Kinetics and mechanism of the aquation of the trinuclear cation, [μ3-oxo-triaqua-hexakis(acetato)tris(iron(III))]in perchloric acid media

The aquation of the title complex cation in aqueous perchloric acid proceeded via two steps, both postulated to be the proton attack on the oxygen atom which binds the acetate ligand to the metal centre, followed by Fe-O bond cleavage. This was followed by rapid decomposition to produce aqueous iron(III) and acetate ions. The first-order rate constants for the first and second steps at 25 °C are: k₁ = (4.16 ± 0.58) × 10⁻² s⁻¹ and k₂ = (2.09 ± 0.42) × 10⁻³ s⁻¹, respectively, and their corresponding activation parameters are . The spontaneous hydrolysis rate constants for the first and second steps were also determined at 25 °C and ionic strength of 1 mol dm⁻³ and they are k₀ = (3.10 ± 0.82) × 10⁻³ s⁻¹ and , respectively. The corresponding activation parameters are .     

Absorption of DNA in the region of vacuum-uv (3–25 eV)

By means of a device that might be considered a modern version of "Ulbricht's sphere" the absorption spectrum and the photoelectric emission of calf thymus DNA was measured in the region of 3 to 25 eV (400 to 50 nm). A tentative explanation of the general shape of the absorption spectrum and of its 6 maxima is given. The results permit a much better insight into some biologic effects of vacuum-uv to be gained than hitherto possible.     

Ligand field,electronic and solvent effects in the non-aqueous electrochemistry of tris(β-dionato)chromium(III) chelates

The electrochemical behaviour of a series of tris-(β-dionato)chromium(III) chelates has been investigated in acetone and acetonitrile. Reduction proceeds in one electron steps involving the chromium ion. Solvent effects are less important than the influence of substituents within the β-dionato moiety. Potentials range from −2.15 to −0.89 V and a linear correlation exists between E_1/2 and the sum of Hammett σ functions of the substituents. Comparison with similarly structured complexes indicates that electronic configuration, ionization potentials and ligand field effects influence the reduction potentials. The paramagnetic complexes behave differently from the diamagnetic ones.     

Specific cation effect on quenching reactions of excited tris(α,α-diimine)ruthenium(II) and tris(2,2-bipyridine)chromium(III) by tris(oxalato)- and tris(malnato)chromates(III) in aqueous solutions

Specific salt effects were studied on the quenching reaction of excited [Ru(N-N)₃]²⁺ (N-N=2,2^′-bipyridine (bpy), 1,10-phenanthrorine (phen)) and [Cr(bpy)₃]³⁺ by [Cr(ox)₃]³⁻ (ox=oxalate ion) and [Cr(mal)₃]³⁻ (mal=malonate ion) in aqueous solutions as a function of alkali metal ions which were added for adjustment of ionic strength. The value of k_q, quenching rate constants, and k₁, energy transfer rate constant in encounter complex, is changed by the cations as the order of Li⁺ > Na⁺ > K⁺ ≈ Rb⁺ ? Cs⁺, although diffusion rate constants are not changed by the co-existing cations. Among the quenching reactions investigated in this work, a ratio of k₁ values in the aqueous solutions whose ionic strength was adjusted with LiCl and KCl, k₁^LiCl/k₁^KCl, is larger for quenching systems of closely approached donor-acceptor pair than loosely bounded pair. These results indicate that co-existing alkali cation tunes the distance between donor and acceptor in encounter complex where energy transfer occurs.     

Synthesis,structure and magnetic properties of the binuclear chromium(III) complex di-μ-hydroxobis [(1,4,7,10-tetraazacyclododecane)chromium(III)] dithionate tetrahydrate, [(cyclen)CrOH]2(S206)2·4H2O

The dark blue dimeric complex di-μ-hydroxo- bis [(1,4,7,10-tetraazacyclododecane)chromium(III)] dithionate tetrahydrate, [Cr(C₈H₂₀N₄)OH]₂(S₂O₆)₂· 4H₂O or [Cr(cyclen)OH]₂(S₂O₆)₂·4H₂O, has been synthesized. The crystal structure of the complex has been determined from threeodimensional counter X-ray data. The complex crystallizes in space group P2₁/n of the monoclinic system with two dimeric formula units in a cell of dimensions a = 8.837(5), b = 14.472(8), c= 13.943(6) Å andβ=95.83(4)^o. The structure has been refined by full-matrix least- squares methods to a final value of the weighted R-factor of 0.059 on the basis of 1774 independent intensities. The geometry of the cyclen macrocycle is unsymmetrical, the observed conformations being λδδλ and its enantiomer. The strained ligand conformation leads to significant deviations from octahedral geometry at the chromium centers, and to a bridged geometry in which the CrOCr angle ø and the Cr···Cr separation of 104.1(1)^o and 3.086(2) Å are the largest observed in dimers of this kind. The magnetic susceptibility of the complex indicates antiferromagnetic coupling, with the ground state singlet lying 21.56(6) cm⁻¹ below the lowest lying triplet state. The structural parameters have been used to calculate the triplet energy by means of the Glerup- Hodgson- Pedersen (GHP) model, and the calculated value of 22.3 cme⁻¹ is very similar to the observed value.     

Specific cation effect on quenching reactions of excited tris(α,α′-diimine) ruthenium(II) and chromium(III) complexes by cyanide complexes in aqueous solutions

Specific salt effects were studied on the quenching reaction of excited [Ru(NN)₃]²⁺ (NN=2,2′-bipyridine(bpy), 1,10-phenanthrorine(phen)) and [Cr(bpy)₃]³⁺ by [Cr(CN)₆]³⁻, [Fe(CN)₆]³⁻ and [Ni(CN)₄]²⁻ in aqueous solutions as a function of alkali metal ions which were added for adjustment of ionic strength. The quenching rate constants in [Ru(NN)₃]²⁺-[Cr(CN)₆]³⁻ and [Cr(bpy)₃]³⁺-[Cr(CN)₆]³⁻ systems are changed by the cations as Li⁺>Na⁺>K⁺≈Rb⁺≈Cs⁺. On the other hand, the rate constants in [Ru(NN)₃]²⁺-[Fe(CN)₆]³⁻ and [Ru(NN)₃]²⁺-[Ni(CN)₄]²⁻ systems, which are diffusion-controlled reactions, are not varied by the alkali metal cations. The obtained order (Li⁺>Na⁺>K⁺≈Rb⁺≈Cs⁺) of the quenching rate constant is quite different from salt effects, Li⁺<Na⁺<K⁺<Rb⁺<Cs⁺, which have been obtained in the electron transfer reactions between complex anions.     

Kinetics and mechanism of the decomposition of μ-amido-μ-hydroxo(tetraamminecobalt(III))(tetraaquacobalt(III)) ion in acidic aqueous solution

The title complex undergoes decomposition in acidic aqueous solution resulting in equimolar concentration of aquapentaamminecobalt(III) and hexa- aquacobalt(II). The kinetic studies over the ranges of 0.048 M ⩽ [H⁺] ⩽ 0.385 M, 25 ⩽ θ_c ⩽ 41.5°C and at I = 0.5 M reveals that the intricate mechanism involves protonation equilibrium of the title complex, followed by a rate determining bridge cleavage. The further follow-up reaction is a fast electron transfer process to form products. The rate expression derived from the mechanism is k_obs = k₁K₁[H⁺]/(1 + K₁[H⁺]) where the values of k, and K, are found to be 8.9 × 10⁻⁴ s⁻¹ and 3.5 M⁻¹ respectively at 25 °C. The results are compared with that obtained for the decomposition reactions of mononuclear aquaammine complexes of cobalt(III).     

Polynuclear chromium(III) carboxlylates: Part 2. Chromium(III) acetate — what's in it?

Chromium(III) acetate has been widely used in industry for decades. The commercial material is an ill-defined substance, which represents a large number of compounds having different compositions, physical properties and appearances. Several samples of Cr(III) acetate, from various commercial sources were examined by ion-exchange chromatography. All the samples were found to contain several species such as [Cr₃O(O₂CCH₃)₆(H₂O)₃]⁺ and other positively charged purple complexes. They also contain various amounts of the neutral violet complex [Cr₈(OH)₈(O₂CCH₃)₁₆] (1) which crystallizes upon slow evaporation of its aqueous solution. 1 is a cyclic octanuclear complex with hydroxo and acetate ligands bridging the adjacent Cr(III) ions. The structure of a well-defined Cr(III) acetate, namely, [Cr(H₂O)₆](O₂CCH₃)₃ (2) has been determined crystallographically and its decomposition products were examined by ion-exchange chromatography. Compound 2 decomposes under ambient conditions, releasing acetic acid and water producing neutral and charged polynuclear Cr(III) complexes.     

Calculation of the Raman frequencies as a function of pressure in the solid phases II and III (III’) of benzene

We calculate here the Raman frequencies of the lattice modes A(A _g ), B(B _2g ) and C(B _1g B _3g ) as a function of pressure at room temperature for the solid phases (II, III and III’) of benzene. This calculation is performed using volume data through the mode Grüneisen parameter. It is found that our calculated frequencies of those lattice modes increase with increasing pressure, as expected. Calculated frequencies are in good agreement with the measurements of the three lattice modes for the solid phases studied in benzene.     

New examples of the exploitation of intermediary ligands in the synthesis of polymeric (μ-Se)Hg-clusters

(PhSe)₂Hg reacts initially with HgX₂ (X = Cl, I) and further with triphenylphosphine/DMF to give [(PhSe)₇Hg₄ClPy]_n (1) and [(PhSe)₇Hg₄I(DMF)]_n (2), polymeric assemblies of (μ-Se)Hg clusters obtained through coordinating intermediary ligands. Each single adamantoid molecule of 1 and 2 presents the Hg^II ions with a distorted tetrahedral configuration linked through asymmetric [μ-(Ph)Se]⁻ bridges. [(PhSe)₇Hg₄ClPy]_n and [(PhSe)₇Hg₄I(DMF)]_n are further examples of extended one-dimensional chains of closed anisotropic ME (E = S, Se, Te) systems. In these reactions the features of the intermediary ligands should determine the template which leads to single adamantane moieties or to fused ones.     

Evidence for the protective effect of ascorbic acid (vitamin C) in treatment with γ-rays and chromium (VI) oxide (CrO3) in somatic cells of Drosophila

Evidence is provided that ascorbic acid (vitamin C), when used as a pretreatment, protects against mutation/recombination induced by γ-rays and chromium (VI) oxide in mwh+/+flr³ larvae in the wing spot test in Drosophila     

Spin-trapping studies on the reactions of Cr(III) with hydrogen peroxide in the presence of biological reductants: is Cr(III) non-toxic?

Cr(III), which is thought to be relatively non-toxic, was reduced to Cr(II) ion by biological reductants such as L-cysteine and NADH and Cr(II) thus formed could easily react with hydrogen peroxide (H2O2) to yield very reactive active oxygen species, hydroxyl radical (.OH). The formation of hydroxyl radical was detected by water-soluble spin-traps, alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO). This result indicates that non-toxic Cr(III) compounds have the possibility of causing dangerous effects to living organism in the presence of biological reductants.     

Evidence for the occurrence of the opioid octapeptide dynorphin-(1–8) in the neurointermediate pituitary of rats

Evidence is provided for the existence of the opioid peptide dynorphin-(1–8) in the neurointermediate pituitary of rats. The octapeptide was isolated by immunoadsorption to antibodies directed against porcine dynorphin-(1–13) followed by a variety of chromatographic separation procedures. The identity of the purified material with dynorphin-(1–8) was indicated by the following criteria: comigration with synthetic dynorphin-(1–8) on gelfiltration chromatography and high-performance liquid chromatography systems and liberation of a peptide with the same chromatographic behavior as leucine-enkephalin after sequential cleavage with trypsin and carboxypeptidase B.Radioimmunological estimations revealed that dynorphin-(1–8) is a major dynorphin-related opioid peptide in the pituitary of rats.     

Anti-diabetic effects of vanadium(III, IV, V)–chlorodipicolinate complexes in streptozotocin-induced diabetic rats

Vanadium(III, IV, V)–chlorodipicolinate (dipic-Cl) complexes, including H[V^III(dipic-Cl)₂] · 5H₂O (V₃dipic-Cl), V^IVO(dipic-Cl)(H₂O)₂ (V₄dipic-Cl) and K[V^VO₂(dipic-Cl)] (V₅dipic-Cl), were prepared with the indicated oxidation states. Our aim was to evaluate the anti-diabetic effects of V₃dipic-Cl, V₄dipic-Cl and V₅dipic-Cl in streptozotocin-induced diabetic rats. Vanadium complexes were orally administered to diabetic rats at concentrations of 0.1–0.3 mg/ml in the drinking water. We found that vanadium–chlorodipicolinate (V–dipic-Cl) complexes at the concentration of 0.1 mg/ml did not exhibit blood glucose-lowering effects when administered to diabetic rats for 20 days. However, the levels of fasting blood glucose in diabetic rats were decreased after treatment with 0.3 mg/ml of V₄dipic-Cl and V₅dipic-Cl complexes for the following 20 days. Although administration of both V₄dipic-Cl and V₅dipic-Cl significantly lowered diabetic hyperglycemia, the vanadium intake from administration of V₄dipic-Cl is nearly 1.5-fold greater compared to that of V₅dipic-Cl. Treatment with the H₂dipic-Cl ligand and all three V–dipic-Cl complexes significantly lowered serum cholesterol, while administration of the V₅dipic-Cl complex lowered serum cholesterol significantly more than administration of the ligand alone. Treatment with ligand alone did not have an effect on serum triglyceride, while administration of the V₄dipic-Cl and V₅dipic-Cl significantly lowered the elevated serum triglyceride associated with diabetes. Oral administration of the ligand and all V–dipic-Cl complexes did significantly lower diabetes elevated serum alkaline phosphatase. Treatment with H₂dipic-Cl ligand and V₄dipic-Cl and V₅dipicCl significantly lowered diabetes elevated aspartate amino transferase. These results indicate that the health of the treated animals did not seem to be further compromised compared to that of diabetic animals. In addition, oral administration of H₂dipic-Cl, V₃dipic-Cl, V₄dipic-Cl and V₅dipic-Cl did not alter diabetic serum creatinine and blood urea nitrogen levels, suggesting no significant side effects of vanadium treatment on renal functions at the dose of 0.3 mg/ml in diabetic rats. The results presented here suggest that the anti-diabetic effects of treatment with V–dipic-Cl complexes were likely associated in part with the oxidation state of vanadium.