Achiral diprotonated porphyrins, forming homoassociates in aqueous solution, lead to spontaneous chiral symmetry breaking. The unexpected result is that the chirality sign of these homoassociates can be selected by vortex motion during the aggregation process. This result is confirmed by means of circular dichroism spectra. These experimental findings are rationalized in terms of the asymmetric influence of macroscopic forces on bifurcation scenarios and by considering the specific binding characteristics of the porphyrin units to form the homoassociates.

The title porphyrin shows non ideal cmc with formation of J-aggregates, due to the formation of intermolecularly stabilized zwitterions, which at high concentration also results in H-aggregates.

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Spontaneous deracemizations is a challenging, multidisciplinary subject in current chirality research. In the absence of any chiral inductors, an achiral substance or a racemic composition is driven into an enantioenriched or even homochiral state through a selective energy input, e.g., chemical potential, photoirradiation, mechanical grinding, ultrasound waves, thermal gradients, etc. The most prominent examples of such transformations are the Soai reaction and the Viedma deracemization. In this review, we track the most recent developments in this topic and recall that many other deracemizations have been reported for solutions from mesophases to conglomerate crystallizations. A compiled set of simply available achiral organic, inorganic, organometallic, and MOF compounds, yielding conglomerate crystals, should give the impetus to realize new experiments on spontaneous deracemizations. Taking into account thermodynamic constraints, modeling efforts have shown that structural features alone are not sufficient to describe spontaneous deracemizations. As a guideline of this review, particular attention is paid to the physicochemical origin and symmetry requirements of such processes.

Stir it up! Comparison of the evolution with time of J‐aggregates of the title porphyrin in stagnant and vortex‐stirred solutions showed that chiral‐sign selection is due to the action of hydrodynamic gradients (shear flows) on particle folding. Brownian dynamics (stagnant solution) result in irregularly folded mesophases, whereas hydrodynamic gradients (vortex stirring) lead to long‐order folding and formation of helical ribbons (see picture).

In a closed system an irreversible enantioselective autocatalysis coupled to a mutual inhibition reaction, corresponding to a fast and low exergonic formation of the heterochiral dimer which reverts to the monomers in the final reaction work-up, yields absolute asymmetric synthesis even in the absence of chiral polarizations. This is due to the very high chiral amplifications of the initial small statistical deviations from the ideal racemic composition. Moreover, this system is sensitive to very small chiral polarizations (energy differences between transition states below the mJ mol(-1) range). This behaviour can also be observed in reversible exergonic reactions, because the racemization time scale is substantially longer than that of the transformation of the initial reagents. The effect of the presence of other reactions likely to occur (i.e. non-catalytic transformations, non-enantioselective catalysis and homodimer formation) is discussed. Even if these decrease the sensitivity of the network in several chemical scenarios, the emergence of kinetically controlled spontaneous symmetry breaking is not hindered. These features, together with the response of the system to a sequential reaction procedure, suggest that a similar type of network is at the heart of the Soai reaction.

The structure of the meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS 4 ) J-aggregates could be determined by X-ray and electron diffraction methods. A sheet-like architecture reveals the relationship between structure and chirality, optics and shapes of the J-aggregate of the meso 4-sulfonatophenyl-and phenyl-10 substituted porphyrins. The structure of the J-aggregates of H 4 TPPS 4 belongs to the chiral space group P2 1 and includes four porphyrin molecules in its unit cell. The intermolecular stabilization of the zwitterionic units by hydrogen bonding and electrostatic interactions between the positively charged central NH groups and the periphery anionic sulfonato groups results in a structure of porphyrins sheets along the [

There are few unambiguous reports describing the transfer of chirality from stirring vortices down to the level of electronic transitions. In this tutorial review the methods reported are discussed as well as the structural trends that seem to be necessary conditions in order to detect this phenomenon.