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PubMed1997

Stepwise Approach to Bimetalic Porphyrin Hosts: Spatially Enforced Coordination of a Nickel(II) Porphyrin.

The synthesis of the Zn(3) 1,1,2-trimer Zn(3)()3 and the NiZn(2) 1,1,2-trimer NiZn(2)()3 by a stepwise convergent route is described. A large affinity for Py(3)()T by both cyclic 1,1,2-trimers, Zn(3)()3 or NiZn(2)()3, with respect to the linear trimers, provides a thermodynamic driving force for the templated cyclization of the new host molecules, which were fully characterized by NMR spectroscopy (COSY and NOESY). The binding properties of several pyridine-containing bidentate and tridentate ligands have been investigated in order to probe the shape and the size of the cavity of the host molecule. Both Py(2)()Pr and Py(2)()Py bind very strongly to Zn(3)()3 and NiZn(2)()3 (ligand affinities in CH(2)Cl(2) at 25 degrees C, >10(8) M(-)(1)), while the tridentate ligand Py(3)()T binds to both Zn(3)()3 and NiZn(2)()3 with a very high binding constant (ligand affinities in CH(2)Cl(2) at 25 degrees C, >10(9) M(-)(1)). This unexpected result for NiZn(2)()3 suggests that the cavity-enforced effective molarity of the third pyridyl of Py(3)()T at the Ni site is high enough to form the first example of a stable 1:1 Ni(II)-pyridyl complex. The resulting Ni(II) paramagnetic complex has been characterized by NMR; the temperature dependence deviates slightly from ideal Curie behavior.

Journal Article↗
PubMed2000

Electronic effects in transition metal porphyrins. 10. Effect of ortho substituents on the temperature dependence of the NMR spectra of a series of spin-admixed perchloratoiron(III) tetrakis(2,6- or 2,4,6-phenyl substituted)porphyrinates.

The perchloratoiron(III) complexes of a series of 2,6-disubstituted tetraphenylporphyrin ligands, where the 2,6-phenyl substituents were -H, -F, -Cl, -Br, or -OMe, as well as two 2,4,6-phenyl-substituted complexes, where the substituents were -Me and -OMe, have been investigated as a function of temperature by 1H NMR spectroscopy. Curvature in the 1/T dependence was evident in most cases. Forced linear extrapolation of the temperature dependence observed over the range of the study yielded Curie plots that include negative slopes with very large positive 1/T intercepts (Cl approximately Br > Me > H) to negative slope with near zero intercept (tri-OMe) to positive slope with very large negative intercept (F, di-OMe). The NMR results were combined with EPR spectroscopic data and curve-fitting procedures based on an expanded Curie law to arrive at a consistent overview of the variety of temperature-dependence behaviors observed. This overview relies upon the premise that, in addition to the ground state observed by EPR spectroscopy, one (or more) thermally accessible excited state(s) are populated to varying degrees over the temperature range of the NMR measurements. If only one excited state is considered, the analysis is consistent with the ground state being a largely intermediate-spin state (S = 3/2) for the majority of the complexes but a largely high-spin state (S = 5/2) for ((2,6-F2)4TPP)FeOClO3 and ((2,6-(OMe)2)4TPP)FeOClO3.

Electron Spin Resonance Spectroscopy↗
PubMed2005

Sol-gel reaction of porphyrin-based superstructures in the organogel phase: creation of mechanically reinforced porphyrin hybrids.

We have demonstrated that a one-dimensional molecular assembly created by an H-aggregated porphyrin.Cu(II) stack can be immobilized, without a morphological change, by sol-gel polycondensation of the peripheral triethoxysilyl groups. The resultant gel prepared according to this flowchart has gained a very high thermal stability as well as a unique mechanical strength.

Journal Article↗
PubMed2000

Three-dimensionally arranged windmill and grid porphyrin arrays by AgI-promoted meso-meso block oligomerization

The syntheses of soluble windmill and grid porphyrin arrays through the AgI-promoted coupling reaction of 1,4-phenylene-bridged linear porphyrin arrays, which are comprised of a central ZnII beta-free porphyrin and flanking peripheral NiII beta-octaalkylporphyrins, are described. The coupling reaction is advantageous in light of its high regioselectivity occurring only at the meso-position of the ZnII beta-free porphyrin as well as its easy extension to large porphyrin arrays. The windmill porphyrin arrays in turn serve as an effective substrate for further coupling reactions, to give three-dimensionally arranged grid porphyrin arrays. Further the grid porphyrin 12-mer (a tetramer of the linear porphyrin trimer) was also coupled to afford grid porphyrins (24-mer, 36-mer, and 48-mer). These porphyrin arrays were isolated in a discrete form by repetitive GPC/HPLC (GPC= gel-permiation chromatography). Competitive experiments with three linear porphyrin trimers bearing different peripheral metalloporphyrins (ZnII, NiII, and Cull), and the trapping experiment of the radical cation at the peripheral porphyrin with AgNO2, suggested that an initial one-electron oxidation of the easily oxidizable peripheral ZnII beta-octaalkylporphyrin with an AgI ion and a subsequent endothermic hole transfer assist the generation of the radical cation at the central ZnII beta-free porphyrin. In all ZnII-metallated windmill porphyrin arrays, the energy level of the S1 state of the meso-meso-linked diporphyrin core is lower than that of the peripheral porphyrins, thereby allowing an energy flow from the peripheral porphyrins to the central diporphyrin core; this has been confirmed by measurements of fluorescence lifetimes and picosecond time-resolved fluorescence spectra. The excitation energy transfer in the arrays encourages their potential use as an light-harvesting antenna.

Journal Article↗
PubMed1997

Photodynamic therapy with 5-aminolaevulinic acid-induced porphyrins of an amelanotic melanoma in vivo.

Of particular interest for photodynamic therapy (PDT) are the endogenously formed and photodynamically active porphyrins produced following topical or systemic application of 65-aminolaevulinic acid (ALA), a haem precursor. Having determined the pharmacokinetics and wavelength dependence of PDT with ALA-induced porphyrins, we analysed the porphyrin metabolites in tumour and surrounding skin. The therapeutic efficacy of PDT using ALA-induced porphyrins was investigated. Amelanotic melanomas (A-Mel-3) were implanted subcutaneously in the back of Syrian golden hamsters (body weight (b.w.), 70-80 g). After 5-7 days, tumours with a volume of approximately 150 mm3 were used for PDT (n = 36). ALA (500 mg kg-1 b.w., pH 6.5) was injected intravenously 45, 90, 150 and 300 min before light irradiation (635 nm, 100 mW cm-2, 100 J cm-2). Tumours with light irradiation only served as controls. The tumour volume was measured after PDT for 28 days. The total porphyrin content was determined in the tumours, the surrounding skin and erythrocytes prior to and 45, 90, 180, 240, 300 and 480 min and 24 h following intravenous injection of ALA (500 mg kg-1 b.w.; n = 32). Porphyrin metabolites were separated by high pressure liquid chromatography (HPLC). Tumour growth was significantly delayed when PDT with ALA was performed 45, 90 or 150 min following intravenous administration. At that time, protoporphyrin (1.8 +/- 0.4 nmol g-1), coproporphyrin (2.2 +/- 0.5 nmol g-1) and uroporphyrin (1.7 +/- 1.4 nmol g-1) were the main metabolites in the tumour tissue. Erythrocytes also contained significant amounts of porphyrins (11.8 +/- 1.3 nmol g-1). The tumour and surrounding skin exhibited a different pattern of porphyrin metabolites. Unexpectedly, a single treatment of PDT with ALA-induced porphyrin resulted in only one complete remission out of six amelanotic melanomas when the final therapeutic outcome was assessed after 28 days. The therapeutic efficacy of PDT with ALA-induced porphyrins can be positively correlated with the fluorescence kinetics previously determined. The analysis of the porphyrin metabolites in amelanotic melanoma by HPLC indicates that the porphyrin accumulation is not due to a decreased activity of ferrochelatase. Moreover, the photodynamic effects may not be mediated solely by porphyrins localized in the tumour parenchyma, but also by significant amounts of porphyrins in the microvasculature. PDT with this endogenous photosensitizer failed to induce complete emission of the treated tumours despite irradiation at the time of maximum porphyrin concentration using the optimum therapeutic wavelength. Thus PDT with ALA-induced porphyrins is less effective in our model relative to that observed for the exogenous photosensitizer Photofrin or synthetic porphycenes after a single treatment.

Aminolevulinic Acid↗
PubMed1995

Evaluation and clinical application of the Enterotest for the determination of human biliary porphyrin composition.

The Enterotest string test is an easy and non-invasive method for sampling duodenal fluid, which has been successfully used for the analysis of duodenal microflora, as well as biliary bile acid and lipid composition. The method was evaluated for determination of porphyrins in duodenal bile in normal subjects and subjects with porphyria, following cholecystokinin induced gall bladder contraction; it is known that analysis of biliary porphyrins is more discriminatory for the diagnosis of asymptomatic porphyria than their analysis in faeces or urine. Moreover, serial analysis of bile from patients with erythropoietic protoporphyria may help in establishing their ability to secrete protoporphyrin in bile and to assess effects of treatment. The binding of various porphyrins to Enterotest strings was investigated by incubating pieces of the string in different human bile samples with low to very high porphyrin concentrations, followed by HPLC analysis of porphyrins both in the native bile and in extracts obtained from the strings. No differences between porphyrin composition in native bile and extracts were observed. Duodenal fluid obtained by means of the Enterotest from volunteers not receiving cholecystokinin showed large variations in porphyrin patterns not resembling those of native bile. Mesoporphyrin, a secondary porphyrin derived from protoporphyrin by bacteria, was often detectable. These data indicate that the duodenal content without cholecystokinin injection does not reflect biliary porphyrin composition. The presence of mesoporphyrin in the whole intestinal tract, but not in serum and bile, suggests that there is no enterohepatic circulation of secondary porphyrins. There was close agreement between the porphyrin ratios found with the standard duodenal intubation technique and the Enterotest, performed simultaneously in one healthy volunteer after induction of gall bladder contraction by cholecystokinin. From these experiments, it was concluded that fluid adsorbed to the Enterotest string after gall-bladder contraction can be used to determine biliary porphyrin composition. Since duodenal bile is diluted gall bladder bile, variable porphyrin concentrations were found when applying the Enterotest in combination with cholecystokinin in the same subject on successive days. However, porphyrin ratios, such as the protoporphyrin to coproporphyrin I ratio, were relatively constant. In subjects with symptomatic variegate porphyria, the Enterotest showed highly aberrant porphyrin patterns, with increased protoporphyrin to coproporphyrin I ratios and, in addition, the presence of some unknown porphyrins. A deviating biliary protoporphyrin/coproporphyrin I ratio in one patient appeared to be a useful diagnostic index for the presence of latent variegate porphyria (or variegate porphyria in remission).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1997

Interactions of DNA with a new electron-deficient tentacle porphyrin: meso-tetrakis[2,3,5,6-tetrafluoro-4-(2-t rimethylammoniumethyl-amine)phenyl]porphy rin.

A new electron-deficient tentacle porphyrin meso-tetrakis[2,3,5,6-tetrafluoro-4-(2-trimethylammoniumethylamine )phenyl]porphyrin (TthetaF4TAP) has been synthesized. The binding interactions of TthetaF4TAP with DNA polymers were studied for comparison to those of an electron-deficient tentacle porphyrin and an electron-rich tentacle porphyrin; these previously studied porphyrins bind to DNA primarily by intercalative and outside-binding modes, respectively. The three tentacle porphyrins have similar size and shape. The basicity of TthetaF4TAP indicated that it has electronic characteristics similar to those of the intercalating electron-deficient tentacle porphyrin. However, TthetaF4TAP binds to calf thymus DNA, [poly(dA-dT)]2, and [poly(dG-dC)]2 in a self-stacking, outside-binding manner under all conditions. Evidence for this binding mode included a significant hypochromicity of the Soret band, a conservative induced CD spectrum, and the absence of an increase in DNA solution viscosity. As found previously for the electron-rich porphyrin, the results suggest that combinations of closely related self-stacked forms coexist. The mix of forms depended on the DNA and the solution conditions. There are probably differences in the detailed features of the self-stacking adducts for the two types of tentacle porphyrins, especially at high R (ratio of porphyrin to DNA). At low R values, the induced CD signal of TthetaF4TAP/CT DNA resembled that of TthetaF4TAP/[poly(dA-dT)]2, suggesting that TthetaF4TAP binds preferentially at AT regions. Competitive binding experiments gave evidence that TthetaF4TAP binds preferentially to [poly(dA-dT)]2 over [poly (dG-dC)]2. Thus, despite the long, positively charged, flexible substituents on the porphyrin, the binding of TthetaF4TAP is significantly affected by base-pair composition. Similar characteristics were found previously for the electron-rich tentacle porphyrin. Thus, significant changes in electron richness have relatively minor effects on this outside binding selectivity for AT regions. TthetaF4TAP is the first porphyrin with electron deficiency and shape similar to intercalating porphyrins that does not appear to intercalate. All porphyrins reported to intercalate have had pyridinium substituents. Thus, the electronic distribution in the porphyrin ring, not just the overall electron richness, may play a role in facilitating intercalation.

Animals↗
PubMedDate not supplied

Urinary porphyrin profiles as a biomarker of mercury exposure: studies on dentists with occupational exposure to mercury vapor.

Porphyrins are formed as intermediates in the biosynthesis of heme. In humans and other mammals, porphyrins with eight, seven, six, five, and four carboxyl groups are excreted in the urine in a well-established pattern. Mercury selectively alters porphyrin metabolism in kidney proximal tubule cells, leading to an altered urinary porphyrin excretion pattern. Previous studies in rats have shown that changes in the urinary porphyrin profile during exposure to mercury as methylmercury hydroxide are uniquely characterized by highly elevated (20- to 30-fold) levels of four- and five-carboxyl porphyrins and by the excretion of an atypical porphyrin ("precoproporphyrin"), which elutes on high performance liquid chromatography (HPLC) approximately midway between penta- and coproporphyrins. Changes in the urinary porphyrin profile are highly correlated with the dose and duration of mercury exposure and persist for up to 20 wk following cessation of mercury treatment. In the present studies, the utility of urinary porphyrin profile changes as a biomarker of mercury exposure in human subjects was evaluated. Urinary porphyrin concentrations were measured in dentists participating in the Health Screening Programs conducted during the 1991 and 1992 annual meetings of the American Dental Association and compared with urinary mercury levels measured in the same subjects. Among dentists with no detectable urinary mercury, mean concentrations of urinary porphyrins were within the established normal ranges for male human subjects. In contrast, among dentists with urinary mercury in excess of 20 micrograms/L, mean urinary concentrations of four- and five-carboxyl porphyrins as well as of precoproporphyrin were elevated three to four times those of unexposed subjects. Significant differences in urinary porphyrin concentrations remained when porphyrin concentrations in spot urine samples were adjusted for creatinine levels. These findings suggest that urinary porphyrin profiles may serve as a useful biomarker of mercury exposure in clinical or epidemiologic studies of mercury-related human health risks.

Animals↗
PubMedDate not supplied

Photodynamic studies and photoinactivation of Escherichia coli using meso-substituted cationic porphyrin derivatives with asymmetric charge distribution.

The photodynamic activities of novel asymmetrically meso-substituted cationic porphyrins, 5,10-di(4-methylphenyl)-15,20-di(4-trimethylammoniumphenyl)porphyrin iodide 1 and 5-(4-trifluorophenyl)-10,15,20-tris(4-trimethylammoniumphenyl)porphyrin iodide 2 and its metal complex with Pd(II) 3, have been investigated in both homogeneous medium bearing photooxidizable substrates and in vitro on a typical gram-negative bacterium Escherichia coli. The amphiphilic character of porphyrin 2 was increased by the presence of a high-lipophilic trifluoromethyl group and its photophysical properties changed by forming a complex with Pd(II). Absorption and fluorescence spectroscopic studies were compared in different media. Fluorescence quantum yields (phi(F)) of 0.16 for 1 in tetrahydrofuran and 0.08 for 2 in N, N-dimethylformamide (DMF) were calculated, whereas no significant emission was detected for Pd(II) porphyrin 3. The singlet molecular oxygen, O(2)((1)Delta(g)), production was evaluated using 9,10-dimethylanthracene in DMF yielding relative values of 1, 0.55 and 0.47 for porphyrins 3, 2 and 1, respectively. A faster decomposition of l-tryptophan was obtained using Pd(II) porphyrin 3 as sensitizer with respect to the free-base porphyrins 1 and 2. In biological medium, the behavior of cationic porphyrins 1-3 were compared with that of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl)porphyrin 4, which was used as a noncationic sensitizer. These porphyrins are rapidly bound to E. coli cells in 5 min and the amount of cell-bound sensitizer is not appreciably changed incubating the cultures for longer times. The recovered porphyrin 2 after one washing step reaches a value of approximately 2.9 nmol/10(6) cells and this amount remains high even after three washes, indicating that this sensitizer is tightly bound to cells. Photosensitized inactivation of E. coli was analyzed using cells without and with one washing step. In both cases, a higher photoinactivation of cells was found for tricationic porphyrin 2 and 3, causing a approximately 5.5 log (99.999%) decrease of cell survival, when treated with 10 microM of sensitizer. Under these conditions, a lower effect was found for porphyrin 1 (approximately 4 log) whereas sensitizer 4 did not produce appreciable photodamage. The results were also confirmed by growth delay experiments. These studies show that the amphiphilic tricationic porphyrin 2 and 3 bearing a trifluoromethyl group can be a promising model for phototherapeutic agents with potential applications in inactivation of bacteria by photodynamic therapy.

Cations↗
PubMed2001

Rational syntheses of cyclic hexameric porphyrin arrays for studies of self-assembling light-harvesting systems.

Two new cyclic hexameric arrays of porphyrins have been prepared in a rational, convergent manner. The porphyrins in each cyclic hexamer are joined by diphenylethyne linkers affording a wheel-like array with a diameter of approximately 35 A. One array is comprised of five zinc (Zn) porphyrins and one free base (Fb) porphyrin (cyclo-Zn(5)FbU) while the other is comprised of an alternating sequence of two Zn porphyrins and one Fb porphyrin (cyclo-Zn(2)FbZn(2)FbU). The prior synthesis employed a one-flask template-directed process and afforded alternating Zn and Fb porphyrins or all Zn porphyrins. More diverse metalation patterns are attractive for manipulating the flow of excited-state energy in the arrays. The rational synthesis of each array employed three Pd-mediated coupling reactions with four tetraarylporphyrin building blocks bearing diethynyl, diiodo, bromo/iodo, or iodo/ethynyl groups. The final ring closure yielding the cyclic hexamer was achieved by reaction of a porphyrin pentamer + porphyrin monomer or the joining of two porphyrin trimers. In the presence of a tripyridyl template, the yields of the 5 + 1 and 3 + 3 reactions ranged from 10 to 13%. The 5 + 1 reaction in the absence of the template proceeded in 3.5% yield, thereby establishing the structure-directed contribution to cyclic hexamer formation. The 3 + 3 route relied on successive ethyne + iodo/bromo coupling reactions. One template-directed route to cyclo-Zn(2)FbZn(2)FbU employed a magnesium porphyrin, affording cyclo-Zn(2)FbZn(2)MgU from which magnesium was selectively removed. The arrays exhibit absorption spectra that are nearly the sum of the spectra of the component parts, indicating weak electronic coupling. Fluorescence spectroscopy showed that the quantum yield of energy transfer in toluene at room temperature from the Zn porphyrins to the Fb porphyrin(s) was 60% in cyclo-Zn(5)FbU and 90% in cyclo-Zn(2)FbZn(2)FbU. Two dipyridyl-substituted porphyrins, a Zn tetraarylporphyrin and a Fb oxaporphyrin, have been synthesized for use as guests in the cyclic hexamers, affording self-assembled arrays for light-harvesting studies.

Journal Article↗
PubMed2002

Photophysical properties of porphyrin tapes.

The novel fused Zn(II)porphyrin arrays (Tn, porphyrin tapes) in which the porphyrin macrocycles are triply linked at meso-meso, beta-beta, beta-beta positions have been investigated by steady-state and time-resolved spectroscopic measurements along with theoretical MO calculations. The absorption spectra of the porphyrin tapes show a systematic downshift to the IR region as the number of porphyrin pigments increases in the arrays. The fused porphyrin arrays exhibit a rapid formation of the lowest excited states (for T2, approximately 500 fs) via fast internal conversion processes upon photoexcitation at 400 nm (Soret bands), which is much faster than the internal conversion process of approximately 1.2 ps observed for a monomeric Zn(II)porphyrin. The relaxation dynamics of the lowest excited states of the porphyrin tapes were accelerated from approximately 4.5 ps for the T2 dimer to approximately 0.3 ps for the T6 hexamer as the number of porphyrin units increases, being explained well by the energy gap law. The overall photophysical properties of the porphyrin tapes were observed to be in a sharp contrast to those of the orthogonal porphyrin arrays. The PPP-SCI calculated charge-transfer probability indicates that the lowest excited state of the porphyrin tapes (Tn) resembles a Wannier-type exciton closely, whereas the lowest excited state of the directly linked porphyrin arrays can be considered as a Frenkel-type exciton. Conclusively, these unique photophysical properties of the porphyrin tapes have aroused much interest in the fundamental photophysics of large flat organic molecules as well as in the possible applications as electric wires, IR sensors, and nonlinear optical materials.

Journal Article↗
PubMed2003

The synthesis and studies towards the self-replication of bis(capped porphyrins).

Connecting two facially-protected porphyrins was expected to lead to an equal mixture of laterally-bridged doubly-protected bis-porphyrins; one in which the two porphyrin units were protected on the same face (syn) and one with the two prophyrin units protected on opposite faces (anti). Addition of a co-factor (bidentate ligand) was expected to lead predominantly to the syn-bis-porphyrin by a templated self-replication process. This concept was explored using Baldwin's capped porphyrin. Bis(capped porphyrins) were synthesised in several steps starting from zinc(II) capped porphyrin 2. Nitration of 2 followed by reduction and photo-oxidation yields a mixture of zinc(II) porphyrindiones 7 and 8 that can separated by HPLC. The condensation of 2 molar eq. of zinc(II) porphyrin-7,8-dione 8 with 1,2,4,5-benzenetetramine leads to the formation of a 1:1 mixture of syn- and anti-dizinc(II) bis(7,8-capped porphyrins), 11 and 12, respectively, that have almost identical spectroscopic properties. These two geometric isomers were distinguished by significant differences in their molecular recognition properties. Likewise the syn- and anti-dizinc(II) bis(2,3-capped porphyrins), 9 and 10, respectively, are synthesised from the related zinc(II) capped porphyrin-2,3-dione 7, and were also identified using molecular recognition studies. The molecular recognition properties of these bis(capped porphyrins) were utilised in studies of self-replicating porphyrin systems. The results show that tetraazaanthraceno-bis-porphyrins 9-12 can catalyse their own formation but self-replication was not observed. These results highlight the potential that these interesting hosts have as templates in supramolecular chemistry, synthesis and catalysis.

Journal Article↗