Metathesis polymer based on 5-trimethylsilylbicyclo[2.2.2]oct-2-ene: Synthesis and gas-transport properties

A new silicon-containing bicyclic monomer 5-trimethylsilylbicyclo[2.2.2]oct-2-ene has been synthesized, and its metathesis polymerization and gas transport properties of the polymer based on it have been studied. The monomer is synthesized by the two-step scheme using the Diels–Alder reaction from 1,3-cyclohexadiene and vinyltrichlorosilane followed by methylation with a Grignard reagent. The resulting 5-trimethylsilylbicyclo[ 2.2.2]oct-2-ene is inactive in metathesis homopolymerization in the presence of first- and second- generation Grubbs catalysts and a Hoveyda–Grubbs catalyst, but it slowly polymerizes when norbornene is present in the reaction mixture. The high-molecular-mass copolymer (M _w = 3.0 × 10⁵, M _w/M _n = 2.8) of 5-trimethylsilylbicyclo[2.2.2]oct-2-ene and norbornene possesses good film-forming properties, and its glass transition temperature is 126°C. The gas-transport properties of the copolymer have been studied.     

Effect of the hyaluronidase microe nvironment on the enzyme structure–function relationship and computational study of the <Emphasis Type="Italic">in silico</Emphasis> molecular docking of chondroitin sulfate and heparin short fragments to hyaluronidase

The review addresses the biochemical interactions of hyaluronidases with components of the natural microenvironment. The effect of subtle structural differences between ligands on the enzyme structure–function relationship regulation is noted. Docking of chondroitin sulfate (CS) trimers (hexasaccharides) and heparin tetramers (octasaccharides) to the 3D model of the bovine testicular hyaluronidase (BTH) was performed by computational chemistry methods in order to elucidate the mechanism of regulation of the enzyme functioning in the body (using virtual screening, molecular dynamics, and calculation of surface electrostatic potential of protein complexes). Several binding sites for glycosaminoglycan (GAG) ligands were found to occur on the hyaluronidase surface. They are identical for CS trimers and heparin tetramers. The calculations showed the possibility of both reversible and irreversible conformational changes of the 3D structure of BTH, depending on the arrangement of negatively charged ligands on its globule. When the changes are irreversible, Glu-149 and Asp-147, which are key amino acid residues for the catalytic activity of BTH, can migrate from the vicinity of the native enzyme active site to the periphery of the protein molecule, thus inducing enzyme inactivation. The interaction of the GAG ligands with the BTH active site is mainly caused by electrostatic forces. Four or five binding sites of the chondroitin sulfate trimer proved to be critical for stabilization of the enzyme structure. Their occupation was sufficient for preventing irreversible deformation of the BTH molecule upon the insertion of the heparin ligand into the active site cavity. Protein stabilization is accompanied by the formation of a particular form of the surface electrostatic potential.     

Six-Nuclear Complexes of Platinum(II) and Palladium(II) with Mercamine and β-Mercaptoethanol

The platinum(II) and palladium(II) complexes [Pt₆(SCH₂CH₂NH₂)₈]Cl₄ and [Pd₆(SCH₂CH₂OH)₈ Cl₄· 5H₂O with mercamine and β-mercaptoethanol, respectively, were synthesized. It was found on the basis of the comparison of IR and X-ray electron spectra of the ligands and complexes, and also of the data of X-ray diffraction analysis that the bidentate coordination of ligands through sulfur and nitrogen atoms is realized in the platinum(II) complex. In the palladium(II) complex β-mercaptoethanol is coordinated in a mixed-mode type. In both complexes sulfur atoms of the ligands occupy a bridging position.     

Chiral zirconium catalysts using multidentate BINOL derivatives for catalytic enantioselective Mannich-type reactions; ligand optimization and approaches to elucidation of the catalyst structure

Catalytic enantioselective Mannich-type reactions of silicon enolates with aldimines were investigated using chiral zirconium catalysts prepared from Zr(O(t)Bu)(4), N-methylimidazole, and newly designed multidentate BINOL derivatives. These new multidentate BINOL ligands were designed on the basis of an assumed transition state structure of a chiral zirconium catalyst derived from two molecules of (R)-6,6'-Br(2)-BINOL. Not only tetradentate BINOL 4 but also tridentate BINOL derivatives were found to be effective, and high enantioselectivities were attained. In a structural study of the most effective zirconium complex prepared from tridentate ligand 6e, several NMR experiments and DFT calculations were carried out. Consequently, the structure of an active catalyst and plausible mechanism of asymmetric induction were elucidated.     

Instrumental neutron activation analysis of prehistoric and ancient bone remains

Instrumental neutron activation analysis (INAA) was used to study the element contents in bones of prehistoric dinosaurs and bones of an ancient bear and an archantrop (ancient person), which were found on the territory of Uzbekistan. Concentrations of more than 25 elements were in the range of 0.043–3600 mg/kg. Multielement analyses of bone and soil samples were carried out by INAA using the WWR-SM research nuclear reactor. Results of measurements have shown that in the dinosaurs bones the concentration of the rare earth elements (REEs) were within 280–3200 mg/kg; the uranium content reached a very high value, up to 180 mg/kg, while in soils coating the dinosaurs bones this content was 4.2 mg/kg; in the bones of the archantrop it was 1.53 mg/kg and in the bones of a standard person its amount is less than 0.016 mg/kg.     

Stability constants of polymer-metal complexes

Conditional stability constants of metal complexes with synthesized copolymers are studied by potentiometric titration. Linear copolymers are found to form more stable complexes than cross-linked sorbents with analogous functional groups. The stability of these complexes decreases in the order Th(IV) > Fe(III) ≈ La(III) > Cu(II).     

Sterically congested uranyl complexes with seven-coordination of the UO2 unit: the peculiar ligation mode of nitrate in [UO2(NO3)2(Rbtp)] complexes

Addition of 1 or 2 molar equiv of Rbtp [Rbtp = 2,6-bis(5,6-dialkyl-1,2,4-triazin-3-yl)pyridine; R = Me, Pr ( n )] to UO 2(OTf) 2 in anhydrous acetonitrile gave the neutral compounds [UO 2(OTf) 2(Rbtp)] [R = Me ( 1), ( n )Pr ( 2)] and the cationic complexes [UO 2(Rbtp) 2][OTf] 2 [R = Me ( 3), Pr ( n ) ( 4)], respectively. No equilibrium between the mono and bis(Rbtp) complexes or between [UO 2(Rbtp) 2][OTf] 2 and free Rbtp in acetonitrile was detected by NMR spectroscopy. The crystal structures of 1 and 3 resemble those of their terpyridine analogues, and 3 is another example of a uranyl complex with the uranium atom in the unusual rhombohedral environment. In the presence of 1 molar equiv of Rbtp in acetonitrile, UO 2(NO 3) 2 was in equilibrium with [UO 2(NO 3) 2(Rbtp)] and the formation of the bis adduct was not observed, even with an excess of Rbtp. The X-ray crystal structures of [UO 2(NO 3) 2(Rbtp)] [R = Me ( 5), Pr ( n ) ( 6)] reveal a particular coordination geometry with seven coordinating atoms around the UO 2 fragment. The large steric crowding in the equatorial girdle forces the bidentate nitrate ligands to be almost perpendicular to the mean equatorial plane, inducing bending of the UO 2 fragment. The dinuclear oxo compound [U(CyMe 4btbp) 2(mu-O)UO 2(NO 3) 3][OTf] ( 7), which was obtained fortuitously from a 1:2:1 mixture of U(OTf) 4, CyMe 4btbp, and UO 2(NO 3) 2 [CyMe 4btbp = 6,6'-bis-(3,3,6,6-tetramethyl-cyclohexane-1,2,4-triazin-3-yl)-2,2'-bipyridine] is a very rare example of a mixed valence complex involving covalently bound U (IV) and U (VI) ions; its crystal structure also exhibits a seven coordinate uranyl moiety, with one bidentate nitrate group almost parallel to the UO 2 fragment. The distinct structural features of [UO 2(kappa (2)-NO 3) 2(Mebtp)], with its high coordination number and a noticeable bending of the UO 2 fragment, and of [UO 2(kappa (2)-NO 3)(kappa (1)-NO 3)(terpy)], which displays a classical geometry, were analyzed by Density Functional Theory, considering the bonding energy components and the molecular orbitals involved in the interaction between the uranyl, nitrate, and Mebtp or terpy moieties. The unusual geometry of the Mebtp derivative with the seven coordinating atoms around the UO 2 fragment was found very stable. In both the Mebtp and terpy complexes, the origin of the interaction appears to be primarily steric (Pauli repulsion and electrostatic); this term represents 62-63% of the total bonding energy while the orbital term contributes to about 37-38%.     

Effect of flow rate on the sorption breakthrough behaviors of uranium(VI), phosphate,and fulvic acid onto a silica column

Five column experiments have been carried out to investigate the effect of flow rate on the breakthrough curves (BTCs) of phosphate, fulvic acid, and uranium(VI) onto a silica column. Both BTCs of phosphate and fulvic acid, and three BTCs of uranium(VI) in the presence and absence of phosphate or fulvic acid at high flow rate published in the previous paper [1] were compared with corresponding initial parts of BTCs at low flow rate in this paper. Each BTC in this paper was expressed as both C/C_o–t and C/C_o–V/V_o plots, where C and C_o are the concentrations in the influent and the effluent respectively, t and V are the time and the effluent volume from the start of injection of pulse solution respectively, V_o is the pore volume of the SiO₂ column. Based on the experimental results and the relationship among V, t, and flow rate F, it was found that there are advantages to using C/C_o–V/V_o plot as BTC to study the effect of flow rate. Based on these comparisons of C/C_o–V/V_o plots at different flow rates and the theoretical analysis from the Bohart–Adams sorption model, it was found that the right shift (increase in V/V_o of breakthrough), the left shift (decrease in V/V_o of breakthrough), and the non-shift (non-change in V/V_o of breakthrough) of initial parts of BTCs with increasing flow rate are certain to occur instead of only left shift and that three different trends of shifts can be mainly attributed to different rate-controlling mechanisms of sorption process.     

Bisindoles. 18. Some electrophilic substitution reactions in the 1,2-di(indol-5-yl)ethane series

A quantum-chemical calculation has been made and the laws of the electron-density distribution in the molecule of 1,2-di(indol-5-yl)ethane have been determined. The electrophilic substitution reactions most characteristic for it have been studied.For communications 15–17, see [1–3].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 73–77, January, 1984.