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PubMed1985

Interstitial porphyrins and tubule degeneration in the hamster Harderian gland.

The Harderian glands of rodents manufacture and store porphyrins and are increasingly used as models for porphyrin biosynthesis. Although porphyrins are normally stored as solid intraluminal accretions, interstitial deposits also occur; in the Harderian gland of the female hamster these are found frequently in ovariectomised or aged animals. The present study (employing double-embedding techniques) suggests that interstitial porphyrin deposits are the result of degenerative processes which conform to an escalating pattern. Initially, tubule epithelial and myoepithelial cells become greatly attenuated and there is neutrophil invasion. Secondly, tubule walls disappear leaving previously intraluminal porphyrin stores free within the interstitium. Finally, large interstitial porphyrin accretions become surrounded by foreign body giant cells or are broken down into smaller deposits within free macrophages. These are often associated with plasma cells. Infiltration of the interstitium by lymphocytes may also occur. It may be that the abnormal localisation of porphyrin in the interstitium (i) evokes an immune response and (ii) is related to elevated blood porphyrin levels found in these animals.

Animals↗
PubMed1984

Inability to elicit rapid cytocidal effects on L1210 cells derived from porphyrin-injected mice following in vitro photoirradiation.

The role of the neoplastic cell in both porphyrin localization and the photochemotherapeutic response was investigated with the use of a series of tumor-localizing porphyrins and the L1210 tumor system. In vivo photoirradiation of DBA/2Ha mice bearing L1210 solid tumors and previously given injections of meso-tetra-(4-sulfonatophenyl)-porphine, meso-tetra-(4-carboxyphenyl)-porphine, or hematoporphyrin derivative (Hpd) indicated that all three chemicals elicited a photodynamic response resulting in necrosis of exposed tissue. Isolation of tumor cells from mice given injections of porphyrin with the use of mild mechanical means and physiologic conditions followed by in vitro photoirradiation of the cells under conditions established to optimize rapid cytocidal effects resulted in no appreciable cell death. A similar situation was noted with the use of spleen cells from mice given injections of Hpd, the spleen cells presumably containing substantial amounts of porphyrin. Both fluorescence microscopy and chemical extraction and quantitation of the porphyrins in the cells indicated that the inability to elicit a rapid cytocidal effect upon in vitro photoirradiation resulted from either the absence of or the presence of only very small amounts of porphyrin. These results indicate that in this particular tumor system the neoplastic cell per se plays only a minor role in porphyrin localization and, as a consequence, cannot be readily killed upon photoirradiation, suggesting that rapid cytocidal effects, due solely to porphyrin contained within the cell, probably do not occur among the majority of parenchymal cells during in vivo photoirradiation.

Animals↗
PubMed1981

Fecal porphyrin abnormalities in a patient with features of Rotor's syndrome.

Detailed porphyrin analysis and additional ultrastructural abnormalities of liver cells are described in a patient with features of Rotor's syndrome. Normal values of porphyrin precursors, delta-aminolevulinic acid and porphobilinogen, and porphyrins were found in plasma, urine, and erythrocytes. However, fecal porphyrin excretion was markedly increased to 406 micrograms/g dry stool weight (normal range less than 100 micrograms/g) constituted predominantly of protoporphyrin 225 micrograms/g (normal range less than 76 micrograms/g),. with a smaller increase in coproporphyrin III of 56 micrograms/g (normal range less than 20 micrograms/g). Increased fecal porphyrin excretion in this patient appears to reflect abnormal hepatic porphyrin excretion. Electron microscopic examination of liver biopsy tissue showed new abnormalities of peroxisomes and mitochondria. The predominant abnormality of mitochondria was "bleb" deformation of the outer membrane and these changes may reflect abnormal hepatic mitochondrial porphyrin metabolism. The significance of abnormalities involving peroxisomes is uncertain. Increased fecal porphyrin excretion may be a feature of Rotor's syndrome that requires further study.

Adult↗
PubMed1996

Abnormal serum porphyrin levels in patients with the acquired immunodeficiency syndrome with or without hepatitis C virus infection.

OBJECTIVE: To define the contributions of human immunodeficiency virus (HIV) and hepatitis C virus infections to the development of porphyria cutanea tarda. DESIGN: Analysis of serum porphyrin levels in a cohort of 167 subjects. Serum samples were divided into 4 groups corresponding to the status of HIV and hepatitis C virus infections: positive-positive, positive-negative, negative-positive, and negative-negative. SETTING: Serum samples positive for HIV were obtained from the serum bank of an acquired immunodeficiency syndrome-HIV research center, and HIV-negative samples were obtained from a regional blood center. MAIN OUTCOME MEASURES: Spectrofluorometric measurement of serum porphyrin levels. RESULTS: The median values of porphyrin were 2.31 nmol/L (interquartile range [difference between the 25th and 75th percentiles]: 4.55) in the positive-positive group, 1.99 nmol/L (interquartile range: 1.63) in the positive-negative group, 1.31 nmol/L (interquartile range: 1.58) in the negative-positive group, and 1.14 nmol/L (interquartile range: 0.92) in the negative-negative group. The fluorescence emission spectra of samples with elevated porphyrin levels were identical with that reported for porphyria cutanea tarda. Elevated porphyrin levels were significantly associated with HIV infection (P < .001) and were observed in patients with an elevated level of alanine aminotransferase (P = .03). Infection with hepatitis C virus was also associated with an elevation in porphyrin levels, although the increase was not statistically significant (P = .16). Porphyrin levels in patients positive for HIV were not correlated with serum urea nitrogen or creatinine levels. None of the patients had symptomatic porphyria cutanea tarda. CONCLUSIONS: Factors associated with increased serum porphyrin levels included HIV infection, elevated alanine aminotransferase levels, and, to a lesser extent, hepatitis C virus infection. These findings suggest that patients with the above risk factors are potentially predisposed to the development of symptomatic porphyria cutanea tarda on further exposure to hepatotoxic agents.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Cellular pharmacological properties of gold(III) porphyrin 1a, a potential anticancer drug lead.

The development of gold(III) complexes as potential anticancer drugs with higher cytotoxicity and fewer side effects than existing metal anticancer drugs has been actively pursued in recent years. In this study, we explored the cellular pharmacological properties of gold(III) porphyrin 1a, an anticancer drug lead we previously described. The cytotoxicity study of gold(III) porphyrin 1a by naphthol blue black (NBB) staining assay demonstrated that the higher cytotoxicity of gold(III) porphyrin 1a was not related to its photosensitizing activity. Serum dependent test revealed that serum proteins exhibited lesser effects on the activity of gold(III) porphyrin 1a. In addition, in vivo and in vitro binding assays showed that gold(III) porphyrin 1a acted on DNA noncovalently, which was differently from cisplatin. Flow cytometric study indicated that gold(III) porphyrin 1a inhibited cell growth partly through abrogating cell cycle at G(0)-G(1), and induced apoptosis in SUNE1 cells. The enhanced expression of p53, a cell cycle-controlling and apoptosis-related protein, further demonstrated that the cell cycle arrest and apoptosis induced by gold porphyrin 1a were p53 dependent. Our results highlighted the potential of gold(III) porphyrin 1a as an anticancer drug.

Animals↗
PubMed2006

Kinetic studies of reactions of iron(IV)-oxo porphyrin radical cations with organic reductants.

Iron(IV)-oxo porphyrin radical cations are observed intermediates in peroxidase and catalase enzymes, where they are known as Compound I species, and the putative oxidizing species in cytochrome P450 enzymes. In this work, we report kinetic studies of reactions of iron(IV)-oxo porphyrin radical cations that can be compared to reactions of other metal-oxo species. The iron(IV)-oxo radical cations studied were those produced from 5,10,15,20-tetramesitylporphryinato-iron(III) perchlorate (1), 5,10,15,20-tetramesitylporphryinato-iron(III) chloride (2), both in CH(3)CN solvent, and that from 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato-iron(III) perchlorate (3) in CH(2)Cl(2) solvent. The substrates studied were alkenes and activated hydrocarbons diphenylmethane and ethylbenzene. For a given organic reductant, various iron(IV)-oxo porphyrin radical cations react in a relatively narrow kinetic range; typically the second-order rate constants vary by less than 1 order of magnitude for the oxidants studied here and the related oxidant 5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato-iron(IV)-oxo porphyrin radical cation in CH(3)CN solvent. Charge transfer in the transition states for epoxidation reactions of substituted styrenes by oxidants 1 and 2, rho(+) values of -1.9 and -0.9, respectively, mirrors results found previously for related species. Competition kinetic reactions with a catalytic amount of porphyrin iron(III) species and a terminal oxidant give relative rate constants for oxidations of competing substrates that are somewhat smaller than the ratios of absolute rate constants. Water in CH(3)CN solutions has an apparent modest stabilizing effect on oxidant 1 as indicated in slightly reduced rate constants for oxidation reactions. The iron(IV)-oxo porphyrin radical cations are orders of magnitude less reactive than porphyrin-manganese(V)-oxo cations and a corrole-iron(V)-oxo species. The small environment effects found here suggest that high energy demanding hydrocarbon oxidation reactions catalyzed by cytochrome P450 enzymes might require highly reactive iron(V)-oxo transients as oxidants instead of the more stable, isomeric iron(IV)-oxo porphyrin radical cations.

Cations↗
PubMed2006

Competing approaches to excitotoxic neuroprotection by inert and catalytic antioxidant porphyrins.

The goal of this study was to determine if novel porphyrins protect cultured cortical neurons from excitotoxic NMDA exposure or oxygen-glucose deprivation (OGD), which model key aspects of cerebral ischemia. Porphyrins were chosen based on conventional and unconventional criteria. Metalloporphyrin catalytic antioxidants possessing a redox-sensitive metal core can exhibit potent and wide-ranging catalytic antioxidant abilities, which are conventionally believed to underlie neuroprotection. We report here that a recent-generation potent peroxynitrite decomposition catalyst, FP-15, protected a majority of neurons against OGD and NMDA toxicity, without suppressing NMDA-mediated intracellular Ca2+ (Cai2+) elevations or whole-cell currents. We have previously shown that neuroprotection against OGD and NMDA toxicity correlated with an ability to suppress neurotoxic Cai2+ elevations and not antioxidant ability. We now evaluate if this unconventional mechanism extends to inert metal-free porphyrins. Neuron cultures were completely protected against OGD and NMDA toxicity by H2-meso-tetrakis(3-benzoic acid)porphyrin (H2-TBAP(3)) or H2-meso-tetrakis(4-sulfonatophenyl)porphyrin (H2-TPPS(4)), although only H2-TPPS(4) suppressed (completely) NMDA-induced Cai2+ rises. H2-meso-tetrakis(3,3'-benzoic acid)porphyrin (H2-TBAP(3,3')) or H2-meso-tetrakis(N-methylpyridynium-4-yl)porphyrin (H2-TM-PyP(4)) provided at least partial protection against OGD and NMDA toxicity and partially suppressed NMDA-induced Cai2+ elevations. Despite the complexity of Ca2+-independent and -dependent based mechanisms, the inventory of porphyrins demonstrating neuroprotection in ischemia-relevant insults is now expanded to include FP-15 and inert metal-free compounds, although with no apparent advantage gained by using FP-15.

Animals↗
PubMed2002

Influence of electronic and structural effects on the oxidative behavior of nickel porphyrins.

With the aim of better understanding the electronic and structural factors which govern electron-transfer processes in porphyrins, the electrochemistry of 29 nickel(II) porphyrins has been examined in dichloromethane containing either 0.1 M tetra-n-butylammonium perchlorate (TBAP) or tetra-n-butylammonium hexafluorophosphate (TBAPF(6)) as supporting electrolyte. Half-wave potentials for the first oxidation and first reduction are only weakly dependent on the supporting electrolyte, but E(1/2) for the second oxidation varies considerably with the type of supporting electrolyte. E(1/2) values for the first reduction to give a porphyrin pi-anion radical are effected in large part by the electronic properties of the porphyrin macrocycle substituents, while half-wave potentials for the first oxidation to give a pi-cation radical are affected by the substituents as well as by nonplanar deformations of the porphyrin macrocycle. The potential difference between the first and second oxidations (Delta/Ox(2) - Ox(1)/) is highly variable among the 29 investigated compounds and ranges from 0 mV (two overlapped oxidations) to 460 mV depending on the macrocycle substituents and the anion of the supporting electrolyte. The magnitude of Delta/Ox(2) - Ox(1)/ is generally smaller for compounds with very electron-withdrawing substituents and when TBAP is used as the supporting electrolyte. This behavior is best explained in terms of differences in the binding strengths of anions from the supporting electrolyte (ClO(4)(-) or PF(6)(-)) to the doubly oxidized species. A closer analysis suggests two factors which are important in modulating Delta/Ox(2) - Ox(1)/ and thus the binding affinity of the anion to the porphyrin dication. One is the type of pi-cation radical (a proxy for the charge distribution in the dication), and the other is the conformation of the porphyrin macrocycle (either planar or nonplanar). These findings imply that the redox behavior of porphyrins can be selectively tuned to display separate or overlapped oxidation processes.

Binding Sites↗
PubMed2003

Excited-state energy-transfer dynamics in self-assembled triads composed of two porphyrins and an intervening Bis(dipyrrinato)metal complex.

The synthesis and characterization of various triads composed of a linear array of two zinc porphyrins joined via an intervening bis(dipyrrinato)metal(II) complex are reported. The preparation exploits the facile complexation of dipyrrins with divalent metal ions to give bis(dipyrrinato)metal(II) complexes [abbreviated (dp)(2)M]. Copper(II) and palladium(II) chelates of dipyrrins (available by oxidation of dipyrromethanes) were prepared in 50-80% yield. A one-flask synthesis of bis(dipyrrinato)zinc(II) complexes was developed by oxidation of a dipyrromethane with DDQ or p-chloranil in the presence of Zn(OAc)(2).2H(2)O in THF ( approximately 80% yield). Three routes were developed for preparing porphyrin-dipyrrins: (1). Suzuki coupling of a boronate-substituted zinc porphyrin (ZnP) and bis[5-(4-iodophenyl)dipyrrinato]Pd(II) to give the (ZnP-dp)(2)Pd triad (50% yield), followed by selective demetalation of the (dp)(2)Pd unit by treatment with 1,4-dithiothreitol under neutral conditions (71% yield); (2). oxidation of a porphyrin-dipyrromethane with p-chloranil in the presence of Zn(OAc)(2).2H(2)O followed by chromatography on silica gel (71% yield); and (3). condensation of a dipyrrin-dipyrromethane and a dipyrromethane-dicarbinol under InCl(3) catalysis followed by oxidation with DDQ (10-16% yield). Four triads of form (ZnP-dp)(2)Zn were prepared in 83-97% yield by treatment of a porphyrin-dipyrrin with Zn(OAc)(2).2H(2)O at room temperature. Free base dipyrrins typically absorb at 430-440 nm, while the bis(dipyrrinato)metal complexes absorb at 460-490 nm. The fluorescence spectra/yields and excited-state lifetimes of the (ZnP-dp)(2)Zn triad in toluene show (1). efficient energy transfer from the bis(dipyrrinato)zinc(II) chromophore to the zinc porphyrins (98.5% yield), and (2). little or no quenching of the resulting excited zinc porphyrin relative to the isolated chromophore. Taken together, these results indicate that bis(dipyrrinato)zinc(II) complexes can serve as self-assembling linkers that further function as secondary light-collection elements in porphyrin-based light-harvesting arrays.

Journal Article↗
PubMed1998

Novel Cofacial Ruthenium(II) Porphyrin Dimers and Tetramers.

A series of cofacially arranged ruthenium(II) porphyrin dimers 1-5 having a variety of axial ligands such as CO, pyridine, and 4-cyanopyridine, were synthesized. Porphyrin tetramers, 6 and 7, which have pyridylporphyrin ligands at the axial positions of the parent cofacial ruthenium(II) dimers, were also prepared. These porphyrin dimers and tetramers were characterized by (1)H NMR spectroscopy, ESI (electrospray ionization)-mass spectroscopy, and elemental analysis. The ruthenium porphyrin dimers and tetramers exhibited characteristic electrochemical and spectroscopic properties caused by interactions between the porphyrin subunits. Stepwise oxidations of the porphyrin rings or the ruthenium ions in the cofacial dimer skeltons were observed in the cyclic voltammograms. The potential differences (DeltaE degrees ' mV) of the oxidation steps were larger than 260 mV for all the porphyrin oligomers. The Soret bands of the cofacial dimers were significantly broadened by excitonic interactions between the two porphyrin subunits. Furthermore, the mixed-valence states of 3-7 showed specific intervalence charge-transfer (IT) bands between the Ru(II) and Ru(III) cores in the near-IR region at around 1500 nm.

Journal Article↗
PubMed2003

Symmetry and bonding in metalloporphyrins. A modern implementation for the bonding analyses of five- and six-coordinate high-spin iron(III)-porphyrin complexes through density functional calculation and NMR spectroscopy.

Bonding interactions between the iron and the porphyrin macrocycle of five- and six-coordinate high-spin iron(III)-porphyrin complexes are analyzed within the framework of approximate density functional theory with the use of the quantitative energy decomposition scheme in combination with removal of the vacant pi orbitals of the porphyrin from the valence space. Although the relative extent of the iron-porphyrin interactions can be evaluated qualitatively through the spin population and orbital contribution analyses, the bond strengths corresponding to different symmetry representations can be only approximated quantitatively by the orbital interaction energies. In contrast to previous suggestions, there are only limited Fe --> P pi back-bonding interactions in high-spin iron(III)-porphyrin complexes. It is the symmetry-allowed bonding interaction between d(z)2 and a(2u) orbitals that is responsible for the positive pi spin densities at the meso-carbons of five-coordinate iron(III)-porphyrin complexes. Both five- and six-coordinate complexes show significant P --> Fe pi donation, which is further enhanced by the movement of the metal toward the in-plane position for six-coordinate complexes. These bonding characteristics correlate very well with the NMR data reported experimentally. The extraordinary bonding interaction between d(z)2 and a(2u) orbitals in five-coordinate iron(III)-porphyrin complexes offers a novel symmetry-controlled mechanism for spin transfer between the axial ligand sigma system and the porphyrin pi system and may be critical to the electron transfer pathways mediated by hemoproteins.

Ferric Compounds↗
PubMed2005

Directly meso-meso linked porphyrin rings: synthesis, characterization, and efficient excitation energy hopping.

Directly meso-meso linked porphyrin rings CZ4, CZ6, and CZ8 that respectively comprise four, six, and eight porphyrins have been synthesized in a stepwise manner from a 5,10-diaryl zinc(II) porphyrin building block. Symmetric cyclic structures have been indicated by their very simple (1)H NMR spectra that exhibit only a single set of porphyrin and their absorption spectra that display a characteristic broad nonsplit Soret band around 460 nm. Energy minimized structures calculated at the B3LYP/6-31G* level indicate that a dihedral angle between neighboring porphyrins decreases in order of CZ6 > CZ8 > CZ4, which is consistent with the (1)H NMR data. Photophysical properties of these molecules have been examined by the steady-state absorption, fluorescence, fluorescence lifetime, fluorescence anisotropy decay, and transient absorption measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly related with the excitation energy migration processes within the porphyrin rings, where the exciton-exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Forster-type incoherent energy hopping model. Consequently, the excitation energy hopping rates have been estimated for CZ4 (119 +/- 2 fs)(-)(1), CZ6 (342 +/- 59 fs)(-)(1), and CZ8 (236 +/- 31 fs)(-)(1), which reflect the magnitude of the electronic coupling between the neighboring porphyrins. Overall, these porphyrin rings serve as a well-defined wheel-shaped light harvesting antenna model in light of very efficient excitation energy hopping along the ring.

Journal Article↗
PubMed2006

A directly fused tetrameric porphyrin sheet and its anomalous electronic properties that arise from the planar cyclooctatetraene core.

Oxidation of a directly meso-meso linked cyclic porphyrin tetramer 2 gave a porphyrin sheet 3. The symmetric square structure of 3 is indicated by its simple 1H NMR spectrum that exhibits only two signals for the porphyrin beta-protons. The absorption spectrum of 3 displays characteristic Soret-like broad bands and weak Q-bands, and its magnetic circular dichroism (MCD) spectrum exhibits a negative Faraday A term at the 762 nm band as a rare case, indicating the absorption as a transition from a nondegenerate level to a degenerate level. A slightly longer S1-state (1.1 ps) and smaller TPA cross section (2750 GM) than a tetrameric linear porphyrin tape also indicate its unique electronic properties. The porphyrin sheet 3 forms stable 1:2 complexes with guest molecules G1 and G2, whose 1H NMR spectra exhibit remarkable downfield shifts for the guest protons that are located just above the cyclooctatetraene (COT) core of 3, whereas the imidazolyl protons bound to the zinc(II) porphyrin local cores are observed at slightly upfield positions. These results have been qualitatively accounted for in terms of the presence of a strong paratropic ring current around the COT core that propagates through the whole pi-electronic network of 3, hence competing with and cancelling the weak diatropic ring currents of the local zinc(II) porphyrins. This explanation was supported by DFT calculation performed at the GIAO-B3LYP/6-31G level, which indicated large positive NICS values within the COT core and small NICS values within the local zinc(II) porphyrins.

Journal Article↗
PubMed2000

Synthesis of thiol-derivatized porphyrin dimers and trimers for studies of architectural effects on multibit information storage

We present the rational design and synthesis of multiporphyrin arrays containing thiol-derivatized linkers for the purpose of multibit molecular information storage. Porphyrin dimers and trimers were synthesized by the Pd-mediated coupling of iodo-substituted and ethynyl-substituted porphyrin building blocks in 5-51% yields. Each porphyrin dimer bears one S-acetylthio group. The architecture of the trimers incorporates a trans-substituted porphyrin (central) bearing two S-acetylthio groups and two diphenylethyne-linked porphyrins (wings) in a trans geometry. The central porphyrin and the wing porphyrins bear distinct substituents and central metals, thereby affording different oxidation potentials. The S-acetylthio groups provide a means for attachment of the arrays to an electroactive surface. The dimers are designed for vertical orientation on an electroactive surface while the trimers are designed for horizontal orientation of the central porphyrin. Altogether seven different arrays were synthesized. Each array forms a self-assembled monolayer (SAM) on gold via in situ cleavage of the S-acetyl protecting group. The SAM of each array is electrochemically robust and exhibits multiple, reversible oxidation waves. In general, however, the trimeric arrays appear to form more highly ordered monolayers that exhibit sharper, better-defined redox features.

Journal Article↗
PubMed2003

Synthesis of cyclic hexameric porphyrin arrays. Anchors for surface immobilization and columnar self-assembly.

To investigate new architectures for the self-assembly of multiporphyrin arrays, a one-flask synthesis of a shape-persistent cyclic hexameric array of porphyrins was exploited to prepare six derivatives bearing diverse pendant groups. The new arrays contain 6-12 carboxylic acid groups, 12 amidino groups, 6 thiol groups, or 6 thiol groups and 6 carboxylic acid groups in protected form (S-acetylthio, TMS-ethyl, TMS-ethoxycarbonyl). The arrays contain alternating Zn and free base (Fb) porphyrins or all Zn porphyrins. The one-flask synthesis entails a template-directed, Pd-mediated coupling of a p/p'-substituted diethynyl Zn porphyrin and a m/m'-substituted diiodo Fb porphyrin. The porphyrin building blocks (trans-A(2)B(2), trans-AB(2)C) contain the protected pendant groups at nonlinking meso positions. A self-assembled monolayer (SAM) of a Zn(3)Fb(3) cyclic hexamer containing one thiol group on each porphyrin was prepared on a gold electrode and the surface-immobilized architecture was examined electrochemically. Together, the work reported herein provides cyclic hexameric porphyrin arrays for studies of self-assembly in solution or on surfaces.

Journal Article↗
PubMed2004

Synthesis of porphyrins bearing hydrocarbon tethers and facile covalent attachment to si(100).

The use of redox-active molecules as the active storage elements in memory chips requires the ability to attach the molecules to an electroactive surface in a reliable and robust manner. To explore the use of porphyrins tethered to silicon via carbosilane linkages, 17 porphyrins have been synthesized. Fourteen porphyrins bear a tether at a single meso site, and three porphyrins bear functional groups at two beta sites for possible two-point attachment. Two high-temperature processing methods (400 degrees C under inert atmosphere) have been developed for rapid (minutes), facile covalent attachment to Si platforms. The high-temperature processing conditions afford attachment either by direct deposition of a dilute solution (1 microM-1 mM) of the porphyrin sample onto the Si substrate or sublimation of a neat sample onto the Si substrate. The availability of this diverse collection of porphyrins enables an in-depth examination of the effects of the tether (length, composition, terminal functional group, number of tethers) and steric bulk of nonlinking substituents on the information-storage properties of the porphyrin monolayers obtained upon attachment to silicon. Attachment proceeds readily with a wide variety of hydrocarbon tethers, including 2-(trimethylsilyl)ethynyl, vinyl, allyl, or 3-butenyl directly appended to the porphyrin and iodo, bromomethyl, 2-(trimethylsilyl)ethynyl, ethynyl, vinyl, or allyl appended to the 4-position of a meso-phenyl ring. No attachment occurs with substituents such as phenyl, p-tolyl, mesityl, or ethyl. Collectively, the studies show that the high-temperature attachment procedure (1) has broad scope encompassing diverse functional groups, (2) tolerates a variety of arene substituents, and (3) does not afford indiscriminate attachment. The high-temperature processing conditions are ideally suited for use in fabrication of hybrid molecular/semiconductor circuitry.

Journal Article↗
PubMed2004

Porphyrin architectures tailored for studies of molecular information storage.

A molecular approach to information storage employs redox-active molecules tethered to an electroactive surface. Zinc porphyrins tethered to Au(111) or Si(100) provide a benchmark for studies of information storage. Three sets of porphyrins have been synthesized for studies of the interplay of molecular design and charge-storage properties: (1) A set of porphyrins is described for probing the effect of surface attachment atom on electron-transfer kinetics. Each porphyrin bears a meso-CH2X group for surface attachment where X = OH, SAc, or SeAc. (2) A set of porphyrins is described for studying the effect of surface-charge density in monolayers. Each porphyrin bears a benzyl alcohol for surface attachment and three nonlinking meso substituents of a controlled degree of bulkiness. (3) A set of porphyrins is described that enables investigation of on-chip patterning of the electrolyte. Each porphyrin bears a formyl group distal to the surface attachment group for subsequent derivatization with a molecular entity that comprises the electrolyte. Taken together, this collection of molecules enables a variety of studies to elucidate design issues in molecular-based information storage.

Journal Article↗
PubMed2006

A theoretical study on the third-order nonlinear optical properties of pi-conjugated linear porphyrin arrays.

By using the Pariser-Parr-Pople (PPP) theory, the second hyperpolarizabilities (gamma) have been calculated for various pi-conjugated porphyrin arrays including "porphyrin tapes": the meso-beta doubly linked porphyrin array Dn and the meso-meso, beta-beta, beta-beta triply linked array Tn. The validity of the PPP theory is checked via a comparison with both the ab initio Hartree-Fock and the B3LYP theories in the case of porphyrin monomers and dimers. It is found that Dn and especially Tn exhibit much more remarkable evolution of gamma/n along with an increasing number of porphyrin units n compared with the butadiyne-bridged array, Yn. As a result, the static third-order susceptibilities chi((3)) of Dn and Tn are expected to be 1 and 3 orders of magnitude larger than that of Yn in the limit n --> infinity, and these advantages of porphyrin tapes become more prominent by taking into account geometrical relaxations of porphyrin units in the arrays. The structure-property relationship in various conjugated polymers including porphyrin arrays is interpreted on the basis of the scaling behaviors of chi((1)) and chi((3)) with the effective conjugation length (ECL) as well as the reciprocal HOMO-LUMO energy gap (1/E(g)). In particular, from the master plot of chi((3)) (and even chi((1))) versus 1/E(g), the pi-conjugation of Tn is noted to indeed be exceptional, because its large susceptibilities cannot be expected from the scaling behavior of ordinary one-dimensional conjugated systems. We also point out that the theory of scaling relationship, chi((3)) approximately 1/E(g)(x)(), is significantly improved by taking into account electron-electron interactions based on the comparison with experiments.

Journal Article↗