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991.
It is commonly believed that the exchange-only optimized effective potential (OEP) method must yield total energies that are above corresponding ground-state Hartree-Fock (HF) energies except for one- and two-electron systems. We present a simple procedure for constructing local (multiplicative) exchange potentials that reproduce exactly the HF energy and density in any finite basis set for any number of electrons. For any finite basis set, no matter how large, there exist infinitely many such OEPs, which questions their suitability for practical applications. 相似文献
992.
Saenz P Cachau RE Seoane G Kieninger M Ventura ON 《The journal of physical chemistry. A》2006,110(41):11734-11751
Several 1:1, 1:2, and 2:2 complexes between BF3 and CH3OH (Met), CH3COOH (AcA), (CH3)2O (DME), (CH3CH2)2O (DEE), and (CH2)2O (EOX) have been studied using ab initio (MP2) and density functional theory (DFT) (PBE, B3LYP) methods and the 6-311++G(3df,2pd) basis set. Geometrical structures and vibrational frequencies are reported, in most cases, for the first time. A detailed comparison of the vibrational frequencies for the O...BF3 vibrational modes, as well as for the nu(OH) band in the methanol and acetic acid complexes with BF3, is performed, and the theoretical frequency shifts are compared with the available experimental information. Thermochemical properties are calculated by employing counterpoise correction to alleviate the basis set superposition error. The DFT enthalpy of complexation of the 1:1 complexes results in the order of stability (AcA)2>AcA:BF3>DEE:BF3>DME:BF3>Met:BF3>EOX:BF3>(Met)2; in contrast, MP2 shows the noticeable difference that the AcA:BF3 complex is much less stable (similar to Met:BF3). The order of stability shows that, even though acetic acid prefers dimerization to complexation with BF3, the case is exactly the opposite for methanol. In both cases, the interaction of BF3 with the dimer gives rise to very stable trimers. However, in contrast to the interaction of BF3 with the methanol dimer being stronger than that with the monomer, the interaction of BF3 with the acetic acid dimer is weaker than that with the monomer. The relative strength of the complexes, discussed in the context of BF3-catalyzed ring opening of epoxides, suggests that the effect of the catalyst in a nonprotogenic solvent should be more properly ascribed to activation of the nucleophile instead of activation of the epoxide. 相似文献
993.
In this work, we demonstrate for the first time that 4-methyl-5-nitrocatechol (4M5NC) and 2,4,5-trihydroxytoluene (2,4,5-THT), two compounds obtained from the 2,4-DNT biodegradation are recognized by polyphenol oxidase as substrates. An amperometric biosensor is described for detecting these compounds and for evaluating the efficiency of the 2,4-DNT conversion into 4M5NC in the presence of bacteria able to produce the 2,4-DNT-biotransformation. The biosensor format involves the immobilization of polyphenol oxidase into a composite matrix made of glassy carbon microspheres and mineral oil. The biosensor demonstrated to be highly sensitive for the quantification of 4M5NC and 2,4,5-THT. The analytical parameters for 4M5NC are the following: sensitivity of (7.5 ± 0.1) × 105 nAM−1, linear range between 1.0 × 10−5 and 8.4 × 10−5 M, and detection limit of 4.7 × 10−6 M. The sensitivity for the determination of 2,4,5-THT is (6.2 ± 0.6) × 106 nAM−1, with a linear range between 1.0 × 10−6 and 5.8 × 10−6 M, and a detection limit of 2.0 × 10−7. Under the experimental conditions, it was possible to selectively quantify 4M5NC even in the presence of a large excess of 2,4-DNT. The suitability of the biosensor for detecting the efficiency of 2,4-DNT biotransformation into 4M5NC is demonstrated and compared with HPLC-spectrophotometric detection, with very good correlation. This biosensor holds great promise for decentralized environmental testing of 2,4-DNT. 相似文献
994.
A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF6) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25 V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48 × 10−6 to 4.95 × 10−5 mol L−1 with a detection limit of 9.15 × 10−7 mol L−1. The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%. 相似文献
995.
Gustavo Santiso‐Quiñones Dr. Alexander Higelin Julia Schaefer Robin Brückner Carsten Knapp Dr. Ingo Krossing Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(27):6663-6677
Naked copper…?? A newly developed simple two‐step route to weakly coordinated CuI starting materials that were used to prepare novel copper–cyclosulfur adducts, including the first M+–S12 complex (see figure, RF= C(CF3)3, C(CH3)(CF3)2, or CH(CF3)2). Reactions with the [Al{OC(CF3)3}4]? counterion mimic gas‐phase chemistry inside a mass spectrometer (to form [Cu(S12)]+).
996.
Let W and M be two finite dimensional subspaces of a Hilbert space H such that H=W⊕M⊥, and let PW‖M⊥ denote the oblique projection with range W and nullspace M⊥. In this article we get the following formula for the singular values of PW‖M⊥
997.
Gustavo M. do Nascimento Tilana B. Silva Paola Corio Mildred S. Dresselhaus 《Journal of Raman spectroscopy : JRS》2010,41(12):1587-1593
Highly dispersed nanocomposites of polyaniline(PANI) and oxidized single wall carbon nanotubes(SWNTs) have been prepared using dodecylbenzenesulfonic acid as dispersant. The materials were characterized via resonance Raman and electronic absorption spectroscopies. The behavior of the composites as a function of the applied potential was also investigated using in situ Raman electrochemical measurements. The results obtained at Elaser = 1.17 eV suggest that a charge‐transfer process occur between PANI and semiconducting nanotubes for samples where the metallic tubes are previously oxidized. The spectroelectrochemical data show that the presence of SWNTs prevents the oxidation of PANI rings. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
998.
Here we propose an experimental set-up in which it is possible to obtain the entanglement of a two-mode Gaussian state, be it pure or mixed, using only simple linear optical measurement devices. After a proper unitary manipulation of the two-mode Gaussian state only number and purity measurements of just one of the modes suffice to give us a complete and exact knowledge of the state’s entanglement. 相似文献
999.
1000.
Fernandes GE Guyot L Chern GD Kneissl M Johnson NM Song Q Xu L Chang RK 《Optics letters》2008,33(6):605-607
We demonstrate output wavelength and intensity switching in a three-element directly coupled microdisk device consisting of one spiral microdisk coupled to two semicircle microdisks. The gapless coupling mechanism used allows individual elements to achieve lasing while achieving optimal transfer of optical power between adjacent microdisks. By controlling the transparency of the center element via injection current, the edge elements can be allowed to exchange their amplified spontaneous emission. In this manner, on-off-on switching of the output intensity, as well as discontinuous shifts in the output wavelength, can be achieved as a function of increasing injection current. 相似文献