Supercritical CO₂ is one of the most important green solvents for biotechnological applications. Due to the high-pressure conditions and gas–liquid properties of the fluid, the structural investigations of the biological macromolecules such as proteins and enzymes in supercritical conditions is problematic. Molecular dynamics simulation has emerged as a good tool to study the molecular-levels phenomena in macromolecule/supercritical CO₂ environments. Many unsolved aspects of such systems have been explored by this method in recent years. One of the most important challenges in biomolecular simulations in supercritical CO₂ is the applied force field for the bio-macromolecules. Most of simulations in supercritical CO₂ have been performed by united-atoms and GROMOS96-based force fields for proteins and enzymes. The reliability of the obtained results should be examined by applying the other protein force fields. There is no comprehensive work about the effect of the force field on a single protein model in supercritical CO₂. In this work, I have applied four famous biomolecular force fields including: GROMOS96 (43a1), CHARMM (27), AMBER (03) and OPLS-AA for simulation of chymotrypsin inhibitor 2 as a model protein in supercritical CO₂ and also in the aqueous conditions. Different structural properties of protein have been examined using the different force fields. Results show that all of the force fields confirm the structural deviations of the protein structure from its native state in supercritical CO₂. GROMOS43a1, similar to the previous simulations, showed the higher flexibility of protein backbone in scCO₂ in comparison to the aqueous condition. In contrast, in simulations with all-atom force fields, the protein flexibility was almost identical in two solvents. Simulations by all of the force fields confirm the previously proposed mechanism for protein denaturation in scCO₂ which states that the changing of the interaction pattern of protein destabilizes the conformation in supercritical CO₂. However, the extent of changes was different among the force fields. While united-atom force field show higher changes and deviations from the native state, all-atom force fields, in agreement with each other, show moderate changes and deviations.

超临界 CO ₂是生物技术应用中最重要的绿色溶剂之一。由于流体的高压条件和气液性质，在超临界条件下对蛋白质和酶等生物大分子的结构研究是有问题的。分子动力学模拟已成为研究大分子/超临界 CO ₂环境中分子水平现象的好工具。近年来，这种方法已经探索了这种系统的许多未解决的方面。超临界 CO ₂中生物分子模拟中最重要的挑战之一是生物大分子的外加力场。大多数超临界 CO ₂模拟已经通过联合原子和基于 GROMOS96 的力场对蛋白质和酶进行了研究。应通过应用其他蛋白质力场来检查所获得结果的可靠性。没有关于力场对超临界 CO _{2 中}单个蛋白质模型的影响的综合工作。在这项工作中，我应用了四个著名的生物分子力场，包括：GROMOS96 (43a1)、CHARMM (27)、AMBER (03) 和 OPLS-AA 来模拟糜蛋白酶抑制剂 2 作为超临界 CO _{2 中}的模型蛋白并且也在水性条件下。已经使用不同的力场检查了蛋白质的不同结构特性。结果表明，所有力场都证实了蛋白质结构与其在超临界 CO _{2 中的}天然状态的结构偏差。GROMOS43a1 与之前的模拟类似，与水性条件相比，scCO ₂中的蛋白质骨架具有更高的灵活性。相比之下，在全原子力场的模拟中，蛋白质的柔韧性在两种溶剂中几乎相同。所有力场的模拟证实了先前提出的 scCO _{2 中}蛋白质变性机制其中指出蛋白质相互作用模式的变化破坏了超临界 CO _{2 中}的构象。然而，不同力场之间的变化程度是不同的。虽然联合原子力场显示出与自然状态的更高变化和偏差，但全原子力场彼此一致，显示出适度的变化和偏差。