Counteranion Dependent Protonation and Aggregation of Tetrakis(4-sulfonatophenyl)porphyrin in Organic Solvents

J-aggregation of 5, 10, 15, 20-tetraphenyl-21H, 23H-porphinetetrasulfonic acid in a molecular crowding environment simulated using dextran

In a molecular crowding environment, different thermodynamics is often observed in a dilute solution. One such example is the promotion of the formation of amyloids, which are causal agents of Alzheimer's disease. Although a considerable number of molecular crowding studies have been reported, its effect remains unclear. In this study, we investigated a J-aggregation of a porphyrin derivative, 5, 10, 15, 20-tetraphenyl-21H,23H-porphinetetrasulfonic acid (TPPS), in a molecular crowding environment simulated by dextran (Dex) in HClO₄, HCl, and NaCl solutions. The changes in the number of monomers in the J-aggregate (n) with the concentration of Dex (C_Dex) depended on the type of solution. No change in n was observed in the NaCl solution, which indicated that the Dex solution did not affect the J-aggregation because of the ionic strength effect. In the HCl solution, the aggregation behavior changed with the pH. Further, at a low pH, the electrostatic interactions promoted J-aggregation by the volume exclusion of Dex, while the aggregation was suppressed at a high pH owing to steric hindrance. A different aggregation mechanism, involving the hydrogen bonding between NH in the center of the TPPS macrocyclic frame and the SO₃H and ClO₄^- functional groups, was responsible for the J-aggregation in the HClO₄ solution. Moreover, the n value increased owing to the volume exclusion effect. We expect that this study will be useful for further elucidation of the molecular crowding effect.

Sn(IV) Porphyrin-Based Ionic Self-Assembled Nanostructures and Their Application in Visible Light Photo-Degradation of Malachite Green

A series of porphyrin-based ionic complexes were prepared through the reaction of two porphyrin precursors, 5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrin H2TPhPyP (1) and trans-dihydroxo [5,10,15,20-tetrakis(4-(2-pyridyl)phenyl)porphyrinato]tin(IV) Sn(OH)2TPhPyP (2), with various acids (HCl, HNO3, CF3COOH, H2SO4, H2CO3, and H3PO4). The complexes were characterized via elemental analysis, 1H nuclear magnetic resonance spectroscopy, electrospray ionization mass spectrometry, Fourier transform infrared (FT-IR) spectroscopy, ultraviolet (UV)-visible spectroscopy, fluorescence spectroscopy, and field-emission scanning electron microscopy (FE-SEM). Each compound exhibited different results for UV-visible, fluorescence, FT-IR, and FE-SEM studies depending on the counter anions. The complexes possessed different self-assembled nanostructures based on electronic interactions between the cations of compounds 1 and 2 with different counter anions. These aggregated species are stabilized by electrostatic forces and the π-π stacking interactions between the two porphyrin rings, in which the counter anions play an important bridging role. The counter anions also play an important role in controlling the morphology and photocatalytic properties of the as-developed materials. The complexes were then used for the photocatalytic degradation of the malachite green (MG) dye in aqueous media under visible light irradiation for up to 70 min. A morphology-dependent photocatalytic degradation of the MG dye was observed for all the ionic complexes, with efficiencies ranging from 50% to 95%.

Substituent Effect on Porphyrin Film-Gas Interaction by Optical Waveguide: Spectrum Analysis and Molecular Dynamic Simulation

Substituent effect on optical gas sensing performance in porphyrin-based optical waveguide detection system was studied by molecular dynamics simulation (MDS), absorption/emission spectrum analysis, and optical waveguide (OWG) detection. The affinities of porphyrin with seven types of substituents (-H, -OH, -tBu, -COOH, -NH2, -OCH3, -SO3-) on para position of meso-phenyl porphyrin toward gas molecules in adsorption process were studied in different size of boxes with the same pressure and concentration. Analyte gases (CO2, H2S, HCl, NO2) were exposed to porphyrin film in absorption spectrophotometer, and in OWG with evanescent field excited by a guiding laser light with 670 nm wavelength. The extent of interaction between host molecule and the guest analytes was analyzed by the number of gas molecules in vicinity of 0.3 nm around substituents of porphyrin molecules. Optical waveguide results reveal that sulfonate porphyrin is mostly responsive to hydrochloride, hydrosulfide gas and nitrogen dioxide gases with strong response intensity. Molecular dynamics and spectral analysis provide objective information about the molecular state and sensing properties. Molecular rearrangements induced by gas exposure was studied by spectral analysis and surface morphology before and after gas exposure taking hydrosulfide gas as an example. Film-gas interaction mechanism was discussed in terms of each gas and substituent group characters.

Potential-Induced Aggregation of Anionic Porphyrins at Liquid|Liquid Interfaces

The adsorption and self-aggregation of anionic porphyrins were studied at the polarized water|1,2-dichloroethane (DCE) interface by polarization-modulation total internal reflection fluorescence (PM-TIRF) spectroscopy. 5,10,15,20-Tetrakis(4-sulfonatophenyl)porphyrin diacid (H₄TPPS^2-) and protoporphyrin IX (H₂PP^2-) exhibited high surface activities at the interface. The selective excitation of interfacial species in PM-TIRF measurements elucidated the potential-induced aggregation mechanism of the porphyrins. The J-aggregates of H₄TPPS^2- were reversibly formed only at the water|DCE interface by applying appropriate potentials even when the porphyrins exist as monomers in the aqueous and organic solutions. In the H₂PP^2- system, the slow aggregation process was found in the negative potential region. The spectral characteristics and the signal phase of PM-TIRF indicated that the H₂PP^2- monomers were adsorbed with relatively standing orientation and that the long axis of the J-aggregates was nearly in plane of the interface. H₂PP^2- was also investigated at the biomimetic phospholipid-adsorbed water|DCE interface. The competitive adsorption of neutral glycerophospholipids effectively inhibited the potential-dependent adsorption and interfacial aggregation processes of H₂PP^2-. The results demonstrated that the aggregation state of the charged species can reversibly be controlled at liquid|liquid interfaces as a function of externally applied potential.

Spectroscopic investigations on chiral J-aggregates induced by tartaric acid in alcoholic solution

Chiral J-aggregates of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS[Formula: see text] have been obtained in ethanol solution triggered by addition of both enantiomeric forms of tartaric acid. A detailed spectroscopic investigation has been performed on aggregates obtained by a well-defined mixture protocol of reactants. Our findings show as both aggregation process and induced supramolecular chirality essentially depend on the concentration of the reactants. Contrary to what occurs in aqueous solution, TPPS4 in ethanol solution shows: (i) at low porphyrin concentration, an aggregation behavior characterized by a L-tartaric acid threshold whereas the D-tartaric does not work even at high concentrations, so revealing an enantiomeric discrimination; (ii) at high porphyrin concentration, a large kinetic discrimination of D- vs. L-enantiomer.

Preparation and characterization of a pH-responsive membrane carrier for meso-tetraphenylsulfonato porphyrin

The pH-responsive PSF-g-P4VP-blended PSF membrane smartly rejects meso-tetraphenylsulfonato porphyrin (TPPS) and induces TPPS to form J-type aggregates.

Determination of LMF binding site on a HSA-PPIX complex in the presence of human holo transferrin from the viewpoint of drug loading on proteins

Holo transferrin (TF) and the natural complex of human serum albumin and protoporphyrin IX (HSA-PPIX) are two serum carrier proteins that can interact with each other. Such an interaction may alter their binding sites. In this study, fluorescence spectroscopy, as well as zeta potential and molecular modeling techniques, have been used to compare the complexes (HSA-PPIX)-LMF and [(HSA-PPIX)-TF]-LMF. The Ka1, Ka2, values of (HSA-PPIX)-LMF and [(HSA-PPIX)-TF]-LMF were 1.1×10(5) M(-1), 9.7×10(6) M(-1), and 2.0×10(4) M(-1), 1.8×10(5) M(-1), respectively, and the n1, n2 values were respectively 1.19, 1.53 and 1.17, 1.65. The second derivative of the Trp emission scan of (HSA-PPIX)-LMF exhibited one negative band at 310 nm, whereas for the [(HSA-PPIX)-TF]-LMF system, we observed one negative band at 316 nm indicating an increase in polarity around Trp. The effect of TF on the conformation of (HSA-PPIX)-TF was analyzed using three-dimensional fluorescence spectroscopy. The phase diagram indicated that the presence of a second binding site on HSA and TF was due to the existence of intermediate structures. Zeta potential analysis showed that the presence of TF increased the positive charges of the HSA-PPIX system. Site marker experiments revealed that the binding site of LMF to HSA-PPIX changed from Sudlow's site IIA to Sudlow's site IIIB in the presence of TF. Moreover, molecular modeling studies suggested the sub-domain IIIB in HSA as the candidate place for the formation of the binding site of LMF on the (HSA-PPIX)-TF complex.

Fluorescence quenching and spectrophotometric methods for the determination of daunorubicin with meso-tera (4-sulphophenyl) porphyrin as probe

In this work, a synthetic meso-tera (4-sulfophenyl) porphyrin (TPPS4) was used as a probe to determine daunorubicin (DNR) by fluorescence quenching and spectrophotometric methods. At pH 4.6 potassium acid phthalate-NaOH buffer solution, a 1:1 complex of DNR interacted with TPPS4 formed via the electrostatic attractions and hydrophobic interactions, thus resulted in TPPS4 fluorescence quenching and absorption spectra change. The maximum excitation wavelength (λex) and the maximum emission wavelength (λem) are 435 nm and 672 nm, respectively. The fluorescence quenching values (ΔF) are the good linear relationship to the concentration of DNR in the range of 0.8-6.0 mgL(-1). The method exhibits high sensitivity with the detection limit (3σ) being 27.0 ng mL(-1). Meanwhile, a decrease of absorbance is detected at 433 nm with the appearance of a new absorption peak at 420 nm. The optimum reaction conditions, influencing factors and the effect of coexisting substances have been investigated in our experiment. The results showed that the method had a good selectivity and could be applied to determine DNR in serum and urine samples. In addition, the combine ratio between DNR and TPPS4 was measured and the charge distribution before and after reaction was calculated by quantum chemistry calculation AM1 method. The type of fluorescence quenching was discussed by the absorption spectra change, Stern-Volmer plots and fluorescence lifetime determination.

Interaction between holo transferrin and HSA-PPIX complex in the presence of lomefloxacin: an evaluation of PPIX aggregation in protein-protein interactions

Human serum albumin (HSA) and holo transferrin (TF) are two serum carrier proteins that are able to interact with each other, thereby altering their binding behavior toward their ligands. During the course of this study, the interaction between HSA-PPIX and TF, in the presence and absence of lomefloxacin (LMF), was for the first time investigated using different spectroscopic and molecular modeling techniques. Fluorescence spectroscopy experiments were performed in order to study conformational changes of proteins. The RLS technique was utilized to investigate the effect of LMF on J-aggregation of PPIX, which is the first report of its kind. Our findings present clear-cut evidence for the alteration of interactions between HSA and TF in the presence of PPIX and changes in drug-binding to HSA and HSA-PPIX complex upon interaction with TF. Moreover, molecular modeling studies suggested that the binding site for LMF became switched in the presence of PPIX, and that LMF bound to the site IIA of HSA. The obtained results should give new insight into research in this field and may cast some light on the dynamics of drugs in biological systems.

Inhibition of aggregation of meso-tetra(4-sulfonatophenyl)-porphyrin (H4TPPS) by urea

The inhibition of the formation of J-aggregates of meso-tetra(4-sulfonatophenyl)-porphyrin ( H 4 TPPS ) by urea is investigated spectroscopically by absorbance, fluorescence, and fluorescence lifetime techniques. In 8 M urea at pH 2 with 0.1 M NaCl , diacid TPPS ( H 4 TPPS ) exists as a monomer up to 75 μM H 4 TPPS where the absorbance is linearly dependent on porphyrin concentration. The extinction coefficient of monomeric H 4 TPPS in 8 M urea at pH 2 with 0.1 M NaCl at 438 nm is 4.43 × 105 M -1. cm -1. No aggregation peaks at 491 nm and 708 nm are found in the 0.5-75 μM concentration range. Aggregated H 4 TPPS (10 μM) molecules in pH 2 buffer dissociate to monomers when the temperature is raised to 65°C. In D 2 O at pH 2, no aggregation is observed. These spectral observations suggest that the H 4 TPPS aggregation involves intermolecular hydrogen bonding.

Spectroscopic studies of aggregation behavior of meso-tetra(4-hydroxyphenyl)porphyrin in aqueous AOT solution

The interactions of two amphiphilic porphyrins with anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in aqueous solutions were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, resonance light scattering technique, fluorescence anisotropy and surface tension measurements. The two porphyrins, meso-tetra(4-hydroxyphenyl)porphyrin (THPP) and meso-tetra(3,5-dibromo-4-hydroxylphenyl)porphyrin (T(DBHP)P), exist as irregular aggregates in aqueous solutions with a broad and low absorption peak near the maximum of monomer peak. The interaction of THPP with AOT leads to the formation of a fluorescent aggregate of porphyrin which was assigned as J-type aggregate according to exciton theory. A long red-shifted Soret band together with a new strong Q-band, a broad emission peak and a sharply peaked resonance light scattering signal are observed for this J-aggregate. The formation of J-aggregate is independent of the initial THPP concentration and can be influenced greatly by ionic strength. The aggregation kinetics has been investigated by UV-vis absorption spectroscopy and fluorescence anisotropy. Conversion of the porphyrin monomers to J-aggregate is observed. The addition of THPP increases the surface tension of solution and changes the critical micelle concentration of AOT. J-aggregate was not observed for T(DBHP)P in AOT solutions which only shows solubilization. The mechanism of aggregation was discussed.

Hydrogen bond controlled adduct formation of meso-tetra(4-sulfonatophenyl)porphyrin with protic acids: a UV-vis spectroscopic study

Interaction of meso-tetra(4-sulfonatophenyl)porphyrin (H2tppS4) with weak and strong protic acid have been studied by UV-vis spectroscopy in water, dichloromethane and methanol. Different shifts of the Soret and Q(0,0) bands in the three solvents, the aggregation of diprotonated species and the stability of porphyrin-acid adducts in the solution, may be explained by the inter- and intramolecular hydrogen bonds. Whilst, the addition of excess amounts of tetra-n-butylammonium chloride to H2tppS4(Cl)2 in dichloromethane has little to no effect on the UV-vis spectrum of the dication, gradual addition of tetra-n-butylammonium hydrogen sulfate to the dichloromethane solution of H2tppS4(H2SO4)2 leads to the degradation of adducts and the release of porphryin. The results of this study clearly show the crucial role played by hydrogen bonds between the porphyrin diprotonated species and the counter ion in the stability of porphyrin diacids in solution.

Stiffness tunable molecular spring washers: high-pressure Raman investigations on porphyrin self-assemblies

The Raman spectra of a series of meso-substituted porphyrin self-assemblies have been measured as a function of pressure up to 13 GPa. In comparison with that for Tpp J-aggregates in our previous investigation [J. Phys. Chem. B, 2008, 112, 15562], a similar phenomenon has been observed in all meso-substituted self-assemblies, such as peaks in the spectrum which show positive linear pressure dependence which provides no evidence of the phase transition and the intensity enhancement of aromatic Psi(3) C-C stretching vibration with pressure. The different slopes of intensity ratios between Psi(3) C-C and C(a)-C(m) stretching vibration to pressure in these meso-substituted porphyrin self-assemblies indicate that the stiffness of molecular spring washers is tunable.

Surfactant-like behavior of short-chain alcohols in porphyrin aggregation

UV/vis absorption and time-resolved fluorescence measurements on alcoholic solutions of meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS(4)) in neutral and acid form have been performed as a function of the alcohol polarity. These solutions show a peculiar behavior that mimics porphyrin in confined water solutions. In alcohols, TPPS(4) exhibits a metastable phase showing the formation of new species in analogy with the confined water environment of AOT microemulsions. Various species have been detected at different pH values and on aging the solutions. Under neutral pH conditions, the porphyrin is present as free base monomer (S415) with a small amount of H-dimeric species (S400). On aging, the S415 leads to the formation of a new species (S423), which has been assigned as a J-type dimer of the neutral porphyrin. The species S400 and S423 are not present in bulk water solution but are typical of TPPS(4) in confined water. On decreasing pH, the S415 almost immediately converts into the diacid form (S438), which evolves toward red-shifted J-aggregates (S490) and blue-shifted H-aggregates (S420). On decreasing alcohol polarity, the kinetic evolution from fresh to aged solution and from the monomeric diacid species to H- and J-aggregates speeds up. Exploiting the amphiphilic character of short chain alcohols and widely varying their polarity, we were able to enhance in bulk conditions the peculiar behavior observed in close proximity to the microemulsion wall.

Acidification and assembly of porphyrin at an interface: counterion matching, selectivity, and supramolecular chirality

The interfacial diprotonation and assemblies of a free-base achiral porphyrin, 5,10,15,20-tetrakis(3,5-dimethoxyphenyl)-21H,23H-porphine, on various acidic subphases were investigated. It has been shown that the compound could be diprotonated in situ on an acidic subphase and can form assemblies. The interfacially organized supramolecular assemblies were transferred onto a solid substrate, and the assemblies showed supramolecular chirality. Interestingly, the supramolecular chirality of the assemblies of the diprotonated species showed a counterion-dependent behavior. For the assemblies fabricated from the aqueous HCl subphases, a strong Cotton effect (CE) could be observed, although the porphyrin itself is achiral. When an aqueous HBr solution was used as the subphase, the assemblies showed a weak CE, whereas no CE could be detected for the assemblies formulated from the HNO3 or HI subphase. Interestingly, when a mixture of HBr and NaCl, or HNO3 and NaCl, was employed as the subphase, the formed assemblies displayed chiral features similar to those fabricated on the HCl subphase, suggesting that the Cl(-) could be preferentially visualized in terms of supramolecular chirality, although the system itself is composed of achiral species. On the basis of the experimental facts and a theoretical calculation, an explanation with regard to the different sizes of the counterions and the distinct binding affinities of the counteranions to the diprotonated porphyrin species has been proposed. Our findings provide new insights into the assembly of the diprotonated porphyrins as well as the interfacially occurring symmetry breaking.

Exciton Coupling of Tetra(p-hydroxyphenyl)porphyrin Controlled by Substituents of Counterions in Triton X-100 Micellar Solution

The interactions of nonionic meso-tetra(p-hydroxyphenyl)porphyrin (THPP) with CX3COOH (X = F, Cl, Br) in Triton X-100 (TX) micellar solution have been investigated by optical absorption, resonance light-scattering, and fluorescence spectroscopies. The double red-shifted absorption bands and strong resonance light scattering (RLS) signal imply that the assemblies induced by trihalo acetic acids belong to J-aggregates. The fluorescence of porphyrin is quenched due to the aggregate formation. The kinetics of assemblies trigged by CBr3COOH is studied via stopped-flow techniques. No characteristics of autocatalyzed reactions are observed, and there is only a log phase. The nature of the exciton coupling of transition dipole moment can be systematically changed by the haloid substituents of the organic counteranion.

Aggregation Properties of Hyperporphyrins with Hydroxyphenyl Substituents

Acidification of tetrakis(4-hydroxyphenyl)porphyrin (THPP) and tetrakis(3,5-dihydroxyphenyl)porphyrin (OHPP) in dichloromethane solutions has been investigated as a function of the nature of the counteranion. These porphyrins exhibit different patterns of behavior, and extended aggregates are formed displaying broad extinction features together with intense components due to resonant light scattering. Especially in the case of haloacids, J-aggregated species are obtained exhibiting large bathochromic shifts both for B- and Q-bands, which extend in the far red region. The optical characteristics of the aggregated and monomeric protonated species are strongly influenced by the nature of the counteranions. A comparison with tetrakis(4-methoxyphenyl)porphyrin (TMPP), which remains always in a monomeric form, demonstrates the key role played by the peripheral hydroxyl groups in stabilizing various porphyrin aggregates.