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PubMed1999

Effects of Metalation State (Free Base, Mg, Zn, Cd) on Excited-State Energy Transfer in Diarylethyne-Linked Porphyrin Dimers.

The ground- and excited-state properties of two new porphyrin dimers have been examined using static and time-resolved optical techniques. One dimer consists of a zinc porphyrin and a magnesium porphyrin (ZnMgU), and the other dimer consists of a cadmium porphyrin and a free base (Fb) porphyrin (CdFbU). In both arrays, the porphyrins are joined by a diarylethyne linker at one meso position with mesityl groups at the nonlinking meso positions. The rates of photoinduced energy transfer are faster for ZnMgU ((9 ps)(-)(1)) and CdFbU ((15 ps)(-)(1)) than found previously for ZnFbU ((24 ps)(-)(1)) and MgFbU ((31 ps)(-)(1)). Only for CdFbU does the yield of excited-state energy transfer (87%) drop below the near-quantitative (>/=99%) level, and this effect derives solely from competition with a very short inherent lifetime ( approximately 100 ps) of the photoexcited Cd porphyrin. The results further illustrate (1) the efficacy of this dimeric architecture for ultrafast excited-state energy transfer, (2) how molecular/electronic properties can be manipulated to tune photoinduced energy flow in multiporphyrin arrays, and (3) key factors impacting effective inter-porphyrin electronic communication, including porphyrin orbital tuning.

Journal Article↗
PubMed2005

Single molecule spectroscopic investigation on conformational heterogeneity of directly linked zinc(II) porphyrin arrays.

We have comparatively investigated the photophysical properties of a series of meso-meso directly linked orthogonal porphyrin arrays (Zn, n = 1, 2, 3, 4, 6, 8, 9, 12, 16, 32, 48, 64, and 96) by ensemble average and single molecule fluorescence spectroscopy. In single molecule fluorescence study, we have recorded the fluorescence intensity trajectories of Zn arrays as the number of porphyrin molecules in the array increases. Up to Z8 in porphyrin arrays, each single array exhibits multiple stepwise photobleaching behaviors in fluorescence intensity trajectories, indicating that each porphyrin unit in the array acts as an individual fluorescent unit due to a maintenance of linear rigid structure of the array. On the other hand, porphyrin arrays longer than Z8 such as Z16, Z32, Z48, and Z64 show complicated photobleaching behaviors in fluorescence intensity trajectories. The origin of complex photobleaching behaviors is believed to be increasing nonradiative decay channels contributed by the enhanced structural nonlinearity in longer arrays. The fluorescence measurements of Zn arrays on single molecule level show a mismatch in the maximum fluorescence intensity level as compared to the solution measurements, which is attributable to the difference in local environment surrounding the porphyrin array. In this work, we have demonstrated the presence of conformational heterogeneity in longer porphyrin arrays by analyzing average survival times and fluorescence spectra of single arrays as the number of porphyrin molecules in the array increases. We believe that the fluorescence properties of porphyrin arrays on single molecule level will provide a platform for further applications as molecular photonic wires.

Journal Article↗
PubMed2004

One-flask synthesis of mono- and trifunctionalized 21-thia and 21-oxaporphyrin building blocks and their application in the synthesis of covalent and noncovalent unsymmetrical porphyrin arrays.

A rapid synthetic route has been developed to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrin systems using simple precursors such as 2[alpha-(aryl)-alpha-hydroxymethyl] thiophene (thiophene mono-ol) and 2[alpha-(aryl)-alpha-hydroxymethyl] furan (furan mono-ol), respectively. Condensation of one equivalent of thiophene or furan mono-ol with two equivalents of aryl aldehyde and three equivalents of pyrrole under porphyrin forming conditions followed by column chromatography resulted in functionalized 21-thia or 21-oxaporphyrins. To synthesize monofunctionalized porphyrins, the mono-ol containing the functionalized aryl group was used. The functionalized aldehydes were used to synthesize trifunctionalized porphyrins. The mono-ol method is versatile and applicable to synthesize mono- and trifunctionalized 21-thia and 21-oxaporphyrins containing functional groups such as iodophenyl, ethynylphenyl, hydroxyphenyl, bromophenyl, and pyridyl groups. The monofunctionalized porphyrin building blocks containing iodophenyl and ethynylphenyl groups were used further to synthesize four unsymmetrical covalent porphyrin dimers containing two different porphyrin cores such as N3S-N4, N3O-N4, and N3S-N3O bridged via diaryl ethyne group and one symmetrical phenylethyne bridged dimer containing two N3S cores. A preliminary photophysical study on these dimers indicated a possibility of energy transfer from one subunit to another. We also demonstrated the use of trifunctionalized porphyrins in the synthesis of two noncovalent unsymmetrical porphyrin tetramers containing one N3S and three N4 porphyrin subunits.

Journal Article↗
PubMed2005

Photoinduced electron transfer in double-bridged porphyrin-fullerene triads.

Electron and energy transfer reactions of porphyrin-porphyrin-fullerene triads (P2P1C) with controllable sandwich-like structures have been studied using spectroscopic and electrochemical methods. The stabile, stacked structure of the molecules was achieved applying a two-linker strategy developed previously for porphyrin-fullerene dyads. Different triad structures with altered linker positions, linker lengths, and center atoms of the porphyrin rings were studied. The final charge-separated (CS) state and the different transient states of the reactions have been identified and energies of the states estimated based on the experimental results. In particular, a complete CS state P2(+) P1C- was achieved in a zinc porphyrin-free-base porphyrin-fullerene triad (ZnP2t9P1C) in both polar (benzonitrile) and nonpolar (toluene) solvents. The lifetime of this state was longer living in the nonpolar solvent. An outstanding feature of the ZnP2t9P1C triad is the extremely fast formation of the final CS state, P2(+) P1C-. This state is formed after primary excitation of either zinc porphyrin or free-base porphyrin chromophores in less than 200 fs. Although the intermediate steps between the locally excited states and the final CS state were not time-resolved for this compound, the process is clearly multistep and the fastest ever observed for porphyrin-based compounds.

Journal Article↗
PubMed1991

Glucose regulated protein induction and cellular resistance to oxidative stress mediated by porphyrin photosensitization.

Photodynamic therapy (PDT) utilizes a tumor localizing porphyrin photosensitizer in the clinical treatment of cancer. At a mechanistic level, porphyrin photosensitization generates reactive oxygen species which initiate oxidative damage to a wide spectrum of biomolecules. Cellular stress proteins are also increased following oxidative stress treatments. In the current study, we examined porphyrin photosensitizing parameters associated with induction of the glucose regulated family of stress proteins. Elevated levels of mRNA encoding glucose regulated proteins (GRPs) as well as increases in GRP protein synthesis were observed for mouse radiation induced fibrosarcoma cells exposed to an extended (16-h) porphyrin incubation prior to light exposure. However, a short (1-h) porphyrin incubation prior to light treatment (designed to produce comparable phototoxicity as PDT using the 16-h porphyrin incubation protocol) was associated with only minimal increases in GRP mRNA levels or GRP protein synthesis. The relationship between GRP levels and PDT sensitivity was examined in radiation induced fibrosarcoma cells pretreated with the calcium ionophore A-23187 in order to overexpress GRPs prior to photosensitization. Resistance to PDT was observed in cells overexpressing GRPs only under photosensitizing conditions associated with the extended porphyrin incubation protocol, and this response was not due to changes in cellular porphyrin uptake. In separate experiments, a transient elevation of GRP mRNA levels was observed in transplanted mouse mammary carcinomas following in vivo PDT treatments. Our results indicate that specific targets of oxidative damage (modulated by porphyrin incubation conditions) instead of generalized cellular exposure to reactive oxygen species are correlated with PDT mediated GRP induction. In this regard, GRP induction may be a useful in vivo biochemical marker of PDT mediated injury. These results also support the hypothesis that GRPs may play a role in modulating sensitivity to cellular stresses including certain types of oxidative injury.

Animals↗
PubMed2000

Porphyrins and metalloporphyrins: versatile circular dichroic reporter groups for structural studies.

During the last few years, porphyrins and metalloporphyrins have attracted widespread attention as chromophores for studies in circular dichroism (CD), an indispensable chiroptical tool for monitoring chiral interactions. This review summarizes the multifaceted properties of porphyrins and metalloporphyrins, powerful CD chromophores that are characterized by their intense and red-shifted Soret band, propensity to undergo pi-pi stacking, facile incorporation of metals, and ease in varying solubility. Such attributes make porphyrins one of the most attractive and sensitive chromophores used in CD studies. They offer possibilities for studying the stereochemistry of chiral porphyrin assemblies, large organic molecules, biopolymers, and compounds available in miniscule quantities. The tendency of porphyrins to undergo pi-pi stacking and zinc porphyrins to coordinate with amines enable the CD exciton chirality method to be extended to configurational assignments of flexible compounds containing only one stereogenic center. Various artificial porphyrin receptors have been synthesized for the recognition of biologically important chiral guests such as carbohydrates, amino acids, and their derivatives. The induced CD of the host porphyrin Soret band reflects the identity of guests and binding modes of host/guest complexation with high sensitivity.

Circular Dichroism↗
PubMed1983

Liquid chromatography of urinary porphyrins for the biological monitoring of occupational exposure to porphyrinogenic substances.

Very sensitive and precise analytical methods for measuring total porphyrin excretion and the relative amounts of different porphyrins in urine are required in order to monitor the biological effects of porphyrinogenic substances in workers and the general population. Many analytical steps of a HPLC method for measuring porphyrins as methyl esters in urine have been perfected. Sensitivity is 0.1 microgram/1 for each type of porphyrin, and average recovery is 92% in the range of 50-450 micrograms/liter porphyrins. The coefficient of variation is 3.4% within a series and 12.5% between series. Chemical oxidation before analysis and appropriate storing of the samples are the key points in achieving high quality results. The urinary excretion of porphyrins in healthy male workers varies within the range 21 to 161 micrograms/liter (95% limits of a group of 78 subjects). Concomitant factors, like drug use or liver disorders, were found to alter urinary porphyrin excretion. The proposed method permits the detection of extremely small alterations in porphyrin excretion resulting from occupational exposure to industrial chemicals such as, for example, mild coproporphyrinuria or early stages of chemical porphyria induced by polyhalogenated arylhydrocarbons.

Adult↗
PubMedDate not supplied

Binding of meso-tetrakis(N-methylpyridiniumyl)porphyrin isomers to DNA: quantitative comparison of the influence of charge distribution and copper(II) derivatization.

Factors influencing the binding of tetracationic porphyrin derivatives to DNA have been comprehensively evaluated by equilibrium dialysis, stopped-flow kinetics, etc., for mesotetrakis (4-N-methylpyridiniumyl)porphyrin [TMpyP (4)]. Technical difficulties have previously precluded a comprehensive study of metalloporphyrins. Since electrostatic interactions with the DNA and metal derivatization of the porphyrins have important consequences, we have investigated in greater detail two isomers of TMpyP (4) (meso-tetrakis(3-N-methylpyridiniumyl)porphyrin, [TMpyP (3)] and meso-tetrakis(2-N-methylpyridiniumyl)porphyrin [TMpyP (2)]) in which the position of the charged centers has been varied. A comprehensive study of the Cu(II) derivatives, e.g., CuTMpyP (4), was possible since the difficulties encountered previously with Ni(II) compounds were not a problem with Cu(II) porphyrins [J. A. Strickland, L. G. Marzilli, M. K. Gay, and W. D. Wilson (1988) Biochemistry 27, 8870-8878]. At 25 degrees C, the apparent equilibrium constants [Kobs] decreased with increasing [Na+] for all porphyrins. The Kobs values were comparable for TMpyP (4) and TMpyP (3) binding to either polyd(G-C).polyd(G-C) [poly[d(G-C)2]] or poly[d(A-T)].poly[d(A-T)] [poly[d(A-T)2]]. For the copper(II) porphyrins, the Kobs values were about fivefold greater. The Kobs value for CuTMpyP (2) binding to poly[d(G-C)2] was too small to measure under typical salt conditions; however, Kobs for binding to poly[d(A-T)2] was about two orders of magnitude smaller than those found for CuTMpyP (4) or CuTMpyP (3). Application of the condensation theory for polyelectrolytes suggests about three charge interactions when CuTMpyP (4), CuTMpyP (3), and TMpyP (3) bind to poly[d(G-C)2] or poly[d(A-T)2], a result comparable to that reported for TMpyP (4). At 20 degrees C and 0.115 M [Na+], incorporation of copper decreased the rates of dissociation from poly[d(A-T)2] by a 100-fold compared to those reported for TMpyP (4) but had little effect on the rates of dissociation from poly[d(G-C)2]. Also, movement of the H3CN+ group from the fourth to the third position of the pyridinium ring enhanced the rates of dissociation from poly[d(A-T)2] but decreased the rates of dissociation from poly[d(G-C)2]. From polyelectrolyte theory, the [Na+] dependence of the dissociation rates from poly[d(G-C)2] is consistent with intercalative binding, while that for poly[d(A-T)2] is consistent with an outside binding model. For calf thymus [CT] DNA at 20 degrees C, a greater decrease in the AT than in the GC imino 1H-nmr signal was observed upon addition of CuTMpyP (2), suggesting selective outside binding to the AT regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Base Sequence↗
PubMed2005

Electrospray tandem mass spectrometry of new porphyrin amino acid conjugates.

Porphyrin amino acid conjugates with one or two porphyrin units were analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The ESI-MS spectra of all the porphyrins studied, obtained in positive ion mode, show the presence of the corresponding protonated molecule [M+H]+; ESI-MS spectra of diporphyrinyl compounds also show the doubly charged ions [M+2H]2+. The fragmentations of these ions induced by collision with argon were studied (ESI-MS/MS). ESI-MS/MS gives detailed structural information about the amino acids associated with the porphyrin. Cleavage of the bonds in the vicinity of the porphyrin moiety and those involving the side chain of amino acid residues gives structural information about this type of association. A fragmentation common to all derivatives corresponds to the cleavage of the phenyl-CO bond. The expected cleavage of the amide bond, that links the porphyrin to the amino acid moiety, is a minor fragmentation, which in some cases is even absent. The MS/MS spectra of the monoporphyrinyl derivatives show product ions characteristic of the amino acid linked to the porphyrin; the fragmentation also indicates when the amino acids has a terminal carboxylic group or a terminal ester group. The fragmentations of the diporphyrinyl compounds occur mainly by the cleavage of the spacer, leading, in the case of the doubly charged ions, to predominantly mono-charged ions, indicating a preferential location of the two protons in separated porphyrinic units.

Amino Acids↗
PubMed2000

Comparison of spectrofluorometric and HPLC methods for the characterization of fecal porphyrins in river otters.

A spectrofluorometric method (B. Grandchamp et al., 1980, Biochem. Biophys. Acta 629, 577-586) developed for the determination of amounts of uroporphyrin I (Uro I), coproporphyrin III (Copro III), and protoporphyrin IX (Proto IX) in skin fibroblasts was compared with a high-performance liquid chromatography (HPLC) method for the analysis of porphyrins in fecal samples of river otters (Lutra canadensis). Heptacarboxylate porphyrin I and coproporphyrin I, two porphyrins determined to be critical in defining the porphyrin profile in fecal samples of river otters with the HPLC method, contributed substantially to the calculation of the concentrations of Uro I and Copro III, respectively, in standard solutions of porphyrins with the spectrofluorometric method. Fluorescent components of the fecal matrix complicated the determination of the concentrations of Uro I, Copro III, and Proto IX with the spectrofluorometric method and resulted in erroneous values for the concentrations of these porphyrins compared with values determined with the HPLC method. These results indicate that the complexity of the sample, particularly with regard to the potential presence of interfering fluorescent compounds, as well as porphyrins additional to Uro I, Copro III, and Proto IX, should be considered prior to the application of the spectrofluorometric method. An alternative HPLC method developed for the rapid characterization of porphyrin profiles in fecal samples of river otters is described.

Alaska↗
PubMedDate not supplied

Castration increases cell damage induced by porphyrins in the Harderian gland of male Syrian hamster. Necrosis and not apoptosis mediates the subsequent cell death.

It is known that the Harderian gland of male Syrian hamster synthesizes a much smaller amount of porphyrins than the gland of the female and that castration greatly increases this synthesis. We have studied in this experimental model the behavior of the different classes of secretory cells and their role in the synthesis of porphyrins, attempting to clarify the participation of these compounds in the cell damage leading to the formation of clear cells previously described in the gland of females. We have also investigated the mechanism underlying the death of these secretory cells after porphyrin accumulation (necrosis vs apoptosis). To achieve this, we have utilized the following techniques: (a) morphometrical; (b) ultrastructural; (c) biochemical (fluorescence spectrophotometry); and (d) molecular (DNA nick-end labeling in methacrylate sections and dot blot analysis). The glands from male hamsters (serving as control) present a very low rate of damaged cells that progressively rises after castration. This rise runs parallel to that of porphyrin synthesis, porphyrin deposits, and the decrease of Type II secretory cells. The damage and subsequent death of the secretory cells in the gland is produced by the deposit of porphyrins in the mitochondrial membrane. This porphyrin accumulation leads to a complete mitochondrial destruction that finally results in cell death and its secretion into the lumen. We finally conclude that this event is not a physiological cell death (apoptosis) but the consequence of the toxic accumulation of porphyrins (necrosis).

5-Aminolevulinate Synthetase↗
PubMed1986

Spectrofluorimetric study of porphyrin incorporation into membrane models--evidence for pH effects.

The effects of hydrophobicity and charges of dicarboxylic porphyrins upon their interactions with membrane model systems are investigated. Four protonation steps are evidenced from fluorescence emission studies of hematoporphyrin IX and its more hydrophobic parent compound lacking of alcoholic chain, deuteroporphyrin IX. They are attributed to the successive protonations of the inner nitrogens of the porphyrin cycle (pK = 4.7 and 2.9 for hematoporphyrin and 4.4 and 2.7 for deuteroporphyrin) and successive deprotonations of propionic groups (pK approximately equal to 5.0 and 5.5 for hematoporphyrin and 5.4 and 6.0 for deuteroporphyrin). These porphyrins, as well as their dimethyl ester forms, are shown to incorporate as monomers into the hydrophobic bilayer of egg phosphatidylcholine small unilamellar vesicles, although the esterified forms are highly aggregated in aqueous solutions. In the case of the non-esterified forms, the incorporation of the porphyrins into the lipidic bilayer is reversible and strongly pH-dependent. A theoretical model is presented which takes into account the various protonation steps and the partition equilibria of the porphyrin between the vesicle lipidic phase and the water medium. The neutral form of the porphyrin (i.e., carboxylic groups protonated) presents the higher affinity, with constants of K approximately equal to 2 X 10(5) and K approximately equal to 6 X 10(6) M-1 (relative to lipid concentration) for hematoporphyrin and deuteroporphyrin, respectively. Protonation of one inner nitrogen leading to the monocationic form is sufficient to prevent incorporation into the hydrophobic bilayer. On the other hand, deprotonation of the peripheral propionic chains leading to anionic forms is less effective. These interactions between vesicles and porphyrins lead to shifts of the apparent pK of nitrogens and carboxylic groups, the latter one being now in the range of physiological pH. These results are discussed with regards to the hypothesis of a possible role of pH in the preferential uptake of porphyrins by tumors.

Hydrogen-Ion Concentration↗
PubMed1982

A tightly bound protein-porphyrin complex isolated from the plasma of a patient with variegate porphyria.

Free acid porphyrins were isolated from plasma of a patient with variegate porphyria. Part of the total porphyrin content--which included protoporphyrin IX, harderoporphyrin and uroporphyrin in a molar ratio of 1.2:1:0.5 and traces of pentacarboxylic porphyrin--was extractable with ethyl acetate/acetic acid as described previously [1]. Unextractable porphyrins remained in the precipitate formed after mixing the lower liquid layer and precipitate from the extraction procedure (Fig. 1, [1]) with excess ethyl acetate/acetic acid. A portion of this precipitate was hydrolyzed in 8 mol/l HCl; its porphyrins were extracted with N-butanol and analyzed by high pressure liquid chromatography; another portion was chromatographed on Sephadex G-150 with 1 mol/l MgCl2, and the major porphyrin-protein pool was hydrolyzed in 8 mol/l HCl, reacted separately with AgNO3 and Ag2SO4, and subjected to cellulose acetate and polyacrylamide-gel electrophoresis. The results support the hypothesis that a dicarboxylic porphyrin, a major portion of which was unextractable by standard procedures [1] and which appeared to be covalently bound to a protein of approximately 68 000 mol. wt. that moved with human serum albumin during cellulose acetate electrophoresis, is the preponderant porphyrin in this plasma.

Carrier Proteins↗
PubMed1992

Age and food restriction alter the porphyrin concentration and mRNA levels for 5-aminolevulinate synthase in rat Harderian gland.

The effects of age and food restriction on the porphyrin concentration in Harderian glands were studied in male Fisher 344 rats. Harderian gland porphyrin concentrations increased with age; this was statistically significant in 20 month old animals compared with 3 month old animals. Food restriction (by 40%) prevented the age-associated rise in porphyrins; thus, in 20 month old food restricted rats had porphyrin concentrations similar to those found in young animals. In a second experiment, we correlated the age-associated rise in Harderian gland porphyrin concentrations with an increase in mRNA levels for 5-aminolevulinate synthase (ALV-S). Both the porphyrin concentration and ALV-S mRNA rose at 12 and 18 months of age, but decreased by 24 months of age. It is concluded that, a) porphyrin biosynthesis in the Harderian glands increases up to 20 months of age but decreases in rats that are 24 months old, and b) food restriction prevents the porphyrin rise associated with age in the Harderian gland of male Fisher 344 rats.

5-Aminolevulinate Synthetase↗
PubMed1995

Porphyrin production and excretion by long-term cultures of adult rat hepatocytes and effect of lead exposure.

Porphyrin production and excretion and the effects of lead exposure were studied in long-term cultures of adult rat hepatocytes cultured on a feeder layer of 3T3 cells after addition of 5-aminolevulinic acid. Porphyrin excretion into the culture medium showed an irregular profile during the first 10 days, with a maximum increase of 50% at day 4 and at day 10 a value similar to that of day 1. Thereafter, porphyrin excretion decreased progressively to 18% of the initial value after 4 weeks. The cellular porphyrin content, after 7 and 28 days in culture, reached values 3.8 and 2.4-fold higher than the corresponding day 1 value. The exposure to 0.5 and 2.4 microM Pb2+ for up to 28 days produced a biphasic effect on porphyrin excretion. Firstly, there was a progressive decrease up to 81% during the first 6 days of lead exposure and, secondly, this effect was followed by an increase reaching control values at day 15 and of up to 6.7-fold after 22 days of exposure to 2.4 microM Pb2+. Similar changes were observed in cellular porphyrin content. The exposure to 0.5 and 2.4 microM Pb2+ for 2 and 4 weeks also produced morphological alterations and release of cytoplasmic enzymes. Our results show that hepatocytes cultured on 3T3 cells produce and excrete porphyrins for 28 days and that exposure for 4 weeks to micromolar lead concentrations alters these functions and cell morphology and produces cytotoxic effects which are better evaluated by monitoring alterations in porphyrin excretion than by enzyme leakage. They also suggest that this culture system is a useful model for assessing the toxic effects of xenobiotics on the biosynthesis of heme by liver cells.

Animals↗
PubMed1992

A review of in vivo studies of porphyrins and unexpected fluorescences. An interpretation of the results.

Clinical applications of porphyrins lead research biologists to characterize these compounds according to their fluorescence. These measurements revealed unexpected fluorescence spectra in addition to those of the injected porphyrins. The general characteristics of the spectra of porphyrins are reviewed. The technique permitting studies on animals in a waking state and the advantages of this method are shown. The studies in this field are reviewed and spectra reproduced. Among the observed fluorescences, those which cannot be attributed to injected porphyrins are divided into two groups. The first group, above 580 nm, seems to result from molecular associations (polymers or micelles of injected porphyrins). The second group, from 560-575 nm, seems to belong to a natural compound. Some spectroscopic observations and some medical reports lead us to identify it as an unusual natural porphyrin and perhaps as metalloporphyrin. Some authors have mentioned a Zn porphyrin. Finally, the importance of continuing the study of this natural porphyrin is discussed.

Animals↗
PubMed1996

Influence of rhodamine 123 on the photosensitizing properties of porphyrins.

The photophysical and photochemical properties of porphyrins were profoundly changed upon addition of rhodamine 123. The Soret band of the porphyrins shifted to higher wavelengths, the fluorescence yield of the porphyrins decreased with unaltered decay rates, and their triplet state was quenched. These observations indicate a strong interaction between porphyrins and rhodamine 123 and formation of 1:1 nonfluorescent complexes, of which the binding constants were determined. Illumination of a porphyrin in the presence of rhodamine 123 resulted in the formation of a porphyrin radical cation, which could be detected with ESR spectroscopy. Quenching of the triplet state of the porphyrins by rhodamine 123 resulted in a decreased singlet oxygen yield and a decrease of the photooxidation of histidine, methionine, tyrosine, and tryptophan. However, the oxidation of thiol compounds was increased and the stoichiometry of the reaction between cysteine and oxygen changed from 2 to 3.8 mol cysteine/ mol oxygen. These results show that the presence of rhodamine 123 converted the for porphyrins prevalent energy transfer (type II) reaction to an electron transfer (type I) reaction.

Cations↗
PubMed2004

Modulation of porphyrin binding to serum albumin by pH.

In this study, we show that the difference in acidity of functional groups in porphyrin photosensitizers provides a meaningful avenue to achieve differential localization and retention of porphyrins in tissues and cells, and in the end could be a positive factor in the photodynamic treatment of cancer (PDT). We have demonstrated that meso-tetraphenylporphyrin derivative with four phosphonate (bond P(double bond O)(bond OH)(2)) moieties exists in aqueous solutions mainly in four forms that differ by a degree of protonation of the porphyrin ring and ionization of the phosphonate group. It is shown that each porphyrin form has different affinities toward the model protein (bovine serum albumin, BSA). Thus pH of the medium significantly modulates the affinity of the phosphonate porphyrin toward BSA. At lower pH (pH 6.0), the phosphonate porphyrin and BSA form a complex with affinity constant of K(b)=6.9 x 10(5) M(-1), while at pH 7.0 the K(b)=6.1 x 10(5) M(-1). At pH 8.0 the association is significantly lower. Because cancerous cells have generally lower pH (pH approximately 6.9) compared to healthy cells (pH approximately 7.4), the pH of such cells could be a decisive factor for cellular retention of the porphyrin in the form of an associate with intracellular proteins. Moreover, we have also demonstrated that the protonation/deprotonation equilibria do not negatively affect the photophysical properties or ability of phosphonate porphyrin to generate singlet oxygen.

Hydrogen-Ion Concentration↗