Molecular relaxation dynamics and self-association of dexamethasone sodium phosphate solutions

Abstract

Detailed concentration-dependent measurements of sound absorption and velocity have been performed in dexamethasone sodium phosphate (DSP) aqueous solutions in the MHz frequency range. A single well-resolved relaxation process dominates the experimental acoustic spectra following a Debye-type distribution function. The analysis of the temperature-dependent ultrasonic relaxation data also revealed analogous effect with concentration on the relaxation spectra. All acoustic parameters were estimated by means of a fitting procedure. The behavior of the relaxation frequency and amplitude with concentration allowed us to assign the observed process to self-association mechanism. Combining the ultrasonic and electric conductivity data, the self-association scheme has been established. The thermodynamic constants and the rate of the aggregation due to hydrophobic interactions have been estimated in view of the Eyring's theory. The concentration dependence of relaxation amplitude and characteristic frequency revealed that the presence of additional relaxation processes in the spectra related to additional mechanisms, such as conformational changes and proton-transfer reaction is excluded and the self-association process considered here was found to dominate in this frequency range. The results have been discussed in view of the fair ability of DSP for hydrophobic interactions and aggregate formation in aqueous environment.

Evidence of Self-Association and Conformational Change in Nisin Antimicrobial Polypeptide Solutions: A Combined Raman and Ultrasonic Relaxation Spectroscopic and Theoretical Study

“…Antibiotics 2023, 12, x FOR PEER REVIEW 9 of 22 6. It is evident that the Cole-Davidson distribution function fit adequately the experimental a/f 2 values.…”

“…The fitting procedure was performed by minimizing the following ratio: (6) which allowed us to estimate the numerous free fitting parameters. Among these fitting parameters, the characteristic relaxation frequency (fr) and the relaxation amplitude (A) are useful since they enable the quantitative characterization of the relaxation effects to be performed.…”

“…It is important to achieve progress on the comprehensive understanding of Nisin behaviour at the molecular level in the solution state, where several structural and dynamic processes may take place, such as self-association, cooperative conformational transitions and protolytic reactions. The combined use of vibrational and acoustic relaxation spectroscopy and theoretical calculations provides important insights into microstructural interactions and dynamical phenomena in the liquid state [6][7][8]. Furthermore, the results of molecular docking studies can be used as a starting model of the molecular interactions among ligand and receptor molecules.…”

The Identification of Structural Changes in the Lithium Hexamethyldisilazide–Toluene System via Ultrasonic Relaxation Spectroscopy and Theoretical Calculations

“…A common ultrasonic medical gel was applied between the cell and the transducers to achieve better contact and thus the maximum sound transmission. Utilizing the same experimental setup, ultrasound velocity measurements were performed via the pulse-echo overlap technique with an experimental error less than ±0.01% [ 23 ].…”

Insight into the Structural and Dynamical Processes of Peptides by Means of Vibrational and Ultrasonic Relaxation Spectroscopies, Molecular Docking, and Density Functional Theory Calculations

“…In general, the relaxation processes observed in molecular systems such as glutathione aqueous solutions can be categorized into thermal and structural processes. Thermal relaxation mechanisms are usually observed in systems where fluctuations in the ultrasonic wave perturb a chemical intra-molecular equilibrium, such as the one detected here between The standard volume change for the conformational change, the association-dissociation reaction, and the protonation and deprotonation reactions can be directly evaluated based on the experimental maximum excess absorption per wavelength µ max , the solution density ρ, the sound velocity u, the absolute temperature T, the gas constant R, and the concentration term Γ from the following equation [40,41]:…”