Fluorescent Turn-On Sensing of Zinc(II) and Alkaline Phosphatase Activity Using a Pyridoxal-5'-Phosphate Derived Schiff Base.

A novel Zn2+ ion and alkaline phosphatase (ALP) selective fluorescence turn-on sensor L was developed by reacting pyridoxal 5'-phosphate (PLP) with hydrazine. Sensor L shows significant flurescence enhancement at 476 nm due to the formation of a L-Zn2+ complex in 1:1 binding stoichiometry with the association constant of 3.1⋅104 M- 1. Using L, the concentration of Zn2+ can be detected down to 2.34 µM, and the practical utility of L was validated by quantifying Zn2+ in real water samples. Additionally, the receptor L was applied to mimic the dephosphorylation reaction catalysed by the enzyme ALP and the resulted fluorescence change was monitored to detect the ALP activity.

Vitamin B6 cofactors guided highly selective fluorescent turn-on sensing of histamine using beta-cyclodextrin stabilized ZnO quantum dots.

Histamine, one of the most important biogenic amines (BAs) is considered as food hazard and therefore various agencies have fixed threshold in different food and beverages. In this manuscript, two novel fluorescent turn-on probes were developed for the instantaneous detection of histamine. The ß-cyclodextrin (ß-CD) capped ZnO quantum dots (QDs) were decorated with the vitamin B6 cofactors like pyridoxal 5'-phosphate (PLP) and pyridoxal (Py) by forming host-guest inclusion complexation between the capped ß-CD and PLP/Py. The cofactors decorated QDs (ZnO@PLP and ZnO@Py) were applied for the sensing of BAs. Addition of histamine to the ZnO@PLP and ZnO@Py solution resulted selective fluorescence enhancement at 473 nm and 460 nm, respectively. Without any interference from the other tested BAs, the fluorescence response of the probes ZnO@PLP and ZnO@Py showed good linearity to histidine concentration from 2.49 to 24.4 µM and 7.44 to 47.6 µM with the detection limit down to 0.59 µM and 0.97 µM, respectively.

Spectroscopic, potentiometric and theoretical studies of novel imino-phenolate chelators for Fe(III).

The present study was targeted to explore the binding properties of two strong chelators for Fe(III) based on tripodal-iminophenolate moiety. Complexation behavior of the tripodal systems cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({2-[(2-hydroxy-benzylidene)-amino]-ethyl}-amide (CYCOENSAL, L(1)) and cis-cis cyclohexane-1,3,5-tricarboxylic acid tris-({3-[(2-hydroxy-benzylidene)-amino]-propyl}-amide (CYCOPNSAL, L(2)) is described. Three protonation constants obtained are assigned for three hydroxyl groups of aromatic ring were employed for the evaluation of the formation constants of the metal complexes. Both ligands liberate three protons each forming monomeric complexes of type FeLH3, FeLH2, FeLH and FeL (L=L(1) and L(2)). The first species FeLH3 depicted at low pH, where the ligands were coordinated through three imine nitrogen and other species form subsequently from FeLH3 in steps upon deprotonation and coordination of the phenolic oxygen giving encapsulated tris(phenolate) complexes. The probable structures of the metal complexes formed in solution were proposed through molecular modeling calculations. L(2) was observed to be highly selective towards Fe(III) as compared to L(1).

Fluorescence 'turn-on' sensor for F- derived from vitamin B6 cofactor.

A novel vitamin B6 Schiff base analog (L) was synthesized by combining vitamin B6 cofactor pyridoxal with 2-aminophenol. Receptor L displays a color change detectable by the naked-eye from yellow to red in the presence of fluoride and acetate due to the formation of hydrogen bonding host-guest complexes in 1 : 1 stoichiometry. Importantly, receptor L showed fluoride-selective 'turn-on' fluorescent response with a detection limit (3σ) of 7.39 × 10(-8) M.

Spectroscopic and computational study of a naphthalene derivative as colorimetric and fluorescent sensor for bioactive anions.

The anion recognition property of a naphthalene based receptor (L) was investigated by naked-eye, UV-Vis, fluorescence, (1)H NMR and computational methods. The receptor L showed fluoride selective naked-eye detectable colorimetric and UV-Vis spectral changes over other tested anions due to the formation of hydrogen bonding complex in 1:1 stoichiometry and/or deprotonation between fluoride and the receptor. Interestingly, the fluorescence of L was quenched by fluoride but enhanced by acetate.

Naphthalene based colorimetric sensor for bioactive anions: experimental and DFT study.

A simple anion selective colorimetric sensor L has been designed by combining 2-hydroxy-1-naphthaldehyde with 2-aminothiophenol. Sensor L portrayed a necked-eye detectable color change from light green to red upon addition of AcO(-), F(-) and H(2)PO(4)(-) anions in CH(3)CN, where as no significant color change was observed upon addition of other anions such as Cl(-), Br(-), I(-) and HSO(4)(-). Sensor L showed selectivity towards AcO(-) under competitive environment, with a detection limit (3σ/S) down to 1.1×10(-7) M. In addition, the anion sensing ability of L was explored in mixed H(2)O/CH(3)CN (v/v) medium. Further, the nature of interactions between the sensor L and AcO(-) was investigated by (1)H NMR and the probable structure of the L-AcO(-) complex was predicted by B3LYP/6-31G(d,p) method.

Iron(III) selective molecular and supramolecular fluorescent probes.

Iron is one of the most important elements in metabolic processes, being indispensable for all living systems and therefore it is extensively distributed in environmental and biological materials. However, both its deficiency and excess from the normal permissible limit can induce serious disorders. Therefore, several analytical techniques have been adopted for the detection of iron. Among the various techniques used for its detection, the method based on fluorescent sensors has received considerable interest in recent years because of its ability to provide online monitoring of very low concentrations without any pre-treatment of the sample together with the advantages of spatial and temporal resolution. In this article, efforts have been made to review the various molecular and supramolecular fluorescent sensors that have been developed for the selective detection of iron(III).

Spectroscopic and pH-metric studies on the complexation of a novel tripodal amine-phenol ligand towards Al(III), Ga(III) and In(III).

The aqueous coordination chemistry of a newly synthesized tripodal amine-phenol ligand, cis,cis-1,3,5-tris{(2-hydroxybenzyl)aminomethyl}cyclohexane (THAC) towards H+, Al3+, Ga3+ and In3+ ions have been investigated in aqueous medium of 0.1 M KCl ionic strength and 25±1 °C by potentiometric and spectrophotometric methods. Three protonation constants assigned to phenolic hydroxyl groups were determined and were used as input data to evaluate the formation constants of the metal complexes. The ligand formed various monomeric metal complex species MLH3, MLH2, MLH, ML and MLH(-1) with Ga(III) and In(III); MLH3, ML and MLH(-1) with Al(III). The calculated stability constants followed the order Ga(III)>In(III)>Al(III), and their pM values at physiological condition were found to be higher than the corresponding transferrin complexes.

Studies on molecular structure and tautomerism of a vitamin B6 analog with density functional theory.

This work presents a computational study on the molecular structure and tautomeric equilibria of a novel Schiff base L derived from pyridoxal (PL) and o-phenylenediamine by using the density functional method B3LYP with basis sets 6-31 G(d,p), 6-31++G(d,p), 6-311 G(d,p) and 6-311++G(d,p). The optimized geometrical parameters obtained by B3LYP/6-31 G(d,p) method showed the best agreement with the experimental values. Tautomeric stability study of L inferred that the enolimine form is more stable than its ketoenamine form in both gas phase and solution. However, protonation of the pyridoxal nitrogen atom (LH) have accelerated the formation of ketoenamine form, and therefore, both ketoenamine and enolimine forms could be present in acidic media.

Potentiometric Study of a Benzene-based Tripodal Triamine as Chelator for Zn(II) Ion.

The complexation of a C3-symmetrical tripodal triamine ligand, N1, N3, N5-tris(2-aminoethyl)benzene-1, 3, 5-tricarboxamide (TAT, L) with Zn(II) ion was investigated at an ionic strength of 0.1 M NaClO4 and 25 ± 1 °C in aqueous medium. Formation of complex species [ZnL(H2O)]2+ and [ZnL(OH)]+ were depicted in solution, where the ligand is tri-coordinated through three amine N-atoms and their stability constants were calculated with the HYPERQUAD 2000 computer program. The pKa of the zinc-bound water molecule is 7.84, making the Zn(TAT) complex a viable model of carbonic anhydrase.