Facile Microwave-Assisted Synthesis of Functionalized Carbon Nitride Quantum Dots as Fluorescence Probe for Fast and Highly Selective Detection of 2,4,6-Trinitrophenol.

Functionalized carbon nitride quantum dots (CNQDs) are fabricated by moderate carbonization of L-tartaric acid and urea in oil acid media by a facile microwave-assisted solvothermal method. The obtained CNQDs are monodispersed with a narrow size distribution (average size of 3.5 nm), and exhibit excellent selectivity and sensitivity of fluorescence quenching for 2,4,6-trinitrophenol (TNP) with a quenching efficiency coefficient Ksv of 4.75 × 104 M-1. This sensing system exhibits a fast response time within 1 min and a wide linear response range from 0.1 to 15 µM. The limit of detection is as low as 87 nM, which is comparable or lower than the other probes. The application of the developed probe to the detection of TNP in spiked water samples yields satisfactory results. The mechanism of fluorescence quenching is also discussed. Graphical Abstract An optical sensor based on functionalized carbon nitride quantum dots (CNQDs) were fabricated from L-tartaric acid and urea by a facile one-pot microwave-assisted solvothermal method, and were effectively utilized to the detection of 2,4,6-trinitrophenol (TNP) based on fluorescence (FL) quenching.

One-pot fabrication of Fe-doped carbon nitride nanoparticles as peroxidase mimetics for H2O2 and glucose detection.

Iron-doped carbon nitride nanoparticles (Fe-CNNPs) were prepared from citric acid, urea and ferric chloride through a convenient one-pot solvothermal method. Oleic acid was used as the reaction medium. The morphology and chemical composition of the obtained Fe-CNNPs were characterized by multiple methods including transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). It is interesting to find that the Fe-CNNPs showed higher catalytic activity than horseradish peroxidase (HRP), and tetramethylbenzidine (TMB) can be catalytically oxidized in the presence of H2O2 to produce a color change in aqueous solution. As H2O2 can be generated in the oxidation process of glucose catalyzed by glucose oxidase (GOD), a novel sensitive method for the detection of glucose with a limit of detection (LOD) of 0.29 µM has been developed combined with the catalytic properties of GOD and Fe-CNNPs. The Fe-CNNPs with peroxidase mimetics activity may have potential applications in biotechnology field.

Nitrogen-doped carbon quantum dots as fluorescent probe for "off-on" detection of mercury ions, l-cysteine and iodide ions.

The application of fluorescent nanoparticles to the detection of inorganic ions and organic compounds has been attracted wide attention recently. In this paper, an "off-on" method for highly sensitive and selective detection of Hg2+ and l-cysteine (l-Cys) or Hg2+ and I- using home-made nitrogen-doped carbon quantum dots (N-CQDs) as fluorescent probe was reported. The N-CQDs with a fluorescence quantum yield of 42.2% were prepared using tartaric acid, citric acid and ethanediamine as the precursors in the oleic acid media. The fluorescence of the obtained N-CQDs could be quenched selectively and sensitively by the addition of Hg2+ (turn-off) with a detection limit of 83.5nM. When l-Cys or I- was added into the N-CQDs-Hg2+ system, the fluorescence was recovered effectively (turn-on). This process could be used to the detection of l-Cys or I- with a detection limit of 45.8 and 92.3nM, respectively.

A facile microwave-assisted fabrication of fluorescent carbon nitride quantum dots and their application in the detection of mercury ions.

A facile microwave-assisted solvothermal method was used to prepare fluorescent carbon nitride quantum dots (CNQDs) using oleic acid as the reaction media at moderate reaction temperature in a short time (5 min). Citric acid monohydrate and urea were used as the precursors. The as-prepared CNQDs were characterized by multiple analytical techniques. The CNQDs exhibited an uncommon excitation wavelength-dependent fluorescence with two maximum emission peaks at 450 and 540 nm. The CNQDs with a quantum yield of 27.1% could serve as an effective fluorescent sensing platform for label-free sensitive detection of Hg(2+) ions with a detection limit of 0.14 µM. This method was also applied to the detection of Hg(2+) ions in tap water samples.

One-pot fabrication of hollow cross-linked fluorescent carbon nitride nanoparticles and their application in the detection of mercuric ions.

Hollow cross-linked fluorescent carbon nitride nanoparticles (CNNPs) were fabricated via a facile one-pot solvothermal process. The obtained CNNPs were characterized by multiple analytical techniques including transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), solid-state nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR). The excitation-dependent fluorescence emission spectra showed significant differences for the CNNPs derived from various proportions of citric acid monohydrate and urea. The fluorescence quantum yield of the obtained CNNPs could reach 31%. The CNNPs exhibited good fluorescence quenching selectivity to mercuric ions. Concentration experiments showed that there existed two parts of linear relationship between fluorescence intensity and concentration of Hg(2+) ions in the range of 0.1-8 and 8-32 µM. The limit of detection (LOD) was estimated to be 0.094 µM. This method can be applied to the detection of Hg(2+) ions in tap water samples.

Development of a composite chiral stationary phase from BSA and ß-cyclodextrin-bonded silica.

A composite chiral stationary phase (CSP) derived from bovine serum albumin (BSA) and ß-cyclodextrin (CD)-bonded silica was prepared. 2,4,6-Trichloro-1,3,5-triazine was used as a cross-linker. The obtained CSP was applied to the enantioseparation of tryptophan, hydrobenzoin, phenylalanine and mandelic acid. The influences of eluent pH value, organic modifier and column temperature on the retention and enantioseparation were discussed. Tryptophan and hydrobenzoin achieved excellent resolution on the composite CSP. For tryptophan, the highest selectivity, 2.79, was achieved with 1% of methanol at pH 8.0. For hydrobenzoin, the selectivity could reach 1.42. The chromatographic results were compared with that on ß-CD-bonded or BSA-immobilized CSP.

Unusual chromatographic enantioseparation behavior of naproxen on an immobilized polysaccharide-based chiral stationary phase.

Enantioseparation of naproxen was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar alcohol modifier in mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. Two unusual phenomena were observed. One was solvent-induced reversal of elution order for the two enantiomers. Not only the type but also the content of polar alcohol modifier could induce the reversal. Another uncommon phenomenon was peak deformation under some chromatographic conditions.

Solvent effect in the chromatographic enantioseparation of 1,1'-bi-2-naphthol on a polysaccharide-based chiral stationary phase.

Enantioseparation of 1,1'-bi-2-naphthol (BINOL) was performed on a polysaccharide-based chiral stationary phase, Chiralcel OD-H, under normal-phase mode. The effects of polar modifier in the mobile phase on the retention, enantioseparation and elution order were investigated in detail. Solvent-induced reversal of elution order for BINOL was observed. When linear alcohols were adopted, R-BINOL was always eluted first. S-BINOL was eluted first when 2-propanol was used as a polar modifier. Enantioseparation could not be obtained when sec-butyl alcohol or tert-butyl alcohol was used as a polar modifier. When isoamyl alcohol or cyclohexanol was used as a polar modifier, favorable enantioseparation was obtained as with 1-pentanol or 1-hexanol; also, R-BINOL was the first-eluted enantiomer. It is worth emphasizing that significantly better enantioseparation was obtained when higher alcohols were used as polar modifier of the mobile phase. A nonlinear characteristic for the lnalpha against 1/T plots was universally observed in this study though the lnk against 1/T plots exhibited a linear feature. Associated with the obtained thermodynamic parameters, some interesting inferences about chiral recognition mechanism were proposed.

4-(4-Pyrid-yl)pyridinium penta-aqua(pyridazine-4,5-dicarboxyl-ato)praseodymate(III).

In the title complex, (C(10)H(9)N(2))[Pr(C(6)H(2)N(2)O(4))(2)(H(2)O)(5)], the Pr atom is nine-coordinated by nine O atoms from two pyridazine-4,5-dicarboxyl-ate anions and five water mol-ecules. It is noteworthy that there is a protonated bipyridine mol-ecule in the structure. Inter-molecular O-H⋯O, O-H⋯N and N-H⋯N hydrogen bonds are present, resulting in a three-dimensional network.

Temperature-induced inversion of elution order in the chromatographic enantioseparation of 1,1'-bi-2-naphthol on an immobilized polysaccharide-based chiral stationary phase.

In this work, the enantioseparations of 1,1'-bi-2-naphthol (BINOL) and its three derivatives were performed on an immobilized polysaccharide-based chiral stationary phase, Chiralpak IA, under normal-phase mode. The effects of the content of polar modifier in the mobile phase and the column temperature on the retention and enantioseparation were investigated in detail. Temperature-induced inversion of elution order for BINOL was observed directly when n-hexane/2-propanol (92/8, v/v) was used as mobile phase. The isoenantioselective temperature (T(iso)) was calculated to be 31.4 degrees C. When n-hexane/2-propanol/THF (93/2/5, v/v/v) was used as mobile phase, the T(iso) value decreased to -8.2 degrees C. Entropically driven enantioseparation which had practical application was obtained successfully (separation factor being 1.189 and 1.332 at 25 degrees C and 50 degrees C, respectively). The corresponding thermodynamic parameters for other three binaphthyl compounds were compared with that for BINOL. Some inferences about chiral recognition mechanism were stressed.

Chromatographic enantioseparations of binaphthyl compounds on an immobilized polysaccharide-based chiral stationary phase.

Seven binaphthyl compounds were enantioseparated by HPLC with an immobilized polysaccharide-based chiral stationary phase, Chiralpak IA. The experiments were performed under normal-phase conditions. Effects of polar modifier and column temperature on the retention time and separation factor were evaluated. All examined compounds obtained complete resolutions. This was the unique one ever reported that 1,1'-bi-2-naphthol and its monoether, diether and diester derivatives could all be enantioseparated on a given CSP. Apparent thermodynamic parameters were also deduced from Van't Hoff plots, and some aspects of chiral recognition mechanism were discussed further.

(R)-1,1'-Binaphthalene-2,2'-diyl dicinnamate.

In the title compound, C(38)H(26)O(4), two cinnamo-yloxy groups are linked in a trans fashion to the two O atoms of optically active (R)-1,10-bi-2-naphthol. The dihedral angle between the mean planes of the two naphthyl groups is 71.8 (1)°. The crystal structure contains inter-molecular C-H⋯O and C-H⋯π inter-actions.