Mechanism for Fluorescence Quenching of Tryptophan by Oxamate and Pyruvate

Conjugation and Solvation-Induced Photoinduced Electron Transfer

Huo Lei Peng, Robert Callender

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Oxamate and pyruvate are isoelectronic molecules. They both quench tryptophan fluorescence with Stern-Volmer constants of 16 and 20 M-1, respectively, which are comparable to that of arcrylamide, a commonly used probe for protein structure. On the other hand, it is well known that neither the carboxylate group of these molecules nor the amide group is a good quencher. To find the mechanism of the quenching by oxamate and pyruvate, density functional theory computations with a polarizable continuum model, solvation based on density, and explicit waters, were performed. Results indicate that both molecules can be an electron acceptor via photoinduced electron transfer. There are two requirements. First, the carboxylate and amide moieties must be in direct contact to bring about noticeable quenching. The conjugation between the amide (or the keto) group and the carboxylate group leads to a lower π∗ orbital, which is the lowest unoccupied molecular orbital (LUMO), and can then accept an electron from the excited tryptophan. Second, since oxamate and pyruvate ions have high electron density, hydrogen bonds with waters, which can be simulated by an explicit water model, are essential. Their LUMO energies are strongly influenced by water in aqueous solution. The above findings demonstrate how tryptophan fluorescence gets quenched in aqueous solution. The findings may be important in dealing with those problems where frontier orbitals are considered, especially with molecules having high electron density.

Original languageEnglish (US)
Pages (from-to)6483-6490
Number of pages8
JournalJournal of Physical Chemistry B
Volume122
Issue number25
DOIs
StatePublished - Jun 28 2018

Fingerprint

pyruvates
tryptophan
Solvation
conjugation
Pyruvic Acid
Tryptophan
solvation
Quenching
electron transfer
Fluorescence
quenching
Amides
Electrons
carboxylates
amides
fluorescence
Molecules
Water
Molecular orbitals
water

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

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title = "Mechanism for Fluorescence Quenching of Tryptophan by Oxamate and Pyruvate: Conjugation and Solvation-Induced Photoinduced Electron Transfer",
abstract = "Oxamate and pyruvate are isoelectronic molecules. They both quench tryptophan fluorescence with Stern-Volmer constants of 16 and 20 M-1, respectively, which are comparable to that of arcrylamide, a commonly used probe for protein structure. On the other hand, it is well known that neither the carboxylate group of these molecules nor the amide group is a good quencher. To find the mechanism of the quenching by oxamate and pyruvate, density functional theory computations with a polarizable continuum model, solvation based on density, and explicit waters, were performed. Results indicate that both molecules can be an electron acceptor via photoinduced electron transfer. There are two requirements. First, the carboxylate and amide moieties must be in direct contact to bring about noticeable quenching. The conjugation between the amide (or the keto) group and the carboxylate group leads to a lower π∗ orbital, which is the lowest unoccupied molecular orbital (LUMO), and can then accept an electron from the excited tryptophan. Second, since oxamate and pyruvate ions have high electron density, hydrogen bonds with waters, which can be simulated by an explicit water model, are essential. Their LUMO energies are strongly influenced by water in aqueous solution. The above findings demonstrate how tryptophan fluorescence gets quenched in aqueous solution. The findings may be important in dealing with those problems where frontier orbitals are considered, especially with molecules having high electron density.",
author = "Peng, {Huo Lei} and Robert Callender",
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T1 - Mechanism for Fluorescence Quenching of Tryptophan by Oxamate and Pyruvate

T2 - Conjugation and Solvation-Induced Photoinduced Electron Transfer

AU - Peng, Huo Lei

AU - Callender, Robert

PY - 2018/6/28

Y1 - 2018/6/28

N2 - Oxamate and pyruvate are isoelectronic molecules. They both quench tryptophan fluorescence with Stern-Volmer constants of 16 and 20 M-1, respectively, which are comparable to that of arcrylamide, a commonly used probe for protein structure. On the other hand, it is well known that neither the carboxylate group of these molecules nor the amide group is a good quencher. To find the mechanism of the quenching by oxamate and pyruvate, density functional theory computations with a polarizable continuum model, solvation based on density, and explicit waters, were performed. Results indicate that both molecules can be an electron acceptor via photoinduced electron transfer. There are two requirements. First, the carboxylate and amide moieties must be in direct contact to bring about noticeable quenching. The conjugation between the amide (or the keto) group and the carboxylate group leads to a lower π∗ orbital, which is the lowest unoccupied molecular orbital (LUMO), and can then accept an electron from the excited tryptophan. Second, since oxamate and pyruvate ions have high electron density, hydrogen bonds with waters, which can be simulated by an explicit water model, are essential. Their LUMO energies are strongly influenced by water in aqueous solution. The above findings demonstrate how tryptophan fluorescence gets quenched in aqueous solution. The findings may be important in dealing with those problems where frontier orbitals are considered, especially with molecules having high electron density.

AB - Oxamate and pyruvate are isoelectronic molecules. They both quench tryptophan fluorescence with Stern-Volmer constants of 16 and 20 M-1, respectively, which are comparable to that of arcrylamide, a commonly used probe for protein structure. On the other hand, it is well known that neither the carboxylate group of these molecules nor the amide group is a good quencher. To find the mechanism of the quenching by oxamate and pyruvate, density functional theory computations with a polarizable continuum model, solvation based on density, and explicit waters, were performed. Results indicate that both molecules can be an electron acceptor via photoinduced electron transfer. There are two requirements. First, the carboxylate and amide moieties must be in direct contact to bring about noticeable quenching. The conjugation between the amide (or the keto) group and the carboxylate group leads to a lower π∗ orbital, which is the lowest unoccupied molecular orbital (LUMO), and can then accept an electron from the excited tryptophan. Second, since oxamate and pyruvate ions have high electron density, hydrogen bonds with waters, which can be simulated by an explicit water model, are essential. Their LUMO energies are strongly influenced by water in aqueous solution. The above findings demonstrate how tryptophan fluorescence gets quenched in aqueous solution. The findings may be important in dealing with those problems where frontier orbitals are considered, especially with molecules having high electron density.

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