4. Copper

Copper-Cystine Biohybrid-Embedded Nanofiber Aerogels Show Antibacterial and Angiogenic Properties

Copper-cystine-based high aspect ratio structures (CuHARS) possess exceptional physical and chemical properties and exhibit remarkable biodegradability in human physiological conditions. Extensive testing has confirmed the biocompatibility and biodegradability of CuHARS under diverse biological conditions, making them a viable source of essential Cu2+. These ions are vital for catalyzing the production of nitric oxide (NO) from the decomposition of S-nitrosothiols (RSNOs) found in human blood. The ability of CuHARS to act as a Cu2+ donor under specific concentrations has been demonstrated in this study, resulting in the generation of elevated levels of NO. Consequently, this dual function makes CuHARS effective as both a bactericidal agent and a promoter of angiogenesis. In vitro experiments have shown that CuHARS actively promotes the migration and formation of complete lumens by redirecting microvascular endothelial cells. To maximize the benefits of CuHARS, they have been incorporated into biomimetic electrospun poly(ε-caprolactone)/gelatin nanofiber aerogels. Through the regulated release of Cu2+ and NO production, these channeled aerogels not only provide antibacterial support but also promote angiogenesis. Taken together, the inclusion of CuHARS in biomimetic scaffolds could hold great promise in revolutionizing tissue regeneration and wound healing.

Classical hydrogen bonding and stacking of chelate rings in new copper(ii) complexes

Three new copper(ii) complexes, viz., [Cu(L)(NO₃)(H₂O)]H₂O 1, [Cu(L)(H₂O)₂]NO₃2 and [Cu₂(L)₂(pyrazine)](ClO₄)₂·4H₂O 3, were prepared using a biomimetic synthesis strategy [HL = 4-chloro-2-{(E)-[2-(pyridin-2-yl)hydrazinylidene]methyl}phenol]. In complex 3, stacking of chelates rings was observed.

Unprecedented copper(ii) mediated in situ formation of gem-diol binuclear complexes: a combined experimental and computational study

The two alkoxo bridged complexes [Cu₂(L¹)₂(HL²)₂(H₂O)](NO₃)₂·2H₂O 1 and [Cu₂(L¹)₂(HL²)₂](NO₃)₂·H₂O 2 have been synthesized by metal assisted hydrolysis with two Schiff bases, where L¹ is 2-benzoylpyridine and HL² is phenyl(pyridin-2-yl)methanediol.

Supramolecular Structure of N,N-Bis(2-hydroxybenzyl)alkylamine: Flexible Molecular Assembly Framework for Host without Guest and Host with Guest

N,N-Bis(2-hydroxybenzyl)alkylamine derivatives form a cage-like assembly consisting of two molecules via inter- and intramolecular hydrogen bonds. The derivatives exhibit themselves as host to accept copper-ion guests under the double-oxygen-bridged dimeric system. Quantum chemical calculation suggested that the host-guest interaction is based on a charge-transfer coordination. Comparison of the crystal structures before and after complexation clarifies a rare example of a host-guest compound where the hosts maintain their cage framework through the change of hydrogen bonds to coordination bonds.

Syntheses, structures, and properties of imidazolate-bridged Cu(II)-Cu(II) and Cu(II)-Zn(II) dinuclear complexes of a single macrocyclic ligand with two hydroxyethyl pendants

The imidazolate-bridged homodinuclear Cu(II)-Cu(II) complex, [(CuimCu)L]ClO(4).0.5H(2)O (1), and heterodinuclear Cu(II)-Zn(II) complex, [(CuimZnL(-)(2H))(CuimZnL(-)(H))](ClO(4))(3) (2), of a single macrocyclic ligand with two hydroxyethyl pendants, L (L = 3,6,9,16,19,22-hexaaza-6,19-bis(2-hydroxyethyl)tricyclo[22,2,2,2(11,14)]triaconta-1,11,13,24,27,29-hexaene), have been synthesized as possible models for copper-zinc superoxide dismutase (Cu(2),Zn(2)-SOD). Their crystal structures analyzed by X-ray diffraction methods have shown that the structures of the two complexes are markedly different. Complex 1 crystallizes in the orthorhombic system, containing an imidazolate-bridged dicopper(II) [Cu-im-Cu](3+) core, in which the two copper(II) ions are pentacoordinated by virtue of an N4O environment with a Cu.Cu distance of 5.999(2) A, adopting the geometry of distorted trigonal bipyramid and tetragonal pyramid, respectively. Complex 2 crystallizes in the triclinic system, containing two similar Cu-im-Zn cores in the asymmetric unit, in which both the Cu(II) and Zn(II) ions are pentacoordinated in a distorted trigonal bipyramid geometry, with the Cu.Zn distance of 5.950(1)/5.939(1) A, respectively. Interestingly, the macrocyclic ligand with two arms possesses a chairlike (anti) conformation in complex 1, but a boatlike (syn) conformation in complex 2. Magnetic measurements and ESR spectroscopy of complex 1 have revealed the presence of an antiferromagnetic exchange interaction between the two Cu(II) ions. The ESR spectrum of the Cu(II)-Zn(II) heterodinuclear complex 2 displayed a typical signal for mononuclear trigonal bipyramidal Cu(II) complexes. From pH-dependent ESR and electronic spectroscopic studies, the imidazolate bridges in the two complexes have been found to be stable over broad pH ranges. The cyclic voltammograms of the two complexes have been investigated. Both of the two complexes can catalyze the dismutation of superoxide and show rather high activity.

Crystallographic, Electrochemical, and Pulsed EPR Study of Copper(II) Polyimidazole Complexes Relevant to the Metal Sites of Copper Proteins(,)

Copper(II) complexes of the following polyimidazole ligands have been synthesized: bis(imidazol-2-yl)methane (BIM), bis(imidazol-2-yl) ketone (BIK), 4-(imidazol-4-ylmethyl)-2-(imidazol-2-ylmethyl)imidazole (TRIM), bis[4-(imidazol-4-ylmethyl)imidazol-2-yl]methane (TIM), and bis[4-(imidazol-4-ylmethyl)imidazol-2-yl] ketone (TIK). Their crystal structures have been determined using X-ray diffraction. [Cu(ClO(4))(2)(BIM)(2)], 1, belongs to the triclinic space group P&onemacr; system, a = 7.161(4) Å, b = 7.986(6) Å, c = 9.865(3) Å, alpha = 76.73(5) degrees, beta = 71.18(3) degrees, gamma = 76.44(5) degrees, Z = 1, T = 291 K; R = 0.035, R(w) = 0.036 for 1668 reflections; Cu-N = 1.998(3) and 2.001(2) Å, Cu-O = 2.574(4) Å, in a tetragonal geometry. [Cu(BIK)(2)](ClO(4))(2), 2, belongs to the monoclinic space group C2/c system, a = 9.029(3) Å, b = 12.497(2)Å, c = 19.197(2) Å, beta = 94.59(2) degrees, Z = 4, T = 291 K; R = 0.056, R(w) = 0.061 for 1052 reflections; Cu-N = 1.961(7) and 1.954(7) Å, in a distorted tetrahedral geometry. [CuCl(TRIM)(CH(3)OH)]Cl, 6, belongs to the monoclinic space group P2(1)/n system, a = 14.192(5) Å, b = 13.832(5) Å, c = 7.913(3) Å, beta = 90.55(4) degrees, Z = 4, T = 291 K; R = 0.062, R(w) = 0.057 for 1377 reflections; Cu-N = 1.987(7), 2.007(7) and 2.007(6) Å, Cu-O = 2.521(7) Å, Cu-Cl = 2.298(2) Å, in a square pyramidal geometry. [Cu(ClO(4))(TIM)](ClO(4)), 4, belongs to the triclinic space group P&onemacr; system, a = 9.604(4) Å, b = 11.508(6) Å, c = 12.003(8) Å, alpha = 58.79(4) degrees, beta = 94.59(2) degrees, gamma = 67.43(3) degrees, Z = 2, T = 291 K; R = 0.057, R(w) = 0.062 for 2084 reflections; Cu-N = 1.985(7), 1.964(7), 1.967(7), and 1.966(7) Å, Cu-O = 2.553(8) Å, in a distorted square pyramidal geometry. [CuCl(TIK)](ClO(4)), 7, belongs to the triclinic space group P&onemacr; system, a = 7.432(3) Å, b = 12.573(3) Å, c = 12.945(2) Å, alpha = 114.94(4) degrees, beta = 92.46(2) degrees, gamma = 103.49(3) degrees, Z = 2, T = 291 K; R = 0.043, R(w) = 0.049 for 2305 reflections; Cu-N = 1.984(5), 1.989(5), 2.012(5), and 1.979(5) Å, Cu-Cl = 2.796(2) Å, in a distorted bipyramidal geometry. In methanol solution, the perchlorato complexes 1, 2, Cu(TRIM)(ClO(4))(2) (3), 4, and Cu(TIK)(ClO(4))(2) (5) exhibited redox potentials from -215 to +284 mV vs NHE together with a visible absorption from 604 to 728 nm. Electron spin-echo envelope modulation (ESEEM) spectroscopy data, particularly the nuclear quadrupole interaction (NQI) parameters e(2)qQ and eta of the remote nitrogen (N1H), were analyzed and interpreted according to the model devised by Jiang et al. (J. Am. Chem. Soc. 1990, 112, 9035) with reference to Cu(HIm)(4)(ClO(4))(2). The results are the following: (i) C2 substitution of the imidazole ring, next to the remote nitrogen (1, 2) decreases the asymmetry parameter eta to ca. 0.75 compared to 1.00 for Cu(HIm)(4)(ClO(4))(2); this effect of C2 substitution on the symmetry of the electric field gradient at N1H appears similar for both the electron-donating methylene substituents (1) and the electron-withdrawing carbonyl group (2). (ii) The electron-donating or -withdrawing properties of the substituent are reflected by the variation of the e(2)qQ parameter, increasing from 1.43 to 1.75 MHz (1) or decreasing to 1.38 MHz (2), and by the nu(+) transition shifting toward higher frequencies from 1.49 to 1.65 MHz (1, 3, 4) or to lower frequencies to 1.29 MHz (2, 5). The use of the eta and nu(+) parameters to assign the Ndelta vs Nepsilon coordination of histidine to the metal and to detect modified histidine in copper-binding proteins is discussed.

Structures of the Copper(I) and Copper(II) Complexes of 2,9-Diphenyl-1,10-phenanthroline: Implications for Excited-State Structural Distortion

The syntheses, crystal structures, and electronic absorption spectra of the copper(I) and copper(II) complexes of 2,9-diphenyl-1,10-phenanthroline (dpp) are reported. The complex [Cu(dpp)(2)](PF(6)) (1) crystallizes in space group P2(1)/c with a = 11.081(4) Å, b = 25.491(8) Å, c = 14.263(5) Å, beta = 92.84(3) degrees, Z = 4, and V = 4024(2) Å(3). For 4813 unique data with F > 4.0sigma(F), R = 5.41% and R(w) = 6.43%. The coordination geometry about the copper(I) center in [Cu(dpp)(2)](+) is best described as distorted tetrahedral with approximate C(2) symmetry. The structure of [Cu(dpp)(2)](+) is largely determined by interligand pi-stacking interactions that occur between the phenyl groups of one ligand and the phenanthroline moiety of the other ligand. Solution-state absorption and (1)H NMR spectra indicate that the [Cu(dpp)(2)](+) complex is fluxional in solution, rocking between two enantiomeric structures of C(2) molecular symmetry through an intermediate of C(s)() symmetry. The complex [Cu(dpp)(2)](ClO(4))(2) (2) crystallizes in space group P&onemacr; with a = 7.809(3) Å, b = 13.027(6) Å, c = 20.344(10) Å, alpha = 87.68(4) degrees, beta = 89.16(4) degrees, gamma = 79.26(4) degrees, Z = 2, and V = 2032(1) Å(3). For 4943 unique data with F > 4.0sigma(F), R = 5.22% and R(w) = 5.37%. The coordination geometry about the copper(II) center in [Cu(dpp)(2)](2+) is best described as flattened tetrahedral with approximate D(2) symmetry. There are no interligand pi-stacking interactions in the structure of [Cu(dpp)(2)](2+). The four-coordinate geometry in [Cu(dpp)(2)](2+) persists in solution on the basis of solution-state and solid-state absorption spectroscopy. Structural distortion in the metal-to-ligand charge-transfer excited state of [Cu(dpp)(2)](+) is discussed on the basis of the structures of 1 and 2.

High Superoxide Dismutase Activity of a Novel, Intramolecularly Imidazolato-Bridged Asymmetric Dicopper(II) Species. Design, Synthesis, Structure, and Magnetism of Copper(II) Complexes with a Mixed Pyrazole-Imidazole Donor Set

A new dinucleating ligand, 1,5-bis(1-pyrazolyl)-3-[bis(2-imidazolyl)methyl] azapentane (Hbpzbiap), containing pyrazoles and imidazoles has been designed and synthesized. The synthesis and characterization of the copper complexes with the ligand Hbpzbiap and its dehydronated form are described. This study is aimed at modeling the active site of copper-zinc superoxide dismutase (SOD). Single crystals of the imidazolato-bridged complex [Cu(2)(bpzbiap)Cl(3)] (1) and non-imidazolato-bridged complex [Cu(2)(Hbpzbiap)Cl(4)] (2) were obtained and their structures determined by X-ray diffraction. Both structures show two copper centers in two different coordination environments: a distorted square pyramid and a distorted tetrahedron. The Cu-nitrogen bond lengths range from 1.919(4) to 2.039(3) Å and are as expected. The copper-copper distances from 5.566(1) to 6.104(1) Å being only slightly shorter than that found in bovine erythrocyte SOD. Temperature-dependent magnetic susceptibility study of 1 shows antiferromagnetic behavior with -2J = 96 cm(-)(1). From pH-dependent electron paramagnetic resonance and electronic spectra, [Cu(2)(bpzbiap)Cl(3)] has been demonstrated to be stable over a quite wide pH range including the physiological pH values. A low concentration of this complex (1) catalyzes the dismutation of superoxide at biological pH. Voltammetric studies indicate a quasi-reversible redox behavior in aqueous solution at pH 7. These results clearly indicate that complex 1 is a good model for superoxide dismutase.