title: Conformational stability and thermal pathways of relaxation in triclosan (antibacterial/excipient/contaminant) in solid-state: combined spectroscopic ((1)H NMR) and computational (periodic DFT) study.
abstract: The mechanism of molecular dynamics in the antibacterial/antifungal agent, triclosan (5-chloro-2-(2',4'-dichlorophenoxy)-phenol), in solid state was studied by (1)H NMR spectroscopy and periodic density functional theory (DFT) calculations. Temperature dependencies of the proton spin-lattice relaxation time (T1) in the ranges 86-293 and 90-250 K (at 15 and 24.667 MHz, respectively) and the second moment (M2) of the (1)H NMR resonant line in the range 103-300 K were measured. Two minima in the temperature dependence of T1 revealed a classical Arrhenius governed activation processes. The low temperature shallow minimum T1(T) of 71 s at 115 K, 15 MHz, which shifts with frequency, was assigned to classical hindered jumps of hydroxyl group around OC axis and with respect to a 5-chloro-2-phenol ring. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points is 9.68 kJ/mol. The pointed high temperature minimum T1(T) of 59 s at 190 K, 15 MHz, which also shifts with frequency, was assigned to the small angle librations by Θlib= ± 9° between two positions of equilibrium differing in energy by 7.42 kJ/mol. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points is 31.1 kJ/mol. Both motions result in a negligible reduction in the (1)H NMR line second moment, thus the second moment delivers an irrelevant description of the molecular motions in triclosan.
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.|Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland.
authors.forename: Jolanta Natalia
authors.initials: JN
authors.lastname: Latosińska
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.|Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Latosińska
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.|Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland.
authors.forename: Marzena Agnieszka
authors.initials: MA
authors.lastname: Tomczak
authors.affiliation: Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland.|Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland.
authors.forename: Wojciech
authors.initials: W
authors.lastname: Medycki
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry*; D004355:Drug Stability; D004785:Environmental Pollutants / Q000737:chemistry*; D005079:Excipients / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition; D011522:Protons; D013696:Temperature; D014260:Triclosan / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D004785:Environmental Pollutants; D005079:Excipients; D011522:Protons; D014260:Triclosan