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Related Concept Videos

Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

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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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Complexation Equilibria: Factors Influencing Stability of Complexes01:09

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In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
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Extraction: Advanced Methods00:56

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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...
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Metal-Ligand Bonds02:51

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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: Chemistry and Properties01:22

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Polydentate ligands are most widely used in complexometric titrations because they form more stable complexes with the metal ions than mono- or bidentate ligands due to the chelate effect. Examples of polydentate ligands are ethylenediaminetetraacetic acid (EDTA), crown ethers, and cryptands. The most important feature of optimal polydentate ligands is the ability to form 1:1 complexes in a single-step process. Amino carboxylic acid derivatives are frequently used as complexing agents. EDTA is...
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Complexometric Titration: Ligands00:43

Complexometric Titration: Ligands

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Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...
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Metal Chelating Crosslinkers Form Nanogels with High Chelation Stability.

Jacques Lux1, Minnie Chan1, Luce Vander Elst2

  • 1Skaggs School of Pharmacy and Pharmaceutical Sciences. KACST-UCSD Center of Excellence in Nanomedicine. Laboratory of Bioresponsive Materials, University of California, San Diego. 9500 Gilman Dr., 0600, PSB 2270, La Jolla, CA-92093-0600, United States.

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New nanogels with metal chelates show improved MRI contrast and stability. This approach enhances relaxivity and reduces gadolinium toxicity for safer medical imaging applications.

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Area of Science:

  • Materials Science
  • Nanotechnology
  • Biomedical Engineering

Background:

  • Hydrogel nanoparticles offer versatile platforms for biomedical applications.
  • Current MRI contrast agents face challenges related to relaxivity and gadolinium toxicity.
  • Metal chelates are crucial for developing effective contrast agents.

Purpose of the Study:

  • To develop novel hydrogel nanoparticles (nanogels) using acyclic or cyclic metal chelates as crosslinkers.
  • To enhance the performance of MRI contrast agents by improving relaxivity and stability.
  • To investigate the potential of these nanogels in reducing gadolinium (Gd3+) toxicity.

Main Methods:

  • Formulation of polyacrylamide-based nanogels (50-85 nm diameter) incorporating metal chelate crosslinkers.
  • Characterization of nanogel properties, including relaxivity and stability against transmetallation.
  • Comparative analysis of relaxivity against a commercial contrast agent (Dotarem®).

Main Results:

  • Nanogels exhibited significantly enhanced relaxivities, up to 6-fold greater than Dotarem®.
  • The nanogel structure was found to slow chelator tumbling frequency, facilitating fast water exchange.
  • Enhanced thermodynamic and kinetic stabilization of Gd3+ within chelators was observed, reducing the risk of free Gd3+ release.

Conclusions:

  • The developed nanogels represent advanced MRI contrast agents with superior relaxivity and stability.
  • The chelate crosslinker strategy effectively mitigates gadolinium toxicity concerns.
  • This approach holds promise for broader applications in medical imaging and radiotherapy using metal-chelating nanoparticles.