Francisco Otón

A Three-State Surface-Confined Molecular Switch with Multiple Channel Outputs

A self-assembled monolayer of a tetrathiafulvalene derivative on indium tin oxide is shown to operate as a ternary redox switch in which the magnetic and optical outputs are employed to provide a readout of the state. This surface-confined molecular switch exhibits excellent reversibility and stability and is thus promising for the development of molecular electronics.

Heteroditopic ferrocene-based ureas as receptors for anions and cations

The synthesis of structurally new types of ferrocene-based ureas, in which the ferrocene moiety is simultaneously attached to two urea groups, have been prepared directly from 1,1-bis(isocyanato)ferrocene 1. Receptors 2a, 2b, and 2d show spectral and electrochemical anion-sensing capability for hydrogenphosphate and fluoride anions, in addition 2d also shows a sensing capability for acetate anion. Heteroditopic receptor 2a, bearing a pyridine binding site, does not complex Cu2+ cations but instead an intramolecular redox reaction takes place to give the oxidized form 2a+. The results obtained by using the heteroditopic receptor 2b, containing two crown ethers units, demonstrate that K+ cations can only be electrochemically detected in the presence of hydrogenphosphate anion. Whereas the new structural motif 2d, in which the two urea groups are part of the macrocycle framework, is a selective electrochemical sensor for Li+ cation in the presence of alkali metal ions. The preferred binding modes and their extent are proposed for the most representative complexes by means of DFT-based theoretical calculations.

Synthesis and biological activity of a 3,4,5-trimethoxybenzoyl ester analogue of epicatechin-3-gallate.

Despite presenting bioavailability problems, tea catechins have emerged as promising chemopreventive agents because of their observed efficacy in various animal models. To improve the stability and cellular absorption of tea polyphenols, we developed a new catechin-derived compound, 3- O-(3,4,5-trimethoxybenzoyl)-(-)-epicatechin (TMECG), which has shown significant antiproliferative activity against several cancer cell lines, especially melanoma. The presence of methoxy groups in its ester-bound gallyl moiety drastically decreased its antioxidant and prooxidant properties without affecting its cell-antiproliferative effects, and the data indicated that the 3-gallyl moiety was essential for its biological activity. As regards its action mechanism, we demonstrated that TMECG binds efficiently to human dihydrofolate reductase and down-regulates folate cycle gene expression in melanoma cells. Disruption of the folate cycle by TMECG is a plausible explanation for its observed biological effects and suggests that, like other antifolate compounds, TMECG could be of clinical value in cancer therapy.

Selective metal-cation recognition by [2.2]ferrocenophanes: the cases of zinc- and lithium-sensing.

The synthesis, electrochemical, optical, and cation-sensing properties of [2.2]ferrocenophanes, in which the two ferrocene subunits are linked through two aldiminic or iminophosphorane moieties, are reported. The new compounds show remarkably selective cation-sensing properties due to the presence of redox-active units (ferrocene) and aza-unsaturated functionalities that are able to act as putative cation-binding sites. In this structural motif, the aldimine groups act as a highly selective binding site for Zn(2+) cations, whereas the iminophosphorane bridges display an unusually strong binding affinity towards Li(+) cations, which could be explained by an additional LiFe interaction. The X-ray structure of the complex 4Li(+) as well as detailed NMR spectroscopic studies, both in solution and in the solid state, support this assessment. Experimental data and conclusions about the cation-sensing capabilities of this family of compounds are supported by DFT calculations.

Coupling Tetracyanoquinodimethane to Tetrathiafulvalene: A Fused TCNQ–TTF–TCNQ Triad

The first marriage of tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) took place in 1973, when an intermolecular 1:1 charge-transfer complex was formed, which led to the discovery of the first organic metal. One year later, Aviram and Ratner theoretically predicted a rectifying behavior for a covalently coupled TTF–s–TCNQ dyad. Since then numerous studies devoted to synthesizing covalent TTF–linker–TCNQ dyads have been undertaken, motivated by potential applications in molecular electronics and optoelectronics. However, the task of covalently coupling a strong p-electron donor to a strong p-electron acceptor is extremely difficult. Many examples of TTF moieties attached to moderate acceptors have been published. 9] Among them, several TTF–quinone dyads and triads have been identified as potential precursors for preparing fused TTF–TCNQ derivatives, but attempts to convert the quinone moiety to the corresponding TCNQ derivative have been in general unsuccessful. 11] One of these examples, a p-benzoquinone–TTF–p-benzoquinone (Q–TTF–Q) fused triad, permitted the study of intramolecular electron transfer (IET) between donor and acceptor and also between acceptor moieties in the mixed-valence compound, thus demonstrating the capability of TTF to behave as a bridge that allows electron transfer. Recently, a small number of well-characterized TTF–linker–TCNQ dyads have been reported, and in all cases intramolecular charge transfer was found. Nonetheless, to date, a TCNQ derivative has never been compactly fused to the TTF core; the closest approach was the attempted synthesis reported by Hudhomme and co-workers. Herein we report the synthesis of the first fused TCNQ–TTF–TCNQ triad, compound 1 (Scheme 1), and the study of the IET processes that take place in the neutral compound 1 as well as in the corresponding mixed-valence derivative 1 .

A ferrocene-based heteroditopic ligand for electrochemical sensing of cations and anions

A ferrocene-based heteroditopic receptor containing urea and crown ether units shows electrochemical responses to dihydrogenphosphate and fluoride anions. K+ cations can only be detected in the presence of dihydrogenphosphate.

Detection of the Early Stage of Recombinational DNA Repair by Silicon Nanowire Transistors

A silicon nanowire-based biosensor has been designed and applied for label-free and ultrasensitive detection of the early stage of recombinational DNA repair by RecA protein. Silicon nanowires transistors were fabricated by atomic force microscopy nanolithography and integrated into a microfluidic environment. The sensor operates by measuring the changes in the resistance of the nanowire as the biomolecular reactions proceed. We show that the nanoelectronic sensor can detect and differentiate several steps in the binding of RecA to a single-stranded DNA filament taking place on the nanowire-aqueous interface. We report relative changes in the resistance of 3.5% which are related to the interaction of 250 RecA·single-stranded DNA complexes. Spectroscopy data confirm the presence of the protein-DNA complexes on the functionalized silicon surfaces.

Conformationally Modulated Intramolecular Electron Transfer Process in a Diaza[2,2]ferrocenophane

A novel conformationally modulated Intramolecular Electron Transfer (IET) phenomenon has been observed due to the cyclic structure of the diaza[2.2]ferrocenophane 3. The corresponding mixed-valence compound of 3, prepared by electrochemical or chemical partial oxidation, interestingly shows the appearance of two absorption bands in the near infrared (NIR) spectral region. These bands are attributable to two intervalence charge-transfer transitions associated to two atropoisomers exhibiting different energy for the IET process. A solvent and temperature control over the atropoisomeric equilibrium have also been observed. The experimental data and conclusions about both the conformational and the electronic properties of compound 3 are also supported by density functional theory calculations.

Benzodicarbomethoxytetrathiafulvalene derivatives as soluble organic semiconductors.

A series of new tetrathiafulvalene (TTF) derivatives bearing dimethoxycarbonyl and phenyl or phthalimidyl groups fused to the TTF core (6 and 15-18) has been synthesized as potential soluble semiconductor materials for organic field-effect transistors (OFETs). The electron-withdrawing substituents lower the energy of the HOMO and LUMO levels and increase the solubility and stability of the semiconducting material. Crystal structures of all new TTF derivatives are also described, and theoretical DFT calculations were carried out to study the potential of the crystals to be used in OFET. In the experimental study, the best performing device exhibited a hole mobility up to 7.5 × 10(-3) cm(2) V(-1) s(-1)).

Electronic and structural characterisation of a tetrathiafulvalene compound as a potential candidate for ambipolar transport properties

We report a joint experimental and theoretical study on the electronic structure and the solid-state organisation of bis(naphthoquinone)-tetrathiafulvalene (BNQ-TTF) as a promising ambipolar semiconductor. Accordingly, organic field-effect transistors (OFETs) fabricated with this material show both hole and electron transport for the first time in TTF derivatives.