Deprotonation and acidity characterization of biomass sugars: a first-principles study

Abstract

Deprotonation of biomass sugars is investigated by high-level electronic structure calculations, considering α- and β-anomers as well as all O and C sites. Structural alterations are generally focused on the deprotonated sites. Proton migration or/and ring opening occurs in 15 of 42 deprotonation processes and more frequently for D-fructofuranose than D-glucopyranose conformers. Other regular patterns of structural changes are observed; e.g., deprotonation at anomeric sites often cause larger structural perturbations, strong H-bonds of O(i)H(i)•••C(i) type are constructed by deprotonation at C sites. Then the enthalpy changes and Gibbs free energies for deprotonation at the various O/C sites are calculated by an economical and sufficiently testified composite method, which are consistent with previous results available. Deprotonation of anomeric groups is always preferred, while not the case for C sites. D-fructofuranose is more acidic than D-glucopyranose, whether for O or C sites. Although O sites are known to deprotonate, some C sites are found to be comparable, or even preferential. Whether for O or C sites, deprotonation is highly regioselective and this clearly indicates the potential utilization for selective conversion of biomass sugars.

Influence of H‐bonds on acidity of deoxy‐hexose sugars

“…[56] Yang et al reported the calculated acidity values (ΔH acid ) for the conjugated base of αand ß-anomers of D-glucopyranose in the range 341-353 and 342-364 kcal.mol −1 and for the conjugated base of αand ß-anomers of D-fructofuranose in different sites in the range 335-355 and 330-385 kcal.mol −1. [57] The acidity value for the conjugated base of αand ßanomers of D-glucopyranose at different sites calculated in the range 341-353 and 342-364 kcal.mol −1 by Salpin et al [58] Our caclculated acidity value for CH 3 -pentose in the range 346-369 kcal.mol −1 and for aldo-pentose in the range 343-355 kcal.mol −1 are in line with available works. [57,58] Moreover, the acidity of ethanol and 2-propanol are 378.3 and 375.1 (kcal.mol −1 ) in the gas phase, respectively.…”

“…[57] The acidity value for the conjugated base of αand ßanomers of D-glucopyranose at different sites calculated in the range 341-353 and 342-364 kcal.mol −1 by Salpin et al [58] Our caclculated acidity value for CH 3 -pentose in the range 346-369 kcal.mol −1 and for aldo-pentose in the range 343-355 kcal.mol −1 are in line with available works. [57,58] Moreover, the acidity of ethanol and 2-propanol are 378.3 and 375.1 (kcal.mol −1 ) in the gas phase, respectively. [59] In comparison with these alcohols, the acidity values of methyl-pentose and aldo-pentose sugars are 346-369 and 343-355 kcal.mol −1 ( Table 2); these results suggest the role of H-bonds in increasing the acidity of deoxy-hexose sugars.…”

“…[25,26] It should be noted that the C-H … O bonds are weaker than the O-H … O bonds. [57] As seen in bonds in DNA and RNA and guanosine. [30,60] As seen in Table 4, the O-H … O distances in the aldo-pentose sugars and their conjugate bases are within 1.53-2.16 Å.…”

Characterization of Protonated Model Disaccharides from Tandem Mass Spectrometry and Chemical Dynamics Simulations

“…[16] Consequently,t he number of deprotonated forms to be considered in the negative modei st oo high to perform chemical dynamics simulations, so we decided to work in the positive-ion mode. However,i nt his case chemical derivatization was mandatory for two reasons.…”

Computational insight into networking H‐bonds in open and cyclic forms of glucose

“…Comparing the predicted acidity values of cyclic glucose and O‐Glc with other sugars is given in Table 1. Yang et al [ 64 ] reported that the calculated acidity values for α‐ and ß‐anomers of D‐glucopyranose range 341–371 and 342–364 kcal.mol −1 , respectively. Salpin et al [ 63 ] predicated the acidity value for α‐ and ß‐anomers of D‐glucopyranose to be in 342–351 and 344–352 kcal.mol −1 range, respectively.…”