Ionizable ligands

The ionizable ligand, EH2, is assigned to Glu270, since chemical modification of this residue with CMC (1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide) decreases the binding affinity of carboxypeptidase A for zinc and lead by more than 60- and 200-fold, respectively. A bridging interaction between the Glu270-coordinated zinc hydroxide is implicated by the ability of Zn and Pb to induce a marked increase in the visible absorption spectrum of the cobalt enzyme within 20 ms of mixing 10 " M Zn or Pb with 10 " M cobalt enzyme. 

Huang reported the unique rare earth complex containing two types of ionized ligands (Hsalen and salen) in 1990 [78]. Eu(Hsalen)(salen) H20 crystallizes in the monoclinic system with a space group P2 a with cell constants a =. 6441 (2) nm, b = 2.0599(3) nm, c=. 0719(2) nm. 

Kd is the dimerization constant of the iron(III) hydroxy-EDTA complex, and a is the relative coneentration of the fully ionized ligand of EDTA and ean be described... 

Table 1 Asymmetric reduction of some a-amino acid precursors 1 at 25 °C in the presence of rhodium complexes containing ionized ligands 3-5 and 7-9.

HOMO fields have been shown to be beneficial for the refinement of 3D-QSAR models for data sets such as the angiotensin converting enzyme (ACE) inhibitors. HOMO fields appear to describe the interaction between the ionized ligand and the metal ion in the molecular binding domain. More recently, molecular orbital fields have been used in the construction of 3D-QSAR models for molecular reactivity end points (e.g., metabolic rate constants). ... 

Step 1 CP2Z1CI2 is converted to the active catalyst by reaction with the promoter methylalumoxane (MAO). A methyl group from MAO displaces one of the chlorine ligands of Cp2ZrCl2. The second chlorine is lost as chloride by ionization, giving a positively charged metallocene. 

This type of isomerism occurs when isomers produce different ions in solution, and is possible in compounds which consists of a complex ion with a counter ion which is itself a potential ligand. The pairs [Co(NH3)5(N03)]S04, [Co(NH3)5(S04)]N03 and [PtCl2(NH3)4]Br2, [PtBr2(NH3)4]Cl2, and the series [CoCl(en)2-(N02)]SCN, [CoCl(en)2(SCN)]N02, [Co(en)2-(N02)(SCN)]C1 are examples of ionization isomers. 

Figure 1 shows the pH-rate profiles of some active complexes. Both Ni2 + and Zn2 + ion complexes of 8 afford saturation curves with inflection at around pH s 6 and 8, respectively, which represent, most likely, the ionization of the hydroxyl group complexed with a Ni2+ or a Zn2+ ion. The pKa = 8.6 was assigned for the ionization of the hydroxyl group of the latter complex 12). The lower pH for the ionization of the Ni2+ ion complex in respect to that of the Zn2+ ion complex indicates that the ligand 8 coordinates to Ni2+ ion more tightly than to Zn2+ ion, which is in conformity with a larger K value (1120 M) for the Ni2 + ion than for the Zn2 + ion complex (559 M) at pH 7.05 (Table 2). 

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