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Related Concept Videos

¹H NMR: Long-Range Coupling01:27

¹H NMR: Long-Range Coupling

The coupling interactions of nuclei across four or more bonds are usually weak, with J values less than 1 Hz. While these are usually not observed in spectra, the presence of multiple bonds along the coupling pathway can result in observable long-range coupling.
In alkenes, spin information is communicated via σ–π overlap, as seen in allylic (four-bond) and homoallylic (five-bond) couplings. These coupling interactions are stronger when the σ bond is parallel to the alkene π orbitals.
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Peptide Bonds02:43

Peptide Bonds

A peptide bond covalently attaches amino acids through a dehydration reaction. One amino acid's carboxyl group and another amino acid's amino group combine, releasing a water molecule. The resulting bond is the peptide bond. The products that such linkages form are peptides. As more amino acids join this growing chain, the resulting chain is a polypeptide. Each polypeptide has a free amino group at one end. This end has the N-terminal, or the amino-terminal, and the other end has a free...
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...

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Analysis of Protein Complex Formation at Micromolar Concentrations by Coupling Microfluidics with Mass Photometry
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Published on: January 26, 2024

Peptide-microgel interactions in the strong coupling regime.

Per Hansson1, Helena Bysell, Ronja Månsson

  • 1Department of Pharmacy, Uppsala University, P.O. Box 580, SE-751 23 Uppsala, Sweden. per.hansson@farmaci.uu.se

The Journal of Physical Chemistry. B
|August 14, 2012
PubMed
Summary

Poly(acrylic acid) microgels shrink when binding peptides, with deswelling increasing with peptide length and charge. A new model captures this behavior, revealing peptide charge, not charge density, dictates microgel collapse.

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Controlled Synthesis and Fluorescence Tracking of Highly Uniform Poly(N-isopropylacrylamide) Microgels
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Controlled Synthesis and Fluorescence Tracking of Highly Uniform Poly(N-isopropylacrylamide) Microgels
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Controlled Synthesis and Fluorescence Tracking of Highly Uniform Poly(N-isopropylacrylamide) Microgels

Published on: September 8, 2016

Area of Science:

  • Polymer Science
  • Supramolecular Chemistry
  • Materials Science

Background:

  • Microgels are versatile polymer networks with tunable properties.
  • Understanding their interactions with biomolecules like peptides is crucial for applications.
  • Poly(acrylic acid) microgels offer pH-responsive behavior due to carboxylic acid groups.

Purpose of the Study:

  • Investigate the interaction between poly(acrylic acid) microgels and oppositely charged peptides.
  • Quantify the impact of peptide length, charge density, pH, and salt concentration on microgel volume.
  • Develop a theoretical model to describe microgel-peptide interactions, particularly in strong coupling regimes.

Main Methods:

  • Micromanipulator-assisted light microscopy to monitor single microgel volume changes.
  • Systematic variation of peptide characteristics (length, charge density) and environmental conditions (pH, salt).
  • Development of a theoretical model incorporating electrostatic attraction and network elasticity.

Main Results:

  • Microgel deswelling (volume reduction) increases with peptide length and charge density.
  • Deswelling is more pronounced at lower pH (pH 5) compared to higher pH (pH 8).
  • A theoretical model accurately predicts microgel swelling behavior and captures phase transitions.

Conclusions:

  • Peptide charge (length) is the primary determinant of microgel deswelling, surpassing charge density.
  • The developed model successfully describes pH- and electrolyte-dependent microgel swelling.
  • A transition between continuous and discrete network collapse was observed, consistent with experimental data.