The Reactions of 6-(Hydroxymethyl)-2,2-dimethyl-1-azaspiro[4.4]nonanes with Methanesulfonyl Chloride or PPh3-CBr4.

Activation of a hydroxyl group towards nucleophilic substitution via reaction with methanesulfonyl chloride or PPh3-CBr4 system is a commonly used pathway to various functional derivatives. The reactions of (5R(S),6R(S))-1-X-6-(hydroxymethyl)-2,2-dimethyl- 1-azaspiro[4.4]nonanes 1a-d (X = O·; H; OBn, OBz) with MsCl/NR3 or PPh3-CBr4 were studied. Depending on substituent X, the reaction afforded hexahydro-1H,6H-cyclopenta[c]pyrrolo[1,2-b]isoxazole (2) (for X = O), a mixture of 2 and octahydrocyclopenta[c]azepines (4-6) (for X = OBn, OBz), or perhydro-cyclopenta[2,3]azeto[1,2-a]pyrrol (3) (for X = H) derivatives. Alkylation of the latter with MeI with subsequent Hofmann elimination afforded 2,3,3-trimethyl-1,2,3,4,5,7,8,8a-octahydrocyclopenta[c]azepine with 56% yield.

Pollution of Beach Sands of the Ob River (Western Siberia) with Microplastics and Persistent Organic Pollutants.

Microplastics (MPs) in aquatic environments can be associated with various substances, including persistent organic pollutants, which add to the problem of plastic ecotoxicity. The abundance of 1-5 mm microplastics and concentrations of particle-adsorbed organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in sandy sediments from three beaches in recreational areas along the upper Ob River in Western Siberia were assessed. MP pollution levels in the Ob River beach sands ranged from 24 ± 20.7 to 104 ± 46.2 items m-2 or, in terms of mass concentration, from 0.26 ± 0.21 to 1.22 ± 0.39 mg m-2. The average abundance of MP particles reached 0.67 ± 0.58 items kg-1 or 8.22 ± 6.13 µg kg-1 in the studied sediments. MP concentrations were significantly higher in number (p < 0.05) and mass (p < 0.01) at the riverbank site downstream of the Novosibirsk wastewater treatment plant (WWTP) outfall compared to these at the upstream and more distant beaches. Most MPs (70-100%) were represented by irregularly shaped fragments. The polymer composition of MPs varied between sites, with a general predominance of polyethylene (PE). The study revealed associations of MPs with PCBs and OCPs not previously detected in the riverbed and beach sediments, suggesting that these substances are circulating in the Ob River basin. Although MP concentrations were higher downstream of the WWTP, the maximum levels of particle-associated OCPs were observed in the beach sands of the site farthest from the urban agglomeration. The pesticides γ-HCH, 4,4-DDT, and 4,4-DDE were detected on MPs at relatively low concentrations. PCBs were more abundant in the studied samples, including 118 dioxin-like congener. The results obtained indicate that the Ob River is susceptible to plastic and persistent organic pollutant (POP) contamination and serve as a starting point for further studies and practical solutions to the problem.

Mechanistic studies of the reactions of nitrone spin trap PBN with glutathiyl radical.

We performed mechanistic studies of the reaction of PBN with the physiologically relevant glutathiyl radical, GS*, formed upon oxidation of the intracellular antioxidant, glutathione, GSH. The scavenging rate constant of GS* by PBN has been measured directly by laser flash photolysis and indirectly by competitive EPR of the spin adduct of PBN and another spin trap, DMPO (5,5-dimethyl-1-pyrroline N-oxide), and was found to be 6.7 x 107 M(-1) s(-1). Reverse decomposition of the paramagnetic PBN-glutathiyl radical adduct to the nitrone and thiyl radical was observed for the first time. The rate constant for the reaction of the monomolecular decomposition of the radical adduct was found to be 1.7 s(-1). Diamagnetic, EPR-invisible products of PBN adduct degradation were studied by 1H NMR and 19F NMR using newly synthesized fluorine-substituted PBN.

Electron paramagnetic resonance spin trapping of glutathiyl radicals by PBN in the presence of cyclodextrins and by PBN attached to beta-cyclodextrin.

The reaction of the glutathiyl radical (GS*) with a widely used spin trap N- tert-butyl-alpha-phenylnitrone (PBN) has been studied in the presence of various methylated beta-cyclodextrins and with PBN covalently bound to dimethylated beta-cyclodextrin (PBN-DIMEB) and permethylated beta-cyclodextrin (PBN-TRIMEB). Scavenging rate constants for GS* by PBN were obtained in the presence of randomly methylated cyclodextrin (RAMEB) and PBN-TRIMEB and found to be close to the rate constant previously measured for PBN. RAMEB and 2,6-di- O-Me-beta-cyclodextrin (DIMEB) were found to be the most efficient in the increasing PBN/GS* lifetime, by a factor of 5.5 for RAMEB and 6.8 for DIMEB compared with the lifetime of PBN/GS*. It is concluded that the presence or "attachment of" beta-cyclodextrins does not influence the scavenging rate constant of GS* but it does lead to stabilization of the spin adducts formed.

Crystalline inclusion complex of a calixarene with a nitroxide.

The first capsular crystalline inclusion complex of para-hexanoyl calix[4]arene with stable nitroxyl radical DEPN has been isolated and showed a low mobility of the radical in the capsule.

Multifrequency EPR study of the mobility of nitroxides in solid-state calixarene nanocapsules.

Multifrequency continuous wave (cw) and echo-detected (ED) electron paramagnetic resonance (EPR) was employed to study the mobility of nitroxides confined in nanocapsules. The complexes p-hexanoyl calix[4]arene with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT) and N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-aminoxyl (DEPN) were studied by X-, W-band and 360 GHz cw EPR at temperatures between 90 and 370 K. Thereby we were able to extract the canonical values of the hyperfine and g-tensors of the encapsulated radicals as well as information on restricted orientational dynamics of the caged spin probes. Comparing cw and ED-EPR data obtained on MT@C6OH we found that between 90 and 200 K the caged nitroxide undergoes isotropic small-angle fluctuations (librations), whereas at higher temperatures restricted rotations of the radical with correlation times of 0.75 x 10(-10) s and 1.2 x 10(-10) s dominate at 325 and 300 K, respectively. The activation energy of the rotational motion of encapsulated MT radicals was evaluated as E(a) = 1.0 kcal mol(-1), which is comparable to the magnitude of van der Waals interactions. Compared to MT, the reorientational motion of DEPN was found to be slower and more isotropic.

Inclusion of 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl in a calixarene nanocapsule in the solid state.

We present an X-ray diffraction (XRD) and multi frequency electron spin resonance (ESR) study of the structure and dynamics of an inclusion complex of p-hexanoyl calix[4]arene (C6OH) with 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl (MT). The single crystal XRD experiments reveal that MT along with ethanol (solvent) molecules are entrapped in a capsular type crystalline lattice of the host C6OH material. ESR measurements were performed at 9.2 GHz/0.33 T (X-band) and at 360 GHz/14 T. In order to avoid ESR line broadening resulting from electron dipole-dipole interaction between nitroxides occupying neighbouring capsules in the crystal lattice, the capsules containing nitroxides were separated from each other by capsules containing diamagnetic dibenzylketone (DBK). Due to the extremely high g-tensor resolution of ESR at 360 GHz, we were able to distinguish, by shifts of their gxx component, between encapsulated nitroxide molecules forming a hydrogen bond between their O-(N) group and the OH group of an ethanol molecule occupying the same capsule and nitroxides missing this interaction. Temperature dependent ESR measurements revealed an orientational anisotropy in the motion of MT encapsulated in C6OH. Solid lipid nanoparticles (SLN) prepared from C6OH and loaded with the nitroxide retained the microcrystalline capsular structure of the pertinent inclusion complex. We found that encapsulated MT in SLNs becomes inaccessible to reducing agents such as sodium ascorbate.