Heat Capacities of l-Histidine,l-Phenylalanine,l-Proline,l-Tryptophan and l-Tyrosine

In an effort to establish reliable thermodynamic data for proteinogenic amino acids, heat capacities for l-histidine (CAS RN: 71-00-1), l-phenylalanine (CAS RN: 63-91-2), l-proline (CAS RN: 147-85-3), l-tryptophan (CAS RN: 73-22-3), and l-tyrosine (CAS RN: 60-18-4) were measured over a wide temperature range. Prior to heat capacity measurements, thermogravimetric analysis was performed to determine the decomposition temperatures while X-ray powder diffraction (XRPD) and heat-flux differential scanning calorimetry (DSC) were used to identify the initial crystal structures and their possible transformations. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval from 262 to 358 K and by power compensation DSC in the temperature interval from 307 to 437 K. Experimental values determined in this work were then combined with the literature data obtained by adiabatic calorimetry. Low temperature heat capacities of l-histidine, for which no literature data were available, were determined in this work using the relaxation (heat pulse) calorimetry from 2 K. As a result, isobaric crystal heat capacities and standard thermodynamic functions up to 430 K for all five crystalline amino acids were developed.     

Single-ion heat capacities, C(p)(298)ion, of solids: with a novel route to heat-capacity estimation of complex anions

Single-ion heat capacities, C(p)(298)(ion), are additive values for the estimation of room-temperature (298 K) heat capacities of ionic solids. They may be used for inferring the heat capacities of ionic solids for which values are unavailable and for checking reported values, thus complementing our independent method of estimation from formula unit volumes (termed volume-based thermodynamics, VBT). Analysis of the reported heat-capacity data presented here provides a new self-consistent set of heat capacities for both cations and anions that is compatible (and thus may be combined) with an extensive set developed by Spencer. The addition of a large range of silicate species permits the estimation of the heat capacities of many silicate minerals. The single-ion heat capacities of individual silicate anions are observed to be strictly proportional to the total number of atoms (Si plus O), n, contained within the silicate anion complex itself (e.g., for the anion Si(2)O(7)(2-), n = 9, for SiO(4)(2-), n = 5), C(p)(silicate anion)/J K(-1) mol(-1) = 13.8n, in a new rule that is an extension of the Neumann-Kopp relationship. The same linear relationship applies to other homologous anion series (for example, oxygenated heavy-metal anion complexes such as niobates, bismuthates, and tantalates), although with a different proportionality constant. A similar proportionality, C(p)(complex anion)/J K(-1) mol(-1) ≈ 17.5n, which may be regarded as a convenient "rule of thumb", also applies, although less strictly, to complex anions in general. The proportionality constants reflect the rigidity of the complex anion, being always less than the Dulong-Petit value of 25 J K(-1) mol(-1). An emergent feature of our VBT and single-ion approaches to an estimation of the thermodynamic properties is the identification of anomalies in measured values, as is illustrated in this paper.     

Recommended vapor pressures for thiophene, sulfolane, and dimethyl sulfoxide

Recommended vapor pressure data for important industrial solvents, thiophene (CAS RN: 110-02-1), sulfolane (CAS RN: 126-33-0), and dimethyl sulfoxide (CAS RN: 67-68-5), were developed by the simultaneous correlation of vapor pressure and related thermal data (heat capacities of condensed phases, ideal gas heat capacities and calorimetrically determined enthalpies of vaporization). For sulfolane and dimethyl sulfoxide, new vapor pressure data were obtained using the static method in the temperature interval from 273 to 308 K. Liquid heat capacities and calorimetric enthalpies of vaporization were taken from the literature and/or determined by Calvet calorimetry. The thermodynamic properties in the ideal gaseous state were calculated using the methods of statistical thermodynamics based on experimental as well as calculated fundamental vibrational frequencies and molecular structure data. Comparisons with literature values are shown for all measured and derived properties.     

Heat capacities and entropies of linear,aliphatic polyesters

New measurements of the heat capacity in the melt of poly(trimethylene succinate) (PTMS), poly(trimethylene adipate) (PTMA), and poly(hexamethylene sebacate) (PHMS) from 310 to 400 K are presented. Based on these data and literature data on eight other molten polylactones and poly(ethylene sebacate) (PES), an addition scheme is developed for linear, aliphatic polyesters that leads to the equation: which represents the ATHAS-recommended melt heat capacities for all linear polyesters. Combining previously discussed solid heat capacities, derived from an approximate frequency spectrum, with the new liquid heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) could be derived using the ATHAS computation scheme. The average value of residual entropy at zero kelvin of 5.3 ± 1.8 J/(K mol) per mobile bead for glassy linear polysters was found to be somewhat higher than for many other polymers in the data bank, but closer to that observed for linear, aliphatic polyamides. The phase transitions of PTMS, PTMA, and PHMS are also analyzed using the quantitative baselines available from the heat capacity study.     

Thermodynamic properties of the aqueous solution of potassium salts of some 4-((alkylcarbonyl)amino)-2-hydroxybenzoic acids at 298 and 313 K

To understand the aggregation behavior of surface-active ligands with a salycilic polar head, we undertook a systematic study of some classes of anionic surfactants where the presence and the position of the -OH and the carboxylic group differ. This paper reports the dilution heats at 298 and 313 K of aqueous solutions of potassium 4-((alkylcarbonyl)amino)-2-hydroxybenzoate (KPAS-C(n) where n stands for the number of carbon atoms in the chain) in KOH at 0.1 m, measured as a function of concentration. From the experimental data, apparent and partial molar enthalpies vs concentration were obtained. By using a pseudo-phase-transition approach, the enthalpy changes upon micelle formation (DeltaH(m)) and assuming that in the restricted range of temperature examined heat capacities are constant, the heat capacity changes have been obtained. Micelle formation enthalpies are seen to be additive with a group contribution for the methylene group of -1.5+/-0.1 kJ mol(-1) per group at 298 K and -2.3+/-0.1 kJ mol(-1) per group at 313 K, comparable with that obtained for similar anionic compounds in the same experimental conditions and for N-alkylnicotinamide chlorides (cationic surfactants). The -CH(2)- group contribution to the micelle formation heat capacities is -53+/-1 J K(-1) mol(-1).     

Heat capacities and entropies of liquid,high-melting-point polymers containing phenylene groups (PEEK,PC, and PET)

The heat capacity at constant pressure of liquid PEEK, poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene), has been measured by scanning calorimetry from 420 to 680 K, and that of PC, poly(4,4′-isopropylidenediphenylene carbonate), from 325 to 610 K. These new data were combined with data-bank data for PC and PET, poly(ethylene terephthalate), over wide temperature ranges. An addition scheme for liquid heat capacities of similar macromolecules has been obtained. In addition, values of absolute entropy, residual entropy for the glassy state, enthalpy, and Gibbs function are estimated for these three polymers. Both melting and glass transition temperatures have been confirmed. The heat capacity increases at the glass transition temperature have been determined by making use of previously calculated solid-state heat capacities.     

Excess heat capacities at T=298.15 K and excess enthalpies at T=293.15 and 298.15 K of aqueous solution of 2-methoxyethanol

Excess isobaric heat capacities of mixture (2-methoxyethanol+water) were measured at T=298.15 K and excess enthalpies at T=293.15 and 298.15 K. Excess enthalpies were extremely exothermic, up to -1290 J mol^-1 atT=293.15 K and -1240 J mol^-1 at T=298.15 K. Excess isobaric heat capacities were positive and very large, approximately 9 J K^-1 mol^-1 at the maximum. In contrast to the data reported by Page and coworkers, the excess heat capacity data were positive in the entire composition range and there was no change in their signs. Consistently, no crossing was found between the curves of excess enthalpies at T=298.15 and 293.15 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reflections on the journey: six short stories

The low-temperature heat capacities of nickel titanate (NiTiO₃), cobalt titanate (CoTiO₃), and cobalt carbonate (CoCO₃) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO₃ and 26 K for NiTiO₃. From our data we calculate standard molar entropies (298.15 K) for NiTiO₃ of 90.9 ± 0.7 J mol^-1 K^-1 and for CoTiO₃ of 94.4 ± 0.8 J mol^-1 K^-1. For CoCO₃, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO₃ of 88.9 ± 0.7 J mol^-1 K^-1.     

Heat capacities and entropies of liquid polyfluoroethylenes and polychloroethylenes

Through new measurements and from literature data, the heat capacity of all liquid polyfluoroethylenes could be established as: above 480 k, and as below 480 K in J/(K mol), where N_F is the mole fraction of F atoms. In connection with previously established heat capacities of the solid polymers, enthalpies, entropies, and residual entropies of the glassy state at 0 K were computed. Data for liquid polychloroethylenes are much less complete, and the thermodynamic functions could only be established for liquid poly(vinyl chloride) and compared with the data for solid poly(vinyl chloride), poly(vinylidene chloride), and polychlorotrifluoroethylene.     

水合烟酸钡的合成、±结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物, 利用室温固相合成方法, 借助于球磨技术, 合成了一种新的化合物——水合烟酸钡. 利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s). 利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容. 在热容曲线上出现了一个明显的吸热峰, 通过对热容曲线的解析, 得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082) K、(16.793±0.084) kJ·mol-1和(51.340±0.164) J·K-1·mol-1. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 另外, 依据Hess定律, 通过设计合理的热化学循环, 选择体积为100 mL、浓度为0.5 mol·L-1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓, 利用溶解焓确定固相反应的反应焓为⊿rH0m=-(84.12±0.38) kJ·mol-1. 最后, 利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1.     

Calculation of heat capacities of light and heavy water by path-integral molecular dynamics

As an application of atomistic simulation methods to heat capacities, path-integral molecular dynamics has been used to calculate the constant-volume heat capacities of light and heavy water in the gas, liquid, and solid phases. While the classical simulation based on conventional molecular dynamics has estimated the heat capacities too high, the quantum simulation based on path-integral molecular dynamics has given reasonable results based on the simple point-charge/flexible potential model. The calculated heat capacities (divided by the Boltzmann constant) in the quantum simulation are 3.1 in the vapor H2O at 300 K, 6.9 in the liquid H2O at 300 K, and 4.1 in the ice Ih H2O at 250 K, respectively, which are comparable to the experimental data of 3.04, 8.9, and 4.1, respectively. The quantum simulation also reproduces the isotope effect. The heat capacity in the liquid D2O has been calculated to be 10% higher than that of H2O, while it is 13% higher in the experiment. The results demonstrate that the path-integral simulation is a promising approach to quantitatively evaluate the heat capacities for molecular systems, taking account of quantum-mechanical vibrations as well as strongly anharmonic motions.     

尿嘧啶和5-溴尿嘧啶的低温热容

采用综合物性测量系统(PPMS)的热容测量模块在1.9-300 K温度区间内对两种药物中间体(尿嘧啶和5-溴尿嘧啶)的低温热容进行了测量与研究. 结果表明, 在测量温区内两种化合物的低温热容随温度的上升而逐步增加, 无任何热异常现象产生; 在相同温度下, 5-溴尿嘧啶的热容数值始终高于尿嘧啶. 利用低温热容理论模型对热容数据进行了拟合, 并计算得到了0-300 K温区的摩尔熵变、焓变等热力学函数. 此外, 通过热容拟合数据计算得到的尿嘧啶和5-溴尿嘧啶在298.15 K的标准摩尔规定熵分别为(132.48±1.32)和(165.39±1.65) J·K^-1·mol^-1.     

右旋布洛芬的低温热容

在80～370 K温度范围内, 用精密自动绝热量热计准确测量了右旋布洛芬的摩尔热容.其固态右旋布洛芬测量值对折和温度X[X=f(T)]的拟和方程为:Cp,m(S)=－39.483X4－66.649X3＋95.196X2＋210.84X＋172.98;相应的液态的拟和方程为 :Cp,m(L)=7.191X3＋4.2774X2＋56.365X＋498.5.并计算得到右旋布洛芬相对于室温(298.15 K)的摩尔焓和摩尔熵.右旋布洛芬的熔点为(324.15±0.02) K.基于摩尔热容的测量,还可获得右旋布洛芬的纯度为99.44％.并对右旋布洛芬和消旋布洛芬的热容进行了对比研究.     

Low Temperature Heat Capacities and Thermodynamic Properties of Zinc L-Threonate Zn(C_4H_7O_5)_2(s) by Adiabatic Calorimetry

Low-temperature heat capacities of the solid compound Zn(C4H7O5)2(s) were measured in a temperature range from 78 to 374 K, with an automated adiabatic calorimeter. A solid-to-solid phase transition occurred in the temperature range of 295?322 K. The peak temperature, the enthalpy, and entropy of the phase transition were determined to be (316.269±1.039) K, (11.194±0.335) kJ?mol-1, and (35.391±0.654) J?K-1?mol-1, respectively. The experimental values of the molar heat capacities in the temperature regions o...     

Low-temperature Heat Capacities and Thermodynamic Properties of Hydrated Sodium Cupric Arsenate [ NaCuAsO4·1.5H2O(s)]

Low-temperature heat capacities of the solid compound NaCuAsO4 · 1.5H2O(s) were measured using a precision automated adiabatic calorimeter over a temperature range of T = 78 K to T = 390 K. A dehydration process occurred in the temperature range of T = 368-374 K. The peak temperature of the dehydration was observed to be TD = (371.828±0.146) K by means of the heat-capacity measurement. The molar enthalpy and entropy of the dehyperimental values of heat capacities for the solid(Ⅰ) and the solid-liquid mixture(Ⅱ) were respectively fitted to two polynomial equations by the least square method. The smoothed values of the molar heat capacities and the fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated at an interval of 5 K.     

Molar heat capacities for (1-butanol + 1,4-butanediol, 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol) as function of temperature

The isobaric molar heat capacities for the binary mixtures (1-butanol + 1,4-butanediol) were determined in the temperature range from (293 to 353) K from measurements of isobaric specific heat capacity in a differential scanning calorimeter. The composition dependencies of the excess molar isobaric heat capacities obtained from the experimental results were fitted by the Redlich-Kister polynomials. Above T = 303.15 K, the excess isobaric molar heat capacities are negative over the whole composition range and absolute values increase with temperature. For temperatures (293.15 and 298.15) K, the excess values show S-shaped character. These excesses are however in general very small; at the temperature 298.15 K smaller than 0.1 J · K⁻¹ · mol⁻¹.Additionally, the isobaric molar heat capacities of 2,3-butanediol, 1,2-butanediol, and 2-methyl-2,4-pentanediol were determined over a similar temperature range. The experimental data for all diols are compared with available literature data and values estimated from group additivity.     

Low-temperature heat capacities and thermodynamic properties of rare-earth triisothiocyanate hydrates (Ⅲ)——Sm(NCS)_3·6H_2O,Gd(NCS)_3·6H_2O,Yb(NCS)_3·6H_2O and Y(NCS)_3·6H_2O

The heat capacities of four RE isothiocyanate hydrates,Sm( NCS)3 6H2O,Gd( NCS)3 6H2O,Yb(NCS)3 6H2O and Y( NCS)3 6H2O,have been measured from 13 to 300 K with a fully-automated adiabatic calorimeter No obvious thermal anomaly was observed for the above-mentioned compounds in the experimental tem-peiatnre ranges.The polynomial equations for calculating the heat capacities of the four compounds in the range of 13-300K were obtained by the least-squares fitting based on the experimental Cp data.The Cp values below 13 K were estimated by using the Debye-Einstem heat capacity functions.The standard molar thermodynamic functions were calculated from 0 to 300 K.Gibbs energies of formation were also calculated.     

Thermophysical properties of 1-hexanol over the temperature range from 303 K to 503 K and at pressures from the saturation line to 400 MPa

Isobaric thermal expansivities, _P(T,p), of 1-hexanol have been measured in a pressure-controlled scanning calorimeter from just above the saturation vapour pressure to 400 Mpa at temperatures from 302.6 K to 503.15 K. The specific volume isotherm, v(T_R,p), at T_R=302.6 K has been derived from measurements of isothermal compressibilities up to 400 MPa and from the specific density at atmospheric pressure. Specific volumes, isothermal compressibilities, thermal pressure coefficients, and isobaric and isochoric heat capacities for the whole pressure and temperature range are derived from these data and from literature data on the saturation vapour pressures and on the isobaric heat capacities at atmospheric or saturation vapour pressure.     

Mechanochemical effect in the iron(III) spin crossover complex [Fe(3-MeO-salenEt2]PF6 as studied by heat capacity calorimetry

Magnetic and thermal properties of the iron(III) spin crossover complex [Fe(3MeO-salenEt)(2)]PF(6) are very sensitive to mechanochemical perturbations. Heat capacities for unperturbed and differently perturbed samples were precisely determined by adiabatic calorimetry at temperatures in the 10-300 K range. The unperturbed compound shows a cooperative spin crossover transition at 162.31 K, presenting a hysteresis of 2.8 K. The anomalous enthalpy and entropy contents of the transition were evaluated to be Delta(trs)H = 5.94 kJ mol(-1) and Delta(trs)S = 36.7 J K(-1) mol(-1), respectively. By mechanochemical treatments, (1) the phase transition temperature was lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossover phenomenon were diminished to Delta(trs)H = 4.94 kJ mol(-1) and Delta(trs)S = 31.1 J K(-1) mol(-1), and (3) the lattice heat capacities were larger than those of the unperturbed sample over the whole temperature range. In spite of different mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets of heat capacity measurements provided basically the same results. The mechanochemical perturbation exerts its effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase of the number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of the diamagnetic cobalt(III) analogue [Co(3MeO-salenEt)(2)]PF(6) also were measured. The lattice heat capacity of the iron compounds has been estimated from either the measurements on the cobalt complex using a corresponding states law or the effective frequency distribution method. These estimations have been used for the evaluation of the transition anomaly.     

Standard molar volumes and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate at temperatures up to 573 K and pressures to 28 MPa

Densities and heat capacities of aqueous solutions of sodium trifluoromethanesulfonate (sodium triflate) of concentrations from 0.025 to 0.3 mol · kg⁻¹ were measured with high temperature, high pressure custom-made instruments at temperatures up to 573 K and at pressures up to 28 MPa. Standard molar volumes and standard molar heat capacities were obtained via extrapolation of the apparent molar properties to infinite dilution. The results for volumetric properties are consistent with earlier literature data, but no previous measurements exist for heat capacities of sodium triflate at superambient conditions. The new data were used for calculating the standard molar volumes and heat capacities for the triflate anion and compared with the results for triflic acid that should be essentially identical within the expected error margins. At temperatures above 473 K an effort was made to refine the processing of literature data for HCl(aq), taking into account its partial association, and subsequently to modify the value for Na⁺ ion calculated from the standard thermodynamic values of NaCl(aq) where its ion pairing was already considered. This approach yields reasonable agreement at high temperatures between the values for triflate ion calculated from its salt and those for triflic acid.