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相关概念视频

Chemical and Solubility Equilibria02:21

Chemical and Solubility Equilibria

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The free energy change associated with dissolving a solute in a liter of solvent is called the free energy of a solution, ΔGsolution. The overall ΔGsolution is expressed as the balance of ΔGinteraction against the always-favorable free-energy of mixing, ΔGmixing. Solution formation is favorable if  ΔGsolution is less than zero, whereas it is unfavorable if ΔGsolution is greater than zero. In short, for a solution to form and complete dissolution to take place,...
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Chemical Equilibria: Systematic Approach to Equilibrium Calculations01:21

Chemical Equilibria: Systematic Approach to Equilibrium Calculations

608
Equilibrium calculations for systems involving multiple equilibria are often complex. For example, to calculate the solubility of a sparingly soluble salt in an aqueous solution in the presence of a common ion, one must consider all the equilibria in this solution. Calculations for these systems can be complicated and tedious, so a systematic approach with a series of steps is often helpful. The process is detailed below.
The first step is to identify all the chemical reactions involved, The...
608
Calculating Equilibrium Concentrations02:05

Calculating Equilibrium Concentrations

47.2K
Being able to calculate equilibrium concentrations is essential to many areas of science and technology—for example, in the formulation and dosing of pharmaceutical products. After a drug is ingested or injected, it is typically involved in several chemical equilibria that affect its ultimate concentration in the body system of interest. Knowledge of the quantitative aspects of these equilibria is required to compute a dosage amount that will solicit the desired therapeutic effect.
A more...
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Calculating Standard Free Energy Changes02:49

Calculating Standard Free Energy Changes

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The free energy change for a reaction that occurs under the standard conditions of 1 bar pressure and at 298 K is called the standard free energy change. Since free energy is a state function, its value depends only on the conditions of the initial and final states of the system. A convenient and common approach to the calculation of free energy changes for physical and chemical reactions is by use of widely available compilations of standard state thermodynamic data. One method involves the...
20.6K
The Small x Assumption02:20

The Small x Assumption

45.8K
If a reaction has a small equilibrium constant, the equilibrium position favors the reactants. In such reactions, a negligible change in concentration may occur if the initial concentrations of reactants are high and the Kc value is small. In such circumstances, the equilibrium concentration is approximately equal to its initial concentration.  This estimation can be used to simplify the equilibrium calculations by assuming that some equilibrium concentrations are equal to the initial...
45.8K
Calculating the Equilibrium Constant02:46

Calculating the Equilibrium Constant

30.7K
The equilibrium constant for a reaction is calculated from the equilibrium concentrations (or pressures) of its reactants and products. If these concentrations are known, the calculation simply involves their substitution into the Kc expression.
For example, gaseous nitrogen dioxide forms dinitrogen tetroxide according to this equation:
30.7K

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相关实验视频

Updated: May 23, 2025

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
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ABCG2:一个里程碑式的电荷模型,用于准确的溶解和自由能量计算.

Xibing He1, Viet H Man1, Wei Yang2

  • 1Department of Pharmaceutical Sciences and Computational Chemical Genomics Screening Center, School of Pharmacy, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States.

Journal of chemical theory and computation
|March 11, 2025
PubMed
概括

我们开发了ABCG2,一种新的原子电荷模型,在分子模拟中实现化学精度. 与GAFF2相结合,它准确地预测了有机分子的溶解和转移自由能量.

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科学领域:

  • 计算化学是一种计算化学.
  • 分子建模分子建模
  • 药物发现 药物发现

背景情况:

  • 准确的原子电荷模型对于分子模拟至关重要.
  • 现有的模型可能对各种有机分子缺乏准确性或可转移性.
  • 一般的AMBER力场 (GAFF2) 是有机系统广泛使用的力场.

研究的目的:

  • 开发和验证ABCG2,一种用于有机分子的新型电荷模型.
  • 为了评估ABCG2与GAFF2在各种热力学性能方面的性能.
  • 为了证明GAFF2/ABCG2组合的准确性,可转移性和通用性.

主要方法:

  • 开发了ABCG2收费模型.
  • 根据FreeSolv数据库对无水化能量进行验证.
  • 在明尼苏达州溶解数据库上测试溶解和转移自由能量.
  • 与整洁液体的密度和蒸发热量进行基准测试.
  • 与受限静电电位 (RESP) 充电方法进行比较.

主要成果:

  • 实现了0.99 kcal/mol的RMSE,用于无水化能量 (FreeSolv),达到化学精度.
  • 获得的RMSE为0.89 kcal/mol的溶解自由能量和0.85 kcal/mol的转移自由能量 (明尼苏达溶解数据库).
  • 在液体密度和蒸发热量方面,其表现与 RESP 的性能相当.
  • 与药物分子的 RESP 相比,显示的电荷波动明显较小.

结论:

  • 该GAFF2/ABCG2组合提供准确和可靠的预测,有机分子的热力学特性.
  • 与RESP相比,ABCG2提供了更好的收费分配稳定性.
  • 该模型在分子模拟中展示了广泛的适用性和可转移性.