Effectivity Functions and Stable Governance Structures

Stability properties of several governance structures are studied by means of their effectivity functions. It is shown that (strong) stability of a governance structure is mainly determined by the collegial nature of the underlying assembly's decision rule.     

Three terminals optoelectronics devices integrated into a silicon on silicon waveguide

In this paper we describe two different kind of optoelectronic devices both based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working. The first device exploits this effect in order to obtain an optical modulation. The second device is an optoelectronic router based on the mode-mixing principle together with the injection-induced optical phase shift. Both devices are integrated into a Silicon on Silicon optical channel waveguide which can be realized using a standard bipolar process. The possibility of using standard, well-known technology presents several advantages with respect to III–V Optoelectronics. The active three terminal device used is a Bipolar Mode Field Effect Transistor (BMFET). Numerical simulation results are presented on both devices.     

Time-scale and excitation energy partition in sequential binary decays induced by heavy-ion collisions at ≃6 MeV·A

We studied the sequential binary decay of the systems ³²S+⁴⁵Sc, ⁷⁶Ge, ⁸⁹Y, ⁵⁹Co, ⁶³Cu and ¹⁹F+⁶³Cu induced by collisions at ≃6 MeV·A. The two stages of the process have reaction-times compatible with the dynamics of different mechanisms. The study of the excitation energy partition shows that the reaction mechanism of the first step has influence on the de-excitation of the primary fragments producing two decay components which have different time scale. Received: 25 March 1997 / Revised version: 2 December 1997     

Evidence against the hopping mechanism as an important electron transfer pathway for conformationally constrained oligopeptides

The rate constant of intramolecular electron transfer through oligopeptides based on the alpha-aminoisobutyric acid residue was determined as a function of the peptide length and found to depend weakly on the donor-acceptor separation. By measuring the electron-transfer activation energy and estimating the energy gap between donor and bridge, we were able to discard the electron hopping mechanism.     

Synthesis and spectroscopic properties of highly water-soluble perylene derivatives

Most known perylene diimides are lipophilic, with few exceptions of hydrophilic derivatives. Even in the latter case, the compounds have limited water solubility and show a strong tendency to self-aggregation. In this paper we present the synthesis of four new perylene derivatives with three and four basic side chains, obtained by functionalizing the bay-area of perylene. These molecules show great solubility in aqueous media as hydrochlorides and their tendency to self-aggregate is remarkably reduced with respect to the previously synthesized two-chained perylene diimides. Their different spectroscopic properties in various solvents and conditions are reported and discussed.     

Polar substituent effects in the bicyclo[1.1.1]pentane ring system: acidities of 3-substituted bicyclo[1.1.1]pentane-1-carboxylic acids

Experimental gas-phase acidities are reported for a series of 3-substituted (X) bicyclo [1.1.1]pent-1-yl carboxylic acids (1, Y = COOH). A comparison with available calculated data (MP2/6-311++G**// B3LYP/6-311+G**) reveals good agreement. The relative substituent effects are shown to be adequately described by a much lower level of theory (B3LYP/6-31+G*). Various correlations are presented which clearly point to polar field effects as being the origin of the relative acidities.     

Intramolecular dissociative electron transfer

Dissociative electron transfers (ET) are reactions in which the ET is associated with the cleavage of a sigma bond. Although a rather satisfactory amount of information is currently available on the intermolecular and heterogeneous dissociative ET reactions, less is known for the corresponding intramolecular processes, despite the relevance of these reactions in both chemistry and biochemistry. This tutorial review focuses on the most recent developments in this area, with particular emphasis on the reactions occurring in well-defined Donor-Spacer-Acceptor molecular systems. The goal is to provide the reader with the essential background to understand and possibly predict the feasibility and rates of these reactions, as well as to stimulate the application of the intramolecular dissociative ET concepts and related issues to still unexplored molecular systems.     

Intramolecular, intermolecular, and heterogeneous nonadiabatic dissociative electron transfer to peresters

The electron transfer to peresters was studied by electrochemical means in N,N-dimethylformamide. The reduction was carried out by three independent methods: (i) heterogeneously, by using glassy carbon electrodes, (ii) homogeneously, by using electrogenerated radical anions as the donors, and (iii) intramolecularly, by using purposely synthesized donor-spacer-acceptor (D-Sp-A) systems. Convolution analysis of the heterogeneous data led to results in excellent agreement with the dissociative electron transfer theory. The homogeneous redox catalysis data also confirmed the reduction mechanism. The cyclic voltammetries of the D-Sp-A molecules could be simulated, leading to determination of the corresponding intramolecular dissociative rate constants. Analysis of the results showed that, regardless of the way by which the acceptor is reduced, the investigated dissociative electron transfers are strongly nonadiabatic and, particularly, that the experimental rates are several orders of magnitude smaller than the adiabatic limit. A possible mechanism responsible for the observed behavior is discussed.     

PHOTOBIOLOGICAL ACTIVITY OF 3,4''-DIMETHYL-8-METHOXYPSORALEN, A LINEAR FUROCOUMARIN WITH UNUSUAL DNA-BINDING PROPERTIES

The furocoumarin derivative 3,4'-dimethyl-8-methoxypsoralen (DMe-8-MOP) exhibits remarkable antiproliferative activity, but is devoid of skin phototoxicity. To gain insight into this peculiar behaviour we investigated non-covalent and covalent binding of DMe-8-MOP to calf thymus DNA, along with DNA-synthesis inhibition and mutagenic activity. The non-covalent interaction of DMe-8-MOP with the nucleic acid is quite poor as shown by equilibrium dialysis, spectroscopic, chiroptical and hydrodynamic techniques. However, it exhibits relevant photobinding ability to DNA using both isolated nucleic acid samples and cellular systems. Unlike the large majority of congeners, DMe-8-MOP undergoes predominantly photochemical monoaddition to the double helical polynucleotide. Upon examination of the products obtained by enzymatic hydrolysis of DMe-8-MOP photomodified DNA, the formation of an unusual furan side adduct is proposed, which could account for the peculiar photochemical and photobiological properties of the 3,4'-dimethyl furocoumarin derivative.