Cheuk-Fai Chow

Single microcrystals of organoplatinum(II) complexes with high charge-carrier mobility

Hydrogen-bonding pyrazolyl and imidazolyl motifs are incorporated into organoplatinum(II) complexes and found to be harmonized with extended π–π and PtII⋯PtII interactions to align the planar cations into a quasi-1-D columnar structure or a quasi-2D framework. A field-effect electron mobility up to 20 cm2V−1s−1 has been recorded with a single-microcrystal transistor. In addition, crystalline samples of one of the organoplatinum(II) complexes show intriguing thermoluminescent and vapoluminescent properties.

Photo-responsive molecularly imprinted hydrogels for the detection of melamine in aqueous media

In this paper, by combination of the specificity of a molecularly imprinted technique, the water solubility of hydrogels and the photoisomerization property of azobenzene chromophores, we report a new and quick detection method for trace melamine in aqueous media based on photo-responsive molecularly imprinted hydrogels (MIHs). The MIHs were fabricated using a water-soluble azobenzene-containing 4-[(4-methacryloyloxy)phenylazo]benzenesulfonic acid (MAPASA) as the functional monomer, 1,3,5-benzenetriol as a mimic template, and tetramethacryloyl triethylene tetramine (TTT) as the cross-linker. The MIHs show specific affinity to melamine with a binding constant of 3.20 × 104 M−1 in aqueous Tris–HCl buffer at pH 7.0. The density of the melamine-specific receptor sites in the MIHs material is 2.69 μmol g−1 MIHs. Upon alternate irradiation at 365 and 440 nm, the MIHs can quantitatively uptake and release melamine. The photoisomerization rate of MIHs is related to the concentration of melamine in the detecting solution, and therefore, a quick detection method for trace melamine is established. Analytical application of the MIHs to detect the melamine concentration in both milk and milk powder has been accomplished successfully with a simple pre-treatment of the samples.

Long aliphatic chain coated rare-earth nanocrystal as polymer-based optical waveguide amplifiers

Oleic acid-coated erbium–ytterbium co-doped NaYF4 nanocrystals, NaY78%F4:Yb20%Er2%, have been synthesized. The cubic nanocrystals were of an average size of 10 nm. The nanocrystals showed excellent redispersibility in common organic solvents and the KMBR® polymer matrix. An optical waveguide amplifier was fabricated by doping 0.1 wt% of the nanocrytals into the KMPR® polymeric host. At a small input signal power of 150 nW and a pump power of 150 mW, an optical gain of 4.81 dB cm−1 at 1535 nm was achieved.

Molecular Engineering of Thiazole Orange Dye: Change of Fluorescent Signaling from Universal to Specific upon Binding with Nucleic Acids in Bioassay.

The universal fluorescent staining property of thiazole orange (TO) dye was adapted in order to be specific for G-quadruplex DNA structures, through the introduction of a styrene-like substituent at the ortho-position of the TO scaffold. This extraordinary outcome was determined from experimental studies and further explored through molecular docking studies. The molecular docking studies help understand how such a small substituent leads to remarkable fluorescent signal discrimination between G-quadruplex DNA and other types of nucleic acids. The results reveal that the modified dyes bind to the G-quadruplex or duplex DNA in a similar fashion as TO, but exhibit either enhanced or quenched fluorescent signal, which is determined by the spatial length and orientation of the substituent and has never been known. The new fluorescent dye modified with a p-(dimethylamino)styryl substituent offers 10-fold more selectivity toward telomeric G-quadruplexes than double-stranded DNA substrates. In addition, native PAGE experiments, FRET, CD analysis, and live cell imaging were also studied and demonstrated the potential applications of this class of thiazole-orange-based fluorescent probes in bioassays and cell imaging.

Novel high proton conductive material from liquid crystalline 4-(octadecyloxy)phenylsulfonic acid

Liquid crystal based sulfonic acid, 4-(octadecyloxy)phenylsulfonic acid, 1, effectively transports protons at 80 °C under non-humidified conditions. At its smectic A liquid crystal state, the proton conductivity of 1 was measured to be 1.1 × 10−2 S cm−1. The proton conductivities of 1 at its molten and solid powder states were found to be 1.2 × 10−4 and 1.5 × 10−7 S cm−1, respectively. A lamellar structure of bilayer stacks of 1 with the sulfonic acid groups in a head-to-head configuration was found within the monodomain of SmA phase of 1 from in situ XRD and DFT calculation. We proposed that the efficient proton transporting property of 1 is highly correlated to the formation of supramolecular pathways between the molecules at its liquid crystal phase.

Photoresponsive surface molecularly imprinted polymer on ZnO nanorods for uric acid detection in physiological fluids

A photoresponsive surface molecularly imprinted polymer for uric acid in physiological fluids was fabricated through a facile and effective method using bio-safe and biocompatible ZnO nanorods as a support. The strategy was carried out by introducing double bonds on the surface of the ZnO nanorods with 3-methacryloxypropyltrimethoxysilane. The surface molecularly imprinted polymer on ZnO nanorods was then prepared by surface polymerization using uric acid as template, water-soluble 5-[(4-(methacryloyloxy)phenyl)diazenyl]isophthalic acid as functional monomer, and triethanolamine trimethacryl ester as cross-linker. The surface molecularly imprinted polymer on ZnO nanorods showed good photoresponsive properties, high recognition ability, and fast binding kinetics toward uric acid, with a dissociation constant of 3.22×10(-5)M in aqueous NaH2PO4 buffer at pH=7.0 and a maximal adsorption capacity of 1.45μmolg(-1). Upon alternate irradiation at 365 and 440nm, the surface molecularly imprinted polymer on ZnO nanorods can quantitatively uptake and release uric acid.

Metallodynamers: Neutral Double‐Dynamic Metallosupramolecular Polymers

Nine neutral dynamic metallosupramolecular polymers (metallodynamers) based on acyl hydrazone derived metal coordination centers (Co(2+), Ni(2+), Zn(2+), and Cd(2+)) were generated through self-assembly polymerization. These are linear coordination polymers with specific optical and mechanical properties. Monomer selection was found to take place in a mixture of subcomponents (carboxyaldehydes and bisacyl hydrazides) driven by hexacoordination to a specific metal ion. Most importantly, the metallodynamers were found to modify their constitution by exchanging and reshuffling their components with another metallodynamer through ligand exchange at the metal coordination site in solution as well as in the neat phase. As a result, the materials undergo remarkable changes in both their mechanical and optical properties.

New pyridinium-based fluorescent dyes: A comparison of symmetry and side-group effects on G-Quadruplex DNA binding selectivity and application in live cell imaging.

A series of C1-, C2-and C3-symmetric pyridinium conjugates with different styrene-like side groups were synthesized and were utilized as G-quadruplex selective fluorescent probes. The new compounds were well-characterized. Their selectivity, sensitivity, and stability towards G-quadruplex were studied by fluorescence titration, native PAGE experiments, FRET and circular dichroism (CD) analyses. These new compounds investigated in the fluorescence assays were preferentially bound with G-quadruplex DNA compared with other type of nucleic acids and it is fascinating to realize the effects of molecular symmetry and associated side groups showing unexpectedly great influence on the fluorescent signal enhancement for the discrimination of G-quadruplexes DNA from other nucleic acids. This may correlate with the pocket symmetry and shape of the G-quadruplex DNA inherently. Among the compounds, a C2-symmetric dye (2,6-bis-((E)-2-(1H-indol-3-yl)-vinyl)-1-methylpyridin-1-ium iodide) with indolyl-groups substituted was screened out from the series giving the best selectivity and sensitivity towards G-quadruplexes DNA, particularly telo21, due to its high equilibrium binding constant (K=2.17×10(5)M(-1)). In addition, the limit of detection (LOD) of the dye to determine telo21 DNA in bioassays was found as low as 33nM. The results of the study give insight and certain crucial factors, such as molecular symmetry and the associated side groups, on developing of effective fluorescent dyes for G-quadruplex DNA applications including G-quadruplex structure stabilization, biosensing and clinical applications. The compound was also demonstrated as a very selective G-quadruplex fluorescent agent for living cell staining and imaging.

Design and synthesis of heterobimetallic donor–acceptor chemodosimetric ensembles for the detection of sulfhydryl-containing amino acids and peptides

A competitive indicator displacement assay has been successfully developed for the ratiometric determination of sulfhydryl-containing amino acids and peptides using heterobimetallic donor-acceptor complexes as chemodosimetric ensembles. Chromotropic cis-[ML2(CN)2](M = FeII, RuII, OsII; L = diimine) are used as signaling indicators and PtII(DMSO)Cl2 acceptor moiety is used as the receptor for the sulfhydryl-containing analytes. A series of three heterobimetallic donor-acceptor complexes: cis-FeII(bpy)2[CN-PtII(DMSO)Cl2]2 (1), cis-Ru(II)(bpy)2[CN-PtII(DMSO)Cl2]2 (2) and cis-Os(II)(bpy)2[CN-PtII(DMSO)Cl2]2 (3) are synthesized and characterized by X-ray crystallography. All the three ensembles are able to produce specific colorimetric/fluorimetric responses to sulfhydryl-containing amino acids (cysteine, homocysteine and methionine) as well as the sulfhydryl-containing small peptide glutathione. The mechanism of the competitive displacement assay is evaluated by examining the thermodynamics of formation of the donor-acceptor linkage and adducts between the acceptor metal and the sulfhydryl-containing analytes as well as by systematic variation of the donor and acceptor metals in the chemodosimetric ensembles.

Colorimetric test paper for cyanide ion determination in real-time

A colorimetric cyanide ion (CN−) sensor 4-[(1E)-2-(2-hydroxyphenyl)ethenyl]-1-allylpyridinium bromide (2-HPEAPB) was synthesized via condensation and N-alkylation reactions using 4-methylpyridine and salicylaldehyde as the starting materials. 2-HPEAPB displayed good selectivity, fast response, and high sensitivity toward CN− over other competing anions in acetonitrile–water (95:5, v/v) with a limit of detection of 8.0 × 10−6 mol L−1 by the naked eye. The sensing mechanism and the influence of pH and temperature on sensing properties were investigated. Colorimetric test paper for CN− was prepared by absorption of 2-HPEAPB to a chromatography paper, which could be used to detect CN− directly and quickly. Analytical application of measuring CN− concentration in an electroplating wastewater in real-time was conducted successfully.