Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
A study on the interaction of nile blue with Uracils: A spectroscopic and computational approach
Graphical abstract
Introduction
Nile blue (NB) has received considerable attention towards biological interaction over other fluorescent based molecules [[1], [2], [3], [4], [5], [6]], due its superior advantages [7]. Nile blue is an interesting molecule (shown in Scheme 1) and belongs to the class of cationic oxazine dyes. The fascinating molecule employed as promising materials for various optical and photonic devices [[8], [9], [10]]. NB is a potent photodynamic therapy agent owing to its absorption of light in the 600–650 nm range. The cationic dye (NB) show high binding affinity towards DNAs and react efficiently with tumor cells than normal tissues to retard the tumor growth [11,12].
NB emits light in the red region of spectrum and employed as an analytical reagent to determine the antioxidant capacity of commercial wine and fruit juice samples [13]. Q.Y. Chen et al. investigated on the determination of nucleic acid by using NB, as a fluorescence probe [14]. NB possesses extensive biological applications. The interaction between NB and DNA was widely reported [15].
Uracil is an essential integral part of RNA and ensues naturally in pyrimidine base pairs. Uracil derivatives find immense applications in biological and pharmacological activities viz., drug delivery, enzyme synthesis [[16], [17], [18]]. For instance, 6-methyl uracil is an antioxidant and also used in the treatment of hepatitis and pancreatitis [19,20]. The pharmacological activity of many drugs correlates with their antioxidant activity [21,22]. Particularly 5-substituted uracil derivatives are important class of non-steriodial anti-inflammatory agents with antioxidant activity. S.A. Grabovskiy et al. reported the structure activity relationship of uracil derivatives against free radicals [23].
Previously we have reported the investigation on 9-aminoacridine, acriflavine and triphenylamine with various antioxidants and TiO2 nanoparticles [[24], [25], [26], [27], [28], [29], [30]]. The ability of sensitizers to undergo excited state electron transfer by various pyrimidines was extensively studied [31]. The foremost objective of us to study the interaction of NB with appropriate biological target and in this perspective, probing the interaction of biologically potent NB with uracil derivatives is of outmost important and chemically relevant to pharmacological research. Fluorescence as a detection method provides high sensitivity down to the single molecule, ease of application, and a subnano-second temporal and sub-micrometer spatial resolution. Fluorescence quenching method is very sensitive and provides direct information on the antioxidant activity of the molecules.
We are interested to understand the fluorescence quenching of NB with various uracils to explore the role of H in quencher molecules and their contribution in antioxidant activity. The quencher molecules chosen in the present study was shown in the Scheme 2. Moreover, it is important to understand the transfer of H from aromatic molecules as it could solve many biological problems [32]. To comprehend the behavioural pattern of molecules, we have performed UV–Vis absorption, steady state fluorescence and lifetime measurements. Understanding the mode of fluorescence quenching of NB with various uracils, our next endeavour focused to assess the extent of antioxidant activity of quencher molecules. Further DFT calculation studies support the release of H from quencher molecules. Finally, deoxyribose degradation assay indicates the antioxidant activity of quencher molecules.
Section snippets
Material
Nile blue, thiouracil, 5-fluorouracil, 5-chlorouracil, 5-bromouracil, 5-iodouracil, 5-methyluracil, 6-nitrouracil, 6-methyluracil were purchased from Sigma-Aldrich. De-oxyribose, ascorbic acid, ferrous sulphate heptahydrate, trichloroacetic acid, thiobarbutric acid were purchased from Hi-media. Double distilled water was used for preparing the solutions. All measurements were performed at room temperature.
Apparatus
Absorption spectra were recorded using JASCO V-630 UV–Vis spectrophotometer. Fluorescence
Result and discussion
NB shows absorption maximum at 636 nm and emission maxima at 669 nm in phosphate buffered media (pH 7.4).
Conclusion
Presently, the photoinduced interactions of NB with various uracil molecules were probed by using spectroscopic techniques and DFT calculations. Ground state complex formation between the molecules was analysed by UV–Visible spectral analysis. The bimolecular quenching rate constant (kq) were calculated, which found to depend on the position and electronic properties of substituent in uracil molecules. Fluorescence quenching experiments were performed at different temperature to calculate the
CRediT authorship contribution statement
S. Sambathkumar: writing - original draft preparation, experimental execution and analysis.
C. Manivannan: contributed in analysis, discussion, review and editing.
S. Baskaran: contributed in computational analysis and discussion.
V. Anbazhagan: contributed in analysis, discussion, review and editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
S.S. thanks to Department of Science and Technology (DST), Fund for Improvement of S&T Infrastructure (FIST), Government of India for the financial support under DST FIST Program 2017 level ‘0’ (SR/FST/College – 111/2017; Dt. 16.01.2018).
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