Reversible Coordination of Dioxygen by Tripodal Tetraamine Copper Complexes Incorporated in a Porous Silica Framework

The present study reports the synthesis and rational design of porous structured materials by using a templating method. A tetraethoxysilylated tripodal tetraamine (TREN) was covalently incorporated in a silica framework with a double imprint: A surfactant template and a metal ion imprint. The presence of a cationic surfactant (CTAB) endowed the material with a high porosity, and the tripodal or square‐pyramidal topology of the ligand was preserved thanks to the use of the silylated Cu^II complex. After removal of the surfactant and de‐metalation, the incorporated tetraamine was quantitatively complexed by CuCl₂ and the material has shown after thermal activation that a reversible binding of O₂ on the metal ions occurred. This chemisorption process was monitored by UV/Vis and EPR spectroscopies, and the Cu:O₂ adduct was postulated to be an end‐on μ‐η¹:η¹‐peroxodicopper(II) complex bridged by a chloride ion. The Cu^I‐active species, formed during the activation step, were fully recovered during several O₂ binding cycles. The high reactivity of the copper complexes and the room‐temperature stability of the dioxygen adduct were explained by the fine adaptability of the tripodal ligand to different geometries, the confinement of the active sites in the hybrid silica that protect them from degradation by a control of the metal‐ion microenvironment, as well as the short‐range lamellar order of the copper complexes in the framework.     

Potential of atmospheric pressure chemical ionization source in GC‐QTOF MS for pesticide residue analysis

The potential applications of a new atmospheric pressure source for GC‐MS analysis have been investigated in this work. A list of around 100 GC‐amenable pesticides, which includes organochlorine, organophosphorus and organonitrogenated compounds, has been used to evaluate their behavior in the new source. Favoring the major formation of the molecular ion in the source has been the main goal due to the wide‐scope screening possibilities that this fact brings in comparison with the traditional, highly fragmented electron ionization spectra. Thus, the addition of water as modifier has been tested as a way to promote the generation of protonated molecules. Pesticides investigated have been classified into six groups according to their ionization/fragmentation behavior. Four of them are characterized by the abundant formation of the protonated molecule in the atmospheric pressure source, mostly being the base peak of the spectrum. These results show that wide‐scope screening could be easily performed with this source by investigating the presence of the protonated molecule ion, MH+. The developed procedure has been applied to pesticide screening in different food samples (nectarine, orange and spinach) and it has allowed the presence of several pesticides to be confirmed such as chlorpyriphos ethyl, deltamethrin and endosulfan sulfate. The availability of a quadrupole time‐of‐flight instrument made it feasible to perform additional MS/MS experiments for both standards and samples to go further in the confirmation of the identity of the detected compounds. Results shown in this paper have been obtained using a prototype source which exhibits promising features that could be applied to other analytical problems apart from those illustrated in this work. Copyright © 2010 John Wiley & Sons, Ltd.     

Chiral discrimination of β‐3‐homo‐amino acids using the kinetic method

Chiral discrimination of seven enantiomeric pairs of β‐3‐homo‐amino acids was studied by using the kinetic method and trimeric metal‐bound complexes, with natural and unnatural α‐amino acids as chiral reference compounds and divalent metal ions (Cu²⁺ and Ni²⁺) as the center ions. The β‐3‐homo‐amino acids were selected for this study because, first of all, chiral discrimination of β‐amino acids has not been extensively studied by mass spectrometry. Moreover, these β‐3‐homo‐amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain (electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of β‐3‐homo‐amino acids could be differentiated. Moreover, it was noted that the β‐3‐homo‐amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of β‐3‐homo‐amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)‐2‐amino‐2‐phenylacetic acid (L ‐Phg) and (S)‐2‐amino‐2‐(4‐hydroxyphenyl)‐acetic acid (L ‐4′‐OHPhg) gave rise to an additional copper‐reduced dimeric fragment ion, [Cu^I(ref)(A)]⁺. The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

Interpretation of vicinal proton–proton coupling constants of heteroaromatic molecules in terms of topological electron density descriptors

The indirect vicinal proton–proton coupling constants for pyrrole, furan, thiophene and 15 related heteroaromatic compounds were calculated using the Khon–Sham approximation. An analysis of the four Ramsey contributions to the coupling constants was carried out showing that the Fermi contact term is always positive and dominant, although the remaining contributions have a nonnegligible net negative contribution. The trends observed for the proton–proton coupling constants were rationalized in terms of the properties of the electron density. It was found that electron delocalization between the corresponding hydrogen atoms plays a major role on the observed behavior with the charges of the carbon atoms bonded to them and the accompanying geometric variations being also of importance in the coupling mechanism. Copyright © 2010 John Wiley & Sons, Ltd.     

Poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene): Synthesis,optical and photovoltaic properties

A new benzodithiophene (BDT)‐based polymer, poly(4,8‐bis(2‐ethylhexyloxy)benzo[1,2‐b:4,5‐b′]dithiophene vinylene) (PBDTV), was synthesized by Pd‐catalyzed Stille‐coupling method. The polymer is soluble in common organic solvents and possesses high thermal stability. PBDTV film shows a broad absorption band covering from 350 nm to 618 nm, strong photoluminescence peaked at 545 nm and high hole mobility of 4.84 × 10^?3 cm²/Vs. Photovoltaic properties of PBDTV were studied by fabricating the polymer solar cells based on PBDTV as donor and PC₇₀BM as acceptor. With the weight ratio of PBDTV: PC₇₀BM of 1:4 and the active layer thickness of 65 nm, the power conversion efficiency of the device reached 2.63% with V_oc = 0.71 V, I_sc = 6.46 mA/cm², and FF = 0.57 under the illumination of AM1.5, 100 mW/cm². © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1822–1829, 2010     

Improved characterization of tomato polyphenols using liquid chromatography/electrospray ionization linear ion trap quadrupole Orbitrap mass spectrometry and liquid chromatography/electrospray ionization tandem mass spectrometry

Tomato (Lycopersicon esculentum Mill.) is the second most important fruit crop worldwide. Tomatoes are a key component in the Mediterranean diet, which is strongly associated with a reduced risk of chronic degenerative diseases. In this work, we use a combination of mass spectrometry (MS) techniques with negative ion detection, liquid chromatography/electrospray ionization linear ion trap quadrupole‐Orbitrap‐mass spectrometry (LC/ESI‐LTQ‐Orbitrap‐MS) and liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS) on a triple quadrupole, for the identification of the constituents of tomato samples. First, we tested for the presence of polyphenolic compounds through generic MS/MS experiments such as neutral loss and precursor ion scans on the triple quadrupole system. Confirmation of the compounds previously identified was accomplished by injection into the high‐resolution system (LTQ‐Orbitrap) using accurate mass measurements in MS, MS² and MS³ modes. In this way, 38 compounds were identified in tomato samples with very good mass accuracy (<2 mDa), three of them, as far as we know, not previously reported in tomato samples. Copyright © 2010 John Wiley & Sons, Ltd.     

Textile‐based Electrochemical Sensing: Effect of Fabric Substrate and Detection of Nitroaromatic Explosives

This study examines the influence of textile substrates upon the behavior of wearable screen‐printed electrodes and demonstrates the attractive sensing properties of these sensors towards the detection of nitroaromatic explosives. Compared to electrodes printed on common cotton or polyester substrates, GORE‐TEX‐based electrochemical sensors display reproducible background cyclic voltammograms, reflecting the excellent water‐repellant properties of the GORE‐TEX fabric. The wetting properties of different printed textile electrodes are elucidated using contact angle measurements. The influence of laundry washing and mechanical stress is explored. The GORE‐TEX‐based printed electrodes exhibit favorable detection of 2,4‐dinitrotoluene (DNT) and 2,4,6‐trinitrotoluene (TNT) explosives, including rapid detection of DNT vapor.