I am attempting to exchange nanoparticle's surface ligand (oleic acid) with another ligand (i.e., citric acid). However, the product yield is too small to get it in powder form and not enough to be measured by FTIR. In that case which tool(s) would be suitable to get the information of exchanged ligand.
N.B.: product is stored as colloidal form.
1H-NMR can do that quite easily, see the attached link for a paper that shows exactly the situation you describe.
Specifically, the alkene and α-alkene protons are very indicative by both resolution and chemical shift of being in either a bound or free state. Use CDCl3 rather than Toluene-D8 for enhanced resolution of this effect. Additionally, the protons both α and β to the carboxylic acid carbon show distinct broadening and chemical shift differences when bound vs free.
http://pubs.acs.org/doi/abs/10.1021/jacs.7b00158
Hi Sandip,
I agree with Chase, proton-NMR can help you to quantify the ligand exchange. You can look for the CH protons in oleic acid to detect the exchange. Citric acid does not have CH protons.
I hope this helps.
Sarang
Dear Sandip, did you tried ATR FTIR? Small amount of solution (drop) can be evaporated from crystal surface and this can be enough to get spectra. Anyway, 1H-NMR is good and sensitive technique, I agree.
Do liquid state IR or ATR FTIR or KBr palate ftir with small drop of the solution. This is the best way to find out NPs surface modification. Or,
Centrifuge the colloidal solution at high speed, to get the ppt, then do IR.
But in every case do sm blanck fire also like, unmodifiedNPs and pure ligand. The change in ftir spectra of the modified NPs with respect to the blancks give you the ans.
what is the continuous phase? Depending on surface ligand particles should be stable in different media. And what about determining oleic acid content before and after modification?
Hello @Titus,
Thanks for your concern to my problem.
FYI, the resultant NPs (supposed to be modified by citric acid ligand) soluble in water (i.e., hydrophilic phase). Uh determining oleic acid content before modification is possible by FTIR, since I have enough powder sample. however, it is quite difficult for me to measure either oleic acid content or citric acid since the yield is too low.
your suggestion(s) in this regards will be appreciated.
Thank you.
not clear about your experimental set-up. Are nanoparticles first in oil phase then in aqueous phase? Does oleic acid stays in oil phase or is it transferred into alkaline water?
Hello @Chase and Sarang,
Thank you for your concern to my problem. Once I tried using p-NMR to solve this problem. However, I failed to extract any data out of it. Let me tell you what was the problem I have encountered. During the run, the p-NMR could not lock the magnetic field of my sample. I chose only oleic acid dispersed in CdCl3 as a control, observed some signal. However, when I loaded the sample (OA-capped NPs dispersed in CdCl3), NMR could not even lock the sample. FYI, Nanoparticle is a complex of NaGdF4:Yb, Er. Gadolinium (Gd) and Erbium (Er) are magnetic in nature. In this scenario, I am speculating that magnetic characteristic of some ions (Gd, Er) may be interfering somehow, which lead to P-NMR can not be able to lock the NPs solutions.
If you have any firm explanations or any suggestion for sample preparation, would be happy to follow.
I am not too sure but I think measuring the zeta potential might help. Oleic acid has only one carboxyl group through which it will bind to the metal NPs and thus, the overall surface charge of the system will have a lower negative potential. On the other hand, citric acid has three carboxyl groups of which many will remain free on the surface even after binding with the metal NPs. They might result in a higher negative zeta potential value for your system.
Thanks, @Sonam,
We did that already, As a result, the zeta potential value shifted from near negative ~-5 mV (for Oleic acid capped NPs) to a far negative value ~ -30 to -40 mV (for Citric acid modified NPs). But guess what, it is not a solid evidence.
ATR-FTIR.The method is very simple and requires a small drop of your sample.
Thanks, @Asma,
I do appreciate your opinion, But, unfortunately, we don't have the liquid sample holder in our FTIR setup. Is there any other you wold like to recommend by which can the liquid sample be measured.
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