Templateless assembly of molecularly aligned conductive polymer nanowires: a new approach for oriented nanostructures

Although oriented carbon nanotubes, oriented nanowires of metals, semiconductors and oxides have attracted wide attention, there have been few reports on oriented polymer nanostructures such as nanowires. In this paper we report the assembly of large arrays of oriented nanowires containing molecularly aligned conducting polymers (polyaniline) without using a porous membrane template to support the polymer. The uniform oriented nanowires were prepared through controlled nucleation and growth during a stepwise electrochemical deposition process in which a large number of nuclei were first deposited on the substrate using a large current density. After the initial nucleation, the current density was reduced stepwise in order to grow the oriented nanowires from the nucleation sites created in the first step. The usefulness of these new polymer structures is demonstrated with a chemical sensor device for H(2)O(2), the detection of which is widely investigated for biosensors. Finally, we demonstrated that controlled nucleation and growth is a general approach and has potential for growing oriented nanostructures of other materials.     

Bond alternation, polarizability, and resonance detuning in methine dyes

We derive structure-property relationships for methine ("Brooker") dyes relating the color of the dye and its symmetric parents to its bond alternation in the ground state and also to the dipole properties associated with its low-lying charge-resonance (or charge-transfer) transition. We calibrate and test these relationships on an array of different protonation states of the green fluorescent protein chromophore motif (an asymmetric halochromic methine dye) and its symmetric parent dyes. The relationships rely on the assumption that the diabatic states that define the Platt model for methine dye color [J. R. Platt, J. Chem. Phys. 25, 80 (1956)] can also be distinguished by their single-double bond alternation and by their charge localization character. These assumptions are independent of the primary constraint that defines the diabatic states in the Platt model--specifically, the Brooker deviation rule for methine dyes [L. G. S. Brooker, Rev. Mod. Phys. 14, 275 (1942)]. Taking these assumptions, we show that the Platt model offers an alternate route to known structure-property relationships between the bond length alternation and the quadratic nonlinear polarizability β. We show also that the Platt model can be parameterized without the need for synthesis of the symmetric parents of a given dye, using the dipole data obtained through spectroscopic measurements. This suggests that the Platt model parameters may be used as independent variables in free-energy relationships for chromophores whose symmetric parents cannot be synthesized or chromophores strongly bound to biomolecular environments. The latter category includes several recently characterized biomolecular probe constructs. We illustrate these concepts by an analysis of previously reported electroabsorption and second-harmonic generation experiments on green fluorescent proteins.     

Tunability of the M(II)M(III)/M(II)(2) and M(III)(2)/M(II)M(III) (M=Mn, Co) couples in bis-μ-O,O'-carboxylato-μ-OR bridged complexes

A comparison of the electrochemical properties of a series of dinuclear complexes [M(2)(L)(RCO(2))(2)](+) with M = Mn or Co, L = 2,6-bis(N,N-bis-(2-pyridylmethyl)-sulfonamido)-4-methylphenolato (bpsmp(-)) or 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato (bpbp(-)) and R = H, CH(3), CF(3) or 3,4-dimethoxybenzoate demonstrates: (i) The electron-withdrawing sulfonyl groups in the backbone of bpsmp(-) stabilize the [M(2)(bpsmp)(RCO(2))(2)](+) complexes in their M(II)(2) oxidation state compared to their [M(2)(bpbp)(RCO(2))(2)](+) analogues. Manganese complexes are stabilised by approximately 550 mV and cobalt complexes by 650 mV. (ii) The auxiliary bridging carboxylato ligands further attenuate the metal-based redox chemistry. Substitution of two acetato for two trifluoroacetato ligands shifts redox couples by 300-400 mV. Within the working potential window, reversible or quasi-reversible M(II)M(III)? M(II)(2) processes range from 0.31 to 1.41 V for the [Co(2)(L)(RCO(2))(2)](+/2+) complexes and from 0.54 to 1.41 V for the [Mn(2)(L)(RCO(2))(2)](+/2+) complexes versus Ag/AgCl for E(M(II)M(III)/M(II)(2)). The extreme limits are defined by the complexes [M(2)(bpbp)(CH(3)CO(2))(2)](+) and [M(2)(bpsmp)(CF(3)CO(2))(2)](+) for both metal ions. Thus, tuning the ligand field in these dinuclear complexes makes possible a range of around 0.9 V and 1.49 V for the one-electron E(M(II)M(III)/M(II)(2)) couple of the Mn and Co complexes, respectively. The second one-electron process, M(II)M(III)? M(III)(2) was also observed in some cases. The lowest potential recorded for the E°(M(III)(2)/M(II)M(III)) couple was 0.63 V for [Co(2)(bpbp)(CH(3)CO(2))(2)](2+) and the highest measurable potential was 2.23 V versus Ag/AgCl for [Co(2)(bpsmp)(CF(3)CO(2))(2)](2+).     

Reversible and selective O2 chemisorption in a porous metal-organic host material

The metal-organic host material [{Co(III)(2)(bpbp)(O(2))}(2)bdc](PF(6))(4) (1·2O(2); bpbp(-) = 2,6-bis(N,N-bis(2-pyridylmethyl)aminomethyl)-4-tert-butylphenolato; bdc(2-) = 1,4-benzenedicarboxylato) displays reversible chemisorptive desorption and resorption of dioxygen through conversion to the deoxygenated Co(II) form [{Co(II)(2)(bpbp)}(2)bdc](PF(6))(4) (1). Single crystal X-ray diffraction analysis indicates that the host lattice 1·2O(2), achieved through desorption of included water guests from the as-synthesized phase 1·2O(2)·3H(2)O, consists of an ionic lattice containing discrete tetranuclear complexes, between which lie void regions that allow the migration of dioxygen and other guests. Powder X-ray diffraction analyses indicate that the host material retains crystallinity through the dioxygen desorption/chemisorption processes. Dioxygen chemisorption measurements on 1 show near-stoichiometric uptake of dioxygen at 5 mbar and 25 °C, and this capacity is largely retained at temperatures above 100 °C. Gas adsorption isotherms of major atmospheric gases on both 1 and 1·2O(2) indicate the potential suitability of this material for air separation, with a O(2)/N(2) selectivity factor of 38 at 1 atm. Comparison of oxygen binding in solution and in the solid state indicates a dramatic increase in binding affinity to the complex when it is incorporated in a porous solid.     

Dicobalt II-II, II-III, and III-III complexes as spectroscopic models for dicobalt enzyme active sites

A matched set of dinuclear cobalt complexes with II-II, II-III, and III-III oxidation states have been prepared and structurally characterized. In [(bpbp)Co2(O2P(OPh)2)2]n+ ( n = 1, 2, or 3; bpbp(-) = 2,6-bis(( N,N'-bis-(2-picolyl)amino)-methyl)-4-tertbutylphenolato), the nonbonded Co...Co separations are within the range 3.5906(17) to 3.7081(11) angstroms, and the metal ions are triply bridged by the phenolate oxygen atom of the heptadentate dinucleating ligand and by two diphenylphosphate groups. The overall structures and geometries of the complexes are very similar, with minor variations in metal-ligand bond distances consistent with oxidation state assignments. The CoIICoIII compound is a valence-trapped Robin-Day class II complex. Solid state 31P NMR spectra of the diamagnetic CoIIICoIII (3) and paramagnetic CoIICoIII (2) and CoIICoII (1) complexes show that 31P isotropic shifts broaden and move downfield by about 3000 ppm for each increment in oxidation state. Cyclic voltammetry corroborates the existence of the CoIICoII, CoIICoIII, and CoIIICoIII species in solution. The redox changes are not reversible in the applied scanning timescales, indicating that chemical changes are associated with oxidation and reduction of the cobalt centers. An investigation of the spectroscopic properties of this series has been carried out for its potential usefulness in analyses of the related spectroscopic properties of the dicobalt metallohydrolases. Principally, magnetic circular dichroism (MCD) has been used to determine the strength of the magnetic exchange coupling in the CoIICoII complex by analysis of the variable-temperature variable-field (VTVH) intensity behavior of the MCD signal. The series is ideal for the spectroscopic determination of magnetic coupling since it can occur only in the CoIICoII complex. The CoIICoIII complex contains a nearly isostructural CoII ion, but since CoIII is diamagnetic, the magnetic coupling is switched off, while the spectral features of the CoII ion remain. Analysis of the MCD data from the CoIICoIII complex has been undertaken in the theoretical context of a 4T1g ground-state of the CoII ion, initially in an octahedral ligand field that is split by both geometric distortion and zero-field splitting to form an isolated doublet ground state. The MCD data for the CoIICoII pair in the [(bpbp)Co2(O2P(OPh)2)2]+ complex were fitted to a model based on weak antiferromagnetic coupling with J = -1.6 cm (-1). The interpretation is confirmed by solid state magnetic susceptibility measurements.     

Identification of components in waste streams by electrospray and tandem mass spectrometry

Highly polar, non-gas-chromatographable compounds have few unambiguous analysis protocols for environmental applications. A recent environmental investigation, concerning the identification of a non-gas-chromatographable yellow component in chemical waste water and in effluents from a biological wastewater treatment plant required the use of a number of analytical approaches. Electrospray mass spectrometry, tandem mass spectrometry, high-performance liquid chromatography, nuclear magnetic resonance, and molecular spectroscopy of commercial and synthesized chlorodinitrophenol isomers were required in order to identify the specific isomer causing the color. The present report summarizes the electrospray ionization and tandem mass spectrometric studies that were used. The mass spectrometric study shows that two different isomers of chlorodinitrophenol exhibit very different collision-induced dissociation (CID) spectra. Differences in the tandem mass spectra can be attributed to the different structures of the anions formed from these two different isomers. Instrumentation that uses electrospray ionization and produces CID mass spectra and optical absorption spectra in a single analysis may be required in order to produce highly specific information on non-gas-chromatographable compounds found in the environment.     

International Intercomparison of Solar UVR Spectral Measurement Systems in Melbourne in 2013

Monitoring ambient solar UVR levels provides information on how much there is in both real time and historically. Quality assurance of ambient measurements of solar UVR is critical to ensuring accuracy and stability and this can be achieved by regular intercomparisons of spectral measurement systems with those of other organizations. In October and November of 2013 a solar UVR spectroradiometer from Public Health England (PHE) was brought to Melbourne for a campaign of intercomparisons with a new Bentham spectrometer of Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and one at the Australian Bureau of Meteorology (BOM), supported by New Zealand's National Institute for Water and Atmosphere (NIWA). Given all three spectroradiometers have calibrations that are traceable to various national standards, the intercomparison provides a chance to determine measurement uncertainties and traceability that support UV measurement networks in Australia, New Zealand and the UK. UV Index measurements from all three systems were compared and ratios determined for clear sky conditions when the scans from each instrument were within 2 min of each other. While wavelengths below 305 nm showed substantial differences between the PHE unit and the two other systems, overall the intercomparison results were encouraging, with mean differences in measured UV Index between the BOM/NIWA and those of PHE and ARPANSA of <0.1% and 7.5%, respectively.     

Unexpected reactions associated with the xanthate‐mediated polymerization of N‐vinylpyrrolidone

The monomer N‐vinylpyrrolidone (NVP) undergoes side reactions in the presence of R group functional xanthates and impurities. The fate of the monomer NVP and a selection of six O‐ethyl xanthates during xanthate‐mediated polymerization were studied via NMR spectroscopy. A high number of by‐products were identified. Significant side reactions affecting NVP include the formation of an unsaturated dimer and hydration products in bulk or in solution in C₆D₆. In addition, the xanthate adjacent to a NVP unit was found to undergo elimination at moderate temperature (60–70 °C), resulting in unsaturated species and the formation of new xanthate species. The presence of the chlorinated compound α‐chlorophenyl acetic acid, ethyl ester, a precursor in the synthesis of the xanthate S‐(2‐ethyl phenylacetate) O‐ethyl xanthate, resulted in a dramatic increase in the rate of side reactions such as unsaturated dimer formation and a high ratio of unsaturated chain ends. The conditions for the occurrence of such side reactions are discussed in this article, with relevance to increasing the control over the polymerization kinetics, endgroup functionality, and control over the molar mass distribution. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6575–6593, 2008