Ruthenium (II) complexes bearing thioether-appended α-iminopyridine ligands: Arene precursors permit access to κ2-N,N and κ3-N,N,S complexes

Herein we report the preparation of a series of Ru(II) complexes featuring α-iminopyridine ligands bearing thioether functionality (NNS^R, where R = Me, CH₂Ph, Ph). Metallation using [(p-cymene)RuCl]₂ permits access to Ru complexes with a κ²-N,N donor set in which the thioether moiety remains uncoordinated. In the presence of a strong field ligand such as acetonitrile or triphenylphosphine, the p-cymene moiety is displaced, and the ligand adopts a κ³-N,N,S binding mode. These complexes are characterized using a combination of solution and solid state methods, including the crystal structure of [(NNS^Me)Ru (NCMe)₂Cl]Cl. The κ²-N,N-Ru(II) complexes are shown to serve as efficient precatalysts for the oxidation of sec-phenethyl alcohol at modest loadings (alcohol: Ru = 20:1), using a variety of external oxidants and solvents. The complex bearing an S-Ph donor was found to be the most active oxidation catalyst of those surveyed, suggesting that the thioether donor plays an active role in the catalytic cycle.     

A classification of continuous wavelet transforms in dimension three

This paper presents a full catalogue, up to conjugacy and subgroups of finite index, of all matrix groups $H<\mathrm{GL}(3,\mathbb{R})$ that give rise to a continuous wavelet transform with associated irreducible quasi-regular representation. For each group in this class, coorbit theory allows to consistently define spaces of sparse signals, and to construct atomic decompositions converging simultaneously in a whole range of these spaces. As an application of the classification, we investigate the existence of compactly supported admissible vectors and atoms for the groups.     

Embedding hypertrees into steiner triple systems

In this paper, we are interested in the following question: given an arbitrary Steiner triple system on vertices and any 3‐uniform hypertree on vertices, is it necessary that contains as a subgraph provided ? We show the answer is positive for a class of hypertrees and conjecture that the answer is always positive.     

Ligand Displacement Reaction Paths in a Diiron Hydrogenase Active Site Model Complex

The mechanism and energetics of CO, 1‐hexene, and 1‐hexyne substitution from the complexes (SBenz)₂[Fe₂(CO)₆] (SBenz=SCH₂Ph) ( 1 ‐CO), (SBenz)₂[Fe₂(CO)₅(η²‐1‐hexene)] ( 1 ‐(η²‐1‐hexene)), and (SBenz)₂[Fe₂(CO)₅(η²‐1‐hexyne)] ( 1 ‐(η²‐1‐hexyne)) were studied by using time‐resolved infrared spectroscopy. Exchange of both CO and 1‐hexyne by P(OEt)₃ and pyridine, respectively, proceeds by a bimolecular mechanism. As similar activation enthalpies are obtained for both reactions, the rate‐determining step in both cases is assumed to be the rotation of the Fe(CO)₂L (L=CO or 1‐hexyne) unit to accommodate the incoming ligand. The kinetic profile for the displacement of 1‐hexene is quite different than that for the alkyne and, in this case, both reaction channels, that is, dissociative (S_N1) and associative (S_N2), were found to be competitive. Because DFT calculations predict similar binding enthalpies of alkene and alkyne to the iron center, the results indicate that the bimolecular pathway in the case of the alkyne is lower in free energy than that of the alkene. In complexes of this type, subtle changes in the departing ligand characteristics and the nature of the mercapto bridge can influence the exchange mechanism, such that more than one reaction pathway is available for ligand substitution. The difference between this and the analogous study of (μ‐pdt)[Fe(CO)₃]₂ (pdt=S(CH₂)₃S) underscores the unique characteristics of a three‐atom S?S linker in the active site of diiron hydrogenases.     

Stereochemical Studies of the Karlotoxin Class Using NMR Spectroscopy and DP4 Chemical‐Shift Analysis: Insights into their Mechanism of Action

After publication of karlotoxin 2 (KmTx2; 1 ), the harmful algal bloom dinoflagellate Karlodinium sp. was collected and scrutinized to identify additional biologically active complex polyketides. The structure of 1 was validated and revised at C49 using computational NMR tools including J‐based configurational analysis and chemical‐shift calculations. The characterization of two new compounds [KmTx8 ( 2 ) and KmTx9 ( 3 )] was achieved through overlaid 2D HSQC NMR techniques, while the relative configurations were determined by comparison to 1 and computational chemical‐shift calculations. The detailed evaluation of 2 using the NCI‐60 cell lines, NMR binding studies, and an assessment of the literature supports a mode of action (MoA) for targeting cancer‐cell membranes, especially of cytostatic tumors. This MoA is uniquely different from that of current agents employed in the control of cancers for which 2 shows sensitivity.     

Total synthesis and biochemical characterization of mirror image barnase

In this study we synthesized and characterized mirror image barnase (B. amyloliquefaciens ribonuclease). d-Barnase was identical to l-barnase, when analyzed by liquid chromatography and mass-spectrometry. Proteolysis of the mirror image enzyme revealed that in contrast to its native counterpart, d-barnase was completely stable to digestive proteases. In enzymatic assays, d-barnase had the reciprocal chiral specificity and was fully active towards mirror image substrates. Interestingly, d-barnase also hydrolyzed the substrate of the native chirality, albeit 4000 times less efficiently. This effect was further confirmed by digesting a native 112-mer RNA with the enzyme. Additional studies revealed that barnase accommodates a range of substrates with various chiralities, but the prime requirement for guanosine remains. These studies point toward using mirror image enzymes as modern agents in biotechnology.     

A Central Limit Theorem for Non-stationary Strongly Mixing Random Fields

In this paper we extend a central limit theorem of Peligrad for uniformly strong mixing random fields satisfying the Lindeberg condition in the absence of stationarity property. More precisely, we study the asymptotic normality of the partial sums of uniformly \(\alpha \)-mixing non-stationary random fields satisfying the Lindeberg condition, in the presence of an extra dependence assumption involving maximal correlations.     

Mechanistic Evidence of a Ni(0/II/III) Cycle for Nickel Photoredox Amide Arylation

This work demonstrates the dominance of a Ni(0/II/III) cycle for Ni-photoredox amide arylation, which contrasts with other Ni-photoredox C-heteroatom couplings that operate via Ni(I/III) self-sustained cycles. The kinetic data gathered when using different Ni precatalysts supports an initial Ni(0)-mediated oxidative addition into the aryl bromide. Using NiCl₂ as the precatalyst resulted in an observable induction period, which was found to arise from a photochemical activation event to generate Ni(0) and to be prolonged by unproductive comproportionation between the Ni(II) precatalyst and the in situ generated Ni(0) active species. Ligand exchange after oxidative addition yields a Ni(II) aryl amido complex, which was identified as the catalyst resting state for the reaction. Stoichiometric experiments showed that oxidation of this Ni(II) aryl amido intermediate was required to yield functionalized amide products. The kinetic data presented supports a rate-limiting photochemically-mediated Ni(II/III) oxidation to enable C−N reductive elimination. An alternative Ni(I/III) self-sustained manifold was discarded based on EPR and kinetic measurements. The mechanistic insights uncovered herein will inform the community on how subtle changes in Ni-photoredox reaction conditions may impact the reaction pathway, and have enabled us to include aryl chlorides as coupling partners and to reduce the Ni loading by 20-fold without any reactivity loss.