Spectroscopic Properties and Conformational Analysis of Methyl Ester of Sinapic Acid in Various Environments

B. Smyk, G. Mȩdza, A. Kasparek, M. Pyrka, Ignacy Gryczynski, M. Maciejczyk

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Abstract

A methyl ester of sinapic acid (MESA) has recently attracted attention due to its antioxidant action. This article presents results of a study on the spectral and physicochemical properties of MESA, using quantum chemistry (QC), steady-state (absorption and fluorescence), and time-resolved fluorescence techniques (TCSPC). The pKa of the phenol group in the ground state was determined (8.6). The pKa∗ values in the excited state calculated from the Förster cycle (1.9) and from fluorescence spectra (8.5) differed significantly but the experimental data suggested that the first was the more probable one. Quantum yields (QYs) for both forms have been determined. The QYs were very low (0.0017 and 0.0007) for nondissociated and dissociated forms, respectively and lifetimes were very short ≤10 ps for both forms. The differences in the probability of H-bond formation in the ground and the excited states were estimated by the application of the SdP polarity scale. Dipole moments in the ground state were calculated using QC. The ratio between dipole moments in the ground and the excited state for free molecule was obtained from Bilot-Kawski (B-K) method. Analysis of all collected results suggests that radical route (through hydrogen atom abstraction) of antioxidant activity of MESA is the more probable one in a water environment at pH below 6.

Original languageEnglish
Pages (from-to)7299-7310
Number of pages12
JournalJournal of Physical Chemistry B
Volume121
Issue number30
DOIs
StatePublished - 3 Aug 2017

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Excited states
esters
Quantum chemistry
Esters
Fluorescence
Dipole moment
antioxidants
quantum chemistry
Quantum yield
Antioxidants
fluorescence
Ground state
acids
Acids
dipole moments
excitation
ground state
Phenol
phenols
Phenols

Cite this

Smyk, B. ; Mȩdza, G. ; Kasparek, A. ; Pyrka, M. ; Gryczynski, Ignacy ; Maciejczyk, M. / Spectroscopic Properties and Conformational Analysis of Methyl Ester of Sinapic Acid in Various Environments. In: Journal of Physical Chemistry B. 2017 ; Vol. 121, No. 30. pp. 7299-7310.
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Spectroscopic Properties and Conformational Analysis of Methyl Ester of Sinapic Acid in Various Environments. / Smyk, B.; Mȩdza, G.; Kasparek, A.; Pyrka, M.; Gryczynski, Ignacy; Maciejczyk, M.

In: Journal of Physical Chemistry B, Vol. 121, No. 30, 03.08.2017, p. 7299-7310.

Research output: Contribution to journalArticleResearchpeer-review

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