Photoluminescence as a Complementary Tool for UV-VIS Spectroscopy to Highlight the Photodegradation of Drugs: A Case Study on Melatonin.

Monica Daescu,Mihaela Baibarac,N'Ghaya Toulbe,C Logofatu,Alin Mogos,Adam Lőrinczi

doi:10.3390/molecules25173820

Abstract

In this work, a complementary ultraviolet-visible (UV-VIS) spectroscopy and photoluminescence (PL) study on melatonin (MEL) hydrolysis in the presence of alkaline aqueous solutions and the photodegradation of MEL is reported. The UV-VIS spectrum of MEL is characterized by an absorption band with a peak at 278 nm. This peak shifts to 272 nm simultaneously with an increase in the band absorbance at 329 nm in the presence of an NaOH solution. The isosbestic point localized at 308 nm indicates the generation of some chemical compounds in addition to MEL and NaOH. The MEL PL spectrum is characterized by a band at 365 nm. There is a gradual decrease in the MEL PL intensity as the alkaline solution concentration added at the drug solution is increased. In the case of the MEL samples interacting with an alkaline solution, a new photoluminescence excitation (PLE) band at 335 nm appears when the exposure time to UV light reaches 310 min. A down-shift in the MEL PLE band, from 321 to 311 nm, as a consequence of the presence of excipients, is also shown. These changes are explained in reference to the MEL hydrolytic products.

Highlights

Melatonin (MEL) is generated in the mammalian pineal gland as a neurohormone [1]
In the case of the MEL-1 sample, as the exposure time to UV light increased to 5 h, one can observe a shift in the absorption band from 278 to 269 nm, which occurs simultaneously with the emergence of a new band in the 300–350 nm spectral range, whose absorbance gradually increases
Spectra of MEL in the absence and presence of NaOH indicates the emergence of new compounds, (ii) both in UV-VIS and photoluminescence excitation (PLE) spectra, the new band localized in the 300–360 nm spectral range belongs to the compounds found to be the result of exposure to UV light, according to Scheme 1, and (iii) the interaction of MEL with NaOH and the photodegradation induced by UV light can be monitored by the variations in the positions and intensities of the PL and PLE bands

Summary

Introduction

Melatonin (MEL) is generated in the mammalian pineal gland as a neurohormone [1]. It is a constituent of many pharmaceutical capsules [2] and is used to control the circadian rhythms and sleep cycle [3]. As reported by Buscemi et al, MEL is rapidly adsorbed

Methods

Results

Conclusion