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At least 19 recordsLinked to original sources
PubMed1998

Synthesis of Vinylene-Co,N-Linked Multi(porphyrin)s by the Addition of Free-Base Porphyrins to a C(2)H(2) Complex of Cobalt(III) Porphyrin and Their Oxidative Rearrangement to Vinylene-N,N'-Linked Multi(porphyrin)s.

The nucleophilic addition reaction of a pyrrole nitrogen of free-base porphyrins to a pi-complexed acetylene ligand in a cationic Co(III) porphyrin intermediate afforded good yields of vinylene-Co,N'-linked bis(porphyrin)s, (Por)Co(III)-CH=CH-(N-Por)H(2). N-substituted porphyrin free bases are N-vinylated regioselectively at the pyrrole adjacent to the original N-substituted pyrrole in this reaction. Tris- and tetrakis(porphyrin)s have been prepared by reacting a vinylene-N,N'-linked bis(meso-tetraarylporphyrin) with (OEP)Co(III)(H(2)O)(2)ClO(4) (OEP: octaethylporphyrin dianion) and acetylene. The tetrakis(porphyrin) proved to be a 1:1 mixture of C(i)()- and C(2)-symmetric regioisomers. These organometallic Co(III) complexes underwent facile oxidative migration of the Co-bound vinyl group to a porphyrin pyrrole nitrogen when treated with Fe(III) salts or HClO(4) to provide moderate to good yields of Co(II) vinylene-N,N'-linked multi(porphyrin) complexes. (Vinylene-N,N')bis(porphyrin) free bases with combinations of different porphyrins have been obtained by this procedure. The homobinuclear (2Co(II), 2Cu(II), and 2Zn(II)) and heterobinuclear (Co(II)Cu(II) and Co(II)Zn(II)) complexes have been prepared and characterized spectroscopically. The single-crystal X-ray analysis of (CH=CH-N,N')[(OEP)Co(II)Cl][(TPP)Zn(II)Cl] (TPP: meso-tetraphenylporphyrin dianion) showed a face-to-face structure with an average inter-ring separation of 4.39 Å (triclinic P&onemacr;; Z = 2; a = 14.806(4), b = 18.703(10), c = 13.796(3) Å, alpha = 97.69(3), beta = 99.57(2), gamma = 96.74(3) degrees ).

Journal Article↗
PubMed2000

3-Cyclobutenyl-1,2-dione-substituted porphyrins. A general and efficient entry to porphyrin-quinone and quinone-porphyrin-quinone architectures.

A new and efficient synthesis of meso-linked porphyrin-quinone dyads and quinone-porphyrin-quinone triads has been developed via the intermediacy of porphyrins bearing 3-cyclobutenyl-1,2-dione and 3-(1-ethenyl)cyclobutenyl-1,2-dione substituents at one or two nonadjacent meso-positions. The free-base porphyrins 5-bromo-10,20-diphenylporphyrin and 5,15-dibromo-10,20-diphenylporphyrin undergo facile palladium-catalyzed Stille coupling with 3-isopropoxy-2-tri-n-butylstannyl-cyclobutene-1,2-dione to produce the corresponding mono- and bis(3-cyclobutenyl-1,2-dione)-substituted porphyrins in good yields. In contrast, the zinc bromoporphyrins reacted with the same tin reagent only slowly and with the formation of side products. The free-base bromoporphyrins also were coupled with tri-n-butylvinyltin to afford vinylporphyrins in very good yields. 5,15-Diphenyl-10-vinylporphyrin was converted into trans-bromovinylporphyrin, which underwent facile Stille coupling with 3-isopropoxy-2-tri-n-butylstannylcyclobutene-1,2-dione to afford the vinylogous 3-cyclobutenyl-1,2-dione-substituted porphyrin. The molecular structure of 5,15-bis(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Z n) was determined by X-ray crystallography. Although the data revealed a fairly large dihedral angle between the cyclobutenedione and the porphyrin rings (57 degrees), the UV-vis spectra of both the mono- and bis(3-cyclobutenyl-1,2-dione)-substituted porphyrins showed B- and Q-band red shifts indicative of strong electronic coupling between the porphyrin and cyclobutenedione chromophores in solution. Introduction of a double bond between the cyclobutenedione and porphyrin rings resulted in a significant red shift of both the B- and Q-bands compared to those of the nonvinylogous system. All porphyrinic cyclobutenediones were metalated with zinc and then, using established cyclobutenedione chemistry, converted into a variety of porphyrin-quinones in excellent yields with aryllithium and vinylic Grignard reagents. From the mono(3-cyclobutenyl-1,2-dione)-substituted porphyrin, 7, a variety of directly linked monoquinone-porphyrin dyads were easily synthesized. Substituents could also be introduced at the free meso-position of 7 by bromination followed by palladium-catalyzed cross-coupling reactions, and additional porphyrinic monoquinones were then prepared from these starting materials. The vinylogous squarylporphyrin was converted into a double bond linked porphyrin-quinone via reaction with phenyllithium followed by thermal rearrangement and oxidation. As a result of the hindered rotation around the C-C bond between the porphyrin and the quinone, pairs of stable, separable, and thermally interconvertable atropisomers of porphyrin-quinones were obtained from 5,15-bis(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Z n). The structure of one of the atropisomers was determined by X-ray crystallography.

Crystallography, X-Ray↗
PubMed2000

3-Cyclobutenyl-1,2-dione-substituted porphyrins. 2. A simple and general entry to quinone-porphyrin-porphyrin-quinone tetrads and related molecules.

The synthesis of meso-linked quinone-porphyrin-porphyrin-quinone tetrads has been accomplished by the simple treatment of a CH2Cl2 solution of zincated 5-substituted-10,20-diphenylporphyrins (where the substituent = 3-cyclobutenyl-1,2-dione, various quinonyl derivatives, and p-anisyl) with 2,3-dichloro-5,6-dicyanoquinone (DDQ). The zincated porphyrinic quinones were synthesized from 5-(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Zn). The meso-linked dimer of 5-(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Zn) was also shown to be a useful precursor to meso-linked quinone-porphyrin-porphyrin-quinone tetrads. This DDQ-based oxidative dimerization appears to be general and effective for various zincated 5-substituted-10,20-diphenylporphyrins bearing both electron-withdrawing and -donating substituents. The oxidative dimerization was very sensitive to the reaction solvent (dimerization occurred in CH2Cl2, not in THF) and required the zincated porphyrins (the corresponding free base porphyrins did not undergo dimerization). When this solvent effect was applied to the reaction of I2/AgO2CCF3 with zincated porphyrins, either the dimeric porphyrins or iodoporphyrins could be selectively prepared simply by selecting methylene chloride or THF as the reaction solvent, respectively.

Cyclobutanes↗
PubMed1996

Synthesis of Linear Amphipathic Porphyrin Dimers and Trimers: An Approach to Bilayer Lipid Membrane Spanning Porphyrin Arrays.

A modular building-block approach has been developed for the construction of linear amphipathic porphyrin arrays. The reaction of meso-(trifluoromethyl)dipyrromethane and an aldehyde under the conditions of the two-step room temperature porphyrin synthesis affords the trans-substituted porphyrin (13-56% yields). A similar reaction with two different aldehydes provides access to porphyrins bearing two different functional groups. An ethyne porphyrin and an iodo porphyrin (either free base or zinc) are selectively joined via Pd(0)-catalyzed coupling reactions, affording a linear array with porphyrins in defined metalation states. Coupling of a zinc-porphyrin bearing iodo and ester groups with a free base porphyrin bearing ethyne and ester groups yielded the zinc-free base porphyrin dimer. Coupling of a bis-ethyne porphyrin with a porphyrin bearing iodo and ester groups afforded the porphyrin trimer. Cleavage of the esters yielded the amphipathic porphyrin dimer and trimer arrays. The arrays with adjacent zinc and free base porphyrins undergo efficient electronic energy transfer. Both amphipathic porphyrin arrays have been incorporated into L-alpha-phosphatidylcholine vesicles. This versatile synthetic strategy provides access to a family of porphyrin arrays for studies of photophysical processes in supramolecular assemblies.

Journal Article↗
PubMed2001

Rh(III) porphyrins as building blocks for porphyrin coordination arrays: from dimers to heterometallic undecamers.

The coordination chemistry of a Rh(III) porphyrin building block was investigated with a view to the construction of heterometallic arrays of porphyrins. The Rh(III) porphyrin was found to coordinate methanol in the solid state and weakly in CDCl(3) solution. Crystallization afforded five coordinate pi stacked Rh(III) porphyrins. The distribution of products from reaction of Rh(III) porphyrin with DABCO, 4,4'-bipyridine, and 4,4'-bipyrimidine could be displaced toward dimeric species by silica gel column chromatography or recrystallization which served to remove excess ligand. Weak coordination to nitriles was observed, although it was sufficiently strong to organize a dimeric complex of 5,5'-dicyano-2,2'-bipyridine in the solid state. Complexes with 4,4'-bipyrimidine and 5,5'-dicyano-2,2'-bipyridine possess uncoordinated chelating nitrogen atoms. Larger heterometallic porphyrin arrays were assembled using a combination of Sn(IV) and Rh(III) porphyrin coordination chemistry. A Sn(IV) porphyrin acted as a core around which were coordinated two isonicotinate groups, carboxylic acid functionalized porphyrins, or porphyrin trimer dendrons. Rh(III) porphyrins were coordinated to pyridyl groups at the periphery of these entities. In this way an eleven porphyrin array, with four different porphyrin metalation states, was assembled. The diamagnetic nature of both the Rh(III) and Sn(IV) porphyrins, the slow ligand exchange kinetics on the NMR time scale, and tight ligand binding permitted the porphyrin arrays to be analyzed by two-dimensional (1)H NMR techniques.

Journal Article↗
PubMed1999

Significant Electronic Effect of Porphyrin Ligand on the Reactivities of High-Valent Iron(IV) Oxo Porphyrin Cation Radical Complexes.

High-valent iron(IV) oxo porphyrin cation radical complexes containing a series of substituents at the meso position of the porphyrin ring (i.e., electron-donating and -withdrawing substituents on phenyl groups) were prepared and used in oxygen atom transfer reactions to elucidate the electronic effect of porphyrin ligands on the reactivities of iron porphyrin complexes. The reactions that we studied with the in situ generated high-valent iron oxo porphyrins were (1) the relative reactivities of the intermediates toward oxygen atom transfer and ROOH disproportionation (ROOH = hydrogen peroxide and tert-butyl hydroperoxide), (2) the mechanism of heterolytic versus homolytic O-O bond cleavage of hydroperoxides, (3) the dependence of oxidizing power of the intermediates on the electronic nature of porphyrin ligands, and (4) the relative rates between oxygen atom transfer and oxygen exchange with labeled H(2)(18)O. We found from these reactivity studies that (1) a high-valent iron oxo porphyrin complex containing electron-donating substituents reacts fast with ROOH in a competitive reaction performed with a mixture of olefin and ROOH, whereas a high-valent iron oxo porphyrin containing electron-withdrawing substituents transfers its oxygen atom to olefin to give an epoxide product at a fast rate, (2) the O-O bond of hydroperoxides is homolytically cleaved by iron porphyrin complexes in aprotic solvent, (3) a high-valent iron oxo complex of electron-deficient porphyrin ligand is a more powerful oxidizing species than that of electron-rich porphyrin ligand in alkane hydroxylation reactions, and (4) the presence of electron-donating substituents on a porphyrin ligand gives a relatively high (18)O incorporation from labeled H(2)(18)O into an oxygenated product when a mixture of olefin and H(2)(18)O is added to a reaction solution containing a high-valent iron oxo intermediate, whereas only a small amount of (18)O incorporation is observed with iron porphyrin complexes containing electron-withdrawing substituents. These results clearly demonstrate that the electronic nature of iron porphyrin complexes is an important factor in determining the reactivities of iron porphyrin complexes in oxygen atom transfer reactions.

Journal Article↗
PubMed2001

A strategy for the assembly of multiple porphyrin arrays based on the coordination chemistry of Ru-centered porphyrin pentamers.

An approach which employs pentameric porphyrin arrays as building blocks toward larger porphyrin arrays is described. Two flexible, and one relatively rigid, Ru-centered porphyrin pentamers (1-3) were synthesized and fully characterized. Their potential as building blocks toward larger porphyrin arrays has been studied via their coordination chemistry using bidentate and tetradentate ligands. DABCO (diazabicyclo[2.2.2]octane) can bind two monomeric porphyrins but was found to be too small to allow the complete formation of a 10-porphyrin array. On the other hand, titration of a larger bridging dipyridyl porphyrin ligand 17 (0.5 equiv) with 1 or 2 and tetrapyridyl ligand 18 (0.25 equiv) with 3 results in the formation of the 11-porphyrin and 21-porphyrin arrays, respectively, with the 21-porphyrin array containing porphyrins in three different metalation states. Changes in the chemical shift of the inner NH protons as well as the ortho- and meso-protons of the pyridyl groups of the porphyrin ligand clearly indicate the formation of large multiple porphyrin complexes. These studies demonstrate that by use of carefully designed building blocks and suitable bridging ligands, porphyrin arrays can be constructed with a dramatic increase in size in relatively few steps. Exploiting the fact that the strength of binding of pyridyl ligands is Ru > Zn > Ni, intra- vs intermolecular competition has been used to investigate aspects of the folding of the array. The photophysical properties of 3 are also described.

Magnetic Resonance Spectroscopy↗
PubMed1995

Correlation between levels of free and protein-bound plasma porphyrin and urinary porphyrins in porphyria cutanea tarda.

Porphyria cutanea tarda (PCT) is a disorder of porphyrin metabolism that leads to massive overproduction and excretion of uroporphyrin. Most plasma porphyrins are bound to albumin and hemopexin. The aim of this work was to analyze the relationship between the concentrations of serum albumin and hemopexin, the levels of total, free and protein-bound plasma porphyrins and the urinary coproporphyrin and uroporphyrin excretion, in PCT patients at different stages of the disease. Urinary porphyrins showed a stronger correlation with total plasma porphyrin levels (r = 0.863) than with the free fraction of plasma porphyrins (r = 0.608). Patients considered in an active stage of PCT, have a higher mean level of total plasma porphyrins (8.80 micrograms/dl +/- 8.75) and a lower mean percentage of free plasma porphyrins (12.79% +/- 11.21) than those patients on remission (0.71 +/- 0.5 microgram/dl and 44.3 +/- 35.3%, respectively). 30% of patients showed hypohemopexinaemia, presumably due to hepatic damage. Despite the high affinity of this protein for porphyrins, no significant correlation was found between plasma porphyrin levels and hemopexin or albumin. It is concluded that (i) the kidney is not merely a passive filter for free plasma porphyrins and (ii) that the formation of hemopexin-porphyrin complex occurs when plasma porphyrins concentrations are increased (i.e. in those patients in an active stage of PCT).

Coproporphyrins↗
PubMed1986

Chemical properties of water-soluble porphyrins. 5. Reactions of some manganese (III) porphyrins with the superoxide and other reducing radicals.

Solution properties of three manganese porphyrins, in monomeric form, were investigated. These were the 'picket-fence-like' porphyrin Mn(III)-alpha,alpha,alpha,beta- tetra-ortho(N-methylisonicotinamidophenyl)porphyrin (Mn(III)PFP) and two 'planar unhindered' porphyrins, the Mn(III)TMPyP (tetrakis (4-N-methylpyridyl)porphyrin) and Mn(III)TAP (tetra(4-N,N,N-trimethylanilinium)porphyrin). The porphyrin properties studied were: the absorption spectra in their manganic and manganous forms; acid/base properties of the aquo complexes; the effect of potential axial ligands (up to a concentration of 0.1 mol dm-3) and their one electron reduction potentials. Knowing these properties, the reaction of the Mn(III) porphyrins with the superoxide radical and other reducing radicals were studied using the pulse radiolysis technique. The second-order reaction rate constant of O2- with the Mn(III) porphyrins, which governs the catalytic efficiency of the metalloporphyrins upon the disproportionation of the superoxide radical, was 5.1 X 10(7) to 4.0 X 10(5) dm3 mol-1 s-1, depending on the pH and the nature of the metalloporphyrin. These values are at least one order of magnitude lower than found for Fe(III)TMPyP. One electron reduction of the three Mn(III) porphyrins by eaq-, CO2-, CH2OH and (CH3)2COH had similar second-order rate constants (10(9)-10(10) dm3 mol-1 s-1). That for (CH3)2(CH2)COH was about 10(5) dm3 mol-1 s-1. Reduction in all cases produced the corresponding Mn(II) porphyrin and no intermediate was found. The oxidation reaction of the Mn(II) porphyrins by O2- was approximately two orders of magnitude faster when compared to the reduction of Mn(III) porphyrins with the same radical. Since the reactivities of O2- towards the three manganese (III) compounds follow their reduction potentials, it is suggested that these reactions are governed by an outer-sphere mechanism. This suggestion is corroborated by the finding that water molecules acting as axial ligands, in these aqueous solution systems, are not replaced by another potential ligand when the latter is in the concentration range of 100 mM or less.

Manganese↗
PubMed1994

Androgenic control of porphyrin in the Harderian glands of the male Syrian hamster is modulated by the photoperiod, which suggests that the sexual differences in porphyrin concentrations in this gland are important functionally.

BACKGROUND: The porphyrin concentrations of the Harderian glands of Syrian hamsters show marked sexual differences, with male levels being much lower than those of females. Porphyrinogenesis is inhibited by androgens, so orchidectomy leads to elevated male porphyrin concentrations; however, a number of other procedures (some of which also lower androgen levels) prevents this. We studied the effects of short-day photoperiods and melatonin on Harderian porphyrin concentrations. METHODS: Intact, castrated, or pinealectomized hamsters of both sexes were exposed to long-day or short-day photoperiods. Intact or castrated hamsters were given melatonin injections in the morning or the afternoon, or were given beeswax pellets containing melatonin. After a variable period, Harderian glands were dissected and porphyrins were measured. RESULTS: Prolonged short-day exposure (13 weeks) led to increased Harderian porphyrin concentrations and this rise was prevented by pinealectomy. The rise in Harderian porphyrins following short-day exposure was small, compared with that following castration. Short-day photoperiods also prevented the rise in porphyrin levels associated with castration and this effect was prevented by removal of the pineal. Melatonin injections, whether given in the morning or in the afternoon, had no effect on Harderian porphyrin concentration of castrated male hamsters. Continuous release melatonin pellets reduced the postcastrational rise in porphyrin levels in one experiment, while having no effect in another. In female hamsters, neither short photoperiods nor melatonin pellets influenced Harderian porphyrin concentrations. CONCLUSIONS: These results suggested that a factor from the pineal gland helps maintain the low levels of porphyrin which are characteristic of male Harderian glands, despite the decrease in androgen levels which typically results from exposure to short days. Morning and afternoon injections of melatonin and continuous release melatonin pellets failed to resolve the question of whether this pineal factor is melatonin. Our results demonstrated that low male and high female porphyrin levels are maintained in Syrian hamsters, despite seasonal variations in the hormonal milieu, suggesting that these sexual differences are important for the (still unestablished) function of the Harderian glands in this species.

Animals↗
PubMed1987

Analysis of porphyrins and enzymes in porphyrin synthesis in Taenia solium cysticercus from man and pig.

Porphyrins and activities of heme biosynthetic enzymes in Taenia solium cysticerci from porcine and human hosts, were examined in order to clarify the possible step where heme synthesis is interrupted. Porphyrins in the vesicular fluid of the parasite were predominantly coproporphyrin, followed by penta-carboxylated porphyrin, which together accounted for 90% of the accumulated porphyrins. Coproporphyrin and penta-carboxylated porphyrin were both type I and III isomers. Small amounts of protoporphyrin and uroporphyrin, and trace amounts of tri-, hexa- and hepta-carboxylated porphyrins were also detected. Fluorescence and phosphorescence spectra and lifetime studies revealed that at least 75% of the porphyrins were bound to metal, probably Zn, while the rest was free. Reverse phase high performance liquid chromatography monitored at an excitation wavelength of 417 nm and at an emission wavelength of 585 nm demonstrated that approximately 90% of these porphyrins were Zn-coproporphyrin. A fluorescence excitation peak at 283 nm with an emission peak at 585 nm and 625 nm indicated that some of the porphyrins were associated with proteins in the vesicular fluid of the parasite. Low levels of delta-aminolevulinic acid dehydratase, porphobilinogen deaminase and uroporphyrinogen decarboxylase activities, and heme concentrations were found in the extract of the parasite walls and scolex, but not in the vesicular fluid. The porphyrin accumulation pattern in this parasite can best be explained by postulating a deficiency of coproporphyrinogen oxidase activity, similar to that in human patients with hereditary coproporphyria. A parasite dissected from a human host was considerably less porphyric than those from pigs, but the pattern of accumulated porphyrins was quite similar in both. In view of their porphyrin contents, T. solium cysticerci could be light sensitive.

Animals↗
PubMed1992

Quantitative determination of porphyrins in rat and human urine and evaluation of urinary porphyrin profiles during mercury and lead exposures.

Measurement of urinary porphyrin excretion patterns (porphyrin profiles) is useful in the diagnosis and evaluation of diseases and disorders of porphyrin metabolism. However, experimental investigation of such disorders with rodent models has been hampered by the lack of an efficient procedure for the isolation and quantitative evaluation of porphyrins in rodent urine. This article describes an analytic procedure that overcomes the principal difficulties encountered with determination of porphyrins in rodent urine, including the loss of porphyrins during their isolation and interference of porphyrin fluorescence by contaminating materials. The procedure entails application of an acidified urine sample to a preconditioned C-18 preparatory column, preferential separation of essentially all potentially interfering contaminants by sequential phosphate-methanol elution, and selective isolation of porphyrins, which are then separated and quantitated by high-performance liquid chromatography and spectrofluorometric techniques. This method has been used to characterize urinary porphyrin excretion patterns in male rats and to define the distinctive changes in porphyrin profiles associated with prolonged exposure to porphyrinogenic metals. The porphyrin excretion patterns of male and female human subjects are also described. This method is applicable to the investigation of urinary porphyrin profile changes associated with exposure to a wide range of porphyrinogenic chemicals in both animals and human subjects.

Animals↗
PubMed1993

Quantitative measurement of porphyrins in biological tissues and evaluation of tissue porphyrins during toxicant exposures.

Porphyrins are formed in most eukaryotic tissues as intermediates in the biosynthesis of heme. Assessment of changes in tissue porphyrin levels occurring in response to the actions of various drugs or toxicants is potentially useful in the evaluation of chemical exposures and effects. The present paper describes a rapid and sensitive method for the extraction and quantitation of porphyrins in biological tissues which overcomes difficulties encountered in previously described methods, particularly the loss of porphyrins during extraction and interference of porphyrin quantitation by coeluting fluorescent tissue constituents. In this procedure 8- through 2-carboxyl porphyrins are quantitatively extracted from tissue homogenates using HCl and methanol and are subsequently separated from potentially interfering contaminants by sequential methanol/phosphate elution on a C-18 preparatory column. Porphyrins are then separated and measured by reversed-phase high-performance liquid chromatography and spectrofluorometric techniques. Recovery of tissue porphyrins using this method is close to 100% with an intraassay variability of less than 10%. We have employed this procedure to measure liver and kidney porphyrin concentrations in male Fischer rats and to define the distinctive changes in tissue porphyrin patterns associated with treatment with the hepatic and renal porphyrinogenic chemicals, allylisopropylacetamide, and methyl mercury hydroxide, respectively. This method is applicable to the measurement of tissue porphyrin changes resulting from drug or toxicant exposures in clinical, experimental or environmental assessments.

Allylisopropylacetamide↗
PubMed1991

Urinary porphyrin profiles as biomarkers of trace metal exposure and toxicity: studies on urinary porphyrin excretion patterns in rats during prolonged exposure to methyl mercury.

Studies were conducted to define the specific changes in the urinary porphyrin excretion pattern (porphyrin profile) and the time course of those changes in rats exposed to mercury as methyl mercury hydroxide (MMH) at 5 or 10 ppm in the drinking water for up to 30 weeks. The urinary porphyrin profile elicited by MMH is uniquely characterized by highly elevated levels of 4- and 5-carboxyl porphyrins, and of a third atypical porphyrin with as yet undetermined chemical characteristics. Changes in the porphyrin profile were observed as early as 1 or 2 weeks following initiation of exposure to MMH at 10 or 5 ppm, respectively, and were sustained as long as 40 weeks following cessation of MMH treatment. The magnitude of the urinary porphyrin profile at either MMH dose level increased progressively during the course of mercury treatment and was highly correlated with the renal mercury concentration. A subsequent decline in the magnitude of the urinary porphyrin profile in animals exposed to 10 ppm MMH for more than 10 weeks was associated with the accumulation of high levels of Hg2+ in kidney cells and loss of renal functional status. These findings demonstrate that mercury elicits a unique change in the urinary porphyrin excretion pattern which is related to the dose and duration of mercury treatment. The association of urinary porphyrin excretion rates with renal mercury content and functional status suggests that urinary porphyrin profiles may serve as a useful biomarker of mercury accumulation and nephrotoxicity during prolonged mercury exposure.

Animals↗
PubMed2003

Theoretical analysis of the porphyrin-porphyrin exciton interaction in circular dichroism spectra of dimeric tetraarylporphyrins.

Chiral bis-porphyrins are currently the subject of intense interest as chiral receptors and as probes in the determination of structure and stereochemistry. To provide an improved framework for interpreting the circular dichroism (CD) spectra of bis-porphyrins, we have calculated the CD spectra of chiral bis-porphyrins from three classes: I, where porphyrins can adopt a relatively wide range of orientations relative to each other; II, porphyrins have a fixed relative orientation; III, porphyrins undergo pi-stacking. The calculations primarily utilized the classical polarizability theory of DeVoe, but were supplemented by the quantum mechanical matrix method. Class I was represented by three isomers of the diester of 5alpha-cholestane-3,17-diol with 5-(4'-carboxyphenyl)-10,15,20-triphenylporphin (2-alphabeta, 2-betaalpha, 2-betabeta). Careful analysis of the torsional degrees of freedom led to two to four minimum-energy conformers for each isomer, in each of which the phenyl-porphyrin bonds had torsional angles near 90 degrees. Libration about these bonds is relatively unrestricted over a range of +/-45 degrees. CD spectra in the Soret region were calculated as Boltzmann-weighted averages over the low-energy conformers for each isomer. Three models were used: the effective transition moment model, in which only one of the degenerate Soret components is considered, along the 5-15 direction; the circular oscillator model, in which both Soret components are given equal weight; and the hybrid model, in which the 10-20 oscillator is given half the weight of the 5-15 oscillator, to mimic the effect of extensive librational averaging about the 5-15 direction. All three models predict Soret exciton couplets with signs in agreement with experiment. Quantitatively, the best results are given by the hybrid and circular oscillator models. These results validate the widely used effective transition moment model for qualitative assignments of bis-porphyrin chirality and thus permit application of the exciton chirality model. However, for quantitative studies, the circular oscillator or hybrid models should be used. The simplified effective transition moment and hybrid models are justified by the librational averaging in the class I bis-porphyrins and should only be used with such systems. Two class II bis-porphyrins were also studied by DeVoe method calculations in the circular oscillator model, which yielded good agreement with experiment. Class III bis-porphyrins were represented by 2-alphaalpha, for which the calculations gave qualitative agreement. However, limitations in the conformational analysis with the close contacts and dynamic effects in these pi-stacked systems preclude quantitative results.

Circular Dichroism↗
PubMed1998

Validity of spot urine samples as a surrogate measure of 24-hour porphyrin excretion rates. Evaluation of diurnal variations in porphyrin, mercury, and creatinine concentrations among subjects with very low occupational mercury exposure.

Porphyrin, mercury, and creatinine levels in single-void urine specimens ("spot samples") were compared with calculated 24-hour urine concentrations among 146 (77 male and 69 female) practicing dentists who are participating in an ongoing study of urinary porphyrin changes as a biomarker of mercury body burden. All subjects had urinary mercury concentrations < or = 5 micrograms/L, a level comparable to that of the general US population and which is below that determined to be associated with mercury-induced changes in urinary porphyrin excretion rates. The results confirmed previous findings of no significant diurnal variation in any of the porphyrin levels normally found in urine or in total porphyrin levels combined among males but describe significant diurnal variations in most porphyrin levels as well as concentrations of total porphyrins combined among females. Similarly, no evidence of large diurnal variation in mercury excretion among males was apparent, whereas significant diurnal variation in the mercury excretion rate among females was found. Creatinine adjustment of porphyrin or mercury concentrations had no significant effect on these findings. Moreover, no evidence of diurnal variation in urinary creatinine excretion among either male or female subjects was obtained, despite substantial between-subject variability in this parameter. These results support the view that spot urine samples may be utilized to derive reasonably accurate estimates of 24-hour porphyrin and mercury excretion rates in male subjects. In contrast, time of day appears to be of considerably greater importance when spot samples are utilized as 24-hour estimates of either porphyrin or mercury excretion rates among females. Additionally, time of day may be an important consideration in studies involving serial (repeated) porphyrin or mercury measurements using spot urine samples, irrespective of gender distribution of study subjects.

Adult↗
PubMed2002

Allosteric Binding of an Ag+ Ion to Cerium(IV) Bis-porphyrinates Enhances the Rotational Activity of Porphyrin Ligands.

A series of cerium(IV) bis-porphyrinate double-deckers [Ce(bbpp)(2)] (BBPP=5,15-bis(4-butoxyphenyl)porphyrin dianion), [Ce(tmpp)(2)] (TMPP=5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin dianion), [Ce(tfpp)(2)] (TFPP=5,10,15,20-tetrakis(4-fluorophenyl)porphyrin dianion), [Ce(tmcpp)(2)] (TMCPP=5,10,15,20-tetrakis(4-methoxycarbonylphenyl)porphyrin dianion), and [Ce(tmpp)(tmcpp)] was prepared. They bind three Ag(+) ions to their concave porphyrin pi subunits (pi-clefts) according to a positive homotropic allosteric mechanism with Hill coefficients (n(H)) of 1.7-2.7. The rotation rates of the porphyrin ligands in [Ce(bbpp)(2)] were evaluated to be 200 s(-1) at 20 degrees C (DeltaG$\rm{^{\ne }_{293}}$=14.1 kcal mol(-1)) and 220 s(-1) at -40 degrees C (DeltaG$\rm{^{\ne }_{233}}$=11.0 kcal mol(-1)) without and with Ag(+) ions, respectively. These results consistently support our unexpected finding that Ag(+) binding can accelerate rotation of the porphyrin ligand. On the basis of UV-visible, (1)H NMR, and resonance Raman spectral measurements, the rate enhancement of the rotational speed of the porphyrin ligands is attributed to conformational changes of the porphyrin in cerium(IV) bis-porphyrinate induced by binding of Ag(+) guest ions in the clefts. This novel concept of positive homotropic allosterism is applicable to the molecular design of various supramolecular and switch-functionalized systems.

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