Interaction Of As(III) with Thiolate-Containing Molecules

The aqueous solutions of arsenous acid with thiolate containing organic ligands such as the meso and racemic forms of 1,4-dithiol-butane-2,3-diol, (dithioerythritol – dte and dithiothreitol - dtt) as well as 2,3-dimercaptopropanol (called also British anti-Lewisite (BAL) or Dimercaprol) were investigated. pH-mertric titrations were performed in solutions with different molar ratios of As(III) and the ligands. The pKa values for As(OH)3, and the ligands determined from these data were in good agreement with the literature data. In all investigated systems containing both As(OH)3 and one of the ligands, the deprotonation steps appeared at a higher pH in the titration curves, than in those of the individual components. This unusual observation was explained by the condensation reactions between the reagents taking place in the pH < 8 range. In some of these systems the pH-metry was combined with NMR and UV spectroscopic measurements. We observed the complexes with 1:1 As(III):ligand composition as being the major species in aqueous solutions. In the case of As(III)-dte system we could crystallize the complex of 1:1 composition from ethanolic solution

Solution properties of iron(III) complexes with 5-fluorosalicylic acid- spectra, speciation, and redox stability

Iron(III)-5-fluorosalicylic acid systems were investigated in water by pH potentiometry combined with UV-VIS spectrophotometry. The data revealed that stable aquated mono-, bis-, and tris(5-fluorosalicylato) iron(III) complexes are formed together with their monohydroxo and dihydroxo analogues. The stability constants of all present iron(III) species were calculated. Based on pH and the metal: ligand ratio dependent distribution of the species, electronic absorption spectra of the complexes in the visible region were obtained. Redox stability was monitored as an ability to undergo both spontaneous and photoinduced reduction of iron(III) to iron(II). Complexes do not undergo any redox changes when in dark neither in methanol nor in water. While aqueous solutions of complexes are stable under the influence of incident visible radiation, steady-state irradiation of the methanolic systems by visible light led to photoreduction of iron(III) to iron(II), the quantum yield of iron(II) photoformation was determined. (C) 2008 Institute of Chemistry, Slovak Academy of Sciences

Competition of zinc(II) with cadmium(II) or mercury(II) in binding to a 12-mer peptide

Speciation of the complexes of zinc(II) with a dodecapeptide (Ac-SCPGDQGSDCSI-NH2), inspired by the metal binding domain of MerR metalloregulatory proteins, have been studied by pH-potentiometric titrations, UV, SRCD (synchrotron radiation circular dichroism) and 1H NMR experiments. (MerR is a family of transcriptional regulators the archetype of which is the Hg2+-responsive transcriptional repressor-activator MerR protein.) The aim of the ligand-design was to retain the advantageous metal binding features of MerR proteins in a model peptide for the efficient capture of toxic metal ions. The peptide binds zinc(II) via two deprotonated Cys-thiol groups and one of the Asp-carboxylates in the ZnL parent complex, possessing a remarkably high stability (logK = 9.93). In spite of the relatively long peptide loop, bis-complexes are also formed with the metal ion under basic conditions. In a competition with cadmium(II) or mercury(II), zinc(II) cannot prevent the binding of toxic metal ions by the thiolate donor groups of the ligand. Around neutral pH one equivalent of mercury(II) was shown to fully replace zinc(II) from the ZnL species. Partial replacement of zinc(II) from the peptide by one equivalent of cadmium(II), relative to zinc(II) and the ligand, is also presumable, nevertheless, spectroscopic data may suggest the formation of mixed metal ion complexes, as well. Based on the obtained results the investigated dodecapeptide can be a promising candidate for capturing toxic metal ions in practical applications

Interactions of an Artificial Zinc Finger Protein with Cd(II) and Hg(II): Competition and Metal and DNA Binding

Cys2His2 zinc finger proteins are important for living organisms, as they—among other functions—specifically recognise DNA when Zn(II) is coordinated to the proteins, stabilising their ββα secondary structure. Therefore, competition with other metal ions may alter their original function. Toxic metal ions such as Cd(II) or Hg(II) might be especially dangerous because of their similar chemical properties to Zn(II). Most competition studies carried out so far have involved small zinc finger peptides. Therefore, we have investigated the interactions of toxic metal ions with a zinc finger proteins consisting of three finger units and the consequences on the DNA binding properties of the protein. Binding of one Cd(II) per finger subunit of the protein was shown by circular dichroism spectroscopy, fluorimetry and electrospray ionisation mass spectrometry. Cd(II) stabilised a similar secondary structure to that of the Zn(II)-bound protein but with a slightly lower affinity. In contrast, Hg(II) could displace Zn(II) quantitatively (logβ′ ≥ 16.7), demolishing the secondary structure, and further Hg(II) binding was also observed. Based on electrophoretic gel mobility shift assays, the Cd(II)-bound zinc finger protein could recognise the specific DNA target sequence similarly to the Zn(II)-loaded form but with a ~0.6 log units lower stability constant, while Hg(II) could destroy DNA binding completely

Circular Dichroism is Sensitive to Monovalent Cation Binding in Monensin Complexes

We present a lock-free version of the light-weight userlevel task management library called Wool, in an aim to show that even extremely well tuned, in terms of synchronization,applications can benefit from lock-free programming.Explicit multi-threading is an efficient way to exploit the offered parallelism of multi-core and multi-processor based systems. However, it can sometimes be hard to expressthe inherited parallelism in programs using a limited number of long lived threads. Often it can be more straightforwardto dynamically create a large number of small tasks that in turn automatically execute on the available threads.Wool is a promising and efficient library and framework that allows the programmer to create user tasks in C with a very low overhead. The library automatically executestasks and balances the load evenly on a given number of threads by utilizing work stealing techniques. However, thesynchronization for stealing tasks is based on mutual exclusion which is known to limit parallelism and efficiency. We have designed and implemented a new lock-free algorithmfor synchronization of stealing tasks in Wool. Experiments show similar or significantly improved performance on a setof benchmarks executed on a multi-core platform