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1.
Importance of the Anchor Group Position (Para versus Meta) in Tetraphenylmethane Tripods: Synthesis and Self‐Assembly Features 下载免费PDF全文
Marcin Lindner Dr. Michal Valášek Jan Homberg Kevin Edelmann Dr. Lukas Gerhard Prof. Dr. Wulf Wulfhekel Dr. Olaf Fuhr Tobias Wächter Prof. Dr. Michael Zharnikov Dr. Viliam Kolivoška Dr. Lubomír Pospíšil Dr. Gábor Mészáros Dr. Magdaléna Hromadová Prof. Dr. Marcel Mayor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13218-13235
The efficient synthesis of tripodal platforms based on tetraphenylmethane with three acetyl‐protected thiol groups in either meta or para positions relative to the central sp3 carbon for deposition on Au (111) surfaces is reported. These platforms are intended to provide a vertical arrangement of the substituent in position 4 of the perpendicular phenyl ring and an electronic coupling to the gold substrate. The self‐assembly features of both derivatives are analyzed on Au (111) surfaces by low‐temperature ultra‐high‐vacuum STM, high‐resolution X‐ray photoelectron spectroscopy, near‐edge X‐ray absorption fine structure spectroscopy, and reductive voltammetric desorption studies. These experiments indicated that the meta derivative forms a well‐ordered monolayer, with most of the anchoring groups bound to the surface, whereas the para derivative forms a multilayer film with physically adsorbed adlayers on the chemisorbed para monolayer. Single‐molecule conductance values for both tripodal platforms are obtained through an STM break junction experiment. 相似文献
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3.
Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light 下载免费PDF全文
Dr. Jiale Wang Dr. Fabiane J. Trindade Caroline B. de Aquino Joana C. Pieretti Prof. Dr. Sergio H. Domingues Prof. Dr. Romulo A. Ando Prof. Dr. Pedro H. C. Camargo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(27):9889-9894
Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl4?(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O2 through the transfer of SPR‐excited hot electrons to O2 molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O2 molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O2 charge‐transfer process. 相似文献
4.
Kevin Kähler Marie Christine Holz Markus Rohe Dr. Jennifer Strunk Dr. Martin Muhler Prof. Dr. 《Chemphyschem》2010,11(12):2521-2529
The adsorption of methanol on pure ZnO and Au‐decorated ZnO nanoparticles and its thermal decomposition monitored by temperature‐programmed desorption (TPD) experiments and by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), both applied under continuous flow conditions in fixed bed reactors, is reported. Two distinguishable methoxy species are formed during methanol adsorption on ZnO differing in the C? O stretching bands. During the subsequent TPD experiments two different H2 peaks are observed, indicating the conversion of methoxy into formate species. By applying different heating rates, activation energies of 109 kJ mol?1 and 127 kJmol?1 for the selective oxidation of the two methoxy species are derived. Correspondingly, the methoxy decomposition results in two distinguishable formate species, which are identified by the asymmetric and symmetric OCO stretching bands on pure ZnO and Au/ZnO. Based on the decreased intensities of the OH bands during methanol adsorption, which are specific for the various ZnO single crystal surfaces, on the different reactivities of these surfaces, and on the formate FTIR bands observed on ZnO single crystal surfaces, the two methoxy and the corresponding formate species are identified to be adsorbed on the exposed less reactive non‐polar ZnO(${10\bar 10}$ ) surface and on the highly reactive polar ZnO(${000\bar 1}$ ) surface. The simultaneous formation of H2, CO, and CO2 at about 550–600 K during the TPD experiments indicate the decomposition of adsorbed formate species. The CO/CO2 ratio decreases with increasing Au loading, and a broad band due to electronic transitions from donor sites to the conduction band is observed in the DRIFT spectra for the Au‐decorated ZnO nanoparticles. Thus, the presence of the Au nanoparticles results in an enhanced reducibility of ZnO facilitating the generation of oxygen vacancies. 相似文献
5.
《Surface and interface analysis : SIA》2004,36(1):43-48
Structure of 4‐biphenylthiolate on Au nanoparticle surfaces has been studied by UV‐Vis absorption spectroscopy, transmission electron microscopy and surface‐enhanced Raman scattering (SERS). 4‐Biphenylthiolate is found to have a standing geometry on Au from the presence of the benzene ring CH stretching band identified at ~3060 cm?1. The ν8a band at 1597 cm?1 in the ordinary Raman spectrum was found to split clearly into two features at 1599 and 1585 cm?1. This result suggests that orientation of the phenyl rings in 4‐biphenylthiolate may be quite different and should not lie in the same plane on Au nanoparticle surfaces. On the basis of the electromagnetic enhancement factor, the dihedral angle could be estimated with a reported value of the tilt angle. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
6.
《Electrochemistry communications》2007,9(8):1892-1898
In the present study, the surface poisoning of electrocatalytic monosaccharide oxidation reactions at gold electrodes were investigated. In the cyclic voltammetric studies, the electrocatalytic oxidation of aldohexose and aldopentose type monosaccharides, aminosugars, acetyl-glucosamine and glucronamide were observed at gold plate electrodes in alkaline medium. However, in controlled-potential electrolytic studies ranging −0.3 to −0.2 V in reaction solutions, current flows during electrolyses decreased quickly with time, except when glucosamine was used as a substrate.Results from surface enhanced infrared adsorption (SEIRA) spectroscopic measurements at an evaporated gold electrode for the electrocatalytic oxidation of glucose in 0.1 mol dm−3 NaOH at −0.3 V and Gaussian simulated spectra indicated that the gluconic acid as a 2-electron oxidation product and/or its analogs adsorbed onto the gold surface. Electrochemical quartz crystal microbalance (EQCM) measurement results, along with surface adsorption results from surface poisoning at the gold electrode during electrolytic reactions, suggested that gluconic acid and/or its analogs adsorbed vertically onto electrode surfaces in a full monolayer packing-like conformation. In the case of the electro oxidation of glucosamine in 0.1 mol dm−3 NaOH at −0.2 V, the obtained SEIRA spectra and EQCM results, clearly indicated that the glucosaminic acid as a 2-oxidation glucosamine product did not strongly bind onto the gold electrode surface. 相似文献
7.
1,2‐Diaminobenzene, popularly known as ortho‐phenylenediamine (PDA), is found to be a prototype spacer for the deposition of gold nanoparticles on the surfaces of Fe3O4 microspheres. Upon carbonization with PDA, the morphology of the product changes significantly, and the resulting nanocomposites exhibit enhanced magnetism beyond the saturation value of Fe3O4. The Fe3O4/Au nanocomposites show good surface‐enhanced Raman spectroscopy activity with a detection limit of 10?15 M . 相似文献
8.
The adsorption characteristics of 1,3‐benzenedithiol (1,3‐BDT) and 1,3‐benzenedimethanethiol (1,3‐BDMT) on Au surfaces are investigated by means of surface‐enhanced Raman scattering, UV/Vis absorption spectroscopy, and cyclic voltammetry (CV). 1,3‐BDMT is found to adsorb via two S–Au linkages at concentrations below monolayer coverage, but to have an upright geometry as the concentration increases on Au nanoparticles. On the other hand, 1,3‐BDT is found to adsorb by forming two S–Au linkages, regardless of concentration, based on the disappearance of the ν(SH)free stretching band. Because of the absence of the methylene unit, 1,3‐BDT appeares not to self‐assemble efficiently on Au surfaces. The UV/Vis absorption spectroscopy and CV techniques are also applied to check the formation of self‐assembled monolayers of 1,3‐BDT and 1,3‐BDMT on Au. Density functional theory calculations based on a simple adsorption model using an Au8 cluster are performed to better understand the nature of the adsorption characteristics of 1,3‐BDT and 1,3‐BDMT on Au surfaces. 相似文献
9.
The conformational changes of cyclohexyl acetylene (CHAL) on gold nanoparticle surfaces were investigated by means of concentration- and temperature-dependent surface-enhanced Raman scattering (SERS). Depending on concentrations and temperatures, the spectral changes of the acetylene ν(C≡C) stretching vibration on gold nanoparticles appeared to be more conspicuous than those of cyclohexyl ring modes. The density functional theory (DFT) calculation was performed at the level of B3LYP/6-31G++(d,p) to compare the energetic stability and vibrational frequencies of the various conformers of cyclohexanethiol (CHT) and CHAL. The DFT calculations were also carried out at the level of B3LYP/LACVP** on the CHAL molecule adsorbed on Au clusters at several sites to explain the spectral changes of the acetylene ν(C≡C) stretching vibration. 相似文献
10.
Bechir Mrabet Aymen Mejbri Samia Mahouche Sarra Gam‐Derouich Mireille Turmine Mourad Mechouet Philippe Lang Hilaire Bakala Moncef Ladjimi Amina Bakhrouf Sven Tougaard Mohamed M. Chehimi 《Surface and interface analysis : SIA》2011,43(11):1436-1443
Poly(oligoethylene glycol methacrylate), POEGMA, brushes were prepared by surface‐initiated atom transfer radical polymerization (SI‐ATRP) on gold‐coated silicon wafers. Prior to ATRP, the substrates were grafted by brominated aryl initiators via the electrochemical reduction of a noncommercial parent diazonium salt of the formula BF4?, +N2‐C6H4‐CH(CH3)Br. The diazonium‐modified gold plates (Au‐Br) served as macroinitiators for ATRP of OEGMA which resulted in hydrophilic surfaces (Au‐POEGMA) that could be used for two distinct objectives: (i) resistance to fouling by Salmonella Typhimurium; (ii) specific recognition of the same bacteria provided that the POEGMA grafts are activated by anti‐Salmonella. The Au‐POEGMA plates were characterized by XPS, polarization modulation‐infrared reflection‐absorption spectroscopy (PM‐IRRAS) and contact angle measurements. Both Beer‐Lambert equation and Tougaard's QUASES software indicated a POEGMA thickness that exceeds the critical ~10 nm value necessary for obtaining a hydrophilic polymer with effective resistance to cell adhesion. The Au‐POEGMA slides were further activated by trichlorotriazine (TCT) in order to covalently bind anti‐Salmonella antibodies (AS). The antibody‐modified Au‐POEGMA specimens were found to specifically attach Salmonella Typhimurium bacteria. This work is another example of the diazonium salt/ATRP process to provide biomedical polymer surfaces. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
11.
Photoresponsive Switches at Surfaces Based on Supramolecular Functionalization with Azobenzene–Oligoglycerol Conjugates 下载免费PDF全文
Olaf Nachtigall Dr. Christian Kördel Leonhard H. Urner Prof. Dr. Rainer Haag 《Angewandte Chemie (International ed. in English)》2014,53(36):9669-9673
The synthesis, supramolecular complexation, and switching of new bifunctional azobenzene–oligoglycerol conjugates in different environments is reported. Through the formation of host–guest complexes with surface immobilized β‐cyclodextrin receptors, the bifunctional switches were coupled to gold surfaces. The isomerization of the amphiphilic azobenzene derivatives was examined in solution, on gold nanoparticles, and on planar gold surfaces. The wettability of functionalized gold surfaces can be reversibly switched under light‐illumination with two different wavelengths. Besides the photoisomerization processes and concomitant effects on functionality, the thermal cis to trans isomerization of the conjugates and their complexes was monitored. Thermal half‐lives of the cis isomers were calculated for different environments. Surprisingly, the half‐lives on gold nanoparticles were significantly smaller compared to planar gold surfaces. 相似文献
12.
The oxidative and reductive electrochemistry of the three isomeric nitroanilines has been studied in neutral (0.1 mol L−1 KClO4) and acidic (0.1 mol L−1 HClO4) aqueous electrolyte solutions by cyclic voltammetry and surface enhanced Raman spectroscopy (SERS). The cyclic voltammograms
recorded for o- and p-nitroanilines with a gold electrode in acidic solution, scanning toward negative potentials, revealed formation of phenylenediamine
not observed in neutral solution. Similar behavior of nitroanilines and phenylenediamines was observed on gold and platinum
electrodes. An oxygen–gold adsorbate stretching mode was detected between 400 and 430 cm−1 in the SER-spectra of the three isomeric nitroanilines in both electrolyte solutions at positive electrode potentials, implying
perpendicular adsorption via the nitro group. 相似文献
13.
《Electrochemistry communications》2002,4(12):973-977
Electroless (or chemical) deposition technique has been used in preparing Au island film electrodes on Si for in situ infrared spectroscopic studies of the electrochemical interface in attenuated total reflection mode. Owing to surface-enhanced infrared absorption (SEIRA) effect, absorption bands of molecules adsorbed on the chemically deposited films were one order of magnitude as large as those observed on smooth Au electrode surfaces. Although the enhancement factor was identical to that observed on vacuum evaporated Au island films, this simple method is superior to vacuum evaporation method with respect to the adhesion of the film, surface contamination, reproducibility, and cost. 相似文献
14.
DMABR (5-(4-Dimethylaminobenzylidene)-rhodanine) is proved to be a very selective reagent for gold as it impregnated on XAD-4. Gold is selectively adsorbed on resin through the formation of Au(I)-DMABR. Distribution coefficients at different pH were determined. The selectivity and interference were studied. Less than 0.1 ppb of Au could be adsorbed on resin. It can be directly determined by NAA or cluted down with cyanide solution and determined by AAS. 相似文献
15.
An overview is presented on the application of surface-enhanced infrared absorption (SEIRA) spectroscopy to biochemical problems.
Use of SEIRA results in high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders
of magnitude and has the potential to enable new studies, from fundamental aspects to applied sciences. This report surveys
studies of DNA and nucleic acid adsorption to gold surfaces, development of immunoassays, electron transfer between metal
electrodes and proteins, and protein–protein interactions. Because signal enhancement in SEIRA uses surface properties of
the nano-structured metal, the biomaterial must be tethered to the metal without hampering its functionality. Because many
biochemical reactions proceed vectorially, their functionality depends on proper orientation of the biomaterial. Thus, surface-modification
techniques are addressed that enable control of the proper orientation of proteins on the metal surface.
Figure Surface enhanced infrared absorption spectroscopy (SEIRAS) on the studies of tethered protein monolayer (cytochrome c oxidase
and cytochrome c) on gold substrate (left), and its potential induced surface enhanced infrared difference absorption (SEIDA)
spectrum 相似文献
16.
《Electroanalysis》2006,18(11):1105-1113
We report for the first time the effective catalytic electrooxidation of nicotinamide adenine dinucleotide (NADH) on the pencil 8B‐scrawled gold electrode of an electrochemical quartz crystal microbalance (EQCM). The EQCM allowed us to quantitatively evaluate the catalytic activity of the pencil‐scrawled Au electrode. With increasing the mass of modified pencil powders, the peak potential for NADH oxidation shifted negatively, with maximum shift of ?0.35 V at saturated pencil modification; the NADH‐oxidation peak current density (jp) was also notably increased, and the jp at saturated pencil modification was found to be larger than those at conventional pencil 8B and bare Au electrodes. Sensitive amperometric detection of NADH was achieved at the gold electrode with saturated pencil modification, with low detection potential (0.4 V versus SCE), low detection limit (0.08 μmol L?1) and wide linear range (0.2–710 μmol L?1). The fluoroelectrochemical measurements of NADH at bare and pencil‐modified gold electrodes were also conducted with satisfactory results. The convenient and low‐cost modification of pencil powders on the Au electrode may have presented a new functional surface of the EQCM, which is recommended for wider applications to bioelectrochemical studies, especially in view of the EQCM's capability of providing abundant in situ information in relevant processes. 相似文献
17.
Pillar[5]arene‐Mediated Synthesis of Gold Nanoparticles: Size Control and Sensing Capabilities 下载免费PDF全文
Borja Gómez Dr. Ignacio Pérez‐Juste Prof. Luis García‐Río Prof. Luis M. Liz‐Marzán Dr. Jorge Pérez‐Juste Dr. Isabel Pastoriza‐Santos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8404-8409
We present a simple procedure for the synthesis of quasi‐spherical Au nanoparticles in a wide size range mediated by macrocyclic host molecules, ammonium pillar[5]arene (AP[5]A). The strategy is based on a seeded growth process in which the water‐soluble pillar[5]arene undergoes complexation of the Au salt through the ammonium groups, thereby avoiding Au nucleation, while acting as a stabilizer. The presence of the pillar[5]arene onto the Au nanoparticle particle surface is demonstrated by surface‐enhanced Raman scattering (SERS) spectroscopy, and the most probable conformation of the molecule when adsorbed on the Au nanoparticles surface is suggested on the basis of theoretical calculations. In addition, we analyze the host–guest interactions of the AP[5]A with 2‐naphthoic acid (2NA) by using 1H NMR spectroscopy and the results are compared with theoretical calculations. Finally, the promising synergetic effects of combining supramolecular chemistry and metal nanoparticles are demonstrated through SERS detection in water of 2NA and a polycyclic aromatic hydrocarbon, pyrene (PYR). 相似文献
18.
Binding property and structure of aromatic isocyanide self‐assembly monolayers on Ag and Au surfaces
《Surface and interface analysis : SIA》2005,37(3):294-299
The binding property of p‐biphenyl isocyanide self‐assembled monolayers (SAMs) on Au and Ag was investigated by temperature‐dependent surface‐enhanced Raman spectroscopy (SERS). p‐Biphenyl isocyanide was found to desorb on Ag at a low temperature of ~393 K whereas it appeared to remain enduring at a high temperature of ~453 K for Au. Structures of p‐biphenyl isocyanide SAMs on Au and Ag flat films were checked by means of near‐edge x‐ray absorption fine structure spectroscopy (NEXAFS) at the two different normal (90° ) and grazing (20° ) angles of the incident x‐ray beam. Our results suggested that the SAMs prepared by p‐biphenyl isocyanide should have a relatively disordered structure even at room temperature on both Au and Ag, as indicated from an insubstantial change in NEXAFS spectra at the two different angles from those of p‐biphenyl thiolate and p‐biphenyl methanethiolate. The weakness of the isocyanide–metal bond in comparison with the sulphur–metal bond may result in both low surface coverage and orientational disorder. A density functional theory calculation method was employed to attempt to explain the difference in stability for phenyl isocyanide on Ag and Au surfaces. Our calculation result yielded a lower binding energy of phenyl isocyanide on Ag than that on Au, consistent with the temperature‐dependent Raman results. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
19.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2018,130(6):1539-1543
Nanoparticulate gold supported on a Keggin‐type polyoxometalate (POM), Cs4[α‐SiW12O40]⋅n H2O, was prepared by the sol immobilization method. The size of the gold nanoparticles (NPs) was approximately 2 nm, which was almost the same as the size of the gold colloid precursor. Deposition of gold NPs smaller than 2 nm onto POM (Au/POM) was essential for a high catalytic activity for CO oxidation. The temperature for 50 % CO conversion was −67 °C. The catalyst showed extremely high stability for at least one month at 0 °C with full conversion. The catalytic activity and the reaction mechanism drastically changed at temperatures higher than 40 °C, showing a unique behavior called a U‐shaped curve. It was revealed by IR measurement that Auδ+ was a CO adsorption site and that adsorbed water promoted CO oxidation for the Au/POM catalyst. This is the first report on CO oxidation utilizing Au/POMs catalysts, and there is a potential for expansion to various gas‐phase reactions. 相似文献
20.
The mechanism of the gold nanocluster‐catalyzed aerobic homocoupling of arylboronic acids has been elucidated by means of DFT calculations with Au20? as a model cluster for the Au:[poly(N‐vinylpyrrolidin‐2‐one)] catalyst. We found that oxygen affects the adsorption of phenylboronic acid and, by lowering the energy barrier, a water molecule enhances dissociation of the C?B bond, which is probably the rate‐determining step. The key role of oxygen is in activating the surface of the gold cluster by generating Lewis acidic sites for adsorption and activation of the phenylboronic acid, leading to the formation of biphenyl through a superoxo‐like species. Moreover, the oxygen adsorbed on the Au nanocluster can act as an oxidant for phenylboronic acid, giving phenol as a byproduct. As shown by NBO analysis, the basic aqueous reaction medium facilitates the reductive elimination process by weakening the Au?C bond, thereby enhancing the formation of biphenyl. The coupling of phenyl and reductive elimination of biphenyl occur at the top or facet site with low‐energy‐barrier through spillover of phenyl group on Au NC. The present findings are useful for the interpretation or design of other coupling reactions with Au NC. 相似文献