Time-Resolved Resonance Raman and Density Functional Theory Investigation of the Intermediates and Mechanism of Photorelease in Benzoin Diethyl Phosphate in Aqueous Solution

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Time-Resolved Resonance Raman and Density
Functional Theory Investigation of the
Intermediates and Mechanism of Photorelease in
Benzoin Diethyl Phosphate in Aqueous Solution
Presented by Yong Du
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Introduction

• What is Phototrigger Compounds?
• protecting groups that require only light of
  particular wavelengths for their cleavage
• Application
• provide a rapid light-induced release of
  bioactive materials such as GABA, L-glutamate,
  cAMP, ATP and nonapeptide Bradykinin.

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• Types of Phototrigger Compounds
• o-nitrobenzyl derivatives
• Benzoin esters
• Benzoin diethyl phosphate
• Phenacyl esters
• P-hydroxyphenacyl diethyl phosphate
• P-methoxyphenacyl diethyl phosphate
• Model compounds
• - 4-methoxyacetophenone

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Benzoin diethyl phosphate Photodeprotection
mechanism
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Research Methods

• To provide direct dynamic and structural
  information and explore the overall reaction
  mechanism, we present here a nanosecond
  time-resolved resonance Raman (ns-TR3) combined
  with the density functional theoretical (DFT)
  calculation for benzoin diethyl phosphate (BDP)
  in a largely aqueous solution.

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Experimental Setup
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DFT Calculation

• Gaussian 98 program suite
• B3LYP method (open shell UB3LYP for triplet)
• 6-311G basis set
• No imaginary frequency mode was observed

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DFT calculation of BDP cation
1
2
10
11
7
3
6
12
9
8
13
4
5
15
14
Triplet cation
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1
10
3
6
7
Singlet cation
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5
8
9
11
15
12
13
14
1
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The optimization structure parameters
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UV spectra of the photochemistry reaction of BDP
in MeCN after 266nm laser irridiation
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TR3 of BDP in 25MeCN/75H2O

• TR3 with 266 nm pump and 532 nm probe

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d
c
b
a
Comparison of DFT calculated Raman spectrum for
the triplet (b) and singlet (d) cation with
ns-TR3 spectrum (a), (c) obtained with 267nm pump
and 532nm probe (at 10ns delay) in 75H2O/25MeCN
solvent.
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Expt and Calc. Raman frequency of BDP triplet
cation
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Expt and Calc. Raman frequency of BDP singlet
cation
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• Combined with the density functional theoretical
  (DFT) calculation to determine the structure and
  vibrational frequencies, the two species has been
  identified and assigned to the heterolytic
  cleavage product of the triplet cation and the
  corresponding singlet cation, respectively.
• The ns-TR3 measurement with the 267 nm probe was
  also performed to monitor the formation dynamics
  of the final solvolytic product. Correlation of
  the kinetics observed for product and the two
  cation intermediates reveals a consecutive
  mechanism for the BDP photoliberation and
  solvolysis reaction.
• Our result sheds new light to the desyl
  deprotection related photochemistry and is
  helpful to improve development of the desyl
  photolabile protection group in the future.

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Thanks!!

• HKUHPCPOWER Cluster provide us a fast and
  convenient way to carry the Density Functional
  Theory calculation for the examined phototrigger
  compounds in our research. This helps to give
  information of structure and bonding properties
  of key chemical reaction intermediates and lead
  to an improved understanding of mechanisms for
  photorelease in benzoin and other kinds of
  phototrigger compounds.