other than TEMPO derivatives could be used in the ESR spin probe technique as probe molecules for determining the structures, sizes, and shapes of the nanospaces.

Safe and efficient degradation of metronidazole using highly dispersed β-FeOOH on palygorskite as heterogeneous Fenton-like activator of hydrogen peroxide

In this study, the highly dispersed β-FeOOH on palygorskite (H-β-FeOOH/PAL) was prepared and investigated as Fenton catalyst for H2O2 activation towards metronidazole (MTZ). Based on electron spin resonance and probe techniques, hydroxyl radicles (•OH) as main reactive oxygen species was confirmed, and much more •OH were generated over H-β-FeOOH/PAL than T-β-FeOOH/PAL using traditional impregnation method. The enhanced Fe(III) to Fe(II) cycle due to the highly dispersed β-FeOOH leads to the fast degradation of metronidazole over H-β-FeOOH/PAL. 92.8% of MTZ degradation efficiency was achieved within 180 min by adding 17 mmol/L H2O2 and 40 mg/L of H-β-FeOOH/PAL at pH 6.0. The bacterial cytotoxicity during MTZ degradation process also decreased with reaction time and achieved zero at 66 min, indicating MTZ was not only efficiently degraded but also safely transformed. Besides, the possible MTZ degradation pathway was further proposed based on the intermediates identified by HPLC-MS.

The orientation order of liquid‐crystalline polymer, measured by ESR and optical dichroism techniques

ABSTRACTMolecular orientation order and rotation mobility of comb‐shaped liquid crystalline polymer forming nematic and smectic mesophases are characterized by spin probe and dichroism technique in the temperature range 100–420 K. The models describing the mechanism of molecular rotations in different temperature ranges were determined by quantitative numerical simulations of ESR spectra. In the vicinity of the glass transition point of the polymer, where the fast amplitude‐restricted molecular reorientations take place, the quasi‐libration model was found to be adequate for the description of ESR spectra, while the often used Brownian rotational diffusion is appropriate at higher temperatures only. Orientation distribution function of probe molecules was characterized quantitatively by order parameters up to sixth rank for a wide temperature range. The orientation order parameters measured via the spin probe technique are shown to correlate with orientation order parameters measured by optical techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 819–825

Properties of Graphite Oxide Powders and Membranes as Revealed by Electron Paramagnetic Resonance Spectroscopy

The spin probe technique was used to study graphite oxide (GO) powders swelled in polar liquids (CH3CN, CH3OH, and H2O) and liquid-free GO membranes (GOM). The nitroxide radicals TEMPO (2,2,6,6-tet ...

Magnetic field effects in nematic and smectic liquid crystals probed by time resolved observation of orientation relaxation of the spin probe

The kinetics of reorientation of the liquid crystal HOPOOB in nematic and smectic phases in the magnetic field was studied by the spin probe technique. The time evolution of the EPR spectrum shape in the course of reorientation in the nematic phase indicates that the mechanism of alignment comprises redistribution between domains of different orientations rather than the turn of the orientation distribution function. A microscopic model of domain structure rearrangement is provided to qualitatively describe the experimental data. In the smectic C phase, partial reorientation is observed upon the action of the magnetic field. A possible mechanism of this process is the reorientation of tilt direction within the smectic layers. It is shown that this process is constrained, and the value of the corresponding elastic constant is estimated.

Drug nanocarriers for cancer chemotherapy based on microemulsions: The case of Vemurafenib analog PLX4720

Oil-in-water (O/W) microemulsions based on Tween 80 as the emulsifier and triacetin as the dispersed oil phase were formulated to be used as delivery vehicles of Vemurafenib analog PLX4720. PLX4720 is a lipophilic antitumor drug against various cancer types correlated with the BRAFV600E mutation. The limits of the single-phase region corresponding to O/W microemulsions as described by ternary phase diagrams were examined. Droplet size measurements determined by dynamic light scattering (DLS) showed mean droplet diameters equal to 10±0.1nm both in the presence and in absence of the drug. Cryogenic-transmission electron microscopy (Cryo-TEM) images of the microemulsions showed the existence of small structures with uniform size distribution having also average diameters of approximately 10nm. Electron paramagnetic resonance (EPR) spectroscopy applying the spin probing technique confirmed PLX4720 location in the oil cores excluding its participation in the surfactants monolayer. Furthermore, cell viability assays on colon cancer cell lines Colo-205 and HT29 showed that microemulsions did not exhibit any cytotoxicity when added in ratios between 0.005% v/v and 0.2% v/v. When the cells were treated with encapsulated PLX4720 at two different concentrations (0.063 and 0.12μΜ) the same response as when dissolved in classic DMSO was observed.

Melanin and humic acid-like polymer complex from olive mill waste waters. Part II. Surfactant properties and encapsulation in W/O microemulsions

A natural melanin and humic acid-like polymer complex from olive mill waste waters (OMWWs) showing surfactant and antiradical properties was encapsulated in food grade water-in-oil (W/O) microemulsions to detect potential interactions with the system's components. Before encapsulation, putative surfactant properties of the polymer complex were investigated through interaction studies with the cationic dye Toluidine blue O (TBO) using spectrophotometry. The limits of the single-phase region corresponding to W/O microemulsions as described by ternary phase diagrams were studied. Structural characteristics of the microemulsions were examined using electrical conductivity, dynamic light scattering (DLS) and electron paramagnetic resonance (EPR) spectroscopy. Antiradical properties of encapsulated polymer complex were investigated using an EPR approach. The existence of a J-aggregation mechanism consisting of head-to-tail arrangement of the dye molecules was proved and attributed to a specific 3D-arrangement of the phenolic constituents of the complex. EPR measurements using the spin probing technique revealed participation of the complex in the surfactants monolayer causing increased membrane fluidity. Droplet size measurements showed a decrease of aqueous droplets size from 19±0.5 to 17±0.8nm upon polymer complex addition. Finally, radical scavenging activity of the complex was retained upon encapsulation and expressed in Trolox equivalents.

Orientation order and rotation mobility of nitroxide biradicals determined by quantitative simulation of EPR spectra.

The problem of quantitative numerical simulation of electron paramagnetic resonance (EPR) spectra of biradical probes in both isotropic and aligned media was solved for the first time. The models suitable for the description of the spectra of the probes, both in the rigid limit and in the presence of rotational motions, were developed and successfully applied to model systems. The simulation of EPR spectra allows obtaining the following information about the molecular structure and dynamics: the values of orientation order parameters, the type of rotation mobility and its quantitative characteristics, and the sign and value of the spin exchange constant of the biradical. Model systems used in this work include solutions of nitroxide biradicals in a viscous solvent (squalane) in the range of temperatures 100-370 K and in the aligned liquid crystal n-octylcyanobiphenyl (8CB, 100-298.5 K). Unexpectedly, it was found that in 8CB the main orientation axis of the biradical molecule is perpendicular to the longest molecular axis.

EPR Spin Probe Study of Local Mobility at the Shungite/Elastomer Interface

Molecular mobility of the polymer composition in the interfacial layer at the boundary of shungite and elastomers (ethylene/propylene copolymer and natural rubber) was investigated by electron paramagnetic resonance spin probe technique. In both cases, the molecular mobility of interfacial layer is approximately one order smaller than the mobility of the bulk polymer. The layer is characterized by high polarity, which is, apparently, due to the penetration of polar molecules and groups in this layer from shungite surface. An attempt was made to estimate the thickness of the interfacial layer (2–4 nm).

Nematic Director Configuration, Local Order and Microviscosity in a PSLC Cell

The director configuration, the local order and the molecular-level reorientational dynamics (microviscosity) of the 5CB liquid crystal (LC) inside a polymer-stabilized LC (PSLC) cell prepared with the 4,4′-bis(6-(acryloyloxy)hexyloxy)biphenyl (BAB6) diacrylic monomer have been studied with the EPR spin probe technique across the nematic and the isotropic phase of the LC. The cells made from glass slides, either clean or coated with an aligning layer, were filled with pure 5CB or with 0.5, 1.0 or 2.0 wt% of BAB6, either in the monomeric state or polymerized. Local orientational order parameter (<P2>) in the non treated cells was always slightly lower than in the coated ones and both were lower than in the bulk LC. Order appeared to be independent of polymerization state or BAB6 concentration up to 1.0 wt%. Reorientational dynamics was essentially bulk-like in all cases, indicating that in our PSLC cells a full molecular mobility is retained. At the concentration of 2.0 wt%, in the coated cell with polymerized BAB6, the monodomain did not reform after a 90° rotation of the cell in the magnetic field, suggesting that the polymer network is, as expected, stabilizing the preexisting director configuration.

EPR spectroscopy and its use in planta—a promising technique to disentangle the origin of specific ROS

While it is widely accepted that reactive oxygen species (ROS) are common players in developmental processes and a large number of adaptations to abiotic and biotic stresses in plants, we still do not know a lot about ROS level control at cellular or organelle level. One major problem that makes ROS hard to quantify and even to identify is their short lifetime. A promising technique that helps to understand ROS level control in planta is the electron paramagnetic resonance (EPR) spectroscopy. Application of the spin trapping method and the spin probe technique by this advanced method enables the quantification and identification of specific ROS in different plant tissues, cells or organelles or under different conditions. This mini review summarizes the knowledge using EPR spectroscopy as a method for ROS detection in plants under different stress conditions or during development. This technique allows disentangling the origin of specific ROS and transient alteration in ROS levels that occur by changes in ROS production and scavenging.

Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation.

The role of orbital differentiation on the emergence of superconductivity in the Fe-based superconductors remains an open question to the scientific community. In this investigation, we employ a suitable microscopic spin probe technique, namely Electron Spin Resonance (ESR), to investigate this issue on selected chemically substituted BaFe2As2 single crystals. As the spin-density wave (SDW) phase is suppressed, we observe a clear increase of the Fe 3d bands anisotropy along with their localization at the FeAs plane. Such an increase of the planar orbital content is interestingly independent of the chemical substitution responsible for suppressing the SDW phase. As a consequence, the magnetic fluctuations in combination with this particular symmetry of the Fe 3d bands are propitious ingredients for the emergence of superconductivity in this class of materials.

Stabilization of active sites in alloyed Pd–Rh catalysts on γ-Al2O3 support

Active components for three-way catalysts containing alloyed Pd–Rh particles with the concentration of the components 0.12 and 0.08wt.%, respectively, were synthesized and studied. The properties of these materials were compared with those of supported catalysts containing one or two precious metals (PM) prepared by mechanical mixing of the components with the same concentrations of PM. The stability of the samples was estimated by in situ prompt thermal aging (PTA) procedure. Photoluminescence (PL) and electron paramagnetic resonance (EPR) were used to show the importance of intrinsic sites of the support in stabilization of single-metal and alloyed Pd-containing clusters with high catalytic activity in CO oxidation. Substantial mutual effect of Pd and Rh in the alloyed particles was revealed. It prevents Pd-containing particles from sintering and hinders diffusion of Rh3+ ions into the bulk of the support at high temperatures. The spin probe technique was used to demonstrate that the alloy formation permits one to improve significantly the catalyst stability to reduction.

ESR and Optical Study of Photo-Orientation in Azobenzene-Containing Liquid-Crystalline Polymer

We report a comprehensive experimental study of photoinduced processes in azobenzene-containing liquid-crystalline polymer. The kinetic and optical characteristics of the photoisomerization reaction and photo-orientation process have been determined. The spin probe technique has been used to elucidate the details of orientation order and rotational mobility of molecular fragments within the liquid-crystalline polymer. The evolution of orientation order parameters <P2>, <P4>, and <P6> in the course of photoinduced ordering of the material as well as the change of liquid-crystalline domain sizes have been studied quantitatively. The obtained experimental results are compared with the predictions of the existing models of photo-orientation.