Novel coumarin-based fluorescent pH indicators,probes and membranes covering a broad pH range

A new family of coumarin-based pH indicators was synthesized. They are sensitive to pH in either weakly acidic or weakly basic solution. The indicators possess moderate to high brightness, excellent photostability and compatibility with light-emitting diodes. The indicators were covalently immobilized on the surface of amino-modified polymer microbeads which in turn were incorporated into a hydrogel matrix to obtain novel pH-sensitive materials. When a mixture of two different microbeads is used, the membranes are capable of optical pH sensing over a very wide range comparable to the dynamic range of the glass electrode (pH 1–11). A new family of coumarin-based pH indicators is synthesized for the use in either weakly acidic or weakly basic solution. The indicators possess moderate to high brightness, excellent photostability and compatibility with light-emitting diodes. Novel pH-sensitive materials are obtained by covalent immobilization of the indicators on the surface of amino-modified polymer microbeads which in turn are incorporated into a hydrogel matrix. Sensing of pH over a very wide range also becomes possible.     

Hybrid fluorescent nanoparticles fabricated from pyridine-functionalized polyfluorene-based conjugated polymer as reversible pH probes over a broad range of acidity-alkalinity

Conjugated polymer nanoparticles (CPNs) were developed based on a polyfluorene-based conjugated polymer with thiophene units carrying pyridyl moieties incorporated in the backbone of polymer chains (PFPyT). Hybrid CPNs fabricated from PFPyT and an amphiphilic polymer (NP1) displayed pH-sensitive fluorescence emission features in the range from pH 4.8 to 13, which makes them an attractive nanomaterial for wide range optical sensing of pH values. The fluorescence of hybrid CPNs based on chemically close polyfluorene derivatives without pyridyl moieties (NP3), in contrast, remains virtually unperturbed by pH values in the same range. The fluorescence emission features of NP1 underwent fully reversible changes upon alternating acidification/basification of aqueous dispersions of the CPNs and also displayed excellent repeatability. The observed pH sensing properties of NP1 are attributed to protonation/deprotonation of the nitrogen atoms of the pyridine moieties. This, in turn, leads to the redistribution of electron density of pyridine moieties and their participation in the π-conjugation within the polymer main chains. The optically transparent amphiphilic polymers also exerted significant influence on the pH sensing features of the CPNs, likely by acting as proton sponge and/or acid chaperone. Figure

pH-sensitive fluorescent nanoparticles were fabricated from pyridine-functionalized conjugated polymer; protonation/deprotonation of the nitrogen atoms of pyridine moieties upon pH changes, which leads to the redistribution of electron density of pyridine moieties and their participation in the π-conjugation with polymer chains, were confirmed.     

Carbon dots with strong excitation-dependent fluorescence changes towards pH. Application as nanosensors for a broad range of pH

In this study, preparation of novel pH-sensitive N-doped carbon dots (NCDs) using glucose and urea is reported. The prepared NCDs present strong excitation-dependent fluorescence changes towards the pH that is a new behavior from these nanomaterials. By taking advantage of this unique behavior, two separated ratiometric pH sensors using emission spectra of the NCDs for both acidic (pH 2.0 to 8.0) and basic (pH 7.0 to 14.0) ranges of pH are constructed. Additionally, by considering the entire Excitation–Emission Matrix (EEM) of NCDs as analytical signal and using a suitable multivariate calibration method, a broad range of pH from 2.0 to 14.0 was well calibrated. The multivariate calibration method was independent from the concentration of NCDs and resulted in a very low average prediction error of 0.067 pH units. No changes in the predicted pH under UV irradiation (for 3 h) and at high ionic strength (up to 2 M NaCl) indicated the high stability of this pH nanosensor. The practicality of this pH nanosensor for pH determination in real water samples was validated with good accuracy and repeatability.     

Two near-infrared highly sensitive cyanine fluorescent probes for pH monitoring

Two near-infrared(NIR) p H-activated heptamethine indocyanine probes with quaternary ammonium unit were designed and synthesized. The absorption and emission titrations indicate that cationic structure improves the cyanine dye's aqueous solubility and these two probes exhibit highly sensitive response to p H in acid condition. Their fluorescence intensities both gradually increase about 25-fold from p H 7.60 to 3.00 with p Ka values of 4.72 and 4.45 respectively, which are suitable for studying acidic organelles in living cells. Moreover, their fluorescence intensities are linearly proportional to p H values in the range of 5.50–4.00. These results are probably attributed to the protonation of the indole nitrogen atoms, which are verified by 1H NMR spectra. Furthermore, these two probes can achieve real-time imaging of cellular p H and detection of p H in situ in living He La cells due to their excellent properties,including good reversibility, desirable photostability, high selectivity, low cytotoxicity and remarkable membrane permeability.     

Fluorescent pH probes for alkaline pH range based on perylene tetra-(alkoxycarbonyl) derivatives

The pH detection in the alkaline range is particularly important in many fields such as leather processing, waste water treatment, paper industry, and metal mining and finishing. Compared with traditional analysis methods such as colorimetric sensors and electrochemical sensors, the fluorescence and colorimetric probes for pH measurements have attracted much more attention due to their advantages of high sensitivity, excellent selectivity, noninvasiveness, low cost, fast response time, the possibility of continuously measurement, etc. However, there are few fluorescent probes fiting for alkaline pH monitoring. Acturally, the design and synthesis of them were more significant for new probes producing. In this study, the design, synthesis, and practical application of two novel fluorescent pH probes for alkaline pH assay were discussed. Both of the two probes were derived from perylene tetra-(alkoxycarbonyl). The red or blue shift of the absorption/fluorescence spectrum was caused by the introduction of electron donor amino or oxygen ring in the bay region. Due to electronic separation of the OH group from the electron-withdrawing core, the probes have high pKa values and cover the pH range from 8 to 12. They exist in either fluorescent acid form or non-fluorescent basic form. It was investigated that the amino substituent at bay region had a higher pKa value than O-heterocyclic annulated perylene, which showed that the adjustable pKa value could be achieved by the modification of electron withdrawing groups. The probes would have a wide use for testing strips measurements and monitoring pH changes in concrete.     

A ratiometric fluorescence sensor with broad dynamic range based on two pH-sensitive fluorophores

This paper describes a novel ratiometric fluorescence sensor for pH measurement. Two pH-sensitive fluorophores, N-allyl-4-(4'-methyl-piperazinyl)-1,8-naphthalimide (AMPN) and meso-5,10,15,20-tetra-(4-allyloxyphenyl)porphyrin (TAPP), which served as referencing indicators for each other, were co-polymerized with acrylamide, hydroxyethyl methacrylate and triethylene glycol dimethacrylate on the silanized glass surface. The proposed sensor is based on the pH-dependent fluorescence intensities of the two fluorophores in different pH ranges. The sensor covers a broad dynamic range of pH 1.5-9.0. It exhibits satisfactory analytical performance in terms of selectivity, reproducibility and stability. The successful fabrication of the proposed sensor provides an alternative concept to utilizing two or more fluorophores for the development of ratiometric sensors covering a broad range of pH.     

Separation and determination of chiral composition in penicillamine tablets by capillary electrophoresis in a broad pH range

A chiral capillary electrophoretic method with nearly full pH window was explored for the separation and determination of dl-penicillamine. A facile one-pot labeling technique was coupled in the method for introduction of chromophore and charge groups onto the analytes to facilitate the electromigration and sensitive detection. By using simply a cost-effective neutral β-cyclodextrin as chiral selector, baseline separation of the dl-penicillamine was achieved from pH 2.0 to over pH 10. Quantification of standard d- and l-penicillamines was demonstrated by taking pH 4.5, 7.4, and 9.7 as the representatives of acidic, neutral, and basic conditions. The working curves were constructed between peak area and concentration, having linear ranges of 8.56-8.56 × 10(2) μg/mL for pH 4.5 and 8.56-1.71 × 10(3) μg/mL for pH 7.4 and 9.7, with correlation coefficients all better than 0.999. The limit of detection (S/N = 3) was 2.58 μg/mL in acidic and neutral conditions or 1.41 μg/mL in basic condition. The method was further validated by assaying the commercial penicillamine tablets, applicable to quantification of the effective enantiomer and the trace impurity of l-penicillamine at a content of down to 0.2, 0.6, and 2.0% for pH 9.7, 4.5, and 7.4, respectively. The recovery determined by spiking technique was in a range from 93.1 to 105 %. The method is easily extendable to the analysis of other chiral amines or amino acids.     

A metal-free carbon dots for wastewater treatment by visible light active photo-Fenton-like reaction in the broad pH range

Carbon dots (Cdots) has been proved to possess the catalytic decomposition of H2O2 in the photocatalytic system. It is a potential photo-Fenton catalyst. Since ...     

Fluorescence probes for monitoring polymerization processes

Several intramolecular charge transfer fluorescence probes, such as the dansyl amides (1a-d), 4-dimethylamino-4′-nitrobiphenyl (2) and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (3), have been developed and evaluated. The fluorescence emission of the probes is sensitive to both the solvent polarity and medium microviscosity. A spectral blue shift, attributed to an increase in microviscosity, was observed as polymerization proceeded. Therefore, these fluorescence probes can be used for monitoring polymerization processes. The correlation between the fluorescence emission intensity ratio and degree of cure is linear in various formulations, which may be cured either photochemically or thermally. The selectivity and sensitivity of the fluorescence probes have been investigated. 4-Dimethylamino-4′-nitrobiphenyl (2) was found to be the most sensitive probe to both solvent polarity and medium microviscosity. © 1996 John Wiley & Sons, Inc.     

Two rhodamine lactam modulated lysosome-targetable fluorescence probes for sensitively and selectively monitoring subcellular organelle pH change

Be a powerful technique for convenient detection of pH change in living cells, especially at subcellular level, fluorescent probes has attracted more and more attention. In this work, we designed and synthesized three rhodamine lactam modulated fluorescent probes RS1, RS2 and RS3, which all respond sensitively toward weak acidity (pH range 4–6) via the photophysical property in buffer solution without interference from the other metal ions, and they also show ideal pKa values and excellent reversibility. Particularly, by changing the lone pair electrons distribution of lactam-N atom with different conjugations, RS2 and RS3 exhibit high quantum yield, negligible cytotoxicity and excellent permeability. They are suitable to stain selectively lysosomes of tumor cells and monitor its pH changes sensitively via optical molecular imaging. The above findings suggest that the probes we designed could act as ideal and easy method for investigating the pivotal role of H⁺ in lysosomes and are potential pH detectors in disease diagnosis through direct intracellular imaging.     

A new mesogenic mixture with antiferroelectric phase only at a broad temperature range

New compounds (S)-4?-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-nonafluoropentyloxy)prop-1-oxy]benzoates were synthesised and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The multicomponent antiferroelectric high tilt mixture with long pitch has been also formulated and characterised. The helical pitch of prepared mixture was estimated with selective reflection method.     

Method for the design of broad energy range focusing reflectrons

A novel method for the design of reflections capable of focusing large kinetic energy ranges is presented. The design method itself is a numerical approach that provides a geometrically flexible alternative to traditional analytical design solutions. This design method has been used to produce a reflectron that provides unit mass resolution for product spectra in a tandem reflectron time-of-flight (TOF) mass spectrometer despite a kinetic energy range of 1950–2700 eV. In this application, the systematic progression of reflectron design results in a practical, nonlinear field reflectron with the use of only two grids. Design improvements are proposed for more flexible systems, although geometric constraints in the current instrument limit their experimental evaluation.     

Determination of pH with acid-base indicators: Implications for optical fibre probes

Results are presented which clearly illustrate the possibilities and limitations of the use of indicators immobilized on optical fibres, in the determination of pH.     

High sensitivity and broad dynamic range infrared multiphoton dissociation for a quadrupole ion trap

Dynamic control of bath gas pressure in a quadrupole ion trap (QIT) achieved high sensitivity and broad dynamic range infrared multiphoton dissociation (IRMPD). Conventional IRMPD is not sensitive because the bath gas pressure in the QIT needs to be kept at less than 1 mTorr for an effective dissociation, whereas the pressure should be about 20 mTorr for maximum trapping efficiency during ion accumulation. By switching the bath gas pressure between about 20 mTorr during the ion accumulation period and less than 0.6 mTorr during the IRMPD period, it was possible to achieve both maximum trapping efficiency and effective IRMPD. An optimized method for gas introduction enables the trapping efficiency to remain constant during the accumulation period, which permits a broad dynamic range measurement.     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Two 1,8-naphthalimide-based proton-receptor fluorescent probes for pH determination

Two newly synthesised 1,8-naphthalimide-based proton-receptor fluorescent probes N-allyl-4-(4’-N,N-diethylpropionamide-acetamido-piperazinyl)-1,8-naphthalimide I and N-(N,N-dibenzylpro- pionamide-acetamido)-4-allyl-1-piperazinyl-1,8-naphthalimide II were synthesised to monitor the change in pH in such a way that the presence of protons can increase the fluorescence intensity of these compounds. Unlike most of the other pH-sensitive probes reported, the probes possess the obvious advantage of being able to detect stronger acids at pH ≈ 2 and a combination of the two probes could detect a wider pH scale from 1.98 to 6.59; this should be very useful for monitoring the pH of the environment.     

Saturation studies of spin probes dissolved in a glass-forming isotropic liquid

Saturation studies of nitroxides in glass-forming dibutyl phthalate were performed to verify that increased spin—lattice relaxation time (T₁) is responsible for intensity reduction as temperature is lowered. Correspondence between onsets of saturation and intensity decrease, matches to T₁ versus temperature and between the observed and calculated intensities all verify the assertion.     

Imines that react with phenols in water over a wide pH range

Cyclic imine derivatives that react with phenols, including tyrosine residues of peptides, have been developed. Reactions of the imines with phenols proceeded in water over a wide pH range (pH 2-10) at room temperature to 37 degrees C and afforded Mannich products without the need of additional catalysts.     

Evaluation of measuring range and interferences for gas-sensing potentiometric probes

The experimental limit of detection and the interferences for any assembled gas sensor are the analytical features of greatest interest. Theoretical and practical studies of CO₂ and SO₂ gas sensors are reported. In the measurement of CO₂, the sample should not be buffered at too acidic a value, although the rate of diffusion at e.g. pH 6.8, may be slower than at low pH. Choice of sample pH can also be used to limit interfering effects. The conditions must be selected on the basis of the required rate of analysis and the selectivity attainable.