Rapid transformation from spherical nanoparticles, nanorods, cubes, or bipyramids to triangular prisms of silver with PVP, citrate, and H2O2

Rapid sphere-to-prism (STP) transformation of silver was studied in aqueous AgNO(3)/NaBH(4)/polyvinylpyrrolidone (PVP)/trisodium citrate (Na(3)CA)/H(2)O(2) solutions by monitoring time-dependent surface plasmon resonance (SPR) bands in the UV-vis region, by examining transmission electron microscopic (TEM) images, and by analyzing emitted gases during fast reaction. Roles of PVP, Na(3)CA, and H(2)O(2) were studied without addition of a reagent, with different timing of each reagent's addition, and with addition of H(2)O(2) to mixtures of spheres and prisms. Results show that prisms can be prepared without addition of PVP, although it is useful to synthesize smaller monodispersed prisms. A new important role of citrate found in this study, besides a known role as a protecting agent of {111} facets of plates, is an assistive agent for shape-selective oxidative etching of Ag nanoparticles by H(2)O(2). The covering of Ag nanoparticles with carboxylate groups is necessary to initiate rapid STP transformation by premixing citrate before H(2)O(2) addition. Based on our data, rapid prism formation starts from the consumption of spherical Ag particles because of shape-selective oxidative etching by H(2)O(2). Oxidative etching of spherical particles by H(2)O(2) is faster than that of prisms. Therefore, spherical particles are selectively etched and dissolved, leaving only seeds of prisms to grow into triangular prisms. When pentagonal Ag nanorods and a mixture of cubes and bipyramids were used as sources of prisms, rod-to-prism (RTP), cube-to-prism (CTP), and bipyramid-to-prism (BTP) transformations were observed in Ag nanocrystals/NaBH(4)/PVP/Na(3)CA/H(2)O(2) solutions. Shape-selective oxidative etching of rods was confirmed using flag-type Ag nanostructures consisting of a triangular plate and a side rod. These data provide useful information for the size-controlled synthesis of triangular Ag prisms, from various Ag nanostructures and using a chemical reduction method, having surface plasmon resonance (SPR) bands at a desired wavelength.     

Characterization of magnetic nanoparticles modified with thiol functionalized PAMAM dendron for DNA recovery

Magnetic nanoparticles (MNPs) modified with the thiol functionalized polyamidoamine (PAMAM) dendron were synthesized to estimate their DNA recovery capabilities. Aminosilane-modified MNPs and MNPs surrounded by a phospholipid (distearoylphosphatidylethanolamine (DSPE)) bilayer were used as core particles. Cystamine-core PAMAM dendrimers were reduced by dithiothreitol to dendron thiols and chemically conjugated to the core particles. Characterization of the synthesis revealed an increase of the surface amine charge from generation 1 (G1) to G6, starting with an aminosilane initiator. Particle size distribution analysis indicated that G6 PAMAM-modified MNPs exhibited monodispersity in an aqueous solution. G6 PAMAM-MNPs and G6 PAMAM-PE-MNPs synthesized by the proposed method have equivalent DNA recovery abilities to PAMAM-MNPs prepared by the conventional divergent synthesis method. In optimized conditions, 96% of λDNA was recovered using G6 PAMAM-PE-MNPs. Therefore, the method for preparing PAMAM-MNPs and PAMAM-PE-MNPs proposed in this study will be a novel approach for producing DNA carriers for efficient DNA purification by magnetic separation.     

Two new monoterpene peroxide glycosides from Aster scaber.

The aerial part of Aster scaber Thunb. (Asteraceae) yielded two new monoterpene peroxide glycosides, (3S)-3-O-(3',4'-diangeloyl-beta-D-glucopyranosyloxy)-7-hydroperoxy-3,7-dimethylocta-1,5-diene (1) and (3S)-3-O-(3',4'-diangeloyl-beta-D-glucopyranosyloxy)-6-hydroperoxy-3,7-dimethylocta-1,7-diene (2), and five known compounds, alpha-spinasterol (3), germacra-4(15),5,10(14)-triene-1-beta-ol (4), 7-methoxy-4(15)-oppositen-1-beta-ol (5), 6alpha-methoxy-4(15)-eudesmane-1beta-ol (6) and alpha-spinasterol 3-O-beta-D-glucopyranoside (7). The structures were established by chemical and spectroscopic methods.     

Controlled release of DNA from zinc and magnesium ion-doped hydroxyapatites

Research on Chemical Intermediates - Hydroxyapatite (HA) is a biocompatible and porous material that is useful for gene delivery. In this study, various Zn- and Mg-doped HA samples were produced by...     

Diverse Approaches for Enantioselective C−H Functionalization Reactions Using Group 9 CpxMIII Catalysts

Transition-metal-catalyzed C−H functionalization reactions with Cp*M^III catalysts (M=Co, Rh, Ir) have found a wide variety of applications in organic synthesis. Albeit the intrinsic difficulties in achieving catalytic stereocontrol using these catalysts due to their lack of additional coordination sites for external chiral ligands and the conformational flexibility of the Cp ligand, catalytic enantioselective C−H functionalization reactions using the Group 9 metal triad with Cp-type ligands have been intensively studied since 2012. In this minireview, the progress in these reactions according to the type of the chiral catalyst used are summarized and discussed. The development of chiral Cp^x ligands the metal complexes thereof, artificial metalloenzymes, chiral carboxylate-assisted enantioselective C−H activations, enantioselective alkylations assisted by chiral carboxylic acids or chiral sulfonates, and chiral transient directing groups are discussed.     

Radical polymerization of allylbiguanide

Monoallyl compounds are not readily homopolymerized by a conventional free‐radical mechanism. However, we successfully performed the radical polymerization of allylbiguanide hydrochloride in a concentrated acid solution (hydrochloric acid or phosphoric acid) in the presence of a radical initiator at 50 °C. The polymer product was precipitated from the reaction solution through the addition of an excess amount of acetone. The precipitated crude polymer [polyallylbiguanide (PAB)] was then purified by dialysis. PAB was confirmed by elemental analysis, infrared spectroscopy, and ¹H NMR. The molecular weight range of PAB was 10,340–113,200, and PAB exhibited a low polydispersity (weight‐average molecular weight/number‐average molecular weight = 1.04–1.68) by multi‐angle laser light scattering. The polymerization of allylbiguanide was quite sensitive to the protonic concentration of the inorganic acid. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1707–1711, 2004     

Synthesis of 6,6-dimethyltricyclo[5.4.0.02,8]undecane-2,9-diol for (ent-)longipinane-type sesquiterpenoids using two types of radical cyclization reactions

A synthetic route to 6,6-dimethyltricyclo[5.4.0.0^2,8]undecane-2,9-diol, a key precursor to (ent-)longipinane-type sesquiterpenoids, is described. This unique core common to (ent-)longipinanes was constructed using two types of intramolecular radical cyclization reactions, namely, intramolecular coupling of an acid chloride and an alkyl iodide mediated by SmI₂, TBAI and HMPA, and the coupling of a ketone and an epoxide mediated by Cp₂TiI₂ and SmI₂.     

Catalytic asymmetric cyano-ethoxycarbonylation reaction of aldehydes using a YLi3 tris(binaphthoxide) (YLB) complex: mechanism and roles of achiral additives

Full details of a catalytic asymmetric cyano-ethoxycarbonylation reaction promoted by a heterobimetallic YLi3 tris(binaphthoxide) complex (YLB 1), especially mechanistic studies, are described. In the cyanation reaction of aldehydes with ethyl cyanoformate, three achiral additives, H2O, tris(2,6-dimethoxyphenyl)phosphine oxide (3a), and BuLi, were required to achieve high reactivity and enantioselectivity (up to >99% yield and up to 98% ee). The roles of achiral additives and the reaction pathway were investigated in detail. In situ IR analysis revealed that the initiation step to generate LiCN from H2O, BuLi, and ethyl cyanoformate is rather slow. On the basis of mechanistic studies of the initiation step to generate an active nucleophilic species, reaction conditions were optimized by using a catalytic amount of acetone cyanohydrin as an initiator. Under the optimized conditions, the induction period decreased and the reaction completed within 9 min using 5 mol % YLB at -78 degrees C. Catalyst loading was successfully reduced to 1 mol %. Kinetic experiments and evaluation of the substituent effects of phosphine oxide revealed that phosphine oxide had beneficial effects on both the reaction rate and the enantioselectivity. The putative active species as well as the catalytic cycle of the reaction are also discussed.