66 results on '"Pasternack RF"'
Search Results
2. DETECTION OF POLY-URONATES THROUGH CHIRALITY TRANSFER TO SUPRAMOLECULAR PORPHYRIN AGGREGATES
- Author
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Samperi, Mario, Occhiuto, ILARIA GIUSEPPINA, DE LUCA, Giovanna, Romeo, Andrea, Pasternack, Rf, and MONSU' SCOLARO, Luigi
- Published
- 2013
3. Insights on Chirality Transfer in Mesoscopic Porphyrins Aggregates
- Author
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Occhiuto, ILARIA GIUSEPPINA, DE LUCA, Giovanna, Villari, V., Romeo, Andrea, Micali, N., Pasternack, Rf, and MONSU' SCOLARO, Luigi
- Published
- 2011
4. Metalloporphyrin Supramolecular Assemblies as Chiroptical Sensor for Polypeptides Conformation
- Author
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De Luca G, Occhiuto I, Romeo A, Monsù Scolaro L, and Pasternack RF
- Published
- 2010
5. Aggregating Cu(II) Porphyrin as Chiroptical Sensor
- Author
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De Luca G, Occhiuto I, Romeo A, Monsù Scolaro L, and Pasternack RF
- Published
- 2010
6. Conformations of protein scaffolds revealed by an aggregating Cu(II) porphyrin: sensing the difference
- Author
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DE LUCA, Giovanna, Romeo, Andrea, MONSU' SCOLARO, Luigi, and Pasternack, Rf
- Published
- 2009
7. Interaction of t-CuPagg with poly-L-glutamate
- Author
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DE LUCA, Giovanna, MONSU' SCOLARO, Luigi, and Pasternack, Rf
- Published
- 2006
8. t-CuPagg metalloporphyrin as sensor for protein helix-coil transition
- Author
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DE LUCA, Giovanna, MONSU' SCOLARO, Luigi, and Pasternack, Rf
- Published
- 2006
9. Kinetic investigation of supramolecular assembling on poly(L-glutamic acid)
- Author
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Scolaro, Lm, Pasternack, Rf, Purrello, Roberto, Romeo, A, and Terracina, A.
- Published
- 1996
10. Controlling J-Aggregates Formation and Chirality Induction through Demetallation of a Zinc(II) Water Soluble Porphyrin.
- Author
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Occhiuto IG, Castriciano MA, Trapani M, Zagami R, Romeo A, Pasternack RF, and Monsù Scolaro L
- Subjects
- Cations, Circular Dichroism, Electrons, Hydrogen-Ion Concentration, Ions, Kinetics, Light, Salts, Scattering, Radiation, Solubility, Spectrophotometry, Ultraviolet, Stereoisomerism, Temperature, Porphyrins chemistry, Zinc chemistry
- Abstract
Under acidic conditions and at high ionic strength, the zinc cation is removed from its metal complex with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS
4 ) thus leading to the diacid free porphyrin, that subsequently self-organize into J-aggregates. The kinetics of the demetallation step and the successive supramolecular assembly formation have been investigated as a function of pH and ionic strength (controlled by adding ZnSO4 ). The demetallation kinetics obey to a rate law that is first order in [ZnTPPS4 ] and second order in [H+ ], according to literature, with k2 = 5.5 ± 0.4 M-2 s-1 at 298 K (IS = 0.6 M, ZnSO4 ). The aggregation process has been modeled according to an autocatalytic growth, where after the formation of a starting seed containing m porphyrin units, the rate evolves as a power of time. A complete analysis of the extinction time traces at various wavelengths allows extraction of the relevant kinetic parameters, showing that a trimer or tetramer should be involved in the rate-determining step of the aggregation. The extinction spectra of the J-aggregates evidence quite broad bands, suggesting an electronic coupling mechanism different to the usual Frenkel exciton coupling. Resonance light scattering intensity in the aggregated samples increases with increasing both [H+ ] and [ZnSO4 ]. Symmetry breaking occurs in these samples and the J-aggregates show circular dichroism spectra with unusual bands. The asymmetry g-factor decreases in its absolute value with increasing the catalytic rate kc , nulling and eventually switching the Cotton effect from negative to positive. Some inferences on the role exerted by zinc cations on the kinetics and structural features of these nanostructures have been discussed., Competing Interests: The authors declare no conflict of interest.- Published
- 2020
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11. Mechanism for Copper(II)-Mediated Disaggregation of a Porphyrin J-Aggregate.
- Author
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Trapani M, Occhiuto IG, Zagami R, De Luca G, Castriciano MA, Romeo A, Scolaro LM, and Pasternack RF
- Abstract
J-aggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3-3.1) in the presence of NiSO
4 or ZnSO4 (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to Δ H≠ = (+163 ± 15) kJ·mol-1 and Δ S≠ = (+136 ± 11) J·K-1 . A mechanism is proposed in which copper(II) cation is in pre-equilibrium with a reactive site at the rim of the J-aggregate. An intermediate copper species is thus formed that eventually leads to the final metallated porphyrin either through an assisted attack of a second metal ion or through a direct insertion of the metal cation into the macrocycle core., Competing Interests: The authors declare no competing financial interest.- Published
- 2018
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12. Effect of zinc cations on the kinetics of supramolecular assembly and the chirality of porphyrin J-aggregates.
- Author
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Romeo A, Castriciano MA, Zagami R, Pollicino G, Monsù Scolaro L, and Pasternack RF
- Abstract
Dilute aqueous solutions of anionic meso -4-sulfonatophenyl-porphyrin (TPPS) extract zinc(ii) ions from glass or quartz surfaces at room temperature and efficiently form the corresponding metal complex (ZnTPPS). The partial or complete formation of ZnTPPS has been probed by UV/Vis spectroscopy and both static and time-resolved fluorescence. The source of zinc(ii) ions has been clearly identified through inductively coupled plasma optical emission spectrometry. The presence of increasing amounts of ZnTPPS slows down the rate of TPPS J-aggregate formation in acid solution. This influences the nucleation step and has a profound impact on the onset of chirality in these species. This evidence indicates the important role of this adventitious metal ion in the interpretation of various spectroscopic and kinetic data for the self-assembly of the TPPS porphyrin and provides some insights into controversial findings on their chirality. The use of this metal derivative as the starting compound for in situ formation of monomeric TPPS is suggested.
- Published
- 2017
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13. Aggregates of a cationic porphyrin as supramolecular probes for biopolymers.
- Author
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Occhiuto IG, Samperi M, Trapani M, De Luca G, Romeo A, Pasternack RF, and Scolaro LM
- Subjects
- Coordination Complexes chemistry, Coordination Complexes pharmacology, Isomerism, Sodium Chloride chemistry, Spores, Bacterial drug effects, Static Electricity, Coordination Complexes chemical synthesis, Copper chemistry, Porphyrins chemistry
- Abstract
The copper(II) derivative of the dicationic trans-bis(N-methylpyridinium-4-yl)diphenylporphyrin (t-CuPagg) forms large fractal aggregates in aqueous solution under moderate ionic strength conditions. A kinetic investigation of the aggregation process allows for a choice of experimental conditions to quickly obtain stable assemblies in solution. These positively charged aggregates are able to interact efficiently with negatively charged chiral species, (including bacterial spores) leading to induced circular dichroism signals in the Soret region of the porphyrin, now acting as a sensitive chiroptical probe.
- Published
- 2015
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14. Kinetic control of chirality in porphyrin J-aggregates.
- Author
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Romeo A, Castriciano MA, Occhiuto I, Zagami R, Pasternack RF, and Scolaro LM
- Abstract
Detailed kinetic investigations demonstrate the fundamental role of kinetic parameters in the expression and transmission of chirality in supramolecular systems. The rate of the aggregation process leading to the formation of J-aggregates strongly affects the size of these nanoassemblies and the chiral induction.
- Published
- 2014
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15. Peripheral stepwise degradation of a porphyrin J-aggregate.
- Author
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Occhiuto I, De Luca G, Trapani M, Scolaro LM, and Pasternack RF
- Subjects
- Cations, Divalent chemistry, Nanostructures chemistry, Salts chemistry, Spectrophotometry, Ultraviolet, Copper chemistry, Metalloporphyrins chemistry
- Abstract
For metalation of the acidic form of tetrakis(4-sulfonatophenyl)porphyrin (dianionic H(4)TPPS(4)) by Cu(II), the order of reagent mixing determines the rate and mechanism of CuTPPS(4) formation. When copper salts are added last, the kinetic profile is fit as a (pseudo)-first-order process. However, J-aggregates of the H(4)TPPS(4) porphyrin are rapidly formed at pH ~ 3 when Cu(II) salts are incorporated in solution prior to porphyrin addition. The subsequent porphyrin units metalation leads to the disassembling of these arrays via a pseudo-zero-order kinetic profile, suggesting an attack of the metal ion at the rims of the nanostructure.
- Published
- 2012
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16. Supramolecular chirality transfer to large random aggregates of porphyrins.
- Author
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Occhiuto I, De Luca G, Villari V, Romeo A, Micali N, Pasternack RF, and Scolaro LM
- Subjects
- Circular Dichroism, Copper chemistry, Polyglutamic Acid chemistry, Spectrophotometry, Ultraviolet, Stereoisomerism, Porphyrins chemistry
- Abstract
Chirality is rapidly induced in a fractal aggregate of the porphyrin t-CuPagg by addition of α-helical poly-glutamate. These results demonstrate a facile transfer of chirality via noncovalent interactions to preformed supramolecular assemblies grown in the absence of a chiral template.
- Published
- 2011
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17. On the kinetics of formation of hemozoin, the malaria pigment.
- Author
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Pasternack RF, Munda B, Bickford A, Gibbs EJ, and Scolaro LM
- Subjects
- 1-Octanol chemistry, Algorithms, Animals, Chloroquine chemistry, Hemeproteins metabolism, Hemin metabolism, Hexanols chemistry, Humans, Kinetics, Malaria parasitology, Methanol chemistry, Models, Chemical, Phosphatidylethanolamines chemistry, Pigments, Biological metabolism, Plasmodium falciparum metabolism, Protozoan Proteins metabolism, Solvents chemistry, Hemeproteins chemistry, Hemin chemistry, Pigments, Biological chemistry, Protozoan Proteins chemistry
- Abstract
We report on the kinetics of formation of hemozoin as a function of hemin concentration and reaction medium. Evidence is presented for the critical role played by interfacial regions in the efficient conversion of hemin to the malaria pigment., (Copyright 2010 Elsevier Inc. All rights reserved.)
- Published
- 2010
- Full Text
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18. Conformations of a model protein revealed by an aggregating Cu(II) porphyrin: sensing the difference.
- Author
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De Luca G, Romeo A, Scolaro LM, and Pasternack RF
- Subjects
- Circular Dichroism, Protein Conformation, Copper chemistry, Metalloporphyrins chemistry, Polyglutamic Acid chemistry
- Abstract
Aggregated t-CuP binds to poly-L-glutamate through supramolecular interactions, revealing itself to be an extremely sensitive probe for the major conformations of the polymeric scaffold.
- Published
- 2010
- Full Text
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19. Probing the mechanism of insulin aggregation with added metalloporphyrins.
- Author
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Sibley SP, Sosinsky K, Gulian LE, Gibbs EJ, and Pasternack RF
- Subjects
- Amyloid chemistry, Hydrogen-Ion Concentration, Kinetics, Microscopy, Atomic Force, Porphyrins chemistry, Insulin chemistry, Metalloporphyrins chemistry
- Abstract
The mechanism of inhibition of insulin-based amyloid gel formation by metal derivatives of tetrakis(4-sulfonatophenyl)porphyrin has been investigated. Time-course UV/vis measurements in conjunction with atomic force microscopy (AFM) were used to study the correlation between observed kinetics and amyloid structure for various concentration ranges of added metalloporphyrins. Observed structures include fibrils as well as circular, ring-like structures formed as a result of the interaction of insulin with porphyrin. In addition, binding studies demonstrate that the effectiveness of inhibition of the various metalloporphyrins is directly related to the strength of binding to insulin. It is suggested that both the electron distribution in the porphyrin core and the tendency to form porphyrin dimers affect both the structure of amyloid formed and the kinetic profile of the reaction.
- Published
- 2008
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20. Formation kinetics of insulin-based amyloid gels and the effect of added metalloporphyrins.
- Author
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Pasternack RF, Gibbs EJ, Sibley S, Woodard L, Hutchinson P, Genereux J, and Kristian K
- Subjects
- Animals, Catalysis, Cattle, Crystallography, X-Ray, Dose-Response Relationship, Drug, Gels chemistry, Hydrogen-Ion Concentration, Insulin metabolism, Ions, Kinetics, Models, Chemical, Porphyrins chemistry, Protein Denaturation, Protein Folding, Time Factors, Amyloid chemistry, Insulin chemistry, Metalloporphyrins chemistry, Pancreas metabolism
- Abstract
The kinetics of insulin-based amyloid gel formation has been studied using extinction and fluorescence detection. The process is treated as autocatalytic, and the kinetic profiles are fit using a nonconventional analysis involving a time-dependent rate constant (factor): k(t) = k(o) + k(c)(k(c)t)(n). The dependence of the kinetic parameters on initial solution conditions of concentration, pH, and ionic strength has been investigated. A mechanism is proposed in which the rate-determining step involves the activation of insulin solute species into partially unfolded, structurally modified monomers, which then aggregate. The influence of added metalloporphyrins on the rate and extent of gel formation is described. Metal derivatives of tetrakis(4-sulfonatophenyl)porphine prove effective at inhibiting the aggregation of insulin via pathways that depend on concentration and identity of the incorporated metal.
- Published
- 2006
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21. Tuning porphyrin/DNA supramolecular assemblies by competitive binding.
- Author
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Scolaro LM, Romeo A, and Pasternack RF
- Subjects
- Binding, Competitive, Circular Dichroism, Molecular Structure, DNA chemistry, DNA metabolism, Porphyrins chemistry, Porphyrins metabolism
- Abstract
Addition of an intercalating but nonaggregating porphyrin, AuT4, to a preformed adduct between DNA and a strongly aggregating porphyrin, t-H2Pagg, permits control of the extent of aggregation of the latter. The size and the intensity of the ICD and RLS signals depend linearly on the concentration of the intercalating dye and decrease markedly on increasing the concentration of the available binding sites on the biopolymer template.
- Published
- 2004
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22. Circular dichroism and the interactions of water soluble porphyrins with DNA.
- Author
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Pasternack RF
- Subjects
- Animals, Binding Sites, Cattle, Circular Dichroism, In Vitro Techniques, Light, Nucleic Acid Conformation, Scattering, Radiation, Solubility, Water, DNA chemistry, DNA metabolism, Porphyrins chemistry, Porphyrins metabolism
- Abstract
The size, sign, and profile of induced circular dichroism (CD) features in the Soret region are reliable indicators of the binding modes of porphyrins and metalloporphyrins to DNA. Porphyrins shown (using such CD criteria) to be intercalators in monodispersed DNA duplexes prove extremely useful for the detection and characterization of organized, condensed forms of nucleic acids (psi-condensates). In addition, certain select porphyrin derivatives can form extended assemblies on nonaggregated DNA templates. A combination of CD and resonance light scattering (RLS) measurements allows for sensitive detection and characterization of these porphyrin arrays., (Copyright 2003 Wiley-Liss, Inc.)
- Published
- 2003
- Full Text
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23. Kinetics of disassembly of a DNA-bound porphyrin supramolecular array.
- Author
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Pasternack RF, Gibbs EJ, Bruzewicz D, Stewart D, and Engstrom KS
- Subjects
- Circular Dichroism, Cyclodextrins chemistry, DNA metabolism, Kinetics, Porphyrins metabolism, Spectrophotometry, Templates, Genetic, DNA chemistry, Porphyrins chemistry, beta-Cyclodextrins
- Abstract
trans-Bis(N-methylpyridinium-4-yl)diphenylporphine forms extended, organized assemblies on DNA templates under appropriate conditions of concentration, ionic strength, and temperature. Addition of beta-cyclodextrin to these arrays leads to their disassembly as evidenced by changes in extinction, circular dichroism, and resonance light scattering spectra. The structure or flexibility of the polymer template has an effect on the rate of disassembly; the reaction is faster on a poly(dG-dC)(2) surface than on ct DNA. The kinetic profiles for the disassembly process can be fit with great precision with a two-kinetic parameter equation in which the rate constant is itself a function of time. The reaction rate, studied in the presence of excess beta-CD, shows a dependence on the mode of detection. A model is presented to account for these observations in which the arrays become increasingly reactive with time due to beta-CD attack at the interior of the porphyrin assemblies as well as the ends.
- Published
- 2002
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24. Aggregation kinetics of extended porphyrin and cyanine dye assemblies.
- Author
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Pasternack RF, Fleming C, Herring S, Collings PJ, dePaula J, DeCastro G, and Gibbs EJ
- Subjects
- Adsorption drug effects, Hydrochloric Acid chemistry, Hydrochloric Acid pharmacology, Hydrogen-Ion Concentration drug effects, Kinetics, Polymers chemistry, Polyvinyls chemistry, Spectrophotometry, Sulfonic Acids chemistry, Porphyrins chemistry, Quinolines chemistry
- Abstract
The kinetics of J-aggregate formation has been studied for two chromophores, tetrakis-4-sulfonatophenylporphine in an acid medium and pseudoisocyanine on a polyvinylsulfonate template. The assembly processes differ both in their sensitivity to initiation protocols and in the reaction profiles they produce. The porphyrin's assembly kinetics, for example, displays an induction period unlike that of the cyanine dye. Two kinetic models are presented. For the porphyrin, an autocatalytic pathway in which the formation of an aggregation nucleus is rate-determining appears to be applicable; for the pseudoisocyanine dye, an equation derived for diffusion-limited aggregation of a fractal object satisfactorily fits the data. These models are shown to be useful for the analysis of kinetic data obtained for several biologically important aggregation processes.
- Published
- 2000
- Full Text
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25. A spectroscopic and thermodynamic study of porphyrin/DNA supramolecular assemblies.
- Author
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Pasternack RF, Goldsmith JI, Szép S, and Gibbs EJ
- Subjects
- Animals, Cattle, Circular Dichroism, Kinetics, Light, Osmolar Concentration, Scattering, Radiation, Solutions, Spectrophotometry methods, Thermodynamics, DNA chemistry, Nucleic Acid Conformation, Porphyrins chemistry, Pyridinium Compounds chemistry
- Abstract
Assemblies of trans-bis(N-methylpyridinium-4-yl)diphenylporphine ions on the surface of calf thymus DNA have been studied using several spectroscopic techniques: absorbance, circular dichroism, and resonance light scattering. The aggregation equilibrium can be treated as a two-state system-monomer and assembly-each bound to the nucleic acid template. The aggregate absorption spectrum in the Soret region is resolved into two bands of Lorentzian line shape, while the DNA-bound monomer spectrum in this region is composed of two Gaussian bands. The Beer-Lambert law is obeyed by both porphyrin forms. The assembly is also characterized by an extremely large, bisignate induced circular dichroism (CD) profile and by enhanced resonance light scattering (RLS). Both the CD and RLS intensities depend linearly on aggregate concentration. The RLS result is consistent with a model for the aggregates as being either of a characteristic size or of a fixed distribution of sizes, independent of total porphyrin concentration or ionic strength. Above threshold values of concentration and ionic strength, the mass action expression for the equilibrium has a particularly simple form: K' = cac-1; where cac is defined as the "critical assembly concentration."offe dependence of the cac upon temperature and ionic strength (NaCl) has been investigated at a fixed DNA concentration. The value of the cac scales as the inverse square of the sodium chloride concentration and, from temperature dependence studies, the aggregation process is shown to be exothermic.
- Published
- 1998
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26. Depolarized resonance light scattering by porphyrin and chlorophyll a aggregates.
- Author
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Parkash J, Robblee JH, Agnew J, Gibbs E, Collings P, Pasternack RF, and de Paula JC
- Subjects
- Animals, Biophysical Phenomena, Biophysics, Cattle, Chlorophyll A, Chromogenic Compounds chemistry, DNA chemistry, Light, Macromolecular Substances, Models, Chemical, Molecular Structure, Quantum Theory, Scattering, Radiation, Chlorophyll chemistry, Porphyrins chemistry
- Abstract
A quantum mechanical model is developed for the observed resonance enhancement of light scattering by aggregates of electronically interacting chromophores. Aggregate size, monomer oscillator strength, extent of electronic coupling, and aggregate geometry are all important determinants of intensity in resonance light scattering (RLS) spectra. The theory also predicts the value of the depolarization ratio (rho(v)(90)) of RLS for a given aggregate geometry. These results are used to interpret the RLS depolarization ratios of four aggregates: tetrakis(4-sulfonatophenyl)porphine aggregated at low pH (rho(v)(90) = 0.17 at 488 nm), trans-bis(N-methylpyridinium-4-yl)-diphenylporphinato copper(II) aggregated in 0.2 M NaCl solution (rho(v)(90) = 0.13 at 450 nm) and on calf thymus DNA (rho(v)(90) = 0.20 at 454 nm), and chlorophyll a aggregates in formamide/water (rho(v)(90) = 0.23 and 0.32 at 469 and 699 nm, respectively). The analysis is consistent with a J-aggregate geometry for all four systems. Furthermore, the specific values of rho(v)(90) allow us to estimate the orientation of the monomer transition dipoles with respect to the long axis of the aggregate. We conclude that depolarized resonance light scattering spectroscopy is a powerful probe of the geometric and electronic structures of extended aggregates of strong chromophores.
- Published
- 1998
- Full Text
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27. Experimental evidence for self-similar structures in the aggregation of porphyrins in aqueous solutions.
- Author
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Mallamace F, Micali N, Trusso S, Scolaro LM, Romeo A, Terracina A, and Pasternack RF
- Published
- 1996
- Full Text
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28. Porphyrin and metalloporphyrin interactions with nucleic acids.
- Author
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Pasternack RF and Gibbs EJ
- Subjects
- Base Sequence, Binding Sites, Light, Models, Molecular, Molecular Conformation, Molecular Sequence Data, RNA, Transfer chemistry, Scattering, Radiation, DNA chemistry, Metalloporphyrins chemistry, Nucleic Acid Conformation, Porphyrins chemistry, RNA chemistry
- Published
- 1996
29. Resonance light scattering: a new technique for studying chromophore aggregation.
- Author
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Pasternack RF and Collings PJ
- Subjects
- Chlorophyll chemistry, Chlorophyll A, Circular Dichroism, DNA metabolism, Molecular Conformation, Porphyrins metabolism, Spectrum Analysis, Light, Porphyrins chemistry, Scattering, Radiation
- Abstract
Light scattering experiments are usually performed at wavelengths away from absorption bands, but for species that aggregate, enhancements in light scattering of several orders of magnitude can be observed at wavelengths characteristic of these species. Resonance light scattering is shown to be a sensitive and selective method for studying electronically coupled chromophore arrays. The approach is illustrated with several examples drawn from porphyrin and chlorin chemistry. The physical principles underlying resonance light scattering are discussed, and the advantages and limitations of the technique are reviewed.
- Published
- 1995
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30. Aggregation of chlorophyll a probed by resonance light scattering spectroscopy.
- Author
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de Paula JC, Robblee JH, and Pasternack RF
- Subjects
- Biophysical Phenomena, Biophysics, Chlorophyll A, Circular Dichroism, Formamides, Hydrogen-Ion Concentration, Kinetics, Light, Molecular Conformation, Scattering, Radiation, Sensitivity and Specificity, Solutions, Spectrophotometry methods, Spectrophotometry statistics & numerical data, Water, Chlorophyll chemistry
- Abstract
We report the resonance light scattering (RLS) spectra of chlorophyll a aggregated in a 9:1 solution of formamide and pH 6.8 phosphate buffer. The aggregate formed after 2 h of mixing, referred to as Chl469, shows a strong scattering feature at 469 nm (Soret band) and a much weaker feature at 699 nm (Qy band). A kinetic investigation confirmed that the aggregation process is cooperative, and also detected one intermediate (Chl458) with a strong RLS spectrum but only a weak CD spectrum. We propose that aggregation proceeds via at least three steps: 1) formation of a nucleating species, probably a dimer of chlorophylls; 2) formation of large aggregates with little or no secondary structure (e.g., Chl458); and 3) conformational change to form helical aggregate (Chl469).
- Published
- 1995
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31. Interaction of water-soluble porphyrins with single- and double-stranded polyribonucleotides.
- Author
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Bustamante C, Gurrieri S, Pasternack RF, Purrello R, and Rizzarelli E
- Subjects
- Chemical Phenomena, Chemistry, Physical, DNA chemistry, Nucleic Acid Conformation, RNA, Double-Stranded chemistry, Solubility, Polyribonucleotides chemistry, Porphyrins chemistry, Water chemistry
- Abstract
CD and uv-visible absorption studies with several tetracationic water-soluble porphyrin derivatives show that some of these species can serve as probes to discriminate between A- and B-conformational forms of single-stranded polynucleotides. It is also observed that these porphyrins can participate in the formation of double helices by forming transient intermediate complexes en-route to duplex formation.
- Published
- 1994
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32. Base pair selectivity in the binding of copper (II) tetrakis (4-N-methylpyridyl)porphine to polynucleotides under closely packed conditions.
- Author
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Dougherty G and Pasternack RF
- Subjects
- Animals, Cattle, DNA chemistry, DNA, Bacterial chemistry, Electron Spin Resonance Spectroscopy, Intercalating Agents chemistry, Metalloporphyrins chemistry, Polynucleotides chemistry
- Abstract
The base pair selectivity of the intercalative binding of the copper porphyrin, copper (II) tetrakis(4-N-methylpyridyl)porphine (Cu(II)TMpyP-4), to DNA has been investigated using a variety of DNA types and the synthetic polynucleotides poly(dG-dC)2 and poly(dA-dT)2. The studies utilize electron paramagnetic resonance of concentrated gels which are thought to mimic the closely packed state of nuclear DNA. The results indicate that intercalation of this porphyrin is preferred for sites containing two adjacent G-C base pairs, irrespective of sequence.
- Published
- 1992
- Full Text
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33. Amphotericin B-phospholipid interactions responsible for reduced mammalian cell toxicity.
- Author
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Perkins WR, Minchey SR, Boni LT, Swenson CE, Popescu MC, Pasternack RF, and Janoff AS
- Subjects
- Amphotericin B toxicity, Candida albicans drug effects, Carbon Radioisotopes, Drug Interactions, Erythrocytes drug effects, Hemolysis drug effects, In Vitro Techniques, Microbial Sensitivity Tests, Microscopy, Electron, Spectrum Analysis, Amphotericin B pharmacology, Phospholipids pharmacology
- Abstract
When interacting with phospholipid in an aqueous environment, amphotericin B forms unusual structures of markedly reduced toxicity (Janoff et al. (1988) Proc. Natl. Acad. Sci. USA 85, 6122-6126). These structures, which appear ribbon-like by freeze-fracture electron microscopy (EM), are found exclusively at amphotericin B to lipid mole ratios of 1:3 to 1:1. At lower mole ratios they occur in combination with liposomes. Circular dichroism (CD) spectra revealed two distinct modes of lipid-amphotericin B interaction, one for liposomes and one for the ribbon-like structures. In isolated liposomes, amphotericin B which comprised 3-4 mole percent of the bulk lipid was monomeric and exhibited a hemolytic activity comparable to amphotericin B suspended in deoxycholate. Above 3-4 mole percent amphotericin B, ribbon-like structures emerged and CD spectra indicated drug-lipid complexation. Minimal inhibitory concentrations for Candida albicans of liposomal and complexed amphotericin B were comparable and could be attributed to amphotericin a release as a result of lipid breakdown within the ribbon-like material by a heat labile extracellular yeast product (lipase). Negative stain EM of the ribbon-like structures indicated that the ribbon-like appearance seen by freeze-fracture EM arises as a consequence of the cross-fracturing of what are aggregated, collapsed single lamellar, presumably interdigitated, membranes. Studies examining complexation of amphotericin B with either DMPC or DMPG demonstrated that headgroup interactions played little role in the formation of the ribbon-like structures. With these results we propose that ribbon-like structures result from phase separation of amphotericin B-phospholipid complexes within the phospholipid matrix such that amphotericin B release, and thus acute toxicity, is curtailed. Formation of amphotericin B-lipid structures such as those described here indicates a possible new role for lipid as a stabilizing matrix for drug delivery of lipophilic substances, specifically where a highly ordered packing arrangement between lipid and compound can be achieved.
- Published
- 1992
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34. Drug binding by branched DNA: selective interaction of tetrapyridyl porphyrins with an immobile junction.
- Author
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Lu M, Guo Q, Pasternack RF, Wink DJ, Seeman NC, and Kallenbach NR
- Subjects
- Base Sequence, Cobalt metabolism, Copper metabolism, Densitometry, Ligands, Manganese, Mesoporphyrins metabolism, Molecular Sequence Data, Nickel metabolism, Zinc metabolism, DNA metabolism, Porphyrins metabolism
- Abstract
The differential binding of a number of water-soluble cationic porphyrins to a branched DNA molecule is reported. Tetrakis(4-N-methylpyridiniumyl)porphine (H2TMpyP-4) interacts near the branch point with an immobile DNA junction formed from four 16-mer strands. Its Cu(II) and Ni(II) derivatives show stronger preferential binding in the neighborhood of the branch point. Axially liganded derivatives, Zn, Co, and Mn, also interact near this branch point, but in a different way. We use the reagents methidiumpropyl-EDTA.Fe(II) [MPE.Fe(II)] and bis(o-phenanthroline)copper(I) [(OP)2Cu(I)] to cleave complexes of DNA duplex controls and the junction with these porphyrins. The resulting cleavage patterns are consistent with previous evidence that the branch point provides a strong site for intercalative binding agents, which is not available in unbranched duplexes of identical sequence. The preferential scission by (OP)2Cu(I) in the presence of Ni and Cu porphyrins near the branch point exceeds that seen for any agents we have studied. This hyperreactivity is not seen in the case of porphyrins with axial ligands, ZnTMpyP-4, CoTMpyP-4, and MnTMpyP-4, although these also interact near the branch point. The Zn derivative tends to protect sites close to the branch point from cutting, while the Co and Mn porphyrins moderately enhance cleavage of sites in this region.
- Published
- 1990
- Full Text
- View/download PDF
35. Catalysis of the disproportionation of superoxide by metalloporphyrins. III.
- Author
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Pasternack RF, Banth A, Pasternack JM, and Johnson CS
- Subjects
- Copper, Edetic Acid, Electrodes, Iron, Kinetics, Manganese, Metalloporphyrins, Oxygen, Superoxide Dismutase metabolism, Superoxides
- Abstract
An assay based on the use of an oxygen electrode has been used to determine the superoxide dismutase-type activity of several metalloporphyrins. Both the iron(III) and manganese(III) derivatives of tetrakis-(4-N-methylpyridyl)porphine were shown to have comparable activity, about 2-3% of that of the enzyme. Comparisons are made between this assay method and the more standard one which depends on the conversion of nitroblue tetrazolium to formazan.
- Published
- 1981
- Full Text
- View/download PDF
36. Hemin binding to serum proteins and the catalysis of interprotein transfer.
- Author
-
Pasternack RF, Gibbs EJ, Hoeflin E, Kosar WP, Kubera G, Skowronek CA, Wong NM, and Muller-Eberhard U
- Subjects
- Caffeine, Hemopexin metabolism, Humans, Hydrogen-Ion Concentration, Kinetics, Mathematics, Protein Binding, Serum Albumin metabolism, Blood Proteins metabolism, Heme analogs & derivatives, Hemin metabolism
- Abstract
The reaction of hemin (Hm) with human hemopexin (Hx) has been studied in a mixed dimethyl sulfoxide (Me2SO)-water solvent system and in aqueous caffeine solutions. In both media, the kinetics could be described by a single, second-order process: (formula - see text) with k = 1.8 X 10(6) M-1 s-1 in 40% Me2SO-water [pH 7.4, mu = 0.2 M (NaCl)] and k = 3.9 X 10(7) M-1 s-1 in water [pH 7.4 mu = 0.2 M (NaCl), [caffeine] = 0.025 M]. The reaction shows an ionic strength dependence consistent with a residual 1+ to 2+ charge in the vicinity of the binding region of the protein. The kinetics of the transfer of hemin from albumin to hemopexin (formula - see text) were studied as a function of concentration, ionic strength, pH, and temperature. In experiments conducted at 3 less than or equal to [Alb]0/[Hx]0 less than or equal to 20 where the transfer kinetics are first order, k' = 5 X 10(-3) S-1 at mu = 0.3 M (NaCl), pH 7.1; the reaction is strongly dependent on ionic strength and choice of electrolyte. The addition of imidazole catalyzes this transfer process via a ligand-mediated pathway with k' = 5 X 10(-3) + 21[Im]T2. At [Alb]0/[Hx]0 = 92, the noncatalyzed transfer reaction is second order. From the kinetic analysis of the reaction under these conditions, an estimate is made of the distribution of hemin between the two proteins at concentration levels which are characteristic of serum. The association of hemin and hemopexin is approximately 30 times faster than that of hemin and albumin, a finding consistent with the recycling function of hemopexin during heme transport to the liver parenchymal cells.
- Published
- 1983
- Full Text
- View/download PDF
37. Some very rapid reactions of porphyrins in aqueous solution.
- Author
-
Pasternack RF, Sutin N, and Turner DH
- Subjects
- Chemical Phenomena, Chemistry, Hydrogen-Ion Concentration, Kinetics, Mathematics, Solutions, Temperature, Porphyrins
- Published
- 1976
- Full Text
- View/download PDF
38. Interactions of porphyrins with nucleic acids.
- Author
-
Pasternack RF, Gibbs EJ, and Villafranca JJ
- Subjects
- Animals, Cattle, Chemical Phenomena, Chemistry, Metalloporphyrins, Spectrophotometry, Structure-Activity Relationship, Thymus Gland, DNA, Poly dA-dT, Polydeoxyribonucleotides, Porphyrins
- Abstract
The interactions of tetrakis(4-N-methylpyridyl)-porphine (H2TMpyP-4) and its copper(II), nickel(II), zinc(II), cobalt(III), iron(III), and manganese(III) derivatives with several nucleic acids have been investigated. Spectrophotometric titrations of H2TMpyP-4 and Cu(II)TMpyP-4 with the synthetic polymer poly(dG-dC) could be analyzed by a nearest-neighbor exclusion model leading to n approximately equal to two base pairs and equilibrium constants of 7.7 X 10(5) M-1 and 8.0 X 10(5) M-1, respectively. The other metal derivatives [except for the nickel(II) porphyrin] do not provide sufficiently large color changes with poly(dG-dC) to allow analysis. In contrast, all of these porphyrins interact with poly(dA-dT) and DNA. For those porphyrins investigated, the binding profiles are not adequately fit by a nearest-neighbor exclusion model but have profiles suggesting that cooperativity effects are important. Spectral and circular dichroic experiments both suggest base specificity. With calf thymus DNA, the copper(II) and nickel(II) derivatives show prominent negative circular dichroism (CD) features and large red shifts and hypochromicity of the Soret absorption band characteristic of GC specificity, as demonstrated with the synthetic polymer. The other metal derivatives show prominent positive induced visible CD features with small red shifts and hypochromicity of the absorption bands in the Soret region characteristic of AT specificity. Only the metal-free derivative has a conservative CD spectrum suggesting distribution among GC and AT sites.
- Published
- 1983
- Full Text
- View/download PDF
39. Anticancer activity of metal compounds with superoxide dismutase activity.
- Author
-
Oberley LW, Leuthauser SW, Pasternack RF, Oberley TD, Schutt L, and Sorenson JR
- Subjects
- Animals, Carcinoma, Ehrlich Tumor drug therapy, Female, Mice, Mice, Inbred CBA, Antineoplastic Agents therapeutic use, Metals therapeutic use, Superoxide Dismutase therapeutic use
- Published
- 1984
- Full Text
- View/download PDF
40. Kinetics of hemoprotein reduction and interprotein heme transfer.
- Author
-
Pasternack RF, Gibbs EJ, Mauk AG, Reid LS, Wong NM, Kurokawa K, Hashim M, and Muller-Eberhard U
- Subjects
- Dithionite pharmacology, Hemopexin metabolism, Humans, Kinetics, Mathematics, Oxidation-Reduction, Protein Binding, Serum Albumin metabolism, Spectrophotometry, Heme metabolism, Hemeproteins metabolism
- Abstract
The transfer of hemin from one protein to another is an event biologically important for the conservation of heme iron. Hemin entering the circulation (or added to serum) is mainly bound by albumin and then transferred to hemopexin [Morgan, W.T., Liem, H.H., Sutor, R.P., & Muller-Eberhard, U. (1976) Biochim. Biophys. Acta 444, 435-445], and we are now investigating which mechanisms may be operative in enhancing this process. The presence of imidazole has been demonstrated to accelerate hemin transfer from albumin to hemopexin [Pasternack, R.F., Gibbs, E.J., Hoeflin, E., Kosar, W.P., Kubera, G., Skowronek, C. A., Wong, N.M., & Muller-Eberhard, U. (1983) Biochemistry 22, 1753-1758]. The present work is an examination of the effect of the reduction of albumin-bound hemin on the rate of its transfer to hemopexin. Hemin (HmIII., ferriprotoporphyrin IX) was reduced to HmII (ferroprotoporphyrin IX) by the addition of sodium dithionite under argon. The reduction kinetics of HmIII to HmII were studied separately in the two complexes: with human serum albumin (HSA), which binds up to 20 mol of heme/mol (the first mole with K congruent to 10(8)), and with hemopexin (HHx), which binds heme equimolarly (K congruent to 10(13)). The rate of reduction of HmIII to HmII on HSA was first order over several half-lives and linearly dependent on [S2O4(2-)]1/2. At [HSA]0/[HmIII] = 3, the kobsd was (5 X 10(-3) + 0.75[S2O4(2-)]1/2, and with [HSA]/[HmIII] approximately 25, the kobsd was (2 X 10(-3)) + 0.25[S2O4(2-)]1/2. The reduction of HmIII to HmII on human hemopexin (HHx) is much more rapid with kobsd = (2.5 X 10(3))[S2O4(2-)]1/2.(ABSTRACT TRUNCATED AT 250 WORDS)
- Published
- 1985
- Full Text
- View/download PDF
41. Model compounds with superoxide dismutase activity: iron porphyrins and other iron complexes [proceedings].
- Author
-
Halliwell B and Pasternack RF
- Subjects
- Models, Biological, Organometallic Compounds, Iron, Metalloporphyrins, Superoxide Dismutase metabolism
- Published
- 1978
- Full Text
- View/download PDF
42. Molecular complexes of nucleosides and nucleotides with a monomeric cationic porphyrin and some of its metal derivatives.
- Author
-
Pasternack RF, Gibbs EJ, Gaudemer A, Antebi A, Bassner S, De Poy L, Turner DH, Williams A, Laplace F, Lansard MH, Merienne C, and Perree-Fauvet M
- Subjects
- Cations chemistry, Molecular Structure, Metalloporphyrins chemistry, Nucleosides chemistry, Nucleotides chemistry, Porphyrins chemistry
- Abstract
Tetrakis(4-7V-methylpyridyl)porphine (H2TMpyP) and a number of its metal derivatives interact extensively with mononucleotides and mononucleosides in aqueous solution. The complexes formed are of a stacking-type involving extensive overlap of the -systems of the porphyrin and purine or pyrimidine bases. Coulombic attractions help stabilize the complexes but there is no evidence for ligation of the bases to axial sites of the metalloporphyrins. Stability constants determined via NMR and spectrophotometric titrations are larger for purine bases than pyrimidines with a given porphyrin derivative. More dramatic influences on stability result from changing porphyrins. Porphyrins having no axial ligands (e.g., metal-free copper(II), palladium(II), and nickel(II) derivatives) or one axial ligand (Zn(II)) produce much larger interactions with a given nucleotide or nucleoside than do metalloporphyrins having two axial ligands (e.g., Mn(III), Fe(III), or Co(III)). The kinetics of the interaction of H2TMpyP with 2'-deoxyadenosine S'-monophosphate (dAMP) were studied via the laser raman temperature-jump method. The measured rate constants are consistent with a simple stacking model for the interaction.
- Published
- 1985
- Full Text
- View/download PDF
43. Interaction of porphyrins and metalloporphyrins with nucleic acids.
- Author
-
Gibbs EJ and Pasternack RF
- Subjects
- Animals, Cattle, Metalloporphyrins metabolism, Nucleic Acids metabolism, Porphyrins metabolism
- Abstract
Differences in the interpretation of the details of the binding of porphyrins and metalloporphyrins to nucleic acids do exist, in part arising from the fact that different experimental techniques require different experimental conditions. For example, uv/vis absorption and CD spectroscopy use mumol/L and 10 to 100 mumol/L concentrations of drug and polymer respectively; whereas NMR uses mmol/l concentrations, increasing the likelihood of DNA aggregation. Differences in solvent conditions can have a profound effect on binding; changes in binding mode with changes in ionic strength have been observed for two of the porphyrins studied. At high levels of drug load the nucleic acid conformation may be changing and/or new modes of binding may become important. Thus, care must be taken when comparing data at different experimental conditions. At the same time that these various complexities for binding make comparison difficult it is precisely because of such complexities that these porphyrins are such sensitive probes of nucleic acid structure and dynamics. It may well be the diversity of binding of these porphyrins that will provide a variety of avenues for therapeutic strategies. It is certainly true that obtaining a complete binding picture for these porphyrins will require extended studies using a variety of techniques and experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
- Published
- 1989
44. Substitution reactions of a water-soluble metalloporphyrin with azide and 1,1,3,3-tetramethyl-2-thiourea.
- Author
-
Pasternack RF, Gillies BS, and Stromsted JP
- Subjects
- Chemical Phenomena, Chemistry, Cobalt, Kinetics, Ligands, Oxidation-Reduction, Thermodynamics, Azides, Metalloporphyrins, Thiourea analogs & derivatives
- Abstract
The substitution reactions of tetrakis-(4-N-methylpyridyl)porphinecobalt (III) (CoIIITMpyP) with azide and with 1,1,3,3-tetramethyl-2-thiourea (TMTU) have been studied as a function of pH at 25 degrees and an ionic strength of 0.5 M. The mechanistic pathway proposed for thiocyanate [1] and pyridine [2] is applicable to these ligands as well once allowance is made for two attacking forms of azide, N3- and HN3. A TMTU axial substituent has about the same influence on the rate of further ligand substitution as does SCN- and a much larger influence than does azide. Similar behavior between bound SCN- and bound TMTU is also shown in electron-transfer reactions with Ru(NH3)62+. Whereas both sulfur-containing ligands enhance the rate relative to the diaquo complex, the azide complex undergoes reduction an order of magnitude more slowly than does the diaquo complex.
- Published
- 1978
- Full Text
- View/download PDF
45. Interactions of porphyrins with purified DNA and more highly organized structures.
- Author
-
Gibbs EJ, Maurer MC, Zhang JH, Reiff WM, Hill DT, Malicka-Blaszkiewicz M, McKinnie RE, Liu HQ, and Pasternack RF
- Subjects
- Animals, Chromatin metabolism, Gold, Kinetics, Liver metabolism, Male, Metalloporphyrins, Rats, Rats, Inbred Strains, Spectrophotometry, Spectrum Analysis, DNA, Polydeoxyribonucleotides, Porphyrins
- Abstract
Studies of the solution properties of gold(III)tetrakis(4-N-methylpyridyl) porphine and its DNA binding characteristics have been conducted utilizing uv/vis absorption spectroscopy, circular dichroism (CD), Mossbauer spectroscopy, and temperature-jump relaxation techniques. These studies indicate that over the concentration range considered this water soluble gold(III) porphyrin does not aggregate, binds axial ligands only weakly with a preference for soft Lewis bases, and is capable of intercalation into nucleic acids of appropriate base pair content. The interaction of this and several other porphyrins with the synthetic polynucleotide poly(dA-dC).poly(dT-dG) has been studied. Spectroscopic signatures for intercalation were found for those derivatives not having axial ligands. Intercalation into chromatin in vitro can also occur with those porphyrins and metalloporphyrins which do not have axial ligands. Finally, studies utilizing microinjection techniques indicate that once within the cell, tetrakis(4-N-methylpyridyl)porphine tends to localize in the nucleus.
- Published
- 1988
- Full Text
- View/download PDF
46. The influence of ionic strength on the binding of a water soluble porphyrin to nucleic acids.
- Author
-
Pasternack RF, Garrity P, Ehrlich B, Davis CB, Gibbs EJ, Orloff G, Giartosio A, and Turano C
- Subjects
- Animals, Cattle, Circular Dichroism, Intercalating Agents, Nucleic Acid Conformation, Osmolar Concentration, Solubility, Spectrophotometry, Thymus Gland, DNA, Polydeoxyribonucleotides, Porphyrins
- Abstract
The ionic strength dependences of the binding of tetrakis (4-N-methylpyridyl)porphine (H2TMpyP) to poly(dG-dC) and calf thymus DNA have been determined. For the former system the results are typical of other intercalators, i.e., a plot of log K vs log [Na+] is linear albeit with a slope which suggests that the "effective charge" of the porphyrin is closer to two than the formal charge of +4. For calf thymus DNA, the binding profile is not completely compatible with the predictions of condensation theory. Whereas the avidity of binding does decrease with increasing [Na+] as predicted, of greater interest is the relocation of the porphyrin from GC-rich regions to AT-rich regions as the ionic strength increases.
- Published
- 1986
- Full Text
- View/download PDF
47. Kinetics of the interaction of hemin liposomes with heme binding proteins.
- Author
-
Cannon JB, Kuo FS, Pasternack RF, Wong NM, and Muller-Eberhard U
- Subjects
- Humans, Kinetics, Lipid Bilayers, Mathematics, Molecular Conformation, Serum Albumin metabolism, Heme metabolism, Liposomes, Phosphatidylcholines, Receptors, Cell Surface metabolism
- Abstract
As a model for the transport of hemin across biological membranes, sonicated phosphatidylcholine liposomes with incorporated hemin were characterized. The interaction of the hemin liposomes with the heme binding proteins albumin, apomyoglobin, and hemopexin was examined as a function of liposome charge and cholesterol content. In all cases, there was an almost complete transfer of hemin from liposome to protein; a rapid phase and a slow phase were observed for the transfer. For negatively charged liposomes (with 11% dicetyl phosphate), the rapid and slow phases showed observed rates of transfer of ca. 2 and 0.01 s-1, respectively, for all three proteins. The presence of cholesterol in the liposomes decreased the observed rates by a factor of 2, and positively charged liposomes (with 11% stearylamine) showed about one-fifth the observed rates of negatively charged liposomes. The observed rates were independent of protein concentration, indicating that the rate-determining step is hemin efflux from the lipid bilayer. The hemin interaction with the phospholipid bilayer is suggested to be primarily hydrophobic with some electrostatic character. The two phases are suggested to arise from two different populations of hemin within the liposomes and are interpreted as arising from two different orientations of hemin within the bilayer.
- Published
- 1984
- Full Text
- View/download PDF
48. Self-assembly of porphyrins on nucleic acid templates.
- Author
-
Gibbs EJ, Tinoco I Jr, Maestre MF, Ellinas PA, and Pasternack RF
- Subjects
- Chemical Phenomena, Chemistry, Physical, Circular Dichroism, Nucleic Acid Conformation, Sodium Chloride, Spectrum Analysis, Nucleic Acids, Porphyrins
- Abstract
The cis and trans isomers of dicationic bis(4-N-methylpyridyl)diphenylporphine show a much greater tendency to aggregate than similar tetracationic porphyrins. Upon binding to nucleic acids these aggregating dicationic porphyrins form long-range structures on the polymer template giving intense circular dichroism signals whose profile reports the helical sense of the DNA.
- Published
- 1988
- Full Text
- View/download PDF
49. The interaction of some water-soluble porphyrins and metalloporphyrins with human serum albumin.
- Author
-
Parr GR and Pasternack RF
- Subjects
- Binding Sites, Hemin, Metalloporphyrins, Protein Binding, Spectrophotometry, Porphyrins, Serum Albumin
- Published
- 1977
- Full Text
- View/download PDF
50. Interactions of water soluble porphyrins with Z-poly(dG-dC).
- Author
-
Pasternack RF, Sidney D, Hunt PA, Snowden EA, and Gibbs EJ
- Subjects
- Circular Dichroism, Kinetics, Nucleic Acid Conformation, Polydeoxyribonucleotides, Porphyrins
- Abstract
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.
- Published
- 1986
- Full Text
- View/download PDF
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