Methyl interaction with surfaces

The molecular modelling approach, taking into account the pyruvate—cinchona alkaloid interaction and the steric constraints imposed by the adsorption on the platinum surface, leads to a reasonable explanation for the enantio-differentiation of this system. Although the prediction of the complex formed between the methyl pyruvate and the cinchona modifiers have been made for an ideal case (solvent effects and a quantum description of the interaction with the platinum surface atoms were not considered), this approach proved to be very helpful in the search of new modifiers. The search strategy, which included a systematic reduction of the cinchona alkaloid structure to the essential functional parts and validation of the steric constraints imposed to the interaction complex between modifier and methyl pyruvate by means of molecular modelling, indicated that simple chiral aminoalcohols should be promising substitutes for cinchona alkaloid modifiers. Using the Sharpless symmetric dihydroxylation as a key step, a series of enantiomerically pure 2-hydroxy-2-aryl-ethylamines... 

In polar solvents, the structure of the acridine 13 involves some zwitterionic character 13 a [Eq. (7)] and the interior of the cleft becomes an intensely polar microenvironment. On the periphery of the molecule a heavy lipophilic coating is provided by the hydrocarbon skeleton and methyl groups. A third domain, the large, flat aromatic surface is exposed by the acridine spacer unit. This unusual combination of ionic, hydrophobic and stacking opportunities endows these molecules with the ability to interact with the zwitterionic forms of amino acids which exist at neutral pH 24). For example, the acridine diacids can extract zwitterionic phenylalanine from water into chloroform, andNMR evidence indicates the formation of 2 1 complexes 39 such as were previously described for other P-phenyl-ethylammonium salts. Similar behavior is seen with tryptophan 40 and tyrosine methyl ether 41. The structures lacking well-placed aromatics such as leucine or methionine are not extracted to measureable degrees under these conditions. 

Mg/Me (Me=Al, Fe) mixed oxides prepared from hydrotalcite precursors were compared in the gas-phase m-cresol methylation in order to find out a relationship between catalytic activity and physico-chemical properties. It was found that the regio-selectivity in the methylation is considerably affected by the surface acid-basic properties of the catalysts. The co-existence of Lewis acid sites and basic sites leads to an enhancement of the selectivity to the product of ortho-C-alkylation with respect to the sole presence of basic sites. This derives from the combination of two effects, (i) The H+-abstraction properties of the basic site lead to the generation of the phenolate anion, (ii) The coordinative properties of Lewis acid sites, through their interaction with the aromatic ring, make the mesomeric effect less efficient, with predominance of the inductive effect of the -O species in directing the regio-selectivity of the C-methylation into the ortho position. 

ENDOR lines predicted by improved DFT calculations for methyl protons at 03(13 ) located at 16.5 MHz were broad and not observable due to incomplete averaging of the methyl proton couplings due to a hindering environment. Thus, the methyl groups at the C5(5 ) and C9(9 ) are located away from the surface of the pore and rapidly rotate, while those at 03(13 ) interact with the surface. Steric hindrance by the terminal bulky trimethyl cyclohexene rings preclude attainment of the requisite distance between Cu2+ and the C7=C8 and C8 =C7 bonds. 

From calculations of the preferred conformation of the ephedrine and pseudo ephedrine molecules the topography of the adrenergic receptor as a flat surface has been deduced (26). This view, however, does not explain the decisive effect of the additional methyl group its relative position should not influence the interaction with the proposed receptor to a large extent (Fig. 7a). However, as the differences in activities are especially high for the ephedrine and pseudo ephedrine isomers, we believe that the receptor must have an intercalated structure similar as projected for the "binding sites" of the silicones (Fig. 7b). ... 

Then, contrary to our previous hypothesis, the reaction proceeds via a Bai2 displacement of aniline on DMC. The product, mono-A -methyl aniline (PhNHMe), plausibly adsorbs into the zeohte in a different way with respect to anihne, because different H-bonds (N H — O-zeolite) take place with the solid. As recently reported by Su et al., A-methyl amines also may interact with NaY by H-bonding between the protons of the methyl group and the oxygen atoms of the zeolite this probably forces the molecule a bit far from the catalytic surface in a fashion less apt to meet DMC and react with it. This behavior can account for the mono-A-methyl selectivity observed, which is specific to the use of DMC in the presence of alkali metal exchanged faujasites in fact, the bis-A-methylation of primary aromatic amines occurs easily with conventional methylating agents (i.e., dimethyl sulfate). ... 

Further, adsorption of methylated phenols (o-cresol and 2,6-xylenol) has given very weak and broad spectral features that were correlated to their weak interaction with the catalyst. Among the ortho-methylated phenols, 2,6-xylenol desorbs fast from the surface at 200 C than o-cresol. These methylated phenols, unlike phenol, desorbed from the catalyst above 200°C that was well below the actual reaction temperature (350°C). Hence, the desorption susceptible nature of the methylated phenols above 200°C facilitated the efficient methylation at 350°C [74]. In contrast to the Cu-containing ferrospinels, CoFc204 shows little interaction [74] of phenol with methanol, when they are co-adsorbed and this might be a limiting factor to the overall reaction. 

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