The synthesis of two series of silylated chalconium borates, 9 and 10, which are based on the peri-naphthyl and peri-acenaphthyl framework, is reported (chalcogen (Ch): O, S, Se, Te). NMR investigations of the selenium- and tellurium-containing precursor silanes 3 d-f and 8 d, f revealed a significant through-space J-coupling between the chalcogen nuclei and the Me SiH group. Experimental and computational results typify the synthesized cations 9 and 10 as chalconium ions. The imposed ring strain weakens the Si-Ch linkage compared to acyclic chalconium ions. This attenuation of the Si-Ch bond strength is more pronounced in the acenaphthene series. Surprisingly, the Si-O bonds in oxonium ions 9 a and 10 a are the weakest Si-Ch linkage in both series. The synthesized silyl chalconium borates are active in hydrodefluorination reactions of alkyl fluorides with silanes. A cooperative activation of the silane by the Lewis acidic (silicon) and by the Lewis basic side (chalcogen) is suggested.
The stability of ionic liquids (ILs) at charged interfaces makes them very attractive in electrochemical applications. In this work, a Langmuir–Blodgett transfer is used to fabricate a monolayer of an amphiphilic 1‐methyl‐3‐octadecylimidazolium perchlorate IL on the Au(111) surface. The IL monolayer immersed in an aqueous electrolyte solution is very stable over a wide potential window. Polarization modulation infrared reflection absorption spectroscopy is used to monitor structural changes in the model of the electrical double layer of the IL in aqueous solution. The imidazolium cation is in direct contact with the Au(111) surface. The imidazolium ring adopts a rigid orientation, inclined toward the metal surface, in the monolayer on the Au(111) surface. The orientation of hydrocarbon chains responds to electric potentials. At low negative surface charge densities of the Au(111) electrode, the hydrocarbon chains in the amphiphilic cation have a large average tilt versus surface normal. A negative potential shift is accompanied by a reorientation of the hydrophobic hydrocarbon chains that adopt an up‐ward orientation, making the film permeable for counter‐ and/or co‐ions. This transition leads to the formation of an ordered, single‐component monolayer of the amphiphilic cation on the electrode surface.
Compatible solutes accumulate in the cytoplasm of halophilic microorganisms, enabling their survival in a high-salinity environment. Ectoine is such a compatible solute. It is a zwitterionic molecule that strongly interacts with surrounding water molecules and changes the dynamics of the local hydration shell. Ectoine interacts with biomolecules such as lipids, proteins, and DNA. The molecular interaction between ectoine and biomolecules, in particular the interaction between ectoine and DNA, is far from being understood. In this paper, we describe molecular aspects of the interaction between ectoine and doublestranded DNA (dsDNA). Two 20 base pairs-long dsDNA fragments were immobilized on a gold surface via a thiol-tether. The interaction between the dsDNA monolayers with diluted and concentrated ectoine solutions was examined by means of X-ray photoelectron and polarization modulation infrared reflection absorption spectroscopies (PM IRRAS). Experimental results indicate that the ability of ectoine to bind water reduces the strength of hydrogen bonds formed to the ribose-phosphate backbone in the dsDNA. In diluted (0.1 M) ectoine solution, DNA interacts predominantly with water molecules. The sugar−phosphate backbone is involved in the formation of strong hydrogen bonds to water, which, over time, leads to a reorientation of the planes of nucleic acid bases. This reorientation destabilizes the strength of hydrogen bonds between the bases and leads to a partial dehybridization of the dsDNA. In concentrated ectoine solution (2.5 M), almost all water molecules interact with ectoine. Under this condition, ectoine is able to interact directly with DNA. Density functional theory (DFT) calculations demonstrate that the direct interaction involves the nitrogen atoms in ectoine and phosphate groups in the DNA molecule. The results of the quantum-chemical calculations show that rearrangements in the ribose-phosphate backbone, caused by a direct interaction with ectoine, facilitates contacts between the O atom in the phosphate group and H atoms in a nucleic acid base. In the PM IRRA spectra, an increase in the number of IR absorption modes in the base pair frequency region proves that the hydrogen bonds between bases become weaker. Thus, a sequence of reorientations caused by interaction with ectoine leads to a breakdown of hydrogen bonds between bases in the double helix.
The structure of cations and anions in ionic liquids is precisely selected to tune their properties for applications in catalysis, electrochemistry, or development of sensors. Substitution of a hydrocarbon by a fluorocarbon chain in either the cation or the anion yields fluorinated ionic liquids (FILs). The ionic character combined with hydrophobic and lipophobic properties of fluorocarbon chains ensure extraordinary surface properties of FILs. The use of fluorocarbons with chains longer than six carbon atoms, due to their impact on the environment and bioaccumulative properties, is banned. In this work we demonstrate that more sustainable imidazolium- and triazolium-based FILs containing two short, partially fluorinated chains [(CH2)2(CF2)5CF3] have amphiphilic properties and form stable monolayers at the air–liquid interface which can be transferred onto a gold substrate by the Langmuir–Blodgett (LB) method. X-ray photoelectron and polarization modulation infrared reflection absorption spectroscopies are used to characterize the composition, conformation, and orientation of FILs in LB monolayers on the gold surface. The positively charged heteroaromatic ring is oriented parallel to the gold surface while the fluorocarbon chains are directed toward air. The fluorocarbon chains adopt a helical conformation. In LB monolayers, the tilt of the helix depends on the chemical structure of the cation and the monolayer transfer conditions. Uniform orientation of the amphiphilic cations in the monolayer assembly yields a hydrophobic surface. Two-dimensional LB films of FILs are proposed here as possible sustainable, functional, ultrathin films and coatings.
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