Resonance raman investigation of equatorial ligand donor effects on the Cu(2)O(2)(2+) core in end-on and side-on mu-peroxo-dicopper(II) and bis-mu-oxo-dicopper(III) complexes

The effect of endogenous donor strength on Cu(2)O(2) bonds was studied by electronically perturbing [[(R-TMPA)Cu(II)]](2)(O(2))](2+) and [[(R-MePY2)Cu](2)(O(2))](2+) (R = H, MeO, Me(2)N), which form the end-on mu-1,2 bound peroxide and an equilibrium mixture of side-on peroxo-dicopper(II) and bis-mu-oxo-dicopper(III) isomers, respectively. For [[(R-TMPA)Cu(II)](2)(O(2))](2+), nu(O-O) shifts from 827 to 822 to 812 cm(-1) and nu(Cu)(-)(O(sym)) shifts from 561 to 557 to 551 cm(-1), respectively, as R- varies from H to MeO to Me(2)N. Thus, increasing the N-donor strength to the copper decreases peroxide pi(sigma) donation to the copper, weakening the Cu-O and O-O bonds. A decrease in nu(Cu-O) of the bis-mu-oxo-dicopper(III) complex was also observed with increasing N-donor strength for the R-MePY2 ligand system. However, no change was observed for nu(O-O) of the side-on peroxo. This is attributed to a reduced charge donation from the peroxide pi(sigma) orbital with increased N-donor strength, which increases the negative charge on the peroxide and adversely affects the back-bonding from the Cu to the peroxide sigma orbital. However, an increase in the bis-mu-oxo-dicopper(III) isomer relative to side-on peroxo-dicopper(II) species is observed for R-MePY2 with R = H < MeO < Me(2)N. This effect is attributed to the thermodynamic stabilization of the bis-mu-oxo-dicopper(III) isomer relative to the side-on peroxo-dicopper(II) isomer by strong donor ligands. Thus, the side-on peroxo-dicopper(II)/bis-mu-oxo-dicopper(III) equilibrium can be controlled by electronic as well as steric effects.     

Geometric and electronic structure of the heme-peroxo-copper complex [(F8TPP)FeIII-(O22-)-CuII(TMPA)](ClO4)

The geometric and electronic structure of the untethered heme-peroxo-copper model complex [(F(8)TPP)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](ClO(4)) (1) has been investigated using Cu and Fe K-edge EXAFS spectroscopy and density functional theory calculations in order to describe its geometric and electronic structure. The Fe and Cu K-edge EXAFS data were fit with a Cu...Fe distance of approximately 3.72 A. Spin-unrestricted DFT calculations for the S(T) = 2 spin state were performed on [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](+) as a model of 1. The peroxo unit is bound end-on to the copper, and side-on to the high-spin iron, for an overall mu-eta(1):eta(2) coordination mode. The calculated Cu...Fe distance is approximately 0.3 A longer than that observed experimentally. Reoptimization of [(P)Fe(III)-(O(2)(2)(-))-Cu(II)(TMPA)](+) with a 3.7 A Cu...Fe constrained distance results in a similar energy and structure that retains the overall mu-eta(1):eta(2)-peroxo coordination mode. The primary bonding interaction between the copper and the peroxide involves electron donation into the half-occupied Cu d(z)2 orbital from the peroxide pi(sigma) orbital. In the case of the Fe(III)-peroxide eta(2) bond, the two major components arise from the donor interactions of the peroxide pi*(sigma) and pi*(v) orbitals with the Fe d(xz) and d(xy) orbitals, which give rise to sigma and delta bonds, respectively. The pi*(sigma) interaction with both the half-occupied d(z)2 orbital on the copper (eta(1)) and the d(xz) orbital on the iron (eta(2)), provides an effective superexchange pathway for strong antiferromagnetic coupling between the metal centers.     

Spectroscopy and bonding in side-on and end-on Cu2(S2) cores: comparison to peroxide analogues

Spectroscopic methods combined with density functional calculations were used to study the disulfide-Cu(II) bonding interactions in the side-on micro -eta(2):eta(2)-bridged Cu(2)(S(2)) complex, [[Cu(II)[HB(3,5-Pr(i)(2)pz)(3)]](2)(S(2))], and the end-on trans- micro -1,2-bridged Cu(2)(S(2)) complex, [[Cu(II)(TMPA)](2)(S(2))](2+), in correlation to their peroxide structural analogues. Resonance Raman shows weaker S-S bonds and stronger Cu-S bonds in the disulfide complexes relative to the O-O and Cu-O bonds in the peroxide analogues. The weaker S-S bonds come from the more limited interaction between the S 3p orbitals relative to that of the O 2s/p hybrid orbitals. The stronger Cu-S bonds result from the more covalent Cu-disulfide interactions relative to the Cu-peroxide interactions. This is consistent with the higher energy of the disulfide valence level relative to that of the peroxide. The ground states of the side-on Cu(2)(S(2))/Cu(2)(O(2)) complexes are more covalent than those of the end-on Cu(2)(S(2))/Cu(2)(O(2)) complexes. This derives from the larger sigma-donor interactions in the side-on micro -eta(2):eta(2) structure, which has four Cu-disulfide/peroxide bonds, relative to the end-on trans- micro -1,2 structure, which forms two bonds to the Cu. The larger disulfide/peroxide sigma-donor interactions in the side-on complexes are reflected in their more intense higher energy disulfide/peroxide to Cu charge transfer transitions in the absorption spectra. The large ground-state covalencies of the side-on complexes result in significant nuclear distortions in the ligand-to-metal charge transfer excited states, which give rise to the strong resonance Raman enhancements of the metal-ligand and intraligand vibrations. Particularly, the large covalency of the Cu-disulfide interaction in the side-on Cu(2)(S(2)) complex leads to a different rR enhancement profile, relative to the peroxide analogues, reflecting a S-S bond distortion in the opposite directions in the disulfide/peroxide pi(sigma) to Cu charge transfer excited states. A ligand sigma back-bonding interaction exists only in the side-on complexes, and there is more sigma mixing in the side-on Cu(2)(S(2)) complex than in the side-on Cu(2)(O(2)) complex. This sigma back-bonding is shown to significantly weaken the S-S/O-O bond relative to that of the analogous end-on complex, leading to the low nu(S)(-)(S)/nu(O)(-)(O) vibrational frequencies observed in the resonance Raman spectra of the side-on complexes.     

Triterpene glycosides of Gypsophila patrinii II. The structure of philoside A

Summary From the roots ofGypsophila patrinii two high-molecular-weight triterpene glycosides have been isolated — philosides A and B. The structure of philoside A has been established; it is a gypsogenin nonaoside.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Branch, Academy of Sciences of the USSR. Correspondence Institute of Soviet Commerce. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 598–603, September–October, 1974.     

Low-temperature UV-visible and NMR spectroscopic investigations of O(2) binding to ((6)L)Fe(II), a ferrous heme bearing covalently tethered axial pyridine ligands

In this report, we describe the reversible dioxygen reactivity of ((6)L)Fe(II) (1) [(6)L = partially fluorinated tetraphenylporphyrin with covalently appended TMPA moiety; TMPA = tris(2-pyridylmethyl)amine] using a combination of low-temperature UV-vis and multinuclear ((1)H and (2)H) NMR spectroscopies. Complex 1, or its pyrrole-deuterated analogue ((6)L-d(8))Fe(II) (1-d(8)), exhibits downfield shifted pyrrole resonances (delta 28-60 ppm) in all solvents utilized [CH(2)Cl(2), (CH(3))(2)C(O), CH(3)CN, THF], indicative of a five-coordinate high-spin ferrous heme, even when there is no exogenous axial solvent ligand present (i.e., in methylene chloride). Furthermore, ((6)L)Fe(II) (1) exhibits non-pyrrolic upfield and downfield shifted peaks in CH(2)Cl(2), (CH(3))(2)C(O), and CH(3)CN solvents, which we ascribed to resonances arising from the intra- or intermolecular binding of a TMPA-pyridyl arm to the ferrous heme. Upon exposure to dioxygen at 193 K in methylene chloride, ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 433 (Soret), 529 (sh), 559 nm] reversibly forms a dioxygen adduct [UV-vis: lambda(max) = 422 (Soret), 542 nm], formulated as the six-coordinate low-spin [delta(pyrrole) 9.3 ppm, 193 K] heme-superoxo complex ((6)L)Fe(III)-(O(2)(-)) (2). The coordination of the tethered pyridyl arm to the heme-superoxo complex as axial base ligand is suggested. In coordinating solvents such as THF, reversible oxygenation (193 K) of ((6)L)Fe(II) (1) [UV-vis: lambda(max) = 424 (Soret), 542 nm] also occurs to give a similar adduct ((6)L)Fe(III)-(O(2)(-)) (2) [UV-vis: lambda(max) = 418 (Soret), 537 nm. (2)H NMR: delta(pyrrole) 8.9 ppm, 193 K]. Here, we are unable to distinguish between a bound solvent ligand or tethered pyridyl arm as axial base ligand. In all solvents, the dioxygen adducts decompose (thermally) to the ferric-hydroxy complex ((6)L)Fe(III)-OH (3) [UV-vis: lambda(max) = 412-414 (Soret), 566-575 nm; approximately delta(pyrrole) 120 ppm at 193 K]. This study on the O(2)-binding chemistry of the heme-only homonuclear ((6)L)Fe(II) (1) system lays the foundation for a more complete understanding of the dioxygen reactivity of heterobinuclear heme-Cu complexes, such as [((6)L)Fe(II)Cu(I)](+), which are models for cytochrome c oxidase.     

Synthesis and spectroscopy of micro-oxo (O(2)(-))-bridged heme/non-heme diiron complexes: models for the active site of nitric oxide reductase

In this paper, we describe the synthesis and study of a series of heme/non-heme Fe-O-Fe' complexes supported by a porphyrin and the tripodal nitrogen ligand TMPA [TMPA = tris(2-pyridylmethyl)amine]. The complete synthesis of [((6)L)Fe-O-Fe(X)](+) (1) (X = OMe(-) or Cl(-), 69:31 ratio), where (6)L is the dianion of 5-(o-O-[(N,N-bis(2-pyridylmethyl)-2-(6-methoxyl)pyridinemethanamine)phenyl]-10,15,20-tris(2,6-difluorophenyl)porphine, is reported. The crystal structure for 1.PF(6) reveals an intramolecular heme/non-heme diferric complex bridged by an Fe-O-Fe' moiety; 90 degree angle (Fe-O-Fe') = 166.7(3) degrees, and d(Fe.Fe') = 3.556 A. Crystal data for C(70)H(57)ClF(12)Fe(2)N(8)O(3)P (1.PF(6)): triclinic, Ponemacr;, a = 13.185(3) A, b = 14.590 (3) A, c = 16.885(4) A, alpha = 104.219(4) degrees, beta = 91.572(4) degrees, gamma = 107.907(4) degrees, V = 2977.3(11) A(3), Z = 2, T = 150(2) K. Complex 1 (where X = Cl(-)) is further characterized by UV-vis (lambda(max) = 328, 416 (Soret), 569 nm), (1)H NMR (delta 27-24 [TMPA -CH(2)-], 16.1 [pyrrole-H], 15.2-10.5 [PY-3H, PY-5H], 7.9-7.2 [m- and p-phenyl-H], 6.9-5.8 [PY-4H] ppm), resonance Raman (nu(as)(Fe-O-Fe') 844 cm(-)(1)), and M?ssbauer (delta(Fe) = 0.47, 0.41 mm/s; deltaE(A) = 1.59, 0.55 mm/s; 80 K) spectroscopies, MALDI-TOF mass spectrometry (m/z 1202), and SQUID susceptometry (J = - 114.82 cm(-)(1), S = 0). We have also synthesized a series of 3-, 4-, and 5-methyl-substituted as well as selectively deuterated TMPA(Fe') complexes and condensed these with the hydroxo complex (F(8))FeOH or (F(8)-d(8))FeOH to yield "untethered" Fe-O-Fe' analogues. Along with selective deuteration of the methylene hydrogens in TMPA, complete (1)H NMR spectroscopic assignments for 1 have been accomplished. The magnetic properties of several of the untethered complexes and a comparison to those of 1 are also presented. Complex 1 and related species represent good structural and spectroscopic models for the heme/non-heme diiron active site in the enzyme nitric oxide reductase.     

Efficient and specific strand scission of DNA by a dinuclear copper complex: comparative reactivity of complexes with linked tris(2-pyridylmethyl)amine moieties

The compound [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) (D(1) = dinucleating ligand with two tris(2-pyridylmethyl)amine units covalently linked in their 5-pyridyl positions by a -CH(2)CH(2)- bridge) selectively promotes cleavage of DNA on oligonucleotide strands that extend from the 3' side of frayed duplex structures at a site two residues displaced from the junction. The minimal requirements for reaction include a guanine in the n (i.e. first unpaired) position of the 3' overhang adjacent to the cleavage site and an adenine in the n position on the 5' overhang. Recognition and strand scission are independent of the nucleobase at the cleavage site. The necessary presence of both a reductant and dioxygen indicates that the intermediate responsible for cleavage is produced by the activation of dioxygen by a copper(I) form of the dinuclear complex. The lack of sensitivity to radical quenching agents and the high level of site selectivity in scission suggest a mechanism that does not involve a diffusible radical species. The multiple metal center exhibits a synergy to promote efficient cleavage as compared to the action of a mononuclear analogue [Cu(II)(TMPA)(H(2)O)](ClO(4))(2) (TMPA = tris(2-pyridylmethyl)amine) and [Cu(OP)(2)](2+) (OP = 1,10-phenanthroline) at equivalent copper ion concentrations. The dinuclear complex, [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4), is even capable of mediating efficient specific strand scission at concentrations where [Cu(OP)(2)](2+) does not detectably modify DNA. The unique coordination and reactivity properties of [Cu(II)(2)(D(1))(H(2)O)(2)](ClO(4))(4) are critical for its efficiency and site selectivity since an analogue, [Cu(II)(2)(DO)(Cl(2))](ClO(4))(2), where DO is a dinucleating ligand very similar to D(1), but with a -CH(2)OCH(2)- bridge, exhibits only nonselective cleavage of DNA. The differences in the reactivity of these two complexes with DNA and their previously established interaction with dioxygen suggest that specific strand scission is a function of the orientation of a reactive intermediate.     

Solvent effects on the conversion of dicopper(II) micro-eta(2):eta(2)-peroxo to bis-micro-oxo dicopper(III) complexes: direct probing of the solvent interaction

A new tridentate ligand, PYAN, is employed to investigate solvent influences for dioxygen reactivity with [Cu(PYAN)(MeCN)]B(C(6)F(5))(4) (1). Stopped-flow kinetic studies confirm that the adducts [[u(II)(PYAN)]2)(O(2))][B(C(6)F(5))(4)](2) (2(Peroxo)) and [[u(III)(PYAN)]2)(O)(2)][B(C(6)F(5))(4)](2) (2(Oxo)) are in rapid equilibrium. Thermodynamic parameters for the equilibrium between 2(Peroxo) and 2(Oxo) re as follows: THF, deltaH degrees approximately -15.7 kJ/mol, deltaS degrees approximately -83 J/K.mol; acetone, deltaH degrees approximately -15.8 kJ/mol, deltaS degrees approximately -76 J/K.mol. UV-visible absorption and resonance Raman spectroscopic signatures demonstrate that the equilibrium is highly solvent dependent; the mixture is mostly 2(Peroxo) in CH(2)Cl(2), but there are significantly increasing quantities of 2(Oxo) along the series methylene chloride --> diethyl ether --> acetone --> tetrahydrofuran (THF). Copper(II)-N(eq) stretches (239, 243, 244, and 246 cm(-)(1) in CH(2)Cl(2), Et(2)O, acetone, and THF, respectively) are identified for 2(Peroxo), but they are not seen in 2(Oxo), revealing for the first time direct evidence for solvent coordination in the more open 2(Peroxo) structure.     

Triterpene glycosides ofPatrinia intermedia

Conclusions It has been established that patrinoside C₁ is -D-xylopyranosido(1 2)--D-glucofuranosido(1 3)--L-rhamnopyranosido(1 3)oleanolic acid.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 1, pp. 22–26, 1969