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24 results on '"Mendez-Arroyo, Jose"'

7. A concerted two-prong approach to the in situ allosteric regulation of bifunctional catalysis† †Electronic supplementary information (ESI) available. CCDC 1469900–1469903. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6sc01454b Click here for additional data file

Author

McGuirk, C. Michael, Mendez-Arroyo, Jose, d'Aquino, Andrea I., Stern, Charlotte L., Liu, Yuan, and Mirkin, Chad A.

Subjects
Chemistry
Abstract

The allosteric regulation of bifunctional catalysis is achieved through the simultaneous use of reversible acid–base and structurally addressable coordination chemistry., Herein, we report the reversible in situ “on–off” allosteric regulation of hydrogen-bond-donating (HBD)–Lewis base co-catalytic activity via a concerted two-prong methodology entailing cooperative acid–base chemistry and a structurally addressable coordination complex. Specifically, a heteroligated Pt(ii) weak-link approach (WLA) tweezer complex containing both a hemilabile squaramide–piperidine-based catalytic ligand and a sodium sulfonate hydrogen-bond-accepting (HBA) ligand was synthesized. Due to the hemilabile nature of the catalyst-containing ligand, the heteroligated complex can be reversibly toggled in situ between a flexible, semi-open state and a rigid, fully closed state upon the addition of elemental ion cues. 1H NMR spectroscopy titration studies show that in the semi-open state interligand hydrogen-bonding prevents substrate recognition by the squaramide unit, while in the fully closed state ligand–ligand interactions are prevented. This results in a catalytically active closed state, whereas in the semi-open state, when the piperidine tertiary amine is deliberately protonated, no catalytic activity is observed. Reversible interconversion between the active fully closed state and the dormant protonated semi-open state is achieved in the presence of substrate upon the concerted addition and abstraction of both a proton and a coordinating elemental anion. In this work, allosteric regulation of catalytic activity is demonstrated for both the Michael addition of nitroethane to β-nitrostyrene and the ring-opening of l-(–)-lactide. Taken together, this work details a potentially generalizable platform for the “on–off” allosteric regulation of a family of HBD–Lewis base co-catalysts capable of catalyzing a broad scope of reactions, including the living ring-opening polymerization of cyclic esters.

Published
2016

11. Giant conductivity switching of LaAlO3/SrTiO3 heterointerfaces governed by surface protonation

Author

Brown, Keith A., He, Shu, Eichelsdoerfer, Daniel J., Huang, Mengchen, Levy, Ishan, Lee, Hyungwoo, Ryu, Sangwoo, Irvin, Patrick, Mendez-Arroyo, Jose, Eom, Chang-Beom, Mirkin, Chad A., Levy, Jeremy, Brown, Keith A., He, Shu, Eichelsdoerfer, Daniel J., Huang, Mengchen, Levy, Ishan, Lee, Hyungwoo, Ryu, Sangwoo, Irvin, Patrick, Mendez-Arroyo, Jose, Eom, Chang-Beom, Mirkin, Chad A., and Levy, Jeremy

Abstract

Complex-oxide interfaces host a diversity of phenomena not present in traditional semiconductor heterostructures. Despite intense interest, many basic questions remain about the mechanisms that give rise to interfacial conductivity and the role of surface chemistry in dictating these properties. Here we demonstrate a fully reversible >4 order of magnitude conductance change at LaAlO3/SrTiO3 (LAO/STO) interfaces, regulated by LAO surface protonation. Nominally conductive interfaces are rendered insulating by solvent immersion, which deprotonates the hydroxylated LAO surface; interface conductivity is restored by exposure to light, which induces reprotonation via photocatalytic oxidation of adsorbed water. The proposed mechanisms are supported by a coordinated series of electrical measurements, optical/solvent exposures, and X-ray photoelectron spectroscopy. This intimate connection between LAO surface chemistry and LAO/STO interface physics bears far-reaching implications for reconfigurable oxide nanoelectronics and raises the possibility of novel applications in which electronic properties of these materials can be locally tuned using synthetic chemistry.

Published
2016

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