Ground-state equilibrium thermodynamics and switching kinetics of bistable [2]rotaxanes switched in solution, polymer gels, and molecular electronic devices

We report on the kinetics and ground-state thermodynamics associated with electrochemically driven molecular mechanical switching of three bistable [2]rotaxanes in acetonitrile solution, polymer electrolyte gels, and molecular-switch tunnel junctions (MSTJs). For all rotaxanes a pi-electron-deficient cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles one of two recognition sites within a dumbbell component. Two rotaxanes (RATTF4+ and RTTF4+) contain tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units, but different hydrophilic stoppers. For these rotaxanes, the CBPQT4+ ring encircles predominantly (>90 %) the TTF unit at equilibrium, and this equilibrium is relatively temperature independent. In the third rotaxane (RBPTTF4+), the TTF unit is replaced by a pi-extended analogue (a bispyrrolotetrathiafulvalene (BPTTF) unit), and the CBPQT4+ ring encircles almost equally both recognition sites at equilibrium. This equilibrium exhibits strong temperature dependence. These thermodynamic differences were rationalized by reference to binding constants obtained by isothermal titration calorimetry for the complexation of model guests by the CBPQT4+ host in acetonitrile. For all bistable rotaxanes, oxidation of the TTF (BPTTF) unit is accompanied by movement of the CBPQT4+ ring to the DNP site. Reduction back to TTF0 (BPTTF0) is followed by relaxation to the equilibrium distribution of translational isomers. The relaxation kinetics are strongly environmentally dependent, yet consistent with a single electromechanical-switching mechanism in acetonitrile, polymer electrolyte gels, and MSTJs. The ground-state equilibrium properties of all three bistable [2]rotaxanes were reflective of molecular structure in all environments. These results provide direct evidence for the control by molecular structure of the electronic properties exhibited by the MSTJs.     

Bispalladacycle‐Catalyzed Michael Addition of In Situ Formed Azlactones to Enones

The development and further evolution of the first catalytic asymmetric conjugate additions of azlactones as activated amino acid derivatives to enones is described. Whereas the first‐generation approach started from isolated azlactones, in the second‐generation approach the azlactones could be generated in situ starting from racemic N‐benzoylated amino acids. The third evolution stage could make use of racemic unprotected α‐amino acids to directly form highly enantioenriched and diastereomerically pure masked quaternary amino acid products bearing an additional tertiary stereocenter. The step‐economic transformations were accomplished by cooperative activation by using a robust planar chiral bis‐Pd catalyst, a Brønsted acid (HOAc or BzOH; Ac=acetyl, Bz=benzoyl), and a Brønsted base (NaOAc). In particular the second‐ and third‐generation approaches provide a rapid and divergent access to biologically interesting unnatural quaternary amino acid derivatives from inexpensive bulk chemicals. In that way highly enantioenriched acyclic α‐amino acids, α‐alkyl proline, and α‐alkyl pyroglutamic acid derivatives could be prepared in diastereomerically pure form. In addition, a unique way is presented to prepare diastereomerically pure bicyclic dipeptides in just two steps from unprotected tertiary α‐amino acids.     

Isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse by high-performance liquid chromatography

The isolation, partial identification and quantitative determination of four guaiphenesin glucuronides in plasma and urine of the horse is described. The identity of the glucuronides was checked by UV and fluorescence spectrophotometry, by NMR spectrometry and by mass spectrometry after permethylation. The applicability of the procedure to pharmacokinetic studies is demonstrated.     

Bildung Siliciumorganischer Verbindungen. 103. Bildung und Struktur von cis- und trans-2,4-Dichloro-2,4-bis(trimethyl-silyl)-1,1,3,3-tetramethyl-1,3-disilacyclobutan

Formation of Organosilicon Compounds. 103. Formation and Structure of cis and trans 2,4-Dichloro-2,4-bis(trimethylsilyl)-1,1,3,3-tetramethyl-1,3-disilacyclobutane The reaction of Me₃Si? CCl₂? SiMe₂Cl with LiBu in THF yields 1,1,3,3-Tetramethyl-2,4-bis(trimethylsilyl) 1,3-disilabicyclo[1.1.0]butane. The product of the first reaction stage is Me₃Si? CCl(Li)-SiMe₂Cl. The 1,3-Disilacyclobutane 2 and 3 were isolated, when Me₃Si? CCl₂? SiMe₂Cl was treated with LiBu in Et₂O. This way the proof is given that 2 and 3 are intermediates of the formation of product 1 . The further products are 4 and 5 (CCl in 2 and 3 substituted by CH) and Me₃Si? CH₂? C(SiMeCl)₂SiMe₃. 2 crystallizes orthorhombically in the space group Fdd 2 (no. 43) with a = 2149.1 pm, b = 2229.2 pm, c = 1763.6 pm and Z = 16 molecules per cell. The central ring of disilacyclobutane is slightly folded (17.9°). The configuration of the C-Atoms in this four membered ring gets closer to a sp² configuration built up by three Si? C bonds. The Cl-atoms approximately have orthogonal positions to these CSi₃ arrangements. The extension of the C? Cl bonds (184.6 pm) and the mutual approximations of the Cl-atoms in the cis-position indicate a high reactivity of the molecule.     

Stochastic dominance equilibria in two-person noncooperative games

Two-person noncooperative games with finitely many pure strategies are considered, in which the players have linear orderings over sure outcomes but incomplete preferences over probability distributions resulting from mixed strategies. These probability distributions are evaluated according to t-degree stochastic dominance. A t-best reply is a strategy that induces a t-degree stochastically undominated distribution, and a t-equilibrium is a pair of t-best replies. The paper provides a characterization and an existence proof of t-equilibria in terms of representing utility functions, and shows that for large t behavior converges to a form of max–min play. Specifically, increased aversion to bad outcomes makes each player put all weight on a strategy that maximizes the worst outcome for the opponent, within the supports of the strategies in the limiting sequence of t-equilibria.The paper has benefitted from the comments of four referees and an associate editor.