Related Experiment Video
Updated: Oct 26, 2025
08:44
Assembly and Characterization of Polyelectrolyte Complex Micelles
Published on: March 2, 2020
11.1K
Looping-in complexation and ion partitioning in nonstoichiometric polyelectrolyte mixtures
Sean Friedowitz1,2, Junzhe Lou1,3, Kayla Patricia Barker3
1Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305, USA.
Science Advances
|July 31, 2021
Summary
Nonstoichiometric mixing of charged molecules drives the formation of membraneless compartments. A "looping-in" phenomenon, influenced by salt concentration and ion entropy, governs polymer behavior in these cellular structures.
Area of Science:
- Biophysics
- Molecular Biology
- Polymer Science
Background:
- Intracellular membraneless compartments form through liquid-liquid phase separation.
- Compositional heterogeneity complicates understanding compartment stability.
Purpose of the Study:
- Investigate the impact of nonstoichiometric mixing on coacervation.
- Quantify polyelectrolyte and ion concentrations in coacervate and supernatant phases.
Main Methods:
- Combined experimental and theoretical approaches.
- Studied synthetic polyacrylamides and polypeptides/DNA.
- Measured ion and polymer concentrations under varying salt conditions.
Main Results:
- Observed a "looping-in" phenomenon where polymer concentration initially increases with salt before decreasing.
- This behavior occurs around physiological salt concentrations.
- A molecular model incorporating ion binding and electrostatics explains the looping-in effect.
Conclusions:
- Nonstoichiometric mixing significantly affects coacervation and compartment stability.
- The looping-in phenomenon is driven by counterion translational entropy in low-salt conditions.
- Reversible ion binding and electrostatic interactions are key to understanding these complex cellular structures.
More Related Videos
Related Concept Videos
01:17Ion Exchange
736
Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or...
736
01:23Complexation Equilibria: Overview
1.0K
Complexation reactions take place when dative or coordinate covalent bonds form between metal ions and ligands. The compounds formed in these reactions are called coordination compounds. The number of bonds formed between the metal ion and the ligands is called its coordination number. Generally, most metal ions in an aqueous solution are solvated by water molecules and thus exist as aqua complexes.
The equilibrium constant of the complexation reaction is represented as the formation constant...
The equilibrium constant of the complexation reaction is represented as the formation constant...
1.0K
01:09Complexation Equilibria: Factors Influencing Stability of Complexes
565
In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
565
01:19Complexation Equilibria: The Chelate Effect
767
In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...
767
03:45Formation of Complex Ions
24.6K
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...
24.6K
02:42Aqueous Solutions and Heats of Hydration
15.9K
Water and other polar molecules are attracted to ions. The electrostatic attraction between an ion and a molecule with a dipole is called an ion-dipole attraction. These attractions play an important role in the dissolution of ionic compounds in water.
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process...
15.9K