Synthesis of hybrid gold-gold sulfide colloidal particles

The nucleation and growth mechanism of nanometer size gold onto gold sulfide colloidal particles by irradiation-induced reduction is reported. The process is characterized by ultraviolet-visible spectroscopy, electronic diffraction, and high-resolution transmission electron microscopy, allowing for observation of several key intermediates and characteristics of the growth mechanism. The formation mechanism of gold on the surface of the gold sulfide particles is shown to depend strongly on the deposition rate. At low dose rate, gold nucleates preferentially onto specific gold-rich Au2S facets {110}, resulting in epitaxial growth. The gold crystal lattice plastically deforms near the interface to accommodate a substantial lattice mismatch. Upon increasing gold precursor concentration, this low dose rate results in growth of elongated gold island on the gold sulfide surface. At a high dose rate, several randomly oriented gold particles are simultaneously produced on gold sulfide, resulting in a layered structure. The absorption spectra of these particles show a dominant surface plasmon band, whose peak wavelength shifts markedly to the red as layered structure is formed.     

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.     

Stereo- and Regiochemical Effect of N,N-Dialkylamide Extractants on the Speciation of Pu Complexes

The relationship between extractant stereochemistry and their extraction performance has only poorly been established. In order to address a part of this concern, we investigated the Pu(IV) liquid-liquid extraction (LLE) by using the N,N-di-(2-ethylhexyl)butyramide (DEHBA), as well as those of its position isomers. DEHBA (ββ-isomer) and N-(2-ethylhexyl)-N-(oct-3-yl)butyramide (EHOBA or αβ-isomer) were synthesized as a mixture of stereoisomer or stereoenriched (R,S)- and (S,S)-diastereoisomers, and were all assessed for Pu^IV LLE. The results showed that both the position and the stereoisomerism of the aliphatic substituents affect Pu^IV complexation and extraction. We found that Pu extraction is lowered by factor 2 to 4 when the ethyl branching group is closer to the complexing site. UV-vis spectroscopy showed that this extraction decrease was affected by steric hindrance inducing a deprivation of Pu inner sphere complex. Effect of stereoisomerism is highlighted for branching closer to the complexing site (α-position). Enantiopure DEHBA stereoisomers provided similar Pu extraction, whereas a slight decrease could be noticed for the more cluttered stereoenriched (αβ)-isomers, which was also concomitant with a smaller population of inner sphere complex. In contrast, the stereoisomers mixture led to a strong decrease of Pu extraction because of an antagonistic association in the mixed complexes.     

Cover Feature: Copper and Nickel Complexes of Oxamate−Phenol Containing Ligands: A Structural Dichotomy in Oxidized Species (Eur. J. Inorg. Chem. 15/2023)

The copper and nickel complexes of two tetradentate ligands derived from bis(aminophenol) and bis(phenol) architectures connected by an oxamate linker were isolated. Depending on the metal and ligand, the complex is isolated with either an intact (deprotonated) ligand ( 1²⁻ ), one-electron oxidized ligand ( 2⁻ ) or quinone form ( 3 ). Surprisingly, the Mannich base is easier to oxidize than the amidophenol derivatives. The complexes were characterized by X-ray diffraction, cyclic voltammetry, UV-Vis-NIR and EPR spectroscopies. Complex 1 shows two reversible oxidation waves assigned to the successive iminosemiquinone/aminophenolate redox systems. Complex 2⁻ shows an intense NIR feature, as well as an EPR signal at g_iso=2.043, consistent with a metallic contribution to the main ligand radical SOMO. Complex 3 shows the typical feature of an isolated Cu(II) complex. Spectro-electrochemistry coupled to DFT calculations demonstrate a ligand-centered oxidative redox chemistry for all the complexes.     

Blow-up of Critical Besov Norms at a Potential Navier–Stokes Singularity

We prove that if an initial datum to the incompressible Navier–Stokes equations in any critical Besov space \({\dot B^{-1+\frac 3p}_{p,q}({\mathbb {R}}^{3})}\), with \({3 < p, q < \infty}\), gives rise to a strong solution with a singularity at a finite time \({T > 0}\), then the norm of the solution in that Besov space becomes unbounded at time T. This result, which treats all critical Besov spaces where local existence is known, generalizes the result of Escauriaza et al. (Uspekhi Mat Nauk 58(2(350)):3–44, 2003) concerning suitable weak solutions blowing up in \({L^{3}({\mathbb R}^{3})}\). Our proof uses profile decompositions and is based on our previous work (Gallagher et al., Math. Ann. 355(4):1527–1559, 2013), which provided an alternative proof of the \({L^{3}({\mathbb R}^{3})}\) result. For very large values of p, an iterative method, which may be of independent interest, enables us to use some techniques from the \({L^{3}({\mathbb R}^{3})}\) setting.     

Asymmetric synthesis of (-)-1-hydroxyquinolizidinone, a common intermediate for the syntheses of (-)-homopumiliotoxin 223G and (-)-epiquinamide

The short and efficient asymmetric synthesis of (-)-1-hydroxyquinolizidinone was achieved in seven steps and 25.2% overall yield from readily available 5-chloropentanal. It is a key intermediate in the formal syntheses of (-)-homopumilotoxin 223G and (-)-epiquinamide.     

Photochemical dehydration of acetamide in a cryogenic matrix

Vacuum ultraviolet (VUV) irradiation of acetamide has been monitored by Fourier transform infrared spectroscopy in argon matrix at 10 K. Several primary photoproducts, including HNCO ratio CH(4) and CO ratio CH(3)NH(2) molecular complexes, and acetimidic acid, which is reported for the first time, were characterized. The acetimidic acid identification was based on comparison between the experimental and theoretical (B3LYP) infrared spectra. Acetimidic acid is found in argon matrix in the (s-Z)-(E) and (s-Z)-(Z) configurations. It is also an intermediate in the VUV decomposition process, its dehydration leads to the formation of CH(3)CN ratio H(2)O molecular complex. The assignment of the complex was achieved by co-depositing the pairs of respective species and by ab initio calculation.     

The marine sponge Plakortis zyggompha: a source of original bioactive polyketides

Three new spiculoic acids 1-3 and two members of a new closely related family of natural products named zyggomphic acids 4 and 5 were isolated from the very little studied marine sponge Plakortis zyggompha. Both families of compounds share a unique trans-hydrindan-2-one skeleton with six stereogenic centers. A total of 15 new metabolites were isolated from this sponge, all are of polyketide origin. The structures were elucidated using LC-MS, 1D, and 2D NMR methods. The absolute stereochemistry was determined by circular dichroism. The large number of close bioactive analogues allowed us to propose preliminary structure-activity relationships as antitumoral and antimycobaterial agents.