Lycopene, but not zeaxanthin, serves as a skeleton for the formation of an orthorhombic organization of intercellular lipids within the lamellae in the stratum corneum: Molecular dynamics simulations of the hydrated ceramide NS bilayer model.

Carotenoids play an important role in the protection of biomembranes against oxidative damage. Their function depends on the surroundings and the organization of the lipid membrane they are embedded in. Carotenoids are located parallel or perpendicular to the surface of the lipid bilayer. The influence of carotenoids on the organization of the lipid bilayer in the stratum corneum has not been thoroughly considered. Here, the orientation of the exemplary cutaneous carotenoids lycopene and zeaxanthin in a hydrated ceramide NS24 bilayer model and the influence of carotenoids on the lateral organization of the lipid bilayer model were studied by means of molecular dynamics simulations for 32 °C and 37 °C. The results confirm that lycopene is located parallel and zeaxanthin perpendicular to the surface of the lipid bilayer. The lycopene-loaded lipid bilayer appeared to have a strong orthorhombic organization, while zeaxanthin-loaded and pure lipid bilayers were organized in a disordered hexagonal-like and liquid-like state, respectively. The effect is stronger at 32 °C compared to 37 °C based on p-values. Therefore, it was assumed that carotenoids without hydroxyl polar groups in their structure facilitate the formation of the orthorhombic organization of lipids, which provides the skin barrier function. It was shown that the distance between carotenoid atoms matched the distance between atoms in the lipids, indicating that parallel located carotenoids without hydroxyl groups serve as a skeleton for lipid membranes inside the lamellae. The obtained results provide reasonable prediction of the overall qualitative properties of lipid model systems and show the importance of parallel-oriented carotenoids in the development and maintenance of the skin barrier function.

A Data Science Approach to Understanding Water Networks Around Biomolecules: The Case of Tri-Alanine in Liquid Water.

Herein, we use recently developed data science algorithms to illustrate the complexity of the water network surrounding the hydrated peptide tri-alanine extracted from molecular dynamics simulations. We estimate the dimensionality of water variables and show that it is sensitive to the underlying secondary structure of the peptide. We show that water wires threading the peptide encode important information on the secondary structure. Interestingly, the free-energy landscape as revealed by the water wires is very rough for α-configurations and rather smooth for ß-configurations. The structured nature of the free-energy landscape is washed out if one uses more standard collective variables such as the number of hydrogen bonds around the peptide. Our results provide fresh insights into the molecular ingredients behind the coupling of protein and solvent degrees of freedom relevant for many biophysical and chemical processes.

Hydrogen Bond Networks and Hydrophobic Effects in the Amyloid ß30-35 Chain in Water: A Molecular Dynamics Study.

We have studied the conformational landscape of the C-terminal fragment of the amyloid protein Aß30-35 in water using well-tempered metadynamics simulations and found that it resembles an intrinsically disordered protein. The conformational fluctuations of the protein are facilitated by a collective reorganization of both protein and water hydrogen bond networks, combined with electrostatic interactions between termini as well as hydrophobic interactions of the side chains. The stabilization of hydrophobic interactions in one of the conformers involves a collective collapse of the side chains along with a squeeze-out of water sandwiched between them. The charged N- and C-termini play a critical role in stabilizing different types of protein conformations, including those involving contact-ion salt bridges as well as solvent-mediated interactions of the termini and the amide backbone. We have examined this by probing the distribution of directed water wires forming the hydrogen bond network enveloping the polypeptide. Water wires and their fluctuations form an integral part of structural signature of the protein conformation.

Synthesis of pH-responsive N-acetyl-cysteine modified starch derivatives for oral delivery.

In this study, a novel type of pH-responsive polymer PyHES-NAC (2-hydroxy-3-(2-propynyloxy) propyl hydroxyethyl starch (PyHES)) - (N-acetyl-cysteine (NAC)) was synthesized. First, PyHES was prepared via hydrophobic modification of hydroxyl groups in hydroxyethyl starch (HES) with propynylglycidyl ether (PGE), and then pH-responsive carboxylic acid group was connected to propynyl group via thiol-yne click reaction with NAC. Aqueous PyHES-NAC solutions exhibited a good transference between hydrophobic (or self-assembly) and hydrophilic static along with the change of pH value and protective properties of drugs under acidic conditions. 10.0% DOX was released under artificial gastric fluid after 2 h, whereas an immediate release (above 80%) was observed under artificial intestinal fluid. Drug loading capacity of PyHES-NAC was increased by the increase of degree of substitution (DS) of hydrophobic propynyl groups in PyHES, and 41 wt% DOX Loading capacity was the highest value in our study area.