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The dielectric permittivity and loss tangent of 1,2-polybutadienes with different chain structures were determined as a function of temperature from-180℃ to 100℃ at different frequencies, and the frequency and structure dependence of the dielectric propertie of 1,2-polybutadienes have been investigated. It is found that a maximum of the permittivity occurs in the glass-transition region. The width of the glasstransition peak increases with increasing frequency while its height has little change. With a rise in the content of 1,2-units, the permittivity decreases and the height of the glass-transition peak slightly grows. A maximum of the width of the glass-transition peak appears when the content of 1,2-units is about 45%. Both the permittivity and dielectric loss drop down as the growth of the content of syndiotactic 1,2-units. 相似文献
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稀土与脂肪族Schiff碱多核配合物的合成及波谱 总被引:2,自引:0,他引:2
在形成多核配合物的诸条件中,认为减小空间位阻颇为重要,设计的直链脂肪族的四甘醇醛与甘氨酸缩合形成的Schiff碱(TAGL)为此提供了有利的条件,且成功地获得了它与稀土离子反应形成的三核配合物(Ln:L=3:1):[Ln~3(TAGL)(NO~3)~7]CH~3OH·nH~2O(Ln=La,Nd,Sm,n=1;Ln=Gd,Dy,Yb,Y,n=2)。以元素分析,IR,NMR等确证其组成,根据EPR谱探讨了Gd(III)配合物的晶体场强,同时见到该类脂肪族Schiff碱及其配合物中δ~H~C~=~N的质子谱向高场明显位移至~5.10。 相似文献
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空气的尘埃中含有一种核苷酸降解酶,这种酶很容易被溶液中痕量的Mg2+等金属离子激活,从而使溶液中的DNA或RNA解链或失活.因而用NMR方法研究核酸的溶液结构时,需要在磷酸缓冲溶液中加入乙二胺四乙酸(EDTA)或其钠盐,保持其浓度大于0.1mmol/L[1~3],利用EDTA与包括Mg2+在内的众多金属离子的强络合作用,解除Mg2+等金属离子对核苷酸降解酶的激活功能,达到保护核酸活性的目的. 相似文献
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距离约束分子动力学计算低聚核苷酸 d(GGTATACC)~2溶液中三维结构 总被引:1,自引:0,他引:1
8聚核苷酸 d(GGTATACC)~2溶液中的三维结构通过简单的高温和低温动力学计算以及能量优化的方法获得。计算中以标准B型双螺旋DNA为初始结构, 加上螺旋间的20个氢键约束和由核磁共振NOESY谱获得的186个NOE约束, 另外还加入二面角约束32个。计算所得的6个低能(-302±5kJ/mol)优势构象的均方根偏差(rmsd值)均小于0.06nm, 平均均方根偏差为0.043nm, 从优化结构反算所得的NOE谱与实验数据相吻合。计算结果表明, 所加各约束项合理, 优化结构具有较高的可信度。 相似文献
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Nine Ln( Ⅲ ) complexes with a novel Schiff base derived from diglycolamine and benzoylacetone (BZDA) have been synthesized and characterized. They can be formulated as [Ln2(BZDA)3(NO3)3](NO3)3· nH2O(Ln=La, Pr, Nd, Sm, n = 4; Ln=Gd, Tb, Er, Yb, Y, n = l). Enamic form mechanism in this β-diketone Schiff base and its complexes were suggested and proved by IR, UV and NMR methods. The 13C spin-lattice relaxation time T1 and the ratios of r(ci-Ln)/r(cj-Ln) were measured by a 500 MHz NMR instrument for elucidating the formation of the stable sk-membered chelate ring structure in these complexes. The EPR spectrum of the Gd( Ⅲ ) complex exhibits the "U" spectral feature and "zero field effect". On the basis of them, the crystal field strength and the local symmetry around Gd3 in the complex have been discussed. 相似文献
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A series of novel heteronuclear Ln(Ⅲ)-Cu(Ⅱ) complexes with noncyclic polyether-amino acid Schiff base were synthesized. The general formula is [LnCu_2(H_2TALY)(NO_3)_5](NO_3)_2' nH_2O(Ln=La, Nd, Sm, Gd, n= 4; Ln=Yb, Y, n=3), where H_2TALY = tetraglycol aldehyde bis-lysine Schiff base. It is the first time to report the synthetic method for this new Cu(Ⅱ) complexes and Ln(Ⅲ)-Cu(Ⅱ) heteronuclear complexes. The complexes were characterized by elemental analysis, IR spectra, TG-DTA, magnetic susceptibility, and especially by a 500 MHz NMR spectrometer for 2D-COSY NMR. Coordination mechanism and structures of complexes have been suggested as well. Of particular interest is the potential that the novel complexes obtained may be used as a catalyst, which prompted us to investigate them. It shows 100% conversion with the viscosity-average molecular weight 120 000 for the polymerization of methyl methacrylate (MMA) without addition of any cocatalyst. Furthermore, the complexes with such aliphatic Schiff bas 相似文献