Boosayarat Tomapatanaget

A-D-A Sensors Based on Naphthoimidazoledione and Boronic Acid as Turn-On Cyanide Probes in Water

Three fluorescence sensors based on naphthoquinoneimidazole and boronic acid (A-D-A system) have been developed with high selectivity for cyanide in water. The fluorescence band at 460 nm was switched on upon substitution of cyanide on sensors in the CTAB micelle.

Anion recognition as a method for templating pseudorotaxane formation

Two thread-shaped cations, pyridinium nicotinamide and imidazolium, as their chloride and hexafluorophosphate salts, were studied with regards to complexation with hydrogen-bond-donating acyclic and macrocyclic ligands. In the latter case, the cations form pseudorotaxanes templated by the chloride anion but not hexafluorophosphate. This formation is a function of the coupling of ion-pairing between the cation and chloride anion and subsequent recognition of the anion by the macrocyclic diamide, which provides the driving force for interpenetration. We propose that this anion template principle is a general method for the construction of pseudorotaxanes and could be applied to other cationic threads, anions, and macrocyclic species.

Lower rim tetra-substituted and upper rim ferrocene amide calix[4]arenes: synthesis, conformation and anion-binding properties

Calix[4]arenes containing ferrocene amide at the upper rim and methoxy or ethoxycarbonylmethoxy (ethyl ester) groups at the lower rim (5a, 5b and 5c) have been synthesized. It was found that tetramethoxy 5a and dimethoxy diethyl ester 5c were conformationally labile and existed in both cone and partial cone conformation in solution. Anion-binding studies by 1H NMR titration in CDCl3 showed that 5b bound Cl− selectively with high stability. Compound 5c formed complexes with Cl− and H2PO4− where the former was more stable. The ratio of cone to partial cone conformation in compound 5a was found to decrease upon binding Cl− and H2PO4− and in a polar solvent.

Self-assembled coordination nanoparticles from nucleotides and lanthanide ions with doped-boronic acid-fluorescein for detection of cyanide in the presence of Cu2+ in water

The sensor molecule, F-oBOH, containing boronic acid-linked hydrazide and fluorescein moieties was synthesized. For anion sensing applications, F-oBOH was studied in aqueous media. Unfortunately, F-oBOH was found to be hydrolyzed in water. Therefore, a new strategy was developed to prevent the hydrolysis of F-oBOH by applying self-assembly coordination nanoparticles network (F-oBOH-AMP/Gd(3+) CNPs). Interestingly, the nanoparticles network displayed the enhancement of fluorescent signal after adding Cu(2+) following by CN(-). The network, therefore, possessed a high selectivity for detection of CN(-) compared to other competitive anions in the presence of Cu(2+). Cyanide ion could promote the Cu(2+) binding to F-oBOH incorporated in AMP/Gd(3+) CNPs to give the opened-ring form of spirolactam resulting in the fourfold of fluorescence enhancement compared to Cu(2+) complexation without CN(-). Additionally, the log K value of F-oBOH-AMP/Gd(3+) CNPs⊂Cu(2+) toward CN(-) was 3.97 and the detection limits obtained from naked-eye and spectrofluorometry detections were 20μM and 4.03μM, respectively. The proposed method was demonstrated to detect CN(-) in drinking water with high accuracy.

Tryptophan receptors containing acridine-based thiourea

Four derivatives of acridine and acridinium compounds (L1, L2, L1H and L2H) comprised thiourea-binding sites were synthesised. The binding abilities of receptors L1, L2, L1H and L2H towards amino acids (l-Trp, l-Phe, l-Leu, l-Ala and l-Gly) were studied by 1H NMR spectroscopy, UV–vis and fluorescence spectrophotometry. Hydrogen bonding interactions between thiourea-binding site of the ligand and the carboxylate groups in zwitterionic amino acids were found to be the main interactions driving complexation to take place. The stoichiometry of 1:1 ligand to amino acid was observed in all cases. Neutral ligands L1 and L2 showed weak binding towards all studied amino acids. The cyclic ligand L1 showed better binding ability towards tryptophan (Trp) than the acyclic ligand L2 did (K for Trp is 307 and 266 M− 1 for L1 and L2, respectively). Interestingly, binding abilities of the protonated ligands, L1H and L2H, towards studied amino acids, especially Trp (K for Trp is 3157 and 2873 M− 1 for L1H and L2H, respectively), were increased due to R–COO− …H…N+–acridinium interactions. Calculated structures of L1H·Trp and L2H·Trp showed that the polyglycol moiety in L1H provided a hydrophobic cavity for binding Trp resulting in a stronger binding affinity of L1H over L2H.

Self-assembly of Gd3+/SDS/HEPES complex and curcumin entrapment for enhanced stability, fluorescence image in cellular system

At present, strategies to disperse hydrophobic molecules in water without altering their chemical structures include conventional surfactant-based micellar and vesicular systems, encapsulation into water dispersible polymeric nanoparticles, and loading onto the surface of various metal nanoparticles. Here, we report a simple and low cost platform to incorporate hydrophobic molecules into a stable water dispersible nanostructure that can significantly increase the stability of the encapsulated materials. The platform is based on the incorporation of hydrophobic molecules into the self-assembled complex of gadolinium ion (Gd3+), sodium dodecyl sulfate (SDS), and 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) called GdSH. After being incorporated, the two model hydrophobic dyes, curcumin and curcumin borondifluoride show approximately 50% and 30% improved stability, respectively. Investigation of the self-assembled 10-14 multilayered 60nm spheres with inter-layer distances of 4.25nm indicates coordination of SDS and HEPES with Gd3+. Incorporation of the hydrophobic molecules into the multilayered spheres results in reduction of the interlayer distance of the multilayer spheres to 4.17nm, suggesting enhanced packing of the hydrophobic chain of SDS and HEPES around the Gd3+. The incorporation of the two curcuminoids into the self-assembled complex also causes an increase in fluorescence quantum yield of the two dyes, thus suggesting spatial confinement of the packed dye molecules. The better cellular uptake of the nanoparticles is responsible for the expected enhancement in fluorescence image of the encapsulated materials.

Highly promising discrimination of various catecholamines using ratiometric fluorescence probes with intermolecular self-association of two sensing elements

Two sensing elements based on fluorescence probes have been employed as the promising discriminating sensors of two catecholamines, dopamine (DA) and norepinephrine (NE), acting as a proper guest linker between two self-recognition sensing components. Surprisingly, in the presence of epinephrine (EPI), sensor NB containing boronic acid connected to a napthalimide unit demonstrated a very strong fluorescence enhancement while a large fluorescence quenching was observed in the case of DA and NE. To differentiate the structural similarity of DA and NE, an appropriately designed small fluorescence sensor CC containing a crown-ether attached to coumarin showed complementary recognition to an ammonium ion based catecholamine. The combination of NB and CC is capable of the differentiation of DA and NE with dual emission bands under a PET mechanism. The dual emission ratio (I475/I384) of the NB–DA–CC complex showed different values from those of the NB–NE–CC complex. Additionally, the PCA analysis using mixed sensors of NB and CC obviously separated DA and NE better than a single sensing element. This systematic approach is the first report showing a high potential for the identification of DA and NE using ratiometric fluorescence sensors with dual emission by two sensing elements.

Synthesis and Fluorescence Sensing Properties of Calix[4]arenes Containing Fluorophores

New fluoroionophores 4 and 5 derived from calix[4]arene triester monoacid chloride with 2-amino-4-(1,3-benzothiazol-2-yl)phenol and 4-aminoquinaldine, respectively, have been synthesized. A preliminary test showed that the fluorescence intensity of 5 was very low, so only 4 was subjected to cation recognition investigation. In methanol, the fluorescence intensity of 4 was quenched by Na+. The fluorescence intensity decreased linearly with increasing Na+ concentration with a stability constant of log K = 2.91 ± 0.08. No significant response was observed for other alkali metal ions under the same experimental conditions.