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相关概念视频

Mixtures of Acids03:27

Mixtures of Acids

The pH of a solution containing an acid can be determined using its acid dissociation constant and its initial concentration. If a solution contains two different acids, then its pH can be determined using one of several methods depending upon the relative strength of the acids and their dissociation constants.
A Mixture of a Strong Acid and a Weak Acid
In a mixture of a strong acid and a weak acid, the strong acid dissociates completely and becomes a source of almost all the hydronium ions...
Structures of Carboxylic Acid Derivatives01:28

Structures of Carboxylic Acid Derivatives

Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Basicity of Aliphatic Amines01:21

Basicity of Aliphatic Amines

Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...
Titration of a Weak Acid with a Weak Base01:08

Titration of a Weak Acid with a Weak Base

Weak acids and bases do not undergo dissociation completely, and titrations between these two are rarely studied. When such studies are performed, say, for the titration of a weak acid with a weak base, the titration curve plots the change in pH as a function of the volume of base added. Take the titration of acetic acid with ammonia, for instance. During the titration, these two species form ammonium acetate and water, but the pH change is slow and gradual.
As a result, there is no simple...
Composition of Polyprotic Acid Solutions as a Function of pH01:19

Composition of Polyprotic Acid Solutions as a Function of pH

Polyprotic acids of the type H2M constitute two ionizable protons. As a result, on titration with a base, they exhibit two equivalence points in the titration curve. During titration, the species H2M, HM−, and M2− will be present in the solution at different points. The fractions of H2M, HM−, and M2− present at the various instances of the titration are denoted by α0, α1, and α2, respectively.
A graph with the alpha values is plotted against the volume of base added during titration. Here, a...
Mixtures of Acids01:19

Mixtures of Acids

The pH of a solution containing an acid can be determined using its acid dissociation constant and initial concentration. If a solution contains two different acids, then its pH can be determined using one of several methods depending on the relative strength of the acids and their dissociation constants.
In a strong and weak acid mixture, the strong acid dissociates completely and becomes a source of almost all the hydronium ions present in the solution. In contrast, the weak acid shows...

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Metabolic Glycoengineering of Sialic Acid Using N-acyl-modified Mannosamines
12:06

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酸与N-乙神经氨基酸 (Neu5Ac) 在具有不同pH值的水溶液中的异常结合特征.

Hidenori Otsuka1, Eiichiro Uchimura, Hiroyuki Koshino

  • 1Department of Materials Science and Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.

Journal of the American Chemical Society
|March 20, 2003
PubMed
概括

酸盐化合物选择性地与N-乙神经胺酸 (Neu5Ac) 结合,这是细胞表面的关键成分. 这一发现为向药物输送和诊断提供了潜力,特别是在生理pH值下.

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科学领域:

  • 碳水化合物化学 碳水化合物化学
  • 生物物理化学 生物物理化学
  • 药用化学 医学化学

背景情况:

  • 酸盐与生物膜上的碳水化合物分子相互作用.
  • N-乙神经胺酸 (Neu5Ac) 是一种在细胞表面发现的重要酸.
  • 了解酸盐与碳水化合物的相互作用对于生物应用至关重要.

研究的目的:

  • 调查酸盐化合物与N-乙神经胺酸 (Neu5Ac) 的结合特征.
  • 为了比较酸盐与Neu5Ac的结合亲和力,与其他常见的糖类如葡萄糖,曼诺糖和银河糖进行比较.
  • 阐明酸盐-Neu5Ac复合物形成的机制和pH依赖性.

主要方法:

  • 使用的多核磁共振光谱仪: (11) B, (1) H, (13) C,和 (15) N.
  • 作为一个模型酸盐化合物,使用了3-) 胺) 酸 (PAPBA).
  • 在各种pH水平的结合相互作用的量化平衡常量 (K).

主要成果:

  • 观察到Neu5Ac/PAPBA结合的异常pH依赖性,随着pH的增加,亲和力下降.
  • 证实了三角形形成的复合体的形成,可能涉及与Neu5Ac的氨基基群的分子内B-N或B-O结合.
  • 在生理pH值7.4时表现出异常高的复合能力,平衡常数大约是葡萄糖的7倍.

结论:

  • 酸对生物膜上的Neu5Ac残留物具有选择性识别.
  • 在生理pH的高度结合亲和力表明潜在的应用在准糖蛋白和化物.
  • 这些发现支持开发基于酸盐的药物,用于涉及Neu5Ac表达细胞的诊断和治疗.