In a handout the following is stated:
Amylose is insoluble in water, therefore a good storage compound e.g. in stroma of chloroplasts
This is with regard to the chemical structure of the molecule.
However it has left me wondering, what is it intrinsically about the structure of a molecule that makes it soluble/insoluble in water?
My thoughts at this stage are perhaps to do with whether the molecule is hydrophobic, and if that is the case - how is amylose hydrophobic?
The availibity of -OH groups for hydrogen bonding with polar water molecules is reduced in amylose due to its coiled nature (resulting in part by H-bonds between the glucose monomers). Amylopectin is even less soluble due to the additional 1-6 glycosidic bonds on the branch chains, further reducing its H bonding potential and therefore reducing solubility in water.
There are a couple of other questions that address this point indirectly: here and here.
In my answers to the first of these questions I mention that amylose is semi-crystalline because of its regular extended structure. I imagine that the semi-crystalline state is more thermodynamically favourable than the solution state, but suspect that a rigorous chemical answer might be quite complex.
Depending on molecular weight of amylose and because of its helical structure formed by two macromolecules makes it partly soluble in water.
Heating amylose solution leads to formation of colloidal suspension of soluble fraction and remining insoluble higher molecular weight fraction of amylose does not dissolve. On cooling this suspension, certain portion of polysaccharide precipitates. This is because of the glycosidic linkages between these glucose molecules.
