Formation of gold nanoparticles in microreactor composed of helical peptide assembly in water

A novel microreactor was prepared by self-assembly of an amphiphilic block copolymer composed of a hydrophobic helical peptide unit with a naphthyl group at the C terminal and a hydrophilic poly(ethylene glycol) unit. The copolymer formed a self-assembly in water, taking a vesicular structure. Noticeably, when the copolymer was dispersed in an Au(3+) aqueous solution, gold nanoparticles were formed without addition of any reducing reagent. The naphthyl groups, which are located at the inner surface of the vesicular assembly, promoted the reduction of Au(3+) ions with accompanying pH decrease.     

Synthesis of block copolymer segments containing different ratios of ethylene and 5-norbornen-2-yl acetate

Block copolymerization of ethylene with 5-norbornen-2-yl acetate (1) by the nickel catalyst system [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide]Ni(eta1-CH2Ph)(PMe3) (2) and Ni(COD)2 (bis(1,4-cyclooctadiene)nickel) (3) produces a variety of block copolymer structures that demonstrate microphase separation. Typical block copolymerizations were carried out in an autoclave charged with a solution of the catalyst mixture and 1 (0.15 M) in toluene. The autoclave was sealed and exposed to PC2H4 = 50 psi for a period of time (T1). A pressure jump to PC2H4 = 1100 psi was then applied and the reaction allowed to proceed for another predetermined interval (T2). Independent experiments were performed to isolate and examine the molecular weight and comonomer composition of the first block. Narrow molecular weight distributions and the increase of polymer molecular weight with increases in T1 or T2 are consistent with a product in which an initial block is formed at low ethylene pressures and quantitatively converted to a block copolymer by the jump to high pressure. Transmission electron microscopy confirms that the materials are microphase separated.     

Seed polymerization of tetraethyl ortho-silicate in the presence of rod-like colloidal particles of anionic palygorskite and cationic β-FeO(OH)

Kinetic analyses were made of the seed polymerization of tetraethyl ortho-silicate (TEOS) in the presence of rod-like colloidal particles of palygorskite and cationic -FeO(OH) by turbidity and dynamic light-scattering measurements. Transmission electron microscopic measurements supported the formation of core-shell particles. The seed polymerization of TEOS took place exclusively on the surfaces of palygorskite. The main cause of the observation is due to the fact that the main component of palygorskite is SiO₂ and the affinity between palygorskite and TEOS is high, though the electrostatic repulsion between them is not favorable for shell formation. The shell formation of silica on a -FeO(OH) particle also proceeded. The electrostatic attraction forces between the anionic polar TEOS monomers and cationic -FeO(OH) particles played an important role in shell formation. These results are consistent with a polymerization mechanism consisting of the formation of small preliminary particles followed by their coalescence on the surfaces of the seeds to give the final large particles coated with silica layers.     

A new series of estrogen receptor modulators: effect of alkyl substituents on receptor-binding affinity

New types of selective estrogen receptor modulators (SERMs) were synthesized and evaluated for their binding affinity and biological effect on reproductive cells. A proposed lead structure (B) was derivatized to provide compounds 30 and 44, which showed good estrogen-receptor binding affinity (K(i) values: 6.3 and 10 nM, respectively), as well as minimal impact on mammary and uterine carcinoma cells. Introduction of an alkyl group in the core structure considerably enhanced receptor-binding affinity of the compounds tested. Synthesis and structure-activity relationships of these compounds are described.     

Nature of the chemical bond formed with the structural metal ion at the A9/G10.1 motif derived from hammerhead ribozymes

We have studied the interaction between metal ions and the metal ion-binding motif in hammerhead ribozymes, as well as the functions of the metal ion at the motif, with heteronuclear NMR spectroscopy. In this study, we employed model RNA systems which mimic the metal ion-binding motif and the altered motif. In Co(NH3)6(III) titrations, we observed large 1H and 31P chemical shift perturbations for the motif and found that outer-sphere complexation of Co(NH3)6(III) is possible for this motif. From the reinvestigation of our previous 15N chemical shift data for Cd(II) binding, in comparison with those of organometallic compounds, we conclude that Cd(II) can form an inner-sphere complex with the nucleobase in the motif. Therefore, the A9/G10.1 site was found to accept both inner-sphere and outer-sphere complexations. The Mg(II) titration for a slightly different motif from the A9/G10.1 site (G10.1-C11.1 to A10.1-U11.1) revealed that its affinity to Mg(II) was drastically reduced, although the ribozyme with this altered motif is known to retain enzymatic activities. This observation suggests that the metal ion at these motifs is not a catalytic center of hammerhead ribozymes.     

Synthesis and photochemical reaction of cyclic oligomers: Synthesis and photopolymerization of novel C‐methylcalix[4]resorcinarene and p‐alkylcalix[n]arene derivatives containing spiro ortho ether groups

New photoreactive calixarene derivatives containing spiro ortho ester groups (calixarenes 3a–3c ) were synthesized by the reaction of 2‐bromomethyl‐1,4,6‐trioxaspiro[4.4]nonane with 2,8,14,20‐tetramethyl‐4,6,10,12,16,18,22,24‐octakis(carboxymethoxy)calix[4]resorcinarene, 5,11,17,23,29,35‐hexamethyl‐37,38,39,40,41,42‐hexakis(carboxymethoxy)calix[6]arene, and 5,11,17,23,29,35,41,47‐octa‐tert‐butyl‐49,50,51,52, 53,54,55,56‐octakis‐(carboxymethoxy)calix[8]arene, which were prepared by the reaction of C‐methylcalix[4]resorcinarene, p‐methylcalix[6]arene, and p‐tert‐butylcalix[8]arene, respectively. The thermal stability of the obtained calixarene derivatives containing spiro ortho ester groups was examined with thermogravimetric analysis, and it was found that these calixarene derivatives had good thermal stability. The photoinitiated cationic polymerization of spiro ortho ester groups in calixarene derivatives 3a–3c was examined with certain photoacid generators in the film state. Interestingly enough, the reaction of calixarene derivatives did not proceed with only photoirradiation; however, the reaction proceeded smoothly when the photoirradiation was followed by heating. Furthermore, calixarene 3a , composed of a C‐methylcalix[4]resorcinarene structure, showed the highest photochemical reactivity in this reaction system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1293–1302, 2002     

A positron annihilation lifetime measurement system with an intense positron microbeam

An intense positron microbeam was formed using an electron linear accelerator. The beam is pulsed to apply positron lifetime spectroscopy to very small samples and to obtain positron lifetime images by scanning it. Positron lifetimes are measured with time resolution of <300 ps and with lateral spatial resolution of 30–100 μm. A counting rate of the γ-ray to measure positron lifetime is about 10³ s⁻¹ which is 10 times higher than that achieved by the radioisotope based microbeam.     

Synthesis of palau’amide and its diastereomers: confirmation of its stereostructure

Four diastereomers of palau’amide (1-4), a cytotoxic cyclodepsipeptide, were synthesized. The ¹H NMR spectrum of 1 was identical to that of natural palau’amide. This established the complete stereostructure of palau’amide.     

New Fluorescence Domain “Excited Multimer” Formed upon Photoexcitation of Continuously Stacked Diaroylmethanatoboron Difluoride Molecules with Fused π‐Orbitals in Crystals

The crystal‐packing structures of seven derivatives of diaroylmethanatoboron difluoride ( 1 a – gBF₂ ) are characterized by no overlap of the π‐conjugated main units of two adjacent molecules (type I), overlap of the benzene ring π‐orbitals of two adjacent molecules (type II), and overlap of the benzene and dihydrodioxaborinine rings π‐orbitals of adjacent molecules (type III). The crystal‐packing structures govern the fluorescence (FL) properties in the crystalline states. The FL domain that is present in type I crystals, in which intermolecular orbital interactions are absent, leads to excited monomer‐like FL properties. In the case of the type II crystals, the presence of intermolecular overlap of the benzene rings π‐orbitals generates new FL domains, referred to as “excited multimers”, which possess allowed S₀–S₁ electronic transitions and, as a result, similar FL lifetimes at longer wavelengths than the FL of the type I crystals. Finally, intermolecular overlap of the benzene and dihydrodioxaborinine ring π‐orbitals in the type III crystals leads to “excited multimer” domains with forbidden S₀–S₁ electronic transitions and longer FL lifetimes at similar wavelengths as that in type I crystals.