Hi all,
I am trying to synthesize chitosan-tpp nanoparticles. I want to show nanoparticle formation via FT-IR. Some peaks shifts are attributed to nanoparticle formation for cs-tpp polymer.
For example amide bond in chitosan is between 1640 cm-1 and 1650 cm-1 in literature. I performed FT-IR experiment and found mine is at 1648 cm-1 for pure chitosan. This value is 1653 cm-1 for cs-tpp crosslinked polymer. Peak shift are very low for this amide bond and other indicator bonds (about 5-6 cm-1 for each bond)
First, I suspected that there was a measurement error. I performed FT-IR experiments thrice and found exactly same results.
Here is my question:
Can these low peak shifts be attributed to nanoparticle formation? Or these peak shifts are not low as I think?
I will be waiting your answers. Thank you all.
Hello dear, the shifts are so many low to infer formation of a compounds. The ideal method for determining formation of nanoparticles is TEM or DLS. Best regards
Dear A. Murillo,
I already performed DLS and SEM and everything seems fine, I just wanted the check with FT-IR but now I am more confused.
A few comments about the systems under your consideration:
1. Chitosan - if fully deacetylated should contain AMINE groups ONLY. In such a purest chitosan NH2-groups absorb at about 1600 cm-1.
2. If the DA degree does not exceed 90-95% (a common case for well deacetylated chitosan) - then principally you should observe very weak peaks of Amide groups (of initial chitin) - as shoulders of NH2 deformation vibrations (at 1600 cm-1).
3. The above means that - if you clearly see the AMIDE peaks - the sample of CH you are working with - has a rather low DA (not higher than 85%).
4. Of 2 AMIDE peaks (A-I which you observe around 1648 should be stronger than A-II and the latter may not be seen at all).
5. Chitosan is a rather hydrophilic compound. Water absorbs at ca. 1645cm-1 - that is the A-I peak of Amide should be strongly overlapped by water absorbance.
THUS basing on the facts described - in my opinion the bands which you observe in the 1653-1648 cm-1 region - should be attributed mostly to absorbance of water.
ALSO - it is well known that the band-shifts for A-i, A-II of Amide and NH2 of Amine as well as def. OH of water n the region of 1650- 1550 cm-1 caused by changes in H-bonding are small - just as you observe - i.e. 5-7 cm-1. BUT by contrast to N-H and O-H stretching (3600-3200 cm-1) - for N-H and O-H deformational vibrations the shift to higher frequencies corresponds - to strengthening of H-bonds.
OK. All-All-All - the above-said means - that In MY View - the effects which you observed - should be related to shifts of H2O peak (neither it Amide nor to Amine peaks)
Regards, Leonid
Dear Leonid V Vladimirov, thank you for your answer.
Now I start to think that problem is my sample. First, I centrifuged the cs-tpp solution, then I collected chitosan pellet and I freeze-dried it. Then I performed FTIR with this freeze dried sample. Do you think it is a correct way to characterize the nanogel?
Well, another question: does neat TPP absorb in the 1645 region ? If it does not - then 1645 cm-1 - should be attributed to water def.; or to A-I of chitin - i.e., of poorly deacetylated chitosan.
Dear Leonid V Vladimirov,
Neat TPP is in powder form, and it does not give peak at 1645 region. Do you think ATR method is appropriate for chitosan-tpp pellet?
The idea to use KBr method for your measurements is NOT GOOD - because KBr itself will absorb much water - which will greatly contribute to total absorbance at 1645 cm-1
Thus , in accord with all the information - which I gave in previous messages - it seems that the IR-methods - can not give you clear information on complex formation. I advise you - try some other analytical method.
Leonid
Dear Azeez Shan and Leoniv V Vladimirov
I think it is better to use NMR in this case. Thank you for your replies.
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