The sources of thermal energy exchange accompanying microbial anabolism

Calculations are made of the thermal energy exchanges accompanying the anabolism of Saccharomyces cerevisiae of four substrates using the equations and . Contrary to a previous postulate cited in the Discussion, the free-energy changes accompanying anabolism are not zero, but can be either positive or negative. However, their magnitude with either sign is small compared to that of catabolism of the same substrates, so that even with free energy changes that are negative it is unlikely anabolism can be considered a spontaneous process.     

On the frequency-dependent specific heat and TMDSC: Constitutive modelling based on thermodynamics with internal state variables

To develop constitutive models to represent the thermomechanically chemically coupled behaviour of curing resins, vulcanizing elastomers or melting and crystallizing polymers the technique of DSC is extremely helpful. In the present study, the method of TMDSC is interpreted and evaluated in the context of thermodynamics with internal state variables. The balance equation of energy and the dissipation principle in the form of the Clausius–Duhem inequality form the theoretical basis of our study. Since the pressure and the temperature are the external variables in DSC, the specific Gibbs free energy is used as thermodynamic potential. It depends on temperature, stress and a set of internal state variables to represent the microstructure of the material on a phenomenological basis. The temperature- and internal variable-induced changes in the Gibbs free energy are approximated by a Taylor series up to second order terms. As a substantial result of this work, closed-form expressions for the dynamic calorimetric response due to harmonic temperature perturbations and the frequency-dependent complex heat capacity are derived. The theory allows a physical interpretation of the complex heat capacity and its underlying phenomena and is in accordance with experimental observations from literature.     

Ionization of five aqueous fluorobenzoic acids: Conductance and thermodynamics

The three monofluorobenzoic acids together with 2,4-difluoro and 2,6-difluorobenzoic acids in aqueous solution are the subject of precision conductance measurements. The experimental data are analyzed to give ionization constants and limiting conductances at temperatures from 0 to 100°C. Walden products for the acid anions are derived from the limiting conductances while the ionization consatants are fitted by statistical methods to the function pK _a (m)=A+B/T+ C logT+DT. Only the 2,6- acid requires the fourth term of the function to fit the data to a precision of better than 0.03%. Mathematical analysis of the pK function gives the standard changes in enthalpy, entropy, and heat capacity. All the acids studied are more acidic than the parent, benzoic acid, as well as more acidic than the isoelectronic methylbenzoic acids. In general the increased acidity is tied to decreases in enthalpy while entropy changes on ionization differn little from those found for the parent acid.     

Aqueous Polymerization of Methyl Methacrylate Initiated by the Potassium Bromate-Thiomalic Acid Redox System

The redox system composed of potassium bromate and thiomalic acid was used to initiate the aqueous polymerization of methyl methacrylate under nitrogen atmosphere at 35 ± 0.2°C. The initial rates of polymerization have been found to be approximately proportional to the first power of the initiator concentration in the range of 2.5 to 6.0 ± 10^?3 M and to the first power (1.15) of monomer concentration in the range of 3.72 to 11.16 ± 10^?2 M The overall rate was independent of activator concentration, approaching a maximum at 10 × 10^?3 M. The overall energy of activation was found to be 8.80 kcal/mol. The initial rate and the maximum conversion attained a maximum value at 35°C in the temperature range of 20 to 45°C.     

A short review and an empirical method for estimating the absorbed enthalpy of formation and the absolute enthalpy of dried microbial biomass for use in studies on the thermodynamics of microbial growth

Calculations are made using the equations Δ_r G = Δ_r H − TΔ_r S and Δ_r X = Δ_r H − Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  − H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

Aqueous iodic acid: Conductance and thermodynamics

Precision conductance measurements are reported on aqueous solutions of iodic acid for 16 concentrations between 17 and 0.7 mM and for 20 temperatures between 5° and 100°C. RlnK _a (m) and _o were calculated at each temperature and the data expressed by suitable temperature functions. From RlnK _a (m) as a function of temperature changes in standard enthalpy, entropy, and heat capacity were calculated. C _p proved to be independent of temperature so that H⁰ was a linear function of temperature. Comparisons have been made with other published data for iodic acid. The pattern of variation of Walden products with temperature was similar to that found earlier for substituted benzoic acids.     

Low-temperature heat capacities and standard molar enthalpy of formation of aspirin

Molar heat capacities (C _p,m) of aspirin were precisely measured with a small sample precision automated adiabatic calorimeter over the temperature range from 78 to 383 K. No phase transition was observed in this temperature region. The polynomial function of C _p,m vs. T was established in the light of the low-temperature heat capacity measurements and least square fitting method. The corresponding function is as follows: for 78 K≤T≤383 K, C _p,m/J mol^-1 K^-1=19.086X ⁴+15.951X ³-5.2548X ²+90.192X+176.65, [X=(T-230.50/152.5)]. The thermodynamic functions on the base of the reference temperature of 298.15 K, {ΔH _T -ΔH _298.15} and {S _T-S _298.15}, were derived. Combustion energy of aspirin (Δ_c U _m) was determined by static bomb combustion calorimeter. Enthalpy of combustion (Δ_c H ^o _m) and enthalpy of formation (Δ_f H ^o _m) were derived through Δ_c U _m as - (3945.26±2.63) kJ mol^-1 and - (736.41±1.30) kJ mol^-1, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molar heat capacities and standard molar enthalpy of formation of 2-amino-5-methylpyridine

The heat capacities (C _p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T _m), the molar enthalpy (Δ_fus H _m⁰), and the molar entropy (Δ_fus S _m⁰) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol⁻¹ and 51.676 J K⁻¹ mol⁻¹, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H _T-H _298.15 and S _T-S _298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU _c(C₆H₈N₂,cr)= −3500.15±1.51 kJ mol⁻¹ and Δ_c H _m⁰ (C₆H₈N₂,cr)= −3502.64±1.51 kJ mol⁻¹, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δ_r H _m⁰ (C₆H₈N₂,cr)= −1.74±0.57 kJ mol⁻¹.     

Reversible and irreversible heat capacity of poly[carbonyl(ethylene‐co‐propylene)] by temperature‐modulated calorimetry

The heat capacity of poly[carbonyl(ethylene‐co‐propylene)] with 95 mol % C₂H₄? CO? (Carilon EP®) was measured with standard differential scanning calorimetry (DSC) and temperature‐modulated DSC (TMDSC). The integral functions of enthalpy, entropy, and free enthalpy were derived. With quasi‐isothermal TMDSC, the apparent reversing heat capacity was determined from 220 to 570 K, including the glass‐ and melting‐transition regions. The vibrational heat capacity of the solid and the heat capacity of the liquid served as baselines for the quantitative analysis. A small amount of apparent reversing latent heat was found in the melting range, just as for other polymers similarly analyzed. With an analysis of the heat‐flow rates in the time domain, information was collected about latent heat contributions due to annealing, melting, and crystallization. The latent heat decreased with time to an even smaller but truly reversible latent heat contribution. The main melting was fully irreversible. All contributions are discussed in the framework of a suggested scheme of six physical contributions to the apparent heat capacity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1565–1577, 2001     

Thermodynamics of the reaction between poly-1,1,2-trichlorobuta-1,3-diene and poly(ethylene imine) to form interpolymer

Thermodynamic parameters of the interpolymer reaction between poly-1,1,2-trichlorobuta1,3-diene and poly(ethylene imine) giving a polymer-polymer compound (incorporating the starting components in a molar ratio of 1 : 2) have been determined by calorimetry. The enthalpy (H°_m), entropy (S°_m), and Gibbs function (G°_m) for this reaction are negative over the whole temperature range studied. The enthalpy of the reaction in chloroform at 298.15 K is about two times smaller, due to the difference in the enthalpies of dissolution of the starting polymers and the enthalpy of swelling of the interpolymer in the same solvent. The glass transition temperature of the interpolymer lies between those of the starting polymers and coincides with the value calculated from the Fox equation. The heat capacity of the interpolymer is smaller than additive values calculated fromC _p ^° of the starting polymers. From the experimentally determinedC _p ^° for the polymers, the thermodynamic functionsC _p ^° (T),H°(T) – H°(O), andS°(T) were calculated for the 0–330 K temperature range, and their configurational entropiesS _c ^° were estimated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2474–2478, October, 1996.     

微孔和介孔材料中的热化学

这篇论文综述了美国加州大学戴维斯分校科学院院士Navrotsky课题组多年来在多孔材料上取得的一系列热化学研究结果。讨论了热化学对微孔、介孔材料的结构稳定性和合成过程的影响。借助多种测热手段对影响骨架结构的热焓、热熵和自由能进行了系统的测量和计算。研究数据表明一系列纯硅分子筛、介孔材料和磷酸铝多孔材料同相应的石英相和块磷铝矿相相比能量上最多只高出15 kJ·mol-1。一系列纯硅分子筛的熵值比石英相高出3.2—4.2 J·K-1·mol-1；在0—12.6 J·K-1·mol-1范围内相对应的自由能几乎没有差别。因此，对不同微孔、介孔材料，其骨架结构在能量上是几乎没有区别的。另外，本文通过介绍一种新型测热方法——原位测热，揭示了分子筛合成过程中的动力学和成核/结晶机理。     

Influence of drawing and heat treatment on surface free energies of polyethylene terephthalate fibers

The surface free energies of polyethylene terepthalate fibers with different draw ratios were experimentally determined by contact angle measurements inn-alkane/water systems. The dispersive component of the surface free energy increased with increasing draw ratio, whereas the nondispersive one remained almost constant. After heat treatment, the dispersive surface free energy increased, but was reduced above 140°C. The nondispersive component increased by heat treatment at 190°C. The increases in the density and birefringence of the fibres due to the drawing and heat treatment suggested that the increase in the dispersive surface free energy was caused by the increase in the atomic density at the fiber surface due to drawing and heat treatment. ESCA results indicated that the increment in the nondispersive surface free energy due to heat treatment was caused by the addition of functional groups to the fiber surface due to heat treatment.     

Measurement of high temperature heat content of silicon by drop calorimetry

Heat content of silicon has been measured in a temperature range of 700-1820 K using a drop calorimeter. Boron nitride was used as a sample crucible. The enthalpy of fusion and the melting point of silicon determined from the heat content-temperature plots are 48.31±0.18 kJ mol^-1 and 1687±5 K, respectively. The heat content and heat capacity equations were derived using the Shomate function for the solid region and the least square method for the liquid region, respectively, and compared with the literature values. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enthalpy changes in formation reactions of zinc and cadmium trimethylenediaminetetraacetates

Calorimetric enthalpy changes in reactions have been measured for the formation of zinc and cadmium trimethylenediaminetetraacetates at 298.15 K and ionic strengths of 0.1. 0.5, 1.0 mol L⁻¹ (KNO₃). The standard thermodynamic parameters of the reactions studied were evaluated from calorimetric and potentiometric measurements under the same conditions. The results obtained were compared with the corresponding data on related compounds.     

The solubilization of alcohols in micellar solutions

The specific conductivities of dodecyldimethylbenzylammonium bromide (C12BBr) have been determined in aqueous butanol and aqueous benzyl alcohol solutions in the temperature range of 5-40°C. From these data the temperature dependent critical micelle concentration (cmc) was determined. The molar fraction of alcohol in the micelle was estimated using the theory suggested by Motomura et al. for surfactant binary mixtures. The thermal properties such as standard Gibbs free energy, enthalpy and entropy of solubilization of alcohols in the micelles were estimated for the phase separation model. The change in heat capacity upon solubilization of alcohol in the micelle has been estimated form the above properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Surface energy of oxides and silicates

Published data and the author’s own data on the surface energy of hydrophilic oxides, silicates, and hydrophobic adsorbents based on them are reviewed. The prospects of using the combined Gibbs-Helmholtz-Young equation to obtain data on the surface pressure, heat of wetting, and wetting contact angle of hydrophilic and hydrophobic adsorbents are demonstrated. These data are used to estimate the thermodynamic characteristics of the surface and interfacial regions at the boundary between the materials and water. It is shown that the boundary layers of water close to the hydrophobic surfaces are more ordered while those close to the hydrophobic surfaces are less ordered than with liquid water. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 133–149, May–June, 2006.     

Micellization of dodecyldimethylethyl- ammonium bromide in aqueous solution

Specific conductivity of aqueous solutions of dodecyldimethylethylammonium bromide has been determined in the temperature range of 15-40°C. The critical micelle concentration (cmc) and ionization degree of the micelles, b, were determined from the data. Thermodynamic functions, such as standard Gibbs free energy, ΔG _m°, enthalpy, ΔG _m°, and entropy, ΔG _m°, of micellization, were estimated by assuming that the system conforms to the mass action model. The change in heat capacity upon micellization, ΔG _m°, was estimated from the temperature dependence of ΔG _m°. An enthalpy-entropy compensation phenomenom for the studied system has been found. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low-temperature heat capacity of α and γ polymorphs of glycine

Low-temperature heat capacity of two polymorphs of glycine (α and γ) was measured from 5.5 to 304 K and thermodynamic functions were calculated. Difference in heat capacity between polymorphs ranges from +26% at 10 K to -3% at 300 K. The difference indicates the contribution into the heat capacity of piezoelectric γ polymorph, probably connected with phase transition and ferroelectricity. Thermodynamic evaluations show that at ambient conditions γ polymorph is stable and α polymorph is metastable. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat capacity of poly(vinyl methyl ether)

The heat capacity of poly(vinyl methyl ether) (PVME) has been measured using adiabatic calorimetry and temperature‐modulated differential scanning calorimetry (TMDSC). The heat capacity of the solid and liquid states of amorphous PVME is reported from 5 to 360 K. The amorphous PVME has a glass transition at 248 K (?25 °C). Below the glass transition, the low‐temperature, experimental heat capacity of solid PVME is linked to the vibrational molecular motion. It can be approximated by a group vibration spectrum and a skeletal vibration spectrum. The skeletal vibrations were described by a general Tarasov equation with three Debye temperatures Θ₁ = 647 K, Θ₂ = Θ₃ = 70 K, and nine skeletal modes. The calculated and experimental heat capacities agree to better than ±1.8% in the temperature range from 5 to 200 K. The experimental heat capacity of the liquid rubbery state of PVME is represented by C_p(liquid) = 72.36 + 0.136 T in J K^?1 mol^?1 and compared to estimated results from contributions of the same constituent groups of other polymers using the Advanced Thermal AnalysiS (ATHAS) Data Bank. The calculated solid and liquid heat capacities serve as baselines for the quantitative thermal analysis of amorphous PVME with different thermal histories. Also, knowing C_p of the solid and liquid, the integral thermodynamic functions of enthalpy, entropy, and free enthalpy of glassy and amorphous PVME are calculated with help of estimated parameters for the crystal. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2141–2153, 2005     

Influence of the size of the formed cycle on the reactivity of free radicals in cyclization reactions

Numerous experimental data for the cyclization of free radicals C·H₂(CH₂)_nCH=CH₂ cyclo-[(CH₂)_n+1CH(C·H₂)], and C·H₂(CH₂)_nCH=CHR cyclo-[(CH₂)_n+1C·HCHR] were analyzed in the framework of the parabolic model. The activation energy of thermoneutral (H _e = 0) cyclization E _e0 decreases linearly with an increase in the energy of cycle strain E _rsc: E _e0(n) (kJ mol–1) = 85.5 – 0.44E _rsc(n) (n is the number of atoms in the cycle). The activation entropy of cyclization S ^# also depends on the cycle size: the larger the cycle, the lower S ^#. A linear dependence of S ^# on the difference between the entropies of formation S° of cyclic hydrocarbon and the corresponding paraffin was found: S ^# = 1.00[S°(cycle) – S°(C_nH_2n+2)]. The E _e0 values coincide for cyclization reactions with the formation of the six-membered cycle and the bimolecular addition of alkyl radicals to olefins.