Speciation of arsenic(III) and arsenic(V) by manganese-mediated stripping voltammetry at gold microelectrode ensemble in neutral and basic medium

New schemes of arsenic speciation by anodic stripping voltammetry are developed at neutral pH based on the difference in electrochemical behaviour of the As(III) and As(V) forms. Detection is performed in sulphite medium (0.1 M Na₂SO₃) in the presence of Mn(II) (10^?6 M), which is known to catalyse the reduction of As(V), making it detectable by ASV. Two speciation schemes are proposed. If As(III) > As(V), then As(III) and total As(III) + As(V) are determined in separate voltammetric cells after oxidation of As(III) to As(V) (5 min ozone purging), similar to previous studies. However, when As(V) > As(III), both As(III) and As(V) can be determined consecutively, within the same cell. In this case, two simple variants were successfully tested, depending on the size of the As(III) peak in comparison to the linearity range. The working electrode is an ensemble of gold microelectrodes obtained by HAuCl₄ electrolysis at a carbon black–polyethylene composite (ratio 30:70). No purging is required, the electrode is sensitive, robust and has a long lifetime. Calculated LODs of As(III) and As(V) are 0.09 μg L^?1 and 0.35 μg L^?1, respectively (3σ, t_dep = 20 s). The proposed procedures are fast, simple and environmental-friendly.     

Comparative regional GDP analysis: case study of Croatia

The focus of this paper is the regional GDP analysis of Croatian Counties. It is a part of an extensive on-going scientific research about Croatian economic challenges within the global recession environment. Although, as EU accession country, Croatia is divided into three NUTS 2 regions, twenty one Croatian Counties show significant economic and social disproportions. In multiple regression model it is researched to what extent regional GDP per capita depends on a set of regional variables (employment, gross investment, production of more important agricultural products, GVA per person employed, construction works value, exports, imports, foreign tourists arrivals, foreign tourist nights, ecology...). Subsequently parameters are evaluated by Monte Carlo simulations which are used for the first time in comparative regional analysis. Also Croatian Counties are classified using Cluster analysis to make a comparative analysis with official spacing into three NUTS 2 regions which are geographical and political areas rather than real and homogenous socio-economic areas.     

Synthesis and antibacterial activity of trinems bearing nitrogen derivatives at C(4)

Optimization of the antibacterial activity of 4-amino trinem, obtained through chemical modification of the basicity of the amino group at position 4, has led to the identification of a very interesting compound characterized by a broad spectrum of activity includingPseudomonas aeruginosa.Medicines Research Centre, GlaxoWellcome S.p. A Via A. Fleming 4, 37100 Verona, Italy. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1553–1559, November, 1998.     

Regioselective synthesis of 1,3,5- and 1,3,4,5-substituted pyrazoles via acylation of N-Boc-N-substituted hydrazones

Acylation of N-Boc-N-methylhydrazones followed by TFA treatment affords regioselective access to substituted pyrazoles. Both regioisomers of 1-methyl-3,5-disubstituted-1H-pyrazoles can be selectively obtained. This procedure can also be employed for the regioselective preparation of fully substituted 1H-pyrazoles.     

Capillary pressure and contact line force on a soft solid

The surface free energy, or surface tension, of a liquid interface gives rise to a pressure jump when the interface is curved. Here we show that a similar capillary pressure arises at the interface of soft solids. We present experimental evidence that immersion of a thin elastomeric wire into a liquid induces a substantial elastic compression due to the solid capillary pressure at the bottom. We quantitatively determine the effective surface tension from the elastic displacement field and find a value comparable to the liquid-vapor surface tension. Most importantly, these results also reveal the way the liquid pulls on the solid close to the contact line: the capillary force is not oriented along the liquid-air interface, nor perpendicularly to the solid surface, as previously hypothesized, but towards the interior of the liquid.     

The [Ru(CN)5(pyS)](4-) complex, an efficient self-assembled monolayer for the cytochrome c heterogeneous electron transfer studies

The organothiol 4-mercaptopyridine (pyS) has been used extensively as facilitator for the assessment of heterogeneous electron transfer reaction of cytochrome c (cyt c). Its efficiency, however, is strongly affected by the instability of the adlayer due to the C-S bond cleavage. The K(4)[Ru(CN)(5)(pyS)].3H(2)O complex was synthesized and characterized aiming its utilization as an inorganic self-assembled monolayer (SAM) that would enhance the gold adlayer stability. The SAM formed by this complex onto gold (RupySAu) was characterized by spectroscopic (FTIRRAS and SERS) and electrochemical (LSV) techniques. The ex situ vibrational SERS and FTIRRAS spectra data of this SAM formed onto gold suggest a sigma interaction between the gold and sulfur atoms of the complex, inducing a perpendicular arrangement in relation to the surface normal. Additionally, SERS and FTIRRAS spectra performed for freshly prepared RupySAu adlayer and for large immersion times in the precursor solution have not shown any significant change that would reflect the degradation of the adlayer. The LSV desorption curves of this SAM indicate an enhancement in the C-S bond strength of the pyS ligand when coordinated to the [Ru(CN)(5)](3-) moiety. Comparatively to the data obtained for the desorption process of the pyS monolayer, the reductive desorption potential, E(rd), of the RupySAu presents a shift of -17 mV. This bond strength intensification leads to an increase in the stability of the monolayer. The voltammetric curves of cyt c carried out with the RupySAu electrode showed electrochemical parameters consistent with those reported for the native protein, as well as the maintenance of the electrochemical kinetic data after repetitive cycles. The results all together suggest that the pi back-bonding effect from the [Ru(CN)(5)](3-) metal center plays an important role in the stability of the RupySAu adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction.     

Colour fading in textiles: A model study on the decomposition of natural dyes

This paper describes an analytical procedure based on GC-MS to identify in textiles the most common flavonoid yellow dyes used in Europe since ancient times, extracted from weld, young fustic, dyer's broom, sawwort and the berries of some species of Rhamnus. Later on, old fustic and quercitron bark were introduced as sources of yellow colours.The method is based on the solvent extraction of flavonoids from raw plant materials (weld, dyer's broom and old fustic), aged and not aged alum-mordanted wool dyed specimens; subsequently, flavonoids are derivatised with N,O-bis(trimethylsilyl)trifluoroacetamide and analysed by GC-MS. The method easily allows the identification of a dyestuff by the detection of the molecular markers apigenin, luteolin, genistein, morin, maclurin, together with 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 2,4,6- trihydroxybenzoic acid, which survive in aged textiles. Two photo-oxidative degradation pathways for colour fading, one involving the mordant metallic ion and the other the light as a catalyst, are suggested.