Ultrasonic Relaxations in Aqueous Solutions of Piperidine and Pyrrolidine

Abstract

In order to examine ultrasonic absorption mechanisms and dynamical properties in aqueous solutions of heterocyclic amines, the absorption coefficients in a frequency range from 3.0 to 220 MHz were measured in solutions of pyrrolidine and piperidine at 25 °C. In the solution of pyrrolidine, a single relaxational absorption associated with a proton transfer reaction was observed, and the rate and thermodynamic parameters were determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength. In the solution of piperidine, another relaxational absorption in addition to that due to the proton transfer reaction was observed in the relatively concentrated solution. It was attributed to a perturbation of an equilibrium associated with an aggregation reaction of nonionized molecules. The mean aggregation number and the rate parameters were estimated from the solute concentration dependence of the relaxation parameters. The results were compared with those observed in aliphatic amine solutions.

Molecular Aggregation in Binary Mixtures of Pyrrolidine, N-Methylpyrrolidine, Piperidine, and N-Methylpiperidine with Water: Thermodynamic, SANS, and Theoretical Studies

“…The corrected preferential solvation parameters point to self-preference of the pyrrolidine and water molecules in binary mixture due to their interactions rather than differences in their volumes . Single relaxational absorption determined in the ultrasound attenuation studies of aqueous solutions of pyrrolidine in the frequency range 3.0–220 MHz was explained by a proton transfer reaction, while aqueous piperidine showed also another relaxation process in this frequency range, associated with an aggregation of nonionized molecules …”

“…10 Single relaxational absorption determined in the ultrasound attenuation studies of aqueous solutions of pyrrolidine in the frequency range 3.0−220 MHz was explained by a proton transfer reaction, while aqueous piperidine showed also another relaxation process in this frequency range, associated with an aggregation of nonionized molecules. 11 Important difference between piperidine and N-methylpiperidine (as well as between pyrrolidine and N-methylpyrrolidine) is the ability to self-association of the former due to N−H•••N bonds. In crystals, neat piperidine and pyrrolidine form chains of hydrogen-bonded molecules.…”

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

“…Deep understanding of the DSP self-association and its thermodynamic profile is crucial for predicting the docking properties of this molecule, which has important implications in effective drug design. Ultrasonic relaxation spectroscopy has been proved as an effective tool in studying association-dissociation mechanisms (Nishikawa et al 1991 ), proton-transfer reactions (Nishikawa et al 1973a , b , 1996 ; Nishikawa and Kamimura 2011 ; Huang et al 1999 ; Tsigoias et al 2020 a), conformational changes (Bae et al 2001 ; Bae et al 2002 ; Kalampounias 2020 ; Stogiannidis et al 2020 ), complexation (Tamm 1961 ; Petrucci 1971 ), backbone segmental motion and normal mode relaxation in polymers (Kouderis et al 2021 ; Siafarika et al 2021 ) and reaction engineering in general (Bernasconi 1976 ). Furthermore, in several cases systematic analysis of the acoustic spectra permits disentangling between different processes taking place in close time scales (Kouderis et al 2021 ).…”