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911.
In recent years scanning near-field optical microscopy (SNOM) has developed into a powerful surface analytical technique for observing specimens with lateral resolution equal to or even better than 100 nm. A large number of applications, from material science to biology, have been reported. In this paper, two different kinds of near-field optical microscopy, aperture and scattering-type SNOM, are reviewed together with recent studies in surface analysis and biology. Here, near-field optical techniques are discussed in comparison with related methods, such as scanning probe and standard optical microscopy, with respect to their specific advantages and fields of application. 相似文献
912.
Grozema FC Best AS van Eijck L Stride J Kearley GJ de Leeuw SW Picken SJ 《The journal of physical chemistry. B》2005,109(16):7705-7712
Polyelectrolyte materials are an interesting class of electrolytes for use in fuel cell and battery applications. Poly(para-phenylene terephthalamide) (PPTA, Kevlar) is a liquid crystalline polymer that, when sulfonated, is a polyelectrolyte that exhibits moderate ion conductivity at elevated temperatures. In this work, quasi-elastic neutron scattering (QENS) experiments were performed to gain insight into the effect of the presence of lithium counterions on the chain dynamics in the material. It was found that the addition of lithium ions decreases the dynamics of the chains. Additionally, the binding of lithium ions to the sulfonic acids groups was investigated by density functional theory (DFT) calculations. It was found that the local surroundings of the sulfonic acid group have very little effect on the lithium-ion binding energy. Binding energies for a variety of different systems were all calculated to be around 150 kcal/mol. The DFT calculations also show the existence of a structure in which a single lithium ion interacts with two sulfonic acid moieties on different chains. The formation of such "electrostatic cross-links" is believed to be the source of the increased tendency to aggregate and the reduced dynamics in the presence of lithium ions. 相似文献
913.
Eva Martínez-Ahumada Mariana L. Díaz-Ramírez Miriam de J. Velsquez-Hernndez Vojtech Jancik Ilich A. Ibarra 《Chemical science》2021,12(20):6772
MOFs are promising candidates for the capture of toxic gases since their adsorption properties can be tuned as a function of the topology and chemical composition of the pores. Although the main drawback of MOFs is their vulnerability to these highly corrosive gases which can compromise their chemical stability, remarkable examples have demonstrated high chemical stability to SO2, H2S, NH3 and NOx. Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. Thus, the interactions of such functional groups (coordinatively unsaturated metal sites, μ-OH groups, defective sites and halogen groups) with these toxic molecules, not only determines the capture properties of MOFs, but also can provide a guideline for the desigh of new multi-functionalised MOF materials. Thus, this perspective aims to provide valuable information on the significant progress on this environmental-remediation field, which could inspire more investigators to provide more and novel research on such challenging task.MOFs are promising candidates for the capture of toxic gases such as SO2, H2S, NH3 and NOx. Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. 相似文献
914.
Castro J Pérez RA Miguel E Sánchez-Brunete C Tadeo JL 《Journal of chromatography. A》2002,947(1):119-127
Rapid analytical methods for the determination of endosulfan isomers and endosulfan-sulfate in air and plant samples were developed. The insecticides were trapped from air using a column containing Florisil and extracted with a low volume of ethyl acetate, assisted by sonication. Pesticide residues were determined by gas chromatography with electron-capture detection using a nonpolar capillary column. Residue identities were confirmed by gas chromatography coupled with mass spectrometry. Recoveries of these compounds from air samples were always higher than 78% with an RSD lower than 11% and the detection limits obtained were at least 0.3 ng/l air. Leaf samples were homogenised with ethyl acetate and extracts cleaned-up on an aluminium oxide column. Pesticides were eluted with a hexane-ethyl acetate (80:20, v/v) mixture. Recoveries obtained from plant samples were higher than 78% with an RSD lower than 14% and detection limits in leaves were 0.02 microg/g for each pesticide. These methods were applied to study the volatilisation of endosulfan from tomato leaves under laboratory conditions. A volatilisation rate near 1% of the initial amount of endosulfan per hour was obtained during the first 24 h at room temperature. 相似文献
915.
The use of a rapid and specific (cross-reactivity<4%) enzyme-linked immunosorbent assay (ELISA) for the determination of alachlor residues in water and vegetable samples is addressed. The analytical method consists of a fast extraction procedure followed by an optimised ELISA. The detection limit was 0.44 microg l(-1), with a linear range from 0.89 to 143.2 microg l(-1). For alachlor extraction from water samples, different solid-phase cartridges (C, Ph, C8 and C2) were assayed using MeOH as eluent. Extracts were diluted (1:4) with distilled water before ELISA. This procedure gave recoveries close to 100% with RSDs<14%. For vegetable samples, alachlor was extracted directly with MeOH and the extracts diluted 1:40 (v/v) with saline buffer prior to ELISA. The results obtained by the proposed procedure correlate well with the reference method (multiresidue extraction-GC-MS) for vegetable samples (r>0.85). 相似文献
916.
A search system is presented that utilizes Fourier domain data. This system removes dominating features from the infrared absorbance data, transforms the data into the Fourier domain and performs a complete library search. The actual matching algorithm is very simple and excellent search results were attained using 16 cm–1 resolution infrared absorbance spectra before transformation. This method can be used to distinguish very similar spectra that cannot be distinguished by many other search methods. 相似文献
917.
van de Waterbeemd H Smith DA Jones BC 《Journal of computer-aided molecular design》2001,15(3):273-286
Lipophilicity, often expressed as distribution coefficients (log D) in octanol/water, is an important physicochemical parameter influencing processes such as oral absorption, brain uptake and various pharmacokinetic (PK) properties. Increasing log D values increases oral absorption, plasma protein binding and volume of distribution. However, more lipophilic compounds also become more vulnerable to P450 metabolism, leading to higher clearance. Molecular size and hydrogen bonding capacity are two other properties often considered as important for membrane permeation and pharmacokinetics. Interrelationships among these physicochemical properties are discussed. Increasing size (molecular weight) often gives higher potency, but inevitably also leads to either higher lipophilicity, and hence poorer dissolution/solubility, or to more hydrogen bonding capacity, which limits oral absorption. Differences in optimal properties between gastrointestinal absorption and uptake into the brain are addressed. Special attention is given to the desired lipophilicity of CNS drugs. In examples using -blockers, Ca channel antagonists and peptidic renin inhibitors we will demonstrate how potency and pharmacokinetic properties need to be balanced. 相似文献
918.
Kanibolotsky A Roquet S Cariou M Leriche P Turrin CO de Bettignies R Caminade AM Majoral JP Khodorkovsky V Gorgues A 《Organic letters》2004,6(13):2109-2112
[structure: see text] In four new dendrimers terminated by 12 electroactive tetrathiafulvalenyl substituents, the tridimensional character of the inter- and intradendrimeric charge and electron transfer, and hence of the electroconductivity, is evidenced by examination of the electronic spectra of their corresponding neutral state and cation radical, dication, and mixed-valence salts, including a closed-shell anion. 相似文献
919.
Geciane Toniazzo Débora de Oliveira Cláudio Dariva Enrique Guillermo Oestreicher Octávio A. C. Antunes 《Applied biochemistry and biotechnology》2005,123(1-3):837-844
The main objective of this work was to investigate the biotransformations of (−)α-pinene, (−)β-pinene, and (+) limonene by
Aspergillus niger ATCC 9642. The culture conditions involved—concentration of cosolvent (EtOH), substrate applied, and sequential addition
of substrates—were investigated. Adaptation of the precultures with small amounts of substrate was also studied. The experiments
were performed in conical flasks with liquid cultures. This strain of A. niger was able to convert only (−)β-pinene into α-terpineol. An optimum conversion of (−)β-pinene into α-terpineol of about 4%
was obtained when the substrate was applied as a diluted solution in EtOH and sequential addition of substrate was used. 相似文献
920.
De Boer JL Ritsema R Piso S Van Staden H Van Den Beld W 《Analytical and bioanalytical chemistry》2004,379(5-6):872-880
Two screening methods were developed for rapid analysis of a great number of urine and blood samples within the framework of an exposure check of the population after a firework explosion. A total of 56 elements was measured including major elements. Sample preparation consisted of simple dilution. Extensive quality controls were applied including element addition and the use of certified reference materials. Relevant results at levels similar to those found in the literature were obtained for Co, Ni, Cu, Zn, Sr, Cd, Sn, Sb, Ba, Tl, and Pb in urine and for the same elements except Ni, Sn, Sb, and Ba in blood. However, quadrupole ICP–MS has limitations, mainly related to spectral interferences, for the analysis of urine and blood, and these cause higher detection limits. The general aspects discussed in the paper give it wider applicability than just for analysis of blood and urine—it can for example be used in environmental analysis. 相似文献