Computational studies on polymer adhesion at the surface of gamma-Al2O3. I. The adsorption of adhesive component molecules from the gas phase

We calculate the minimum energy paths and reaction energies of the adsorption of the epoxide adhesive components diglycidylesterbisphenol A (DGEBA), diethyltriamine (DETA), and the adhesion promoter 3-aminopropylmethoxysilane (AMEO) at two different sites on a model of the native Al2O3 surface, using the nudged elastic band algorithm in conjunction with self-consistent charge-density functional based tight binding. Our results show that the chosen combination of methods is well suited to obtain an overview of the reaction mechanisms and kinetics of the adsorption of organic molecules on inorganic surfaces. The obtained MEP-s show that there is preference for the adsorption of the adhesion promoter, AMEO, over the resin, DGEBA, while the adsorption of the curing agent, DETA, is unfavorable. Our approach also gives an insight into the ranges of the mechanical and electronic influences of the adsorption process on the interface, which neither full ab initio methods nor force field approaches can provide. These results will help to develop a quantum mechanics-molecular mechanics multiscale embedding scheme for more detailed studies of organic/inorganic hybrid interface reactions.     

Identification of a novel series of alkylitaconic acids in wood cultures of Ceriporiopsis subvermispora by gas chromatography/mass spectrometry.

A novel series of long-chain unsaturated dicarboxylic acids consisting of a long aliphatic chain attached to the C-3 position of itaconic acid has been identified by gas chromatography/mass spectrometry during in vitro decay of eucalypt wood by the white-rot basidiomycete Ceriporiopsis subvermispora. The major compounds were identified as tetradecyl-, 7-hexadecenyl- and hexadecylitaconic acids by their mass fragmentation patterns. Other members of the same compound series, identified as dodecanyl-, tridecanyl-, tetradecenyl-, pentadecanyl-, octadecenyl- and octadecanylitaconic acids, were present in very minor amounts or traces. Whereas hexadecenylitaconic acid has already been reported in cultures of C. subvermispora, to our knowledge this is the first report of the presence of the other alkylitaconic acids in fungal cultures. These new alkylitaconic-type metabolites may constitute a source for peroxidizable lipids involved in lignin degradation during wood decay by C. subvermispora and other white-rot basidiomycetes.     

Quenching of giant hysteresis effects in La(1-z)Y(z)Hx switchable mirrors

Hydrogen atoms adsorbed on TiO2(110)-(1x1) surfaces have been characterized by scanning tunneling microscopy (STM) combined with electron stimulated desorption (ESD) technique. Certain amounts of H atoms are unexpectedly found on the TiO2 surfaces annealed at 900 K. Two forms of adsorption were discriminated in STM images from the different sensitivity to ESD and tentatively assigned to hydroxyl-type (O-H) and hydride-type (Ti-H) species.     

Methode zur biochemischen Untersuchung des Proteinstoffwechsels mit Hilfe der Doppelmarkierungstechnik

Die ³H/¹⁴C-Doppelmarkierungstechnik wird zu Proteinstoffwechseluntersuchungen eingesetzt. Dabei treten Probleme der Optimierung des Meßverfahrens sowie einer rationellen und Fehlerquellen erfassenden Auswertung auf. Eine für biochemische Untersuchungen des Proteinstoffwechsels anwendbare Methodik wird beschrieben.     

Steric and Chain Length Effects in the (${\sqrt {(3)} }$×${\sqrt {(3)} }$)R30° Structures of Alkanethiol Self‐Assembled Monolayers on Au(111)

The translational and orientational potential energy surfaces (PESs) of n‐alkanethiols with up to four carbon atoms are studied for (${\sqrt {(3)} }$ ×${\sqrt {(3)} }$ )R30° self‐assembled monolayers (SAMs). The PESs indicate that methanethiol may form SAM structures that are not accessible for long‐chain thiols. The tilt of the thiol molecules is determined by a compromise between the preferred binding geometry at the sulfur atom and the steric requirements of the alkane chains. The Au? S bond lengths, offset from the bridge position (brg), and the Au? S? C bond angles result in tilt angles of the S? C bond in the range of 55–60°. As DFT/generalized gradient approximation systematically underestimates chain–chain interactions, the binding energies are corrected by comparison to MP2 interaction energies of alkane dimers in SAM‐like configurations. The resulting thiol binding energies increase by approximately 1 kcal mol^?1 per CH₂ group, which results in a substantial stabilization of long‐chain SAMs due to chain–chain interactions. Furthermore, as the chain length increases, the accessible range of backbone tilt angles is constrained due to steric effects. The combination of these two effects may explain why SAM structures with long‐chain thiols exhibit higher order in experiments. For each thiol two favorable SAM structures are found with the sulfur head group at the fcc‐brg and hcp‐brg positions, respectively. These domains may coexist in thermal equilibrium. In combination with the symmetry of the gold (111) surface, this raises the possibility of up to six different domains on single‐crystal terraces. Reconstructions by an adatom or vacancy of ethanethiol SAMs with (${\sqrt {(3)} }$ ×${\sqrt {(3)} }$ )R30° lattice are also studied using PES scans. The results indicate that adsorption of thiols next to a vacancy is favorable and may lead to point defects inside SAMs.