Control of metal ion size-based selectivity through chelate ring geometry. metal ion complexing properties of 2,2'-biimidazole.

Some metal ion complexing properties of 2,2'-biimidazole (BIM) are presented. The ligand BIM forms minimum steric strain complexes with hypothetical metal ions with M-N (metal-nitrogen) bond lengths of 4.2 A, in contrast to more usual ligands such as bipy (2,2'-bipyridyl) that prefer metal ions with M-N bond lengths of 2.51 A. This metal ion size-based preference of BIM suggests that ligands with such architecture could be used to produce selectivity (differences in log K(1)) for very large metal ions. To test this hypothesis, the crystal structure of [Pb(BIM)(2)(ClO(4))(2)](2) (1) was determined as the first example of a complex of BIM with a large metal ion. In addition, formation constants (log K(1)) for BIM with metal ions ranging from the very small Cu(II) to the very large Ba(II) ion were determined to examine the effect of the architecture of BIM on metal ion selectivity. The structure of 1 gave: Triclinic, P1, a = 8.314(2) A, b = 8.677(2) A, c = 14.181(3) (A), alpha = 91.143(3) degrees , beta = 104.066(2) degrees , gamma = 106.044(3) degrees , V = 949.5(4) A(3), Z = 1, R = 0.030. Pb(II) in 1 is eight-coordinate, with relatively short Pb-N bonds to the two BIM ligands ranging from 2.366(5) to 2.665(5) A, while the four Pb-O bonds are very long at 2.826(5) to 3.123(5) A. This is typical of the structure of Pb(II) complexes that have a stereochemically active lone pair of electrons, which is postulated to be situated in the vicinity of the long Pb-O bonds. The geometry of the chelate rings formed by BIM with Pb(II) in 1 is analyzed, and it is shown that these are closer in structure to the minimum-strain chelate ring formed by BIM with a very large metal ion than is the case for structures reported in the literature with smaller metal ions. The formation constants (log K(1)) determined for BIM at 25 degrees C in 0.1 M NaClO(4) by UV-visible spectroscopy are as follows: Cu(II), 6.35; Ni(II), 4.89; Zn(II), 3.42; Cd(II), 3.86; Ca(II), -0.2; Pb(II), 3.2; Ba(II), 0.2. The log K(1) values for BIM complexes show that, as expected from the geometry of the chelate ring formed by BIM, the complexes of BIM with small metal ions such as Cu(II) are considerably weaker than with ligands such as bipy, where the ligand architecture is more favorable for forming chelate rings with small metal ions. In contrast, for very large metal ions such as Pb(II) or Ba(II), the log K(1) values for BIM complexes are larger than for bipy. The use of ligand architecture in BIM-type ligands to engineer selectivity for very large metal ions is discussed. Some fluorescence results for BIM and its complexes are presented. BIM itself fluoresces very strongly, while all of its complexes except for Ca(II) show diminished fluorescence intensity, ranging from small shifts and decreases for Ba(II) to very large decreases for Cd(II), which may be due to the distortion of the ligand geometry in its complexes by metal ions that are too small for low-strain coordination with BIM.

Refinements in husbandry, care and common procedures for non-human primates: Ninth report of the BVAAWF/FRAME/RSPCA/UFAW Joint Working Group on Refinement.

Preface Whenever animals are used in research, minimizing pain and distress and promoting good welfare should be as important an objective as achieving the experimental results. This is important for humanitarian reasons, for good science, for economic reasons and in order to satisfy the broad legal principles in international legislation. It is possible to refine both husbandry and procedures to minimize suffering and improve welfare in a number of ways, and this can be greatly facilitated by ensuring that up-to-date information is readily available. The need to provide such information led the British Veterinary Association Animal Welfare Foundation (BVAAWF), the Fund for the Replacement of Animals in Medical Experiments (FRAME), the Royal Society for the Prevention of Cruelty to Animals (RSPCA) and the Universities Federation for Animal Welfare (UFAW) to establish a Joint Working Group on Refinement (JWGR) in the UK. The chair is Professor David Morton and the secretariat is provided by the RSPCA. This report is the ninth in the JWGR series. The RSPCA is opposed to the use of animals in experiments that cause pain, suffering, distress or lasting harm and together with FRAME has particular concerns about the continued use of non-human primates. The replacement of primate experiments is a primary goal for the RSPCA and FRAME. However, both organizations share with others in the Working Group, the common aim of replacing primate experiments wherever possible, reducing suffering and improving welfare while primate use continues. The reports of the refinement workshops are intended to help achieve these aims. This report produced by the British Veterinary Association Animal Welfare Foundation (BVAAWF)/Fund for the Replacement of Animals in Medical Experiments (FRAME)/Royal Society for the Prevention of Cruelty to Animals (RSPCA)/Universities Federation for Animal Welfare (UFAW) Joint Working Group on Refinement (JWGR) sets out practical guidance on refining the husbandry and care of non-human primates (hereinafter primates) and on minimizing the adverse effects of some common procedures. It provides a valuable resource to help understand the physical, social and behavioural characteristics and needs of individual primates, and is intended to develop and complement the existing literature and legislative guidelines. Topics covered include refinements in housing, husbandry and common procedures such as restraint, identification and sampling, with comprehensive advice on issues such as primate communication, assessing and facilitating primate wellbeing, establishing and maintaining social groups, environmental and nutritional enrichment and animal passports. The most commonly used species are the key focus of this resource, but its information and recommendations are generally applicable to other species, provided that relevant individual species characteristics are taken into account.