Efficient Spin-Selective Electron Transport at Low Voltages of Thia-Bridged Triarylamine Hetero[4]helicenes Chemisorbed Monolayer

The Chirality Induced Spin Selectivity (CISS) effect describes the capability of chiral molecules to act as spin filters discriminating flowing electrons according to their spin state. Within molecular spintronics, efforts are focused on developing chiral-molecule-based technologies to control the injection and coherence of spin-polarized currents. Herein, for this purpose, we study spin selectivity properties of a monolayer of a thioalkyl derivative of a thia-bridged triarylamine hetero[4]helicene chemisorbed on a gold surface. A stacked device assembled by embedding a monolayer of these molecules between ferromagnetic and diamagnetic electrodes exhibits asymmetric magnetoresistance with inversion of the signal according to the handedness of molecules, in line with the presence of the CISS effect. In addition, magnetically conductive atomic force microscopy reveals efficient electron spin filtering even at unusually low potentials. Our results demonstrate that thia[4]heterohelicenes represent key candidates for the development of chiral spintronic devices.

Construction and Characterizations of Antibacterial Surfaces Based on Self-Assembled Monolayer of Antimicrobial Peptides (Pac-525) Derivatives on Gold

Background: Infection that is related to implanted biomaterials is a serious issue in the clinic. Antimicrobial peptides (AMPs) have been considered as an ideal alternative to traditional antibiotic drugs, for the treatment of infections, while some problems, such as aggregation and protein hydrolysis, are still the dominant concerns that compromise their antimicrobial efficiency in vivo. Methods: In this study, antimicrobial peptides underwent self-assembly on gold substrates, forming good antibacterial surfaces, with stable antibacterial behavior. The antimicrobial ability of AMPs grafted on the surfaces, with or without glycine spaces or a primer layer, was evaluated. Results: Specifically, three Pac-525 derivatives, namely, Ac-CGn-KWRRWVRWI-NH2 (n = 0, 2, or 6) were covalently grafted onto gold substrates via the self-assembling process for inhibiting the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). Furthermore, the alkanethiols HS(CH)10SH were firstly self-assembled into monolayers, as a primer layer (SAM-SH) for the secondary self-assembly of Pac-525 derivatives, to effectively enhance the bactericidal performance of the grafted AMPs. The -(CH)10-S-S-G6Pac derivative was highly effective against S. aureus and E. coli, and reduced the viable amount of E. coli and S. aureus to 0.4% and 33.2%, respectively, after 24 h of contact. In addition, the immobilized AMPs showed good biocompatibility, promoting bone marrow stem cell proliferation. Conclusion: the self-assembled monolayers of the Pac-525 derivatives have great potential as a novel therapeutic method for the treatment of implanted biomaterial infections.

Electrostatic control over temperature-dependent tunnelling across a single-molecule junction

Understanding how the mechanism of charge transport through molecular tunnel junctions depends on temperature is crucial to control electronic function in molecular electronic devices. With just a few systems investigated as a function of bias and temperature so far, thermal effects in molecular tunnel junctions remain poorly understood. Here we report a detailed charge transport study of an individual redox-active ferrocene-based molecule over a wide range of temperatures and applied potentials. The results show the temperature dependence of the current to vary strongly as a function of the gate voltage. Specifically, the current across the molecule exponentially increases in the Coulomb blockade regime and decreases at the charge degeneracy points, while remaining temperature-independent at resonance. Our observations can be well accounted for by a formal single-level tunnelling model where the temperature dependence relies on the thermal broadening of the Fermi distributions of the electrons in the leads.

Synthesis, self-assembly and characterization of a novel push–pull thiophene-based chromophore on a gold surface

A self-assembled dense monolayer based on a non-charged push–pull chromophore is clearly evidenced by electrochemical, XPS and STM analysis. Associated with good film properties a conducting behavior consistent with the structure of the SAM-organized push–pull is also shown.

Tetrairon(III) single-molecule magnet monolayers on gold: insights from ToF-SIMS and isotopic labeling

To work as magnetic components in molecular electronics and spintronics, single-molecule magnets (SMMs) must be reliably interfaced with metals. The organization on gold of a Fe4 SMM carrying two acetyl-protected thiol groups has been studied by exploiting the surface sensitivity of time-of-flight secondary ion mass spectrometry (ToF-SIMS), additionally powered by the use of an isotopic labeling strategy. Deposition from millimolar dichloromethane solutions results in a higher surface coverage and better packed monolayers as compared with previous protocols based on more diluted solutions. Fe4 complexes are chemically tethered to the surface via a single Au-S bond while they still contain an intact SAc group.

Controlling leakage currents: the role of the binding group and purity of the precursors for self-assembled monolayers in the performance of molecular diodes

This paper describes that the performance of molecular diodes based on self-assembled monolayers (SAMs) depends on the type of anchoring group and purity of the precursors of these SAMs. The SAMs were formed on ultrasmooth template-stripped silver (Ag(TS)) surfaces, which served as the bottom-electrode, and a eutectic alloy of gallium-indium was used as the top-electrode. When these junctions incorporate SAMs of the form S(CH2)11Fc (≡ SC11Fc) derived from HSC11Fc, they are good molecular diodes and rectify currents with rectification ratios R (≡ |J(-1.0 V)|/|J(+1.0 V)|) of ∼1.0 × 10(2). Replacing the thiol by disulfide or thioacetate functionalities in the precursor resulted in molecular diodes with values of R close to unity. Cyclic voltammetry and angle resolved X-ray photoelectron spectroscopy indicated that the SAMs derived from the disulfide or thioacetate precursors have lower surface coverages and are more defective than SAMs derived from thiols. In the junctions these defective SAMs caused defects and increased the leakage currents. The purity of the thiol-precursor is also crucial: 3 or 5% of disulfide present in the thiol caused a 28 or 61% decrease in R, respectively, and >15% of disulfide lowered R to unity, while the yield in nonshorting junctions remained unchanged. Our results show that the type of binding group, and the puritiy of the thiols, are crucial parameters in the experimental design of molecular electronic devices to ensure optimal device performance by keeping leakage currents to a minimum.