Cocatalysis by epoxides in the polymerization of tetrahydrofuran with trityl hexachloroantimonate initiator

The polymerization of tetrahydrofuran (THF) with (C₆H₅)₃C⁺SbCl₆^- initiator is markedly accelerated by small concentrations of propylene oxide or other epoxides. Molar concentrations of propylene oxide 4 to 10 times those of the carbonium-ion salt showed increasing conversion to polymer. The equilibrium conversion level at different temperatures with epoxides is the same as in their absence; the approach to equilibrium is first-order in THF. NMR experiments in the presence of propylene oxide indicate the formation of a trityl ether intermediate. The cocatalysis effect is interpreted on the basis of an acceleration in the initiation process in the system.     

Thermodynamic study of Cd(II) complex formation with tripodal N-donor ligands in DMSO

The complex formation of Cd(II) with N-donor ligands in dimethylsulfoxide (DMSO) is investigated by means of potentiometry and titration calorimetry. The ligands considered in this work are tripodal polyamines and polypyridines: 2,2′,2″-triaminotriethylamine (TREN), tris(2-(methylamino)ethyl)amine (Me₃TREN), tris(2-(dimethylamino)ethyl)amine (Me₆TREN), tris[(2-pyridyl)methyl]amine (TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA). These ligands are characterized by a systematic modification of the donor groups to relate their structure to the thermodynamics of the complexes formed. The TREN and Me₃TREN ligands form highly stable species. The stability of the complex formed with the fully methylated Me₆TREN is much lower than with other polyamines and the enthalpic and entropic terms suggest an incomplete coordination to the metal ion. In general, the TPA ligand forms complexes less stable than TREN and Me₃TREN as a result of the combination of higher structural rigidity of TPA and lower basicity of pyridine moiety with respect to primary and secondary amines. Pyridine-containing ligands display, in general, a less unfavorable formation entropy than tripodal polyamines here considered. In particular, TPA forms a more stable 1:1 species with respect to Me₆TREN due to the entropic term, being the enthalpy less negative. The ligand BTPA is able to form only a monometallic complex, where the metal ion is likely to be encapsulated as indicated by the obtained thermodynamic parameters.     

Enantioselective Cytotoxicity of Chiral Diphosphine Ruthenium(II) Complexes Against Cancer Cells

The chiral cationic complex [Ru(η¹-OAc)(CO)((R,R)-Skewphos)(phen)]OAc ( 2 ^R ), isolated from reaction of [Ru(η¹-OAc)(η²-OAc)(R,R)-Skewphos)(CO)] ( 1 ^R ) with phen, reacts with NaOPiv and KSAc affording [RuX(CO)((R,R)-Skewphos)(phen)]Y (X=Y=OPiv 3 ^R ; X=SAc, Y=OAc 4 ^R ). The corresponding enantiomers 2 ^S - 4 ^S have been obtained from 1 ^S containing (S,S)-Skewphos. Reaction of 2 ^R and 2 ^S with (S)-cysteine and NaPF₆ at pH=9 gives the diastereoisomers [Ru((S)-Cys)(CO)(PP)(phen)]PF₆ (PP=(R,R)-Skewphos 2 ^R -Cys; (S,S)-Skewphos 2 ^S -Cys). The DFT energetic profile for 2 ^R with (S)-cysteine in H₂O indicates that aquo and hydroxo species are involved in formation of 2 ^R -Cys. The stability of the ruthenium complexes in 0.9 % w/v NaCl solution, PBS and complete DMEM medium, as well as their n-octanol/water partition coefficient (logP), have been evaluated. The chiral complexes show high cytotoxic activity against SW1736, 8505 C, HCT-116 and A549 cell lines with EC₅₀ values of 2.8–0.04 μM. The (R,R)-Skewphos derivatives show higher cytotoxicity compared to their enantiomers, 4 ^R (EC₅₀=0.04 μM) being 14 times more cytotoxic than 4 ^S against the anaplastic thyroid cancer 8505 C cell line.     

Diffusion determines the recurrent graph

We consider diffusion on discrete measure spaces as encoded by Markovian semigroups arising from weighted graphs. We study whether the graph is uniquely determined if the diffusion is given up to order isomorphism. If the graph is recurrent then the complete graph structure and the measure space are determined (up to an overall scaling). As shown by counterexamples this result is optimal. Without the recurrence assumption, the graph still turns out to be determined in the case of normalized diffusion on graphs with standard weights and in the case of arbitrary graphs over spaces in which each point has the same mass.     

Solvent effect on the thermodynamics of Ag(I) coordination to tripodal polypyridine ligands

An investigation on the thermodynamics of complex formation between Ag(I) ion and two tripodal ligands tris[(2-pyridyl)methyl]amine (TPA) and 6,6′-bis-[bis-(2-pyridylmethyl)aminomethyl]-2,2′-bipyridine (BTPA) has been carried out in the aprotic solvents dimethylsulfoxide (DMSO) and dimethylformamide (DMF) by means of potentiometry and titration calorimetry. The results for TPA are compared with those already obtained for other aliphatic tripodal polyamines. In general, the TPA ligand forms complexes less stable than 2,2′,2″-triaminotriethylamine (TREN) and tris(2-(methylamino)ethyl)amine (Me₃TREN) as a result of the combination of higher structural rigidity of TPA and lower σ-donor ability of pyridinic moieties with respect to primary and secondary amines. The same trend is found if the stability of Ag(I) complex with TPA is compared with that of tris(2-(dimethylamino)ethyl)amine (ME₆TREN), despite the pyridinic nitrogen is formally a tertiary one. Theoretical calculations run to explain the reasons of this weaker interaction indicate that this difference is due to solvation, rather than to steric or σ-donor effects. The ligand BTPA is able to form bimetallic species whose relative stability is largely influenced by the different solvation of Ag(I) ion in DMSO and DMF rather than by the difference in the dielectric constants of these two media.     

Simultaneous micellar electrokinetic chromatographic determination of isomeric fatty acid hydroperoxides and corresponding hydroxy fatty acids

The high selectivity and efficiency of micellar electrokinetic chromatography with a borax-sodium dodecylsulfate (SDS) or meglumin-SDS buffer make possible the rapid separation of hydroperoxy and hydroxy fatty acids and the non-oxidised unsaturated fatty acids from which they are derived. Nearly all the isomers of the hydroperoxides and hydroxy fatty acids derived from oleic, linoleic, alpha- and gamma-linolenic and arachidonic acids can be determined both qualitatively and quantitatively within ca. 10 min. The system has as many as 1 x 10(6) theoretical plates, and the detection limits with UV diode array detection at 195 or 234 nm are in the micromolar range.     

Ultrafast all-optical demultiplexer based on monolithic Mach–Zehnder interferometer with integrated semiconductor optical amplifiers

A monolithically integrated and fully packaged Mach–Zehnder interferometer with semiconductor optical amplifiers (MZI-SOA) is demonstrated as polarisation-independent high-speed demultiplexer for up to 160 Gbit/s optical time division multiplexed (OTDM) data streams.