Thermal stability and molecular dynamics of triclosan in solid state studied by 35Cl–NQR spectroscopy and DFT calculations

Conformations and intermolecular interactions pattern in solid chloroxylenol and triclosan (API of anti‐infective agents and drugs). A 35Cl NQR, 1H‐14 N NQDR, X‐ray and DFT/QTAIM study

“…The difference between 35 Cl NQR frequency at 90 and 100 K is in fact within the width of the line, thus negligibly small. The smooth changes in NQR frequency with increasing temperature from 77 to 300 K and similar parameters of the unit cells at RT and at 90 K ( a = 12.5225 Å, b = 12.5225 Å and c = 6.6809 Å, Table vs a = 12.6410 Å, b = 12.6410 Å and c = 6.7163 Å) confirm no phase transformation from RT to 90 K during the data collection. The 35 Cl NQR frequencies in triclosan labelled as Cl(2'), Cl(4') and Cl(5), Table , are within the range expected from the mono‐chlorophenol and di‐chlorophenol derivatives …”

“…For Cl(5) and Cl(2'), both involved in above mentioned contacts, imposing rigidity of the molecular structure, the slope coefficients of the temperature dependencies of 35 Cl‐NQR frequencies are close (−6⋅10 −5 and −5⋅10 −5 1/K) and smaller than those for the unbound Cl(4') (−9⋅10 −5 1/K). Additionally, the electron density and its Laplacian at BCP of Cl(2') ···O bond is noticeably smaller at 90 K than at RT (0.068 vs 0.114 and 0.0252 vs 0.0435, Table ); thus, Cl(2') is strongly bonded, and it is apparently less mobile than the other chlorine atoms.…”

“…Equation is derived by assuming that a single torsional mode dominates the temperature dependence of the NQR frequency. Assuming the coefficient values obtained from the fit of Eqn to the experimental data, Table , it is possible to predict the differences in 35 Cl NQR frequencies at Cl(5), Cl(4') and Cl(2') sites in triclosan resulting from a 10 ° decrease in temperature (i.e. from 100 to 90 K) which is equal to 0.017, 0.023 and 0.013 MHz.…”

“…Our previous studies of triclosan, only by 35 Cl NQR and DFT, aimed to determine the thermal stability of triclosan, have not indicated any phase transitions, which would suggest the conformation stability. However, they also proved that unambiguous determination of the actual conformation realised in the solid state of the two possible ones is impossible on the basis of 35 Cl‐NQR and DFT calculations only . Some light on the stability of conformation can be shed by the information about the presence and strength of weak intramolecular C‐H···π interaction that locks up the molecular conformation of diphenyl ether which structurally resembles triclosan .…”

Temperature-dependent Photodegradation in UV-resonance Raman Spectroscopy

“…The energy of ~1 kJ/mol is equivalent to the activation energy of inner-molecular bond rotation. 22 In the case of a macromolecule, such as BChl, the inner-molecular rotation plays an important role for chemical reactions, which will lead to degradation of the molecule.…”