Navigation

Recent Publications

More...

Home

Time-Resolved Spectroscopic Studies of Selected Photoredox and Photodeprotection Reactions of Aromatic Carbonyl Compounds in Aqueous Solutions

phillips - Posted on 25 November 2016

Project Description: 

Time-resolved absorption (fs-TA and ns-TA) and TR3 spectroscopy experiments will be performed to investigate the photoredox and/or photodeprotection reactions of derivatives of selected benzophenone (BP) and anthraquinone (AQ) compounds so as to characterize the excited states and reactive intermediates and reaction mechanisms for the compounds of interest. 2 Time-resolved absorption (fs-TA and ns-TA) and TR3 spectroscopy experiments will be done to investigate how the substituent and leaving group properties influence the deprotection reactions of ketoprofen (KP) based phototrigger compounds in aqueous solutions of varying pH. This will help better understand how substituents with varying properties and located at different positions will affect the behavior and outcome for the photodeprotection reactions of interest. 3 Time-resolved absorption (fs-TA and ns-TA) and TR3 spectroscopy experiments will be performed to investigate benzophenone alcohols like 2-(3’-benzoyl)phenethyl alcohol that undergo a base catalyzed elimination of formaldehyde and form a 3-methylbenzophenone side product. Experiments will also be done in aqueous solutions of varying pH values in order to better understand why this reaction only appears to be appreciable in strongly basic and acidic solutions but only trace amounts of the reaction were observed in neutral and slightly basic aqueous solutions. 4 Time-resolved absorption (fs-TA and ns-TA) and TR3 spectroscopy experiments will be done to study photoenolization based photorelease reactions for selected ortho-alkyl substituted aromatic carbonyl compounds that have a good leaving group on the ortho-alkyl substituent or the -position next to the aromatic carbonyl in aqueous solutions of varying pH values. This work aims to develop an improved understanding of the reaction mechanisms, and what role the water and pH conditions play in the photoenolization reactions and the release mechanism(s) of interest. 5 Time-resolved absorption (fs-TA and ns-TA) and TR3 spectroscopy experiments will be performed to examine photoenolization based photorelease reactions for selected ortho-alkyl substituted aromatic carbonyl compounds in which the cleavage of the leaving group occurs by intramolecular relactonization of the photoenol alcohol group with an ester moiety. This work will help gain a better understanding of the reaction mechanisms and the role water and pH conditions play in the photoenolization and intramolecular relactonization of the photoenol alcohol group with an ester moiety. 6 The accumulated experimental and computational results gained in objectives 1-5 will be compared to each other in order to help determine similarities and differences in their excited states, intermediates, substituent effects and pH dependence for their associated photochemistry. This may be helpful to determine promising trends and/or properties that may be useful to explore in the design of improved photoredox and photodeprotection compounds for use in particular applications with certain aqueous pH conditions.

Researcher name: 
David Lee Phillips
Researcher position: 
Chair Professor
Researcher department: 
Department of Chemistry
Researcher email: 
phillips@hku.hk
Research Project Details
Project Duration: 
09/2015 to 08/2018
Project Significance: 
A number of kinds of aromatic carbonyl containing compounds are able to undergo very efficient photoredox reactions and/or photodeprotection reactions in aqueous solutions within some pH value ranges. We are interested in investigating some benzophenone (BP) and anthraquinone (AQ) containing compounds that can undergo efficient water assisted photoredox and/or photodeprotection reactions and also the photodeprotection reactions based on ketoprofen (KP), BP alcohols like 2-(3’- benzoyl)phenethyl alcohol, ortho-alkyl substituted aromatic carbonyl compounds that have a good leaving group on the ortho-alkyl substituent or the alpha-position next to the aromatic carbonyl and ortho-alkyl substituted aromatic carbonyl compounds in which the cleavage of the leaving group occurs by intramolecular relactonization of the photoenol alcohol group with an ester moiety. These kinds of compounds can be developed as a photoremovable protecting group (PRPG) for great range of leaving groups like inorganic phosphates, nucleotides, carboxylates, formaldehye, amines and applications as PRPGs in drug delivery, organic synthesis, triggering protein folding and unfolding and others. The compounds of interest in our proposal briefly described above have been mainly examined using product analysis studies and limited nanosecond time resolved transient absorption experiments. We propose to use several time-resolved spectroscopy methods to directly observe and characterize the excited states and intermediates from the ultrafast time scale to formation of final products in order to investigate and determine the intermediates and reaction mechanisms of selected photochemical reactions for the compounds of interest. We plan to systematically examine substituent and water hydrogen bonding and pH effects on the photochemical reactions of interest that are detailed in the objectives below and in the subsequent sections of the proposal. This time-resolved spectroscopy study will help provide a better understanding of how substitutions and solvent environmental factors affect the structure, properties and chemical reactivity of the observed intermediate species. This information can then be employed to determine structure-reactivity relationships. The results gained from this proposed research may be useful to help design and develop better aromatic carbonyl compounds for specific applications as PRPG compounds and synthetic methods for novel reactions.
Results Achieved: 
We have published the following paper on this project recently: 1. “Ketyl Radical Formation Via Proton-Coupled Electron Transfer in Aqueous Solution Versus Hydrogen Atom Transfer in Isopropanol After Photoexcitation of Aromatic Carbonyl Compounds,” X. T. Zhang, J. Ma*, S. B. Li, M. D. Li, X. G. Guan, X. Lan, R. X. Zhu and D. L. Phillips*, J. Org. Chem. 81, 5330-5336 (2016). 2. “To Photoredox or Not in Neutral Aqueous Solutions for Selected Benzophenone and Anthraquinone Derivatives,” X. T. Zhang, J. Ma* and D. L. Phillips*, J. Phys. Chem. Lett. 7, 4860-4864 (2016). 3. “Competition Between “Meta-Effect” Photochemical Reactions of Selected Benzophenone Compounds Having Two Different Substituents at Meta Positions,” J. Ma*, H. Li, X. T. Zhang, M. D. Li and D. L. Phillips*, J. Org. Chem. 81, 9553–9559 (2016).
Remarks: 
None