Preprogramming of Porphyrin−Nucleic Acid Assemblies via Variation of the Alkyl/Aryl Substituents of Phosphonium Tetratolylporphyrins

The structural features of poly(dG-dC).poly(dG-dC) at complexation with some porphyrins

The binding peculiarities of the water-soluble meso-tetra-(4N-hydroxyethylpyridyl) porphyrin (H₂TOEtPyP4) and its Cu- and Co-derivatives (CuTOEtPyP4 and CoTOEtPyP4) with synthetic double-stranded alternating polynucleotide poly(dG-dC).poly(dG-dC) were investigated by UV/Vis absorption and circular dichroism (CD) methods. It was shown that the porphyrins with planar structure such as H₂TOEtPyP4 and CuTOEtPyP4 interact with poly(dG-dC).poly(dG-dC) via intercalation at low relative concentrations (r = [porphyrin]/[polynucleotide]), while at high r - via intercalation and external binding modes. In the case of no planar porphyrin CoTOEtPyP4 complexation occurs only by external binding mode. The binding constant K_b and the exclusion parameter n calculated for H₂TOEtPyP4, CuTOEtPyP4 and CoTOEtPyP4 porphyrins with poly(dG-dC).poly(dG-dC) complexes was 1.50 x10⁷, M^-1 (n = 1.76); 9.29 x10⁷, M^-1 (n = 1.18); and 0.28 x10⁷, M^-1 (n = 2.65) correspondingly. The values of binding parameters for each porphyrin-poly(dG-dC).poly(dG-dC) complexes demonstrated good agreement with the proposed binding models. Communicated by Ramaswamy H. Sarma.

Lipid Membrane Adsorption Determines Photodynamic Efficiency of β-Imidazolyl-Substituted Porphyrins

Photosensitizers (PSs) represent a group of molecules capable of generating reactive oxygen species (ROS), such as singlet oxygen (SO); thus, they are considered to be promising agents for anti-cancer therapy. The enhancement of the photodynamic efficiency of these compounds requires increasing the PS activity in the cancer cell milieu and exactly at the target cells. In the present work, we report the synthesis, lipid membrane binding and photodynamic activity of three novel cationic PSs based on β-imidazolyl-substituted porphyrin and its Zn(II) and In(III) complexes (1H2, 1Zn and 1In). Comparison of the behavior of the investigated porphyrins at the bilayer lipid membrane (BLM) demonstrated the highest adsorption for the 1In complex and the lowest one for 1Zn. The photodynamic efficiency of these porphyrins was evaluated by determining the oxidation rate of the styryl dye, di-4-ANEPPS, incorporated into the lipid membrane. These rates were proportional to the surface density (SD) of the porphyrin molecules at the BLM and were roughly the same for all three porphyrins. This indicates that the adsorption of these porphyrins at the BLM determines their photodynamic efficiency rather than the extinction or quantum yield of singlet oxygen.

Tuning photochemical properties of phosphorus(v) porphyrin photosensitizers

Photosensitizing and emission properties of P(v) porphyrins were studied. The nature of the axial ligands, occupying the apical position on the P centre adopting an octahedral coordination geometry, strongly influences singlet oxygen generation and charge transfer and allows switching between the two processes.

Ground and excited state interactions of metalloporphyrin PtTMPyP4 with polynucleotides [poly(dG-dC)]2 and [poly(dA-dT)]2

The ground- and excited-state interactions of Pt(ii) meso-tetrakis(4-N-methylpyridyl)porphyrin (PtTMPyP4) with polynucleotides [poly(dG-dC)]2 and [poly(dA-dT)]2 have been investigated using UV/visible, circular dichroism, and steady-state and time-resolved emission spectroscopy. PtTMPyP4 intercalates into [poly(dG-dC)]2 with K∼ 10(6) M(-1). When bound to [poly(dG-dC)]2 in aerated solution there is a six-fold emission enhancement with 18 nm red-shift in emission maximum. Emission lifetimes are biexponential. In the presence of [poly(dA-dT)]2 at least two distinct groove-binding modes are observed, depending on the binding ratio. In [poly(dA-dT)]2 the emission intensity increases by a maximum factor of 17 with no shift in the emission spectrum. Three exponentials were required for lifetime fitting. The lower extent of emission enhancement in the presence of [poly(dG-dC)]2 suggests that a slow electron transfer may take place to guanine, which is significantly less efficient than that previously observed for PtTMPyP4 in the presence of guanosine 5'-monophosphate (GMP). The results are compared to those previously recorded with free base H2TMPyP4.

Water-soluble porphyrin-phosphonate conjugates as potential photodynamic therapy photosensitizers

Two novel water-soluble porphyrin-phosphonate conjugates were synthesized and characterized. Although both conjugates showed significant potential in photodynamic therapy, the variety of their structure induced the obvious differences in the binding manner with calf thymus DNA, the cytotoxicity and the cellular sublocalization.

Porphyrins bearing quaternary azaaromatic moieties

In this review, porphyrins bearing quaternary azaaromatic moieties are described as follows: firstly those with useful physicochemical properties, then, species showing biological activities and finally, porphyrins bound with fullerenes and with cyclodextrins.

Polyphosphonium polymers for siRNA delivery: an efficient and nontoxic alternative to polyammonium carriers

A water-soluble polyphosphonium polymer was synthesized and directly compared with its ammonium analog in terms of siRNA delivery. The triethylphosphonium polymer shows transfection efficiency up to 65% with 100% cell viability, whereas the best result obtained for the ammonium analog reaches only 25% transfection with 85% cell viability. Moreover, the nature of the alkyl substituents on the phosphonium cations is shown to have an important influence on the transfection efficiency and toxicity of the polyplexes. The present results show that the use of positively charged phosphonium groups is a worthy choice to achieve a good balance between toxicity and transfection efficiency in gene delivery systems.

Triplet-state dynamics of a metalloporphyrin photosensitiser (PtTMPyP4) in the presence of halides and purine mononucleotides

The photophysical properties of Pt(II) meso-tetrakis(4-N-methylpyridyl)porphyrin (PtTMPyP4) have been investigated in the presence of purine mononucleotides using emission and transient UV/visible/near-IR spectroscopy. While both adenosine 5'-monophosphate (AMP) and guanosine 5'-monophosphate (GMP) form 1:1 and 1:2 complexes with PtTMPyP4, the effect on the triplet lifetime is different. With AMP, complexation gives rise to an enhancement of lifetime and quantum yield due to shielding from dissolved oxygen and a slight decrease in the non-radiative decay rate. When complexed with GMP, quenching is observed consistent with photoinduced electron transfer from guanine to triplet-excited PtTMPyP4, due to both dynamic quenching of the porphyrin and to short-lived emission from 1:1 (67 ns) and 1:2 (400 ns) complexes. No charge-separated photoproducts are observed by transient UV/vis/near-IR absorption spectroscopy on the nanosecond timescale, suggesting that rapid reverse electron transfer may prevent type 1 DNA damage.

Transfer of chirality for memory and separation

Transfer of chirality is an intriguing issue worth studying to understand better the origin of life and for possible technological applications. In the last few years we have been working in this area studying the chain of events that begins with induction, reaches a permanent transfer (chiral memory) and extends in some cases to a (quasi-)reversible situation in which induced and permanently memorized chirality coexists. This can happen thanks to a designed blend of thermodynamics and kinetics.

Vibrational and electronic circular dichroism study of the interactions of cationic porphyrins with (dG-dC)10 and (dA-dT)10

The interactions of two different porphyrins, without axial ligands-5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin-Cu(II) tetrachloride (Cu(II)TMPyP) and with bulky meso substituents-5,10,15,20-tetrakis(N,N,N-trimethylanilinium-4-yl)porphyrin tetrachloride (TMAP), with (dG-dC)10 and (dA-dT)10 were studied by combination of vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) spectroscopy at different [oligonucleotide]/[porphyrin] ratios, where [oligonucleotide] and [porphyrin] are the concentrations of oligonucleotide per base-pair and porphyrin, respectively. The combination of VCD and ECD spectroscopy enables us to identify the types of interactions, and to specify the sites of interactions: The intercalative binding mode of Cu(II)TMPyP with (dG-dC)(10), which has been well described, was characterized by a new VCD "marker" and it was shown that the interaction of Cu(II)TMPyP with (dA-dT)10 via external binding to the phosphate backbone and major groove binding caused transition from the B to the non-B conformer. TMAP interacted with the major groove of (dG-dC)10, was semi-intercalated into (dA-dT)10, and caused significant variation in the structure of both oligonucleotides at the higher concentration of porphyrin. The spectroscopic techniques used in this study revealed that porphyrin binding with AT sequences caused substantial variation of the DNA structure. It was shown that VCD spectroscopy is an effective tool for the conformational studies of nucleic acid-porphyrin complexes in solution.

Tetraphenylporphyrin-cobalt(III) bis(1,2-dicarbollide) conjugates: from the solution characteristics to inhibition of HIV protease

Tetraphenylporphyrin conjugates with one (PB1) and four (PB4) cobalt(III) bis(1,2-dicarbollide) substituents were synthesized and the physicochemical and photophysical properties as well as inhibition of HIV-1 protease were described. In methanol, both PB1 and PB4 were monomeric producing the triplet states and singlet oxygen after excitation. The triplet states of PB4 were quickly protonated. Porphyrins exhibited a small decrease of the quantum yields of the singlet oxygen formation (17% for PB4 and 13% for PB1) as compared with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin. On the contrary, no singlet oxygen was detected in aqueous solutions because of strong aggregation. Light scattering and atomic force microscopy (AFM) measurements documented that the behavior of aggregates in aqueous solutions is fairly complex and depends on pH, concentration, and aging. The aggregation started from spherical particles in neutral solutions. In acidic solutions, extended aggregation occurred because of slow protonation of the porphyrin pyrrole nitrogen atoms. Both PB1 and PB4 are new representatives of nonpeptide HIV-1 protease inhibitors. Their activity increased with the increasing number of the cobalt(III) bis(1,2-dicarbollide) substituents and was characterized with the IC50 values of 290+/-44 nM for PB1 and 77+/-13 nM for PB4.

Synthesis, characterization, and saccharide binding studies of bile acid-porphyrin conjugates

Synthesis and characterization of bile acid-porphyrin conjugates (BAPs) are reported. Binding of saccharides with BAPs in aqueous methanol was studied by monitoring changes in the visible absorption spectral of the porphyrin-moieties. Although these studies clearly showed absorbance changes, suggesting quite high if non-selective binding, the mass spectral studies do not unambiguously support these results.

Ground-state interactions of spermine-substituted naphthalimides with mononucleotides

Water soluble spermine, spermine-naphthalimide, and pyridinium-substituted 1,8-naphthalimide derivatives have been synthesized as nucleotide-specific binding agents. Both mono- and bifunctionalized spermine compounds were studied. The photophysical properties of each compound were studied by using time-resolved and steady-state fluorescence and absorption spectroscopies. The fluorescence decay of the mononaphthalimides was adequately fit to a single exponential decay, and in all cases, the lifetime (2.4 ns) was independent of the imide substitutent. In the case of the bisnaphthalimide, emission from both the monomer and ground-state dimer forms was observed. The fluorescence quantum yield of the monomer (0.03) was significantly smaller than that of the mononaphthalimides (0.27). The dimer emission was red-shifted relative to that of the monomer. The singlet-state lifetime of the dimer was found to be 20 ns. In all cases, only absorption from the triplet excited state was observed, indicating no evidence of a naphthalimide radical anion from dimer excitation. The ground-state interactions of the naphthalimides with four nucleotides were investigated. Nucleotide selectivity was evaluated by determining their individual binding constants (Keq). The association constants were measured by using absorption, time-resolved fluorescence, and combined time-resolved and steady-state fluorescence. The equilibrium binding constant was largest for association of the spermine-substituted mononaphthalimide with adenosine monophosphate (Keq=550 M-1) or guanosine monophosphate (Keq=440 M-1). The dimer form of the disubstituted spermine also showed binding constants in excess of 200 M-1 with the purine nucleotides. The association constant for binding of the pyridinium-substituted naphthalimide showed little dependence on the structure of the nucleotide.

Interaction of porphyrins with a dendrimer template: self-aggregation controlled by pH

The interaction between self-aggregated porphyrins such as 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and 5,10,15,20-tetrakis(4-phosphonatophenyl)porphyrin (TPPP), and a generation 5 (G5) PAMAM dendrimer template is governed by minute differences of porphyrin acido-basic properties. While at neutral pH both monomeric TPPS and TPPP form complexes with G5, decreasing pH did not lead to porphyrin ring protonation (pK(a) approximately 5) but rather to the preferential formation of H-aggregates (probably H-dimers), most likely due to protonation of the G5. Upon further acidification of the solution, this face-to-face orientation of the porphyrin units is being converted to edge-to-edge aligned J-aggregates with a tightly defined structure. This process starts by protonation of the porphyrin ring at pH below 2.3 and 2.8 for TPPS and TPPP, respectively. The AFM imaging of porphyrin/G5 nanostructures obtained at pH 0.7 shows the formation of long nanorods of TPPS with partially aggregated G5 and small aggregates of TPPP connected to individual G5 molecules.

Novel cationic transport agents for oligonucleotide delivery into primary leukemic cells

Novel cationic compounds forming complexes with oligodeoxyribonucleotides (ODNs) were prepared, and their ability to transport ODNs into cultured primary leukemic cells was tested. Two cationic porphyrin derivatives (2 and 3) were found to be at least 1 order of magnitude more efficient in this respect than commercially available agents. The ODN transporting capacity of novel compounds was dependent on the magnitude and the nature of their positive charges as well as on the porphyrin/ODN molar ratio. Porphyrin-ODN complexes were internalized into cells, and their dissociation was demonstrated by accumulation of fluorescein isothiocyanate-ODN fluorescence in the nucleus. Importantly, porphyrin 3 significantly protected complexed ODN against degradation and efficiently mediated the specific antisense effect on targeted v-Myb expression, resulting in reproducible growth inhibition of treated cells. Low toxicity, serum compatibility, and water solubility of porphyrin 3 make this compound a promising novel tool for modulation of gene expression in primary leukemic cells.