No abstract

The adsorption of alkanes on a gold substrate is simulated by a simple computational scheme that combines the "glue model" for gold, a standard force field for alkanes, and a combination of the charge equilibration model and the Born-Mayer potential for their interaction. The adsorption energies of 10 short chains on the Au(111) surface are reproduced with an average error of less than 1 kcal mol -1 . The results allow extension of the use of the model to investigate the appeareance/disappeareance of ordered deposition on gold of longer alkanes. The unexpected transition to disorder occurs for chains between 18 and 26 carbon atoms and has been ascribed to the mismatch between the Au(111) lattice and the CH2 group periodicity, a feature that here is shown to hinder the formation of short, i.e., docking, C-Au distances.

Thin films of a benzylic amide macrocycle, the common component of a wide class of mechanically interlocked molecules, are prepared by vapor deposition on Au(111). The films are characterized by monochromated X-ray photoelectron spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS). The relative amounts of carbon, nitrogen, and oxygen are consistent with the formation of intact molecular species. At monolayer coverage, the relative intensity of out-of-plane to in-plane phenyl ring vibrational modes indicates that the macrocycle adopts a nearly flat-lying conformation. The formation of a chemisorption bond is evidenced by the presence of a Au-O stretching vibration and a low binding energy component in the O 1s core level region assigned to interfacial bonding. A decrease in film order and the absence of a preferred molecular orientation is observed at higher coverages. Computer modeling of the adsorption of the macrocycle on the surface rationalizes the experimental observations.

The adsorption of organic molecules on inorganic surfaces is a thriving field with applications that range from adhesion, lubrication and chromatographic separation to the modification of the properties of plasticized polymeric materials (e.g., varying the surface and interior concentration of reinforcing fillers), and even to the biocompatibility of artificial internal organs.Gold surfaces are a prime example of ™well-behaved∫ inorganic surfaces because their reactivity and reconstruction patterns are usually well-understood. While the Au(111) surface is the most studied and exploited because of its high stability, probably second is the more reactive Au(110), which reconstructs into a (1 Â 2) missing row motif, in which alternate rows of atoms along [11 ≈ 0] are removed to produce stable (111) microfacets with 8.16 ä periodicity and 1.4 ä height.[1] In recent years, C 60 has become one of the most investigated molecules both because of its highly symmetrical shape and because of its properties, foremost among them its electron-accepting capacity. The interaction of C 60 with gold surfaces has attracted much interest and the structural properties of the C 60 /metal interface have been studied for Au(111), [2] Au(110), [3] Au(001), [4] and also for polycrystalline Au substrates.[5] The Au(110) missing row (1 Â 2) reconstructed surface provides a corrugated surface, which places more stringent geometric constraints than Au(111) on the We can see in Figure 5 that the free energy of solvation is linearly related to the shift of the n CO vibration of acetaminophen for both expanded solvents. This linear behaviour between IR spectroscopic data and the free energy of solvation has been previously reported. [14] This result shows that the n CO mode is a well-adapted probe to check the acetaminophen solubility sensitivity to CO 2 -expanded solvent changes.To conclude, our results show that high-pressure IR spectroscopy is a valuable tool to investigate, at the molecularmicroscopic level, macroscopic phenomena occurring in CO 2 -expanded solutions, such as the solubility behaviour of suitable solutes such as 1.