Palladium(I) carbonyl carboxylate clusters cyclo-[Pd2(μ-CO)2(μ-OCOR)2]n (n = 2 or 3): Structure and reactivity

The interaction of palladium(+1) cluster Pd₄(μ-CO)₄(μ-OAc)₄ with saturated and unsaturated carboxylic acids was studied. It was found, that the substitution of acetates groups on others carboxylates leads to the clusters with different nuclearity. Palladium(+1) carbonyl carboxylate complexes of composition [Pd(μ-CO)(μ-OCOR)]_n, where R = CF₃, CCl₃, CH₂Cl, MeCH = CMe, Me, Prⁱ, Bu, Buⁱ, Bu^tert, n-C₅H₁₁ and n = 4 or 6 were synthesized. According to X-ray data all clusters possess cyclic planar metal cores with alternate pairs of μ-carbonyl and μ-carboxylate ligands. The presence of bulky alkyl fragments in the carboxylate ligand increases the nuclearity of the cluster compared to that of the starting palladium(+1) carbonyl acetate of composition Pd₄(μ-CO)₄(μ-OAc)₄ due, apparently, to steric hindrance.     

Structure of radical cations of saturated heterocyclic compounds with two heteroatoms as studied by electron paramagnetic resonance, electron-nuclear double resonance, and density functional theory calculations

The radical cations of piperazine, morpholine, thiomorpholine, and thioxane were investigated by electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy in a solid Freon matrix. Optimized geometry and magnetic parameters of the radical cations were calculated using a density functional theory (DFT)/Perdew-Burke-Ernzerhof (PBE) method. Both experimental and theoretical results suggest that all the studied species adopt chair (or distorted chair) conformations. No evidence for the boat conformers with intramolecular sigma-bonding between heteroatoms were obtained. In the cases of morpholine and thioxane, the oxygen atoms are characterized by relatively small spin populations, whereas a major part of spin density is located at N and S atoms, respectively. The thiomorpholine radical cation exhibits nearly equal spin population of N and S atoms. In most cases (except for thioxane), the calculated magnetic parameters agree with the experimental data reasonably well.     

Analysis and elimination of artifacts in indirect covariance NMR spectra via unsymmetrical processing

Indirect covariance NMR offers an alternative method of extracting spin-spin connectivity information via the conversion of an indirect-detection heteronuclear shift-correlation data matrix to a homonuclear data matrix. Using an IDR (inverted direct response)-HSQC-TOCSY spectrum as a starting point for the indirect covariance processing, a spectrum that can be described as a carbon-carbon COSY experiment is obtained. These data are analogous to the autocorrelated 13C-13C double quantum INADEQUATE experiment except that the indirect covariance NMR spectrum establishes carbon-carbon connectivities only between contiguous protonated carbons. Cyclopentafuranone and the complex polynuclear heteroaromatic naphtho[2',1':5,6]-naphtho[2',1':4,5]thieno[2,3-c]quinoline are used as model compounds. The former is a straightforward example because of its well-resolved proton spectrum, while the latter, which has considerable resonance overlap in its congested proton spectrum, gives rise to two types of artifact responses that must be considered when using the indirect covariance NMR method.     

Tautomeric equilibria in the reaction products of asymmetric 1,3-diamines with β-dicarbonyl compounds

The reaction products of 1,3-butanediamine and 2-methyl-2,4-pentanediamine with β-keto aldehydes were shown by ¹H and ¹³C NMR spectroscopy to exist as tautomeric mixtures in solutions, comprising one cyclic and two open-chain forms due to the non-equivalence of the amino groups. The chain products exist as Z- and E-isomers. After equilibration, the products from 1,3-butanediamine contain relatively less of the cyclic form than those from 2-methyl-2,4-pentanediamine. The products of 2-methyl-2,4-pentanediamine with p-substituted aroylacetaldehydes, exhibit a linear correlation between log K of the ring-chain equilibria and Hammett's σ values of the aromatic ring substituents. α-Substitution of β-keto aldehydes notably increased the relative amounts of the chain E-isomers in their condensation products and also resulted in the formation of two diastereomers for each of the cyclic products. No ring-chain equilibria were observed in the products of 1,3-butanediamine and 2-methyl-2,4-pentanediamine with β-diketones, β-keto esters, or β-keto amides.     

Biomimetic total synthesis of (+)-himbacine

On treatment with trifluoroacetic acid butenolide 14 undergoes N-Boc deprotection and condensation followed by an iminium ion activated intramolecular Diels-Alder cycloaddition to give the (+)-himbacine precursor 11 on reductive work up. Compound 11 was converted into (+)-himbacine in four synthetic steps. [reaction: see text]     

Diastereoselective synthesis of (2S)-2-[(R)-1H-indol-3-yl(phenyl)methyl]-2,3-dihydro-1H-inden-1-one

Double asymmetric induction in Michael reactions has been studied. Enantioselective alkylation of a cyclic ketone (1-indanone) with α-phenyl-nor-gramine was carried out. The relative configuration of (2S^∗)-2-[(R^∗)-1H-indol-3-yl(phenyl)methyl]-2,3-dihydro-1H-inden-1-one was established by X-ray diffraction. The relative configuration of (R^∗,R^∗,S^∗)- and (S^∗,R^∗,S^∗)-2-1H-indol-3-yl(phenyl)methyl]-2,3-dihydro-1H-inden-1-ols was established by ¹H NMR studies.     

Gold nanoparticle patterning of silicon wafers using chemical e-beam lithography

This paper demonstrates a novel facile method for fabrication of patterned arrays of gold nanoparticles on Si/SiO2 by combining electron beam lithography and self-assembly techniques. Our strategy is to use direct-write electron beam patterning to convert nitro functionality in self-assembled monolayers of 3-(4-nitrophenoxy)-propyltrimethoxysilane to amino functionality, forming chemically well-defined surface architectures on the 100 nm scale. These nanopatterns are employed to guide the assembly of citrate-passivated gold nanoparticles according to their different affinities for amino and nitro groups. This kind of nanoparticle assembly offers an attractive new option for nanoparticle patterning a silicon surface, as relevant, for example, to biosensors, electronics, and optical devices.     

Electrochemical and structural study of LiCoPO<Subscript>4</Subscript>-based electrodes

LiCoPO₄ samples were synthesized by two different techniques (high-temperature solid-state reaction and lower-temperature synthesis using NH₄CoPO₄·H₂O as precursor) and tested as cathode materials for 5-V lithium batteries. An irreversible lithium deinsertion was observed for the high-temperature sample. In contrast, the application of lower-temperature synthesis led to a significant improvement of the lithium storage reversibility. Different delithiation mechanisms in LiCoPO₄ were found for the samples obtained by different synthetic techniques. The nature of capacity fading during cycling of the cells is discussed.     

Polyelectrolyte-mediated protein adsorption: fluorescent protein binding to individual polyelectrolyte nanospheres

We have used confocal fluorescence microscopy with single molecule sensitivity to characterize uptake and release of fluorescent protein (mEosFP) molecules by individual spherical polyelectrolyte brush (SPB) nanoparticles that were immobilized on a glass surface. The SPB particles consisted of a solid core particle of 100 nm diameter onto which long polyelectrolyte chains were affixed. They could be loaded with up to 30 000 mEosFP molecules in a solvent of low ionic strength. The concentration dependence of protein loading can be described with a simple bimolecular binding model, characterized by an equilibrium dissociation coefficient of 0.5 microM. Essentially complete release of the bound proteins was observed after increasing the ionic strength by adding 250 mM NaCl to the solvent. Fluorescence emission spectra and time-resolved fluorescence intensity decays were measured on individual, mEosFP-loaded SPB nanoparticles, and also on the dissolved mEosFP before and after adsorption. These results indicate that the mEosFP molecules remained structurally intact in this procedure. Hence, the present investigation demonstrates unambiguously that polyelectrolyte-mediated protein adsorption onto SPB particles presents a viable process for protein immobilization.