Search PubMed⌕ Search

Biomedical subjects

Shih-Yuan Liu

Publications and source records attributed to Shih-Yuan Liu.

4 recordsLinked to original sources
PubMed2006

Mechanistic studies of Hangman salophen-mediated activation of O-O bonds.

Stopped-flow kinetic studies of a HSX-Mn-SalophOMe (1) catalyst provide spectroscopic evidence for the direct generation of a manganese(V) oxo salophen from a manganese(III) perbenzoate. The O-O bond heterolysis reaction that produces the oxo is not facilitated by intramolecular proton transfer from the acid hanging group of the HSX platform. Instead, the hanging group stabilizes the catalyst against oxidative degradation and, consistent with recent predictions of theory, is geometrically matched to promote the end-on coordination of a H2O2 substrate prior to its oxidation at the manganese(V) oxo center.

Catalysis↗
PubMed2005

Synthesis, resolution, and aldol reactions of a planar-chiral Lewis acid complex.

The synthesis and resolution of a new planar-chiral Lewis acid complex is described. The compound is applied to asymmetric Mukaiyama aldol reactions, leading to the formation of the desired product with good stereoselectivity. The sense of stereoselection is as predicted by the design, which exploits the ability of the Lewis acid to simultaneously serve as a sigma and a pi acceptor. Mechanistic observations are consistent with rate-determining formation of an aldehyde-Lewis acid complex, followed by rapid nucleophilic addition.

Journal Article↗
PubMed2005

Hangman salophens.

We report here a modular approach for the construction of a new class of compounds, the Hangman salophens. In the Hangman motif, an acid-base functionality "hangs" over the face of a redox cofactor. In contrast to more synthetically intractable porphyrin-based Hangman systems, Hangman salophens permit the facile control of their proton and redox properties for the study of the proton-coupled electron transfer (PCET) activation of small molecules. By investigating the catalase-like disproportionation of H2O2, we show that the presence (1) of a strong proton-donating hanging group (i.e., carboxylic acid) and (2) of electron-donating groups on the redox-active salen imparts significant catalytic activity for the O-O bond activation of small molecule substrates. The contribution of the new ligand framework to furthering our understanding of how PCET can be implemented in the design of active/selective catalysts will be discussed.

Catalase↗