Dear Sandeep Hembram ,

First of all the answer to your question depends on which and what type of chitosan you talk about.

Still in general: It is clear that the amino group in chitosan has a pKa value round 6.5, which leads to significant protonation in neutral solution, which will increase with increasing the acidity (thus decreasing pH). This makes chitosan water-soluble and capable to binding to negatively charged surfaces, see for excellent examples:

Dong Woog Lee, et al. (2013). Strong adhesion and cohesion of chitosan in aqueous solutions. Langmuir. 29 (46): 14222–14229.

http://scholar.google.nl/scholar_url?url=https%3A%2F%2Fcyberleninka.org%2Farticle%2Fn%2F325386.pdf&hl=nl&sa=T&oi=ggp&ct=res&cd=1&d=17037662882552067896&ei=GMGxXL-AIs6PmwG-hpDYBA&scisig=AAGBfm2CK4ARhHUsW_dgIxppjQPPMM9YXw&nossl=1&ws=1163x605&at=Strong%20Adhesion%20and%20Cohesion%20of%20Chitosan%20in%20Aqueous%20Solutions

Chanoong Lim, et al. (2015). Contact time- and pH-dependent adhesion and cohesion of low molecular weight chitosan coated surfaces". Carbohydrate Polymers. 117 (6): 887–894.

https://escholarship.org/content/qt36d7m7fh/qt36d7m7fh.pdf

The pKa of the hydroxyl group you want to create will be higher (not sure but I guess above 14-15), so at neutral pH it will behave differently. Whether it will be more waterphobic (or better put more hydrophobic) depends on what you are looking at. In principle you know from basic chemistry that both NH- and OH-groups have the ability to form hydrogen bonds so both capable to give good solubility in aqueous solutions.

How they react under different pH conditions and so on: have a good look at the advised papers (and references mentioned in these papers).

Hope this will help you any further.

Dear Sandeep Hembram,

Our colleague Rob Keller covered the whole topic. I would like to add that solubility of chitosan depends not only on the amount of amino groups but also on the molecular weight of the polymer. The ratio between acetyl and amine groups is what differentiates chitosan from chitin. In cellulose the hydroxyls are present instead of the acetyl and amine groups. So if you replace most -NH2 groups, your sample will tend to behave like cellulose.

I would also suggest the following references:

Chapter Solubility and Solution Behaviour of Chitin and Chitosan

Article A Review on Chitin and Chitosan Polymers: Structure, Chemist...

I hope this helps you.

Regards

you can modify the amino groups by Actylation which change the amino group to CH2CH3 group