Greasy Cations Bind to Neutral Macromolecules in Aqueous Solution
Umay Eren Ertekin1, Halil Ibrahim Okur1,2
1Department of Chemistry, Faculty of Science, Bilkent University, 06800 Ankara, Turkey.
The Journal of Physical Chemistry Letters
|June 5, 2024
Summary
The study reveals that bulky quaternary ammonium cations bind directly to poly(N-isopropylacrylamide) (PNIPAM), influencing its phase transition. Greasier cations exhibit stronger binding and salting-out effects, comparable to Hofmeister anions.
Area of Science:
- Polymer Science
- Solution Chemistry
- Biophysical Chemistry
Background:
- Ions significantly impact macromolecule solution properties.
- Cationic effects on macromolecules are less understood than anionic effects.
- Quaternary tetraalkylammonium cations are investigated for their influence on polymer phase transitions.
Purpose of the Study:
- To systematically investigate the effect of various quaternary tetraalkylammonium cations on the phase transition of poly(N-isopropylacrylamide) (PNIPAM).
- To elucidate the binding interactions between these cations and PNIPAM in aqueous solutions.
- To correlate cation properties with their observed effects on PNIPAM solubility and phase behavior.
Main Methods:
- Solubility measurements of PNIPAM in the presence of different tetraalkylammonium salts.
- Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy to probe cation-macromolecule interactions.
- Attenuated Total Reflection Fourier-Transform Infrared (ATR-FTIR) spectroscopy to identify binding sites.
- Analysis of cation hydration entropies and their relation to salting-out effects.
Main Results:
- Direct binding of greasier tetraalkylammonium cations to the isopropyl group of PNIPAM was observed.
- Nonlinear, Langmuir-type chemical shift responses in ¹H NMR at isopropyl signals indicated specific binding.
- ATR-FTIR data suggested the amide oxygen is not the primary direct binding site.
- Salting-out effects of cations correlated with their hydration entropies, with weakly hydrated cations showing stronger effects.
Conclusions:
- Weakly hydrated quaternary ammonium cations can bind strongly to PNIPAM, similar to Hofmeister anions.
- The binding interaction is primarily with the hydrophobic isopropyl groups of PNIPAM.
- Cation hydration entropy is a key factor determining their effectiveness in inducing PNIPAM phase transitions.
More Related Videos
07:11Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator
Published on: November 1, 2018
7.1K
14:43Microfluidic On-chip Capture-cycloaddition Reaction to Reversibly Immobilize Small Molecules or Multi-component Structures for Biosensor Applications
Published on: September 23, 2013
10.8K
Related Concept Videos
03:00Solubility
17.5K
Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules,...
A solution is a homogeneous mixture composed of a solvent, the major component, and a solute, the minor component. The physical state of a solution—solid, liquid, or gas—is typically the same as that of the solvent. Solute concentrations are often described with qualitative terms such as dilute (of relatively low concentration) and concentrated (of relatively high concentration).
In a solution, the solute particles (molecules,...
17.5K
01:09Complexation Equilibria: Factors Influencing Stability of Complexes
363
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...
363
02:51Metal-Ligand Bonds
20.7K
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
20.7K
02:42Aqueous Solutions and Heats of Hydration
14.7K
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...
14.7K
01:19Complexation Equilibria: The Chelate Effect
501
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...
501
01:23Complexation Equilibria: Overview
666
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...
666