NMR Reveals That a Highly Reactive Nonheme FeIV=O Complex Retains Its Six-Coordinate Geometry and S=1 State in Solution

The [Fe^IV(O)(Me₃NTB)]²⁺ (Me₃NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, ¹H NMR spectroscopy was used to determine that 1 does not have C₃-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme Fe^IV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 Fe^IV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the Fe^IV=O center to rationalize nonheme oxoiron(IV) reactivity.     

A mathematical model for bioconvection flow of Williamson nanofluid over a stretching cylinder featuring variable thermal conductivity,activation energy and second-order slip

Journal of Thermal Analysis and Calorimetry - The significant bioconvection phenomenon with the utilization of nanoparticles encountered fundamental industrial and technological applications in...     

Synthesis and characterization of degradable hyperbranched poly(2‐ethyl‐2‐oxazoline)

Hyperbranched poly(2‐ethyl‐2‐oxazoline) was synthesized by a combination of cationic ring‐opening polymerization and the oxidation of thiol to disulfide groups. A three‐arm star poly(2‐ethyl‐2‐oxazoline) (PEtOx) was first synthesized using 1,3,5‐tris(bromomethyl) benzene as an initiator. The star PEtOx was end‐capped with potassium ethyl xanthate. Similarly, a linear PEtOx was synthesized and end‐capped with potassium ethyl xanthate using benzyl bromide as an initiator. Hyperbranched PEtOx was then obtained by in situ cleaving and subsequent oxidation of the star PEtOx and linear PEtOx mixture with n‐butylamine as both a cleaving agent and a base in tetrahydrofuran. The linear PEtOx was used to prevent the formation of gel. The hyperbranched PEtOx can be cleaved with dithiothreitol to trithiol and monothiol polymer. The hyperbranched PEtOx shows no remaining thiols using Ellman's assay. The resulting hyperbranched PEtOx was hydrolyzed to a novel hyperbranched polyethyleneimine with degradable disulfide linkages. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2030–2037     

Numerical analysis of dual variable of conductivity in bioconvection flow of Carreau–Yasuda nanofluid containing gyrotactic motile microorganisms over a porous medium

Journal of Thermal Analysis and Calorimetry - The increasing need of the modern era of technology for better ways to increase the heat transfer performance of thermal systems has made nanoliquids...     

Influence of pH on nanosized Mn–Zn ferrite synthesized by sol–gel auto combustion process

Sol–gel auto combustion process was employed to synthesize nanosized Mn–Zn ferrite at different pH values (<1, 5, 6, 7, 8 and 10). Although self propagating combustion behavior of gel was noted at pH 5 but more effective combustion was observed at pH 6. The smoldering effect was observed in gel prepared at pH 7, 8 and 10, whereas pH < 1 showed localized burning. Thermogravimetric (TG) and X-ray diffraction (XRD) analyses were done to investigate the effect of pH on the combustion behavior, particle size and the formation of desired magnetic (spinel) phase. From TG curves of burnt powders, activation energy of ignition reaction at each pH value was calculated. The results showed that fuel to oxidant ratio and the amount of gel residuals decided the value of activation energy required to further purify the burnt powders. Calcination parameters (time and temperature in air) of powders P1 and P6 synthesized at pH < 1 and pH 6 were also determined. B–H loop results showed that calcined powder C6 was more ferromagnetic than C1 due to fully developed spinel phase and larger particle size.     

Oblique interaction of electrostatic nonlinear structures in relativistically degenerate dense magnetoplasmas

We have investigated the interaction of obliquely propagating ion acoustic solitary waves in a magnetoplasma with relativistically degenerate electrons. Using the quantum hydrodynamics model and by employing the extended Poincaré–Lighthill–Kuo technique, we have derived a set of Korteweg de Vries equations for two solitons. We have observed that the system under consideration allows the formation of only compressive solitons and their velocities remain in the sub-acoustic limit. Furthermore, phase shifts of solitons as a result of their interaction have been calculated. The phase shifts have been observed to be dependent on the obliqueness and the physical parameters of plasma. It has also been noticed that phase shifts remain negative for the whole range of parameters generally found in white dwarf stars. We have observed that the phase shifts enhance with the enhancement in number density, however, the converse happens when the magnetic field is enhanced. It has also been observed that the phase shift is slightly greater for the solitons that are less oblique as compared to their more oblique counterparts. Furthermore, we have estimated the spatial scales of interaction of solitons using the parameters found in white dwarf stars.     

Characterization of Glycan Structures of Chondroitin Sulfate-Glycopeptides Facilitated by Sodium Ion-Pairing and Positive Mode LC-MS/MS

Purification and liquid chromatography-tandem mass spectrometry (LC-MS/MS) characterization of glycopeptides, originating from protease digests of glycoproteins, enables site-specific analysis of protein N- and O-glycosylations. We have described a protocol to enrich, hydrolyze by chondroitinase ABC, and characterize chondroitin sulfate-containing glycopeptides (CS-glycopeptides) using positive mode LC-MS/MS. The CS-glycopeptides, originating from the Bikunin proteoglycan of human urine samples, had ΔHexAGalNAcGlcAGalGalXyl-O-Ser hexasaccharide structure and were further substituted with 0-3 sulfate and 0-1 phosphate groups. However, it was not possible to exactly pinpoint sulfate attachment residues, for protonated precursors, due to extensive fragmentation of sulfate groups using high-energy collision induced dissociation (HCD). To circumvent the well-recognized sulfate instability, we now introduced Na⁺ ions to form sodiated precursors, which protected sulfate groups from decomposition and facilitated the assignment of sulfate modifications. Sulfate groups were pinpointed to both Gal residues and to the GalNAc of the hexasaccharide structure. The intensities of protonated and sodiated saccharide oxonium ions were very prominent in the HCD-MS2 spectra, which provided complementary structural analysis of sulfate substituents of CS-glycopeptides. We have demonstrated a considerable heterogeneity of the bikunin CS linkage region. The realization of these structural variants should be beneficial in studies aimed at investigating the importance of the CS linkage region with regards to the biosynthesis of CS and potential interactions to CS binding proteins. Also, the combined use of protonated and sodiated precursors for positive mode HCD fragmentation analysis will likely become useful for additional classes of sulfated glycopeptides.

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Comparison of α-chloralose,medetomidine and isoflurane anesthesia for functional connectivity mapping in the rat

Functional connectivity measures based upon low-frequency blood-oxygenation-level-dependent functional magnetic resonance imaging (BOLD fMRI) signal fluctuations have become a widely used tool for investigating spontaneous brain activity in humans. Still unknown, however, is the precise relationship between neural activity, the hemodynamic response and fluctuations in the MRI signal. Recent work from several groups had shown that correlated low-frequency fluctuations in the BOLD signal can be detected in the anesthetized rat — a first step toward elucidating this relationship. Building on this preliminary work, through this study, we demonstrate that functional connectivity observed in the rat depends strongly on the type of anesthesia used. Power spectra of spontaneous fluctuations and the cross-correlation-based connectivity maps from rats anesthetized with α-chloralose, medetomidine or isoflurane are presented using a high-temporal-resolution imaging sequence that ensures minimal contamination from physiological noise. The results show less localized correlation in rats anesthetized with isoflurane as compared with rats anesthetized with α-chloralose or medetomidine. These experiments highlight the utility of using different types of anesthesia to explore the fundamental physiological relationships of the BOLD signal and suggest that the mechanisms contributing to functional connectivity involve a complicated relationship between changes in neural activity, neurovascular coupling and vascular reactivity.     

Framing the novel aspects of irreversibilty in MHD flow of Williamson nanomaterial with thermal radiation near stagnation point

Journal of Thermal Analysis and Calorimetry - Here, MHD stagnation point flow of non-Newtonian fluid over a stretchable surface is considered. Process of modeling is characterized for basic...     

Efficient post-plasma catalytic degradation of toluene via series of Co–Cu/TiO2 catalysts

Research on Chemical Intermediates - Volatile organic compounds (VOCs) represent a very important class of pollutants that causes serious health effects. There is an urgent requirement to establish...