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Related Concept Videos

Anticoagulant Drugs: Low-Molecular-Weight Heparins01:30

Anticoagulant Drugs: Low-Molecular-Weight Heparins

Hemostasis is a crucial process that prevents excessive blood loss from damaged blood vessels. It involves various mechanisms such as vasoconstriction, platelet adhesion and activation, and fibrin formation. The importance of each mechanism depends on the type of vessel injury. In contrast, thrombosis is the abnormal formation of a blood clot within the blood vessels, leading to potential complications if the clot obstructs blood flow. Thrombosis can be caused by increased coagulability of the...
EDTA: Chemistry and Properties01:22

EDTA: Chemistry and Properties

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...
Ion Exchange01:17

Ion Exchange

Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...
Complexometric Titration: Ligands00:43

Complexometric Titration: Ligands

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...
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...
Masking and Demasking Agents01:19

Masking and Demasking Agents

EDTA titrations may necessitate masking and demasking agents to temporarily protect a particular metal ion in a mixture from the EDTA reaction. These agents facilitate the sequential analysis of the metal ions by forming stable complexes with some—but not all—metal ions during certain steps.
There are many masking agents, such as cyanide, fluoride, triethanolamine, thiourea, and 2,3-bis(sulfanyl)propan-1-ol (formerly 2,3-dimercapto-1-propanol), with the masking agent chosen based on the metal...

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Polycationic calix[8]arenes able to recognize and neutralize heparin.

Tommaso Mecca1, Grazia M L Consoli, Corrada Geraci

  • 1CNR-Istituto di Chimica Biomolecolare, Via del Santuario, 110, I-95028, Valverde (CT), Italy.

Organic & Biomolecular Chemistry
|October 7, 2006
PubMed
Summary

Calix[8]arene polycations exhibit superior heparin binding due to a unique induced fit mechanism, outperforming protamine and polylysine. These compounds offer high specificity and affinity for heparin neutralization in solution and blood.

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Area of Science:

  • Supramolecular chemistry
  • Biochemistry
  • Pharmacology

Background:

  • Heparin is a critical anticoagulant, but its antagonists like protamine and polylysine have limitations.
  • Understanding molecular interactions with heparin is key for developing effective anticoagulants and reversal agents.

Purpose of the Study:

  • To investigate the complexation performance of calix[8]arene polycations with heparin.
  • To compare the binding mechanism of calix[8]arene polycations with known heparin antagonists (protamine, polylysine).

Main Methods:

  • Fluorescence spectroscopy
  • Nuclear Magnetic Resonance (NMR) titration
  • Activated partial thromboplastin time (aPTT) assays
  • Comparative analysis with protamine and polylysine

Main Results:

  • Calix[8]arene polycations demonstrate exceptional complexation with heparin via a mutual induced fit mechanism.
  • This adaptability significantly enhances recognition compared to the rigid protamine and less ordered polylysine.
  • Calixarene derivatives show high specificity and affinity for heparin neutralization in both aqueous solutions and blood.
  • Effective neutralization of low molecular weight heparin (LMWH) was observed, an effect not fully achieved by protamine.

Conclusions:

  • The flexible macrocyclic scaffold of calix[8]arene enables superior heparin binding through induced fit.
  • Calixarene polycations represent a promising class of compounds for heparin antagonism and neutralization.
  • These findings have implications for anticoagulant therapy and the management of heparin-related complications.