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Showing papers in "ChemInform in 2000"


Journal ArticleDOI
TL;DR: This paper presents a new approach to solvent-free organic synthesis called “Solvent-free synthesis with real-time stoichiometry” that combines high-performance liquid chromatography and high-tech electronics.
Abstract: Solvent-free organic synthesis , Solvent-free organic synthesis , کتابخانه دیجیتال جندی شاپور اهواز

1,004 citations



Journal ArticleDOI
TL;DR: The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established as mentioned in this paper.
Abstract: Flavonoids are phenolic substances isolated from a wide range of vascular plants, with over 8000 individual compounds known. They act in plants as antioxidants, antimicrobials, photoreceptors, visual attractors, feeding repellants, and for light screening. Many studies have suggested that flavonoids exhibit biological activities, including antiallergenic, antiviral, antiinflammatory, and vasodilating actions. However, most interest has been devoted to the antioxidant activity of flavonoids, which is due to their ability to reduce free radical formation and to scavenge free radicals. The capacity of flavonoids to act as antioxidants in vitro has been the subject of several studies in the past years, and important structure-activity relationships of the antioxidant activity have been established. The antioxidant efficacy of flavonoids in vivo is less documented, presumably because of the limited knowledge on their uptake in humans. Most ingested flavonoids are extensively degraded to various phenolic acids, some of which still possess a radical-scavenging ability. Both the absorbed flavonoids and their metabolites may display an in vivo antioxidant activity, which is evidenced experimentally by the increase of the plasma antioxidant status, the sparing effect on vitamin E of erythrocyte membranes and low-density lipoproteins, and the preservation of erythrocyte membrane polyunsaturated fatty acids. This review presents the current knowledge on structural aspects and in vitro antioxidant capacity of most common flavonoids as well as in vivo antioxidant activity and effects on endogenous antioxidants.

737 citations



Journal ArticleDOI
TL;DR: The femtosecond resolution (1 fs = 10^(−15) s) is the ultimate achievement for studies of the fundamental dynamics of the chemical bond as discussed by the authors, which is the wellspring of the field of femtochemistry.
Abstract: Over many millennia, humankind has thought to explore phenomena on an ever shorter time scale. In this race against time, femtosecond resolution (1 fs=10^(−15) s) is the ultimate achievement for studies of the fundamental dynamics of the chemical bond. Observation of the very act that brings about chemistry—the making and breaking of bonds on their actual time and length scales—is the wellspring of the field of femtochemistry, which is the study of molecular motions in the hitherto unobserved ephemeral transition states of physical, chemical, and biological changes. For molecular dynamics, achieving this atomic-scale resolution using ultrafast lasers as strobes is a triumph, just as X-ray and electron diffraction, and, more recently, STM and NMR spectroscopy, provided that resolution for static molecular structures. On the femtosecond time scale, matter wave packets (particle-type) can be created and their coherent evolution as a single-molecule trajectory can be observed. The field began with simple systems of a few atoms and has reached the realm of the very complex in isolated, mesoscopic, and condensed phases, as well as in biological systems such as proteins and DNA structures. It also offers new possibilities for the control of reactivity and for structural femtochemistry and femtobiology. This anthology gives an overview of the development of the field from a personal perspective, encompassing our research at Caltech and focusing on the evolution of techniques, concepts, and new discoveries.

333 citations


Journal ArticleDOI
Masahiro Irie1

238 citations


Book ChapterDOI
TL;DR: A review of several classes of organic compounds capable of multiple hydrogen-bond recognition is presented in this paper with a focus on the factors that contribute to complex stability, including the properties of the donor and acceptor groups.
Abstract: Hydrogen bonding is a directional and moderately strong intermolecular force. Compounds that present multiple hydrogen-bond donor and acceptor groups have proven to be extremely important in creating new self-assembled structures. A review of several classes of organic compounds capable of multiple hydrogen-bond recognition is presented with a focus on the factors that contribute to complex stability.

237 citations


Book ChapterDOI
TL;DR: In this article, it was shown that photosynthetic bicarbonate uptake in less supersaturated waters can lead to micrite precipitation within the sheath, which is restricted to species which prefer oligotrophic, phosphate-poor environments.
Abstract: Calcification in cyanobacteria depends on water chemistry as well as on physiological and morphological factors such as photosynthetic bicarbonate uptake and the existence of a suitable sheath. Physicochemical precipitation under high levels of supersaturation leads to the dense encrustation of the filaments, forming a solid micrite tube, while photosynthetic bicarbonate uptake in less supersaturated waters can lead to micrite precipitation within the sheath. Both forms of calcification are restricted to species which prefer oligotrophic, phosphate-poor environments. In this way, various environmental factors such as the saturation state of the water with respect to calcium carbonate minerals and the concentration of dissolved CO2 and phosphate may be reflected in the occurrence of fossil calcifying cyanobacteria.

194 citations


Journal ArticleDOI
TL;DR: In this article, the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence was explored and the properties of known magnetically ordered ferro-electric materials were examined.
Abstract: Multiferroic magnetoelectrics are materials that are both ferromagnetic and ferroelectric in the same phase. As a result, they have a spontaneous magnetization that can be switched by an applied magnetic field, a spontaneous polarization that can be switched by an applied electric field, and often some coupling between the two. Very few exist in nature or have been synthesized in the laboratory. In this paper, we explore the fundamental physics behind the scarcity of ferromagnetic ferroelectric coexistence. In addition, we examine the properties of some known magnetically ordered ferroelectric materials. We find that, in general, the transition metal d electrons, which are essential for magnetism, reduce the tendency for off-center ferroelectric distortion. Consequently, an additional electronic or structural driving force must be present for ferromagnetism and ferroelectricity to occur simultaneously.

189 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed study of the growth mechanism of WS2 nanotubes has been undertaken, which is reported hereby, and a series of experiments were conducted to define the key parameters, which determine the shape of the WS2 Nanotubes.
Abstract: Recently, a method to produce bulk quantities of pure multiwall WS2 nanotubes, which could reach several microns in length, has been developed. A detailed study of the growth mechanism of these WS2 nanotubes has been undertaken, which is reported hereby. A series of experiments were conducted to define the key parameters, which determine the shape of the WS2 nanotubes. An alternative approach for the synthesis of WS2 nanotubes, starting from long WO3-x nanowhiskers, which can be extended for the synthesis of other nanotubes, is described as well.

185 citations




Journal ArticleDOI
TL;DR: In this article, a lock-and-key approach is used to detect compounds in the presence of controlled backgrounds and interferences, which requires the synthesis of a separate, highly selective sensor for each analyte to be detected.
Abstract: Conventional approaches to chemical sensors have traditionally made use of a “lock-and-key” design, wherein a specific receptor is synthesized in order to strongly and highly selectively bind the analyte of interest.1-6 A related approach involves exploiting a general physicochemical effect selectively toward a single analyte, such as the use of the ionic effect in the construction of a pH electrode. In the first approach, selectivity is achieved through recognition of the analyte at the receptor site, and in the second, selectivity is achieved through the transduction process in which the method of detection dictates which species are sensed. Such approaches are appropriate when a specific target compound is to be identified in the presence of controlled backgrounds and interferences. However, this type of approach requires the synthesis of a separate, highly selective sensor for each analyte to be detected. In addition, this type of approach is not particularly useful for analyzing, classifying, or assigning human value judgments to the composition of complex vapor mixtures such as perfumes, beers, foods, mixtures of solvents, etc.

Journal ArticleDOI
TL;DR: In this article, the crystal structure of compounds with the general formula AB 2 X 4, which crystallize with the same atomic structure as the mineral spinel, MgAl 2 O 4, is reviewed.
Abstract: This paper reviews the crystal structure of compounds with the general formula AB 2 X 4 , which crystallize with the same atomic structure as the mineral spinel, MgAl 2 O 4 . Three degrees of freedom associated with the detailed atomic arrangements of spinels are considered here: (i) the lattice parameter, a; (ii) the anion parameter, u; and (iii) the cation inversion parameter, i. Oxide spinels are used as examples to explore the interrelationships between these parameters.


Journal ArticleDOI
TL;DR: In this article, a hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum.
Abstract: Masses of single-walled carbon nanotubes (SWNTs) with a large mean diameter of about 1.85 nanometers, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. A hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum. Moreover, 78.3 percent of the adsorbed hydrogen (3.3 weight percent) could be released under ambient pressure at room temperature, while the release of the residual stored hydrogen (0.9 weight percent) required some heating of the sample. Because the SWNTs can be easily produced and show reproducible and modestly high hydrogen uptake at room temperature, they show promise as an effective hydrogen storage material.

Journal ArticleDOI
TL;DR: In this article, the physical, chemical, electrochemical and mechanical properties of pure and doped ceria, predominantly in the temperature range from 200 to 1000°C, are investigated.
Abstract: This paper gives an extract of available data on the physical, chemical, electrochemical and mechanical properties of pure and doped ceria, predominantly in the temperature range from 200 to 1000°C. Several areas are pointed out where further research is needed in order to make a better basis for the evaluation of the real potential and limits for the practical application of ceria in solid oxide fuel cells and other solid state electrochemical devices.



Journal ArticleDOI
TL;DR: In this paper, a method for the synthesis of needle-shaped titanium oxide (TiO2) nanotubes was proposed. But the method was not suitable for the case of amorphous raw materials, and it required the use of distilled water and HCl aqueous solution.
Abstract: We report a new method for the synthesis of titanium oxide (TiO2) nanotubes. When anatase-phase- or rutile-phase-containing TiO2 was treated with an aqueous solution of 5–10 M NaOH for 20 h at 110 °C and then with HCl aqueous solution and distilled water, needle-shaped TiO2 products were obtained (diameter ≈ 8 nm, length ≈ 100 nm). The needle-shaped products are nanotubes with inner diameters of approximately 5 nm and outer diameters of approximately 8 nm. The formation mechanism of titania nanotubes is discussed in terms of the detailed observation of the products by transmission electron microscopy: the crystalline raw material is first converted to an amorphous product through alkali treatment, and subsequently, titania nanotubes are formed after treatment with distilled water and HCl aqueous solution.



Book ChapterDOI
TL;DR: In this paper, the EPR g-tensor of the Fe(II)-dioxygen adduct and the catalytic site in many mono-iron biomolecules has been analyzed.
Abstract: Iron-peroxo Fe(III)O2 and hydroperoxo Fe(III)OOH systems are important intermediates between the initial Fe(II)-dioxygen adduct and the “activated” form of the catalytic site in many mono-iron biomolecules. To the same peroxidic level correspond, in diiron enzymes, bridged peroxo Fe(III)-O-O-Fe(III) intermediates. This review is concerned with the preparation and spectroscopic characterization of such intermediates in non-heme chemical systems, the properties of the natural systems being quoted as references. Although none have been crystallized, it seems very likely that Fe(III)OOH systems present a η 1 - coordination mode for the hydroperoxo group. These Fe(III)OOH units have given clear signatures in UV-vis, resonance Raman and mass spectrometry. By EPR it was found that in Fe(III)OOH, the Fe(III) is low-spin (S = 1/2) and we propose here a simple rationalization of the characteristics of the EPR g-tensor. The electronic properties of the Fe(III)(η1-OOH) known so far, point toward a strong Fe-O bond and a weak O-O bond, in total agreement with the reactivity scheme implying a cleavage of the O-O bond to lead formally to a Fe(V)O unit. Alkylperoxo systems are also included in this review. Fe(III)-peroxo systems Fe(III)O2 have been prepared and described. They contain high-spin Fe(III) and those identified seem to be of the η 2 type. The Fe-O bond is weaker and the O-O one is stronger than in the Fe(III)OOH systems. The implication of these Fe(III)O2 units in catalysis is unclear. “Complementary” systems, such as Fe(III)(η 1-OO) or Fe(III)(η 2-OOH) have been evoked in publications but not identified spectroscopically. These systems certainly deserve to be actively looked for.

Journal ArticleDOI
TL;DR: In this article, the solution-and solid-phase synthesis of guanidines have been accomplished with a reagent called guanidine reagent, which is used in both solution and solid phase synthesis.
Abstract: ® chemists helping chemists in research and industry Both the solution-and solid-phase synthesis of guanidines have been accomplished with this reagent. 43,416-7

Book ChapterDOI
TL;DR: The most important progress made in the last ten years in the production of new electrophilic selenium reagents as well as in their reactivity towards unsaturated compounds are presented and discussed as discussed by the authors.
Abstract: The most important progress made in the last ten years in the production of new electrophilic selenium reagents as well as in their reactivity towards unsaturated compounds are presented and discussed Several new selenium-promoted, ring-closure reactions are illustrated and the factors controlling the selectivity of the cyclization process are discussed One-pot selenenylation-deselenenylation sequences, which occur using only catalytic amounts of the organoselenium reagents, are presented Finally, the efficient asymmetric syntheses, which are carried out with the recently described chiral non-racemic electrophilic selenenylating agents, are also surveyed



Journal ArticleDOI
TL;DR: In this paper, a review of applications of particulate biofilm reactors (e.g., upflow sludge blanket, Biofilm Fluidized Bed, Expanded Granular Sludge Blanket, biofilm Airlift Suspension, Internal Circulation Reactor) is presented.
Abstract: The review presented in this paper focuses on applications of particulate biofilm reactors (e.g. Upflow Sludge Blanket, Biofilm Fluidized Bed, Expanded Granular Sludge Blanket, Biofilm Airlift Suspension, Internal Circulation reactors). Several full-scale applications for municipal and industrial wastewater treatment are presented and illustrated, and their most important design and operation aspects (e.g. biofilm formation, hydrodynamics, mass transfer, mixing) are analysed and discussed. It is clear from the review that this technology can be considered a grown up technology for which good design and scale-up guidelines are available.