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Photodissociation dynamics of hydroxybenzoic acids.

Yi Lin Yang¹, Yuri Dyakov, Y T Lee

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.

The Journal of Chemical Physics

|January 26, 2011

Summary

Intramolecular hydrogen bonding in tyrosine chromophores prevents excited-state dissociation, explaining amino acid photostability under UV light. This finding offers a new mechanism for understanding ultraviolet photon interactions with biological molecules.

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Area of Science:

Photochemistry
Biophysical Chemistry
Molecular Dynamics

Background:

Aromatic amino acids exhibit high UV absorption and low fluorescence.
Ultrafast internal conversion was thought to ensure photostability.
Recent studies suggest excited-state dissociation contradicts observed photostability.

Purpose of the Study:

Investigate photodissociation dynamics of tyrosine chromophores.
Explore the role of intramolecular hydrogen bonding in photostability.
Provide an alternative mechanism for amino acid photostability.

Main Methods:

Studied 2-, 3-, and 4-hydroxybenzoic acid photodissociation.
Utilized multimass ion imaging techniques in a molecular beam at 193 nm.
Performed ab initio calculations on potential energy surfaces.

Main Results:

Dissociation from the excited state is quenched in conformers with intramolecular hydrogen bonding.
Ab initio calculations reveal significant changes in excited and ground state potential energy surfaces.
Intramolecular hydrogen bonding plays a crucial role in excited-state dynamics.

Conclusions:

Intramolecular hydrogen bonding is key to the photostability of aromatic amino acids.
This study provides a novel molecular mechanism for UV photostability.
Findings challenge previous assumptions about ultrafast internal conversion.