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91.
Carbon nanotubes are a kind of new carbon-based nanomaterials, which have drawn great attention in many application fields. The potential of single-walled carbon nanotubes (SWCNTs) as solid-phase microextraction (SPME) adsorbent for the preconcentration of environmental pollutants has been investigated in recent years. In the present study, the feasibility of SWCNTs as SPME adsorbent for the determination of monobutyltin, dibutyltin and tributyltin in seawater samples was studied. To achieve this aim, the potential factors affecting the SPME efficiency, including extraction time, extraction temperature, desorption time, desorption temperature, and salinity were optimized. The developed method showed good performance according to the ICH (International Conference on Harmonization of Technical Requirements for Analytical Methods) criteria. The acquired calibration curves were linear (r ≥ 0.992) over the concentration range from ≤12 to 2000 ng L−1. For all of the analytes, the limit of detection at signal-to-noise ratio of 3 was below 5 ng L−1. Furthermore, in comparison with the commercial carboxen/polydimethylsiloxane fiber, the developed SWCNT fiber showed better thermal stability (over 350 °C) and longer life span (over 150 times). The application of the proposed method in environmental analyses was shown by analyzing seawater samples from the harbors on the Persian Gulf for butyltin residues. Some of the butyltins were detected in the analyzed samples. Results of the present study demonstrate the feasibility of the SWCNTs as SPME adsorbent for the determination of butyltins in seawater samples. 相似文献
92.
Fidelity and Mutual Entropy in Mixed States for Fermi-resonance Coupling Vibrations of CS2 下载免费PDF全文
states of Fermi-resonance coupling vibrations in molecule CS2. It is demonstrated that those fidelities are dominant-positively correlated with each other, one of which by Wang et al. (Phys. Lett. A 373, 58 (2008)) is the most striking in dominant anti-correlation with quantum mutual entropy. That is useful for molecular quantum computing and quantum information. 相似文献
93.
Tomislav P. ivkovi 《Journal of mathematical chemistry》2009,45(4):1060-1101
Mathematical formalism of the Low Rank Perturbation method (LRP) is applied to the vibrational isotope effect in the harmonic
approximation with a standard assumption that force field does not change under isotopic substitutions. A pair of two n-atom isotopic molecules A and B which are identical except for isotopic substitutions at ρ atomic sites is considered. In the LRP approach vibrational frequencies ω
k
and normal modes of the isotopomer B are expressed in terms of the vibrational frequencies ν
i
and normal modes of the parent molecule A. In those relations complete specification of the normal modes is not required. Only amplitudes at sites τ affected by the isotopic substitutions and in the coordinate direction s (s = x, y, z) are needed. Out-of-plane vibrations of the (H,D)-benzene isotopomers are considered. Standard error of the LRP frequencies
with respect to the DFT frequencies is on average . This error is due to the uncertainty of the input data (± 0.5 cm−1) and in the absence of those uncertainties and in the harmonic approximation it should disappear. In comparing with experiment,
one finds that LRP frequencies reproduces experimental frequencies of (H,D)-benzene isotopomers better () than scaled DFT frequencies () which are designed to minimize (by frequency scaling technique) this error. In addition, LRP is conceptually and numerically
simple and it also provides a new insight in the vibrational isotope effect in the harmonic approximation. 相似文献
94.
95.
Michael Schleeger Christoph Wagner Michiel J. Vellekoop Bernhard Lendl Joachim Heberle 《Analytical and bioanalytical chemistry》2009,394(7):1869-1877
Fourier-transform infrared (FT-IR) difference spectroscopy has been proven to be a significant tool in biospectroscopy. In
particular, the step-scan technique monitors structural and electronic changes at time resolutions down to a few nanoseconds
retaining the multiplex advantage of FT-IR. For the elucidation of the functional mechanisms of proteins, this technique is
currently limited to repetitive systems undergoing a rapid photocycle. To overcome this obstacle, we developed a flow-flash
experiment in a miniaturised flow channel which was integrated into a step-scan FT-IR spectroscopic setup. As a proof of principle,
we studied the rebinding reaction of CO to myoglobin after photodissociation. The use of microfluidics reduced the sample
consumption drastically such that a typical step-scan experiment takes only a few 10 ml of a millimolar sample solution, making
this method particularly interesting for the investigation of biological samples that are only available in small quantities.
Moreover, the flow cell provides the unique opportunity to assess the reaction mechanism of proteins that cycle slowly or
react irreversibly. We infer that this novel approach will help in the elucidation of molecular reactions as complex as those
of vectorial ion transfer in membrane proteins. The potential application to the oxygen splitting reaction of cytochrome c
oxidase is discussed.
An erratum to this article can be found at 相似文献
96.
The multireference configuration interaction (MRCI) electronic energy calculations with different basis sets have been performed on the ground state (X1Σ) and three low-lying excited states (3Σ, 1Π and 3Π) of HgCd dimer. The obtained potential energy curves (PECs) are fit to analytical potential energy functions (APEFs) using the Murrell–Sorbie potential function. Spectroscopic constants are calculated using the APEFs. Based on the PECs, the vibrational levels of each state are predicted. Our equilibrium positions of the X1Σ state and 3Π state are in excellent agreement with the experimental reports. 相似文献
97.
Shamsipur M Dastjerdi LS Haghgoo S Armspach D Matt D Aboul-Enein HY 《Analytica chimica acta》2007,601(1):130-138
19F NMR spectroscopy was applied to the quantitative determination of fluoxetine enantiomers using different chiral recognition agents in pharmaceutical formulations. Several parameters affecting the enantioresolution including the type and concentration of chiral selector, concentration of fluoxetine and temperature were studied. The chiral selectors investigated are the cyclic oligosaccharides α-, β- and γ-cyclodextrin and a diamino derivative of methylated α-cyclodextrin (DAM-α-CD), linear polysaccharides (maltodextrin with dextrose equivalents of 4.0-7.0, 13.0-17.0 and 16.5-19.5) and the macrocyclic antibiotic vancomycin. Among the chiral selectors used, DAM-α-CD turned out to give the best resolution of the 19F NMR signals of (R)- and (S)-fluoxetine. The calibration curve was linear for (R)- and (S)-fluoxetine over the range 0.10-1.35 mg mL−1, the detection limits (S/N = 3) being 5.9 and 7.5 μg mL−1 for the pure solutions of (R)- and (S)-fluoxetine, respectively. The recovery studies performed on pharmaceutical samples ranged from about 90 to 110% with relative standard deviations of <8%. The results showed that the proposed method is rapid, precise and accurate. Applying statistical Student's t-test revealed insignificant difference between the real and measured contents at the 95% confidence level. 相似文献
98.
Ab initio calculations using the MP2/cc-pVTZ basis set do an excellent job of predicting the inversion barrier (247 vs. 232 cm−1) and dihedral angle (26°) of cyclopentene. DFT calculations also do an excellent job of predicting the vibrational frequencies of the d0, d1, d4, and d8 isotopomers. They have also allowed the reassignments of several of the vibrational frequencies. 相似文献
99.
It is well known that water plays a fundamental role for living beings, because the nature of water transformations provides for the ability to preserve biostructures. Solute can be classified as “kosmotropes” or “chaotropes” depending on the interaction strength with water. In the case of solutes destroying the natural hydrogen bonded network of water, called “kosmotropes” or “structure-makers”, the denaturation processes can be inhibited.
The aim of this work is to investigate the vibrational behaviour of maltose/H2O mixtures in order to characterise the changes induced by the sugar on the H2O hydrogen-bonded network. The obtained findings point out that maltose has a destructuring effect on the water tetrahedral network and emphasise its kosmotrope character. 相似文献
100.
Anant D. Kulkarni Dhurba Rai Libero J. Bartolotti Rajeev K. Pathak 《Journal of Molecular Structure》2007,824(1-3):32-38
Methyl hydrogen peroxide (MHP) exhibits a tendency to form a stable dimer by hydrogen-bonding. Ab initio theoretical investigations on methyl hydrogen peroxide dimer (MHPD) carried out herein lead to several energetically stable structures that have a direct bearing on the reactivity of the monomer in terms of its molecular electrostatic potential (MESP). To gauge the role played by the electron-correlation in lending stability to MHP and its dimer, we employ the density functional theory (DFT) (as implemented by B3LYP-functional), and subsequently second order Møller-Plesset (MP2) perturbation theory, using the basis sets 6-31G(d, p) and 6-311++G(2d, 2p). Simulated infra-red vibrational spectra lead to spectral intensity redistribution upon dimerization. Energetically the lowest MHPD is endowed with inversion symmetry and has two hydrogen bonds, while three other structures emerge: one energetically very close with two H-bonds, and the two others, with three H-bonds each, yet higher by about 2 kcal mol−1. 相似文献