The key role of vibrational entropy in the phase transitions of dithiazolyl-based bistable magnetic materials

The neutral radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA) is a prototype of molecule-based bistable materials. TTTA crystals undergo a first-order phase transition between their low-temperature diamagnetic and high-temperature paramagnetic phases, with a large hysteresis loop that encompasses room temperature. Here, based on ab initio molecular dynamics simulations and new X-ray measurements, we uncover that the regular stacking motif of the high-temperature polymorph is the result of a fast intra-stack pair-exchange dynamics, whereby TTTA radicals continually exchange the adjacent TTTA neighbour (upper or lower) with which they form an eclipsed dimer. Such unique dynamics, observed in the paramagnetic phase within the whole hysteresis loop, is the origin of a significant vibrational entropic gain in the low-temperature to high-temperature transition and thereby it plays a key role in driving the phase transition. This finding provides a new key concept that needs to be explored for the rational design of novel molecule-based bistable magnetic materials.journal articl

Clinopodium gilliesii (Benth.) Kuntze

Clinopodium gilliesii (Benth.) Kuntze is an aromatic species from the Andean region, from southern Peru to northern-central Argentina. It is mainly known as muña-muña and its leaves and tender stems are used as a flavoring and medicinal: stimulant, against mountain sickness, aphrodisiac, digestive, antispasmodic, among others traditional uses. Its bioactive constituents are essential oils, to which the plant owes its aroma and many of its therapeutic properties. The presence of flavonoids and phenolic compounds has also been detected. The essential oil composition of aerial organs is variable according to geographical location and ecological conditions, soil-type, weather-conditions and altitude of the population. Regarding its popular uses, the majority of uses has not been validate by pre-clinical tests, therefore they require experimental founding. Some of its biological activities, e.g.: aphrodisiac (in particular, erectile dysfunction), against some gastrointestinal disorders, antibacterial, antifungal, antiplasmodial, trypanocidal, insect repellent, antioxidant, and cytotoxic activities have already been analyzed. Some data about the similar species: C. bolivianum (Benth.) Kuntze and C. odorun (Griseb.) Harley is additionally commented.Fil: Hurrell, Julio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Etnobotánica y Botánica Aplicada; Argentin