Exploring Regioselective Bond Cleavage and Cross‐Coupling Reactions using a Low‐Valent Nickel Complex

Recently, esters have received much attention as transmetalation partners for cross‐coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}₂(μ‐η²:η²‐C₆H₆)] (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η²‐carbonyl complexes. In contrast, acetylthioesters underwent rapid C_acyl?S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross‐coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η²‐carbonyl complex, phenyl esters were found to predominantly undergo C_aryl?O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2‐naphthyl acetate was also found to undergo clean C_aryl?O bond cleavage, and although stoichiometric cross‐coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.     

Focused ion beam preparation of samples for X‐ray nanotomography

The preparation of hard material samples with the necessary size and shape is critical to successful material analysis. X‐ray nanotomography requires that samples are sufficiently thin for X‐rays to pass through the sample during rotation for tomography. One method for producing samples that fit the criteria for X‐ray nanotomography is focused ion beam/scanning electron microscopy (FIB/SEM) which uses a focused beam of ions to selectively mill around a region of interest and then utilizes a micromanipulator to remove the milled‐out sample from the bulk material and mount it on a sample holder. In this article the process for preparing X‐ray nanotomography samples in multiple shapes and sizes is discussed. Additionally, solid‐oxide fuel cell anode samples prepared through the FIB/SEM technique underwent volume‐independence studies for multiple properties such as volume fraction, average particle size, tortuosity and contiguity to observe the characteristics of FIB/SEM samples in X‐ray nanotomography.     

Polyhydrido Copper Nanoclusters with a Hollow Icosahedral Core: [Cu30H18{E2P(OR)2}12] (E=S or Se; R=nPr,iPr or iBu)

Although atomically precise polyhydrido copper nanoclusters are of prime interest for a variety of applications, they have so far remained scarce. Herein, this work describes the synthesis of a dithiophosphate-protected copper(I) hydride-rich nanocluster (NC), [Cu₃₀H₁₈{S₂P(OnPr)₂}₁₂] ( 1_H ), fully characterized by various spectroscopic methods and single-crystal X-ray diffraction. The X-ray structure of 1_H reveals an unprecedented central Cu₁₂ hollow icosahedron. Six faces of this icosahedron are capped by Cu₃ triangles, the whole Cu₃₀ core being wrapped by twelve dithiophosphate ligands and the whole cluster has ideal S₆ symmetry. The locations of the 18 hydrides in 1_H were ascertained by a single-crystal neutron diffraction study. They are composed of three types: capping μ₃-H, interstitial μ₄-H (seesaw) and μ₅-H ligands (square pyramidal), in good agreement with the DFT simulations. The numbers of hydrides and ligand resonances in the ¹H NMR spectrum of 1_H are in line with their coordination environment in the solid state, retaining the S₆ symmetry in solution. Furthermore, two new Se-protected polyhydrido copper nanoclusters, [Cu₃₀H₁₈{Se₂P(OR)₂}₁₂] ( 2_H : R=iPr 3_H : R=iBu) were synthesized from their sulfur relative 1_H via ligand displacement reaction and their X-ray structures feature the exceptional case where both the NC shape and size are fully conserved during the course of ligand exchange. DFT and TD-DFT calculations allow understanding the bonding and optical properties of clusters 1_H – 3_H . In addition, the reaction of 1_H with [Pd(PPh₃)₂Cl₂] in the presence of terminal alkynes led to the formation of new bimetallic Cu−Pd alloy clusters [PdCu₁₄H₂{S₂P(OnPr)₂}₆(C≡CR)₆] ( 4 : R=Ph; 5 : R = C₆H₄F).     

Neuronal metabolomics by ion mobility mass spectrometry: cocaine effects on glucose and selected biogenic amine metabolites in the frontal cortex, striatum, and thalamus of the rat

We report results of studies of global and targeted neuronal metabolomes by ambient pressure ion mobility mass spectrometry. The rat frontal cortex, striatum, and thalamus were sampled from control nontreated rats and those treated with acute cocaine or pargyline. Quantitative evaluations were made by standard additions or isotopic dilution. The mass detection limit was ～100 pmol varying with the analyte. Targeted metabolites of dopamine, serotonin, and glucose followed the rank order of distribution expected between the anatomical areas. Data was evaluated by principal component analysis on 764 common metabolites (identified by m/z and reduced mobility). Differences between anatomical areas and treatment groups were observed for 53 % of these metabolites using principal component analysis. Global and targeted metabolic differences were observed between the three anatomical areas with contralateral differences between some areas. Following drug treatments, global and targeted metabolomes were found to shift relative to controls and still maintained anatomical differences. Pargyline reduced 3,4-dihydroxyphenylacetic acid below detection limits, and 5-HIAA varied between anatomical regions. Notable findings were: (1) global metabolomes were different between anatomical areas and were altered by acute cocaine providing a broad but targeted window of discovery for metabolic changes produced by drugs of abuse; (2) quantitative analysis was demonstrated using isotope dilution and standard addition; (3) cocaine changed glucose and biogenic amine metabolism in the anatomical areas tested; and (4) the largest effect of cocaine was on the glycolysis metabolome in the thalamus confirming inferences from previous positron emission tomography studies using 2-deoxyglucose.

Synthesis of Anomerically Pure,Furanose‐Free α‐Benzyl‐2‐amino‐2‐deoxy‐d‐altro‐ and d‐manno‐pyranosides and Some of Their Derivatives

The anomerically pure benzyl α‐d‐glycoside of 2‐amino‐2‐deoxy‐mannopyranoside was synthesized from d‐glucopyranose via 2‐amino‐2‐deoxy‐d‐altrose intermediates. Unlike the direct synthesis from mannosamine in the literature, our method provides furanose‐free products. A new method for the preparation of cis‐2,3‐oxazolidinones of 2‐amino‐2‐deoxy‐sugars was developed. A selective removal of the glycosidic benzyl group in the presence of 4,6‐O‐benzylidene protection was developed, which may provide new routes for the synthesis of oligosaccharides. Furanose‐free derivatives of α‐benzyl‐2‐amino‐2‐deoxy‐mannopyranuronic acids synthesized here offered possibilities for direct comparisons to prior literature preparations.     

THE USE OF CARBOXYMETHYL ETHOXYLATE SURFACTANT TO DISSOLVE VITAMIN K1 AND TO OBTAIN LOW INTERFACIAL TENSION AND STABLE EMULSION SYSTEMS

Abstract

The presence of vitamin K₁ in human body is important for preventing the hemorrhagic disease. Due to its very long side chain, vitamin K₁ is highly insoluble in water. We have successfully dissolve a substantial amount of vitamin K₁ in solutions of a commercial surfactant containing carboxymethyl ethoxylates (Hüls B433) and obtained low interfacial tension (IFT) and stable emulsion systems. This paper will present the details of these experiments. The solubilization of vitamin K₁ was estimated from UV absorption. The IFT values were measured by using a spinning drop apparatus and all particle sizes were determined by using laser light scattering. By using the Hüls B433 surfactant and an optimum amount of CaCl₂, we can dissolve vitamin K₁ in water and obtain low IFT systems in the order of 10^?2 dyne/cm. The emulsions obtained in these systems are stable and contain droplet sizes below 65 nm. The dissolution of vitamin K₁ and the IFT behavior in these systems follow the rules for crude oil and prefer larger surfactant micelles.     

DETERMINATION OF LONG-TERM STABILITY OF VITAMIN E EMULSION AND FORMATION OF MICROEMULSIONS BY USING LASER LIGHT SCATTERING AND UV ABSORPTION MEASUREMENTS

This paper presents methods of determining the long-term stability of vitamin E emulsion and formation of microemulsions. Several emulsion systems formed by using anionic, zwitterionic and cationic surfactants have been studied in the presence and absence of NaCI. Several conclusions can be drawn: (1) by using UV absorption and particle size measurements, one may be able to predict the long-term stability of an emulsion or the possibility of forming a microemulsion by measuring the initial properties of an emulsion, (2) in order to form a stable vitamin E emulsion or microemulsion, the initial properties of the emulsion should have the following features : (a) the particle size is ≤ 200 nm, (b) the surfactant system has a saturation value ≥ 1 and (c) the surfactant system can dissolve a substantial amount of vitamin E without causing an increase of the emulsion droplet size and (3) the saturation value and the stability of many vitamin E emulsion systems can be increased by adding an optimum amount of NaCI.