title: Microsolvation effects on the excited-state dynamics of protonated tryptophan.
abstract: To better understand the complex photophysics of the amino acid tryptophan, which is widely used as a probe of protein structure and dynamics, we have measured electronic spectra of protonated, gas-phase tryptophan solvated with a controlled number of water molecules and cooled to approximately 10 K. We observe that, even at this temperature, the bare molecule exhibits a broad electronic spectrum, implying ultrafast, nonradiative decay of the excited state. Surprisingly, the addition of two water molecules sufficiently lengthens the excited-state lifetime that we obtain a fully vibrationally resolved electronic spectrum. Quantum chemical calculations at the RI-CC2/aug-cc-pVDZ level, together with TDDFT/pw based first-principles MD simulations of the excited-state dynamics, clearly demonstrate how interactions with water destabilize the photodissociative states and increase the excited-state lifetime.
authors.affiliation: Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Sébastien R
authors.initials: SR
authors.lastname: Mercier
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Boyarkin
authors.forename: Anthi
authors.initials: A
authors.lastname: Kamariotis
authors.forename: Matteo
authors.initials: M
authors.lastname: Guglielmi
authors.forename: Ivano
authors.initials: I
authors.lastname: Tavernelli
authors.forename: Michele
authors.initials: M
authors.lastname: Cascella
authors.forename: Ursula
authors.initials: U
authors.lastname: Rothlisberger
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Rizzo
mesh_terms: D008958:Models, Molecular; D011522:Protons; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D011522:Protons; D014364:Tryptophan