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101.
102.
The high-pressure iron borate α-FeB2O4 was synthesized under high-pressure and high-temperature conditions in a Walker-type multianvil apparatus at 7.5 GPa and 1100 °C. The monoclinic iron borate crystallizes with eight formula units in the space group P21/c with the lattice parameters a=715.2(2), b=744.5(2), c=862.3(2) pm, and β=94.71(3)°. The compound is built up exclusively from corner-sharing BO4-tetrahedra, isotypic to the monoclinic phases β-SrGa2O4, CaAl2O4-II, and CaGa2O4. Additionally, the structure is closely related to the orthorhombic compound BaFe2O4. The structure consists of layers of six-membered rings, which are interconnected to a three-dimensional network. The iron cations are coordinated by six and seven oxygen atoms. Next to synthesis and crystal structure of the new high-pressure borate, structural coherences to other structure types are discussed. 相似文献
103.
Mechanochemical Synthesis of 3d Transition‐Metal–1,2,4‐Triazole Complexes as Precursors for Microwave‐Assisted and Thermal Conversion to Coordination Polymers with a High Influence on the Dielectric Properties
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Franziska A. Brede Dr. Johanna Heine Prof. Dr. Gerhard Sextl Prof. Dr. Klaus Müller‐Buschbaum 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(8):2708-2718
The complexes [MCl2(TzH)4] (M=Mn ( 1 ), Fe ( 2 ); TzH=1,2,4‐1H‐triazole) and [ZnCl2(TzH)2] ( 3 ) have been obtained by mechanochemical reactions of the corresponding divalent metal chloride and 1,2,4‐1H‐triazole. They were successfully used as precursors for the formation of coordination polymers either by a microwave‐assisted reaction or by thermal conversion. For manganese, the conversion directly yielded [MnCl2TzH] ( 4 ), whereas for the iron‐containing precursor, [FeCl2TzH] ( 6 ), was formed via the intermediate coordination polymer [FeCl(TzH)2]Cl ( 5 ). For cobalt, the isotypic polymer [CoCl(TzH)2]Cl ( 7 ) was obtained, but exclusively by a microwave‐induced reaction directly from CoCl2. The crystal structures were resolved from single crystals and powders. The dielectric properties were determined and revealed large differences in permittivity between the precursor complexes and the rigid chain‐like coordination polymers. Whereas the monomeric complexes exhibit very different dielectric behaviour, depending on the transition metal, from “low‐k” to “high‐k” with the permittivity ranging from 4.3 to >100 for frequencies of up to 1000 Hz, the coordination polymers and complexes with strong intermolecular interactions are all close to “low‐k” materials with very low dielectric constants up to 50 °C. Therefore, the conversion procedures can be used to deliberately influence the dielectric properties from complex to polymer and for different 3d transition‐metal ions. 相似文献
104.
105.
Andrews KW Schweitzer A Zhao C Holden JM Roseland JM Brandt M Dwyer JT Picciano MF Saldanha LG Fisher KD Yetley E Betz JM Douglass L 《Analytical and bioanalytical chemistry》2007,389(1):231-239
As part of a study initiating the development of an analytically validated Dietary Supplement Ingredient Database (DSID) in
the United States (US), a selection of dietary supplement products were analyzed for their caffeine content. Products sold
as tablets, caplets, or capsules and listing at least one caffeine-containing ingredient (including botanicals such as guarana,
yerba mate, kola nut, and green tea extract) on the label were selected for analysis based on market share information. Two
or three lots of each product were purchased and analyzed using high-pressure liquid chromatography (HPLC). Each analytical
run included one or two National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) and two
products in duplicate. Caffeine intake per serving and per day was calculated using the maximum recommendations on each product
label. Laboratory analysis for 53 products showed product means ranging from 1 to 829 mg caffeine/day. For products with a
label amount for comparison (n = 28), 89% (n = 25) of the products had analytically based caffeine levels/day of between −16% and +16% of the claimed levels. Lot-to-lot
variability (n = 2 or 3) for caffeine in most products (72%) was less than 10%. 相似文献
106.
Dwyer JT Holden J Andrews K Roseland J Zhao C Schweitzer A Perry CR Harnly J Wolf WR Picciano MF Fisher KD Saldanha LG Yetley EA Betz JM Coates PM Milner JA Whitted J Burt V Radimer K Wilger J Sharpless KE Hardy CJ 《Analytical and bioanalytical chemistry》2007,389(1):37-46
This article illustrates the importance of having analytical data on the vitamin and mineral contents of dietary supplements
in nutrition studies, and describes efforts to develop an analytically validated dietary supplement ingredient database (DSID)
by a consortium of federal agencies in the USA. Preliminary studies of multivitamin mineral supplements marketed in the USA
that were analyzed as candidates for the DSID are summarized. Challenges are summarized, possible future directions are outlined,
and some related programs at the Office of Dietary Supplements, National Institutes of Health are described. The DSID should
be helpful to researchers in assessing relationships between intakes of vitamins and minerals and health outcomes. 相似文献
107.
Feiler AA Stiernstedt J Theander K Jenkins P Rutland MW 《Langmuir : the ACS journal of surfaces and colloids》2007,23(2):517-522
Friction force measurements have been conducted with a colloid probe on mica and silica (both hydrophilic and hydrophobized) after long (24 h) exposure to high-humidity air. Adhesion and friction measurements have also been performed on cellulose substrates. The long exposure to high humidity led to a large hysteresis between loading and unloading in the friction measurements with separation occurring at large negative applied loads. The large hysteresis in the friction-load relationship is attributed to a contact area hysteresis of the capillary condensate which built up during loading and did not evaporate during the unloading regime. The magnitude of the friction force varied dramatically between substrates and was lowest on the mica substrate and highest on the hydrophilic silica substrate, with the hydrophobized silica and cellulose being intermediate. The adhesion due to capillary forces on cellulose was small compared to that on the other substrates, due to the greater roughness of these surfaces. 相似文献
108.
Johanna Faist Werner Seebacher Marcel Kaiser Reto Brun Robert Saf Robert Weis 《Monatshefte für Chemie / Chemical Monthly》2009,31(6):1261-1268
Abstract
Aroyl derivatives of 2-aminobicyclo-octanes and 2-azabicyclo-nonanes have been synthesized and tested for their activities against the causative organisms of East African trypanosomiasis and malaria tropica. The acylation induced in general loss of antiprotozoal activity, but a single compound showed good antiplasmodial activity against a multiresistant strain of Plasmodium falciparum. 相似文献109.
Santiago JM Keffer DJ Counce RM 《Langmuir : the ACS journal of surfaces and colloids》2006,22(12):5358-5365
We performed a series of experiments designed to elucidate the effects of the presence of sodium dodecyl sulfate (SDS) surfactant and an applied electrical field on the wetting behavior in a system containing a sessile droplet of phenylmethyl polysiloxane (PMPS) oil on a polished stainless steel surface submersed in aqueous solution. The voltage difference ranged from -3 to +3 V, which is at least 3 orders of magnitude smaller than from comparable recent work. We report the measured equilibrium contact angle of the droplet as a function of surfactant concentration and field strength. We then modeled the system. We solved the Laplace equation to obtain the 3D field within our system. We expanded the three surface tensions (oil droplet-aqueous solution (oa), oil droplet-metal surface (os), and aqueous solution-metal surface (as)) in a Taylor series with respect to surfactant concentration and local field strength. We use these three surface tensions in Young's equation to obtain the theoretical contact angle of the organic droplet. We demonstrate that the large changes in contact angle due to the simultaneous presence of small concentrations of surfactant and small voltage differences can be accounted for by changes in the oa and as surface tensions. 相似文献
110.
Phytoestrogens occur naturally in plants and are structurally similar to mammalian estrogens. The lignans are a class of phytoestrogen and can be metabolized to the biologically active enterolignans, enterodiol, and enterolactone by a consortium of intestinal bacteria. Secoisolariciresinol diglucoside (SDG), a plant lignan, is metabolized to enterodiol and, subsequently, enterolactone. Matairesinol, another plant lignan, is metabolized to enterolactone. Other dietary enterolignan precursors include lariciresinol, pinoresinol, syringaresinol, arctigenin, and sesamin. Enterolignan exposure is determined in part by intake of these precursors, gut bacterial activity, and host conjugating enzyme activity. A single SDG dose results in enterolignan appearance in plasma 8-10 h later--a timeframe associated with colonic bacterial metabolism and absorption. Conjugation of enterolignans with sulfate and glucuronic acid occurs in the intestinal wall and liver, with the predominant conjugates being glucuronides. Controlled feeding studies have demonstrated dose-dependent urinary lignan excretion in response to flaxseed consumption (a source of SDG); however, even in the context of controlled studies, there is substantial interindividual variation in plasma concentrations and urinary excretion of enterolignans. The complex interaction between colonic environment and external and internal factors that modulate it likely contribute to this variation. Knowledge of this field, to date, indicates that understanding the sources of variation and measuring the relevant panel of compounds are important in order to use these measures effectively in evaluating the impact of lignans on human health. 相似文献