# Spectroscopic Analysis of the TiO2 Nanoparticles Influence on the Interaction of 5,10,15,20-(Tetra-4-carboxyphenyl)porphyrin with Human Serum Albumin

## TL;DR

This study explores how TiO2 nanoparticles affect the interaction of a porphyrin photosensitizer with human serum albumin, using various spectroscopic techniques and molecular docking.

## Contribution

The study provides new insights into the binding behavior of TiO2-TCPP complexes with HSA and their impact on protein conformation.

## Key findings

- Molecular docking and UV-Vis absorption confirmed consistent binding constants for TCPP–HSA.
- LIF data showed slightly lower affinity for TiO2-TCPP compared to free TCPP, possibly due to competitive binding.
- FTIR revealed conformational changes in HSA upon interaction with both TCPP and TiO2-TCPP.

## Abstract

Photodynamic therapy is a cancer treatment that relies on a photosensitizer (PS) to generate reactive oxygen species upon light activation, thereby destroying cancer cells. The photophysical properties of porphyrins make them effective PSs, while nanoparticles (NPs) enhance their delivery and stability. The bioavailability and targeting efficiency of NPs-PS complexes may be improved through transport via human serum albumin (HSA). This study investigates the HSA binding affinity with 5,10,15,20-(Tetra-4-carboxyphenyl)porphyrin (TCPP) and with TiO2-TCPP complexes. The interactions were analyzed using UV-Vis absorption, laser-induced fluorescence (LIF), and FTIR spectroscopy. Molecular docking was performed and provided consistent binding constant values for the TCPP–HSA complex with UV-Vis absorption measurements. LIF data revealed a slightly lower affinity when compare free porphyrin with TiO2-TCPP, possibly due to competitive binding between TiO2 and HSA. Docking simulations indicated that TCPP favorably interacts with amino acid residues located in subdomains IB and IIIA of HSA, supporting a preferential binding near Sudlow site I. FTIR measurements revealed conformational changes in HSA for both its interactions with TCPP and TiO2-TCPP, including alterations in α-helical content and reorganization of the hydrogen bonding network within the polypeptide backbone.