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131.
Sarrión MN Santos FJ Galceran MT 《Rapid communications in mass spectrometry : RCM》2000,14(23):2271-2281
Headspace solid-phase microextraction combined with gas chromatography/ion trap tandem mass spectrometry (HS-SPME/GC/ITMS/MS) was used for the analysis of 12 halobenzenes from soil samples. For MS/MS optimisation, the experiments were performed by precursor ion selection and software controlled operations. Collision-induced dissociation (CID) can be achieved by two different approaches, resonant and non-resonant excitation modes. Different results were obtained using the two approaches, and the resonant excitation mode was chosen as the best for all halobenzenes. Parameters such as the CID excitation amplitude, excitation RF storage level and CID bandwidth frequency were optimised to maximise the formation of halobenzene product ions. A 100-microm polydimethylsiloxane fibre was used for the isolation and preconcentration of the analytes. The HS-SPME/GC/ITMS/MS method was applied to the analysis of halobenzenes in an agricultural soil sample. The halobenzenes were quantified by standard addition, which led to good reproducibility (RSD between 4.7 and 9.2%) and detection limits in the low pg/g range. The method was validated by comparing the results with those obtained in a European inter-laboratory exercise. 相似文献
132.
Estefania Fernandez-Bartolome Arturo Gamonal Jos Santos Saeed Khodabakhshi Eider Rodríguez-Snchez E. Carolina Saudo Nazario Martín Jos Snchez Costa 《Chemical science》2021,12(25):8682
Weak forces can play an essential role in chemical reactions. Controlling such subtle forces in reorganization processes by applying thermal or chemical stimuli represents a novel synthetic strategy and one of the main targets in supramolecular chemistry. Actually, to separate the different supramolecular contributions to the stability of the 3D assemblies is still a major challenge. Therefore, a clear differentiation of these contributions would help in understanding the intrinsic nature as well as the chemical reactivity of supramolecular ensembles. In the present work, a controlled reorganization of an hexakis[60]fullerene-based molecular compound purely governed by the weakest van der Waals interactions known, i.e. the dihydrogen interaction – usually called sticky fingers – is illustrated. This pre-reorganization of the hexakis[60]fullerene under mild conditions allows a further selective hydrogenation of the crystalline material via hydrazine vapors exposure. This unique two-step transformation process is monitored by single-crystal to single-crystal diffraction (SCSC) which allows the direct observation of the molecular movements in the lattice and the subsequent solid–gas hydrogenation reaction.Weak forces play an essential role in chemistry. Controlling these supramolecular interactions will contribute to the creation dynamic absorbent materials with a variety of technological applications as chemosensors and environmental remediation. 相似文献
133.
This paper deals with the synthesis of six σ-cyclohexylethynyl complexes of CoII and FeII and their characterization by chemical analysis, infrared and 1H NMR spectra, and magnetic measurements. Four of them are six-coordinate complexes, unsubstituted or substituted, namely K4[M(C≡C—C6H11)6] nNH3(M = Co, n = 2; M = Fe, n = 0), K2[Co(C≡C6H11)4(NH3)2] and K4[Fe(CN)4-(C≡C—C6H11)2]. Two are four-coordinate complexes of formula [(Ph3P)2M-(C≡C6H11)2] (M = Co, Fe). All are low-spin complexes, the magnetic moment for the six-coordinate Co(II) complexes, measured at various temperatures, being intermediate between low- and high-spin values. 相似文献
134.
In this work a simple, fast, sensitive and selective flow-based procedure for the chemiluminometric determination of carvedilol, a recent non-cardioselective β-blocker with noteworthy antioxidant activity, is proposed. The developed methodology takes advantage of the antioxidant capacity of carvedilol to inhibit the chemiluminescence response resulting from the oxidation of luminol by hypochlorite, by acting as a hypochlorite scavenger. The analytical process was implemented in a multi-pumping flow system that employs multiple solenoid actuated micro-pumps as the only active components. These acted as solution insertion, propelling and commuting units assuring an easily controlled, low cost, compact and reliable analytical system.A linear working range for carvedilol concentrations ranging from 1.2 × 10−7 to 3.0 × 10−6 mol l−1 (r > 0.999, n = 6), was obtained, with a detection limit of 8.7 × 10−9 mol l−1. The system handles about 65 samples per hour yielding precise results (R.S.D. < 1.3%, n = 10). Recoveries within 95 and 104% were obtained. 相似文献
135.
[Reaction: see text]. An efficient approach for the parallel solid-phase synthesis of novel heterocyclic azoniaspiro ring systems is described. The target compounds, the 1,8,9-trisubstituted 10-oxo-3,9-diaza-6-azoniaspiro[5.5]undecanes, were obtained starting from resin-bound reduced dipeptides. The azoniaspiro cation was formed by intramolecular attack of a tertiary nitrogen on pendent alpha-bromocarbonyl. N-3 acylated and N-3 alkylamino carbonyl derivatives of the 1,8,9-trisubstituted 10-oxo-3,9-diaza-6-azoniaspiro[5.5]undecanes were obtained following in solution treatment of the N-3 azoniaspiro derivatives with different carboxylic acids and isocyanates. 相似文献
136.
An equation of state for a multicomponent mixture of nonadditive hard spheres in d dimensions is proposed. It yields a rather simple density dependence and constitutes a natural extension of the equation of state for additive hard spheres proposed by us [A. Santos, S. B. Yuste, and M. Lopez de Haro, Mol. Phys. 96, 1 (1999)]. The proposal relies on the known exact second and third virial coefficients and requires as input the compressibility factor of the one-component system. A comparison is carried out both with another recent theoretical proposal based on a similar philosophy and with the available exact results and simulation data in d=1, 2, and 3. Good general agreement with the reported values of the virial coefficients and of the compressibility factor of binary mixtures is observed, especially for high asymmetries and/or positive nonadditivities. 相似文献
137.
Antonio S. Santos Arnaldo C. Pereira Maria D. P. T. Sotomayor César R. T. Tarley Nelson Durán Lauro T. Kubota 《Electroanalysis》2007,19(5):549-554
This work evaluated an amperometric biosensor based on multi‐wall carbon nanotubes (MWCNT), chemically modified with methylene blue (Met) and horseradish peroxidase (HRP), for detection of phenolic compounds. The dependences of the biosensor response due to the enzyme immobilization procedure, HRP amounts, pH and working potential were investigated. The amperometric response for catechol using the proposed biosensor showed a very wide linear response range (1 to 150 μmol L?1), good sensitivity (50 nA cm?2 μmol?1 L), excellent operational stability (after 300 determinations the response remained at 97%) and very good storage stability (lifetime>3 months). Based on all these characteristics, it is possible to affirm that the material is promising for phenol detection due to its good electrochemical response and enzyme stabilization. The biosensor response for various phenolic compounds was investigated. 相似文献
138.
Wagner B. De Almeida Hélio F. Dos Santos Patrick J. O'Malley 《Structural chemistry》1995,6(6):383-389
The potential energy surface (PES) for the herbicide diuron (DCMU), a photosystem II inhibitor, has been extensively investigated using the quantum-mechanical semiempirical molecular orbital methods AM1 and PM3 and molecular mechanics method. A detailed conformational search has been carried out which revealed the occurrence of four genuine minimum energy structures. The relative stability of the conformers and rotational barriers to conformational interconversion were evaluated using distinct theoretical approaches. The results showed that thetrans form of the diuron molecule is more stable than thecis form in all methods, and so it may possibly be the biologically active isomer. 相似文献
139.
The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac2O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from l-cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The thermolysis of (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazine-3-carboxylic acid in Ac2O gave 5-acetyl-2-phenyl-2,3-dihydrothiazole. The structures of methyl (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylate 1a and methyl (2R,4R)-N-chlorocarbonyl-2-(2-hydroxyphenyl)thiazolidine-4-carboxylate 9 were determined by X-ray crystallography. 相似文献
140.
AkshatKumar Nigam Robert Pollice Mario Krenn Gabriel dos Passos Gomes Aln Aspuru-Guzik 《Chemical science》2021,12(20):7079
Inverse design allows the generation of molecules with desirable physical quantities using property optimization. Deep generative models have recently been applied to tackle inverse design, as they possess the ability to optimize molecular properties directly through structure modification using gradients. While the ability to carry out direct property optimizations is promising, the use of generative deep learning models to solve practical problems requires large amounts of data and is very time-consuming. In this work, we propose STONED – a simple and efficient algorithm to perform interpolation and exploration in the chemical space, comparable to deep generative models. STONED bypasses the need for large amounts of data and training times by using string modifications in the SELFIES molecular representation. First, we achieve non-trivial performance on typical benchmarks for generative models without any training. Additionally, we demonstrate applications in high-throughput virtual screening for the design of drugs, photovoltaics, and the construction of chemical paths, allowing for both property and structure-based interpolation in the chemical space. Overall, we anticipate our results to be a stepping stone for developing more sophisticated inverse design models and benchmarking tools, ultimately helping generative models achieve wider adoption.Interpolation and exploration within the chemical space for inverse design. 相似文献