Encapsulation of ZnS:Mn2+ nanocrystals with diblock copolymers

The encapsulation of the nanocrystalline manganese‐doped zinc sulfide (ZnS:Mn) in poly(styrene‐b‐2vinylpyridine) (PS‐PVP) diblock copolymers is reported. Below the critical micelle concentration in the absence of nanocrystals (NCs), inverse micelles of PS‐PVP were induced by adding ZnS:Mn NCs, the presence of which was confirmed by scanning force microscope and dynamic light scattering. In toluene, a PS‐selective solvent, the less‐soluble PVP blocks preferentially surround the ligand‐coated ZnS:Mn NCs. For PS‐PVP encapsulated ZnS:Mn NCs, the ratio of blue emission to orange emission of ZnS:Mn NCs is dependent on both the concentration of PS‐PVP and the solvent quality. The pyridine of PVP blocks form complexes with the Zn atoms via the nitrogen lone pair and thus the sulfur vacancies are passivated. As a result, the defect‐related blue emission is selectively quenched even when the micelles are not formed. As the concentration of PS‐PVP encapsulating the ZnS:Mn NCs increases, the intensity of blue emission decreases. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3227–3233, 2006     

A novel cyclic dithiocarbonate having siloxane moiety; Approach to curable siloxane oligomer

A novel 5‐membered cyclic dithiocarbonate (DTC) having a siloxane moiety, 5‐(3‐trimethoxysilylpropyloxymethyl)‐1,3‐oxathiolane‐2‐thione, was synthesized from the corresponding epoxide precursor by its cycloaddition with carbon disulfide. The siloxane group underwent condensation reaction by the treatment with water and a basic or acidic catalyst, to afford the corresponding oligomer having siloxane main chain and DTC pendant. The resulting oligomer was liquid and soluble in organic solvents such as THF and chloroform. Treatment of the oligomer with amines resulted in selective ring‐opening reaction of the DTC group, generating a thiol group, which underwent oxidative coupling reaction to make the oligomer successfully cured. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4422–4430, 2005     

Novel fluorescent asparaginyl-N-acetyl-d-glucosamines (Asn-GlcNAc) for the resolution of oligosaccharides in glycopeptides, based on enzyme transglycosylation reaction

Several fluorescent asparaginyl-N-acetyl-d-glucosamines (Asn-GlcNAcs), i.e., DBD-Asn-GlcNAc, NBD-Asn-GlcNAc, NDA-Asn-GlcNAc, PS-Asn-GlcNAc, FITC-Asn-GlcNAc, DMEQ-Asn-GlcNAc and DBD-PZ-Boc-Asn-GlcNAc, were synthesized as the acceptors for the resolution of oligosaccharides in glycopeptides. The resolution of oligosaccharides is based on the transglycosylation reaction with end-β-N-acetylglucosaminidase (Endo-M), isolated from Mucor hiemalis. The synthesis of each fluorescent acceptor was carried out in a one-pot reaction of Asn-GlcNAc and the corresponding fluorescent tagging reagent. The transglycosylation reaction using Endo-M proceeds at RT in neutral phosphate buffer (pH 6.0) and reached maxima at around 30 min. When Fmoc-Asn-GlcNAc (acceptor) was enzymatically reacted with Disialo-Asn (donor) in the presence of Endo-M, the ratio of Disialo-Asn-Fmoc (transglycosylation product) was almost comparable with the decreasing ratio of Fmoc-Asn-GlcNAc. Therefore, the transglycosylation activity of Endo-M from Disialo-Asn (donor) and fluorescent-Asn-GlcNAc (acceptor) was calculated from the decreasing ratio of fluorescent-Asn-GlcNAc. The order was NDA-Asn-GlcNAc > DBD-Asn-GlcNAc Fmoc-Asn-GlcNAc > NBD-Asn-GlcNAc DMEQ-Asn-GlcNAc > DNS-Asn-GlcNAc > PS-Asn-GlcNAc > FITC-Asn-GlcNAc. On the other hand, the activity with a fluorescent acceptor (DBD-PZ-Boc-Asn-GlcNAc), labeled to a carboxylic acid group in the Asn residue, was the strongest among the synthesized acceptors.     

Facile synthesis and crosslinking reaction of trifunctional five‐membered cyclic carbonate and dithiocarbonate

The trifunctional five‐membered cyclic carbonate 2 and dithiocarbonate 3 were successfully synthesized by the reaction of trifunctional epoxide 1 with carbon dioxide and carbon disulfide, respectively. The crosslinking reactions of 2 with p‐xylylenediamine or hexamethylenediamine were carried out in dimethyl sulfoxide at 100 °C for 48 h to produce the corresponding crosslinked poly(hydroxyurethane)s quantitatively. The crosslinking reactions of 3 with both p‐xylylenediamine and hexamethylenediamine, followed by acetylation of thiol moiety, produced the corresponding crosslinked poly(thioester–thiourethane)s quantitatively. The obtained crosslinked poly(hydroxyurethane)s were thermally more stable than the analogous crosslinked poly(thioester–thiourethane)s, probably because of less thermal stability of thiourethane moiety than hydroxyurethane moiety. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5983–5989, 2004     

Samarium enolate on crosslinked polystyrene beads. III. Anionic initiator for well‐defined synthesis of poly(hydroxyethyl methacrylate) on solid support

A solid‐supported samarium enolate successfully initiated the polymerization of 2‐(trimethylsilyloxy)ethyl methacrylate (TMS‐HEMA) through the living anionic process. In addition, the silyl group was readily removed by treatment of the beads with a weak acid to afford the corresponding well‐defined poly(methacrylate) having a hydroxyethyl group in the side chain (PHEMA). The hydroxyl group of the immobilized PHEMA on the beads was successfully acetylated to give poly(2‐acetoxyethyl methacrylate), which could be quantitatively isolated from the beads by trifluoroacetic acid treatment. Moreover, the hydroxyl group of the immobilized PHEMA could be utilized as an initiator for acid promoted ring opening polymerization of lactone to yield the corresponding graft copolymer. In this method, the residual and excess reagents could be removed by filtration, which demonstrated the applicability of the present technique to a novel method for construction of functional polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4417–4423, 2004     

Ring‐opening grafting polymerization of cyclic monomers onto human hair

Natural human hair was successfully modified by the graft polymerization of trimethylene carbonate, β‐propiolactone, ε‐caprolactone, glycidol, ε‐caprolactam, and 5,5‐dimethyl‐1,3‐dioxane‐2‐thione. In contrast, we could not modify natural human hair by the graft polymerization of oxetane under similar conditions. The model reaction suggested that the main initiating species in these polymerizations were the amino, thiol, and hydroxyl groups in hair, which could induce ring‐opening polymerization. Among the tested monomers, β‐propiolactone was most effective for hair modification with its graft polymer, whose concentration was as high as 0.5 g/g of hair though polymerization under mild conditions. The effects of the hair pretreatment and polymerization temperature on the weight ratio of the grafted polymers were also investigated. Hair modified by grafted polymers was characterized with scanning electron microscopy and Fourier transform infrared measurements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 736–744, 2007     

La0.7Ce0.3MnO3 epitaxial films fabricated by a pulsed laser deposition method

La_0.7Ce_0.3MnO₃ epitaxial films were successfully fabricated via a pulsed laser deposition method by controlling the experimental conditions. A series of experiments with varying the oxygen pressure and the substrate temperature demonstrated that the use of appropriate conditions is crucial for fabricating the epitaxial thin films. The existence of such suitable conditions was thermodynamically interpreted in terms of the stability of Mn²⁺ ion. Both XRD and EPMA measurements indicated that La_0.7Ce_0.3MnO₃ thin films fabricated herein form single phases, although it was difficult to present the direct experimental evidence to prove that Ce ion can really exist within the perovskite structure. The resultant films with oxygen annealing showed a metal-insulator transition and ferromagnetic property with Curie temperature of 275 K.     

Determination of tin by resin-suspension electrothermal atomic absorption spectrometry after enrichment as the complex with ammonium pyrrolidinedithiocarbamate.

A resin-phase extraction method has been optimized for the trace determination of tin(II) by ETAAS. Tin(II) was extracted on a finely divided anion exchange resin as the complex with ammonium pyrrolidinedithiocarbamate (APDC). The resin was collected on a membrane filter and then dispersed in 1.00 ml of 1 mol l(-1) nitric acid containing 100 microg of Pd(II) and 60 microg of Ni(II). The resulting resin suspension was subjected to GFAAS. The proposed method was applied to the determination of tin(II) in hydrochloric acid.