Pyrene-stacked nanostructures constructed in the recombinant tobacco mosaic virus rod scaffold

The effect of pyrenes introduced into a tobacco mosaic virus (TMV) coat protein monomer on the formation and stability of the TMV assembly was investigated. The possible arrangement of the pyrenes in the inner cavity of the TMV rod was also estimated. The pyrene derivative was introduced to four specific amino acids in the cavity of the TMV rod structure. Rod-structure formation was examined by atomic force microscopy (AFM). Two pyrene-attached mutants (positions 99 and 100) assembled to increase the length of the rod structures by 2.5 microm at pH 5.5. The interaction of the pyrene moieties in the TMV cavity was investigated by steady-state and time-resolved spectroscopic analysis. Strong excimer emission with significantly short wavelength (465 nm) was observed from the two mutants mentioned above. Excitation and UV-visible spectra indicate that the pyrene moieties form pi-stacked structures in the TMV cavity. Details of the pyrene interaction were investigated by analyzing the fluorescence lifetime of the excimer. Results suggest that the pyrenes formed preassociated rigid structures with partially overlapped geometry in the restricted space of the TMV cavity. The pyrenes effectively stabilize the TMV rod through a pi-stacking interaction in a well-ordered way, and the single pyrene moiety introduced into the monomer affects the overall formation of the TMV rod structure.     

Color-tunable fluorescent organogels: columnar self-assembly of pyrene-containing oligo(glutamic acid)s

New fluorescent gelators containing pyrene moieties and dendritic oligopeptides have been developed. These molecules self-assemble into 1D helical columnar structures that lead to the formation of 3D fibrous random networks. The resulting gel materials show monomer emission of pyrenes because the hydrogen-bonded array of the oligopeptide moieties greatly suppresses the formation of pyrene excimers. In contrast, in the sol states green excimer emission of the pyrenes is observed because of the dissociation of intermolecular hydrogen bonds. This is the first example of the reverse-mode color switching of fluorescence for supramolecular pyrene assemblies.     

Chloride selective calix[4]arene optical sensor combining urea functionality with pyrene excimer transduction

A neutral 2-site chloride selective compound has been developed (3), based on a 1,3-alternate tetrasubstituted calix[4]arene providing a preorganized supramolecular scaffold. The resultant supramolecular cavity is among the first to combine urea functional groups bridged with single methylene spacers to pyrene moieties. It combines a naturally and synthetically proven H-bonding system with the elegant ratiometric fluorescent signaling properties of an intramolecular pyrene excimer system, triggered by conformational changes upon anion coordination. The excimer emission of 3 is quenched, with a simultaneous rise in the monomer emission solely by the chloride anion among a wide variety of anions tested. 3 has an association constant of 2.4 x 10(4) M(-1) with chloride. The suitability and advantages of ratiometric optical sensor compounds like 3 for use in practical sensor devices is discussed. 3 has an LOD of 8 x 10(-6) M with chloride in acetonitrile-chloroform (95:5 v/v). A dynamic fluorescence study revealed a response time of < 3 s. A recently developed and simple HPLC-based purification method complimented conventional organic work up methods to yield pure product.     

A Selective Cucurbit[8]uril-Peptide Beacon Ensemble for the Ratiometric Fluorescence Detection of Peptides

A convenient supramolecular strategy for constructing a ratiometric fluorescent chemosensing ensemble, consisting of a macrocyclic host (cucurbit[8]uril CB[8]), and a pyrene-tagged amphiphilic peptide beacon (AP 1), is reported. AP 1 unfolds upon encapsulation of the pyrene termini into the hydrophobic CB[8] cavity. This changes pyrene excimer to monomer emission. Substrates with higher affinity for the CB[8] cavity can displace AP 1 from the ensemble. The released AP 1 folds again to form a pyrene excimer, which allows for the ratiometric fluorescence monitoring of the substrate. In this report, the ensemble capacity for ratiometric fluorescence monitoring of biological substrates, such as amino acid derivatives, specific peptides, and proteins, in aqueous media is demonstrated.     

New cyclen-cored dendrimers functionalized with pyrene: Synthesis characterization,optical and photophysical properties

New cyclen (1,4,7,10-teraazacyclododecane) cored dendrimers up to the second generation, functionalized with 4, 8 and 16 pyrene units, respectively, were synthesized following a convergent procedure. All new compounds were characterized by NMR spectroscopies and ESI or MALDI TOF mass spectrometry. The optical and photophysical properties of the new dendrimers were studied in THF solution. Absorption spectra showed the typical absorption bands of pyrene moieties. In the fluorescence spectra, monomer as well as excimer emission were observed for all compounds. An increased proportion of excimer emission was observed in the dendrimer of the highest generation.     

Fluoride-sensing calix-luminophores based on regioselective binding

Bifunctional (fluorescence and visible light absorption) anion-sensing compounds 1 and 2 based on calix[4]arene platform with 4-nitrophenylazo and pyrene moieties have been developed. The two NHs of the amide groups of 1 bind the fluoride anion through the H-bonding. This changes the characteristic excimer emission and forms a new emission peak from a static excimer. In 2, two OHs bind the fluoride anion, and this changes the characteristic absorption spectrum. The DFT calculation supports the regioselective binding of the fluoride anion, which is responsible for the different sensing property.     

Molecule-binding dependent assembly of split aptamer and γ-cyclodextrin: A sensitive excimer signaling approach for aptamer biosensors

A highly sensitive and selective fluorescence aptamer biosensors for the determination of adenosine triphosphate (ATP) was developed. Binding of a target with splitting aptamers labeled with pyrene molecules form stable pyrene dimer in the γ-cyclodextrin (γ-CD) cavity, yielding a strong excimer emission. We have found that inclusion of pyrene dimer in γ-cyclodextrin cavity not only exhibits additive increases in quantum yield and emission lifetime of the excimer, but also facilitates target-induced fusion of the splitting aptamers to form the aptamer/target complex. As proof-of-principle, the approach was applied to fluorescence detection of adenosine triphosphate. With an anti-ATP aptamer, the approach exhibits excimer fluorescence response toward ATP with a maximum signal-to-background ratio of 32.1 and remarkably low detection limit of 80 nM ATP in buffer solution. Moreover, due to the additive fluorescence lifetime of excimer induced by γ-cyclodextrin, time-resolved measurements could be conveniently used to detect as low as 0.5 μM ATP in blood serum quantitatively.     

Synthesis of double-armed lariat ethers with pyrene moieties at each end of two sidearms and their fluorescence properties in the presence of alkali metal and alkaline earth metal cations

Two types of double-armed lariat ether derivatives having pyrene moieties at each end of two sidearms, (3x + 1)-crown-x derivatives 1 (x = 5), 2 (x = 6), and 3 (x = 4) (type A) and 3y-crown-y derivatives, 6 (y = 5) and 7 (y = 6) (type B), were synthesized, and their complexation behavior toward alkali metal and alkaline earth metal cations was examined by fluorescence spectroscopy. Pyrene excimer emission decreased accompanied by an increase in monomer emission upon metal ion complexation. This finding is ascribed to the change of the spatial distance of two pyrene rings by movement suppression of both the crown ring and one of the two sidearms based on complexation with the metal cation. The selectivity for alkaline earth metal cations was highly dependent on the fitness of the host cavity and the guest size. Although most of the fluorophores did not respond to alkali metal cations, only trans-7a containing an 18-crown-6 ring showed K(+) selectivity.     

Insertion of two pyrene moieties into oligodeoxyribonucleotides for the efficient detection of deletion polymorphisms

For the detection of deletion polymorphisms, two pyrene moieties are tethered to an oligodeoxyribonucleotide (ODN) on both sides of the intervening base; one- and two-base deletions can be selectively detected by the strength of the excimer emission.     

Fluorescent visualization of the conformational change of aromatic amide or urea induced by N-methylation

The conformational change of amide structure of benzanilide or urea structure of N,N′-diphenylurea induced by methylation of the secondary nitrogen was visualized by introduction of pyrene moieties on the benzene ring. In contrast to the extended trans-form of secondary amide and urea, which showed monomer fluorescence emission of pyrene, the corresponding N-methylated compounds exist in cis-form, which exhibited excimer emission.     

Excited-state energy transfers in single-walled carbon nanotubes functionalized with tethered pyrenes

Single-walled carbon nanotubes were co-functionalized with pyrenemethanol and 3,5-dihexadecanyloxybenzyl alcohol in different ratios with the purpose of altering the content of pyrene moieties tethered to the nanotube surface. The functionalized nanotube samples were characterized by using established instrumental techniques. The absorption and emission results of the samples suggest that there are significant “intramolecular” excited-state energy transfers from both pyrene monomer and excimer to the linked nanotube, though the energy transfer efficiencies may be different between the monomer and excimer. The excimer formation can be limited by reducing the pyrenemethanol fraction to simplify the excited state processes, but contributions from the luminescence of the well-functionalized carbon nanotubes in the same wavelength region becomes an additional complication. Mechanistic implications of the photophysical results are discussed.     

Fluorescence Switches Triggered by Metal Ions

Molecular switches 1 with a modular architecture whose functional principle is based on conformational changes around two acetylene axes were developed. By systematic screening of various metal ions, it was found that especially Pb²⁺ ions effectively trigger the switching event. The reporting of this event takes place by the change of the ratio between excimer and monomer fluorescence emission of two pyrene moieties.     

A calixarene based fluorescent Sr2+ and Ca2+ probe

A fluorescent probe, PyCalix, which has two pyrene moieties at the lower rim of a calix[4]arene fixed in the cone conformation was synthesized and its complexation behavior with alkali and alkaline earth cations was studied by fluorescence spectrometry. The compound showed intramolecular excimer emission at approximately 480 nm in the fluorescence spectra. Upon complexation with alkaline earth metal cations, a decrease of excimer emission was observed. The decrease of excimer emission was accompanied by an increase of monomer emission of pyrenes at 397 nm. The order of complexation constants of PyCalix with metal ions was Sr(+ approximately Ca2+ > Ba2+ > Mg2+ > K+ > Na+ > Cs+ for all reagents. PyCalix doped polyvinyl chloride (PVC) membrane was fabricated and our results showed that this membrane can be used for selective detection of Sr2+.     

Indium(III)-induced fluorescent excimer formation and extinction in calix[4]arene-fluoroionophores

New fluorogenic or/and chromogenic calix[4]arenes 1-3 with two facing amide groups linked to fluorescent pyrene units are synthesized. Orientations of the pyrene units are remote from each other in 1 and face-to-face pi-stacked in 2, which produces different photophysical properties. In the excited state, the two pyrene units of 2 form a strong intramolecular excimer displaying an emission at 472 nm with a relatively weak monomer emission at 395 nm. In contrast, 1 exhibits only a monomer emission at 398 nm because intramolecular hydrogen bonding between the phenolic OH oxygens and the amide hydrogens prevents pi-stacking of the two pyrene groups. Fluorescence changes upon addition of various metal ions show that 1 has a remarkably high selectivity for In(3+) over the other metal ions tested. Compound 1 forms 2:1 (metal:ligand), as well as 1:1 complexes, with In(3+), with fluorescence varying uniquely with the complex stoichiometry. Compound 3, which possess two pyrene units and two chromogenic azo groups, shows almost the same binding behavior toward metal ions as does 1, together with additional bathochromic shifts of the absorption maximum. Compared with 1, compound 3 emits a considerably weaker fluorescence, which is attributed to electron transfer from the pyrene units to the nitro groups of the phenylazo moieties.     

Dinuclear Diphosphine Complexes of Gold(I) Alkynyls,the Effects of Alkynyl Substituents onto Photophysical Behavior

A series of dinuclear diphosphine complexes of gold(I) alkynyls containing bis(diphenylphosphanyl)ethane/propane and alkynyl ligands with aromatic substituents (biphenyl, pyrene, and azobenzene) was synthesized and characterized using X‐ray crystallography and NMR spectroscopy. Photophysical parameters of the compounds obtained strongly depend on the nature of aromatic substituents in the alkynyl ligands. Azobenzene containing derivatives are non‐luminescent, whereas biphenyl and pyrene containing complexes display moderate emission both in solution and in solid state. The complexes with biphenyl substituents display strong heavy atom effect and show typical phosphorescent emission. In contrast, the complexes containing pyrene chromophore are fluorescent that points to the absence of spin orbit coupling in these systems, which additionally display static excimer emission in solid phase due to ground state π‐stacking of the pyrene moieties.     

Synthesis of bispyrenyl sugar-aza-crown ethers as new fluorescent molecular sensors for Cu(II)

Two N-pyrenylacetamide-substituted sugar-aza-crown ethers have been synthesized as new fluorescent chemosensors. The designed ligands 1 and 2 exhibit fluorescence characteristics of a pyrene monomer and a dynamic excimer emission when compared to N-pyrenylacetamide as a model compound. Both ligands displayed a Cu2+-sensitive fluorescence quenching with a 1:1 stoichiometry and high stability constants (log K = 6.7 for 1 and 7.8 for 2). The quenching effect was rationalized on the basis of photoinduced electron transfer from the excited pyrene to the complexed Cu2+ cation, while the changes in excimer-to-monomer ratio were explained by a conformational analysis through DFT calculations. The predicted structure suggests that the Cu2+ cation is coordinated with the two carbonyl groups and the sugar-aza-crown ethers which rigidified the complex structure and placed the two pyrene moieties far apart.     

A fluoride-selective PCT chemosensor based on formation of a static pyrene excimer

[reaction: see text] Calixarene-based fluorescent chemosensor 1 with two fluorogenic pyrene units conjugated to amide groups as guest recognition sites is synthesized. Complexation of F(-) by 1 causes a red shift of its absorption band to 400 nm (Deltalambda = 54 nm) and a blue shift of the excimer emission to 470 nm (Deltalambda = 12 nm) together with enhanced fluorescence intensity. The blue-shifted excimer emission is attributed to a pyrene dimer formed in the ground state, a so-called static excimer.     

Unambiguous detection of target DNAs by excimer-monomer switching molecular beacons

A new class of molecular beacons were developed in which pyrene fluorophores were connected both at 3' and 5' ends of a single-stranded oligonucleotide. The two pyrene-based fluorophores were synthesized from the same starting material, so that the preparation of the beacons was simplified. The detection strategy of the beacons for target DNAs is based on "excimer-monomer emission switching" of the pyrene fluorophores: excimer emission of the pyrene moieties changed to monomer one when the beacons hybridized with the targets. This type of two-state mode of fluorescence allows unambiguous detection of the target DNAs because strict 1:1 correlation between the nonhybridized and the hybridized beacons can be monitored by the presence of isoemissive points of the fluorescence changes. The beacons can detect target 19-mer DNAs and can discriminate the targets from their single-nucleotide mismatches at 1 nM concentration. Advantages of the excimer-monomer switching molecular beacons were discussed in comparison with conventional ones.     

Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag ion

New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag⁺ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu²⁺, and Hg²⁺ quench both the monomer and excimer emission of pyrene acutely. The ¹H NMR results indicated that Ag⁺ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene.     

Protease Probes that Enable Excimer Signaling upon Scission

Peptide‐based probes that fluoresce upon proteolytic cleavage are invaluable tools for monitoring protease activity. The read‐out of protease activity through pyrene excimer signaling would be a valuable asset because the large Stokes shift and the long lifetime of the excimer emission facilitate measurements in autofluorescent media such as blood serum. However, proteolytic cleavage abolishes rather than installs the proximity relationships required for excimer signaling. Herein, we introduce a new probe architecture to enable the switching on of pyrene excimer emission upon proteolytic scission. The method relies on hairpin‐structured peptide nucleic acid (PNA)/peptide hybrids with pyrene units and anthraquinone‐based quencher residues positioned in a zipper‐like arrangement within the PNA stem. The excimer hairpin peptide beacons afforded up to a 50‐fold enhancement of the pyrene excimer emission. Time‐resolved measurements allowed the detection of matrix metalloprotease 7 in human blood serum.