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61.
Yang Qin Frieder Jäkle 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):149-157
The binding of Lewis bases to organoboron polymeric Lewis acids has been studied and the parameters that determine the complexation
equilibrium have been investigated, which include (i) the strength of the individual Lewis acids and Lewis bases, (ii) concentration,
and (iii) temperature. While the strongly Lewis acidic borane polymers poly(4-bis(pentafluorophenyl)borylstyrene) (PS-BPf) and poly(4-(di-2-thienylboryl)styrene) (PS-BTh) form isolable complexes with strong Lewis bases such as 4-t-butylpyridine (tPy), a temperature dependent equilibrium is established with weaker bases such as THF. Similarly, the weakly Lewis acidic
boronate polymer poly(4-diethoxyborylstyrene) (PS-BOEt) undergoes a temperature dependent equilibrium with the strong Lewis base 4-dimethylaminopyridine (DMAP), while poly(4-pinacolatoborylstyrene)
(PS-BPin) does not significantly bind to pyridine bases. Decomplexation of PS-BTh·
t
Py is achieved by treatment with the stronger Lewis acid, B(C6F5)3, thereby confirming the reversible nature of the polymeric Lewis acid–base adducts.
This paper is dedicated to Professor Ian Manners in gratitude of his guidance throughout the years and recognition of his
scientific accomplishments 相似文献
62.
Kaneshiro ES 《Lipids》2004,39(8):753-761
Pneumocystis can transiently colonize healthy individuals without causing adverse symptoms, and most people test positive for exposure
to this organism early in life. However, it can cause Pneumocystis pneumonia (PcP) in people with impaired immune systems and is a major cause of death in HIV/AIDS. Although it has close affinities
to the Ascomycetes, Pneumocystis has features unlike those of any single group of fungi. For example, Pneumocystis does not synthesize ergosterol, which is consistent with the inefficacy of amphotericin B and some triazoles in clearing
PcP. Pneumocystis sterols include distinct Δ7 24-alkylsterols. Metabolic radiolabeling experiments demonstrated that P. carinii synthesizes sterols de novo. Cholesterol is the most abundant sterol in Pneumocystis; most, if not all, is scavenged from the mammalian host lung by the pathogen. The P. carinii erg7, erg6, and erg11 genes have been cloned, sequenced, and expressed in heterologous systems. The recombinant P. carinii S-adenosyl-l-methionine:C-24 sterol methyl transferase (SAM:SMT) has a preference for lanosterol over zymosterol as substrate, and the
enzyme can catalyze the transfer of either one or two methyl groups to the C-24 position of the sterol side chain. Two different
sterol compositions were detected among human-derived P. jirovecii; one was dominated by C28 and C29 sterols, and the other had high proportions of higher molecular mass components, notably the C32 sterol pneumocysterol. The latter phenotype apparently represents organisms blocked at 14α-demethylation of the sterol nucleus.
These studies suggest that SAM:SMT is an attractive drug target for developing new chemotherapy for PcP. 相似文献
63.
A series of polyimide–silica hybrid films with silica contents up to 30 wt % were successfully prepared by the sol‐gel reaction of tetraethoxysiliane in the presence of poly(amic acid) containing pendent hydroxyl groups. The films were yellow and transparent when the silica content was less than 11 wt %. The chemical structure of the films was characterized by Fourier transform infrared spectroscopy, and the morphology of the films was investigated by scanning electronic microscopy and atomic force microscopy. Thermogravimetric analysis, differential scanning calorimetry, and stress–strain tests were used to measure the performance of the films. The results indicate that the glass‐transition temperatures and decomposition temperatures of the hybrid films increased with increasing silica content, whereas the tensile strength had a maximum with the variety of silica contents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2210–2214, 2003 相似文献
64.
循环结构是C语言程序设计中的重难点,其掌握情况对于后续章节的学习效果尤为关键。本文以什么是循环、何时需要使用循环以及如何使用循环三个问题为主线,通过精心选择的教学案例和灵活有效的教学方法来进行解答,以激发学生兴趣,培养编程思想。 相似文献
65.
66.
介绍板壳式换热器的主要特点和应用。当壳体与板束温差较大时,笔者通过对产品开发的生产实践,提出解决板壳式换热器要否设置膨胀节的类似判定方法。 相似文献
67.
A few Ca-containing mono-metallofullerenes, i.e. Ca@C76, Ca@C88, Ca@C90 (I, II), were synthesized by an improved DC arc discharge method and isolated by a multi-stage HPLC method for the first time. These isomer-separated metallofullerenes were characterized by LD-TOF MS and UV-vis-NIR spectrometry. Their HOMO-LUMO band gaps and possible molecular geometries are discussed according to the absorption spectra in this report. In addition, the cyclic and differential pulse voltammetry of Ca@C76 was conducted in MeCN/C6H5CH3 (1:4 v/v). The voltammograms of Ca@C82 (II, III) and Ca@C84 (II) were also recorded. Their electrochemical behaviors are discussed compared with those of corresponding ytterbium metallofullerenes. The features of the Ca metallofullerenes’ electronic structures are also discussed. 相似文献
68.
何庆复 《武汉理工大学学报(材料科学英文版)》2009,24(3):428-431
Behaviour of hardening and serration yield of a Fe-Ni-Cr alloy under isothermal cycling (ISC) and out-phase TMF was studied
on the basis of varied hysteresis loops. Cycling hardening and serrated yielding for ISC depend on the temperature and the
total strain range, stronger hardening with serrated yielding at higher strain range under ISC at 600 °C, but no hardening
and serrated yielding occurred under ISC at 800 °C. Stronger hardening with stress serration occurred at the thermal path
going to the lowest temperature, no stress serration occurred at the highest temperature under the out-phase. The hardening
also depends on the total strain range, higher total strain range with lower cycling temperature resulted in a stronger hardening
and remarkable serration yielding behavior. Weaker hardening without serrated yielding occurred at near 800 °C may due to
an obvious cycling stress drop under out-phase TMF. Change in the shape of the hysteresis loops also expresses the degree
of the damage of the tested alloy under out-phase and ISC. 相似文献
69.
章桥新 《武汉理工大学学报(材料科学英文版)》2009,24(6):871-874
Silver powder was fabricated by spray pyrolysis, using 2%–20% AgNO3 solution, 336–500 mL/h flux of AgNO3 solution, 0.28–0.32 MPa flux of carrier gas and in the 620–820 °C temperature range. The effects of furnace set temperature,
concentration of AgNO3 aqueous solution, flux of AgNO3 aqueous solution as well as carrier gas on the morphology and particle size distribution of silver powder, were investigated.
The experimental results showed that with the high concentration of AgNO3 aqueous solution, the average grain size of silver decreased with the increasing of furnace set temperature. But the gain
size distribution was not homogenous, the discontinuous grain growth occurred. With the low concentration of AgNO3 aqueous solution, the higher furnace set temperature made the nano sliver grains sintered together to grow. Nano silver powder
about 100 nm was fabricated by spray pyrolysis, using 2wt% AgNO3 solutions, 336 mL/h flux of AgNO3 aqueous solution, 0.32 MPa flux of carrier gas at 720 °C furnace set temperature. 相似文献
70.
Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite
as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed
by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress
relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction
and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer.
The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The
results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural
bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link
and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress
relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of
the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient
reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular
cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite
hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing
cycles and the HA content.
Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century
Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403) 相似文献