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Related Concept Videos

Formation of Complex Ions03:45

Formation of Complex Ions

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...
Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

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...
Extraction: Advanced Methods00:56

Extraction: Advanced Methods

Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
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...
Colors and Magnetism03:02

Colors and Magnetism

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 eye.
Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...

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Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells
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Published on: December 13, 2016

Effective charge saturation in ferritin cages.

Takumi Kuwata1, Yuusuke Murakami1, Daisuke Sato1

  • 1Department of Biosciences, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo, 192-8577, Japan.

Scientific Reports
|June 16, 2026
PubMed
Summary

Ferritin proteins have a maximum negative charge limit. Mutating surface residues surprisingly revealed that Escherichia coli and Pseudo-nitzschia multiseries ferritins possess maximal negative charges, unlike animal ferritins.

Keywords:
Dissociation constantElectrostatic potentialFerritinNet chargeProtein cage

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Protein Chemistry

Background:

  • Ferritins are highly conserved metalloproteins that store iron.
  • They assemble into spherical 24-subunit cages, crucial for cellular iron homeostasis.
  • The surface charge of ferritins can influence their interactions and functions.

Purpose of the Study:

  • To investigate the net charge limit of ferritin proteins.
  • To explore the role of surface glutamate and aspartate residues in determining ferritin net charge.
  • To compare the net charge characteristics of bacterial, marine diatom, and animal ferritins.

Main Methods:

  • Site-directed mutagenesis was used to create net-charge mutants of Escherichia coli ferritin (EcFtn) and Pseudo-nitzschia multiseries ferritin (PmFtn).
  • Nondenaturing polyacrylamide gel electrophoresis (PAGE) and ζ-potential measurements were employed to assess the effective negative charges of the wild-type and mutant proteins.
  • Amino acid sequence analysis was performed to compare charge characteristics across different species.

Main Results:

  • Contrary to expectations, increasing the number of glutamate (Glu) and aspartate (Asp) residues did not increase the effective negative charge of the mutant ferritins.
  • Conversely, decreasing the number of Glu and Asp residues led to a decrease in effective negative charge.
  • Both EcFtn and PmFtn exhibited properties suggesting they possess the maximum possible negative charges for their structures.
  • Sequence analysis indicated that bacterial and plant ferritins generally have near-maximum negative charges, while animal ferritins have significantly fewer.

Conclusions:

  • Ferritin proteins appear to have a physical limit to their net negative charge.
  • EcFtn and PmFtn are likely at or near this maximal negative charge capacity.
  • Significant differences in surface charge exist between bacterial/plant and animal ferritins, potentially impacting their biological roles.