**4. Conclusions**

In the present study, the antipsychotic drug QTP was characterized for its binding interaction to HSA using spectroscopic and biochemical methods and computational approaches. The results obtained from the QTP-HSA binding interactions showed moderate binding affinity of QTP toward HSA. In addition, the involvement of hydrogen bonding and hydrophobic interactions was observed. The spectroscopic studies suggest a complex formation between QTP and HSA, and the system follows a static quenching mechanism. Conversely, the thermodynamic parameters of the HSA-QTP system calculated via fluorescence spectroscopy at different temperatures indicate a spontaneous and exothermic process and indicate the predominant forces to be hydrophobic interactions.

Further, the site-displacement assay and molecular docking results confirm the QTP binding region at subdomain IB of HSA. The CD spectra and UV-Vis spectroscopy identified changes in the secondary structure of HSA upon its interaction with QTP. In addition, QTP did not inhibit the esterase-like activity of HSA. This study is essential and is expected to help understand the drug's mechanisms and pharmacokinetics for further clinical research and novel drug delivery systems.

**Author Contributions:** Conceptualization: T.A.W., S.Z.; Methodology: T.A.W., S.Z.; Software: T.A.W., N.A.A.; Formal analysis: A.I.A.K., S.Z.; Investigation: N.A.A., T.A.W., S.Z, A.I.A.K.; Resources: T.A.W.; Writing: S.Z., T.A.W.; Review & Editing N.A.A., T.A.W. Project administration: T.A.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** Researchers Supporting Project (RSP-2021/357), King Saud University, Riyadh, Saudi Arabia.

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Data Availability Statement:** Data will be available on request to corresponding author.

**Acknowledgments:** The authors extend their appreciation to the Researchers Supporting Project number (RSP-2021/357), King Saud University, Riyadh, Saudi Arabia, for funding this work.

**Conflicts of Interest:** The authors declare no conflict of interest.
