The early stages of methane activation over Zn-modified H-MFI catalysts obtained by high-temperature reaction with zinc vapor have been studied by 13 C MAS NMR in situ. Methane 99.9% enriched with 13 C was used as labeled reactant. The spectroscopic data pointed to formation of zinc methyl species at ambient temperature just after methane adsorption onto the zeolite sample. The results suggest that methane activation occurs via dissociative adsorption over acid-base Zn-O pairs involving Zn 2+ cations and negatively charged oxygen atoms of the zeolite framework. The nature of the sites responsible for the dissociation is discussed.

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Abstract:We explored the neuroprotective properties of natural plant-derived antioxidants plastoquinone and thymoquinone (2-demethylplastoquinone derivative) modified to be specifically accumulated in mitochondria. The modification was performed through chemical conjugation of the quinones with penetrating cations: Rhodamine 19 or tetraphenylphosphonium. OPEN ACCESSMolecules 2015, 20 14488Neuroprotective properties were evaluated in a model of middle cerebral artery occlusion. We demonstrate that the mitochondria-targeted compounds, introduced immediately after reperfusion, possess various neuroprotective potencies as judged by the lower brain damage and higher neurological status. Plastoquinone derivatives conjugated with rhodamine were the most efficient, and the least efficiency was shown by antioxidants conjugated with tetraphenylphosphonium. Antioxidants were administered intraperitoneally or intranasally with the latter demonstrating a high level of penetration into the brain tissue. The therapeutic effects of both ways of administration were similar. Long-term administration of antioxidants in low doses reduced the neurological deficit, but had no effect on the volume of brain damage. At present, cationic decylrhodamine derivatives of plastoquinone appear to be the most promising anti-ischemic mitochondria-targeted drugs of the quinone family. We suggest these antioxidants could be potentially used for a stroke treatment.

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A mitochondria-targeted chimeric compound consisting of a rhodamine derivative linked to a plastoquinone molecule (10-(6'-plastoquinonyl)decylrhodamine, SkQR1) was studied under conditions of acute brain or kidney damage. A protective effect of this compound was demonstrated in a model of focal brain ischemia, rat kidney ischemia/reperfusion, myoglobinuria (rhabdomyolysis, or crush syndrome), and pyelonephritis. We found that a single intraperitoneal injection of SkQR1 diminishes the size of the ischemic zone in the brain and improves performance of a test characterizing neurological deficit in ischemic animals. Control substance not containing plastoquinone appeared to be not neuroprotective. The data show that SkQR1 is a nephroprotectant and neuroprotectant, which can be due to the antioxidative action of this Skulachev cation.

Mesenchymal stem cells isolated from human placenta and in vitro labeled with fluorescent magnetic microparticles were intravenously injected to rats 2 days after induction of focal cerebral ischemia (endovascular model). According to MRT findings, transplantation of mesenchymal stem cells led to an appreciable reduction of the volume of ischemic focus in the brain. Two or three weeks after transplantation, labeled cells accumulated near and inside the ischemic focus, in the hippocampus, and in the subventricular zone of both hemispheres. Only few human mesenchymal stem cells populating the zone adjacent to the ischemic focus started expressing astroglial and neuronal markers. On the other hand, transplantation of mesenchymal stem cells stimulated proliferation of stem and progenitor cells in the subventricular zone and migration of these cells into the ischemic zone. Positive effects of transplantation of these cells to rats with experimental ischemic stroke are presumably explained by stimulation of proliferation of resident stem and progenitor cells of animal brain and their migration into the ischemic tissue and adjacent areas. Replacement of damaged rat neurons and glial cells by transplanted human cells, if it does take place, is quite negligible.

We propose porous silicon nanoparticles (PSi NPs) with natural oxide coating as biocompatible and bioresorbable contrast agents for magnetic resonant imaging (MRI). A strong shortening of the transversal proton relaxation time (T2) was observed for aqueous suspensions of PSi NPs, whereas the longitudinal relaxation time (T1) changed moderately. The longitudinal and transversal relaxivities are estimated to be 0.03 and 0.4 l/(g·s), respectively, which are promising for biomedical studies. The proton relaxation is suggested to undergo via the magnetic dipole-dipole interaction with Si dangling bonds on surfaces of PSi NPs. MRI experiments with phantoms have revealed the remarkable contrasting properties of PSi NPs for medical diagnostics.