Homonuclear and heteronuclear transition metal complexes by syn-proportionation reactions

Redox processes consisting of disproportionation and syn-proportionation are reviewed with special attention to metal complexes containing carbon-based ligands, i.e. carbon monoxide or unsaturated hydrocarbons. An introduction and a survey of reactions aimed to show the large applicability of syn-proportionation reactions in the field of coordination chemistry, is followed by examples of the use of these redox processes for the preparation of catalytic precursors. The latter studies derive from the idea that if a syn-proportionation reaction can be carried out between two complexes containing different metals in different oxidation states, inter-metallic systems could be formed which may act as active catalysts, e.g. for polymerization reactions.     

Genetic structure of populations of the closely related species of Melanopsis (Gastropoda: Cerithiacea) in Israel

Population genetic structure in the species of Melanopsis were studied by means of cellulose acetate gel allozyme electrophoresis, on 26 Melanopsis populations from Israel: six of Melanopsis buccinoidea Olivier, 1801, eight of Melanopsis saulcyi Bourguignat, 1853, one of Melanopsis meiostoma Heller et Sivan, 2000 , 11 of Melanopsis costata Olivier, 1804, represented by two subspecies: M. costata costata Olivier, 1804 and M. costata jordanica Roth, 1839. 14 loci (nine polymorphic) were scorable: Aat, Alp, Est-1, Est-2, Gpi, Hbdh, Idh-1, Idh-2, Iddh, Mdh, Mdhp, Mpi, Pgdh, Pgm. Gametic disequilibrium was postulated. D-statistics was computed, indicating limited migration, not epistatic selection as the source of disequilibrium. Exact multilocus and multipopulation tests showed a statistically significant heterozygote deficit in 18 populations and seven polymorphic loci. Inbreeding, Wahlund's effect and codominant mode of selection were postulated as causing homozygote excess. Mantel test indicated a statistically significant association between the pairwise θ and geographic distance, and no association between Nm and the geographic distance. The mean gene flow estimates Nm, derived from either θ or private alleles technique, were consistent. Hierarchical F-statistics showed slight differences between the taxa. The process of speciation within the genus seems not yet completed.     

The interaction of microsomal cytochrome P450 2B4 with its redox partners, cytochrome P450 reductase and cytochrome b(5)

Cytochrome P450 2B4 is a microsomal protein with a multi-step reaction cycle similar to that observed in the majority of other cytochromes P450. The cytochrome P450 2B4-substrate complex is reduced from the ferric to the ferrous form by cytochrome P450 reductase. After binding oxygen, the oxyferrous protein accepts a second electron which is provided by either cytochrome P450 reductase or cytochrome b₅. In both instances, product formation occurs. When the second electron is donated by cytochrome b₅, catalysis (product formation) is ∼10- to 100-fold faster than in the presence of cytochrome P450 reductase. This allows less time for side product formation (hydrogen peroxide and superoxide) and improves by ∼15% the coupling of NADPH consumption to product formation. Cytochrome b₅ has also been shown to compete with cytochrome P450 reductase for a binding site on the proximal surface of cytochrome P450 2B4. These two different effects of cytochrome b₅ on cytochrome P450 2B4 reactivity can explain how cytochrome b₅ is able to stimulate, inhibit, or have no effect on cytochrome P450 2B4 activity. At low molar ratios (<1) of cytochrome b₅ to cytochrome P450 reductase, the more rapid catalysis results in enhanced substrate metabolism. In contrast, at high molar ratios (>1) of cytochrome b₅ to cytochrome P450 reductase, cytochrome b₅ inhibits activity by binding to the proximal surface of cytochrome P450 and preventing the reductase from reducing ferric cytochrome P450 to the ferrous protein, thereby aborting the catalytic reaction cycle. When the stimulatory and inhibitory effects of cytochrome b₅ are equal, it will appear to have no effect on the enzymatic activity. It is hypothesized that cytochrome b₅ stimulates catalysis by causing a conformational change in the active site, which allows the active oxidizing oxyferryl species of cytochrome P450 to be formed more rapidly than in the presence of reductase.     

The human pituitary nitroproteome: detection of nitrotyrosyl-proteins with two-dimensional Western blotting, and amino acid sequence determination with mass spectrometry

Nitric oxide is an important mediator that participates in reduction-oxidation (redox) mechanisms and in cellular signal transduction pathways. Two types of post-translational modifications are induced by nitric oxide: S-nitrosylation of cysteine residues and nitration of tyrosine residues. Two-dimensional gel electrophoresis-based Western blotting was used to detect, and liquid chromatography (LC)-tandem mass spectrometry (MS/MS) to determine the amino acid sequence of, several different nitrated proteins in the human pituitary. Proteins from several 2D gel spots, which corresponded to the strongly positive anti-nitrotyrosine Western blot spots, were subjected to in-gel trypsin-digestion and LC-MS/MS analysis. MS/MS, SEQUEST analysis, and de novo sequencing were used to determine the nitration site of each nitrated peptide. A total of four different nitrated peptides were characterized and were matched to four different proteins: synaptosomal-associated protein, actin, immunoglobulin alpha Fc receptor, and cGMP-dependent protein kinase 2. Those nitrotyrosyl-proteins participate in neurotransmission, cellular immunity, and cellular structure and mobility.     

The Arabidopsis thaliana genome encodes at least four thioredoxins m and a new prokaryotic-like thioredoxin

Screening of cDNA libraries at low stringency and complete sequencing of EST clones with homology to thioredoxins allowed us to characterize five new prokaryotic type Arabidopsis thaliana thioredoxins. All present N-terminal extensions with characteristics of transit peptides. Four are clustered in a phylogenetic tree with the chloroplastic thioredoxin m from red and green algae and higher plants, and their transit peptides have typical characteristics of chloroplastic transit peptides. One is clearly divergent and defines a new prokaryotic thioredoxin type that we have named thioredoxin x. Its transit peptide sequence presents characteristics of both chloroplastic and mitochondrial transit peptides. The five corresponding genes are expressed at different levels, but mostly in green tissues and in in-vitro cultivated cells.     

The structural and electrochemical consequences of hydrogenating copper N2S2 Schiff base macrocycles

A series of cis and trans tetradentate copper macrocyclic complexes, of ring size 14-16, that employ amine and thioether donor groups are reported. Apart from 5,6,15,16-bisbenzo-8,13-diaza-1,4-dithia-cyclohexadecane copper(I) (cis-[Cu(H₄N_buS_en)]⁺) all of the complexes are obtained in the copper(II) form. Crystallographic analysis shows that the copper(II) complexes all adopt a distorted planar geometry around the copper. In contrast, cis-[Cu(H₄N_buS_en)]⁺ is found to adopt a distorted tetrahedral geometry. The complexes were subjected to electrochemical analysis in water and acetonitrile. The effect of the solvent, positions of the donor atoms (cis/trans) on E^1/2 is discussed as is the comparison of the electrochemical behaviour of these complexes with their parent Schiff base macrocycles.     

Copper-thioarylazoimidazole complexes: Structures, photochromism and redox interconversion between Cu(II) ↔ Cu(I) and correlation with DFT calculation

Reaction of Cu(ClO₄)₂·6H₂O, SRaaiNR′ (1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole) and NH₄SCN (1:1:2 mol ratio) affords distorted square pyramidal, [Cu^II(SRaaiNR′)(SCN)₂] (3) compound while identical reaction with [Cu(MeCN)₄](ClO₄) yields -SCN- bridged coordination polymer, [Cu^I(SRaaiNR′)(SCN)]_n (4). These two redox states [Cu^II and Cu^I] are interconvertible; reduction of [Cu^II(SRaaiNR′)(SCN)₂] by ascorbic acid yields [Cu^I(SRaaiNR′)(SCN)]_n while the oxidation of [Cu^I(SRaaiNR′)(SCN)]_n by H₂O₂ in presence of excess NH₄SCN affords [Cu^II(SRaaiNR′)(SCN)₂]. They are structurally confirmed by single crystal X-ray diffraction study. Cyclic voltammogram of the complexes show Cu(II)/Cu(I) redox couple at ∼0.4 V and azo reductions at negative to SCE. UV light irradiation in MeCN solution of [Cu^I(SRaaiNR′)(SCN)]_n (4) show trans-to-cis isomerisation of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation while the process is thermally accessible. Quantum yields (?_t→c) of trans-to-cis isomerisation are calculated and free ligands show higher ? than their Cu(I) complexes. The activation energy (E_a) of cis-to-trans isomerisation is calculated by controlled temperature experiment. Copper(II) complexes, 3, do not show photochromism. DFT and TDDFT calculation of representative complexes have been used to determine the composition and energy of molecular levels and results have been used to explain the solution spectra, photochromism and redox properties of the complexes.     

Impact of cytokine and cytokine receptor gene polymorphisms on cellular immunity after smallpox vaccination

We explored associations between SNPs in cytokine/cytokine receptor genes and cellular immunity in subjects following primary smallpox vaccination. We also analyzed the genotype–phenotype associations discovered in the Caucasian subjects among a cohort of African-Americans. In Caucasians we found 277 associations (p < 0.05) between gene SNPs and inter-individual variations in IFN-α, IL-12p40, IL-1β, IL-2, and TNF-α secretion levels. A collection of SNPs in the IL1RN, IL2RB, IL4R, IL6, IL10RB, IL12A, and IL12RB2 genes had consistent associations among both Caucasians and African-Americans. A regulatory SNP (rs452204) in the IL1RN gene was significantly associated with higher levels of IL-2 secretion in an allele dose-dependent manner in both race groups (p = 0.05 for Caucasians and p = 0.002 for African-Americans). IL12RB2 polymorphism rs3790567 was associated with a dose-related decrease in IL-1β secretion (p = 0.009 for Caucasians and p = 0.01 for African-Americans). Our results demonstrate that variations in smallpox vaccine-induced cytokine responses are modulated by genetic polymorphisms in cytokine and cytokine receptor genes.     

Oxidative stress and inflammation in cerebral cavernous malformation disease pathogenesis: Two sides of the same coin

Cerebral Cavernous Malformation (CCM) is a vascular disease of proven genetic origin, which may arise sporadically or is inherited as an autosomal dominant condition with incomplete penetrance and highly variable expressivity. CCM lesions exhibit a range of different phenotypes, including wide inter-individual differences in lesion number, size, and susceptibility to intracerebral hemorrhage (ICH). Lesions may remain asymptomatic or result in pathological conditions of various type and severity at any age, with symptoms ranging from recurrent headaches to severe neurological deficits, seizures, and stroke. To date there are no direct therapeutic approaches for CCM disease besides the surgical removal of accessible lesions. Novel pharmacological strategies are particularly needed to limit disease progression and severity and prevent de novo formation of CCM lesions in susceptible individuals.Useful insights into innovative approaches for CCM disease prevention and treatment are emerging from a growing understanding of the biological functions of the three known CCM proteins, CCM1/KRIT1, CCM2 and CCM3/PDCD10. In particular, accumulating evidence indicates that these proteins play major roles in distinct signaling pathways, including those involved in cellular responses to oxidative stress, inflammation and angiogenesis, pointing to pathophysiological mechanisms whereby the function of CCM proteins may be relevant in preventing vascular dysfunctions triggered by these events. Indeed, emerging findings demonstrate that the pleiotropic roles of CCM proteins reflect their critical capacity to modulate the fine-tuned crosstalk between redox signaling and autophagy that govern cell homeostasis and stress responses, providing a novel mechanistic scenario that reconciles both the multiple signaling pathways linked to CCM proteins and the distinct therapeutic approaches proposed so far. In addition, recent studies in CCM patient cohorts suggest that genetic susceptibility factors related to differences in vascular sensitivity to oxidative stress and inflammation contribute to inter-individual differences in CCM disease susceptibility and severity.This review discusses recent progress into the understanding of the molecular basis and mechanisms of CCM disease pathogenesis, with specific emphasis on the potential contribution of altered cell responses to oxidative stress and inflammatory events occurring locally in the microvascular environment, and consequent implications for the development of novel, safe, and effective preventive and therapeutic strategies.     

Manipulating the proximal triad His-Asn-Arg in human myeloperoxidase

In mammalian peroxidases the proximal histidine is in close interaction with a fully conserved asparagine which in turn is hydrogen bonded with an arginine that stabilizes the propionate substituent of pyrrol ring D in bent conformation. In order to probe the role of this rigid proximal architecture for structural integrity and catalysis of human myeloperoxidase (MPO), the variants Asn421Asp, Arg333Ala and Arg333Lys have been recombinantly expressed in HEK cell lines. The standard reduction potential of the Fe(III)/Fe(II) couple of Asn421Asp was still wild-type-like (−50 mV at pH 7.0) but the spectral properties of the ferric and ferrous forms as well as of higher oxidation states showed significant differences. Additionally, rates of ligand binding and oxidation of both one- and two-electron donors were diminished. The effect of exchange of Arg333 was even more dramatic. We did not succeed in production of mutant proteins that could bind heme at the active site. The importance of this His–Asn–Arg triad in linking the heme iron with the propionate at pyrrol ring D for heme insertion and binding as well as in maintenance of the architecture of the substrate binding site(s) at the entrance to the heme cavity is discussed.