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Constant-pH Simulations of a Coarse-Grained Model of Polyfunctional Weak Charged Biopolymers

A coarse-grained model of linear polyfunctional weak charged biopolymers was implemented, formed of different proportions of acid-base groups resembling the composition of humic substances. These substances are mainly present in dissolved organic matter in natural water. The influence of electrostatic interactions computing methods, factors concerning the structure of the chain, different functional groups, and the ionic strength on polyelectrolytes were studied. Langevin dynamics with constant pH simulations were performed using the ESPResSO package and the Python-based Molecule Builder for ESPResSo (pyMBE) library. The coverage was fitted to a polyfunctional Frumkin isotherm, with a mean-field interaction between charged beads. The composition of the chain affects the charge while ionic strength affects both the charge and the radius of gyration. Additionally, the parameters intrinsic to the polyelectrolyte model were well reproduced by fitting the polyfunctional Frumkin isotherm. In contrast, the non-intrinsic parameters depended on the ionic strength. The method developed and applied to a polyfunctional polypeptide model, that resembles a humic acid, will be very useful for characterizing biopolymers with several acid-base functional groups, where their structure, the composition of the different functional groups, and the determination of the main intrinsic proton binding constants and their proportion are not exactly known.

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The Signature of Fluctuations of the Hydrogen Bond Network Formed by Water Molecules in the Interfacial Layer of Anionic Lipids

As the water molecules found at the interface of lipid bilayers exhibit distinct structural and reorientation dynamics compared to water molecules found in bulk, the fluctuations in their hydrogen bond (HB) network are expected to be different from those generated by the bulk water molecules. The research presented here aims to gain an insight into temperature-dependent fluctuations of a HB network of water molecules found in an interfacial layer of multilamellar liposomes (MLVs) composed of anionic 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine (DMPS) lipids. Besides suspending DMPS lipids in phosphate buffer saline (PBS) of different pH values (6.0, 7.4, and 8.0), the changes in HB network fluctuations were altered by the incorporation of a non-polar flavonoid molecule myricetin (MCE) within the hydrocarbon chain region. By performing a multivariate analysis on the water combination band observed in temperature-dependent FTIR spectra, the results of which were further mathematically analyzed, the temperature-dependent fluctuations of interfacial water molecules were captured; the latter were the greatest for DMPS in PBS with a pH value of 7.4 and in general were greater for DMPS multibilayers in the absence of MCE. The presence of MCE made DMPS lipids more separated, allowing deeper penetration of water molecules towards the non-polar region and their restricted motion that resulted in decreased fluctuations. The experimentally observed results were supported by MD simulations of DMPS (+MCE) lipid bilayers.

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Neurite Growth and Electrical Activity in PC-12 Cells: Effects of H3 Receptor-Inspired Electromagnetic Fields and Inherent Schumann Frequencies

Cells are continually exposed to a range of electromagnetic fields (EMFs), including those from the Schumann resonance to radio waves. The effects of EMFs on cells are diverse and vary based on the specific EMF type. Recent research suggests potential therapeutic applications of EMFs for various diseases. In this study, we explored the impact of a physiologically patterned EMF, inspired by the H3 receptor associated with wakefulness, on PC-12 cells in vitro. Our hypothesis posited that the application of this EMF to differentiated PC-12 cells could enhance firing patterns at specific frequencies. Cell electrophysiology was assessed using a novel device, allowing the computation of spectral power density (SPD) scores for frequencies between 1 Hz and 128 Hz. T-tests comparing SPD at certain frequencies (e.g., 29 Hz, 30 Hz, and 79 Hz) between the H3-EMF and control groups showed a significantly higher SPD in the H3 group (p < 0.050). Moreover, at 7.8 Hz and 71 Hz, a significant correlation was observed between predicted and percentages of cells with neurites (R = 0.542). Key findings indicate the efficacy of the new electrophysiology measure for assessing PC-12 cell activity, a significant increase in cellular activity with the H3-receptor-inspired EMF at specific frequencies, and the influence of 7.8 Hz and 71 Hz frequencies on neurite growth. The overall findings support the idea that the electrical frequency profiles of developing cell systems can serve as an indicator of their progression and eventual cellular outcomes.

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