Formal Nickelate(−I) Complexes Supported by Group 13 Ions

Formal nickelate(?I) complexes bearing Group 13 metalloligands (M=Al and Ga) were isolated. These 17 e^? complexes were synthesized by one‐electron reduction of the corresponding Ni⁰→M^III precursors, and were investigated by single‐crystal X‐ray diffraction, EPR spectroscopy, and quantum chemical calculations. Collectively, the experimental and computational data support: 1) the strengthening of the Ni?M bond upon one‐electron reduction, and 2) the delocalization of the unpaired spin across the Ni and M atoms. An intriguing electronic configuration is revealed where three valence electrons occupy two σ‐type bonding interactions: Ni(3d )²→M and σ‐(Ni?M)¹. The latter is an unusual Ni?M σ‐bonding molecular orbital that comprises primarily the Ni 4p_z and M np_z/ns atomic orbitals.     

Stereochemical basis for the anti-chlamydial activity of the phosphonate protease inhibitor JO146

JO146, a mixture of two diastereomers of a peptidic phosphonate inhibitor for Chlamydial HtrA (CtHtrA), has reported activity against Chlamydia species in both human and koala. In this study we isolated the individual diastereomers JO146-D1 and JO146-D2 (in ≥90% purity) and assessed their individual inhibitory activity against the serine protease human neutrophil elastase (HNE) which is structurally and functionally related to CtHtrA, as well as in Chlamydia trachomatis cell culture. JO146-D2 [S,S,R-Boc-Val-Pro-Val^P(OPh)₂], the isomer with the physiologically relevant valine at P1, had an approximate 2.5 – fold increase in in vitro HNE inhibition potency over JO146-D1 [S,S,S-Boc-Val-Pro-Val^P(OPh)₂] and greater than 100 – fold increase in cellular anti-chlamydial activity compared to JO146-D1 which possesses the unnatural valine at P1. JO146 and the individual diastereomers had excellent selectivity for the serine protease HNE over the potential off-target serine proteases trypsin and chymotrypsin. Docking studies supported the biological data with a geometrically unfavoured interaction observed between the P1 valine residue of JO146-D1 and the enzyme S1 sub-pocket.     

Chiral trans-carboxylic trifluoromethyl 2-imidazolines by a Ag2O-catalyzed Mannich-type reaction

Trifluoromethyl aldimines derived from α-amino esters have proven to be very good starting materials to obtain the title compounds. A Ag₂O-catalyzed Mannich-type/cyclization cascade reaction starting from suitable α-isocyano acetates leads to enantiopure valuable trans-carboxylic trifluoromethyl substituted 2-imidazolines by a highly stereoselective addition without the need to add organocatalysts.     

Synthesis and reactivity against Cp2TiCl of 4-isoprenyl-β-lactams. Trapping of N-titanoimidoyl radicals from cyanoformyl-2-azetidinones

A Staudinger reaction between methoxyketene and two different imines formed from citral afforded, after chemical transformation, the (E/Z)-4-alkenylepoxy-2-azetidinones 2, 3 and 4. These compounds, by reaction with Cp₂TiCl, did not cyclize to afford the expected polycyclic β-lactams, but the corresponding allylic alcohols 12, 13 and 15 were obtained instead. Unexpectedly, the treatment of cyanoepoxide (E)-3 with Cp₂TiCl also gave the hydroxyl aldehyde (E)-14 whose formation suggests to us that a possible radical reduction of the cyano group might have occurred, and we lastly succeeded in the capture of the N-titanoimidoyl radicals. The behaviour observed for the isoprenoid side chain in the Staudinger reaction, the reactions with Cp₂TiCl, as well as the trapping of N-titanoimidoyl radicals generated from benzocyanoformyl-2-azetidinones with the Ti(III) reagent, are discussed.     

On weight functions which admit explicit Gauss-Turán quadrature formulas

The main purpose of this paper is the construction of explicit Gauss-Turán quadrature formulas: they are relative to some classes of weight functions, which have the peculiarity that the corresponding -orthogonal polynomials, of the same degree, are independent of . These weights too are introduced and discussed here. Moreover, highest-precision quadratures for evaluating Fourier-Chebyshev coefficients are given.

     

Hypercomplex structures on four-dimensional Lie groups

The purpose of this paper is to classify invariant hypercomplex structures on a -dimensional real Lie group . It is shown that the -dimensional simply connected Lie groups which admit invariant hypercomplex structures are the additive group of the quaternions, the multiplicative group of nonzero quaternions, the solvable Lie groups acting simply transitively on the real and complex hyperbolic spaces, and , respectively, and the semidirect product . We show that the spaces and possess an of (inequivalent) invariant hypercomplex structures while the remaining groups have only one, up to equivalence. Finally, the corresponding hyperhermitian -manifolds are determined.

     

Influence of structure on binding of chlorophylls to peptide ligands

Four classes of chlorophyll (Chl), a, b, c, and d, are involved in photosynthesis within cyanobacteria, algae, and plants. These classes have different evolutionary origins, chemical properties, and biological functions. Our results demonstrate that peptide-bound ligands provided by the imidazole group of histidine and the charge-compensated glutamate-arginine ion pair readily form coordination bonds with Chls a and d but do not interact significantly with Chls b and c. These ligands are apparently not sufficiently strong Lewis bases to displace strongly coordinated water from Chls b and c. These differences determine specificity of binding of Chls in light-harvesting complexes and play an important role in assembly of stable Chl-protein complexes, which has had a profound impact on the evolution of photosynthetic organisms.     

1,3-dipolar cycloaddition reactions of azomethine ylides on enantiomerically pure (E)-γ-alkoxy-α,β-unsaturated esters.

Enantiomerically pure (E)-γ-alkoxy-α,β-unsaturated esters were reacted with azomethine ylides obtained from glycine imines in the presence of LiBr and diazabicycloundecene (DBU), to afford tetrasubstituted pyrrolidines with complete regiocontrol and fair to excellent diastereoselectivity (only two diastereoisomers formed in up to 96: 4 diastereoisomeric ratio). The results are compared with those of other 1,3-dipolar cycloadditions, and the origin of stereocontrol is discussed.     

Self-assembled monolayers and electrostatically self-assembled multilayers of polyalkylviologens on sulfonate-modified gold and indium–tin–oxide electrodes

Self-assembly (SA) of polyviologens with linear alkyl spacers PVn (n = 3–10) on sulfonate-primed gold and ITO electrode surfaces has been investigated by CV, QCM, XPS and AFM. The polymers form stable and relatively dense monolayers even from 10⁻⁴ M PVn concentration. The viologen surface density is decreased as n is increased but for n = 10 and on alkylsulfonate-primed surfaces a strong adsorption takes place, with decreased redox potential and very narrow cyclic voltammogram of the absorbed layer due to organized structures on the surface.Stable and regular electrostatically self-assembled (ESA) multilayers are built on sulfonate-primed surfaces with PV3 and polysulfonates. From XPS analysis, the composition of the PVn/polysulfonate multilayers corresponds to a 1:1 ratio of polyanion and polycation charges, i.e., no extra non-polymeric ion is present, independently from the alkane chain length. The rate of electron transfer within the multilayers (diffusion coefficient = ca. 10⁻⁹ cm² s⁻¹) is higher than for analogous bulk materials.