Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors

This review article focuses primarily on the work carried in our laboratories over the last few years using luminescent and colorimetric sensors, where the anion recognition occurs through hydrogen bonding in organic or aqueous solvents. This review begins with the story of the discovery of fluorescent photoinduced electron transfer (PET) sensors for anions using charged neutral urea or thiourea receptors where both fluorescent and NMR spectroscopic methods monitored anion recognition. This work led to the development of dual luminescent and colorimetric anion sensors based on the use of the ICT based naphthalimide chromophore, where ions such as fluoride gave rise to changes in both the fluorescence and the absorption spectra of the sensors, but at different concentrations. Here, the former changes were due to hydrogen bonding interactions, whereas the latter was due to the deprotonation of acidic protons, giving rise to the formation of the bifluoride anion (HF2−). Modification of the 4-amino-l,8-naphthalimide moiety has facilitated the formation of colorimetric anion sensors that work both in organic or aqueous solutions. Such charge neutral receptor motifs have also been incorporated into organic scaffolds with norbomyl and calixarene backbones, which have enabled us to produce anion directed self-assembled structures.

Peptide-fluorescent bacteria complex as luminescent reagents for cancer diagnosis

Currently in clinic, people use hematoxylin and eosin stain (H&E stain) and immunohistochemistry methods to identify the generation and genre of cancers for human pathological samples. Since these methods are inaccurate and time consuming, developing a rapid and accurate method to detect cancer is urgently demanded. In our study, binding peptides for lung cancer cell line A549 were identified using bacteria surface display method. With those binding peptides for A549 cells on the surface, the fluorescent bacteria (Escherichia coli with stably expressed green fluorescent protein) were served as specific detecting reagents for the diagnosis of cancers. The binding activity of peptide-fluorescent bacteria complex was confirmed by detached cancer cells, attached cancer cells and mice tumor xenograft samples. A unique fixation method was developed for peptide-bacteria complex in order to make this complex more feasible for the clinic use. This peptide-fluorescent bacteria complex has great potential to become a new diagnostic tool for clinical application.

Luminescent probes for the bioimaging of small anionic species in vitro and in vivo

The ability to spatiotemporally identify the formation of specific anionic species, or track changes in their concentration inside living systems, is of critical importance in deciphering their exact biological roles and effects. The development of probes (also called bioimaging agents and intracellular sensors) to achieve this goal has become a rapidly growing branch of supramolecular chemistry. In this critical review the challenges specific to the task are identified and for a select range of small anions of environmental and biological relevance (fluoride, chloride, iodide, cyanide, pyrophosphate, bicarbonate, hydrosulphide, peroxynitrite, hypochlorite and hypobromite) a comprehensive overview of the currently available in vitro and in vivo probes is provided.

Bimodal magneto-luminescent dysprosium (DyIII)-potassium (KI)-oxalate framework: magnetic switchability with high anisotropic barrier and solvent sensing

We report synthesis, characterization, and properties of a multifunctional oxalate framework, {KDy(C₂O₄)₂(H₂O)₄}_n (1) (C₂O₄^2- = oxalate dianion) composed of two absolutely different metal ions in terms of their size, charge, and electronic configuration. Dehydrated framework (1′) exhibits permanent porosity and interesting solvent (H₂O, MeOH, CH₃CN, and EtOH) vapor sorption characteristics based on specific interactions with unsaturated alkali metal sites on the pore surface. Compound 1 shows solvent responsive bimodal magnetic and luminescence properties related to the DyIII center. Compound 1 exhibits reversible ferromagnetic to antiferromagnetric phase transition upon dehydration and rehydration, hitherto unknown for any lanthanide based coordination polymer or metal-organic frameworks. Both the compounds 1 and 1′ exhibit slow magnetic relaxation with very high anisotropic barrier (417 ± 9 K for 1 and 418 ± 7 K for 1′) which has been ascribed to the single ion magnetic anisotropy of the Dy^III centers. Nevertheless, compound 1 shows a metal based luminescence property in the visible region and H₂O molecules exhibit the strongest quenching effect compared to other solvents MeOH, MeCN, and EtOH, evoking 1′ as a potential H₂O sensor.

Narrowed bandgaps and stronger excitonic effects from small boron nitride nanotubes

The bandgap of boron nitride nanotubes (BNNTs) is generally considered to be independent on tube radius and chirality. However, we have observed that the bandgaps of BNNTs do depend on the tube size. Photoluminescence excitation spectroscopy with variable photon energies in vacuum ultraviolet (VUV) range revealed that the bandgap becomes smaller when the tube diameter decreases. This is consistent with red-shifted luminescent emissions. The strong interactions between excitons and phonons are possibly responsible for the bandgap narrowing as the function of nanotube size. 2009 Elsevier B.V. All rights reserved.

Mechanisms of light producing chemical reactions

An array of experimental and computational methods has been implement to elucidate the mechanisms of light producing chemical reactions that are important in nature and the laboratory.

Electrochemiluminescent monomers for solid support syntheses of Ru(II)-PNA bioconjugates : multimodal biosensing tools with enhanced duplex stability

The feasibility of devising a solid support mediated approach to multimodal Ru(II)-peptide nucleic acid (PNA) oligomers is explored. Three Ru(II)-PNA-like monomers, [Ru(bpy)2(Cpp-L-PNA-OH)]2+ (M1), [Ru(phen)2(Cpp-L-PNA-OH)]2+ (M2), and [Ru(dppz)2(Cpp-L-PNA-OH)]2+ (M3) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2′,3′-c]phenazine, Cpp-L-PNA-OH = [2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycine), have been synthesized as building blocks for Ru(II)-PNA oligomers and characterized by IR and 1H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. As a proof of principle, M1 was incorporated on the solid phase within the PNA sequences H-g-c-a-a-t-a-a-a-a-Lys-NH2 (PNA1) and H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-lys-NH2 (PNA4) to give PNA2 (H-g-c-a-a-t-a-a-a-a-M1-lys-NH2) and PNA3 (H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-M1-lys-NH2), respectively. The two Ru(II)-PNA oligomers, PNA2 and PNA3, displayed a metal to ligand charge transfer (MLCT) transition band centered around 445 nm and an emission maximum at about 680 nm following 450 nm excitation in aqueous solutions (10 mM PBS, pH 7.4). The absorption and emission response of the duplexes formed with the cDNA strand (DNA: 5′-T-T-T-T-T-T-T-A-T-T-G-C-T-T-T-3′) showed no major variations, suggesting that the electronic properties of the Ru(II) complexes are largely unaffected by hybridization. The thermal stability of the PNA·DNA duplexes, as evaluated from UV melting experiments, is enhanced compared to the corresponding nonmetalated duplexes. The melting temperature (Tm) was almost 8 °C higher for PNA2·DNA duplex, and 4 °C for PNA3·DNA duplex, with the stabilization attributed to the electrostatic interaction between the cationic residues (Ru(II) unit and positively charged lysine/arginine) and the polyanionic DNA backbone. In presence of tripropylamine (TPA) as co-reactant, PNA2, PNA3, PNA2·DNA and PNA3·DNA displayed strong electrochemiluminescence (ECL) signals even at submicromolar concentrations. Importantly, the combination of spectrochemical, thermal and ECL properties possessed by the Ru(II)-PNA sequences offer an elegant approach for the design of highly sensitive multimodal biosensing tools.

Selective excitation of concomitant electrochemiluminophores : tuning emission color by electrode potential

ECL in 3D: Selective electrogenerated chemiluminescence (ECL) of several ruthenium and iridium complexes simultaneously in solution can be controlled by electrode potential (see picture; λem=emission wavelength). These luminescent redox systems create a range of new possibilities for multi-analyte ECL detection, assessment of interdependent electrochemical/spectroscopic properties, and color tuning in light-emitting devices.

Preparation and characterization of graphitic carbon nitride through pyrolysis of melamine

Graphitic carbon nitride (g-C₃N₄) has been synthesized via a two-step pyrolysis of melamine (C₃H₆N₆) at 800°C for 2 h under vacuum conditions. X-ray diffraction (XRD) patterns strongly indicate that the synthesized sample is g-C₃N₄. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) morphologies indicate that the product is mainly composed of graphitic carbon nitride. The stoichiometric ratio of C:N is determined to be 0.72 by elemental analysis (EA). Chemical bonding of the sample has been investigated by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). Electron energy loss spectroscopy (EELS) verifies the bonding state between carbon and nitrogen atoms. Optical properties of the g-C₃N₄ were investigated by PL (photoluminescence) measurements and UV–Vis (ultraviolet–visible) absorption spectra. We suppose its luminescent properties may have potential application as component of optical nanoscale devices. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were also performed.

Iridium(III) N-heterocyclic carbene complexes: an experimental and theoretical study of structural, spectroscopic, electrochemical and electrogenerated chemiluminescence properties

Four cationic heteroleptic iridium(III) complexes have been prepared from methyl- or benzyl-substituted chelating imidazolylidene or benzimidazolylidene ligands using a Ag(I) transmetallation protocol. The synthesised iridium(III) complexes were characterised by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for three complexes were determined by single crystal X-ray diffraction. A combined theoretical and experimental investigation into the spectroscopic and electrochemical properties of the series was performed in order to gain understanding into the factors influencing photoluminescence and electrochemiluminescence efficiency for these complexes, with the results compared with those of similar NHC complexes of iridium and ruthenium. The N^C coordination mode in these complexes is thought to stabilise thermally accessible non-emissive states relative to the case with analogous complexes with C^C coordinated NHC ligands, resulting in low quantum yields. As a result of this and the instability of the oxidised and reduced forms of the complexes, the electrogenerated chemiluminescence intensities for the compounds are also low, despite favourable energetics. These studies provide valuable insights into the factors that must be considered when designing new NHC-based luminescent complexes.

A comparison of novel organoiridium(III) complexes and their ligands as a potential treatment for prostate cancer

A range of 1,4-substituted 2-pyridyl-N-phenyl triazoles were synthesised and evaluated for their antiproliferative properties against lymph node cancer of the prostate (LNCaP) and bone metastasis of prostate cancer (PC-3) cells. Excellent-to-low IC50 values were determined (5.6-250 μM), and a representative group of 4 ligands were then complexed to iridium(III) giving highly luminescent species. Re-evaluation of these compounds against both cell lines was then undertaken and improved potency (up to 72-fold) was observed, giving IC50 values of 0.36-11 μM for LNCaP and 0.85-5.9 μM for PC-3. Preliminary screens for in vivo toxicity were conducted using a zebrafish model showing a wide range of induced toxicity depending of the compound evaluated. Apoptosis and Caspase-3 levels were also determined and showed no statistical difference between some of the treated specimens and the controls. This study may identify novel therapeutic agents for advanced stage of prostate cancer in humans.

Analytically useful blue chemiluminescence from a water-soluble iridium(iii) complex containing a tetraethylene glycol functionalised triazolylpyridine ligand

We examine [Ir(df-ppy)2(pt-TEG)](+) as the first highly water soluble, blue-luminescent iridium(iii) complex for chemiluminescence detection. Marked differences in selectivity were observed between the new complex and the conventional [Ru(bpy)3](2+) reagent, which will enable this mode of detection to be extended to new areas of application.