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Related Concept Videos

Valence Bond Theory02:42

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
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Overview of Valence Bond Theory
Spin–Spin Coupling: One-Bond Coupling01:17

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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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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.
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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.
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Spin delocalization over type zero copper.

Alexey Potapov1, Kyle M Lancaster, John H Richards

  • 1Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.

Inorganic Chemistry
|March 22, 2012
PubMed
Summary
This summary is machine-generated.

Researchers studied "type zero" copper sites in Pseudomonas aeruginosa azurin mutants. These sites exhibit enhanced electron transfer, with their low EPR A(zz)(Cu) values attributed to orbital dipolar contributions, not dramatically increased spin delocalization.

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Area of Science:

  • Biochemistry and Biophysics
  • Bioinorganic Chemistry
  • Electron Transfer Mechanisms

Background:

  • Pseudomonas aeruginosa azurin is a model protein for studying copper centers.
  • Mutants C112D/M121X create unique "type zero" copper sites with distinct electronic properties.
  • Type zero sites exhibit small A(zz)(Cu) splitting and enhanced electron transfer activity compared to type 2 Cu(II) in C112D mutants.

Purpose of the Study:

  • To elucidate the origin of the reduced A(zz)(Cu) value in type zero copper sites.
  • To investigate the degree of spin delocalization over ligands in type zero versus type 2 copper sites.
  • To understand the relationship between electronic structure, geometry, and electron transfer properties.

Main Methods:

  • Characterization of double mutants (C112D/M121X) and single mutant (C112D) of Pseudomonas aeruginosa azurin.
  • Electron Paramagnetic Resonance (EPR) spectroscopy at X- and W-band frequencies.
  • Hyperfine spectroscopy techniques to map ligand hyperfine couplings ( (14)N and (13)C).

Main Results:

  • Spin delocalization differs between type zero and type 2 copper sites.
  • Type zero sites show smaller (14)N hyperfine couplings (25-40% reduction) but larger (13)C carboxylate couplings (approx. 50% increase) from D112.
  • The reduced A(zz)(Cu) in type zero sites is primarily due to increased orbital dipolar contribution linked to a larger g(zz) value and distorted tetrahedral geometry.

Conclusions:

  • Spin delocalization in type zero copper sites is not significantly greater than in type 2 C112D mutants.
  • The low A(zz)(Cu) value is mainly a consequence of geometric distortion and its effect on orbital dipolar contributions.
  • Enhanced spin delocalization onto the D112 carboxylate in type zero mutants suggests improved electron transfer pathways involving this residue.