Showing papers on "Fluorescence spectrometry published in 2005"

The development of the DIGE system: 2D fluorescence difference gel analysis technology.

Abstract: Two-dimensional (2D) gel electrophoresis is a powerful technique enabling simultaneous visualization of relatively large portions of the proteome. However, the well documented issues of variation and lack of sensitivity and quantitative capabilities of existing labeling reagents, has limited the use of this technique as a quantitative tool. Two-dimensional difference gel electrophoresis (2D DIGE) builds on this technique by adding a highly accurate quantitative dimension. 2D DIGE enables multiple protein extracts to be separated on the same 2D gel. This is made possible by labeling of each extract using spectrally resolvable, size and charge-matched fluorescent dyes known as CyDye DIGE fluors. 2D DIGE involves use of a reference sample, known as an internal standard, which comprises equal amounts of all biological samples in the experiment. Including the internal standard on each gel in the experiment with the individual biological samples means that the abundance of each protein spot on a gel can be measured relative (i.e. as a ratio) to its corresponding spot in the internal standard present on the same gel. Ettan DIGE is the system of technologies that has been optimized to fully benefit from the advantages provided by 2D DIGE.

Evolution of Fluorescein as a Platform for Finely Tunable Fluorescence Probes

Abstract: Fluorescence imaging is the most powerful technique currently available for continuous observation of dynamic intracellular processes in living cells. Suitable fluorescence probes are naturally of critical importance for fluorescence imaging, but only a very limited range of biomolecules can currently be visualized because of the lack of flexible design strategies for fluorescence probes. At present, design is largely empirical. Here we show that the carboxylic group of traditional fluorescein dyes, formerly considered indispensable, has been replaced with other substituents, affording various kinds of new fluoresceins. Further, by breaking out of the traditional structure of fluorescein, we developed the first and totally rational design strategy for novel fluorescence probes based on a strict photochemical basis. The value of this approach is exemplified by its application to develop a novel, highly sensitive, and membrane-permeable fluorescence probe for β-galactosidase, which is the most widely used r...

Inhibition assay of biomolecules based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles.

Abstract: An inhibition assay method was developed based on the modulation in the FRET efficiency between quantum dots (QDs) and gold nanoparticles (AuNPs) in the presence of the molecules which inhibit the interactions between QD- and AuNP-conjugated biomolecules. For the functionalization, AuNPs were first stabilized by chemisorption of n-alkanethiols and then capped with the first generation polyamidoamine (G1 PAMAM) dendrimers. By employing a streptavidin−biotin couple as a model system, avidin was quantitatively analyzed as an inhibitor by sensing the change in photoluminescence (PL) quenching of SA−QDs by biotin−AuNPs. The detection limit for avidin was about 10 nM. It is anticipated that the PL quenching-based sensing system can be used for the quantitative analysis and high throughput screening of molecules which inhibit the specific biomolecular interactions.

Carbocyanine dyes as efficient reversible single-molecule optical switch

Abstract: We demonstrate that commercially available unmodified carbocyanine dyes such as Cy5 (usually excited at 633 nm) can be used as efficient reversible single-molecule optical switch, whose fluorescent state after apparent photobleaching can be restored at room temperature upon irradiation at shorter wavelengths. Ensemble photobleaching and recovery experiments of Cy5 in aqueous solution irradiating first at 633 nm, then at 337, 488, or 532 nm, demonstrate that restoration of absorption and fluorescence strongly depends on efficient oxygen removal and the addition of the triplet quencher β-mercaptoethylamine. Single-molecule fluorescence experiments show that individual immobilized Cy5 molecules can be switched optically in milliseconds by applying alternating excitation at 633 and 488 nm between a fluorescent and nonfluorescent state up to 100 times with a reliability of >90% at room temperature. Because of their intriguing performance, carbocyanine dyes volunteer as a simple alternative for ultrahigh-densit...

Fluorescent Amplifying Recognition for DNA G-Quadruplex Folding with a Cationic Conjugated Polymer: A Platform for Homogeneous Potassium Detection

Abstract: Single-stranded DNA with G-rich sequences can fold into secondary structures, G-quadruplexes, via intramolecular hydrogen-bonding interactions. This conformational change can be detected by a homogeneous assay method based on fluorescence resonance energy transfer (FRET) from a water-soluble cationic conjugated polymer (CCP) to a fluorescein chromophore labeled at the terminus of the G-quadruplex DNA. The space charge density around the DNA controls the efficiency of FRET from the CCP to the fluorescein. The higher FRET efficiency for the CCP/G-quadruplex pair is correlated to the stronger electrostatic interactions between the more condensed G-quadruplex and the CCP in comparison to the CCP/ssDNA pair. Since the potassium ion can specifically bind to the G-quadruplex DNA, the G-quartet-DNA/CCPs assembly can also be used as a platform to sense the potassium ion in water with high selectivity and sensitivity.

Stabilization of dissolved organic matter by sorption to the mineral soil

Abstract: The main process by which dissolved organic matter (DOM) is retained in forest soils is likely to be sorption in the mineral horizons that adds to stabilized organic matter (OM) pools. The objectives of this study were to determine the extent of degradation of sorbed OM and to investigate changes in its composition during degradation. DOM of different origins was sorbed to a subsoil and incubated for 1 year. We quantified mineralized C by frequent CO2 measurements in the headspace of the incubation vessels and calculated mean residence times by a double exponential model. Mineralization of C of the corresponding DOM in solution was used as a control to estimate the extent of DOM stabilization by sorption. Changes in the composition of sorbed OM during the incubation were studied by spectroscopic (UV, fluorescence) and isotope (13C, 14C) measurements after hot-water extraction of OM. The fraction of sorbed organic C mineralized during the incubation was only one-third to one-sixth of that mineralized in solution. The mean residence time of the most stable OM sample was estimated to increase from 28 years in solution to 91 years after sorption. For highly degradable DOM samples, the portion of stable C calculated by a double exponential model nearly doubled upon sorption. With less degradable DOM the stability increased by only 20% after sorption. Therefore, the increase in stability due to sorption is large for labile DOM high in carbohydrates and relatively small for stable DOM high in aromatic and complex molecules. Nevertheless, in terms of stability the rank order of OM types after sorption was the same as in solution. Furthermore, the extent of sorption of recalcitrant compounds was much larger than sorption of labile compounds. Thus, sorptive stabilization of this stable DOM sample was four times larger than for the labile ones. We conclude that stabilization of OM by sorption depends on the intrinsic stability of organic compounds sorbed. We propose that the main stabilization processes are selective sorption of intrinsically stable compounds and strong chemical bonds to the mineral soil and/or a physical inaccessibility of OM to microorganisms. The UV, fluorescence and 13C measurements indicated that aromatic and complex compounds, probably derived from lignin, were preferentially stabilized by sorption of DOM. The 13C and 14C data showed that degradation of the indigenous OM in the mineral soil decreased after sorption of DOM. We estimated DOM sorption stabilizes about 24 Mg C ha−1 highlighting the importance of sorption for accumulation and preservation of OM in soil.

Enhanced fluorescence cyanide detection at physiologically lethal levels : Reduced ICT-based signal transduction

Abstract: Three water-soluble fluorescent probes have been specifically designed to determine free cyanide concentrations up to physiologically lethal levels, >20 microM. The probes have been designed in such a way as to afford many notable sensing features, which render them unique with regard to signal transduction, photophysical characteristics, and their application to physiological cyanide determination and safeguard. The probes are readily able to reversibly bind free aqueous cyanide with dissociation constants around 4 microM3. Subsequent cyanide binding modulates the intramolecular charge transfer within the probes, a change in the electronic properties within the probes, resulting in enhanced fluorescence optical signals as a function of increased solution cyanide concentration. The ground-state chelation with cyanide produces wavelength shifts, which also enable the probes to sense cyanide in both an excitation and emission ratiometric manner, in addition to enhanced fluorescence signaling. This has enabled a generic cyanide sensing platform to be realized that is not dependent on fluorescent probe concentration, probe photodegradation, or fluctuations in the intensity of any employed excitation sources, ideal for remote cyanide sensing applications. Further, the >600 nm fluorescence emission of the probes potentially allows for enhanced fluorescence ratiometric cyanide sensing in the optical window of tissues and blood, facilitating their use for the transdermal monitoring of cyanide for mammalian safeguard or postmortem in fire victims, both areas of active research.

Chemical Sensors for Electronic Nose Systems

Abstract: Chemical sensors have been widely used for the analysis of volatile organic compounds. Employing chemical sensors in an array format with pattern recognition provides a higher degree of selectivity and reversibility leading to an extensive range of applications. When such systems are used for odour analysis they are termed ‘electronic noses’. Application of electronic noses ranges from the food industry, medical industry to environmental monitoring and process control. Many types of different gas sensors have been employed in the array. These include conducting polymers, metal oxide semiconductors, piezoelectric, optical fluorescence and amperometric gas sensors The transducer principle of these sensors is varied and is discussed in detail within this review. Examples of the current trends in sensor array technology as well as the applications to which the sensor-based noses have been applied are also discussed.

Copper Ion-Selective Fluorescent Sensor Based on the Inner Filter Effect Using a Spiropyran Derivative

Abstract: A highly selective copper(II) ion fluorescent sensor has been designed based on the UV−visible absorption of a spiropyran derivative coupled with the use of a metal porphyrin operative on the fluorescence inner filter effect. Spiropyrans, which combine the characteristics of metal binding and signal transduction, have been widely utilized in cationic ion recognition by UV−visible spectroscopy. In the present work, the viability of converting the absorption signal of the spiropyran molecule into a fluorescence signal was explored. On account of overlap of the absorption band of the spiropyran (λabs = 547 nm) in the presence of copper ion with the Q-band of an added fluorophore, zinc meso-tetraphenylporphyrin (λabs = 556 nm), the effective light absorbed by the porphyrin and concomitantly the emitted light intensity vary as a result of varying absorption of the spiropyran via fluorescence inner filter effect. The metal binding characteristic of the spiropyran presents an excellent selectivity for copper ion...

Highly Sensitive Near-Infrared Fluorescent Probes for Nitric Oxide and Their Application to Isolated Organs

Abstract: Novel near-infrared (NIR) fluorescent probes for nitric oxide (NO) have been designed, synthesized, and evaluated. Their NIR fluorescence was increased in an NO concentration-dependent manner under physiological conditions, and their reaction efficiency with NO was at least 53 times higher than that of a widely used NO probe, DAF-2. They were confirmed to function in isolated intact rat kidneys. Because NIR light can penetrate deeply into tissues, these probes may have potential for in vivo NO imaging.

High-affinity adaptors for switchable recognition of histidine-tagged proteins.

Abstract: We aspired to create chemical recognition units, which bind oligohistidine tags with high affinity and stability, as tools for selectively attaching spectroscopic probes and other functional elements to recombinant proteins. Several supramolecular entities containing 2-4 nitrilotriacetic acid (NTA) moieties were synthesized, which additionally contained an amino group, to which fluorescein was coupled as a sensitive reporter probe. These multivalent chelator heads (MCH) (termed bis-, tris-, and tetrakis-NTA) were characterized with respect to their interaction with hexahistidine (H6)- and decahistidine (H10)-tagged targets. Substantially increased binding stability with increasing number of NTA moieties was observed by analytical size exclusion chromatography. The binding enthalpies as determined by isothermal titration calorimetry increased nearly additively with the number of possible coordinative bonds between chelator heads and tags. Yet, a substantial excess of histidines in the oligohistidine tag was required for obtaining fully additive binding enthalpies. Dissociation kinetics of MCH/oligohistidine complexes measured by fluorescence dequenching showed an increase in stability by 4 orders of magnitude compared to that of mono-NTA, and subnanomolar affinity was reached for tris-NTA. The gain in free energy with increasing multivalency was accompanied by an increasing loss of entropy, which was ascribed to the high flexibility of the binding partners. Numerous applications of these MCHs for noncovalent, high affinity, yet reversible tethering of spectroscopic probes and other functional elements to the recombinant proteins can be envisioned.

Synthetic micelle sensitive to IR light via a two-photon process.

Abstract: A micellar assembly of molecules constituted of poly(ethylene glycol) as the hydrophilic component and 2-diazo-1,2-naphthoquinone as the hydrophobic component was shown to be destroyed in a two-photon photoreaction triggered by infrared light with release of an encapsulated fluorescent probe molecule.

Charge-mediated recognition of N-terminal tryptophan in aqueous solution by a synthetic host.

Abstract: The molecular recognition of peptides and proteins in aqueous solution by designed molecules remains an elusive goal with broad implications for basic biochemical research and for sensors and separations technologies. This paper describes the recognition of N-terminal tryptophan in aqueous solution by the synthetic host cucurbit[8]uril (Q8). Q8 is known to form 1:1:1 heteroternary complexes with methyl viologen (MV) and a second aromatic guest. Here, the complexes of Q8·MV with (i) the four natural aromatic α-amino acids, (ii) four singly charged tryptophan derivatives, and (iii) four tryptophan-containing tripeptides were characterized by isothermal titration calorimetry, mass spectrometry, and UV−visible, fluorescence, and 1H NMR spectroscopy. We find that Q8·MV binds Trp−Gly−Gly with high affinity (Ka = 1.3 × 105 M-1), with 6-fold specificity over Gly−Trp−Gly, and with 40-fold specificity over Gly−Gly−Trp. Analysis of the nine indole-containing compounds suggests that peptide recognition is mediated by...

Stress responses to polycyclic aromatic hydrocarbons in Arabidopsis include growth inhibition and hypersensitive response-like symptoms.

Abstract: Polycyclic aromatic hydrocarbons (PAHs) are of global environmental concern because they cause many health problems including cancer and inflammation of tissue in humans. Plants are important in removing PAHs from the atmosphere; yet, information on the physiology, cell and molecular biology, and biochemistry of PAH stress responses in plants is lacking. The PAH stress response was studied in Arabidopsis (Arabidopsis thaliana) exposed to the three-ring aromatic compound, phenanthrene. Morphological symptoms of PAH stress were growth reduction of the root and shoot, deformed trichomes, reduced root hairs, chlorosis, late flowering, and the appearance of white spots, which later developed into necrotic lesions. At the tissue and cellular levels, plants experienced oxidative stress. This was indicated by localized H 2 O 2 production and cell death, which were detected using 3, 3'-diaminobenzidine and trypan blue staining, respectively. Gas chromatography-mass spectrometry and fluorescence spectrometry analyses showed that phenanthrene is internalized by the plant. Gene expression of the cell wall-loosening protein expansin was repressed, whereas gene expression of the pathogenesis related protein PR1 was induced in response to PAH exposure. These findings show that (i) Arabidopsis takes up phenanthrene, suggesting possible degradation in plants, (ii) a PAH response in plants and animals may share similar stress mechanisms, since in animal cells detoxification of PAHs also results in oxidative stress, and (iii) plant specific defence mechanisms contribute to PAH stress response in Arabidopsis.

Tunable Inhibition and Denaturation of α-Chymotrypsin with Amino Acid-Functionalized Gold Nanoparticles

Abstract: Water-soluble gold nanoparticles bearing diverse l-amino acid terminals have been fabricated to probe the effect of receptor surface on protein surface binding. The interaction of these nanoparticles with α-chymotrypsin (ChT) was investigated by activity assay, gel electrophoresis, zeta-potential, circular dichroism, and fluorescence spectroscopy. The results show that both electrostatic and hydrophobic interactions between the hydrophobic patches of receptors and the protein contribute to the stability of the complex. The microscopic binding constants for these receptor−protein systems are 106−107 M-1, with the capacity of the nanoparticle receptors to bind proteins determined by both their surface area and their surface charge density. Furthermore, it is found that the hydrophilic side chains destabilize the ChT structure through either competitive hydrogen bonding or breakage of salt bridges, whereas denaturation was much slower with hydrophobic amino acid side chains. Significantly, correlation betwee...

Kinetics of 5α-Cholestan-3β-yl N-(2-Naphthyl)carbamate/n-Alkane Organogel Formation and Its Influence on the Fibrillar Networks

Abstract: The kinetics and mode of nucleation and growth of fibers by 5α-cholestan-3β-yl N-(2-naphthyl)carbamate (CNC), a low-molecular-mass organogelator (LMOG), in n-octane and n-dodecane have been investigated as their sols were transformed isothermally to organogels. The kinetics has been followed in detail by circular dichroism, fluorescence, small-angle neutron scattering, and rheological methods. When treated according to Avrami theory, kinetic data from the four methods are self-consistent and describe a gelation process involving one-dimensional growth and “instantaneous nucleation”. As expected from this growth model, polarized optical micrographs of the self-assembled fibrillar networks (SAFINs) show fibrous aggregates. However, their size and appearance change abruptly from spherulitic to rodlike as temperature is increased. This morphological change is attended by corresponding excursions in static and kinetic CD, fluorescence and rheological data. Furthermore, the rheological measurements reveal an un...

Amounts and degradability of dissolved organic carbon from foliar litter at different decomposition stages

Abstract: Litter is one of the main sources of dissolved organic carbon (DOC) in forest soils and litter decomposition is an important control of carbon storage and DOC dynamics. The aim of our study was to evaluate (i) effects of tree species on DOC production and (ii) relationships between litter decomposition and the amount and quality of DOC. Five different types of leaves and needles were exposed in litterbags at two neighboring forest sites. Within 12 months we sampled the litterbags five times and leached aliquots of field moist litter in the laboratory. In the collected litter percolates we measured DOC concentrations and recorded UV and fluorescence spectra in order to estimate the aromaticity and complexity of the organic molecules. Furthermore, we investigated the biodegradability of DOC from fresh and decomposed litter during 6 weeks incubations. Fresh sycamore maple litter released the largest amounts of DOC reaching about 6.2% of litter C after applying precipitation of 94 mm. We leached 3.9, 1.6, 1.0 and 3.3% carbon from fresh mountain ash, beech, spruce and pine litter, respectively. In the initial phase of litter decomposition significantly decreasing DOC amounts were released with increasing litter mass loss. However, after mass loss exceeds 20% DOC production from needle litter tended to increase. UV and fluorescence spectra of percolates from pine and spruce litter indicated an increasing degree of aromaticity and complexity with increasing mass loss as often described for decomposing litter. However, for deciduous litter the relationship was less obvious. We assume that during litter decomposition the source of produced DOC in coniferous litter tended toward a larger contribution from lignin-derived compounds. Biodegradability of DOC from fresh litter was very high, ranging from 30 to 95% mineralized C. DOC from degraded litter was on average 34% less mineralizable than DOC from fresh litter. Taking into account the large DOC production from decomposed needles we can assume there is an important role for DOC in the accumulation of organic matter in soils during litter decomposition particularly in coniferous forests.

Discovery of O-GlcNAc Transferase Inhibitors

Abstract: O-GlcNAcylation of serine and threonine residues is a dynamic and essential post-translational modification involved in signaling pathways in eukaryotes. Studies of O-GlcNAcylation would be aided by small-molecule inhibitors of O-GlcNAc transferase (OGT), the sole enzyme know to mediate this modification, but discovery of such molecules has been hampered by poor expression of cloned OGT and lack of suitable high-throughput screens. This Communication describes the development an expression system to access large amounts of the catalytic domain of OGT and the implementation of a fluorescence-based substrate analogue displacement assay that has led to the discovery of a set of OGT inhibitors. This work lays the foundation for both structural and functional analysis of the catalytic domain of OGT.

Preconcentration of proteins on microfluidic devices using porous silica membranes.

Abstract: Fluorescently labeled proteins were electrophoretically concentrated on microfabricated devices prior to separation and laser-induced fluorescence detection on the same device. The proteins were concentrated using a porous silica membrane between adjacent microchannels that allowed the passage of buffer ions but excluded larger migrating molecules. Concentrated analytes were then injected into the separation column for analysis. Two basic microchip designs were tested that allowed sample concentration either directly in the sample injector loop or within the microchannel leading from the sample reservoir to the injector. Signal enhancements of ∼600-fold were achieved by on-chip preconcentration followed by SDS−CGE separation. Preconcentration for CE analysis in both coated and uncoated open channels was also demonstrated. Fluorescently labeled ovalbumin could be detected at initial concentrations as low as 100 fM by using a combination of field-amplified injection and preconcentration at a membrane prior ...

Structural and thermodynamic studies on cation-Pi interactions in lectin-ligand complexes: high-affinity galectin-3 inhibitors through fine-tuning of an arginine-arene interaction.

Abstract: The high-resolution X-ray crystal structures of the carbohydrate recognition domain of human galectin-3 were solved in complex with N-acetyllactosamine (LacNAc) and the high-affinity inhibitor, methyl 2-acetamido-2-deoxy-4-O-(3-deoxy-3-[4-methoxy-2,3,5,6-tetrafluorobenzamido]-β-d-galactopyranose)-β-d-glucopyranoside, to gain insight into the basis for the affinity-enhancing effect of the 4-methoxy-2,3,5,6-tetrafluorobenzamido moiety The structures show that the side chain of Arg144 stacks against the aromatic moiety of the inhibitor, an interaction made possible by a reorientation of the side chain relative to that seen in the LacNAc complex Based on these structures, synthesis of second generation LacNAc derivatives carrying aromatic amides at 3‘-C, followed by screening with a novel fluorescence polarization assay, has led to the identification of inhibitors with further enhanced affinity for galectin-3 (Kd ≥ 320 nM) The thermodynamic parameters describing the binding of the galectin-3 C-terminal to

Detection of single bacterial pathogens with semiconductor quantum dots.

Abstract: Semiconductor quantum dots (QDs) have been used in a simple fluorometric assay to detect single cells of the pathogenic Escherichia coli O157:H7 serotype. Composed of CdSe/ZnS core/shell QDs conjugated to streptavidin, this system exhibits 2 orders of magnitude more sensitivity than a similar assay using a common organic dye. Selectivity for this pathogenic bacterial strain over a common lab strain (E. coli DH5alpha), which is gained from the use of specific biotinylated antibodies, is also demonstrated for QD labeling. Under continuous excitation, these QDs retain high fluorescence intensities for hours, whereas a typical organic dye bleaches within seconds, allowing for more rapid and accurate identification of E. coli O157:H7 in single-cell fluorescence-based assays. This indirect QD labeling method, based on antibody-antigen and streptavidin-biotin interactions, is flexible enough to expand to other systems and has great potential for use in simultaneous multicolor detection schemes.

Performance of Fluorescence Correlation Spectroscopy for Measuring Diffusion and Concentration

Abstract: Fluorescence correlation spectroscopy (FCS) has become an important tool for measuring diffusion, concentration, and molecular interactions of cellular components. The interpretation of FCS data critically depends on the measurement set-up. Here, we present a rigorous theory of FCS based on exact wave-optical calculations. Six of the most important optical and photophysical factors that influence FCS are studied: fluorescence anisotropy, cover-slide thickness, refractive index of the sample, laser-beam geometry, optical saturation, and pinhole adjustment. Our theoretical framework represents a general attempt to link all relevant parameters of the experimental set-up with the measured correlation function.

Microarray immunoassay for phenoxybenzoic acid using polymer encapsulated Eu:Gd2O3 nanoparticles as fluorescent labels.

Abstract: Currently, detection in microarray bioanalysis is based mainly on the use of organic dyes. To overcome photobleaching and spectral overlaps we applied a new type of fluorophore, crystalline europium-doped gadolinium oxide (Eu:Gd2O3) nanoparticles, as labels in immunoassay microarrays. The Eu:Gd2O3 nanoparticles synthesized by spray pyrolysis offer narrow red emission, large Stokes shift, photostable laser-induced fluorescence with a long lifetime (1 ms). The amino functionalization of the particles was achieved by poly(l-lysine) (PL) encapsulation. The formation of a stable PL shell was confirmed by TEM analysis, colloidal stability studies, and quantification of the surface reactive amino groups. The PL-encapsulated particles were covalently conjugated to antibodies and successfully applied as reporters in a competitive fluorescence microimmunoassay for phenoxybenzoic acid (PBA), a generic biomarker of human exposure to pyrethroid insecticides. Microarrays were fabricated by microcontact printing of BSA−...

Photophysics and Biological Applications of the Environment-Sensitive Fluorophore 6-N,N-Dimethylamino-2,3-naphthalimide

Abstract: We have synthesized a new environment-sensitive fluorophore, 6-N,N-dimethylamino-2,3-naphthalimide (6DMN). This chromophore exhibits valuable fluorescent properties as a biological probe with emission in the 500−600 nm range and a marked response to changes in the environment polarity. The 6DMN fluorescence is red-shifted in polar protic environments, with the maximum emission intensity shifting more than 100 nm from 491 nm in toluene to 592 nm in water. Additionally, the fluorescence quantum yield decreases more than 100-fold from chloroform (Φ = 0.225) to water (Φ = 0.002). The scope and applications of the 6DMN probe are expanded with the synthesis of an Fmoc-protected amino acid derivative (5), which contains the fluorophore. This unnatural amino acid has been introduced into several peptides, demonstrating that it can be manipulated under standard solid-phase peptide synthesis conditions. Peptides incorporating the new residue can be implemented for monitoring protein−protein interactions as exemplif...

A family of main-chain polymeric Lewis acids: synthesis and fluorescent sensing properties of boron-modified polythiophenes.

Abstract: A new family of main-chain organoborane polymeric Lewis acids (PTh−BAr) that contain Lewis acidic boron groups embedded into a polythiophene backbone has been prepared under mild conditions through tin−boron exchange reaction. When phenyl and pentafluorophenyl groups are attached to boron, blue and green luminescence is observed, respectively, while the attachment of ferrocenyl substituents leads to a characteristic red color. The incorporation of readily accessible highly Lewis acidic groups into the conjugated polymer backbone provides an opportunity for sensing of Lewis basic substrates. For instance, treatment of the polymer containing phenyl substituents on boron with pyridine leads to efficient quenching of the fluorescence, while the polymer containing ferrocenyl groups changes color from dark red to light orange.