# Insulin and Human Serum Albumin Interactions with Core–Shell Fe3O4@SiO2 Nanoparticles Functionalized with Carboranes

## TL;DR

This study explores how specific nanoparticles interact with human serum albumin and insulin, causing structural changes that could impact their function in medical applications.

## Contribution

The novelty lies in analyzing the enthalpy–entropy-driven interactions of functionalized Fe3O4@SiO2 nanoparticles with two specific proteins using multiple experimental techniques.

## Key findings

- Human serum albumin (HSA) undergoes significant structural changes when interacting with nanoparticles, reducing its α-helix content from 87.59% to 40.9%.
- Insulin shows weaker interaction with nanoparticles compared to HSA, with only a 15% decrease in α-structure content.
- Nanoparticle exposure alters the microenvironment around tryptophan residues, increasing hydrophobicity for both proteins.

## Abstract

In a biological medium,
nanoparticles (NPs) can spontaneously
interact
with proteins, adsorb onto their surface, and cause conformational
and orientation changes of the proteins. As a result, the protein
function is influenced in a complex manner. Therefore, a detailed
understanding of the nature and specificity of protein–nanoparticle
interactions is crucial for the application of functional NPs in medicine.
In the presented work, we studied the interactions of GMA-treated
SiO2 NPs with the Fe3O4 core and
attached carborane compounds (Fe3O4/TEOS/TMSPM/GMA/Carborane),
designed for boron neutron capture therapy, with human serum albumin
(HSA) and insulin. We combined different techniques: spectrofluorometry,
circular dichroism spectroscopy, and isothermal titration calorimetry
to address this issue. The results show that the adsorption of protein
onto the NP surface is enthalpy–entropy-driven, with ensuing
structural changes of the protein. As for albumin, the percentage
of the α-helix structure in the protein is significantly reduced
from 87.59 (free protein) to 40.9% for an NP concentration of 1.8
mg/mL, while the content of the β-sheet and random coil increases
from 0.48 to 8.78% and from 11.93 to 50.32%, respectively. The interaction
between NPs and small protein–insulin is weaker than that for
HSA, confirming less negative ΔH and a 15%
decrease in the α-structure content for the highest concentration
of NPs. For both proteins, the exposure on Fe3O4/TEOS/TMSPM/GMA/Carborane affects the polarity of the microenvironment
around Trp, which is consequently exposed to a more hydrophobic environment.
Calculated values of the radius of gyration and the minimum distance
between the proteins and the NPs indicate a stronger interaction and
closer binding proximity to the NPs, corroborating experimental observations
of the higher binding affinity of HSA to NPs.