相关实验视频
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Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
分子动力学研究气体酸盐的形成
Changman Moon1, Paul C Taylor, P Mark Rodger
1Department of Chemistry, The University of Warwick, Coventry, U.K. CV4 7AL, UK.
Journal of the American Chemical Society
|April 17, 2003
概括
分子动力学模拟揭示了甲水合物集群形成2D,然后是3D结构,具有挑战性的核化模型. 观察到的II型水合物结构与最近的实验发现一致.
科学领域:
- * 计算化学和材料科学.
- *专注于分子动力学模拟和相位过渡.
背景情况:
- *甲水合物形成对于储能和气候研究至关重要.
- *以前的模型表明快速的3D核形成,但实验证据仍有争议.
研究的目的:
- * 在分子水平上研究甲水合物的自发形成.
- *将模拟结果与现有的水合物核化理论和实验数据进行比较.
主要方法:
- *采用了长期规模的分子动力学模拟.
- * 在不同的温度和压力条件下模拟甲和液态水接口 (起初300 K,30 bar;然后250 K,300 bar).
主要成果:
- * 在冷却 (20K次冷却) 后观察到甲水合物的快速生长.
- *水合物集群最初是2D排列,然后发展为3D结构.
- * 观察到II型水合物结构,尽管I型对甲具有热力学稳定性,与衍射实验一致.
结论:
- * 模拟结果支持水合物核化的局部顺序模型.
- *这些发现挑战了传统的3D核化模型,表明了2D到3D的增长途径.
- *II型结构的出现为甲水合物形成机制提供了洞察力.
相关概念视频
Ions as Acids and Bases
Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Determining the pH of Salt Solutions
The pH of a salt solution is determined by its component anions and cations. Salts that contain pH-neutral anions and the hydronium ion-producing cations form a solution with a pH less than 7. For example, in ammonium nitrate (NH4NO3) solution, NO3− ions do not react with water whereas NH4+ ions produce the hydronium ions resulting in the acidic solution. In contrast, salts that contain pH-neutral cations and the hydroxide ion-producing anions form a solution with a pH greater than 7. For...
Polyprotic Acids
Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
Acid Strength and Molecular Structure
Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
Molecular Structure and Acidity
An acid can be deprotonated to form a conjugate base or an anion. If the produced anion is more stable, then the acid is stronger. On the contrary, if the anion is unstable, then the acid is weaker. Hence, to determine the acidity of the compound, the stability of its conjugate base is studied using various factors.
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...

