Following in Emil Fischer's Footsteps: A Site-Selective Probe of Glucose Acid-Base Chemistry.

Sebastian Malerz,Wilson Quevedo,Claudia Goy,Tillmann Buttersack,Lukáš Tomaník,Florian Trinter,Karen Mudryk,Iain Wilkinson,Uwe Hergenhahn,Stephan Thürmer,Robert Seidel,Bernd Winter,Dominik Stemer,Petr Slavíček

doi:10.1021/acs.jpca.1c04695

Abstract

Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (pKa) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first pKa reveal a change in glucose’s lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid–base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.

Highlights

Glucose is a ubiquitous monosaccharide of major significance in living organisms.[1,2] It is the precursor of many oligo- and polysaccharides that mediate cell−cell communication,[3] build up the scaffold of cells,[4−6] or serve as energy storage units.[7−10] It is a natural energy source synthesized via the conversion of solar energy into chemical energy by plants during photosynthesis.[11,12] it plays a central role in the metabolic pathways that govern the flow of energy and matter that sustain life.[13]
We have investigated the pH-dependent molecular structure changes in glucose by performing LJ-photoelectron spectroscopy (PES) experiments over the valence and C 1s spectral regions
With the support of electronic structure calculations, we show how aqueous-phase PES data can be applied to determine the first acid dissociation constant and, more importantly, to unambiguously identify the deprotonation site

Summary

Introduction

Glucose is a ubiquitous monosaccharide of major significance in living organisms.[1,2] It is the precursor of many oligo- and polysaccharides that mediate cell−cell communication,[3] build up the scaffold of cells,[4−6] or serve as energy storage units.[7−10] It is a natural energy source synthesized via the conversion of solar energy into chemical energy by plants during photosynthesis.[11,12] it plays a central role in the metabolic pathways that govern the flow of energy and matter that sustain life.[13]. There remains much to be learned about the acid−base properties of this fundamental molecule. This is perhaps surprising because the structure of glucose has been intensively studied since the turn of the 19th century, when Emil Fischer (Nobel Prize in Chemistry 1902) reported the chemical synthesis of D-(+)-glucose and demonstrated its stereoisomeric forms.[16,17] But it is only with advancing experimental and theoretical methods,[18−21] in particular, photoelectron spectroscopy (PES) from an aqueous solution,[22−25] that previously inaccessible molecular structural details can be resolved

Methods

Results

Conclusion