Single-molecule conductance through multiple π-π-stacked benzene rings determined with direct electrode-to-benzene ring connections

Understanding electron transport across π-π-stacked systems will help to answer fundamental questions about biochemical redox processes and benefit the design of new materials and molecular devices. Herein we employed the STM break-junction technique to measure the single-molecule conductance of multiple π-π-stacked aromatic rings. We studied electron transport through up to four stacked benzene rings held together in an eclipsed fashion via a paracyclophane scaffold. We found that the strained hydrocarbons studied herein couple directly to gold electrodes during the measurements; hence, we did not require any heteroatom binding groups as electrical contacts. Density functional theory-based calculations suggest that the gold atoms of the electrodes bind to two neighboring carbon atoms of the outermost cyclophane benzene rings in η(2) fashion. Our measurements show an exponential decay of the conductance with an increasing number of stacked benzene rings, indicating a nonresonant tunneling mechanism. Furthermore, STM tip-substrate displacement data provide additional evidence that the electrodes bind to the outermost benzene rings of the π-π-stacked molecular wires.     

Inhibition effect of horehound (Marrubium vulgare L.) extract towards C38 steel corrosion in HCl solution

The corrosion inhibition properties of horehound (Marrubium vulgare L.) extract (HE) in 1 M hydrochloric acid medium was carried out using electrochemical methods (polarization curve and electrochemical impedance spectroscopy). Experiments were performed by concentration of the inhibitor and temperature effect. The results showed variation in inhibition performance of this plant extract. The Langmuir model was tested to describe the adsorption behavior of the inhibitor on the C38 steel surface. Some thermodynamic functions of dissolution processes were also determined.     

Synthesis and structural characterization of new polynuclear complexes of 1-hydroxymethyl-3,5-dimethylpyrazole with Ni(II) and Fe(II)

The complexation of the simple 1-hydroxymethyl-3,5-dimethylpyrazole (HL) ligand with Fe and Ni salts leads to interesting polynuclear complexes in good yield. X-ray diffraction reveals that the resulting complexes (μ₄-L)₄Ni₄Cl₄(H₂O)₄ and (μ₂-L)₄(μ₃-L)₂Fe₈Cl₁₆(μ₄-O)₆ adopt cubane-type and open-cubane-type structures in the solid state.     

Total synthesis and biological evaluation of (-)apicularen A and analogues thereof

Apicularen A (1) and related benzolactone acylenamines belong to a growing class of novel natural products possessing highly cytotoxic properties. The challenging structure of 1 includes a 10-membered macrolactone ring, a tetrahydropyran system, an o,m-substituted phenol and a doubly unsaturated acyl group attached on the side chain enamine functionality. The total synthesis of apicularen A described herein involves a strategy equivalent to its proposed biosynthesis and entails a reiterative two-step procedure featuring allylation and ozonolytic cleavage to grow the molecule's chain by one acetate unit at a time. The developed synthetic technology was applied to the construction of a series of apicularen A analogues whose biological evaluation established a set of structure-activity relationships in this new area of potential importance in cancer chemotherapy.     

Phytochemical compounds and anti-corrosion activity of Veronica rosea

The aim of this work is the phytochemical study of the butanolic extract of the aerial parts of Veronica rosea. Four compounds 1–4 have been isolated using different chromatographic methods. The structures of these compounds were determined by NMR spectral analysis and mass spectroscopy. The adsorption and anticorrosion effects of this extract were investigated towards the corrosion of copper in 1 M HNO₃ aqueous by the weight loss technique and potentiodynamic polarization. The results showed that the butanolic extract is a good inhibitor and the inhibition efficiency increases with increasing of concentration of the inhibitor. The adsorption of this extract on the copper specimen surface was spontaneous and obeyed the Langmuir’s adsorption isotherm. Large value of adsorption equilibrium Constant (K _ads = 35 L g^?1) was obtained. The polarization experiments confirmed the data obtained by gravimetric weight-loss. Tafel plot of polarization curves indicates that the extract acts as a mixed type inhibitor.     

Production, bleaching, and characterization of pulp from Stipa tenacissima

Alfa grass pulping was successfully performed in hydro-organic acid medium under mild conditions (107°C, atmospheric pressure, cooking time: 3 h). Use of an acetic acid/formic acid/water mixture as pulping liquor was perfectly suitable for selective isolation of pulp, lignin, and hemicelluloses. The unbleached pulp obtained in good yield was first delignified by peroxyacids in organic acid medium and then bleached with hydrogen peroxide in a basic medium to give pulp offering good physico-chemical and mechanical characteristics.     

Polyazomethines Bearing Furan Moieties. Solution Polycondensation of Bis(furanic diamine)s and Aromatic Dialdehydes

A series of new polyazomethines containing furan moieties was synthesized by polycondensation of bifuranic diamine monomers with commercially available aromatic dialdehydes viz., terephthaldehyde (TPA), isophthaldehyde (IPA). Inherent viscosities and number average molecular weights of polyazomethines were in the range 0.90–1.56 dL/g and 10460–17850 (SEC, polystyrene standard), respectively indicating formation of medium to reasonably high molecular weight polymers. The resulting polyazomethines were characterized by solubility tests, viscosity measurements, FTIR, NMR, UV spectroscopy, differential scanning calorimetric (DSC), and thermogravimetric analysis (TGA). These furan-based polyazomethines were essentially amorphous and exhibited glass transition temperatures (Tg) in the 150–190°C range. The temperature at 10% wt loss (T₁₀), determined from TGA of polyazomethines were in the range 300–380°C, indicating their good thermal stability.