排序方式: 共有70条查询结果,搜索用时 0 毫秒
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León I Montero R Castaño F Longarte A Fernández JA 《The journal of physical chemistry. A》2012,116(25):6798-6803
Mass-resolved excitation spectroscopic techniques are usually limited to systems with a chromophore, that is, a functional group with electronic transitions in the Vis/UV, with lifetimes from hundreds of picoseconds to some microseconds. In this paper, we expand such techniques to any system, by using a combination of nanosecond IR pulses with nonresonant ionization with 800 nm femtosecond laser pulses. Furthermore, we demonstrate that the technique can achieve conformational specificity introducing an additional nanosecond IR laser. As a proof-of-principle, we apply the technique to the study of phenol(H(2)O)(1), propofol(H(2)O)(1) γ-butyrolactone(H(2)O)(n), n = 1-3, and (H(2)O)(2) complexes. While monohydrated phenol and propofol clusters permit a direct comparison with a well-studied system including an aromatic chromophore, γ-butyrolactone is a cyclic nonaromatic molecule, whose mass-resolved spectroscopy cannot be tackled by conventional techniques. Finally, we further demonstrate the potential of the technique by obtaining the first mass-resolved IR spectrum of the neutral water dimer, a nice example of a system whose ionization-based detection had not been possible to date. 相似文献
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León I Millán J Cocinero EJ Lesarri A Castaño F Fernández JA 《Physical chemistry chemical physics : PCCP》2012,14(25):8956-8963
Propofol is a general anaesthetic that exerts its action by interaction with the GABA(A) receptor. Crystallographic studies suggest that there is a direct interaction between propofol and the phenolic residue of a tyrosine in the channel. In this study we create propofol···phenol clusters by their co-expansion in jets. The complex is probed using a set of mass-resolved spectroscopic strategies: 2-color REMPI, UV/UV hole-burning, IR/UV double resonance and the novel technique IR/IR/UV triple resonance. The existence of at least six different isomers in the expansion is demonstrated. All the isomers are stabilized by interactions between their aromatic rings. Additionally, in some conformers the OH moieties form hydrogen bonds in some of the isomers, with propofol and phenol alternating their donor-acceptor roles, while in others the -OH···OH angle points to a dipole-dipole interaction. Interpretation of the data in the light of dispersion-corrected DFT calculations shows that shallow barriers separate all the isomers, both in the ground and excited electronic states. Comparison of the structures of the complex with the X-ray diffraction data is also offered. 相似文献
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The movement of a few large diameter spheres immersed in a granular medium composed of smaller beads in a rotating cylinder is studied. We evidence attractions and repulsions between the large spheres depending on the rotation frequency. The large spheres also show relative position fluctuations which are Gaussian. A complete study of this problem sheds new light on the problem of size segregation in granular materials and points to the importance of fluctuation-induced interactions. 相似文献
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Iker Montes-Burgos Dorota Walczyk Patrick Hole Jonathan Smith Iseult Lynch Kenneth Dawson 《Journal of nanoparticle research》2010,12(1):47-53
Before commencing any nanotoxicological study, it is imperative to know the state of the nanoparticles to be used and in particular
their size and size distribution in the appropriate test media is particularly important. Particles satisfying standards can
be commercially purchased; however, these invariably cannot be used directly and need to be dispersed into the relevant biological
media. Often such changes in the environment or ionic strength, or a change in the particle concentration, results in some
aggregation or a shift in the particle size distribution. Such unexpected aggregation, dissolution or plating out, if unaccounted
for, can have a significant effect on the available nanoparticle dose and on interpretation of any results obtained thereafter.
Here, we demonstrate the application of characterisation instrumentation that sizes nanoparticles based on their Brownian
motion in suspension. Unlike classical light-scattering techniques, the nanoparticle tracking and analysis (NTA) technique
allows nanoparticles to be sized in suspension on a particle-by-particle basis allowing higher resolution and therefore better understanding of aggregation than ensemble methods (such as dynamic
light scattering (DLS) and differential centrifugation sedimentation (DCS)). Results will be presented from gold (standard)
nanoparticles in biologically relevant media that emphasise the importance of characterisation of the nanoparticle dispersion.
It will be shown how the NTA technique can be extended to multi-parameter analysis, allowing for characterization of particle
size and light scattering intensity on an individual basis. This multi-parameter measurement capability allows sub-populations
of nanoparticles with varying characteristics to be resolved in a complex mixture. Changes in one or more of such properties
can be followed both in real time and in situ. 相似文献
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Runhai Chen Guorui Qin Shihui Li Alison J. Edwards Ross O. Piltz Iker Del Rosal Laurent Maron Dongmei Cui Jianhua Cheng 《Angewandte Chemie (International ed. in English)》2020,59(28):11250-11255
Hydrogenolysis of alkyl‐substituted cyclopentadienyl (CpR) ligated thorium tribenzyl complexes [(CpR)Th(p‐CH2‐C6H4‐Me)3] ( 1 – 6 ) afforded the first examples of molecular thorium trihydrido complexes [(CpR)Th(μ‐H)3]n (CpR=C5H2(tBu)3 or C5H2(SiMe3)3, n=5; C5Me4SiMe3, n=6; C5Me5, n=7; C5Me4H, n=8; 7 – 10 and 12 ) and [(Cp#)12Th13H40] (Cp#=C5H4SiMe3; 13 ). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra‐nuclear octahydrido thorium dibenzylidene complex [(Cpttt)Th(μ‐H)2]4(μ‐p‐CH‐C6H4‐Me)2 (Cpttt=C5H2(tBu)3) ( 11 ) was also isolated. All of the complexes were characterized by NMR spectroscopy and single‐crystal X‐ray analysis. Hydride positions in [(CpMe4)Th(μ‐H)3]8 (CpMe4=C5Me4H) were further precisely confirmed by single‐crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12 . 相似文献
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PMLABe Diol Synthesized by Ring‐Opening Polymerization of Racemic Benzyl β‐Malolactonate Initiated by Rare‐Earth Trisborohydride Complexes: An Experimental and DFT Study 下载免费PDF全文
Iker del Rosal Teddy Mevel Prof. Dr. Peter W. Roesky Prof. Dr. Laurent Maron Dr. Sophie M. Guillaume 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14387-14402
Polymer diols are a class of polymeric building blocks of high interest for the synthesis of complex macromolecular edifices. Rare‐earth borohydride complexes are known as efficient initiators for the ring‐opening polymerization (ROP) of cyclic esters, directly affording α,ω‐dihydroxy‐telechelic polyesters. Here, were report the direct synthesis of poly(benzyl β‐malolactonate) (PMLABe) diols, from the ROP of racemic (benzyl β‐malolactonate) (rac‐MLABe), a valuable and renewable monomer, initiated by the homoleptic [Ln(BH4)3(thf)3] (Ln=La, Nd, and Sm) complexes. These initiators enabled the controlled ROP of this β‐lactone, affording well‐defined syndiotactic‐enriched (Pr≈0.83) PMLABes (Mn up to 21 300 g mol?1, ÐM≈1.5) as evidenced by size exclusion chromatography, 1H and 13C NMR spectroscopy, and MALDI‐ToF mass spectrometry analyses. The first and second insertions of rac‐MLABe, as assessed by DFT calculations, revealed more favorable stationary front‐side than migratory back‐side insertions, the thermodynamically and kinetically competitive ROP on two distinct arms with that on a one arm‐only, and the thermodynamically slightly favored formation of syndiotactic‐enriched PMLABes. 相似文献
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Dr. Pelin Sözen‐Aktaş Dr. Iker Del Rosal Dr. Eric Manoury Prof. Funda Demirhan Prof. Agustí Lledós Prof. Rinaldo Poli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):3969-3985
The speciation of compounds [Cp*2M2O5] (M=Mo, W; Cp*=pentamethylcyclopentadienyl) in different protic and aprotic polar solvents (methanol, dimethyl sulfoxide, acetone, acetonitrile), in the presence of variable amounts of water or acid/base, has been investigated by 1H NMR spectrometry and electrical conductivity. Specific hypotheses suggested by the experimental results have been further probed by DFT calculations. The solvent (S)‐assisted ionic dissociation to generate [Cp*MO2(S)]+ and [Cp*MO3]? takes place extensively for both metals only in water/methanol mixtures. Equilibrium amounts of the neutral hydroxido species [Cp*MO2(OH)] are generated in the presence of water, with the relative amount increasing in the order MeCN≈acetone<MeOH<DMSO. Addition of a base (Et3N) converts [Cp*2M2O5] into [Et3NH]+[Cp*MO3]?, for which the presence of a N? H???O?M interaction is revealed by 1H NMR spectroscopy in comparison with the sodium salts, Na+[Cp*MO3]?. These are fully dissociated in DMSO and MeOH, but display a slow equilibrium between free ions and the ion pair in MeCN and acetone. Only one resonance is observed for mixtures of [Cp*MO3]? and [Cp*MO2(OH)] because of a rapid self‐exchange. In the presence of extensive ionic dissociation, only one resonance is observed for mixtures of the cationic [Cp*MO2(S)]+ product and the residual undissociated [Cp*2M2O5] because of a rapid associative exchange via the trinuclear [Cp*3M3O7]+ intermediate. In neat methanol, complex [Cp*2W2O5] reacts to yield extensive amounts of a new species, formulated as the mononuclear methoxido complex [Cp*WO2(OMe)] on the basis of the DFT study. An equivalent product is not observed for the Mo system. The addition of increasing amounts of water results in the rapid decrease of this product in favor of [Cp*2W2O5] and [Cp*WO2(OH)]. 相似文献
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Heteronuclear NMR Spectroscopy as Surface‐Selective Technique: A Unique Look at the Hydroxyl Groups of γ‐Alumina 下载免费PDF全文
Dr. Mostafa Taoufik Dr. Kai C. Szeto Dr. Nicolas Merle Dr. Iker Del Rosal Dr. Laurent Maron Dr. Julien Trébosc Dr. Grégory Tricot Dr. Régis M. Gauvin Dr. Laurent Delevoye 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3856-3856
Invited for the cover of this issue are the groups of Régis M. Gauvin at the Université Lille Nord de France, Laurent Maron from the Université de Toulouse, and Mostafa Taoufik from the Université Lyon 1. The image depicts data on the topology of the surface hydroxyl groups of γ‐alumina as a postcard. Read the full text of the article at 10.1002/chem.2013004883. 相似文献