New Evidence About the Spontaneous Symmetry Breaking: Action of an Asymmetric Weak Heat Source

In the present study, we show how, in a stagnant water solution of uncharged
aggregated achiral porphyrin-based molecules, a mirror-symmetry breaking (SB) can be induced
and controlled by means of a weak asymmetric thermal gradient. In particular, it is shown that the
optical activity of the aggregate porphyrin solution can be generated and reversed, in sign, only
acting on the thermal ramp direction (heating or cooling). In order to avoid data
misinterpretation, the aggregate structure modifications with the temperature change and the
linear dichroism contribution to circular dichroism spectra were evaluated. A model simulation,
using a finite element analysis approach describing the thermal flows, shows that small thermal
gradients are able to give rise to asymmetric heat flow. The results reported here can be considered
new evidence about the spontaneous symmetry breaking phenomenon induced by very weak forces having an important role in
the natural chiral selective processes.