Highly selective colorimetric detection of cysteine and homocysteine in water through a direct displacement approach

The complex CuQ₂ (HQ = 8-hydroxy-7-(4-tolyldiazenyl)quinoline-5-sulfonic acid) has been synthesized and used as a colorimetric probe for the specific detection of cysteine and homocysteine in water through a displacement reaction. The detection can be performed either by the spectroscopy from the increased UV–vis absorbance at 498 nm or by the change of color from yellow to red upon addition of cysteine or homocysteine to the solution of the complex. The experimental results show no interference by other amino acids to the detection of cysteine and homocysteine.     

A fluorescent probe for the dual detection of mercury ions and thiols based on a simple coumarin derivative

A fluorescent probe based on a simple coumarin derivative could recognise mercury ions (Hg(ii )) and thiols selectively in aqueous solution. The addition of Hg(ii ) induced a blue shift of the fluorescence emission band of the probe while the fluorescence was almost quenched by the addition of p‐toluenethiol or cysteine (Cys). The detection limit of the probe towards Hg(ii ) and Cys was 8 µmol/L. The probe could be used for the detection of Hg(ii ) and thiols by the naked eye under ultraviolet light irradiation.     

Water-soluble poly(p-phenylene) incorporating methoxyphenol units: Highly sensitive and selective chemodosimeters for hypochlorite

A series of water-soluble poly(p-phenylene)s (PPPs), named N-PPPx (x = 10, 25 and 50), were directly synthesized by Suzuki coupling in aqueous solution. The structures of the polymers were characterized by ¹H NMR and elemental analysis. The polymers exhibit similar absorption and emission spectra with three absorption maxima at ca. 205, 290 and 350 nm, and emission maximum at 420 nm in phosphate buffer saline (PBS) solution. Upon addition of hypochlorite, N-PPPx shows a decrease of absorption band at ca. 350 nm and a fluorescent quenching. Compared to their model compound PMOPP, N-PPPx shows a significantly amplified fluorescent quenching. Moreover, the K_sv is decreased with the increasing content of methoxyphenol moieties in N-PPPx. In view of the sensitivity and selectivity, N-PPP10 and N-PPP25 are very promising polymeric fluorescent probes to hypochlorite under the aqueous condition.     

Detecting Cysteine in Bioimaging with a Near-Infrared Probe Based on a Novel Fluorescence Quenching Mechanism

Near-infrared (NIR) fluorescent probes are very significant for detecting cysteine in biological systems. Herein, we report a highly selective and sensitive NIR turn-on fluorescent probe (BDP-NIR) based on BODIPY with large Stokes shift (105 nm) for detecting Cys. We clarified the sensing mechanism based on the different thiol-induced S_NAr substitution/rearrangement reaction of the probe with cysteine and homocysteine/glutathione, which leads to the corresponding amino- and thiol-BODIPY dyes with distinct photophysical properties. Moreover, a novel mechanism of fluorescence quenching was demonstrated by density functional theory calculation. The reason for the fluorescence quenching of the probe might be intersystem crossing (from singlet to triplet excited state). Moreover, BDP-NIR had a high linear dynamic range of 0–500 μM, which was promising for detecting cysteine quantificationally. Significantly, BDP-NIR was capable of sensing endogenous cysteine in living cells and in vivo.     

Synthesis of novel stilbene-alkoxysilane fluorescent brighteners, and their performance on cotton fiber as fluorescent brightening and ultraviolet absorbing agents

Two novel fluorescent brightening agents (compounds 3a-b shown in Figure 1) were synthesized, using a facile three-step synthetic route, from 4,4′-diamino-2,2′-disulfonic-stilbene, cyanuric chloride, and a readily cross-linkable 3-aminopropyltrimethoxy silane. The products contain hydrolytically active trimethoxysilyl, (-Si(OCH)₃), functional groups that readily hydrolyze in the presence of water, and subsequently generate a water insoluble silicon cross-linked-network (Si-O-Si) via a condensation process. The cross-linked product hydrolyzes on treatment with hot aqueous sodium hydroxide to silanols (-Si(OH)₃) to form compounds 4a-b which are readily water soluble and produce a clear fluorescent solution. The silanol forms of compounds 4a-b were used for further characterization and performance evaluation. The structures of compounds 4a-b were characterized by ¹H-NMR, Fourier-Transform infrared (FT-IR) spectroscopy and negative electrospray ionization mass (⁻ESI-MS) spectroscopy. Compounds were applied to cotton fiber as fluorescent brightening agents and their performance was evaluated by measuring the degree of whiteness, ultraviolet protection factor (UPF), fluorescence and acid fastness. Results showed that application of 0.25% (o.w.f) of compounds 4a-b impart a high degree of whiteness (CIE WI = 144, 139) as well as good ultraviolet protection factor (UPF = 29, 27) on cotton fiber exhibiting a significant increase in whiteness and UV blocking properties compared to untreated substrate (CIE WI = 81, UPF = 5). Acid fastness tests of both compounds showed a slight change in fluorescence emission intensities as a function of pH. In acidic solutions, a shift in emission maximum occurs at pH 3 from 434 to 453 nm and from 435 to 457 nm, due to the protonation of amino and sulfonic groups of stilbene fluorophore which substantially reduces the quenching process.     

A highly selective and sensitive benzothiazole‐based ‘turn‐on’ fluorescent sensor for Hg2+ ion

A simple benzothiazole‐based fluorescent probe (TDA) for the determination of Hg²⁺ ion in aqueous solutions was synthesised in one step and characterised by ¹H NMR, ¹³C NMR, APT, COSY, FTIR, and elemental analysis. TDA shows a significant fluorescence change upon the interaction of Hg²⁺ ion in DMF–water (v/v = 1/1), while only minor changes in fluorescence intensity are observed with 18 other metal ions. Fluorescence enhancement by a factor of 15 is achieved upon selective interaction with Hg²⁺ ion. The Hg²⁺ ion detection process is found to be pH dependent; therefore, TDA could be feasible within a pH range of 4.0–7.0.     

Fractionation and analysis of fluorescent products of lipid peroxidation

The fluorescence excitation spectrum of model conjugated Schiff base compounds that arise from the reaction of malonaldehyde with amino acids was shown to contain a maximum at 260–280 nm in addition to the previously observed maximum at 350–390 nm. Excitation at either maximum results in emission at a single maximum at 440–480 nm. The excitation and emission maxima of the model fluorescent compounds, together with the characteristic reductions in fluorescence intensity caused by alkaline pH or heavy metal coordination, provide criteria with which to examine lipid peroxidation products for the presence of the conjugated Schiff base fluorophore. Silicic acid column chromatography and silica gel thin layer chromatography were employed to fractionate the fluorescent products of model lipid peroxidation systems and of rat testicular lipid soluble extracts. These products contained large families of compounds whose fluorescence characteristics were the same as those of the Schiff base floorophores. The fractionation methods used enabled more thorough fluorescence characterization of many of the products of lipid peroxidation, but the fluores-cence criteria available do not provide definitive proof of structure.     

Spectroscopic evaluation of a novel multi-element sensitive fluorescent probe derived from 2-(2′-phenylbenzamide)benzimidazole: Selective discrimination of Al3 + and Cd2 + from their congeners

A novel fluorescent chemosensor 2 exhibiting excited-state intramolecular proton transfer (ESIPT) process has been synthesized by condensation approach, among which 2 could be used as a multielement sensitive fluorescent probe for both Al^3 + and Cd^2 +. The emission wavelength of 2 underwent blue shift of 78 nm upon binding with these ions. The cation-induced inhibition of ESIPT phenomenon was responsible for these fluorescence changes. Moreover, the absorption spectra of 2 showed changes with F⁻ and AcO⁻ ions also. TD-DFT studies well displayed the blue shift in the emission wavelength of 2 upon binding with Al^3 + ions.     

Synthesis and properties of new water-soluble aliphatic hyperbranched poly(amido acids) with high pH-dependent photoluminescence

Water-soluble fluorescent hyperbranched poly(amido acids) (HBPAAs), based on wholly aliphatic structures were prepared through direct self-condensation of N-(3-aminopropyl) diethano succinate amine (APDESA, AB₂ monomer) in the presence of N,N-dicyclohexylcarbodiimide (DCC) as a condensation agent. The resulting HBPAAs were soluble in water, DMF and THF, and the structure of synthesized AB₂ monomer and polymers was confirmed by IR, ¹H, and ¹³C NMR measurements. TEM image indicated that the HBPAAs self-assembled in H₂O to form a spherical micelle with a diameter ranging from 30 to 50 nm. A significant pH-dependent profile of fluorescent intensity in the pH range from 3 to 10 was observed, wherein pH 4 provided a critical jump as the solution pH was increased. Further increasing the pH to 10 decreased the fluorescence because of partial hydrolysis. Strong fluorescence emission was observed at 395 nm in aqueous media and the fluorescence quantum yields are to 23%. These amphiphilic HBPAAs, with excellent water-solubility, void-rich space, multiple functional peripheries and high blue fluorescence, have potential uses as tracing nanocarriers and molecular-level containers.     

Preparation of polymer latex particles carrying salt-responsive fluorescent graft chains

We prepared the novel fluorescent polymer latex particles which can change their fluorescence intensity in response to the increasing NaCl concentration in water. Core polymer latex particles were synthesized by emulsifier-free emulsion polymerization of styrene and 2-(2-chloroisobutyroyloxy)ethyl methacrylate. Hydrophilic polymer chains containing epoxy groups were grafted from the core particles by surface-initiated atom transfer radical copolymerization of methoxy polyethyleneglycol methacrylate (MEO_xMA, x = 4 or 9) and glycidyl methacrylate in aqueous media. After azidation of epoxy groups in graft chains, a water-soluble fluorescent dansyl derivative was successfully coupled with the graft chains by copper-catalyzed azide-alkyne cycloaddition in aqueous media. The wavelength of maximum fluorescence intensity of polymer particles carrying graft chains with longer PEG side chains (x = 9) was slightly blue-shifted (7 nm) and the fluorescence intensity increased (1.35 times) with an increase in NaCl concentration as opposed to polymer particles with shorter PEG chains (x = 4).     

A luminescent coordination polymer for selective,sensitive, and recyclable sensing of nitrobenzene in aqueous solution

A luminescent coordination polymer, [Cd(H₂biim)₂SO₄]·3H₂O (JLNU-1, JLNU = Jilin Normal University); H₂Biim = 2,2′-biimidazole, has been prepared by hydrothermal method and characterized by corresponding analytical tools. JLNU-1 exhibits outstanding chemical stability in aqueous solution and solvent-dependent luminescent behaviour. In particular, stable suspension of JLNU-1 in nitrobenzene showed highest quenching. The emission spectra were nearly completely quenched at a concentration of 100 ppm nitrobenzene in aqueous solution. JLNU-1 can be regenerative for 6 cycles by centrifugation of the solution after use and washing several times with H₂O. Therefore, JLNU-1 can be used as a fluorescent probe for sensitive and recyclable sensing of small-molecule pollutant nitrobenzene in aqueous solution.     

A boronic acid-based fluorescent hydrogel for monosaccharide detection

A boronic acid-based anthracene fluorescent probe was functionalised with an acrylamide unit to incorporate into a hydrogel system for monosaccharide detection. In solution, the fluorescent probe displayed a strong fluorescence turn-on response upon exposure to fructose, and an expected trend in apparent binding constants, as judged by a fluorescence response where D-fructose>D-galactose>D-mannose>D-glucose. The hydrogel incorporating the boronic acid monomer demonstrated the ability to detect monosaccharides by fluorescence with the same overall trend as the monomer in solution with the addition of D-fructose resulting in a 10-fold enhancement (≤0.25 mol/L).     

Evolution of ZnS Nanoparticles via Facile CTAB Aqueous Micellar Solution Route: A Study on Controlling Parameters

Synthesis of semiconductor nanoparticles with new photophysical properties is an area of special interest. Here, we report synthesis of ZnS nanoparticles in aqueous micellar solution of Cetyltrimethylammonium bromide (CTAB). The size of ZnS nanodispersions in aqueous micellar solution has been calculated using UV-vis spectroscopy, XRD, SAXS, and TEM measurements. The nanoparticles are found to be polydispersed in the size range 6–15 nm. Surface passivation by surfactant molecules has been studied using FTIR and fluorescence spectroscopy. The nanoparticles have been better stabilized using CTAB concentration above 1 mM. Furthermore, room temperature absorption and fluorescence emission of powdered ZnS nanoparticles after redispersion in water have also been investigated and compared with that in aqueous micellar solution. Time-dependent absorption behavior reveals that the formation of ZnS nanoparticles depends on CTAB concentration and was complete within 25 min.     

Two coumarin formhydrazide compounds as chemosensors for copper ions

Two coumarin formhydrazide compounds as chemosensors for copper ions have been synthesized. The compounds can recognize copper ion with obvious absorption spectral change and fluorescence decrease in aqueous solution. The detection limit of the compound with terminal diethylamino group to Cu^2 + in aq.-HEPES buffer acetonitrile (3:7, v/v, pH = 7.4) with fluorescence spectra as detected signal is 0.00041 μM. One carbonyl and amine group in one sensor molecule may complex with one copper ion to form 1:1 complex.     

Photophysical properties and photostability of novel symmetric polycyclicphenazine-type fluorescent dyes and the dye-doped films

Novel symmetric polycyclicphenazine-type fluorescent dyes have been synthesized and characterized in solution and in polymer films. The dyes exhibited two strong absorption bands at around 365-428 nm and 519-567 nm and an intense fluorescence band at around 560-600 nm (Ф = 0.70-0.87) in 1,4-dioxane. The dye-doped polymer films showed excellent wavelength conversion function that efficiently convert ultraviolet and yellow lights into red light (Ф = 0.61-0.92). Moreover, the photostability of the dye-doped PS, PMMA, and PLA films has been investigated.     

In situ polycondensation of amino acid modified liposomes and their properties

Three amphiphilic amino acids based on glutamic acid, i.e. S-[1-carboxy-2-([N-bistetradecyl- -glutamate]carbon-yl)ethyl]cysteine (1), S-[1-carboxy-2-([N-bishexadecyl- -glutamate]carbonyl)ethyl]cysteine (2), S-[1-carboxy-2-([N-bis-octadecyl- -glutamate]carbonyl)ethyl]cysteine (3), were synthesized. The aggregation behavior of them in water or buffer solution was studied. It was found that upon hydration and sonication in water, they could form stable liposomes. This kind of amino acid modified liposome was then polycondensed locally on the liposome surface to form a polypeptide-surfaced liposome and the peptide formation was detected by Fr-IR, GPC, etc. The effect of polycondensation of amino acid on the properties of liposomes were studied by detecting the phase transition temperatures with DSC or measuring the leakage of the encapsulated fluorescent probe from the liposomes. It was observed that the phase transition temperatures of the peptide liposomes moved down and the polycondensation of amino acid moieties obviously increased the leakage of the encapsulated molecules.     

A turn-off fluorescence sensor for cyanide detection which in turn inhibit 2-way ESIPT investigated by experimental and theoretical study

A ligand based on 3-((quinoline-7-yl) methyeleneamino) phenazine-2-ol) (HAPQA) has been designed and synthesized for the selective detection of cyanide ions. The ligand HAPQA exhibits excited-state intramolecular proton transfer (ESIPT) with a long wavelength emission fluorescent (575 nm) which gradually quenches with the addition of cyanide ions. The photophysical properties of the probe as well as its selectivity towards CN⁻ ions are explored using UV–visible, emission spectroscopy and time-resolved fluorescence spectroscopic studies. The ligand exhibits strong H-bonding-mediated inhibition of 2-way excited-state intramolecular proton transfer (ESIPT) in HAPQA selectively with cyanide ions over all other ions. The deep orange colour fluorescence of the ligand in acetonirile turns into bright green coloured solution in presence of cyanide ions with a detection limit of 0.60 μM. DFT calculations has been done to study the ground and excited state energy optimized structure and proposed mechanism which is in harmony with the experimental findings and the ESIPT process observed in ligand HAPQA. Thus, the receptor can be used as a Colorimetric and fluorescent sensor for the determination of CN⁻ ion.     

Assessment of quality changes in frozen sardine (Sardina pilchardus) by fluorescence detection

The formation of fluorescent compounds was tested as a quality assessment during the frozen storage of sardine at −18°C (up to 24 mon) and at −10°C (up to 120 d). The fluorescence ratio between two excitation/emission maxima (393/463 and 327/415 nm) was studied in the aqueous (δF _aq) and organic (δF _or) extracts after Bligh and Dyer extraction of the white muscle. Fluorescence results were compared to common quality indices [total volatile base-nitrogen (TVB-N); conjugated dienes; thiobarbituric acid index (TBA-i); and free fatty acids (FFA)]. δF _aq showed good correlations with storage time (r=0.80 and r=0.72 at −18 and −10°C, respectively) and TBA-i (r=0.92 and r=0.81). Principal-component analysis grouped δF _aq with quality indices that are sensitive for the assessment of fish damage during frozen storage at both temperatures (TBA-i and FFA at −18°C; BVT-N, TBA-i, and FFA at −10°C). According to these results, fluorescence detection of interaction compounds in the aqueous phase can provide an accurate method to assess quality differences during frozen storage of fish.     

Synthesis of pH Sensitive Organic-Inorganic Polymer Hybrids

Summary The synthesis of pH sensitive organic-inorganic polymer hybrids from poly(2-hydroxyethyl methacrylate) derivatives and alkoxysilane is described. To a reaction mixture of poly(2-hydroxyethyl methacrylate) derivatives, tetramethoxysilane, 2,7-bis(carboxyethyl)-4- or 5-carboxyfluorescein (BCECF) as a fluorescent probe, and ten equivalents of HCl aqueous solution in methyl ethyl ketone / propanol (7/3, v/v) were added. The resulting mixture was kept stirring at room temperature for 1 h and was heated at 40 °C for 2 weeks. The changes of the pH were estimated as changes in the fluorescence intensity with the pH sensitive fluorescence probe BCECF trapped within the obtained polymer hybrid. Consequently, the pH value was found to be proportionate to the fluorescence intensity.     

Photoluminescence of Cu(I)(PPh3)2(8-quinolinolate)

The complex Cu(I)(PPh₃)₂(oxinate) with oxine = 8-quinolinole is luminescent under ambient conditions. In the solid state it shows an emission which originates from the lowest-energy oxinate ILCT state. It consists of a fluorescence and a phosphorescence. In solution saturated with argon, a single broad emission band appears which seems to be composed of a more intense fluorescence and a much weaker phosphorescence at longer wavelength. If this solution is saturated with air, the complete emission band becomes less intense. This is quite surprising, since the oxinate ILCT fluorescence of other oxinate complexes is not quenched by oxygen. It is conceivable that the fluorescence largely consists of a delayed fluorescence. When the emitting triplet is depopulated by a thermally activated transition to the fluorescent singlet, both emissions, the delayed fluorescence and the phosphorescence, may undergo a luminescence quenching. For a simple comparison, the photoluminescence of Ag(PPh₃)₂(oxinate) was also briefly examined. The absorption and emission spectra of this silver complex in solution at r.t. resemble those of the copper complex.