Does Thermosalient Effect Have to Concur with a Polymorphic Phase Transition? The Case of Methscopolamine Bromide

Teodoro Klaser,Michele Zema,José Fernandes,Željko Skoko,Serena Tarantino,Jasminka Popović

doi:10.3390/cryst8070301

Teodoro Klaser, Michele Zema + Show 4 more

Open Access

https://doi.org/10.3390/cryst8070301

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Abstract

In this paper, we report for the first time an observed thermosalient effect that is not accompanied with a phase transition. Our experiments found that methscolopamine bromide—a compound chemically very similar to another thermosalient material, oxitropium bromide—exhibited crystal jumps during heating in the temperature range of 323–340 K. The same behavior was observed during cooling at a slightly lower temperature range of 313–303 K. Unlike other thermosalient solids reported so far, no phase transition was observed in this system. However, similar to other thermosalient materials, methscolopamine showed unusually large and anisotropic thermal expansion coefficients. This indicates that the thermosalient effect in this compound is caused by a different mechanism compared to all other reported materials, where it is governed by sharp and rapid phase transition. By contrast, thermosalient effect seems to be a continuous process in methscolopamine bromide.

Highlights

Materials that exhibit mechanical response to external stimuli in the form of jumping, bursting, curling, bending, etc. are at the frontier of research into potential actuators at the nanoscale.Molecular crystals that exhibit such behavior are extremely interesting from a scientific aspect, and from a technological point of view due to the rapidness of their actuation
Thermosalient compounds are known to belong to different classes of materials—from simple organic molecules to organometallic compounds, from metal complexes all the way to inorganic solid—all thermosalient compounds exhibit three common features: 1) crystallinity, 2) negative thermal expansion for at least of one of the cell parameters, and 3) a phase transition concomitant with a sudden change of cell parameters
Results presented this work show that thermosalient possible even without presented in this work that thermosalient effectwe is have possible evenacquired withoutinphase transition and phase transition and show that despite all the knowledge already this field, there is thatstill despite all the knowledge we have already acquired in this field, there is still a long way before a long way before the mystery of thermosalient effect is resolved

Summary

Introduction

Materials that exhibit mechanical response to external stimuli (heat or light) in the form of jumping, bursting, curling, bending, etc. are at the frontier of research into potential actuators at the nanoscale. In the light of all the new cognitions on thermosalient behavior and several after published a comprehensive study on TS materials, we again return to the anticholinergic agent first published a comprehensive study on TS materials, we again return to the anticholinergic oxitropium bromide, whichwhich sparked our initial in this field [14].field. We do this by examining methscopolamine bromide, a compound chemically very similar to oxitropium thisbromide. By examining methscopolamine bromide, a compound chemically very similar to oxitropium. We use variation temperature study to show that methscopolamine bromide exhibits thermosalient behavior without any associated phase transition. Methscopolamine exhibits thermosalient behavior without anyIndeed, associated phase transition. This is contrarybromide to all previously reported thermosalient materials.

Materials and Methods

Hot-Stage Microscopy

Hot-Stage Microscopy and Thermal Analysis

In variable temperature ofmethscopolamine methscopolamine bromide