Seeding Chiral Ensembles of Prolinated Porphyrin Derivatives on Glass Surface: Simple and Rapid Access to Chiral Porphyrin Films.

Gabriele Magna,Manuela Stefanelli,Tanja Traini,Gaio Paradossi,Mario Luigi Naitana,Fabio Domenici,Mariano Venanzi,Donato Monti,Gianlorenzo Bussetti,Corrado Di Natale,Roberto Paolesse

doi:10.3389/fchem.2021.804893

Gabriele Magna, Manuela Stefanelli + Show 9 more

Open Access

https://doi.org/10.3389/fchem.2021.804893

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Abstract

An easy and fast method to achieve chiral porphyrin films on glass is herein reported. The on-surface formation of organized supramolecular architectures with distinctive and remarkable chiroptical features strictly depends on the macrocycles used, the solvent chosen for the casting deposition, and most importantly, on the roughness of the glass slide. Dynamic light scattering studies performed on 10−4–10−6 M porphyrin solutions revealed the presence of small porphyrin aggregates, whose size and number increase depending on the initial concentration. Once transferred on surface, these protoaggregates act as nucleation seeds for the following, self-assembling into larger structures upon solvent evaporation, with a process driven by a fine balance between intermolecular and molecule–substrate interactions. The described method represents a straightforward way to fabricate porphyrin-based chiral surfaces onto a transparent and economic substrate in few minutes. The results obtained can be particularly promising for the development of sensors based on stereoselective optical active films, targeting the detection of chiral analytes of practical relevance, such as the so-called emerging pollutants released in the environment from agrochemical, food, and pharmaceutical manufacturing.

Highlights

The understanding of chirality at solid surfaces is of ever-growing importance, and an increasing number of studies have been reported over the years to shed light on the fundamentals and practices in achieving chiral surfaces with definite enantioselectivity (Gellman, 2010; Zaera, 2017; Albano et al, 2020; Xu et al, 2021)
The achievement of a convenient signal for the detection is highly desirable. With this aim in mind, we have carried out the studies reported, concerning the development of a straightforward method to fabricate optically active films on glass by drop-casting of (L) or (D)-prolinated porphyrin building blocks dissolved in suitable organic solvents (Scheme 1)
For all the films tested, UV-vis spectra showed broad Soret bands, with peaks lying in the 435–440 nm range, red shifted if compared with the corresponding porphyrin solution (420–424 nm range), indicating that macrocycles are aggregated in J-type structures at solid state

Summary

INTRODUCTION

The understanding of chirality at solid surfaces is of ever-growing importance, and an increasing number of studies have been reported over the years to shed light on the fundamentals and practices in achieving chiral surfaces with definite enantioselectivity (Gellman, 2010; Zaera, 2017; Albano et al, 2020; Xu et al, 2021). Over the course of our research, we found that various amphiphilic porphyrin derivatives bearing a stereogenic information on the peripheral molecular positions form chiral mesoscopic structures of tunable size in different hydro–organic media, depending on the interplaying of structural motifs and solvent bulk properties (i.e., type and relative ratio of the hydro–organic mixture used, ionic strength, and monomer concentration) (Monti et al, 2010; Caroleo et al, 2019; Stefanelli et al, 2020a) Within this set of tetrapyrroles, cationic derivatives functionalized with a peripheral (L)-proline moiety have been exploited for the preparation of chiral films to be applied for sensor development. The easiness and the versatility of the described protocol make it a viable approach in fabricating chiral films based on porphyrins for stereoselective sensor applications

RESULTS AND DISCUSSION

Conclusion and future perspectives

DATA AVAILABILITY STATEMENT