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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Calculation of Standard Transformed Entropies of Formation of Biochemical Reactants and Group Contributions at Specified pH
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Calculation of Standard Transformed Entropies of Formation of Biochemical Reactants and Group Contributions at Specified pH

机译：在特定pH下计算生化反应物形成的标准转化熵和基团贡献

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When the pH is specified, the criterion for spontaneous change and equilibrium is stated in terms of the transformed Gibbs energy G' that is defined by a Legendre transform introducing pH as an intensive variable. The change in the standard transformed Gibbs energy of reaction Δ_rG'°gives the apparent equilibrium constant K', and the standard transformed enthalpy Δ_rH'°gives the temperature coefficient of K'. The corresponding standard transformed entropy of reaction Δ_rS'°is less often discussed but is often easier to interpret in terms of structure. The standard transformed entropies of formation of 44 biochemical reactants are calculated at 298.15 K, 1 bar, pH 7, and ionic strengths of 0, 0.10, and 0.25 M from values of the standard Gibbs energies of formation Δ_fG°and standard enthalpies of formation Δ_fH°of the species involved. These values are used the calculate Δ_rS'°for 19 biochemical reactions to illustrate the role that entropy plays in these reactions. Δ_fS'°values for biochemical reactants at a specified pH can also be calculated from standard molar entropies of the species involved in a reactant. The standard transformed formation properties of biochemical reactants can be estimated by adding up group contributions. The contributions of 15 groups to Δ_fG'°and Δ_fH'°at pH 7 and three ionic strengths are calculated and used to estimate Δ_fG'°and Δ_fH'°for seven reactants. This shows that standard transformed formation properties can be estimated for biochemical reactants for which there are no equilibrium or calorimetric data.
机译：当指定了pH值时，自发变化和平衡的标准以转换后的吉布斯能量G'表示，吉布斯能量G'由Legendre变换定义，引入pH作为强度变量。反应的标准变换吉布斯能量的变化Δ_rG′°给出表观平衡常数K′，而标准变换焓Δ_rH′°给出K′的温度系数。反应的相应标准转换熵Δ_rS'°较少被讨论，但通常在结构上更易于解释。根据形成标准吉布斯能量Δ_fG°和形成标准焓Δ_fH的值，计算出44种生化反应物形成的标准转化熵在298.15 K，1 bar，pH 7和离子强度分别为0、0.10和0.25 M时所涉及物种的°。这些值用于19个生化反应的Δ_rS'°计算，以说明熵在这些反应中的作用。特定pH下生化反应物的Δ_fS'°值也可以根据反应物所涉及的物质的标准摩尔熵来计算。生化反应物的标准转化形成特性可以通过将基团贡献相加来估算。计算15个基团在pH 7时对Δ_fG'°和Δ_fH'°的贡献以及三个离子强度，并用于估算七个反应物的Δ_fG'°和Δ_fH'°。这表明可以为没有平衡或量热数据的生化反应物估计标准的转化形成特性。

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