Stereochemical Aspects in the Asymmetric Michael Addition of Chiral Imines to Substituted Electrophilic Alkenes

The Michael-type addition of chiral imines, derived from racemic alpha-substituted cyclanones and optically active 1-phenylethylamine, to electrophilic alkenes, in neutral conditions, constitutes one of the most efficient methods for the stereocontrolled construction of quaternary carbon centers. In order to create an additional stereogenic center at the alpha- or beta-position to the quaternary one, the behavior of a variety of alpha- and beta-substituted alkenyl acceptors was examined. In general, these additions are highly regioselective, the alkylation taking place predominantly, if not exclusively, at the more substituted alpha-side of the imine function; however, in some cases (electrophilic alkenes 28 and 49), significant amounts (10-15%) of regioisomeric adducts were obtained. With the exception of methyl propiolate 52, a remarkable control of the absolute configuration of the adducts were always observed with these Michael acceptors. According to the general rule we have previously proposed, the alkylation process takes place preferentially on the less hindered pi-face of the more substituted secondary enamine, in tautomeric equilibrium with the starting imine. An excellent diastereocontrol was always obtained by using the present alpha- and beta-substituted alkenes. These stereochemical outcomes can be interpreted by invoking that the reaction proceeds through a compact approach of the reactants, the hydrogen atom at the nitrogen center of the enamine being transferred to the alpha-vinylic carbon atom of the acceptor, concertedly with the creation of the C-C bond. In this respect the "endo-approach" 58, in which the electron-withdrawing group of the acceptor faced to the nitrogen atom of the enamine (case of acceptors 10, methyl methacrylate, 24, 28, 43, 47, and 49) largely prevails over the "exo-approach" 59 (case of acceptor 38). This predominant "endo-preference" can be reasonably interpreted in terms of a cooperative effect between steric and stereoelectronic factors.     

Inversvoltammetrische Untersuchung von Cyanidspuren am h?ngenden Quecksilbertropfen

Zusammenfassung Cyanidspuren lassen sich in Gegenwart von Kupfer(II)-ionen mit Hilfe der inversen Voltammetrie am hängenden Hg-Tropfen unter Anreicherung quantitativ bestimmen. Wahrscheinlich beruht diese Möglichkeit auf der Bildung von unlöslichem CuCN auf der Elektrodenoberfläche. Man kann entweder die Abnahme des Cu-Peaks oder die Bildung des Oxydationspeaks bei + 0,17 V den Bestimmungen zugrunde legen. Untersuchungen über den Einfluß von SCN^–, Cl^–, Br^{– –} und J^– ergaben, daß die CN^–-Bestimmung unter bestimmten Konzentrationsverhältnissen möglich ist.

---

Summary Traces of cyanide can be quantitatively determined by inverse voltammetry in the presence of copper(II) ions after accumulation at the hanging mercury drop. Probably the determination is due to the formation of insoluble CuCN at the surface of the electrode. It is possible to determine the decrease of the copper peak or the formation of the second oxidation peak at +0.17 V. The investigation of the influence of SCN^–, Cl^–, Br^– and J^– showed that the determination of CN^– is possible in the presence of certain proportions of concentrations of these ions.

     

Oxygen-17 nuclear magnetic resonance: The effects of remote unsaturation on 17o-chemical shifts in polycyclic ethers

Natural-abundance ¹⁷O-NMR spectra of 7-oxanorbornane exo-3-oxatricyclo [3.2.1.0^2.4]octane and their unsaturated derivatives (endo cyclic and exocyclic double bonds) have been measured. Linear correlation laws were observed for $\text{δ}{}_{\mathrm{o}}\text{δ}{}_{\mathrm{c}}$ of these ethers/corresponding hydrocarbons. The “cyclization shifts” for δ_o in ethers were not correlated by the “cyclization shifts” for δ_c of the corresponding hydrocarbons.     

Stereochimie de la des benzoates d'argent sur des diesters iododesoxy ns: I- Action des benzoates d'argent sur des di-o-aroyl-1,2 iododesoxy-3 ns-glycerols

The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R¹ and R² on the substrates to stabilize a positive charge. Rearrangements are at minimum with R¹ and R² electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed.     

Indirekte inversvoltammetrische Bestimmung von Elementen unter Anwendung von Verdr?ngungsreaktionen

Zusammenfassung Unter Anwendung von Verdrängungsreaktionen lassen sich nichtamalgambildende Elemente inversvoltammetrisch indirekt bestimmen. Eisen läßt sich indirekt über die Freisetzung von Blei aus dem Blei-ÄDTA-Komplex und inversvoltammetrische Bestimmung des freigesetzten Bleianteils bis zu einer Konzentration von etwa 4·10^–8 Mol/l erfassen. Die relative Standardabweichung betrug im Konzentrationsbereich 4·10^–7 bis 2·10^–6Mol/l ± 10%.Indirekte Bestimmungen von Calcium, Strontium und Barium sind über die Verdrängung von Zink aus dem Zink-ÄDTA-Komplex in Gegenwart von Ammoniak als Hilfskomplexbildner möglich. Im Konzentrations-bereich 6·10^–7 bis 3·10^–6 Mol/l ergab sich eine relative Standardabweichung von 6%.

---

Summary Elements forming no amalgams can be determined indirectly by inverse voltammetry using exchange reactions. Iron displacing lead from lead-EDTA complex is determined by anodic stripping voltammetry of lead down to a concentration of about 4×10^–8 M. In the concentration range from 4×10^–7 to 2×10^–6 M a relative standard deviation of ±10% has been obtained. Indirect determinations of calcium, strontium and barium are possible by displacement of zinc from zinc-EDTA in presence of ammonia. In the concentration range from 6×10^–7 to 3×10^–6 M the relative standard deviation amounts to 6%.

     

Préparation,configuration et réduction électrochimique d'α-cyano β-nitrostyrènes. Synthèse d'amino-5 isoxazoles

Z α-Cyano-β-nitrostyrenes were prepared by nitration with dinitrogentetroxide of the corresponding α-cyanostyrenes. Elsomers were obtained by photoirradiation of Z isomers. The electrochemical reduction of these cyanonitro compounds generates the α-cyanooximes which lead, according to the experimental conditions(ring closure or hydrolysis), either to 5-aminoisoxazoles or to β-ketonitriles.     

Study of Langmuir and Langmuir-Blodgett films of odorant-binding protein/amphiphile for odorant biosensors

To make ultrathin films for the fabrication of artificial olfactory systems, odorant biosensors, we have investigated mixed Langmuir and Langmuir-Blodgett films of odorant-binding protein/amphiphile. Under optimized experimental conditions (phosphate buffer solution, pH 7.5, OBP-1F concentration of 4 mg L(-1), target pressure 35 mN m(-1)), the mixed monolayer at the air/water interface is very stable and has been efficiently transferred onto gold supports, which were previously functionalized by self-assembled monolayers (SAMs) with 1-octadecanethiol (ODT). Atomic force microscopy and electrochemical impedance spectroscopy were used to characterize mixed Langmuir-Blodgett (LB) films before and after contact with a specific odorant molecule, isoamyl acetate. AFM phase images show a higher contrast after contact with the odorant molecule due to the new structure of the OBP-1F/ODA LB film. Non-Faradaic electrochemical spectroscopy (EIS) is used to quantify the effect of the odorant based on the electrical properties of the OBP-1F/ODA LB film, as its resistance strongly decreases from 1.18 MOmega (before contact) to 25 kOmega (after contact).     

Biosensors based on enzyme field-effect transistors for determination of some substrates and inhibitors

This paper is a review of the authors' publications concerning the development of biosensors based on enzyme field-effect transistors (ENFETs) for direct substrates or inhibitors analysis. Such biosensors were designed by using immobilised enzymes and ion-selective field-effect transistors (ISFETs). Highly specific, sensitive, simple, fast and cheap determination of different substances renders them as promising tools in medicine, biotechnology, environmental control, agriculture and the food industry.The biosensors based on ENFETs and direct enzyme analysis for determination of concentrations of different substrates (glucose, urea, penicillin, formaldehyde, creatinine, etc.) have been developed and their laboratory prototypes were fabricated. Improvement of the analytical characteristics of such biosensors may be achieved by using a differential mode of measurement, working solutions with different buffer concentrations and specific agents, negatively or positively charged additional membranes, or genetically modified enzymes. These approaches allow one to decrease the effect of the buffer capacity influence on the sensor response in an aim to increase the sensitivity of the biosensors and to extend their dynamic ranges.Biosensors for the determination of concentrations of different toxic substances (organophosphorous pesticides, heavy metal ions, hypochlorite, glycoalkaloids, etc.) were designed on the basis of reversible and/or irreversible enzyme inhibition effect(s). The conception of an enzymatic multibiosensor for the determination of different toxic substances based on the enzyme inhibition effect is also described.We will discuss the respective advantages and disadvantages of biosensors based on the ENFETs developed and also demonstrate their practical application.     

The effect of σ and π singly-excited configurations in the calculation of excited states by the CNDO and INDO approximations

The CNDO/2 and INDO approximations (with their original parametrization) are utilized for the calculation of transition energies. The effect of including all ( and ) singly excited configurations is assessed in C₂H₄, H₂CO, HCOOH and HCONH₂, and the results are compared to experimental transitions and to the available non-empirical calculations. The effect of extensive mixing is then considered in larger molecules.

---

Zusammenfassung Die Näherungen CNCO/2 und INDO (mit ihrer ursprünglichen Parametrisierung) werden für die Berechnung von Übergangsenergien benutzt. Der Effekt des Einschlusses aller ( und ) einfach angeregter Konfigurationen wird untersucht für C₂H₄, H₂CO, HCOOH und HCONH₂ und die Ergebnisse werden mit experimentellen Übergängen und den verfügbaren nicht-empirischen Rechnungen verglichen. Die Überlegungen werden dann auf größere Moleküle ausgedehnt.

---

Résumé Les procédés CNDO/2 et INDO (avec leur paramétrisation originale) sont utilisés pour calculer des énergies de transition. L'effet du mélange de toutes les configurations monoexcitées ( et ) est étudié pour C₂H₄, H₂CO, HCOOH et HCONH₂, les résultats sont comparés aux transitions expérimentales et aux calculs non-empiriques disponibles. L'étude est étendue à de plus grandes molécules.

     

Gibbs functions for transfer of divalent metal cations from water to water + methanol mixtures using potentiometry, polarography and solubility measurements

Gibbs functions for transfer from water to methanol and to a full range of water + methanol mixtures were obtained for Cu²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ using potentiometric or polarographic measurements in these solvents. In addition, data were obtained from the solubility products of the alkaline-earth iodates. From values obtained by the different methods and literature data, a table of selected values is given.