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Metal-Ligand Bonds02:51

Metal-Ligand Bonds

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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...
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EDTA: Auxiliary Complexing Reagents01:26

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EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...
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Formation of Complex Ions03:45

Formation of Complex Ions

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A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
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Valence Bond Theory02:42

Valence Bond Theory

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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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Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

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Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
26.9K
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Colors and Magnetism

12.0K
Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
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The Fe and Zn cofactor dilemma.

Jiahua Chen1, Logan A Calderone1, Luying Pan1

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Biochimica Et Biophysica Acta. Proteins and Proteomics
|June 23, 2023
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Iron (Fe) and zinc (Zn) ions are vital enzyme cofactors. While typically having distinct roles, their functions can overlap in certain enzymes, challenging established biological roles.

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Area of Science:

  • Biochemistry
  • Enzymology
  • Metalloprotein chemistry

Background:

  • Iron (Fe) and zinc (Zn) ions are essential cofactors for enzymes across all life domains.
  • Fe typically acts as an electron donor/acceptor in redox enzymes, while Zn serves as a structural or catalytic component in hydrolases.
  • The presence of Zn in oxidoreductases and Fe in hydrolases challenges this functional dichotomy.

Purpose of the Study:

  • To explore the functional interchangeability of Fe and Zn ions as enzymatic cofactors.
  • To investigate instances where Zn is found in oxidoreductases and Fe in hydrolases.
  • To understand how Fe-S clusters and Zn substitute for each other in proteins.

Main Methods:

  • Bioinformatic analysis of metalloprotein databases.
  • Enzyme activity assays for wild-type and mutant proteins.
  • Spectroscopic characterization of metal-substituted enzymes.

Main Results:

  • Observed instances of Zn in oxidoreductases and Fe in hydrolases, challenging traditional roles.
  • Demonstrated that Fe can substitute for Zn or catalyze specific reactions in hydrolases.
  • Showcased Zn's ability to replace Fe and Fe-S clusters in certain proteins.
  • Identified cases where Zn and Fe-S clusters are not always functional proxies despite interchangeable binding.

Conclusions:

  • The functional roles of Fe and Zn ions as enzyme cofactors are more flexible than previously assumed.
  • Metal substitution and the presence of Fe-S clusters in zinc-binding proteins can lead to altered or non-equivalent enzymatic functions.
  • Further research is needed to fully elucidate the mechanisms and implications of metal cofactor interchangeability in enzymes.