Hydroxy-amide Functionalized Azolium Salts for Cu-Catalyzed Asymmetric Conjugate Addition: Stereocontrol Based on Ligand Structure and Copper Precatalyst

A series of hydroxy-amide functionalized azolium salts have been designed and synthesized for Cu-catalyzed asymmetric conjugate addition reaction. The (CH₂)₂-bridged hydroxy-amide functionalized azolium ligand precursors <b>2</b>, in addition to the previously reported CH₂-bridged azolium salts <b>1</b>, have been prepared from readily available enantiopure β-amino alcohols. The combination of a Cu species with <b>1</b> or <b>2</b> efficiently promoted the 1,4-addition reaction of cyclic enones with dialkylzincs. For example, the reaction of 2-cyclohepten-1-one (<b>17</b>) with Bu₂Zn in the presence of catalytic amounts of Cu­(OTf)₂ and <b>1</b> gave (<i>S</i>)-3-butylcycloheptanone (<b>20</b>) in 99% yield and 96% ee. On the other hand, when the reaction was carried out under the influence of Cu­(OTf)₂ combined with <b>2</b>, (<i>R</i>)-<b>20</b> in preference to (<i>S</i>)-<b>20</b> was obtained in 98% yield and 80% ee. In this manner, the enantioselecvity was switched by controlling the structure of chiral ligand. Additionally, the reversal of enantioselectivity was also achieved by changing the Cu precatalyst from Cu­(OTf)₂ to Cu­(acac)₂ with the same ligand. The combination of Cu­(acac)₂ with CH₂-bridged azolium salt <b>1</b> in the reaction of <b>17</b> with Bu₂Zn led to formation of (<i>R</i>)-<b>20</b> as a major product in 55% yield and 80% ee. This result was in contrast to the Cu­(OTf)₂/<b>1</b> catalytic system, where the 1,4-adduct with opposite configuration was obtained. Moreover, use of the Cu­(acac)₂/<b>2</b> catalytic system produced (<i>S</i>)-<b>20</b>, while (<i>R</i>)-<b>20</b> was formed by the Cu­(OTf)₂/<b>2</b> catalytic system. Thus, it was found that either varying the linker of the chiral ligands or changing the counterion of Cu species between a OTf and acac ligand initially on the metal led to dual enantioselective control in the 1,4-addition reaction

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

A simple, high-concentration (up to 0.6 M Cu salt) synthesis of sub-10-nm copper nanoparticles (Cu NPs) was developed in ethylene glycol at room temperature under ambient air conditions using 1-amino-2-propanol (AmIP) as the stabilizer. Monodispersed AmIP-Cu NPs of 3.5 ± 1.0 nm were synthesized in a high yield of ∼90%. Thus, nearly 1 g of sub-10-nm Cu NP powder was obtained using a one-step synthesis for the first time. It is proposed that metallacyclic coordination stability of a five-membered ring type between the Cu and AmIP causes the high binding force of Am IP onto the Cu surface, resulting in the superior stability of the AmIP-Cu NPs in a solution. The purified powder of AmIP-Cu NPs can be redispersed in alcohol-based solvents up to high Cu contents of 45 wt % for the preparation of Cu nanoink. The resistivity of the conductive Cu film obtained from the Cu nanoink was 30 μΩ cm after thermal heating at 150 °C for 15 min under a nitrogen flow. The long-term resistance stability of the Cu film under an air atmosphere was also demonstrated

Desorption/Ionization Efficiency of Common Amino Acids in Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (SALDI-MS) with Nanostructured Platinum

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) using inorganic nanoparticles has been reported as an organic matrix-free approach. However, the correlation of desorption/ionization (DI) efficiency with analyte chemical structures in SALDI-MS is not clear. In this study, we investigated the DI efficiency of 20 common amino acids and several peptides in SALDI-MS with Pt nanoparticles with thin projections on the surface (termed with Pt nanoflowers, Pt Nfs) on silicon substrates. The fluorocarbon-based hydrophobic perfluorodecyltrichlorosilane (FDTS)-Pt Nf substrates enabled the simultaneous analysis of all 20 common amino acids in negative-ion mode, whereas MALDI-MS was able to detect only two amino acids, proline and glutamic acid, from the same mixture in negative-ion mode. The SALDI-MS produced high ion yields for arginine and proline in positive-ion mode as well as for glutamic acid and aspartic acid in negative-ion mode. A linear correlation was found between the ion yield and the gas-phase proton affinity or acidity of amino acids in SALDI-MS, consistent with the MALDI-MS analysis of amino acids, although the linear correlation in the SALDI-MS was poor in comparison with that of MALDI-MS. It was suggested that the ion yields of amino acids (i.e., the DI process) are mainly determined by the same factors regardless of the ionization method employed in both MALDI performed using organic matrix and organic matrix-free SALDI

Functionalized Graphene-Coated Cobalt Nanoparticles for Highly Efficient Surface-Assisted Laser Desorption/Ionization Mass Spectrometry Analysis

Graphene-coated cobalt nanoparticles surface-functionalized with benzylamine groups (CoC–NH₂ nanomagnets) were shown to effectively enrich analytes for surface-assisted laser desorption/ionization mass spectrometry (affinity SALDI-MS) analysis. These CoC–NH₂ nanomagnets are highly suited for use with affinity SALDI-MS because their mean diameter of 30 nm, high specific surface area of 15 m² g^–1, and high-strength saturation magnetization of 158 emu g^–1 led to efficient extraction of analytes by magnetic separation, which in turn enabled excellent SALDI-MS performance. Surface modification of CoC nanomagnets with benzylamine groups increased the yield of peptide ions and decreased fragmentation of benzylpyridinium ions, so-called “thermometer ions” formed through soft ionization. The CoC–NH₂ nanomagnets were used to extract perfluorooctanesulfonate from large volumes of aqueous solutions by magnetic separation, which was identified directly by SALDI-MS analysis with high sensitivity even at the sub-part-per-trillion level (∼0.1 ng/L). The applicability of CoC–NH₂ nanomagnets in conjunction with SALDI-MS for the enrichment and detection of pentachlorophenol, bisphenol A, and polyfluorinated compounds (PFCs) with varying chain length, which are environmentally significant compounds, as well as small drugs, was also evaluated

Optical Properties of 2‑Methacryloyloxyethyl Phosphorylcholine-Protected Au₄ Nanoclusters and Their Fluorescence Sensing of C‑Reactive Protein

We present the solution synthesis of thiolated 2-methacryloyloxyethyl phosphorylcholine (MPC)-protected Au nanoclusters (NCs). This water-soluble lipid-mimetic MPC was first used for the size focusing synthesis of thiolate (SR)-protected Au_<i>n</i>(SR)_<i>m</i> NCs. Au₂₅(MPC)₁₈ and Au₄(MPC)₄ NCs are selectively synthesized, without the need for electrophoretic or chromatographic isolation of size mixed products, by including ethanol or not in the solvent. The Au₄(MPC)₄ NCs emit at yellow wavelengths (580–600 nm) with a quantum yield (3.6%) and an average lifetime of 1.5 μs. Also for the first time, we report C-reactive protein (CRP) sensing using Au NCs, with a detection limit (5 nM) low enough for the clinical diagnosis of inflammation. This is based on the quenching effect of specific CRP–MPC interactions on the fluorescence of the Au₄(MPC)₄ NCs