Unusual spectroscopic properties of PPE/TiO2 composite and its sensor response to TNT

A composite from a broad bandgap polymer, poly(phenylene ethylene) (PPE), and nano-sized TiO₂ particles was found to be able to sense 2,4,6-trinitrotoluene (TNT) for TNT sensor. Fluorescence quenching induced by charge transfer from PPE to nano-sized TiO₂ was observed in toluene solution. At high TiO₂ composition, a strong exciplex band occurred at 550 nm. Under prolonged light irradiation at 400 nm, unusual fluorescence gains took place at 460 nm, companied with a very small change in the UV–vis absorbance. After 30 min light irradiation, the fluorescence at 460 nm reached a maximum, but the peak at 550 nm disappeared. This composite showed amplified sensor response to TNT compared to the pristine PPE film, which can be potentially used as sensing material for detecting TNT based explosives.

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.

Blue electrogenerated chemiluminescence from water-soluble iridium complexes containing sulfonated phenylpyridine or tetraethylene glycol derivatized triazolylpyridine ligands

Incorporating phenylpyridine- and triazolylpyridine-based ligands decorated with methylsulfonate or tetraethylene glycol (TEG) groups, a series of iridium(III) complexes has been created for green and blue electrogenerated chemiluminescence under analytically useful aqueous conditions, with tri-n-propylamine as a coreactant. The relative electrochemiluminescence (ECL) intensities of the complexes were dependent on the sensitivity of the photodetector over the wavelength range and the pulse time of the applied electrochemical potential. In terms of the integrated area of corrected ECL spectra, with a pulse time of 0.5 s, the intensities of the Ir(III) complexes were between 18 and 102 % that of [Ru(bpy)3 ](2+) (bpy=2,2'-bipyridine). However, when the intensities were measured with a typical bialkali photomultiplier tube, the signal of the most effective blue emitter, [Ir(df-ppy)2 (pt-TEG)](+) (df-ppy=2-(2,4-difluorophenyl)pyridine anion, pt-TEG=1-(2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethyl)-4-(2-pyridyl)-1,2,3-triazole), was over 1200 % that of the orange-red emitter [Ru(bpy)3 ](2+) . A combined experimental and theoretical investigation of the electrochemical and spectroscopic properties of the Ir(III) complexes indicated that the greater intensity from [Ir(df-ppy)2 (pt-TEG)](+) relative to those of the other Ir(III) complexes resulted from a combination of many factors, rather than being significantly favored in one area.

Molecular architecture of Aβ fibrils grown in cerebrospinal fluid solution and in a cell culture model of Aβ plaque formation

OBJECTIVES: The detailed structure of brain-derived Aβ amyloid fibrils is unknown. To approach this issue, we investigate the molecular architecture of Aβ(1-40) fibrils grown in either human cerebrospinal fluid solution, in chemically simple phosphate buffer in vitro or extracted from a cell culture model of Aβ amyloid plaque formation. METHODS: We have used hydrogen-deuterium exchange (HX) combined with nuclear magnetic resonance, transmission electron microscopy, seeding experiments both in vitro and in cell culture as well as several other spectroscopic measurements to compare the morphology and residue-specific conformation of these different Aβ fibrils. RESULTS AND CONCLUSIONS: Our data reveal that, despite considerable variations in morphology, the spectroscopic properties and the pattern of slowly exchanging backbone amides are closely similar in the fibrils investigated. This finding implies that a fundamentally conserved molecular architecture of Aβ peptide fold is common to Aβ fibrils.

New dibutyltin(IV) ladders: syntheses, structures and, optimization and evaluation of cytotoxic potential employing A375 (melanoma) and HCT116 (colon carcinoma) cell lines in vitro

Synthesis and spectroscopic properties of seven new dibutyltin(IV) compounds of 2-{(E)-4-hydroxy-3-[(E)-4-(aryl)iminomethyl]phenyldiazenyl}benzoic acids (L(n)HH'; n=2-8) with general formula {[Bu2Sn(L(n)H)]2O}2 (1-7) are reported. The compounds were characterized by elemental analysis and by UV-Visible, fluorescence, IR, (1)H, (13)C and (119)Sn NMR spectroscopies. Solid state structures of dibutyltin(IV) compounds 1-3, 6 and 7 were accomplished from single crystal X-ray crystallography which reveal the common ladder-type structure with two endo- and two exo-Sn atoms. The redox properties of L(n)HH' (n=2-4, 7 and 8) and their diorganotin(IV) compounds 1-3, 6 and 7 were also investigated by cyclic voltammetry. In general, the dibutyltin(IV) derivatives exhibited significant in vitro cytotoxic potency towards A375 (melanoma) and HCT116 (colon carcinoma) cell lines as determined by several experiments, like Live and Dead assay, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay, LDH (lactate dehydrogenase), cleavage of caspases and PARP (poly(ADP-ribose)polymerase), and DNA fragmentation. Dibutyltin(IV) compounds increase cell death without cytolysis and decreases membrane fluidity, without interfering with p53. Among the dibutyltin(IV) compounds, compound 6 was found to be the most potent, with an IC50 value of 78nM. A mechanism of action for tumor cell death is proposed.

Simultaneous control of spectroscopic and electrochemical properties in functionalised electrochemiluminescent tris(2,2'-bipyridine)ruthenium(II) complexes

Using a combination of electrochemical, spectroscopic and computational techniques, we have explored the fundamental properties of a series of ruthenium diimine complexes designed for coupling with other molecules or surfaces for electrochemiluminescence (ECL) sensing applications. With appropriate choice of ligand functionality, it is possible to manipulate emission wavelengths while keeping the redox ability of the complex relatively constant. DFT calculations show that in the case of electron withdrawing substituents such as ester or amide, the excited state is located on the substituted bipyridine ligand whereas in the case of alkyl functionality it is localised on a bipyridine. The factors that dictate annihilation ECL efficiency are interrelated. For example, the same factors that determine ΔG for the annihilation reaction (i.e. the relative energies of the HOMO and LUMO) have a corresponding effect on the energy of the excited state product. As a result, most of the complexes populate the excited state with an efficiency (Φex) of close to 80% despite the relatively wide range of emission maxima. The quantum yield of emission (Φp) and the possibility of competing side reactions are found to be the main determinants of ECL intensity.

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.

Electrochemical and spectroscopic investigation of redox processes for labile metal dithiocarbamate complexes

Although metal dithiocarbamate complexes have been studied extensively, there is in sate cases a distinct lack of data concerning redox properties and the products thereof. This is particularly true for complexes of the late transition and main group metals which are important in agriculture, industry, and chemical analysis. Hence, using electrochemical techniques, the redox behaviour of dithiocarbamate complexes of zinc, cadmium, mercury, lead, and tellurium has been examined. The products of oxidation and reduction have also been characterized by spectroscopic techniques (NMR, EPR, UV, and IR), mass spectrometry, conductivity, and Where possible, crystallographic study of an isolated compound. The species studied were without exception labile with the result that electrochemistry at mercury electrodes was influenced by the great stability of the mercury dithiocarbamate (Hg(RR’dtc) 2) complexes. Investigation of the latter showed that oxidative processes in the presence of mercury led to a new class of expounds: polymeric mercury dithiocarbamato cations. Oily one of these could be isolated as a solid, with the formula [Hg5(RR’dtc) 8](C104)2 For R=R’=ethyl the crystal structure was determined. For other metal dithiocarbamates the electrochemical behaviour at mercury electrodes in many ways paralleled that of the mercury analogues. Thus oxidative processes involved oxidation of electrode mercury to form mixed metal cationic species. Polarographic reduction led to the metal amalgam, usually via formation of mercury dithiocarbamate. Electrochemical studies at inert electrode materials such as platinum yielded distinctly different responses, with both oxidation and reduction being more difficult. Oxidation products at platinum electrodes gave identical polarographic responses to those firm mercury electrodes due to rapid interaction of the former with electrode mercury. The results are in sharp contrast to much of the previous work on transition metal dithiocarbamates for which electrochemical redox processes are often metal based arid not explicated by interaction with the electrode material.

Qualitative spectroscopic characterization of the matrix-silane coupling agent interface across metal fibre reinforced ion exchange resin composite membranes

The characterization of novel metal reinforced electro-dialysis ion exchange membranes, for water desalination, by attenuated total reflectance Fourier transform infrared spectroscopy mapping is presented in this paper. The surface of the porous stainless steel fibre meshes was treated in order to enhance the amount of surface oxide groups and increase the material hydrophilicity. Then, the metal membranes were functionalized through a sol-gel reaction with silane coupling agents to enhance the affinity with the ion exchange resins and avoid premature metal oxidation due to redox reactions at the metal-polymer interface. Polished cross sections of the composite membranes embedded into an epoxy resin revealed interfaces between metallic frameworks and the silane layer at the interface with the ion exchange material. The morphology of the metal-polymer interface was investigated with scanning electron microscopy and Fourier transform infrared micro-spectroscopy. Fourier transform infrared mapping of the interfaces was performed using the attenuated total reflectance mode on the polished cross-sections at the Australian Synchrotron. The nature of the interface between the metal framework and the ion exchange resin was shown to be homogeneous and the coating thickness was found to be around 1 μm determined by Fourier transform infrared micro-spectroscopy mapping. The impact of the coating on the properties of the membranes and their potential for water desalination by electro-dialysis are also discussed.

Miscibility, UV resistance, thermal degradation, and mechanical properties of PMMA/SAN blends and their composites with MWCNTs

Poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends, with varying concentrations, were prepared by melt-mixing technique. The miscibility is ensured by fixing the acrylonitrile (AN) content of styrene acrylonitrile (SAN) as 25% by weight. The blends were transparent as well. The Fourier transform infrared spectroscopic (FTIR) studies did not reveal any specific interactions, supporting the well accepted 'copolymer repulsion effect' as the driving mechanism for miscibility. Addition of SAN increased the stability of PMMA towards ultraviolet (UV) radiations and thermal degradation. Incorporation of even 0.05% by weight of multi-walled carbon nanotubes (MWCNTs) significantly improved the UV absorbance and thermal stability. Moreover, the composites exhibited good strength and modulus. However, at higher concentrations of MWCNTs (0.5 and 1% by weight) the thermo-mechanical properties experienced deterioration, mainly due to the agglomeration of MWCNTs. It was observed that composites with 0.05% by weight of finely dispersed and well distributed MWCNTs provided excellent protection in most extreme climatic conditions. Thus, PMMA/SAN/MWCNTs composites can act as excellent light screens and may be useful, as cost-effective UV absorbers, in the outdoor applications.