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Molecular‐Level Understanding of Ground‐ and Excited‐State OH⋅⋅⋅O Hydrogen Bonding Involving the Tyrosine Side Chain: A Combined High‐Resolution Laser Spectroscopy and Quantum Chemistry Study
Author(s) -
Biswal Himansu S.,
Bhattacharyya Surjendu,
Wategaonkar Sanjay
Publication year - 2013
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201300670
Subject(s) - chemistry , hydrogen bond , excited state , ground state , chromophore , acceptor , crystallography , spectroscopy , intermolecular force , ab initio , photochemistry , computational chemistry , molecule , organic chemistry , atomic physics , physics , quantum mechanics , condensed matter physics
The present study combines both laser spectroscopy and ab initio calculations to investigate the intermolecular OH⋅⋅⋅O hydrogen bonding of complexes of the tyrosine side chain model chromophore compounds phenol (PH) and para ‐cresol ( p CR) with H 2 O, MeOH, PH and p CR in the ground (S 0 ) state as well as in the electronic excited (S 1 ) state. All the experimental and computational findings suggest that the H‐bond strength increases in the S 1 state and irrespective of the hydrogen bond acceptor used, the dispersion energy contribution to the total interaction energy is about 10–15 % higher in the S 1 state compared to that in the S 0 state. The alkyl‐substituted (methyl; +I effect) H‐bond acceptor forms a significantly stronger H bond both in the S 0 and the S 1 state compared to H 2 O, whereas the aryl‐substituted (phenyl; −R effect) H‐bond donor shows a minute change in energy compared to H 2 O. The theoretical study emphasizes the significant role of the dispersive interactions in the case of the p CR and PH dimers, in particular the CH⋅⋅⋅O and the CH⋅⋅⋅π interactions between the donor and acceptor subunits in controlling the structure and the energetics of the aromatic dimers. The aromatic dimers do not follow the acid–base formalism, which states that the stronger the base, the more red‐shifted is the XH stretching frequency, and consequently the stronger is the H‐bond strength. This is due to the significant contribution of the dispersion interaction to the total binding energy of these compounds.