Fibril-like aggregate formation of peptide carboxylate Langmuir films analyzed by surface pressure, surface dipole moment, and infrared spectroscopy

The fibril formation process of a synthetic peptidolipid compound in a Langmuir monolayer at the air-water interface has been analyzed by surface pressure and surface dipole moment-area isotherms, followed by infrared spectral analysis of related Langmuir-Blodgett films. Thus far, the analysis of randomly oriented molecular assemblies has been a difficult matter, especially for spectroscopic measurements. In the present study, the Langmuir film isotherms were discussed in detail, and they have readily been correlated to the infrared spectra. For the spectral analysis, infrared multiple-angle incidence resolution spectroscopy (MAIRS) was employed, which was compared to the results by conventional techniques. Since the peptide assemblies greatly responded to a metal surface, the reflection-absorption technique was not useful for our analysis. Instead, MAIRS was found to be powerful to reveal the anisotropic structure of the Langmuir films, and a disordered molecular architecture has been revealed via the molecular orientation analysis. As a result, the fibril-like aggregation formation process during the monolayer compression, which was suggested by previous topographical study, has been found to be due to the stiff domain formation in the Langmuir films.     

Which One is Bulkier: The 3,5‐Dimethylphenyl or the 2,6‐Dimethylphenyl Group? Development of Size‐Complementary Molecular and Macromolecular [2]Rotaxanes

We developed novel size‐complementary molecular and macromolecular rotaxanes using a 2,6‐dimethylphenyl terminal group as the axle‐end‐cap group in dibenzo‐24‐crown‐8‐ether (DB24C8)‐based rotaxanes, where the 2,6‐dimethylphenyl group was found to be less bulky than the 3,5‐dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6‐dimethylphenyl group as the axle‐end‐cap were synthesized using unsubstituted and fluorine‐substituted DB24C8. Base‐induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size‐complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate‐determining step was that in which the wheel is getting over the end‐cap group, and deslipping proceeded via a hopping‐over mechanism. Finally, the present deslipping behavior was applied to a stimulus‐degradable polymer as an example for the versatile utility of this concept in the context of stimulus‐responsive materials.     

Release control of fragrances by complexation with β-cyclodextrin and its derivatives

The release control of fragrances, benzyl acetate (BA), citral (CR), linalool (LL), citronellol (CL) and linalyl acetate (LA), was conducted using β-cyclodextrin (β-CyD), 2-hydroxypropyl-β-CyD (HP-β-CyD) and 2,6-di-O-methyl β-CyD (DM-β-CyD). The release rate of the fragrances from 30% ethanol/water solution was significantly suppressed by the complexation with these CyDs, and the suppressing effect increased in the order of β-CyD?<?HP-β-CyD?<?DM-β-CyD. The concentration-dependent change of the release rate was quantitatively analyzed to obtain the stability constant (Kc) of the fragrance-CyD complexes. These Kc values were in good agreement with those determined by the solubility method. The results suggest that the release of fragrances can be prolonged by the complexation with β-CyDs and their effects can be controlled by choosing appropriate CyD derivatives with higher Kc values and by setting proper concentrations of the host molecules.     

Design and synthesis of N–acetylglucosamine derived 5a-carbasugar analogues as glycosidase inhibitors

An efficient synthesis of new six-membered carbasugars in both L-form and D-form starting from N–acetylglucosamine is described. The key synthetic steps involved regioselective protection and deprotection, Ferrier carbocyclization, Peterson olefination, hydroboration and stereoselective epoxidation followed by regioselective epoxide ring opening reactions. These six-membered carbasugars showed moderate glycosidase inhibitory activity and one of the compounds was found selective towards β-galactosidase inhibitory activity.     

NMR characterization of α- and β-mannopyranurono-2,6-lactones

Determining the stereochemistry at the anomeric position of glycosides is imperative in chemical synthesis. As for 1,2-cis-β-glycosides such as β-mannosides, ¹³C-¹H coupling constants, ¹J_CHs, are conventionally used when glycosides are in an ordinary chair conformation. In this work, we searched for appropriate criteria to determine the stereochemistry of products in a recently developed glycosylation reaction using 2,6-lactones. As a result, we found that α-glycosides exhibited vicinal coupling constants of around 3.0?Hz?at the anomeric proton, as well as a long-range coupling between protons at C-1 and C-5, whereas β-glycosides had coupling constants of 1.2?Hz?at most. These figures are expected to be useful for future assignments. In addition, the observations obtained from this study revealed the conformation of glycosides with a 2,6-lactone moiety.     

Mixed-valent tetranuclear manganese complexes with pentadentate Schiff-base ligand having a Y-shaped core

Reaction of pentadentate Schiff-base ligands, 1,3-bis(3-methoxysalicylideneamino)-2-propanol (H₃msap) with manganese(II) salts afforded tetranuclear mixed-valent manganese complexes, [Mn₄(msap)₂(CH₃CO₂)₃(CH₃O)(H₂O)]·H₂O (1) and [Mn₄(msap)₂(C₆H₅CO₂)₃(CH₃O)] (2), which were characterized by elemental analysis, infrared and diffused reflectance spectra and temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of these complexes showed that four manganese atoms are chelated by two Schiff-base ligands and further coordinated by syn–syn bridging, syn–anti bridging, and monodentate or bidentate-carboxylato groups, forming a Y-shaped cluster made up of two Mn^II and two Mn^III atoms. Diffused reflectance spectra are featureless, showing broad bands around at near-UV and visible regions. Magnetic moments decrease with lowering of temperature, showing an antiferromagnetic behavior of these complexes.     

On the use of Montgomery multiplication in the computation of binary BBP-type formulas for mathematical constants

The Ramanujan Journal - In this paper, we propose a method of using Montgomery multiplication in the computation of binary Bailey–Borwein–Plouffe (BBP)-type formulas for mathematical...     

Asymmetrically modified silica particles: a simple particulate surfactant for stabilization of oil droplets in water

Spherical silica particles that are able to assemble at a phase boundary of a dual-phase mixture of water and an immiscible organic solvent were prepared by a partial modification of their surface hydroxyl groups with an alkylsilylation agent. Scanning electron microscopic observation of these particles in which their remaining surface hydroxyl groups had been selectively modified with colloidal gold particles revealed that each particle has an asymmetric surface structure: one side of the surface is hydrophilic and the other is hydrophobic. We found that these particles could form a micellar structure in water in the presence of an organic solution of a toluene/polystyrene mixture. The micellar structure was evidenced by formation of golf-ball-like polystyrene particles with dimples imprinting morphologies of the hydrophobic part of modified silica particles.