Microhydration of protonated biomolecular building blocks: protonated pyrimidine. Issue 23 (3rd June 2020)

• Record Type: Journal Article
• Authors: Chatterjee, Kuntal; Dopfer, Otto
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 23(2020)
• Page Start: 13092
• Page End: 13107
• Publication Date: 2020-06-03
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp02110e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The protonation site and evolution of the hydration network in microsolvated protonated pyrimidine clusters, H + Pym–(H2 O) n with n = 1–4, has been explored by infrared spectroscopy and density functional theory calculations. Abstract : Protonation and hydration of biomolecules govern their structure, conformation, and function. Herein, we explore the microhydration structure in mass-selected protonated pyrimidine–water clusters (H + Pym–W n, n = 1–4) by a combination of infrared photodissociation spectroscopy (IRPD) between 2450 and 3900 cm −1 and density functional theory (DFT) calculations at the dispersion-corrected B3LYP-D3/aug-cc-pVTZ level. We further present the IR spectrum of H + Pym–N2 to evaluate the effect of solvent polarity on the intrinsic molecular parameters of H + Pym. Our combined spectroscopic and computational approach unequivocally shows that protonation of Pym occurs at one of the two equivalent basic ring N atoms and that the ligands in H + Pym–L (L = N2 or W) preferentially form linear H-bonds to the resulting acidic NH group. Successive addition of water ligands results in the formation of a H-bonded solvent network which increasingly weakens the NH group. Despite substantial activation of the N–H bond upon microhydration, no intracluster proton transfer occurs up to n = 4 because of the balance of relative proton affinities of Pym and W n and the involved solvation energies. Comparison to neutral Pym–W n clusters reveals the drastic effects of protonation on microhydration with respect to both structure and interaction strength.