Synthesis of Low-Valent Dinuclear Group 14 Compounds with Element–Element Bonds by Transylidation

Dinuclear low-valent compounds of the heavy main group elements are rare species owing to their intrinsic reactivity. However, they represent desirable target molecules due to their unusual bonding situations as well as applications in bond activations and materials synthesis. The isolation of such compounds usually requires the use of substituents that provide sufficient stability and synthetic access. Herein, we report on the use of strongly donating ylide-substituents to access low-valent dinuclear group 14 compounds. The ylides not only impart steric and electronic stabilization, but also allow facile synthesis via transfer of an ylide from tetrylene precursors of type ^RY₂E to ECl₂ (E=Ge, Sn; ^RY=TolSO₂(PR₃)C with R=Ph, Cy). This method allowed the isolation of dinuclear complexes amongst a germanium analogue of a vinyl cation, [(^PhY)₂GeGe(^PhY)]⁺ with an electronic structure best described as a germylene-stabilized Ge^II cation and a ylide(chloro)digermene [^CyY(Cl)GeGe(Cl)^CyY] with an unusually unsymmetrical structure.     

High-throughput mass finger printing and Lewis blood group assignment of human milk oligosaccharides

The structural diversity of human milk oligosaccharides (HMOs) strongly depends on the Lewis (Le) blood group status of the donor which allows a classification of these glycans into three different groups. Starting from 50 μL of human milk, a new high-throughput, standardized, and widely automated mass spectrometric approach has been established which can be used for correlation of HMO structures with the respective Lewis blood groups on the basis of mass profiles of the entire mixture of glycans together with selected fragment ion spectra. For this purpose, the relative abundance of diagnostically relevant compositional species, such as Hex₂Fuc₂ and Hex₃HexNAc₁Fuc₂, as well as the relative intensities of characteristic fragment ions obtained thereof are of key importance. For each Lewis blood group, i.e., Le(a − b+), Le(a + b−), and Le(a − b−), specific mass profile and fragment ion patterns could be thus verified. The described statistically proven classification of the derived glycan patterns may be a valuable tool for analysis and comparison of large sets of milk samples in metabolic studies. Furthermore, the outlined protocol may be used for rapid screening in clinical studies and quality control of milk samples donated to milk banks.     

Selective Antimicrobial and Antibiofilm Disrupting Properties of Functionalized Diamond Nanoparticles Against Escherichia coli and Staphylococcus aureus

Diamond nanoparticles (NDs) have demonstrated great promise as useful materials in a variety of biomedical settings. In this paper, the antimicrobial and antibiofilm activities of variously functionalized NDs against two common bacterial targets Gram‐negative bacterium Escherichia coli and Gram‐positive bacterium Staphylococcus aureus are compared. Hydroxylated (ND‐OH), aminated (ND‐NH₂), carboxylated (ND‐COOH), mannose (ND‐Mannose), tri‐thiomannoside (ND‐Man₃), or tri‐thiolactoside (ND‐Lac₃)‐modified NDs are fabricated and evaluated in the present work. Of these, the mannose‐modified NDs are found to interfere most strongly with the survival of S. aureus, but not to influence the growth of E. coli. In contrast, particles featuring lactosyl units have the opposite effect on S. aureus growth. Sugar‐functionalized NPs reported to display antibacterial effects are rare. Only ND‐COOH particles are seen to have any effect on the growth profile of E. coli, but the effects are moderate. On the other hand, both ND‐NH₂ and ND‐COOH are found to inhibit E. coli‐induced biofilm formation at levels comparable to the known E. coli biofilm disruptor, ampicillin (albeit at concentrations of 100 μg mL^?1). However, none of the modified particles examined here reveal any significant activity as disruptors of S. aureus‐induced biofilm formation even at the highest concentrations studied.     

CARBAMOYL AND THIOCARBAMOYL DERIVATIVES OF N-BENZYL-AMINOMETHYL-DIMETHYL-PHOSPHINE OXIDE

A series of thirteen new carbamoyl and thiocarbamoyl derivatives of N-benzyl-aminomethyl-dimethyl-phosphine oxide have been synthesized and characterized. The compounds were prepared via interaction of N-benzyl-aminomethyl-dimethyl-phosphine oxide with the corresponding isocyanates or isothiocyanates. The composition of the synthesized novel compounds was proved by elemental analysis for nitrogen and the structures were confirmed by IR,¹H-, ³¹P-³¹P{¹H} NMR spectroscopy and by mass spectrometry.     

Urea and Thiourea Derivatives of Bis(dimethyl-phosphinoylmethyl)-amine

A group of hitherto unknown 1-aryl-3,3-bis(dimethyl-phosphinoylmethyl)-, 1-benzyl-3,3-bis(dimethyl-phosphinoylmethyl)- and 1-cyclohexyl-3,3-bis(dimethyl-phosphinoylmethyl) ureas and thioureas 1-10 have been synthesized, characterized, and are reported in this article. The compounds were prepared via reaction of corresponding isocyanates or isothiocyanates with the secondary phosporus-containing amine: bis(dimethyl-phosphinoylmethyl)-amine. The composition of the novel compounds was proved by elemental analysis, corresponding structures were confirmed by IR, 1 H-, 31 P-, 31 P{ 1 H}-NMR spectroscopy and by mass spectrometry.     

Dynamics and heterogeneity of Pb(II) binding by SiO2 nanoparticles in an aqueous dispersion

Pb(II) binding by SiO(2) nanoparticles in an aqueous dispersion was investigated under conditions where the concentrations of Pb(2+) ions and nanoparticles are of similar magnitude. Conditional stability constants (log K) obtained at different values of pH and ionic strength varied from 4.4 at pH 5.5 and I = 0.1 M to 6.4 at pH 6.5 and I = 0.0015 M. In the range of metal to nanoparticle ratios from 1.6 to 0.3, log K strongly increases, which is shown to be due to heterogeneity in Pb(II) binding. For an ionic strength of 0.1 M the Pb(2+)/SiO(2) nanoparticle system is labile, whereas for lower ionic strengths there is loss of lability with increasing pH and decreasing ionic strength. Theoretical calculations on the basis of Eigen-type complex formation kinetics seem to support the loss of lability. This is related to the nanoparticulate nature of the system, where complexation rate constants become increasingly diffusion controlled. The ion binding heterogeneity and chemodynamics of oxidic nanoparticles clearly need further detailed research.     

N-Heterocyclic Olefins on a Silicon Surface

The adsorption of N-heterocyclic olefins (NHOs) on silicon is investigated in a combined scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory study. We find that both of the studied NHOs bind covalently, with ylidic character, to the silicon adatoms of the substrate and exhibit good thermal stability. The adsorption geometry strongly depends on the N-substituents: for large N-substituents, an upright adsorption geometry is favored, while a flat-lying geometry is found for the NHO with smaller wingtips. These different geometries strongly influence the quality and properties of the obtained monolayers. The upright geometry leads to the formation of ordered monolayers, whereas the flat-lying NHOs yield a mostly disordered, but denser, monolayer. The obtained monolayers both show large work function reductions, as the higher density of the flat-lying monolayer is found to compensate for the smaller vertical dipole moments. Our findings offer new prospects in the design of tailor-made ligand structures in organic electronics and optoelectronics, catalysis, and material science.     

Computer-Driven Development of Ylide Functionalized Phosphines for Palladium-Catalyzed Hiyama Couplings

Palladium-catalyzed couplings of silicon enolates with aryl electrophiles are of great synthetic utility, but often limited to expensive bromide substrates. A comparative experimental study confirmed that none of the established ligand systems allows to couple inexpensive aryl chlorides with α-trimethylsilyl alkylnitriles. In contrast, ylide functionalized phosphines (YPhos) led to encouraging results. A statistical model was developed that correlates the reaction yields with ligand features. It was employed to predict catalyst structures with superior performance. With this cheminformatics approach, YPhos ligands were tailored specifically to the demands of Hiyama couplings. The newly synthesized ligands displayed record-setting activities, enabling the elusive coupling of aryl chlorides with α-trimethylsilyl alkyl nitriles. The preparative utility of the catalyst system was demonstrated by the synthesis of pharmaceutically meaningful α-aryl alkylnitriles, α-arylcarbonyls and biaryls.