Crystal-growth inhibition of solid porphyrin micro-crystals by G4 PAMAM dendrimer

We report on the effect of G4 PAMAM dendrimer on the formation of a previously reported solid porphyrin micro-crystals formed by two oppositely charged porphyrins [meso-tetra(N-methy-4-pyridyl)porphyrin tetratosylate (TMPyP) and zinc-tetrakis(4-sulphonatophenyl)porphyrin (Zn-TPPS)], by self-assembly at room temperature without acidification. The crystals were characterized by UV–visible spectroscopy, fluorescence spectroscopy, optical microscopy, and powder X-ray diffraction techniques. The addition of the G4 PAMAM dendrimer to the starting solution of the monomer porphyrins alters the size and morphology of the crystals as well as their absorbance and fluorescence spectra. However, the dendrimer is not incorporated in the structure.     

Intermolecular interactions in monolayers of porphyrins

Monolayers containing solely porphyrins with or without aliphatic chains or porphyrins mixed with phospholipids are studied on water on solid surfaces. The systems are manipulated on the water surface and characterized by film balance techniques, fluorescence microscopy, fluorescence and absorption spectroscopy and, after transfer onto solid supports, by optical and electron microscopy techniques. The data presented contain information on the interrelation between molecular and monolayer structure and on porphyrin-porphyrin and porphyrin-lipid interactions.Homogeneous monolayers can be formed only for porphyrins containing aliphatic chains or in dilution with lipids in the fluid phase. An ordered structure is obtained for zinc 3,8-bis(1'-heptadecenyl)deuteroporphyrin dimethylester (ZnHDPDME) that exhibits two aliphatic chains attached to one edge and two (hydrophilic) ester groups to the opposite edge of the porphyrin moiety. If these groups are bound to the same edge, a disordered structure with little tendency to aggregate formation is obtained.None of the porphyrins are soluble in the solid phase of phospholipids. As this is presumably due to the high packing density given by the area per hydrocarbon chain this is suggested to hold also for other aliphatic matrices including fatty acids.A strong decrease in fluorescence yield with increasing molecular density is observed for ZnHDPDME diluted in phospholipids. This suggests a change in the coordination of the central zinc atom of the porphyrin. As the environment can be changed in a defined and continuous way these systems offer the possibility of studying the relation between the microscopic surroundings and the optical properties.     

Micro-contact printing of polydiacetylene liposomes using hydrophilic stamps

Micron-sized polydiacetylene (PDA) liposome patterns have been fabricated on titanium (Ti) substrates using a micro-contact printing (micro-CP) technique. Two types of stamps (PDMS and agarose) and inking methods ("soaking" and "dropping") are used for micro-CP, and we compare their effect on the morphology of the PDA patterns. The size and morphology of the patterned PDA liposomes are analysized by optical and fluorescence microscopies and atomic force microscopy (AFM). When the agarose stamp is inked by the "dropping" method, PDA patterns are most efficiently transferred to the Ti substrate. However, the thickness of the transferred PDA patterns is not homogeneous, with the edge of the transferred pattern being thicker than its center. In contrast, when the PDMS stamp is used for micro-CP, the center of the pattern is thicker than the edge. Red fluorescence patterns are readily obtained by heat treatment of the PDA-immobilized solid substrate. The intensity of the fluorescence of the samples is consistent with the results of optical microscopy and AFM experiments.     

Optical determination of bacterial exosporium sugars using immobilized porphyrins

Three porphyrins were tested as possible candidates for identification and quantification of the presence of sugars known to be contained in the exosporium of the bacterial endospores of some Clostridium and Bacillus species. The effect of the sugars on both absorbance and fluorescence characteristics of the immobilized porphyrins was investigated for possible application as a wipe test to indicate the presence of these sugars. Changes in porphyrin absorbance spectra were unique for each sugar with limits of detection as low as 2 ppb using immobilized porphyrins and 0.2 ppb using porphyrins in solution. Meso-tetra(4-boronic acid) porphyrin (TPPB) is likely the most useful porphyrin of those tested for detection of the sugars. Detection of methyl a-L-rhamnopyranoside between 13 and 1450 parts per billion (ppb), L-rhamnose between 15 and 150 ppb, L(-)-fucose between 80 and 1300 ppb, and D(+)-galactosamine between 18 and 1700 ppb is demonstrated using TPPB.     

Influences of hydrophilic and hydrophobic substituents on the organization of supramolecular assemblies of porphyrin derivatives formed at the air/water interface

Monolayers and Langmuir–Blodgett (LB) films of several kinds of porphyrin derivatives that have different substituted alkyl chain length, chain numbers and central metals were studied by π-A isotherms, UV–Vis, polarized UV–Vis and fluorescence spectroscopy and low angle X-ray diffractometry (LAXD). The orientation angles of porphyrin rings and alkyl chains were derived from the polarized UV–Vis spectra and LAXD patterns of the monolayers or LB films, respectively. The rings of the freebase porphyrins with different alkyl chain length or number have similar orientation angles in the films due to the same hydrophilic groups on the rings, and those of metal porphyrins have different orientation angles from each other. The orientation of the alkyl chains is related to the special positions of the chains on the rings and the orientation of the rings. The influences of the hydrophilicity of the hydrophilic groups and the alkyl chain number and length on the organization of the supramolecular assemblies of the porphyrin derivatives were discussed.     

Plasmon Enhanced Fluorescence Based on Porphyrin–Peptoid Hybridized Gold Nanoparticle Platform

A porphyrin–peptoid‐hybridized silica‐coated gold nanoparticle is developed, which is inspired by the protein–chlorophyll ensemble found in photosynthetic antenna. In the natural antenna, chlorophylls are integrated into dense assemblies that are supported by frameworks of proteins, which ensure optimal pigment arrangement for effective light harvesting. In the subject platform, porphyrins are conjugated to the peptoid helix scaffold in a structurally well‐defined alignments and subsequently immobilized on the surface of nanoparticles. This prevents intermolecular aggregation among porphyrins and allows high resolution analysis of the effect of porphyrin configuration on the optical properties of the system. Interestingly, under the influence of plasmon from the gold nanoparticle core, the fluorescence of porphyrin is enhanced up to 24‐fold at the wavelength where the plasmon resonance matches the porphyrin excitation wavelength. In addition, differences in porphyrin configuration result in spectral modification of their fluorescence emissions. Particularly, the peptoid bearing two porphyrins at a distance of 6 Å shows the most significant alteration in fluorescence. The platform can facilitate extensive studies on the relationship between porphyrin arrangement design and their photophysical interaction in antenna complexes.     

Near unity photon-to-electron conversion efficiency of photoelectrochemical cells built on cationic water-soluble porphyrins electrostatically decorated onto thin-film nanocrystalline SnO₂ surface

Thin transparent SnO(2) films have been surface modified with cationic water-soluble porphyrins for photoelectrochemical investigations. Free-base and zinc(II) derivatives of three types of cationic water-soluble porphyrins, (P)M, viz., tetrakis(N-methylpyridyl)porphyrin chloride, (TMPyP)M, tetrakis(trimethylanilinium)porphyrin chloride, (TAP)M, and tetrakis(4'-N-methylimidazolyl-phenyl)porphyrin iodide, (TMIP)M, (M = 2H or Zn) are employed. The negative surface charge and the porous structure of SnO(2) facilitated binding of positively charged porphyrins via electrostatic interactions, in addition to strong electronic interactions in the case of (TMPyP)M binding to nanocrystalline SnO(2). The SnO(2)-porphyrin binding in solution was probed by absorption spectroscopy which yielded apparent binding constants in the range of 1.5-2.6 × 10(4) M(-1). Both steady-state and time-resolved fluorescence studies revealed quenching of porphyrin emission upon binding to SnO(2) in water suggesting electron injection from singlet excited porphyrin to SnO(2) conduction band. Addition of LiClO(4) weakened the ion-paired porphyrin-SnO(2) binding as revealed by reversible emission changes. Over 80% of the quenched fluorescence was recovered in the case of (TMPyP)M and (TAP)M compounds but not for (TMIP)M suggesting stronger binding of the latter to SnO(2) surface. Photoelectrochemical studies performed on FTO/SnO(2)/(P)M electrodes revealed incident photon-to-current conversion efficiencies (IPCE) up to 91% at the peak maxima for the SnO(2)-dye modified electrodes, with very good on-off switchability. The high IPCE values have been attributed to the strong electrostatic and electronic interactions between the dye, (TMPyP)M and SnO(2) nanoparticles that would facilitate better charge injection from the excited porphyrin to the conduction band of the semiconductor. Electrochemical impedance spectral measurements of electron recombination resistance calculations were supportive of this assignment.     

Speciation of new tri- and tetra-glucoconjugated tetrapyrrolic macrocycles (porphyrins and chlorins): an electronic molecular spectroscopy study

In this work, we study the physicochemical properties of some newly developed glycoconjugated photosensitizers that can be used in photodynamic therapy (PDT) of cancers: meso-tri- and tetra-(meta-O-beta-D-glucosyloxyphenyl)porphyrins and meso-, tri-, and tetra-(meta-O-beta-D-glucosyloxyphenyl)chlorins. Their properties are compared to the non-glycosylated hydroxylated parent compounds meso-tetra-(meta-hydroxyphenyl) porphyrin and meso-tetra-(meta-hydroxyphenyl)chlorin. It was found that at the ground state, all porphyrins present, independent of the substitution, have the same mean ionization constant (pKa = 2.7), corresponding to two indistiguishable steps of protonation of tetrapyrrolic nitrogens. On the other hand, in the case of chlorins, one proton process can be observed and the corresponding nitrogen exhibits a slightly superior basicity (pKa = 3.0) with respect to porphyrins. Hydroxylated compounds present a second transition at high pH corresponding to the ionization of phenol groups (pKa = 10.5). Consequently, all photosensitizers are not charged at physiological pH (approximately 7.4), and so the ionization process does not influence their activity in biological media. Ionization induces very important variations in photosensitizer absorption and emission spectra. For example, absorption in the red region (band V), one of the most important characteristics of a good photosensitizer, is only important for diprotonated porphyrins and neutral chlorins. As far as fluorescence emission is concerned, neutral chlorins are almost six times more fluorescent than the corresponding neutral porphyrins (phi(chlorin)/phi(porphyrin) approximately = 6). It should be emphasized that the spectra modifications induced by pH variations can find interesting applications in the optimization of visible and fluorescence detection in high-performance liquid chromatography (HPLC) as well as in the development of direct, rapid fluorimetric analytical methods.     

Noncovalent functionalization of carbon nanotubes with porphyrins: meso-tetraphenylporphine and its transition metal complexes

Noncovalent functionalization of carbon nanotubes with meso-tetraphenylporphine (H2TPP) and its metal(II) complexes NiTPP and CoTPP was studied by means of different experimental techniques and theoretical calculations. As follows from the experimental adsorption curves, free H2TPP ligand exhibits the strongest adsorption of three porphyrins tested, followed by CoTPP and NiTPP. At the highest porphyrin concentrations studied, the adsorption at multi-walled carbon nanotubes was about 2% (by weight) for H2TPP, 1% for CoTPP, and 0.5% for NiTPP. Transmission electron microscopy observations revealed carbon nanotubes with a variable degree of surface coverage with porphyrin molecules. According to scanning electron microscopy, the nanotubes glue together rather than debundle; apparently, a large porphyrin excess resulting in polymolecular adsorption is essential for exfoliation/debundling of the nanotube ropes. The nanotube/porphyrins hybrids were studied by infrared and Raman spectroscopy, as well as by scanning tunneling microscopy. Electronic structure calculations were performed at the B3LYP/LANL2MB theoretical level with the unsubstituted porphine (H2P) and its Co(II) complex, on one hand, and open-end armchair (5,5) (ANT) and zigzag (8,0) (ZNT) SWNT models, on the other hand. The interaction of H2P with ANT was found to be by 3.9 kcal mol(-1) stronger than that of CoP. At the same time, CoP+ZNT complex is more stable by 42.7 kcal mol(-1) as compared to H2P+ZNT According to these calculated results, the free porphyrins interact less selectively with zigzag and armchair (i.e., semiconducting and metallic) nanotubes, whereas the difference becomes very large for the metal porphyrins. HOMO-LUMO structure, electrostatic potential and spin density distribution for the paramagnetic cobalt(II) complexes were analyzed.     

Atomic force microscopic observation of the molecular orientation in ultrathin films of alkanoic acid-derivatized porphyrins on a mica surface

The observation of the molecular orientation of alkanoic acid-derivatized porphyrins in ultrathin films deposited on mica was carried out by atomic force microscopy. It was observed that the tetraacid derivative 5, 10, 15, 20-tetra(N-10-carboxydecyl-pyridinium-4-yl) porphyrin was arranged as a monolayer with the porphyrin macrocycle oriented coplanar to the mica surface. On the other hand, the diacid derivative protoporphyrin IX Zn(II) formed a bilayer with the hydrophobic part inside and the hydrophilic part in the periphery. Therefore, in this case, the porphyrin macrocycle is roughly perpendicular to the mica surface.     

Porphyrin colorimetric indicators in molecular and nano-architectures

One of the most important outcomes of organic nanotechnologies could be development of well-integrated systems for sensing of particular chemical species. Use of color indicators is an attractive approach to guest reporting. Of the known chromophores, porphyrin and its derivatives are the most widely studied functional chromophores in a diverse range of research fields. In this review, recent developments in colorimetric indicator functions of porphyrin derivatives and related compounds in their molecular and nano-architectures are reviewed according to the classification: (i) rather simple porphyrin derivatives, (ii) porphyrin conjugates, (iii) porphyrins embedded in bulk materials, and (iv) porphyrins in organized films. Porphyrin derivatives with unusual structures, such as expanded and N-confused ones have been used for color indicators in specific cases. Electron and energy transfers in porphyrins conjugated with other functional moieties resulted in dynamic sensing systems including switch-on and switch-off actions. Immobilization of porphyrin color indicators in appropriate matrices is important for practical applications. Use of supramolecular films such as self-assembled monolayers, Langmuir-Blodgett films, and layer-by-layer assemblies as porphyrin nanoarchitectures often offers opportunities for colorimetric outputs based on control of their aggregate structures.     

Central metal effect on the organization of porphyrin LB films

Monolayers and Langmuir–Blodgett (LB) films of 5,10,15,20-tetra-4-oxy (2-stearic acid) phenylporphyrin (TSPP) and its complexes TSPPCu(II) and TSPPMn(III)Cl have been studied. π–A isotherms show that the molecular areas of the three molecules are similar to one another, while the polarized UV-vis spectra of the transferred films show different tilt angles of macrocycles with respect to the substrates: TSPP, 31°; TSPPCu(II), 0°; TSPPMn(III)Cl, 52°. The UV-vis spectra show that the π–π interactions between porphyrin macrocycles in monolayers of these three porphyrins are different. The Brewster angle microscopy (BAM) observations suggest that the monolayer behavior is also dependent on the central metal ions. These results indicate that the central metal ions have great influence on the organization of the films.     

Increasing mouse embryonic fibroblast cells adhesion on superhydrophilic vertically aligned carbon nanotube films

We have analyzed the adhesion of mouse embryonic fibroblasts (MEFs) genetically modified by green fluorescence protein (GFP) gene cultured on vertically-aligned carbon nanotubes (VACNTs) after 6 days. The VACNTs films grown on Ti were obtained by microwave plasma chemical vapor deposition process using Fe catalyst and submitted to an oxygen plasma treatment, for 2 min, at 400 V and 80 mTorr, to convert them to superhydrophilic. Cellular adhesion and morphology were analyzed by scanning electron, fluorescence microscopy, and thermodynamics analysis. Characterizations of superhydrophilic VACNTs films were evaluated by contact angle and X-Ray Photoelectron Spectroscopy. Differences of crowd adhered cells, as well as their spreading on superhydrophilic VACNTs scaffolds, were evaluated using focal adhesion analysis. This study was the first to demonstrate, in real time, that the wettability of VACNTs scaffolds might have enhanced and differential adherence patterns to the MEF-GFP on VACNTs substrates.     

Chitosan as a bioadhesive agent between porphyrins and phospholipids in a biomembrane model

Porphyrins are currently used in photodynamic therapy as photosensitizers. In this paper we studied the interaction of two charged porphyrins, 5, 10, 15, 20-mesotetrakis(N-metyl-4-pyridyl) porphyrin, (TMPyP/chloride salt) cationic, and 5, 10, 15, 20-meso-tetrakis(sulfonatophenyl) porphyrin, (TPPS4/sodium salt) anionic, nanoassembled in phospholipid Langmuir monolayers and Langmuir-Blodgett films. Furthermore, we used chitosan to mediate the interaction between the porphyrins and the model membrane, aiming to understand the role of the polysaccharide in a molecular level. The effect of the interaction of the photosensitizers on the fluidity of the lipid monolayer was investigated by using dilatational surface elasticity. We also used photoluminescence (PL) spectroscopy to identify the porphyrins adsorbed in the phospholipid films. We observed an expansion of the monolayer promoted by the adsorption of the porphyrins into the lipid-air interface which was more pronounced in the case of TMPyP, as a consequence of a strong electrostatic interaction with the anionic monolayer. The chitosan promoted a higher adsorption of the porphyrins on the phospholipid monolayers and enabled the porphyrin to stay in its monomeric form (as confirmed by PL spectroscopy), thus demonstrating that chitosan can be pointed out as a potential photosensitizer delivery system in photodynamic therapy.     

Electrospinning of polystyrene/dicyanopyrazine-linked porphyrin nanofibers

We have fabricated fluorescing polystyrene/dicyanopyrazine-linked porphyrin (PS/4-TDCPP) nanofibers using the electrospinning technique. UV-vis spectroscopy shows a strong Soret band and two relatively weak Q bands from the PS/4-TDCPP films and fibers, and reveals that the 4-TDCPP molecules are homogeneously dispersed in the films and fibers. Scanning electron microscopy (SEM) reveals the effect of solvent and collecting distance on the morphology of the electro-spun PS/4-TDCPP fibers. Fibers spun from a 50% dimethlyformamide (DMF), 50% methylethylketone (MEK) solution have ultra-fine structures with an average diameter of 300 nm. In the case of fibers from pure DMF and DMF:MEK (1:3) solutions, beads are formed along the length of the fibers. Variation of the collecting distance from 20 to 30 cm does not induce significant differences in the morphology of the electro-spun PS/4-TDCPP fibers. However, at a collecting distance of 15 cm, many beads are formed along the fibers. Acid-sensing capability of the PS/4-TDCPP fibers is demonstrated by fluorescence microscopy.     

A nanohybrid material of SWNTs covalently functionalized with porphyrin for light harvesting antenna: synthesis and photophysical properties

Novel covalently porphyrin functionalized single-walled carbon nanotubes (SWNTs) were synthesized using carboxylic group functionalized carbon nanotubes (o-SWNTs) with meso-aniline substituted porphyrin. The structure and morphology of this SWNT nanohybrid material were fully characterized with FTIR, Raman, UV-Vis-NIR spectra as well as TGA and TEM measurements. The energy transfer efficiency from porphyrin to SWNTs and porphyrin fluorescence quenching mechanism were studied by means of steady state fluorescence and time-resolved fluorescence measurement. The fast and efficient electron transfer occurring in this nanohybrid illustrates that they can be utilized as a good candidate for light harvesting materials in molecular photonic devices and solar energy utilization.     

基于卟啉及其衍生物的硫化氢检测进展

硫化氢既是有毒 物质又是生物体内重要气体信号分子,所以对硫化氢检测的研究十分重要。卟啉及其衍生物作为传感器材料,具有良好的化学稳定性和光学稳定性,与硫化氢结合后会产生光电变化,是检测硫化氢的优良材料。简述了硫化氢的检测手段、卟啉的性质以及卟啉与硫化氢的反应原理,并按照不同的传感器类别综述了卟啉在硫化氢检测中的应用,同时还对卟啉在硫化氢检测的应用领域进行了展望。     

Tetra-anionic porphyrin loading onto ZnO nanoneedles: A hybrid covalent/non covalent approach

A stepwise surface functionalization procedure, based on hybrid covalent and non-covalent approach is herein proposed to anchor tetra-anionic meso-tetrakis(4-sulfonatophenyl)porphyrin on ZnO nanorods. Carboxyalkylphosphonic acids have been proven effective to form stable self-assembled monolayers through the surface grafting of –PO₃H₂ headgroups. The exposed carboxylic functionalities are suitable for the successful grafting of cationic poly-l-lysine that drives, in water, the non-covalent anchoring of the anionic porphyrin. A stepwise surface characterization, provided by X-ray photoelectron spectroscopy, elucidates the multilayers deposition and surface composition after each process step, thus, giving interesting insights on the chemical speciation of the exposed functionalities. UV–vis spectroscopy confirms the role of ZnO morphology to increase the porphyrin loading onto the investigated surfaces. The proposed approach is effective to achieve deposition of anionic porphyrins on ZnO nanostructures and combines the robustness of covalent functionalization with the versatility and full reversibility of the non-covalent strategies.     

Substrate effect of STM-induced luminescence from porphyrin molecules

We investigated scanning tunneling microscope (STM)-induced luminescence from Meso-tetrakis (3,5-di-tertiarybutyl-phenyl) porphyrin (H₂TBPP) thin films on various metal substrates (copper, platinum and silver) under ambient conditions. Molecular fluorescence similar to the corresponding photoluminescence was observed from the H₂TBPP/Ag and H₂TBPP/Pt, but not H₂TBPP/Cu, depending on the spectra of the surface plasmons of the substrates. The results support the mechanism that intense molecular fluorescence from porphyrin film on the noble metals is a result of enhancement of molecular excitation by substrate surface plasmons.     

Porous one-dimensional nanostructures through confined cooperative self-assembly

We report a simple confined self-assembly process to synthesize nanoporous one-dimensional photoactive nanostructures. Through surfactant-assisted cooperative interactions (e.g., π-π stacking, ligand coordination, and so forth) of the macrocyclic building block, zinc meso-tetra (4-pyridyl) porphyrin (ZnTPyP), self-assembled ZnTPyP nanowires and nanorods with controlled diameters and aspect ratios are prepared. Electron microscopy characterization in combination with X-ray diffraction and gas sorption experiments indicate that these materials exhibit stable single-crystalline and high surface area nanoporous frameworks with well-defined external morphology. Optical characterizations using UV-vis spectroscopy and fluorescence imaging and spectroscopy show enhanced collective optical properties over the individual chromophores (ZnTPyP), favorable for exciton formation and transport.