A solvent-resistant halogen bond

The effect of solvent on the stabilities of complexes involving a single H-bond or halogen-bond (X-bond) has been quantified. Association constants for binary complexes of 4-(phenylazo)phenol, molecular iodine, tetramethylurea and tetramethylthiourea have been measured in fifteen different solvents by UV/vis absorption and 1H NMR titration experiments. The stabilities of the H-bonded complexes decrease by more than three orders of magnitude with increasing solvent polarity. In contrast, the X-bonded complex of molecular iodine with tetramethylthiourea is remarkably insensitive to the nature of the solvent (association constants measured in alkanes and alcohols are similar). The results suggest that, in contrast to H-bonds, where electrostatics determine thermodynamic stability, charge-transfer interactions make a major contribution to the stability of these X-bonded complexes rendering them resistant to increases in solvent polarity

Synthesis of Mono- and Diiron Dithiolene Complexes as Hydrogenase Models by Dithiolene Transfer Reactions, Including the Crystal Structure of [{Ni(S2C2Ph2)}6]

The dithiolene transfer reaction between the nickel bis(dithiolene) complex [Ni(S2C2Ph2)2] and iron carbonyls has been re-investigated, and the conditions for the production of the dinuclear product [Fe2(μ-S2C2Ph2)(CO)6] have been optimized. Interception of a purple intermediate, thought to be [Fe(CO)3(S2C2Ph2)], in the reaction of [Fe(CO)5] with [Ni(S2C2Ph2)2] by the addition of PPh3 affords the new dark blue mononuclear complex [Fe(CO)2(PPh3)(S2C2Ph2)] in good yield. The fate of the nickel dithiolene fragments in these reactions has also been established by crystallographic characterization of the hexamer [{Ni(S2C2Ph2)}6] and the trinuclear cluster [Ni3(μ-S2C2Ph2)3(PPh3)2]. The substitution reactions of [Fe2(μ-S2C2Ph2)(CO)6] with PPh3 in the presence of Me3NO to give monosubstituted [Fe2(μ-S2C2Ph2)(CO)5(PPh3)] and disubstituted [Fe2(μ-S2C2Ph2)(CO)4(PPh3)2] are also reported

Structural investigation into the threading intercalation of a chiral dinuclear ruthenium(II) polypyridyl complex through a B-DNA oligonucleotide

Herein we report the separation of the three stereoisomers of the DNA light-switch compound [{Ru(bpy)2}2(tpphz)]4+ (tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2‴,3‴-j]phenazine) by column chromatography and the characterization of each stereoisomer by X-ray crystallography. The interaction of these compounds with a DNA octanucleotide d(GCATATCG).d(CGATATGC) has been studied using NMR techniques. Selective deuteration of the bipyridyl rings was needed to provide sufficient spectral resolution to characterize structures. NMR-derived structures for these complexes show a threading intercalation binding mode with slow and chirality-dependent rates. This represents the first solution structure of an intercalated bis-ruthenium ligand. Intriguingly, we find that the binding site selectivity is dependent on the nature of the stereoisomer employed, with Λ RuII centers showing a better intercalation fit

2,2′:4,4′′:4′,4′′′-Quaterpyridine: synthesis, crystal-structure description, and Hirshfeld surface analysis

The title compound, 2,2′:4,4′′:4′,4′′′-quaterpyridine (Qtpy), C20H14N4, crystallizes in the triclinic P\overline{1} space group and has half of the mol­ecule in the asymmetric unit, corresponding to 4,4′-bi­pyridine (4,4′-bpy) that serves as the building block for the mol­ecule. C4,4′-bpy—N—C4,4′-bpy and/or N—C4,4′-bpy—C4,4′-bpy bond-angle parameters show that the 4,4′-bpy ligands are highly rigid, displaying values lower than the linear bond angle of 180°. In the crystal, the 4,4′-bpy units are seen to be facing each other in relatively close proximity. The most important inter­actions on the Hirshfeld Surface of the compound are C—H...N/H...N—C inter­actions (constituting 10.6% and 7.6% of the total surface)

Dithiolene transfer to the molybdenum nitrosyl complex [CpMo(CO)2(NO)]: Formation of bimetallic complexes

The reaction of the nitrosyl complex [CpMo(CO)2(NO)] (Cp = η-C5H5) with the nickel dithiolene complex [Ni(S2C2Ph2)2] produces the expected dimolybdenum complex [Mo2(NO)2(μ-S2C2Ph2)2Cp2], but only as a minor product (13% yield). The major product (41%) consists of two separable isomers of the tetranuclear complex [Mo2Ni2(NO)2(μ-S2C2Ph2)4Cp2], which comprises two CpMo(NO)Ni(S2C2Ph2)2units joined through bridging sulfur atoms. The isomers differ in the orientation of one dimeric unit in relation to the other. All three compounds have been structurally characterised

Chan–Lam amination of secondary and tertiary benzylic boronic esters

We report a Chan–Lam coupling reaction of benzylic and allylic boronic esters with primary and secondary anilines to form valuable alkyl amine products. Both secondary and tertiary boronic esters can be used as coupling partners, with mono-alkylation of the aniline occurring selectively. This is a rare example of a transition-metal-mediated transformation of a tertiary alkylboron reagent. Initial investigation into the reaction mechanism suggests that transmetalation from B to Cu occurs through a single-electron, rather than a two-electron process

Turning intercalators into groove binders: synthesis, photophysics and DNA binding properties of tetracationic mononuclear ruthenium(ii)-based chromophore-quencher complexes.

The synthesis of two new tetracationic mononuclear RuII complexes containing the tetrapyridyl [3,2-a:2',3'-c:3'',2''-h:2''',3'''-j] phenazine ligand in which the uncoordinated site has been converted into a dicationic ethylene-bipyridyldiylium unit is reported. The structure of the complexes is fully assigned through detailed NMR studies and, in one case, through an X-ray crystallography study. Voltammetry, optical spectroscopy and computational studies confirm that the bipyridyldiylium moiety has a low-lying reduction that quenches the 3MLCT-based emission usually observed in such systems. The new complexes interact with DNA in a quite different manner to their dicationic analogues: they both bind to duplex DNA with micromolar affinity through groove binding. These observations are rationalized through a consideration of their structural and electronic properties

Synthesis of boronic ester γ‐lactam building blocks

Saturated heterocycles are found widely in biologically active compounds such as medicinal drugs and agrochemicals. However, boronic acid‐derived building blocks for these structures have limited availability, particularly in comparison to heteroaromatic boronic acids. We report the preparation of boronic ester γ‐lactams through a Cu‐catalysed conjugate borylation‐cyclisation protocol. Using a chiral catalyst, this can be performed in high enantioselectivity. Exploration of the further transformations of these reagents suggest that the boronic esters have much potential as chemical building blocks

Effect of washed versus unwashed red blood cells on transfusion‐related immune responses in preterm newborns

Objectives. Transfusion with washed packed red blood cells (PRBCs) may be associated with reduced transfusion-related proinflammatory cytokine production. This may be because of alterations in recipient immune responses. Methods. This randomised trial evaluated the effect of transfusion with washed compared with unwashed PRBCs on pro-inflammatory cytokines and endothelial activation in 154 preterm newborns born before 29 weeks’ gestation. Changes in plasma cytokines and measures of endothelial activation in recipient blood were analysed after each of the first three transfusions. Results. By the third transfusion, infants receiving unwashed blood had an increase in IL-17A (P = 0.04) and TNF (P = 0.007), whereas infants receiving washed blood had reductions in IL-17A (P = 0.013), TNF (P = 0.048), IL-6 (P = 0.001), IL-8 (P = 0.037), IL-12 (P = 0.001) and IFN-c (P = 0.001). The magnitude of the post-transfusion increase in cytokines did not change between the first and third transfusions in the unwashed group but decreased in the washed group for IL-12 (P = 0.001), IL-17A (P = 0.01) and TNF (P = 0.03), with the difference between the groups reaching significance by the third transfusion (P < 0.001 for each cytokine). Conclusion. The proinflammatory immune response to transfusion in preterm infants can be modified when PRBCs are washed prior to transfusion. Further studies are required to determine whether the use of washed PRBCs for neonatal transfusion translates into reduced morbidity and mortality.Tara M Crawford, Chad C Andersen, Nicolette A Hodyl, Sarah A Robertson and Michael J Star

Managing to lead in private enterprise in China: Work values, demography and the development of trust

Previous work on trust has focused on employee trust in management. However, issues of how leaders develop trust in their followers in leader-member exchange (LMX) are under-explored. Based on theories of leader-member exchange, attribution and industrial convergence, this study investigates how the work values of leaders influence the development of their trust in followers and how this is moderated by demographic factors. A survey of 219 leaders was conducted in privately owned enterprises in China. The findings suggest that the work value of centralization is negatively related to leader trust in follower predictability. Group orientation and formalization are positively related to the development of trust in follower good faith. Moreover, age and level of formal education are found to moderate significantly the relationships between leader work values and development of their trust in followers within the context of China. Copyright © 2007 SAGE Publications