Tautomers of Gas-Phase Erythrose and Their Interconversion Reactions: Insights from High-Level ab Initio Study

Abstract

D-Erythrose is a C4 monosaccharide with a biological and potential astrobiological relevance. We have investigated low-energy structures of d-erythrose and their interconversion in the gas phase with the highest-level calculations up-to-date. We have identified a number of structurally distinct furanose and open-chain isomers and predicted α ↔ α and β ↔ β furanose interconversion pathways involving the O-H rotamers. We have estimated relative Gibbs free energies of the erythrose species based on the CCSD(T)/aug-cc-pVTZ electronic energies and MP2/aug-cc-pVTZ vibrational frequencies. By using natural bond orbital theory we have also quantified a stabilization of erythrose conformers and interconversion transition states by intramolecular H-bonds.

Anomerization reaction of bare and microhydrated d‐erythrose via explicitly correlated coupled cluster approach. Two water molecules are optimal

“…To be consistent with the nomenclature used before, the α‐ and β‐furanose ( fur ) anomers of bare erythrose are indicated as “ a ” and “ b ,” and clockwise and counterclockwise arrangements of their intramolecular H‐bonds are abbreviated as “ c ” and “ cc ,” respectively. In addition, the standard notation for envelope (E) and twist (T) furanose ring puckerings is used; for the low‐energy erythrose conformers considered, we also preserve the original “ n ” numbers in front of their designations to avoid confusion (cf., Table ).…”

“… The conformers were found in Ref. (the original nomenclature is preserved); the α‐anomer 1fur‐ 2 E‐a‐cc corresponds to the global minimum on the potential energy surface of d ‐erythrose.…”

“…Figure depicts stationary points of the anomerization reaction of bare d ‐erythrose (a complete path). This reaction path leads from the α‐furanose anomer corresponding to the global minimum on the PES of erythrose, and spectroscopically observed species, to the low‐lying β‐furanose anomer found previously by us . All the stationary points have been characterized at both the M06‐2X/6‐311++G(d,p) and MP2/aug‐cc‐pVTZ levels.…”

“…On the theoretical side, the erythrose tautomers were examined using density functional theory and ab initio schemes . The recent ab initio calculations revealed that the FTMW detected α‐erythrofuranose conformer resided in the global minimum on the potential energy surface (PES) of erythrose.…”

“…Among the methods used, the G4 performed best against the CCSD(T)-F12 reference at estimating the ring-opening barrier heights for both the hydrated and bare erythrose conformers. Our results for the hydrated species are most relevant to an experimental study of the anomerization reaction of D-erythrose to be carried out in microsolvation environment.To be consistent with the nomenclature used before, [43] the aand b-furanose (fur) anomers of bare erythrose are indicated Scheme 1. Ring-opening for a-D-erythrose.…”