A novel insight into the femtosecond induced nonlinear response of monoamine neurotransmitters through experimental and in silico approaches.

Monoamine neurotransmitters, such as serotonin and melatonin, are of significant scientific interest due to their widespread influence across various tissues. They play crucial roles in the hormonal and neuronal systems, controlling numerous physiological processes, including antioxidant, neuroprotective, anticancer, cardiovascular function, platelet aggregation, and psychiatric disorders. In this study, we present a direct analysis revealing the nonlinear optical properties of serotonin and melatonin under femtosecond (fs) pulsed laser excitation through the Z-scan and quantum chemical methods. Under the specified Z-scan experimental conditions, these monoamine neurotransmitters exhibit positive refractive and absorptive nonlinearities. Here, the origin of this nonlinearity is attributed to the electronic polarization effect. Specifically, nonlinear refraction is influenced by the self-focusing effect, while nonlinear absorption is governed by the reverse saturable absorption effect (RSA). The experimental data from the Z-scan method correlate with the quantum chemical method, and we observe that, at the highest experimental concentration (550 mM), the theoretical values of ⟨γ⟩ for serotonin and melatonin are approximately 15.78% and 33.84%, respectively, of the experimental values. Several novel chemical reactivity descriptors are calculated using the quantum chemical method to comprehend various aspects of pharmacological science. Furthermore, molecular docking simulations are carried out to conduct a thorough investigation into the binding affinity and poses of serotonin and melatonin with their receptors. The prediction of non-bonding weak interactions of serotonin and melatonin assures potent binding with their receptors. The findings of this research could provide valuable understanding, aiding in the development of novel therapeutic approaches focused on processes regulated by serotonin and melatonin.