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Green fluorescent proteins (GFPs) have become powerful markers for numerous biological studies due to their robust fluorescence properties, site-specific labeling, pH sensitivity, and mutations for multiple-site labeling. Fluorescence correlation spectroscopy (FCS) studies have indicated that fluorescence blinking of anionic GFP mutants takes place on a time scale of 45-300 ms, depending on pH, and have been attributed to external proton transfer. Here we present experimental evidence indicating that conformational change in the protein &beta-barrel is a determining step for the external protonation of GFP-S65T (at low pH) using time-resolved fluorescence and polarization anisotropy measurements. While the average anionic fluorescence lifetime of GFP-S65T is reduced by approximately 18% over a pH range of 3.6-10.0, the fluorescence polarization anisotropy decays mostly as a single exponential with a rotational time of phi = 17 +/- 1 ns, which indicates an intact beta-barrel with a hydrodynamic volume of 78 +/- 5 nm3. In contrast, the total fluorescence (525 +/- 50 nm) of the excited neutral state of S65T reveals a strong correlation between the fluorescence lifetime, structural conformation, and pH. The average fluorescence lifetime of the excited neutral state of S65T as a function of pH yields pKa approximately 5.9 in agreement with literature values using steady-state techniques. In contrast to the intact beta-barrel at high pH, the anisotropy of neutral S65T (at pH 相似文献
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The First Integrals and Related Properties of a Class of Quintic Systems with a Uniform Isochronous Center 下载免费PDF全文
In this paper, we give all the first integrals of the quintic systems which have a uniform isochronous center,
and use them to determine the qualitative behavior of the periodic solutions of their equivalent non-autonomous systems. Meanwhile, we clearly describe the local phase portraits of singularity at infinity. 相似文献
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TiO2 *nH2 O凝胶预处理对水热合成SrTiO3 粉的影响 总被引:2,自引:0,他引:2
以TiCl4为钛源, 首先制备TiO2 * nH2O凝胶, 然后在80℃的水热条件下制备了SrTiO3粉.利用X射线衍射(XRD)、透射电子显微镜(TEM)和红外光谱(FTIR)研究了TiO2 * nH2O凝胶水洗方式、阴离子(Cl-和NO3-)以及TiO2 * nH2O热处理对SrTiO3粉性能的影响.结果表明, 水洗和热处理都能使TiO2 * nH2O凝胶产生晶化; TiO2 * nH2O的晶化程度对产物SrTiO3颗粒的粒度和粒度分布有很大影响,以非晶质TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度大且粒度分布宽.以结晶TiO2 * nH2O为钛源制备的SrTiO3颗粒粒度小且粒度分布窄,而且可以得到纳米颗粒.水热反应液相中存在Cl-或NO3-能使产物SrTiO3颗粒粒度稍有增大.综合以上结果, TiO2 * nH2O凝胶水洗对产物颗粒的影响主要是由于使凝胶产生了晶化,而由阴离子脱除产生的影响很小.因此,在不考虑阴离子对其它工程化影响(如设备腐蚀等)的前提下,可采用热处理代替水洗. 相似文献
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以TiCl4为钛源,首先制备TiO2*nH2O凝胶,然后在80℃的水热条件下制备了SrTiO3粉.利用X射线衍射(XRD)、透射电子显微镜(TEM)和红外光谱(FTIR)研究了TiO2*nH2O凝胶水洗方式、阴离子(Cl-和NO3-)以及TiO2*nH2O热处理对SrTiO3粉性能的影响.结果表明,水洗和热处理都能使TiO2*nH2O凝胶产生晶化;TiO2*nH2O的晶化程度对产物SrTiO3颗粒的粒度和粒度分布有很大影响,以非晶质TiO2*nH2O为钛源制备的SrTiO3颗粒粒度大且粒度分布宽.以结晶TiO2*nH2O为钛源制备的SrTiO3颗粒粒度小且粒度分布窄,而且可以得到纳米颗粒.水热反应液相中存在Cl-或NO3-能使产物SrTiO3颗粒粒度稍有增大.综合以上结果,TiO2*nH2O凝胶水洗对产物颗粒的影响主要是由于使凝胶产生了晶化,而由阴离子脱除产生的影响很小.因此,在不考虑阴离子对其它工程化影响(如设备腐蚀等)的前提下,可采用热处理代替水洗. 相似文献
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Liping Wen Yuexin Yu Shoufu Li 《Journal of Computational and Applied Mathematics》2009,230(2):351-359
This paper is concerned with the stability and asymptotic stability of θ-methods for the initial value problems of nonlinear stiff Volterra functional differential equations in Banach spaces. A series of new stability and asymptotic stability results of θ-methods are obtained. 相似文献
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Sufficient conditions for the stability and asymptotic stability of the theoretical solutions to nonlinear systems of functional differential and functional equations are derived. 相似文献
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In this paper, we answer the question: under what conditions a class of rigid differential systems have a composition center. We give the sufficient and necessary conditions for these systems to have a center at origin point. At the same time, we give the formula of focal values and the highest order of fine focus. 相似文献
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On the equivalence of two differential equations by means of reflecting functions coinciding 下载免费PDF全文
In this article, we discuss the equivalence of two differential systems by using the method of reflecting functions. We obtain some necessary and sufficient conditions under which certain differential equations are equivalent. Given these results, new types of differential systems equivalent to the given systems can be found. We also discussed the qualitative behavior of the periodic solutions of such differential systems. These results are new, in the sense that they generalize previous discussions on the equivalence of differential systems. 相似文献
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