Proposal of a New Hydrogen‐Bonding Form to Maintain Curdlan Triple Helix

Publisher Website
Google Scholar
Abstract
Curdlan and other β‐1,3‐D‐glucans form right‐handed triple helices, and it has been believed that the intermolecular H‐bond is present at the center of the helix to maintain the structure. In this H‐bond model, three secondary OH groups form an inequilateral hexagonal shape perpendicular to the helix axis. This hexagonal form seems to be characteristic for β‐1,3‐D‐glucans and is widely accepted. We carried out MOPAC and ab initio calculations for the curdlan helix, and we propose a new intermolecular H‐bonding model. In our model, the H‐bonds are formed between the O(2)‐atoms on different x‐y planes along the curdlan helix, hence the H‐bonds are not perpendicular to the helix axis. The new H‐bonds are connected along the helix, traversing three curdlan chains to make a left‐handed helix. Therefore, the H‐bonding array leads to a reverse helix of the main chain. According to our MOPAC calculation, this model is more stable than the previous one. We believe that the continuous H‐bonding array is stabilized by cooperative phenomena in the polymeric system.