# Molecular insights into nilvadipine–hemoglobin interactions: conformational dynamics and binding mechanisms

## TL;DR

This study explores how the drug nilvadipine interacts with hemoglobin, revealing a stable, hydrophobic binding that could influence drug delivery and safety.

## Contribution

The study provides a detailed molecular and thermodynamic characterization of nilvadipine–hemoglobin interactions using combined experimental and computational methods.

## Key findings

- Nilvadipine binds to hemoglobin with a 1:1 stoichiometry and hydrophobic interactions as the main driving force.
- Molecular docking and MD simulations reveal a stable binding pose involving hydrogen bonds and hydrophobic contacts.
- The Hb–Nilvadipine complex remains structurally robust during simulations, suggesting minimal disruption to hemoglobin's global fold.

## Abstract

Understanding the molecular basis of drug–protein interactions is essential for predicting pharmacokinetics and potential off-target effects. Here, we employ a combined experimental and computational approach to characterize the binding of Nilvadipine (a dihydropyridine calcium channel blocker) to hemoglobin (Hb). Using Soret band absorption and steady-state fluorescence spectroscopy across 298–310 K, we observed pronounced static quenching of Hb's intrinsic fluorescence, yielding Stern–Volmer constants (KSV) in the order of 104 M−1 and 1 : 1 binding stoichiometry. Thermodynamic parameters derived from van't Hoff analysis (ΔH° > 0, ΔS° > 0, and ΔG° < 0) highlighted hydrophobic interactions as the primary driving force and confirmed the spontaneity of complex formation. Förster resonance energy transfer (FRET) measurements further positioned Nilvadipine at ∼3.0 nm from Hb's fluorophores, consistent with a static, ground-state complex. Molecular docking identified a preferential binding pose stabilized by hydrogen bonds with ASN68 and ASP64, hydrophobic contacts involving ALA82, LEU83, and LEU86, and interactions with the heme group, yielding a computed binding energy of −5.50 kcal mol−1 in close agreement with spectroscopically derived ΔG°. Over 100 ns of molecular dynamics (MD) simulations, the Hb–Nilvadipine complex remained structurally robust, with backbone RMSD values <0.2 nm, minor radius of gyration (Rg) reduction, limited per-residue fluctuations (RMSF < 0.3 nm), and negligible changes in solvent-accessible surface area (SASA). Together, these data demonstrate that Nilvadipine forms a stable, hydrophobically driven complex with Hb without perturbing its global fold, suggesting that Hb may serve as a transient reservoir for the drug in circulation. This integrative study provides a detailed roadmap for interrogating small-molecule binding to blood proteins and offers insights valuable for drug delivery, safety assessment, and the design of Hb-based carriers.

Understanding the molecular basis of drug–protein interactions is essential for predicting pharmacokinetics and potential off-target effects.