Theoretical study of species formed by IA and IB metals or ions and a CN ligand

Multireference second-order perturbation calculations have been carried out for copper and sodium complexes involving one CN ligand. Neutral compounds are strongly linked, cyanides M-CN being more stable than isocyanides M-NC (M = Cu, Na) as in the case of the pair HCN/HNC. Cations are much less strongly linked, Cu-NC⁻ being predicted to be the only system having a fairly bound structure, at variance with the dominance of the cyanide form in the HCN⁺/HNC⁺ pair.     

Molecular Recognition by a Short Partial Peptide of the Adrenergic Receptor: A Bottom‐Up Approach

Receptor–neurotransmitter molecular recognition is key for neurotransmission. Although crystal structures of the receptors are known, the mechanism for recognition is not clear. Reported here is the ultraviolet (UV) and infrared (IR) spectra of complexes between a partial peptide (SIVSF), mimicking the binding motif of a catechol ring in the adrenergic receptor, and various ligands. The UV spectra show that two isomers coexist in the complex of SIVSF with properly recognized ligands, such as protonated adrenaline (adrenalineH⁺). From IR spectra, they are assigned to catechol‐ and amino‐bound structures. The catechol‐bound structure is not observed when the ligand is replaced by nonproper molecules, such as noradrenalineH⁺. The results suggest that SIVSF not only recognizes the catechol ring but can distinguish differences in the amine side chain. The method provides a new possibility for screening molecules as potential therapeutics for activating the receptor.     

Evolving Systems of Stochastic Differential Equations

Journal of Theoretical Probability - We introduce Evolving Systems of Stochastic Differential Equations. This model generalizes the well-known stochastic differential equations with Markovian...     

Finite-state approximations for denumerable state discounted markov decision processes

A finite-state iterative scheme introduced by White [9] to approximate the optimal value function of denumerable-state Markov decision processes with bounded rewards, is extended to the case of unbounded rewards. Convergence theorems that, when applied to the case of bounded rewards, give stronger results than those in [9] are proved. Moreover, bounds on the rates of convergence under several assumptions are given and the extended scheme is used to obtain policies with asymptotic optimality properties.This research was supported in part by the Consejo Nacional de Ciencia y Tecnología under Grant PCCBBNA 020630, and in part by the Universidad Autónoma Agraria Antonio Narro.     

Electrostatic effect of specifically adsorbed electroinactive ions upon electrode processes: Part VI. Dimethylglyoxime electroreduction from weakly acidic aqueous solutions in the presence of I− and SCN−

An investigation of the _d-effect in the absence of ionic specific adsorption shows that the overall charge of the reactants in dimethylglyoxime (DMG) electroreduction on mercury from aqueous solutions of pH?2 equals+1, in agreement with a protonation reaction either preceding (DMG + H⁺DMGH^++e → products) or else simultaneous with (DMG + H⁺ + e → products) the charge transfer. In the presence of the specifically adsorbed supporting anions I^? and SCN^? the logarithm Φ of the rate constant for DMG electroreduction corrected for diffuse-layer effects decreases linearly with an increase in the absolute value |q_i| of the charge density at the inner Helmholtz plane due to the adsorbed anions. This behaviour is explained semiquantitatively by assuming that protonation takes place simultaneously with charge transfer, with the DMG molecule in the adsorbed state and the H₃O⁺ ion in the non-adsorbed state. In this way the H₃O⁺ ion, due to the screening effect of the surrounding diffuse-layer ions, escapes the accelerating attractive effect exerted by the adsorbed I^? or SCN^? ions; on the other hand these latter anions exert a retarding repulsive effect upon the electron transfer from the metal to the adsorbed DMG molecule.     

A generator of peroxynitrite activatable with red light

The generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) as “unconventional” therapeutics with precise spatiotemporal control by using light stimuli may open entirely new horizons for innovative therapeutic modalities. Among ROS and RNS, peroxynitrite (ONOO⁻) plays a dominant role in chemistry and biology in view of its potent oxidizing power and cytotoxic action. We have designed and synthesized a molecular hybrid based on benzophenothiazine as a red light-harvesting antenna joined to an N-nitroso appendage through a flexible spacer. Single photon red light excitation of this molecular construct triggers the release of nitric oxide (˙NO) and simultaneously produces superoxide anions (O₂˙⁻). The diffusion-controlled reaction between these two radical species generates ONOO⁻, as confirmed by the use of fluorescein-boronate as a highly selective chemical probe. Besides, the red fluorescence of the hybrid allows its tracking in different types of cancer cells where it is well-tolerated in the dark but induces remarkable cell mortality under irradiation with red light in a very low concentration range, with very low light doses (ca. 1 J cm⁻²). This ONOO⁻ generator activatable by highly biocompatible and tissue penetrating single photon red light can open up intriguing prospects in biomedical research, where precise and spatiotemporally controlled concentrations of ONOO⁻ are required.

Excitation of a molecular hybrid with highly biocompatible red light generates cytotoxic peroxynitrite, produces red fluorescence useful for cell tracking and induces remarkable cancer cell death at very low concentrations and very low light doses.     

A study of the gas-phase reaction between protonated acetaldehyde and methanol

Protonated acetaldehyde is methylated on the oxygen during interaction with methanol in the gas phase. The ionic product of the ion/molecule reaction between methanol and protonated acetaldehyde is identical with C-protonated methylvinyl ether (high-pressure ionization), and with the (M − C₂H₅)⁺ fragment ion of sec-butyl methyl ether (following electron ionization), and also with the (M − OCH₃)⁺ fragment ion of acetaldehyde dimethylacetal (following electron ionization). The structures of these ions and the mechanism of their formation were established by isotope-labeling experiments and collision-induced dissociation mass spectra of model compounds obtained with three different types of tandem mass spectrometers (BEQQ, triple-quadrupole, and a penta-quadrupole instrument). Gas phase synthesis of the product ion from [²H₃]-methanol or [²H₄]-acetaldehyde provided insight into its mode of formation and collision-induced dissociation.     

Potassium ion transport by valinomycin across a Hg-supported lipid bilayer

A biomimetic membrane consisting of a lipid bilayer tethered to a mercury electrode via a hydrophilic spacer was investigated in aqueous KCl by potential-step chronocoulometry and electrochemical impedance spectroscopy, both in the absence and in the presence of the ionophore valinomycin. Impedance spectra, recorded from 1 x 10(-2) to 1 x 10(5) Hz over a potential range of 0.8 V, are satisfactorily fitted to a series of four RC meshes, which are straightforwardly related to the different substructural elements of the biomimetic membrane. The frequency-independent resistances and conductances of both the lipid bilayer and the hydrophilic spacer show a maximum when plotted against the applied potential. This behavior is interpreted on the basis of a general approximate approach that applies the concepts of impedance spectroscopy to a model of the electrified interphase and to the kinetics of potassium ion transport assisted by valinomycin across the lipid bilayer.