The Manipulation of Hydrophobicity in Catalyst Design for Applications of Aerobic Alcohols Oxidation and Electrocatalytic Water Oxidation

Handle URI:
http://hdl.handle.net/10754/610561
Title:
The Manipulation of Hydrophobicity in Catalyst Design for Applications of Aerobic Alcohols Oxidation and Electrocatalytic Water Oxidation
Authors:
Chen, Batian ( 0000-0002-9228-5829 )
Abstract:
Hydrophobicity is the generalized characteristic of non-polar substances that brings about their exclusion from aqueous phases. This property, entropic in its nature, drives key self-assembly and phase separation processes in water. Protein folding, the formation of DNA double helix, the existence of lipid bilayers and the wetting properties of leaf surfaces are all due to hydrophobic interactions. Inspired by Nature, we aimed to use hydrophobicity for creating novel and improved catalytic systems. (I) A number of fluorous amphiphilic star block-copolymers containing a tris(benzyltriazolylmethyl)amine motif have been prepared. These polymers assembled into well-defined nanostructures in water, and their mode of assembly could be controlled by changing the composition of the polymer. The polymers were used for enzyme-inspired catalysis of alcohol oxidation. (II) An enzyme-inspired catalytic system based on a rationally designed multifunctional surfactant was developed. The resulting micelles feature metal-binding sites and stable free radical moieties as well as fluorous pockets that attract and preconcentrate molecular oxygen. In the presence of copper ions, the micelles effect chemoselective aerobic alcohol oxidation under ambient conditions in water, a transformation that is challenging to achieve nonenzymatically. (III) Development of a facile means of photo/electrocatalytic water splitting is one of the main barriers to establishing of a solar hydrogen economy. Of the two half-reactions involved in splitting water into O2 and H2, water oxidation presents the most challenge due to its mechanistic complexity. A practical water oxidation catalyst must be highly active, yet inexpensive and indefinitely stable under harsh oxidative conditions. Here, I shall describe the synthesis of a library of molecular water oxidation catalysts based on the Co complex of tris(2-benzimidazolylmethyl)amine, (BimH)3. A wide range of catalysts differing in their electronic properties, surface affinity, and steric bulk was explored. We identified hydrophobicity as the key variable in mediating the catalytic competence of Co-(BimH)3 complexes. The change in this parameter correlates both with the conformational mobility of the ligand core and the structural changes in the local solvent environment around the catalytic metal site. The optimal ligand identified is superhydrophobic due to three fluorinated side chains. The corresponding Co complex catalyzes water electrooxidation efficiently, with an onset potential equal to that for the well-established CoPi heterogeneous system, albeit with a dramatically higher turnover frequency (TOF) and in the absence of soluble Co salts. As an added benefit, the hydrophobic catalyst can be immobilized through physisorption, and remains stable after prolonged controlled-potential electrolysis. A DFT calculation was also performed to understand the catalytic pathway.
Advisors:
Rodionov, Valentin
Committee Member:
Hadjichristidis, Nikolaos ( 0000-0003-1442-1714 ) ; Takanabe, Kazuhiro ( 0000-0001-5374-9451 ) ; Moshkov, Mikhail ( 0000-0003-0085-9483 ) ; Sidorov, Vlamidir
KAUST Department:
Physical Sciences and Engineering (PSE) Division; Chemical Science Program
Program:
Chemical Sciences
Issue Date:
17-May-2016
Type:
Dissertation
Appears in Collections:
Dissertations; Physical Sciences and Engineering (PSE) Division; Chemical Science Program

Full metadata record

DC FieldValue Language
dc.contributor.advisorRodionov, Valentinen
dc.contributor.authorChen, Batianen
dc.date.accessioned2016-05-23T12:28:06Z-
dc.date.available2016-05-23T12:28:06Z-
dc.date.issued2016-05-17-
dc.identifier.urihttp://hdl.handle.net/10754/610561-
dc.description.abstractHydrophobicity is the generalized characteristic of non-polar substances that brings about their exclusion from aqueous phases. This property, entropic in its nature, drives key self-assembly and phase separation processes in water. Protein folding, the formation of DNA double helix, the existence of lipid bilayers and the wetting properties of leaf surfaces are all due to hydrophobic interactions. Inspired by Nature, we aimed to use hydrophobicity for creating novel and improved catalytic systems. (I) A number of fluorous amphiphilic star block-copolymers containing a tris(benzyltriazolylmethyl)amine motif have been prepared. These polymers assembled into well-defined nanostructures in water, and their mode of assembly could be controlled by changing the composition of the polymer. The polymers were used for enzyme-inspired catalysis of alcohol oxidation. (II) An enzyme-inspired catalytic system based on a rationally designed multifunctional surfactant was developed. The resulting micelles feature metal-binding sites and stable free radical moieties as well as fluorous pockets that attract and preconcentrate molecular oxygen. In the presence of copper ions, the micelles effect chemoselective aerobic alcohol oxidation under ambient conditions in water, a transformation that is challenging to achieve nonenzymatically. (III) Development of a facile means of photo/electrocatalytic water splitting is one of the main barriers to establishing of a solar hydrogen economy. Of the two half-reactions involved in splitting water into O2 and H2, water oxidation presents the most challenge due to its mechanistic complexity. A practical water oxidation catalyst must be highly active, yet inexpensive and indefinitely stable under harsh oxidative conditions. Here, I shall describe the synthesis of a library of molecular water oxidation catalysts based on the Co complex of tris(2-benzimidazolylmethyl)amine, (BimH)3. A wide range of catalysts differing in their electronic properties, surface affinity, and steric bulk was explored. We identified hydrophobicity as the key variable in mediating the catalytic competence of Co-(BimH)3 complexes. The change in this parameter correlates both with the conformational mobility of the ligand core and the structural changes in the local solvent environment around the catalytic metal site. The optimal ligand identified is superhydrophobic due to three fluorinated side chains. The corresponding Co complex catalyzes water electrooxidation efficiently, with an onset potential equal to that for the well-established CoPi heterogeneous system, albeit with a dramatically higher turnover frequency (TOF) and in the absence of soluble Co salts. As an added benefit, the hydrophobic catalyst can be immobilized through physisorption, and remains stable after prolonged controlled-potential electrolysis. A DFT calculation was also performed to understand the catalytic pathway.en
dc.language.isoenen
dc.subjectHydrophobicityen
dc.subjectFluorousen
dc.subjectAerobic Oxidationen
dc.subjectWater Oxidationen
dc.titleThe Manipulation of Hydrophobicity in Catalyst Design for Applications of Aerobic Alcohols Oxidation and Electrocatalytic Water Oxidationen
dc.typeDissertationen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberHadjichristidis, Nikolaosen
dc.contributor.committeememberTakanabe, Kazuhiroen
dc.contributor.committeememberMoshkov, Mikhailen
dc.contributor.committeememberSidorov, Vlamidiren
thesis.degree.disciplineChemical Sciencesen
thesis.degree.nameDoctor of Philosophyen
dc.person.id124271en
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