The Long-Lasting Story of One Sensor Development: From Novel Ionophore Design toward the Sensor Selectivity Modeling and Lifetime Improvement

The metalloporphyrin ligand bearing incorporated anion-exchanger fragment, 5-[4-(3-trimethylammonium)propyloxyphenyl]-10,15,20-triphenylporphyrinate of Co(II) chloride, CoTPP-N, has been tested as anion-selective ionophore in PVC-based solvent polymeric membrane sensors. A plausible sensor working mechanism includes the axial coordination of the target anion on ionophore metal center followed by the formed complex aggregation with the second ionophore molecule through positively charged anion-exchanger fragment. The UV-visible spectroscopic studies in solution have revealed that the analyte concentration increase induces the J-type porphyrin aggregation. Polymeric membranes doped with CoTPP-N showed close to the theoretical Nernstian response toward nitrite ion, preferably coordinated by the ionophore, and were dependent on the presence of additional membrane-active components (lipophilic ionic sites and ionophore) in the membrane phase. The resulting selectivity was a subject of specific interaction and/or steric factors. Moreover, it was demonstrated theoretically and confirmed experimentally that the selection of a proper ratio of ionophore and anionic additive can optimize the sensor selectivity and lifetime.

AGGREGATION OF MS-MONOPYRIDYL-Β-OCTAALKYLPORPHYRINS IN DICHLOROMETHANE IN PRESENCE OF Pd(II)

Aggregation of 13,17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-4-yl) porphyrin (I), 13,17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-3-yl)porphyrin (II) and 13.17-diethyl-2,3,7,8,12,18-hexamethyl-5-(pyridin-2-yl)porphyrin (III) in the presence of trans-bis(benzonitrile)palladium(II) dichloride was studied by dynamic light scattering and electronic absorption spectroscopy in dichloromethane at 293 K. The average aggregate size and the nature of their distribution were determined. Using scanning electron microscopy, it was determined the size and composition of clusters formed by aggregates of complexes of the palladium(II) cation with the studied porphyrins. It was shown that minimal acetic acid additions lead to the destruction of the corresponding clusters. At the same time, complete destruction of the aggregates does not occur even with a 100-fold molar excess of acid.We used the Zetasizer Nano ZS (model ZEN3600, Malvern Instruments), equipped with a 633nm laser and non-invasive backscattering (NIBS) technology when the scattered light detector is positioned at an angle of 173° to the incident light. Confirmation of porphyrin aggregation was performed by additional study of the structure using a Hitachi TM4000Plus desktop electron microscope equipped with a 4-segment highly sensitive semiconductor detector and a secondary electron detector for low vacuum mode. Elemental analysis of the obtained aggregates in the cluster was performed using a silicon drift detector with a working area of 30 mm2, combined with a Hitachi TM4000Plus microscope. It was found that aggregates consisting of a para-pyridyl derivative of alkylporphyrin and trans-bis (benzonitrile) palladium (II) dichloride are formed in dichloromethane at 293 K. The best results of porphyrin structures were observed for mixtures of 13,17-diethyl-2,3,7,8,12,18-5-hexamethyl-5-(pyridine-4-yl)porphyrin with TRANS-bis(benzonitrile)- palladium (II) dichloride in a ratio of 1:3, which is probably due to less spatial shielding of the reaction center of the macrocycle and, as a result, better stabilization of the resulting particles. The size of a cluster consisting of individual aggregates was measured using scanning electron microscopy. An elemental analysis of a single aggregate was obtained.

Amphiphilic Porphyrin Aggregates: A DFT Investigation

Owing to the attractive potential applications of porphyrin assemblies in photocatalysis, sensors, and material science, studies presently concerning porphyrin aggregation are widely diffused. π–π stacking, H-bonding, metal coordination, hydrophobic effect, and electrostatic forces usually drive porphyrin interaction in solution. However, theoretical studies of such phenomena are still limited. Therefore, a computational examination of the different porphyrin aggregation approaches is proposed here, taking into account amphiphilic [5-{4-(3-trimethylammonium)propyloxyphenyl}-10,15,20-triphenylporphyrin] chloride, whose aggregation behavior has been previously experimentally investigated. Different functionals have been adopted to investigate the porphyrin dimeric species, considering long-range interactions. Geometry optimization has been performed, showing that for the compound under analysis, H-type and cation–π dimers are the most favored structures that likely co-exist in aqueous solution. Of note, frontier orbital delocalization showed an interesting interaction between the porphyrin units in the dimer at the supramolecular level.

Effect of zinc cations on the kinetics of supramolecular assembly and the chirality of porphyrin J-aggregates

The key role of adventitious zinc(ii) ions, extracted from glass and quartz surfaces, in the kinetics of porphyrin aggregation and in the subsequent expression of their chirality is discussed herein.