Stereoelectronic properties of metalloenzymes. 10. a refined model that mimics the type II copper(II) site in galactose oxidase22See Ref. [1] for a partial listing of other articles in this series.
“…On adding CN - to 2 , g ∥ decreases and A ∥ slightly increases with considerable overlapping of the parallel and perpendicular regions of the spectrum (Figure ). These spectral changes, which are in line with the above blue shift, are similar to those observed for certain tridentate bis(phenolate) copper(II) complexes of Bereman,5d but are in contrast to those for axial addition of CN - to [Cu(cyclops)] + . They are expected 5d of the replacement of the equatorial CH 3 COO - by the relatively strongly coordinating ligand like CN - to form a CuN 4 coordination plane.…”
Section: Resultssupporting
confidence: 83%
“…Further, the g ∥ / A ∥ quotient for CN - (120) and N 3 - (130) addition to 2 are similar to those for GOase:anion adducts and falls within the range (105−135 cm) expected for square planar structures, suggesting that the coordination sphere in the adducts is not distorted from square based geometry. Moreover, the results of anion binding studies of [Cu(bpnp)Cl] complex are relevant to the identification of an additional axial binding site in the enzyme. 5c,d Thus the electronic properties of Cu(II) both in the present models and in the active site of GOase is tuned by several factors such as nature of in-plane donor atoms and effective charge on the copper, equatorial, or axial ligation, etc. 5 EPR spectra of 2 (a) and its adducts with N 3 - (b) and CN - (c) in water/methanol (4:1 v/v) glass at 77 K.…”
Section: Resultsmentioning
confidence: 97%
“…On the other hand, both g ∥ and A ∥ values simultaneously decrease for N 3 - addition to 2 . The replacement of the weakly coordinated CH 3 COO - by N 3 - , which possesses diffusely distributed negative charge, leads to an increased delocalization of the unpaired spin density away from the copper nucleus, and hence an increased copper−ligand covalency. 5d,34a A similar decrease in g ∥ and A ∥ values has been observed 5d but for CN - addition to a model complex of Bereman, which has been also ascribed to a similar increase in covalency involving probably the deprotonated isoindoline ring in the complex. The present spectral changes for 2 blue shift and decrease in g ∥ are remarkably similar to those obtained for GOase enzyme on adding these ions.…”
Section: Resultsmentioning
confidence: 99%
“…To establish the structural and spectroscopic consequences of phenolate donors in this enzyme, we initiated a study of monomeric copper(II) complexes containing phenolate and imidazole donors as structural models toward GOase. Bereman et al have studied a number of copper(II) complexes of tridentate ligands with various donor atoms in an attempt to duplicate the unusual reactivity patterns and accompanying spectral changes of the copper(II) center in GOase upon anion binding. In fact one of these complexes 5d correctly predicted the active site structure of the enzyme even before its crystal structure was published.…”
The crystal structures of [Cu(bpnp)(SCN)].NH(4)SCN (1), [Cu(bpnp)(CH(3)COO)].CH(3)OH.C(8)H(10) (2), and [Cu(bpnp)ClO(4)] (3) [Hbpnp = 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol] reveal a distorted square pyramidal geometry around Cu(II) with an unusual axial coordination of phenolate. The mononuclear complex [Cu(bpnp)(SCN)].NH(4)SCN crystallizes in the triclinic space group P&onemacr; with a = 10.796(2) Å, b = 10.804(2) Å, c = 12.559(2) Å, alpha = 71.38(1) degrees, beta = 72.68(1) degrees, gamma = 61.69(1) degrees, and Z = 2. The mononuclear acetate [Cu(bpnp)(CH(3)COO)].CH(3)OH.C(8)H(10) crystallizes in the triclinic space group P&onemacr; with a = 10.480(6) Å, b = 12.116(4) Å, c = 12.547(3) Å, alpha = 98.77(3) degrees, beta = 113.37(3) degrees, gamma = 100.78(3) degrees, and Z = 2. The binuclear perchlorate complex crystallizes in the monoclinic space group C2/c with a = 13.417(3) Å, b = 20.095(2) Å, c= 16.401(2) Å, alpha = 102.21(2) degrees, and Z = 8. The coordination plane in all these complexes is comprised of the tertiary amine and two pyridine nitrogens. The fourth equatorial position is occupied by SCN(-)/CH(3)COO(-) in the mononuclear complexes but by the coordinated phenolate ion from the adjacent molecule in the perchlorate complex, resulting in its dimerization. The unusual occupation of phenolate ion in the axial site is possibly due to the steric constraint at copper imposed by the 5,5,6-chelate ring sequence. The thiocyanate/acetate coordination geometry is reminiscent of the active site of the radical copper enzyme galactose oxidase (GOase) with an axial phenolate and equatorial SCN(-)/CH(3)COO(-) ligands. Further, the present complexes exhibit several spectral features also similar to this enzyme. The addition of chloride or thiocyanate or acetate ions dissociates the dimeric structure of the perchlorate complex to produce the corresponding monomeric derivatives. The study of the interaction of the acetate complex with N(3)(-) and CN(-) ions provide insight into the anion binding properties of the enzyme. The sensitivity of the acetate complex to protons suggests the facile dissociation of the axial phenolate which then acts as a base to bind to protons. The implication of this reaction to the GOase mechanism is discussed.
“…On adding CN - to 2 , g ∥ decreases and A ∥ slightly increases with considerable overlapping of the parallel and perpendicular regions of the spectrum (Figure ). These spectral changes, which are in line with the above blue shift, are similar to those observed for certain tridentate bis(phenolate) copper(II) complexes of Bereman,5d but are in contrast to those for axial addition of CN - to [Cu(cyclops)] + . They are expected 5d of the replacement of the equatorial CH 3 COO - by the relatively strongly coordinating ligand like CN - to form a CuN 4 coordination plane.…”
Section: Resultssupporting
confidence: 83%
“…Further, the g ∥ / A ∥ quotient for CN - (120) and N 3 - (130) addition to 2 are similar to those for GOase:anion adducts and falls within the range (105−135 cm) expected for square planar structures, suggesting that the coordination sphere in the adducts is not distorted from square based geometry. Moreover, the results of anion binding studies of [Cu(bpnp)Cl] complex are relevant to the identification of an additional axial binding site in the enzyme. 5c,d Thus the electronic properties of Cu(II) both in the present models and in the active site of GOase is tuned by several factors such as nature of in-plane donor atoms and effective charge on the copper, equatorial, or axial ligation, etc. 5 EPR spectra of 2 (a) and its adducts with N 3 - (b) and CN - (c) in water/methanol (4:1 v/v) glass at 77 K.…”
Section: Resultsmentioning
confidence: 97%
“…On the other hand, both g ∥ and A ∥ values simultaneously decrease for N 3 - addition to 2 . The replacement of the weakly coordinated CH 3 COO - by N 3 - , which possesses diffusely distributed negative charge, leads to an increased delocalization of the unpaired spin density away from the copper nucleus, and hence an increased copper−ligand covalency. 5d,34a A similar decrease in g ∥ and A ∥ values has been observed 5d but for CN - addition to a model complex of Bereman, which has been also ascribed to a similar increase in covalency involving probably the deprotonated isoindoline ring in the complex. The present spectral changes for 2 blue shift and decrease in g ∥ are remarkably similar to those obtained for GOase enzyme on adding these ions.…”
Section: Resultsmentioning
confidence: 99%
“…To establish the structural and spectroscopic consequences of phenolate donors in this enzyme, we initiated a study of monomeric copper(II) complexes containing phenolate and imidazole donors as structural models toward GOase. Bereman et al have studied a number of copper(II) complexes of tridentate ligands with various donor atoms in an attempt to duplicate the unusual reactivity patterns and accompanying spectral changes of the copper(II) center in GOase upon anion binding. In fact one of these complexes 5d correctly predicted the active site structure of the enzyme even before its crystal structure was published.…”
The crystal structures of [Cu(bpnp)(SCN)].NH(4)SCN (1), [Cu(bpnp)(CH(3)COO)].CH(3)OH.C(8)H(10) (2), and [Cu(bpnp)ClO(4)] (3) [Hbpnp = 2-(bis(pyrid-2-ylmethyl)aminomethyl)-4-nitrophenol] reveal a distorted square pyramidal geometry around Cu(II) with an unusual axial coordination of phenolate. The mononuclear complex [Cu(bpnp)(SCN)].NH(4)SCN crystallizes in the triclinic space group P&onemacr; with a = 10.796(2) Å, b = 10.804(2) Å, c = 12.559(2) Å, alpha = 71.38(1) degrees, beta = 72.68(1) degrees, gamma = 61.69(1) degrees, and Z = 2. The mononuclear acetate [Cu(bpnp)(CH(3)COO)].CH(3)OH.C(8)H(10) crystallizes in the triclinic space group P&onemacr; with a = 10.480(6) Å, b = 12.116(4) Å, c = 12.547(3) Å, alpha = 98.77(3) degrees, beta = 113.37(3) degrees, gamma = 100.78(3) degrees, and Z = 2. The binuclear perchlorate complex crystallizes in the monoclinic space group C2/c with a = 13.417(3) Å, b = 20.095(2) Å, c= 16.401(2) Å, alpha = 102.21(2) degrees, and Z = 8. The coordination plane in all these complexes is comprised of the tertiary amine and two pyridine nitrogens. The fourth equatorial position is occupied by SCN(-)/CH(3)COO(-) in the mononuclear complexes but by the coordinated phenolate ion from the adjacent molecule in the perchlorate complex, resulting in its dimerization. The unusual occupation of phenolate ion in the axial site is possibly due to the steric constraint at copper imposed by the 5,5,6-chelate ring sequence. The thiocyanate/acetate coordination geometry is reminiscent of the active site of the radical copper enzyme galactose oxidase (GOase) with an axial phenolate and equatorial SCN(-)/CH(3)COO(-) ligands. Further, the present complexes exhibit several spectral features also similar to this enzyme. The addition of chloride or thiocyanate or acetate ions dissociates the dimeric structure of the perchlorate complex to produce the corresponding monomeric derivatives. The study of the interaction of the acetate complex with N(3)(-) and CN(-) ions provide insight into the anion binding properties of the enzyme. The sensitivity of the acetate complex to protons suggests the facile dissociation of the axial phenolate which then acts as a base to bind to protons. The implication of this reaction to the GOase mechanism is discussed.
“…While only one complex of Zn(II) with isoindolines had been previously synthesized, a number of Cu(II) isoindoline complexes have been reported. Of the latter all but Cu(4‘-MeL) 2 contain ancillary anionic ligands, for example, hydroxide, carbonate, and acetate, , and exist in a variety of geometries including square planar, square pyramidal, and trigonal bipyramidal. All, however, exist with significant distortions from ideal geometry, and only one, [{Cu(4‘-MeL)} 3 {Cu(4‘-MeL)O}(μ-OH) 3 ], contains a Cu(II) center comparable in structure to that of 2 .…”
Deprotonation of the tridentate isoindoline ligand 1,3-bis[2-(4-methylpyridyl)imino]-isoindoline, 4'-MeLH, and reaction with hydrated zinc(II) perchlorate produces an unexpected trinuclear Zn(II) complex, [Zn(3)(4'-MeL)(4)](ClO(4))(2).5H(2)O (1), whereas reaction with hydrated copper(II) perchlorate in methanol produces the expected mononuclear product, [Cu(4'-MeL)(H(2)O)(2)]ClO(4) (2). X-ray diffraction shows that the trinuclear Zn(II) complex (1) contains a linear zinc backbone, and the arrangement of ligands about the outer chiral zinc(II) atoms is helical. The two terminal zinc ions exhibit approximate C(2) site symmetry, with tetrahedral coordination by two pyrrole and two pyridyl nitrogen atoms of the potentially tridentate isoindoline ligands. The central zinc ion exhibits approximate tetrahedral symmetry, with coordination by four pyridyl nitrogen atoms of four different isoindoline ligands. Pyridyl-pyrrole intramolecular pi-stacking interactions contribute to the stability of the trinuclear cation. The structure of the mononuclear copper(II) complex cation in 2 is best described as a distorted trigonal bipyramid. The isoindoline anion binds Cu(II) in both axial positions and one of the equatorial positions; water molecules occupy the other two equatorial positions.
The copper complexes [Cu(4-MeBPI)(OAc)] (4), [Cu(4-Me-10-tBuBPI)(OAc)] (5) and [Cu(BTI)(OAc)] (6) [BPI = 1,3-bis(2-pyridylimino)isoindole, BTI = 1,3-bis(2-thiazolylimino)isoindole] were prepared by reaction of the protio ligands with copper(II) acetate. Compounds 4 and 6 were characterized by X-ray diffraction, establishing distorted square-planar coordination geometries of the copper ions. Two monoclinic modifications of 6 (6a and 6b) were found, both crystallizing in the space group P2 1 /c, but possessing different cell parameters. In contrast to 6a, which is monomeric in the crystal, the second monoclinic modification 6b has a more complicated crystal structure, which is composed of both monomeric complex units such as those found in 6a and infinite chains
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