X-射线小角光散射(SAXS)研究全氟磺酸树脂中空纤维膜中的离子簇结构

本文用SAXS(Small Angle X-ray Scattering)方法对全氟磺酸树脂中空纤维膜中的离子簇结构进行了研究.在散射角2θ=2°左右,出现由离子簇产生的散射峰;并就离子交换容量、不同阳离子形式、含水量及不同拉伸等对离子簇散射峰位的影响进行了研究讨论.并计算了有关离子簇半径和每个离子簇中的离子数目.     

电喷雾多级串联质谱法研究碱金属硝酸盐和亚硝酸盐簇合物离子的裂解行为

在正常毛细管温度(200 ℃)下,利用电喷雾质谱(ESI-MS)研究了NaNO3、KNO3、NaNO2和KNO2形成的新型簇合物离子,采用电喷雾多级串联质谱(ESI-MSn)研究了簇合物离子裂解行为.实验结果表明: NaNO3和KNO3溶液产生的簇合物离子及这些离子的裂解方式相似;NaNO2溶液产生的簇合物离子比NaNO3和KNO3溶液产生的复杂;KNO2溶液产生了含有Na+离子的簇合物离子,通过分析KNO2簇合物离子的裂解行为证明了Na+与NO-2的亲合势大于K+.此外,还研究了离子源金属毛细管温度和溶液浓度对簇合物离子形成的影响.     

团簇尺寸对奇数和偶数磷团簇离子信号强度差异的影响

磷原子形成的奇数和偶数团簇离子的信号存在明显的强度差异. 当团簇离子尺寸n>25时, 奇数团簇离子的信号强度一般会远远超过其邻近的偶数团簇离子. 为更好地理解团簇尺寸对这一现象的影响, 本文通过真空中激光溅射红磷的方法, 利用质谱对磷团簇离子进行了研究和分析. 结果表明这种方法可以产生较大尺寸(n~500)的磷团簇离子. 进一步对团簇离子的强度分布进行分析表明: 随着正负离子团簇尺寸的增加, 奇/偶数离子强度差异都会逐渐减小. 根据它们的变化趋势, 可以预测: 当n>1000时, 奇/偶数离子强度交替的现象可能会消失. 这一结果正反映出团簇在从原子演变到凝聚态物质过程中的桥梁作用.     

嵌段聚氨酯阴离子离聚物的小角X射线散射研究

用小角Ｘ射线散射研究了嵌段聚氨酯阴离子离聚物中不同离子化程度对离子聚集体形态结构的影响．结果表明：离子含量少时，主要以非聚集离子或多重离子对的形式存在；离子含量多时，主要以离子簇的形式存在．聚氨酯离子化后，有利于软、硬段的微相分离．     

N_2H_4-CH_3OH氢键团簇体系的从头计算

用从头计算法研究了 (N2 H4-CH3OH)氢键团簇体系。分别在HF/6 31G 和HF/6 31G 水平上对它们的中性和离子团簇进行几何全优化 ,得到了 3种中性混合团簇稳定构型和离子混合团簇稳定构型 ,并对其能量和稳定性进行了比较。讨论了 3种不同构型离子团簇可能的解离通道。给出了质子化混合团簇的稳定构型 ,并对其可能的解离通道进行了讨论。文中最后计算出N2 H4,CH3OH ,(N2 H4-CH3OH)团簇的质子亲和能 (PA) ,分别为 :2 0 6.7kcal/mol,1 78.3kcal/mol,2 2 7.5kcal/mol,其中质子亲和能PAcalc[N2 H4]与实验值PAexp[N2 H4]=2 0 4 .8kcal/mol符合得很好。     

用从头算法研究高氯酸钠溶液中存在的离子缔合物种及缔合过程

采用量子化学计算方法在HF/6-31+G*水平下对高氯酸钠溶液中可能存在的离子缔合物种及浓度升高时溶液中发生的离子缔合过程进行了研究. 高氯酸根与水合钠离子可形成溶剂共享离子对、接触离子对、三离子及多离子团簇等离子缔合物种, 当体系中水比较充足时, 钠离子可以保持较规整的六配位八面体构型, 而当水分子比较少时, 则生成不规则的五配位构型. 以上水合离子缔合物种中的ν₁-ClO₄^-频率与水合硝酸根中的参比值相比, 分别发生4.7, 8.5及14~17 cm^-1的蓝移, 除以影响因子后, 其与实验结果符合得很好. 通过将计算结果与实验结果进行对比, 高氯酸钠溶液在浓度升高时发生离子缔合的过程可简略表示为“自由水合离子→溶剂共享型离子对→单齿接触离子对→阳-阴-阳型三离子团簇→链状多离子团簇→网状多离子团簇→无定形晶体”. 这个过程与硫酸镁相似, 而与硝酸镁、高氯酸镁和硝酸钠不同.     

EMIM离子液体离子簇模型的量子化学计算

以1-乙基-3-甲基咪唑(EMIM)卤化物、氟硼酸盐、三溴化物和二碘溴酸盐、氯铝酸和溴铝酸盐等不同种类EMIM离子液体为研究对象,对多阳离子、多阴离子的离子簇模型进行了量子化学计算研究.首先在B3LYP/6-311++G(d, p)水平上(I使用6-311G(d, p)基组)对{[EMIM]X_n}^(n-1)- (X = Cl, Br, I, BF₄, AlCl₄, AlBr₄, Br₃, IBrI, FHF; n = 2, 3)和{[EMIM]₂X_n'}^(n'-2)- (n' = 3, 4, 5)离子簇进行构型优化,并对卤化物和氟硼酸盐进行了振动光谱计算.结果表明所采用理论模型在键长、键角等结构参数及红外振动光谱方面均与实验结果符合较好.同时对不同离子簇模型中阴、阳离子间相互作用能与实验熔点之间的关系进行了研究,发现采用{[EMIM]₂X_n'}^(n'-2)--模型时EMIM离子液体实验熔点与阴、阳离子间相互作用能之间呈现近线性关系.     

532 nm纳秒激光电离产生Xez＋(z ≤ 11)高价离子

利用25 ns脉冲Nd-YAG 532 nm激光,在1011 W•cm－2的光场强度下,研究了Xe原子团簇的激光电离过程,观察到较强的高价离子信号,其中最高价态达＋11.不同脉冲束位置和束源压力的实验表明,仅当激光作用于脉冲束中段时才能观察到高价离子,且高价离子信号强度随束源压力的增加而迅速增强,说明束中大尺寸团簇的存在与高价离子的形成密切相关.通过实验,认为高价离子可能来源于电离原子团簇而形成的纳米尺度等离子体小球对激光光场的共振吸收.     

1,4-二氧六环和氨分子氢键团簇的从头算

在不同基组水平上,对１,４－二氧六环和氨分子氢键团簇体系进行了从头算分子转道法研究,优化得到中性团簇,离子团簇和碎片离子（质子化团簇离子和非质子化团簇离子）平衡几何构型,研究结果表明：中性团簇最稳定构型为Ｒ－ＨＮ２－ＨＮＮ２（Ｒ：１,４－二氧六环）,离子团簇由于发生质子转移,其构型与中 团簇有较大的淡同,两类碎片离子Ｒ（ＮＨ３）＋和Ｒ（ＮＨ３）Ｈ＾＋与中性团簇Ｒ（ＮＨ３）的结构也有所不同     

金属离子Na+ , Li+ , Mg2+与硫酸根离子形成的无水缔合物种的从头算量子化学研究

计算并讨论了Na+, Li+和Mg2+ 3种离子与SO42-离子形成离子缔合物的结构以及阳离子的结合对ν1-SO42-频率的影响. 结果表明, 在缔合物结构方面, 阳离子数目越少, 离子间斥力越小, 越容易形成阳离子与硫酸根间距离更短, 结合更紧密的双齿缔合结构; 而当阳离子数目增加时, 特别是当具有2个正电荷的Mg2+离子数目较多时, 离子间的斥力使多离子团簇不稳定, 易形成阳离子与硫酸根间距离更长的单齿缔合结构. 有2种阳离子作用可影响ν1-SO42-频率, 一种是极化作用, 可使ν1-SO42-频率红移; 另一种是成键作用, 可使ν1-SO42-频率蓝移. 当金属离子数目≤2时, 阳离子的极化作用占主导地位, 第一个阳离子能使ν1-SO42-频率发生红移, 而当阳离子数目增多时, 不同方向结合的其它阳离子可以削弱第一个阳离子的极化作用, 因此导致多离子团簇中ν1-SO42-频率红移的减小. 当阳离子数目≥3时, 极化作用影响减小, 成键作用占据主导地位, 导致ν1-SO42-频率更大蓝移的单齿缔合结构取代双齿结构, 并使多离子团簇中的ν1-SO42-频率继续发生蓝移.     

Structural analysis of polyelectrolyte film absorbing metal ion by SAXS utilizing with X-ray anomalous dispersion effect

A distribution of Cu ions in polyelectrolyte film (Nafion) is directly observed with a small-angle X-ray scattering (SAXS) method utilizing an X-ray anomalous dispersion effect. A partial structure factor of the Cu ions, GAA(q), can be derived from the SAXS profiles obtained by scanning the incident X-ray energy around the Cu K absorption edge. GAA(q) has two peaks, indicating that the Cu ions hierarchically distribute in Nafion film. In addition, a standard SAXS also shows that Nafion film has a hierarchical structure. These results mean that the Cu ions locate in the domain where the hydrophilic bases aggregate.     

3,4-聚异戊二烯的磺化反应及其离聚体的结构研究

本工作合成了磺化的3,4-聚异戊二烯及其离子聚合体,IR和NMR谱图证明对3,4-聚异戊二烯的磺化反应是成功的,并且磺酸基团主要与3,4-链节的侧基双键发生反应。WAXD对磺化3,4-聚异戊二烯及其离聚体的研究表明,磺化度的增加使离聚体的结晶能力降低,SAXS结果表明,在离子含量为3.29mol％的离聚体中,未观察到离子簇聚集,只观察到多重离子对的散射。     

Small-angle X-ray scattering from a dual-component organogel to exhibit a charge transfer interaction

The structure of a dual-component organogel consisting of methyl 4,6-O-(p-aminobenzylidene)-alpha-D-glucopyranoside and methyl 4,6-O-(p-nitrobenzylidene)-alpha-D-glucopyranoside in diphenyl ether was investigated with small-angle X-ray scattering (SAXS). The individual components gelatinized the solvent to yield a colorless gel and the gel fiber consisted of the crystal, providing the crystalline peaks at the same diffraction angles as those of the solid samples. When the components were mixed in equimolar ratio and dissolved in diphenyl ether, a yellow gel was formed and the crystalline peaks disappeared. For all compositions, the SAXS profiles were well fitted by a cylinder model. The cross-sectional radius of gyration, r(c), was determined from the cross-sectional Guinier plot (qI vs q(2), where I and q are the scattering intensity and the magnitude of the scattering vector). The value of r(c) reached a minimum of 3.0 nm at the equimolar composition. By correcting the data for the thermal scattering background, we obtained the entire SAXS profile for the equimolar dual-component gel. From this profile, the radial electron density distribution was determined and the radius of the cylinder was estimated to be 2.6 nm. The electron density distribution thus obtained revealed that four gelator molecules are packed in the sectional direction. This model was consistent with the size of the gelator molecules.     

Three-dimensional ion mass chromatograms of oil hydrocarbon and heteroatomic compound types

The type composition of oil and oil products is usually determined by either the summation of all individuals of this compound type found from GC or GC/MS data or using appropriate generalized analytical features specific for a compound type as a whole. The specific representation of mass spectra of a complex mixture as a table of 14 homological series allows the analyst to visualize characteristic ion clusters specific for the compound types. These ion clusters form a “type mass spectrum” for each compound type. In the mass chromatograms of ions of a homologous ion series, these ion clusters form peculiar three-dimensional chromatographic peaks, whose width along the retention time axis corresponds to the isomer distribution for the homologue, molecular mass distribution (if molecular ions are considered), or structural features of the system of fused rings (for fragment ions) and “volume,” the concentration of the compound type. Three-dimensional chromatographic peaks for compound types are similar to usual peaks for individual compounds in ion mass chromatograms.     

Computerized separation of chromatographically unresolved peaks

A computerized peak deconvolution software and mass spectra were successfully applied for the deconvolution of overlapped peak cluster in the chromatogram obtained separating the complex mixture of pesticides by retention time locking gas chromatography-mass spectroscopy. The method based on the unique fragment ions in the spectra can be used for deconvolution of peak clusters if mass spectra of overlapped peaks differ. This method allows determining actual retention times of overlapped peaks. Peak areas found by this method however, cannot be used naturally for the quantitative purposes as the abundance of fragment ions used for this deconvolution procedure can dramatically differ. Computer assisted deconvolution of peaks in the peak clusters gives more realistic peak area ratios as at this method it is supposed equal response for all peaks overlapped in a cluster.     

Solvent/gelator interactions and supramolecular structure of gel fibers in cyclic bis-urea/primary alcohol organogels

An organogel system consisting of trans-(1S,2S)-bis(ureidododecyl)cyclohexane (SS-BUC) and a series of primary alcohols was explored with optical polarizing microscopy (OPM), electron microscopy, circular dichroism (CD), wide-angle X-ray scattering (WAXS), and synchrotron small-angle X-ray scattering (SAXS). OPM, SAXS, and especially WAXS showed that the gel fiber of SS-BUC/methanol gels essentially consists of SS-BUC crystal itself. SAXS showed that the SS-BUC crystal in the gel takes a lamella with a domain spacing of 5.2 nm. When we left the gel at room temperature, the spacing decreased to 3.1 nm after several months. This distance change may correspond to the structural transition from a double-layer structure to an intercalated-layer structure, which was proposed by Feringa et al. (Chem.-Eur. J. 1999, 5, 937-950) as a possible arrangement of the molecular packing. When the gels in ethanol, propanol, butanol, or octanol were examined, they never showed crystalline peaks in WAXS and SAXS, indicating the amorphous nature of the gels. With increasing the alkyl chain length from ethanol to octanol, dramatic changes were observed in the CD spectrum in the 200-500-nm range. Because these CD changes are correlated to the absorbance of urea, those can be considered as the evidence that the solvents strongly relate to the spatial arrangement between the adjacent urea groups. For the amorphous gels, the cross-sectional correlation function [gammaCu] was directly obtained by the inverse Hankel transform of the SAXS data. The value of gammaCu for the gels is decreased with increasing u (distance between the two scattering bodies, see eq 5). Furthermore, it more rapidly decreases than that of the rigid cylinder model. This feature can be explained by the speculation that many solvent molecules permeate into the SS-BUC fiber. There was a clear difference between ethanol and the other gels, indicating that the solvents with a longer alkyl chain give the more permeated and diffused fiber. This permeated fiber (i.e., wet fiber) can rationalize the dramatic CD change, by presuming that the permeated solvent molecules alter the molecular stacking form.     

Time-resolved small angle X-ray scattering study of sol-gel precursor solutions of lead zirconate titanate and zirconia

The evolution of nanostructure in sol-gel derived lead zirconate titanate (PZT) and zirconia precursor sols at different hydrolysis ratios was investigated by small angle X-ray scattering (SAXS). The shape of the clusters in the zirconia sol could be described by the length-polydisperse cylindrical form factor. The zirconia-based clusters were characterized by a cross-sectional radius, r(0), of 0.28 nm and a practically monodisperse length of ca. 1.85 nm. These clusters were probably constructed of zirconia-related tetrameric building blocks. Similar cylindrical structural motifs were observed in PZT precursor sols with [H(2)O]/[Zr+Ti]=9.26 and 27.6, but the polydispersity in length was much higher. Clear scattering contributions from Ti and Pb centers were not detected, which was interpreted in terms of a homogeneous distribution of unbound lead ions in solution and the relatively low scattering intensity from any Ti-based clusters or oligomers that may have been present in the sols.     

Aggregation behavior of pyridinium based ionic liquids in water--surface tension, 1H NMR chemical shifts, SANS and SAXS measurements

The aggregation behavior of short alkyl chain ionic liquids (ILs), namely 1-butyl, or 1-hexyl or 1-octylpyridinium and 1-octyl-2-, or -3-, or -4-methylpyridinium chlorides, in water has been assessed using surface tension, electrical conductance, (1)H NMR, small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) measurements. Critical aggregation concentrations (CACs), adsorption (at air/water interface) and thermodynamic parameters of aggregation have been reported. The values of CAC and area per adsorbed molecule decrease with the number of carbon atoms in the alkyl chain. The aggregation process is driven by both favorable enthalpy and entropy contributions. An attempt was made to examine the morphological features of the aggregates in water using SANS and SAXS methods. SANS and SAXS curves displayed diffuse structural peaks that could not be model fitted, and therefore, we calculated the mean aggregation numbers from the Q(max) assuming that IL molecules typically order into cubic type clusters.     

Effects of ionic strength on SAXS data for proteins revealed by molecular dynamics simulations

The combination of small-angle X-ray solution scattering (SAXS) experiments and molecular dynamics (MD) simulations is now becoming a powerful tool to study protein conformations in solution at an atomic resolution. In this study, we investigated effects of ionic strength on SAXS data theoretically by using MD simulations of hen egg white lysozyme at various NaCl concentrations from 0 to 1 M. The calculated SAXS excess intensities showed a significant dependence on ion concentration, which originates from the different solvent density distributions in the presence and absence of ions. The addition of ions induced a slow convergence of the SAXS data, and a ～20 ns simulation is required to obtain convergence of the SAXS data with the presence of ions whereas only a 0.2 ns simulation is sufficient in the absence of ions. To circumvent the problem of the slow convergence in the presence of ions, we developed a novel method that reproduces the SAXS excess intensities with the presence of ions from short MD trajectories in pure water. By applying this method to SAXS data for the open and closed forms of transferrin at 1 M ion concentration, the correct form could be identified by simply using short MD simulations of the protein in pure water for 0.2 ns.     

Formation of charged clusters during electrospray ionization of organic solute species

Electrospray dispersion of solutions into a bath gas can produce solute ions with many charges per molecule. In contrast to such multiple charging, it can also result in ‘fractional charging’ by which cluster ions are formed with more than one solute molecule per charge. Examples of such fractional charging or clustering are presented and discussed. In the case of arginine solutions, which are reported in some detail, ion masses corresponding to clusters containing as many as 24 solute molecules and up to four charges were identified. The number and size of these cluster ions increased markedly with increase in the initial solute concentration. When co-solutes consisting of acids, salts or bases were present, at up to millimolar concentrations in the initial solution, clustering was often strongly suppressed, especially by strong acids and their salts. This clustering phenomenon not only provides insight into the chemistry of solute precipitation in solution, but also offers a means of producing new kinds of clusters for experimental studies.