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91.
Sivakumar S van Veggel FC Raudsepp M 《Journal of the American Chemical Society》2005,127(36):12464-12465
White light was generated from a single silica thin film made with Yb0.75La0.2Eu0.05F3, La0.45Yb0.5Er0.05F3, and La0.75Yb0.2Tm0.05F3 nanoparticles by exciting with a single source near-infrared light (980 nm CW diode laser). Eu3+ and Tm3+ ions are responsible for red and blue emission, respectively. Er3+ ion is responsible for green as well as red emission. The Commission Internationale de l'Eclairage (CIE) coordinates of the resulting light were easily adjusted by controlling the concentration of Ln3+ (Eu3+, Er3+, Tm3+) ions in the nanoparticles as well as the concentration of Ln3+-doped nanoparticles in the sol-gel thin layer. 相似文献
92.
Semiempirical AM1 calculations were performed for quantum chemically optimized minimum-energy conformations of L -alanine oligomers (A)n at n = 7 and their derivatives containing one, two, or three proline residues at various positions along the peptide chain. The effect of proline residues on the peptide conformation was quantified in terms of the conformational “strain energy” and also analyzed in terms of the spatial compatibility of peptides. The defined “strain energy” corresponds to the transformation of the polyalanine peptide from its minimum conformation to the conformation corresponding to that of the proline-containing peptide. The results of calculations indicate that the “strain effect” of proline residues is additive at all locations along the peptide chain, except at the first and the second positions of its N-terminal part. Also, the regular α-helical polyalanine structure was most significantly altered by the presence of some specific motifs around the proline location in the peptide. This, in turn, has its implications in the prediction of the protein secondary structure, as well as in the design of peptide inhibitors and substrates for enzymes and receptors. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 391–396, 1998 相似文献
93.
Silvia Rang Tiiu Strenze Mati Müürisepp Olaf Eisen 《Journal of mass spectrometry : JMS》1984,19(4):193-195
The field ionization mass spectra of monosubstituted cyclopentenes and cyclohexenes with C1-C7 n-alkyl and C4-C5 isoalkyl substituents in positions 1 and 3 have been investigated and compared with the previously reported electron impact mass spectra of these compounds. The cleavage of the C? C bond β to the double bond in the non-isomerized molecular ion was found to be a typical degradation reaction of the higher homologues in the strong electric field. So, by means of the field ionization mass spectra, the >C1 alkyl substituent can be readily located in the parent molecule. The electron impact mass spectra exhibit a less specific fragment ion distribution for positional isomers due to the extensive molecular ion isomerization prior to decomposition, but provide useful information on the ring size. For structure determination it is appropriate to use both ionization techniques. 相似文献
94.
Käärik Maike Arulepp Mati Kozlova Jekaterina Aruväli Jaan Mäeorg Uno Kikas Arvo Kisand Vambola Tamm Aile Leis Jaan 《Journal of Solid State Electrochemistry》2022,26(11):2365-2378
Journal of Solid State Electrochemistry - The present study considers TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC) as potential electrode materials for pH-neutral... 相似文献
95.
The authors study the continuity estimate of the solutions of almost harmonic maps with the perturbation term f in a critical integrability class (Zygmund class) Ln/2 logq L, n is the dimension with n ≥ 3. They prove that when q > n/2 the solution must be continuous and they can get continuity modulus estimates. As a byproduct of their method, they also study boundary continuity for the almost harmonic maps in high dimension. 相似文献
96.
Wang H Ng MK Wang L Yu L Lin B Meron M Xiao Y 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(14):3246-3253
This paper reports the synthesis and characterization of a new class of diblock copolymers (co-oligomers), rod-rod conjugated diblock copolymers. A general synthetic strategy is outlined, and the structures of the copolymers (oligothiophene-co-oligophenylenevinylene) are fully characterized. It was found that these copolymers exhibit efficient intramolecular energy transfer. An interesting self-assembly ability of these rod--rod copolymers was also revealed. 相似文献
97.
Ivar Kruusenberg Jaan Leis Mati Arulepp Kaido Tammeveski 《Journal of Solid State Electrochemistry》2010,14(7):1269-1277
Electroreduction of oxygen in alkaline solution on glassy carbon (GC) electrodes modified with different carbon nanomaterials
has been studied. Electrochemical experiments were carried out in 0.1 M KOH employing the rotating disk electrode and rotating
ring-disk electrode methods. The GC disk electrodes were modified with carbon nanomaterials using polytetrafluoroethylene
as a binder. Four different carbon nanomaterials were used: multiwalled carbon nanotubes, carbon black powder, and two carbide-derived
carbons (CDC). For the first time, the electrocatalytic behavior of CDC materials toward oxygen reduction is explored. Electrochemical
characterization of the materials showed that all the carbon nanomaterial-modified GC electrodes are highly active for the
reduction of oxygen in alkaline solutions. 相似文献
98.
Bojana Beljkaš Jovana Matić Ivan Milovanović Pavle Jovanov Aleksandra Mišan Ljubiša Šarić 《Accreditation and quality assurance》2010,15(10):555-561
The objective of this research was to test suitability of the Dumas combustion method to completely substitute the Kjeldahl
method in routine laboratory determination of crude protein content in cereals and oilseeds. The validation of the method
demonstrated that it is able to determine crude protein content in cereals and oilseeds in an efficient and accurate manner,
with a detection limit w(N) = 0.006%, quantification limit w(N) = 0.019%, repeatability precision RSD
r = 0.41%, intra-laboratory reproducibility precision RSD
R = 0.74%, trueness, expressed in terms of bias b = 0.43%, and linear response between (2.36–19.2) mg N. Measurement uncertainty, expressed as relative expanded uncertainty
(coverage factor k = 2, confidence level 95%), was calculated from validation data (U
rel = 2.24%). In order to examine the relationship between two methods, 15 cereal grain and oilseed samples were analyzed using
Dumas and Kjeldahl procedure. The Kjeldahl procedure gave slightly lower w(N) values than the Dumas procedure: w
K(N) = 0.9905 w
D(N) = 0.0376 (R
2
= 0.9996). Relative standard deviations and results of homogeneity test obtained during analysis of complex cereal products
(cereal breakfast and muesli bars) show that the Dumas combustion method may be less suitable for analysis of such samples
compared to Kjeldahl method. 相似文献
99.
Leiske DL Meckes B Miller CE Wu C Walker TW Lin B Meron M Ketelson HA Toney MF Fuller GG 《Langmuir : the ACS journal of surfaces and colloids》2011,27(18):11444-11450
Interactions between amphiphilic block copolymers and lipids are of medical interest for applications such as drug delivery and the restoration of damaged cell membranes. A series of monodisperse poly(ethylene oxide)-poly(butylene oxide) (EOBO) block copolymers were obtained with two ratios of hydrophilic/hydrophobic block lengths. We have explored the surface activity of EOBO at a clean interface and under 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) monolayers as a simple cell membrane model. At the same subphase concentration, EOBO achieved higher equilibrium surface pressures under DPPC compared to a bare interface, and the surface activity was improved with longer poly(butylene oxide) blocks. Further investigation of the DPPC/EOBO monolayers showed that combined films exhibited similar surface rheology compared to pure DPPC at the same surface pressures. DPPC/EOBO phase separation was observed in fluorescently doped monolayers, and within the liquid-expanded liquid-condensed coexistence region for DPPC, EOBO did not drastically alter the liquid-condensed domain shapes. Grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XRR) quantitatively confirmed that the lattice spacings and tilt of DPPC in lipid-rich regions of the monolayer were nearly equivalent to those of a pure DPPC monolayer at the same surface pressures. 相似文献
100.
Lendrum CD Ingham B Lin B Meron M Toney MF McGrath KM 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):4430-4438
2-Hydroxyacids display complex monolayer phase behavior due to the additional hydrogen bonding afforded by the presence of the second hydroxy group. The placement of this group at the position α to the carboxylic acid functionality also introduces the possibility of chelation, a utility important in crystallization including biomineralization. Biomineralization, like many biological processes, is inherently a nonequilibrium process. The nonequilibrium monolayer phase behavior of 2-hydroxyoctadecanoic acid was investigated on each of pure water, calcium chloride, sodium bicarbonate and calcium carbonate crystallizing subphases as a precursor study to a model calcium carbonate biomineralizing system, each at a pH of ~6. The role of the bicarbonate co-ion in manipulating the monolayer structure was determined by comparison with monolayer phase behavior on a sodium chloride subphase. Monolayer phase behavior was probed using surface pressure/area isotherms, surface potential, Brewster angle microscopy, and synchrotron-based grazing incidence X-ray diffraction and X-ray reflectivity. Complex phase behavior was observed for all but the sodium chloride subphase with hydrogen bonding, electrostatic and steric effects defining the symmetry of the monolayer. On a pure water subphase hydrogen bonding dominates with three phases coexisting at low pressures. Introduction of calcium ions into the aqueous subphase ensures strong cation binding to the surfactant head groups through chelation. The monolayer becomes very unstable in the presence of bicarbonate ions within the subphase due to short-range hydrogen bonding interactions between the monolayer and bicarbonate ions facilitated by the sodium cation enhancing surfactant solubility. The combined effects of electrostatics and hydrogen bonding are observed on the calcium carbonate crystallizing subphase. 相似文献