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1.
Weber JM Ioffe IN Berndt KM Löffler D Friedrich J Ehrler OT Danell AS Parks JH Kappes MM 《Journal of the American Chemical Society》2004,126(27):8585-8589
Ultraviolet photoelectron spectroscopy in an ion beam was used to investigate the electronic properties of isolated DNA oligonucleotides [dA(5)-4H](4-) and [dT(5)-4H](4-), carrying four excess negative charges. We find the fourth adiabatic electron affinity to be slightly negative for [dA(5)-4H](4-), while it is positive for [dT(5)-4H](4-). This implies a significant influence of the base composition on energetics, which is in turn relevant for analytic applications and also for charge transport properties. 相似文献
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We report laser photoelectron spectra of the doubly negatively charged fullerenes C(76) (2-), C(78) (2-), and C(84) (2-) at 2.33, 3.49, and 4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment energies, as well as estimates for the repulsive Coulomb barriers are obtained. These results are discussed in the context of electrostatic models. They reveal that fullerenes are similar to conducting spheres, with electronic properties scaling with their size. The experimental spectra are compared with the accessible excited states of the respective singly charged product ions calculated in the framework of time dependent density functional theory. 相似文献
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Ehrler OT Yang JP Sugiharto AB Unterreiner AN Kappes MM 《The Journal of chemical physics》2007,127(18):184301
Femtosecond time-resolved pump-probe photoelectron spectroscopy was used to study elementary relaxation processes occurring in isolated phthalocyanine-tetrasulfonate tetra-anions ([MPc(SO3)4]4-, M=Cu,Ni, and "free-base" [H2Pc(SO3)4]4-) following Q band excitation by one-photon absorption at 775 nm. Whereas the Cu and Ni systems decay rapidly by means of internal conversion without electron loss, the free-base phthalocyanine primarily undergoes excited state tunneling electron emission. This reflects less efficient coupling to lower lying states within the corresponding spin manifold. Results are interpreted in terms of (time-dependent) density functional theory calculations of ground and electronically excited states and kinetically modeled to yield the associated rates. 相似文献
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Note on Biotransformations with Halobacterium halobium: Reduction of Ethyl 3-Oxobutanoate and Hydrolysis of Ethyl 3-Hydroxybutanoate. Cooperative Effects of Reductase and Hydrolase The archaebacterium Halobacterium halobium, growing in saturated NaCl solution, is tested for its ability to achieve biotransformations. We found that this microorganism does accept only a small variety of compounds as substrates. Ethyl acetoacetate ( 1 ) is reduced to ethyl (S)-3-hydroxybutanoate ( 2 ) of optical purity of 40–76%, but in low chemical yields. The reduction is accompanied by hydrolysis of the hydroxy-ester to 3-hydroxybutanoic acid ( 3 ). Hydrolysis of rac-ester 2 by Halobacterium halobium gives (R)- 2 of optical purity of up to 88%, depending upon reaction time, together with the almost racemic hydroxy-acid 3 , both in low chemical yields. Hopes that the ‘extremist’ Halobacterium halobium would be able to effect unique conversions were not fulfilled. 相似文献
5.
Ehrler OT Griffin GB Young RM Neumark DM 《The journal of physical chemistry. B》2009,113(13):4031-4037
We have used ultrafast time-resolved photoelectron imaging to measure charge transfer dynamics in iodide-doped acetonitrile clusters I(-)(CH(3)CN)(n) with n = 5-10. Strong modulations of vertical detachment energies were observed following charge transfer from the halide, allowing interpretation of the ongoing dynamics. We observe a sharp drop in the vertical detachment energy (VDE) within 300-400 fs, followed by a biexponential increase that is complete by approximately 10 ps. Comparison to theory suggests that the iodide is internally solvated and that photodetachment results in formation of a diffuse electron cloud in a confined cavity. We interpret the initial drop in VDE as a combination of expansion of the cavity and localization of the excess electron on one or two solvent molecules. The subsequent increase in VDE is attributed to a combination of the I atom leaving the cavity and rearrangement of the acetonitrile molecules to solvate the electron. The n = 5-8 clusters then show a drop in VDE of around 50 meV on a much longer time scale. The long-time VDEs are consistent with those of (CH(3)CN)(n)(-) clusters with internally solvated electrons. Although the excited-state created by the pump pulse decays by emission of a slow electron, no such decay is seen by 200 ps. 相似文献
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We report the laser photoelectron spectra of doubly negatively charged C84 (D2 and D(2d)) using 532 nm and 355 nm radiation. From these spectra, values for the second electron affinity and vertical detachment energy, as well as upper and lower limits for the repulsive Coulomb barrier, are obtained. These values are discussed in the context of classical electrostatic models. The experimental spectra are compared with the accessible excited states of the C-84 product ion calculated in the framework of time dependent density functional theory. 相似文献
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Vonderach M Ehrler OT Matheis K Weis P Kappes MM 《Journal of the American Chemical Society》2012,134(18):7830-7841
Fractionation according to ion mobility and mass-to-charge ratio has been used to select individual isomers of deprotonated DNA oligonucleotide multianions for subsequent isomer-resolved photoelectron spectroscopy (PES) in the gas phase. Isomer-resolved PE spectra have been recorded for tetranucleotides, pentanucleotides, and hexanucleotides. These were studied primarily in their highest accessible negative charge states (3-, 4-, and 5-, respectively), as provided by electrospraying from room temperature solutions. In particular, the PE spectra obtained for pentanucleotide tetraanions show evidence for two coexisting classes of gas-phase isomeric structures. We suggest that these two classes comprise: (i) species with excess electrons localized exclusively at deprotonated phosphate backbone sites and (ii) species with at least one deprotonated base (in addition to several deprotonated phosphates). By permuting the sequence of bases in various [A(5-x)T(x)](4-) and [GT(4)](4-) pentanucleotides, we have established that the second type of isomer is most likely to occur if the deprotonated base is located at the first or last position in the sequence. We have used a combination of molecular mechanics and semiempirical calculations together with a simple electrostatic model to explore the photodetachment mechanism underlying our photoelectron spectra. Comparison of predicted to measured photoelectron spectra suggests that a significant fraction of the detected electrons originates from the DNA bases (both deprotonated and neutral). 相似文献
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Three HECs with a high MS (HEC 1: 1.89, HEC 2: 1.94, HEC 3: 3.03) were analyzed with respect to their substituent distribution and tandem reaction in the glucosyl unit by GLC of the corresponding glucitol acetates, and along the polymer chain by MALDI-ToF-MS after a multi-step sample preparation. For comparison of the experimental data with a random pattern an extended Bernoulli plot was applied to calculate a random distribution for the composition of un-, mono-, di-, tri-, and up to heptasubstituted glucosyl units (c0, c1, c2, ... c7). 相似文献