Two different molecular conformations found in chitosan type II salts

Fourth 3D Structure of the Chitosan Molecule: Conformation of Chitosan in Its Salts with Medical Organic Acids Having a Phenyl Group

“…A similar situation has been found in all type II salts. 8,10,11) These facts indicate that the chitosan conformation in the type III salt is the fourth 3D structure of chitosan next to the relaxed 2 W 1 7,20) and 4 W 1 12) helical conformation of type II chitosan salts. Theˆber repeat of the presented type III salt, 2.550 nm, and a 5th-order meridional re‰ection suggest that the chain conformation of the salt was a 5-fold helix.…”

“…11) We have recently found another conformation of chitosan in a type II salt of chitosan-HI, having the 4 W 1 helix with a disaccharide as an asymmetric unit. 12) Chitosan and partially N-acetylated chitosan are expected to be applied as drug carriers in drug delivery system (DDS). 13,14) The ascorbic acid salt of chitosan has recently received strong attention, since ascorbic acid is known to enhance such chitosan functions as the adsorption of transition metals, inhibition of fat digestion, and prevention of dental periodontitis.…”

Contact time- and pH-dependent adhesion and cohesion of low molecular weight chitosan coated surfaces

“…In addition, hysteresis was observed between approach (which is purely repulsive) and separation force curves (adhesive) even after very short contact time (t ct < 5 s). These results indicate that a rearrangement and/or possible structural change -possibly from the relaxed two-fold helix to the extended two-fold helix (Lertworasirikul, Tsue, Noguchi, Okuyama, & Ogawa, 2003;Okuyama, Noguchi, Miyazawa, Yui, & Ogawa, 1997) -of LMW chitosan molecules have occurred due to the external force in a confined space which caused the LMW chitosan layer to be more compact and adhesive to the opposing mica substrate. The adhesions of LMW chitosan to mica were ∼40% less than those of previous studied higher molecular weight chitosan (∼150 kDa) to mica (Lee, Lim, et al, 2013).…”

“…Imposing external force to contact two coated surfaces, the hydrogen bond, which is short ranged and attractive, can be established whereas the electrostatic interaction is still repulsive. So, it takes time to connect enough number of hydrogen bonds by changing its solution secondary structure from relaxed two-fold helix to extend two-fold helix, in order to overcome the electrostatic repulsion (Lertworasirikul et al, 2003;Okuyama et al, 1997). This explains the existence of t crit at pH 3.0 and when t ct < t crit , only a small fraction of the amine groups of LMW chitosan molecules may participate in hydrogen bonds.…”

The Molecular Structure and Conformational Dynamics of Chitosan Polymers: An Integrated Perspective from Experiments and Computational Simulations

“…This pattern suggests a two-fold helix even though the corresponding asymmetric unit is rather d i s t i n c t f r o m t h a t o f t y p e I w h e r e t h e asymmetric unit has only one glucosamine residue. The main difference between the type I and type II conformations is that the latter is almost four times longer than chitosan, and originated the designation of relaxed two-fold helix ( Figure 2E) [92,[134][135][136]. A type II salt variant, called Type IIa, has a similar fiber repeat (4.05 nm), but with an asymmetric unit consisting of a glucosamine dimer in a 4/1 helical symmetry.…”