Bioinorganic chemistry最新文献

The resonance Raman (RR) spectra of a series of triaryl formazans and several of their metal complexes have been recorded. The spectra of the free formazans display several bands of weak to medium intensity that are unaffected by physical state or metal complex formation. However, strong bands in the 1050–1200 cm⁻¹ and 1330–1430 cm⁻¹ regions are sensitive to both the physical state of the formazan and to the formation of metal complexes. This observation, coupled with the intensity of these bands, leads to the conclusion that they are fundamentals of CN, φN, CN, and NN stretching character that are diagnostic of conformation of the formazyl linkage. The bands ascribed to ν(CN) and ν(NN) in the 1330–1430 cm⁻¹ region may also be used as indicators of the formation of metal complexes.

The results of the RR studies of the free and complexed formazans are compared with spectra obtained for the inhibitor complex formed between liver alcohol dehydrogenase and 2-carboxy-2′-hydroxy-5′-sulfoformazylbenzene (zincon). Similarities between the spectra of zincon bound to the enzyme and the various model complexes lead to the conclusion that zincon is coordinated to the enzyme zinc atom but that the formazyl linkage is in an “open” rather than “closed” conformation on the enzyme surface, whereas the simple zinc complex is in the “closed” conformation.

Absorption and emission data are reported for species resulting from addition of acids, alkali, and metal salts to H₂(Etio) (etioporphyrin) and H₂(TPP) (tetraphenylporphyrin) in various organic solvents. With acid addition, dications of both TPP and Etio are observed in equilibrium with free base, and a monocation of Etio is also observed in acetone, but not in benzene. The fluorescence yield of H₄(TPP)Cl₂ was approximately 0.1, and that of H₄(TPP)Br₂, about 0.01 in acetone. The fluorescence yield of H₄(Etio)Cl₂ was approximately twice that of H₄(Etio)Br₂ in THF. With alkali addition, absorption spectra show a predicted variation with metal, and all species show strong fluorescence and weak phosphorescence, which is consistent with only a small heavy atom effect. In addition, three distinct species were observed in the fluorescence of Na₂(TPP) complexes in THF at 77 K. With metal salt addition, spectra closely resembling monocation and dication spectra are produced in acetone for Etio and TPP, respectively. For all cases studied, except perhaps uranyl salts with TPP, fluorescence yields agreed to within about 25% of that of H₃(Etio) acetate for Etio complexes and about 25% of that of H₄(TPP)Cl₂ for TPP complexes, indicating shielding of the metal salt from the porphyrin π cloud by solvent molecules.

Weanling rats were fed a low-lithium diet (0.005-0.015 ppm) and the same diet supplemented with 0.5 ppm lithium. They were carried through three generations and observations made on growth rate, reproductive performance, and lithium concentration of tissues. Analyses were performed by flame emission using a nitrous oxide-acetylene flame. Tissues and fluids analyzed included whole blood, plasma, milk, adrenal gland, pituitary, salivary gland, thymus, brain, liver, kidney, spleen, heart, lung, skin, testis, ovary, uterus, and femur. The results are only suggestive of a physiological role for trace quantities of lithium. The fertility of second- and third-generation females [10] was inferior to that of the lithium supplemented group, but lithium had no effect on growth rate. Most significantly, the lithium concentrations in the pituitary and adrenal glands were relatively high and maintained constant through two generations regardless of dietary lithium. The lithium concentrations in other tissues were lowered by low dietary intake and in at least two cases, heart and kidney, continued to decrease with successive generations.

Visible spectra of manganese(II), cobalt(II), and zinc(II) complexes of N-methyldeuteroporphyrin IX dimethyl ester are similar to each other in both energies and intensities of absorption bands. These spectra are also quite similar to the spectrum of the monoprotonated ligand, as found earlier for complexes of N-methyltetraphenylporphyrin. Luminescence intensities of N-methyldeuteroporphyrin complexes, however, are dependent on identity of the metal ion and axial ligand, varying in the order: free ligand /gt Cl-Zn(II) complex /gt Br-Zn(II) complex ⪢ Mn(II) complex, Co(II) complex. Complexation of metal ions to N-methyltetraphenylporphyrin results in reduction in emission, with intensities of the complexes varying in the order: Zn(II) /gt Cd(II) ⪢ Fe(II), Mn(II), Co(II). Formation of ion pairs consisting of a porphyrin cation and a metal-containing anion results in a fluorescence spectrum similar to that of the porphyrin ion pair formed by addition of HCl, without substantial quenching. Luminescence spectra provide conclusive evidence for the formation of ion pairs rather than “sitting-atop” complexes under conditions where the nature of such species has been controversial.

Black pigment of polybilirubinate is found in most types of human gallstones. It behaves as a cationic exchange resin and adsorbs transition-metal ions from the bile in the gallbladder. It is suggested that the role of transition-type metals is minimal and the ions occur only as a result of the cationic exchange properties of the pigment.

The complex of thymidine with (NH₃)₃Pt(OH₂) or (en)Pt(OH₂)₂, where en = ethylenediamine, have been prepared in aqueous solution at pH = 7. The isolated complexes, corresponding to the formula [(NH₃)₃Pt(ThdH₋₁)]NO₃ and (en)Pt(ThdH₋₁)₂ where ThdH₋₁ = mono anion of thymidine, have been characterized by nmr, ir, and uv spectra. The binding site is the N(3) position of ThdH₋₁.

The equilibrium constant for (NH₃)₃Pt(OH₂) + ThdH₋₁ ⇌ (NH₃)₃Pt(ThdH₋₁), in which the equilibrium of binding is pH dependent, was estimated from integrated intensity ratio of the proton of position 6 of thymidine, and log K was 10.4 ± 0.1. In the case of (en)Pt(ThdH₋₁)₂, the log K₁ for (en)Pt(OH₂)₂ + ThdH₋₁ ⇌ (en)Pt(OH₂)(ThdH₋₁) was 10.3 ± 0.1, and the log K₂ for (en)Pt(OH₂)(ThdH₋₁) + ThdH₋₁ ⇌ (en)Pt(ThdH₋₁)₂ was 7.4 ± 0.1.

The kinetics of reduction of sperm-whale aquometmyoglobin by excess dithionite ion was studied at 25°C, pH 6.9–9.8, and ionic strength 0.50 M (adjusted with potassium nitrate). The dependence of the pseudo first-order rate constant for the disappearance of metmyoglobin on hydrogen and dithionite ion concentrations is (k₁[S₂O₄²⁻] + k₂[S₂O₄²⁻]^{$\text{1}\text{2}$})[H⁺]/(K_a + [H⁺]), where k₁ = 52 ± 11 M⁻¹ s⁻¹, k₂ = 40.9 ± 2.3 M^{$\text{1}\text{2}$} s⁻¹, and K_a (the ionization constant of the water coordinated to the iron) = (5.79 ± 0.49) × 10⁻¹⁰ M. The rate law is interpreted on the basis of parallel pathways for the reaction of aquometmyoglobin with S₂O₄²⁻ and SO₂⁻, the hydroxometmyoglobin in equilibrium with the aquo form being unreactive. From a comparison of the rate constants for anation of aquometmyoglobin and the rate constant for reduction by SO₂⁻, it is inferred that an outer-sphere redox mechanism is operative. It is postulated that the activation process for reduction of aquometmyoglobin requires considerable stretching of the Fe-OH₂ bond, and this model is utilized to assign an outer-sphere mechanism to the reduction by S₂O₄²⁻. The dithionite reduction of cyanometmyoglobin proceeds in two stages. The first stage proceeds at a rate that is dependent on dithionite concentration and corresponds to the outer-sphere reduction of cyanometmyoglobin. The second stage proceeds at a rate that is independent of dithionite concentration and corresponds to the dissociation of the transient cyanodeoxymyoglobin intermediate produced in the first stage. The results of the present investigation are compared with those obtained in three independent, previous studies.

A spectral study of bilirubin and bilirubin dimethyl ester complexes with a variety of metal ions indicates that bilirubin forms two different types of complexes, interacting either with the pyrrole nitrogens or with the propionic acid side chains. A combination of the two types is possible. The proposed structure of these complexes is in accord with the most recent structural information for bilirubin.

Intraperitoneal injections of α-mercapto-β-(2-furyl)acrylic acid (MFA) induced incorporation of zinc into a low-molecular-weight metailoprotein fraction in ratqiver cytosol. Cytosol of control rats contained little or none of this material, α-Mercapto-β-(2-thienyl)acrylic acid induced less incorporation of zinc in this fraction than did MFA. Twenty-two hours after administration of ⁶⁵ZnSO₄ (50 μmol/kg) and MFA (200 μmol/kg), serum concentrations of both total and radioisotopic zinc were markedly elevated, compared to serum concentrations in rats administered only ⁶⁵ZNSO₄. Further, in liversof MFAtreated rats, radioisotopic zinc concentration was significantly greater in all cytosol zinc-containing proteins resolved by gel chromatogzaphy, but total zinc was elevated only in the metallothionein fraction and not in proteins of higher molecular weight. This appears to be the first example of induction of a metallothionein-like protein by a procedure not involving food restriction or administration of metal salts.

The design and use of iron(III) chelates in the oral treatment of iron-deficiency anemia is discussed in terms of the following criteria: (1) the ability of a chelate to exist as a monomeric species even at physiological pH values, (2) the rate of transfer of iron from the chelate to the iron-transporting protein - apotransferrin, (3) the rate of depolymerization of ferric citrate polymer by the free ligand, and (4) its nontoxicity and ability to regenerate hemoglobin levels in anemic rats.

Detailed species distribution studies, stability constants, and kinetic data for iron(III) acetohydroxamate (criteria 1–3 above) show that it remains monomeric at physiological pH values and undergoes very rapid iron transfer with apotransferrin. Detailed animal studies show a significant increase in regeneration of hemoglobin in rats fed 2 ml of 4 mM Fe(III) acetohydroxamate daily when compared to rats fed similarly with Fe(III) citrate. A strong potential is thus indicated for Fe(III) acetohydroxamate as a source of iron in the anemic animal.