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Synthesis and characterization of carborane BODIPYs were described. UV and fluorescence spectra were studied. DFT calculations were performed to study the geometrical structures and chemical reactivity descriptors of synthesized compounds.

A multistep general synthetic strategy towards polytopic carboranyl-terminated (semi)clathrochelate metal complexes, based on the template synthesis, transmetallation, amide condensation and 1,3-dipolar cycloaddition reactions, is developed.

A series of new BODIPY conjugates containing maleimide or carborane-succinimide-triazole functional groups were prepared from synthetically available azido-substituted BODIPYs. The structure of new synthesized compounds was characterized by UV-vis, IR, NMR and mass spectrometry. The crystal structures of BODIPY-maleimide conjugates were determined by single crystal X-ray diffraction study. The carborane-containing BODIPYs can be promising agents for photodynamic and boron neutron capture therapy.

Triton B-catalyzed Michael reaction as a green chemistry process was used for the functionalization of carbon- and boron-substituted carboranes with α,β-unsaturated nitriles and esters.

Carborane maleimides were prepared in good yields through the thermal cyclization of maleamic acids prepared by the reaction of 3-amino-o-carborane with maleic or 3-bromomaleic anhydrides, respectively. The selective reactivity of synthesized maleimides towards S-nucleophiles was demonstrated. As a result a series of boronated thiosuccinimide- or thiomaleimide-substituted compounds including boron rich ones was obtained and fully characterized. Furthermore the opportunity of variation with substitution patterns may lead to the development of potential candidates for biological applications or the development of new materials.

Copper-containing agents are promising antitumor pharmaceuticals due to the ability of the metal ion to react with biomolecules. In the current study, we demonstrate that inorganic Cu2+ in the form of oxide nanoparticles (NPs) or salts, as well as Cu ions in the context of organic complexes (oxidation states +1, +1.5 and +2), acquire significant cytotoxic potency (2–3 orders of magnitude determined by IC50 values) in combinations with N-acetylcysteine (NAC), cysteine, or ascorbate. In contrast, other divalent cations (Zn, Fe, Mo, and Co) evoked no cytotoxicity with these combinations. CuO NPs (0.1–1 µg/mL) together with 1 mM NAC triggered the formation of reactive oxygen species (ROS) within 2–6 h concomitantly with perturbation of the plasma membrane and caspase-independent cell death. Furthermore, NAC potently sensitized HCT116 colon carcinoma cells to Cu–organic complexes in which the metal ion coordinated with 5-(2-pyridylmethylene)-2-methylthio-imidazol-4-one or was present in the coordination sphere of the porphyrin macrocycle. The sensitization effect was detectable in a panel of mammalian tumor cell lines including the sublines with the determinants of chemotherapeutic drug resistance. The components of the combination were non-toxic if added separately. Electrochemical studies revealed that Cu cations underwent a stepwise reduction in the presence of NAC or ascorbate. This mechanism explains differential efficacy of individual Cu–organic compounds in cell sensitization depending on the availability of Cu ions for reduction. In the presence of oxygen, Cu+1 complexes can generate a superoxide anion in a Fenton-like reaction Cu+1L + O2 → O2−. + Cu+2L, where L is the organic ligand. Studies on artificial lipid membranes showed that NAC interacted with negatively charged phospholipids, an effect that can facilitate the penetration of CuO NPs across the membranes. Thus, electrochemical modification of Cu ions and subsequent ROS generation, as well as direct interaction with membranes, represent the mechanisms of irreversible membrane damage and cell death in response to metal reduction in inorganic and organic Cu-containing compounds.

Maleimide-containing fluorinated porphyrins and chlorins were prepared based on the reaction of Zn(II) or Ni(II) complexes of 5,10,15,20-tetrakis(4-amino-2,3,5,6-tetrafluorophenyl)porphyrin and chlorin with maleic anhydride. Porphyrin maleimide derivatives were also prepared by the reaction of 5,10,15,20-tetrakis(4-azido-2,3,5,6-tetrafluorophenyl)porphyrinato Zn(II) or Ni(II) with N-propargylmaleimide via the CuAAC click reaction to afford fluorinated porphyrin–triazole–maleimide conjugates. New maleimide derivatives were isolated in reasonable yields and identified by UV–vis, 1H NMR, 19F NMR spectroscopy and mass-spectrometry.

Fluoroalkanesulfonyl bromides, RFSO2Br, RF = CF3, CF2CO2Et, CF2CF2OCH3, were used for addition of fluoroalkyl groups to the double bonds of allylcarboranes. These synthetic transformations were smoothly proceeded in good yields using the copper-catalysis approach to afford a variety of bromofluoroalkyl-containing target molecules. Nucleophilic substitution of the bromo substituent in some prepared compounds was shown to lead to further diverse carborane functionalization.

The structure of PdTPP and ZnTPP molecules have been studied at first time by a combined gas-phase electron diffraction and mass spectrometry (GED/MS) complemented by quantum-chemical calculations. Four conformers have been found in which four phenyl fragments are turned in different directions from their perpendicular position relative to the porphyrin plane. The structures with turned orientation of phenyl fragments demonstrate an energy balance between orbital conjugation of phenyls with porphyrin framework and steric repulsion of the phenyl and pyrrole fragments. Comparison of PdTPP and unsubstituted PdP as well as ZnTPP and ZnP complexes within the framework of NBO analysis shows that characteristics of the M N coordination bond do not practically change when meso-substituents are introduced. In contrast, the Cα-Cm bond lengths at the meso-substituent, the Cα-Cm-Cα bond angle, and the energy of the frontier orbitals are changed significantly. The change in these parameters indicates the electron-donor nature of the phenyl fragments. Strong donor-acceptor interactions between LP(N) and both 4dx2-y2 and 5s AO (Pd) causes a significant transfer of the electron density from the donor atom N on Pd resulting the extremely low effective net charge on the palladium atom and determining the high donor and acceptor properties of PdP and PdTPP complexes.

Boron containing polyhedra (carboranes) are three-dimensional delocalized aromatic systems. These structures have been shown to transport protons through lipid membranes and mitochondria. Conjugation of carboranes to various organic moieties is aimed at obtaining biologically active compounds with novel properties. Taking advantage of 1,2,3-triazoles as the scaffolds valuable in medicinal chemistry, we synthesized 1-(o-carboranylmethyl)-4-pentyl-1,2,3-triazole (c-triazole) and 1-(o-carboranylmethyl)-4-pentyl-1,2,3-triazolium iodide (c-triazolium). Both compounds interacted with model lipid membranes and exhibited a proton carrying activity in planar bilayers and liposomes in a concentration- and pH-dependent manner. Importantly, mechanisms of the protonophoric activity differed; namely, protonation-deprotonation reactions of the triazole and the o-carborane moieties were involved in the transport cycles of c-triazole and c-triazolium, respectively. At micromolar concentrations, c-triazole and c-triazolium stimulated respiration of isolated rat liver mitochondria and depolarized their membrane potential, with c-triazole being more potent. In living K562 (human chronic myelogenous leukemia) cells, both c-triazolium and c-triazole altered the mitochondrial membrane potential as determined by a decreased intracellular accumulation of the potential-dependent dye tetramethylrhodamine ethyl ester. Finally, cell viability testing demonstrated a cytotoxic potency of c-triazolium and, to a lesser extent, of c-triazole against K562 cells, whereas non-malignant fibroblasts were much less sensitive. In all tests, the reference boron-free benzyl-4-pentyl-1,2,3-triazole showed little-to-no effects. These results demonstrated that carboranyltriazoles carry protons across biological membranes, a property potentially important in anticancer drug design.

The enantiomerically pure N- and C-protected derivatives of planar-chiral (3-amino-1,2-dicarba-closo-dodecaboran-1-yl)acetic acid (>99% ee) have first been obtained in good yields via a combination of HPLC separation and synthetic procedures. Assignment of absolute configuration of the carborane fragments has been made based on the X-ray diffraction data of diastereoisomeric derivatives of (S)-amino acids.

A synthetic strategy for obtaining structurally flexible hybrid iron(II) carboranoclatrochelates functionalized with biorelevant groups, based on a combination of a 1,3-dipolar cycloaddition reaction with nucleophilic substitution of an appropriate chloroclathrochelate precursor, was developed. In its first stage, a stepwise substitution of the dichloroclathrochelate precursor with amine N-nucleophiles of different natures in various solvents was performed. One of its two chlorine atoms with morpholine or diethylamine in dichloromethane gave reactive monohalogenoclathrochelate complexes functionalized with abiorelevant substituents. Further nucleophilic substitution of their remaining chlorine atoms with propargylamine in DMF led to morpholine- and diethylamine-functionalized monopropargylamine cage complexes, the molecules of which contain the single terminal C≡C bond. Their “click” 1,3-cycloaddition reactions in toluene with ortho-carborane-(1)-methylazide catalyzed by copper(II) acetate gave spacer-containing di- and tritopic iron(II) carboranoclatrochelates formed by a covalent linking between their different polyhedral(cage) fragments. The obtained complexes were characterized using elemental analysis, MALDI-TOF mass, UV-Vis, 1H, 1H{11B}, 11B, 11B{1H}, 19F{1H} and 13C{1H}-NMR spectra, and by a single crystal synchrotron X-ray diffraction experiment for the diethylamine-functionalized iron(II) carboranoclathrochelate. Its encapsulated iron(II) ion is situated almost in the center of the FeN6-coordination polyhedron possessing a geometry intermediate between a trigonal prism and a trigonal antiprism with a distortion angle φ of approximately 28°. Conformation of this hybrid molecule is strongly affected by its intramolecular dihydrogen bonding: a flexibility of the carborane-terminated ribbed substituent allowed the formation of numerous C–H…H–B intramolecular interactions. The H(C) atom of this carborane core also forms the intermolecular C–H…F–B interaction with an adjacent carboranoclathrochelate molecule. The N–H…N intermolecular interaction between the diethylamine group of one hybrid molecule and the heterocyclic five-membered 1H-[1,2,3]-triazolyl fragment of the second molecule of this type caused formation of H-bonded carboranoclathrochelate dimers in the X-rayed crystal.

Condensation of amino groups in 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin with pentafluorobenzaldehyde resulted in corresponding Schiff bases and was shown to be a convenient route for the preparation of fluorinated porphyrin derivatives. Compounds thus obtained were easily transformed into the corresponding amines using sodium borohydride. Fluorinated carboranyl porphyrins were prepared via the nucleophilic substitution of the para-fluorine atom of pentafluorophenyl-substituted amine porphyrin derivatives with carborane S-nucleophiles. The alternative synthetic route to the fluorinated carboranyl porphyrins included the condensation of para-carboranyl-substituted tetrafluorobenzaldehyde with corresponding meso-aminoporphyrins. All prepared porphyrins were characterized by different spectroscopic techniques such as UV-vis, IR, 1H, 11B, 19F NMR and mass spectra.

New (S)-homocysteine derivatives containing a meta-carborane fragment were synthesized. m-Carboranyl-(S)-homocysteine sulfoxide was obtained as a mixture of diastereoisomers. The reduction of the side-chain carboxy group of N-tert-butoxycarbonyl-(S)-aspartic acid α-tert-butyl ester with sodium tetrahydridoborate was not accompanied by racemization.

CAN-catalyzed reactions between α-ferrocenyl ethanol or ferrocenyl methanol and S-, N- and O-carborane nucleophiles are reported. This approach is an efficient and simple procedure for the preparation of carborane derivatives containing ferrocenyl units. Energy and geometry optimizations of some carboranylthio-, carboranylamino- and carboranyloxy-substituted ferrocenes have been calculated using the density functional theory. A series of new ferrocene-containing carborane 1,2,3-triazoles have been synthesized in good yields through a facile copper-mediated 1,3-dipolar cycloaddition reactions of alkynyl ferrocenes with [(o-carboran-1-yl)methyl]azide. Molecular structure of carborane-substituted ferrocenyl triazole was established by single crystal X-ray diffraction study. Representative examples of all ferrocenyl carboranes prepared were characterized by IR, 1H and 11B NMR spectroscopy.

A chlorin–phorbin dimer with the carborane fragment attached to the dimer via amide bond has been synthesized. The obtained boronated dimer is of interest for a further study as a promising agent for combined application in boron neutron capture and photodynamic therapy of oncological diseases.

A new method for the synthesis of carborane-containing carbonates by the reaction of CO2 with the corresponding epoxides was developed. The reaction can be facilitated by an additional hydroxyl group in the catalyst. The crystal structure of 1-phenyl-2-(1,3-dioxolan-2-onylmethyl)-C2B10H10 was determined by single crystal X-ray diffraction. The carborane-containing carbonates can be considered as precursors for the synthesis of advanced heat- and impact-resistant polycarbonates and agents for boron neutron capture therapy.

9-Substituted 1,2-bis(diphenylphosphanyl)-o-carboranes were synthesized from the corresponding 9-R-o-carboranes (R = I, i-Pr, SMe), and their complexes with chromium, molybdenum, and palladium were obtained. The coordination chemical shifts calculated from the 31P NMR spectra of the complexes and free ligands showed that the substituent at B9 of carborane affects the strength of the ligand-to-metal binding, but the latter is determined to a greater extent by the nature of the metal and its ligand environment.

Local morphological features and piezoelectric properties of films and bulk crystals of ortho-carboranyl derivatives of (S)-asparagine and (S)-glutamine have been investigated at nanoscale by atomic force and piezoresponse force microscopies. Both films and bulk crystals of the studied compounds demonstrated a very high piezoelectric response exceeding that of lithium niobate. The crystal structure has been studied by single crystal X-ray diffraction.

Tetrapyrrolic macrocycles are suitable for a variety of chemical modifications aimed at new agents for binary antitumor treatment and diagnosis. Previously we have reported that the conjugation of one single carborane cage to the chlorin e6 macrocycle, a modification designed for tumor sensitization in photodynamic (PDT) and boron neutron capture (BNCT) therapies, yielded the derivative with a higher photosensitizing potency in the models of transplanted rodent tumors. This effect was mechanistically linked to the localization of the carboranylchlorin in membrane organelles due to the carborane moiety. Further exploring the potential of modified tetrapyrrolic compounds as photoradiosensitizers we synthesized the chlorin derivative carrying four closo-carborane cages (44 boron atoms) and 16 fluorine atoms at the periphery of the macrocycle (fluorinated tetracarboranylchlorin, compound 1). For comparison of the properties of 1, its fluorine free congener (tetracarboranylchlorin 6) was obtained. The water soluble 1 and 6 accumulated preferentially in cells selected for resistance to chemotherapeutic drugs (multidrug resistance and cisplatin resistance) than in the parental non-selected counterparts. Compounds 1 and 6 showed a negligible dark cytotoxicity. In contrast, a monochromatic light illumination of cells loaded with low micromolar concentrations of 1 or 6 triggered rapid (within minutes) photonecrosis as determined by the entry of propidium iodide or SYTOX dyes into the parental as well as into resistant cells. In vivo 1 or 6 (up to 80 mg/kg i.p.) caused no general toxicity in Balb/c or C57BL6 mice. Illumination with a monochromatic light of B16 melanoma transplants in mice injected with 5 mg/kg 1 or 6 caused a significant shrinkage of tumor foci, with no re-growth in 77.8% animals by day 21 post PDT. BNCT on C6 rat glioma xenografts in Balb/c nu/nu mice injected i.p. with 5 mg/kg 1 led to a decrease of tumor foci and cure of animals by day 29 whereas the radiosensitizing potency of 6 was less pronounced. This difference was attributable to a limited intratumoral accumulation of 6. Altogether, an extensive modification of the chlorin macrocycle periphery with polyfluorines and polycarboranes yielded potent and well tolerable compounds for PDT and BNCT.

A series of new carboranyl organosilicon monomers have the potential to be used as high temperature oils, as building blocks in sol-gel processes and as an additive in composites. The versatile and easy preparation of the four polyhedral carboranyl derivatives are based on UV initiated hydrothiolation. The compounds were isolated in good yields (65–95%) and characterized by 1H, 11B, 13C and 29Si NMR, IR spectroscopy, HRMS ESI and elemental microanalysis. Assignment of 1H and 13C NMR spectra was made on the basis of 2D experiments of COSY, HMQC and HMBC.

This paper presents a synthesis of new boron-substituted carborane-carbosilane dendrimers of the zero (G0-4 cages), first (G1-8 cages), third (G3-32 cages), and fifth (G5-128 cages) generations. The structures and purity of the compounds obtained were confirmed by using a set of physicochemical methods of analysis: 1H, 29Si, 13C{1H} and 11B{1H} NMR, IR spectroscopy, and gel permeation chromatography. Their properties were studied by DSC, TGA, DLS and viscometry in solution.

The new sixteen functional carboranyl substituted octasilsesquioxane was obtained and fully characterized by NMR-, IR - spectroscopy and Mass-spectrometry, its molecular and crystalline structure was established by X-ray analysis in single crystal. The thermal behavior of the compound obtained was studied by means of TGA and DSC.

An efficient triflic acid catalyzed regioselective alkylation of 5-R-1H-tetrazoles with readily available allylcarboranes is reported. The suggested synthetic procedure allows the formation of a variety of carboranyl-substituted tetrazoles in a good yield under mild conditions. Transformations of newly synthesized carboranyl tetrazoles under UV irradiation were studied. Allylcarboranes as starting materials were prepared via Pd-catalyzed cross-coupling reaction of iodocarboranes with allylmagnesium bromide.

Local piezoelectric and ferroelectric properties as well as morphology of single crystals and films of two novel chiral organic compounds derived from chiral 2-methoxy and 2-amino acids have been investigated. The crystals demonstrated piezoelectric response exceeding that of lithium niobate. The piezoelectric response was registered also in compound films. Piezoelectric properties and domain structure of single crystals and films have been studied by piezoresponse force microscopy.

A series of novel meso- triazoloporphyrin-carborane conjugates was prepared in good yields via the copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of Zn(II) or Pd(II) 5,10,15,20-tetrakis[4-(2-propargyloxy)-2,3,5,6-tetrafluorophenyl]porphyrin or Zn(II) 5,10,15,20-tetra(p-propargyloxyphenyl)porphyrin with 1-azidomethyl-o-carborane in CH2Cl2. Zinc metalloporphyrins were demetallated under acidic conditions to afford the corresponding free-base triazolo-carborane porphyrins in excellent yields. All new compounds were characterized by MS, NMR and UV–vis spectroscopy and their photophysical properties were studied.

Compounds which are rich in boron and nitrogen have the potential to find application as high-energy material. In the present article quantum-chemical calculations (DFT B3LYP/6-311 + G*) of geometric and electronic structures, enthalpies of formation, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energies and the detonation properties of 22 molecules of carboranyl tetrazoles were carried out. The method of the estimation of enthalpies of formation of carboranyl tetrazoles based on full energies of the molecules and semi empirical parameters for solid carbon (graphite) and boron was proposed. The enthalpies of formation of carboranyl tetrazoles were evaluated. Theoretical terahertz frequencies for potential high-energy density materials (HEDMs) were computed which allows the opportunity for the remote detection of these compounds. According to the results of calculations the most promising HEDMs among studied compounds were found to be 9,12-bis(2-(5-phenyl-tetrazol-2-yl)propyl)-o-carborane; 9,10-bis(2-(5-phenyl-tetrazol-2-yl)propyl)-m-carborane; 5,5’-(butan-1,4-diyl)-{9,12-bis[2-(tetrazol-2-yl)prop-1-yl]-о-carborane}. Based on the calculated frontier molecular orbital energy gap these energetic materials are even less impact sensitive than classical diaminotrinitrobenzene (DATB) and trinitroaniline (TNA). These compounds are characterized by the maxima magnitudes of the evaluation of the enthalpies of formation (EOF) and can be considered as promising HEDMs as their EOF values are notably higher than those of well-known trinitrotoluene (TNT) and hexogen (RDX, Research Department eXplosive).

The maleimide moiety is widely used in drug design. To explore the properties of maleimide containing photosensitizers we obtained a series of new β-maleimide functionalized meso-arylporphyrins through acylation of β-amino group in porphyrins with maleic anhydride followed by condensation of maleic acid monoamides. The selective reactivity of porphyrin maleimides toward thiols was demonstrated using mercaptocarboranes and cysteine. New derivatives retained the ability of tetrapyrrolic macrocyclic compounds to absorb light in visible spectral region and to generate triplet states and reactive oxygen species upon photoactivation. Importantly, illumination of cells loaded with a cell permeable 2-{3-[(o-carboran-1′-yl)thio]pyrrolidine-2,5-dione-1-yl}-5,10,15,20-tetraphenylporphyrin triggered rapid (within the initial minutes) generation of superoxide anion radical concomitantly with a decrease of mitochondrial membrane potential, and then the loss of the plasma membrane integrity and cell death. Thus, the maleimide-substituted porphyrins represent a new chemotype of polyfunctionalized compounds for an in-depth investigation as photosensitizers in cancer and beyond.

Friedel-Crafts acylation reaction of ferrocene with carborane carboxylic acid chlorides was shown to be a facile and convenient route for the preparation of carboranyl ferrocenyl oxo-derivatives in high yield. Compounds thus obtained were easily transformed into the corresponding alcohols using lithium aluminum hydride whereas their conversion into the corresponding ferrocenylalkyl carboranes was reached with monochloroalane. Substitution of hydroxyl group in carboranyl ferrocenyl alcohols with S-nucleophile in the presence of CAN as a catalyst was investigated.

Novel neutral and anionic fluorinated carboranylporphyrins for boron neutron capture therapy (BNCT) and photodynamic therapy (PDT) were synthesized by the reaction of 5,10,15,20-pentafluorophenylporphyrin and its copper(II), zinc(II), and palladium(II) complexes with closo-mercaptocarboranes and cesium 1-mercapto-1-carba-closo-dodecaborate. Preliminary evaluation of biological activity reveals that anionic carboranylporphyrins are promising agents for BNCT and PDT.

The porphyrin-based photosensitizers capable of binding to DNA are perspective drug candidates. Here we report the interactions with calf thymus DNA of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium)porphyrin (P1) and its derivatives containing Zn(II) or Ni(II) in the coordination sphere. These interactions were studied with absorption and circular dichroism spectroscopy. NiP1 and ZnP1 formed different types of complexes with DNA. NiP1 intercalated into the double helix, whereas ZnP1 bound the DNA groove. Compound P1 displayed both binding modes. The ZnP1-DNA binding constant was approximately three times smaller than the respective values for P1-DNA and NiP1-DNA complexes. Light induced degradation of the reactive oxygen species (ROS) trap 1,3-diphenylisobenzofuran in the presence of P1 and its metal derivatives revealed that NiP1 was a weaker photooxidative agent, whereas P1 and ZnP1 generated ROS to similar extents. Nevertheless, the DNA photodamaging effect of ZnP1 was the most pronounced. Illumination of the supercoiled plasmid caused single-strand DNA photocleavage in the presence of P1 and ZnP1; double strand breaks were detectable with micromolar concentrations of ZnP1. The concentration of ZnP1 required for plasmid photonicking was two times smaller than that of P1 and ~20 times lower than that for NiP1. Thus, the modes of P1, NiP1 and ZnP1 binding to DNA determine the differential photodamaging potency of these porphyrins. A greater accessibility to the solvent of the groove binder ZnP1, compared to the shielded intercalator NiP1 and the intercalated P1 molecules, allows for an efficient local generation of ROS followed by DNA photocleavage.

Porphyrins are a chemical class that is widely used in drug design. Cationic porphyrins may bind to DNA guanine quadruplexes. We report the parameters of the binding of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium) porphyrin (P1) and 5,10,15,20-tetrakis(N-etoxycarbonylmethyl-4-pyridinium) porphyrin (P2) to antiparallel telomeric G-quadruplex formed by d(TTAGGG)4 sequence (TelQ). The binding constants (K i ) and the number of binding sites (N j ) were determined from absorption isotherms generated from the absorption spectra of complexes of P1 and P2 with TelQ. Compound P1 demonstrated a high affinity to TelQ (K i = (40 ± 6) × 106 M−1, N 1 = 1; K 2 = (5.4 ± 0.4) × 106 M−1, N 2 = 2). In contrast, the binding constants of P2-TelQ complexes (K 1 = (3.1 ± 0.2) × 106 M−1, N 1 = 1; K 2 = (1.2 ± 0.2) × 106 M−1, N 2 = 2) were one order of magnitude smaller than the corresponding values for P2-TelQ complexes. Measurements of the quantum yield and fluorescence lifetime of the drug’s TelQ complexes revealed two types of binding sites for P1 and P2 on the quadruplex oligonucleotide. We concluded that strong complexes can result from the interaction of the porphyrins with TTA loops whereas the weaker complexes are formed with G-quartets. The altered TelQ conformation detected by the circular dichroism spectra of P1-TelQ complexes can be explained by the disruption of the G-quartet. We conclude that peripheral carboxy groups contribute to the high affinity of P1 for the antiparallel telomeric G-quadruplex.