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81.
82.
A simple semi-empirical approximation for the exchange energy (Ex), coupled with a tractable representation of the Coulomb energy (EC), has been found to yield very accurate results for the isotropic part of the interaction energy (Eint = Ex + EC) between two closed shell systems. The expression for Eint is based on the knowledge of the first order Coulomb energy and the first three terms in the asymptotic long range expansion of the second order Coulomb energy for the interaction and contains but one adjustable parameter which occurs in Ex. The usefulness of this approach for evaluating Eint is tested critically by using the non-bonded H(1s)H(1s) (3Σu+) interaction as a model (accurate values of the total interaction energy, the exchange energy, and various orders of Coulomb energies, are available for a wide range of R for this system). The results obtained for both Eint and (dEint/dR) are inremarkable agreement with the exact results of Kotos and Wolniewicz for R > 3 ao. Since the law of corresponding states for inert gas pairs holds equally well for the HH(3Σu+) interaction, our analysis of this simple system yields valuable information on the reliability of the approach for other van der Waals dimers. 相似文献
83.
Molecular diodes based on conjugated diblock co-oligomers 总被引:2,自引:0,他引:2
This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system. This system consists of two conjugated blocks with opposite electronic demand. The molecular structure exhibits a built-in electronic asymmetry, much like a semiconductor p-n junction. Electrical measurements by scanning tunneling spectroscopy (STS) clearly revealed a pronounced rectifying effect. Definitive proof for the molecular nature of the rectifying effect in this conjugated diblock molecule is provided by control experiments with a structurally similar reference compound. 相似文献
84.
Jacob J. Habeeb Farouq F. Said Dennis G. Tuck 《Journal of organometallic chemistry》1980,190(4):325-334
The electrochemical oxidation of indium metal in cells of the type
leads to the formation of RInX2 compounds; if 2,2′-bipyridine is also present, the products are the adducts RInX2·bipy (R = CH3, C2H5, C6H5, C6H5CH2, C6F5; X = Cl, Br, I (not all combinations)). When R′4NX is present instead of bipy, the products are the salts R′4N[RInX3]. The electrochemical oxidation apparently proceeds via the general mechanism discussed previously. Anomalous results with CH3I or C2H5I are discussed in the light of the known solution chemistry of organoindium(III) compounds. 相似文献
85.
Xi Xing Beth Reed Mi Kyung Bahng Peng Wang Hin Koo Woo Sun Jong Baek Chee Shing Lam Cheuk Yiu Ng¤ 《化学物理学报(中文版)》2008,21(3):193-201
We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X=Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed. 相似文献
86.
Sophorolipids are well-known glycolipid biosurfactants, produced mainly by non-pathogenic yeast species such as Candida bombicola with high yield. Its unique environmental compatibility and high biodegradable properties have made them a focus in the present review for their promising applications in diverse areas. This study aims to examine current research trends of sophorolipids and evaluate their applications in food and health. A literature search was conducted using different research databases including PubMed, ScienceDirect, EBSCOhost, and Wiley Online Library to identify studies on the fundamental mechanisms of sophorolipids and their applications in food and health. Studies have shown that various structural forms of sophorolipids exhibit different biological and physicochemical properties. Sophorolipids represent one of the most attractive biosurfactants in the industry due to their antimicrobial action against both Gram-positive and Gram-negative microorganisms for applications in food and health sectors. In this review, we have provided an overview on the fundamental properties of sophorolipids and detailed analysis of their applications in diverse areas such as food, agriculture, pharmaceutical, cosmetic, anticancer, and antimicrobial activities. 相似文献
87.
Chang-Tong Yang Pei Ing Ngam Vanessa Jing Xin Phua Sidney Wing Kwong Yu Gogna Apoorva David Chee Eng Ng Hian Liang Huang 《Molecules (Basel, Switzerland)》2022,27(21)
Yttrium-90 (90Y) microspheres are widely used for the treatment of liver-dominant malignant tumors. They are infused via catheter into the hepatic artery branches supplying the tumor under fluoroscopic guidance based on pre-therapy angiography and Technetium-99m macroaggregated albumin (99mTc-MAA) planning. However, at present, these microspheres are suspended in radiolucent media such as dextrose 5% (D5) solution. In order to monitor the real-time implantation of the microspheres into the tumor, the 90Y microspheres could be suspended in omnipaque contrast for allowing visualization of the correct distribution of the microspheres into the tumor. The radiochemical purity of mixing 90Y-microspheres in various concentrations of omnipaque was investigated. The radiochemical purity and feasibility of mixing 99mTc-MAA with various concentrations of a standard contrast agent were also investigated. Results showed the radiochemical feasibility of mixing 90Y-microspheres with omnipaque is radiochemically acceptable for allowing real-time visualization of radioembolization under fluoroscopy. 相似文献
88.
In this paper,we are interested in HSS preconditioners for saddle point lin- ear systems with a nonzero(2,2)-th block.We study an approximation of the spectra of HSS preconditioned matrices and use these results to illustrate and explain the spectra obtained from numerical examples,where the previous spectral analysis of HSS precon- ditioned matrices does not cover. 相似文献
89.
Kuan-Chieh Ching Elaine J. Chin Mario Wibowo Zann Y. Tan Lay-Kien Yang Deborah C. Seow Chung-Yan Leong Veronica W. Ng Siew-Bee Ng Yoganathan Kanagasundaram 《Molecules (Basel, Switzerland)》2023,28(1)
Thiopeptides are macrocyclic natural products with potent bioactivity. Nine new natural thiopeptides (1–9) were obtained from a Nonomuraea jiangxiensis isolated from a terrestrial soil sample collected in Singapore. Even though some of these compounds were previously synthesized or isolated from engineered strains, herein we report the unprecedented isolation of these thiopeptides from a native Nonomuraea jiangxiensis. A comparison with the literature and a detailed analysis of the NMR and HRMS of compounds 1–9 was conducted to assign their chemical structures. The structures of all new compounds were highly related to the thiopeptide antibiotics GE2270, with variations in the substituents on the thiazole and amino acid moieties. Thiopeptides 1–9 exhibited a potent antimicrobial activity against the Gram-positive bacteria, Staphylococcus aureus with MIC90 values ranging from 2 µM to 11 µM. In addition, all compounds were investigated for their cytotoxicity against the human cancer cell line A549, none of the compounds were cytotoxic. 相似文献
90.
Silvio Curia Feifei Ng Marie-Emrentienne Cagnon Victor Nicoulin Adolfo Lopez-Noriega 《Molecules (Basel, Switzerland)》2021,26(5)
This article presents the evaluation of diblock and triblock poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate) amphiphilic copolymers (PEG-PTMCs) as excipients for the formulation of long-acting injectables (LAIs). Copolymers were successfully synthesised through bulk ring-opening polymerisation. The concomitant formation of PTMC homopolymer could not be avoided irrespective of the catalyst amount, but the by-product could easily be removed by gel chromatography. Pure PEG-PTMCs undergo faster erosion in vivo than their corresponding homopolymer. Furthermore, these copolymers show outstanding stability compared to their polyester analogues when formulated with amine-containing reactive drugs, which makes them particularly suitable as LAIs for the sustained release of drugs susceptible to acylation. 相似文献