用模型拟合法研究1,2-聚丁二烯分子运动

本文采用Cole-Cole,Fuoss-Kirkwood经验相关时间分布模型和构象跳跃,高聚物局部主链运动阻尼取向扩散分子模型,对1,2-聚丁二烯在溶液中的~(13)C-NMR自旋-晶格弛豫时间nT_1和核Overhauser效应(NOE)值进行了数值拟合。用拟合所得分子运动参数讨论了1,2-聚丁二烯微观分子运动对链结构和温度的依赖性。     

用核磁共振研究浓溶液中高聚物缠结

研究~(13)C-NMR弛豫过程能提供聚合物分子水平上缠结(拓扑和凝聚)的信息.1,2-聚丁二烯在质量分数为25％浓溶液中主链上各基团约有20％产生缠结网络,这个量与样品中1,2-链节含量和溶剂种类无关。而侧链上的端基=CH_2几乎全部是非网络型的,表现为在结点自由地滑动。     

用~(13)C-NMR研究 1,2-聚丁二烯的分子运动——1,2-聚丁二烯分子运动对微观结构的依赖性

本工作用200兆赫脉冲傅里叶变换 NMR 波谱仪测定了一系列1,2-聚丁二烯样品在溶液中~13C核自旋-晶格弛豫时间(T_1)和核Overhauser效应(NOE)。较系统地研究了1,2-聚丁二烯的分子运动与化学结构、序列结构和大分子链节构成的关系,分析了乙烯基的内旋转运动。实验结果表明,顺1,4-链节中各碳的nT_1值比1,2-链节中相应各碳的nT_1值长1倍左右;对于相同的链节,当其两旁由1,2-链节变为顺1,4-链节时,其各类碳的nT_1值都大大增加;随着1,2-链节增加,各类碳的nT_1值都明显缩短。乙烯基叔碳的nT_1值大于端碳,经计算表明,引起乙烯基叔、端碳的nT_1值不相等的主要因素是乙烯基在垂直于主链的平面上的摆动。     

1,2-聚丁二烯分子运动的~(13)C-NMR研究——Ⅱ.分子运动的温度依赖性

本文用200MHz脉冲傅利叶变换波谱仪测定了1,2-聚丁二烯样品在不同温度下的~(13)C-T_(19)NOE,线宽和化学位移等~(13)G自旋弛豫参数,研究了1,2-聚丁二烯分子运动的温度依赖性.结果发现,在-10—-30℃之间,样品中各碳核的NOE和谱线宽度随温度变化的曲线斜率增加,表明此时长程链运动冻结;各碳核nT_1随温度的变化均在-45℃左右出现极小值.     

~(13)C-NMR化学位移与聚合物的构象——Ⅰ.1,2-聚丁二烯乙烯基叔碳(-CH=)的~(13)C-NMR谱研究

本文应用半经验方法来解析无规1,2-聚丁二烯乙烯基叔碳(—CH=)的~(13)C-NMR谱图。研究指出只有主链CH与乙烯基叔碳之间的gauche排列和由此产生的屏蔽效应对后者的化学位移的改变作出了贡献。因此,可以直接利用键概率来归属十个五元组立构异构体的排列顺序。由于上述原因,得到了对于无规1,2-聚丁二烯乙烯基叔碳的~(13)C-NMR谱的一种新的归属,并且通过研究全同和间同1,2-聚丁二烯的~(13)C-NMR谱图予以证明。     

~(13)C-NMR研究聚丁二烯的序列结构

本文采用~13C-NMR方法研究了不同催化体系制备的聚丁二烯。经分析指出,聚丁二烯分子链的三种序列(顺-1,4-序列、反-1,4-序列和1,2-序列)和十七类脂碳碳核为~13C-NNR谱贡献了十六个谱峰。经数据的解析,得到一组计算聚丁二烯脂碳部分各谱峰化学位移的经验参数。在本文条件下,应用该组参数得到的计算值与实验值符合较好。本文确认了聚丁二烯反-1,4-序列第四峰(T_4)的存在。初步研究了聚丁二烯~13℃-NMR谱图的定量处理问题。     

聚丁二烯~(13)C-NMR谱图中一个新的共振吸收峰(T_4)

<正> 最近解析锂系和铁系含乙烯基聚丁二烯的~(13)C-NMR谱图,发现并确认了一个新的共振吸收峰。即聚丁二烯反式1,4-序列的第四峰,简称T_4峰。 Furukawa等对钼系和章哲彦等对铁系等二元聚顺-1,4-1,2-丁二烯的研究都指出在聚丁二烯的~(13)C-NMR谱图上,有四个谱峰属于顺1,4-序列。本文给出其化学位     

聚酯-聚氨酯溶液的~(13)C-NMR弛豫研究——自旋晶格弛豫与聚氨酯分子在溶液中的局部片段运动

本文对由己二酸丁二醇酯(数均分子量为2000)、4,4′-二苯基甲烷二异氰酸酯(MDI)和扩链剂1,4-丁二醇(BDO)形成的不同分子量的聚氨酯溶液进行了~(13)C核磁共振研究。在氘代二甲基亚砜溶液中,应用JEOL FX-60Q核磁共振仪测定了聚氨酯链中不同嵌段上CH_2和CH碳的自旋晶格弛豫时间(T_1)。利用所得数据对聚氨酯分子的链运动进行了分析和讨论。     

~(13)C核磁共振(四)

9 ~(13)C自旋-晶格弛豫时间(T_1)的测量及应用 9.1 测定T_1的方法 9.1.1 倒向—恢复法此法是用(180°-τ-90°)_n脉冲系列作用于样品。磁化矢量M_0在180°脉冲作用下倒向(图20b),在自旋-晶格弛豫过程中,磁化矢量从-M_0经0到 M_0弛豫,在这一过程中,即过了时间τ后,90°脉冲将部份弛豫的磁化矢量M_τ旋转到X(?)Y平面中,并在接收线圈中感应出FID信号。如果τ很短,M_τ还是负的(M_τ<0),90°脉冲(?)_1,作用后M_τ沿X向负Y轴旋转(图20c),     

~(13)C-NMR研究铁系聚丁二烯(顺1,4-1,2)的链结构

前已报道,以高活性铁催化剂可以制得性能良好的含顺-1,4-1,2结构的等二元聚丁二烯。文献已有用~(13)C-NMR研究以钴,钼催化剂合成的这种等二元聚合物的报导。本工作用~(13)C-NMR进行了研究,得到的聚合物的~(13)C-NMR图谱表明,聚合物的脂碳部分共有十一个共振峰,烯碳部分有九个峰。通过改进Furukawa的经验参数,并应用Randall的方法,这些共振峰的归属得到了令人满意的结果。确认该聚合物是双烯和单烯的无规共聚物,但偏离Bernoulli分布,趋向于一级Markov分布。     

固体核磁共振弛豫在高分子研究中的应用

本文综述了近年来固体核磁弛豫方法在高分子研究中的应用，共分５个部分加以介绍：（１）自旋－晶格弛豫过程；（２）在旋转坐标系中的＾１３Ｃ自旋－晶格弛豫过程；（３）交叉极化速率和旋转坐标系中的＾１Ｈ自旋－晶格弛豫过程；（４）自旋－自旋弛豫过程；（５）动态结构导致的线形变化。本文主要讨论磁性核的各种弛豫过程以及它们与分子结构和分子运动的关系。     

Structural analysis of alanine tripeptide with antiparallel and parallel beta-sheet structures in relation to the analysis of mixed beta-sheet structures in Samia cynthia ricini silk protein fiber using solid-state NMR spectroscopy

The structural analysis of natural protein fibers with mixed parallel and antiparallel beta-sheet structures by solid-state NMR is reported. To obtain NMR parameters that can characterize these beta-sheet structures, (13)C solid-state NMR experiments were performed on two alanine tripeptide samples: one with 100% parallel beta-sheet structure and the other with 100% antiparallel beta-sheet structure. All (13)C resonances of the tripeptides could be assigned by a comparison of the methyl (13)C resonances of Ala(3) with different [3-(13)C]Ala labeling schemes and also by a series of RFDR (radio frequency driven recoupling) spectra observed by changing mixing times. Two (13)C resonances observed for each Ala residue could be assigned to two nonequivalent molecules per unit cell. Differences in the (13)C chemical shifts and (13)C spin-lattice relaxation times (T(1)) were observed between the two beta-sheet structures. Especially, about 3 times longer T(1) values were obtained for parallel beta-sheet structure as compared to those of antiparallel beta-sheet structure, which could be explicable by the difference in the hydrogen-bond networks of both structures. This very large difference in T(1) becomes a good measure to differentiate between parallel or antiparallel beta-sheet structures. These differences in the NMR parameters found for the tripeptides may be applied to assign the parallel and antiparallel beta-sheet (13)C resonances in the asymmetric and broad methyl spectra of [3-(13)C]Ala silk protein fiber of a wild silkworm, Samia cynthia ricini.     

Precise Molecular Weight Determination and Structure Characterization of End-functionalized Polymers: An NMR Approach via Combination of One-dimensional and Two-dimensional Techniques

We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS).The peaks in 1H-NMR spectra corresponding to main-chain,side-chain and chain-end groups are assigned by 1H-1H gCOSY,1H-13C gHSQC and gHMBC spectra.For the first time,the spin-lattice relaxation time (T1) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW).As a result,a much higher delay time (d1) for chain-ends (d1 ＞ 20T1) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS,which is in accordance with the value estimated by GPC.An improved method for the polymer MW determination is established,by combination of different NMR techniques to distinguish the peaks,and a large dl setting to achieve quantitative NMR analysis.     

含氟离聚体的多相结构及大分子链运动的NMR研究

本文用~(13)C自旋-自旋弛豫时间T_2表征了以丙烯酸-1,1,5-三氢全氟戊酯-丙烯酸共聚物为基础的离聚体体系的多相结构和大分子链段运动特性,结果表明:离子微区和聚合物基体之间存在界面层,聚合物主链的运动活性与离聚体的共聚物组成、金属离子特性、离子化程度、离子微区的稳定性和离子微区内的精细结构均有密切关系.     

Nuclear relaxation of H2 and H2@C60 in organic solvents

The 1H nuclear spin-lattice relaxation time (T1) of H2 and H2@C60 in organic solvents varies with solvent, and it varies proportionally for H2 and for H2@C60. Since intermolecular magnetic interactions are ruled out, the solvent must influence the modulating processes of the relaxation mechanisms of H2 both in the solvent cage and inside C60. The temperature dependence of T1 also is very similar for H2 and H2@C60, T1 going through a maximum by varying the temperature in solvents which allow a wide range of temperatures to be explored. This behavior is attributed to the presence of dipolar and spin-rotation mechanisms which have an opposite dependence on temperature.     

Acceleration of carbon-13 spin-lattice relaxation times in amino acids by electrolytes

A series of amino acids and carboxylic acids were determined by 13C NMR spectroscopy.The results showed that addition of 3M MgCl2 led to the 13C NMR integral area of samples being well proportional to number of carbon atoms that produce the particular signal with reliability over 95%. Measurements of 13C spin-lattice relaxation times (T1's) are reported for a number of amino acids. T1's of all the carbons in amino acids generally tend to decrease with the increase of the concentration of electrolytes, and the presence of magnesium slats is of significant. Carboxylic carbons in amino acids are the most sensitive "acceptor" of the 13C spin-lattice relaxation accelerating effects in electrolytes, and the 13C spin-lattice relaxation accelerating ability of electrolytes is Mg(ClO4)2 ＞MgCl2 ＞CaCl2 ＞NaCl ＞KCl ＞LiClO4 ＞NaOH. In general, T1's of C1 carbons in nonpolar a-amino acids are higher than those in polar and basic a-amino acids both in aqueous and 3M MgCl2 medium. In aliphatic straight-chain amino acids, a-, a-, a-, ai- and a- amino acids, T1's of C1 carbons tend to reduce with the increase of inserted carbon numbers between amino and carboxylic groups compared with Gly. T1's can be decreased even more when amino acids are mixed in 3M MgCl2, but T1's of carbons in amino acids decrease slightly with increase of the concentration of amino acids in 3M MgCl2. The mechanisms of the observed phenomena are discussed in terms of intermolecular interaction and paramagnetic impurity in electrolytes, large contributions of intermolecular interaction which is enhanced in electrolytes concentrate on the incoming "unsaturation" of the primary solvation shell of cations with the increase of electrolytes concentration and complexes formation of amino acids with metal ions. In electrolytes, amino acids are "anchored" to cations and molecule tumbling is slowed down, molecular rigidity is increased and molecular size is "enlarged", all of these are helpful to accelerate the 13C spin-lattice relaxation. Atlast, MgCl2 is proposed as an efficient relaxation agent for analysis of amino acids and some carboxylic acids.Samples were dissolved with the aid of supersonic which has the effect of degassing, and they were degassed again with supersonic for 30 seconds right before determination. All of the 13C NMR was obtained with a Bruker DPX-300 NMR instrument, using NOE-suppressed inverse gated decoupling with a recycle delay 8.00s and a sweep width 30120.48Hz, experiment temperature is integral of the carbon with the smallest chemical shift is calibrated as 10.00. Spin-lattice relaxation times (T1's) were determined by using inversion recovery according to Bruker avance user's guide.The pulse sequence is (T-90.°-T-180°-o-90t°) n.     

Spin-lattice relaxation and rotational motion of aromatic triplet-state molecules in supercooled alkane solvents (part 1)

The phosphorescence of phenazine (PZ) and quinoxaline (QX) was investigated after pulsed laser excitation in the glass-transition range of several alkane solvents. Three relaxation processes of PZ and QX in the metastable triplet state, T1, were studied as a function of temperature: (1) the decay of the selective population of the strongly phosphorescent triplet substate T1x due to spin-lattice relaxation (SLR), (2) the time-dependent red shift of the phosphorescence spectrum due to the solvation of triplet-state molecules, and (3) the decay of the phosphorescence polarization due to orientational relaxation (OR). Various aspects and connections of the mechanisms governing the three relaxation phenomena are discussed. The relaxation dynamics were characterized at temperatures above the glass-transition temperature of the respective solvent, where the fundamental processes involved are strongly dependent upon the solvent viscosities. For the systems treated here, OR and solvation were satisfactorily described by a Vogel-Fulcher-Tammann temperature behavior. SLR also depends on properties of the alkane solvent above the glass transition. Upon cooling, SLR becomes independent of the specific solvent properties and is based on mechanisms that are typical for amorphous glasses or solids. (This particular aspect will be the subject of a subsequent publication, part 2).     

New application of proton nuclear spin relaxation unraveling the intermolecular structural features of low-molecular-weight organogel fibers

Proton nuclear spin relaxation has been for the first time extensively used for a structural and dynamical study of low-molecular-weight organogels. The gelator in the present study is a modified phenylalanine amino acid bearing a naphthalimide moiety. From T(1) (spin-lattice relaxation time in the laboratory frame) and T(1ρ) (spin-lattice relaxation time in the rotating frame) measurements, it is shown that the visible gelator NMR spectrum below the liquid-gel transition temperature corresponds to a so-called isotropic compartment, where gelator molecules behave as in a liquid phase but exchange rapidly with the molecules constituting the gel structure. This feature allows one to derive, from accessible parameters, information about the gel itself. Nuclear Overhauser effect spectroscopy (NOESY) experiments have been exploited in view of determining not only cross-relaxation rates but also specific longitudinal rates. The whole set of relaxation parameters (at 25 °C) leads to a correlation time of 5 ns for gelator molecules within the gel structure and 150 ps for gelator molecules in the isotropic phase. This confirms, on one hand, the flexibility of the organogel fibers and, on the other hand, the likely presence of clusters in the isotropic phase. Concerning cross-relaxation rates, a thorough theoretical investigation in multispin systems of direct and relayed correlations in a NOESY spectrum allows one to make conclusions about contacts (around 2-3 ?) not only between naphtalimide moieties of different gelator molecules but also between the phenyl ring and the naphtalimide moiety again of different gelator molecules. As a result, not only is the head-to-tail structure of amino acid columns confirmed but also the entangling of nearby columns by the naphthalimide moieties is demonstrated.