Convergence of the projected gradient method for quasiconvex multiobjective optimization

We consider the projected gradient method for solving the problem of finding a Pareto optimum of a quasiconvex multiobjective function. We show convergence of the sequence generated by the algorithm to a stationary point. Furthermore, when the components of the multiobjective function are pseudoconvex, we obtain that the generated sequence converges to a weakly efficient solution.     

New Approach for the Construction of the Coumarin Frame and Application in the Total Synthesis of Natural Products

A new synthetic approach is described for building the coumarin scaffold through the Lewis acid‐promoted cyclization of novel aryl 3‐(dimethylamino)prop‐2‐enoates 2a – 2f . The latter precursors were prepared via aminomethylenation of the corresponding aryl acetates 4a – 4f with the Bredereck reagent. This approach was used for the synthesis of biologically active natural compounds 1a – 1f , through a three‐step procedure starting from the corresponding phenols.     

Analysis of nucleotides binding to chromatography supports provided by nuclear magnetic resonance spectroscopy

The epitope mapping of nucleotides bound to three chromatography supports is accomplished using saturation transfer difference (STD)-NMR spectroscopy. This experiment involves subtracting a spectrum in which the support was selectively saturated from one recorded without support saturation. In the difference spectrum only the signals of the ligands that bind to the support and received saturation transfer remain. The nucleotide protons in closer contact with the support have more intense signals due to a more efficient transfer of saturation. We investigate the effects on the binding to the nucleotides by the introduction of a spacer arm between l-histidine and Sepharose. Our NMR experiments evidence a clear contribution of the spacer to the interaction with all the nucleotides, increasing the mobility of the amino acid and giving different STD responses. This enhanced mobility originates the reinforcement of the interactions with the sugar moiety and phosphate group of 5'-CMP and 5'-TMP or the base of 5'-GMP and 5'-UMP. Hence, with this study we show that by using STD NMR technique on chromatographic systems it is possible to provide a fast, robust and efficient way of screening the atoms involved in the binding to the supports.     

Optimization of the derivatization reaction and the solid-phase microextraction conditions using a D-optimal design and three-way calibration in the determination of non-steroidal anti-inflammatory drugs in bovine milk by gas chromatography-mass spectrometry

An experimental design optimization is reported of an analytical procedure used in the simultaneous determination of seven non-steroidal anti-inflammatory drugs (NSAIDs) in bovine milk by gas chromatography with mass spectrometry detection (GC-MS). This analytical procedure involves a solid-phase microextraction (SPME) step and an aqueous derivatization procedure of the NSAIDs to ethyl esters in bovine milk. The following NSAIDs are studied: ibuprofen (IBP), naproxen (NPX), ketoprofen (KPF), diclofenac (DCF), flufenamic acid (FLF), tolfenamic acid (TLF) and meclofenamic acid (MCL). Three kinds of SPME fibers - polyacrylate (PA), polydimethylsiloxane/divinylbenzene (PDMS/DVB) and polydimethylsiloxane (PDMS) - are compared to identify the most suitable one for the extraction process, on the basis of two steps: to determine the equilibrium time of each fiber and to select the fiber that provides the best figures-of-merit values calculated with three-way PARAFAC-based calibration models at the equilibrium time. The best results were obtained with the PDMS fiber. Subsequently, 8 experimental factors (related to the derivatization reaction and the SPME) were optimized by means of a D-optimal design that involves only 14 rather than 512 experiments in the complete factorial design. The responses used in the design are the sample mode loadings of the PARAFAC decomposition which are related to the quantity of each NSAID that is extracted in the experiment. Owing to the fact that each analyte is unequivocally identified in the PARAFAC decomposition, a calibration model is not needed for each experimental condition. The procedure fulfils the performance requirements for a confirmatory method established in European Commission Decision 2002/657/EC.     

A structure-based analysis of the vibrational spectra of nitrosyl ligands in transition-metal coordination complexes and clusters

The vibrational spectra of nitrogen monoxide or nitric oxide (NO) bonded to one or to several transition-metal (M) atom(s) in coordination and cluster compounds are analyzed in relation to the various types of such structures identified by diffraction methods. These structures are classified in: (a) terminal (linear and bent) nitrosyls, [M(σ-NO)] or [M(NO)]; (b) twofold nitrosyl bridges, [M₂(μ₂-NO)]; (c) threefold nitrosyl bridges, [M₃(μ₃-NO)]; (d) σ/π-dihaptonitrosyls or “side-on” nitrosyls; and (e) isonitrosyls (oxygen-bonded nitrosyls).Typical ranges for the values of internuclear N–O and M–N bond-distances and M–N–O bond-angles for linear nitrosyls are: 1.14–1.20 Å/1.60–1.90 Å/180–160° and for bent nitrosyls are 1.16–1.22 Å/1.80–2.00 Å/140–110°. The [M₂(μ₂-NO)] bridges have been divided into those that contain one or several metal–metal bonds and those without a formal metal/metal bond (M?M). Typical ranges for the M–M, N–O, M–N bond distances and M–N–M bond angles for the normal twofold NO bridges are: 2.30–3.00 Å/1.18–1.22 Å/1.80–2.00 Å/90–70°, whereas for the analogous ranges of the long twofold NO bridges these are 3.10–3.40 Å/1.20–1.24 Å/1.90–2.10 Å/130–110°. In both situations the N–O vector is approximately at right angle to the M–M (or M?M) vector within the experimental error; i.e. the NO group is symmetrical bonded to the two metal atoms. In contrast the threefold NO bridges can be symmetrically or unsymmetrically bonded to an M₃-plane of a cluster compound. Characteristic values for the N–O and M–N bond-distances of these NO bridges are: 1.24–1.28 Å/1.80–1.90 Å, respectively. As few dihaptonitrosyl and isonitrosyl complexes are known, the structural features of these are discussed on an individual basis.The very extensive vibrational spectroscopy literature considered gives emphasis to the data from linearly bonded NO ligands in stable closed-shell metal complexes; i.e. those which are consistent with the “effective atomic number (EAN)” or “18-electron” rule. In the paucity of enough vibrational spectroscopic data from complexes with only nitrosyl ligands, it turned out to be very advantageous to use wavenumbers from the spectra of uncharged and saturated nitrosyl/carbonyl metal complexes as references, because the presence of a carbonyl ligand was found to be neutral in its effect on the ν(NO)-values. The wide wavenumber range found for the ν(NO) values of linear MNO complexes are then presented in terms of the estimated effects of net ionic charges, or of electron-withdrawing or electron-donating ligands bonded to the same metal atom. Using this approach we have found that: (a) the effect for a unit positive charge is [plus 100 cm^?1] whereas for a unit negative charge it is [minus 145 cm^?1]. (b) For electron-withdrawing co-ligands the estimated effects are: terminal CN [plus 50 cm^?1]; terminal halogens [plus 30 cm^?1]; bridging or quasi-bridging halogens [plus 15 cm^?1]. (c) For electro donating co-ligands they are: PF₃ [plus 10 cm^?1]; P(OPh)₃ [?30 cm^?1]; P(OR)₃ (R = alkyl group) [?40 cm^?1]; PPh₃ [?55 cm^?1]; PR₃ (R = alkyl group) [?70 cm^?1]; and η⁵-C₅H₅ [?60 cm^?1]; η⁵-C₅H₄Me [?70 cm^?1]; η⁵-C₅Me₅ [?80 cm^?1]. These values were mostly derived from the spectra of nitrosyl complexes that have been corrected for the presence of only a single electronically-active co-ligand. After making allowance for ionic charges or strongly-perturbing ligands on the same metal atom, the adjusted ‘neutral-co-ligand’ ν(NO)*-values (in cm^?1) are for linear nitrosyl complexes with transition metals of Period 4 of the Periodic Table, i.e. those with atomic orbitals (…4s3d4p): [ca. 1750, Cr(NO)]; [1775,Mn(NO)]; [1796,Fe(NO)]; [1817,Co(NO)]; [ca. 1840, Ni(NO)]. Period 5 (…5s4d5p): [1730 Mo(NO)]; [—, Tc(NO)]; [1745,Ru(NO)]; [1790,Rh(NO)]; [ca. 1845, Pd(NO)]. Period 6 (…6s4f5d6p), [1720,W(NO)]; [1730,Re(NO)]; [1738,Os(NO)]; [1760,Ir(NO)]; [—, Pt] respectively. Environmental differences to these values, e.g. data taken in polar solutions or in the crystalline state, can cause ν(NO)* variations (mostly reductions) of up to ca. 30 cm^?1.Three spectroscopic criteria are used to distinguish between linear and bent NO groups. These are: (i) the values of ν(¹⁴NO) themselves, and (ii) the isotopic band shift – (IBS) – parameter which is defined as [ν(¹⁴NO)–ν(¹⁵NO)], and, (iii) the isotopic band ratio – (IBR) – given by [ν(¹⁵NO/ν¹⁴NO)]. The former is illustrated with the ν(¹⁴NO)-data from trigonal bipyramidal (TBP) and tetragonal pyramidal (TP) structures of [M(NO(L)₄] complexes (where M = Fe, Co, Ru, Rh, Os, Ir and L = ligand). These values indicate that linear (180–170°) and strongly bent (130–120°) NO groups in these compounds absorb over the 1862–1690 cm^?1 and 1720–1525 cm^?1-regions, respectively. As was explicitly demonstrated for the linear nitrosyls, these extensive regions reflect the presence in different complexes of a very wide range of co-ligands or ionic charges associated with the metal atom of the nitrosyl group. A plot of the IBS parameter against M–N–O bond-angle for compounds with general formulae [M(NO)(L)_y] (y = 4, 5, 6) reveals that the IBS-values are clustered between 45 and 30 cm^?1 or between 37 and 25 cm^?1 for linear or bent NO groups, respectively. A plot of IBR shows a less well defined pattern. Overall it is suggested that bent nitrosyls absorb ca. 60–100 cm^?1 below, and have smaller co-ligand band-shifts, than their linear counterparts.Spectroscopic ν(NO) data of the bridging or other types of NO ligands are comparatively few and therefore it has not been possible to give other than general ranges for ‘neutral co-ligand’ values. Moreover the bridging species data often depend on corrections for the effects of electronically-active co-ligands such as cyclopentadienyl-like groups. The derived neutral co-ligand estimates, ν(NO)*, are: (a) twofold bridged nitrosyls with a metal–metal bond order of one, or greater than one, absorb at ca. 1610–1490 cm^?1; (b) twofold bridged nitrosyl ligands with a longer non-bonding M?M distance, ca. 1520–1490 cm^?1; (c) threefold bridged nitrosyls, ca. 1470–1410 cm^?1; (d) σ/π dihaptonitrosyl, [M(η²-NO)], where M = Cr, Mn and Ni; ca. 1490–1440 cm^?1. Isonitrosyls, from few examples, appear to absorb below ca. 1100 cm^?1.To be published DFT calculations of the infrared and Raman spectra of complexes with formulae [M(NO)_4?n(CO)_n] (M = Cr, Mn, Fe, Co, Ni, and n = 0, 1, 2, 3, 4, respectively) are used as models for the assignments of the ν(MN) and δ(MNO) bands from more complex metal nitrosyls.     

Nitrogen/gold codoping of the TiO2(101) anatase surface. A theoretical study based on DFT calculations

The interaction between implanted nitrogen atoms, adsorbed gold atoms, and oxygen vacancies at the anatase TiO(2)(101) surface is investigated by means of periodic density functional theory calculations. Substitutional and interstitial configurations for the N-doping have been considered, as well as several adsorption sites for Au adatoms and different types of vacancies. Our total energy calculations suggest that a synergetic effect takes place between the nitrogen doping on one hand and the adsorption of gold and vacancy formation on the other hand. Thus, while pre-implanted nitrogen increases the adsorption energy for gold and decreases the energy required for the formation of an oxygen vacancy, pre-adsorbed gold or the presence of oxygen vacancies favors the nitrogen doping of anatase. The analysis of the electronic structure and electron densities shows that a charge transfer takes place between implanted-N, adsorbed Au and oxygen vacancies. Moreover, it is predicted that the creation of vacancies on the anatase surface modified with both implanted nitrogen and supported gold atoms produces migration of substitutional N impurities from bulk to surface sites. In any case, the most stable configurations are those where N, Au and vacancies are close to each other.     

Mode-locked all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator

Active mode-locking of long-cavity all-fiber ring laser based on broad bandwidth in-fiber acousto-optic modulator (AOM) is reported. The proposed AOM combines the advantages of intermodal coupling induced by standing flexural acoustic waves in a double-ended tapered fiber. We focus our attention on the effects of large tapered transitions to improve the bandwidth modulation. Our approach permits the implementation of broad modulation bandwidth (13 nm), high modulation depth (50 %), and low optical loss (1.1 dB) in an 80-μm configuration. The effects of the AOM in the laser performance are also investigated. Transform-limit optical pulses of 25 ps temporal width and 2.7 W peak power were obtained at 2.46 MHz repetition rate.     

On the use of the photoacoustic technique for the measurement of the thermomechanical properties of semiconductor two-layer systems

The photoacoustic technique is used in semiconductor two-layer systems for the determination of thermal properties and thermal expansion coefficient. The two-layer systems studied were amorphous silicon-glass and Al_0.2Ga_0.8As---GaAs. Our results show that the proposed method is a reliable technique for the characterization of other semiconductor two-layers systems.     

Sensory Equipment of the Antennal Flagellum of Several Species of Damalinia (Phthiraptera: Trichodectidae)

Sensilla comprising the sensory equipment of the antennal flagellum of eight species of Damalinia were studied using light and scanning electron microscopy. The sensillar complex consists of three pore organs and two sensilla coeloconica in both males and females. No relationship between their relative position in different genera and species has been found. The ‘pit organs' of the sensilla coeloconica have different shapes according to species. In the apex of the male flagellum, teeth are present in the species studied but the number and shapes are different. Adjacent to the teeth is a cluster of sensilla basiconica. At high magnification, no pores were found in the sensilla walls but their more or less blunt tips have small pores. The inner face of the male flagellum can be serrated or non-serrated.     

Use of p-nitrobenzyloxycarbonyl (pNZ) as a permanent protecting group in the synthesis of Kahalalide F analogs

p-Nitrobenzyloxycarbonyl (pNZ) is used for the permanent protection of ornithine in the synthesis of derivatives of the anti-tumor cyclodepsipeptide Kahalalide F that contain acid labile residues.