Polystyryl-supported TBD as an efficient and reusable catalyst under solvent-free conditions

Polystyryl supported-TBD (PSTBD) is an efficient and reusable heterogeneous basic catalyst under solvent-free conditions for a variety of organic transformations such as 1,2-epoxide ring-opening, aldol-type condensation and Michael addition.     

Blood lead monitoring in Italy: Assessment of the quality of results obtained between 1992 and 1994

Between 1992 and 1994, a new screening campaign for blood Pb monitoring in the Italian general population was carried out. Since the first campaign (started in 1978, in accomplishment of the European Community Directive 77/312/EEC) a working group of the Laboratory of Clinical Biochemistry at the Italian National Institute of Health (Istituto Superiore di Sanità), as the Reference Centre (RC), has coordinated the activity of various laboratories spread over the national territory. Appropriate quality assurance procedures, including an external quality assessment scheme (EQAS), were elaborated. Within the EQAS, three or four trials were carried out every year. Each laboratory participating in the trial analyzed eight control samples prepared from cow blood at different Pb concentrations. The results obtained by each peripheral laboratory and the RC between 1992 and 1994 have been compared by regression analysis. The same statistical method was adopted to compare the results obtained by each peripheral laboratory and the RC in the duplicate analysis of about 10 per cent of the human samples collected during the 1992–1994 monitoring campaign. There was no evidence of systematic differences between the regression lines obtained on control and human samples. In spite of the lower Pb concentration in the control samples analyzed during the 1992–1994 campaign, the analytical performance of the laboratories was better than that obtained in the previous screening campaign (1985–1986). Blood Pb levels observed in human samples collected between 1992 and 1994, confirm the downward time trend observed in the campaigns carried out in 1978–1979, 1980–1981 and 1985–1986. This study confirms that the results obtained in an EQAS are representative of the actual performance in the analysis of real (human) samples.     

A Combined Theoretical and Experimental Approach to the Study of the Structural and Electronic Properties of Curcumin as a Function of the Solvent

Curcumin, a chemical compound present in the well-known Indian spice turmeric, has uses in many different fields ranging from medicinal chemistry to the dye industry. Its poor water solubility, though, makes Curcumin difficult to handle, making it less appealing for potential uses. The principal aim of this work is to perform a computational study of the structural and electronic properties of Curcumin {IUPAC name: 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione} in several solvents, and a comparison with experimental data. Rotameric equilibria, vibrational and thermochemical analysis, and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied, both in vacuum and in three selected solvents. Different computational techniques have been applied and the results compared. Combined approaches resulted in very satisfactory results. Interesting results have emerged, which suggest subsequent investigations about the nature of the excited states and potential derivatives of Curcumin that possibly have non-linear optical applications, as a π-core for innovative materials in laser engineering and photonics.     

Synergistic Properties of Arabinogalactan (AG) and Hyaluronic Acid (HA) Sodium Salt Mixtures

The properties of mixtures of two polysaccharides, arabinogalactan (AG) and hyaluronic acid (HA), were investigated in solution by the measurement of diffusion coefficients D of water protons by DOSY (Diffusion Ordered SpectroscopY), by the determination of viscosity and by the investigation of the affinity of a small molecule molecular probe versus AG/HA mixtures in the presence of bovine submaxillary mucin (BSM) by ¹HNMR spectroscopy. Enhanced mucoadhesive properties, decreased mobility of water and decreased viscosity were observed at the increase of AG/HA ratio and of total concentration of AG. This unusual combination of properties can lead to more effective and long-lasting hydration of certain tissues (inflamed skin, dry eye corneal surface, etc.) and can be useful in the preparation of new formulations of cosmetics and of drug release systems, with the advantage of reducing the viscosity of the solutions.     

Large bending behavior of creased paperboard. II. Structural analysis

The mechanics of a paradigmatic typical carton corner with five creases is analyzed theoretically, in closed form. A general kinematical analysis of the mechanism (in finite rotation) is presented, assuming the versor of the intermediate crease, s, as a 2-degree-of-freedom Lagrangian parameter. The rotation θ_c of the cth crease is derived, together with the existence domain and a discussion of the singular configurations.The actions, driving the carton during a prescribed quasi-static erection program, are derived in a very efficient manner using the Virtual Works Equation, taking into account a non-linear anholonomic bending constitutive law of the creased paperboard. In particular, the active and reactive components of the moment ?, driving s along its path, are identified. No resort to the tangent stiffness computation is required. Some numerical examples illustrate the rotation and the driving forces obtained for both monotone-loading and complex loading–unloading erection paths.The presented results, “exact” within the scope of the restrictive hypotheses assumed, may be used in a preliminary design approach as well as a benchmark for more realistic FEM or CAE simulators.     

Competitive evaluation of threshold functions in the priced information model

In Charikar et al. (J. Comput. Syst. Sci. 64(4):785–819, 2002) the authors proposed a new model for studying the function evaluation problem based on a variant of the classical decision tree problem for Boolean functions. In this variant each variable of the function to evaluate has an associated cost which has to be paid in order to read the value of the variable. Given a function f and an assignment σ to the variables of f, the performance of an algorithm for evaluating f is measured via the competitive ratio, i.e., the ratio of the total cost spent by the algorithm and the cost of the cheapest set of variables constituting a certificate for the value of the function on the given assignment.     

Conformational analysis of hydrazones. 1H dynamic nuclear magnetic resonance and solvent effects in aryl- and 2-furylaldehyde ethylaminoacetylhydrazones

Aryl- and 2-furylaldehyde ethylaminoacetylhydrazones were examined in different solvents and over a wide temperature range with ¹H NMR in order to study their conformational properties. Nearly equal amounts of the E/Z isomers, relative to the C?N bond, are present, even when the solvents and the substituents on the aldimino carbon produce small changes in the isomeric mixture. The activation parameters of the thermal isomerization process were measured, and the results are in the line with a lateral-shift type mechanism, also supported by theoretical calculations on a model compound. No other internal process was noted from the low-temperature spectral behaviour, and this was interpreted in terms of a highly biased equilibrium concerning the rotation around the C(O)? N bond. Chemical shifts obtained in different solvents also enable the most stable arrangement of the whole molecule of these compounds to be postulated.     

3-nitrocoumarins as dienophiles in the Diels-Alder reaction in water. An approach to the synthesis of nitrotetrahydrobenzo[c]chromenones and dihydrodibenzo[b,d]furans

The [4 + 2] cycloadditions of 3-nitrocoumarin (1a), 6-chloro-3-nitrocoumarin (1b), and 6-, 7-, and 8-hydroxy-3-nitrocoumarins (1c, 5, and 6) with (E)-piperylene (7), isoprene (8), 2,3-dimethyl-1,3-butadiene (9), 2-methoxy-1,3-butadiene (10), 2,3-dimethoxy-1,3-butadiene (11), and cyclopentadiene (12) were investigated in aqueous medium, in organic solvent and under solventless conditions. The reactions performed in water occurred in heterogeneous phase but were faster than those executed in toluene or dichloroethane (DCE). 1a-c, 5, and 6 behaved as 2pi components in the Diels-Alder cycloadditions with 7-10 and 12, and exo adducts were preferentially or exclusively produced. Surprisingly 1a, behaved as a 4pi component in the cycloaddition in water with 11 and 4-substituted 3-nitrochromanones 20 and 21 were isolated. The cycloadditions of hydroxy-3-nitrocoumarins 1c, 5, and 6 with 1,3-diene 9 did not work in water or in organic solvent, but did work under solventless conditions. Nitrotetrahydrobenzo[c]chromenones 13-16, 24, and 25, originating from the normal electron-demand Diels-Alder reactions, were converted into dihydrodibenzo[b,d]furans 27-31 in water, via one-pot Nef-cyclodehydration reactions.     

A convenient strategy of dimerization by microwave heating and using 2,5-diketopiperazine as scaffold

A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating.     

The influence of ligand field effects on the magnetic exchange of high-spin Co(II)-semiquinonate complexes

[Co(Me(4)cyclam)(tropolonate)](PF(6)) was synthesised and structurally characterised. Its electronic and W-band EPR spectra have been analysed by means of the angular overlap calculation of the Spin Hamiltonian parameters that provided also a satisfactory reproduction of the temperature dependence of the magnetic susceptibility. The present results can be interpreted assuming a pseudo-octahedral character for the Co(II) center. This prompted us to reconsider the model formerly used for the analysis of the magnetic coupling between hs-Co(II) and the paramagnetic o-semiquinonate ligand in the corresponding derivatives [Co(Me(4)cyclam)(PhenSQ)](PF(6)) and [Co(Me(4)cyclam)(DTBSQ)](PF(6)). These results indicate that the effect of the magnetic coupling is active only below 50 K and that a more refined model of exchange coupling between Co(II) and semiquinonato ligands is needed to quantitatively analyze the magnetic behaviour of this class of systems.