溶液中尼龙11的NMR弛豫研究

用 2DNMR(HMQC)技术归属了溶液中尼龙 11分子的主要1H和13 C NMR共振信号 ,并通过变温和变浓度 1H NMR弛豫时间的测定 ,得到了尼龙 11溶液中氢键结构变化的动力学信息 .结果表明 ,溶液中尼龙 11分子的弛豫行为与一般高聚物不同 ,随着温度升高 ,尼龙链间相互作用逐渐减弱 ,尼龙分子与溶剂小分子间相互作用逐渐增强 ,尼龙链间氢键逐渐离解 ,而离解出来的自由NH和CO基团又与溶剂小分子间生成氢键 .尼龙 11链卷曲堆积成无规线团状 ,一部分溶剂被包裹在内部并和α CO质子成为一个整体而一起运动 .变浓度实验弛豫过程呈现双指数特性 ,快弛豫部分随体系浓度增加而增多 ,表明聚合物溶液中凝聚缠结含量的增大 ,这种凝聚缠结是由溶液中氢键引起分子链物理交联成网而形成的 .随着浓度增加 ,溶液逐渐变成局部粘度较大的类似软固体     

季铵盐型双子表面活性剂C14-s-C14·2Br的聚集行为

用1H NMR弛豫、2D NOESY研究了双子表面活性剂14-s-14胶束在重水溶液中的聚集行为. 1H NMR自旋-晶格、自旋-自旋弛豫实验表明, 联结基团质子及其邻近的亚甲基质子的运动受到严重限制, 表明这些质子形成胶束疏水核的壳层；而远离极性头的疏水质子的运动则相对自由, 说明其位于胶束的内部. 14-s-14系列(s=2, 3, 4)的弛豫实验结果还表明, 联结基团越短, 分子的碳氢链在疏水核中的排列越紧密. 与14-4-14的对应单链表面活性剂TTAB相比, 它们的分子运动更受限制. 14-4-14的2D NOESY 谱给出了与16-4-16类似的交叉峰信息, 这表明14-4-14同16-4-16一样, 形成了表面不平滑的球形胶束. 因此, 烷烃链的长短对胶束中分子的排列方式没有影响.     

乙烯-丙烯酸共聚物非晶区结构和分子运动的固体核磁共振研究

利用固体高分辨1 3CCP MAS和变温固体质子宽线技术对乙烯 丙烯酸共聚物 (EAA)非晶区的结构和分子运动进行了研究 ,结果发现 ,非晶区中羧基之间可以形成氢键 ,其数量随着共聚物中丙烯酸共聚单体含量的增加而增加 ,使得共聚物中非晶区分子运动能力随非晶区相对含量的增加而减弱 ,这是一种与一般的乙烯共聚物相反的变化趋势 .通过交叉极化方法间接测量了非晶区中乙烯链段的1 H自旋 自旋弛豫时间 (T2 ) ,表明非晶区中乙烯链段的运动同样受到氢键的束缚 .随着温度的升高 ,羧基之间的氢键发生解离 ,非晶区的柔性增强     

尼龙6升温过程的二维红外相关分析研究

通过二维红外相关分析来研究尼龙6在25～200℃范围内酰胺氢键和碳氢链段的结构变化．结果证明,尼龙6中酰胺氢键的吸收峰和主链上亚甲基的伸缩振动对于温度变化所导致的结构变化是十分敏感的,因此可以通过对二维红外相关谱图的分析,确定尼龙6在升温过程中酰胺氢键的解离和碳氢链段结构变化的先后顺序．     

C6H5—H…X分子间氢键的理论计算

利用密度泛函理论B3LYP方法, 在6-311+G(3df,2p)水平上对C6H5—H…X型分子间氢键进行了几何构型优化、氢键相互作用能、电子密度分布等计算. 其中C6H6为质子供体, HCOH、H2O、NH3、CH2NH和HCN为质子受体. 从电荷布居分析、自然键轨道等角度详细地讨论了C6H5—H…X 体系中, 共轭π键、O和N的不同键型结构对氢键形成的影响以及孤电子对与C—H 反键轨道之间的相互作用(n→σ*)等.     

CO_2在复合溶液MDEA-AMP中的溶解度

测定了CO2在复合溶液N-甲基二乙醇胺(MDEA)+2-氨基-2-甲基-1-丙醇(AMP)中的溶解度,研究了气相CO2浓度、温度和复合溶液的组分对溶解度的影响。实验获得了温度分别为25℃、30℃和40℃时,CO2在复合溶液MDEA-AMP中的溶解度。实验表明,溶解度随气相中CO2浓度升高或随AMP在复合溶液中的摩尔分数升高而升高,随温度升高而降低。     

聚亚甲基绿的性质

在 10～ 6 0℃范围内 ,测定了聚亚甲基绿的循环伏安图和交流阻抗图 ,测定了循环伏安所用电解质溶液的电导率随温度的变化 .在不同温度下 ,聚亚甲基绿的循环伏安图上均有一阳极峰和一阴极峰 ,阳极峰和阴极峰的峰电流均随温度升高而增加 ,即电极反应速率随温度升高而增加 .交流阻抗的结果表明 ,聚亚甲基绿的电荷传递电阻Rct随温度升高而增大 .热重 (TG)实验表明聚亚甲基绿热失重是分三步进行的 ,聚合物在 2 6 3 .1℃时发生分解 .扫描电镜 (SEM)结果显示聚亚甲基绿表面呈颗粒状     

尼龙-6 18的晶型转变研究

以偶偶尼龙-6 18为例, 通过示差扫描量热分析(DSC), 广角X射线衍射(WAXD)与傅里叶变换红外光谱(FTIR)等方法研究了其Brill转变的过程, 探索了脂肪族聚酰胺的晶型转变的本质. X射线衍射结果表明， 随着温度的升高, 尼龙-6 18由三斜晶系转变为假六方晶型, 同时其DSC曲线上出现一个较宽的吸热峰. 红外光谱结果表明, 在其晶型转变过程中, 晶体内氢键强度逐渐减弱, 与酰胺键相连的C—C和C—N键发生扭曲. 酰胺基团之间的亚甲基链段的振动逐渐增强, 部分亚甲基单元由反式构象变成旁式构象, 最后整齐排列的亚甲基链段逐渐变得无序化.     

温控近红外光谱用于胺类化合物氢键相互作用研究

氢键对于蛋白质等生物分子的结构与功能具有重要影响.基于近红外光谱对含氢基团的高灵敏响应及其温度效应,研究了脂肪胺中氮氢基团的结构及相互作用.采用独立成分分析对不同温度、不同浓度样品的光谱进行分析,得到光谱中的三种独立成分,分别对应于氮氢基团的非氢键键合、线型氢键键合和环状氢键键合三种结构形式.随着温度的升高,两种键合形式的氮氢基团逐步转化为非氢键键合形式.环状键合的氮氢基团先解离为线型键合形式,再解离为非氢键键合形式.随着脂肪伯胺侧链的增长,NH基团的光谱吸收受温度影响减弱,且线型键合形式受温度的影响较环状键合形式小.     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.     

Nuclear magnetic resonance relaxation studies of polyacrylamide solution

 The cohesive interaction among polymer chains in a polyacrylamide (PAAm)–D₂O solution has been studied by NMR relaxation. The NMR relaxation times of PAAm in the good solvent D₂O were measured at different temperatures. The results show that the solution system has a high local viscosity and that its relaxation characteristic is soft-solid-like. The temperature dependence of the relaxation behavior of the solution is obviously different from that of ordinary polymer solutions. The difference lies in the relaxation behavior of the methylene protons in the main chain of PAAm, as shown by analyzing the relaxation process with single exponential and biexponential decays. As the temperature increases, the solvation is weakened, leading polymer chains to form curling coils, thus hindering the movement of the methylene protons among the main chains. It can be expected from the existence of 80% fast-relaxing protons that there are a zhigh number of entanglements among the polymer chains in PAAm solution. The information about entanglements among the polymer chains can be deduced from the biexponential dependence of the spin–spin relaxation on the concentration of the polymer solutions. Received: 14 April 1999/Accepted in revised form: 12 October 1999     

Chirality-organized ferrocene receptor bearing podand dipeptide chains (-L-Ala-L-Pro-NHPyMe) for the selective recognition of dicarboxylic acids

[structure: see text] The ferrocene receptor bearing the podand dipeptide chains (-l-Ala-l-Pro-NHPyMe) was found to provide a chirality-organized binding site through two intramolecular interchain hydrogen bonds between CO (Ala) and NH (another Ala) of each podand dipeptide chain. The size-selective and chiral recognition of dicarboxylic acids was achieved by multipoint hydrogen bonds of the binding site.     

Enantiomerisation of tetrahedral homochiral [M4L6] clusters: synchronised four Bailar twists and six atropenantiomerisation processes monitored by temperature-dependent dynamic 1H NMR spectroscopy

Temperature-dependent 1H NMR studies prove homochiral, racemic [([symbol: see text])/([symbol: see text])]-((NH4)4[symbol: see text] [Mg4(L1)6]) (1) to be kinetically stable on the NMR timescale. Due to steric reasons, rotation around the central C-C single bond in (L1)2- is blocked, which prevents 1 from enantiomerisation. Most interestingly, however, the 1H NMR spectrum of racemic 2a reveals dynamic temperature dependence. This phenomenon can be explained by simultaneous Bailar twists at the four octahedrally coordinated magnesium centres, synchronised with the sterically unhindered atropenantiomerisation processes around the C-C single bonds of the six ligands (L2)2-, leading to the unprecedented enantiomerisation ([symbol: see text])-2a [symbol: see text] ([symbol: see text])-2a. The profound nondissociative rearrangement occurs without the formation of diastereoisomers. Supplementary support for the interpretation of the temperature-dependent dynamic 1H NMR spectra of 2a is presented by additional studies of [([symbol: see text])/([symbol: see text])]-((EtNH3)4 [symbol: see text] [Mg4(L2)6]) (2b). In 2a and 2b, the ether methylene protons exhibit identical temperature dependence. However, with addition, the methylene protons of the ethyl ammonium groups of 2b display similar temperature dependence as the ligand ether methylene protons.     

STRUCTURAL PHASE TRANSITION OF ALIPHATIC NYLONS VIEWED FROM THE WAXD/SAXS AND VIBRATIONAL SPECTRAL MEASUREMENTS AND MOLECULAR DYNAMICS CALCULATION

The crystalline phase transition of aliphatic nylon 10/10 has been investigated on the basis of the simultaneous measurement of wide-angle and small-angle X-ray scatterings, the infrared spectral measurement and the molecular dynamics calculation. An interpretation of infrared spectra taken for a series of nylon samples and the corresponding model compounds was successfully made, allowing us to assign the infrared bands of the planar-zigzag methylene segments reasonably. As a result the methylene segmental parts of molecular chains were found to experience an order-to-disorder transition in the Brill transition region, where the intermolecular hydrogen bonds are kept alive although the bond strength becomes weaker at higher temperature. The small-angle X-ray scattering data revealed a slight change in lamellar stacking mode in the transition region. The crystal structure has been found to change more remarkably in the temperature region immediately below the melting point, where the conformationally disordered chains experienced drastic rotational and translational motions without any constraints by hydrogen bonds, and the lamellar thickness increased largely along the chain axis. These experimental results were reasonably reproduced by the molecular dynamics calculation performed at the various temperatures.     

用核磁共振技术研究氢键的键合方式

为了了解怎样利用核磁共振技术研究氢键的键合方式,本文以联酰胺衍生物为例,分别运用变温核磁共振氢谱和变浓度核磁共振氢谱分析了羰基(CO)与氨基(H—N)之间形成氢键的形式。结果表明,本文举例中联酰胺基团中的CO与H—N以分子间氢键形式存在。     

Giant dielectric anisotropy and relaxor ferroelectricity induced by proton transfers in NH+...N-bonded supramolecular aggregates

A huge dielectric effect has been observed in a pure and water-soluble hydrogen-bonded organic crystal, 1,4-diazabicyclo[2.2.2]octane hydroiodide [C6H13N2]+.I(-) (dabcoHI). In this structure, the dabco cations are NH+...N bonded into linear aggregates, where the protons are disordered at two nitrogen atoms and the crystal acquires the symmetry of space group P6m2. This nonpolar crystal exhibits a barely temperature-dependent dielectric constant exceeding 1000 at ambient conditions. The dielectric response is extremely anisotropic, more than 2 orders of magnitude higher along the linear hydrogen bonded chains than in perpendicular directions. The physics underlying this effect originates from proton transfers in the NH+...N bonds, leading to disproportionation defects and formation of polar nanodomains, which, on the macroscopic scale, results in one-dimensional relaxor ferroelectricity. Such properties are unprecedented for the materials with hydrogen bonds highly polarizable due to proton disorder. The proton disordering in dabcoHI is analogous to this in H2O ice, where the hydrogen bonds remain disordered until the lowest temperature.     

Dinuclear calcium complex with weakly NH...O hydrogen-bonded sulfonate ligands

The novel intramolecularly NH...O hydrogen-bonded Ca(II)-aryl sulfonate complex, [Ca2(SO3-2-t-BuCONHC6H4)2(H2O)4]n(2-t-BuCONHC6H4SO3)2n (1), sulfonate anion, (HNEt3)(SO3-2-t-BuCONHC6H4) (2a), (PPh4)(SO3-2-t-BuCONHC6H4) (2b), (n-Bu4N)(SO3-2-t-BuCONHC6H4) (2c), and sulfonic acid, 2-t-BuCONHC6H4SO3H (3), were synthesized. The structures of 1, 2a, and 2b depict the presence of the formation of NH...O hydrogen bonds between the amide NH and S-O oxygen for a series of compounds as determined by IR and 1H NMR analyses both in the solid state and in the solution state. Thus, the NH...O hydrogen bonds with neutral amide groups are available for investigation of the electronic state of the O- anion. The combined data from the IR and 1H NMR spectra indicate that the sulfonic acid, sulfonate anion, and Ca(II) complex have a substantially weak intramolecular NH...O hydrogen bond between the SO3 oxygen and amide NH. In the detailed comparison with the intense NH...O hydrogen bonds for the carboxylate, weak NH...O hydrogen bonds for sulfonate is due to the strong conjugation of the SO3- group with the lower nucleophilicity.     

Large variations in acidity of terminal amide bonds in histamine-containing peptides as measured by proton DNMR

The main objective of these studies is to quantitatively estimate pK variations of individual amide bonds as a function of the ionization state of end groups in peptides, determined on measuring macro- and micro- (if any) ionization constants. ¹H NMR spectra of aqueous solutions of eight model substrates were consequently recorded using a water suppression sequence, within large pH ranges. A set of programs was devised to treat NMR data over the entirety of pH-dependent NMR patterns, in order to smooth out errors arising in handling individual spectra. Rates of amide proton abstraction by hydroxide ions were obtained from the coalescence of methylene coupled protons and the decrease of NH bond signal intensities, allowing us to estimate and discuss peptide pKs on assuming back reprotonation at a diffusion-limited rate. Cis–trans isomerization rates in two substrates bearing a tert-Butyloxycarbonyl terminal group were put in parallel with the acidity of carbamic protons.     

Chirality organization of ferrocenes bearing podand dipeptide chains: synthesis and structural characterization

A variety of ferrocenes bearing podand dipeptide chains have been synthesized to form an ordered structure in both solid and solution states and have been investigated by 1H NMR, FT-IR, CD, and X-ray crystallographic analyses. Conformational enantiomerization through chirality organization was achieved by the intramolecular hydrogen bondings between the podand dipeptide chains. The single-crystal X-ray structure determination of the ferrocene 2 bearing the podand dipeptide chains (-D-Ala-D-Pro-OEt) revealed two C2-symmetric intramolecular hydrogen bondings between CO (Ala) and NH (another Ala) of each podand dipeptide chain to induce the chirality-organized structure. The molecular structures of the ferrocene 1 composed of the podand L-dipeptide chains (-L-Ala-L-Pro-OEt) and 2 are in a good mirror image relationship, indicating that they are conformational enantiomers. An opposite helically ordered molecular arrangement was formed in the crystal packing of 2 as compared with 1. The ferrocene 2 exhibited induced circular dichroism (CD), which appeared at the absorbance of the ferrocene moiety. The mirror image of the CD signals between 1 and 2 was observed, suggesting that the chirality-organized structure via intramolecular hydrogen bondings is present even in solution. The ferrocene 4 bearing the podand dipeptide chains (-Gly-L-Leu-OEt) also showed an ordered structure in the crystal based on two intramolecular hydrogen bondings between CO (Gly) and NH (another Gly) of each podand dipeptide chain, together with intermolecular hydrogen bondings between CO adjacent to the ferrocene unit and NH (neighboring Leu) to create the highly organized self-assembly. A different self-assembly was observed in the crystal of the ferrocene 5 composed of the podand dipeptide chains (-Gly-L-Phe-OEt), wherein each molecule is bonded to two neighboring molecules through two pairs of symmetrical intermolecular hydrogen bonds to form a 14-membered intermolecularly hydrogen-bonded ring. These ordered structures based on the intramolecular hydrogen bondings in the solution state are also confirmed by 1H NMR and FT-IR.