Spectroscopic studies on the chiral recognition of ketoprofen enantiomers using different selectors / Asma Omar Obaid

Asma , Omar Obaid (2022) Spectroscopic studies on the chiral recognition of ketoprofen enantiomers using different selectors / Asma Omar Obaid. PhD thesis, Universiti Malaya.

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Abstract

Ketoprofen is a chiral drug marketed as a racemic mixture for medicinal use. The physiological reactions of R-ketoprofen and S-ketoprofen within the human body differ considerably; therefore, enantiorecognition is a necessary process that can be done using chiral selectors that interact differently with only one enantiomer. In this study, the potential of different chiral selectors for recognizing ketoprofen enantiomers was investigated. Gold and silver nanoparticles (AuNPs and AgNPs) were synthesized and characterized then used for recognition of ketoprofen. AgNPs with ketoprofen enantiomers showed significant differences in the appearance and spectra obtained, while no differences were obtained between R- and S-ketoprofen when using AuNPs. Then beta-cyclodextrin (β-CD) and hydroxypropyl-beta-cyclodextrin (HPβ-CD) inclusion complexes with R- and S-ketoprofen were investigated as selectors for ketoprofen enantiomers. The different relative intensities and characteristic band shifts of the two enantiomers from Raman spectra suggest different interactions when complexed with β- CD/HPβ-CD. Raman experiments revealed a noticeable diminishing of the C=C vibration and ring deformation, which indicate the embedding of ketoprofen inside the β-CD cavity. Both enantiomers showed a stoichiometry ratio of a 1:1 inclusion complex with β-CD and HPβ-CD. The binding constant of R-ketoprofen (2750 M-1) and (1038 M-1) is higher than S-ketoprofen (1299 M-1) and (799 M-1) with β-CD and HPβ-CD, respectively. These values indicate that β-CD forms inclusion complexes more preferentially with Rketoprofen than S-ketoprofen. This investigation was followed by qualitative surface enhanced Raman spectroscopy (SERS) studies of β-CD/HPβ-CD inclusion complexes with ketoprofen enantiomers using AgNPs and AuNPs as SERS substrate. In the second part, the potential of L-cysteine capped with AgNPs (L-Cys-AgNPs) or AuNPs (L-Cys AuNPs) as chiral selectors for recognition of ketoprofen enantiomers have been studied. Colorimetric sensors represent easy, inexpensive, simple and very effective visual chiral recognition methods for the recognition of ketoprofen enantiomers. Rapid aggregation of NPs occurred in the addition of R-ketoprofen, resulting in visible colour changes. The chiral assay described in this work is easily distinguished with the naked eyes or using a UV-Vis spectrometer. Both L-Cys-AgNPs and L-Cys-AuNPs sensors revealed a good linear response to ketoprofen enantiomers in the concentration range of 8.33–33.33 μM. The methods excel by their simplicity, low cost and good availability of materials. Both qualitative and quantitative analysis were performed to test the capability of these colorimetric sensors.

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