Spectro-electrochemistry of cobalt and iron tetrasulphonated phthalocyanines

Generation of high-spin iron(I) in a protein environment using cryoreduction

High-spin Fe(1+) sites are potentially important in iron-sulfur proteins but are rare in synthetic compounds and unknown in metalloproteins. Here, we demonstrate a spectroscopically characterized example of high-spin non-heme Fe(1+) in a protein environment. Cryoreduction of Fe(2+)-substituted azurin at 77 K with (60)Co γ radiation generates a new species with a S = (3)/2 (high-spin) Fe(1+) center having D > 0 and E/D ~ 0.25. This transient species is stable in a glycerol-water glass only up to ~170 K. A combination of electron paramagnetic resonance and Mössbauer spectroscopies provides a powerful means of identifying a transient high-spin Fe(1+) site in a protein scaffold.

Synthesis of tetra(tricarbethoxy)- and tetra(dicarboxy)- substituted soluble phthalocyanines

Pd (II), Co (II), Cu (II) and Zn (II) phthalocyanines with a tricarbethoxyethyl substituent on each benzo group were prepared from 4-(1,1,2-tricarbethoxyethyl)-phthalonitrile and the corresponding divalent metal salt at 170°C. Transesterification occurred when the reaction was carried out in pentanol. Treatment of the palladium complex with sodium ethoxide at room temperature and further acidification resulted with tetra(1,2-dicarboxyethyl)phthalocyaninatopal-ladium. Its UV-vis spectrum in aqueous solution indicated dimeric and monomeric species at pH ≈ 12, but at pH ≈ 6 only the dimeric form were present.

A novel route to 4-chloro-5-alkyl-phthalonitrile and phthalocyanines derived from it

A new route to the synthesis of 4-chloro-5-alkyl-phthalonitrile derivatives was shown by the displacement reaction of 4,5-dichloro-phthalonitrile and diethylmalonate, a CH -acidic precursor, in the presence of K 2 CO 3. Cyclotetramerization of 1-chloro-3,4-dicyano-6-(1,1-dicarbethoxy-methyl)benzene and the metal salt without any solvent gave the corresponding metallophthalocyanines ( M = Co , Cu or Pd ). Transesterification occurred when the reaction was carried out in hexanol in the presence of DBU to obtain the metal-free derivative. Treatment of 1-chloro-3,4-dicyano-6-(1,1-dicarbethoxy-methyl)benzene with sodium ethoxide at ambient temperature and further acidification resulted in 2,9,16,23-tetra(carboxymethyl)-3,10,17,24-tetrachloro-phthalocyaninatopalladium(II) with partial decarboxylation. Its electronic spectrum in aqueous solution indicated no appreciable change over a pH range from 7 to 12.

A computational analysis of electromerism in hemoprotein Fe(I) models

The electronic structures of formally Fe(I) centers in thiolate- and imidazole-ligated hemoproteins are examined with density functional theory. The S = 1/2 spin state of the imidazole-ligated model apparently features a net total of one unpaired electron on the porphyrin, suggestive of a macrocycle-centered reductive process; however, this spin density originates from two different orbitals, each carrying 0.5 spin units on the porphyrin. Under these conditions, the system may be described as S = 3/2 Fe(I) (d(xy)(2)d(xz)(1)d(yz)(1)dz2(1)) antiferromagnetically coupled to a porphyrin triplet state; nevertheless, there is still the caveat that the iron d (xz) and d (yz) orbitals are strongly mixed with porphyrin orbitals, to such an extent that they each harbor 0.5 spin units and hence an alternative description as Fe(II) or Fe(III) cannot be ruled out. Electromerism phenomena are described in the formally Fe(I) systems examined here, with electronic structures varying between Fe(II) and Fe(III) in various spin states, coupled either ferro- or antiferromagnetically to porphyrin radicals. The main factors controlling this electromerism appear to be the identity of the axial ligand, the iron-axial ligand bond length, and the overall spin state; heme deformations, ligand charge, or medium polarity do not appear to qualitatively affect the electronic structures of these systems.

'Super-reduced' iron under physiologically-relevant conditions

EPR spectroscopy is employed to demonstrate chemical production of formally Fe(i) and Fe(0) states of phthalocyanines in water at room temperature, and physiologically-relevant pH.

Physicochemical Properties and Sensing Ability of Metallophthalocyanines/Chitosan Nanocomposites

Electroactive nanostructured films of chitosan (Ch) and tetrasulfonated metallophthalocyanines containing nickel (NiTsPc), copper (CuTsPc), and iron (FeTsPc) were produced via the electrostatic layer-by-layer (LbL) technique. The multilayer formation was monitored with UV-vis spectroscopy by measuring the increase of the Q-band absorption from metallophthalocyanines. Results from transmission and reflection infrared spectroscopy suggested specific interactions between SO(3)(-) groups from metallophthalocyanines and NH(3)(+) from chitosan. The electroactive multilayered films assembled onto an ITO electrode were characterized by cyclic voltammetry, with Ch/NiTsPc films showing higher stability and well-defined voltammograms displaying reversible redox peaks at 0.80 and 0.75 V. These films could be used to detect dopamine (DA) in the concentration range from 5.0 x 10(-6) to 1.5 x 10(-4) mol L(-1). Also, ITO-(Ch/NiTsPc)(n)() electrodes showed higher electrocatalytic activity for DA oxidation when compared with a bare ITO electrode. On the other hand, only the Ch/FeTsPc and Ch/CuTsPc modified electrodes could distinguish between DA and ascorbic acid. These results demonstrate that versatile electrodes can be prepared by incorporation of different metallophthalocyanine molecules in LbL films, which may be used in bioanalytical applications.

Synthesis, Spectroscopy, and Electrochemistry of Tetra-tert-butylated Tetraazaporphyrins, Phthalocyanines, Naphthalocyanines, and Anthracocyanines, together with Molecular Orbital Calculations

Tetraazaporphyrins (TAPs), phthalocyanines (Pcs), naphthalocyanines (Ncs), and anthracocyanines (Acs) with four tert-butyl groups attached at similar positions have been synthesized, and their electronic absorption, magnetic circular dichroism (MCD), IR, and voltammetric properties were studied and interpreted with the help of quantum-mechanical calculations. Through the preparation of a series of compounds with the same number of the same substituent, the effects of the increase in the size of the ring system were clearly derived. The main results may be summarized as follows. 1) The Q band shifts to longer wavelength and its intensity increases, but with decreasing degree of change with increasing molecular size. If the size of the effect of benzene directly fused to the TAP skeleton is set at unity, the effects of the second and third benzene units are roughly 0.8 and 0.5, respectively. 2) The splitting of the Q bands in metal-free compounds decreases with increasing molecular size, so that the Q bands of H2Nc and H2Ac appear as single bands. 3) The magnitude of the orbital angular momentum of the excited state of the ligand decreases with increasing molecular size. 4) Interestingly, the ring current, as judged from the positions of pyrrole proton signals in the 1H NMR spectrum, appears to decrease with increasing molecular size. 5) The first reduction potential becomes less negative, but only slightly, whereas the first oxidation potential shows a marked shift to less positive values with increasing molecular size, indicating that the HOMO destabilizes significantly as the molecule becomes larger. 6) In 5), the extent of the HOMO destabilization with molecular size differs depending on the central metal, so metals producing smaller destabilization effects can allow larger macrocycles. Of the metals studied, the most effective is cobalt, and the practical size limit is represented by the Acs. 7) The IR spectra become simpler the larger the molecule, and the main bands were assigned by DFT calculations. 8) The trend in experimentally determined redox potentials and electronic absorption and MCD spectra were reasonably reproduced by MO calculations using the ZINDO/S Hamiltonian. 9) EPR data for several metallocomplexes are also reported.