共查询到20条相似文献,搜索用时 15 毫秒
1.
Sophie C. Patrick Dr. Robert Hein Andrew Docker Prof. Paul D. Beer Prof. Jason J. Davis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(39):10201-10209
Sensing anionic species in competitive aqueous media is a well-recognised challenge to long-term applications across a multitude of fields. Herein, we report a comprehensive investigation of the electrochemical anion sensing performance of novel halogen bonding (XB) and hydrogen bonding (HB) bis-ferrocene-(iodo)triazole receptors in solution and at self-assembled monolayers (SAMs), in a range of increasingly competitive aqueous organic solvent media (ACN/H2O). In solution, the XB sensor notably outperforms the HB sensor, with substantial anion recognition induced cathodic voltammetric responses of the ferrocene/ferrocenium redox couple persisting even in highly competitive aqueous solvent media of 20 % water content. The response to halides, in particular, shows a markedly lower sensitivity to increasing water content associated with a unique halide selectivity at unprecedented levels of solvent polarity. The HB sensor, in contrast, generally displayed a preference towards oxoanions. A significant surface-enhancement effect was observed for both XB/HB receptive films in all solvent systems, whereby the HB sensor generally displayed larger responses towards oxoanions than its halogen bonding analogue. 相似文献
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Fezile Lakadamyali Dr. Anna Reynal Dr. Masaru Kato Prof. James R. Durrant Dr. Erwin Reisner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(48):15464-15475
A visible‐light driven H2 evolution system comprising of a RuII dye ( RuP ) and CoIII proton reduction catalysts ( CoP ) immobilised on TiO2 nanoparticles and mesoporous films is presented. The heterogeneous system evolves H2 efficiently during visible‐light irradiation in a pH‐neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self‐assembled system occurs at the ligand framework of CoP , which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H2 (mol CoP )?1 and above 200,000 mol H2 (mol TiO2 nanoparticles)?1 in water. Our studies support that a molecular Co species, rather than metallic Co or a Co‐oxide precipitate, is responsible for H2 formation on TiO2. Electron transfer in this system was studied by transient absorption spectroscopy and time‐correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO2 in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long‐lived TiO2 conduction band electron is formed with a half‐lifetime of approximately 0.8 s. Electron transfer from the TiO2 conduction band to the CoP catalysts occurs quantitatively on a 10 μs timescale and is about a hundred times faster than charge‐recombination with the oxidised RuP . This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors. 相似文献
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Dr. Samuel Dessources Dr. Claudia Morais Dr. Têko W. Napporn Prof. K. Boniface Kokoh 《Chemphyschem》2016,17(23):3964-3973
Hydrogen oxidation and evolution reactions (HOR and HER) are studied on PtxNi1?x/C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant‐free method enables the preparation of well‐dispersed and effective catalysts for the processes involved in the anode of H2/O2 fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt‐based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt‐based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j0) and kinetic current densities, and the rate‐determining steps of the reaction mechanisms are determined for each Pt–Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j0 values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials. 相似文献
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Suzanne M. Jansze Dr. Alfonso Martínez‐Felipe Prof. John M. D. Storey Dr. Antonius T. M. Marcelis Prof. Corrie T. Imrie 《Angewandte Chemie (International ed. in English)》2015,54(2):643-646
The liquid crystalline phase behavior of 4‐[6‐(4′‐cyanobiphenyl‐4‐yl)hexyloxy]benzoic acid (CB6OBA) and 4‐[5‐(4′‐cyanobiphenyl‐4‐yloxy)pentyloxy]benzoic acid (CBO5OBA) is described. Both acids show an enantiotropic nematic phase attributed to the formation of supramolecular complexes by hydrogen bonding between the benzoic acid units. In addition, CB6OBA provides the first example of hydrogen bonding driving the formation of the twist‐bend nematic phase. The observation of the twist‐bend nematic phase for CB6OBA, but not CBO5OBA, is attributed to the more bent molecular shape of the complexes formed by the former, reinforcing the view that shape is a key factor in stabilizing this new phase. Temperature‐dependent FTIR spectroscopy reveals differences in hydrogen bonding between the two nematic phases shown by CB6OBA which suggest that the open hydrogen‐bonded complexes may play an important role in stabilizing the helical arrangement found in the twist‐bend nematic phase. 相似文献
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Dr. Yue Wang Dr. Zhi Yu Dr. Wei Ji Yoshito Tanaka Huimin Sui Prof. Bing Zhao Prof. Yukihiro Ozaki 《Angewandte Chemie (International ed. in English)》2014,53(50):13866-13870
Efficient and generic enantioselective discrimination of various chiral alcohols is achieved by using surface‐enhanced Raman scattering (SERS) spectroscopy through charge–transfer (CT) contributions. The relative intensities of the peaks in the SERS spectra of a chiral selector are strongly dependent on the chirality of its surroundings. This highly distinct spectral discrepancy may be due to the tendency of chiral isomers to form intermolecular hydrogen‐bonding complexes with the chiral selector in different molecular orientations, resulting in different CT states and SERS intensities of the adsorbates in the system. This study opens a new avenue leading to the development of novel enantiosensing strategies. A particular advantage of this approach is that it is label‐free and does not employ any chiral reagents, including chiral light. 相似文献
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Pronay Kumar Biswas Abir Goswami Suchismita Saha Prof. Dr. Michael Schmittel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(62):14095-14099
The dynamics of hydrogen bonding do not only play an important role in many biochemical processes but also in Nature's multicomponent machines. Here, a three-component nanorotor is presented where both the self-assembly and rotational dynamics are guided by hydrogen bonding. In the rate-limiting step of the rotational exchange, two phenolic O-H–N,N(phenanthroline) hydrogen bonds are cleaved, a process that was followed by variable-temperature 1H NMR spectroscopy. Activation data (ΔG≠298=46.7 kJ mol−1 at 298 K, ΔH≠=55.3 kJ mol−1, and ΔS≠=28.8 J mol−1 K−1) were determined, furnishing a rotational exchange frequency of k298=40.0 kHz. Fully reversible disassembly/assembly of the nanorotor was achieved by addition of 5.0 equivalents of trifluoroacetic acid (TFA)/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) over three cycles. 相似文献
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Malcolm E. Tessensohn Melvyn Lee Prof. Dr. Hajime Hirao Prof. Dr. Richard D. Webster 《Chemphyschem》2015,16(1):160-168
Voltammetric experiments with 9,10‐anthraquinone and 1,4‐benzoquinone performed under controlled moisture conditions indicate that the hydrogen‐bond strengths of alcohols in aprotic organic solvents can be differentiated by the electrochemical parameter ΔEpred=|Epred(1)?Epred(2)|, which is the potential separation between the two one‐electron reduction processes. This electrochemical parameter is inversely related to the strength of the interactions and can be used to differentiate between primary, secondary, tertiary alcohols, and even diols, as it is sensitive to both their steric and electronic properties. The results are highly reproducible across two solvents with substantially different hydrogen‐bonding properties (CH3CN and CH2Cl2) and are supported by density functional theory calculations. This indicates that the numerous solvent–alcohol interactions are less significant than the quinone–alcohol hydrogen‐bonding interactions. The utility of ΔEpred was illustrated by comparisons between 1) 3,3,3‐trifluoro‐n‐propanol and 1,3‐difluoroisopropanol and 2) ethylene glycol and 2,2,2‐trifluoroethanol. 相似文献
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Propagation rate coefficients (kp) for 2‐hydroxyethyl acrylate (HEA) have been determined by pulsed‐laser polymerization (PLP) combined with size‐exclusion chromatography (SEC) between 20 and 60 °C using pulse repetition rates of 50 and 100 Hz. The success of PLP–SEC under these conditions suggests that HEA is not subjected to the intramolecular chain transfer to polymer (backbiting) reactions dominant for other acrylates; 13C NMR analysis shows that the quaternary carbon observed in PLP‐generated poly(butyl acrylate) (pBA) samples is not observed in pHEA. These results are related to H‐bonding in the system, as it is shown that the introduction of H‐bonding by addition of n‐butanol to BA suppresses backbiting, and the disruption of H‐bonding by addition of dimethylformamide to HEA leads to an increased level of backbiting.
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Dr. Stephan Hagspiel Dr. Felipe Fantuzzi Dr. Merle Arrowsmith Annalena Gärtner Maximilian Fest Jonas Weiser Prof. Dr. Bernd Engels Prof. Dr. Holger Helten Prof. Dr. Holger Braunschweig 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(49):e202201398
The reaction of a cyclic alkyl(amino)carbene (CAAC)-stabilized thiazaborolo[5,4-d]thiazaborole (TzbTzb) with strong Brønsted acids, such as HCl, HOTf (Tf=O2SCF3) and [H(OEt2)2][BArF4] (ArF=3,5-(CF3)2C6H3), results in the protonation of both TzbTzb nitrogen atoms. In each case X-ray crystallographic data show coordination of the counteranions (Cl−, OTf−, BArF4−) or solvent molecules (OEt2) to the doubly protonated fused heterocycle via hydrogen-bonding interactions, the strength of which strongly influences the 1H NMR shift of the NH protons, enabling tuning of both the visible (yellow to red) and fluorescence (green to red) colors of these salts. DFT calculations reveal that the hydrogen bonding of the counteranion or solvent to the protonated nitrogen centers affects the intramolecular TzbTzb-to-CAAC charge transfer character involved in the S0→S1 transition, ultimately enabling fine-tuning of their absorption and emission spectral features. 相似文献
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Dr. Zhen Yin Dr. Wu Zhou Yongjun Gao Prof. Dr. Ding Ma Prof. Dr. Christopher J. Kiely Prof. Dr. Xinhe Bao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(16):4887-4893
Monodisperse bimetallic Pd–Cu nanoparticles with controllable size and composition were synthesized by a one‐step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd and Cu precursors afforded nanoparticles with different compositions, such as Pd85–Cu15, Pd56–Cu44, and Pd39–Cu61. The nanoparticles were separated from the solution mixture by extraction with non‐polar solvents, such as n‐hexane. Monodisperse bimetallic Pd–Cu nanoparticles with narrow size‐distribution were obtained without the need for a size‐selection process. Capping ligands that were bound to the surface of the particles were removed through heat treatment when the as‐prepared nanoparticles were loaded onto a Vulcan XC‐72 carbon support. Supported bimetallic Pd–Cu nanoparticles showed enhanced electrocatalytic activity towards methanol oxidation compared with supported Pd nanoparticles that were fabricated according to the same EG method. For a bimetallic Pd–Cu catalyst that contained 15 % Cu, the activity was even comparable to the state‐of‐the‐art commercially available Pt/C catalysts. A STEM‐HAADF study indicated that the formation of random solid‐solution alloy structures in the bimetallic Pd85–Cu15/C catalysts played a key role in improving the electrochemical activity. 相似文献
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Zintl‐Phase Sr3LiAs2H: Crystal Structure and Chemical Bonding Analysis by the Electron Localizability Approach 下载免费PDF全文
Xian‐Juan Feng Yurii Prots Matej Bobnar Marcus Peter Schmidt Walter Schnelle Prof. Jing‐Tai Zhao Prof. Yuri Grin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14471-14477
The compound Sr3LiAs2H was synthesized by reaction of elemental strontium, lithium, and arsenic, as well as LiH as hydrogen source. The crystal structure was determined by single‐crystal X‐ray diffraction: space group Pnma; Pearson symbol oP28; a = 12.0340(7), b = 4.4698(2), c = 12.5907(5) Å; V = 677.2(1) Å3; RF = 0.047 for 1021 reflections and with 36 parameters refined. The positions of the hydrogen atoms were first revealed by the electron localizability indicator and subsequently confirmed by crystal structure refinement. In the crystal structure of Sr3LiAs2H the metal atoms are arranged in a Gd3NiSi2‐type motif, whereas the hydrogen atoms are arranged in a distorted tetrahedral environment formed by strontium. The calculated band structure revealed that Sr3LiAs2H is a semiconductor, which is in agreement with its diamagnetic behavior. Thus, Sr3LiAs2H is considered as a (charge‐balanced) Zintl phase. 相似文献
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In former investigations on hydrogen spillover through the gas phase the glass surface seemed to be important. Two methods were used here to test this: (a) filling the reaction zone with glass powder; (b) same with silanized glass. High conversion with normal and negligible ones with silanized glass provide clear proof for the above assumption. 相似文献
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Dr. Katharyn Fletcher Prof. Dr. Uwe H. F. Bunz Prof. Dr. Andreas Dreuw 《Chemphyschem》2016,17(17):2650-2653
We computed the mechanism of fluorescence quenching of benzaldehyde in water through relaxed potential energy surface scans. Time‐dependent density functional theory calculations along the protonation coordinate from water to benzaldehyde reveal that photoexcitation to the bright ππ* (S3) state is immediately followed by ultrafast decay to the nπ* (S1) state. Evolving along this state, benzaldehyde (BA) abstracts a hydrogen atom, resulting in a BAH. and OH. radical pair. Benzaldehyde does not act as photobase in water, but abstracts a hydrogen atom from a nearby solvent molecule. The system finally decays back to the ground state by non‐radiative decay and an electron transfers back to the OH. radical. Proton transfer from BAH+ to OH? restores the initial situation, BA in water. 相似文献
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Boer Liu Xi Chen Glenn A. Spiering Robert B. Moore Timothy E. Long 《Molecules (Basel, Switzerland)》2021,26(15)
This work reveals the influence of pendant hydrogen bonding strength and distribution on self-assembly and the resulting thermomechanical properties of A-AB-A triblock copolymers. Reversible addition-fragmentation chain transfer polymerization afforded a library of A-AB-A acrylic triblock copolymers, wherein the A unit contained cytosine acrylate (CyA) or post-functionalized ureido cytosine acrylate (UCyA) and the B unit consisted of n-butyl acrylate (nBA). Differential scanning calorimetry revealed two glass transition temperatures, suggesting microphase-separation in the A-AB-A triblock copolymers. Thermomechanical and morphological analysis revealed the effects of hydrogen bonding distribution and strength on the self-assembly and microphase-separated morphology. Dynamic mechanical analysis showed multiple tan delta (δ) transitions that correlated to chain relaxation and hydrogen bonding dissociation, further confirming the microphase-separated structure. In addition, UCyA triblock copolymers possessed an extended modulus plateau versus temperature compared to the CyA analogs due to the stronger association of quadruple hydrogen bonding. CyA triblock copolymers exhibited a cylindrical microphase-separated morphology according to small-angle X-ray scattering. In contrast, UCyA triblock copolymers lacked long-range ordering due to hydrogen bonding induced phase mixing. The incorporation of UCyA into the soft central block resulted in improved tensile strength, extensibility, and toughness compared to the AB random copolymer and A-B-A triblock copolymer comparisons. This study provides insight into the structure-property relationships of A-AB-A supramolecular triblock copolymers that result from tunable association strengths. 相似文献
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Elo Kibena Dr. Margus Marandi Dr. Uno Mäeorg Luna B. Venarusso Dr. Gilberto Maia Dr. Leonard Matisen Dr. Aarne Kasikov Prof. Väino Sammelselg Dr. Kaido Tammeveski 《Chemphyschem》2013,14(5):1043-1054
An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X‐ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi‐reversible voltammogram of the Fe(CN)63?/4? redox couple on bare Au and a sigmoidal shape for the GBC‐ and FBK‐modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)63?/4? response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)63?/4? redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge‐transfer rates to the Fe(CN)63? probe for the GBC‐ and FBK‐modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer. 相似文献