Broadening the reactivity spectrum of a phthalocyanine catalyst while suppressing its nucleophilic, electrophilic and radical degradation pathways

A robust molecule that resists degradation via nucleophilic, electrophilic and radical attacks is described. Coordinated O(2) is reduced catalytically, producing efficiently thyil radicals in spite of the extreme electronic deficiency of the catalyst.     

Deuterium isotope effects on iron core formation in ferritin

We present comparative Mössbauer investigations of nanosized FeOOH and FeOOD biomineral phases nucleated within the 7-nm diameter cavity of horse-spleen apoferritin in order to assess deuterium isotopic effects on nanoscale, bioinorganic lattice structures with extended hydrogen bond networks. Differences in magnetic anisotropy energy, packing density and degree of crystallinity in the resulting iron oxo-hydroxide nanophases obtained via D₂O (heavy water) vs. H₂O (light water) solution chemistry are noted. These observations point to the possibility of stabilizing new thermodynamic states in the solid-state by utilizing isotope effects, with important implications for new synthetic pathways to novel nano materials.     

Spectroscopy and electronic structure of electron deficient zinc phthalocyanines

The effect of introduction of perfluoro alkyl groups into phthalocyanines, as evidenced by the spectroscopic properties of 1,4,8,11,15,18,22,25-octa-fluoro-2,3,9,10,16,17,23,24-octa-perfluoro isopropyl zinc phthalocyanine, ZnF(64)Pc(-2) and its ring-reduced radical anion species, [ZnF(64)Pc(-3)](-), are reported. A combination of UV-visible absorption and magnetic circular dichroism (MCD) spectroscopy, ESI and MALDI-TOF mass spectrometry, cyclic and differential pulse voltammetry, and complete theoretical calculations using INDO/S and DFT techniques reveals that the substitution of all sixteen hydrogen atoms in protio ZnPc(-2) by eight F and eight i-C(3)F(7) groups red shifts the Q and pi --> pi transitions and narrows the HOMO-LUMO gap while simultaneously preventing ring photooxidation and stabilizing the radical anion. The [ZnF(64)Pc(-3)](-) species, which is in equilibrium in solution with the neutral complex when a reducing agent is present, is unusually stable. The above effects are attributed to the strong electron withdrawing properties of the peripheral substituents, which render ZnF(64)Pc extremely electron deficient.     

Synthesis and characterization of fluorinated tris(pyrazolyl)borate complexes. Observation of an (eta 5-pyrazole)-K+ interaction in the solid state

Cyclopentadienyl (Cp) ligands have received considerable attention mainly because of their pi six-electron donation capability. Tris(pyrazolyl)borate ligands (Tp) are often compared with Cp because of their identical charge, number of donated electrons, and similar facial coordinating geometry. Their six-electron donation, however, is formally sigma-type. The X-ray structure of the [TpCF3,CH3CuK(mu 4-CO3)KTpCF3,CH3]2 aggregate, 1, reveals for the first time an unprecedented eta 5-TpCF3,CH3 potassium bonding interaction. 1 crystallizes in the triclinic space group P1 with a = 12.0411(2) A, b = 14.9791(2) A, c = 16.0567(3) A, alpha = 71.301(1) degrees, beta = 69.785(1) degrees, gamma = 66.539(1) degrees, and Z = 2. Both K-F and K-mu 4-CO3(2-) interactions stabilize the aggregate, as suggested by the lack of hexanuclear aggregation and K incorporation in the absence of fluorine groups or when O=CO2(2-) is replaced by CH3-CO2-. In the latter case we have isolated the complex [CuTpCF3,CH3(CH3CO2)], 2, which retains a Cu coordination sphere similar to that encountered in the TpCF3,CH3Cu subset of 1. The mononuclear complex 2 crystallizes in the monoclinic space group P2(1)/c with a = 14.1474(2) A, b = 14.1474(2) A, c = 19.0456(6) A, beta = 99.012(2) degrees, and Z = 4. The novel eta 5-coordination mode revealed in 1 suggests that Tp ligands might function not only as sigma donors but also as Cp-like pi donors. The eta 5-coordination mode might therefore constitute a new potential common denominator of these two important classes of ligands.     

Enhanced acidity, photophysical properties and liposome binding of perfluoroalkylated phthalocyanines lacking C-H bonds

The acid-base, spectroscopic, photophysical and liposome-binding properties of the recently synthesized free base, 29H,31H,1,4,8,11,15,18,22,25-octafluoro-2,3,9,10,16,17,23, 24-octakisperfluoro(isopropyl) phthalocyanine, F64PcH2, are reported. The perfluoroalkylation of the phthalocyanine core renders the hydrogen atoms acidic, with a pK(a) = 6. The F64Pc(-2) dianion is detected already at pH 3, by singular-value decomposition analysis of electronic spectra. F64Pc(-2) generates 1O2 with quantum yields phi(delta) = 0.252 (in MeOH) and 0.019 in liposomes. Metallation of the Pc macrocycle to yield F64PcZn increases phi(delta) to 0.606 and 0.126 in MeOH and liposomes, respectively. Surprisingly, F64Pc(-2) (but not F64PcH2 or F64PcZn) binds strongly to liposomes, with a binding constant K(b) = 25 (mg/mL)(-1). The fully protonated F64PcH2, but not the zwitterionic F64Pc(-2), might favor hydrogen bonding, thus reducing its lipophilicity. Similarly, the Lewis acidity of Zn in F64PcZn, and thus its ability to bind water within a hydrophobic perfluoroalkyl pocket, is significantly enhanced by the fluorinated substituents.