Non-covalent assemblies of negatively charged boronated porphyrins with different cationic moieties

A unique approach to non-covalent electron and energy transfer is described that is based on the formation of salt bridges between oppositely charged porphyrin units. A new class of electrostatically linked dimeric and pentameric porphyrins was synthesized by interaction of novel anionic boron containing porphyrins such as 5-(benzamidodecahydro-closo-dodecaborate)-10,15,20-triphenylporphyrin (N1) and meso-tetrakis-benzamidodecahydro-closo-dodecaborate)porphyrin (N2) and a variety of cationic meso-tetraarylporphyrin units. A bipyridine linked dimer (N1 · bpy · N1) was also prepared by employing N,N′-dimethyl-4,4′-bipyridinium (bpy) as a spacer between two mono-anionic species. A quinone-porphyrin dyad was also prepared for electron or energy transfer demonstration. All the synthesized assemblies were characterized by NMR, IR, UV-Vis, and mass spectroscopy. Significant spectral changes occurred in the absorption spectra of these non-covalent porphyrin assemblies compared to those of the reference monomers, indicating the presence of electronic interaction between the adjacent porphyrin units. Resonance light scattering was also used to study the formation of these assemblies in solution.     

Noncovalent functionalization of single-walled carbon nanotubes with water-soluble porphyrins

We have employed water-soluble porphyrin molecules [meso-(tetrakis-4-sulfonatophenyl) porphine dihydrochloride] to solubilize single-walled carbon nanotubes (SWNTs), resulting in aqueous solutions that are stable for several weeks. The porphyrin-nanotube complexes have been characterized with absorption and fluorescence spectroscopy and with AFM. We find that the porphyrin/SWNT interaction is selective for the free base form, and that this interaction stabilizes the free base against protonation to the diacid. Under mildly acidic conditions nanotube-mediated J-aggregates form, which are unstable in solution and result in precipitation of the nanotubes over the course of a few days. Porphyrin-coated SWNTs can be precisely aligned on hydrophilic poly(dimethylsiloxane) (PDMS) surfaces by combing SWNT solution along a desired direction and then transferred to silicon substrates by stamping. Parallel SWNT patterns have been fabricated in this manner.     

Electrochemistry of porphyrins and related macrocycles

The electrochemistry of metallomacrocycles is known to depend on a variety of factors, some of which are related to the nature of the macrocycle, some to the central metal ion and some to the solution conditions. This present paper presents a brief overview of metalloporphyrin and metallocorrole redox reactivity while outlining the most important structural factors which influence the reversible half-wave potentials for oxidation or reduction of these complexes in non-aqueous media. Electronic Publication     

Selective interactions of cationic porphyrins with G-quadruplex structures

G-quadruplex DNA presents a potential target for the design and development of novel anticancer drugs. Because G-quadruplex DNA exhibits structural polymorphism, different G-quadruplex typologies may be associated with different cellular processes. Therefore, to achieve therapeutic selectivity using G-quadruplexes as targets for drug design, it will be necessary to differentiate between different types of G-quadruplexes using G-quadruplex-interactive agents. In this study, we compare the interactions of three cationic porphyrins, TMPyP2, TMPyP3, and TMPyP4, with parallel and antiparallel types of G-quadruplexes using gel mobility shift experiments and a helicase assay. Gel mobility shift experiments indicate that TMPyP3 specifically promotes the formation of parallel G-quadruplex structures. A G-quadruplex helicase unwinding assay reveals that the three porphyrins vary dramatically in their abilities to prevent the unwinding of both the parallel tetrameric G-quadruplex and the antiparallel hairpin dimer G-quadruplex DNA by yeast Sgs1 helicase (Sgs1p). For the parallel G-quadruplex, TMPyP3 has the strongest inhibitory effect on Sgs1p, followed by TMPyP4, but the reverse is true for the antiparallel G-quadruplex. TMPyP2 does not appear to have any effect on the helicase-catalyzed unwinding of either type of G-quadruplex. Photocleavage experiments were carried out to investigate the binding modes of all three porphyrins with parallel G-quadruplexes. The results reveal that TMPyP3 and TMPyP4 appear to bind to parallel G-quadruplex structures through external stacking at the ends rather than through intercalation between the G-tetrads. Since intercalation between G-tetrads has been previously proposed as an alternative binding mode for TMPyP4 to G-quadruplexes, this mode of binding, versus that determined by a photocleavage assay described here (external stacking), was subjected to molecular dynamics calculations to identify the relative stabilities of the complexes and the factors that contribute to these differences. The DeltaG(o) for the external binding mode was found to be driven by DeltaH(o) with a small unfavorable TDeltaS(o) term. The DeltaG(o) for the intercalation binding model was driven by a large TDeltaS(o) term and complemented by a small DeltaH(o) term. One of the main stabilizing components of the external binding model is the energy of solvation, which favors the external model over the intercalation model by -67.94 kcal/mol. Finally, we propose that intercalative binding, although less favored than external binding, may occur, but because of the nature of the intercalative binding, it is invisible to the photocleavage assay. This study provides the first experimental insight into how selectivity might be achieved for different G-quadruplexes by using structural variants within a single group of G-quadruplex-interactive drugs.     

Synthesis and characterization of cationic iodonium macrocycles

A synthetic strategy for the high-yield preparation of iodonium containing macrocycles such as rhomboids, a square, and a pentagon is described, with the long-term objective of preparing iodonium compounds for potential molecular electronics applications. Two cationic rhomboid shaped molecules were prepared for the first time (55-70%) by the treatment of compounds 11 and 12a or 12b with Me3SiOTf. The reaction of dication 8 with 6 in the presence of Me3SiOTf gave an iodonium containing molecular square in 70% yield. In addition, a pentagon-shaped macromolecule was prepared in 60% yield. These iodonium-containing charged macromolecules were characterized by multinuclear NMR, mass spectrometry, and physical means.     

Equipping metallo-supramolecular macrocycles with functional groups: assemblies of pyridine-substituted urea ligands

A series of di-(m-pyridyl)-urea ligands were prepared and characterized with respect to their conformations by NOESY experiments and crystallography. Methyl substitution in different positions of the pyridine rings provides control over the position of the pyridine N atoms relative to the urea carbonyl group. The ligands were used to self-assemble metallo-supramolecular M(2)L(2) and M(3)L(3) macrocycles which are generated in a finely balanced equilibrium in DMSO and DMF according to DOSY NMR experiments and ESI FTICR mass spectrometry. Again, crystallography was used to characterize the assemblies. Methyl substitution in positions next to the pyridine nitrogen prevents coordination, while the other ligands form small metallo-supramolecular macrocycles. The incorporated urea carbonyl groups provide hydrogen bonding sites which converge towards the center of the assemblies.     

Indirect spectrophotometric determination of trace cyanide with cationic porphyrins

Three highly sensitive methods for the determination of cyanide have been developed, based on the fact that the complexation of silver ions with three cationic porphyrins, 5,10,15,20-tetrakis-(1-methyl-2-pyridinio)porphine [T(2-MPy)P], 5,10,15,20-tetrakis(1-methyl-3-pyridinio)porphine [T(3-MPy)P] and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphine [T(4-MPy)P], in alkaline media is inhibited by cyanide and the decrease in absorbance of the silver(II) complex is proportional to the cyanide concentration. Sensitivities of the procedures developed are 0.133, 0.126 and 0.234 ng/cm(2), respectively for an absorbance of 0.001. Cadmium(II), copper(II), mercury(II), zinc(II), iodide and sulfide interfere with the cyanide determination. One of the proposed methods was applied to the determination of cyanide in waste-water samples, with satisfactory results.     

Synthesis and aggregation of cationic porphyrins

Tetra(N-R-pyridinium-4-yl)porphyrin and tetra(N-R-pyridinium-3-yl)porphyrin derivatives were synthesized with R = 3, 6, and 8 carbon alkene, alcohol and carboxylic acid chains. Self-aggregation of these systems was studied at I = 0.1 using visible spectroscopy. N-Alkyl chain length and functionality were determined to play the dominant role in aggregation of the cationic porphyrins. Position of peripheral charge (meta vs. para) also influenced spectral changes and the nature of the aggregate.     

Noncovalent binding between fullerenes and protonated porphyrins in the gas phase

Noncovalent interactions between protonated porphyrin and fullerenes (C?? and C??) were studied with five different meso-substituted porphyrins in the gas phase. The protonated porphyrin-fullerene complexes were generated by electrospray ionization of the porphyrin-fullerene mixture in 3:1 dichloromethane/methanol containing formic acid. All singly protonated porphyrins formed the 1:1 complexes, whereas porphyrins doubly protonated on the porphine center yielded no complexes. The complex ion was mass-selected and then characterized by collision-induced dissociation with Xe. Collisional activation exclusively led to a loss of neutral fullerene, indicating noncovalent binding of fullerene to protonated porphyrin. In addition, the dissociation yield was measured as a function of collision energy, and the energy inducing 50% dissociation was determined as a measure of binding energy. Experimental results show that C?? binds to the protonated porphyrins more strongly than C??, and electron-donating substituents at the meso positions increase the fullerene binding energy, whereas electron-withdrawing substituents decrease it. To gain insight into π-π interactions between protonated porphyrin and fullerene, we calculated the proton affinity and HOMO and LUMO energies of porphyrin using Hartree-Fock and configuration interaction singles theory and obtained the binding energy of the protonated porphyrin-fullerene complex using density functional theory. Theory suggests that the protonated porphyrin-fullerene complex is stabilized by π-π interactions where the protonated porphyrin accepts π-electrons from fullerene, and porphyrins carrying bulky substituents prefer the end-on binding of C?? due to the steric hindrance, whereas those carrying less-bulky substituents favor the side-on binding of C??.     

Noncovalent assemblies of CdSe semiconductor quantum dots and an amphiphilic long-chain meso-arylporphyrin

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Supramolecular systems based on cationic surfactants and amphiphilic macrocycles

The effect of the structure of mono- and dicationic surfactants and amphiphilic calixarenes on their aggregation properties, aggregate morphology, and catalytic activity in reactions of nucleophilic substitution in esters is analyzed.     

Noncovalent trapping and stabilization of dinuclear ruthenium complexes within a coordination cage

A dinuclear ruthenium complex, [(η(5)-indenyl)Ru(CO)(2)](2), was noncovalently enclathrated within a self-assembled coordination cage. In the cavity, rapid cis-trans isomerization and ligand exchange between the terminal and bridging carbonyls were suppressed, and only the carbonyl-bridged cis configuration was observed by X-ray crystallographic analysis.     

Photocycloreversion-reaction of a cage molecule and related cyclobutanes with cationic sensitizers

Irradiation of 1, 2, or 3 in acetonitrile in the presence of cationic sensitizer 7 or 8 afforded the cycloreversion product 4, 5 or 6, respectively. A wide range in quantum yields were found and these were dependent on the substrates and sensitizers.     

Acid-base properties and DNA-binding of water soluble N-confused porphyrins with cationic side-arms

Water soluble N-confused porphyrins, 5,10,15,20-tetrakis(alpha-pyridinio-p-tolyl)-2-aza-21-carbaporphyrin (pPyNCP) and its N-methyl derivative, 2-N-methyl-5,10,15,20-tetrakis(alpha-pyridinio-p-tolyl)-2-aza-21-carbaporphyrin (NMe-pPyNCP), have been synthesized by introducing cationic side-arms at the meso-positions of N-confused porphyrin. Their acid-base properties (pK(1-4)) and DNA-binding ability in aqueous solutions were elucidated in comparison with the corresponding porphyrin derivative. Photophysical behaviors of pPyNCP were largely influenced by buffer compositions and DNA structures, whereas NMe-pPyNCP is considerably robust against these factors. In addition, significant enhancement of the fluorescence was observed with NMe-pPyNCP by the addition of DNA. The unique properties of pPyNCP and NMe-pPyNCP stem from the confused pyrrole rings in the macrocycle.     

Photophysical properties and antibacterial activity of meso-substituted cationic porphyrins

A series of derivatives of 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphine, where one N-methyl group was replaced by a hydrocarbon chain ranging from C6 to C22, were characterized for their photophysical and photosensitizing properties. The absorption and fluorescence features of the various compounds in neutral aqueous solutions were typical of largely monomeric porphyrins, with the exception of the C22 derivative, which appeared to be extensively aggregated. This was confirmed by the very low triplet quantum yield and lifetime of the C22 derivative as compared with 0.2-0.7 quantum yields and 88-167 micros lifetimes for the other porphyrins. The photophysical properties and photosensitizing activity toward N-acetyl-L-tryptophanamide of the C22 porphyrin became comparable to those typical of the other derivatives in 2% aqueous sodium dodecyl sulfate, where the C22 compound is fully monomerized. All the porphyrin derivatives exhibited at micromolar concentrations photoinactivation activity against both Staphylococcus aureus and Escherichia coli, even though the gram-negative bacteria were markedly less photosensitive. The photosensitizing efficiency was influenced by (1) the amount of cell-bound porphyrin, which increased with increasing length of the hydrocarbon chain; and (2) the tendency to undergo partial aggregation in the cell, which seems to be especially important for the C22 derivative.     

1,3,5,7-Tetrasubstituted adamantanes as frameworks in the design of assemblies of porphyrin macrocycles

A new strategy for the synthesis of adamantane-containing polyphenols of a porphyrin series has been suggested on the basis of Suzuki–Miyaura reaction between 1,3,5,7-tetrakis(4'-iodophenyl)adamantane and a monoboryl derivative of substituted porphyrin. The synthesis of this porphyrin assembly on the adamantane core followed by chemical transformations of this compound has provided a possibility to synthesize the corresponding polyphenol derivative. The latter has been used in the development of positive photoresists for nanolithography with exposure to radiation at a wavelength 13.5 nm capable of producing topological structures with a resolution of 16 nm.     

Long-range assemblies on poly(dG-dC)2 and poly(dA-dT)2: phosphonium cationic porphyrins and the importance of the charge

The present paper describes synthesis and spectroscopic properties of novel cationic meso-tetraphenylporphyrins bearing two (trans) (P2) or three (P3) triphenylphosphonium substituents. The porphyrin aggregation in aqueous solutions is discussed in detail. Porphyrin binding to and self-organization onto long-range assemblies on poly(dA-dT)2 or poly(dG-dC)2 were probed by combination of absorption, fluorescence, circular dichroism (CD), transient and resonance light-scattering (RLS) techniques. The higher hydrophobicity of P2 is manifested by more extensive self-organization. Induced CD and intensive RLS indicate binding to the chiral environment on the nucleic acids exterior and exciton coupling between adjacent porphyrin moieties. The CD spectra of P2 on poly(dG-dC), and poly(dA-dT)2 suggest that the binding geometry is essentially independent of the base sequence. The fluorescence lifetime of about 4 ns was attributed to the long-range assembly. In the case of P3 the distinctly different CD spectra induced by GC or AT base-pair regions reveal that the number of the substituents determines how closely the porphyrin can approach the specific electronic environment on the nucleic acid exterior. The fluorescence lifetime of the P3 assembly is about 2 ns.     

Synthesis and DNA binding of novel water-soluble cationic methylcobalt porphyrins

Organocobalt derivatives of tetracationic water-soluble porphyrins are difficult to prepare via the typical reductive alkylation of the Co(II)(por) (porH(2) = porphyrin ligand). None have been reported. The problem may arise because the porphyrin core is made relatively electron poor by the positively charged peripheral groups. We have circumvented this problem by using the [Co(III)(NH(3))(5)CH(3)](2+) reagent, which inserts the Co(III)-CH(3) moiety directly into porH(2) in water under basic conditions. The method afforded two new [CH(3)Co(por)](4+) derivatives, [CH(3)CoTMpyP(4)](4+) and [CH(3)CoTMAP](4+), where [TMpyP(4)](4+) and [TMAP](4+) are the coordinated, NH-deprotonated forms of meso-tetrakis(N-methyl-4-pyridiniumyl)porphyrin and meso-tetrakis(N,N,N-trimethylaniliniumyl)porphyrin, respectively. The binding of the two new [CH(3)Co(por)](4+) cations to DNA and to the synthetic DNA polymers [poly(dA-dT)](2) and [poly(dG-dC)](2) was studied. Using published criteria by which changes in DNA viscosity and in the visible and CD spectra in the Soret region can be used to assess DNA binding, we conclude that both are outside binders. A large hypochromicity of the Soret bands of the [CH(3)Co(por)](4+) cations observed upon outside binding to DNA may indicate a high degree of self-stacking. The visible absorption and CD spectra of the [CH(3)Co(por)](4+) cations in the presence of 1:1 mixtures of [poly(dA-dT)](2) and [poly(dG-dC)](2) are nearly identical to those with [poly(dA-dT)](2) alone and are very different from those of [poly(dG-dC)](2) alone. Thus, both cations show a high preference for outside binding at AT-rich over GC-rich DNA sites. Upon binding of each of the [CH(3)Co(por)](4+) cations to all of the DNA polymers, the Soret bands exhibit blue shifts, whereas the Soret bands of the corresponding [(H(2)O)(2)Co(por)](5+) cations exhibit red shifts. The blue shifts strongly suggest that the [CH(3)Co(por)](4+) cations, particularly [CH(3)CoTMAP](4+), become five-coordinate forms to some extent on DNA binding; this result is the first good evidence for the presence at equilibrium of five-coordinate CH(3)Co(III)(N(4)) forms in water.     

Spectrophotometric and analogue derivative spectrophotometric determination of ultramicro amounts of cadmium with cationic porphyrins

alpha,beta,gamma,delta-Tetrakis(1-methylpyridinium-3-yl)porphine [T(3-MPy)P] and alpha,beta,gamma,delta-tetrakis(1-methylpyridinium-4-yl)porphine [T(4-MPy)P] have been found to react rapidly with cadmium to give coloured complexes in weakly alkaline media at room temperature. Simple and practical methods for the determination of cadmium at ng/ml levels by conventional and analogue derivative spectrophotometry have been proposed. The analogue method gives higher sensitivity. T(3-MPy)P gives higher sensitivity than T(4-MPy)P. The interference of various foreign cations and anions has also been examined and in many cases eliminated or reduced. Adsorption of the porphyrins and their cadmium complexes onto the glassware, which is usually observed under the conditions of reaction and causes significant errors in the determination, can be suppressed almost completely by addition of fairly large amounts of a salt such as sodium chloride.