水簇中发现H_3O~+离子

<正> 美国宾夕法尼亚州立大学化学物理学家A.Welford Castleman Jr.及毕业生杨晓麟、魏启金及奚绍山(译音)组成研究小组,对水簇结构进行研究,发现水簇有几种组分,认为最突出的是20水分子及21水分子(亦可称20体,21体,H~+(H_2O)_(20)、及H~+(H_2O)_(21))。这是气相簇离子,也可以说是气相水,性质在水蒸气与液态水之间,是一种弱的聚合。     

微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现：甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。     

微波电场对甘油水溶液体系中氢键的影响

通过分子动力学模拟考察微波电场对不同水含量甘油溶液中氢键的影响。研究发现:甘油含量高时,甘油分子在溶液中以较大的团簇结构存在,水分子以较小的团簇结构或游离状态存在,电场作用下,大的甘油分子团簇变成较小的团簇并且变得更加有序;随着电场强度继续增加,甘油分子整体结构变化不大,但是团簇结构边缘甘油分子氢键断裂,变成游离状态。对于水分子而言,其较小的团簇结构在电场作用下被打开,团簇结构消失,水分子在电场方向上整齐排布,且电场强度继续增大,其结构变化不大,同样个别水分子氢键断裂变成游离状态。因此,甘油浓度高时,水分子间氢键数减少,甘油分子氢键数先增大后略微减少;甘油浓度低时,水分子氢键数先增大后略有减少,甘油分子间氢键减少。     

用AIM理论研究水体系中K~+与水分子之间的成键

碱金属中的钾离子与水分子形成的K+-H2O团簇在生物体钾离子通道的选择中起到了重要的作用。本文用Car-Parrinello动力学方法(CPMD)和AIM理论对团簇中钾离子与水分子形成的键进行研究。结果表明钾离子与一、二两个水合层中的水分子均发生作用。在300K时,第一水合层钾离子的配位数为5.10,键能为11.99 kcal/mol。因为K+-H2O之间形成的较强的键,所以第一水合层中离子与水的结合在250K~350K时很稳定。     

电气石对液态水团簇和沼泽红假单胞菌脱氢酶活性的影响

用化学个分析、X射线衍射分析、原子力显微镜等方法对内蒙古产黑色电气石进行测试表征。研究了电气石对液态水团簇和沼泽红假单胞菌脱氧酶活性的影响。结果显示：电气石使蒸馏水17^O核磁共振的半高幅宽变窄,降低了水分子缔合度。电气石提高了细胞脱氢酶活性,并使脱氧酶对pH值变化的稳定性增强。电气石对体系pH调控的结果表明：电气石使不同起始pH值溶液的pH值均趋向8．0左右。电气石提高脱氧酶活力除了电气石影响水的团簇外,还与其保持体系恒定的弱碱性pH有关。     

基于分子动力学水分和离子在水化硅酸钙纳米孔道中的传输特性研究

水化硅酸钙凝胶是水泥水化产物中最基本的粘结相,水分子和离子在凝胶孔中的传输从根本上决定着水泥混凝土材料的服役寿命.采用分子动力学方法系统地研究了水分子、氯离子和钠离子在1nm、2nm、3nm和4nm的水化硅酸钙凝胶孔中的传输过程.基于径向分布函数和均方位移的离子轨迹分析发现在纳米孔道中离子和水分子展现出异于毛细水的分子结构和动力学特性:水分子有序性排布、离子大量在界面吸附和扩散速度急剧下降.这种分子结构与动力学的特性是因为水化硅酸钙界面处硅链中的非桥接氧会与水分子形成稳定的氢键连接,而钠离子可以形成Na-O化学键,同时表面的钙离子也可以与氯离子形成CaCl2团簇体.此外,随着孔径的增大,离子和水分子的扩散系数逐渐由0.15×10-9m2/s、0.7×10-9m2/s增大到1.3×10-9m2/s、3×10-9m2/s,这很接近于实验测得的毛细水的扩散系数,说明在纳米尺度上,孔径的约束和界面化学键作用是决定离子和水分子传输的关键因素.     

高频电磁阻垢及其机理研究

利用自行设计组装的高频电磁水处理器进行阻垢实验,运用物理方法结合扫描电镜对垢样进行了分析,结果表明,该装置具有阻垢效果。采用紫外光谱和17O核磁共振技术探讨了装置的防垢机理,结果表明,该电磁水处理器能够改变水分子团簇大小,使水的活性增强。对处理过程中水的电导率的测量表明,经处理的水具有记忆效应。     

非饱和及饱和状态下水化硅酸钙孔道中水分和离子传输的分子动力学研究

水分子和离子在纳米孔道中的传输是混凝土材料的耐久性的重要影响因素.利用分子动力学方法可以模拟水分子和离子在非饱和及饱和状态下的毛细传输过程,进而探究纳米孔道中水分和离子的传输规律以及与C-S-H界面之间的相互作用特性.非饱和状态下,水分子和离子的传输主要受到毛细作用的驱使,以半月板形界面沿3.4 nm的水化硅酸钙孔道向上侵入;饱和状态下的水分子的传输主要是上下部水分子互相扩散而形成的交互传输过程,使得水分子沿孔道的扩散速度减慢.且饱和状态下,孔道界面处水化层更为紧密稳定,易形成离子簇,直接阻碍了后续水分子和离子的进入.因此,非饱和状态下水分子携带离子在纳米孔道中的传输速度远快于饱和状态.     

天然气-水-活性剂混合体系在石英表面吸附微观机理研究

构建了天然气-水-活性剂混合体系与α-石英晶面构成的界面超分子结构模型,采用分子动力学方法研究了温度为350 K和325 K,活性剂为甲醇的情况下,岩石对天然气分子以及水分子的界面吸附行为的影响.研究发现甲醇分子可降低水分子与α-石英表面的结合能从而起到降低水锁的危害,并从分子动力学的角度解释了解除水锁危害的微观机理.     

氧化镁壁面上水纳米液滴润湿性的分子动力学模拟

采用分子动力学模拟技术,研究氧化镁壁面-水纳米液滴体系的润湿特性。探讨了温度对密度分布及接触角的影响,研究了水分子在氧化镁近壁处的排布规律。模拟结果表明,氧化镁壁面具有润湿水纳米液滴的特性;随着温度的升高,氧化镁壁面-水纳米液滴体系的接触角不断减小,即润湿性不断增强。氧化镁近壁处的水分子中的两个氢原子,一个靠近氧化镁壁面,另一个远离氧化镁壁面。     

Proton Transfer Processes in Water Clusters

Elucidation of some of the basic mechanisms and principles of proton transfer in clusters is achieved by systematic evaluation of experimental and theoretical results that were obtained throughout the last decade from the authors' studies on ionic water clusters and, more recently, on protonated rare gas clusters. Among the processes studied are: Blackbody radiation-induced, stepwise desolvation of clusters when stored in an ion trap; ionic dissociation and recombination of HCl in water clusters; metal oxidation in aqueous clusters; formation of nascent hydrogen in reactions of solvated metal cations with acids; and the behavior of ionic water clusters as acidic or basic micro-solutions. Infrared spectroscopic studies of size-selected water clusters are expected to advance our knowledge of structure and dynamics of water clusters and of excess protons therein.     

Biocompatible glutathione capped gold clusters as one- and two-photon excitation fluorescence contrast agents for live cells imaging

The one- and two-photon excitation emission properties of water soluble glutathione monolayer protected gold clusters were investigated. Strong two-photon emission was observed from the gold clusters. The two-photon absorption cross section of these gold clusters in water was deduced from the z-scan measurement to be 189?740 GM, which is much higher compared to organic fluorescent dyes and quantum dots. These gold clusters also showed high photo-stability. The MTT assay showed that these gold clusters have low toxicity even at high concentrations. We have successfully demonstrated their applications for both one and two-photon excitation live cell imaging. The exceptional properties of these gold clusters make them a promising alternative for one- and two-photon bio-imaging and other nonlinear optical applications.     

Adsorption of Some Atmospherically Important Molecules onto Large Water Clusters: SO2, SO3, HCl,and ClONO2

The adsorption of a range of atmospherically important molecules (SO₂, SO₃, HCl, and ClONO₂) on large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50–450 water molecules. SO₂ and HCl were found to stick with low efficiency to the water cluster, retaining their chemical identity. In contrast, both SO₃ and ClONO₂ undergo heterogeneous reactions on the surface of the water cluster forming, respectively, H₂SO₄ and HOCl with HNO₃. For SO₃, calculations show that the large barrier that exists in the gas-phase to the reaction of SO₃ with water is removed for water clusters of a sufficient size because of stabilization of the transition state by solvation. For ClONO₂, the barrier to reaction is much larger and cannot be removed by solvation for any size cluster. In this case, it is likely that reaction takes place on the water cluster by the ionic dissociation of ClONO₂ in a similar manner to that observed for ClONO₂ on ice films.     

A Facile Strategy to Prepare Small Water Clusters via Interacting with Functional Molecules

Although small water clusters (SWCs) are important in many research fields, efficient methods of preparing SWCs are still rarely reported, which is mainly due to the lack of related materials and understanding of the molecular interaction mechanisms. In this study, a series of functional molecules were added in water to obtain small water cluster systems. The decreasing rate of the half-peak width in a sodium dodecyl sulfate (SDS)–water system reaches ≈20% at 0.05 mM from ¹⁷O nuclear magnetic resonance (NMR) results. Based on density functional theory (DFT) and molecular dynamics (MD) simulation calculation, it can be concluded that functional molecules with stronger negative electrostatic potential (ESP) and higher hydrophilicity have a stronger ability to destroy big water clusters. Notably, the concentrations of our selected molecule systems are one to two magnitudes lower than that of previous reports. This study provides a promising way to optimize aqueous systems in various fields such as oilfield development, protein stability, and metal anti-corrosion.     

Intracluster ion molecule reactions following the generation of Mg+ within polar clusters

In this work we investigated the intracluster ion molecule reactions following the generation of Mg(+) within the polar clusters (water, methanol, ether and acetonitrile), using time of flight mass spectrometry. In the case of Mg(+)/water and Mg(+)/methanol, dehydrogenation reactions are observed after the addition of five molecules. However, no dehydrogenation reactions are observed in the case of Mg(+)/ether or Mg(+)/acetonitrile clusters. This confirms the role of the H atom in (O-H) in the dehydrogenation reaction, and rules out any contribution from the H atom in the CH(3) group. In addition, the magic numbers in the time of flight (TOF) mass spectra of the Mg(+)X(n) clusters (X = H(2)O, CH(3)OH, CH(3)OCH(3) and CH(3)CN) have been investigated. Finally, the role of ground electronic magnesium ion Mg(+)((2)S(1/2)), and excited electronic magnesium ion Mg(+)((2)P(1/2)) in the dehydrogenation reaction were investigated using Ion Mobility Mass spectrometry. The results offer direct evidence confirming the absence of the electronically excited, Mg(+)((2)P(1/2)).     

The formation of the S‐shaped edge‐on lamellae on the thin porous polylactic acid membrane via phase separation induced by water microdroplets

Biodegradable polymers have received increased attention due to their potential application in the medicine and food industries; in particular, poly(lactic acid) (PLA) is a primary biopolymer because of its excellent biocompatibility and absorbability features. In this study, a porous PLA membrane was fabricated by phase separation using water microdroplets produced by an ultrasonic atomizer as a coagulation bath. The formation of S‐type clusters was attributed to the slow exchange rate between solvent and coagulant, which provided time for the movement of polymer molecules. The effect of preparation conditions on the structure of S‐type clusters, including polymer concentration in solution and ambient temperature was investigated. The PLA porous membrane prepared from water micro‐droplets with different morphology compared with the sample fabricated from distilled water has potential application in fields of tissue engineering and artificial organ generation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43355.     

MOLECULAR DYNAMICS SIMULATIONS OF FILLED AND EMPTY CAGE-LIKE WATER CLUSTERS IN LIQUID WATER AND THEIR SIGNIFICANCE TO GAS HYDRATE FORMATION MECHANISMS

Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetimes of these clusters are calculated according to their Lindemann index δ (t) using the criteria of δ≥0.07. For both the filled and empty clusters, we find the dynamics of bulk water determines the lifetimes of cage-like water clusters, and that the lifetime of 512 62 cage-like cluster is the same as that of 512 cage-like cluster. Although the methane molecule indeed makes the filled cage-like cluster more stable than the empty one, the empty cage-like cluster still has chance to be long-lived compared with the filled clusters. These observations support the labile cluster hypothesis on the formation mechanisms of gas hydrates.     

Changes of Water Hydrogen Bond Network with Different Externalities

It is crucial to uncover the mystery of water cluster and structural motif to have an insight into the abundant anomalies bound to water. In this context, the analysis of influence factors is an alternative way to shed light on the nature of water clusters. Water structure has been tentatively explained within different frameworks of structural models. Based on comprehensive analysis and summary of the studies on the response of water to four externalities (i.e., temperature, pressure, solutes and external fields), the changing trends of water structure and a deduced intrinsic structural motif are put forward in this work. The variations in physicochemical and biological effects of water induced by each externality are also discussed to emphasize the role of water in our daily life. On this basis, the underlying problems that need to be further studied are formulated by pointing out the limitations attached to current study techniques and to outline prominent studies that have come up recently.