Electronic Transitions of Protonated and Deprotonated Amino Acids in Aqueous Solution in the Region 145–300 nm Studied by Attenuated Total Reflection Far-Ultraviolet Spectroscopy

Abstract

The electronic transitions of 20 naturally occurring amino acids in aqueous solution were studied with attenuated total reflection far-ultraviolet (ATR-FUV) spectroscopy in the region from 145 to 300 nm. From the measured ATR spectra of sample solutions, the FUV absorption spectra attributed to the amino acids were separated from the intense solvent absorption by using a modified Kramers-Kronig transformation method. The FUV absorption spectra of the amino acids reflect the protonation states of the backbone and side-chain structures. The contributions of the side chains to the spectra were also examined from the difference spectra subtracting the corresponding Gly spectrum from each spectrum. The observed spectra were compared mostly with the electronic transition studies of the molecular fragments of the amino acids in gas phase. The FUV spectra of the amino acids exhibited the intra- and intermolecular electronic interactions of the solute-solute as well as the solute-solvent, and those are essential factors to elucidate UV photochemical processes of the amino acids in aqueous solution.

Action spectroscopy of a protonated peptide in the ultraviolet range

“…The absorption tail for alkyl sulfides extends slightly below 230 nm (5.4 eV). 39,60 Our data show extensive fragmentations of the S-CH3 and CH2-S bonds already at 5.2 eV, see figure 4, which decrease with increasing photon energy. A feature is observed in figure 4 at 6.8 eV (182.3 nm), which could correspond to the second n S σ * transition observed for isolated alkyl sulfides 60,61 or to the peptide π 2 π 3 * transition, since this feature match very well the maximum of the a-ion yield, which has been assigned to the NV1 transition (see below).…”

“…Previous studies have focused mostly on the near UV range with some excursion in the VUV using laser lines. 9,21,36,[38][39][40][41][42][43][44][45][46][47] Our measurements lead us to propose a tentative rationalization of the photochemistry of peptides, summarize in figure 5. The observed fragmentation yields arise from the convolution of the photoabsorption cross section of the precursor with the fragmentation efficiency and relaxation pathways of the particular excited state populated.…”

“…The ion yields associated with this loss shows a peak at 7.1 eV, which match the transition of the ππ * feature observed for Arg in solution. 39 However, the involvement of Leu in this loss cannot be ruled out as it could contribute to the ion yield at higher photon energy.…”

Electron dynamics in complex environments with real-time time dependent density functional theory in a QM-MM framework

“…Formamide represents the simplest model for the peptidic bond. The interest in the application of UV spectroscopy to the structural, dynamical, and electronic characterization of the peptidic linkage in proteins, has motivated a lot of experimental [27][28][29][30][31] and theoretical [32][33][34][35][36][37][38][39][40][41] research on the excitations and absorption of formamide, acetamide, and other related molecules. The UV spectrum of formamide is characterized by an intense band at 7.4 eV involving non-bonding and antibonding π orbitals (denoted π nb → π * ), 27,30 which experiences a red-shift of 0.5 eV in aqueous solution.…”

Far- and deep-ultraviolet surface plasmon resonance sensors working in aqueous solutions using aluminum thin films

“…The plasma frequencies of Au and Ag are 1.37 × 10 16  s −1 and 1.36 × 10 16  s −1 , respectively 10, 11 , and Au and Ag thin films are widely utilized for visible-SPR sensors. Although many target molecules of SPR sensors such as DNA and proteins have no absorbance in the visible region, they have strong absorption and high refractive indices in the FUV-DUV region 12, 13 . In addition, the penetration depth of the evanescent wave in the FUV-DUV region is less than 50 nm, which is much shorter than that in the visible region.…”