Speaker
Description
The physicochemical properties of life-essential molecules such as carbohydrates, amino acids, and DNA arise from a series of complex intramolecular and intermolecular interactions within aqueous cellular environments. Knowledge of the aqueous-phase electronic structure of these important biomolecules is indispensable to understand structure–function relationships, chemical activity, and higher-level biological function. The advent of liquid-jet photoelectron spectroscopy (LJ-PES) has enabled these studies, due to the sensitivity and site-selectivity of the technique to local chemical environments. Herein, we highlight our recent efforts to expand the utility of LJ-PES to the study of acid–base and chiral properties of biomolecules by focusing first on the model systems glucose and alanine.
Glucose is a ubiquitous monosaccharide in living organisms. Its fundamental role as a primary energy source, structural unit, and facilitator of cellular communication is inherently related to its aqueous-phase acid–base chemistry. By applying core-level (C 1s) LJ-PES, we probed pH-dependent electronic-structure changes at specific deprotonation sites in the molecule. We also investigated the occurrence of charge sharing upon deprotonation of glucose and determined the acid dissociation constant (pKa) while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Our work demonstrates the utility of photoemission titration as a valuable tool for determining pKas of other polyprotic acids that cannot be readily measured using traditional methods.[1]
Chirality is omnipresent in biology and plays a significant role in determining the intermolecular interaction propensity of different species, both due to steric and electronic considerations. Nevertheless, the capacity to site-selectively probe chirality of biologically relevant molecules in aqueous solution has proven elusive. Leveraging photoemission circular dichroism (PECD), the forward-backward asymmetry in photoemission from chiral molecules stimulated with circularly polarized light was clearly observed in the chiral liquid fenchone. We then deconvoluted the site-selective chiral behavior of aqueous-phase alanine, one of the most basic amino acids. Despite contrasting energy windows for maximizing PECD intensity and minimizing inelastic scattering of photoelectrons in the liquid-phase,[2] we report encouraging dichroic trends in the photoemission intensity asymmetry observed. Refinement of liquid-phase PECD promises to enable the measurement and monitoring of site-selective chirality in more complex aqueous-phase biomolecules.
Our findings highlight the capacity of LJ-PES as a general technique to site-selectively probe acid–base and chiral properties of biomolecules. Although both glucose and alanine are relatively simple species, we expect the methods demonstrated here to be applicable to larger biomolecules as well.
[1] S. Malerz, K. Mudryk, L. Tomaník, D. Stemer, U. Hergenhahn, T. Buttersack, F. Trinter, R. Seidel, W. Quevedo, C. Goy, I. Wilkinson, S. Thürmer, P. Slavíček, and B. Winter.
J. Phys. Chem. A, 2021, 125, 32, 6881−6892.
[2] S. Malerz, F. Trinter, .U. Hergenhahn, A. Ghrist, H. Ali, C. Nicolas, C.-M. Saak, C. Richter, S. Hartweg, L. Nahon, C. Lee, C. Goy, D.M. Neumark, G. Meijer, I. Wilkinson, B. Winter and S. Thürmer.
Phys. Chem. Chem. Phys., 2021, 23, 8246-8260.
| Abstract Number (department-wise) | MP 19 |
|---|---|
| Department | MP (Meijer) |
