Mössbauer studies at Milli-Kelvin temperature region

Using a³He dilution refrigerator, Mössbauer measurements at extremely low temperatures have been carried out. From the nuclear polarization of⁵⁷Fe in an Fe metal foil absorber, the lowest temperature was determined to be 5mK.⁵⁷Fe results on a triangular Fe³⁺cluster complex and¹¹⁹Sn results on RPd₂Sn(R=Er, Tm) are briefly presented.     

Metallic superlattices

Multilayered metal films with artificial superstructures are prepared by alternate deposition of two elements in ultrahigh vacuum. Preparation and characterization for Fe-Mg and Fe-V superlattices are described. From hyperfine field measurements, chemical profiles of interfaces are discussed. Magnetic properties of extremely thin Fe layers sandwiched in between Mg layers are studied by means of Mőssbauer absorption spectroscopy.     

Amorphous-to-crystalline transformation of ultrathin Fe Layers:57Fe Mössbauer study of artificial multilayers

Multilayered films consisting of ultrathin Fe layers with spacer layers of other materials, such as Mg, Nd, or C, have been prepared by using vacuum deposition techniques. The properties of Fe layers have been investigated from⁵⁷Fe Mössbauer spectroscopy. If the stacking is nonepitaxial, the structure of the Fe layers is amorphous as long as the thickness is less than a critical value. It is found that a structural transformation from amorphous to crystalline (bcc) generally takes place in the course of nonepitaxial film growth.     

Biselides A-E: novel polyketides from the Okinawan ascidian Didemnidae sp.

Five new polyketides, biselides A (1), B (2), C (3), D (4), and E (5), were isolated from the Okinawan ascidian Didemnidae sp. Their structures were determined by spectroscopic analysis. Biselides A (1), B (2), and C (3) showed cytotoxicity against human cancer cells NCI-H460 and MDA-MB-231.     

Novel heparan sulfate mimetic compounds as antitumor agents

Heparan sulfate glycosaminoglycans (HSGAGs) are involved in tumor cell growth, adhesion, invasion, and migration, due to their interactions with various proteins. In this study, novel HSGAG-mimetic compounds (KI compounds) were designed and synthesized. As a result of cell-based assays, KI-105 was found to exert potent inhibitory activities against migration and invasion of human fibrosarcoma HT1080 cells. The present results indicate that a novel invasion/migration inhibitor, KI-105, can increase the adherence of HT1080 cells. It was conceivable that this cellular effect was caused by an increase in the amount of cell-surface HSGAGs and focal adhesions. Although further investigations are needed to decipher the molecular mechanism of KI-105, it is suggested that heparanase and Cdc42 are involved in its biological effects.     

Isolation and structure of koshikalide,a 14-membered macrolide from the marine cyanobacterium Lyngbya sp.

A 14-membered macrolide, koshikalide (1), was isolated from the marine cyanobacterium Lyngbya sp., and its planar structure was elucidated by spectroscopic analysis. The relative stereochemistry of C-11 and C-13 was elucidated by NOESY experiments and by an analysis of ¹H–¹H coupling constants. Koshikalide (1) exhibited weak cytotoxicity against HeLa S₃ cells.     

Co-gelation mechanism of xanthan and galactomannan

Synergistic gelation of dilute (0.1% total gums) mixed solutions of xanthan and galactomannan isolated from seeds of Delonix regia was investigated. Gelation occurred in a mixed solution of xanthan and galactomannan at 0.1% total gums at room temperature (25 °C). The flow curves of mixed solutions of native xanthan and galactomannan showed plastic behavior. The maximum elastic modulus was obtained when the ratio of the xanthan to galactomannan was 2:1 at room temperature (25 °C). The largest elastic modulus was observed in the mixture solution of deacetylated xanthan. However, a small elastic modulus was obtained in the mixture with depyruvated xanthan. The results obtained supported the interaction mechanism between xanthan and galactomannan (locust bean gum) previously proposed, and the pyruvate methyl groups might also take part in the interaction.     

Recent Progress of Thioester Method

Introduction Theavailabilityofsite specificallymodifiedpep tidesisofvitalimportanceforbiochemicalandbiophys icalstudies.Biologicalmethods,suchasexpression usingbacteria,areuseful.Theyare,however,notal waysapplicabletothesynthesisofpeptideswithsite specifi…     

The Effects of Side-Chain Configurations of a Retro–Inverso-Type Inhibitor on the Human T-Cell Leukemia Virus (HTLV)-1 Protease

In this study, the effects of side-chain configurations of D-Ile residues of a retro–inverso (RI)-type inhibitor on the human T-cell leukemia virus type 1 (HTLV-1) protease containing a hydroxyethylamine dipeptide isostere were clarified. Prior to evaluation using the RI-type inhibitor, the effects of side-chain configurations of Ile residues of the substrate peptide on the HTLV-1 protease were examined to estimate the influence of side-chain configurations on enzyme activity. Based on the estimation of the influence of side-chain configurations on protease affinity, the RI-type inhibitors containing a D-allo-Ile residue in the corresponding substrate sequence, instead of a D-Ile residue, were synthesized via 9-fluorenylmethoxycarbonyl-based solid-phase peptide synthesis. Refolded recombinant HTLV-1 protease (1-116, L40I) was used for the simple and short evaluation of the inhibitory activities of the synthesized RI-type inhibitors. The results clearly indicated that mimicking the whole topology, comprising both the main- and side-chain structures of the parent inhibitor, is effective for the design of potent RI-modified protease inhibitors.     

A versatile tRNA aminoacylation catalyst based on RNA

Aminoacyl-tRNA synthetase (ARS) ribozymes have potential to develop a novel genetic coding system. Although we have previously isolated such a ribozyme that recognizes aromatic amino acids, it could not be used as a versatile catalyst due to its limited ability of aminoacylation to a particular tRNA used for the selection. To overcome this limitation, we used a combination of evolutionary and engineering approaches to generate an optimized ribozyme. The ribozyme, consisting of 45 nucleotides, displays a broad spectrum of activity toward various tRNAs. Most significantly, this ribozyme is able to exhibit multiple turnover activity and charge parasubstituted Phe analogs onto an engineered suppressor tRNA (tRNA(Asn)(CCCG)). Thus, it provides a useful and flexible tool for the custom synthesis of mischarged tRNAs with natural and nonnatural amino acids.