Structure and principles of self-assembly of giant “sea urchin” type sulfonatophenyl porphine aggregates

Abstract

Principles of molecular self-assembly into giant hierarchical structures of hundreds of micrometers in size are studied in aggregates of meso-tetra(4-sulfonatophenyl)porphine (TPPS4). The aggregates form a central tubular core, which is covered with radially protruding filamentous non-branching aggregates. The filaments cluster and orient at varying angles from the core surface and some filaments form bundles. Due to shape resemblance, the structures are termed giant sea urchin (GSU) aggregates. Spectrally resolved fluorescence microscopy reveals J- and H-bands of TPPS4 aggregates in both the central core and the filaments. The fluorescence of the core is quenched while filaments exhibit strong fluorescence. Upon drying, the filament fluorescence gets quenched while the core is less affected, showing stronger relative fluorescence. Fluorescence-detected linear dichroism (FDLD) microscopy reveals that absorption dipoles corresponding to J-bands are oriented along the filament axis. The comparison of FDLD with scanning electron microscopy (SEM) reveals the structure of central core comprised of multilayer ribbons, which wind around the core axis forming a tube. Polarimetric second-harmonic generation (SHG) and third-harmonic generation microscopy exhibits strong signal from the filaments with nonlinear dipoles oriented close to the filament axis, while central core displays very low SHG due to close to centrosymmetric organization. Large chiral nonlinear susceptibility points to helical arrangement of the filaments. The investigation shows that TPPS4 molecules form distinct aggregate types, including chiral nanotubes and nanogranular aggregates that associate into the hierarchical GSU structure, prototypical to complex biological structures. The chiral TPPS4 aggregates can serve as harmonophores for nonlinear microscopy.

Digital polarimetric second harmonic generation microscopy of partially oriented fiber structures

“…For modeling of collagen fibers, a molecular susceptibility ratio of is assumed. For an example of fibers with achiral molecular susceptibility ratio above 3, fibrillar TPPS 4 aggregates with are considered (28). Main fiber configurations affecting the SHG intensity, I , R and C ratios in the focal volume are presented in the following sections.…”

Polarimetric response of second harmonic generation in microscopy of chiral fibrillar structures

“…The filaments of meso-tetra(4-sulfonatophenyl)porphine (TPPS 4 ) aggregates from the giant sea urchin (GSU) type aggregate preparations were used for investigations (22). The preparation of TPPS 4 aggregates is described elsewhere (22). Briefly, a 10 − 3 M stock solution of TPPS 4 was prepared by dissolving the powder (Sigma Aldrich, St. Louis, Missouri, USA) in distilled water.…”

“…(2) zxx = 1.4 for collagen (7,14,18,26,27) and |χ (2) zzz | χ (2) zxx = 6.5 for TPPS 4 (20,22) fibers. For α=0°, R ′ will have the same value as the molecular susceptibility ratio (see eq.…”

“…(3, 4). The characteristic molecular values are taken for collagen (7, 14, 18, 26, 27) and for TPPS 4 (20, 22) fibers. For α =0°, R ′ will have the same value as the molecular susceptibility ratio (see eq.…”

“…The study employs polarization-in polarization-out (PIPO) SHG microscopy (7, 14, 21) to investigate collagen ultrastructural organization in rat tail tendon, rabbit cornea and pig cartilage tissues, and chiral fibers of mesotetra (4-sulfonatophenyl) porphine (TPPS 4 ) molecules in giant “sea urchin” (GSU) aggregates (22). Digital nonlinear microscopy modeling results published in the preceding paper (20) will be used to interpret the experimental polarimetric results.…”