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31.
M. Rosario De La Fuente Enrique Martín Miguel Ángel Pérez Jubindo Carmen Artal Blanca Ros José Luis Serrano 《Liquid crystals》2013,40(1):151-155
We present an achiral diacrylate that shows a phase transition from the synclinic smectic C phase (SmC) to the anticlinic smectic C (SmCalt). This last phase has been previously reported only for swallow-tailed or dimeric compounds. Our studies using differential scanning calorimetry, X-ray diffraction, polarizing optical microscopy and broad band dielectric spectroscopy suggest the existence of this mesophase in this bifunctional smectogen. 相似文献
32.
33.
Dr. Mónica Arrate Dr. Aritz Durana Dr. Paula Lorenzo Prof. Dr. Ángel R. de Lera Prof. Dr. Rosana Álvarez Dr. José M. Aurrecoechea 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13893-13900
Carbonyl‐tethered propargylic benzoates undergo intramolecular carbonylpropargylation upon treatment with Et2Zn in the presence of a catalytic amount of Pd0 with the formation of 2‐alkynylcyclopentanol products. A ligand/solvent effect on the cis/trans selectivity (referring to the relative positions of alkynyl and OH groups) of ring‐closure has been found. In a non‐coordinating solvent (benzene), increasing the electron‐donating ability of the phosphine ligand (while decreasing its dissociation ability) leads to an increased tendency towards the trans product. On the other hand, the combination of a coordinating solvent (THF) and PPh3, an easily dissociated phosphine, results in the exclusive formation of cis products. Experimental and computational results are compatible with a divergent behavior of an allenylethylpalladium intermediate that partitions between competitive carbonyl‐addition and transmetalation pathways, each leading to a different diastereoisomer. These results also suggest that the dissociating ability of the phosphine regulates that behavior. 相似文献
34.
Dr. Ángel J. Jiménez Michael Sekita Dr. Esmeralda Caballero Dr. M. Luisa Marcos Dr. M. Salomé Rodríguez‐Morgade Prof. Dr. Dirk M. Guldi Prof. Tomás Torres 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(43):14506-14514
In a novel electron‐donor–acceptor conjugate, phthalocyanine (Pc) and perylenediimide (PDI) are connected through a trans‐platinum(II) diacetylide linker to yield Pc‐Pt‐PDI 1 . In the ground state, the presence of PtII disrupts the electronic communication between the two electroactive components, as revealed by UV/Vis spectroscopy and electrochemical studies. The photophysical behavior of 1 is compared with that of the corresponding Pc‐PDI electron‐donor–acceptor conjugate 2 in terms of charge separation and charge recombination. The insertion of PtII between Pc and PDI impacts the results in a longer‐lived Pc . +/PDI . ? radical ion‐pair state. In addition, the intermediately formed Pc triplet excited state is formed with higher quantum yields in 1 than in 2 . 相似文献
35.
Determination of estrogens in environmental water samples using 1,3‐dipentylimidazolium hexafluorophosphate ionic liquid as extraction solvent in dispersive liquid–liquid microextraction 下载免费PDF全文
Bárbara Socas‐Rodríguez Javier Hernández‐Borges María Asensio‐Ramos Antonio V. Herrera‐Herrera Jose A. Palenzuela Miguel Ángel Rodríguez‐Delgado 《Electrophoresis》2014,35(17):2479-2487
In this work, the potential of a symmetric dialkyl‐substituted ionic liquid (IL), 1,3‐dipenthylimidazolium hexafluorophosphate ([PPIm][PF6]), as extraction solvent in dispersive liquid–liquid microextraction (DLLME) has been studied for the analysis of a group of three natural (estriol, 17β‐estradiol, and 17α‐estradiol) and four synthetic (17α‐ethynylestradiol, diethylstibestrol, dienestrol, and hexestrol) estrogenic compounds as well as one mycotoxin with estrogenic activity (zearalenone) in different types of water samples (Milli‐Q, mineral, and wastewater). Separation, determination, and quantification were developed by HPLC‐DAD and a fluorescence detector (FD) connected in series. Factors influencing the IL‐DLLME procedure (sample pH, amount of IL, type and volume of disperser solvent, ionic strength, and assistance of vortex agitation) were investigated and optimized by means of a step‐by‐step approach. Once the optimum extraction conditions were established (10 mL of water at pH 8, 60 mg of [PPIm][PF6], 500 μL of ACN as disperser solvent and vortex agitation for 1 min), the calibration curves of the whole method (IL‐DLLME‐HPLC‐DAD/FD) were obtained and precision and accuracy were evaluated. It was demonstrated that the developed methodology was repeatable, accurate, and selective with limits of detection in the 0.30–0.57 μg/L and 13.8–37.1 μg/L range for FD and DAD, respectively. Relative recovery values were higher than 85% for the different types of water samples and the Student's t test demonstrated that there were not significant differences between the added and the found concentration. 相似文献
36.
Determination of sulfonamides in milk samples by HPLC with amperometric detection using a glassy carbon electrode modified with multiwalled carbon nanotubes 下载免费PDF全文
A sensitive and accurate method for determining five sulfonamides based on HPLC with amperometric detection and using a glassy carbon electrode modified with multiwalled carbon nanotubes is proposed. Optimal conditions for the quantitative separation of selected sulfonamides were studied, and glassy carbon electrodes with and without modification with carbon nanotubes were systematically investigated as electrodic materials. Statistical analysis of the obtained results demonstrated that these modified electrodes achieved considerably better stability and sensitivity than the conventional unmodified ones. Detection limits were in the 1.2–6.0 ng/mL range. The usefulness of the method was demonstrated by the analysis of milk samples, taking into account the European legislation on residues in food products, following both a screening method to classify the samples and a confirmation method to provide more detailed information in the case of positive samples. 相似文献
37.
Nardana Sivendran Florian Belitz Daniel Sowa Prendes Dr. Ángel Manu Martínez Prof. Dr. Rochus Schmid Prof. Dr. Lukas J. Gooßen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202103669
Trihalide salts were found to efficiently promote photochemical dediazotizing halogenations of diazonium salts. In contrast to classical Sandmeyer reactions, no metal catalysts are required to achieve high yields and outstanding selectivities for halogenation over competing hydridodediazotization. Convenient protocols are disclosed for synthetically meaningful brominations, iodinations, and chlorinations of diversely functionalized derivatives. 相似文献
38.
Sánchez-Calderón Ismael Merillas Beatriz Bernardo Victoria Rodríguez-Pérez Miguel Ángel 《Journal of Thermal Analysis and Calorimetry》2022,147(22):12523-12533
Journal of Thermal Analysis and Calorimetry - Nowadays, developing advanced, highly insulating materials for minimizing heat losses in buildings is of utmost relevance. Thus, there is a constant... 相似文献
39.
Alejandra Medrano-Banda Dr. Alfonso Crespo-Yapur Dr. Miguel Ángel Velasco-Soto Dr. Marcelo Videa 《ChemistryOpen》2022,11(2):e202100241
The synthesis of hybrid platinum materials is fundamental to enable alkaline water electrolysis for cost-effective H2 generation. In this work, we have used a galvanostatic method to co-deposit PtNi films onto polycrystalline gold. The surface concentrations of Ni (ΓNi) and Pt (ΓPt) were calculated from electrochemical measurements; the ΓPt/ΓNi ratio and electrocatalytic activity of these materials towards hydrogen evolution reaction (HER) in 1 M KOH show a strong dependence on the current density pulse applied during the electrodeposition. Analysis of the Tafel parameters hints that, on these deposits, HER proceeds through a Volmer-Heyrovsky mechanism. The galvanostatically deposited PtNi layers present a high current output per Pt gram, 3199 A gPt−1, which is significantly larger compared to other PtNi-based materials obtained by more extended and more complex synthesis methods. 相似文献
40.
Felipe J. Llanes-Estrada Tim Van Cauteren Ángel P. Martín 《The European Physical Journal C - Particles and Fields》2007,51(4):945-952
We study the multiple solutions of the truncated propagator Dyson–Schwinger equation for a simple fermion theory with Yukawa
coupling to a scalar field. Upon increasing the coupling constant g, other parameters being fixed, more than one non-perturbative
solution breaking chiral symmetry becomes possible and we find these numerically. These “recurrences” appear as a mechanism
to generate different fermion generations as quanta of the same fundamental field in an interacting field theory, without
assuming any composite structure. The number of recurrences or flavors is reduced to the question of the value of the Yukawa
coupling, and it has no special profound significance in the standard model. The resulting mass function can have one or more
nodes and the measurement that potentially detects them can be thought of as a collider-based test of the virtual dispersion
relation for the charged lepton member of each family. This requires the three independent measurements of the charged lepton’s energy,
three-momentum and off-shellness. We illustrate how this can be achieved for the (more difficult) case of the tau lepton.
PACS 12.15.Ff; 11.30.Rd 相似文献