吡啶团簇的飞秒光电离和从头计算研究

用飞秒激光电离飞行时间质谱研究了吡啶分子团簇在400 nm波长下的多光子光电离,实验观测到一系列的质子化和非质子化团簇离子.结果表明,质子转移也能发生在弱氢键结合的分子间.通过分析离子峰宽和离子信号强度随气源压力的变化,得到质子化团簇离子来源于大团簇离子的碎裂,而非质子化团簇离子是中性团簇直接电离的结果.从头计算结果表明,吡啶团簇是通过弱氢键C-H…N 结合在一起的,并且团簇离子离解倾向于生成质子化产物.     

乙二醇的分子间氢键结构动力学的飞秒非线性红外光谱

利用稳态线性红外光谱和飞秒泵浦-探测红外光谱技术, 研究了在乙腈(MeCN)、丙酮(AC)、四氢呋喃(THF)和二甲基亚砜(DMSO)溶剂中乙二醇(EG)的结构和羟基(―OH)伸缩振动动力学. 结果表明, 乙二醇的―OH伸缩振动的频率位置、峰宽以及振动弛豫动力学都表现出强烈的溶剂依赖性. 乙二醇溶液中至少存在两种形式的分子间氢键, 一种是溶质-溶剂团簇的分子间氢键, 另一种是溶质-溶质团簇的分子间氢键. 量子化学计算预测的―OH伸缩振动频率的溶剂依赖性与我们的红外光谱实验观测结果一致. 进一步, 我们发现在乙腈中参与形成溶质-溶剂团簇氢键的乙二醇―OH伸缩振动具有最慢的弛豫动力学, 丙酮和四氢呋喃次之, 而最快的弛豫动力学过程发生在二甲基亚砜中. 在每一溶剂条件下, 乙二醇/乙二醇溶质团簇中―OH伸缩振动弛豫都更快一些. 本文结果有助于认识在溶质-溶质、溶质-溶剂分子团簇共存的体系中不同分子间氢键的结构动力学特性.     

拉曼光谱法测定冷冻对CuCl2与牛血清白蛋白作用的影响

用CuCl2溶液密度和粘度的变化表征溶液团簇结构的变化,发现CuCl2溶液经冷冻处理后,由于在水的微观结构上形成许多靠氢键结合的小水分子团簇结构,水分子氢键网络的缔合程度变大,溶液密度降低,粘度增大。采用激光显微共聚焦拉曼光谱法对冷冻前后CuCl2溶液与BSA相互作用进行研究,结果表明:Cu2+与BSA作用后,BSA酰胺I带特征峰发生位移,β-折叠构象增加,二硫键构象和酪氨酸外环境发生变化。CuCl2溶液经冷冻-解冻处理后,引起BSA酰胺I带特征峰发生位移的程度和对酪氨酸残基的影响变小,这种相互作用趋弱的效应与水分子团簇结构的变化有关。     

N-甲基吡咯烷酮与乙醇溶液介电常数的特异性研究

本文通过测量微波频率下N-甲基吡咯烷酮和乙醇溶液在不同配比下的介电常数,发现N-甲基吡咯烷酮与乙醇溶液的介电常数的实部和虚部在特定浓度下小于任意单独一种物质介电常数。分析表明电介质溶液特定浓度下分子间团簇结构会影响溶液的介电常数。此结果为研究微波促进化学反应理论机理提供了实验依据。     

C4H5N-(NH3)n氢键团簇的多光子电离与从头计算

在355和532nm激光波长下用TOF质谱仪研究了C4H5N-(NH3)n系列氢键团簇体系的多光子电离.实验发现,两波长下除了得到一系列团簇离子外,还观测到一系列质子化产物C4H5N-(NH3)n－H＋.这些质子化产物来自于光电离过程中团簇内部的质子转移反应;系列离子出现反常强度变化,即离子强度较离子明显减小;从头计算结果表明,上述现象是由于中性团簇稳定性的差异造成的.     

拉曼光谱与理论计算研究金属离子Cu溶液弱相互作用力

采用理论计算和实验光谱对金属离子Cu~(2+)-丁基二硫代碳酸盐及水溶液中弱相互作用力进行了研究.通过拉曼光谱特征峰的位移、强度变化和温度变化对溶液中金属离子Cu~(2+)微团簇结构的影响进行了讨论,得到了伴生元素Fe存在下,丁基二硫代碳酸盐溶液中的微团簇结构、铜溶液(H_2O)_n(n=2～6)团簇和[Cu(H_2O)_n]~(2+)(n=2～6)团簇随着温度的变化和影响逐渐减小的规律,发现实验与理论计算的结果一致.     

应用ABEEM/MM模型研究水分子团簇(H2O)n (n=11～16)的性质

应用ABEEM/MM 模型计算了较大的水分子团簇(H2O)n (n=11~16)的各种性质,如：优化的几何构型, 氢键个数, 结合能, 稳定性, ABEEM 电荷分布, 偶极矩, 以及结构参数、平均氢键个数和强度, 增加的团簇结合能等.结果表明,从立方体结构到笼状结构的过渡出现在n=12的水分子团簇中,随着类似于笼状结构特点的不断增强,五元环的富集程度有所增加.     

白酒中乙醇分子和水分子四聚缔合的理论研究

白酒新酒老熟的过程,可以理解为白酒中乙醇分子和水分子之间相互作用的过程,老熟使得乙醇分子与水分子的缔合形态发生了变化,从而引起白酒"口感"的变化。乙醇分子与水分子的缔合形态可以通过其形成的聚合团簇进行理解,而形成的团簇形式往往由氢键相互作用所决定。乙醇分子与水分子能够形成的团簇类型众多,本文着眼于乙醇分子与水分子之间形成的四聚缔合团簇,使用理论计算的方法,对团簇的结构和稳定性、氢键相互作用、红外光谱和振动分析等进行了深入的研究,以期对白酒中两类分子之间的存在形态有更好的理解。     

应用ABEEM/MM力场模型研究水分子团簇(H2O)n(n=7～35)的性质

应用ABEEM/MM模型研究和计算了水分子团簇(H2O)n(n=7～35)的各种性质,如:优化的几何构型,氢键个数,结合能,稳定性,ABEEM电荷分布,偶极矩,以及结构参数、平均氢键个数和强度、团簇的递增结合能等,并描述了六聚水区域中所反映的从二维结构(从二聚水到五聚水)到三维结构(n>6的水分子团簇)的过渡,又进一步地预测了从立方体结构到笼状结构的过渡出现在n=12的水分子团簇中,随着类似于笼状结构特点的不断增强,五元环的富集程度有所增加.以上研究不仅系统研究和分析了水团簇的各种性质,而且对比Ab initio研究和实验结果,进一步验证了ABEEM/MM模型的合理性以及参数的正确性和可转移性.     

脂肪族氨基酸二肽与水团簇的理论研究

用ABEEMσπ/MM模型和MP2/6-31+G(d)//B3LYP/6-31G(d)方法研究水合效应对脂肪族氨基酸二肽的影响.从结构和能量两方面说明Leu残基在蛋白质中起成旋作用,Val和Ⅱe残基在蛋白质中起解旋作用.同时得出:水分子严重影响了二肽分子的骨架二面角;对于结合相同数目水分子的团簇倾向于形成含有环状氢键的结构,并且含有环状氢键团簇的结合能大于含有链状氢键团簇的结合能.     

Needleless electrospinning of poly(acrylic acid) superabsorbent: Fabrication,characterization and swelling behavior

In this work, nanofibrous hydrogel has been fabricated from needleless electrospinning of Poly(acrylic acid) (PAA) in an aqueous solution with different concentrations. First, all solution samples were characterized for pH, surface tension, conductivity and viscosity. Next, electrospinnability of the PAA-water dope solution was investigated using the needleless electrospinning technique under constant conditions. Results indicated that the PAA-water solution was not electrospinnable. Therefore, the neutralization of carboxylic groups in the PAA chemical structure using the NaOH solution was investigated to enhance the PAA electrospinnability. Morphology observation revealed that the fiber diameters ranged from 40 to 250 nm and increased with increasing the solution concentrations. Increasing the neutralization degree (10%, 15% and 20% with 50 wt% NaOH solution) led to increase the dope viscosity and conductivity. The resultant nanofibers could be rendered water-insoluble by incorporating 1,4-butanediol diglycidyl-ether in the PAA-water dope solution, then heat-induced crosslinking was performed using a microwave at different curing times (1–5 min) and temperatures (45–105 °C). The nanofibrous hydrogel mat was then characterized by FTIR. The resulting nanofibrous hydrogel showed remarkable water absorption capacity up to 17,000% and 51,000% (within 15 min) in the standard saline solution and distilled water, respectively.     

Collision energy transfer in collision of NH(4) (+)(NH(3))(n-1) (n=3-9) with ND(3)

An incorporation of ND(3) into protonated ammonia cluster ions NH(4)(+)(NH(3))(n-1) (n=3-9), together with a dissociation of the cluster ions, was observed in the collision of the cluster with ND(3) at collision energies ranging from 0.04 to 1.4 eV in the center-of-mass frame. The branching fractions of the cluster ion species produced in the reactions were obtained as a function of the collision energy. The branching fractions of the incorporation products were successfully explained in terms of the Rice-Ramsperger-Kassel (RRK) theory at collision energies lower than the binding energy of the cluster ion. In addition, the internal energy distributions of the parent cluster ions were determined, and found to be in good agreement with those predicted using the evaporative ensemble model. In incorporations at collision energies lower than the binding energy of the cluster ion, all of the collision energy was transferred to the internal energy of the cluster ions; subsequently, an evaporation of ammonia molecules occurred in an equilibrium process after a complete energy redistribution in the clusters. In contrast, at collision energies higher than the binding energy of the cluster ion, a release of an ammonia molecule from the incorporation products occurred in a nonequilibrium process. The transition from the complex mode to the direct mode in the incorporation was observed at collision energies approximately equal to the binding energy. On the other hand, the collision energy dependence of the cross sections for the dissociation and for a nonreactive collision were estimated by a RRK simulation in which the collision energy transfer was interpreted by using the classical hard-sphere collision model. A relationship between reactivity and reaction modes in the collision of NH(4)(+)(NH(3))(4) with ND(3) is discussed via a comparison of the experimental results with the RRK simulation.     

乌青铜型BaNd2Ti4O12微波介质陶瓷的电导和介电损耗

用固相反应合成了乌青铜型钛酸盐陶瓷BaNd₂Ti₄O₁₂, 并用电化学阻抗和微波介质谐振测试表征了不同热处理和钽掺杂对电导和微波介电损耗的影响. 电导率随退火气氛(空气, 氧气和氮气)的变化与缺陷反应平衡2O_O^×↔2V_O^··+O₂↑+2e'和Ti_Ti^×+e'↔Ti'_Ti随氧分压的变化一致, 表明BaNd₂Ti₄O₁₂具有n型导电性质. 在空气和氧气中退火有利于减少包括V_O^×, Ti'_Ti和弱束缚电子在内的本征缺陷因而降低电导. 而在低氧分压的氮气中进行退火处理, 增加了缺陷的浓度, 同时提高了电导率. 在空气/氧气/氮气中的退火处理对微波介电损耗没有明显的影响, 表明本征缺陷对微波介电损耗的影响可以忽略. 空气退火处理样品的电导率和微波介电损耗低于空气淬火处理的样品; 其中电导的变化与缺陷反应平衡相关, 但空气退火降低微波介电损耗可能与退火消除晶格热应力有关. 五价钽的掺杂降低了电导但增大了微波介电损耗. 本研究表明空气退火处理能有效地改善BaNd₂Ti₄O₁₂陶瓷的品质因子Q×f, 其值提高了约12%.     

Ions in size-selected aqueous nanodrops: sequential water molecule binding energies and effects of water on ion fluorescence

The effects of water on ion fluorescence were investigated, and average sequential water molecule binding energies to hydrated ions, M(z)(H(2)O)(n), at large cluster size were measured using ion nanocalorimetry. Upon 248-nm excitation, nanodrops with ~25 or more water molecules that contain either rhodamine 590(+), rhodamine 640(+), or Ce(3+) emit a photon with average energies of approximately 548, 590, and 348 nm, respectively. These values are very close to the emission maxima of the corresponding ions in solution, indicating that the photophysical properties of these ions in the nanodrops approach those of the fully hydrated ions at relatively small cluster size. As occurs in solution, these ions in nanodrops with 8 or more water molecules fluoresce with a quantum yield of ~1. Ce(3+) containing nanodrops that also contain OH(-) fluoresce, whereas those with NO(3)(-) do not. This indirect fluorescence detection method has the advantages of high sensitivity, and both the size of the nanodrops as well as their constituents can be carefully controlled. For ions that do not fluoresce in solution, such as protonated tryptophan, full internal conversion of the absorbed 248-nm photon occurs, and the average sequential water molecule binding energies to the hydrated ions can be accurately obtained at large cluster sizes. The average sequential water molecule binding energies for TrpH(+)(H(2)O)(n) and a doubly protonated tripeptide, [KYK + 2H](2+)(H(2)O)(n), approach asymptotic values of ~9.3 (n ≥ 11) and ~10.0 kcal/mol (n ≥ 25), respectively, consistent with a liquidlike structure of water in these nanodrops.     

Massive cluster impact mass spectrometry: a new desorption method for the analysis of large biomolecules.

A new ion desorption method is described that utilizes a primary beam of massive, multiply charged cluster ions to generate secondary ions of peptides in a glycerol matrix. The massive cluster ion beam is generated via electrohydrodynamic emission using a 1.5 M solution of ammonium acetate in 30% aqueous glycerol. Negative ion spectra of peptides obtained using this technique show greatly decreased relative intensities for fragment ions and 'chemical noise' background when compared to spectra obtained using a xenon atom primary beam. The near absence of fragments derived from radiation damage to the sample solution is attributed to the impact of primary particles with energies less than 1 eV/nucleon.     

Concentration Dependence of the Activation Energy of Conductivity in Aqueous Sodium Selenite and Potassium Tellurite

The temperature and concentration dependences of conductivity have been studied for aqueous solutions of sodium selenite and potassium tellurite. The corresponding empirical equations have been derived. The activation energies of conductivity in both electrolytes are calculated for different solution concentrations. The ascertained dependence is interpreted in the light of Samoilov's theory on positive and negative hydration of ions. Analysis of the results suggests that the larger the positive hydration of ions, the higher the activation energies of conductivity for the salts.     

Intramolecular switching between dipolar resonance structures in singlet and triplet excited states detected by TRMC

Transient changes in the real and imaginary component of the complex permittivity of a flash-photolyzed solution can be monitored with nanosecond time resolution using the time-resolved microwave conductivity (TRMC) technique. Effects caused by rapid (picosecond), flip—flop switching between dipolar resonance structures in the S₁ and T₁ states of molecules with mirror symmetry have been observed.     

B2C3簇的结构和振动光谱的理论研究

用量子化学从头计算方法研究了Ｂ２Ｃ３簇各种可能的空间结构，计算了相应的振动光谱和结合能。对Ｂ２Ｃ３最稳定构型的电子结构进行了深入的分析和讨论。     

聚碳硅烷热解SiC陶瓷结构与微波吸收性能

以聚碳硅烷(PCS)为原料,通过800-1200℃热解制备了PCS-SiC陶瓷,采用SEM、XRD与拉曼光谱对样品形貌、晶相及自由碳结构进行了表征。测量了样品直流电导率,并用矩形波导法测试了试样在8.2-12.4 GHz(X波段)频率范围的复介电常数,根据传输线理论计算出不同厚度材料的反射损耗。结果表明,随着热解温度的升高,样品电导率升高,同时复介电常数实部与虚部增加,吸波性能得到改善。PCS-SiC陶瓷中自由碳石墨化是引起极化能力及电导损耗提高的原因。     

Glutamic acid cation based ionic liquids: microwave synthesis, characterization, and theoretical study

Some new members of amino acid ionic liquids (ILs) with glutamic acid (Glu) cation were studied. GluBF4, GluCl, GluNO3, and Glu2SO4 were synthesized using the one-step microwave synthesis method, and their physicochemical properties, including the IR spectrum, melting point, conductivity, solubility, and thermostability, were investigated in detail experimentally. Systematic theoretical study on the series molecules were also performed by quantum chemistry calculation. Geometry optimization on the single molecule was carried out with the B3LYP/6-311++G** level of theory, and the vibration frequencies of each optimized molecule were analyzed at the same level. The binding energies were calculated, and the basis set superposition error (BSSE) was corrected by the counterpoise method (CP). A close relation between the experimental melting points and the intramolecular interaction was found: the smaller the absolute value of the biding energy between ions is, the lower the melting point would be. This conclusion shows the probability of designing ILs with the help of theoretical way in the future exploitation.