Bottom-Up Hierarchical Self-Assembly of Chiral Porphyrins through Coordination and Hydrogen Bonds

Abstract

A series of chiral synthetic compounds is reported that show intricate but specific hierarchical assembly because of varying positions of coordination and hydrogen bonds. The evolution of the aggregates (followed by absorption spectroscopy and temperature-dependent circular dichroism studies in solution) reveal the influence of the proportion of stereogenic centers in the side groups connected to the chromophore ring in their optical activity and the important role of pyridyl groups in the self-assembly of these chiral macrocycles. The optical activity spans two orders of magnitude depending on composition and constitution. Two of the aggregates show very high optical activity even though the isolated chromophores barely give a circular dichroism signal. Molecular modeling of the aggregates, starting from the pyridine-zinc(II) porphyrin interaction and working up, and calculation of the circular dichroism signal confirm the origin of this optical activity as the chiral supramolecular organization of the molecules. The aggregates show a broad absorption range, between approximately 390 and 475 nm for the transitions associated with the Soret region alone, that spans wavelengths far more than the isolated chromophore. The supramolecular assemblies of the metalloporphyrins in solution were deposited onto highly oriented pyrolitic graphite in order to study their hierarchy in assembly by atomic force microscopy. Zero and one-dimensional aggregates were observed, and a clear dependence on deposition temperature was shown, indicating that the hierarchical assembly took place largely in solution. Moreover, scanning electron microscopy images of porphyrins and metalloporphyrins precipitated under out-ofequilibrium conditions showed the dependence of the number and position of chiral amide groups in the formation of a fibrillar nanomaterial. The combination of coordination and hydrogen bonding in the complicated assembly of these molecules -where there is a clear hierarchy for zinc(II)-pyridyl interaction followed by hydrogen-bonding between amide groups, and then van der Waals interactions -paves the way for the preparation of molecular materials with multiple chromophore environments.

Tumor Microenvironment‐Triggered Supramolecular System as an In Situ Nanotheranostic Generator for Cancer Phototherapy

“…These observations imply that appropriate intermolecular interactions between Mn 2+ and DVDMS molecules are necessary to form well-defined nanoDVD, which might be due to the competition of the interactions of the Mn 2+ and porphyrin ring/carboxylate radicals from DVDMS, and DVDMS π – π stacking. [7b,9] As expected, dynamic light scattering (DLS) data illustrated an increase in the average hydrodynamic size of nanoDVD with an increase in the [Mn 2+ ]/[DVDMS] ratio (Figure S1H, Supporting Information), but the electronegativity of the nanoDVD was reduced as the amount of Mn 2+ increased (Figure S1I, Supporting Information). Meanwhile, X-ray photoelectron spectroscopy (XPS) data further confirmed the nanoDVD supramolecular assemblies (Figure S2, Supporting Information).…”

“…[7] Considering the structure of DVDMS photosensitizers with unique spectroscopic and photochemical properties, it is strongly desirable to develop DVDMS-based supramolecular nanomaterials as a versatile and effective nanoplatform in cancer theranostics. Because Mn 2+ features a hexacoordinate nature due to its 3d 5 4s 0 outermost shell electrons, [7b,8] we reasoned that, by using supramolecular assembly, [7b,9] Mn 2+ could coordinate with the porphyrin ring and carboxylate radicals from DVDMS molecules (Figure 1A(a)) to form DVDMS nanoassemblies (Figure 1A(b)), which could potentially address the need for high-performance photosensitizers in cancer phototherapy.…”

Boosting Self‐Assembly Diversity in the Solid‐State by Chiral/Non‐Chiral ZnII‐Porphyrin Crystallization

“…( R )‐Methyl 2‐(4‐formylphenoxy)propionate was prepared by modifying a prior procedure to improve the yield . 5,10,15,20‐Tetrakis[( R,R,R,R )‐methyl‐2‐phenoxypropanoate]porphyrin, here denoted 4 R ‐H 2 PPP, was synthesized according to the procedure described elsewhere …”

Zinc Oxide–Porphyrin Hybrid Rhombuses: Catalytically Active Microstructures via Self‐Assembly

“…Driving forces can be hydrogen bonding, metal coordination, π–π interactions, ionic interactions, or the hydrophobic effect. In particular, the combination of different types of noncovalent interaction allows for a multitude of different structures …”