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Related Concept Videos

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,...
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.
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Intermolecular Forces03:13

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions (attractive or repulsive) between charged species (permanent, partial, or temporary charges) and exist with varying strengths between ions, polar, nonpolar, and neutral molecules. The different types of intermolecular forces are ion–dipole, dipole–dipole, hydrogen bonds, and dispersion; among these, dipole–dipole, hydrogen bonds, and dispersion...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...

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Related Experiment Video

Updated: Jun 4, 2026

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
14:44

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Published on: December 16, 2013

Correlation forces between helical macro-ions in the weak coupling limit.

D J Lee1

  • 1Max-Planck Institute für Physik Komplexer Systeme, Nöthnizer Straße 38, D-01187, Dresden, Germany. domolee@hotmail.com

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|February 22, 2011
PubMed
Summary
This summary is machine-generated.

Electrostatic forces between macro-ions include mean field and correlation contributions. Correlation forces, significant for divalent ions, decrease with increasing salt concentration, impacting macro-ion interactions in solutions.

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High-Speed Magnetic Tweezers for Nanomechanical Measurements on Force-Sensitive Elements
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Area of Science:

  • Physical Chemistry
  • Colloid Science
  • Biophysics

Background:

  • Electrostatic interactions are crucial for macro-ion behavior in solutions.
  • Understanding these forces is key to fields like DNA condensation and protein association.
  • Existing models often focus on mean-field contributions, neglecting correlation effects.

Purpose of the Study:

  • To analyze and quantify correlation forces between cylindrical macro-ions.
  • To derive analytical expressions for different correlation contributions.
  • To investigate the influence of ion valency and salt concentration on these forces.

Main Methods:

  • Expansion in the number density of condensed ions.
  • Derivation of analytical expressions for electrostatic contributions.
  • Analysis of forces for general and helical macro-ion configurations.
  • Modeling DNA-like charge distributions.

Main Results:

  • Identified three distinct correlation force contributions: solvation energy changes, image repulsion, and attractive Oosawa force.
  • Found that correlation forces are negligible for univalent ions at physiological salt concentrations.
  • Divalent ions exhibit small but significant correlation forces, which decrease with increasing salt concentration.
  • The Oosawa force's dependence on molecular orientation was analyzed for DNA-like charge distributions.

Conclusions:

  • Correlation forces play a role in macro-ion interactions, particularly for multivalent ions.
  • Salt concentration significantly modulates correlation forces, reducing their magnitude.
  • The findings provide a more comprehensive understanding of electrostatic interactions in complex ionic systems.