Coherent control of cross-peaks in chirality-induced two-dimensional optical signals of excitons

Polarization tuning of the interference of chirality-induced tensor components is used to simulate the suppression of diagonal peaks and amplification of cross peaks in femtosecond two-dimensional photon echo signals of excitons in a chiral porphyrin dimer. Superpositions of various tensor components which generate the optimized signals are constructed using a genetic learning algorithm. Exciton couplings and bath correlations may be extracted from these highly resolved signals.

Modulation of the Singlet−Singlet Through-Space Energy Transfer Rates in Cofacial Bisporphyrin and Porphyrin−Corrole Dyads

A new series of relatively flexible cofacial donor-acceptor dyads for singlet-singlet energy transfer with the corrole or etio-porphyrin free base and zinc porphyrin as the acceptor and donor, respectively, were synthesized and characterized (represented as (PMes2COx)ZnH3 (13), (PMes2CO)ZnH3 (14), and (PMes2CX)ZnH3 (15)) where (PMes2COx = [2-[5-(5,15-dimesitylcorrol-10-yl)-diphenylether-2'-yl]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), (PMes2CO = [5-[5-(5,15-dimesitylcorrol-10-yl)-dibenzofuran-4-yl]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), and (PMes2CX = [5-[5-(5,15-dimesitylcorrol-10-yl)-9,9-dimethylxanthen-4-yl)]-13,17-diethyl-2,3,7,8,12,18-hexamethylporphyrin]), respectively) along with the homobismacrocycles (DPOx)ZnH2 (17) and (DPOx)Zn2 (18) (where (DPOx = 2,2'-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]diphenylether) as comparison standards. The rate for energy transfer (kET) extracted by the measurements of fluorescence lifetimes are of the same order of magnitude as those recently reported for the rigidly held face-to-face dyads ((DPB)ZnH2 (1), (DPX)ZnH2 (2), (DPA)ZnH2 (3), (DPO)ZnH2 (4), and (DPS)ZnH2 (5) where (DPB = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]biphenylene), (DPX = 4,5-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]-9,9-dimethylxanthene), (DPA = 1,8-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]anthracene), (DPO = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzofuran), and (DPS = 4,6-bis[5-(2,8,13,17-tetraethyl-3,7,12,18-tetramethylporphyrinyl)]dibenzothiophene), respectively), but for the first time, it is shown that the presence of a bulky group located between the acceptor and the donor moiety influences the transfer rate. The presence of perpendicular mesityl groups on the acceptor macrocycle prevents the two macrorings from interacting strongly; therefore, kET is slower. On the other hand, by rendering the rigid spacer flexible (i.e., changing the dibenzofuran rigid spacer to the flexible diphenylether assembling fragment), kET increases due to stronger intermacrocycle interactions. This study is complemented by DFT computations (B3LYP/3-21G*) as a molecular modeling tool where subtle structural features explain the changes in kET. During the course of this study, X-ray structures of 17 and 18 were investigated and exhibit a linear stacking of the bismacrocycles where intermolecular porphyrin-porphyrin interactions are observed (dinter(Zn...Zn) = 4.66 and 4.57 A, for 17 and 18, respectively).

Interest of RGD-containing linear or cyclic peptide targeted tetraphenylchlorin as novel photosensitizers for selective photodynamic activity

Destruction of the neovasculature is essential for tumor eradication by photodynamic therapy. Since the over-expression of integrins is correlated with tumor angiogenesis, we conjugated a photosensitizer (5-(4-carboxyphenyl)-10,15,20-triphenylchlorin or porphyrin) to the alpha(v)beta(3) integrin specific peptide RGD (H-Arg-Gly-Asp-OH) motif as a common sequence. We reported an efficient solid-phase synthesis of a new family of peptidic photosensitizers with linear or cyclic[RGDfK] RGD motif and compared conjugates in vitro selectivity and photodynamic activity. The conjugates were characterized by (1)H NMR, MALDI, UV-visible spectroscopy and singlet oxygen formation was performed. Chlorins containing linear and constrained RGD motif were incorporated up to 98- and 80-fold more, respectively, than the unconjugated photosensitizer over a 24-h exposure in human umbilical vein endothelial cells (HUVEC) over-expressing alpha(v)beta(3) integrin. Peptidic moiety also led to a non-specific increased cellular uptake by murine mammary carcinoma cells (EMT-6), lacking RGD binding receptors. Survival measurements demonstrated that HUVEC were greatly sensitive to conjugates-mediated photodynamic therapy.

DFT/TDDFT study of lanthanide(III) mono- and bisporphyrin complexes

The electronic structure, molecular structure, and electronic spectra of lanthanide(III) mono- and bisporphyrin complexes are investigated using a DFT/TDDFT method. These complexes include YbP(acac), YbP(2), [YbP(2)](+), YbHP(2), and [YbP(2)](-) (where P = porphine and acac = acetylacetonate). To shed some light on the origin of the out-of-plane displacement of Yb in YbP(acac), unligated model systems, namely, planar D(4h) and distorted C(4nu) YbP, were calculated. For comparison, the calculations were also extended to include the C and [Ce(IV)P(2) ](+) systems. Even without an axial ligand, the lanthanide atom lies considerably above the porphyrin plane; the distortion of the YbP molecular structure from a planar D(4h) to the nonplanar C(4nu) symmetry leads to a considerable energy lowering. The axial ligand makes the metal out-of-plane displacement even larger, and it also changes the redox properties of the lanthanide monoporphyrin. The ground-state configurations of YbP(2) and YbHP(2) were determined by considering several possible low-lying states. YbP(2) is confirmed to be a single-hole radical. The special redox properties of the bisporphyrin complexes can well be accounted for by the calculated ionization potentials and electron affinities. The TDDFT results provide a clear description of the UV-vis and near-IR absorption spectra of the various lanthanide porphyrins.

Atropisomers of meso-Conjugated Uracyl Porphyrin Derivatives and Their Assembling Structures

[reaction: see text] We have synthesized a 5,15 meso-substituted methyluracyl porphyrin derivative bearing 6-methyluracyl units directly at the meso positions. The atropisomerization was regulated by steric replusion between the methyl substituents. When the atropisomers were mixed with alkylated melamine as a complementary hydrogen-bonding unit, the hydrogen-bonded assemblies were analyzed by diffusion-ordered spectroscopy (DOSY) in solution, which clarified that the alphabeta isomer formed a face-to-face dimer, whereas the alphabeta isomer took a zigzag structure.

Diffuse interstellar bands: a comprehensive laboratory study

As a result of the search for the identity of the chromophores responsible for producing the diffuse interstellar bands, a comprehensive exposition of experimental data is presented, which implicates the following molecules: (1) The extremely stable organic molecules, magnesium tetrabenzoporphyrin (MgTBP) and H(2)TBP. (2) A paraffin matrix (referred to as "grains") containing TBPs. (3) A low concentration of pyridine (also within the grains), whose transmission window at 2175 A, accounts for the ubiquitous UV bump. The blue emission spectra associated with the central star, HD44179, of the Red Rectangle displays the fluorescence excitation spectra of bare MgTBP. This unique spectrum matches the low temperature lab data of MgTBP in the vapor phase. An effective grain temperature of 2.728 K (+/-0.008) was deduced, based on MgTBP's lowest measured vibrational state of 341 GHz.

Ground- and excited-state tautomerism in porphycenes

Owing to short distances between the inner nitrogen atoms and, therefore, strong intramolecular hydrogen bonds, porphycenes display completely different tautomeric properties than porphyrins, their constitutional isomers. Tunneling splitting caused by delocalization of two inner hydrogen atoms is observed for porphycenes isolated in supersonic jets. The barrier to tautomerization is higher in the lowest excited singlet state than in the ground state. Still, rapid exchange of inner hydrogen atoms is detected in S1. The mechanism of tautomerization involves synchronous double hydrogen tunneling, activated by excitation of a low-frequency mode, which modulates the NH...N separation. This separation can also be strongly altered by peripheral substitution. In porphycenes with alkyl substituents on the ethylene bridges, the NH...N distances become extremely small. For these derivatives, both trans and cis tautomeric forms are detected. Tautomerism in porphycenes was also monitored on a single-molecule level.

Synthesis of N-Confused Phlorins via an Addition/Cyclization Pathway

The syntheses of N-confused phlorins are provided by reactions of N-confused porphyrins with nitrilimines and with dialkyl acetylenedicarboxylate. Both reactions involve zwitterionic intermediates and proceed through an addition/cyclization pathway.

Theoretical Solar-to-Electrical Energy-Conversion Efficiencies of Perylene−Porphyrin Light-Harvesting Arrays

The efficiencies of organic solar cells that incorporate light-harvesting arrays of organic pigments were calculated under 1 sun of air mass 1.5 solar irradiation. In one set of calculations, photocurrent efficiencies were evaluated for porphyrin, phthalocyanine, chlorin, bacteriochlorin, and porphyrin-bis(perylene) pigment arrays of different length and packing densities under the assumption that each solar photon absorbed quantitatively yielded one electron in the external circuit. In another more realistic set of calculations, solar conversion efficiencies were evaluated for arrays comprising porphyrins or porphyrin-(perylene)2 units taking into account competitive excited-state relaxation pathways. A system of coupled differential equations for all reactions in the arrays was solved on the basis of previously published rate constants for (1) energy transfer between the perylene and porphyrin pigments, (2) excited-state relaxation of the perylene and porphyrin pigments, and (3) excited-state electron injection into the semiconductor. This formal analysis enables determination of the optimal number of pigments in an array for solar-to-electrical energy conversion. The optimal number of pigments depends on the molar absorption coefficient and the density at which the arrays can be packed on an electrode surface. Taken together, the ability to employ fundamental photophysical, kinetic, and structural parameters of modular molecular architectures in assessments of the efficiency of solar-to-electrical energy conversion should facilitate the design of molecular-based solar cells.

22π Smaragdyrin Molecular Conjugates with Aromatic Phenylacetylenes and Ferrocenes: Syntheses, Electrochemical, and Photonic Properties

Syntheses, spectroscopic, electrochemical, and third-order nonlinear optical susceptibilities of a series of 22pi smaragdyrins and their corresponding Rh(I) derivatives bearing phenylacetylene substituents and ferrocene-containing substituents are reported. The synthetic strategy involved a [3 + 2] acid-catalyzed oxidative coupling reaction of the appropriate dipyrromethane and oxatripyrrane. The desired meso substituents, such as phenylacetylenylphenyl and the ferrocenes, were incorporated to the dipyrromethane unit prior to the oxidative coupling reaction. The optical absorption, emission characteristics, and the quantum yield of the smaragdyrin conjugates depends on the nature of the substituent, nature of linker group, and the spacer length. Theoretical studies at the DFT level suggest high delocalization of electrons confined to only four of the five available heterocyclic rings for the free bases. However, upon Rh(I) metalation, the pi-electron delocalization is extended to all the heterocyclic rings. The two-photon absorption cross section (TPA) values sigma(2) measured through the open aperture Z-scan method, increases linearly with enhanced pi-electron delocalization for the smaragdyrins containing phenylacetylene substituents. The meta branching of substituents decreases sigma(2) values. Introduction of Rh(I) to the smaragdyrin cavity enhances the sigma(2) values by about 3-10 orders of magnitude, attributed to the increased aromatic character upon Rh(I) insertion. The calculated molecular electrostatic potential (MESP) and harmonic oscillator model of aromaticity (HOMA) for the free bases and the Rh(I) derivatives justifies such a conclusion. A linear correlation observed for the second oxidation potential of Rh(I) derivatives and corresponding free bases also support the increased aromaticity upon Rh(I) insertion. The electrochemical data for ferrocene-containing smaragdyrins reveal easier ring oxidation by about 50-130 mV and harder ferrocene oxidation by 40-180 mV suggesting electron-donating nature of the ferrocene upon linking with the smaragdyrin system. The TPA cross section value of 88782 GM observed for 5g represents one of the highest values known for a metalloexpanded porphyrin derivative.

C−F Bond Activation by Modified Sulfinatodehalogenation: Facile Synthesis and Properties of Novel Tetrafluorobenzoporphyrins by Direct Intramolecular Cyclization and Reductive Defluorinative Aromatization of Readily Available β-Perfluoroalkylated Porphyrins

A facile and efficient synthesis of various novel fluorinated extended porphyrins has been developed. The method is based on the direct intramolecular cyclization and reductive defluorinative aromatization of readily available beta-perfluoroalkylated porphyrins by highly selective C-F bond activation under modified sulfinatodehalogenation reaction conditions. Various beta-(omega-chloroperfluoroalkyl)-meso-tetraphenylporphyrins prepared readily by sulfinatodehalogenation reaction or palladium-catalyzed cross-coupling reaction were treated with Na2S2O4/K2CO3 (10:10 equiv per RF tail) in DMSO at 100 degrees C for 10-30 min, resulting in good yields of novel beta-tetrafluorobenzo-meso-tetraphenylporphyrins. That further reduction of C-F bonds of the products was not observed under the optimal conditions indicates the high selectivity of the reaction. It was found that the amount of sodium dithionite, base, and central metal ion of substrate porphyrins play important roles in the reaction. Detailed mechanism investigations and systematic studies on X-ray crystallographic structure and photophysical and electrochemical properties of a series of new tetrafluorobenzoporphyrins are also reported.

Built-in Axial Base Binding on Phenanthroline-Strapped Zinc(II) and Iron(III) Porphyrins

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.

Delivery of photosensitisers and light through mucus: investigations into the potential use of photodynamic therapy for treatment of Pseudomonas aeruginosa cystic fibrosis pulmonary infection

Respiratory disease is the main cause of morbidity and mortality in patients with cystic fibrosis (CF). In such patients chronic Pseudomonas aeruginosa infection is virtually impossible to eradicate using antibiotic therapy. Photodynamic antimicrobial chemotherapy (PACT) could be one potential alternative antimicrobial method. As photosensitisers could be delivered to the lungs of CF patients via inhalation, the current in vitro study investigated the potential use of PACT in the treatment of P. aeruginosa CF pulmonary infection. Delivery of red light (635 nm) and two photosensitisers (toluidine blue O (TBO) and meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP)) across artificial CF mucus was successfully achieved. Artificial CF mucus reduced the measured fluence of incident light in an almost exponential manner with increasing depth. The presence of dissolved photosensitisers also reduced light fluence. TMP diffused more efficiently across artificial CF mucus than TBO. However, receiver compartment concentrations of both drugs after 6 h were of the same order as those required to achieve high rates of kill (>99%) of P. aeruginosa isolates growing both planktonically and in biofilms. TMP required significantly higher concentrations (2.5 mg ml(-1)) than TBO to achieve high rates of kill (>99%) of P. aeruginosa isolates growing planktonically. Higher concentrations (5.0 mg ml(-1)) of both photosensitisers were required to achieve high rates of kill (>99%) of P. aeruginosa isolates growing in biofilms. When photosensitisers were prepared in artificial mucus, higher concentrations were required to achieve reasonably high kill rates (>80%) of P. aeruginosa (PAO1) growing both planktonically and in biofilm.

Calix[4]arene-Linked Bisporphyrin Hosts for Fullerenes: Binding Strength, Solvation Effects, and Porphyrin−Fullerene Charge Transfer Bands

A calix[4]arene scaffolding has been used to construct bisporphyrin ("jaws" porphyrin) hosts for supramolecular binding of fullerene guests. Fullerene affinities were optimized by varying the nature of the covalent linkage of the porphyrins to the calixarenes. Binding constants for C60 and C70 in toluene were explored as a function of substituents at the periphery of the porphyrin, and 3,5-di-tert-butylphenyl groups gave rise to the highest fullerene affinities (26,000 M(-1) for C60). The origin of this high fullerene affinity has been traced to differential solvation effects rather than to electronic effects. Studies of binding constants as a function of solvent (toluene < benzonitrile < dichloromethane < cyclohexane) correlate inversely with fullerene solubility, indicating that desolvation of the fullerene is a major factor determining the magnitude of binding constants. The energetics of fullerene binding have been determined in terms of DelatH and DeltaS and are consistent with an enthalpy-driven, solvation-dependent process. A direct relationship between supramolecular binding of a fullerene guest to a bisporphyrin host and the appearance of a broad NIR absorption band have been established. The energy of this band moves in a predictable manner as a function of the electronic structure of the porphyrin, thereby establishing its origin in porphyrin-to-fullerene charge transfer.

Fungal Heme Oxygenases: Functional Expression and Characterization of Hmx1 from Saccharomyces cerevisiae and CaHmx1 from Candida albicans

Heme oxygenases convert heme to free iron, CO, and biliverdin. Saccharomyces cerevisiae and Candida albicans express putative heme oxygenases that are required for the acquisition of iron from heme, a critical process for fungal survival and virulence. The putative heme oxygenases Hmx1 and CaHmx1 from S. cerevisiae and C. albicans, respectively, minus the sequences coding for C-terminal membrane-binding domains, have been expressed in Escherichia coli. The C-terminal His-tagged, truncated enzymes are obtained as soluble, active proteins. Purified ferric Hmx1 and CaHmx1 have Soret absorption maxima at 404 and 410 nm, respectively. The apparent heme binding Kd values for Hmx1 and CaHmx1 are 0.34 +/- 0.09 microM and 1.0 +/- 0.2 microM, respectively. The resonance Raman spectra of Hmx1 reveal a heme binding pocket similar to those of the mammalian and bacterial heme oxygenases. Several reductants, including ascorbate, yeast cytochrome P450 reductase (CPR), human CPR, spinach ferredoxin/ferredoxin reductase, and putidaredoxin/putidaredoxin reductase, are able to provide electrons for biliverdin production by Hmx1 and CaHmx1. Of these, ascorbate is the most effective reducing partner. Heme oxidation by Hmx1 and CaHmx1 regiospecifically produces biliverdin IXalpha. Spectroscopic analysis of aerobic reactions with H2O2 identifies verdoheme as a reaction intermediate. Hmx1 and CaHmx1 are the first fungal heme oxygenases to be heterologously overexpressed and characterized. Their heme degradation activity is consistent with a role in iron acquisition.

Interaction of photosensitizers with liposomes containing unsaturated lipid

Small unilamellar liposomes were made of dipalmitoyl-phosphatidylcholine and dioleoyl-phosphatidylcholine, and photosensitized by a symmetrically or an asymmetrically substituted glycosilated tetraphenyl-porphyrin derivative. As differential scanning calorimetry and electron paramagnetic resonance spectroscopy (EPR) revealed these porphyrin derivatives were localized in different depth within the lipid bilayer. Both porphyrin derivatives were able to induce photoreaction and consequent structural changes in the membrane. 5-, 12-, or 16-doxyl stearic acid labeled lipid bilayers were applied and the efficiency of photoinduced reaction was followed by the decay of their EPR signal amplitude. Light dose-dependent destruction of nitroxide radical proved to be dependent on the position of spin label. In this process the porphyrin localized in closer connection with the double bond of unsaturated fatty acid was more effective. EPR signal decay was also dependent on the unsaturated fatty acid content of the liposome and the oxygen saturation of the solvent.

Resonance Raman Studies of β-Substituted Porphyrin Systems with Unusual Electronic Absorption Properties

Zn(II) and Cu(II) porphyrins with beta-conjugated barbiturate functional groups have low-energy electronic transitions which are unusual in that there are two strong bands in the Soret region. Resonance excitation of the two bands shows that each has features characteristic of both the porphyrin and barbiturate groups, with some perturbation to these features caused by the interaction of the two chromophores. The resonance Raman (RR) spectrum (lambda(exc)=413.1 nm) of the 412 nm band shows two bands at 1722 and 1743 cm(-1) attributable to C==O stretches in the substituent. Changes in frequency of porphyrin core modes due to the differing metal centres are reproduced by density functional theory calculations. The Q band RR spectra show modes with anomalous polarization which may be attributed to A(2g) modes, however no overtone or combination bands are observed.

Synthesis and properties of a novel phenylazomethine dendrimer with a tetraphenylmethane core

[structure: see text] A new type of phenylazomethine dendrimer with a tetraphenylmethane core was synthesized by a convergent method. The properties of the dendrimer were confirmed by thermal, rheological, TEM, and AFM measurements. A stepwise radial complexation was clearly observed with SnCl(2).

Supramolecular Polypseudorotaxanes Composed of Star-Shaped Porphyrin-Cored Poly(ε-caprolactone) and α-Cyclodextrin

Star-shaped porphyrin-cored poly(epsilon-caprolactone) (SPPCL) was synthesized using a tetrahydroxyethyl-terminated porphyrin as a core initiator and stannous octoate as a catalyst in bulk at 120 degrees C. The molecular weight of as-synthesized polymer could be adjusted linearly by controlling the molar ratio of epsilon-caprolactone to porphyrin core initiator, and the molecular weight distribution was reasonably narrow. Supramolecular polypseudorotaxanes were prepared by inclusion complexation of SPPCL with alpha-cyclodextrin (alpha-CD) and thoroughly characterized by means of FT-IR, 1H NMR, 13C CP/MAS NMR, DSC, TGA, and WAXD. The results demonstrated that the porphyrin-cored polypseudorotaxanes formed through alpha-CD molecules threading onto the branch chains of star-shaped SPPCL polymers, and they had a channel-type crystalline structure. Meanwhile, the original crystallization of SPPCL polymers within the polypseudorotaxanes was completely suppressed in the alpha-CD cavities. Moreover, inclusion complexation between SPPCL and alpha-CD enhanced the thermal stability of both the guest SPPCL polymers and the host alpha-CD. Furthermore, both the SPPCL polymers and the polypseudorotaxanes showed similar fluorescent and UV-vis spectra compared with porphyrin core initiator. Consequently, this will not only provide potentially porphyrin-cored poly(epsilon-caprolactone) and its polypseudorotaxanes for photodynamic therapy but also improve the compatibility between poly(epsilon-caprolactone) and peptide drugs for drug delivery.

Resonance Raman Study of Ferric Heme Adducts of Dehaloperoxidase from Amphitrite ornata

The study of axial ligation by anionic ligands to ferric heme iron by resonance Raman spectroscopy provides a basis for comparison of the intrinsic electron donor ability of the proximal histidine in horse heart myoglobin (HHMb), dehaloperoxidase (DHP), and horseradish peroxidase (HRP). DHP is a dimeric hemoglobin (Hb) originally isolated from the terebellid polychaete Amphitrite ornata. The monomers are structurally related to Mb and yet DHP has a peroxidase function. The core size marker modes, v2 and v3, were observed using Soret excitation, and DHP-X was compared to HHMb-X for the ligand series X = F, Cl, Br, SCN, OH, N3, and CN. Special attention was paid to the hydroxide adduct, which is also formed during the catalytic cycle of peroxidases. The Fe-OH stretching frequency was observed and confirmed by deuteration and is higher in DHP than in HHMb. The population of high-spin states of the heme iron in DHP was determined to be intermediate between HHMb and HRP. The data provide the first direct measurement of the effect of axial ligation on the heme iron in DHP. The Raman data support a modified charge relay in DHP, in which a strongly hydrogen-bonded backbone carbonyl (>C=O) polarizes the proximal histidine. The charge relay mechanism by backbone carbonyl >C=O-His-Fe is the analogue of the Asp-His-Fe of peroxidases and Glu-His-Fe of flavohemoglobins.

Phosphate group effects upon the equilibrium of iron(III) meso-tetrakis (4-N-methylpyridiniumyl) porphyrin in aqueous solution

Iron(III) meso-tetrakis (4-N-methylpyridiniumyl) porphyrin (FeTMPyP) undergoes a complex equilibrium in aqueous solution as a function of pH. Use of phosphate buffers, a common practice in biomedical applications of porphyrins, suggests the complexation of phosphate anion at the sixth coordination position to the iron, which contributes to the complexity of the equilibrium in the pH range from 1 to 4. In the absence of phosphate the equilibrium is simplified in a similar way as in the presence of high salt concentrations. Combined use of optical absorption, (1)H NMR and infrared spectroscopies, together with the literature data, suggest the formation of hexacoordinated monoaqueous-phosphate FeTMPyP complex in a limited acidic pH range. Discussion of the behavior of cationic FeTMPyP as compared to anionic iron(III) meso-tetrakis (4-sulfonatophenyl) porphyrin (FeTPPS(4)) is presented in regard to equilibrium of different species to explain the observed complex equilibrium.

Absorbance change and static quenching of fluorescence of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) by trinitrotoluene (TNT)

Meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) interacts with trinitrotoluene (TNT) and forms a 1:1 complex with a new absorbance peak at 422 nm. TNT quenches TPPS emission intensity at 645 and 702 nm when excited at 413 nm. The TPPS-TNT complex is formed in the ground state on the basis of a linear Stern-Volmer plot indicative of static quenching. The association constants determined from absorbance and fluorescence studies are in excellent agreement.

Nanoparticles for two-photon photodynamic therapy in living cells

We describe here a nontoxic two-photon photodynamic nanoparticle platform and its cellular application. We demonstrate that the dye's potential toxicity can be circumvented by its permanent encapsulation into a biocompatible nanoparticle polymer matrix; this was examined by dye leaching experiments and confirmed by cell uptake experiments. Infrared two-photon nanoplatform phototoxicity was demonstrated for rat C6 glioma cells, while the controls showed no dark toxicity for these living cells.

Incorporation of designed extended chromophores into amphiphilic 4-helix bundle peptides for nonlinear optical biomolecular materials

Multipigment ensembles that feature (porphinato)metal components and appropriate ethyne- and oligoyne-based chromophore-to-chromophore connectivity can manifest large optical polarizabilities and hyperpolarizabilities by design. Their vectorial orientation and local environment are controlled upon incorporation into designed amphiphilic 4-helix bundle peptides via axial histidyl ligation without disturbing the peptide's helical secondary structure. The chromophore/peptide stoichiometry can be tuned by varying the peptide's oligomeric state. The chromophore/peptide complexes are thermally stable, making them ideal candidates for the fabrication of nonlinear optical biomolecular materials.

Molecular modeling of anti-parallel G-quadruplex DNA/TMPyP complexes

We carried out the molecular modeling of anti-parallel G-quadruplex/TMPyP complex, molecular dynamics simulation and estimation of binding free energy using MM-PBSA method to validate groove binding model in addition to external stacking one. We found that not total electrostatic but van der Waals energy contributes to the negative binding free energies in both models.