Schulzeines A-C, new alpha-glucosidase inhibitors from the marine sponge Penares schulzei

Three new alpha-glucosidase inhibitors, schulzeines A-C (1-3), were isolated from the marine sponge Penares schulzei. Their structures were elucidated by spectral analysis and chemical degradations to be the isoquinoline alkaloids, encompassing two amino acids, and C(28) fatty acid, the last of which was sulfated. Absolute stereochemistry of schulzeines was determined by application of the modified Mosher analysis to fragments obtained by chemical degradation. Schulzeines A-C inhibit alpha-glucosidase with IC(50) values of 48-170 nM.     

Hybrid Mesoporous-Silica Materials Functionalized by Pt(II) Complexes: Correlation between the Spatial Distribution of the Active Center, Photoluminescence Emission, and Photocatalytic Activity

[Pt(tpy)Cl]Cl (tpy: terpyridine) was successfully anchored to a series of mesoporous-silica materials that were modified with (3-aminopropyl)triethoxysilane with the aim of developing new inorganic-organic hybrid photocatalysts. Herein, the relationship between the luminescence characteristics and photocatalytic activities of these materials is examined as a function of Pt loading to define the spatial distribution of the Pt complex in the mesoporous channel. At low Pt loading, the Pt complex is located as an isolated species and exhibits strong photoluminescence emission at room temperature owing to metal-to-ligand charge-transfer ((3) MLCT) transitions (at about 530?nm). Energy- and/or electron-transfer from (3) MLCT to O(2) generate potentially active oxygen species, which are capable of promoting the selective photooxidation of styrene derivatives. On the other hand, short Pt???Pt interactions are prominent at high loading and the metal-metal-to-ligand charge-transfer ((3) MMLCT) transition is at about 620?nm. Such Pt complexes, which are situated close to each other, efficiently catalyze H(2) -evolution reactions in aqueous media in the presence of a sacrificial electron donor (EDTA) under visible-light irradiation. This study also investigates the effect of nanoconfinement on anchored guest complexes by considering the differences between the pore dimensions and structures of mesoporous-silica materials.     

Improved complementary polymer pair system: switching for enzyme activity by PEGylated polymers

The development of technology for on/off switching of enzyme activity is expected to expand the applications of enzyme in a wide range of research fields. We have previously developed a complementary polymer pair system (CPPS) that enables the activity of several enzymes to be controlled by a pair of oppositely charged polymers. However, it failed to control the activity of large and unstable α-amylase because the aggregation of the complex between anionic α-amylase and cationic poly(allylamine) (PAA) induced irreversible denaturation of the enzyme. To address this issue, we herein designed and synthesized a cationic copolymer with a poly(ethylene glycol) backbone, poly(N,N-diethylaminoethyl methacrylate)-block-poly(ethylene glycol) (PEAMA-b-PEG). In contrast to PAA, α-amylase and β-galactosidase were inactivated by PEAMA-b-PEG with the formation of soluble complexes. The enzyme/PEAMA-b-PEG complexes were then successfully recovered from the complex by the addition of anionic poly(acrylic acid) (PAAc). Thus, dispersion of the complex by PEG segment in PEAMA-b-PEG clearly plays a crucial role for regulating the activities of these enzymes, suggesting that PEGylated charged polymer is a new candidate for CPPS for large and unstable enzymes.     

In situ time-resolved DXAFS study of Rh nanoparticle formation mechanism in ethylene glycol at elevated temperature

A combination of in situ time-resolved DXAFS and ICP-MS techniques reveals that the formation process of Rh nanoparticles (NPs) from rhodium trichloride trihydrate (RhCl(3)·3H(2)O) in ethylene glycol with polyvinylpyrrolidone (PVP) at elevated temperature is a first-order reaction, which indicates that uniform size Rh NPs appear consecutively and these Rh NPs do not aggregate with each other.     

Electrocatalytic Oxidation of Amines on a Mediator‐Modified Electrode by Electrochemical Copolymerization of Nitroxyl Radical Precursor Containing Pyrrole Side Chain and Bithiophene

This paper describes the electrocatalytic oxidation of amines on TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxyl)‐modified electrodes prepared by electrochemical copolymerization of TEMPO precursor containing pyrrole side chain and 2,2′‐bithiophene. The modified electrode exhibits electrocatalytic activity for the oxidation of primary and secondary amines. Cyclic voltammetric studies showed that the peak current of the cyclic voltammogram increased linearly with increasing concentration of amine in the sample solution.     

Designed self-assembly of molecular necklaces

This paper reports an efficient strategy to synthesize molecular necklaces, in which a number of small rings are threaded onto a large ring, utilizing the principles of self-assembly and coordination chemistry. Our strategy involves (1) threading a molecular "bead" with a short "string" to make a pseudorotaxane and then (2) linking the pseudorotaxanes with a metal complex with two cis labile ligands acting as an "angle connector" to form a cyclic product (molecular necklace). A 4- or 3-pyridylmethyl group is attached to each end of 1,4-diaminobutane or 1,5-diaminopentane to produce the short "strings" (C4N4(2+), C4N3(2+), C5N4(2+), and C5N3(2+)), which then react with a cucurbituril (CB) "bead" to form stable pseudorotaxanes (PR44(2+), PR43(2+), PR54(2+), and PR53(2+), respectively). The reaction of the pseudorotaxanes with Pt(en)(NO(3))(2) (en = ethylenediamine) produces a molecular necklace [4]MN, in which three molecular "beads" are threaded on a triangular framework, and/or a molecular necklace [5]MN, in which four molecular "beads" are threaded on a square framework. Under refluxing conditions, the reaction with PR44(2+) or PR54(2+) yields exclusively [4]MN (MN44T or MN54T, respectively), whereas that with PR43(2+) or PR53(2+) produces exclusively [5]MN (MN43S or MN53S, respectively). The products have been characterized by various methods including X-ray crystallography. At lower temperatures, on the other hand, the reaction with PR44(2+) or PR54(2+) affords both [4]MN and [5]MN. The supermolecules reported here are the first series of molecular necklaces obtained as thermodynamic products. The overall structures of the molecular necklaces are strongly influenced by the structures of pseudorotaxane building blocks, which is discussed in detail on the basis of the X-ray crystal structures. The temperature dependence of the product distribution observed in this self-assembly process is also discussed.     

Dithienylethenes with a novel photochromic performance

Dithienylethenes with low decoloration quantum yields and thermal reversibility at high temperature above 100 degrees C were prepared. Introduction of bulky alkoxy substituents at 2- and 2'-positions of the thiophene rings strongly suppressed the cycloreversion quantum yields. The quantum yields were lower than 10(-3), and the photogenerated color remained stable enough under room light. On the other hand, the bulky alkoxy substituent decreased the thermal stability of the colored closed-ring isomers at high temperature. The color of the dithienylethene with cyclohexyloxy substituents faded out in less than 1 min at 160 degrees C.