Surface Rearrangement of Water-Immersed Hydrophobic Solids by Gaseous Nanobubbles

Interactions of gaseous (ambient) nanobubbles (10–100 nm diameter) with different hydrophobic materialsTeflon, polystyrene, paraffin, and basal plane highly ordered pyrolytic graphite (HOPG)are studied by AFM <i>in situ</i> and <i>ex situ</i>. Exactly identical surface locations are examined before and after exposure to ambient gas nanobubbles in deionized water and compared for nanomorphological changes. While freely flooded/immersed surfaces, regularly occupied by nanobubbles, do not exhibit resolvable alterations, significant surface rearrangement is found on whole flooded area after mild pressure drop (10 kPa) applied on the solid–liquid interface. Nanopattern and its characteristic dimension appear to be material specific and solely reflect surface–nanobubble interaction. Mild, nonswelling, noncorrosive conditions (20 °C, deionized water) prevent intervention of chemical reaction and high-energy-demanding processes. Experimental results, in accordance with the presented model, indicate that the mild pressure drop triggers expansion of pinned nanobubbles, imposing local tensile stress on the solid surface. Consequently, nanobubbles should be considered as large-area nanoscale patterning elements

Carboranedithiols: Building Blocks for Self-Assembled Monolayers on Copper Surfaces

Two different positional isomers of 1,2-dicarba-<i>closo</i>-dodecaboranedithiols, 1,2-(HS)₂-1,2-C₂B₁₀H₁₀ (<b>1</b>) and 9,12-(HS)₂-1,2-C₂B₁₀H₁₀ (<b>2</b>), have been investigated as cluster building blocks for self-assembled monolayers (SAMs) on copper surfaces. These two isomers represent a convenient system in which the attachment of SH groups at different positions on the skeleton affects their acidic character and thus also determines their reactivity with a copper surface. Isomer <b>1</b> exhibited etching of polycrystalline Cu films, and a detailed investigation of the experimental conditions showed that both the acidic character of SH groups and the presence of oxygen at the copper surface play crucial roles in how the surface reaction proceeds: whether toward a self-assembled monolayer or toward copper film etching. We found that each positional isomer requires completely different conditions for the preparation of a SAM on copper surfaces. Optimized conditions for the former isomer required the exposure of a freshly prepared Cu surface to vapor of <b>1</b> in vacuum, which avoided the presence of oxygen and moisture. Adsorption from a dichloromethane solution afforded a sparsely covered Cu(0) surface; isomer <b>1</b> effectively removes the surface copper­(I) oxide, forming a soluble product, but apparently binds only weakly to the clean Cu(0) surface. In contrast, adsorption of the latter, less volatile isomer proceeded better from a dichloromethane solution than from the vapor phase. Isomer <b>2</b> was even able to densely cover the copper surface cleaned up by the dichloromethane solution of <b>1</b>. Both isomers exhibited high capacity to remove oxygen atoms from the surface copper­(I) oxide that forms immediately after the exposure of freshly prepared copper films to ambient atmosphere. Isomer <b>2</b> showed suppression of Cu film oxidation. A number of methods including X-ray photoelectron spectroscopy (XPS), X-ray Rutherford back scattering (RBS), proton-induced X-ray emission (PIXE) analysis, atomic force microscopy (AFM), cyclic voltammetry, and contact angle measurements were used to investigate the experimental conditions for the preparation of SAMs of both positional isomers on copper surfaces and to shed light on the interaction between these molecules and a polycrystalline copper surface

Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts

Ruthenium olefin metathesis catalysts bearing a polar quaternary ammonium group in N-heterocyclic ligand were immobilized on silica and siliceous mesoporous molecular sieves with different pore sizes (SBA-15 and MCM-41). The activity of the heterogeneous catalysts was found to increase with an increase in pore size of the support used, with the best results observed for SBA-15-supported catalyst. The influence of reaction conditions (temperature, solvent, catalyst, and substrate concentration) on the efficiency of new heterogeneous catalysts was established. A significant influence of the counterion present in the ruthenium complex on the activity of immobilized catalysts was also found: those derived from chloride containing ion exhibited the highest activity. High activity in ring-closing metathesis of substrates as citronellene, 1,7-octadiene, and diallyl compounds as well as in cross-metathesis of unsaturated aliphatic compounds with methyl acrylate was observed under optimized conditions. In some cases, heterogenization led to catalysts with efficiency higher than those observed for corresponding homogeneous complexes

Decaborane Thiols as Building Blocks for Self-Assembled Monolayers on Metal Surfaces

Three <i>nido</i>-decaborane thiol cluster compounds, [1-(HS)-<i>nido</i>-B₁₀H₁₃] <b>1</b>, [2-(HS)-<i>nido</i>-B₁₀H₁₃] <b>2</b>, and [1,2-(HS)₂<i>-nido</i>-B₁₀H₁₂] <b>3</b> have been characterized using NMR spectroscopy, single-crystal X-ray diffraction analysis, and quantum-chemical calculations. In the solid state, <b>1</b>, <b>2</b>, and <b>3</b> feature weak intermolecular hydrogen bonding between the sulfur atom and the relatively positive bridging hydrogen atoms on the open face of an adjacent cluster. Density functional theory (DFT) calculations show that the value of the interaction energy is approximately proportional to the number of hydrogen atoms involved in the interaction and that these values are consistent with a related bridging-hydrogen atom interaction calculated for a B₁₈H₂₂·C₆H₆ solvate. Self-assembled monolayers (SAMs) of <b>1</b>, <b>2</b>, and <b>3</b> on gold and silver surfaces have been prepared and characterized using X-ray photoelectron spectroscopy. The variations in the measured sulfur binding energies, as thiolates on the surface, correlate with the (CC2) calculated atomic charge for the relevant boron vertices and for the associated sulfur substituents for the parent B₁₀H₁₃(SH) compounds. The calculated charges also correlate with the measured and DFT-calculated thiol ¹H chemical shifts. Wetting-angle measurements indicate that the hydrophilic open face of the cluster is directed upward from the substrate surface, allowing the bridging hydrogen atoms to exhibit a similar reactivity to that of the bulk compound. Thus, [PtMe₂(PMe₂Ph)₂] reacts with the exposed and acidic B–H–B bridging hydrogen atoms of a SAM of <b>1</b> on a gold substrate, affording the addition of the metal moiety to the cluster. The XPS-derived stoichiometry is very similar to that for a SAM produced directly from the adsorption of [1-(HS)-7,7-(PMe₂Ph)₂-<i>nido</i>-7-PtB₁₀H₁₁] <b>4</b>. The use of reactive boron hydride SAMs as templates on which further chemistry may be carried out is unprecedented, and the principle may be extended to other binary boron hydride clusters

The Scope of Direct Alkylation of Gold Surface with Solutions of C₁–C₄ <i>n</i>‑Alkylstannanes

Treatment of cleaned gold surfaces with dilute tetrahydrofuran or chloroform solutions of tetraalkylstannanes (alkyl = methyl, ethyl, <i>n</i>-propyl, <i>n</i>-butyl) or di-<i>n</i>-butylmethylstannyl tosylate under ambient conditions causes a self-limited growth of disordered monolayers consisting of alkyls and tin oxide. Extensive use of deuterium labeling showed that the alkyls originate from the stannane and not from ambient impurities, and that trialkylstannyl groups are absent in the monolayers, contrary to previous proposals. Methyl groups attached to the Sn atom are not transferred to the surface. Ethyl groups are transferred slowly, and propyl and butyl rapidly. In all cases, tin oxide is codeposited in submonolayer amounts. The monolayers were characterized by ellipsometry, contact angle goniometry, polarization modulated IR reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy with ferrocyanide/ferricyanide, which revealed a very low charge-transfer resistance. The thermal stability of the monolayers and their resistance to solvents are comparable with those of an <i>n</i>-octadecanethiol monolayer. A preliminary examination of the kinetics of monolayer deposition from a THF solution of tetra-<i>n</i>-butylstannane revealed an approximately half-order dependence on the bulk solution concentration of the stannane, hinting that more than one alkyl can be transferred from a single stannane molecule. A detailed structure of the attachment of the alkyl groups is not known, and it is proposed that it involves direct single or multiple bonding of one or more C atoms to one or more Au atoms

Self-Assembled <i>p</i>‑Carborane Analogue of <i>p</i>‑Mercaptobenzoic Acid on Au{111}

The <i>p</i>-carborane cluster analogue of <i>p</i>-mercaptobenzoic acid, 1-HS-12-COOH-1,12-C₂B₁₀H₁₀, has been synthesized and characterized using nuclear magnetic resonance spectroscopy, single-crystal X-ray diffraction analysis, quantum-chemical calculations, and scanning tunneling microscopy. The single-crystal structure and selected packing aspects are discussed and presented in comparison with the two-dimensional periodic arrangements. Scanning tunneling micrographs, recorded under ambient conditions, are used to compare pure monolayers of 1-HS-1,12-C₂B₁₀H₁₁ to coadsorbed monolayers of both the parental precursor and carboxyl-functionalized <i>p</i>-carboranethiolate on Au{111}. Monolayers of both constituents are further characterized by X-ray photoelectron spectroscopy, which shows good agreement between the stoichiometry of each pure monolayer and the nominal stoichiometries of the respective molecules. Results indicate that most of the molecules of both derivatives adsorb as thiolates but that a small fraction of each adsorbs as thiols, without complete SH bond scission, and consequently are labile relative to desorption. Wetting-angle measurements confirm the hydrophilic character of monolayers containing the carboxylic acid constituents. Mixed self-assembled monolayers with functionalized constituents of high axial symmetry provide a convenient basis for grafting two- and three-dimensional structures

Competing Intermolecular and Molecule–Surface Interactions: Dipole–Dipole-Driven Patterns in Mixed Carborane Self-Assembled Monolayers

Carboranedithiol isomers adsorbing with opposite orientations of their dipoles on surfaces are self-assembled together to form mixed monolayers where both lateral dipole–dipole and lateral thiol–thiolate (S–H···S) interactions provide enhanced stability over single-component monolayers. We demonstrate the first instance of the ability to map individual isomers in a mixed monolayer using the model system carboranedithiols on Au{111}. The addition of methyl groups to one isomer provides both an enhanced dipole moment and extra apparent height for differentiation via scanning tunneling microscopy (STM). Associated computational investigations rationalize favorable interactions of mixed pairs and the associated stability changes that arise from these interactions. Both STM images and Monte Carlo simulations yield similarly structured mixed monolayers, where approximately 10% of the molecules have reversed dipole moment orientations but no direct chemical attachment to the surface, leading to homogeneous monolayers with no apparent phase separation. Deprotonating the thiols by depositing the molecules under basic conditions eliminates the lateral S–H···S interactions while accentuating the dipole–dipole forces. The molecular system investigated is composed of isomeric molecules with opposite orientations of dipoles and identical surface packing, which enables the mapping of individual molecules within the mixed monolayers and enables analyses of the contributions of the relatively weak lateral interactions to the overall stability of the assemblies