Microextraction of steroidal hormones from urine samples using natural deep eutectic solvents: insights into chemical interactions using molecular dynamics simulations.

Natural deep eutectic solvents (NADES) are gaining significant attention in analytical chemistry due to attractive physico-chemical properties associated with sustainable aspects. They have been successfully evaluated in different fields, and applications in sample preparation have increased in the last years. However, there is a limited knowledge related to chemical interactions and mechanism of intermolecular action with specific analytes. In this regard, for the first time, this study exploited a computational investigation using molecular dynamics (MD) predictions combined with experimental data for the extraction/determination of steroidal hormones (estriol, ß-estradiol, and estrone) in urine samples using NADES. The ultrasound-assisted liquid-liquid microextraction (UALLME) approach followed by high-performance liquid chromatography with diode array detection (HPLC-DAD) was employed using menthol:decanoic acid as extraction solvent. Experimental parameters were optimized through multivariate strategies, with the best conditions consisting of 3 min of extraction, 150 µL of NADES, and 3 mL of sample (tenfold diluted). According to molecular dynamics predictions confirmed by experimental data, a molar ratio that permitted the highest efficiency consisted of menthol:decanoic acid 2:1 v/v. Importantly, computational simulations revealed that van der Waals interactions were the most significant contributor to the interaction energy of analytes-NADES. Using the optimized conditions, limits of detection (LOD) ranged from 3 and 8 µg L-1, and precision (n = 3) varied from 8 to 19%. Intraday precision was evaluated at 3 concentrations: low (LOQ according to each analyte), medium (100 µg L-1), and high (750 µg L-1). Accuracy was successfully assessed through recoveries that ranged from 82 to 98%. In this case, molecular dynamics simulations proved to be an important tool for in-depth investigations of interaction mechanisms of DES with different analytes.

Interaction of Statherin-Derived Peptide with the Surface of Hydroxyapatite: Perspectives Based on Molecular Dynamics Simulations.

INTRODUCTION: Statherin-derived peptide (StatpSpS) has shown promise against erosive tooth wear. To elucidate its interaction with the hydroxyapatite (HAP) surface, the mechanism related to adsorption of this peptide with HAP was investigated through nanosecond-long all-atom molecular dynamics simulations. METHODS: StatpSpS was positioned parallel to the HAP surface in 2 orientations: 1 - neutral and negative residues facing the surface and 2 - positive residues facing the surface. A system containing StatpSpS without HAP was also simulated as control. In the case of systems with HAP, both partially restrained surface and unrestrained surface were constructed. Structural analysis, interaction pattern, and binding-free energy were calculated. RESULTS: In the peptide system without the HAP, there were some conformational changes during the simulation. In the presence of the surface, only moderate changes were observed. Many residues exhibited short and stable distances to the surface, indicating strong interaction. Specially, the residues ASP1 and SER2 have an important role to anchor the peptide to the surface, with positively charged residues, mainly arginine, playing a major role in the further stabilization of the peptide in an extended conformation, with close contacts to the HAP surface. CONCLUSION: The interaction between StatpSpS and HAP is strong, and the negative charged residues are important to the anchoring of the peptide in the surface, but after the initial placement the peptide rearranges itself to maximize the interactions between positive charged residues.

In vitro antimicrobial, antibiofilm photodynamic activity, and molecular dynamic simulations of tetra-cationic porphyrinmembrane interactions against foodborne microorganisms.

This manuscript presents a new report on the in vitro antimicrobial photo-inactivation of foodborne microorganisms (Salmonella spp. and Listeria monocytogenes) using tetra-cationic porphyrins. Isomeric tetra-cationic porphyrins (3MeTPyP, 4MeTPyP, 3PtTPyP, and 4PtTPyP) were tested, and antimicrobial activity assays were performed at specific photosensitizer concentrations under dark and white-light LED irradiation conditions. Among the tested bacterial strains, 4MeTPyP exhibited the highest efficiency, inhibiting bacterial growth within just 60 min at low concentrations (17.5 µM). The minimal inhibitory concentration of 4MeTPyP increased when reactive oxygen species scavengers were present, indicating the significant involvement of singlet oxygen species in the photooxidation mechanism. Furthermore, the checkerboard assay testing the association of 4MeTPyP showed an indifferent effect. Atomic force microscopy analyses and dynamic simulations were conducted to enhance our understanding of the interaction between this porphyrin and the strain's membrane.