共查询到20条相似文献,搜索用时 31 毫秒
1.
Cataliotti RS Palombo F Paolantoni M Sassi P Raudino A 《The Journal of chemical physics》2007,126(4):044505
Rayleigh-Brillouin spectra have been measured in a range of temperatures and compositions of t-butyl alcohol/2,2(')-dimethylbutane liquid mixture. The mixture mole fraction has been varied from pure alkane (x(TBA)=0) to pure alcohol (x(TBA)=1) at temperatures between 283 and 323 K. In the same composition and temperature ranges the authors also executed measurements of mass density, shear viscosity, and refractive index. From light scattering spectra the authors have extracted the hypersound velocities and adiabatic compressibilities and evaluated their excess values. Moreover, the authors attempted to evaluate the isothermal (40 degrees C) Landau-Placzek ratios at various mole fractions, but these values proved to be subject to significant errors due to great uncertainty in the central component intensity measurements. Thus, in discussing the results, this latter quantity was considered only from a qualitative point of view. These results highlight a nonideal behavior of the studied liquid mixture with a probable azeotropic composition around x(TBA)=0.7 due to formation of small clusters of hydrogen-bonded alcohol tetramers that are completely surrounded by solvent molecules and analogous or smaller clusters. These clusters, shaped as inverse micelles, offer their hydrophobic moiety towards the molecules that constitute the solvation shell, resulting in a low polarity solution structure that minimizes the solute-solvent interactions. Differences in thermal and compositional behavior of excess molar volumes and adiabatic compressibilities have been interpreted by attributing different weights to the solute-solvent interaction forces and to the hydrogen bond connectivity effects. 相似文献
2.
Nanodroplets containing mixtures of silicone oil and squalene are dispersed in a simple aqueous surfactant solution, quenched in liquid ethane, and examined using cryogenic transmission electron microscopy (CTEM). Depending on the phase of ice that forms around the nanodroplets and on the composition of the oil mixture, nanoinclusions can be observed inside oil nanodroplets, independent of surfactant type. Our observations suggest that these nanoinclusions arise from nucleation of vapor cavities as the water freezes and expands while the oil remains liquid during the quench. 相似文献
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We have investigated the rotational dynamics of lithium thiocyanate (LiNCS) dissolved in various polar solvents with time and polarization resolved vibrational spectroscopy. LiNCS forms multiple distinct ionic structures in solution that can be distinguished with the CN stretch vibrational frequency of the different ionic assemblies. By varying the solvent and the LiNCS concentration, the number and type of ionic structures present in solution can be controlled. Control of the ionic structure provides control over the volume, shape, and dipole moment of the solute, critical parameters for hydrodynamic and dielectric continuum models of friction. The use of solutes with sizes comparable to or smaller than the solvent molecules also helps amplify the sensitivity of the measurement to the short-ranged solute-solvent interaction. The measured orientational relaxation dynamics show many clear and distinct deviations from simple hydrodynamic behavior. All ionic structures in all solvents exhibit multi-exponential relaxation dynamics that do not scale with the solute volume. For Lewis base solvents such as benzonitrile, dimethyl carbonate, and ethyl acetate, the observed dynamics strongly show the effect of solute-solvent complex formation. For the weak Lewis base solvent nitromethane, we see no evidence for solute-solvent complex formation, but still see strong deviation from the predictions of simple hydrodynamic theory. 相似文献
5.
采用可极化的连续介质模型(PCM), 运用密度泛函理论(DFT), 在B3LYP/6-31+G**水平下研究了溶剂极性对有机π共轭配体N,N'-Bis-(3-pyridyl)ethylene-bis-urea(BPEBU)中syn-anti构象的分子几何和电子结构的影响, 并借助分子动力学模拟的方法, 采用明确溶剂模型研究了溶质-溶剂分子间的相互作用. 密度泛函理论计算结果表明, 随着溶剂极性的增强, BPEBU中尿素基上的CO键和N-H键以及吡啶环上的C-N键被明显极化, 使羰基氧原子和吡啶氮原子的电负性明显增强, 尿素基的N-H键上氢原子的正电荷也显著增加. 分子动力学模拟统计的结果表明, 在极性较强的乙醇溶液中, 有明确的O…H-O, N…H-O和N-H…O等3种氢键作用存在, 而在丙酮溶液中, 只有N…H-O一种氢键作用存在, 而且与乙醇溶液中的N…H-O作用相比要弱些. 另外, 采用密度泛函理论方法结合连续/明确的混合溶剂模型, 优化得到了溶质-溶剂三聚体的超分子簇结构, 与分子动力学模拟的第一溶剂层中的超分子结构相比, 两者定性一致. 相似文献
6.
The hydration behavior of two planar nanoscopic hydrophobic solutes in liquid water at normal temperature and pressure is investigated by calculating the potential of mean force between them at constant pressure as a function of the solute-solvent interaction potential. The importance of the effect of weak attractive interactions between the solute atoms and the solvent on the hydration behavior is clearly demonstrated. We focus on the underlying mechanism behind the contrasting results obtained in various recent experimental and computational studies on water near hydrophobic solutes. The length scale where crossover from a solvent separated state to the contact pair state occurs is shown to depend on the solute sizes as well as on details of the solute-solvent interaction. We find the mechanism for attractive mean forces between the plates is very different depending on the nature of the solute-solvent interaction which has implications for the mechanism of the hydrophobic effect for biomolecules. 相似文献
7.
Solutions of blockcopolymers (POE-b-PI-b-POE) in fluids of interacting aqueous nanodroplets (W/O microemulsions) are studied. The interaction strength between the (pseudo) two components is measured by the shift of the percolation temperature relative to that of the pure microemulsion. A quantitative measure of the interaction, the differential heat of solution, is thermodynamically related to the slopes of the equilibrium temperature of the system with varying monomeric nanodroplet concentration and the experimental percolation line in the presence of copolymer. 相似文献
8.
Krishna Medda Prasanta Chatterjee Mohan Pal Sanjib Bagchi 《Journal of solution chemistry》1990,19(3):271-287
The longest wavelength band of n-alkyl pyridinium iodides (NAPI) in solution, which is due to charge transfer processes within a contact ion pair species, serves as an empirical measure of solute-solvent interaction for a polar solute in polar solvents. An attempt has been made to correlate the energy of the transition with the chemical potential of the dipolar ion pair in a solvent. The latter quantity has been calculated using a dielectrically saturable Block-Walker reaction field model. It has been found that, for protic solvents there is a good linear correlation between the two parameters enabling the calculation of the transition energy in water. An alternative correlation involving the individual molecule dipole reaction field is also discussed. For dipolar aprotic solvents both correlations yield poorer results indicating a single parameter correlation is not sufficient. In alcoholic binary systems the solute-solvent interaction is a linear function of the bulk reaction fields of the component solvents. But in the case of aprotic-alcoholic solvents, where specificities of interaction differ, the solute sees an environment the composition of which differs from that of the bulk. 相似文献
9.
Fluorescence behavior and specific interactions of an ionic liquid in ethylene glycol derivatives 总被引:2,自引:0,他引:2
The excitation-wavelength- and concentration-dependent fluorescence response of an ionic liquid (IL), 1-octyl-3-methylimidazolium tetrafluoroborate [Omim][BF(4)], in the ethylene glycol derivatives, [CH(3)(OCH(2)CH(2))n-OH, n = 1-3], has been critically examined in the entire composition range. The pure IL exhibited a large red shift beyond an excitation wavelength of 390 nm, showing the heterogeneous nature of the liquid. Concentration dependence of the fluorescence spectra in the organic solvent-rich region favors the association of IL molecules into the aggregated structures. The maximum of the fluorescence spectra shifted toward blue with the increase of organic component concentration in all of the mixtures, reflecting an appreciable solute-solvent interaction. Very high concentrations of the organic liquid in the mixtures resulted in the inversion of the spectral shift toward red, indicating the dominance of pi-pi* transitions over the n-pi* transitions as a consequence of imidazolium ring stacking. (1)H NMR and FT-IR investigations over the whole composition range of the mixtures showed multiple hydrogen-bonded interactions of varying strengths between the unlike molecules and the existence of associated species of the IL in the dilute region. Both the specific interactions between unlike molecules and the tendency of aggregation of IL molecules in the dilute region reduced with the introduction of the -OC(2)H(4) group in the glycol derivative. A comparison of specific interactions with the volumetric properties of the similar mixtures shows that the packing efficiency depending on differences in the shape and size of the molecules mainly decides the overall magnitude of deviations from ideality. 相似文献
10.
IR probes have been extensively used to monitor local electrostatic and solvation dynamics. Particularly, their vibrational frequencies are highly sensitive to local solvent electric field around an IR probe. Here, we show that the experimentally measured vibrational frequency shifts can be inversely used to determine local electric potential distribution and solute-solvent electrostatic interaction energy. In addition, the upper limits of their fluctuation amplitudes are estimated by using the vibrational bandwidths. Applying this method to fully deuterated N-methylacetamide (NMA) in D(2)O and examining the solvatochromic effects on the amide I' and II' mode frequencies, we found that the solvent electric potential difference between O(═C) and D(-N) atoms of the peptide bond is about 5.4 V, and thus, the approximate solvent electric field produced by surrounding water molecules on the NMA is 172 MV/cm on average if the molecular geometry is taken into account. The solute-solvent electrostatic interaction energy is estimated to be -137 kJ/mol, by considering electric dipole-electric field interaction. Furthermore, their root-mean-square fluctuation amplitudes are as large as 1.6 V, 52 MV/cm, and 41 kJ/mol, respectively. We found that the water electric potential on a peptide bond is spatially nonhomogeneous and that the fluctuation in the electrostatic peptide-water interaction energy is about 10 times larger than the thermal energy at room temperature. This indicates that the peptide-solvent interactions are indeed important for the activation of chemical reactions in aqueous solution. 相似文献
11.
A level-set method is developed for numerically capturing the equilibrium solute-solvent interface that is defined by the recently proposed variational implicit solvent model [Dzubiella, Swanson, and McCammon, Phys. Rev. Lett. 104, 527 (2006); J. Chem. Phys. 124, 084905 (2006)]. In the level-set method, a possible solute-solvent interface is represented by the zero level set (i.e., the zero level surface) of a level-set function and is eventually evolved into the equilibrium solute-solvent interface. The evolution law is determined by minimization of a solvation free energy functional that couples both the interfacial energy and the van der Waals type solute-solvent interaction energy. The surface evolution is thus an energy minimizing process, and the equilibrium solute-solvent interface is an output of this process. The method is implemented and applied to the solvation of nonpolar molecules such as two xenon atoms, two parallel paraffin plates, helical alkane chains, and a single fullerence C(60). The level-set solutions show good agreement for the solvation energies when compared to available molecular dynamics simulations. In particular, the method captures solvent dewetting (nanobubble formation) and quantitatively describes the interaction in the strongly hydrophobic plate system. 相似文献
12.
A. B. Naik M. L. Narwade P. S. Bodakhe G. G. Muley 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2014,88(1):37-41
Density, ultrasonic speed in pure solvent acetonitrile (AN) and ligand solution of substituted pyrimidine in pure AN were measured at different temperatures (298.15, 303.15, 308.15, 313.15, and 318.15 K). Acoustical parameters such as adiabatic compressibility, intermolecular free length, acoustical impedance and relative association were determined from the experimental data of density and ultrasonic speed. The effect of temperature variations on the strength of molecular interaction has been studied. An excellent correlation represents in terms of solute-solvent interaction at all temperatures. 相似文献
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Photoisomerization of two cyanine derivatives, 3,3(')-diethyloxadicarbocyanine iodide (DODCI) and merocyanine 540 (MC 540), has been investigated in an ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate and aqueous glycerol (93 wt % glycerol +7 wt % water) by measuring fluorescence lifetimes and quantum yields. The aim of this work is to understand how the rates of photoisomerization of DODCI and MC 540 are influenced by specific solute-solvent interactions besides the viscosity of the medium. For DODCI, it has been observed that the nonradiative rate constants, which represent the rates of photoisomerization, are almost identical in the ionic liquid and aqueous glycerol at given temperature, indicating that viscosity is the sole parameter that governs the rate of photoisomerization. In contrast, the photoisomerization rate constants of MC 540 have been found to be a factor of 2 higher in aqueous glycerol compared to the ionic liquid. The observed behavior is due to the zwitterionic character of MC 540, a consequence of which, the twisted state gets stabilized by the solute-solvent hydrogen bonding interactions in aqueous glycerol, thus lowering the barrier for isomerization. 相似文献
15.
A potential of mean torque is derived for a solute at infinite dilution in a uniaxial liquid crystal solvent, which contains terms originating from the dispersion interaction, and the electrostatic interaction between quadrupole moments on both molecules. It is shown that the electrostatic term is non-zero only if the solute-solvent vectors are distributed with lower than spherical symmetry. If this distribution has cylindrical symmetry then both the electrostatic and dispersion terms in the potential of mean torque are shown to depend on order parameters for the orientational distribution of the solute-solvent vectors, as well as on the order parameters of the solvent molecules. 相似文献
16.
Pavone M Cimino P Crescenzi O Sillanpää A Barone V 《The journal of physical chemistry. B》2007,111(30):8928-8939
The role of stereoelectronic, environmental, and short-time dynamic effects in tuning the hyperfine and gyromagnetic tensors of a prototypical nitroxide spin probe has been investigated by an integrated computational approach based on extended Lagrangian molecular dynamics and discrete-continuum solvent models. Trajectories were generated in two protic solvents as well as in the gas phase for reference; structural analysis of the dynamics, and comparison with optimized solute-solvent clusters, allowed for the identification of the prevailing solute-solvent hydrogen-bonding patterns and helped to define the strategy for the computation of magnetic parameters. This was performed in a separate step, on a large number of frames, by a high-level DFT approach coupling the PBE0 hybrid functional with a tailored basis set and with proper account of specific and bulk solvent effects. Remarkable changes in solvation networks are found on going from aqueous to methanol solution, thus providing a rationalization of indirect experimentally available evidence. The computed magnetic parameters are in satisfactory agreement with the available measured values and allow for an unbiased evaluation of the role of different effects in tuning the overall EPR observables. Apart from their intrinsic interest, our results pave the route toward the development of tunable detection protocols based on specific spectroscopic signatures. 相似文献
17.
Cerda-Monje A Aizman A Tapia RA Chiappe C Contreras R 《Physical chemistry chemical physics : PCCP》2012,14(28):10041-10049
Multiparameter linear energy-density relationships to model solvent effects in room temperature ionic liquids (RTILs) are introduced and tested. The model incorporates two solvent dependent and two specific solute-solvent parameters represented by a set of electronic indexes derived from the conceptual density functional theory. The specific solute-solvent interactions are described in terms of the electronic chemical potential for proton migration between the anion or cation and the transition state structure of a specific reaction. These indexes provide a quantitative estimation of the hydrogen bond (HB) acceptor basicity and the hydrogen bond donor acidity of the ionic solvent, respectively. A sound quantitative scale of HB strength is thereby obtained. The solvent dependent contributions are described by the global electrophilicity of the cation and nucleophilicity of the anion forming the ionic liquid. The model is illustrated for the kinetics of cycloaddition of cyclopentadiene towards acrolein. In general, cation HB acidity outweighs the remaining parameters for this reaction. 相似文献
18.
Phase change contrast agents (PCCAs) have been studied in the medical ultrasound field for nearly three decades. Their ability to convert from a liquid core droplet to an acoustically active microbubble has enhanced the possibilities of medical ultrasound, enabling new imaging approaches as well as therapeutic directions. However, traditional PCCAs are formulated with perfluorocarbons which are a liquid at standard temperature and pressure, requiring a high amount of energy to transition the encapsulated droplets to gas form, possibly resulting in undesired bioeffects. A new generation of low-boiling point PCCAs, which are formulated from gaseous perfluorocarbons in a metastable liquid state, seeks to overcome these limits. These super-heated liquid perfluorocarbon nanodroplets display longer circulation kinetics than microbubbles, their activation produces unique acoustic signatures, and their small particle size holds potential for extravascular applications. Low-boiling point nanodroplets can be phase-transitioned when activated with ultrasound at pressures and frequencies approved for diagnostic imaging. From the first publication almost 10 years ago, low-boiling point PCCA research has expanded rapidly, and recent advances in super-resolution imaging, drug delivery and neuromodulation made possible by these nanodroplets are just a few examples of this growing field of research. In this review, we discuss low-boiling point phase change contrast agents and their applications in ultrasound imaging and therapeutics. 相似文献
19.
G B Dutt 《Chemphyschem》2005,6(3):413-418
Solute-solvent interactions play an important role in determining the physicochemical properties of liquids and solutions. As a consequence, understanding these interactions has been one of the long-standing problems in physical chemistry. This Minireview describes our approach towards attaining this goal, which is to investigate rotational relaxation of a pair of closely related, medium-sized nondipolar solutes in a set of appropriately chosen solvents. Our studies indicate that solute-solvent hydrogen bonding significantly hinders solute rotation. We have also examined the role of solvent size both in the absence and presence of specific interactions and it has been observed that the size of the solvent has a bearing on solute rotation especially in the absence of specific interactions. Our results point to the fact that only strong solute-solvent hydrogen bonds have the ability to impede the rotation of the solute molecule because, in such a scenario, hydrogen-bonding dynamics and rotational dynamics transpire on comparable time scales. This aspect has been substantiated by measuring the reorientation times of the chosen solutes in solvents such as ethanol and trifluoroethanol, which have distinct hydrogen-bond donating and accepting abilities, and correlating them with solute-solvent interaction strengths. As an alternative treatment, it has been shown that specific interactions between the solute and the solvent can be modeled as dielectric friction with the extended charge distribution model. This approach is not unrealistic considering the fact that specific as well as non-specific interactions are electrostatic by nature and the differences between them are subtle. 相似文献
20.
The rotational correlation time (tau(2R)) is determined for D(2)O (polar) and C(6)D(6) (apolar) in 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF(6)]) by measuring (2)H (D) nuclear magnetic resonance spin-lattice relaxation time (T(1)) in the temperature range from -20 to 110 degrees C. The tau(2R) ratio of water to benzene (tau(WB)) was used as a measure of solute-solvent attraction. tau(WB) is 0.73 and 0.52 in [bmim][Cl] and [bmim][PF(6)], respectively, whereas the molecular volume ratio is as small as 0.11. The slowdown of the water dynamics compared to the benzene dynamics in ionic liquids is interpreted by the Coulombic attractive interaction between the polar water molecule and the anion. As for the anion effect, the rotational dynamics of water solvated by Cl(-) is slower than that solvated by PF(6) (-), whereas the rotational dynamics of benzene is similar in the two ionic liquids. This is interpreted as an indication of the stronger solvation by the anion with a larger surface charge density. The slowdown of the water dynamics via Coulombic solvation is actually significant only at water concentrations lower than approximately 9 mol dm(-3) at room temperature, and it is indistinguishable at temperatures above approximately 100 degrees C. The quadrupolar coupling constants determined for D(2)O and C(6)D(6) in the ionic liquids were smaller by a factor of 2-3 than those in the pure liquid state. 相似文献