Hydrogen bond strength modulates the mechanical strength of ferric-thiolate bonds in rubredoxin

It has long been recognized that hydrogen bonds formed by protein backbone amides with cysteinyl S(γ) atoms play important roles in modulating the functional and structural properties of the iron-sulfur centers in proteins. Here we use single molecule atomic force microscopy, cyclic voltammetry, and protein engineering techniques to investigate directly how the strength of N-H···S(γ) hydrogen bonds in the secondary coordination sphere affects the mechanical stability of Fe(III)-thiolate bonds of rubredoxin. Our results show that the mechanical stability of Fe(III)-thiolate bonds in rubredoxin correlates with the strength of N-H···S(γ) hydrogen bonds as reflected by the midpoint reduction potential, providing direct evidence that N-H···S(γ) hydrogen bonds play important roles in modulating the mechanical and kinetic properties of the Fe(III)-thiolate bonds of iron-sulfur proteins and corroborating the important roles of the protein environment in tuning the properties of metal-thiolate bonds.     

First asymmetric total syntheses of (-)-subincanadines a and B, skeletally rearranged pentacyclic monoterpenoid indole alkaloids in aspidospermasubincanum

We achieved the first asymmetric total syntheses of novel Aspidosperma indole alkaloids, (-)-subincanadines A and B, which involve an intramolecular diastereoselective Pictet-Spengler cyclization and an intramolecular Nozaki-Hiyama-Kishi reaction as key steps in the total syntheses.     

Docosahexaenoic acid and eicosapentaenoic acid induce changes in the physical properties of a lipid bilayer model membrane

We investigated the effect of fatty acids such as stearic acid (SA, 18:0), oleic acid (OA, 18:1), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6) on a dipalmitoylphosphatidylcholine (DPPC) bilayer by determining the phase transition temperature, fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH), and detergent insolubility. Treatment with unsaturated fatty acid broadened and shifted the phase transitions of the DPPC bilayer to a lower temperature. The phase transition temperature and the value of fluorescence anisotropy of DPH at 37 degrees C decreased progressively with increasing treatment amounts of unsaturated fatty acid. A large amount of the DPPC bilayer treated with unsaturated fatty acid was dissolved in Triton X-100, obtaining a low level of detergent insolubility. These modifications of the bilayer physical properties were most pronounced with DHA and EPA treatment. These data show that unsaturated fatty acids, particularly DHA and EPA, induce a marked change in the lipid bilayer structure. The composition of fatty acids in the DPPC bilayer was similar after treatment with various unsaturated fatty acids, suggesting that the different actions of unsaturated fatty acids are attributed to change in the molecular structure (e.g., kinked conformation by double bonds). We further explored the change in physical properties induced by fatty acids dispersed in a water-in-oil-in-water multiple emulsion and found that unsaturated fatty acids acted efficiently on the DPPC bilayer, even when incorporated in emulsion form.     

An efficient one-pot synthesis of β-enamino ketones from endo glucal via hypervalent iodine

β-Enamino ketones were successfully synthesized by reaction of endo glycals with primary or secondary amines in the presence of hypervalent iodine reagent in one pot. After the oxidation and protonation taking place on hypervalent iodine agent in acidic condition, endo glucals were effectively converted into the uncyclic β-alkoxyvinyl ketones. Further substitution of β-alkoxyvinyl ketones with primary or secondary amines provided the corresponding β-enamino ketone derivatives in 57-67% yields.     

Improved sonolytic hydrolysis of peptides in aqueous solution with addition of 1,4-benzenedithiol

Described here is the sonolytic hydrolysis of peptides achieved by treatment of aqueous solution to which the radical scavenger 1,4-benzenedithiol (1,4-BDT), which has hydrogen donating ability, has been added. Mass spectrometric analysis of the products of sonolytic hydrolysis gave information about amino acid sequence of the peptides without any byproducts. The additive 1,4-BDT improves the sonolytic hydrolysis of peptides in terms of the rate of hydrolysis reaction and the amount of additive required when compared to catechol, a previously reported additive. The sonolytic hydrolysis of peptides differs from both acid hydrolysis and hydrogen atom-induced dissociation named matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD), in characteristics. We propose a mechanistic reaction for the sonolytic hydrolysis of peptides, based on the mechanisms of both acid hydrolysis and MALDI-ISD processes. The sonolytic hydrolysis of peptides upon addition of hydrogen donating radical scavengers can be rationalized via the attachment of a hydrogen atom to the carbonyl oxygen with subsequent hydrolysis.     

An experimental investigation of the stability of converging cylindrical shock waves in air

An experimental study was made of the stability of converging cylindrical shock waves. The experiments were conducted on annular shock tubes equipped with a double exposure holographic interferometer in the Stoßwellenlabor, RWTH Aachen, and in the Institute of High Speed Mechanics, Tohoku University, Sendai, for shock Mach numbers of 1.1 to 2.1 in air. By comparing these two different shock tube experiments, it is found that in the former facility the mode-three instability is predominant at the center of convergence, whereas the mode-four instability appears in the latter setup. The instabilities are denoted in this way because the shock and the flow field behind it reveal a remarkable triangular and quadrangular symmetry, respectively. It is concluded that the converging cylindrical shock wave is always unstable and sensitive to the structure of the annular shock tube. Usefulness of holographic interferometry to this kind of shock wave research is also demonstrated.To Prof. Dr. sq. techn. Dr.-Ing. e.h. Fritz Schultz-Grunow on the occasion of his 80th birthday     

Structure of χ3-Borophene Studied by Total-Reflection High-Energy Positron Diffraction (TRHEPD)

We have investigated the structure of χ₃-borophene on Ag(111), a monolayer material of boron atoms, via total-reflection high-energy positron diffraction (TRHEPD). By comparing the experimental rocking-curves with ones for several structures calculated by using dynamical diffraction theory, we confirmed that the χ₃-borophene layer has a flat structure. The distance from the topmost layer of the metal crystal is 2.4 Å, which is consistent with results reported by X-ray standing wave-excited X-ray photoelectron spectroscopy. We also demonstrated that the in-plane structure of χ₃-borophene is compatible with the theoretical predictions. These structural properties indicate that χ₃-borophene belongs to a group of epitaxial monolayer sheets, such as graphene, which have weak interactions with the substrates.     

Reduction of atmospheric turbulence using optical duplicate system in free-space optical communications

Optical Review - To reduce the effect of atmospheric turbulence and stabilize the optical link in free-space optical (FSO) communications, we have proposed to use an optical duplicate system (ODS)...