BSA–AuNPs@Tb–AMP metal–organic frameworks for ratiometric fluorescence detection of DPA and Hg2+

An easy and effective strategy for synthesizing a ratiometric fluorescent nanosensor has been demonstrated in this work. Novel fluorescent BSA–AuNPs@Tb–AMP (BSA, bovine serum albumin; AMP, adenosine 5′‐monophosphate; AuNPs, Au nanoparticles) metal–organic framework (MOF) nanostructures were synthesized by encapsulating BSA–AuNPs into Tb–AMP MOFs for the detection of 2,6‐pyridinedicarboxylic acid (DPA) and Hg²⁺. DPA could strongly co‐ordinate with Tb³⁺ to replace water molecules from the Tb³⁺ center and accordingly enhanced the fluorescence of Tb–AMP MOFs. The fluorescence of BSA–AuNPs at 405 nm remained constant. While the fluorescence of BSA–AuNPs at 635 nm was quenched after Hg²⁺ was added, the fluorescence of Tb–AMP MOFs remained constant. Accordingly, a ratiometric fluorescence nanosensor was constructed for detection of DPA and Hg²⁺. The ratiometric nanosensor exhibited good selectivity to DPA over other substances. The F₅₄₅/F₄₀₅ linearly increased with increase of DPA concentration in the range of 50 nM to 10 μM with a detection limit as low as 17.4 nM. F₆₃₅/F₄₀₅ increased linearly with increase of Hg²⁺ concentration ranging from 50 nM to 1 μM with a detection limit as low as 20.9 nM. Additionally, the nanosensor could be successfully applied for the determination of DPA and Hg²⁺ in running water.     

An assay for inorganic mercury(II) based on its post-catalytic enhancement effect on the potassium permanganate-luminol system.

A strong chemiluminescence (CL) response is observed when potassium permanganate solution is injected into basic luminol solution. When the CL reaction terminates, subsequent injection of Hg2+ solution into the reaction mixture results in a new CL reaction. Based on the post-catalytic enhancement effect of Hg2+ on the potassium permanganate-luminol system in basic media, a fast and simple CL-coupled flow injection analysis for the determination of Hg2+ was developed. In optimum conditions, CL intensity is proportional to Hg2+ concentration over the range 1.0 x 10(-8)-1.0 x 10(-5) g/mL, with a detection limit of 2.0 x 10(-9) g/mL. The relative standard deviation (RSD) is 3.6% for 1.0 x 10(-7) g/mL Hg2+ (n = 11). After pretreatment with sulphydryl cotton fibre, environmental water samples were analysed by the proposed method for total mercury determination with satisfactory results. The results were in good agreement with those given by hydride generation-cold vapour atomic absorption spectrometry (HG-CVAAS).     

Hg2+‐selective ratiometric and colorimetric probe based on dansyl–rhodamine and its staining function in cell imaging

A new ratiometric probe composed of a dansyl–rhodamine dyad for the detection of Hg²⁺ via fluorescence resonance energy transfer was designed and synthesized. Rhodamine, dansyl chloride, and hydrazide were selected as the acceptor, donor, and reaction site, respectively. It displayed high selectivity and sensitivity to Hg²⁺ with obvious colour change and fluorescence change due to Hg²⁺‐assisted hydrolysis of rhodamine hydrazide. A good linear relationship ranging from 0 to 16 μM and 0–28 μM for the Hg²⁺ concentration was found based on absorbance and fluorescence assay, respectively. Detection limits of absorbance and fluorescence for Hg²⁺ were calculated to be 1.22 μM and 9.10 μM, respectively.     

Resonance scattering spectral detection of ultratrace Hg(II) using herring sperm DNA modified nanogold probe as catalyst

Herring sperm DNA (hsDNA) was used to modify 10 nm nanogold to obtain a resonance scattering (RS) probe (AuhsDNA) for detection of Hg²⁺. In the presence of salt, Hg²⁺ interacts with AuhsDNA to form stable Hg²⁺–hsDNA complexes, and releases nanogold particles to form larger nanogold clusters that can be removed by membrane filtration. The excess AuhsDNA in the filtrate solution exhibits a catalytic effect on the reaction between hydroxylamine (NH₂OH) and Cu(II). The excess AuhsDNA decreased with the addition of Hg²⁺, which led the RS intensity at 602 nm to decrease. The decreased RS intensity (Δl_{602 nm}) had a linear response to Hg²⁺ concentration in the range of 0.4–400 nM, with a detection limit of 0.2 nM Hg²⁺. This RS method was applied for the detection of Hg²⁺ in water samples, with sensitivity, selectivity and simplicity. Copyright © 2009 John Wiley & Sons, Ltd.     

Glucose biosensor based on nano-SiO2 and “unprotected” Pt nanoclusters

The “unprotected” Pt nanoclusters (average size 2 nm) mixed with the nanoscale SiO₂ particles (average size 13 nm) were used as a glucose oxidase immobilization carrier to fabricate the amperometric glucose biosensor. The bioactivity of glucose oxidase (GOx) immobilized on the composite was maintained and the as-prepared biosensor demonstrated high sensitivity (3.85 μA mM⁻¹) and good stability in glucose solution. The Pt–SiO₂ biosensor showed a detection limit of 1.5 μM with a linear range from 0.27 to 4.08 mM. In addition, the biosensor can be operated under wide pH range (pH 4.9–7.5) without great changes in its sensitivity. Cyclic voltammetry measurements showed a mixed controlled electrode reaction.     

Phylogenetic relationships of the callitrichinae (Platyrrhini,Primates) based on β2‐microglobulin DNA sequences

The phylogenetic relationships of callitrichine primates have been determined by DNA sequence analyses of exons 1, 2, and 3 of the β₂‐microglobulin gene. Parsimony, distance, and maximum likelihood analyses of ca. 900 base pairs of 21 taxa, representing all callitrichine genera, indicated that Saguinus was the most basal offshoot. Within Saguinus, S. fuscicollis appeared as the first divergent lineage followed by an unresolved trichotomy formed by S. mystax/S. imperator, S. midas/S. bicolor, and S. oedipus. A second callitrichine lineage was formed by Leontopithecus; each of the three species studied showed identical nucleotide sequences. Callimico appeared as the sister taxon of Callithrix/Cebuella. Genetic distances within this latter group were very small, although a stronger association between Cebuella and species of the Callithrix argentata group was observed. The inclusion of Cebuella in the genus Callithrix is suggested. These studies indicated that tamarins are more plesiomorphic than marmosets in agreement with the phyletic dwarfism hypothesis. Am. J. Primatol. 48:225–236, 1999. © 1999 Wiley‐Liss, Inc.     

Modeling of α(1–4) chain arrangements in α(1–4)(1–6) glucans: The action and outcome of β-amylase and Pseudomonas stutzeri amylase on an α(1–4)(1–6) glucan model

Simulated enzymic debranching of a β-limit dextrin model, prepared from a computed construct made by random extension and branching, and given the CCL value of w-maize amylopectin (and equal amounts of external chains with ECL values of 2 and 3) has been related to experimental chromatograms of the debranched β-limit dextrin of the amylopectin. The profile was similar to those from gel chromatograms and IEC-PAD chromatography.The equivalent lengths in glucosyl units of grid-links (g-links) of internal and external chains in constructs were calculated from the ICL and ECL values of amylopectin and models produced from the constructs with the appropriate lengths for internal and external chains. These derived models were subjected to simulated hydrolysis by Pseudomonas stutzeri amylase and the products compared with those of the experimental distribution from w-maize amylopectin. With the model the amounts of maltotetraose and maltodextrins released were similar to the experimental values but the distribution of branched maltodextrins was quite different. Unlike w-maize amylopectin – a polymer with the cluster structure – which has given a profile of molecular sizes of maltodextrins with low amounts of single and small numbers of internal chains and with a peak at a M_W of about 14,000 (13 chains), in the model the proportion of maltodextrin with one internal chain was high and as d.p. increased the amounts decreased exponentially. This would be expected if the distribution of internal chains in the core was random. It is suggested that in the core of a model prepared from a construct made with alternating probabilities of extension – one in which this probability is high relative to branching, and a second in which it is low – may give clusters of branched maltodextrins with short internal chains which are joined by longer chains; more closely approximating the distribution of internal chains of different lengths in amylopectin.An arrangement for amylopectin molecules in the starch granule has been proposed. In this, they have a wafer-like, discoidal shape, composed of the amorphous zone overlain with the double helical, crystalline region. The flat macromolecules are concentrically layered with the former on the inside and the latter oriented to the outside of the granule.     

Imidazolate-bridged dicopper(II) and copper(II)–zinc(II) complexes of macrocyclic ligand with methylimidazol pendants: Model study of copper(II)–zinc(II) superoxide dismutase

Two new homo- and hetero-dinuclear complexes, [Cu₂L(im)](ClO₄)₃4H₂O (1) and [CuZnL(im)](ClO₄)₃4H₂O (2) (where Im=1H-1midazole and L = 3, 6, 9, 16, 19, 22-hexaaza-6, 19-bis(1H-imidazol-4-ylmethyl)tricycle[22, 2, 2, 2^11,14]triaconta-1, 11, 13, 24, 27, 29-hexaene) were synthesized and characterized as model compounds for the active site of copper(II)–zinc(II) superoxide dismutase (Cu₂Zn₂–SOD). X-ray crystal structure analysis revealed that the metal centers in both complexes exhibit distorted trigonal-bipyramid coordination geometry and the CuCu and CuZn distances are both 6.02 Å. Magnetic and ESR spectral measurements of 1 showed antiferromagnetic exchange interactions between the imidazolate-bridged Cu(II) ions. The ESR spectrum of 2 displays typical signals of mononuclear Cu(II) complex, demonstrating the formation of heterodinuclear complex 2 rather than a mixture of homodinuclear Cu(II)/Zn(II) complexes. pH-dependent ESR and UV–visible spectral measurements manifest that the imidazolate exists as a bridging ligand from pH 6 to 11 for both complexes. The IC₅₀ values of 1.96 and 1.57 μM [per Cu(II) ion] for 1 and 2 suggest that they are good models for the Cu₂Zn₂–SOD.     

DNA‐based chemiluminescent nanoprobes for highly sensitive and selective detection of mercury(II) ion

A simple and sensitive DNA‐stablized gold nanoparticle (AuNP)‐based chemiluminescent (CL) probe for detecting mercury ion (Hg²⁺) in aqueous solution has been developed. The CL strategy relies upon the catalytic activity of unmodified AuNPs on the luminol–H₂O₂ CL reaction, and the interaction of unmodified AuNPs with DNA. The unmodified AuNPs can effectively differentiate unstructured and folded DNA. The DNA desorbs from AuNPs in the presence of Hg²⁺, leading to the increase in CL signal. By rationally varying the number of thymine in single‐strand oligonucleotides, the detection range could be tuned. Employing single‐strand oligonucleotides with 14 thymine in the detecting system, a sensitive linear range for Hg²⁺ ions from 5.0 × 10^–10 to 1.0 × 10^–7 mol/L and a detection limit of 2.1 × 10^–10 mol/L are obtained. Changing the number of thymine to 10 and 6, it leads to a narrow detection range but a high sensitivity. Besides, DNA‐based CL nanoprobes exhibit a remarkable selectivity for Hg²⁺ ions over a variety of competing metal ions. Copyright © 2012 John Wiley & Sons, Ltd.     

Determination of oxytetracycline hydrochloride in milk and egg white samples using Ru(bipy)32+–Ce(SO4)2 chemiluminescence

A novel, rapid and sensitive chemiluminescence (CL) method for the determination of oxytetracycline hydrochloride (OTCH) is described in this paper. The presented method was based on the fact that OTCH could immensely enhance the CL of the reaction of cerium sulfate and tris(2,2‐bipyridyl) ruthenium (II) in acidic medium. Under optimal experimental conditions, CL intensity was favorably linear for OTCH in the range 5.0 × 10^?7 to 5.0 × 10^?5 g/ml, with a detection limit of 1.5 × 10^?7 g/ml (S/N = 3). The relative standard detection was 4.76% for 5.0 × 10^?6 g/ml (n = 11). This method was successfully applied to the analysis of OTCH in milk and egg white samples. According to the results of the kinetic curves for OTCH in the Ru(bipy)₃²⁺–Ce(SO₄)₂ CL system, together with CL and ultraviolet (UV)–visible spectra, the possible mechanism of the CL reaction is discussed briefly.     

Cellular localization of the K+‐dependent Na+–Ca2+ exchanger NCKX5 and the role of the cytoplasmic loop in its distribution in pigmented cells

NCKX5 is a bidirectional K⁺‐dependent Na⁺–Ca²⁺ exchanger, which belongs to the SLC24A gene family. In particular, the A111T mutation of NCKX5 has been associated with reduced pigmentation in European populations. In contrast to other NCKX isoforms, which function in the plasma membrane (PM), NCKX5 has been shown to localize either in the trans‐Golgi network (TGN) or in melanosomes. Moreover, sequences responsible for retaining its intracellular localization are unknown. This study addresses two major questions: (i) clarification of intracellular location of NCKX5 and (ii) identification of sequences that retain NCKX5 inside the cell. We designed a set of cDNA constructs representing NCKX5 loop deletion mutants and NCKX2–NCKX5 chimeras to address these two questions after expression in pigmented MNT1 cells. Our results show that NCKX5 is not a PM resident and is exclusively located in the TGN. Moreover, the large cytoplasmic loop is the determinant for retaining NCKX5 in the TGN.     

Polymer composite fluorescent hydrogel film based on nitrogen‐doped carbon dots and their application in the detection of Hg2+ ions

A simple microwave‐assisted solvothermal method was used to prepare fluorescent nitrogen‐doped carbon dots (N‐CDs) with high fluorescence quantum yield (79.63%) using citric acid and N‐(2‐hydroxyethyl)ethylenediamine as starting materials. The PVAm‐g‐N‐CDs grafted products were synthesized by amide bond formation between the carboxylic groups of N‐CDs and amine groups of polyvinylamine (PVAm). Fluorescent hydrogel films (PVAm‐g‐N‐CDs/PAM) were synthesized by interpenetration polymer network polymerization of PVAm‐g‐N‐CDs and acrylamide (AM). When used for ion detection, we found that the fluorescence of the hydrogel films was clearly quenched by addition of Hg²⁺. Repeatability tests on using the hydrogel films for Hg²⁺ detection showed that they could be applied at least three times. The PVAm‐g‐N‐CDs/PAM could serve as an effective fluorescent sensing platform for sensitive detection of Hg²⁺ ions with a detection limit of 0.089 μmol/L. This work may offer a new approach for developing recoverable and sensitive N‐CDs‐based sensors for biological and environmental applications.     

Electron transfer reactions of ruthenium(II)–bipyridine complexes carrying tyrosine moiety with quinones

Three ruthenium(II)–bipyridine complexes carrying a tyrosine moiety were synthesized and photophysical and electron transfer studies with quinones were carried out using absorption and emission spectral techniques. The binding efficiency of quinones with ruthenium(II)–bipyridine complexes was also studied using these techniques. The binding efficiency was moderate and similar for all complexes with all quinones. The quenching modes were also similar and efficient for all complexes with all quinones. The quenching processes were diffusion controlled. The rate of electron transfer was calculated using semiclassical theory. Copyright © 2013 John Wiley & Sons, Ltd.     

A ratiometric fluorescence sensor based on carbon quantum dots realized the quantitative and visual detection of Hg2+

In this paper, based on the fluorescence of carbon quantum dots (CQDs) quenched by mercury ions (Hg²⁺) and the nonresponse of Hg²⁺ to rhodamine B fluorescence, a dual emission ratio fluorescence sensor was constructed to realize the quantitative detection of Hg²⁺. Under excitation at 365 nm, the fluorescence spectrum showed double emission peaks at 437 nm and 590 nm, corresponding to the fluorescence emissions of CQDs and rhodamine B, respectively. This method quantitatively detected Hg²⁺ based on the linear relationship between the ratio of the intensities of the two emission peaks F₄₃₇/F₅₉₀ and the concentration of Hg²⁺. The detection range was 10–70 nM, and the limit of detection (S/N = 3) was 3.3 nM. In addition, this method could also realize the qualitative and semiquantitative detection of Hg²⁺ according to the fluorescence colour change of the probe under ultraviolet light. After various evaluations, the method could be successfully applied to the quantitative and visual detection of Hg²⁺ in tap water, and demonstrated excellent selectivity, anti-interference performance, and repeatability of the method.     

CD measurements of β‐amyloid (1–40) and (1–42) in the condensed phase

Circular dichroism (CD) spectroscopy of proteins/peptides in thin films can provide valuable information on the structures in the aggregated states; however, it is difficult to estimate the secondary structure content quantitatively due to artifact signals arising from macroscopic anisotropies which is unique to the solid phase. Using a Universal Chiroptical Spectrophotometer (UCS‐1) together with the measurement and analytical procedures we have developed, we could obtain artifact‐free CD spectra of cast and Langmuir‐Blodgett (L‐B) films of synthetic peptides, Aβ (1–40) and (1–42) which are related to Alzheimer's disease. The work gave insights into the mechanisms for structural transformation and amyloid‐like aggregation. © 2010 Wiley Periodicals, Inc. Biopolymers 95: 127–134, 2011.     

The luminescence properties of Sr2–1.5x−1.5yP2O7:xDy3+,yCe3+ phosphor for near‐UV‐based white LEDs synthesized by a chemical co‐precipitation method

A series of Sr₂P₂O₇:Dy³⁺, Sr₂P₂O₇:Ce³⁺ and Sr₂P₂O₇:Dy³⁺,Ce³⁺ phosphors was synthesized via the one‐step calcination process for the precursors prepared by co‐precipitation methods. The phases, morphology, quantum efficiency and photoluminescence properties of the obtained phosphors were characterized systematically. These results show that the near‐spherical particles prepared through calcining the precursors by means of ammonium dibasic phosphate co‐precipitation (method 3) have the smallest particle size and strongest emission intensity among the three methods in the paper. With Dy³⁺ concentration increasing in Sr₂P₂O₇:Dy³⁺ phosphors, the luminescence intensity first increases, reaches maximum, and then decreases. A similar trend was followed by Sr₂P₂O₇:Ce³⁺ with Ce³⁺concentration increasing. A successful attempt was made to initiate the energy transfer mechanism from Ce³⁺ to Dy³⁺ in the host lattice and an overlap between the emission band of Ce³⁺ and the excitation band of Dy³⁺ indicated that the Ce³⁺ → Dy³⁺ energy transfer may indeed exist. It is clear that the photoluminescence intensity of Dy³⁺ as well as the quantum efficiency of the phosphor can be enhanced markedly by co‐doping Ce³⁺. Sr₂P₂O₇:Dy³⁺,Ce³⁺ has its (CIE) chromaticity coordinates in the bluish‐white‐light region, near the standard illuminant D₆₅. The CIE 1913 chromaticity coordinates of Sr₂P₂O₇:Dy³⁺ phosphors fall in the white‐light region, and are adjacent to the ideal white‐light coordinates. In addition, the colour temperature and colour tone of Sr₂P₂O₇:Dy³⁺ could be adjusted by changing the relative concentration of Dy³⁺. In short, Sr₂P₂O₇:Dy³⁺ can be a promising single‐phased white‐light emitting phosphor for near‐UV (NUV) w‐LEDs.     

A new fluorescent chemosensor for cadmium(II) based on a pyrene‐appended piperidone derivative and its β‐cyclodextrin complex

We report, in this article, a piperidin‐4‐one derivative carrying pyrenyl fluorescent reporter groups which acts as a Cd²⁺ ion sensor. The compound is synthesized and characterized using IR and NMR spectral techniques. The compound forms an inclusion complex with β‐cyclodextrin. It selectively binds to Cd²⁺ ions in water and aqueous β‐cyclodextrin media. The stoichiometry of the host–guest complex of the compound with β‐cyclodextrin is 1:2. The ligand–metal ion binding stoichiometry is 1:1 both in water and in β‐cyclodextrin. The linear concentration range of detection of the metal ion is reported. Cyclodextrin complex formation does not affect the metal ion selectivity of the compound.     

Chemiluminescence determination of chlorpheniramine using tris(1,10‐phenanthroline)–ruthenium(II) peroxydisulphate system and sequential injection analysis

A sequential injection (SI) method was developed for the determination of chlorpheniramine (CPA), based on the reaction of this drug with tris(1,10‐phenanthroline)–ruthenium(II) [Ru(phen)₃²⁺] and peroxydisulphate (S₂O₈^2–) in the presence of light. The instrumental set‐up utilized a syringe pump and a multiposition valve to aspirate the reagents [Ru(phen)₃²⁺ and S₂O₈^2–] and a peristaltic pump to propel the sample. The experimental conditions affecting the chemiluminescence reaction were systematically optimized, using the univariate approach. Under the optimum conditions linear calibration curves of 0.1–10 µg/ml were obtained. The detection limit was 0.04 µg/ml and the relative standard deviation (RSD) was always < 5%. The procedure was applied to the analysis of CPA in pharmaceutical products and was found to be free from interferences from concomitants usually present in these preparations. Copyright © 2008 John Wiley & Sons, Ltd.