I am trying to develop Curcumin bioconjugates by esterifying -OH moieties of Curcumin aromatic rings.
By performing UV spectrophotometric analysis of the conjugate (red curve) in a mixture DMSO/H2O, there is an uplifting of the peak in the UV region (between 250-270 nm) and a lowering of the Cur (1,6-heptadiene-3,5-dione) conjugated system peculiar peak at 420-440 nm in the VIS region.
Compared to the behaviour of bare Cur solubilized in pure DMSO (blue curve), where its UV profile is opposed (lower peak in the UV region and a higher peak at ≃ 430nm).
Could the uplifting in the UV region be attributable to an auxochrome effect of phenolic -OH after esterification ? Note: it is noteworthy that the polymer scaffold chosen for the esterification is not UV active, according to the absence of any insaturation within its structure. Thanks in advance to who will give a hand.
I dont know if Cur properties can remain intact after exposure to the esterification process:
1) I guess that the OH groups can be involved in the UV properties of the molecule with enol-keto tautoremism. So, if you convert one alchol to esther this equilibrium cannot exist, changing the absorption/emission properties of the dye (the same happens with others dyes)
2)This molecule could react also through intramolecular michael adition, yielding another molecule different than the Cur.
Furthermore, you should compare the UV-VIS spectra using the same solvent to be sure that you are assigning the sorption bands properly (pure DMSO or the H2O/DMSO mixture for both compounds)
FTIR examination to confirm the esterification reaction and the disappearance of hydroxyl groups .
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