Pyrenyl Units Research Articles

Pyrene-Modified Cyclic Peptides Detect Cu2+ Ions by Fluorescence in Water

The detection of metal ions is an option for maintaining water quality and diagnosing metal ion-related diseases. In this study, we successfully detected metal ions using fluorescent peptides in water. First, we prepared seven linear (L1–L7) and seven cyclic (C1–C7) peptides containing two pyrenyl (Pyr) units and assessed the response to various metal ions by fluorescence. The results indicated that C1, which contains a hexameric cyclic peptide moiety consisting of Pyr and Gly units, did not show a fluorescent response to metal ions, while the linear L1 corresponding to C1 showed a response to Cu2+, but its selectivity was found to be poor through a competition assay for each metal ion. We then assessed C2–C7 and L2–L7, in which Gly was replaced by His units at various positions in the same manner. The results showed that C2–C7 responded to Cu2+ in a manner dependent on the His position. Additionally, superior selectivity was observed in C7 through a competition assay. These results demonstrate that the structural restriction of peptides and the sequence affect the selective detection of Cu2+ and reveal that peptides with an appropriate structure can accomplish the fluorescent detection of Cu2+ specifically.

Controlling Excimer-Origin Circularly Polarized Luminescence of Bipyrenyl-Arginine Peptides by Cyclodextrin in Water

Abstract It is important to optimize the photoexcited-state conformation of chiral luminescent molecules to enhance the intensity of circularly polarized luminescence (CPL) and control the direction of CPL rotation. In pyrenyl peptide luminophores, the intensity and sign of CPL is determined by the solvent and intramolecular distance between pyrenyl units in addition to peptide chirality. However, the control of CPL properties in water is difficult, and new methods to control CPL in water are required. In this study, we achieved amplification and control of the sign of excimer-origin CPL by adding γ-cyclodextrin to a flexible bipyrenyl peptide luminophore with two arginine groups in water.

Front Cover: Synthesis, Photophysics, Computational Approaches, and Biomolecule Interactive Studies of Metalloporphyrins Containing Pyrenyl Units: Influence of the Metal Center (Eur. J. Inorg. Chem. 12/2022)

The Front Cover shows the design of meso-tetra-(1-pyrenyl)porphyrin derivatives, which interact with biomolecules. These porphyrins were fully characterized by photophysical and theoretical methods. The presence of metal species in the porphyrin core influences the ground and excited states. Biomolecule interaction experiments show that these porphyrins interact spontaneously in the minor groove of CT-DNA and in subdomain IB in the BSA pocket. The interaction depends on the nature of the metal ion. The cover was designed by Júlio A. F. Arvellos (scientific designer). More information can be found in the Research Article by B. Almeida Iglesias and co-workers.

Synthesis, Photophysics, Computational Approaches, and Biomolecule Interactive Studies of Metalloporphyrins Containing Pyrenyl Units: Influence of the Metal Center

AbstractA classical methodology to design free‐basemeso‐tetra‐(1‐pyrenyl)porphyrin (H2TPyrP) and their corresponding metalloporphyrins containing Zn(II), Cu(II), Ni(II), Co(III), and Mn(III) was described. These porphyrins were characterized in terms of structure, photophysical, and interactions profile withcalf‐thymusdeoxyribonucleic acid (CT‐DNA) and bovine serum albumin (BSA).H2TPyrPexhibited five characteristic bands in the visible wavelength: Soret (432 nm) and Q‐bands (520–650 nm range), while the metalloporphyrins showed some spectrum shifts according to the nature of the ion, which were also explored by time‐dependent density functional theory (TD‐DFT) calculations. The fluorescence and singlet oxygen quantum yield (Φfl, ΦΔ, respectively) decreased with the presence of metal species in the porphyrin core. The porphyrins interact spontaneously via a ground‐state association in the minor groove of CT‐DNA following the increasing order of binding:CuTPyrP<H2TPyrP<CoTPyrP<MnTPyrP<NiTPyrP<ZnTPyrP, while for BSA the suitable complex geometry for Co(III) and Mn(III) complexes increased the binding capacity.

A Conjugated Molecular Crown Containing a Single Pyrenyl Unit: Synthesis, Characterization, and Photophysical Properties

A Conjugated Molecular Crown Containing a Single Pyrenyl Unit: Synthesis, Characterization, and Photophysical Properties

Controlling the sign of Excimer‐Origin Circularly Polarised Luminescence by Balancing Hydrophilicity/Hydrophobicity in Bipyrenyl Arginine Peptides

AbstractDetermining the conformation of a chiral luminescent molecule in its ground state as well as in its photoexcited state is difficult. In the case of a pyrenyl peptide, the sign of its circularly polarised luminescence (CPL) is determined by the solvent or the intramolecular distance between its pyrenyl units; consequently, a new method for controlling CPL in water is required. Herein, we report that chiral LL‐oligopeptide luminophores bearing two fluorescent pyrenyl and hydrophilic arginine units exhibit clear excimer‐origin circularly polarised luminescence (CPL) at 480–510 nm in aqueous solution. The CPL sign is tuneable by altering the number and positions of the arginine units on the edges of the chiral peptide backbone.

Hybridizing Oligonucleotides with Hydrophobic Peptide Nucleic Acids Assists Their Cellular Uptake through Aggregate Formation.

We applied hybridization between hydrophobic peptide nucleic acids (PNAs) and oligodeoxynucleotides (ODNs) to achieve their cellular uptake without any need for transfection reagents. We employed a pyrenyl unit as a hydrophobic functional group and introduced it at the terminus of the PNA strand. The pyrene-tethered PNA (PyPNA) strongly bound with its complementary ODNs to generate amphiphiles; the resulting hybrids formed aggregates that showed efficient cellular uptake and high biological stability. Aggregates containing a functional DNA aptamer that bound to the PyPNA penetrated the cell membrane smoothly, with the aptamer exerting its original function in living cells. Thus, PyPNA efficiently assisted the additive-free cellular uptake of ODNs.

Photophysical and electrochemical properties of two trans-A2B-corroles: differences between phenyl or pyrenyl groups at the meso-10 position.

The present study reports on the optical and photophysical properties of trans-A2B-corroles possessing pyrenyl units attached at the meso-10-position and compares them with those of model trans-A2B-corroles having phenyl substituents at that position. In contrast to the model meso-substituted corrole, the new pyrenyl-corrole shows slightly red-shifted absorption bands and blue-shifted emission, slightly higher fluorescence quantum yield, and more importantly, it shows better photo-stability under white-light illumination. Theoretical calculations were used to determine the electronic transitions and geometries of the singlet and triplet excited states (TD-DFT and NTO). Moreover, we demonstrate that the pyrenyl-corrole in analogy to previously studied model corroles is able to generate reactive oxygen species (ROS) under visible light using photo-degradation of 1,3-diphenylisobenzofuran (DBPF), a singlet oxygen quencher, and EPR spectroscopy allied with the spin-trapping method is used for identifying singlet oxygen species. The results show that the pyrenyl unit attached at the meso-10-position of the corrole increases the photo-stability and efficiency in ROS generation compared to the phenyl substituent.

Label-free sensing of abasic DNA using pyrenylamido triazolyl aromatic amino acid scaffold as AIE probe

We report a label-free strategy for switch-on sensing of abasic DNA using aggregation-induced emission (AIE) probe, pyrenylamido triazolyl aromatic amino acid scaffold (PyAm-ArTAA). In aqueous media and buffer the probe molecule aggregates through the electrostatic as well as hydrophobic π-π stacking interaction resulting in strong fluorescence emission. Thus, the probe is found to be useful in sensing of an abasic site opposite to adenosine (A) base of a T-rich 13-mer DNA via an enhancement of fluorescence intensity. Intercalative stacking interaction of pyrenyl unit within the minor groove and alongside the abasic site opposite of base A possibly play an essential role in the success of label-free sensing of abasic DNA by the probe.

Heterotrimetallic complexes of iron and ruthenium based on vinyliminium dithiocarboxylate ligands

The diiron vinyliminium compounds [Fe2{μ-η1:η3-C(R2) = C(H)C=N(Me)R1}(μ-CO)(CO)(Cp)2]OSO2CF3 (R1 = Xyl = 2,6-C6H3Me2, R2 = Me; R1 = Me, R2 = CO2Me) provide a versatile entry point for many subsequent transformations, such as their reaction with carbon disulfide to provide zwitterionic dithiocarboxylate products. These compounds react with the coordinatively-unsaturated ruthenium vinyl precursors [Ru(CH=CHR3)Cl(CO)(PPh3)2] (R3 = C6H4Me-4, 1-Pyrenyl) to yield heterotrimetallic Fe2Ru compounds, exhibiting vinyl moieties at both iron and ruthenium centres. The emission associated with the pyrenyl unit is enhanced in the diiron vinyliminium ruthenium pyrenyl complex compared to the diethyldithiocarbamate analogue.

Circular dichroism and circularly polarised luminescence of bipyrenyl oligopeptides, with piperidines added in the peptide chains.

Upon combining chiral peptides (the most basic chiral source) with pyrene moieties, we found that chiral oligopeptides bearing two-pendant pyrenyl units exhibited circularly polarised luminescence (CPL) originating from intramolecular excimers at 450-490 nm in various solvents, and the sign of their CPL signals depended on the type of solvent employed. The CPL and circular dichroism signs and intensities could be tuned by the introduction of a piperidine unit into the chiral peptide chain; thus, the obtained structure could be considered a practical Lock ON-OFF system for oligopeptide luminophores.

Excited State Dynamics of a Photobiologically Active Ru(II) Dyad Are Altered in Biologically Relevant Environments.

In this study femtosecond and nanosecond time-resolved transient absorption spectroscopy was used to investigate the influence of ionic strength and complexity on the excited state dynamics of a Ru(II)-based metal-organic dyad. The bis-heteroleptic complex [Ru(bpy)2(ippy)]2+ (1), where bpy = 2,2'-bipyridine and ippy = 2-(1-pyrenyl-1H-imidazo[4,5-f][1,10]phenanthroline, is a potent photosensitizer for in vitro photodynamic therapy (PDT) and photodynamic inactivation (PDI) of microorganisms owing to a long-lived triplet excited state derived from a metal-to-ligand charge-transfer (3MLCT) state that is equilibrium with an intraligand (3IL) state. The prolonged lifetime provides ample opportunity for bimolecular quenching of this state by oxygen; thus singlet oxygen (1O2) sensitization is very efficient. In simple aqueous solution, fast cooling within the 3MLCT manifold is followed by energy transfer to an 3IL state, which is facilitated by rotation of a pyrenyl unit about the imidazo-pyrenyl (ip) coannular bond. For solutions of 1 in high ionic strength simulated biological fluid (SBF), a more physiologically relevant solvent that contains a complex mixture of ions at pH 7.4, femtosecond studies revealed an additional excited state, possibly based on an ion-ligand interaction. This new state appearing in high ionic strength SBF was not observable in water, simple buffers, or low ionic strength SBF. These photoinduced dynamics were also affected by the presence of biomolecules such as DNA in simple buffer, whereby relaxation on the picosecond time scale was accelerated from 39 to 18 ps with DNA intercalation by 1. The increased rate of coplanarization of the pyrene and the imidazole units was attributed to DNA-induced conformational restriction of the pyrenyl unit relative to the ip bond. Quantitative changes to excited state decay rates of 1 in solutions of high ionic strength were also observed when probed on the microsecond time scale. Notably, the thermalized excited state decay pathways were altered substantially with DNA intercalation, with access to some states being completely blocked. Experimentally, this manifested in the absence of the slowest microsecond decay channel, which is normally observed for 1 in solution. The quantitative and qualitative observations from this study highlight the importance of employing biologically relevant solvents and potential biomolecule targets when the excited state dynamics and photophysical properties (under cell-free conditions) responsible for the potent photobiological effects are assessed in the context of photodynamic therapy and photodynamic inactivation.

Can the Excited State Energy of a Pyrenyl Unit Be Directly Transferred to a Perylene Bisimide Moiety?

A pyrenyl unit (Py) was chemically connected to a perylene bisimide (PBI) moiety through a long and flexible linker, 4,7,10-trioxa-1,13-tridecanediamine (TOA), resulting in a fluorescent dyad, PBI-TOA-Py. Ultraviolet-visible absorption and fluorescence studies revealed that the two fluorescent units of PBI-TOA-Py behave independently. However, efficient Förster resonance energy transfer (FRET) from the Py unit to the PBI moiety in solution state was also observed. Temperature and solvent effect studies demonstrated that the energy transfer efficiency is highly dependent upon solution temperature and solvent nature. Specifically, for the dimethylformamide (DMF) solution of PBI-TOA-Py, the FRET efficiency is close to 88% at temperatures below ∼40 °C, but the efficiency greatly decreases to nearly zero when the temperature exceeds ∼80 °C. Moreover, addition of HAc into the DMF solution at room temperature could reduce the energy transfer efficiency to nearly zero, suggesting that the excited state energy of Py cannot be directly transferred to the PBI structure even though they are properly and chemically bonded. On the basis of the observations and time-resolved studies, it is believed that the observed efficient FRET from the Py unit to the PBI moiety occurs mainly through Py excimer formation, which could be a result of intermolecular association of the compound. Thus, the applications of the fluorescent dyad in solvent discrimination and trace water determination in organic solvents were verified through example studies.

Non-doped red-green-blue electroluminescence for fumaronitrile and fluorene bridge with pyrenyl or phenanthrylamino group

A red-emitting bis(4-(N-(1-pyrenyl)-3,5-dimethylphenylamino)phenyl)fumaronitrile (3) and a green-emitting 2,7-bis(N-1-pyrenyl-3,5-dimethylphenylamino)-9,9-diethylfluorene (4) were synthesized, while a red emissive bis(4-(N-(9-phenanthryl)-3,5-dimethylphenylamino)phenyl)fumaronitrile (5) and a blue 2,7-bis(N-9-phenanthryl-3,5-dimethylphenylamino)-9,9-diethylfluorene (6) were reported previously. The bulky and non-planar phenanthryl or pyrenyl amino substituent created steric torsional hindrance to restrict intermolecular aggregation and to promote high carrier mobility, thermal stability and luminous efficiency. The red non-doped devices for donor–π–acceptor 3 and 5 showed electroluminescent (EL) peaks at 668 and 652nm with luminance (external quantum) efficiencies of 3.45cd/A (6.89%), and 2.52cd/A (3.74%), respectively. 4 exhibited EL peak at 500nm with efficiency of 2.18cd/A (0.81%). The device based on 6 was centered at 460nm with efficiency of 1.86cd/A (1.16%). The large planar pyrenyl group had stronger electron-donating ability than phenanthryl group, so the EL emissions from 3 and 4 redshifted compared with those from the homologous 5 and 6. EL efficiency was improved more effectively by pyrenyl unit than by phenanthryl unit. The prepared compounds were multifunctional materials with emitting and hole-transporting properties.

A Porphyrin-Based Discrete Tetragonal Prismatic Cage: Host-Guest Complexation and Its Application in Tuning Liquid-Crystalline Behavior.

The host-guest complexation between a porphyrin-based 3D tetragonal prism (H) and electron-rich pyrene is investigated. This host-guest molecular recognition is further utilized to suppress the liquid-crystalline behavior of a nematic molecule (G) containing cyanobiphenyl mesogens functionalized with a pyrenyl unit. Furthermore, coronene, with an increased number of π-electrons, is used as a competitive guest to recover the liquid-crystalline behavior of G. This supramolecular approach provides a glimpse of the new possibilities to modulate the structures of the mesophases.

Phthalate mediated hydrogelation of a pyrene based system: a novel scaffold for shape-persistent, self-healing luminescent soft material

Two-component super-hydrogelation triggered by the acid-base interaction of a L-histidine appended pyrenyl derivative (PyHis) and phthalic acid (PA) was reported. The use of isomeric isophthalic or terephthalic acid or other comparable acids in place of PA does not lead to salt formation and therefore hydrogelation is not observed. Excimer formation of the pyrenyl unit has not been detected although the PyHis : PA = 1: 1 system undergoes extensive self-assembly in aqueous solution. The synergistic effect of intermolecular H-bonding forces, pi-pi stacking, electrostatic interactions, etc. is found to be responsible for robust hydrogel formation. Development of chiral supramotecular assemblies has been verified through circular dichroism spectroscopy. Morphological investigations involving the PyHis : PA = 1: 1 system show vesicular nano-structures with a definite bilayer width at relatively low concentrations. The latter fuses to construct coiled-coil left-handed helical fibers upon increase in the concentrations of the gelators. The intertwining of the resultant helical fibers eventually results in hydrogel formation. The probable bilayer packing in the self-assembled structures has been probed using X-ray diffraction (XRD) studies and lanthanide sensitization, which suggests that the polar imidazolium hydrogen phthalate unit of the gelator forms the head group and faces the hydrophilic water environment while the hydrophobic pyrenyl units sit inside the hydrophobic core of the bilayer. The hydrogel exhibits multi-stimuli responsiveness including thixotropic behavior. In addition, shape-persistent as well as rapid self-healing behaviour of the hydrogel was established. Furthermore load-bearing characteristics of the hydrogel have also been demonstrated.

In vitro multiwavelength PDT with 3IL states: teaching old molecules new tricks.

The purpose of the present investigation was to ascertain whether (3)IL excited states with microsecond lifetimes are universally potent for photodynamic applications, and if these long-lived states are superior to their (3)MLCT counterparts as in vitro PDT agents. A family of blue-green absorbing, Ru(II)-based transition metal complexes derived from the π-expansive dppn ligand was prepared and characterized according to its photodynamic activity against HL-60 cells, and toward DNA in cell-free media. Complexes in this series that are characterized by low-energy and long-lived (3)IL excited states photocleaved DNA with blue, green, red, and near-IR light. This panchromatic photodynamic effect translated to in vitro multiwavelength photodynamic therapy (PDT) with red-light cytotoxicities as low as 1.5 μM (EC50) for the parent complex and 400 nM for its more lipophilic counterpart. This potency is similar to that achieved with Ru(II)-based dyads containing long-lived (3)IL excitons located on appended pyrenyl units, and appears to be a general property of sufficiently long-lived excited states. Moreover, the red PDT observed for certain members of this family was almost 5 times more potent than Photofrin with therapeutic indices 30 times greater. Related Ru(II) complexes having lowest-lying (3)MLCT states of much shorter duration (≤1 μs) did not yield DNA photodamage or in vitro PDT with red or near-IR light, nor did the corresponding Os(II) complex with a submicrosecond (3)IL excited state lifetime. Therefore, metal complexes that utilize highly photosensitizing (3)IL excited states, with suitably long lifetimes (≫ 1 μs), are well-poised to elicit PDT at wavelengths even where their molar extinction coefficients are very low (<100 M(-1) cm(-1)). Herein we demonstrate that such unexpected reactivity gives rise to very effective PDT in the typical therapeutic window (600-850 nm).

Synthesis, optical properties and explosive sensing performances of a series of novel π-conjugated aromatic end-capped oligothiophenes

Four novel terthiophene (3T) derivatives, have been synthesized by employing Grignard coupling reaction via end-capping of naphthyl (NA) or pyrenyl (Py) unit to the one or two ends of 3T. It has been shown that both increasing electron donating strength and extending conjugation are effective approaches to improve the photochemical stability of the oligothiophene. Fluorescence studies demonstrated that the emission of the 3T derivatives is sensitive to the presence of some important nitro-containing explosives in their ethanol solution, in particular, 2,4,6-trinitrophenol (PA) and 3,5-dinitro-2,6-bispicrylamino pyridine (PYX). As an example, the detection limits of 4 to PA and PYX were determined to be 6.21×10−7mol/L and 8.95×10−7mol/L, respectively. Based on the discovery, a colorimetric detection method has been developed. The sensitive and selective response of the modified 3T to the explosives have been tentatively attributed to the adsorptive affinity of the compounds to the explosives, and to the higher probability of the electron transfer from the electron-rich 3T derivatives to the electron-poor nitro-containing explosives. No doubt, present study broadens the family of fluorophores which may be employed for the development of fluorescent sensors.

Synthesis and photophysical properties of polyethylene containing pyrenyl units in the side chain

Copolymerization of ethylene and diallyl-bis(pyren-1-yl)-silane (APyS) was investigated with zirconocene catalysts, rac-ethylenebis(indenyl)zirconium dichloride (1) and diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2), using methylaluminoxane as a cocatalyst. APyS was copolymerized via both 1,2-insertion and cyclization insertion, and cyclization selectivity, ratio of cyclized insertion unit, of APyS in the copolymers obtained with Catalyst 1 was higher than that obtained with Catalyst 2. Catalyst 2 showed a higher reactivity for APyS than Catalyst 1. Photophysical properties of the copolymer were investigated by UV–vis and photoluminescence (PL) spectroscopy, and absorption and fluorescence derived from pyrenyl groups were detected in the copolymers. Chloroform solution of the copolymer showed emission derived from both monomer and eximer of pyrenyl units. Only the emission derived from eximer of pyrenyl units was observed in the cast film. The polarized PL spectrum of an oriented film showed anisotropy, and the polarization excitation parallel to the drawing direction showed high fluorescence intensity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

A pyrenyl-PNA probe for DNA and RNA recognition

The design and the synthesis of a PNA oligomer containing a pyrenyl residue in the backbone were performed. PNA sequence was chosen complementary to a "G rich" target sequence involved in G-quadruplex formation. The pyrenyl unit replaced a nucleobase in the middle of the PNA through covalent linkage to the backbone by a carboxymethyl unit. A systematic study on the binding properties of this probe towards DNA and RNA complementary strands was carried out by UV and fluorescence spectroscopy. UV melting curves indicated that the PNA probe binds more tightly to RNA rather than to DNA. Thermodynamic data obtained by Van't Hoff fitting of the melting curves indicated that, in the case of RNA, a more favorable interaction occurs between the pyrenyl unit and the RNA nucleobases, leading to a very favorable enthalpic contribution.The fluorescence analysis showed specific quenching of the pyrene emission associated to the formation of the full-match PNA-DNA or PNA-RNA duplexes. Again, this behavior was more evident in the case of RNA, consistently with the stronger interaction of the pyrenyl unit with the complementary strand. In order to study the sequence specificity of the pyrenyl-PNA probe (pyr-PNA), recognition experiments on mismatched DNA and RNA sequences were also performed.