Colloidal gold nanoparticles as catalyst for carbon-carbon bond formation: application to aerobic homocoupling of phenylboronic acid in water

Gold nanoparticles (<2 nm) stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP NPs) were prepared by reduction of AuCl4- with NaBH4 in the presence of PVP and characterized via an array of methods including optical absorption spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray absorption near-edge structure, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. We demonstrate for the first time that the Au:PVP NPs act as catalyst toward homocoupling of phenylboronic acid in water under aerobic conditions. Suppression of biphenyl formation under anaerobic conditions indicates that molecular oxygen dissolved in water is intimately involved in the coupling reactions. A mechanism of the aerobic homocoupling catalyzed by the Au:PVP NPs is proposed on the basis of a crucial role of dissolved oxygen, steric effects on the product yields, and the well-established mechanism for the Pd(II)-based catalysts.     

Molecular recognition by indoleacetic acid-imprinted polymers – effects of 2-hydroxyethyl methacrylate content

Molecularly imprinted polymers for indole-acetic acid were prepared by co-polymerizing N,N-dimethylaminoethyl methacrylate, 2-hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate. The dependence of the affinity and selectivity of the imprinted polymers on HEMA content was evaluated chromatographically. The affinity was improved by increasing the HEMA content; the selectivity of the imprinted polymer was best when the HEMA content was approximately 30%, irrespective of monomer content.     

Glutathione-protected gold clusters revisited: bridging the gap between gold(I)-thiolate complexes and thiolate-protected gold nanocrystals

Small gold clusters (approximately 1 nm) protected by molecules of a tripeptide, glutathione (GSH), were prepared by reductive decomposition of Au(I)-SG polymers at a low temperature and separated into a number of fractions by polyacrylamide gel electrophoresis (PAGE). Chemical compositions of the fractionated clusters determined previously by electrospray ionization (ESI) mass spectrometry (Negishi, Y. et al. J.Am. Chem. Soc. 2004, 126, 6518) were reassessed by taking advantage of freshly prepared samples, higher mass resolution, and more accurate mass calibration; the nine smallest components are reassigned to Au10(SG)10, Au15(SG)13, Au18(SG)14, Au22(SG)16, Au22(SG)17, Au25(SG)18, Au29(SG)20, Au33(SG)22, and Au39(SG)24. These assignments were further confirmed by measuring the mass spectra of the isolated Au:S(h-G) clusters, where h-GSH is a homoglutathione. It is proposed that a series of the isolated Au:SG clusters corresponds to kinetically trapped intermediates of the growing Au cores. The relative abundance of the isolated clusters was correlated well with the thermodynamic stabilities against unimolecular decomposition. The electronic structures of the isolated Au:SG clusters were probed by X-ray photoelectron spectroscopy (XPS) and optical spectroscopy. The Au(4f) XPS spectra illustrate substantial electron donation from the gold cores to the GS ligands in the Au:SG clusters. The optical absorption and photoluminescence spectra indicate that the electronic structures of the Au:SG clusters are well quantized; embryos of the sp band of the bulk gold evolve remarkably depending on the number of the gold atoms and GS ligands. The comparison of these spectral data with those of sodium Au(I) thiomalate and 1.8 nm Au:SG nanocrystals (NCs) reveals that the subnanometer-sized Au clusters thiolated constitute a distinct class of binary system which lies between the Au(I)-thiolate complexes and thiolate-protected Au NCs.     

A nucleobase that releases reporter tags upon DNA oxidation

We have developed a novel nucleosbase, edaG, that efficiently releases various reporter units upon one-electron oxidation. The edaG-selective degradation of ODNs was achieved by various mild oxidizing agents. The oxidant-dependent molecular releasing technique is quite useful not only for DNA-based drug releasing systems but also for the detection of long-range hole transport through DNA without time-consuming analysis.     

Preparation of molecularly imprinted polymers with thiourea group for phosphate

Molecularly imprinted polymers selective for phosphate were prepared with the two types of functional monomers, 1-allyl-2-thiourea and N-methyl-N′-(4-vinylphenyl)-thiourea, and the binding abilities of the polymers were evaluated. Phenylphosphonic acid or diphenyl phosphate were used as the template molecules and the imprinted polymers prepared with 1-allyl-2-thiourea as functional monomer showed high binding ability to phosphate in aqueous media and nearly 90% of phosphate could be recovered. Also, the imprinted polymer prepared with N-methyl-N′-(4-vinylphenyl)-thiourea as functional monomer had a high binding ability and specific interaction with phosphate in acetonitrile solution and over 90% of phosphate-derivatives could be recovered selectively.     

Stable, specific, and reversible base pairing via Schiff base

We here present a novel covalently linked base pair via Schiff base formation between 5-formyluracil (fU) and 5-aminocytosine (AmC). Formation of the Schiff base linkage proceeds reversibly and does not require any additives. The cross-linked DNA is very stable under denaturing conditions, whereas it completely dissociates upon heating at 90 degrees C. The pairing ability of AmC and fU is very specific and is applicable to the detection of fU, which is the major oxidative lesion of T in DNA. We propose the Schiff base linkage as a new artificial base pairing scheme to create functional DNAs.     

Ubiquitous 8 and 29 kDa gold:alkanethiolate cluster compounds: mass-spectrometric determination of molecular formulas and structural implications

The molecular formulas and charge state distributions of thus-far known ubiquitous alkanethiolate-protected gold clusters with core-masses of 8 and 29 kDa were assessed using electrospray ionization mass spectrometry. The 8 and 29 kDa clusters were determined to be composed of single species, [Au38(SCn)24]z and [Au144(SCn)59]z, respectively, with charge states of z >/= 0. Possible geometric structures for Au38(SCn)24 and Au144(SCn)59 are discussed, based on the structures of relevant systems that have been recently determined experimentally and theoretically: [Au25(SR)18]- and Au102(SR)44, in which the Au cores are protected by monomers [-SR-Au-SR-] and/or dimers [-SR-Au-SR-Au-SR-]. Their preferential formation and chemical robustness are proposed as being associated with high stability due to geometric factors, while the Au-thiolate interface takes on common motifs regardless of the underlying Au core.     

Heterogeneity of osmium oxidation efficiency at consecutive thymines

Consecutive thymine sequences were oxidized more efficiently with a mixture including potassium osmate, potassium hexacyanoferrate(III), and bipyridine than an isolated thymine, and, in particular, osmium oxidation at the 5'T of TT progressed much more rapidly, compared with those of other thymines.     

Microfluidic synthesis and catalytic application of PVP-stabilized, approximately 1 nm gold clusters

Small PVP-stabilized gold clusters were successfully prepared by the homogeneous mixing of continuous flows of aqueous AuCl 4 (-) and BH 4 (-) in a micromixer. Spectroscopic characterization revealed that microfluidic synthesis could yield monodisperse Au:PVP clusters with an average diameter of approximately 1 nm, which is smaller than clusters produced by conventional batch methods. These approximately 1 nm Au:PVP clusters exhibited higher catalytic activity for the aerobic oxidation of p-hydroxybenzyl alcohol than did Au:PVP clusters prepared by batch methods.     

Magnetic properties of hexagonal strontium ferrite thick film synthesized by sol–gel processing using SrM nanoparticles

Strontium ferrite SrFe₁₂O₁₉ (SrM) thick films have been synthesized using a spinning coating sol–gel process. The coating sol was formed from SrFe₁₂O₁₉ powders dispersed in the strontium ferrite raw sol. XRD, TEM, SEM, vibrating sample magnetometer (VSM) and ac susceptometer were employed to evaluate the structure, composition and magnetic properties of SrFe₁₂O₁₉ thick films. The results indicated that a uniform and crack-free coating of Strontium ferrite with ∼15 μm thickness can be produced with a good deal of consistency. The magnetization hysteresis loops were almost the same for magnetic fields both applied in parallel and perpendicular.