Pyrrole Units Research Articles

Synthesis and the effect of substituent position upon unsymmetrical isomeric diarylethenes bearing a pyrrole unit

Four unsymmetrical diarylethenes bearing a pyrrole moiety were synthesized, and the structures of two isomeric compounds were determined by single-crystal X-ray diffraction analysis. The properties of these compounds, including photochromism, fluorescence and electrochemical properties of these diarylethenes were also investigated systematically. Each of the four diarylethene derivatives exhibited good photochromism and functioned as an effective fluorescent photoswitch both in solution and in PMMA films. The absorption maxima, the quantum yields of cyclization and cycloreversion, and the fluorescence quantum yields of the open-ring isomers increased whereas the emission peaks decreased evidently when the methoxy group was attached at any of the three positions on the terminal benzene ring. Compared with the analogous diarylethenes bearing a pyrazole moiety, the introduction of the pyrrole moiety could increase the absorption maxima and decrease the cycloreversion quantum yields significantly. Cyclic voltammograms testified that methoxy group and its substituted position could effectively modulate the electrochemical behaviours of these diarylethene derivatives.

Abstract 3521: Pharmacological modulation of Topoisomerase IIα expression and confluence-induced resistance to etoposide by a novel fluorescent HxIP polyamide

Abstract Pyrrole (P)-Imidazole (I) containing polyamides are small synthetic molecules which can target predetermined DNA sequences with high affinity and modulate gene expression by interfering with the binding of transcription factors to DNA. As a model system we have previously used the inverted CCAAT box 2 (ICB2) of the topoisomerase IIα promoter and shown that targeted polyamides inhibit the binding of the transcription factor NF-Y and induce expression of topo IIα in confluent cancer cells. Critical to this approach is the need for low molecular weight polyamides that readily enter in the nucleus. In this study, the fluorophore p-anisylbenzimidazolecarboxamido (Hx) moiety was rationally designed to mimic the recognition of A/T base pairs by two consecutive pyrrole units. The hybrid polyamide HxIP is the first example of a small fluorescent molecule that fluoresces significantly more intensely upon binding to its target sequence, 5′-TACGAT-3′ of the 5′-flank of ICB2. Sequence specificity was confirmed by DNAse I footprinting, with HxIP binding with increased affinity compared to the corresponding triamides/tetraamides (f-PIP/PPIP). Thermal denaturation, circular dichroism, and Surface Plasmon Resonance studies confirmed the sequence specificity of HxIP. A dose-dependent inhibition of protein binding to ICB2 by HxIP with complete abolition at concentrations >3 μM was seen in an Electrophoretic Mobility Shift Assay (EMSA). A supershift assay confirmed NF-Y binding to the target sequence. HxIP was also able to displace bound protein factors from DNA at the same concentrations. The incorporation of Hx in the hybrid molecule provides an intrinsic probe to directly monitor cellular uptake and migration into the nucleus. Confocal microscopy in both fixed and live NIH3T3 and A549 cells showed that HxIP is readily taken up by cells and quickly localises in the cell nucleus within 5 minutes. Exposure of confluent cells to 20-40 μM HxIP resulted in time-dependent upregulation of topo IIα expression, reaching levels comparable to those of proliferating cells within 24h as shown by immunoblotting analysis. Confluence-associated repression of topo IIα expression contributes to cellular resistance to agents such as etoposide. De-repression of topo IIα by pre-incubation with HxIP was shown to resensitise NIH3T3 cells to the cytotoxic effect of etoposide (MTT assay) and enhance its DNA damaging effects by increasing levels of etoposide-induced DNA strand breaks as assessed by the single cell gel electrophoresis (comet) assay and the phosphorylation of H2AX. Subcellular localisation of HxIP and potential synergies with etoposide treatment is currently being investigated in vivo against human tumour xenografts. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3521.

Protonated [4n]π and [4n+2]π Octaphyrins Choose Their Möbius/Hückel Aromatic Topology

Protonation-triggered conformational changes of meso-octakis(pentafluorophenyl) [36]octaphyrin and [38]octaphyrin have been investigated. The X-ray crystal structures and (1)H NMR analyses revealed that the protonation process cuts off intramolecular hydrogen bonds between aminic and iminic pyrrole units and, at the same time, produces intermolecular hydrogen-bond network between aminic pyrrole unit and counter-anions. Such a replacement induces some pyrrole inversion, leading to Mobius aromatic conformation for [36]octaphyrin and to Huckel aromatic conformation for [38]octaphyrin. These protonated octaphyrins show similar structures only with a subtle difference in tilted pyrrole angles, which results in their different topologies. This feature strongly suggests that the macrocycles control their topologies by pyrrole rotation to gain [4n]pi Mobius or [4n+2]pi Huckel aromatic stabilization, depending on the number of pi-electrons. Detailed photophysical properties such as absorption/fluorescence, excited singlet/triplet state lifetimes, and two-photon absorption cross-section values have been presented for both protonated [36] and [38]octaphyrins in conjunction with their Mobius or Huckel aromaticity.

Synthesis and biophysical studies of hairpin polyamides targeting the Brn-3b and GATA-3 transcriptional sites

Hairpin polyamide analogs of distamycin A (1) were designed and synthesized to evaluate their ability to bind 5′-ATAGA-3′ and 5′-AGATA-3′ sequences which are important elements for controlling the function of the Brn-3b and GATA-3 transcriptional factors, respectively. The hairpin polyamides are composed of pyrrole and imidazole units linked together via a γ-aminobutyrate (GABA) unit. Hairpins 2b (Py-Py-Im-γ-Py-Py-Py) and 2c (Im-Py-Py-γ-Py-Py-Py) were synthesized to target the respective Brn-3b and GATA-3 cognate sequences. Preliminary biophysical studies including thermal denaturation and circular dichroism were performed and the results ascertained the binding of hairpins 2a and 2b to their respective cognate DNA sequences.

Colorimetric fluoride sensors based on deprotonation of pyrrole–hemiquinone compounds

The combination of pyrrole and hemiquinone units produced a novel prototype of efficient colorimetric fluoride sensors, and the presence of the tautomerism effect provides additional means of modulating the sensing behavior.

Electrochemistry and Spectroelectrochemistry of β,β′-Fused Quinoxalinoporphyrins and Related Extended Bis-porphyrins with Co(III), Co(II), and Co(I) Central Metal Ions

A series of cobalt(II) and cobalt(III) porphyrins with fused quinoxaline rings at one or more beta,beta'-pyrrolic units of the macrocycle were synthesized and characterized as to their electrochemical properties in nonaqueous media. Their UV-visible spectra were also measured before and during oxidation or reduction in a thin-layer cell. The investigated quinoxalinoporphyrins are represented as (PQ)Co, (QPQ)CoCl, (PQ(2))CoCl, Co(P)-TA-(P)Co, and Co(PQ)-(QP)Co, where PQ = the dianion of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)-quinoxalino[2,3-b']porphyrin, QPQ = the dianion of the corresponding linear bisquinoxalino[2,3-b':12,13-b'']porphyrin, PQ(2) = the dianion of the corresponding corner bisquinoxalino[2,3-b':7,8-b'']porphyrin, and (P)-TA-(P) = the tetraanion of the bis-porphyrin with 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrins fused at opposite ends of tetraazaanthracene. (P)Co and (P)CoCl were also characterized where P = the dianion of 5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrin. Each compound could be cycled between their Co(III), Co(II), and Co(I) forms under the application of a given oxidizing or reducing potential, although a one-electron reduction of the Co(II) quinoxalinoporphyrins led to a product with mixed Co(I) and porphyrin pi-anion radical character followed by generation of a pure Co(I) pi-anion radical species at more negative potentials. The effect of the position and number of quinoxaline groups on the redox potentials and mechanisms of each electron transfer were elucidated, and comparisons made to structurally similar compounds containing both redox active and redox inactive central metal ions. Surprisingly, the position and number of quinoxaline groups on the macrocycle has little or no effect on the redox potentials for the Co(II) --> Co(III) or Co(III) --> Co(II) processes, but this is not the case for other electron transfer reactions where significant differences are seen between the examined compounds. Significant interactions are also observed between the two porphyrin macrocycles of the laterally bridged dicobalt(II) bis-porphyrin dyad Co(P)-TA-(P)Co in its singly and doubly reduced form, but only weak interactions are seen between the two Co(PQ) units of the single bond biquinolalinyl-bridged dicobalt(II) bis-porphyrin dyad Co(PQ)-(QP)Co.

Palladium‐Catalyzed Sequential Reactions via Allene Intermediates for the Rapid Synthesis of Fused Polycyclic Pyrrole Derivatives

AbstractIn this paper, we report a novel sequential reaction sequence consisting of a series of processes including Sonogashira coupling, propargyl‐allenyl isomerization, [3+2] cycloaddition, denitrogenation, and highly selective biradical coupling reaction, providing an efficient synthesis of fused polycyclic pyrrole derivatives. The reaction features one CC bond and two CN bonds formed to construct the pyrrole unit, together with two rings efficiently assembled in one stroke.

5,10,10,15,20,20-Hexamethylcalix[4]pyrrole 5,15-diethyl diester

In the title compound, C32H40N4O4, the pyrrole rings and ester groups adopt a 1,3-alternate conformation in which the alternating pyrrole and ester units are in opposite directions. The structure displays N—H⋯O hydrogen bonding and exhibits disorder [site occupancies of 0.81(2) and 0.71(2)] in the peripheral ethyl groups.

Novel hyperbranched molecules containing pyrrole units from diacetylene compounds

Novel hyperbranched molecules containing pyrrole units were obtained from ortho-, meta-, and para-diaminodiphenyldiacetylenes, as AB2 type monomers by one-step polymerization. Diacetylenic fragments reacted with terminal amino groups in the presence of copper chloride to give pyrrole units. Diaminodiphenyldiacetylene monomers have been synthesized from ethynilanilines in three steps. The novel monomers and hyperbranched molecules were characterized by NMR, IR and thermal analysis.

Strong CH⋅⋅⋅Halide Hydrogen Bonds from 1,2,3‐Triazoles Quantified Using Pre‐Organized and Shape‐Persistent Triazolophanes

The structures associated with halide (F-, Cl-, Br-) complexation inside CH hydrogen-bonding macrocyclic receptors, called triazolophanes, are characterized using density functional theory (DFT). The associated binding energies in the gas and solution phases are evaluated. The ruffles in the empty triazolophane become smoothed-out upon Cl(-)- and Br(-)-ion binding directly into the middle of the cavity. The largely pre-organized cavity morphs into an elliptical shape to facilitate shorter hydrogen bonds in the north and south regions and longer ones west and east. The smaller F- ion sits in, and flattens-out, only the north (or south) region. The 1,2,3-triazoles show shorter CH...Cl- contacts than for the phenylenes. Both Cl- and Br- show the same binding geometries but Cl- has a larger binding energy consistent with its stronger Lewis basicity. Model triads were used to decompose the overall binding energy into those of its components. In the course of this triad analysis, anion polarization was identified and its contribution to the triad...Cl- binding energy estimated. Consequently, the binding energies for the individual aryl units within the comparatively non-polarized triazolophanes were estimated. The 1,2,3-triazoles are twice as strong as the phenylenes thus contributing most of the interaction energy to Cl(-)-ion binding. Therefore, the 1,2,3-triazoles appear to approach the hydrogen bond strengths of the NH donors of pyrrole units.

Computational note on the chemical reactivity of pyrrole derivatives

The nanosciences and their companion nanotechnologies are a hot topic all around the world. They promise the development of revolutionary new materials. These materials are based on nanostructures so they could be called Molecular Nanostructured Materials (MNMs). These MNMs have a lot of potential applications, and among them we could mention getting energy and a cleaner environment, creating new sources of energy by generating hydrogen and utilizing our current sources of energy more efficiently at the microscopic level. Organic heterocycles are systems of growing interest in materials science in view of the potential technological applications in fields such as electronics, photonics, sensors, or corrosion protection. The pyrrole-derived MNMs could be the starting materials for Organic Photovoltaics and for High-Performance OLEDs (Organic Light-Emitting Devices). The objective of this work is to perform a detailed calculation of the molecular structure of some pyrrole derivatives as well as of their dimers, and to predict the chemical reactivity of them using concepts derived from Density Functional Theory (or Conceptual DFT) [1] like the electronegativity, hardness, global electrophilicity and the condensed Fukui functions. These compounds have several desirable characteristics related to their use in Organic Photovoltaics and OLEDS: (i) they contain the pyrrole group, with molecular parameters similar to the thiophene derivatives that have been shown to be useful as MNMs; (ii) the p-conjugated derivatives are generally efficient fluorophores, and as such, useful for the fabrication of nanobiosensors; (iii) they can be used as an attractive building block for Organic Molecular Materials. The analysis of the chemical reactivity parameters will help to identify which of the pyrrole derivatives will be more prone to react with functionalized fullerenes in order to be able to design an Organic Photovoltaics device. The studied molecules are phenyl-(4-phenyl-1H-pyrrole-3-yl)methanone (Molecule 1) [2–4], (4-methoxy-phenyl)-(4-phenyl1H-pyrrole-3-yl)-methanone (Molecule 2) [2–4], [4-(4-methoxyphenyl)-1H-pyrrole-3-yl]-phenylmethanone (Molecule 3) [2–4], and their dimers called Molecule 1-1, Molecule 2-2 and Molecule 3-3, respectively. For this reason, we have calculated the molecular structure of the parent molecules pyrrole and anisole through the use of two different theory levels, PBE/DND and PBE/TNP. The molecular structures of the parent molecules obtained from each calculation were compared with the experimental results by aligning both structures and calculating the Root Mean-Square Deviation (RMSD). The agreement is very good: the standard error of the differences between the experimental and the calculated bond lengths and bond angles being very low for both model chemistries (an average value of 0.03). Moreover, the results for both model chemistries are the same. The conclusion is that with the PBE/ DND model chemistry it is possible to obtain accurate values for the molecular structures without the need to resort to other model chemistry with a higher computational cost. The next step in our study was to perform a conformational analysis on every one of the studied molecules in order to obtain the most stable structure at the semiempirical AM1 level. This was performed by modifying the distances angles of the moieties connected to the pyrrole unit. The resulting structures were used as the starting point for geometry optimizations with the PBE/DND model chemistry. The results for the optimized molecular structures of the six molecules are presented in Figs. 1 and 2 of the Supplementary Materials. Listings showing the values of the interatomic bond lengths and bond angles for the six studied molecules are provided in the form of Tables in the Supplementary Materials section accompanying this work.

Theoretical study on nonlinear optical properties of the Li+[calix[4]pyrrole]Li−dimer, trimer and its polymer with diffuse excess electrons

The static (hyper)polarizabilities of the dimer and trimer with diffuse excess electrons, [Li(+)[calix[4]pyrrole]Li(-)](n), are firstly investigated by the DFT(B3LYP) method in detail. For the dimer and trimer, a Li atom inside each calix[4]pyrrole unit is ionized to form a diffuse excess electron. The results show that the dimer and trimer containing two and three excess electrons, respectively, have very large first hyperpolarizablities as 2.3 x 10(4) and 4.0 x 10(4) au, which are 30 and 40 times larger than that of the corresponding [calix[4]pyrrole](n) (n = 2, 3) without Li atom. Also, beta values of dimer and trimer are twice and four times as large as that of monomer containing one excess electron. Obviously, not only excess electron but also the number of excess electron plays an important role in increasing the first hyperpolarizability. Moreover, the (hyper)polarizabilities of the [Li(+)[calix[4]pyrrole]Li(-)](n) polymer are investigated at ab initio level by using the elongation finite-field (elongation FF) method. All the oligomers of the [Li(+)[calix[4]pyrrole]Li(-)](n) with many excess electrons exhibit very large first hyperpolarizability and large second hyperpolarizability. The present investigation shows that by introducing several and more excess electrons into the nonlinear optical (NLO) materials will be an important strategy for improving their NLO properties, which will be helpful for design of NLO materials.

Pyrrolamidocalix[4]arenes: new receptors for anion recognition

Pyrrolamidocalix[4]arenes 1– 4, members of a new class of anion receptors bearing pyrrolic units at the upper rim of calix[4]arene macrocycle, have been readily synthesized in good yields. Derivatives 1 and 3, with unsubstituted pyrrole units, show a good selectivity for H 2 PO 4 - over F − and AcO −, while the presence of electron-withdrawing NO 2 substituents in 2 and 4 inverts the selectivity favoring more basic AcO − and F −. In addition, it is demonstrated that the flexibility of calix[4]arene skeleton, present in 1 but absent in 3, is very important in the fitting process that leads the amidopyrrole moieties to wrap the tetrahedral H 2 PO 4 - guest.

Synthesis of 2‐(Selenophen‐2‐yl)pyrroles and Their Electropolymerization to Electrochromic Nanofilms

Bridging pyrrole and selenophene chemistries: Molecular assemblies have been developed that allow scrutiny of the electronic communication between pyrrole and selenophene nuclei. Divergent syntheses of 2-(selenophen-2-yl)pyrroles and their N-vinyl derivatives from available 2-acylselenophenes and acetylenes in a one-pot procedure have been devised (see scheme), which provide access to these exotic heterocyclic ensembles.The divergent syntheses of 2-(selenophen-2-yl)pyrroles and their N-vinyl derivatives from available 2-acylselenophenes and acetylenes in a one-pot procedure make these exotic heterocyclic ensembles accessible. Now we face a potentially vast area for exploration with a great diversity of far-reaching consequences including conducting electrochromic polymers with repeating of pyrrole and selenophene units (emerging rivalry for polypyrroles and polyselenophenes), the synthesis of functionalized pyrrole-selenophene assembles for advanced materials, biochemistry and medicine, exciting models for theory of polymer conductivity.

Redetermination ofL-tryptophan hydrobromide

The redetermined crystal structure of the title compound, C11H13N2O2 +·Br−, is reported. Data collection at 100 K about three crystallographic axes resulted in a crystal structure with significantly higher precision in comparison to the two-dimensional data collected at 176 K [Takigawa et al. [(1966) Bull. Chem. Soc. Jpn, 39, 2369–2378]. The carboxyl group and indole ring system are planar, with maximum deviations of 0.002 (2) and 0.007 (2) Å, respectively, and make an angle of 70.17 (1)° with each other. The mol­ecules are arranged in double layers of carboxyl and amino groups parallel to the ab plane, stabilized by an extensive network of N—H⋯Br and O—H⋯Br hydrogen bonds. The polar layer is held together by a network of three N—H⋯Br hydrogen bonds and one O—H⋯Br hydrogen bond. In the non-polar layer, the indole rings are linked mainly by electrostatic N—H⋯C inter­actions between the polarized bond N—H (H is δ+) of the pyrrole unit and two of the ring C atoms (δ−) of the benzene rings of adjacent mol­ecules. The distances of these electrostatic inter­actions are 2.57 and 2.68 Å, respectively. C—H⋯O and C—H⋯π inter­actions are also present.

Pyrrole containing ionic liquid as tecton for construction of ordered mesoporous silica with aligned polypyrrole nanowires in channels

Two types of ionic liquid (IL) based surfactants bearing a terminal pyrrole moiety were synthesized, and used as both structure-directing agents and monomers to prepare mesostructured silica with densely packed pyrrole units within channels via a hydrothermal synthesis procedure. A systematic study was carried out to address the influence of the relative concentration of the IL and the type of head group and counter ions on the mesostructure. As a main result, it was found that both the prepared imidazolium- and pyridium-based surfactants displayed a significantly strong tendency towards formation of a highly ordered two-dimensional (2D) hexagonal mesostructure in a broad range of conditions with excellent reproducibility. In situpolymerization of the pyrrole groups closely packed in the central region of the formed silica pore channels led to the desired mesostructured silica with well-distinct aligned polypyrrole (PPy) molecular wires in channels, which are clearly visible under TEM after the removal of silica framework. It is found that, due to the spatial confinement of the silica framework, the encapsulated PPys are elongated and straight, leading to longer conjugation length.

Conjugated Ladder-Type Heteroacenes Bearing Pyrrole and Thiophene Ring Units: Facile Synthesis and Characterization

Ladder-type heteroacenes containing pyrrole and thiophene rings, dibenzo[b,b']thieno[2,3-f:5,4-f']-carbazoles (DBTCZ, 1), and diindolo[3,2-b:2',3'-h]benzo[1,2-b:4,5-b']bis[1]benzothiophene (DIBBBT, 2), were facilely synthesized through proper precursors (7, 11, and 18) respectively. The key step is a triflic acid induced intramolecular electrophilic coupling reaction of corresponding aromatic methyl sulfoxides with activated aromatic building blocks, which enables regioselective ring closure. Both precursors (7 and 11) toward DBTCZ gave the symmetrical product but with solubilizing alkyl chains in two different fashions. DIBBBT was also synthesized as the extended ladder-type heteroacene with defined structure. These obtained heteroacenes are fully characterized (mass spectrometry, NMR, elemental analysis), and their X-ray analysis and optical and electrochemical properties are reported.

1,4-Dithiaheterocycle-fused porphyrazines: Synthesis, characterization, voltammetric and spectroelectrochemical properties

Porphyrazines (M = H, Mg, Zn and Co) with a 2,3-dicyano-5-phenyl-5,6-dihydro-1,4-dithiin group fused to each pyrrole unit were synthesized and characterized starting with the corresponding unsaturated dicarbonitrile derivative. The voltammetric and spectroelectrochemical characterizations of the metallo-porphyrazines (M = 2H +, Mg 2+, Zn 2+ and Co 2+) substituted with 2,3-dicyano-5-phenyl-5,6-dihydro-1,4-dithiin groups on peripheral positions are described. Cyclic voltammetry and differential pulse voltammetry studies showed that while metal-free, magnesium, and zinc porphyrazines represented well-defined one-electron ligand-based reductions and ligand-based one-electron oxidation couples, cobalt porphyrazine gave both metal-based and ligand-based reduction and oxidation couples. Assignments of the redox couples were confirmed by spectroelectrochemical measurements.

Aromatic Conjugation Pathways in Porphyrins

Abstract The π-current density induced in a polycyclic π-system is strongly dependent on molecular geometry, so that information on main aromatic pathways cannot be extracted straightforwardly from the π-current density. Using our graph theory of aromaticity and ring-current diamagnetism, we re-interpreted the π-current densities and aromatic stabilization energies of porphyrins consistently and found that main pathways of π-electron circulation along the macroscopic ring are not those of aromatic stabilization. Four five-site circuits instead proved to be the main origin of aromaticity in porphyrins. In general, currents are induced in all possible circuits in a π-system. Superposition of all these circuit currents gives rise to the apparent bifurcation of the π-current across each pyrrolic unit. Local π-currents induced in pyrrolic rings represent those induced in the corresponding five-site circuits.

Electrochemical synthesis and corrosion performance of poly(pyrrole-co- o-anisidine)

The electrochemical synthesis of poly( o-anisidine) homopolymer and its copolymerization with pyrrole have been investigated on mild steel. The copolymer films have been synthesized from aqueous oxalic acid solutions containing different ratios of monomer concentrations: pyrrole: o-anisidine, 9:1, 8:2, 6:4, 1:1. The characterization of polymer films were achieved with FT-IR, UV–visible spectroscopy and cyclic voltammetry techniques. The electrochemical synthesis of homogeneous-stable poly( o-anisidine) film with desired thickness was very difficult on steel surface. Therefore its copolymer with pyrrole has been studied to obtain a polymer film, which could be synthesized easily and posses the good physical–chemical properties of anisidine. The kinetics and rate of copolymer film growth were strongly related to monomer feed ratio. The introduction of pyrrole unit into synthesis solution increased the rate of polymerization and the substrate surface became covered with polymer film soon, while this process required longer periods in single o-anisidine containing solution. The protective behavior of coatings has been investigated against steel corrosion in 3.5% NaCl solution. For this aim electrochemical impedance spectroscopy (EIS) and anodic polarization curves were utilized. The synthesized poly( o-anisidine) coating exhibited significant protection efficiency against mild steel corrosion. It was shown that 6:4 ratio of pyrrole and anisidine solution gave the most stable and corrosion protective copolymer coating.