Pilar Cea

Simplifying the conductance profiles of molecular junctions: the use of the trimethylsilylethynyl moiety as a molecule–gold contact

Conductance across a metal|molecule|metal junction is strongly influenced by the molecule-substrate contacts, and for a given molecular structure, multiple conductance values are frequently observed and ascribed to distinct binding modes of the contact at each of the molecular termini. Conjugated molecules containing a trimethylsilylethynyl terminus, -C≡CSiMe(3) give exclusively a single conductance value in I(s) measurements on gold substrates, the value of which is similar to that observed for the same molecular backbone with thiol and amine based contacting groups when bound to under-coordinated surface sites.

Density and Speed of Sound for Binary Mixtures of a Cyclic Ether with a Butanol Isomer

Densities and speeds of sound of the binary mixtures 1,3-dioxolane + 1-butanol, 1,3-dioxolane + 2-butanol, 1,4-dioxane + 1-butanol, and 1,4-dioxane + 2-butanol have been measured at 25 and 40°C. The excess molar volumes and excess isentropic compressibility coefficients were calculated from experimental data and fitted to a Redlich–Kister polynomial function. Results were analyzed in terms of molecular interactions and compared with literature data.

Electrochemical Single-Molecule Transistors with Optimized Gate Coupling

Electrochemical gating at the single molecule level of viologen molecular bridges in ionic liquids is examined. Contrary to previous data recorded in aqueous electrolytes, a clear and sharp peak in the single molecule conductance versus electrochemical potential data is obtained in ionic liquids. These data are rationalized in terms of a two-step electrochemical model for charge transport across the redox bridge. In this model the gate coupling in the ionic liquid is found to be fully effective with a modeled gate coupling parameter, ξ, of unity. This compares to a much lower gate coupling parameter of 0.2 for the equivalent aqueous gating system. This study shows that ionic liquids are far more effective media for gating the conductance of single molecules than either solid-state three-terminal platforms created using nanolithography, or aqueous media.

Speed of sound and isentropic compressibility of the ternary mixture (2-Butanol + n-Hexane + 1-Butylamine) and the constituent binary mixtures at 298.15 K and 313.15 K

Abstract Densities and speeds of sound for (2-Butanol + n -Hexane + 1-Butylamine) at 298.15K and 313.15 K, and the constituent binary mixtures (2-Butanol + n -Hexane), (2-Butanol + 1-Butylamine) at 298.15 K and 313.15 K, and ( n -Hexane + 1-Butylamine), at 313.15 K have been measured. The isentropic compressibilities, the excess isentropic compressibilities, and the speeds of sound deviations have been calculated for both the binary and the ternary systems, from the experimental data. The isentropic compressibilities have been compared with calculated values from the Free Length Theory (FLT) and Collision Factor Theory (CFT).

Excess molar enthalpies of 1,3-dioxolane, or 1,4-dioxane with isomeric butanols

Using a flow-mixing calorimeter, excess molar enthalpies of 1,3-dioxolane, or 1,4-dioxane, with isomeric butanols were determined at the temperatures of 298.15 K and 313.15 K. All the studied systems show positive excess molar enthalpies. The results are compared with calculated values from the UNIFAC model.

A monolayer study on interactions of docetaxel with model lipid membranes.

Docetaxel (DCT) is an antineoplastic drug for the treatment of a wide spectrum of cancers. DCT surface properties as well as miscibility studies with l-alpha-dipalmitoyl phosphatidylcholine (DPPC), which constitutes the main component of biological membranes, are comprehensively described in this contribution. Penetration studies have revealed that when DCT is injected under DPPC monolayers compressed to different surface pressures, it penetrates into the lipid monolayer promoting an increase in the surface pressure. DCT is a surface active molecule able to decrease the surface tension of water and to form insoluble films when spread on aqueous subphases. The maximum surface pressure reached after compression of a DCT Langmuir film was 13 mN/m. Miscibility of DPPC and DCT in Langmuir films has been studied by means of thermodynamic properties as well as by Brewster angle microscopy (BAM) analysis of the mixed films at the air-water interface, concluding that DPPC and DCT are miscible and they form non-ideally mixed monolayers at the air-water interface. Helmholtz energies of mixing revealed that no phase separation occurs. In addition, Helmholtz energies of mixing become more negative with decreasing areas per molecule, which suggests that the stability of the mixed monolayers increases as the monolayers become more condensed. Compressibility values together with BAM images indicate that DCT has a fluidizing effect on DPPC monolayers.

Excess volumes and excess viscosities of binary mixtures of 2-chlorobutane with isomeric butanols at 298.15 K

Abstract This paper reports excess volumes and excess viscosities for binary mixtures of 2-chlorobutane with isomeric butanols at 298.15 K. Excess properties were correlated by means of a Redlich-Kister type equation. A qualitative interpretation of the results in terms of OH-OH and Cl-OH interactions is presented. The Prigogine-Flory-Patterson and Blomfield-Dewan theories have been used to analyze the results. Experimental isentropic compressibilities are also reported.

Preparation of nascent molecular electronic devices from gold nanoparticles and terminal alkyne functionalised monolayer films

A metal–molecule–GNP assembly has been fabricated using an acetylene-terminated phenylene–ethynylene molecular monolayer, namely 4-((4-((4-ethynylphenyl)ethynyl)phenyl)ethynyl)benzoic acid (HOPEA), sandwiched between a gold substrate bottom electrode and gold nanoparticle (GNP) top contact electrode. In the first stage of the fabrication process, a monolayer of directionally oriented (carboxylate-to-gold) HOPEA was formed onto the bottom electrode using the Langmuir–Blodgett (LB) technique. In the second stage, the gold-substrate supported monolayer was incubated in a solution of gold nanoparticles (GNPs), which resulted in covalent attachment of the GNPs on top of the film via an alkynyl carbon–Au σ-bond thereby creating the metallic top electrode. Adsorption of the GNPs to the organic LB film was confirmed by both UV-vis absorption spectroscopy and X-ray photoemission spectroscopy (XPS), whilst the contact angle showed changes in the physical properties of the film surface as a result of top-coating of the LB film with the GNPs. Importantly, surface-enhanced Raman scattering (SERS) confirmed the covalent attachment of the metal particles to the LB film by formation of Au–C σ-bonds via a heterolytic cleavage of the alkyne C–H bond. Electrical properties of these nascent metal–molecule–GNP assemblies were determined from I–V curves recorded with a conductive-AFM in the Peak Force Tunneling AFM (PF-TUNA™) mode. The I–V curves obtained from these structures rule out the formation of any significant number of short-circuits due to GNP penetration through the monolayer, suggesting that this strategy of self-assembly of GNPs to alkyne-terminated monolayers is an effective ‘soft’ procedure for the fabrication of molecular junctions without damaging the organic layer.

Viscosities of the ternary mixture (cyclohexane + tetrahydrofuran + chlorocyclohexane) at 298.15 and 313.15 K

Abstract Viscosities of the ternary mixture (cyclohexane+tetrahydrofuran+chlorocyclohexane) and the binary mixtures (cyclohexane+tetrahydrofuran and cyclohexane+chlorocyclohexane) have been measured at normal pressure at the temperatures of 298.15 and 313.15 K. The viscosity data for the binary and ternary mixtures were fitted to a McAllister-type equation [R.A. McAllister, AIChE J. 6 (1960) 427–431]. Viscosity deviations for the binary and ternary mixtures were fitted to Redlich–Kisters and Cibulkas equations [I. Cibulka, Coll. Czech. Chem. Commun. 47 (1982) 1414–1419]. The group contribution method proposed by Wu [D.T. Wu, Fluid Phase Equilib. 30 (1986) 149–156] has been used to predict the viscosity of the binary and ternary systems.

Excess Molar Enthalpies of Cyclic Ethers with Cyclohexane, Methylcyclohexane, or Chlorocyclohexane

Excess molar enthalpies for mixtures of tetrahydrofuran, tetrahydropyran, 2-methyltetrahydrofuran or 2,5-dimethyltetrahydrofuran with cyclohexane, methylcyclohexane, or chlorocyclohexane were determined at 25°C. The excess enthalpies are positive for the mixtures containing cyclohexane or methylcyclohexane, but negative for the mixtures containing chlorocyclohexane. The results were used with the Prigogine–Flory–Patterson theory to predict the corresponding excess molar volumes.