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Date: 17-1-2018
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The Chelate Effect
The chelate effect is the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal.
The macrocyclic effect follows the same principle as the chelate effect, but the effect is further enhanced by the cyclic conformation of the ligand. Macrocyclic ligands are not only multi-dentate, but because they are covalently constrained to their cyclic form, they allow less conformational freedom. The ligand is said to be "pre-organized" for binding, and there is little entropy penalty for wrapping it around the metal ion. For example heme b is a tetradentate cyclic ligand which is strongly complexes transition metal ions, including (in biological systems) Fe+2.
Figure 4
: (left) A free, unbound porphorin ligand and (right) Heme b macrocyclic ligand that binds iron in hemoglobin
Some other common chelating and cyclic ligands are shown below:
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"الرعاية التلطيفية".. تحسين جودة حياة المرضى هي السر
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العلماء الروس يطورون طريقة جديدة لإعادة تدوير النفايات البلاستيكية
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اختتام المراسم التأبينية التي أهدي ثوابها إلى أرواح شهداء المق*ا*و*مة
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