The structure and dynamics of water inside armchair carbon nanotube

In this paper we present some simulation results about the behaviour of water molecules inside a single wall carbon nanotube (SWNT). We find that the confinement of water in an SWNT can induce a wave-like pattern distribution along the channel axis, similar phenomena are also observed in biological water channels. Carbon nanotubes(CNTs) can serve as simple nonpolar water channels. Molecular transport through narrow CNTs is highly collective because of tight hydrogen bonds in the protective environment of the pore. The hydrogen bond net is important for proton and other signal transports. The average dipoles of water molecules inside CNTs (7,7), (8,8) and (9,9) are discussed in detail. Simulation results indicate that the states of dipole are affected by the diameter of SWNT. The number of hydrogen bonds, the water--water interaction and water--CNT interaction are also studied in this paper.     

Structure of water in mesoporous organosilica by calorimetry and inelastic neutron scattering

In this paper, we describe the preparation of mesoporous organosilica samples with hydrophilic or hydrophobic organic functionality inside the silica channel. We synthesized mesoporous organosilica of identical pore sizes based on two different organic surface functionality namely hydrophobic (based on octyltriethoxysilane OTES) and hydrophilic (3-aminopropyltriethoxysilane ATES) and MCM-41 was used as a reference system. The structure of water/ice in those porous silica samples have been investigated over a range temperatures by differential scanning calorimetry (DSC) and inelastic neutron scattering (INS). INS study revealed that water confined in hydrophobic mesoporous organosilica shows vibrational behavior strongly different than bulk water. It consists of two states: water with strong and weak hydrogen bonds (with ratio 1:2.65, respectively), compared to ice-Ih. The corresponding O-O distances in these water states are 2.67 and 2.87 ?, which strongly differ compared to ice-Ih (2.76 ?). INS spectra for water in hydrophilic mesoporous organosilica ATES show behavior similar to bulk water, but with greater degree of disorder.     

Selective interaction water-hydrophilic/hydrophobic impurities observed by four-photon Brillouin spectroscopy

The four-photon scattering spectra of water in the aqueous solution/suspension of various hydrophilic/hydrophobic impurities in the range ±3 cm^?1 (±90 GHz) have been observed. We have found the strong dependence of the Brillouin resonance frequency upon the connectivity of the impurities and water molecules. The Brillouin shift is attributed to the local restructuring of the hydrogen bond network in water inside the interface layer that is sensitive to the hydrophilic/hydrophobic properties. In fact, it results in variations in the isothermal compressibility and sound velocity.     

亲水性两性离子聚合物刷的构象与结构

本文应用分子场理论,研究暴露于水蒸气中的亲水性两性离子聚合物(HP)刷的构象与结构.理论模型考虑HP-水(P-W)氢键和水-水(W-W)氢键效应,以及HP单体之间的偶极-偶极相互作用.研究发现,P-W与W-W氢键决定着HP的水合性,P-W氢键形成,会诱导HP刷溶胀.我们通过考察HP单体间的偶极-偶极相互作用发现,随着偶极-偶极相互作用增强,HP链在垂直培基表面沿着链方向,形成了结节状结构.这是由于HP单体之间的偶极-偶极静电吸引作用导致单体间汇聚结节,这种结节在刷内产生了较强的排斥体积作用,因此,这种HP刷具有抗污性能.在较高的接枝密度环境下,由于HP链间单体之间的偶极-偶极静电吸引作用,会形成链间单体-单体的结节,在刷内形成结节网络状凝胶结构,这种结构的出现,会使得HP刷呈现极强的抗污性.另外,当体系中水蒸气浓度增加、水合相互作用增强时,增加的P-W氢键将平衡HP单体之间的偶极-偶极相互作用,使得结节解开,聚合物链伸展.我们的理论结果符合实验观测,由此表明,P-W氢键效应,以及HP单体之间的偶极-偶极相互作用决定着HP刷的构象转变和结构特性,刷内出现的两性离子聚合物链内单体间的结节和链间单体结节状凝胶结构,是两性离子聚合物刷呈现较强抗污性的本质特性.     

Hydrogen-bond dynamics near a micellar surface: origin of the universal slow relaxation at complex aqueous interfaces

The dynamics of hydrogen bonds among water molecules themselves and with the polar head groups (PHG) at a micellar surface have been investigated by long molecular dynamics simulations. The lifetime of the hydrogen bond between a PHG and a water molecule is found to be much longer than that between any two water molecules, and is likely to be a general feature of hydrophilic surfaces of organized assemblies. Analyses of individual water trajectories suggest that water molecules can remain bound to the micellar surface for more than 100 ps. The activation energy for such a transition from the bound to a free state for the water molecules is estimated to be about 3.5 kcal/mol.     

Water Dynamics at Interfaces and Solutes: Disentangling Free Energy and Diffusivity Contributions

The dynamics of single water molecules in bulk and at interfaces is studied by means of molecular dynamics simulations. We use a recently developed stochastic method based on the Fokker-Planck equation to disentangle the contributions of the free energy and diffusivity profiles on the local dynamics. The strong variations found in the diffusivity profiles are crucial for accurately modeling the water kinetics. A comparison of hydrophobic and hydrophilic substrates and solutes yields significant differences in the diffusivities, which can be attributed to the presence of hydrogen bonds.     

Femtosecond laser-induced surface wettability modification of polystyrene surface

In this paper, we demonstrated a simple method to create either a hydrophilic or hydrophobic surface. With femtosecond laser irradiation at different laser parameters, the water contact angle (WCA) on polystyrene’s surface can be modified to either 12.7° or 156.2° from its original WCA of 88.2°. With properly spaced micro-pits created, the surface became hydrophilic probably due to the spread of the water droplets into the micro-pits. While with properly spaced micro-grooves created, the surface became rough and more hydrophobic. We investigated the effect of laser parameters on WCAs and analyzed the laser-treated surface roughness, profiles and chemical bonds by surface profilometer, scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). For the laser-treated surface with low roughness, the polar (such as C—O, C=O, and O—C=O bonds) and non-polar (such as C—C or C—H bonds) groups were found to be responsible for the wettability changes. While for a rough surface, the surface roughness or the surface topography structure played a more significant role in the changes of the surface WCA. The mechanisms involved in the laser surface wettability modification process were discussed.     

The role of water in the design of glycosidic linkage flexibility

In this paper we show how a variety of computational methods are used to understand the role that water plays in the solution conformational dynamics of carbohydrates. A comparison is made between maltose and a designed disaccharide (α-D-Glc-NAc-(1→4)-β-D-Glc-3-NH₂) in which the cross glycosidic linkage hydrogen bonds have been significantly strengthened. However, despite the stronger intramolecular hydrogen bonds in the maltose derivative, the correlation times for glycosidic dihedral angle fluctuations are approximately the same for the two sugars. Upon investigation of the water in the first hydration shells for the two disaccharides, high water probability densities were found between the functional groups straddling the glycosidic linkage that bonds the two monosaccharides together. This probability density corresponds to single water molecules forming bridging hydrogen bonds between the functional groups on either side of the linkage for periods of 3.66 ps in the case of maltose and 8.36 ps in the case of the amine derivative. Ab initio studies of saccharide structure interaction with single water molecules reveal that these intermolecular (sugar-solvent) hydrogen bonds are of similar strength to the intramolecular (sugar-sugar) hydrogen bonds. This combination of molecular dynamics and ab initio computational methods demonstrates that increasing the internal hydrogen bond strength in oligosaccharides does not lead to significantly slower internal molecular motion of these sugars in solution. The intermolecular hydrogen bonds formed with water compete equally with the intramolecular hydrogen bonds in the sugar. This result has important implications when considering hydrophobic versus hydrophilic effects in glycoproteins.     

高压液态重水的拉曼光谱研究

应用金刚石压腔结合拉曼光谱技术研究了重水在291 K,0.1～800 MPa条件下的拉曼谱图。结果表明：压力增大的过程中,重水的拉曼伸缩振动光谱向低频方向移动,并且频移和压力基本呈线性相关。频移没有突变,没有发生相的转变。将重水的拉曼谱峰分解为代表分子内O—D振动的高频峰和代表分子间氢键振动的低频峰。研究这两种不同类型谱峰的性质,发现代表分子间氢键的低频峰峰面积在不同的压力范围内呈现出不同的变化特征,压力对分子间氢键的影响并不是持续不变的。拉曼峰的峰面积反映的是产生这种拉曼峰的振动的数目,峰面积的变化反映了特征振动数目的变化。由于分子间氢键的强相互作用,水分子总是倾向于形成对称的空间五分子四面体结构,因此最大峰面积代表了最稳定的五分子团簇结构。     

Modulation of Relaxivity,Suspension Stability,and Biodistribution of Dendronized Iron Oxide Nanoparticles as a Function of the Organic Shell Design

Nanoparticles (NPs) with a mean diameter of 10 nm are functionalized with three dendrons: D1 a PEGylated PAMAM dendron of generation 0.5, D2 a hydrophilic oligoethyleneglycol‐derivatized dendron (D2) displaying a phosphonic acid at the focal point, and D2–2P the same dendron than D2 but with two phosphonic acid anchoring agents. Their grafting is confirmed by IR spectroscopy and elemental analysis. All dendronized NPs are stable over a long period of time in suspensions in water and in different physiological media and display a mean hydrodynamic diameter smaller than 50 nm whatever the molecule architecture. NMRD profiles and relaxivity measurements highlight the influence of the molecule architecture on the water diffusion close to the magnetic core thus influencing the relaxation properties at low magnetic field. The high hydrophilic architecture of the dendron D2 by contrast to dendron D1 allows maintaining the colloidal stability in different conditions while ensuring a very good accessibility of water molecule close to the magnetic core. Coupling of a fluorescent dye on dendrons have allowed investigating the biodistribution of dendronized NPs, which are found to be quickly eliminated through urinary and hepatobiliary pathways within 4 h. Furthermore, no enhanced permeation and retention effect in tumors can be observed.     

Freezing of water confined at the nanoscale

Freezing of water in hydrophilic nanopores (D=1.2 nm) is probed at the microscopic scale using x-ray diffraction, Raman spectroscopy, and molecular simulation. A freezing scenario, which has not been observed previously, is reported; while the pore surface induces orientational order of water in contact with it, water does not crystallize at temperatures as low as 173?K. Crystallization at the surface is suppressed as the number of hydrogen bonds formed is insufficient (even when including hydrogen bonds with the surface), while crystallization in the pore center is hindered as the curvature prevents the formation of a network of tetrahedrally coordinated molecules. This sheds light on the concept of an ubiquitous unfreezable water layer by showing that the latter has a rigid (i.e., glassy) liquidlike structure, but can exhibit orientational order.     

激发态下甘氨酸与水分子间氢键性质研究

在生物体中氨基酸通常以水作为溶剂,是形成细胞的重要成分.在该环境下,分子间氢键的产生会对氨基酸分子与水分子的结构和性质产生影响.为了研究其在基态和激发态下的性质,本文利用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对甘氨酸分子和H₂O分子在基态和激发态下的分子间氢键的静电势、键长、自然键轨道(NBO)电荷、分子中的原子理论(AIM)分析、Wiberg键级b、红外(IR)光谱、空穴-电子轨道和基态与激发态之间的电子转移进行了理论研究.结果表明：分子间氢键的形成会导致分子结构的改变和红外光谱振动频率的移动.在激发态下,分子间氢键有不同程度的增强或减弱.该计算结果为氢键的形成和激发态下分子间氢键的研究提供理论依据.     

The effect of working pressure on the chemical bond structure and hydrophobic properties of PET surface treated by N ion beams bombardment

Polyethylene terephthalate (PET) surface was bombarded by N ion beams at room temperature. Varying the working pressure of the ion beams, PET surfaces with different composition and properties were obtained. Characterization by X-ray photoelectron spectrometry showed that only on film surface, ester bonds, especially C-O bonds, were broken and N element chemical bonded with C. The influence depth was less than 5 nm because of the lower ion energy (about 10³ eV). Contact angle results revealed that with increasing the working pressure of ion beams, the contact angle of PET surface to pure water increased from 51° to 130°. With these results, one conclusion could be deduced that the hydrophilic and hydrophobic properties of PET surface could be influenced by N atom chemical bond with C, which in turn is controlled by the working pressure of N ion beams.     

醇类抑制剂对甲烷水合物形成的影响

在本工作中,甲烷水合物的生长动力学是通过甲醇、乙醇、乙二醇三种不同醇类抑制剂存在下的分子动力学模拟研究的.模拟结果发现,三种醇类都可作为甲烷水合物的抑制剂,醇类分子中的亲水性羟基极大地破坏了水合物笼的结构,并且羟基可以与局部的液态水分子形成氢键,从而增加了形成水合物笼型结构的难度,导致甲烷水合物的生长速率降低.对于甲醇分子,甲醇分子的亲水性羟基与水分子形成氢键从而破坏了水分子结构,而亲油性甲基对周围的水分子具有簇效应,两者都会降低水合物生长速率;对于乙二醇和乙醇分子,它们只含有羟基,特别是乙二醇分子含有两个羟基,其对H₂O分子有很强的吸附作用,导致水合物生长速率降低.在抑制效果方面,甲醇分子最优,乙二醇稍微优于乙醇.     

Water behavior in the neighborhood of hydrophilic and hydrophobic membranes: Lessons from molecular dynamics simulations

The study of properties of water in the vicinity of surfaces poses a fascinating challenge. In this article we studied the behavior of water molecules in the neighborhood of membranes. We addressed the question of how these water molecules are influenced by the membranes’ hydrophilicity. Three systems were studied through molecular dynamics simulations: water in the presence of a hydrophilic membrane (PL), water in the presence of a hydrophobic (PB) one and water in the absence of membranes (BULK). Additionally, in order to study the dependence of the effect of the membrane on the behavior of neighboring water molecules with temperature, each system was simulated at three different temperatures (K): 250, 300 and 350. For each condition, kinetic and structural features were studied. The first feature involved the calculation of diffusion coefficients and activation energy. The second feature was evaluated through the study of water density and hydrogen bond distribution. From the present study we concluded that: (1) density studies underestimate the influence of both hydrophilic and hydrophobic membranes on the neighboring water molecules; (2) the hydrophilic and hydrophobic membranes disturb the hydrogen bond network within distances ranging from 1 to 8 nm, depending on the nature of the membrane and the temperature conditions; (3) the presence of a hydrophobic surface results in an enhancement of the natural hydrogen bond network present in liquid water, to a greater extent than what even an ordered Ih ice structure is able to achieve (i.e. PL membrane); (4) the structural enhancement due to the presence of a hydrophobic surface involves roughly 18 to 24 water hydration layers, for ambient and above temperature conditions.     

Proton transport through water-filled carbon nanotubes

Proton transfer along 1D chains of water molecules inside carbon nanotubes is studied by simulations. Ab initio molecular dynamics and an empirical valence bond model yield similar structures and time scales. The proton mobility along 1D water chains exceeds that in bulk water by a factor of 40, but is reduced if orientational defects are present. Excess protons interact with hydrogen-bonding defects through long-range electrostatics, resulting in coupled motion of protons and defects.     

Percolation transition of hydration water: from planar hydrophilic surfaces to proteins

The formation of a spanning hydrogen-bonded network of hydration water is found to occur via a 2D percolation transition in various systems: smooth hydrophilic surfaces, the surface of a single protein molecule, protein powder, and diluted peptide solution. The average number of water-water hydrogen bonds at the percolation threshold varies from 2.0 to 2.3, depending on temperature, system size, and surface properties. Calculation of nH allows an easy estimation of the percolation threshold of hydration water in various systems, including biomolecules.     

Fabrication of superhydrophobic wood surfaces via a solution-immersion process

Superhydrophobic wood surfaces were fabricated from potassium methyl siliconate (PMS) through a convenient solution-immersion method. The reaction involves a hydrogen bond assembly and a polycondensation process. The silanol was formed by reacting PMS aqueous solution with CO₂, which was assembled on the wood surface via hydrogen bonds with the wood surface -OH groups. The polymethylsilsesquioxane coating was obtained through the polycondensation reaction of the hydroxyl between wood and silanol. The morphology of products were characterized using a scanning electron microscope (SEM), the surface chemical composition was determined using energy dispersive X-ray analysis (EDXA), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TGA) and contact angle measurement. Analytical results revealed that rough protuberances uniformly covered the wood surface, thus transforming the wood surface from hydrophilic to superhydrophobic. The water contact angle of the superhydrophobic wood surface was about 153° and a sliding angle was 4.6°.     

含水量对PAM/PVA互穿网络水凝胶性能的影响

应用分子动力学方法对PAM/PVA互穿网络水凝胶体系进行研究.发现该水凝胶体系的内聚能密度、结合能随着水含量的增加而增加,即体系的稳定性更强.由静态力学性能分析发现随体系含水量的增加,弹性系数、工程模量以及延展性均减小.此外,通过对相关函数的分析,发现H₂O分子与其周围原子、官能团之间主要是通过氢键相互作用,形成氢键的强弱关系为O_water >O_PVA >O_PAM >N_PAM,与形成氢键的可能性(难易)关系一致.     

水玻璃化过程的氢键结构特性

为了解玻璃化过程氢键结构特性,采用分子模拟的手段计算了三种压力下的水玻璃化过程氢键的角度、距离、生命期和数量.计算结果显示:(i)氢键角度呈现泊松分布的特征,随着温度降低分布氢键角度分布范围变窄,峰值变高,在0～13°范围,随温度降低,分布数值变大;而在大于13°,随温度降低,分布数值变小;(ii)氢键距离也呈现泊松分...