Chemoenzymatic Posttranslational Modification Reactions for the Synthesis of Ψ[CH2NH]‐Containing Peptides

The Ψ[CH₂NH] reduced amide bond is a peptide isostere widely used in the development of bioactive pseudopeptides. Reported here is a method of chemoenzymatic posttranslational modification for the synthesis of Ψ[CH₂NH]‐containing peptides converted from ribosomally expressed peptides. The posttranslational conversion composed of an enzymatic cyclodehydration and facile two‐step chemical reduction achieves deoxygenation of a specific amide bond present in a nonprotected peptide in water. This method generates the Ψ[CH₂NH] bond in peptides and is applicable to various peptide sequences, potentially enabling the preparation of a library of Ψ[CH₂NH]‐containing peptides.     

Chemoenzymatic Posttranslational Modification Reactions for the Synthesis of Ψ[CH2NH]-Containing Peptides

The Ψ[CH₂NH] reduced amide bond is a peptide isostere widely used in the development of bioactive pseudopeptides. Reported here is a method of chemoenzymatic posttranslational modification for the synthesis of Ψ[CH₂NH]-containing peptides converted from ribosomally expressed peptides. The posttranslational conversion composed of an enzymatic cyclodehydration and facile two-step chemical reduction achieves deoxygenation of a specific amide bond present in a nonprotected peptide in water. This method generates the Ψ[CH₂NH] bond in peptides and is applicable to various peptide sequences, potentially enabling the preparation of a library of Ψ[CH₂NH]-containing peptides.     

Pummerer rearrangement of 1-deoxy-5-thioglucopyranose oxides; novel synthesis of 5-thioglucopyranose derivatives

The Pummerer rearrangement of 3,4-O-isopropylidene-1-deoxy-5-thiopyranose oxide derivatives took place at the C1 position regioselectively to give the corresponding 5-thiopyranoses. The reaction mechanism of this reaction is also discussed.     

Morphological change of a diblock copolymer film induced by selective doping of a photoactive chromophore

Tetrakis‐5,10,15,20‐(4‐carboxyphenyl)porphyrine (TCPP) was position‐selectively introduced into a diblock copolymer film of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) with a sea–island microphase structure. By immersing the PS‐b‐P4VP film into a solution of TCPP/methanol, TCPP was introduced into the island parts comprising P4VP phase. The morphology of the island parts depended on the immersion time and TCPP concentration. A schematic model for the morphological change caused by the phase‐selective introduction of TCPP was proposed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 368–375, 2007     

Degradation behavior in InGaAs/GaAs strained-quantum well lasers

Facet degradation mechanisms of a 980-nm InGaAs/GaAs strained-quantum well laser are analyzed by monitoring the optical-beam induced current. It is clarified that the behavior of defects around the facets govern the long-term stability as well as catastrophic-optical damage generation during operation.     

Mechanistic studies on the N-formylation of amines with CO2 and hydrosilane catalyzed by a Cu–diphosphine complex

The reaction mechanism, reaction intermediates, and catalytically active species of the Cu–diphosphine-catalyzed N-formylation of amines (R¹R²NH) with CO₂ and hydrosilane were investigated. The NMR and kinetic experiments show that the catalytically active species is a Cu-hydride–diphosphine complex, which was generated from the Cu precursor, diphosphine ligand, and hydrosilane. Isotopic experiments using ¹³CO₂ and deuterated hydrosilane revealed the incorporation of the carbonyl group of CO₂ and the H atom of Si–H moiety into the formamide (R¹R²NCHO) product. The formation of a Cu-formate species as an intermediate of the reaction was clarified by in situ ¹H and ¹³C NMR studies.     

Light can transform the secondary structure of silk protein

Fibroin is the main component of silk and is expected to be used as a novel functional material in medicine and bioelectronics. The main secondary structures of this protein are of the random-coil and the β-sheet types. In this study, we carried out laser-induced transformation of the secondary structure, from the random-coil type to the β-sheettype, in solid fibroin films. We prepared two types of fibroin films with the random-coil structure. One is a fibroin film doped with a dye as a photosensitizer with a small amount (1 wt %), and the other is a neat fibroin film. The former was excited at 532 nm and the latter was excited at 266 nm. Irradiations were carried out with fluences much lower than each ablation threshold. The excitation of the dye at 532 nm did not affect the secondary structure of the random-coil type. By contrast, 266-nm laser irradiation, which excites tryptophan (an amino-acid residue) involved in fibroin, created the β-sheetdomain in the film. The structural transformation was revealed by infrared absorption spectroscopy and atomic force microscopy. Received: 1 August 2001 / Accepted: 2 August 2001 / Published online: 2 October 2001     

Highly reliable spot-size converter integrated laser diodes over a wide temperature range for access network systems

In this paper, we present highly reliable high-temperature spot-size converter integrated laser diodes (LDs) fabricated using a full-wafer process with dry etching and MOVPE. The lasers lase at 150°C and operate stably for 10,000 h at 85°C and 10 mW. The median lifetime is estimated to be over 10⁵ h. We also demonstrate a novel screening test procedure for a bar configuration of LDs, which can greatly reduce optical module cost.