Copper axial coordination

The EPR spectra of phenol adsorbed on the encapsulated copper acetate in the presence of O2 clearly indicated the formation of an axially coordinated copper-phenol... 

Axial Coordination to Copper (II)—Peptide Complexes. Although inplane coordination dominates the thermodynamic, kinetic, and spectral properties of the Cu( II)-peptides, axial coordination also is important. While the carboxylate groups in Cu(H.3G4)2" and Cu(H 2GGhis)"... 

Intriguingly, the blue copper sites, especiaUy those with a carbonyl oxygen at the axial coordination position, display high affinity for Zn + ions. Mutants in which the Met is replaced by Gin or Glu preferentiaUy bind Zn + when expressed in heterologous systems, e.g., Escherichia coli. Examples include azurin, amicyanin, nitrite reductase, and possibly also plastocyanin (Diederix et al., 2000 Hibino et al., 1995 Murphy et al., 1995 Nar et al., 1992a Romero et al., 1993). In the case of azurin it has been shown that both wild-type and the Met—Gin mutant have the same affinity for both Zn +and Cu + (Romero ci a/., 1993). In addition, EXAFS studies showed that some preparations of blue copper proteins purihed from their natural sources also contain small fractions of Zn derivatives (DeBeer George, personal communication). 

Figure 7-67 shows the crystal structure of (C5H5)Fe[C5H4-CH2-NH-(CH2)2-NH-CH2-C5H4]Fe(C5H5) 2Cu(N03)2 [188]. Because of the axial coordination of the two nitrate anions, the central copper (n) ion assumes octahedral coordination. Both the ferrocenyl fragments are in a nearly eclipsed conformation. 

In the present study, we synthesized dibromo(l,4,8,ll-tetraazacyclotetradecane)copper(II) ([CuBr2(cyclam)]) and diaqua(l,4,8,ll-tetraazacyclotetradecane)copper(II) difluoride four hydrate ([Cu(cyclam)-(H20)2]F2 4H20) complexes and performed single crystal structure analysis and X-ray absorption near-edge structure (XANES) measurements in crystals and in aqueous solution. Furthermore, DV-Xa molecular orbital calculations have been made for models based on these results, and the structures and electronic states of the [Cu(cyclam)] complexes in crystals and in aqueous solution are discussed, in particular, on the axial coordination to Cu(II). 

Zr(IV), and Ce(IV) as the central metal ion. Copper(II) porphyrins are among the most studied of the paramagnetic metalloporphyrins. The Cu(II) complexes show a low-temperature luminescence that arises from the and states that exist in thermal equilibrium. These two states are derived from the lowest excited triplet state on the porphyrin ring, which is split because of the presence of a unpaired electron on the Cu(II) center. Transient absorption measurements show that the ambient temperature excited-state decay times are lowered when a ligand is associated with the axial coordination positions of the tetracoordinate Cu(Il) porphyrin complex. The excited state lifetimes of Cu(II) porphyrin complexes in solution can be either dependent or independent of the temperature and solvent. For the octaethylporphyrin complex Cu(OEP) the excited state lifetime increases as the temperature is lowered, and also as the solvent polarity is increased. By contrast, the excited state lifetime of the tetraphenylporphyrin Cu(TPP) is insensitive to both the temperature and the polarity of the solvent. This difference in their photophysical behavior is likely due to a difference in the energy gap between the charge transfer state and the T/ T states in the pair of complexes. 

Compound 11 forms a gel with cyclohexane at room temperature. From small-angle neutron scattering (SANS) measurements it was found that the molecules are stacked on top of each other linked by axial copper-oxygen coordination bonds. The stacks consist of a polar core (copper and oxygen) surrounded by a hydrophobic shell (aliphatic tails). These stacks in turn are part of the three dimensional network which forms the gel. 

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