Computational insight into networking H-bonds in open and cyclic forms of galactose

• Published in: Journal of molecular structure 2022-05, Vol.1255, p.132432, Article 132432
• Main Authors: Kotena, Zahrabatoul Mosapour, Fattahi, Alireza
• Format: Article
• Language: English
• Subjects: AIM; Bifurcated; Galactose; H-bonds; NBO; Open and cyclic forms; Trifurcated
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2022.132432

•A cooperative network of trifurcated and bifurcated in addition to normal H-bonds were found in the conjugate base of O-Gal. In contrast, bifurcated and normal H-bond were observed in the conjugate base of cyclic galactose and neutral form of O-Gal.•Based on acidity values (ΔHacid), galactose in open form (O-Gal) is more acidic than its cyclic form (Gal).•The acidity value for galactose in open and cyclic forms exhibit significantly lower values (i.e., stronger acid) compared to the reported acidity value for α-/ß- anomers of D-glucopyranose and simple alcohols because their conjugate bases are more stabilized through intramolecular H-bonds like trifurcated and bifurcated H-bonds. In this work, the intramolecular H-bonds in galactose were studied using DFT at the B3LYP/6–311++G (d,p) levels of theory, atoms in molecules (AIM), and natural bond orbital (NBO). AIM and NBO analysis revealed a cooperative network of trifurcated, bifurcated, and normal H-bonds for the conjugate bases of open galactse (O-Gal). While for the conjugate base of the cyclic form of galactose, we identified bifurcated and normal H-bonds, which may highlight a crucial feature of the biological activity of a whole class of natural sugars. The O-H…O bonds are categorized as mostly electrostatic, strong H-bonds and more favorable, whereas for multiple interactions involving C=O...H, C-H…O and C-H…H-C (dihydrogen bonding) interactions are categorized as weak H-bonds bonds in the conjugate base of considered sugar. The theoretical results indicated that based on acidity values (ΔHacid), galactose in open form (O-Gal) is more acidic than cyclic form (Gal).The acidity value for galactose in open and cyclic forms exhibit significantly lower values (i.e., stronger acid) compared to the reported acidity value for α-/ß- anomers of D-glucopyranose and simple alcohols because their conjugate bases are more stabilized through intramolecular H-bonds like trifurcated and bifurcated, which are studied in details using AIM and NBO analysis.