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61.
Peter C. H. Hollman Martijn B. Katan 《Fresenius' Journal of Analytical Chemistry》1987,326(7):690-695
Summary In order to determine the influence of laboratory procedures on nutrient values in different food tables and data banks, an interlaboratory study was set up. Nineteen laboratories participated, and received well-homogenized samples of egg powder, full-fat milk powder, whole rye and wheat meal, biscuits and french beans to perform analyses of macronutrients by their own routine methods. For dry weight the results agreed very well; the results for ash agreed rather well. For protein the coefficient of variation between laboratories (CVbetween) ranged from 2.8% to 6.4%. The CVbetween for total fat ranged from 5.4% to 54%. For available carbohydrates the CVbetween ranged from 9% to 27%. The CVbetween for total dietary fiber ranged from 23% to 84%. It is concluded that leading laboratories produce widely different values for macronutrients in common foods. Reference materials of certified nutrient concentration are needed. 相似文献
62.
Palermo V Otten MB Liscio A Schwartz E de Witte PA Castriciano MA Wienk MM Nolde F De Luca G Cornelissen JJ Janssen RA Müllen K Rowan AE Nolte RJ Samorì P 《Journal of the American Chemical Society》2008,130(44):14605-14614
The physicochemical properties of organic (multi)component films for optoelectronic applications depend on both the mesoscopic and nanoscale architectures within the semiconducting material. Two main classes of semiconducting materials are commonly used: polymers and (liquid) crystals of small aromatic molecules. Whereas polymers (e.g., polyphenylenevinylenes and polythiophenes) are easy to process in solution in thin and uniform layers, small molecules can form highly defined (liquid) crystals featuring high charge mobilities. Herein, we combine the two material types by employing structurally well-defined polyisocyanopeptide polymers as scaffolds to precisely arrange thousands of electron-accepting molecules, namely, perylenebis(dicarboximides) (PDIs), in defined chromophoric wires with lengths of hundreds of nanometers. The polymer backbone enforces high control over the spatial location of PDI dyes, favoring both enhanced exciton and charge transfer. When blended with an electron-donor system such as regioregular poly(3-hexylthiophene), this polymeric PDI shows a relative improvement in charge generation and diffusion with respect to monomeric, aggregated PDI. In order to correlate this enhanced behavior with respect to the architecture, atomic force microscopy investigations on the mixtures were carried out. These studies revealed that the two polymers form interpenetrated bundles having a nanophase-segregated character and featuring a high density of contact points between the two different phases. In order to visualize the relationship between the architecture and the photovoltaic efficiency, Kelvin probe force microscopy measurements were carried out on submonolayer-thick films. This technique allowed for the first time the direct visualization of the photovoltaic activity occurring in such a nanoscale phase-segregated ultrathin film with true nanoscale spatial resolution, thus making possible a study of the correlation between function and architecture with nanoscale resolution. 相似文献
63.
Accurate calculations of electrostatic potentials and treatment of substrate polarizability are critical for predicting the permeation of ions inside water-filled nanopores. The ab initio molecular dynamics method, based on density functional theory (DFT), accounts for the polarizability of materials, water, and solutes, and it should be the method of choice for predicting accurate electrostatic energies of ions. In practice, DFT coupled with the use of periodic boundary conditions in a charged system leads to large energy shifts. Results obtained using different DFT packages may vary because of the way pseudopotentials and long-range electrostatics are implemented. Using maximally localized Wannier functions, we apply robust corrections that yield relatively unambiguous ion energies in select molecular and aqueous systems and inside carbon nanotubes. Large binding energies are predicted for ions in metallic carbon nanotube arrays, while Na+ and Cl- energies are found to exhibit asymmetry in water that is smaller than but comparable with those computed using nonpolarizable water force fields. 相似文献
64.
Ferroelectric switching and electrochemistry of pyrrole substituted trialkylbenzene‐1,3,5‐tricarboxamides 下载免费PDF全文
Xiao Meng Andrey V. Gorbunov W. S. Christian Roelofs Stefan C. J. Meskers René A. J. Janssen Martijn Kemerink Rint P. Sijbesma 《Journal of Polymer Science.Polymer Physics》2017,55(8):673-683
We explore a new approach to organic ferroelectric diodes using a benzene‐tricarboxamide (BTA) core connected with C10 alkyl chains to pyrrole groups, which can be polymerized to provide a semiconducting ferroelectric material. The compound possesses a columnar hexagonal liquid crystalline (LC) phase and exhibits ferroelectric switching. At low switching frequencies, an additional process occurs, which leads to a high hysteretic charge density of up to ~1000 mC/m2. Based on its slow rate, the formation of gas bubbles, and the emergence of characteristic polypyrrole absorption bands in the UV–Vis–NIR, the additional process is identified as the oxidative polymerization of pyrrole groups, enabled by the presence of amide groups. Polymerization of the pyrrole groups, which is essential to obtain semiconductivity, is limited to thin layers at the electrodes, amounting to ~17 nm after cycling for 21 h. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 673–683 相似文献
65.
We propose a novel concept for creating high-Q cavities in photonic crystal slabs (PCSs) composed of photosensitive material. To date, high-Q cavities have been realized through the use of double heterostructures where the lattice geometry is altered via nanolithography. Here, we show that selective postexposure to light of a uniform PCS composed of photosensitive material, altering the refractive index permanently, can also yield high-Q microcavities. We show theoretically that high-Q cavities (up to Q = 1 x 10(6)) can be achieved with photoinduced index changes that are well within what can be achieved in chalcogenide glasses. 相似文献
66.
Martena MJ van der Wielen JC van de Laak LF Konings EJ de Groot HN Rietjens IM 《Analytical and bioanalytical chemistry》2007,389(1):263-275
In traditional chinese medicine several Aristolochia species are used. Aristolochia spp. contain a mixture of aristolochic acids (AAs), mainly AA I and AA II which are nephrotoxicants and carcinogens. After
AA-related nephropathy (AAN) and urothelial cancer were described in female patients in Belgium following intake of AA-contaminated
herbal preparations, herbs with AAs were prohibited worldwide. Confusing nomenclature can cause AA contamination of certain
Chinese traditional herbal preparations (THPs). Here we report the results of investigations by the Dutch Food and Consumer
Product Safety Authority (VWA) into the presence of AAs in THPs sampled on the Dutch market using a liquid-chromatography–-mass
spectrometry method. Between 2002 and 2006 we sampled 190 Chinese THPs using recent information on Chinese THPs potentially
containing AAs. AA I was found in 25 samples up to a concentration of 1,676 mg/kg. AA II was also found in 13 of these samples
up to 444 mg/kg. All 25 positive samples including Mu Tong, Fang Ji, Tian Xian Teng and Xi Xin were part of a group of 68 THPs
identified as possibly containing AAs. In a worst-case scenario, use of a sample of Mu Tong with the highest AA content over
a 7-day period would result in the same intake levels of AAs which significantly raised the cancer risk in the Belgian AAN
cases. Our results show that contaminated THPs still can be found on the market following worldwide publicity. Therefore,
it can be concluded that testing of possibly AA-contaminated THPs is still essential.
Figure Various Chinese Herbs 相似文献
67.
Pierik A Boamfa M van Zelst M Clout D Stapert H Dijksman F Broer D Wimberger-Friedl R 《Lab on a chip》2012,12(10):1897-1902
Quantitative real-time polymerase chain reaction (qrtPCR) is widely used as a research and diagnostic tool. Notwithstanding its many powerful features, the method is limited in the degree of multiplexing to about 6 due to spectral overlap of the available fluorophores. A new method is presented that allows quantitative amplification detection at higher multiplexing by the integration of amplification in solution and monitoring via hybridization to a microarray in real-time. This method does not require any manipulation of the PCR product and runs in a single closed chamber. Employing labeled primers, one of the main challenges is to measure surface signals against a high fluorescence background from solution. A compact, confocal scanner is employed, based on miniaturized optics from DVD technology and combined with a flat thermocycler for simultaneous scanning and heating. The feasibility of this method is demonstrated in singleplex with an analytical sensitivity comparable to routine qrtPCR. 相似文献
68.
F Wang MA Gillissen PJ Stals AR Palmans EW Meijer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(37):11761-11770
The design of supramolecular motifs with tuneable stability and adjustable supramolecular polymerisation mechanisms is of crucial importance to precisely control the properties of supramolecular assemblies. This report focuses on constructing π-conjugated oligo(phenylene ethynylene) (OPE)-based one-dimensional helical supramolecular polymers that show a cooperative growth mechanism. Thus, a novel set of discotic molecules comprising a rigid OPE core, three amide groups, and peripheral solubilising wedge groups featuring C(3) and C(2) core symmetry was designed and synthesised. All of the discotic molecules are crystalline compounds and lack a columnar mesophase in the solid state. In dilute methylcyclohexane solution, one-dimensional supramolecular polymers are formed stabilised by threefold intermolecular hydrogen bonding and π-π interactions, as evidenced by (1) H?NMR measurements. Small-angle X-ray and light scattering measurements reveal significant size differences between the columnar aggregates of C(3) - and C(2) -symmetrical discotics, that is, the core symmetry strongly influences the nature of the supramolecular polymerisation process. Temperature-dependent CD measurements show a highly cooperative polymerisation process for the C(3) -symmetrical discotics. In contrast, the self-assembly of C(2) -symmetrical discotics shows a smaller enthalpy release upon aggregation and decreased cooperativity. In all cases, the peripheral stereogenic centres induce a preferred handedness in the columnar helical aggregates. Moreover, one stereogenic centre suffices to fully bias the helicity in the C(2) -symmetrical discotics. Finally, chiral amplification studies with the C(3) -symmetrical discotics were performed by mixing chiral and achiral discotics (sergeants-and-soldiers experiment) and discotics of opposite chirality (majority-rules experiment). The results demonstrate a very strong sergeants-and-soldiers effect and a rather weak majority-rules effect. 相似文献
69.
Pinkse MW Heck AJ Rumpel K Pullen F 《Journal of the American Society for Mass Spectrometry》2004,15(10):1392-1399
Nanoflow electrospray ionization time of flight mass spectrometry (ESI-TOF-MS) was used to study activation properties of the cGMP-dependent protein kinase (PKG). Our nanoflow ESI-TOF-MS analysis confirms that PKG mainly occurs as a 153 kDa homodimer and is able to bind four cGMP molecules, which is in agreement with the known stoichiometry. Binding order and stoichiometry of cGMP, the non-hydrolysable ATP analog beta,gamma-imidoadenosine 5'-triphosphate (AMPPNP) and Mn2+ for PKG were characterized as model for the active PKG-cGMP-ATP/Mg2+ complex. Already in the absence of cGMP, a noncovalent complex between PKG and two molecules of AMPPNP could be observed by ESI-TOF-MS. Binding of AMPPNP to PKG was strongly enhanced by the addition of MnCl2 to the spray solution. This is in agreement with binding of AMPPNP/Mn2+ in the ATP binding pocket of PKG since all protein kinases require a metal ion to accompany ATP in the ATP-binding pocket for proper positioning of the beta and gamma phosphates. Additionally, this finding could imply that within the inactive conformation of PKG, the autoinhibition-domain, when in contact with the substrate-docking domain, does not block the entrance to the ATP-binding site. In the presence of cGMP, less of the fully saturated PKG-(cGMP)4(AMPPNP/Mn2+)2 complex was observed, suggesting that the PKG-ATP interaction is weakened in the active conformation of PKG. Additionally, limited proteolysis in combination with native-ESI MS showed to be a useful tool to study the contact regions on the PKG-dimer and also allowed the rapid determination of the overall autophosphorylation status of the protein. These measurements indicated that autophosphorylation mainly occurs within the first 80 aminoterminal residues and involves in total 3-4 phosphates per subunit. 相似文献
70.
Ewoud van Tricht Lars Geurink Francisca Galindo Garre Martijn Schenning Harold Backus Marta Germano Govert W. Somsen Cari E. Snger van de Griend 《Electrophoresis》2019,40(18-19):2277-2284
A CZE method was validated and implemented for fast and accurate in‐process determination of adenovirus concentrations of downstream process samples obtained during manufacturing of adenovirus vector‐based vaccines. An analytical‐quality‐by‐design approach was embraced for method development, method implementation, and method maintenance. CZE provided separation of adenovirus particles from sample matrix components, such as cell debris, residual DNA and proteins. The intermediate precision of the virus particle concentration was 6.9% RSD and the relative bias was 2.3%. In comparison, the CZE method is intended to replace a quantitative polymerase chain reaction method which requires three replicates in three analytical runs to achieve an intermediate precision of 8.1% RSD. Given that, in addition, the time from sampling till reporting results of the CZE method was less than 2 h, whereas quantitative polymerase chain reaction requires 3 days, it follows that the CZE method enables faster processing times in downstream processing. 相似文献