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101.
Reka Geczy Niels Johan Christensen Kim K. Rasmussen Ildik Klomista Manish K. Tiwari Pratik Shah Seong Wook Yang Morten J. Bjerrum Peter W. Thulstrup 《Angewandte Chemie (International ed. in English)》2020,59(37):16091-16097
Fluorescent, DNA‐stabilized silver nanoclusters (DNA‐AgNCs) are applied in a range of applications within nanoscience and nanotechnology. However, their diverse optical properties, mechanism of formation, and aspects of their composition remain unexplored, making the rational design of nanocluster probes challenging. Herein, a synthetic procedure is described for obtaining a high yield of emissive DNA‐AgNCs with a C‐loop hairpin DNA sequence, with subsequent purification by size‐exclusion chromatography (SEC). Through a combination of optical spectroscopy, gel electrophoresis, inductively coupled plasma mass spectrometry (ICP‐MS), and small‐angle X‐ray scattering (SAXS) in conjunction with the systematic study of various DNA sequences, the low‐resolution structure and mechanism of the formation of AgNCs were investigated. Data indicate that fluorescent DNA‐AgNCs self‐assemble by a head‐to‐head binding of two DNA hairpins, bridged by a silver nanocluster, resulting in the modelling of a dimeric structure harboring an Ag12 cluster. 相似文献
102.
Meera A. Shah Samuel Raynes Dr. David C. Apperley Dr. Russell A. Taylor 《Chemphyschem》2020,21(7):673-679
The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH3]+ species was confirmed by 13C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the 13C MAS NMR spectrum, resulting from two distinct [Zn-CH3]+ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH3]+ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure–function correlations for methane conversion over zinc-exchanged zeolites. 相似文献
103.
Rabindra N. Roy Lakshmi N. Roy Kathleen A. Allen Casey J. Mehrhoff Isaac B. Henson Jessica M. Stegner Alexis L. Jenkins Ankita A. Shah Stephen D. Rocchio 《Journal of solution chemistry》2012,41(6):1044-1053
In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg?1. The residual liquid junction potentials (??E j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7. 相似文献
104.
In this Letter we investigate the propagation of coupled nonlinear Alfven-spin and helicon-spin waves in a composite medium having the properties of both magnetic and semiconducting materials. We arrive at the nonlinear evolution equations for these coupled waves using the reductive perturbation method for which we obtain soliton solutions. We also discuss the limiting cases for the two materials separately. 相似文献
105.
A simple and sensitive spectrophotometric method has been developed for the determination of sparfloxacin in bulk and pharmaceutical
formulations, and in artificial urine. Sparfloxacin was oxidized into a red colored product using ammonium monovanadate in
acidic media. The proposed method was successfully applied to the determination of sparfloxacin in different pharmaceutical
formulations (tablets) and in a spiked urine sample. The influence of commonly used excipients on the determination of sparfloxacin
was studied. Percentage recoveries in the range of 98.0 ± 0.14 % to 100.0 ± 0.20 % were obtained. The observed data have been
evaluated statistically which showed high accuracy and precision. 相似文献
106.
107.
Babak Momeni Ehsan Shah Hosseini Murtaza Askari Mohammad Soltani Ali Adibi 《Optics Communications》2009,282(15):3168-697
A combination of negative refraction and diffraction compensation in a superprism-based photonic crystal structure is used to demonstrate a compact on-chip photonic crystal spectrometer. This structure provides strong dispersion and signal isolation, which are essential for forming an efficient and compact spectrometer. Performance of these spectrometers as spectral pattern detectors is discussed. The experimental results show that a PC structure with 80 μm × 220 μm dimension can locate a single spectral feature with better than 10 pm accuracy over a bandwidth of 50 nm around 1550 nm center wavelength at an output signal-to-noise ratio of 13 dB. 相似文献
108.
For a non-compact harmonic manifold M, we establish an integral formula for the derivative of a harmonic function on M. As
an application we show that for the harmonic spaces having minimal horospheres, bounded harmonic functions are constant. The
main result of this article states that the harmonic spaces having polynomial volume growth are flat. In other words, if the
volume density function Θ of M has polynomial growth, then M is flat. This partially answers a question of Szabo namely, which
density functions determine the metric of a harmonic manifold. Finally, we give some natural conditions which ensure polynomial
growth of the volume function. 相似文献
109.
Temperature dependent Mössbauer measurements are done on the samples of La1–x
Ca
x
Mn1–y
57Fe
y
O3 with x=0 and 0.25, and y=0.01. With decreasing temperature, the specimen with x=0.25 shows a paramagnetic to ferromagnetic transition around 175 K. In the specimen x=0.0, the temperature dependence of both the center shift () and the recoilless fraction (f) can be fitted very well with the Debye theory with a
D=320±50 K. But for the specimens with x=0.25, f and show distinct deviations from the Debye behavior in the temperature range in which the resistivity shows a sharp decrease. Dips observed in both the f and around the transition temperature suggest that the Jahn–Teller distortion observed in these systems is dynamic in nature. 相似文献
110.
R.F. Leheny Jagdeep Shah R.L. Fork C.V. Shank A. Migus 《Solid State Communications》1979,31(11):809-813
Carrier relaxation following excitation with subpicosecond optical pulses, determined from time resolved nearband gap transmission spectrum changes, is described for GaAs. For n < 5×1017cm-3 the observed relaxation can be related to carrier-phonon interaction, but at higher densities the rate of relaxation is significantly slowed, possibly due to carrier screening. 相似文献