TssA forms a gp6-like ring attached to the type VI secretion sheath

The type VI secretion system (T6SS) is a supra-molecular bacterial complex that resembles phage tails. It is a killing machine which fires toxins into target cells upon contraction of its TssBC sheath. Here, we show that TssA1 is a T6SS component forming dodecameric ring structures whose dimensions match those of the TssBC sheath and which can accommodate the inner Hcp tube. The TssA1 ring complex binds the T6SS sheath and impacts its behaviour in vivo. In the phage, the first disc of the gp18 sheath sits on a baseplate wherein gp6 is a dodecameric ring. We found remarkable sequence and structural similarities between TssA1 and gp6 C-termini, and propose that TssA1 could be a baseplate component of the T6SS. Furthermore, we identified similarities between TssK1 and gp8, the former interacting with TssA1 while the latter is found in the outer radius of the gp6 ring. These observations, combined with similarities between TssF and gp6Nterminus or TssG and gp53, lead us to propose a comparative model between the phage baseplate and the T6SS

Iridium-catalyzed C–H borylation of pyridines

The iridium-catalysed C–H borylation is a valuable and attractive method for the preparation of aryl and heteroaryl boronates. However, application of this methodology for the preparation of pyridyl and related azinyl boronates can be challenged by low reactivity and propensity for rapid protodeborylation, particularly for a boronate ester ortho to the azinyl nitrogen. Competition experiments have revealed that the low reactivity is due to inhibition of the active catalyst through coordination of the azinyl nitrogen lone pair at the vacant site on the iridium. This effect can be overcome through the incorporation of a substituent at C-2. Moreover, when this is sufficiently electron-withdrawing protodeborylation is sufficiently slowed to permit isolation and purification of the C-6 boronate ester. Following functionalization, reduction of the directing C-2 substituent provides the product arising from formal ortho borylation of an unhindered pyridine ring

Improved syntheses of bis(ethynyl)-para-carboranes, 1,12-(RC C)(2)-1,12-C2B10H10 and 1,10-(RC equivalent to C)(2)-1,10-C2B8H8 (R = H or Me3Si).

Copper-mediated cross-coupling reactions of the 12-vertex and 10-vertex para carboranes, 1,12-C2B10H12 and 1,10-C2B8H10, with trans-1-iodo-2-chloroethene gave the bis(trans-2-chloroethenyl) carboranes, 1,12-(ClCHdouble bond; length as m-dashCH)2-1,12-C2B10H10 and 1,10-(ClCHdouble bond; length as m-dashCH)2-1,10-C2B8H8, respectively, in good yield. The molecular structures of both compounds were determined by X-ray crystallography, verifying the trans disposition of the chloride and carboranyl substituents across the double bonds. These vinyl carboranes can be converted to bis(ethynyl) carboranes, 1,12-(RCtriple bond; length of mdashC)2-1,12-C2B10H10 and 1,10-(RCtriple bond; length of mdashC)2-1,10-C2B8H8 (R = H or Me3Si), easily, and in high yields. These findings provide the most convenient routes to bis(ethynyl) carboranes from the commercially available carboranes, 1,12-C2B10H12 and 1,10-C2B8H10 reported to date

A solid-state dehydration process associated with a significant change in the topology of dihydrogen phosphate chains, established from powder X-ray diffraction

The anhydrous crystalline phase of chloroquine bis-(dihydrogen phosphate) is obtained by dehydration of the corresponding hydrate phase, but in common with many solid-state dehydration processes, the product is obtained as a polycrystalline powder, thus limiting the opportunity to carry out structural characterization using single crystal X-ray diffraction techniques. Instead, structure determination of the anhydrous phase has exploited the capabilities of modern powder X-ray diffraction techniques, employing the direct-space Genetic Algorithm technique for structure solution followed by Rietveld refinement. The results reveal that the dehydration process is associated with a significant change in the topology of hydrogen bonded chains of dihydrogen phosphate anions, arising from a change in the hydrogen bonding arrangement within the chains, together with a significant change in the conformation of the chloroquine cation

Trimetallic complexes featuring Group 10 tetracyanometallate dianions as bridging ligands.

The trimetallic complexes {Ru(PPh3)2Cp}2{μ-M(CN)4} and {Ru(dppe)Cp*}2{μ-M(CN)4} (M = Ni, Pd, Pt) have been prepared from reactions of RuCl(PPh3)2Cp or RuCl(dppe)Cp* with the appropriate tetracyanometallate salt, and structurally characterised. While a similar reaction of FeCl(dppe)Cp with K2[Pt(CN)4] afforded {Fe(dppe)Cp}2{μ-Pt(CN)4}, the iron cyanide complex Fe(CN)(dppe)Cp was isolated as the only iron containing product from reaction of FeCl(dppe)Cp with K2[Ni(CN)4]. The trimetallic complexes can be oxidised in two sequential one-electron steps. Spectroelectrochemical experiments reveal weak NIR absorption bands in the mono-oxidised complexes which are not present in the binuclear complex K[Ru(dppe)Cp*{Pt(CN)4}], and are therefore attributed to RuII → RuIII charge transfer processes. The coupling parameter, Vab, extracted using Hush-style analysis falls in the range 250 ± 50 cm−1, consistent with the weak interaction between the Group 8 metal centres. The energy of the IVCT process is dominated by reorganisation energy of the Group 8 metal–ligand fragment

Ligand redox non-innocent behaviour in ruthenium complexes of ethynyl tolans

A small series of half-sandwich bis(phosphine) ruthenium acetylide complexes [Ru(CCC6H4CCSiMe3)(L2)Cp′] and [Ru(CCC6H4CCC6H4R-4)(L2)Cp′] (R = OMe, Me, CO2Me, NO2; L2 = (PPh3)2, Cp′ = Cp; L2 = dppe; Cp′ = Cp∗) have been synthesised. One-electron oxidations of these complexes gave the corresponding radical cations, which were significantly more chemically stable in the case of the Ru(dppe)Cp∗ derivatives. The representative complex [Ru(CCC6H4CCC6H4OMe-4)(dppe)Cp∗] was further examined by spectroelectrochemical (IR and UV–Vis–NIR) methods. The results of the spectroelectrochemical studies, supported by DFT calculations, indicate that the hole is largely supported by the ‘RuCCC6H4’ moiety in a manner similar to that described previously for simple aryl ethynyl complexes, rather than being more extensively delocalized along the entire conjugated ligand

Structural Insights into the Molecular Organisation of the S-layer from Clostridium difficile

Clostridium difficile expresses a surface layer (S‐layer) which coats the surface of the bacterium and acts as an adhesin facilitating interaction of the bacterium with host enteric cells. The S‐layer contains a high‐molecular‐weight S‐layer protein (HMW SLP) and its low‐molecular‐weight partner protein (LMW SLP). We show that these proteins form a tightly associated non‐covalent complex, the H/L complex, and we identify the regions of both proteins responsible for complex formation. The 2.4 Å X‐ray crystal structure of a truncated derivative of the LMW SLP reveals two domains. Domain 1 has a two‐layer sandwich architecture while domain 2, predicted to orientate towards the external environment, contains a novel fold. Small‐angle X‐ray scattering analysis of the H/L complex shows an elongated molecule, with the two SLPs arranged ‘end‐to‐end’ interacting with each other through a small contact area. Alignment of LMW SLPs, which exhibit high sequence diversity, reveals a core of conserved residues that could reflect functional conservation, while allowing for immune evasion through sequence variation. These structures are the first described for the S‐layer of a bacterial pathogen, and provide insights into the assembly and biogenesis of the S‐layer

The synthesis, structure, and electrochemical properties of Fe(C≡CC≡N)(dppe)Cp and related compounds.

The cyanoacetylide complex Fe(C≡CC≡N)(dppe)Cp (3) is readily obtained from sequential reaction of Fe(C≡CSiMe3)(dppe)Cp with methyllithium and phenyl cyanate. Complex 3 is a good metalloligand, and coordination to the metal fragments [RhCl(CO)2], [Ru(PPh3)2Cp]+, and [Ru(dppe)Cp*]+ affords the corresponding cyanoaceylide-bridged heterobimetallic complexes. In the case of the 36-electron complexes [Cp(dppe)Fe-C≡CC≡N-MLn]n+, spectroscopic and structural data are consistent with a degree of charge transfer from the iron centre to the rhodium or ruthenium centre via the C3N bridge, giving rise to a polarized ground state. Electrochemical and spectroelectrochemical methods reveal significant interactions between the metal centres in the oxidized (35 electron) derivatives, [Cp(dppe)Fe-C≡CC≡N-MLn](n+1)+. Key words: cyanide, cyanoacetylide, crystal structure