Spectroelectrochemical investigation of a flavoprotein with a flavin-modified gold electrode

A flavin-modified gold electrode was developed in order to catalyze the electrochemical oxidoreduction of flavoproteins. Surface modification was carried out by a two-step procedure. In the first step a mixed self-assembled monolayer obtained by adsorption of activated and nonactivated 3,3'-dithiopropionic acid (free acid and N-succinimidyl ester) was formed, followed by the covalent attachment of a N(10)-hexylamino-alkylated flavin derivative via an amide bond in the second step. The electrochemical properties of the flavin-modified electrode are presented and discussed. The redox potential of the attached flavin was measured at various pH values and the electron-transfer rate constant between electrode and flavin was determined as k0 = 5 s(-1) independent of pH. The flavin-modified electrode was successfully applied to the electrochemical and spectroelectrochemical investigation of the flavoprotein WrbA from Escherichia coli that shows some structural similarities to flavodoxins. It is concluded that the electron transfer "electrode --> flavin --> flavoprotein" occurs by a two-step hopping mechanism where the first step is rate determining. Kinetic details are discussed. Furthermore, it turned out that, in contrast to flavodoxins, where the semiquinone state is stabilized, WrbA rapidly takes up two electrons, directly leading to the fully reduced form. The presented electrode surface modification may generally lend itself for spectroelectrochemical investigations of flavoproteins.     

Optical resolution methods

Despite the large number of elaborate enantioselective syntheses for the preparation of a single enantiomer to achieve industrial and scientific goals, the separation and purification of enantiomers (components of racemic compounds) is also necessary. Hence, we present the most often used thought-provoking modern methods based on momentous recognitions (e.g. spontaneous resolution, induced crystallization, resolution by formation of diastereomers, resolution by formation of non-covalent diastereomers, resolution by diastereomeric salt formation, resolution by diastereomeric complex formation, "half equivalent" methods of resolution, separation by crystallization, separation by distillation, separation by supercritical fluid extraction, resolution with mixtures of resolving agents, resolution with a derivative of the target compound, enantioselective chromatography, resolution by formation of covalent diastereomers, resolution by substrate selective reaction, kinetic resolution without enzymes, kinetic resolution by enzyme catalysis, hydrolytic and redox enzymes, kinetic and thermodynamic control, resolutions combined with 2nd order asymmetric transformations, enrichment of partially resolved mixtures, role of the solvent and methods of optimization in the separation of diastereoisomers, non-linear effects and selected examples of resolution on an industrial scale).     

The minimal spanning tree and the upper box dimension

We show that the -weight of an MST over points in a metric space with upper box dimension has a bound independent of if d$"> and does not have one if .

     

Intentional systems: Review of neurodynamics, modeling, and robotics implementation

We present an intentional neurodynamic theory for higher cognition and intelligence. This theory provides a unifying framework for integrating symbolic and subsymbolic methods as complementary aspects of human intelligence. Top-down symbolic approaches benefit from the vast experience with logical reasoning and with high-level knowledge processing in humans. Connectionist methods use bottom-up approach to generate intelligent behavior by mimicking subsymbolic aspects of the operation of brains and nervous systems. Neurophysiological correlates of intentionality and cognition include sequences of oscillatory patterns of mesoscopic neural activity. Oscillatory patterns are viewed as intermittent representations of generalized symbol systems, with which brains compute. These dynamical symbols are not rigid but flexible. They disappear soon after they emerged through spatio-temporal phase transitions. Intentional neurodynamics provides a solution to the notoriously difficult symbol grounding problem. Some examples of implementations of the corresponding dynamic principles are described in this review.     

Reactions of diols and epoxides Communication 10. Synthesis of 3-alkyl- and 3-aryl-oxetanes

Conclusions New synthesis of 3-methyl-, 3-ethyl-, 3-propyl-, 3-isopropyl-, 3-butyl-, 3-t-butyl-, 3-cyclohexyl-, 3-phenyl-, and 3-benzyl-oxetanes are described, and their more important physical constants are given. These cyclic ethers can be prepared in fairly good yields (40–60%) from the corresponding chloro acetates.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1241–1244, July, 1966.     

The d + d reactions at low energies I. The structure of4He in the vicinity of the d-d threshold

Polarization data concerning the polarization of the outgoing nucleons from the²H(d, n)³He and²H(d, p)³H reactions have been analysed in order to search for a resonanceJ =1^– near the d-d threshold in⁴He. The data were analysed in the theoretical framework of theR-matrix approach. The non-resonant behaviour of these polarization observables showed no evidence for aJ =1^– level of the⁴He at 24.1 MeV.