The Structure of Simple Molecular Liquids

Liquid structure is described by the pair-correlation function. If the liquied particles are molecules then the respective correlation function depends on distance and several angular variables; hence, for the sake of simplicity a symmetry-adapted representation must be used. The most important structural parameters of this molecular pair-correlation function can be determined approximately by a combination of several scattering experiments, such as neutron (employing different isotopes), X-ray and electron diffraction. Light scattering, dielectric, and nuclear magnetic relaxation experiments provide further, albeit less direct, access to such determinations. Some results obtained by measurements on chloroform are reported. Theoretical computations of these structural parameters are also discussed.     

超高效液相色谱-三重四极杆质谱法测定化妆品中秋水仙碱、秋水仙胺和秋水仙碱苷EI北大核心CSCD

建立了一种同时测定化妆品中秋水仙碱、秋水仙胺和秋水仙碱苷的超高效液相色谱-三重四极杆质谱分析方法。试样经正己烷饱和的甲醇-乙腈(1∶1,V/V)混合溶剂超声提取,蜡基类样品经正己烷溶解分散后提取,膏霜类样品在提取液中加入乙酸铵以改善样品乳化情况,提取液离心过滤后,以5 mmol/L乙酸铵(含0.1%甲酸)-甲醇作为流动相梯度洗脱,经ACQUITY UPLC BEH C_(18)色谱柱分离后,采用超高效液相色谱-三重四极杆质谱在电喷雾正离子电离模式和多反应监测(MRM)模式检测。3种化合物在0.5~10μg/L范围内线性关系良好,相关系数大于0.995,检出限为3.0μg/kg,定量限为10.0μg/kg,在10.0,20.0,100μg/kg 3个加标水平下的平均回收率为81.5%~109.2%,相对标准偏差为0.5%~8.7%。该方法适用于化妆品中秋水仙碱、秋水仙胺和秋水仙碱苷的测定。     

Determination of 15 polycyclic aromatic hydrocarbons in lotus root by QuEChERS-high performance liquid chromatographyEI北大核心CSCD

A method for the determination of 15 priority polycyclic aromatic hydrocarbonsPAHsin lotus root by QuEChERS technique combined with high performance liquid chromatography HPLC was established. Lotus root samples were extracted by acetonitrilefiltrated after salting out and purified by C18 and primary secondary aminePSAsorbent. Then the 15 kinds of PAHs were analyzed by HPLC with diode array detector or fluorescence detector after being separated by Athena PAHs column. When the 15 kinds of PAHs were analyzed by diode array detectorthe linear relationships were good between 0.02 and 1.0 mg/L with the correlation coefficients above 0.99 for all the 15 kinds of PAHs. The limits of quantitation were 0.02 mg/kg for allthe average recoveries of the 15 kinds of PAHs were 84.7%-117.1%and the relative standard deviations were 0.73%-11%. When the 14 kinds of PAHsexcept for acenaphthyleneanalyzed by fluorescence detectorthe linear relationships were good between 0.001 and 1.0 mg/L with the correlation coefficients above 0.99 for all the 14 kinds of PAHs except for acenaphthylene. The limits of quantitation were 5 μµg/kg for allthe average recoveries of the 14 kinds of PAHsexcept for acenaphthylenewere 69.1%-111.8%and the relative standard deviations were 0.18%-9.7%. Diode array detector and fluorescence detector are complementary. Diode array detector can analyze all the PAHsbut its sensitivity is relatively low. Fluorescence detector is not suitable for acenaphthylene with weak fluorescence signalbut its sensitivity is much higher than that of diode array detector. This method is suitable for simultaneously and quickly determination of 15 kinds of PAHs in lotus root. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Non-hydrodynamic modes in viscoelastic behaviour of simple fluids

ABSTRACT

We discuss the role of non-hydrodynamic processes in viscoelastic transition in pure liquids. In particular, using both analytical results and molecular dynamics simulations, we clarify the effect of the shear stress relaxation on the transverse dynamics. We use as an example the Lennard-Jones fluids. We analyse the frequency dependence of the shear modulus and its connection to the non-hydrodynamic shear relaxation mode. The analysis of the relaxation times of the non-hydrodynamic modes in longitudinal and transverse dynamics makes evidence that the emergence of the non-hydrodynamic transverse excitations outside the propagation gap is not directly connected to the onset of the positive sound dispersion.     

Tandem catalysis in ionic liquids: a recyclable catalytic synthesis of benzofuran derivatives

A convenient, recyclable catalytic synthesis of benzofuran-2-acetic esters 2 by sequential Pd(0)-catalyzed deallylation—Pd(II)-catalyzed carbonylative heterocyclization of 1-(2-allyloxyphenyl)-2-yn-1-ols 1 in ionic liquids is presented. Reactions were typically carried out in BmimBF₄ as the solvent at 100 °C and under 30 atm of CO, in the presence of catalytic amounts (1 mol %) of PdI₂ in conjunction with KI (1 equiv), PPh₃ (4 mol %), MeOH (28 equiv), and H₂O (2 equiv). The solvent-catalyst system could be recycled several times without appreciable loss of catalytic activity.     

Proposed lower bound for the shear viscosity to entropy density ratio in some dense liquids

Starting from relativistic quantum field theories, Kovtun et al. (2005) have quite recently proposed a lower bound η/s??/(4πkB), where η is the shear viscosity and s the volume density of entropy for dense liquids. If their proposal can eventually be proved, then this would provide key theoretical underpinning to earlier semiempirical proposals on the relation between a transport coefficient η and a thermodynamic quantity s. Here, we examine largely experimental data on some dense liquids, the insulators nitrogen, water, and ammonia, plus the alkali metals, where the shear viscosity η(T) for the four heaviest alkalis is known to scale onto an ‘almost universal’ curve, following the work of Tankeshwar and March a decade ago. So far, all known results for both insulating and metallic dense liquids correctly exceed the lower bound prediction of Kovtun et al.     

Study of clusters of interest for liquid ionic alloys

Calculations are reported of the total energies and related quantities of sequences of small clusters of the form A_m Pb_n, where A is an alkali atom, n <6 and m < 9. The object of this study is to shed light on the stoichiometry and the possible formation of complexes in A-Pb liquid alloys. The calculations are performed using empty core pseudopotentials and the spherical average approximation for the cluster. The results are insensitive to the choice of alkali atom apart from a smooth trend with the progression from Li to Cs. The calculated total energies suggest that clusters with compositions A₄Pb and A₄Pb₄ are very stable against a change in the number of Pb or A atoms and support the possibility of these clusters forming in the liquid alloys. This stability arises from an electronic shell-closing effect.     

Macroscopic properties of smectic liquid crystals

We discuss the macroscopic behavior of smectic C_G liquid crystals. Smectic C_G is the most general tilted smectic phase that is fluid in the layers. It is characterized by global C₁ symmetry. Consequently, it is ferroelectric, pyroelectric and piezoelectric, opening up a number of possible applications for such a phase. As smectic C_G-phase has a macroscopic hand due to its structure, it is a natural candidate to explain the recent experimental observations of left and right-handed helices in a system composed of achiral molecules. We also discuss critically to what extent smectic C_G could be important for liquid crystalline phases formed by banana-shaped molecules. Phase transitions involving a smectic C_G phase and defects of its in-plane director are briefly discussed. Received: 25 March 1998 / Revised: 15 June 1998 / Accepted: 15 July 1998     

Brillouin scattering in liquid sulfur dioxide: relaxational behaviour

The frequency dependence of hypersonic absorption and the dispersion of hypersonic speed in liquid sulfur dioxide (SO₂) were determined at (293.75±0.30) K and at (284.65±0.30) K by Brillouin spectroscopy. The results are used to experimentally establish the second relaxation step in the double vibrational relaxation of these quantities in the liquid phase, which was first conjectured by R. Bass and J. Lamb, Proc. R. Soc. Ser. A (1958) 243, 94. This second relaxation takes place at approximately 1.5 GHz for both temperatures within experimental error, whereas the first relaxation step, previously determined by ultrasonic spectroscopy, takes place at approximately 23 MHz. In the course of this investigation, some evidence was found that for the temperatures considered the shear viscosity relaxes in the hypersonic frequency range.