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991.
The behavior of the symmetrical ethane-bridged bis(Zn porphyrin) (1) has been investigated at the air-water interface. The molecular organization of floating films of pure 1 and its mixture with amphiphilic substances, such as arachidic acid and n-octadecylamine, was inspected by means of surface pressure-area isotherms, Brewster angle microscopy and reflection spectroscopy in the UV-Vis region. The overall results suggest the presence in all cases of mainly the anti conformer of 1 even when the dimer was spread on pure water, through the ligation of water molecules to the zinc atoms in the axial positions. It was also demonstrated for the first time that the syn-to-anti conformational transition of the porphyrin dimer can be accelerated by the ligation of suitable amphiphiles even at the liquid-air interface. In particular, it is noted that n-octadecylamine, and arachidic acid (to a lesser extent), added to the system as amphiphiles, drive the syn ? anti equilibrium of 1 towards the anti form through the axial ligation of the amino or carboxylate group to the zinc atoms. 相似文献
992.
Helen O. Leung Oluwatoyin M. Ibidapo Mary B. Bianchi 《Journal of Molecular Spectroscopy》2003,222(1):3-14
The rotational spectra of six isotopomers of the linear and bent isomers of HF-N2O have been collected in the 7-18 GHz region with a Fourier transform microwave spectrometer. The nuclear hyperfine structure in the spectra produced by HF spin-spin coupling interaction and nuclear quadrupole coupling interactions due to the D nucleus of DF and the nuclei of N2O have been resolved and analyzed. In the linear isomer, H in HF is bonded to the terminal N in N2O. The NF bond lengths are 2.9808(2) Å for the HF-containing isotopomers and 2.9732(2) Å for the DF-containing isotopomers. The zero point angles are 23.1° for HF and 31-34° for N2O. The hyperfine constants suggest that the HF bond is lengthened by 0.0105 Å upon complexation and that the electric field gradients of the two nitrogen nuclei in N2O are perturbed differently in the complex. In the bent isomer, the hydrogen bond is formed between HF and O in N2O. The intermolecular distances are 3.4942(2) Å for the HF-containing isotopomers and 3.4436(2) Å for the DF-containing isotopomers, with HF and N2O forming angles of 34° and 46°, respectively, with the intermolecular axis. The nuclear quadrupole coupling constants of the two nitrogen nuclei do not indicate electric field gradient perturbation in this isomer. 相似文献
993.
Peroxynitrite, as a derivative of nitric oxide, is a potent oxidant. It reacts with several biological molecules, makes cellular and tissue damages, and is related with many diseases; therefore, it is of major concern in current medical research works. In this work, a special perm-selective cellulose acetate membrane sampler is used to implement flow injection analysis (FIA)/chemiluminscence (CL)-detection method for the detection of peroxynitrite with Luminol CL-reagent. Optimum detection conditions were established, and the permeability of peroxynitrite through cellulose acetate (CA) membrane, as well as the interference from matrix constituents were studied. The proposed method has the high sensitivity of the CL-detection and the selectivity of perm-selective membrane sampler. The obtained detection limit of 1×10−11 M (without dialysis membrane) and 1×10−10 M (with dialysis membrane), makes it possible to monitor the elusive peroxynitrite in biological samples. The mechanism of luminol CL-emission generated during oxidation by peroxynitrite and the kinetics of peroxynitrite decomposition were also studied using FIA/CL-detection set-up. 相似文献
994.
Massimo Gottardi Lorenzo Gonzo Stefano Gregori Valentino Liberali Andrea Simoni Guido Torelli 《Analog Integrated Circuits and Signal Processing》2003,34(2):143-154
This paper presents a front-end circuit for optical rotary encoders. The light pulses modulated by the encoder disc are transduced into current signals, which are pre-processed and converted into digital waveforms related to the disc angular position information. The proposed front-end circuit is compensated against temperature drifts. Digitally programmable calibration is provided to account for spreads in impinging light pulse power. Measurement results on integrated prototypes are shown, demonstrating correct operation of the front-end with an optical input power from 0.5 W to 3 W up to a signal frequency of 500 kHz in a temperature range from 0 °C to 80 °C. 相似文献
995.
996.
R. R. Mahajan P. S. Makashir J. P. Agrawal 《Journal of Thermal Analysis and Calorimetry》2001,65(3):935-942
Complexes of nitrocellulose (NC – low and high nitrogen content) with copper oxide (CuO) have been synthesized and studied
for morphological behaviour on heating from room temperature to 500°C with the help of hot stage microscopy (HSM).
During decomposition, NC:CuO complexes show contraction of fibrous boundaries followed by mass movement of matrix, with the
evolution of brown yellow colour gas at higher temperatures as compared to NC alone.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
997.
G. B. Parravicini A. Stella M. C. Ungureanu P. G. Merli A. Migliori P. Cheyssac R. Kofman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):219-222
Both theoretical and experimental works give evidence that
gallium exhibits solid phases labelled , , , besides the
stable phase strongly dependent both on the size and the
confinement conditions. An experimental technique was used based
on capacitance and conductance measurements
vs. temperature in the
audiofrequency range. This technique is particularly sensitive
to the conditions of the investigated particle surface that
plays a fundamental role in the melting and more generally in
the phase transition processes. In particular the strict
relation between the derivative of the capacitance with respect
to the temperature, dC/dT, and the entropy of the system is
considered. In gallium nanoparticles 20 nm in radius, only the
phase is shown to occur. Further the transition to liquid phase
was detected. The melting process was found to start about 65 K
below the full melting temperature value. In the case of
particles 10 nm in radius, where different metastable phases may
occur, the capacitance vs.
temperature curve was found to display abrupt changes of the
slope. The singularities are associated to a well defined
transition temperature. 相似文献
998.
Yasutaka Takahashi Ayako Ohsugi Takeshi Arafuka Tomokazu Ohya Takayuki Ban Yutaka Ohya 《Journal of Sol-Gel Science and Technology》2000,17(3):227-238
The effects of several hydroxyketones such as acetol, actoin, -ketobutanol themselves and their combinations with monoethanolamine (MEA) or ethylenediamine (ED) on the stabilization of titanium tetraisopropoxide (TTIP) in isopropanol solution are examined. Acetoin itself and the imine derivatives of acetol and acetoin were found to show extraordinarily strong stabilizing effect for the alkoxide. The properties including the crystal modifications and refractive index of TiO2 films that were dip-coated using each stabilized solution are examined and discussed in comparison with those of the films obtained from the diethanolamine (DEA) systems. The effect of UV-light irradiation to the gel films on the crystallization of TiO2 is also examined and discussed. 相似文献
999.
We used the isotope selectivity of 57Fe Mössbauer spectroscopy to investigate changes in the magnetic properties of polycrystalline hematite exposed to ferrous iron (Fe(II)). We found that sorption of 56Fe(II), followed by interfacial electron exchange, alters the bulk magnetic properties of 57hematite. After reaction with 56Fe(II), we observed partial suppression of the Morin transition of 57hematite to below 13 K. This is significantly lower than the Morin temperature (T M) of ~230 K measured for isotopically enriched polycrystalline 57hematite, as well as the T M of 264?±?2 K reported for normal polycrystalline hematite. 相似文献
1000.
Thin solid polymer electrolytes based on polyethylene oxide (PEO) and silver triflate (AgCF3SO3) dispersed with various concentrations of aluminum oxide (Al2O3) nanoparticles have been prepared by solution casting technique. These thin polymer films are found to have thickness of
the order of 30 to 100 μm. The X-ray diffraction (XRD) patterns have indicated the amorphous nature of the polymer electrolyte.
The differential scanning calorimeter (DSC) traces showed slight change in the glass transition temperature (T
g) whereas the degree of crystallization (X
c) decreases markedly due to the addition of alumina nanoparticles. Fourier transform infrared (FTIR) spectral analysis of
all these samples has revealed the presence of absorption bands around 1,000 cm−1; thus indicating the complexation of silver ions with oxygen in PEO. Employing the Wagner’s polarization technique as the
standard method, the total ionic transference number for the complexed polymer electrolyte was found to be approximately unity
thereby revealing that the significant contribution to electrical conduction was due to ions only.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, December 7–9,
2006 相似文献