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Related Concept Videos

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...
Noncovalent Attractions in Biomolecules02:35

Noncovalent Attractions in Biomolecules

Noncovalent attractions are associations within and between molecules that influence the shape and structural stability of complexes. These interactions differ from covalent bonding in that they do not involve sharing of electrons.
Four types of noncovalent interactions are hydrogen bonds, van der Waals forces, ionic bonds, and hydrophobic interactions.
Hydrogen bonding results from the electrostatic attraction of a hydrogen atom covalently bonded to a strong-electronegative atom like oxygen,...
Noncovalent Attractions in Biomolecules02:35

Noncovalent Attractions in Biomolecules

Noncovalent attractions are associations within and between molecules that influence the shape and structural stability of complexes. These interactions differ from covalent bonding in that they do not involve sharing of electrons.
Four types of noncovalent interactions are hydrogen bonds, van der Waals forces, ionic bonds, and hydrophobic interactions.
Hydrogen bonding results from the electrostatic attraction of a hydrogen atom covalently bonded to a strong-electronegative atom like oxygen,...
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: 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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Single-Molecule Measurement of Protein Interaction Dynamics Within Biomolecular Condensates
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Helical transfer through nonlocal interactions.

Xiaojian Wu1, Sunjun Ji, Yi Li

  • 1College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, PR China.

Journal of the American Chemical Society
|April 8, 2009
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Chiral bola-type enantiomers form physical gels in water, enabling templated synthesis of helical silica nanostructures. This method controls mesoporous silica architectures and helicity for advanced materials.

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Area of Science:

  • Supramolecular Chemistry
  • Materials Science
  • Nanotechnology

Background:

  • Chiral bola-type amphiphiles can self-assemble into ordered structures.
  • Self-assembled structures can serve as templates for nanomaterial synthesis.

Purpose of the Study:

  • To synthesize chiral bola-type enantiomers and utilize their self-assemblies as templates for creating mesoporous silica nanostructures with controlled helicity.
  • To investigate the influence of acidic and basic conditions on the templating process and the resulting silica structures.

Main Methods:

  • Synthesis of chiral bola-type enantiomers (ll-12PyBr and dd-12PyBr).
  • Sol-gel transcription using amphiphile self-assemblies as templates.
  • Characterization of silica nanostructures using powder X-ray diffraction.

Main Results:

  • Left-handed and right-handed helical 1,4-phenylene-silica bundles were successfully prepared under acidic conditions using specific enantiomers as templates.
  • 1,4-phenylene-silica bundles were obtained under basic conditions, with higher order observed in the packing of aromatic rings within the pore walls.
  • Helical silica, 1,3-phenylene-silica, ethene-silica, and ethane-silica bundles were also synthesized using the chiral templates.

Conclusions:

  • Chiral bola-type amphiphile self-assemblies are effective templates for controlling the helicity and mesoporous structure of silica nanostructures.
  • The pH conditions significantly influence the order and potentially the handedness of the templated silica materials.
  • This templating approach offers a versatile route for fabricating various helical silica architectures with potential applications in chiral separations and catalysis.