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相关概念视频

Chirality02:25

Chirality

22.1K
Chirality is a term that describes the lack of mirror symmetry in an object. In other words, chiral objects cannot be superposed on their mirror images. For example, our feet are chiral, as the mirror image of the left foot, the right foot, cannot be superposed on the left foot.
Chiral objects exhibit a sense of handedness when they interact with another chiral object. For example, our left foot can only fit in the left shoe and not in the right shoe. Achiral objects — objects that have...
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Molecules with Multiple Chiral Centers02:25

Molecules with Multiple Chiral Centers

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Molecules that possess multiple chiral centers can afford a large number of stereoisomers. For instance, while some molecules like 2-butanol have one chiral center, defined as a tetrahedral carbon atom with four different substituents attached, several molecules like butane-2,3-diol have multiple chiral centers. A simple formula to predict the number of stereoisomers possible for a molecule with n chiral centers is 2n. However, there can be a lower number where some of the stereoisomers are...
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Chirality in Nature02:30

Chirality in Nature

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Chirality is the most intriguing yet essential facet of nature, governing life’s biochemical processes and precision. It can be observed from a snail shell pattern in a macroscopic world to an amino acid, the minutest building block of life. Most of the snails around the world have right-coiled shells because of the intrinsic chirality in their genes. All the amino acids present in the human body exist in an enantiomerically pure state, except for glycine - the sole achiral amino acid.
12.1K
Chirality at Nitrogen, Phosphorus, and Sulfur02:30

Chirality at Nitrogen, Phosphorus, and Sulfur

5.6K
Chirality is most prevalent in carbon-based tetrahedral compounds, but this important facet of molecular symmetry extends to sp3-hybridized nitrogen, phosphorus and sulfur centers, including trivalent molecules with lone pairs. Here, the lone pair behaves as a functional group in addition to the other three substituents to form an analogous tetrahedral center that can be chiral.
A consequence of chirality is the need for enantiomeric resolution. While this is theoretically possible for all...
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Prochirality02:05

Prochirality

3.7K
The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
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¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons00:58

¹H NMR Chemical Shift Equivalence: Enantiotopic and Diastereotopic Protons

1.3K
Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...
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凝结和同步在对齐的状活性物质中.

Yujia Wang1, Bruno Ventéjou2, Hugues Chaté2,3,4

  • 1Center for Soft Condensed Matter Physics and Interdisciplinary Research, <a href="https://ror.org/05t8y2r12">Soochow University</a>, Suzhou 215006, China.

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概括

在循环游泳者中,自发密度分离形成了凝结物,而不是相位分离. 这些类似的结构吸收粒子并同步,挑战了典型的活性物质行为.

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科学领域:

  • 物理 物理学 物理
  • 活动物质物理学 活动物质物理学
  • 统计力学 统计力学

背景情况:

  • 二维活性物质通常表现出相位分离.
  • 循环游泳者是研究活性物质集体行为的模型系统.
  • 了解自发模式形成是活性物质物理学的关键.

研究的目的:

  • 为了研究自发密度隔离在密集的系统对齐圆游泳者自发密度隔离的性质.
  • 描述新出现的结构及其属性.
  • 将这些发现与已建立的相隔模型进行比较.

主要方法:

  • 在粒子和连续层面进行模拟.
  • 分析具有铁磁和阴磁对齐的系统.
  • 包括相同的和无序的奇拉性.

主要成果:

  • 密度分离表现为一种凝结现象,与相位分离不同.
  • 凝结物形成状或旋转的极地包结构.
  • 这些凝结物吸收了很大一部分颗粒,并随着质量增加而保持大小.
  • 凝聚会导致同步,尽管在2D中存在局部相互作用.

结论:

  • 这项研究揭示了二维活性物质系统中一种新的凝结机制.
  • 新兴的同步结构挑战了传统的相位分离模式.
  • 提出了一个现象学理论来解释观察到的凝聚和同步.