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PubMed2006

Porphyrin accumulation in mitochondria is mediated by 2-oxoglutarate carrier.

Heme (Fe-protoporphyrin IX), an endogenous porphyrin derivative, is an essential molecule in living aerobic organisms and plays a role in a variety of physiological processes such as oxygen transport, respiration, and signal transduction. For the biosynthesis of heme or the mitochondrial heme proteins, heme or its biosynthetic precursor porphyrin must be transported into mitochondria from cytosol. The mechanism of porphyrin accumulation in the mitochondrial inner membrane is unclear. In the present study, we analyzed the mechanism of mitochondrial translocation of porphyrin derivatives. We showed that palladium meso-tetra(4-carboxyphenyl)porphyrin (PdTCPP), a phosphorescent porphyrin derivative, accumulated in the mitochondria of several cell lines. Using affinity latex beads, we showed that 2-oxoglutarate carrier (OGC), the mitochondrial transporter of 2-oxoglutarate, bound to PdTCPP, and in vitro PdTCPP inhibited 2-oxoglutarate uptake into mitochondria in a competitive manner (Ki = 15 microM). Interestingly, all types of porphyrin derivatives examined in this study competitively inhibited 2-oxoglutarate uptake into mitochondria, including protoporphyrin IX, coproporphyrin III, and hemin. Furthermore, mitochondrial accumulation of porphyrins was inhibited by 2-oxoglutarate or OGC inhibitor. These results suggested that porphyrin accumulation in mitochondria is mediated by OGC and that porphyrins are able to competitively inhibit 2-oxoglutarate uptake into mitochondria. This is the first report of a putative mechanism for accumulation of porphyrins in the mitochondrial inner membrane.

Amino Acid Sequence↗
PubMed1986

Interactions of water soluble porphyrins with Z-poly(dG-dC).

The water soluble porphyrin tetrakis(4-N-methylpyridyl)porphine (H2TMpyP) and its copper(II) derivative (CuTMpyP) convert Z-poly(dG-dC) to the B-form. For H2TMpyP, the fraction Z character (fr-Z) is given by fr-Z = 1.0 - 21 rO and for CuTMpyP, fr-Z = .94 - 12 rO where rO identical to [Porphyrin]O/[DNA]O. Neither the manganese(III) derivative of of this porphyrin (MnTMpyP) nor tetrakis(2-N-methylpyridyl)porphine (H2TMpyP-2) is nearly as effective at causing the conversion. The former two porphyrins have been shown to intercalate into B-poly(dG-dC) whereas the latter two porphyrins do not. The kinetics of the Z----B conversion are independent of porphyrin or poly(dG-dC) concentration for 1/rO greater than 6. At smaller values of 1/rO, the conversion rate is greatly increased for H2TMpyP and CuTMpyP. The interaction of these porphyrins with Z-poly(dG-dC) follows simple first order kinetics in this latter concentration range. It is proposed that for small values of 1/rO the sequence of events begins with a porphyrin-unassisted distortion of the Z-duplex (with a rate constant of 0.6 s-1) followed by a rapid uptake of porphyrin in what may be an intercalative mode. The porphyrin thus located in Z-regions brings about rapid conversion to the B-form. Binding of H2TMpyP or CuTMpyP to B-regions of a predominantly Z-strand leads to conversion of Z to B. However, this conversion process is considerably slower than when the porphyrins bind directly to Z-regions.

Circular Dichroism↗
PubMed1999

Urinary porphyrin excretion measurements in healthy neonates.

The objective of this study was to establish normal reference ranges for porphyrins in healthy neonates. There is little information about urinary porphyrin excretion in this age group. This knowledge may provide an early diagnostic tool for detecting subtle alterations or latent forms in disorders of heme biosynthesis. Fifty healthy neonates were selected from the Department of Obstetrics. Total urinary porphyrins in random specimens were analysed by a spectrofluorometry method. The measurement of porphyrin fractions was made by fluorometric high-performance liquid chromatography (HPLC). The results were adjusted to urinary creatinine excretion to correct any imprecision and interindividual variation in body mass. The urinary total porphyrin had a median value of 331.50 (nmol/L). A statistically significant relationship between total porphyrin (nmol/L) and creatinine (mmol/L) was found (p < 0.01). The porphyrin/creatinine ratio showed a median value of 56.30 nmol/mmol creatinine. The study of individual porphyrins revealed that coproporphyrin and uroporphyrin were the major porphyrins excreted in neonates (coproporphyrin represents 81.98% and uroporphyrin 16.64% of total porphyrin); in both cases, isomer I was predominant with median values of 22.36 and 6.25 nmol/mmol creatinine, respectively. No significant relationships were found between porphyrin excretion and sex, gestational age, weight, or height. Our data provide the reference limits for porphyrins in neonates as a diagnostic guideline for evaluation of subtle alterations in heme biosynthesis.

Age Factors↗
PubMed2004

Thermodynamic analysis of porphyrin binding to Momordica charantia (bitter gourd) lectin.

Owing to the use of porphyrins in photodynamic therapy for the treatment of malignant tumors, and the preferential interaction of lectins with tumor cells, studies on lectin-porphyrin interaction are of significant interest. In this study, the interaction of several free-base and metalloporphyrins with Momordica charantia (bitter gourd) lectin (MCL) was investigated by absorption spectroscopy. Difference absorption spectra revealed that significant changes occur in the Soret band region of the porphyrins on binding to MCL. These changes were monitored to obtain association constants (Ka) and stoichiometry of binding. The tetrameric MCL binds four porphyrin molecules, and the stoichiometry was unaffected by the presence of the specific sugar, lactose. In addition, the agglutination activity of MCL was unaffected by the presence of the porphyrins used in this study, clearly indicating that porphyrin and carbohydrate ligands bind at different sites. Both cationic and anionic porphyrins bind to the lectin with comparable affinity (Ka =10(3)-10(5) m(-1)). The thermodynamic parameters associated with the interaction of several porphyrins, obtained from the temperature dependence of the Ka values, were found to be in the range: DeltaH degrees = -98.1 to -54.4 kJ.mol(-1) and DeltaS degrees =-243.9 to -90.8 J.mol(-1).K(-1). These results indicate that porphyrin binding to MCL is governed by enthalpic forces and that the contribution from binding entropy is negative. Enthalpy-entropy compensation was observed in the interaction of different porphyrins with MCL, underscoring the role of water structure in the overall binding process. Analysis of CD spectra of MCL indicates that this protein contains about 13%alpha-helix, 36%beta-sheet, 21%beta-turn, and the rest unordered structures. Binding of porphyrins does not significantly alter the secondary and tertiary structures of MCL.

Circular Dichroism↗
PubMed1993

Effect of UVA and blue light on porphyrin biosynthesis in epidermal cells.

To study porphyrin biosynthesis in normal human keratinocytes and A431 cells derived from human epidermoid carcinoma, cultured cells were incubated with delta-aminolevulinic acid (ALA), the precursor of porphyrin synthesis, and accumulation of porphyrins was measured spectrofluorometrically. Both human keratinocytes and A431 cells accumulated porphyrins in a time-dependent and a dose-dependent fashion. Protoporphyrin was the predominant porphyrin accumulated by both cell types. Porphyrin accumulation was enhanced by Ca Mg ethylenediaminetetraacetic acid, a ferrochelatase inhibitor, and the enhancement was reversed by the addition of iron, suggesting the utilization of iron by ferrochelatase. The effect of light on porphyrin accumulation was evaluated by exposing the ALA-loaded A431 cells to ultraviolet-A (UVA) and blue light radiation, followed by continued incubation with ALA for 2-48 h. There was an enhancement of porphyrin accumulation 2-48 h after the radiation as compared with nonirradiated controls. Consistent with this finding, ferrochelatase activity decreased in these cells at 24 h and 48 h. These data demonstrate that human keratinocytes and A431 cells are capable of porphyrin biosynthesis, and that exposure of porphyrin-containing A431 cells to light, which includes the Soret band spectrum, decreases the ferrochelatase activity, which is responsible, at least in part, for the further increase in porphyrin level.

Calcium↗
PubMed1997

Ex vivo application of delta-aminolevulinic acid induces high and specific porphyrin levels in human skin tumors: possible basis for selective photodynamic therapy.

In photodynamic therapy with topically applied delta-aminolevulinic acid porphyrins are acting as photosensitizers. The profile of porphyrin metabolites in normal or in neoplastic skin after administration of delta-aminolevulinic acid has not been determined in detail yet. Thus, to study porphyrin biosynthesis in human skin an organ culture model was developed. Explant pieces of normal skin, keratoacanthoma, and basal cell carcinoma were incubated with 1 mM delta-aminolevulinic acid for 36 h. Levels of delta-aminolevulinic acid, porphyrins and porphyrin metabolites were measured in tissues and supernatants. After incubation with delta-aminolevulinic acid, higher porphyrin levels were demonstrated in tumors as compared to normal skin. In supernatants, most of formed porphyrins, preferentially highly carboxylated porphyrin metabolites, were measured. The pattern of synthesized porphyrins differed between normal and neoplastic skin explants. In tissues of basal cell carcinomas protoporphyrin was preferentially shown and tissues of keratoacanthomas were characterized by a predominance of coproporphyrin as compared to normal skin. The results show that explant cultures offer an easy approach to examine the porphyrin biosynthesis of various tissues. The tumor-specific delta-aminolevulinic acid metabolism indicates additional porphyrin metabolites such as coproporphyrin apart from protoporphyrin as effective photosensitizers and may offer a novel approach to tumor-selective photodynamic damage.

Aminolevulinic Acid↗
PubMed1994

Determination of porphyrins in bile using high performance liquid chromatography and some clinical applications.

A simple and fast HPLC method for the determination of porphyrins in bile without extraction is described. Porphyrins were determined in bile from control subjects and from patients after orthotopic liver transplantation, including three patients with erythropoietic protoporphyria. It was found that: 1) coproporphyrin I is the predominant porphyrin in bile of controls, accompanied by some coproporphyrin III and protoporphyrin, whereas protoporphyrin mostly but not always is the predominant porphyrin in the bile of erythropoietic protoporphyria patients. In two of the three erythropoietic protoporphyria patients, the bile contained a hundred times more protoporphyrin than that of non-porphyric orthotopic liver transplantation patients. The third erythropoietic protoporphyria patient remained cholestatic and was unable to excrete sufficient amounts of protoporphyrin. 2) All investigated bile samples contained no secondary porphyrins derived from protoporphyrin, i.e. no deutero-, pempto-, or mesoporphyrin. Even when extracts of bile and serum were concentrated fifty to a hundred times, no traces of deutero-, pempto- and mesoporphyrin were detected. This complete absence of secondary porphyrins suggests that an enterohepatic circulation of dicarboxylic porphyrins from the distal gastrointestinal tract does not exist. 3) The HPLC chromatograms contain peaks from unknown compounds. No correlation between porphyrins and these compounds was found. Porphyrin profiles were followed in the bile of some orthotopic liver transplantation patients. Three episodes are recognizable. During the first three days after orthotopic liver transplantation there is a very high coproporphyrin excretion. There is then a lag of one to three weeks, in which no or very low porphyrin concentrations are detectable, followed by the restoration of normal biliary porphyrin patterns.

Bile↗
PubMed1999

The photodynamic and non-photodynamic actions of porphyrins.

Porphyrias are a family of inherited diseases, each associated with a partial defect in one of the enzymes of the heme biosynthetic pathway. In six of the eight porphyrias described, the main clinical manifestation is skin photosensitivity brought about by the action of light on porphyrins, which are deposited in the upper epidermal layer of the skin. Porphyrins absorb light energy intensively in the UV region, and to a lesser extent in the long visible bands, resulting in transitions to excited electronic states. The excited porphyrin may react directly with biological structures (type I reactions) or with molecular oxygen, generating excited singlet oxygen (type II reactions). Besides this well-known photodynamic action of porphyrins, a novel light-independent effect of porphyrins has been described. Irradiation of enzymes in the presence of porphyrins mainly induces type I reactions, although type II reactions could also occur, further increasing the direct non-photodynamic effect of porphyrins on proteins and macro-molecules. Conformational changes of protein structure are induced by porphyrins in the dark or under UV light, resulting in reduced enzyme activity and increased proteolytic susceptibility. The effect of porphyrins depends not only on their physico-chemical properties but also on the specific site on the protein on which they act. Porphyrin action alters the functionality of the enzymes of the heme biosynthetic pathway exacerbating the metabolic deficiencies in porphyrias. Light energy absorption by porphyrins results in the generation of oxygen reactive species, overcoming the protective cellular mechanisms and leading to molecular, cell and tissue damage, thus amplifying the porphyric picture.

Darkness↗
PubMed1992

Hypophysectomy prevents the castration-induced increase in porphyrin concentrations in the harderian glands of the male golden hamster: a possible role for prolactin.

The Harderian glands of golden hamsters contain high concentrations of porphyrin pigments, with female hamsters having considerably higher porphyrin concentrations than males. Castration of male hamsters leads to a rapid increase in porphyrin concentrations; testosterone treatment of females has the opposite effect, suggesting a central role for androgens in inhibiting the realization of high porphyrin concentrations by this organ. Previous studies in our laboratories have shown, however, that administration of a dopamine agonist to castrated hamsters prevents the normal increase in Harderian porphyrins from occurring. This suggests that prolactin is necessary for low androgen levels to lead to maximal increases in Harderian porphyrin concentrations. The present study tested the hypothesis that prolactin is involved in the control of Harderian porphyrin levels in the golden hamster. Although hypophysectomy of male hamsters reduced serum testosterone to levels in castrated hamsters, the resultant increase in Harderian porphyrin concentrations was much less than that seen after a similar period of castration. Furthermore, combining the two procedures (castration and hypophysectomy) also led to a blunted increase in Harderian porphyrin, suggesting that a pituitary hormone is necessary for low testosterone levels to lead to increased porphyrins. Evidence that this pituitary hormone is prolactin comes from the observations that eliminating all pituitary hormones except prolactin, by severing the connection of the pituitary with the hypothalamus or transplanting the pituitary to a distant site (beneath the kidney capsule) led to greatly augmented Harderian porphyrin levels, in intact or castrated male hamsters.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

[The determination of porphyrin carbon isotope composition by gas chromatography-isotope ratio monitoring mass spectrometry technique].

The porphyrin carbon isotope composition can be used to explore the precursor of porphyrin, oil-oil and oil-source rock correction and calculation of paleo P CO2. The conventional method is limited because of its time consuming and large sample size (several mg of individual porphyrin) required. Therefore, it hampers the application of porphyrin carbon isotope composition into the chemistry and geoscience. The present paper describes a quantification method to prepare bis-(tert-butyldimethylsiloxy) silicon (IV) [(TBDMSO)2Si(IV)] porphyrin which is sufficiently volatile at 300 degrees C and can be used for GC-IRMS analysis. The analysis of carbon isotope composition of aetio I as the form of free base, nickel, demetalization derivative, silicon(IV) and (TBDMSO)2Si(IV) have shown that aetio I porphyrin has no obvious isotope fractionation in the whole synthesis procedure for (TBDMSO)2Si(IV) porphyrin. The carbon isotope study on the porphyrin mixtures of aetio I and OEP indicates that isotope exchange between porphyrins during the synthesis of (TBDMSO)2Si(IV) porphyrin is absent. The method can be applied to the determination of porphyrin carbon isotope compositions. The advantages of the method are time saving, less sample size and lower standard deviation.

Carbon Isotopes↗
PubMed1986

Structural requirements for porphyrin inhibition of the hemin-controlled protein kinase and maintenance of protein synthesis in reticulocytes.

The role of hemin in the maintenance of protein synthesis in reticulocyte lysates was examined by comparing the effects of various porphyrins and metalloporphyrins on the protein kinase activity of the hemin-controlled repressor and on protein synthesis. The porphyrin requirements for maintenance of protein synthesis were relatively specific. Iron and cobalt metalloporphyrins sustained protein synthesis whereas other metalloporphyrins, metal-deficient porphyrins, and non-porphyrin precursor and degradation products of protoporphyrin IX were ineffective. These same compounds were examined for their effectiveness in inhibiting the protein kinase activity of the hemin-controlled repressor with initiation factor 2 (eIF-2). Most of the metalloporphyrins and porphyrins tested were inhibitory. The presence of the iron atom in the porphyrin was not essential for inhibition, but the maintenance of the integrity of the porphyrin ring was imperative. The porphyrins which inhibited the hemin-regulated protein kinase contained vinyl groups or ethyl groups, or were protonated in the 2- and 4-positions of the porphyrin ring, whereas those with bulky or acidic groups in these positions were ineffective. Precursor and degradation products of protoporphyrin IX and synthetic porphyrins modified at other positions had no effect on the enzyme. Both hemin and protoporphyrin IX inhibited phosphorylation of eIF-2 exogenously added to a reticulocyte lysate; however, hemin sustained protein synthesis in the lysate, whereas protoporphyrin IX did not. These results suggest that regulation of the protein kinase phosphorylating the alpha subunit of eIF-2 is not the only point at which hemin modulates protein synthesis in reticulocytes and reticulocyte lysates, since a correlation between inhibition of protein synthesis, inhibition of protein kinase activity, and phosphorylation of eIF-2 is not observed with all porphyrins.

Animals↗
PubMed1996

Altered porphyrin metabolism as a biomarker of mercury exposure and toxicity.

Changes in urinary porphyrin excretion patterns (porphyrin profiles) have been described in response to a variety of drugs and chemicals. The present studies were conducted to define the specific changes in the urinary porphyrin profile associated with prolonged exposure to mercury and mercury compounds. In rats, exposure for a prolonged period to mercury as methyl mercury hydroxide was associated with urinary porphyrin changes, which were uniquely characterized by highly elevated levels of 4- and 5-carboxyl porphyrins and by the expression of an atypical porphyrin ("precoproporphyrin") not found in urine of unexposed animals. These distinct changes in urinary porphyrin concentrations were observed as early as 1-2 weeks after initiation of mercury exposure, and increased in a dose- and time-related fashion with the concentration of mercury in the kidney, a principal target organ of mercury compounds. Following cessation of mercury exposure, urinary porphyrin concentrations reverted to normal levels, consistent with renal mercury clearance. In human studies, a comparable change in the urinary porphyrin profile was observed among subjects with occupational exposure to mercury as mercury vapor sufficient to elicit urinary mercury levels greater than 20 micrograms/L. Urinary porphyrin profiles were also shown to correlate significantly with mercury body burden and with specific neurobehavioral deficits associated with low level mercury exposure. These findings support the utility of urinary porphyrin profiles as a useful biomarker of mercury exposure and potential health effects in human subjects.

Adult↗
PubMed1996

Porphyrin abnormalities in acquired immunodeficiency syndrome.

OBJECTIVE: To examine prospectively porphyrin metabolism in a human immunodeficiency virus (HIV)-positive population. SETTING: Specialist referral unit at the Department of Genitourinary Medicine, St James's Hospital, Dublin, Ireland. PATIENTS: Twenty-eight men and 5 women (age range, 18-35 years). Twenty-nine were current or previous intravenous drug abusers. Four were thought to have sexually acquired HIV infection. All had a history of acquired immunodeficiency syndrome-defining illnesses. The patients were selected as a consecutive sample from the inpatient department. Eligibility criteria were cooperation with urine and stool collection and confirmed HIV seropositivity. The patients were matched to 2 groups: 1 with normal results of porphyrin studies and the other with abnormal findings from porphyrin studies. INTERVENTION: None. MAIN OUTCOME MEASURES: Plasma, urine, and stool porphyrin excretion patterns. RESULTS: Of the 33 patients in the study, 13 (40%) had increased urinary porphyrin excretion. All but 2 of these patients were seropositive for hepatitis C virus. No study patient had clinical evidence of porphyria. Four patients (12%), however, had urine and stool porphyrin excretion patterns that were classic for porphyria cutanea tarda. All 4 of these patients were hepatitis C virus-positive. Patients with porphyrinuria had a greater degree of immunosuppression (P = .002) than those with normal porphyrin metabolism, and they were more likely to be taking zidovudine (P = .009). CONCLUSIONS: Commonly, porphyrin metabolism is abnormal in persons with established HIV infection. Hepatitis C may contribute to abnormal porphyrin metabolism. An unexpected number of patients studied had porphyrin excretion patterns that were characteristic of porphyria cutanea tarda, and all of these were hepatitis C virus-positive. A diagnosis of porphyria cutanea tarda, especially in a young patient, should prompt investigation for underlying HIV and hepatitis C virus infections. Dermatologists should be aware of the infectious risk associated with the vesicles and erosions in these patients. Porphyrin studies should be performed in any patient with HIV and photosensitivity.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Factors affecting the electronic ground state of low-spin iron(III) porphyrin complexes.

To determine the factors affecting the ground-state electron configuration of low-spin Fe(III) porphyrin complexes, we have examined the (1)H NMR, (13)C NMR, and EPR spectra of a series of low-spin bis-ligated Fe(III) porphyrin complexes [Fe(Por)L(2)](+/-), in which the positions of porphyrin substituents and the coordination ability of axial ligands are different. The seven porphyrins used in this study are meso-tetraalkylporphyrins (TRP: R is propyl, cyclopropyl, or isopropyl), meso-tetraphenylporphyrin (TPP), meso-tetrakis(2,3,4,5,6-pentafluorophenyl)porphyrin, and 5,10,15,20-tetraphenyl-2,3,7,8,12,13,17,18-octaalkylporphyrins (ORTPP: R is methyl or ethyl). The porphyrin cores of TRP are more or less S(4)-ruffled depending on the bulkiness of the alkyl substituents, while those of ORTPP are highly S(4)-saddled. Three types of axial ligands are examined which have the following characteristics in ligand field theory: they are (i) strong sigma-donating imidazole (HIm), (ii) strong sigma-donating and weak pi-accepting cyanide (CN(-)), and (iii) weak sigma-donating and strong pi-accepting tert-butyl isocyanide ((t)BuNC). In the case of the bis(HIm) complexes, only the isopropyl complex, [Fe(T(i)PrP)(HIm)(2)](+), has shown the less common (d(xz), d(yz))(4)(d(xy))(1) ground state; the other six complexes have exhibited the common (d(xy))(2)(d(xz), d(yz))(3) ground state. When the axial imidazole is replaced by cyanide, even the propyl and cyclopropyl complexes have shown the (d(xz), d(yz))(4)(d(xy))(1) ground state; the TPP and ORTPP complexes have still maintained the common (d(xy))(2)(d(xz), d(yz))(3) ground state. In the case of the bis((t)()BuNC) complexes, all the complexes have shown the (d(xz), d(yz))(4)(d(xy))(1) ground state. However, the contribution of the (d(xz), d(yz))(4)(d(xy))(1) state to the electronic ground state differs from complex to complex; the (d(xz), d(yz))(4)(d(xy))(1) contribution is the largest in [Fe(T(i)PrP)((t)()BuNC)(2)](+) and the smallest in [Fe(OETPPP)((t)BuNC)(2)](+). We have then examined the electronic ground state of low-spin [Fe(OEP)((t)BuNC)(2)](+) and [Fe(ProtoIXMe(2))((t)BuNC)(2)](+); OEP and ProtoIXMe(2) represent 2,3,7,8,12,13,17,18-octaethylporphyrin and protoporphyrin-IX dimethyl ester, respectively. These porphyrins have a(1u) HOMO in contrast to the other seven porphyrins that have a(2u) HOMO. The (13)C NMR and EPR studies have revealed that the contribution of the (d(xz), d(yz))(4)(d(xy))(1) state in these complexes is as small as that in [Fe(OETPP)((t)BuNC)(2)](+). On the basis of these results, we have concluded that the low-spin iron(III) porphyrins that have (i) strong axial ligands, (ii) highly saddle shaped porphyrin rings, (iii) porphyrins with a(1u) HOMO, and (iv) electron withdrawing substituents at the meso positions tend to maintain the common (d(xy))(2)(d(xz), d(yz))(3) ground state.

Electron Spin Resonance Spectroscopy↗
PubMed2001

Methylammonium groups at the solid walls of nanometer-sized, water-filled monolayer gaps as binding sites for a tetraanionic porphyrin.

Long-chain hydrosulfides containing two secondary amide functions and either electron-poor or electron-rich carbon-carbon double bonds were self-assembled on gold surfaces around a flat-lying, octaanionic porphyrin. Rigid and reactive surface monolayers with 2 nm-wide, porphyrin-based gaps were thus obtained. The gold electrodes were then immersed in water, and the double bonds on the gaps' surfaces reacted with methylamine. It was added to the double bonds either by Michael addition or by bromination with hypobromite followed by methylamine substitution. Only the double bonds at the border of the gaps were accessible to methylamine dissolved in the bulk water volume and could react. The walls of the rigid membrane gaps now contained methylammonium groups at the sites of the double bonds in defined heights. A tetracationic copper(II) porphyrinate could not diffuse any more into the gap and did not quench the fluorescence of the octaanionic porphyrin on the bottom of the gap. A tetraanionic porphyrin, on the other hand, was fixated by the ring of ammonium groups. The bound porphyrin then acted as molecular cover for the gap with respect to ferricyanide transport from bulk water to the electrode. It was removed by raising the pH to a value of 12, where the methylammonium groups were neutralized to amines. Lowering the pH to 7 again and addition of more of the anionic porphyrin reclosed the gap.The porphyrin "cover" should be localized at distances of 8-10 and 20 A from the bottom porphyrin by multiple charge interactions. The 8-10 A distance is ideal for studies of photoinduced electron transfer between two porphyrin monomers of different redox potential. Furthermore it was found, that redox-active tyrosine could be trapped in the water volume above the porphyrin on gold.

Journal Article↗
PubMed2000

Synthesis of thiol-derivatized ferrocene-porphyrins for studies of multibit information storage

One approach toward storage of multiple bits of information at the molecular level requires the construction of molecular architectures comprised of multiple redox-active units. Four new ferrocene-porphyrins have been synthesized to investigate questions concerning (1) the scope of redox-active molecules that can be employed in molecular information-storage schemes and (2) writing/reading rates as well as retention of charge in redox-active units located at different sites in a molecular architecture. Three of the ferrocene-porphyrins have linkers of different lengths between the ferrocene and porphyrin. The fourth ferrocene-porphyrin has two ferrocenes positioned at the lateral sites on the porphyrin. The latter architecture is designed to provide a shorter distance between the electroactive surface and the ferrocene while maintaining an upright orientation of the porphyrin. Each ferrocene-porphyrin affords three cationic oxidation states (ferrocene monocation, porphyrin monocation, porphyrin dication) in addition to the neutral state, thereby affording the capability of storing two bits of information. Each ferrocene-porphyrin bears an S-acetyl or S-(N-ethyl)carbamoyl-protected thiol moiety, thereby avoiding handling of free thiols. Each ferrocene-porphyrin forms a self-assembled monolayer (SAM) on gold via in situ cleavage of the thiol protecting group. The SAM of each array is electrochemically robust and exhibits three well-resolved, reversible oxidation waves.

Journal Article↗
PubMed2000

Synthesis of "Porphyrin-linker-Thiol" molecules with diverse linkers for studies of molecular-based information storage

The attachment of redox-active molecules such as porphyrins to an electroactive surface provides an attractive approach for electrically addressable molecular-based information storage. Porphyrins are readily attached to a gold surface via thiol linkers. The rate of electron transfer between the electroactive surface and the porphyrin is one of the key factors that dictates suitability for molecular-based memory storage. This rate depends on the type and length of the linker connecting the thiol unit to the porphyrin. We have developed different routes for the preparation of thiol-derivatized porphyrins with eight different linkers. Two sets of linkers explore the effects of linker length and conjugation, with one set comprising phenylethyne units and one set comprising alkyl units. One electron-deficient linker has four fluorine atoms attached directly to a thiophenyl unit. To facilitate the synthesis of the porphyrins, convenient routes have been developed to a wide range of aldehydes possessing a protected S-acetylthio group. An efficient synthesis of 1-(S-acetylthio)-4-iodobenzene also has been developed. A set of porphyrins, each bearing one S-acetyl-derivatized linker at one meso position and mesityl moieties at the three remaining meso positions, has been synthesized. Altogether seven new aldehydes, eight free base porphyrins and eight zinc porphyrins have been prepared. The zinc porphyrins bearing the different linkers all form self-assembled monolayers (SAMs) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each porphyrin is electrochemically robust and exhibits two reversible oxidation waves.

Journal Article↗
PubMed2004

Porphyrins bearing arylphosphonic acid tethers for attachment to oxide surfaces.

Synthetic molecules bearing phosphonic acid groups can be readily attached to oxide surfaces. As part of a program in molecular-based information storage, we have developed routes for the synthesis of diverse porphyrinic compounds bearing phenylphosphonic acid tethers. The routes enable (1) incorporation of masked phosphonic acid groups in precursors for use in the rational synthesis of porphyrinic compounds and (2) derivatization of porphyrins with masked phosphonic acid groups. The precursors include dipyrromethanes, monoacyldipyrromethanes, and diacyldipyrromethanes. The tert-butyl group has been used to mask the dihydroxyphosphoryl substituent. The di-tert-butyloxyphosphoryl unit is stable to the range of conditions employed in syntheses of porphyrins and multiporphyrin arrays yet can be deprotected under mild conditions (TMS-Cl/TEA or TMS-Br/TEA in refluxing CHCl(3)) that do not cause demetalation of zinc or magnesium porphyrins. The porphyrinic compounds that have been prepared include (1) A(3)B-, trans-AB(2)C-, and ABCD-porphyrins that bear a single phenylphosphonic acid group, (2) a trans-A(2)B(2)-porphyrin bearing two phenylphosphonic acid groups, (3) a chlorin that bears a single phenylphosphonic acid group, and (4) a porphyrin dyad bearing a single phenylphosphonic acid group. For selected porphyrin-phosphonic acids, the electrochemical characteristics have been investigated for molecules tethered to SiO(2) surfaces grown on doped Si. The voltammetric behavior indicates that the porphyrin-phosphonic acids form robust, electrically well-behaved monolayers on the oxide surface.

Journal Article↗