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相关概念视频

SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

10.5K
Kinetic Studies and Significance
In a chemical reaction, a relationship exists between the concentration of reactants and the rate at which the reaction proceeds. The study to measure this relationship is known as the kinetics of a chemical reaction. Kinetic studies are used to deduce the rate law of a chemical reaction, which provides information about the species involved during the transition state of the rate-determining step. Thus, kinetic studies help to derive the mechanism of a...
10.5K
Precipitation Processes01:12

Precipitation Processes

6.5K
The experimental conditions in a gravimetric analysis should be optimized to maximize the particle size and purity of the obtained precipitate. Ideally, the concentration of the precipitating reagent should be low with effective stirring to maintain low relative supersaturation for the growth of large crystals. In homogeneous precipitation, the precipitant is slowly generated by a chemical reaction in the solution to avoid local reagent excesses. For example, urea decomposes gradually to...
6.5K
Recrystallization: Solid–Solution Equilibria01:10

Recrystallization: Solid–Solution Equilibria

4.2K
Recrystallization is a purification technique used to separate impurities from solid compounds. In this technique, no chemical reactions occur. Instead, it exploits physical properties only, specifically, the solubility differences between the desired compound and impurities, either at a single temperature or at different temperatures, and under other selected conditions. The solid-solution equilibrium (solubility equilibrium) of each component in the solution represents a binary phase...
4.2K
SN1 Reaction: Kinetics02:05

SN1 Reaction: Kinetics

9.9K
In an SN2 reaction, the reaction rate depends on both the type of nucleophile and the substrate. A hindered tertiary alkyl halide is practically inert to the SN2 mechanism despite using a strong nucleophile.
However, Sir Christopher Ingold and Edward D. Hughes, who studied the kinetics of various nucleophilic substitution reactions, noticed that a tertiary alkyl halide does undergo a nucleophilic substitution reaction in the presence of a weak nucleophile. While studying the substitution...
9.9K
Anionic Chain-Growth Polymerization: Mechanism01:04

Anionic Chain-Growth Polymerization: Mechanism

2.6K
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael...
2.6K
Predicting Products: SN1 vs. SN202:27

Predicting Products: SN1 vs. SN2

17.6K
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
17.6K

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Updated: Mar 15, 2026

Optimizing the Growth of Endothiapepsin Crystals for Serial Crystallography Experiments
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在异质冰形成过程中堆叠顺序进化的动力学.

Xudan Huang1,2, Zifeng Yuan3, Chon-Hei Lo3

  • 1Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

Physical review letters
|March 13, 2026
PubMed
概括
此摘要是机器生成的。

这项研究揭示了蒸汽沉积过程中冰晶生长的原子化机制. 我们观察到由表面和对称效应驱动的从立方体到六角形冰的独特过渡,为材料设计提供了新的见解.

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Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
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科学领域:

  • 材料科学 材料科学 材料科学
  • 晶体学 晶体学是指结晶学.
  • 表面科学是一门学科.

背景情况:

  • 密集包装的多态材料中的堆叠顺序尚未得到充分理解.
  • 控制晶体生长对于设计先进材料至关重要.

研究的目的:

  • 阐明在蒸汽沉积过程中控制冰晶生长的原子化机制.
  • 研究表面和对称性在冰结晶中的作用.

主要方法:

  • 在现场低温传输电子显微镜 (cryo-TEM) 用于实时观察.
  • 分子动力学 (MD) 模拟以支持实验发现.

主要成果:

  • 观察到异质的冰核和与再结晶和分叉的生长.
  • 通过堆叠无序的层,确定了从立方冰到六角冰的连贯表轴过渡.
  • 归因于对表面受约束,对称性破坏效应的结晶偏好,最大限度地减少自由能量.

结论:

  • 表面和对称性对冰的结晶具有重要影响.
  • 提供了对晶体生长机制的基本见解.
  • 提供了设计具有控制结构的新材料的指导原则.