Structure of holothurin A a biologically active triterpene-oligoglycoside from the sea cucumber holothuria leucospilota brandt

On the basis of chemical and physicochemical evidence, the structure of holothurin A, a biologically active major obligoglycoside o lanostane-type triterpene holothurigenol ($\text{2}$), has been elucidated to be $\text{8}$.     

Anomalous High Pressure Properties in Fullerene Superconductors

Abstract

Correlations among lattice parameter, external pressure, and critical temperature T_c has been surveyed on fullerene superconductors with a wide range of lattice parameters and various valence states. The observed value of dT_c/dP for Na₂Rb_0.5Cs_0.5C₆₀ and Li₃CsC₆₀, having small interfullerene separations, is about a few times lager than that of K₃C₆₀. In contrast, small dT_c/dP values are found in fullerides with expanded unit cells, such as (NH₃)_xNaAA^?C₆₀ (A, A^? = K, Rb and Cs) and A₃Ba₃C₆₀. Interestingly, the chemical and physical pressure effects on T_c are considerably different in these fullerides with large interfullerene spacings. Our results suggest that the pressure dependence is scaled by an interfullerene distance when the interfullerene distances is small, but that this scaling fails when the unit cell is expanded.     

Application of 15N NMR Spectroscopy to Studies of the Intermolecular Interaction of Biomolecules

Abstract

Nitrogen nuclei are frequently located at the interaction sites of biomolecules; for example, amide nitrogens in the peptide are the key to maintaining the peptide backbone conformation by hydrogen bonding. Histidine, tryptophan, and arginine side chains contain nitrogen atoms which are often located at the active sites of enzymes. Heterocyclic compounds like purine and pyrimidine bases are substances essential to information transfer by base pair formation of nucleic acids. Also some other co-factors and dyes, such as flavins, porphyrins and chlorophylls, are nitrogen-containing substances which regulate energy tranduction in biological systems. Lecithin and phosphatidylethanolamine are the principal components of the phospholipids from biomembranes. To detect interaction sites and to study the interaction mechanism of these biomolecules, the use of nitrogen NMR seems promising. Although more than 99% of naturally occurring nitrogen element has the ¹⁴N nuclei, a disadvantage of the use of ¹⁴N magnetic resonance has been recognized. It has a spin quantum number I = 1 and the associated quadrupole moment provides a very broad resonance signal of about 100～1000 Hz. Thus, for detection of small changes of the chemical environment, use of ¹⁴N magnetic resonance is not adequate. The natural abundance of ¹⁵N nuclei with a spin quantum number I = 1/2 (which give a sharp resonance signal) is only 0.3% (Table 1). But recent developments in the instrumentation of NMR spectroscopy have made it possible to observe the resonance of the nuclei with low natural abundance. Fourier transform (FT) NMR can save thousands of times the accumulation time to improve the signal to noise ratio of ¹⁵N spectra [1-3]. Also superconducting magnets with wide bores have made possible the use of thick sample tubes of 25 mmΦ and observation of the ¹⁵N resonance of substances of low solubility [4]. In spite of such instrumental development, the observation of the 15N resonance is still not easy because of its low sensitivity; about of proton magnetic resonance. In the application of ¹⁵N NMR in biological systems, we often encounter quite low solubility of biomacromolecules and also sometimes need to measure the concentration dependency of ¹⁴N chemical shifts. For such experiments, enrichment of ¹⁵N nuclei in the molecules is required. Chemical syntheses starting from the simple ¹⁵N containing compounds as an ¹⁵N source and also biological syntheses by bacterial fermentation using the ¹⁵N source in culture media are employed for ¹⁵N enrichment. Enrichment at specific positions of biomolecules is useful for spectral assignments and also for analyses of the pathways of biosyntheses [5].     

Direct measurement of interactions between stimulation-responsive drug delivery vehicles and artificial mucin layers by colloid probe atomic force microscopy

A novel thermo- and pH-sensitive nanogel particle, which is a core-shell structured particle with a poly(N-isopropylacrylamide) (p(NIPAAm)) hydrogel core and a poly(ethylene glycol) monomethacrylate grafted poly(methacrylic acid) (p(MMA-g-EG)) shell, is of interest as a vehicle for the controlled release of peptide drugs. The interactions between such nanogel particles and artificial mucin layers during both approach and separation were successfully measured by using colloid probe atomic force microscopy (AFM) under various compression forces, scan velocities, and pH values. While the magnitudes of the compression forces and scan velocities did not affect the interactions during the approach process, the adhesive force during the separation process increased with these parameters. The pH values significantly influenced the interactions between the nanogel particles and a mucin layer. A large steric repulsive force and a long-range adhesive force were measured at neutral pH due to the swollen p(MMA-g-EG) shell. On the other hand, at low pH values, the steric repulsive force disappeared and a short-range adhesive force was detected, which resulted from the collapse of the shell layer. The nanogel particles possessed a pH response that was sufficient to protect the incorporated peptide drug under the harsh acidic conditions in the stomach and to effectively adhere to the mucin layer of the small intestine, where the pH is neutral. The relationships among the nanogel particle-mucin layer interactions, pH conditions, scan velocities, and compression forces were systemically investigated and discussed.     

Switchable antenna: a star-shaped ruthenium/osmium tetranuclear complex with azobis(bipyridine) bridging ligands

A star-shaped Ru/Os tetranuclear complex, in which a central Os unit is linked to three peripheral Ru units by 4,4'-azobis(2,2'-bipyridine) (azobpy) bridging ligands, was prepared to examine the unique photodynamics regulated by its redox state. The Ru/Os tetranuclear complex exhibits Ru-based luminescence at 77 K, whereas the three-electron reduction (one for each azobpy) of the Ru/Os complex results in luminescence from the Os unit. The photoexcited state of the Ru/Os complex rapidly decays into low energy metal-to-ligand charge-transfer states, in which the excited electron is localized in the azobpy ligand in the form of azobpy(.-). Upon the one-electron reduction of the azobpy ligands, the above-mentioned low-energy states become unavailable to the photoexcited complex. As a result, an energy transfer from the Ru-based excited state to the Os-based excited state becomes possible. Ultrafast transient absorption measurements revealed that the energy transfer process consists of two steps; intramolecular electron transfer from the terminal bipyridine ligand (bpy(.-)) to form azobpy(2-) followed by a metal-to-metal electron transfer. Thus, the Ru/Os tetranuclear complex collects light energy into the central Os unit depending on the redox state of the bridging ligands, qualifying as a switchable antenna.     

Effects of oligoDNA template length and sequence on binary self-assembly of a nucleotide bolaamphiphile

Templated self-assembly of nucleotide bolaamphiphile 1 (in which a 3'-phosphorylated thymidine moiety is connected to each end of a long oligomethylene chain) with a 10-, 20-, 30-, or 40-meric single-stranded oligoadenylic acid (2, 3, 4, or 5) led to the formation of right-handed helical nanofibers in 0.1x Tris/EDTA (TE) buffer solutions. The helical pitch increased as the length of the oligoadenylic acid template increased. DNA composed of oligoadenylic and oligocytidylic acid sequences (6, 7, and 8) also acted as templates to induce the formation of helical nanofiber structures. The diameter of the nanofibers remained constant (6-6.6 nm) irrespective of the template used. The binary self-assembly of 1 with 4 also produced higher-order, double-stranded nanofibers.     

Lower closure point of adsorption hysteresis in ordered mesoporous silicas

To examine the nature of the lower closure point of adsorption hysteresis in ordered mesoporous silicas, we measured the temperature dependence of the adsorption-desorption isotherm of nitrogen for three kinds of ordered silicas with cagelike pores and three kinds of ordered silicas with cylindrical pores. The lower closure point pressure of nitrogen in the cagelike pores with sufficiently small necks, that is, the cavitation pressure of a confined liquid, did not depend appreciably on the cage size in the temperature region far away from a hysteresis critical temperature (Tch) but its cage-size dependence was noticeable in the vicinity of Tch. The lower closure point in the cylindrical pores depended on the pore size, and its thermal behavior was totally different from that in the cagelike pores. Nevertheless, the hysteresis critical points of nitrogen in the ordered mesoporous silicas, which are defined as a threshold of temperatures (Tch) and pressure above which reversible capillary condensation takes place in a given size and shape of pores, fell on a common line in a temperature-pressure diagram regardless of the pore geometries. We consider this finding as evidence that capillary evaporation in the cylindrical pores follows a cavitation process in the vicinity of Tch in the same way as that in the cagelike pores and also that the low limit of the hysteresis loop that has been long recognized since 1965 is due to the occurrence of a vapor bubble in a stretched metastable liquid confined to the pores with decreasing pressure (cavitation).     

Anionic Polymerization of New Dual-Functionalized Styrene and α-Methylstyrene Derivatives Having Styrene or α-Methylstyrene Moieties

Anionic polymerizations of four new dual-functionalized styrene and α-methylstyrene derivatives, 3-(4-(4-isopropenylphenoxy)butyl)styrene ( 4 ), 3-(4-(2-isopropenylphenoxy)butyl)-α-methylstyrene ( 5 ), 4-(4-(4-isopropenylphenoxy)butyl)-α-methylstyrene ( 6 ), and 4-(4-(2-vinylphenoxy)butyl)styrene ( 7 ), were carried out in THF at -78 °C with sec-BuLi as an initiator. Both 4 and 5 underwent anionic polymerization in a living manner to quantitatively afford functionalized polystyrenes and poly(α-methylstyrene)s having α-methylstyrene moiety in each monomer unit and precisely controlled chain lengths. On the other hand, insoluble polymers were obtained by the anionic polymerization of 6 and 7 under the same conditions. The positional effect of substituent on anionic polymerization was discussed.     

Anti-Obesity Effects of Matoa (Pometia pinnata) Fruit Peel Powder in High-Fat Diet-Fed Rats

Fruit peels, pericarps, or rinds are rich in phenolic/polyphenolic compounds with antioxidant properties and potentially beneficial effects against obesity and obesity-related non-communicable diseases. This study investigated the anti-obesity effects of matoa (Pometia pinnata) and salak (Salacca zalacca) fruit peel. Neither matoa peel powder (MPP) nor salak peel powder (SPP) affected the body weight, visceral fat weight, or serum glucose or lipid levels of Sprague–Dawley rats when included as 1% (w/w) of a high-fat diet (HFD). However, MPP significantly decreased the hepatic lipid level. MPP at a dose of 3% (w/w) of the HFD decreased body weight, visceral fat, and serum triglyceride levels as well as the hepatic lipid content. The inhibitory effect of MPP on hepatic lipid accumulation was not enhanced when its concentration was increased from 1% to 3% of the HFD. The anti-obesity effect of matoa was partly explained by the inhibitory effect of the matoa peel extract on fatty acid-induced secretion of ApoB-48 protein, a marker of intestinal chylomicrons, in differentiated Caco-2 cell monolayers. We identified hederagenin saponins that are abundant in MPP as potential anti-obesity substances. These results will contribute towards the development of functional foods with anti-obesity effects using the matoa fruit peel.