The selective oxidation of alcohols in aqueous phase over supported metal catalysts is facilitated by high-pH conditions. We have studied the mechanism of ethanol and glycerol oxidation to acids over various supported gold and platinum catalysts. Labeling experiments with (18)O(2) and H(2)(18)O demonstrate that oxygen atoms originating from hydroxide ions instead of molecular oxygen are incorporated into the alcohol during the oxidation reaction. Density functional theory calculations suggest that the reaction path involves both solution-mediated and metal-catalyzed elementary steps. Molecular oxygen is proposed to participate in the catalytic cycle not by dissociation to atomic oxygen but by regenerating hydroxide ions formed via the catalytic decomposition of a peroxide intermediate.

http://science.sciencemag.org/content/sci/330/6000/74.full.pdf

Reactivity of the Gold/Water Interface During Selective Oxidation Catalysis

Reactions of transition metal dihydrogen complexes

A shortened form of the self-splicing ribosomal RNA (rRNA) intervening sequence of Tetrahymena thermophila acts as an enzyme in vitro. The enzyme catalyzes the cleavage and rejoining of oligonucleotide substrates in a sequence-dependent manner with Km = 42 microM and kcat = 2 min-1. The reaction mechanism resembles that of rRNA precursor self-splicing. With pentacytidylic acid as the substrate, successive cleavage and rejoining reactions lead to the synthesis of polycytidylic acid. Thus, the RNA molecule can act as an RNA polymerase, differing from the protein enzyme in that it uses an internal rather than an external template. At pH 9, the same RNA enzyme has activity as a sequence-specific ribonuclease.

https://science.sciencemag.org/content/sci/231/4737/470.full.pdf

The intervening sequence RNA of Tetrahymena is an enzyme.

HKUST-1, a metal–organic framework (MOF) material containing CuII-paddlewheel-type nodes and 1,3,5-benzenetricarboxylate struts, features accessible CuII sites to which solvent or other desired molecules can be intentionally coordinated As part of a broader investigation of ionic conductivity in MOFs, we unexpectedly observed substantial proton conductivity with the “as synthesized” version of this material following sorption of methanol Although HKUST-1 is neutral, coordinated water molecules are rendered sufficiently acidic by CuII to contribute protons to pore-filling methanol molecules and thereby enhance the alternating-current conductivity At ambient temperature, the chemical identities of the node-coordinated and pore-filling molecules can be independently varied, thus enabling the proton conductivity to be reversibly modulated The proton conductivity of HKUST-1 was observed to increase by ∼75-fold, for example, when node-coordinated acetonitrile molecules were replaced by water molecules In c

/pdf/coordination-chemistry-control-of-proton-conductivity-in-the-4dcw6zab1d.pdf

Coordination-Chemistry Control of Proton Conductivity in the Iconic Metal−Organic Framework Material HKUST-1

Publisher Summary This chapter presents the reversible hydration of carbonyl compounds. The formation of stable solid hydrates is well known for aldehydes and ketones containing several electronegative substituents and for some di- and triketones. The chapter discusses the chemical and biological reactivity of carbonyl compounds in aqueous solution, and they have proved kinetically very convenient for studying problems of homogeneous catalysis. The hydration equilibrium constants are briefly described. Later, the experimental methods and results relevant to acidity of carbonyl hydrates are discussed. The kinetics of hydration and dehydration reactions is also presented. Hydration and dehydration reactions have proved particularly convenient for studying catalysis by acids and bases over a wide range of structures and catalytic power. The absolute rate constants are relatively low even with very strong acids or bases, and diffusion-controlled rates are not approached for either the forward or reverse reactions.

P. Ballinger

Papers

Acid Ionization Constants of Alcohols. II. Acidities of Some Substituted Methanols and Related Compounds1,2