State-by-State Investigation of Destructive Interference in Resonance Raman Spectra of Neutral Tyrosine and the Tyrosinate Anion with the Simplified Sum-over-States Approach

Jerry B Cabalo,Semion K Saikin,Dmitrij Rappoport,Erik D Emmons,Alán Aspuru-Guzik

doi:10.1021/jp506948h

Jerry B Cabalo, Semion K Saikin + Show 3 more

Open Access

https://doi.org/10.1021/jp506948h

Copy DOI

Abstract

UV resonance Raman scattering is uniquely sensitive to the molecular electronic structure as well as intermolecular interactions. To better understand the relationship between electronic structure and resonance Raman cross section, we carried out combined experimental and theoretical studies of neutral tyrosine and the tyrosinate anion. We studied the Raman cross sections of four vibrational modes as a function of excitation wavelength, and we analyzed them in terms of the contributions of the individual electronic states as well as of the Albrecht A and B terms. Our model, which is based on time-dependent density functional theory (TDDFT), reproduced the experimental resonance Raman spectra and Raman excitation profiles for both studied molecules with good agreement. We found that for the studied modes, the contributions of Albrecht's B terms in the Raman cross sections were important across the frequency range spanning the L(a,b) and B(a,b) electronic excitations in tyrosine and the tyrosinate anion. Furthermore, we demonstrated that interference with high-energy states had a significant impact and could not be neglected even when in resonance with a lower-energy state. The symmetry of the vibrational modes served as an indicator of the dominance of the A or B mechanisms. Excitation profiles calculated with a damping constant estimated from line widths of the electronic absorption bands had the best consistency with experimental results.

Highlights

UV Resonance Raman Scattering (RRS) spectroscopy is a powerful analytical technique permitting sensitive detection of hazardous materials as well as of structural change within biological systems
We used the simplified sum-over-states approach within the framework of time-dependent density functional theory (TDDFT) to investigate the influence of the molecular electronic structure on the RRS cross section
The simplified sum-over-states approach has been used to study the influence of highenergy electronic states on the RRS spectrum of neutral tyrosine and tyrosinate anion at high pH with state-specific detail

Summary

Introduction

UV Resonance Raman Scattering (RRS) spectroscopy is a powerful analytical technique permitting sensitive detection of hazardous materials as well as of structural change within biological systems. UV-RRS was used to measure hydrophilic interactions, in particular the H-bond strength between water solvent molecules and the polar groups on the aromatic side chain.[4,5,6,7] RRS has been used to investigate the interactions between metal atoms in metallo-enzymes[810] and nearby amino acid residues serving as coordinating ligands.[10,11,12] RRS has been used for examining tertiary protein structure such as the α and ψ angles of the peptide linkages in proteins,[13] as well as the hydrophobicity around aromatic amino acid residues.[14] Clearly, the RRS signal is sensitive to intermolecular interactions or any process that affects the electronic structure. Because of the wide applicability of RRS for the study of interactions in biological environments, a fundamental understanding of how the signal responses of vibrational modes within a molecule are impacted by the electronic structure is important. The impact can be reflected in both frequency shifts as well as subtle changes in Raman intensities.[13, 15,16,17]

Methods

Results

Conclusion