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Present work reports interaction between water and amino acid lysine for understanding the physicochemical properties that will be useful in the structure formation of protein. The dielectric relaxation of aqueous lysine was systematically investigated over a temperature range spanning from 298.15 K to 278.15 K, encompassing frequencies ranging from 10 MHz to 30 GHz, and across a concentration range of 0.152 M to 0.610 M. Within this study, aqueous lysine revealed the presence of two distinct relaxation modes. The low-frequency relaxation process (l-process) is primarily associated with the relaxation of lysine molecules, whereas the high-frequency relaxation process (h-process) is attributed to water molecules interacting with lysine. Several key dielectric parameters, including static dielectric constant (εj), relaxation time (τj), dipole moment (µj), correlation factor (gj), and the number of water molecules rotationally bonded by solute molecules (Zib), were meticulously determined. These parameters were interpreted in terms of molecular interactions, hydrogen bonding, hydrophobicity, and Lys-Lys binding. Additionally, various thermodynamic parameters such as molar enthalpy (ΔHj), molar entropy (ΔSj), and molar free energy (ΔFj) were calculated to provide further insights into the system's characteristics and behavior.Communicated by Ramaswamy H. Sarma.

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Concentration-dependent dielectric response for non-steroidal anti-inflammatory drugs (NSAIDs): Aceclofenac (ACF) and Diclofenac (DCF) in the aqueous leucine solution have been reported at different concentrations and temperatures (298.15 K to 283.15 K). The time domain reflectometry technique in the frequency region of 1 GHz to 30 GHz was used for the present study. Complex permittivity (ε*), static dielectric constant (ε), dielectric relaxation time (τ), dipole moment (µ) and Kirkwood correlation factor (g) have been calculated and discussed in terms of the molecular interaction of water and the used drugs. To give more insights into the structural dynamics of drug-induced amino acids, the study includes molar enthalpy of activation (ΔH), entropy of activation (ΔS), and free energy of activation (ΔF). The overall study concludes that the drug (DCF) having a potent inhibitor of cyclooxygenase found a higher static dielectric constant (ε0) than that of the drug (ACF) having more carbon (C), hydrogen (H), and oxygen (O) in the chain, which is more efficient in controlling pain.Communicated by Ramaswamy H. Sarma.

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H-Bonding abilities of ionic liquids (ILs) along with hydrophobicity and cooperativity effects increases their hydration numbers making them capable for dissolving sparingly soluble organic molecules in aqueous or polar nonaqueous media, and hence ILs are potential candidates in pharmaceutical and medicinal sciences besides the different technological and academic interests. In this work, dielectric spectra were measured and analyzed for diethylammonium-based protic ionic liquids (PILs), imidazolium-based aprotic ionic liquids (APILs), and their aqueous solutions (∼0.02 to ∼0.8 mol·dm-3) over a frequency range from 0.01 to 50 GHz using time domain reflectometry at 298.15 K. The Cole-Cole (CC) model for neat ILs and a combination of the Debye and Cole-Cole (D+CC) models for their aqueous solutions best describes the experimental dielectric relaxation spectra. Higher values of static permittivity and relaxation time were observed for less viscous PILs compared to more viscous APILs due to the existence of hydrogen bonding in PILs, ionic translational motion, and the existence of transient, short-lived proton transfer responsible for solvent polarization. For aqueous solutions of ionic liquids, the fast collective relaxation of solvent (bulk water) observed at higher frequencies (∼20 GHz) and slow relaxation is detected at lower frequency (∼5 to ∼10 GHz) due to hydrophobic hydration with or without cooperative H-bonding effect. The apparent concentrations of bulk water, cbwap, and slow water, cswap, were used to obtain effective hydration numbers to understand the ion solvation. Hydration numbers revealed that imidazolium-based APILs are weakly hydrated than the diethylammonium-based PILs. Static permittivity and relaxation time of pure ILs and of aqueous solutions of studied ILs are discussed in terms of effect on alkyl chain length of cation/anion, H-bonding abilities of ions, dipole moments of ions, viscosity, hydrophobic effects, etc.

RESUMEN

Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10 MHz to 7 GHz in the temperature region 25 to 10 °C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε 0), high-frequency limiting static permittivity (ε ∞), average relaxation time (τ 0), and thermodynamic parameters such as free energy (∆F τ), enthalpy (∆H τ), and entropy of activation (∆S τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.

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The values of complex permittivity for alcohol-1,4-dioxane (DX) mixtures with various concentrations have been determined in the frequency range 10 MHz to 20 GHz using the time domain reflectometry (TDR) method. Numbers of hydrogen bonds between alcohol-alcohol and alcohol-dioxane pairs are estimated from the values of the static dielectric constant by using the Luzar model. The model provides a satisfactory explanation of the experimental results related to the static dielectric constant. The binding energies for alcohol-alcohol (pair 11) and alcohol-DX (pair 12) are estimated to be -13.98 and -16.25 kJ/mol, respectively. The results have also been compared with previous results of the ethyleneglycol-DX system.

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Complex permittivity has been determined for mixtures of ethyleneglycol-1,4-dioxane (EG-DX) with various concentrations in the frequency range from 100 MHz to 30 GHz at 25 degrees C by time domain reflectometry (TDR). A primary process with an asymmetric shape and a Debye-type small-amplitude high-frequency process are observed for each mixture. The deviation of the relaxation time for the primary process from that of the ideal mixture shows a maximum value at a mole fraction of 1,4-dioxane, xDX approximately =0.8. The static permittivity for the mixtures can be explained using the Luzar model by assuming the formation of two types of hydrogen-bonded dimers, one between EG-EG (pair 1) and the other between EG-DX (pair 2). The number of these pairs is also estimated as a function of concentration. These results of the relaxation time and static permittivity are interpreted on the basis of a model of two kinds of cooperative domains coexisting in the mixtures.