Supramolecular Surface Modification and Solubilization of Single‐Walled Carbon Nanotubes with Cyclodextrin Complexation

A novel approach to solubilize single‐walled carbon nanotubes (SWCNTs) in the aqueous phase is described by employing supramolecular surface modification. We use cyclodextrin complexes of synthetic molecules that contain a planar pyrene moiety or a bent, shape‐fitted triptycene moiety as a binding group connected through a spacer to an adamantane moiety that is accommodated in the cyclodextrin cavity. The binding groups attach to the sidewalls of SWCNTs through a π–π stacking interaction to yield a supramolecular system that allows the SWCNTs to dissolve in the aqueous phase through the formed hydrophilic cyclodextrin shell. The black aqueous SWCNT solutions obtained are stable over a period of months. They are characterized through absorbance, static, and time‐resolved fluorescence spectroscopy as well as Raman spectroscopy, TEM, and fluorescence‐decay measurements. Furthermore, the shape‐fitted triptycene‐based system shows a pronounced selectivity for SWCNTs with a diameter of 1.0 nm.     

Near‐Infrared Fluorescent Probe with New Recognition Moiety for Specific Detection of Tyrosinase Activity: Design,Synthesis, and Application in Living Cells and Zebrafish

Fluorescence imaging of tyrosinase (a cancer biomarker) in living organisms is of great importance for biological studies. However, selective detection of tyrosinase remains a great challenge because current fluorescent probes that contain the 4‐hydroxyphenyl moiety show similar fluorescence responses to both tyrosinase and some reactive oxygen species (ROS), thereby suffering from ROS interference. Herein, a new tyrosinase‐recognition 3‐hydroxybenzyloxy moiety, which exhibits distinct fluorescence responses for tyrosinase and ROS, is proposed. Using the recognition moiety, we develop a near‐infrared fluorescence probe for tyrosinase activity, which effectively eliminates the interference from ROS. The high specificity of the probe was demonstrated by imaging and detecting endogenous tyrosinase activity in live cells and zebrafish and further validated by an enzyme‐linked immunosorbent assay. The probe is expected to be useful for the accurate detection of tyrosinase in complex biosystems.     

Near‐Infrared Fluorescent Probe with New Recognition Moiety for Specific Detection of Tyrosinase Activity: Design,Synthesis, and Application in Living Cells and Zebrafish

Fluorescence imaging of tyrosinase (a cancer biomarker) in living organisms is of great importance for biological studies. However, selective detection of tyrosinase remains a great challenge because current fluorescent probes that contain the 4‐hydroxyphenyl moiety show similar fluorescence responses to both tyrosinase and some reactive oxygen species (ROS), thereby suffering from ROS interference. Herein, a new tyrosinase‐recognition 3‐hydroxybenzyloxy moiety, which exhibits distinct fluorescence responses for tyrosinase and ROS, is proposed. Using the recognition moiety, we develop a near‐infrared fluorescence probe for tyrosinase activity, which effectively eliminates the interference from ROS. The high specificity of the probe was demonstrated by imaging and detecting endogenous tyrosinase activity in live cells and zebrafish and further validated by an enzyme‐linked immunosorbent assay. The probe is expected to be useful for the accurate detection of tyrosinase in complex biosystems.     

Synthesis, optical, electrochemical, and thermal studies on triazole-based dendrimers with diphenylamine as surface group

Fréchet-type dendrimers with hole-transporting diphenylamine as surface group and electron-transporting triazole moiety as building block have been synthesized by convergent synthetic strategy through ‘click chemistry’ methodology. First generation dendrimer exhibits longer relaxation time, higher quantum yield in the fluorescence spectrum, and better thermal stability than the zero and second generation dendrimers. CV studies showed irreversible reduction potential and the formation of radical cation due to diphenylamine moiety.     

Fluororeactands for the Detection of Saccharides Based on Hemicyanine Dyes with a Boronic Acid Receptor

Three hemicyanine dyes with boronic acid receptor functions have been synthesized in a two step procedure. These dyes are capable of forming a covalent bond between their boronic acid moiety and the diol moiety of saccharides which causes fluorescence to change. In detail, the indicator dyes exhibit absorbance maxima at around 460 nm and emission at around 600 nm, show increases in fluorescence upon exposure to saccharides and can be used in aqueous solution at physiological pH.     

A PEGylated Fluorescent Turn‐On Sensor for Detecting Fluoride Ions in Totally Aqueous Media and Its Imaging in Live Cells

Owing to the considerable significance of fluoride anions for health and environmental issues, it is of great importance to develop methods that can rapidly, sensitively and selectively detect the fluoride anion in aqueous media and biological samples. Herein, we demonstrate a robust fluorescent turn‐on sensor for detecting the fluoride ion in a totally aqueous solution. In this study, a biocompatible hydrophilic polymer poly(ethylene glycol) (PEG) is incorporated into the sensing system to ensure water solubility and to enhance biocompatibility. tert‐Butyldiphenylsilyl (TBDPS) groups were then covalently introduced onto the fluorescein moiety, which effectively quenched the fluorescence of the sensor. Upon addition of fluoride ion, the selective fluoride‐mediated cleavage of the Si? O bond leads to the recovery of the fluorescein moiety, resulting in a dramatic increase in fluorescence intensity under visible light excitation. The sensor is responsive and highly selective for the fluoride anion over other common anions; it also exhibits a very low detection limit of 19 ppb. In addition, this sensor is operative in some real samples such as running water, urine, and serum and can accurately detect fluoride ions in these samples. The cytotoxicity of the sensor was determined to be Grade I toxicity according to United States Pharmacopoeia and ISO 10993‐5, suggesting the very low cytotoxicity of the sensor. Moreover, it was found that the senor could be readily internalized by both HeLa and L929 cells and the sensor could be utilized to track fluoride level changes inside the cells.     

Steroid-porphyrin conjugate for saccharide sensing in protic media

A new saccharide receptor in protic media has been designed and synthesized. The receptor combines advantages of steroids, which are responsible for saccharide binding, and of the porphyrin moiety acting as a signalling component of the molecule due to changes in UV-vis electronic spectra. The synthesis is based on condensation of steroid aldehyde with pyrrole to form the porphyrin unit with four protected steroid moieties. After deprotection, meso-substituted porphyrin contains 12-hydroxy groups on the steroidal part. The receptor is soluble in aqueous solutions and exhibits high complexation affinity towards saccharides. Because the receptor extensively aggregates in water, most of the experiments were performed in 50% aqueous 2-propanol where aggregation is significantly eliminated. Binding is evidenced by spectral changes in the Soret region of the receptor in UV-vis absorption spectra allowing the evaluation of the binding constants. Additional confirmation of binding is obtained using 1H NMR, Raman and IR spectroscopies and the surface plasmon resonance technique. The receptor exhibits higher selectivity for oligosaccharides over monosaccharide. The results point to the importance of a combination of multiple binding via H-bonding and hydrophobic interactions.     

Novel bifunctional acridine-acridinium conjugates: synthesis and study of their chromophore-selective electron-transfer and DNA-binding properties

Novel bifunctional conjugates 1-3, with varying polymethylene spacer groups, were synthesized, and their DNA interactions have been investigated by various biophysical techniques. The absorption spectra of these systems showed bands in the regions of 300-375 and 375-475 nm, corresponding to acridine and acridinium chromophores, respectively. When compared to 1 (Phi(f) = 0.25), bifunctional derivatives 2 and 3 exhibited quantitative fluorescence yields (Phi(f) = 0.91 and 0.98) and long lifetimes (tau = 38.9 and 33.2 ns). The significant quenching of fluorescence and lifetimes observed in the case of 1 is attributed to intramolecular electron transfer from the excited state of the acridine chromophore to the acridinium moiety. DNA-binding studies through spectroscopic investigations, viscosity, and thermal denaturation temperature measurements indicate that these systems interact with DNA preferentially through intercalation of the acridinium chromophore and exhibit significant DNA association constants (K(DNA) = 10(5)-10(7) M(-1)). Compound 1 exhibits chromophore-selective electron-transfer reactions and DNA binding, wherein only the acridinium moiety of 1 interacts with DNA, whereas optical properties of the acridine chromophore remain unperturbed. Among bifunctional derivatives 2 and 3, the former undergoes DNA mono-intercalation, whereas the latter exhibits bis-intercalation; however both of them interact through mono-intercalation at higher ionic strength. Results of these investigations demonstrate that these novel water-soluble systems, which exhibit quantitative fluorescence yields, chromophore-selective electron transfer, and DNA intercalation, can have potential use as probes in biological applications.     

Highly sensitive and selective chemosensor for Cu2+ detection based on a N-propargyl rhodamine 6G-hydrazide derivative

A novel fluorescence "turn-on" probe for Cu2+ detection has been designed based on a Cu2+ triggered spirolactam ring-opening reaction.The synthetic probe is a double-responsive fluorescent and colorimetric Cu2+-specific sensor.In aqueous solution,it exhibits high selectivity and excellent sensitivity.With a significant color change visible to the naked eye at the concentration of 3 μM(ca.0.19 mg/L),about one magnitude lower than the WHO(World Health Organization) recommended level(2.0 mg/L) for Cu2+ ions in drinking water,the probe could be used to monitor Cu2+ ions in drinking water.     

Modular solid-phase synthetic approach to optimize structural and electronic properties of oligoboronic acid receptors and sensors for the aqueous recognition of oligosaccharides

This article describes the design and optimization of the first entirely modular, parallel solid-phase synthetic approach for the generation of well-defined polyamine oligoboronic acid receptors and fluorescence sensors for complex oligosaccharides. The synthetic approach allows an effective building of the receptor polyamine backbone, followed by the controlled diversification of the amine benzylic side chains. This approach enabled the testing, in a modular fashion, of the effect of different arylboronic acid units substituted with unencumbering para electron-withdrawing or electron-donating groups. The feasibility of this approach toward automated synthesis was also investigated with the assembly of a sublibrary of receptors by means of the Irori MiniKan technology. Several sublibraries of anthracene-capped sensors containing two or three arylboronic acids were synthesized, and their binding to a series of model disaccharides was examined in neutral aqueous media. The calculation of association constants by fluorescence titrations confirmed that subtle changes in the structures of the interamine spacers in the polyamine backbone can have a significant effect on the stability of the resulting complexes. Most importantly, this study led to the determination of the preferred electronic characteristics for the arylboronate units, and suggests that a new generation of receptors containing very electron-poor arylboronic acids could lead to a significant improvement of binding affinities.     

Surface recognition and fluorescence sensing of histone by dansyl-appended cyclophane-based resorcinarene trimer

A cyclophane-based resorcinarene trimer (3) bearing a dansyl moiety as an environmentally sensitive fluorophore was prepared by stepwise condensation of a tetraaza[6.1.6.1]paracyclophane skeleton with a dansyl moiety and three resorcinarene derivatives having heptacarboxylic acid residues in this sequence. The dansyl-appended cyclophane exhibited the following fluorescence properties regarding solvent polarity dependency and histone surface recognition: With increasing dioxane contents in dioxane/water solvents, the fluorescence intensity originating from the dansyl moiety of 3 increased along with a concomitant blue shift of the fluorescence maximum (lambdaem). The microenvironmentally sensitive fluorescence properties of dansyl fluorophore were maintained, even when the dansyl moiety was covalently attached to a cyclophane. Most interestingly, the cyclophane-based resorcinarene trimer exhibited recognition and fluorescence sensing capabilities toward histone, a small basic protein of eukaryotic chromatins. The fluorescence intensity originating from 3 increased along with a concomitant blue shift of lambdaem upon the addition of histone, reflecting the formation of 3-histone complexes. A relatively large fluorescence polarization (P) value was obtained for the 3-histone complexes (0.15), reflecting highly restricted conformations of 3, and the obtained P value was much larger than that of 3 alone in aqueous medium (0.07). The binding constant (K) of 3 with histone (unit basis) was estimated to be 2.1 x 106 M-1. On the other hand, upon the addition of acetylated histone (Ac-histone) to an aqueous solution containing 3, the extent of change in fluorescence intensity originating from the dansyl group of 3 was almost negligible, indicating that the electrostatic interactions between 3 and Ac-histone were weak. In addition, the fluorescence spectral changes were also small or negligible upon the addition of other proteins such as albumin, ovalbumin, peanut agglutinin, myoglobin, concanavalin A, cytochrome c, and lysozyme, having isoelectric points of 4.7, 4.8, 5.7-6.7, 6.8, 7.1, 9, and 11.0, respectively, to an aqueous solution containing 3.     

Potentiometric,NMR, and Fluorescence‐Emission Studies on the Binding of Adenosine 5′‐Triphosphate (ATP) by Open‐Chain Polyamine Receptors Containing Naphthylmethyl and/or Anthrylmethyl Groups

The interaction in aqueous solution of adenosine 5′‐triphosphate (ATP) with a series of open‐chain polyamines linked at one or both ends to anthrylmethyl or naphthylmethyl fragments was followed by potentiometric titration, ¹H‐, ¹³C‐, and ³¹P‐NMR spectroscopy, and by steady‐state fluorescence measurements. The results revealed greater stabilities for the compounds containing one anthracene moiety than for those with one naphthalene moiety, the stabilities of the compounds with both ends N‐substituted with naphthylmethyl groups being close to those containing just one anthrylmethyl unit. The ¹H‐NMR spectra showed that in all systems, there is involvement of π‐π stacking interactions in the stabilization of the adduct species. The competitive effect of the anions afforded by the supporting electrolyte was checked in some of the studied systems working at two different ionic strenghts (0.15M and 1.0M NaCl). The joint analysis of the spectrofluorimetric titrations and pH‐metric species‐distribution curves showed that for all the ATP? receptor systems, a quenching of the fluorescence occurred upon protonation of the adenine N(1)atom. Steady‐state fluorescence and time‐correlated single‐photon‐counting analysis of a system made up of ATP and a bis‐chromophoric polyamine receptor containing anthracene and naphthalene fluorophores established that the energy‐transfer process between the naphthalene and anthracene moieties is still operative despite the presence of ATP.     

Design and synthesis of novel rhodamine-based chemodosimeters derived from [2.2]paracyclophane and their application in detection of Hg2+ion

For a better insight into the spectroscopic properties of [2.2]paracyclophane in fluorescent probes, a novel rhodamine-based chemodosimeter bearing [2.2]paracyclophane 4a has been designed and synthesized. The probe 4a exhibits a highly selective and sensitive response to Hg²⁺ over other transition metal ions in aqueous solution. Its detection limit is determined to be 77 nM. The significant changes in the fluorescence color could be used for the naked-eye detection. Furthermore, the probe 4a shows good membrane permeability and can be applied to detect intracellular Hg²⁺ in human lung adenocarcinoma cells (A549 cells). The crystal structure and spectral properties of its congener 4b that contains one 12-bromo [2.2]paracyclophane group and rhodamine moiety are also investigated for a comparison.     

Hydroperoxynaphthalimide Derivative-mediated Oxidation of Heme Proteins on Photoirradiation: Horseradish Peroxidase

Abstract— Horseradish peroxidase (HRP) was photoirradiated in the presence of organic peroxide (1, hydroperoxynaphthalimide derivative) at around 353 nm and 0°C. This compound bound to a heme pocket of HRP as shown by its inhibitory effect on catalysis by HRP ( K _i= 5.5 times 10⁻⁵ M) and subsequently it formed an intermediate in the same way as H202. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) suggested cleavage of the peptide chain of HRP on photoirradiation with 1. From CD spectra and SDS-PAGE, it was presumed that the destruction of both secondary structure and heme of the enzyme occurred to some extent upon photoirradiation, which resulted in a decrease in the catalytic activity. The absorption spectra also suggested that the heme group of the enzyme was destroyed, and the fluorescence spectra showed that the Trp residue in the photoirradiated HRP was oxidized to N -formylkynurenine by a hydroxyl radical generated from 1. Energy transfer from the excited naphthalimide moiety or hydrogen abstraction also seemed to make some contribution to the alteration of the heme group.     

Characterization of N-Acetylated Heme Undecapeptide and Some of Its Derivatives in Aqueous Media: Monomeric Model Systems for Hemoproteins

The heme undecapeptide of cytochrome c has been converted to a bis(N-acetylated) derivative by reaction with acetic anhydride. The structure of the product has been confirmed by liquid secondary-ion mass spectrometry. As anticipated, the N-acetylated molecule exhibits much less tendency to aggregate in aqueous solution than its heme undecapeptide precursor. Around neutral pH, one axial ligand on the heme iron is provided by the same histidine residue as in the native cytochrome. The other axial ligand can be varied by the addition of exogenous donor species to produce a range of hemoprotein model compounds exhibiting mixed axial ligation. Contrary to the findings of Othman et al. [Biochemistry 1994, 33, 15437-15448] concerning heme octapeptide, the N-acetylated undecapeptide showed no tendency to bind more than one exogenous ligand per heme. At concentrations approaching millimolar and in the absence of exogenous ligands, the N-acetylated molecule may either be monodispersed, exhibiting a characteristic high-spin (S = (5)/(2)) ferric heme electron paramagnetic resonance (EPR) signal, or exist in an EPR-silent and presumably aggregated form. Interestingly, the system displays a novel dependence on the buffer with regard to which of these two forms is present in a given sample. There is no evidence in any of the spectra for the existence of an intermediate-spin (S = (3)/(2)) ferric heme as suggested by Wang and Van Wart [J. Phys. Chem. 1989, 93, 7925-7931] to be present in aqueous solutions of N-acetylated heme octapeptide. Also, in contrast to another earlier report concerning the underivatized undecapeptide [Clore et al. Inorg. Chim. Acta 1981, 56, 143-148], the N-acetylated molecule showed no evidence of catalase activity. In fact, the heme chromophore was surprisingly unstable in the presence of hydrogen peroxide.     

A novel fluorescent and colorimetric anion sensor based on thiourea derivative in competitive media

A novel and simple fluorescent receptor bearing thiourea moiety as recognition site was described. The recognition behavior of the receptor toward different anions was investigated in DMSO/H(2)O (95:5 v/v) and dry DMSO through two various channels: the colorless-yellow color change and a remarkable enhancement of the fluorescence. And the enhancement of the fluorescence was attributed to an anion-induced increase of the rigidity of the host molecule.     

Synthesis and H+, Cu2+, and Zn2+ coordination behavior of a bis(fluorophoric) bibrachial lariat aza-crown

The synthesis, protonation behavior, and Cu2+ and Zn2+ coordination chemistry of the novel bibrachial aza lariat ether (naphthalen-1-ylmethyl)[2-(20-[2-[(naphthalen-1-ylmethyl)amino]ethyl]-3,6,9,17,20,23,29,30-octaazatricyclo[23.3.1.1*11,15*]triaconta-1(29),11(30),12,14,25,27-hexaen-6-yl)ethyl]amine (L) are discussed. The macrocycle, which has two aminoethyl naphthyl moieties symmetrically appended to a 2:2 azapyridinophane structure, displays, in the pH range 2-11, six protonation steps that correspond to the protonation of the secondary amino groups. Steady-state fluorescence measurements show emissions due to the monomer and to the excimer formed between the two naphthalene fragments of the macrocycle. The time-resolved fluorescence data, obtained by the time-correlated single photon counting technique, show that a significant percentage of excimer is preformed as ground-state dimers. The ligand L forms with the metal ions Cu2+ and Zn2+ mono- and dinuclear complexes in aqueous solution. The influence of metal coordination in the fluorescence emission of L is analyzed. The acid-base, coordination capabilities, and emissive behavior of L are compared with those presented by its synthetic precursor L1, which has a tripodal tris(2-aminoethyl)amine structure functionalized at one of its terminal amino groups with a naphthyl moiety.     

Dopamine selective molecularly imprinted polymers via post-imprinting modification

A novel synthetic dopamine receptor bearing bidentate binding sites were prepared by covalent imprinting using a disulfide linkage which is cleaved and oxidized to a non-covalent sulfoxide recognition group. The used templates have dopamine-like structures connected to an allyl moiety via a disulfide and to a 4-vinylphenyl group via a cyclic boronic diester. After the polymerization, the ester bonds were hydrolyzed and the disulfide bond was reduced to remove the template moiety from the polymer matrix, followed by the oxidation to transform the thiol residues into sulfonic acid (post imprinted process). The imprinted polymer adsorbed dopamine selectively in aqueous solution with the two-point interaction, i.e. the formation of cyclic boronic diester and electrostatic interaction with the sulfonic acid residue.     

Fluorophore appended saccharide cyclophane: self-association, fluorescent properties, heterodimers with cyclodextrins, and cross-linking behavior with peanut agglutinin of dansyl-modified saccharide cyclophane

A saccharide cyclophane bearing an environment-sensitive fluorophore (1) was prepared by introducing not only three branches with a terminal galactose residue but also one with a dansyl moiety into a tetraaza[6.1.6.1]paracyclophane skeleton. Self-association behavior of the dansyl-appended saccharide cyclophane was characterized in aqueous media by fluorescence spectroscopy and dynamic light scattering measurements. At least in the concentrations below 1.0 x 10(-5) M, saccharide cyclophane 1 existed in a monomeric state, whereas it tended to form self-aggregated complexes in the higher concentration. Solvent polarity dependency on the emission spectra of 1 was examined by fluorescence spectroscopy. With increasing dioxane contents in dioxane/water solvents, the fluorescence intensity originating from the dansyl moiety of 1 increased along with a concomitant blue shift of the fluorescence maximum (lambda(em)). In the monomeric state of 1 in water, the dansyl moiety of 1 was not fully included into its cyclophane cavity but partially exposed to the bulk aqueous phase. In the higher concentration ranges in an aggregate state, however, the dansyl group of 1 was located in the apolar cyclophane cavity whose microenvironment was equivalent to the polarity of 1-butanol evaluated on the basis of a correlation between lambda(em) and solvent polarity. This indicates an intermolecular inclusion of the dansyl moiety within the cyclophane. When cyclodextrin (CD) was mixed with 1, the dansyl group of 1 was bound to an internal cavity of CD such as gamma-CD, beta-CD, 6-O-alpha-glucosyl-beta-CD, and 6-O-alpha-maltosyl-beta-CD with binding constants of 7.5 x 10(2), 7.8 x 10(2), 7.7 x 10(2), and 6.0 x 10(2) M(-1), respectively. Such a supramolecular assembling of dansyl-modified cyclophane 1 and CDs caused changes of the fluorescence spectra as well as appearance of induced CD bands in aqueous media. Furthermore, saccharide cyclophane 1 was selectively bound to peanut agglutinin (PNA), galactoside-binding lectin, which was readily monitored by a visible turbidity of the solution due to a cross-linking agglutination of these components, as well as by fluorescence spectroscopy.     

Hormone-receptor-relationships: synthesis and characteristics of N-epsilon-dansyllysine 21-adrenocorticotropin-(1-24)-tetrakosipeptide

We are investigating interactions between hormones and their potential receptor molecules by means of biologically active, synthetic hormone derivatives. The substituents are so chosen that they can supply quantitative information about specific contacts or convert the hormone to an ‘affinity marker’. We describe the synthesis of N^ε-dansyllysine²¹-adrenocorticotropin-(1–24)-tetrakosipeptide. In fat cells and in adrenal cells of the rat the dansyl substituent does not seem to impair the interaction between the peptide moiety and its biological receptors. It allows for affinity studies by fluorescence depolarisation and for measurement of intramolecular and intermolecular distances by means of energy transfer (fluorescence sensibilisation).