Ultraviolet and visible Brillouin scattering study of viscous relaxation in 3-methylpentane down to the glass transition

Brillouin light scattering spectra from transverse and longitudinal acoustic waves in liquid and supercooled 3-methylpentane have been collected from room temperature down to 80 K, just above the glass transition. Spectra at different wave vectors have been obtained using 532 nm and 266 nm excitation. We found evidence of a shear relaxation with a characteristic time of 100 s at the glass transition which only partly accounts for the relaxation observed in the propagation and attenuation of the longitudinal modes. The inclusion of a relaxing bulk viscosity contribution with a relaxation time of the order of 10(2) ns at the glass transition is found to adequately reproduce the experimental data including transient grating data at a much lower frequency. A consistent picture of relaxed shear and bulk moduli as a function of temperature is derived. These two quantities are found to be related by a linear relation suggesting that a Cauchy-like relation holds also above the glass transition.     

Communication: Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids

The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, and longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-parameter liquids.     

Heat capacity, Raman, and Brillouin scattering studies of M2O-MgO-WO3-P2O5 glasses (M=K,Rb)

The authors report the results of temperature-dependent Brillouin scattering from both transverse and longitudinal acoustic waves, heat capacity studies as well as room temperature Raman scattering studies on M2O-MgO-WO3-P2O5 glasses (M=K,Rb). These results were used to obtain information about structure and various properties of the studied glasses such as fragility, elastic moduli, ratio of photoelastic constants, and elastic anharmonicity. They have found that both glasses have similar properties but replacement of K+ ions by Rb+ ions in the glass network leads to decrease of elastic parameters and P44 photoelastic constant due to increase of fragility. Based on Brillouin spectroscopy they show that a linear correlation between longitudinal and shear elastic moduli holds over a large temperature range. This result supports the literature data that the Cauchy-type relation represents a general rule for amorphous solids. An analysis of the Boson peak revealed that the form of the frequency distribution of the excess density of states is in agreement with the Euclidean random matrix theory. The reason of the observed shift of the maximum frequency of the Boson peak when K+ ions are substituted for Rb+ ions is also briefly discussed.     

Determination of Elastic Moduli and Compliances of Viscoelastic Liquids Using the Dynamic Light Scattering Technique

Relations between the dynamic light scattering spectrum and the mechanical compliances and longitudinal stress moduli of viscoelastic liquids are provided. The result provides a basis for determination of mechanical relaxation spectra using the dynamic light scattering technique. The method of Computating the longitudinal modulus and the compliance spectra from the time correlation of density fluctuations of poly (propylene glycol), as determined by the photon correlation spectroscopy technique is illustrated.     

New regularities and an equation of state for liquids

Three regularities have been introduced for liquids (T < T_C and ρ > ρ_C) based on average potential energy. The experimental data have been used to show the validity of the regularities. First, there exists near-linearity relation between and ρ for all isotherms of a liquid, where P_i and ρ are internal pressure and density, respectively. Second, changes linearly with ρ for each isotherm of any liquid, where Z and V_m are compressibility factor and molar volume, respectively. Third, a new regularity using the definition of bulk modulus and our new equation of state between reduced bulk modulus and density has been introduced, that is versus ρ must be linear for all isotherms of a liquid where B_r is the reduced bulk modulus.

A new equation of state has been also derived. The density of some liquids in the extensive ranges of temperature and pressure has been calculated using the new equation of state. The densities calculated from this equation agree with experiment to better than 0.3%. The new equation of state can predict internal pressure, thermal expansion coefficient, and isothermal compressibility of liquids within experimental error.     

Triggered ligand release coupled to framework rearrangement: generating crystalline porous coordination materials

A robust 3-D porous structure of formula [Ln2(PDC)3(DMF)2](infinity) has been constructed from lanthanide cations (Ln = Er3+ or Y3+) and the non-linear anionic bridging ligand, pyridine-3,5-dicarboxylate (PDC2-) in dimethylformamide (DMF). The solvated framework polymers {[M2(PDC)3(DMF)2].n(solv)}(infinity) (M = Er, Y) undergo a solid-state, crystal-to-crystal reaction upon heating and are converted via loss of both sorbed and coordinated solvent and rearrangement of the framework core to give a desolvated and porous form with retention of structural integrity. This structural transfer is the first crystallographically characterized system with lanthanide metal ions. These porous products are shown to be effective absorbants for H2, N2, and benzene.     

Electric birefringence and streaming-electric birefringence of synthesized imogolite: the anisotropy of electric polarizability

Imogolite synthesized from sodium orthosilicate and aluminum trichloride was fractionated into four fractions by centrifuging at 12,000 x g (1h). The supernatant, which did not deposit by three times centrifugations, was used for all measurements. The signal of birefringence under a reversing electric pulse showed that the permanent dipole moment is negligibly small at low fields. The electric birefringence under a rectangular electric pulse is positive. The saturated value is proportional to the concentration of imogolite in the range of 0-0.1mg/ml and decreases rapidly with an increase of added salt concentration for NaCl and AgNO(3). It slightly depends on the pH of solution and is biggest in pure water. Then we have determined the anisotropy of electric polarizability (Deltaalpha) for imogolite in pure water at 0.05 mg/ml. Deltaalpha we obtained from the method decreases rapidly at low fields and slowly at high fields as shown in references [M. Matsumoto, Colloids Surf. A 148 (1999) 75, M. Matsumoto, Biophys. Chem. 58 (1996) 173]. It is approximately shown by the following expression, Deltaalpha=Deltaalpha(infinity)+(Deltaalpha(0)-Deltaalpha(infinity))/(1+KE), (Deltaalpha(0):Deltaalpha at E=0, Deltaalpha(infinity):Deltaalpha at E=infinity). Using this relation we can draw the curve of electric birefringence as a function of electric field and compare it with experimental values. The results, when Deltaalpha(0)=1.17x10(-28)Fm(2), Deltaalpha(infinity)=0.005x10(-28)Fm(2) and K=0.00031 m/V, are in good agreement with each other. In order to explain the reason why the anisotropy of electric polarizability rapidly decreases with an increase of electric field we propose that the difference of electrophoretic mobility between parts of colloidal particle causes the orientation of a rod like particle. The theoretical electric birefringence as a function of electric field we obtained is considerably in good agreement with the experimental values.     

由纯组元性质预估过量体积和过量焓——新关联方程的提出

在各种预估溶液过量性质的方法中,以统计力学为基础的Flory法常被采用。在此基础上,Pollin和Fried按虚拟双流体理论所提出的方法使预估的准确性有所提高。其他还可以提到Lieberman以Van der Waals方程为基础的预估方法。本文的目的是从反映液体实际PVT性质的函数关系出发,提出相应的状态方程,并用于推导预估液体溶液过量性质的新关联方程。     

Determination of the elastic moduli of polymer films by a new ultrasonic reflection method

The development and first applications of a new ultrasonic reflection method for determination of the viscoelastic properties of polymer films are reported. The complex shear modulus G* and the complex longitudinal modulus L*=K*+ 4/3 G* of the samples are derived from the measured complex reflection coefficients of an ultrasonic shear and longitudinal wave, respectively. From G and L the Young's modulus E, the compression modulus K and the Poisson ratio ν can be calculated for isotropic materials. A LiNbO₃-transducer (10° rotated Y-cut) is used for the simultaneous excitation of longitudinal and transversal ultrasonic waves, which allows to determine different elastic constants by one measurement. A measuring cell with normal incidence of the ultrasonic waves is used. The equipment has been applied to study the time dependence of the moduli during film formation from an aqueous polymer dispersion and the isothermal curing of an epoxy resin. Furthermore, the temperature dependence of the elastic constants of a carbon-black filled rubber and during non-isothermal crystallization of a semi-crystalline polymer has been studied.     

Measurement of the stress-relaxation modulus in the primary transition region

Difficulties have been encountered in experimentally measuring the stress-relaxation modulus for systems with steep slopes in the primary transition region. The usually applied “factor-of-ten” rule is shown to apply in these cases as well as in cases where the relaxation is slower; with the steep slope, however, the rule offers little help, since the decay in the modulus is so fast that stresses are usually very small at times when direct modulus calculations may be made. A technique is suggested which allows calculation of the modulus in this difficult region. A slow constant strain-rate deformation is followed by a constant strain period. Modulus values for times during the constant strain rate period are calculated using well known relationships. Long-time values are calculated from the definition of the modulus (the factor-of-ten rule being employed) and a recursion relation is developed which is used for modulus calculations during the constant strain period at relatively short times where effects of strain rate are important. Starting values for the recursion relation are long-time moduli which can be calculated directly.     

2'''',3''''-双脱氢-2'''',3''''双脱氧胸苷5''''-亚磷酸苄酯的ESI-MS~n中的一种新颖的重排反应

爱滋病(AIDS)是一种严重威胁人类健康的传染性疾病。研究和开发新的、高疗效的抗AIDS的药物已成了生物学家、化学家和药物学家的主要的研究方向之一。2',3'-双脱氢.2',3'-双脱氧胸苷(d4T)是HIV逆转录酶抑制剂,它们是美国FDA通过的可用于治疗AIDS的一类药物。由于d4T等本身对HIV无活性,只有经细胞代谢成5'-磷酸化产物后才对HIV产生抑制作用,因此很有必要对d4T进行结构改造,而对上述药物的结构进行改造是研制新的抗AIDS的化学药物最简捷的途径。因此,我们合成了一系列的d41、5'-亚磷酸酯的衍生物,并对它们的电喷雾质谱进行了详细的研究。研究发现了2',3'-双脱氢,2',3'双脱氧胸苷(d4T)-5'-氢亚磷酸苄酯的一种新颖的重排反应,并对其机理进行了进一步的研究。有关结果不仅有助于对这类化合物的结构分析,而且对它们的合成、药物性质以及药物代谢等方面的研究都具有重要意义。     

Rapid ligand substitution reactions in ionic liquids studied by stopped-flow technique

Detailed kinetic studies on ligand substitution reactions of [M(II)(terpy)Cl](+) complexes (M = Pt, Pd; terpy = 2,2':6',2'-terpyridine) with thiourea as entering nucleophile were for the first time performed in the imidazolium based ionic liquid [emim][NTf(2)] using stopped-flow techniques, opening the route to study fast reactions of transition metal complexes in ionic liquids.     

Vectorial property dependence in bis {4'-(n-pyridyl)-2,2':6',2"-terpyridine}iron(II) and ruthenium(II) complexes with n = 2, 3 and 4

A comparative structural and spectroscopic investigation of the complexes [M(1)2]2+, [M(2)2]2+ and [M(3)2]2+ in which M = Fe or Ru, and ligands 1, 2 and 3 are 4'-(2-pyridyl)-, 4'-(3-pyridyl)- and 4'-(4-pyridyl)-2,2':6',2"-terpyridine, respectively, is reported. The complexes [Ru(1)2]2+, [Ru(2)2]2+ and [Ru(3)2]2+ undergo mono- and bis-N-methylation. The consequences of methylation on the absorption spectra and electrochemical properties are discussed; the solid-state structure of the bis(N-methylated) derivative of [Ru(2)2][PF6]2 is presented.     

New layered materials: syntheses, structures, and optical and magnetic properties of CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3

Four new quaternary selenides CsGdZnSe3, CsZrCuSe3, CsUCuSe3, and BaGdCuSe3 have been synthesized with the use of traditional high-temperature solid-state experimental methods. These compounds are isostructural with KZrCuS3, crystallizing with four formula units in the orthorhombic space group Cmcm. Cell constants (A) at 153 K are CsGdZnSe3 4.1684(7), 15.765(3), 11.0089(18); CsZrCuSe3 3.903(2), 15.841(10), 10.215(6); CsUCuSe3 4.1443(7), 15.786(3), 10.7188(18); and BaGdCuSe3 4.1839(6), 13.8935(19), 10.6692(15). The structure of these ALnMSe3 compounds (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of 2 to infinity [LnMSe3(n-)] (n = 1, 2) layers separated by A atoms. The Ln atom is octahedrally coordinated to six Se atoms, the M atom is tetrahedrally coordinated to four Se atoms, and the A atom is coordinated to a bicapped trigonal prism of eight Se atoms. Because there are no Se-Se bonds in the structure, the oxidation state of A is 1+ (Cs) or 2+ (Ba), that of Ln is 3+ (Gd) or 4+ (Zr, U), and that of M is 1+ (Cu) or 2+ (Zn). CsGdZnSe3 and BaGdCuSe3, which are paramagnetic, obey the Curie-Weiss law and have effective magnetic moments of 7.87(6) and 7.85(5) muB for Gd(3+), in good agreement with the theoretical value of 7.94 muB. Optical transitions at 1.88 and 2.92 eV for CsGdZnSe3 and 1.96 eV for BaGdCuSe3 were deduced from diffuse reflectance spectra.     

Cs3AgAs4Se8 and CsAgAs2Se4: selenoarsenates with infinite 1 infinity[AsSe2]- chains in different Ag+ coordination environments

Two quaternary silver selenoarsenates Cs3AgAs4Se8 (I) and CsAgAs2Se4 (II) have been discovered by methanothermal reaction of Li3AsSe3 with AgBF4 in the presence of the respective alkali metal sources Cs2CO3 and CsCl. Orange crystals of Cs3AgAs4Se8 (I) were formed after reaction at 120 degrees C for 72 h, whereas red CsAgAs2Se4 (II) was obtained under slightly different conditions at 140 degrees C for 70 h. Both compounds possess novel two-dimensional (2D) polyanions consisting of infinite 1 infinity[AsSe2]- chains that are interconnected by Ag+ ions in different coordination patterns. In I, a double layer of 1 infinity[AsSe2]- chains is bridged by distorted trigonal planar coordinated Ag+ atoms to form a 2 infinity[AgAs4Se8]3- layer with a thickness of about 11.3 A. The nonbonding Ag...Ag distances are about 4.220 A, and large cavities within the layers accommodate for three of the four crystallographic Cs+ cations. The double amount of Ag+ atoms per AsSe2 chain unit in II leads to simple layers 2 infinity[AgAs2Se4]- [=[Ag2As4Se8]2-] in which the Ag+ atoms are arranged in rows between the 1 infinity[AsSe2]- chains, with alternating Ag...Ag distances of 3.053(3) and 3.488(3) A. Hereby the 1 infinity[AsSe2]- polyanions show a disorder within the central (-As-Seb)- chain (b = bridging), while the positions of the terminal Se atoms (Set) remain unaffected. The thermal, optical, and spectroscopic properties of the compounds are reported. Both I and II melt with decomposition and are wide band gap semiconductors with values of 2.07 and 1.79 eV, respectively. Raman spectroscopic data show typical band patterns expected for infinite [AsSe2]- chains. Crystal Data: Cs3AgAs4Se8 (I), monoclinic, C2/c, a = 25.212(2) A, b = 8.0748(7) A, c = 22.803(2) A, beta = 116.272(2) degrees, Z = 8; CsAgAs2Se4 (II), monoclinic, P2(1)/n, a = 10.9211(1) A, b = 6.5188(2) A, c = 13.7553(3) A, beta = 108.956(1) degrees, Z = 4.     

二氧化硅分散体系在应力剪切过程中粘弹性及能耗研究

通过动态应力剪切研究了以乙二醇、丙二醇和丁二醇为分散介质的雾化二氧化硅分散体系的粘弹性以及能耗. 研究发现, 随着应力的增大, 体系都经历了线性粘弹区、剪切变稀区以及剪切增稠区. 在线性粘弹区, 储能模量(G′)、耗能模量(G′′)随着应力(σ)的增大保持不变；在剪切变稀区, G′随着σ的增大而减小, 且乙二醇、丙二醇、丁二醇分散体系的减小幅度依次递减, 而G′′基本保持不变；在剪切增稠区, G′、G′′都随着σ的增大而增大. 在所研究的应力范围内, G′′都大于G′, 体系主要体现粘性, 消耗能量为主. 同时还发现在低剪切应力区, 体系所消耗的能量(Ed)都随着最大应变(γ0)成二次方关系增长, 而在剪切增稠区, 当n=2.79、4.93、4.88时, EG/SiO2、PG/SiO2、BG/SiO2的Ed分别随γ0以指数关系增长.     

Simultaneous determination of stable isotopically labelled L-histidine and urocanic acid in human plasma by stable isotope dilution mass spectrometry.

A capillary gas chromatographic-mass spectrometric method for the simultaneous determination of stable isotopically labelled L-histidine (L-[3,3-2H2,1',3'-15N2]histidine, L-His-[M + 4]) and urocanic acid ([3-2H,1',3'-15N2]urocanic acid, UA-[M + 3]) in human plasma was developed using DL-[2,3,3,5'-2H4,2'-13C,1',3'-15N2]histidine (DL-His-[M + 7]) and [2,3,5'-2H3,2'-13C,1',3'-15N2]urocanic acid (UA-[M + 6]) as internal standards. L-Histidine and urocanic acid were derivatized to alpha N-(trifluoroacetyl)-imN-(ethoxycarbonyl)-L-histidine n-butyl ester and imN-(ethoxycarbonyl)urocanic acid n-butyl ester. Quantification was carried out by selected ion monitoring of the molecular ions of the respective derivatives of L-His-[M + 4], DL-His-[M + 7], UA-[M + 3] and UA-[M + 6]. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring plasma concentrations of L-His-[M + 4] and UA-[M + 3] following administration of trace amounts of L-His-[M + 4] to humans.     

Alkali cation extraction by calix[4]crown-6 to room-temperature ionic liquids. The effect of solvent anion and humidity investigated by molecular dynamics simulations

We report a molecular dynamics study on the solvation of M+ (Na+ to Cs+) alkali cations and of their LM+ complexes with a calix[4]arene host (L = 1,3-dimethoxy-calix[4]arene-crown-6 in the 1,3-alternate conformation) in the [BMI][PF6] and [BMI][Tf2N] room-temperature ionic liquids "ILs" based on the BMI+ (1-butyl-3-methylimidazolium) cation. The comparison of the two liquids and the dry versus humid form of the former one (with a 1:1 ratio of H2O and BMI+PF6- species) reveals the importance of humidity: in [BMI][PF6]-dry as in the [BMI][Tf2N] liquid, the first solvation shell of the "naked" M+ ions is composed of solvent anions only (four PF6- anions, and from four to five Tf2N- anions, respectively, quasi-neutralized by a surrounding cage of BMI+ cations), while in the [BMI][PF6]-humid IL, it comprises from one to three solvent anions and about four H2O molecules. In the LM+ complexes, the cation is shielded from solvent, but still somewhat interacts with a solvent anion in the dry ILs and with water in the humid IL. We also report tests on M+ interactions with solvent anions PF6- and Tf2N- in the gas phase, showing that the AMBER results are in satisfactory agreement with QM results obtained at different levels of theory. The question of ion recognition by L is then examined by free energy perturbation studies in the three liquids, predicting a high Cs+/Na+ selectivity upon liquid extraction from an aqueous phase, in agreement with experimental results on a parent calixarene host. A similar Cs+/Na+ selectivity is predicted upon complexation in a homogeneous IL phase, mainly due to the desolvation energy of the free cations. Thus, despite their polar character, ionic liquids qualitatively behave as classical weakly polar organic liquids (e.g., choroform) as far as liquid-liquid extraction is concerned but more like polar liquids (water, alcohols) as far as complexation in a single phase is concerned.     

A novel layered titanoniobate LiTiNbO5: topotactic synthesis and electrochemistry versus lithium

A new layered titanoniobate, LiTiNbO5, an n = 2 member of the A(x)M(2n)O(4n+2) family, has been synthesized using a molten salt reaction between HTiNbO5 and an eutectic "LiOH/LiNO3". This compound crystallizes in the P2(1)/m space group with a = 6.41 A, b = 3.77 A, c = 8.08 A, and beta = 92 degrees . It exhibits |TiNbO5|(infinity) layers similar to HTiNbO5, but differs from the latter by a "parallel configuration" of its |TiNbO6|(infinity) ribbons between the two successive layers. The topotactic character of the reaction suggests that exfoliation plays a prominent role in the synthesis of this new form. This new phase intercalates reversibly 0.8 lithium through a first-order transformation leading to a capacity of 94 mAh/g at a potential of 1.67 V vs Li/Li+.     

Study of aldehyde oxidase by micellar electrokinetic chromatography separation of O6‐benzylguanine and 8‐oxo‐O6‐benzylguanine

A separation method for O⁶‐benzylguanine (O⁶‐BG) and 8‐oxo‐O⁶‐benzylguanine (8‐oxo‐O⁶‐BG) is developed by using MEKC. This study includes the optimization of separation and incubation parameters for both off‐line and on‐line procedures. The BGE consisted of 25 mM sodium phosphate buffer‐methanol (70:30, v/v), apparent pH 7.4, in which SDS and methyl‐β‐cyclodextrin were dissolved yielding final concentrations of 50 and 15 mM, respectively. Separations were performed at 15 kV using an untreated fused‐silica capillary (40 cm length, effective length is 30 cm) with the detection wavelength at 195 nm. The capillary was kept at 15°C. Good performances were demonstrated for the repeatability and linearity. The LOQ was determined to be 14 μM for 8‐oxo‐O⁶‐BG (S/N = 10). The accuracy values showed a bias of +7.9% for 50 μM and –7.0% for 100 μM. Premix and transverse diffusion of laminar flow profiles (TDLFP) methods were used for on‐line mixing and reaction of the substrate O⁶‐BG with aldehyde oxidase. Both procedures were successful in mixing as well as subsequent separation of the substrate and the metabolite, while the repeatability of TDLFP (14.7% (n = 3)) was much better than the premix technique.