Hexametallic manganese clusters with bulky derivatised salicylaldoximes

The reaction of Mn(ClO(4))(2)·6H(2)O with Ph-saoH(2) (Ph-saoH(2) = 2-hydroxybenzophenone oxime) in MeCN in the presence of sodium propionate forms the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(MeCN)(2)]·5.27MeCN (1·5.27MeCN) (prop = propionate). Repeating the same reaction in EtOH produces the complex [Mn(III)(6)O(2)(Ph-sao)(6)(prop)(2)(EtOH)(4)] (2). Complexes 1 and 2 may be considered as structural isomers, since they display the same metallic core but different coordination modes of the propionate ligands; bridging in 1 and terminal in 2. Performing similar reactions and switching from sodium propionate to sodium adamantane-carboxylate (NaO(2)C-ada) and sodium pivalate (Napiv) in the presence of NEt(4)OH yields the complexes [Mn(III)(6)O(2)(Ph-sao)(6)(O(2)C-ada)(2)(MeOH)(4)] (3) and [Mn(III)(6)O(2)(Ph-sao)(6)(piv)(2)(EtOH)(4)]·0.5Et(2)O (4·0.5Et(2)O), respectively. All four complexes contain the same {Mn(III)(3)O(Ph-sao)(3)} building block. Variable temperature magnetic susceptibility and magnetization studies show that all complexes possess an S = 4 ground-state.     

Electronic characterization of lithographically patterned microcoils for high sensitivity NMR detection

Nuclear magnetic resonance (NMR) offers a non-destructive, powerful, structure-specific analytical method for the identification of chemical and biological systems. The use of radio frequency (RF) microcoils has been shown to increase the sensitivity in mass-limited samples. Recent advances in micro-receiver technology have further demonstrated a substantial increase in mass sensitivity [D.L. Olson, T.L. Peck, A.G. Webb, R.L. Magin, J.V. Sweedler, High-resolution microcoil H-1-NMR for mass-limited, nanoliter-volume samples, Science 270 (5244) (1995) 1967–1970]. Lithographic methods for producing solenoid microcoils possess a level of flexibility and reproducibility that exceeds previous production methods, such as hand winding microcoils. This paper presents electrical characterizations of RF microcoils produced by a unique laser lithography system that can pattern three dimensional surfaces and compares calculated and experimental results to those for wire wound RF microcoils. We show that existing optimization conditions for RF coil design still hold true for RF microcoils produced by lithography. Current lithographic microcoils show somewhat inferior performance to wire wound RF microcoils due to limitations in the existing electroplating technique. In principle, however, when the pitch of the RF microcoil is less than 100 μm lithographic coils should show comparable performance to wire wound coils. In the cases of larger pitch, wire cross sections can be significantly larger and resistances lower than microfabricated conductors.     

Comparison of protein immobilisation methods onto oxidised and native carbon nanofibres for optimum biosensor development

The properties of native and oxidised graphene layered carbon nanofibres are compared, and their utilisation in enzyme biosensor systems using different immobilisation methods are evaluated. The efficient oxidation of carbon nanofibres with concentrated H₂SO₄/HNO₃ is confirmed by Raman spectroscopy while the introduction of carboxylic acid groups on the surface of the fibres by titration studies. The oxidised fibres show enhanced oxidation efficiency to hydrogen peroxide, while at the same time they exhibit a more efficient and selective interaction with enzymes. The analytical characteristics of biosensor systems based on the adsorption or covalent immobilisation of the enzyme glucose oxidase on carbon nanofibres are compared. The study reveals that carbon nanofibres are excellent substrates for enzyme immobilisation allowing the development of highly stable biosensor systems. Figure Immobilization of proteins on carbon nanofibres     

Solid ink-printed filter paper as a green adsorbent material for the solid-phase extraction of UV filters from water samples

This work describes the development of a new green solid-phase extraction approach, which is based on the use of low-cost extraction discs composed of plain filter papers that are covered with a synthetic wax-like coating. The filter papers are printed in a commercial solid ink printer, which dispenses a synthetic wax-like ink on the surface of the paper, to cover the hydrophilic cellulose fibre matrix with an interface of lipophilic domains where non-polar analytes can partition through hydrophobic interactions. The modified paper filters were used to extract hydrophobic organic compounds from water samples following the customary procedure of solid-phase extraction without sorbent preconditioning and needless of high-vacuum sources. As a proof-of-concept application, a series of non-polar organic UV filters were used as model analytes to optimise the extraction parameters and evaluate the performance of the method in spiked water samples. Based on this principle, a new sample preparation platform with low environmental footprint has been developed that enables extraction to be carried out using low-cost, environmental benign and non-toxic conventional materials. The advantages and disadvantages of the method, alongside with its future prospects towards the development of custom-made ‘printed extraction kits’, are envisioned and discussed.     

Formation, characterization, and chemistry of undecanoic acid-terminated silicon surfaces: patterning and immobilization of DNA

This paper describes a simple strategy for DNA immobilization on chemically modified and patterned silicon surfaces. The photochemical modification of hydrogen-terminated Si(111) with undecylenic acid leads to the formation of an organic monolayer covalently attached to the surface through Si-C bonds without detectable reaction of the carboxylic acid group, providing indirect support of a free radical mechanism. Chemical activation of the acid function was achieved by a simple chemical route using N-hydroxysuccinimide (NHS) in the presence of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride. Single strand DNA with a 5'-dodecylamine group was then coupled to the NHS-activated surface by amide bond formation. Using a previously reported chemical patterning approach, we have shown that DNA can be immobilized on silicon surfaces in spatially well-resolved domains. Methoxytetraethyleneglycolamine was used to inhibit nonspecific adsorption. The resulting DNA-modified surfaces have shown good specificity and chemical and thermal stability under hybridization conditions. The sequential reactions on the surface were monitored by ATR-FTIR, X-ray Photoelectron Spectroscopy, and fluorescence spectroscopy.     

Atomic force microscopy measurements of peptide-wrapped single-walled carbon nanotube diameters.

With a vertical resolution of 0.1 nm, atomic force microscopy (AFM) height measurements can be used to determine accurately the diameter of single-walled carbon nanotubes (SWNT) with the assumption that they have circular cross sections. The aim of this article is to draw attention to the need to optimize operating parameters in tapping mode for quantitative AFM height (diameter) analysis of SWNTs. Using silicon tip/cantilever assemblies with force constants ranging from 0.9 to 40 N m(-1), we examined the effect of applied force on the apparent diameter of SWNT wrapped with a 29-residue amphiphilic alpha-helical peptide. A decrease in apparent height (SWNT diameter) with increasing applied force was observed for the higher force constant cantilevers. Cantilevers having force constants of 0.9 and 3 N m(-1) demonstrated minimal vertical sample compression with increasing applied force. The effects of AFM image pixel density and scan speed on the measured height (diameter) of SWNTs were also assessed.     

Synthesis and spectroscopic Investigation of Mixed-Ligand Copper Chelates containing 2-hydroxyaryloximes and N-disubstituted dithiocarbamates. Crystal and molecular structure of trans-bis[propanone, 1-(2-hydroxy-phenyl)oximato] copper(II)

A series of mixed-ligand copper(II) chelates containing the anion of 2-hydroxyaryloxime(oxime) and N,N-disubstituted dithiocarbamate(dtc), [Cu(dtc)(oxime)], was prepared and characterised. The spectra (IR, ESR, electronic excitation) indicate that the CuNOS₂ chromophore attains square planar geometry. The ESR observables suggest appreciable covalency. In the case of [Cu(Et₂dtc)(oxime)] chelates, however, the observed data suggest distortion from square planar arrangement to a square pyramidal, indicative of a possible dimerism. In addition, the structure of the trans-bis[propanone, 1-(2-hydroxyphenyl)-oximato]copper(II), Cu(C₉H₁₀NO₂)₂ was determined by X-ray diffraction (monoclinic, space group P2₁/n, a = 12.072(7) Å, b = 5.204(2) Å, c = 13.571(6) Å, β = 103.72(1)°, Z = 2). The molecule consists of discrete Cu(ppox)₂ monomeric units, where the Cu atom is in the equatorial plane bonded to two nitrogen atoms and two oxygen at distances of 1.949(2) and 1.882(2) Å, respectively.     

Thermodynamics of micellization of tapered statistical copolymers of ethylene oxide and propylene oxide in water

Two tapered statistical copolymers were prepared by the oxyanionic polymerization of ethylene oxide and propylene oxide and characterized by gel permeation chromatography and 13C NMR spectroscopy. We denote the copolymers t-E/P38 and t-E/P30, where E = oxyethylene, OCH2CH2, and P = oxypropylene, OCH2CH(CH3), and the number denotes the mole percentage P. In each case the copolymer chain length was ca. 100 oxyalkylene units. The association of the copolymers to form micelles in aqueous solution was checked by dynamic light scattering. The critical micelle temperatures (cmt) of the copolymers at several concentrations were determined by static light scattering and dye solubilization, and values of the apparent standard enthalpy of micellization (DeltamicHapp0) were obtained. For both copolymers, a low value of DeltamicHapp0 was found when the copolymer concentration exceeded ca. 150 g dm(-3).     

An experimental design approach employing artificial neural networks for the determination of potential endocrine disruptors in food using matrix solid-phase dispersion

Matrix solid-phase dispersion (MSPD) as a sample preparation method for the determination of two potential endocrine disruptors, linuron and diuron and their common metabolites, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl) urea (DCPU) and 3,4-dichloroaniline (3,4-DCA) in food commodities has been developed. The influence of the main factors on the extraction process yield was thoroughly evaluated. For that purpose, a 3^(4–1) fractional factorial design in further combination with artificial neural networks (ANNs) was employed. The optimal networks found were afterwards used to identify the optimum region corresponding to the highest average recovery displaying at the same time the lowest standard deviation for all analytes. Under final optimal conditions, potato samples (0.5 g) were mixed and dispersed on the same amount of Florisil. The blend was transferred on a polypropylene cartridge and analytes were eluted using 10 ml of methanol. The extract was concentrated to 50 μl of acetonitrile/water (50:50) and injected in a high performance liquid chromatography coupled to UV–diode array detector system (HPLC/UV–DAD). Recoveries ranging from 55 to 96% and quantification limits between 5.3 and 15.2 ng/g were achieved. The method was also applied to other selected food commodities such as apple, carrot, cereals/wheat flour and orange juice demonstrating very good overall performance.