Synthesis and Photophysical Properties of Polyfluorene With Dipicolylamine Groups on the Side Chain: Highly Selective and Sensitive Detection of Histidine

Two new polyfluorenes with dipicolylamine (DPA) pendant, PF‐TDPA and PF‐HDPA, are designed and synthesized by pre‐ and post‐functionalization, respectively. PF‐TDPA with a rigid side chain shows a selective fluorescence quenching upon the addition of Cu²⁺ in a mixture solution of tetrahydrofuran and 4‐(2‐hydroxyethyl)‐1‐piperazineethanesulfonic acid (HEPES) buffer. What is more, the PF‐TDPA/Cu²⁺ complex can selectively detect histidine over other amino acids with a fluorescence recovery. In contrast, PF‐HDPA with a flexible spacer exhibits a fluorescence quenching to Cu²⁺ but slightly fluorescence recovery after the addition of histidine. This indicates that the proper distance between the two DPA groups play an important role in the detection of histidine.     

A Novel Fluorescent Probe Based on Perylene Derivative for Hg2+ Ions and Biological Thiols and its Application in Live Cell Imaging and Theoretical Calculations

The selective and sensitive detection of biothiols; cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) in aqueous solutions is of considerable importance because of their pivotal roles in maintaining the reducing environment in the cells. This study describes a strategy for the determination of biothiols based on the PDI/Met‐Hg²⁺complex platform. We designed and fabricated methionine modified perylene diimide molecule as a selective sensing probe for Hg²⁺ ions in aqueous solutions ( PDI/Met‐Hg ²⁺). The complex between perylene bisimide derivative ( PDI/Met) and Hg²⁺ was investigated and it demonstrated turn‐on fluorescence response for the detection of the biological thiols. Besides, PDI/Met displayed fluorescence quenching response in the presence of mercury ions and the emission intensity of PDI/Met‐Hg²⁺ was recovered after transferring biothiols (Cys, Hcy, and GSH). Thus, PDI/Met could be utilized as a fluorescent chemosensor for the sequential recognition of mercury ions and biological thiols.     

New Electrocatalytic Reactions at a Mercury Electrode in the Presence of Homocysteine or Cysteine and Cobalt or Nickel Ions

Homocysteine (Hcy) and cysteine (Cys) mercury thiolate layers were prepared by anodic polarization of a mercury electrode in amino acid containing solutions and then investigated in the cathodic regime in the presence of Ni²⁺ or Co²⁺ ions. The sulfhydryl function in the mercury thiolate undergoes a slow disintegration resulting in surface‐attached mercury sulfide. During the cathodic scan, Hg²⁺ substitution by Ni²⁺ or Co²⁺ yields minute amounts of the relevant metal sulfide. Such a species catalyzes hydrogen evolution at ?1.3 V vs. Ag|AgCl|KCl(3 M). Hcy experiences a faster decomposition and, consequently, displays a stronger catalytic effect. Each compound catalyzes the reduction of Ni²⁺ or Co²⁺, but only Cys (bound in metal complexes) induces typical catalytic hydrogen evolution processes such as the Brdi?ka reaction (with Co²⁺; pH around 9), or the catalytic hydrogen prewave (CHP) (with Ni²⁺; pH near 7). On the other hand, Hcy catalyzes the hydrogen evolution in the presence of Co²⁺ at ?1.5 V in the same way than sulfur derivatives with no amine function do. Metal sulfide formation does not interfere with CHP and Brdi?ka processes. Correlations between the physical state of the metal sulfide (adsorbed molecule or aggregate form) and its catalytic properties are discussed and possible analytical applications suggested.     

Polymer‐based colorimetric and “turn off” fluorescence sensor incorporating benzo[2,1,3]thiadiazole moiety for Hg2+ Detection

A conjugated polymer was synthesized by the polymerization of 4,7‐dibromobenzo[2,1,3]thiadiazole ( M‐1 ) with tri{1,4‐diethynyl‐2,5‐bis(2‐(2‐methoxyethoxy)‐ethoxy)}‐benzene ( M‐2 ) via Pd‐catalyzed Sonogashira reaction. The polymer shows strong orange fluorescence. The responsive optical properties of the polymer on various metal ions were investigated through photoluminescence and UV–vis absorption measurements. The polymer displays highly sensitive and selective on‐off Hg²⁺ fluorescence quenching property in tetrahydrofuran solution in comparison with the other cations including Mg²⁺, Zn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Cd²⁺, and Pb²⁺. More importantly, the fluorescent color of the polymer sensor disappears after addition of Hg²⁺, which could be easily detected by naked eyes. The results indicate that this kind of polymer sensor incorporating benzo[2,1,3]thiadiazole moiety as a ligand can be used as a novel colorimetric and fluorometric sensor for Hg²⁺ detection. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Cobalt(III)‐Mediated Permanent and Stable Immobilization of Histidine‐Tagged Proteins on NTA‐Functionalized Surfaces

We present the cobalt(III)‐mediated interaction between polyhistidine (His)‐tagged proteins and nitrilotriacetic acid (NTA)‐modified surfaces as a general approach for a permanent, oriented, and specific protein immobilization. In this approach, we first form the well‐established Co²⁺‐mediated interaction between NTA and His‐tagged proteins and subsequently oxidize the Co²⁺ center in the complex to Co³⁺. Unlike conventionally used Ni²⁺‐ or Co²⁺‐mediated immobilization, the resulting Co³⁺‐mediated immobilization is resistant toward strong ligands, such as imidazole and ethylenediaminetetraacetic acid (EDTA), and washing off over time because of the high thermodynamic and kinetic stability of the Co³⁺ complex. This immobilization method is compatible with a wide variety of surface coatings, including silane self‐assembled monolayers (SAMs) on glass, thiol SAMs on gold surfaces, and supported lipid bilayers. Furthermore, once the cobalt center has been oxidized, it becomes inert toward reducing agents, specific and unspecific interactions, so that it can be used to orthogonally functionalize surfaces with multiple proteins. Overall, the large number of available His‐tagged proteins and materials with NTA groups make the Co³⁺‐mediated interaction an attractive and widely applicable platform for protein immobilization.     

Structure of a di-zinc complex of a bis-calix[4]arene conjugate and its sensing of cysteine among the amino acids

Abstract

A triethylene glycol di-imine locked triazole linked bis-calix[4]arene conjugate (L) and its Zn²⁺ complex [Zn₂L], were synthesised, characterised and the three-dimentional (3-D) structure of the complex was established by single crystal XRD. In this complex, the Zn²⁺ centre exhibits distorted tetrahedral geometry with N₂O₂ binding core. The complex showed selectivity towards cysteine (Cys) with greater sensitivity followed by histidine (His) among the naturally occurring amino acids studied based on fluorescence and absorption spectroscopy. The fluorescence quenching of the complex is much greater with Cys as compared to that of His. The detection limit of Cys is 650 ppb. Release of Zn²⁺ from its complex [Zn₂L] followed by its capture by –SH containing molecules was shown based on absorption and emission spectroscopy. This was also shown in one case by ¹H NMR spectroscopy.     

Synthesis and Characterization of a Water‐Soluble Carboxylated Polyfluorene and Its Fluorescence Quenching by Cationic Quenchers and Proteins

We have developed a new intermediate monomer, 2,7‐[bis(4,4,5,5‐tetramethyl‐1,3,2‐dioxaborolan‐2‐yl)‐9,9‐bis(3‐(tert‐butyl propanoate))]fluorene, that allows the easy synthesis of water‐soluble carboxylated polyfluorenes. As an example, poly[9,9′‐bis(3′′‐propanoate)fluoren‐2,7‐yl] sodium salt was synthesized by the Suzuki coupling reaction, and the properties of the polymer were studied in aqueous solutions of different pH. Fluorescence quenching of the polymer by different cationic quenchers (MV²⁺, MV⁴⁺, and NO₂MV²⁺; MV=methyl viologen) was studied, and the quenching constants were found to be dependent on the charge and electron affinity of the quencher molecule and the pH of the medium. The largest quenching constant was observed to be 1.39×10⁸ M ^?1 for NO₂MV²⁺ at pH 7. The change in polymer fluorescence upon interaction with different proteins was also studied. Strong fluorescence quenching of the polymer was observed in the presence of cytochrome c, whereas weak quenching was observed in the presence of myoglobin and bovine serum albumin. Lysozyme quenched the polymer emission at low protein concentrations, and the quenching became saturated at high protein concentrations. Under similar experimental conditions, the polymer showed improved quenching efficiencies toward cationic quenchers and a more selective response to proteins relative to other carboxylated conjugated polymers.     

Bipyridinophane‐containing conjugated polymers modulated with an intramolecular aromatic C?H/π interaction

Bipyridinophane–fluorene conjugated copolymers have been synthesized via Suzuki and Heck coupling reactions from 5,8‐dibromo‐2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane and suitable fluorene precursors. Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P7 ) exhibits large absorption and emission redshifts of 20 and 34 nm, respectively, with respect to its planar reference polymer Poly[2,7‐(9,9‐dihexylfluorene)‐co‐alt‐1,4‐(2,5‐dimethylbenzene)] ( P11 ), which bears the same polymer backbone as P7 . These spectral shifts originate from intramolecular aromatic C? H/π interactions, which are evidenced by ultraviolet–visible and ¹H NMR spectra as well as X‐ray single‐crystal structural analysis. However, the effect of the intramolecular aromatic C? H/π interactions on the spectral shift in poly[9,9‐dihexylfluorene‐2,7‐yleneethynylene‐co‐alt‐5,8‐(2,11‐dithia[3]paracyclo[3](4,4′)‐2,2′‐bipyridinophane)] ( P10 ) is much weaker. Most interestingly, the quenching behaviors of these two conjugated polymers are largely dependent on the polymer backbone. For example, the fluorescence of P7 is efficiently quenched by Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Mn²⁺, and Ag⁺ ions. In contrast, only Cu²⁺, Co²⁺, and Ni²⁺ ions can partially quench the fluorescence of P10 , but much less efficiently than the fluorescence of P7 . The static Stern–Volmer quenching constants of Cu²⁺, Co²⁺, and Ni²⁺ ions toward P7 are of the order of 10⁶ M^?1, being 1300, 2500, and 37,300 times larger than those of P10 , respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4154–4164, 2006     

A Novel Surface‐tethered Analysis Method for Mercury (II) ion Detection via Self‐assembly of Individual Electrochemiluminescence Signal Units

A novel analysis strategy based on the analyte‐induced surface‐tethered (AIST) of electrochemiluminescence (ECL) signal nanoparticles was first proposed for detection of Mercury (II) ion (Hg²⁺). In this work, luminol@Au‐cysteamine‐thymine (luminol@Au‐Cys‐T) multifunctional nanoarchitecture was designed as ECL signal units in the experimental process. Through a specific T‐Hg²⁺‐T coordination, luminol@Au‐Cys‐T composites were gravitationally self‐assembled to the electrode surface, which was coated with tris (2‐aminoethyl) amine functionalized graphene oxide@perylene‐3,4,9,10‐tetracarboxylic acid‐thymine (GO@PTCA‐TAEA‐T) complex film. This simple strategy of AIST of signal molecules could amplify the response signal and vastly enhance the sensitivity. Under the optimum condition, the linear relationship of Hg²⁺ concentration variation from 0.005 nM to 5 nM with a limit of detection (LOD) down to 0.002 nM (S/N=3), which also offered an alternative analytical approach with excellent performance of stability and selectivity. The regression equation was y=−414.52+2305.02 lgC_(Hg²⁺₎ (pM). This Hg²⁺ ECL sensor had a good application prospects for the analysis of real samples.     

Lighting‐Up of the Dye Malachite Green with Mercury(II)–DNA and Its Application for Fluorescence Turn‐Off Detection of Cysteine and Glutathione

This work describes a novel strategy for the highly sensitive and selective detection of cysteine (Cys) and glutathione (GSH) based on the Hg²⁺–AGRO100–malachite green (MG) complex system. The dye MG, which has a very low quantum yield in aqueous solution by itself, can bind with the thymine‐rich DNA AGRO100 in the presence of Hg²⁺ ions to generate a striking fluorescence intensity enhancement of 1000‐fold. As sulfur‐containing amino acids, Cys and GSH effectively sequester Hg²⁺ ions from the Hg²⁺–AGRO100–MG complex structure to switch the ‘lit‐up’ chemosensor to the ‘off’ state (about a 50‐fold fluorescence intensity decrease), thus providing a facile, but effective, method to probe for Cys/GSH. The fluorescence titration, UV absorption, CD, and Raman spectra provide some insight into the structural and chemical basis for the enhancement effect. The formation of the Hg²⁺–AGRO100–MG complex significantly affects the electronic structure and conformation of the MG molecule by leading to an extended π system, which is the likely origin of the observed striking fluorescence intensity enhancement. Notably, the proposed sensing platform exhibits exquisite selectivity and sensitivity toward Cys/GSH with limits of detection of 5 nM for Cys and 10 nM for GSH, respectively. Furthermore, the straightforward assay design avoids labeling of the probe, uses only commercially available materials, and still displays comparable sensitivity and excellent selectivity.     

Highly Sensitive Ratiometric Chemosensor for Selective ′Naked‐Eye′ Nanomolar Detection of Co2+ in Semi‐Aqueous Media

An easy‐to‐prepare chemosensor, (E)‐1‐(phthalazine‐4‐yl)‐2‐(1‐(pyridine‐2‐yl)ethylidene) hydrazine ( 3 ), structurally characterized by single X‐ray crystallography, is developed for the selective and sensitive detection of Co²⁺ in aqueous media. Chemosensor 3 shows both absorption and fluorescence responses to Co²⁺ by forming a 1:1 complex (among the surveyed metal ions) with a detection limit down to 50 nM . It can also be used as a ′naked‐eye′ sensor due to the outstanding visible and emission color changes from yellow to red and blue to orange, respectively.     

Synthesis,characterization of novel rotaxanes depend on cyclodextrins

We have developed a colorimetric chemosensor for the selective and sensitive detection of Cys based on the complex (CA-2Pb²⁺) between a commercially available natural organic dye, carminic acid (CA) and Pb²⁺ in pure aqueous solution at physiological pH. The addition of Cys to the CA-2Pb²⁺ solution resulted in a distinct color change from purple to red together with a remarkable absorption spectral change by the restoration of CA through a displacement mechanism with formation of the Cys-Pb²⁺ complex, whereas other amino acids and glutathione induce no or minimal spectral and color changes. Moreover, the other amino acids and GSH do not affect the detection ability of CA-2Pb²⁺ for Cys. The reversibility even through several cycles was established for practical applications. The results indicate that CA-2Pb²⁺ may be useful as a potential colorimetric and naked-eye chemosensor for Cys over Hcy and GSH in aqueous solution.     

Novel polyamidoamine‐based hydrogel with an innovative molecular architecture as a Co2+‐, Ni2+‐, and Cu2+‐sorbing material: Cyclovoltammetry and extended X‐ray absorption fine structure studies

An amphoteric polyamidoamine (PAA)‐based hydrogel, named INT‐PAA1, with a novel molecular architecture was prepared and studied as a Co²⁺‐, Ni²⁺‐, and Cu²⁺‐sorbing material. This hydrogel was obtained by the synthesis of a PAA in the presence of a second presynthesized PAA carrying many primary amino groups as side substituents, which acted as a macromolecular crosslinking agent. Therefore, it had an intersegmented structure. INT‐PAA1 exhibited a remarkable sorption capacity and sorption rate for Co²⁺, Ni²⁺, and Cu²⁺ that were advantageously in situ monitored by cyclic voltammetry. An extended X‐ray absorption fine structure spectroscopy characterization of the Co²⁺/INT‐PAA1 complex was also performed. The very fast and quantitative metal‐ion uptake, made apparent by an intense coloring of the hydrogel, showed remarkable potential for environmental applications such as heavy‐metal detection, recovery, and elimination. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2316–2327, 2006     

Synthesis,Characterization, and Reactivity of Cobalt(III)–Oxygen Complexes Bearing a Macrocyclic N‐Tetramethylated Cyclam Ligand

Mononuclear metal–dioxygen species are key intermediates that are frequently observed in the catalytic cycles of dioxygen activation by metalloenzymes and their biomimetic compounds. In this work, a side‐on cobalt(III)–peroxo complex bearing a macrocyclic N‐tetramethylated cyclam (TMC) ligand, [Co^III(15‐TMC)(O₂)]⁺, was synthesized and characterized with various spectroscopic methods. Upon protonation, this cobalt(III)–peroxo complex was cleanly converted into an end‐on cobalt(III)–hydroperoxo complex, [Co^III(15‐TMC)(OOH)]²⁺. The cobalt(III)–hydroperoxo complex was further converted to [Co^III(15‐TMC‐CH₂‐O)]²⁺ by hydroxylation of a methyl group of the 15‐TMC ligand. Kinetic studies and ¹⁸O‐labeling experiments proposed that the aliphatic hydroxylation occurred via a Co^IV–oxo (or Co^III–oxyl) species, which was formed by O? O bond homolysis of the cobalt(III)–hydroperoxo complex. In conclusion, we have shown the synthesis, structural and spectroscopic characterization, and reactivities of mononuclear cobalt complexes with peroxo, hydroperoxo, and oxo ligands.     

Photophysical and Complexation Behavior of (4-Dimethylamino-benzylidene)-(4,6-dimethyl-pyrimidin-2-yl)-amine

The absorption and fluorescence characteristics of (4‐dimethylamino‐benzylidene)‐(4,6‐dimethyl‐pyrimidin‐2‐yl)‐amine (SB) have been investigated in different solvents. Both the absorption and emission spectra of SB exhibit red shifts as the solvent polarity increases. This indicats a change in dipole moment of molecules upon excitation as a result of intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was discussed on the bases of positive and negative solvatokinetic effects. The effect of some divalent transition metal ions such as Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺on the absorption and fluorescence spectra of SB is also investigated. The results were consistent with formation of highly colored metal‐ SB complex which is responsible for the extreme quenching of the fluorescence of SB. The variations of both the formation constant of the complex and Stern‐Volmer constant were correlated with the electronic structure of the used metal ion.     

氮掺杂荧光碳点用于Co2+的超灵敏检测及细胞成像

首次以金银花和乙二胺为原料,通过水热法合成出性能优异的氮掺杂碳点(N-CDs)。制备的N-CDs具有丰富的官能团、良好的水溶性、低细胞毒性、高的荧光稳定性和良好的生物相容性。在最佳条件下,N-CDs能够高选择性地检出Co²⁺,N-CDs的荧光强度在0.5～3.6 nmol·L^-1范围内被Co²⁺线性猝灭,检出限低至1.38 nmol·L^-1,其猝灭机制属于内滤效应和静态猝灭。该方法也已成功应用于实际样品的精确分析。此外,N-CDs还可用于细胞成像及细胞内Co²⁺传感。     

In Vitro Monitoring of Picogram Levels of Captopril in Human Urine Using Flow Injection Chemiluminescence with Immobilized Reagent Technique

Abstract

A flow‐injection procedure for detection of captopril using a Co²⁺‐captopril complex formed on line based enhancement of luminol and dissolved oxygen chemiluminescence is described. The chemiluminescence reagents, luminol and Co²⁺, were both immobilized on ion exchange resin in the flow injection system. When captopril solution flowed through the immobilized Co²⁺ column, the Co²⁺‐captopril (1:2) complex formed on line could greatly enhanced the chemiluminescence intensity generated from the reaction between luminol and dissolved oxygen. The increment of chemiluminescence emission was correlated with the captopril concentration in the range from 7 to 1000 pg mL^?1, and the detection limit was 2 pg mL^?1 (3σ). One analysis cycle, including sampling and washing, could be accomplished in 0.5 min with relative standard deviations of less than 3.0% (n=11). The proposed method was applied directly in the assay of human urine without any pretreatment and it was found that the captopril concentration reached its maximum after being administrated orally for 1.5 hours, with the mean excretion ratio in 6.5 hours of 54.3% in the body of volunteers. The possible chemiluminescence mechanism was discussed.     

Binding Interaction of Captopril with Metal Ions: A Fluorescence Quenching Study

The binding interaction of captopril (CPL) with biologically active metal ions Mg²⁺, Ca²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ was investigated in an aqueous acidic medium by fluorescence spectroscopy. The experimental results showed that the metal ions quenched the intrinsic fluorescence of CPL by forming CPL‐metal complexes. It was found that static quenching was the main reason for the fluorescence quenching. The quenching constant in the case of Cu²⁺ was highest among all quenchers, perhaps due to its high nuclear charge and small size. Quenching of CPL by metal ions follows the order Cu²⁺>Ni²⁺>Co²⁺>Ca²⁺>Zn²⁺>Mn²⁺>Mg²⁺. The quenching constant K_sv, bimolecular quenching constant K_q, binding constant K and the binding sites "n" were determined together with their thermodynamic parameters at 27 and 37°C. The positive entropy change indicated the gain in configurational entropy as a result of chelation. The process of interaction was spontaneous and mainly ΔS‐driven.     

Effects of Divalent Metal Ions on Electrochemiluminescence Sensor with Ru(bpy)32+ Immobilized in Eastman‐AQ Membrane

Different effects of divalent metal ions on electrochemiluminescence (ECL) sensor with Ru(bpy)₃²⁺ immobilized in Eastman‐AQ membrane were investigated. Mg²⁺, Ca²⁺ and Fe²⁺ can elevate the ECL of Ru(bpy)₃²⁺/proline; while metal ions that underwent redox reactions on the electrode such as Mn²⁺ and Co²⁺ presented intensive quenching effects on Ru(bpy)₃²⁺ ECL. Also, the quenching effect of Mn²⁺ on the ECL sensor with Ru(bpy)₃²⁺ immobilized in Eastman‐AQ membrane enhanced to about 30‐folds compared with the case that Ru(bpy)₃²⁺ was dissolved in phosphate buffer, and the enhanced quenching effects of Mn²⁺ were studied.     

Differential Pulse Polarography of the Zn2+ Complexation by Glutathione Fragments Cys‐Gly and gamma‐Glu‐Cys

The metal binding properties of glutathione (GSH) and their fragments γ‐Glu‐Cys and Cys‐Gly are of biological and environmental interest. In this work a differential pulse polarographic study of the Zn²⁺/γ‐Glu‐Cys and Zn²⁺/Cys‐Gly systems was carried out for a better understanding of the results obtained in previous studies on the Zn²⁺‐GSH system. In the case of γ‐Glu‐Cys, complexation with Zn²⁺ was not detected. In the case of Cys‐Gly, the parallel analysis, by multivariate curve resolution with alternating least squares, of data from the titration of peptide with metal and of metal with peptide suggested the presence of two types of bound Zn²⁺. This could be attributed to Zn²⁺ strongly bound to two sulfur atoms of two peptides, to form a complex of 1 : 2 stoichiometry, and to Zn²⁺ weakly bound to carboxylate and/or amino groups.