Selective formation of AAB- and ABC-type heterotrimeric alpha-helical coiled coils

The alpha-helical coiled coils have a representative amino acid sequence of (abcdefg)(n) heptad repeats. We previously reported that two peptides named IZ-2A and IZ-2W formed an (IZ-2A)(2)/IZ-2W heterotrimer with an Ala-Ala-Trp interaction in the hydrophobic core. In this paper, we describe the selective formation of AAB- and ABC-type heterotrimers. To increase the selectivity of the AAB-type heterotrimeric formation, Lys residues at the f position were mutated to either an Ala or a Gln residue to form IZ-2A(fA) or IZ-2W(fQ). Separately, both IZ-2A(fA) and IZ-2W(fQ) have a random structure at pH 7 and 20 degrees C. However, together IZ-2A(fA) and IZ-2W(fQ) form a 2:1 complex with a thermal transition midpoint (Tm) of 48 degrees C. This procedure was applied to prepare the ABC-type heterotrimer, in which two sets of Ala-Ala-Trp interactions were designed in the hydrophobic core. Interhelical interaction between the e and g positions and the alpha-helical propensity of the amino acid at the f position were also considered in the design. The resultant three peptides selectively formed the ABC-type heterotrimer with a Tm of 51 degrees C. Other peptide combinations had random coil properties.     

Flow amperometric detection of indigo for enzyme-linked immunosorbent assays with use of screen-printed electrodes

A simple and automated methodology for a sensitive electrochemical detection of enzyme immunoassays that employ alkaline phosphatase (AP) as label has been developed. A flow injection system with programmable pump, valve and cell functions, amperometric detection of indigo and screen-printed electrodes (SPEs) are responsible for the advantages of this methodology. Amperometric detection at a low potential of indigo, the product of the enzymatic hydrolysis of the substrate 3-indoxyl phosphate (IP), is combined with a flow injection system. This incorporates in the flow cell a disposable screen-printed board provided with a graphite working electrode. No electrode pretreatment is necessary to obtain reproducible signals. The system was applied to the determination by an enzyme-linked immunosorbent assays (ELISA) of pneumolysin (PLY), a toxin related to respiratory infections. Linear calibration curves for low and high concentration ranges were obtained. These were also performed in a proteic matrix and linearity was also obtained.     

Large-scale separation of metallic and semiconducting single-walled carbon nanotubes

In the applications of single-walled carbon nanotubes (SWNTs), it is extremely important to separate semiconducting and metallic SWNTs. Although several methods have been reported for the separation, only low yields have been achieved at great expense. We show a separation method involving a dispersion-centrifugation process in a tetrahydrofuran solution of amine, which makes metallic SWNTs highly concentrated to 87% in a simple way.     

Synthesis of optically active forms of (E)-6-isopropyl-3,9-dimethyl-5,8-decadienyl acetate,the pheromone of the yellow scale

Highly optically pure enantiomers of (E)-6-isopropyl-3,9-dimethyl-5,8-decadienyl acetate, the sex pheromone of the yellow scale (Aniodiella citrina), were stereoselectively from synthesized from(R)-(+)-citronellic acid. Only the (s)-enantiomer was bioactive.     

Beta-1,3-glucan polysaccharides as novel one-dimensional hosts for DNA/RNA, conjugated polymers and nanoparticles

Beta-1,3-glucan polysaccharides have triple-stranded helical structures whose sense and pitch are comparable to those of polynucleotides. We recently revealed that the beta-1,3-glucans could interact with certain polynucleotides to form triple-stranded and helical macromolecular complexes consisting of two polysaccharide-strands and one polynucleotide-strand. This unique property of the beta-1,3-glucans has made it possible to utilize these polysaccharides as potential carriers for various functional polynucleotides. In particular, cell-uptake efficiency of the resultant polysaccharide/polynucleotide complexes was remarkably enhanced when functional groups recognized in a biological system were introduced as pendent groups. The beta-1,3-glucans can also interact with various one-dimensional architectures, such as single-walled carbon nanotubes, to produce unique nanocomposites, in which the single-walled carbon nanotubes are entrapped within the helical superstructure of beta-1,3-glucans. Various conductive polymers and gold nanoparticles are also entrapped within the helical superstructure in a similar manner. In addition, diacetylene monomers entrapped within the helical superstructure can be photo-polymerized to afford the corresponding poly(diacetylene)-nanofibers with a uniform diameter. These findings indicate that the beta-1,3-glucans are very attractive and useful materials not only in biotechnology but also in nanotechnology. These unique properties of the beta-1,3-glucans undoubtedly originate from their inherent, very strong helix-forming character which has never been observed for other polysaccharides.     

Effects of dipole moment, linkers, and chromophores at side chains on long-range electron transfer through helical peptides

Octadecapeptides carrying a ferrocene moiety at the molecular terminal were self-assembled on gold, and long-range electron transfer from the ferrocene moiety to gold was investigated by electrochemical methods. Effects on electron transfer of dipole moment of helical peptides, linkers connecting the peptide to gold, and chromophores introduced into the side chains were discussed. Cyclic voltammetry of the monolayers in an aqueous solution revealed that long-range electron transfer over 40 A occurred along the peptide molecule. Chronoamperometry showed that the long-range electron transfer should be ascribed to a hopping mechanism with use of amide groups as hopping sites. Electron transfer through the long peptide was not significantly accelerated by the dipole moment. However, the linker remarkably affected electron transfer depending on whether it was a methylene chain or a phenylene group, suggesting that local electron transfer between gold and the peptides should be the slowest step to determine the overall rate. Pyrenyl groups introduced into the side chains in the middle of the peptide molecule did not noticeably change electron transfer, probably because pyrenyl groups were too distant to allow direct electron transfer between them. Electrostatic potential profiles across the peptide monolayers were also calculated to explain reasonably the several interesting features in the present peptide systems.     

Synthetic studies on oxindole spiro-lactones with thalliumd(III) trinitrate: A formal total synthesis of (±)-tryptoquivaline G

(±)-Tryptoquivaline G was formally synthesized through shortened steps from tryptophan, in which oxidation with thallium(III) trinitrate(TTN) was effected at the crucial stage. The present work also constitutes the first synthesis of oxindole lactones carrying 2-alkyl quinazolinones.     

Synthesis of racemic and optically active forms of lineatin,the unique tricyclic pheromone of trypodendron lineatum (olivier)

(±) - 33,7 - Trimethyl - 2,9 - dioxatricyclo[3.3.1.0^4,7]nonane 1 and (±) - 3,3,7 - trimethyl - 2,9-dioxatricyclo [4.2.1.0^4,7]nonane 2 were synthesized. The former was shown to be (±)-lineatin, an ambrosia beetle pheromone. A selective synthesis of (±)-lineatin was devised, which was modified to yield the both enantiomers of lineatin via optical resolution of an intermediate.     

Magnetic structure of the europium fulleride ferromagnet Eu(6)C(60)

The powder neutron diffraction technique has been used for the direct observation of magnetic scattering below a Curie temperature of approximately 14 K in the fullerene-based molecular ferromagnet Eu6C60. Europium is in the divalent state with a magnetic moment of 7.1(3) muB per atom, and the configurational symmetry of the magnetic structure is body-centered cubic. Close contacts between Eu2+ and neighboring C60 units provide the signature of orbital hybridization, which can evidently account for the conducting and magnetic properties of the material.     

The synthesis of hexahydrooxoepithiopyridinedicarboximides by the reaction of thioamides with N-substituted maleimides

The synthesis of hexahydrooxoepithiopyridinedicarboxyimide (5: X₂ = N-Ph) by the reaction of thioamides 1 with N-substituted maleimide ( 2a ) was examined. The reaction of primary thioamides, such as thiobenzamide and p-toluthioamide with N-phenylmaleimide gives compounds 5 together with corresponding 4-hydroxy-1,3-thiazoles 4 . However, a similar reaction of secondary thioamides, such as N-methylthioacetamide, thiobenzanilide, with N-phenylmaleimide did not provide compounds 5 without addition of acid. The reaction pathway and the configuration of 5 were also investigated.