A Highly Selective and Sensitive Fluorescent Chemosensor for Detecting Al3+ Ion in Aqueous Solution and Plant Systems.

The solubilized form of aluminum, Al3+, is present under acid soil conditions and toxic to both animals and plants. Detecting and quantifying Al3+ is vital for both chemistry and biology. A new Schiff-based fluorescent turn-on sensor (probe L) for the selective detection of the Al3+ ion was synthesized by coupling 2-hydroxy-1-naphthaldehyde and 2-aminoisoindoline-1,3-dione, and the structure was characterized by nuclear magnetic resonance spectra. The probe L exhibited an excellent selective and sensitive response to the Al3+ ion over other metal ions in DMSO-H2O (1:9 v/v). Fluorescence quantification revealed that probe L was promising for the detection and accumulation of Al3+. Treating rice seedlings with Al3+ at 25⁻200 µM inhibited their growth. Al3+ treatment produced reactive oxygen species in rice roots. Practical applications of the fluorescent probe for the quantification of Al3+ in water samples and rice seedlings are demonstrated. Detecting the Al3+ ion with the probe L is easy and a potential alternative to existing analytical methods. The method can be used for detecting the Al3+ content of aqueous solution and plant systems. The novel fluorescent probe L has good potential for monitoring Al3+ content in the environment and biological systems.

A Selective Colorimetric and Turn-on Fluorescent Chemosensor for Hg2+ in Aqueous Solution.

A simple colorimetric and turn-on fluorescence receptor FT (thiophene appended fluorescein-hydrazone derivative) was prepared and its cation-sensing properties were investigated. Receptor FT displayed a selective colorimetric change (from colorless to orange color) upon binding to Hg2+ in DMSO/H2O (1:9, v/v) solution. The association constant of FT-Hg2+ complex was calculated to be 3.03 × 109 M-1, and the detection limit for Hg2+ was found to be 0.24 ppm.

A colorimetric sensor for the selective detection of fluoride ions.

A colorimetric receptor L was prepared. Receptor L can selectively sense F- based on distinct color changes among a series of ions. It can selectively sense F- through an intramolecular hydrogen bond interaction. A Job plot indicated a 1:1 complexation stoichiometry between receptor L and F- . The association constant for L-F- in CH3 CN was determined as 9.70 × 104  M-1 using a Stern-Volmer plot.

A selective colorimetric chemosensor for Fe3.

Two simple colorimetric receptors PS and PP (thiophene and pyridine appended derivative) were prepared and their cation sensing properties were investigated. Receptors PS and PP displayed a selective colorimetric change (from colorless to orange) upon binding to Fe3+ in MeOH solution. The association constants for receptors PS-Fe3+ and PP-Fe3+ in MeOH were determined to be 1.15 × 106 and 4.31 × 106  M-1 , respectively, using Hill plots. The detection limits of PS and PP were 490.7 ppm and 393.7 ppm, respectively.

A fluorescent chemosensor based on naphthol for detection of Zn(2).

A simple naphthol-based fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an 'off-on-type' mode with high selectivity in the presence of Zn(2+) ion. The selectivity of 1 for Zn(2+) is the consequence of combined effects of chelation-enhanced fluorescence (CHEF), C = N isomerization and π-π stacking interaction between the two naphthalene rings.

A highly selective and turn-on fluorescence sensor for detection of cyanide.

2-Hydroxy-1-naphthaldehyde (receptor 1) serves as a selective chemosensor for cyanide anion (CN(-)). In the presence of CN(-), an enhanced fluorescent intensity and red shift were observed. The observed complexation between receptor 1 and CN(-) may cause from a formation of phenoxide anion by nucleophilic addition of the CN(-) to carbonyl group.

A quinoline derivative as an efficient sensor to detect selectively Al³âº ion.

A quinoline-based Schiff base 1 has been utilized as a fluorescence chemosensor for the selective detection of Al(3+). The receptor 1 exhibited a high association constant (3.67 × 10(5) M(-1)) with submicromolar detection limit (0.18 ppm) towards Al(3+) in CH3CN solution.

A Schiff-based sensor with turn-on fluorescence for selective detection of Hg2+.

A simple Schiff-base colorimetric receptor 1 was prepared. It exhibits an 'off­on-type' mode with high sensitivity in the presence of Hg2+. The change in color is very easily observed by the naked eye in the presence of Hg2+, whereas other metal cations do not induce such a change. A Job plot indicated a 1 : 1 complexation stoichiometry between receptor 1 and Hg2+. The association constant for 1­Hg2+ in Tetrahydrofuran (THF) was determined to be 1.3 × 10(9)M-1 using a Hill plot.

A turn-on indole-based sensor for hydrogen sulfate ion.

A simple indole-based receptor 1 was prepared by a simple Schiff-base reaction of 1H-indole-3-carbaldehyde with ethane 1,2-diamine and its fluoroionophoric properties toward anions were investigated. Indole-based receptor 1 acts as a selective turn-on fluorescent sensor for HSO4(-) in methanol among a series of tested anions. Fluorescence spectroscopy, ultraviolet and nuclear magnetic resonance imaging support that the HSO4(-) indeed interacted with imine nitrogen and the proton of nitrogen in indole ring.

A turn-on and reversible Schiff base fluorescence sensor for Al3+ ion.

A simple Schiff-base receptor 2 was prepared. It exhibits an "off-on-type" mode with high sensitivity in the presence of Al3+. The receptor 2 exhibited a high association constant with submicromolar detection for Al3+ in EtOH­H2O (95:5 v/v) solution. The addition of EDTA quenches the fluorescence of the receptor 2·Al3+ complex offering receptor 2 as a reversible chemosensor.

Indole-based fluorescent sensors for selective detection of Hg2+.

A series of indole-based fluorescent chemosensors 1-4 were prepared and investigated characteristick features with transition metal ions. Sensors 1 and 2 were selective for Hg(2+) ion among a series of metal ions in H2O-DMSO with association constants of 4.60×10(4) and 5.90×10(4) M(-1) and detection limits of 140 and 101.6 µM, respectively.

A Schiff-based colorimetric fluorescent sensor with the potential for detection of fluoride ions.

A simple Schiff-based colorimetric fluorescent receptor 1 was prepared. It exhibits a "turn-on-type" mode with high sensitivity in the presence of F(-). The change in color is very easily observed by the naked eye in the presence of F(-), whereas other anions do not induce such a change. Job plot indicated a 1:2 complexation stoichiometry between receptor 1 and F(-). The association constant for 1-F(-) in CH3CN was determined as 1.32*10(5) M(-2) by a Hill plot.

A turn-on and reversible fluorescence sensor for Al3+ ion.

A simple 2-hydroxy-1-naphthaldehyde (receptor 1) serves as a selective chemosensor for Al(3+) based on chelation-enhanced fluorescence (CHEF). The receptor 1 exhibited a high association constant with micromolar detection for Al(3+) in EtOH-H(2)O solution.

A turn-on and reversible fluorescence sensor for zinc ion.

A simple Schiff base type fluorescent receptor was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an "off-on-type" mode with high selectivity in the presence of Zn(2+) ion. The addition of EDTA quenches the fluorescence of receptor 1-Zn(2+) complex, making receptor 1 a reversible chemosensor. The selectivity of 1 for Zn(2+) is the consequence of combined effects of CHEF, C=N isomerization and inhibition of ESIPT.

A fluorescence enhancement-based sensor for hydrogen sulfate ion.

Sugar-aza-crown ether-based cavitand 1 can act as a selective turn-on fluorescence sensor for hydrogen sulfate ion in methanol among a series of tested anions. Spectroscopic studies, particularly NMR spectroscopy, revealed that the C-H hydrogen bonding between 1,2,3-triazole ring of cavitand 1 and hydrogen sulfate ion is crucial for the high selectivity of the receptor for hydrogen sulfate.

A simple and highly selective receptor for iodide in aqueous solution.

We synthesized a simple fluorescent receptor 3 bearing two boronic acid groups as recognition sites. The recognition behaviour of receptor 3 towards various anions was evaluated in THF/H(2)O (1:1, v/v) solution. Receptor 3 showed high selectivity for iodide among a series of anions. Fluorescence spectroscopy and computational calculations revealed that the electrostatic interaction played a crucial role in its high selectivity for iodide.

Aminoglycoside-mimicking carbonized polymer dots for bacteremia treatment.

Bacteremia and associated bacterial sepsis are potentially fatal and occur when the host response to microbial invasion is impaired or compromised. This motivated us to develop carbonized polymer dots (CPDsMan/AA) from a mixture of mannose (Man) and positively charged amino acids [AAs; lysine, arginine (Arg), or histidine] through a one-step mild pyrolysis procedure, which effectively inhibited drug-resistant bacterial strains isolated from septic patients. The as-prepared CPDsMan/AA showed broad-spectrum antibacterial activity, including multidrug-resistant bacteria, even in human plasma. The minimal inhibitory concentration of CPDsMan/Arg is ca. 1.0 µg mL-1, which is comparable to or lower than those of other tested antibiotics (e.g., ampicillin, gentamicin, and vancomycin). In addition to directly disrupting bacterial membranes, the CPDsMan/Arg feature a structure similar to aminoglycoside antibiotics that could bind to 16S rRNA, thereby blocking bacterial protein synthesis. In vitro cytotoxic and hemolytic assays demonstrated the high biocompatibility of the CPDsMan/AA. In addition, in vivo studies on methicillin-resistant Staphylococcus aureus-infected mice treated with the CPDsMan/Arg showed a significant decrease in mortality-even better than that of antibiotics. Overall, the synthesis of the CPDsMan/AA is cost-efficient, straightforward, and effective for treating bacteremia. The polymeric features of the CPDsMan/Arg, including cationic charges and specific groups, can be recognized as a safe and broad-spectrum biocide to lessen our reliance on antibiotics to treat systemic bacterial infections in the future.

Synthesis of highly selective indole-based sensors for mercuric ion.

Two indole-based fluorescent chemosensors 1 and 2 were prepared and investigated characteristic features with transition metal ions. Sensors 1 and 2 were selective for Hg(2+) ion, among a series of metal ions, in aqueous ethanol (H(2)O-EtOH, 1:2, v/v) with association constants of 5.74 × 10(3) and 4.46 × 10(3) M(-1) and detection limits of 7.4 and 6.8 µM, respectively. Computational results revealed that sensor 1 or 2 with Hg(2+) ion formed 1:1 complex with a central, sandwich-coordinated Hg(2+) ion. Computational calculations provided evidence that a sandwich-coordinated Hg(2+) ion center was formed and the polyoxyethylene spacer acted as a scaffold for bringing functional ligands into a suitable geometry.

Hydrolysis of cellulose in synergistic mixtures of ß-glucosidase and endo/exocellulase Cel9A from Thermobifida fusca.

The synergism between the endo/exocellulase, Cel9A, and ß-glucosidase (ßgl) of Thermobifida fusca was investigated. Wild type ßgl or S319C, a ßgl mutant with significantly improved cellobiase activity, were added to Cel9A. Both wild type and mutant ßgl enhanced the Cel9A hydrolysis of carboxymethyl cellulose (CMC) and filter paper by 50-100% compared to Cel9A alone. No enhancement occurred with addition of E388A, an inactive form of ßgl. HPLC analysis showed that, with Cel9A alone, the resulting hydrolysate of glucose and cellobiose contained about half glucose; after addition of equimolar amounts of either wild type ßgl or mutant S319C to Cel9A, the hydrolysate contained more than 85% glucose. ßgl thus acted synergistically with Cel9A by converting cello-oligomers to glucose; this reduced the soluble sugar accumulation during hydrolysis of cellulose.

Effect of bis-triazoles on a ribose-based fluorescent sensor.

We synthesized two ribosyl-based fluorescent sensors. Both sensors have an anthracene as the fluorophore, but they differ in the recognition site for metal ions. One (3) has two ribosyl esters, and the other (6) has two triazole groups linked to two ribosyl esters. Among the metal ions examined in MeOH, compound 3 displayed a large chelation-enhanced fluorescence (CHEF) effect with Hg(2+) and Cu(2+) ions, and compound 6 displayed a large chelation-quenched fluorescence (CHQF) effect with Cu(2+) and Ni(2+) ions. The results demonstrated that the absence (sensor 3) and presence (sensor 6) of an incorporated bis-triazole group in a ribosyl-based fluorescent sensor conferred different preferences and distinct binding modes for metal ions.