The asymmetric hydrogenation of alpha-ketoesters on cinchona-modified supported platinum particles is a prototype reaction in heterogeneous chiral catalysis. The catalysis literature shows that the reaction is highly metal-specific, that it displays rate-enhancement with respect to the racemic reaction on the nonmodified surface, and that the observed stereoselectivity is a sensitive function of substrate and modifier structure. This set of observations has proven difficult to rationalize within the context of existing models for the mechanism of the Orito reaction. The most widely discussed mechanistic models are based on the formation of chemisorbed 1:1 complexes through H-bonding between the quinuclidine function of the cinchona modifier and the prochiral, keto-carbonyl, function of the substrate. Recent surface science studies, as well as advances in the area of C-H...O hydrogen bonding, suggest that chemisorption-induced polarization may lead to an aromatic-carbonyl H-bonding interaction between the aromatic anchor of the modifier and the coadsorbed substrate. By specifying that the aromatic C-H...O interaction is to the prochiral carbonyl and that it is accompanied by a H-bonding interaction between the ester carbonyl and the quinuclidine function, we show that it is possible to rationalize essentially all of the catalysis literature for the Orito reaction in terms of a single molecular mechanism. The generality of the proposed mechanistic model is demonstrated by addressing data from the literature for a representative range of substrates, modifiers, solvents, and metals. Results of catalytic tests on an asymmetric diketone substrate are presented in support of the model.

Methyl pyruvate undergoes CH bond scission on Pt(111) at room temperature to trigger surface-mediated enol formation and subsequent self-assembly into enol superstructures. This process may be inhibited by performing the experiment below the temperature for CH bond scission or, at room temperature, by using a background pressure of H2. Superstructure formation is not due to a polymerization reaction. Hence, it is unlikely that rate enhancement of the enantioselective hydrogenation of methyl pyruvate on cinchona-modified Pt catalysts is simply due to the absence of a substrate polymerization reaction under reaction conditions.

Trifluoroacetophenone (TFAP) forms C O...H-C bonded dimers and trimers at room temperature on Pt(111). It is proposed that these systems mimic the prochiral carbonyl-chiral modifier interaction in the enantioselective hydrogenation of TFAP on cinchona-modified Pt catalysts. That is, the activation of TFAP in homomolecular assemblies at racemic sites is expected to be roughly the same as in the diastereomeric complex formed at chiral sites. This interpretation suggests a reason why alpha-phenyl ketones do not display a strong measured rate enhancement effect in the Orito reaction.

The chemical transformation and subsequent self-assembly of chiral alcohols on platinum was studied using three different pairs of prochiral ketones and their alcohol products. The ketones were chosen because they represent three different types of substrates in the asymmetric hydrogenation on chirally modified platinum catalysts. Scanning tunneling microscopy and high-resolution electron energy loss vibrational spectroscopy data were combined to show that methyl lactate transforms into the enol tautomer of methyl pyruvate on Pt(111) at room temperature. Specifically, the chiral alcohol undergoes dehydrogenation leading to the same adsorbed enol assemblies that are formed directly through the adsorption of the prochiral α-ketoester. Similarly, 1-phenylethanol transforms into assemblies of the enol tautomer of acetophenone. The interrelationship between surface reactivity and self-assembly was further explored by studying the oxidation of 1-phenyl-2,2,2-trifluoroethanol to form CH···O bonded 2,2,2-trifluoroacetophenone assemblies. In terms of catalytic function, these self-assembly processes provide insight on the optimization of the asymmetric hydrogenation of activated ketones on chirally modified platinum catalysts.

Treatment with citalopram for 12 weeks in depressed CAD patients is associated with enhanced production of nitric oxide despite the co-administration of commonly prescribed anti-platelet regimens including aspirin and clopidogrel. Clinical implications of these findings are unclear, but improved endothelial function is implied by the increased NO production, suggesting that citalopram may be of particular benefit for patients with comorbid depression and vascular disease including CAD, stroke, peripheral artery disease, and diabetes.