CF3C(O)F水合作用的热力学和动力学理论研究

由于氟氟烃（CFCs）对大气臭氧层有破坏作用，人们拟以另外的化合物来代替它，CF3CX2H（X＝H，CI，F）可能是一类合适的取代物．但人们对它及其反应产物对大气的影响还不清楚.CFaC（0）F是CFaCX。H大气光氧化过程的终产物之一[1－3］，其在大气中的后继反应行为将直接关系到CF2     

Calorimetric Control of Aluminium Casting Quality

Differential scanning calorimetry (DSC) combined with an entrained droplet technique [1] has been successfully used on a series of melt spun alloys with deliberate impurity additions to study the nucleation related aspects of secondary phase selection during solidification of dilute Al alloys. This paper illustrates how DSC is a sensitive tool for determining the effect impurities can have on the nucleation of secondary phases, and hence material properties of these alloys. Stepped cooling/isothermal holding profile DSC has also been used in preliminary investigations of the thermodynamic range of formation of the Al—Fe eutectic phases and their nucleation and growth solidification kinetics.This revised version was published online in November 2005 with corrections to the Cover Date.     

Cyclofructan 6 based stationary phases for hydrophilic interaction liquid chromatography

New stationary phases for hydrophilic interaction liquid chromatography (HILIC) were synthesized by covalently attaching native cyclofructan 6 (CF6) to silica gel. The chromatographic characteristics of the new stationary phases were evaluated and compared to three different types of commercial HILIC columns. The CF6 columns produced considerably different retention and selectivity patterns for various classes of polar analytes, including nucleic acid compounds, xanthines, β-blockers, salicylic acid and its derivatives, and maltooligosaccharides. Univariate optimization approaches were examined including organic modifier (acetonitrile) contents and buffer pH and salt concentration. The thermodynamic characteristic of the CF6 stationary phase was investigated by considering the column temperature effect on retention and utilizing van't Hoff plots. CF6 based stationary phases appear to have exceptionally broad applicability for HILIC mode separations.     

Techniques of differential scanning calorimetry for quantification of low contents of amorphous phases

Differential scanning calorimetry (DSC) is one of the most frequently used techniques for analyzing small concentrations of amorphous phases in a crystalline matrix. In recent years novel enhanced DSC approaches have been intensively looked for to improve parameters such as sensitivity, accuracy, and detection limit of the technique. Low levels of amorphous phases can be quantitatively determined in DSC by measuring the heat capacity change associated with the glass transition. In this short review the potentials provided by the HyperDSC and StepScan DSC techniques are discussed. Examples illustrate the advantages and disadvantages of the techniques and compare their abilities to detect small glass transitions and determine low contents of amorphous phases in samples which are mostly crystalline.     

Novel fluorinated liquid crystals. II. The synthesis and phase transitions of a novel type of ferroelectric liquid crystals containing 1,4-tetrafluorophenylene moiety

4-[(S)-2-Methylbutoxycarbonyl]phenyl 4-[(4-n-alkoxy-2,3,5,6-tetrafluorophenyl)ethynyl]benzoates have been prepared from the starting material 1-pentafluorophenyl-2-trimethylsilylacetylene. Polarizing microscope textural observation and DSC measurements of the phase transitions of these novel compounds showed that they were liquid crystals with chiral smectic C phase (S*_C), smectic A(S_A) and cholesteric (Ch) phases. The effects of the alkoxy chain length on the transition temperatures and enthalpies were also studied.     

Thermal behaviour of styrene butadiene rubber/poly(ethylene-co-vinyl acetate) blends

The thermal behaviour of styrene butadiene rubber (SBR)/poly (ethylene-co-vinyl acetate) (EVA) blends was studied by using thermogravimetry (TG) and differential scanning calorimetry (DSC). The effects of blend ratio, cross-linking systems and compatibilization on the thermal stability and phase transition of the blends were analyzed. It was found that the mass loss of the blends at any temperature was lower than that of the components, highlighting the advantage of blending SBR and EVA. The addition of compatibilizer was also found to improve the thermal stability. DSC studies indicated the thermodynamic immiscibility of SBR/EVA system even in the presence of the compatibilizer. This is evident from the presence of two different glass transition temperatures, corresponding to SBR and EVA phases in both compatibilized and uncompatibilized blends.     

Calorimetric and spectroscopic studies characterization of newborn rat’ blood serum after maternal administration of cyclophosphamide

Differential scanning microcalorimetry (DSC) and UV–VIS absorption spectroscopy were used to obtain the characteristics of blood serum from newborn rat’ after maternal treatment with cyclophosphamide in comparison with control. The obtained DSC curves reveal a complex endothermic peak due to the unfolding process of various serum proteins. Thermal profiles and absorption spectra of blood serum are sensitive to the age of newborns as well as to effect of maternal administration of cyclophosphamide. The most significant disturbances in serum proteome were observed for 14-day old newborns. The thermodynamic parameters: enthalpy change (∆H), the normalized first moment (M₁) of the thermal transition with respect to the temperature axis and the ratio of C _p^ex at 70 and 60 °C describing denaturation contributions of globulin forms in respect to unliganded albumin with haptoglobin was estimated. Moreover, the second derivative spectroscopy in the UV region was used to resolve the complex protein spectrum. The differences in blood serum detected by DSC and UV–VIS confirm a potential usefulness of these methods for diagnostic and monitoring changes with age as well as the pathological state of blood serum.     

Effects of solvents and solutes on glass-transition thermodynamics and kinetic fragility for amine and alcohol solutions of inorganic salts

Journal of Thermal Analysis and Calorimetry - We have used differential scanning calorimetry (DSC) to investigate the thermodynamic and kinetic properties of the glass transition of simple amine...     

Phase transitions and conformational changes in an antiferroelectric liquid crystal 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC)

The thermodynamic properties and conformational structures in the crystalline and liquid crystalline phases of 4-(1-methylheptyloxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC) have been investigated by Raman scattering, X-ray diffraction and differential scanning calorimetry (DSC). MHPOBC can assume two different crystalline states at room temperature depending on crystallization conditions, and heating transforms the metastable crystal to the stable one before melting. In the liquid crystalline phases, Raman scattering spectra have revealed not only the flip-flop twisting vibration of the biphenyl group but also the internal rotation around C-C bonds between the carbonyl groups and the corresponding benzene rings.     

Scan-rate-dependent melting transitions of interleukin-1 receptor (type II): elucidation of meaningful thermodynamic and kinetic parameters of aggregation acquired from DSC simulations

The role of thermal unfolding as it pertains to thermodynamic properties of proteins and their stability has been the subject of study for more than 50 years. Moreover, exactly how the unfolding properties of a given protein system may influence the kinetics of aggregation has not been fully characterized. In the study of recombinant human Interleukin-1 receptor type II (rhuIL-1R(II)) aggregation, data obtained from size exclusion chromatography and differential scanning calorimetry (DSC) were used to model the thermodynamic and kinetic properties of irreversible denaturation. A break from linearity in the initial aggregation rates as a function of 1/T was observed in the vicinity of the melting transition temperature (T(m) approximately 53.5 degrees C), suggesting significant involvement of protein unfolding in the reaction pathway. A scan-rate dependence in the DSC experiment testifies to the nonequilibrium influences of the aggregation process. A mechanistic model was developed to extract meaningful thermodynamic and kinetic parameters from an irreversibly denatured process. The model was used to simulate how unfolding properties could be used to predict aggregation rates at different temperatures above and below the T(m) and to account for concentration dependence of reaction rates. The model was shown to uniquely identify the thermodynamic parameters DeltaC(P) (1.3 +/- 0.7 kcal/mol-K), DeltaH(m) (74.3 +/- 6.8 kcal/mol), and T(m) with reasonable variances.     

Gas phase SN2 reactions of halide ions with trifluoromethyl halides: front- and back-side attack vs. complex formation

Density functional theory computations and pulsed-ionization high-pressure mass spectrometry experiments have been used to explore the potential energy surfaces for gas-phase S(N)2 reactions between halide ions and trifluoromethyl halides, X(-) + CF(3)Y --> Y(-) + CF(3)X. Structures of neutrals, ion-molecule complexes, and transition states show the possibility of two mechanisms: back- and front-side attack. From pulsed-ionization high-pressure mass spectrometry, enthalpy and entropy changes for the equilibrium clustering reactions for the formation of Cl(-)(BrCF(3)) (-16.5 +/- 0.2 kcal mol(-1) and -24.5 +/- 1 cal mol(-1) K(-1)), Cl(-)(ICF(3)) (-23.6 +/- 0.2 kcal mol(-1)), and Br(-)(BrCF(3)) (-13.9 +/- 0.2 kcal mol(-1) and -22.2 +/- 1 cal mol(-1) K(-1)) have been determined. These are in good to excellent agreement with computations at the B3LYP/6-311+G(3df)//B3LYP/6-311+G(d) level of theory. It is shown that complex formation takes place by a front-side attack complex, while the lowest energy S(N)2 reaction proceeds through a back-side attack transition state. This latter mechanism involves a potential energy profile which closely resembles a condensed phase S(N)2 reaction energy profile. It is also shown that the Cl(-) + CF(3)Br --> Br(-) + CF(3)Cl S(N)2 reaction can be interpreted using Marcus theory, in which case the reaction is described as being initiated by electron transfer. A potential energy surface at the B3LYP/6-311+G(d) level of theory confirms that the F(-) + CF(3)Br --> Br(-) + CF(4) S(N)2 reaction proceeds through a Walden inversion transition state.     

A convenient tool for studying the stability of proteins and nucleic acids

The aim of this work is to discuss the thermodynamic properties, obtained by differential scanning calorimetry (DSC), of the thermal transition of proteins and nucleic acids and to analyze these data using statistical thermodynamic relations. The denaturation of the ordered, specific structures of biological macromolecules is a cooperative process and in many cases the macromolecules undergo a two-state transition. Differential scanning calorimetry, giving direct thermodynamic information, has proved to be very useful in clarifying the energetics of macromolecule transitions and in characterizing their thermal stability. Here, various examples are discussed: i) the equilibrium thermal denaturation of ribonuclease A, a model for the use of DSC by following the temperature-unfolding of the proteins, a monomolecular transition; ii) the equilibrium thermal dissociation of a DNA double helix in two strands, an example of how DSC is used to follow a bimolecular process; iii) an example of the use of DSC for studying the melting of unimolecular and tetramolecular DNA quadruple-helices.     

低相变温度锌卟啉液晶的合成与表征

卟啉液晶作为一种功能型盘状液晶,已经受到了科学家们的高度重视^[1]。自1980年Goodby^[2]首次合成出简单的卟啉液晶以来;各国学者对卟啉液晶的合成做了相应的研究工作,但其液晶相变温度偏高^[3,4],相区宽度偏窄^[3]。本文首次合成出相变温度较低,相区宽,含有8,10,12和14碳的酰氧基的四种卟啉液晶5、10、15、20－四（对－酰氧基）苯基卟啉液晶5、10、15、20－四（对－酰氧基）苯基卟啉锌（Ⅱ）配合物[分别简称为TOPPZn,TDPPZn,TLPPZn,TMPPZn]。研究4种配合物的液晶行为,其液晶相相变温度最低始于－36．4℃,相区宽达175℃,是一种具有应用前景的卟啉液晶。     

Comparison of the thermal behavior and conformational changes in partially and fully hydrated dipalmitoylphosphatidylcholine systems

The temperature dependence of conformational changes for partially and fully hydrated DPPC systems through two physicochemical techniques, namely DSC and Raman spectroscopy, is studied. DSC experiments have shown a different thermal behavior between the two considered systems, indicating the effective role of water in the thermal behavior. A temperature resolution of inter- and intramolecular interactions during the main melting phase transition was achieved by using three different Raman intensity ratios, which confirm that the main phase transition represents a two-stage transition. Van’t Hoff plots for the C–C, C–H, C=O and C₄N⁺ stretching modes, in a temperature range just below the main transition temperature, have been used to compare the thermodynamic parameters extracted by the two physicochemical techniques. The significance of these results can be summarized as follows: (a) DSC and Raman spectroscopy have shown complementary results indicating that DPPC exists in partially or fully hydrated states; (b) thermodynamic parameters ΔΗ and ΔS calculated in both techniques for the two different hydration states of DPPC were in harmony; (c) water more significantly affects the thermal and dynamic properties of fully hydrated DPPC bilayers than of the partially hydrated DPPC; and (d) water disturbs the head-group packing, the alkyl chains interactions and the mesophase region. It appears that the amount of water plays a vital role in the bilayer structure. As more and more extensive studies appear in the literature on biomolecules or drug membrane interactions, this information will be valuable in understanding the role of water in these interactions.     

Density of configurational states from first-principles calculations: the phase diagram of Al-Na surface alloys.

The structural phases of Al(x)Na(1-x) surface alloys have been investigated theoretically and experimentally. We describe the system using a lattice-gas Hamiltonian, determined from density functional theory, together with Monte Carlo (MC) calculations. The obtained phase diagram reproduces the experiment on a quantitative level. From calculation of the (configurational) density of states by the recently introduced Wang-Landau MC algorithm, we derive thermodynamic quantities, such as the free energy and entropy, which are not directly accessible from conventional MC simulations. We accurately reproduce the stoichiometry, as well as the temperature at which an order-disorder phase transition occurs, and demonstrate the crucial role, and magnitude, of the configurational entropy.     

Mesomorphic properties of a homologous series of chiral liquid crystals containing the α-chloroester group

The mesomorphic properties of the N*, S*_c and higher ordered smectic phases have been investigated for a homologous series of 4-[(S)-2-chlor-3-methylbutanoyloxy]-4'-(4-n-alkyloxy-benzoyloxy)biphenyls. They have been characterized by optical texture observation, differential scanning calorimetry (DSC), small angle X-ray scattering and electro-optic measurements. The compounds exhibit a strongly twisted cholesteric phase and smectic phases with large spontaneous polarization and tilt angle values. One or two higher ordered, monotropic smectic phases were found which significantly differ in their rotational viscosity.     

Transitions between disordered phases in supercooled liquid silicon

We have investigated the transitions between disordered phases in supercooled liquid silicon using computer simulations. The thermodynamic properties were directly obtained from the free energy, which was computed using the recently proposed reversible scaling method. The calculated free energies of the crystalline and liquid phases of silicon at zero pressure, obtained using the environment dependent interatomic potential, are in excellent agreement with the available experimental data. The results show that, at zero pressure, a weak first-order liquid-liquid transition occurs at 1135 K and a continuous liquid-amorphous transition takes place at 843 K. These results are consistent with the existence of a second critical point for the liquid-liquid transition at a negative pressure.     

Heat-induced conformational transition of cytochrome c observed by temperature gradient gel electrophoresis at acidic pH

Temperature-gradient gel electrophoresis (TGGE) has been used to study the thermal unfolding of ferricytochrome c in low and high concentrations of acetic acid. It has been observed that the mobility of cytochrome c is a linear function of temperature when the system is characterized by a homogeneous population of conformation-state, single molecular species. Within the transition temperature range, the mobility clearly displays the characteristic sigmoidal shape describing the transitions of protein unfolding. The data obtained by TGGE were used to estimate the apparent thermodynamic parameters (enthalpy change deltaHvh and transition temperature Tm), associated with the transition of unfolding. The accuracy of the apparent thermodynamic parameters obtained by this method agrees within error limits with the values obtained by direct calorimetric measurements using differential scanning calorimetry (DSC).     

Thermodynamic properties of cycloketones: A DSC study

In this paper, we describe the study of the thermodynamic properties of all cycloketones, from cyclobutanone to cyclododecanone, through DSC measurements in order to reveal possible new glassy crystalline phases. This work presents revised phase diagrams of the four previously known plastic crystals of the series, namely cyclohexanone, cycloheptanone, cyclooctanone, and cyclononanone. In particular, it has been shown that the last three crystals exhibit two phase sequences, a stable one and a metastable one, which could be attained through reproducible heat treatments. Contrary to what could be expected by comparison with the cyclo-alcohol series, only two compounds, namely cyclooctanone and cyclononanone, exhibit glassy crystalline phases. Finally, the thermodynamic data related to the various phase transitions of all these compounds have been determined.     

Thermotropic liquid crystalline α-[bis(2-hydroxyethyl)amino]ω-(4 ′-methoxybiphenyl-4-oxy)alkane hydrochlorides

Liquid crystalline α-[bis(2-hydroxyethyl)amino]- ω -(4′-methoxybiphenyl-4-oxy)alkane hydrochlorides with different spacer lengths (6, 8, 10 methylene units) have been synthesized and characterized by NMR, DSC, polarizing optical microscopy and X-ray diffraction. The melting temperatures of the hydrochlorides decrease with increasing number of methylene units in the spacer. Highly ordered and very viscous liquid crystalline (LC1) smectic phases are formed on melting. Upon further heating these phases are transformed into a less viscous smectic C phase (LC2). The temperature of the LC1-LC2 transition decreases and the temperature of the LC2 to isotropic phase transition (LC2-I transition) increases with increasing number of methylene units in the spacer.