The metal-sulphur active sites of hydrogenases catalyse hydrogen evolution or uptake at rapid rates. Understanding the structure and function of these active sites--through mechanistic studies of hydrogenases, synthetic assemblies and in silico models--will help guide the design of new materials for hydrogen production or uptake. Here we report the assembly of the iron-sulphur framework of the active site of iron-only hydrogenase (the H-cluster), and show that it functions as an electrocatalyst for proton reduction. Through linking of a di-iron subsite to a {4Fe4S} cluster, we achieve the first synthesis of a metallosulphur cluster core involved in small-molecule catalysis. In addition to advancing our understanding of the natural biological system, the availability of an active, free-standing analogue of the H-cluster may enable us to develop useful electrocatalytic materials for application in, for example, reversible hydrogen fuel cells. (Platinum is currently the preferred electrocatalyst for such applications, but is expensive, limited in availability and, in the long term, unsustainable.).

The synthesis and characterisation of the first {2Fe2S}cluster bearing both CO and CN ligands is described; the iron atoms are linked by the bridging 1,3-propanedithiolate unit that has been identified in the crystallographic structure of the {2Fe2S} sub-unit of the H-centre of the all-iron hydrogenase from Desulfovibrio desulfuricans.

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Simple SummaryMaintaining a high standard of animal welfare is essential in zoos, and methods of animal welfare assessment should aim to evaluate positive as well as negative states. The indicators that are useful in assessing these are discussed as there is huge variability in the available information about the natural biology for some zoo species. Wild baselines are not always the most accurate indicator of what is right for an animal in captivity, which makes the identification of factors to include within species-specific welfare assessment even more challenging. There is no “one size fits all” welfare strategy as it should account for the range of biological requirements and needs, which it is not possible to define for some zoo species. The different approaches for welfare assessment are reviewed, including the development of the Animal Welfare Assessment Grid which offers an evidence-based tool for continual welfare assessment, using technology where appropriate, to facilitate decision making and lead to improvements in the animals’ quality of life.AbstractZoos are required to maintain a high standard of animal welfare, and this can be assessed using a combination of resource-based and animal-based indices usually divided into behavioural indicators, physiological indicators and clinical/pathological signs. Modern animal welfare assessments should aim to encompass positive affective states and the indicators that are useful in assessing these are discussed. When developing factors to be scored for each species, there is huge variability in the available information about the natural biology for some zoo species and even less information concerning those animals in captivity. Wild baselines are not always the most accurate indicator of what is right for an animal in captivity, which makes the identification of factors to include within species-specific welfare assessment even more challenging. When planning a welfare strategy for any species, it is important that the full range of their biological requirements and needs are considered, but this can be challenging for some zoo species and it is not possible to define a “one size fits all” welfare strategy. The different approaches for welfare assessment are reviewed, including the development of the Animal Welfare Assessment Grid which offers an evidence-based tool for continual welfare assessment, using technology where appropriate, to facilitate decision making and lead to improvements in the animals’ quality of life.

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The reaction, under carbon monoxide, of [Fe(NS 3 )(CO)] 2 [NS 3 = N(CH 2 CH 2 S) 3 32 ] with [NiCl 2 (dppe)] gives the structurally characterised dinuclear thiolate-bridged complex [{Fe(NS 3 )(CO) 2 -S,SA}NiCl(dppe)], which has structural features similar to those of the active site of NiFehydrogenase.

Reaction of [Fe(acac) 3 ], (NEt 4 )OAc and N(CH 2 CH 2 SH) 3 in MeCN in the presence of NO gives (NEt 4 )[Fe(NS 3 )(NO)] (1) [where NS 3 = N(CH 2 CH 2 S) 3 ]. Complex 1 reacts with metal chloride solvates, giving insoluble compounds of stoichiometry MFe 2 (NO) 2 (NS 3 ) 2 , probably having the structure [M{Fe(NS 3 )(NO)} 2 -S,SЈ] [M = Fe (2), Co (3), Ni (4), Cu (5)], the nitrosyl analogues of known structurally characterised carbonyl compounds. 1 also reacts with HBF 4 ؒ Et 2 O, giving the tetranuclear complex [{Fe(NO) 2 {Fe(NS 3 )}-S,SЈ} 2 -S,SЈ] (6), which adds small molecules, L, giving the binuclear complexes [Fe(NO) 2 {Fe(NS 3 )(L)}-S,SЈ] [L = CO (7), CNMe (8), NO (9), CN Ϫ (10)]. Complexes 6-9 are more conveniently prepared by treatment of [Fe(NS 3 )(L)] Ϫ precursors with half an equivalent of [{Fe(NO) 2 } 2 (µ-I) 2 ]. Reaction of (NEt 4 )[Co(NS 3 )(CN)] with half an equivalent of [{Fe(NO) 2 } 2 (µ-I) 2 ] gives [Fe(NO) 2 {Co(NS 3 )(CN)}-S,SЈ] (11). Treatment of the [Fe(NS 3 )L] precursors used to make 7-9 with one equivalent of [{Fe(NO) 2 } 2 (µ-I) 2 ] gives another series of complexes, [{Fe(NO) 2 I}-S{Fe(NS 3 )(L)}-SЈ,SЉ{Fe(NO) 2 }] [L = CO (12), CNMe (13), NO (14)].Products were characterised by microanalyses, IR and Mössbauer spectra; X-ray crystal structure determinations were carried out on 1, 6, 7, 9, 10, 13 and 14. Magnetic measurements at room temperature showed evidence of spin pairing in all the polynuclear complexes. DALTON