For example: If you consider agarose, by seeing the structure is it possible to predict whether it is charged or neutral when added in water? I have attached the image of structure of agarose. This is just a doubt. If anyone could explain with any other polymer too it would be okay.
It will depend on how acidic or basic the functional groups are.
In your example of agarose, it has several hydroxyl groups. Because the hydroxyls are weakly acidic, you would expect that some of the protons would dissociate from the polymer when added to water, giving the polymer a negative charge.
Dear Mithra. Aliphatic alcohols generally have a very low dissociation constant and thus high pKa of approx 15-17, so solutions of alcohols are theoretically acidic as indicated by Mark, but the effect is so small that the pH of alcohol solutions should be very close to neutral. Agarose is thus considered to be neutral because it does not contain any groups that are more acidic (eg carboxylic acid groups) or basic amines (or other basic groups). Have you made a solution of a grade that has a relatively low gel temperature and measured the pH?
Dear Mithra,
I'm agree with the other answers...the agarose, such as all sugar should be neutral becouse the dissociation oh the alchol is very limiteted in water.
Relating an example, my experience is on dendrimers of poly propilene imine (PPI dendrimers). The amine groups (tertiary and primary) confer a positive charge to the dendrimers. The complete substitusion of the primary amine groups with maltose or maltotrionse units produce an external shell of sugar which changes the charge of the macromolecule, from positive to neutral. Hovewer, the partial (about 50%) substitution produce an imperfect glyco-shell (we call open shell) and the charge of the dendrimers remain positive.
to modify the charge of a macromolecule is important that the ionizable groups are manifold. in the case of dendrimers, plays an important role also the arrangement of these groups ... molecules of maltose (neutral charge) overshadow the effect of numerous amino groups (positive charge) because shield amines and do not allow the interaction with the 'water ... when the shell is imperfect water is able to interact with the amine and the charge remains positive.
a common example of a polysaccharide with no neutral chargeis hyaluronic acid ... I have also worked with this macromolecule ... the presence of a COOH cruppo for each repeat unit gives the macromolecule a character slightly acid (pH = from 5.5. to 7.5).
some of my work for references
glycodendriemrsAdd your answer
Macromolecules 2013(46):3215−3227, DOI: 10.1021/ma400352m
Polymer Chemistry 2012(3):3239, DOI: 10.1039/c2py20649h
hyaluronic acid
Journal of Materials Chemistry B 2014; DOI: 10.1039/c3tb21824d
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