Steroidal glycosides from the underground parts of Solanum sodomaeum

A new steroidal glycoside has been isolated from the underground parts of Solanum sodomaeum L., along with seven known steroidal glycosides. Their chemical structures were determined on the basis of spectroscopic data and chemical evidence, and the structure of one known pregnane type glycoside was corrected. In addition, their antiproliferative activity against human promyelocytic leukemia (HL-60) cells was investigated, and five compounds exhibited stronger activity than cisplatin.     

Lateral organization of a membrane protein in a supported binary lipid domain: direct observation of the organization of bacterial light-harvesting complex 2 by total internal reflection fluorescence microscopy

A unique method is described for directly observing the lateral organization of a membrane protein (bacterial light-harvesting complex LH2) in a supported lipid bilayer using total internal reflection fluorescence (TIRF) microscopy. The supported lipid bilayer consisted of anionic 1,2-dioleoyl-sn-glycero-3-[phospho-rac-(1'-glycerol)] (DOPG) and 1,2-distearoly-sn-3-[phospho-rac-(1'-glycerol)] (DSPG) and was formed through the rupture of a giant vesicle on a positively charged coverslip. TIRF microscopy revealed that the bilayer was composed of phase-separated domains. When a suspension of cationic phospholipid (1,2-dioleoyl-sn-glycero-3-ethylphosphocholine: EDOPC) vesicles (approximately 400 nm in diameter), containing LH2 complexes (EDOPC/LH2 = 1000/1), was put into contact with the supported lipid bilayer, the cationic vesicles immediately began to fuse and did so specifically with the fluid phase (DOPG-rich domain) of the supported bilayer. Fluorescence from the incorporated LH2 complexes gradually (over approximately 20 min) spread from the domain boundary into the gel domain (DSPG-rich domain). Similar diffusion into the domain-structured supported lipid membrane was observed when the fluorescent lipid (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lissamine-rhodamine B sulfonyl: N-Rh-DOPE) was incorporated into the vesicles instead of LH2. These results indicate that vesicles containing LH2 and lipids preferentially fuse with the fluid domain, after which they laterally diffuse into the gel domain. This report describes for first time the lateral organization of a membrane protein, LH2, via vesicle fusion and subsequent lateral diffusion of the LH2 from the fluid to the gel domains in the supported lipid bilayer. The biological implications and applications of the present study are briefly discussed.     

Synthesis of pyrroles: reaction of chromium N-alkylaminocarbene complexes with alpha,beta-unsaturated aldehydes

N-alkylaminocarbene complexes of chromium were found to react with alpha,beta-unsaturated aldehydes to give pyrroles in good yields.     

Electronic and local structural changes in Li(2+x)Ti3O7 ramsdellite compounds upon electrochemical Li-ion insertion reactions by X-ray absorption spectroscopy

Electronic and local structural changes in ramsdellite-type Li(2+x)Ti3O7 compound were investigated by X-ray absorption spectroscopy (XAS) measurements. Upon electrochemical Li-ion insertions, the host lattice with ramsdellite structure is retained, indicated by X-ray powder diffraction. Ti K-edge extended X-ray absorption fine structure (EXAFS) analysis shows, however, slight local structural distortions around Ti ions. The energy shifts and the changes in the peak intensity of Ti K-edge and Ti L-edge XAS reveal the reducing oxidation states of Ti ions as the amount of electrochemically-inserted Li-ion increases. Equally important, oxide ions have a significant effect on the electronic transfer process, suggested by O K-edge XAS. These results on electronic structural changes were interpreted using the Zaanen-Sawatzky-Allen scheme.     

The first stable tetraarylacenaphthenequinodimethanes exhibiting electrochromism with ‘write-protect’ option: preparation, highly deformed structure, and reversible interconversion with acenaphthylene-5,6-diyl dicationic dyes

Severely deformed title quinodimethanes [1,2-bis(diarylmethylene)acenaphthenes] 1 have been designed and prepared as novel electrochromic materials, which can be reversibly interconverted with the deeply colored dicationic dyes 1²⁺ with acenaphthylene-1,2-diyl skeleton. The X-ray analysis of 1 revealed that the inner two aryl groups are forced to overlap in proximity, which can account for the facile electrocyclization process to the isomer. By combination of reversible electrochemical transformation with irreversible isomerization process, the present system provides a prototype for novel molecular response systems equipped with the ‘write-protect’ option.     

Surface properties and enzymatic degradation of end-capped poly(l-lactide)

Surface properties and enzymatic degradation of poly(l-lactide) (PLLA) end-capped with hydrophobic dodecyl and dodecanoyl groups were investigated by means of advancing contact angle (θ_a) measurement, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The θ_a values of end-capped PLLA films were larger than those of non-end-capped PLLA films, suggesting that the hydrophobic dodecyl and dodecanoyl groups were segregated on the film surface. The weight changes of end-capped PLLA thin films during enzymatic degradation in the presence of proteinase K were monitored by using a QCM technique. The relatively fast weight loss of PLLA film occurred during first few hours of degradation, followed by a decrease in the erosion rate. The erosion rate of PLLA films at the initial stage of degradation was dependent on the chain-end structure of PLLA molecules, and the value decreased with an increase in the amount of hydrophobic functional groups. The surface morphologies of PLLA thin films before and after degradation were characterized by AFM. After the enzymatic degradation, the surface of non-end-capped PLLA films was blemished homogeneously. In contrast, the end-capped PLLA thin films were degraded heterogeneously by the enzyme, and many hollows were formed on the film surface. From these results, it has been concluded that the introduction of hydrophobic functional groups at the chain-ends of PLLA molecules depressed the erosion rate at the initial stage of enzymatic degradation.     

Computational analysis of the proton translocation from Asp96 to schiff base in bacteriorhodopsin

The potential energy change during the M --> N process in bacteriorhodopsin has been evaluated by ab initio quantum chemical and advanced quantum chemical calculations following molecular dynamics (MD) simulations. Many previous experimental studies have suggested that the proton transfer from Asp96 to the Schiff base occurs under the following two conditions: (1) the hydrogen bond between Thr46 and Asp96 breaks and Thr46 is detached from Asp96 and (2) a stable chain of four water molecules spans an area from Asp96 --> Schiff base. In this work, we successfully reproduced the proton-transfer process occurring under these two conditions by molecular dynamics and quantum chemical calculations. The quantum chemical computation revealed that the proton transfer from Asp96 to Shiff base occurs in two-step reactions via an intermediate in which an H(3)O(+) appears around Ala215. The activation energy for the proton transfer in the first reaction was calculated to be 9.7 kcal/mol, which enables fast and efficient proton pump action. Further QM/MM (quantum mechanical/molecular mechanical) and FMO (fragment molecular orbital) calculations revealed that the potential energy change during the proton transfer is tightly regulated by the composition and the geometry of the surrounding amino acid residues of bacteriorhodopsin. Here, we report in detail the Asp96 --> Schiff base proton translocation mechanism of bacteriorhodopsin. Additionally, we discuss the effectiveness of combining quantum chemical calculations with truncated cluster models followed by advanced quantum chemical calculations applied to a whole protein to elucidate its reaction mechanism.     

Dielectric relaxation behavior of aqueous solutions of carbobetaines with varying intercharge distances

The dielectric relaxation behavior of aqueous triethylammonioalkanoate (carbobetaine: Et(3)nCB) solutions was examined as a function of frequency from 1.00 x 10(6) to 2.00 x 10(10) Hz (6.28 x 10(6) to 1.26 x 10(11) rad s(-1) in angular frequency); number of intercharge methylene groups, n = 1, 3, 4, 5, and 10; and solute concentration, c. Two major relaxation modes, fast and slow, were found in all solutions examined. Et(3)nCB systems with n = 5 and 10 possessed another, medium, relaxation mode with relaxation time tau(Dh) at high c values (above the contact concentration of solutes) in addition to the fast and slow modes. The fast mode with a relaxation time, tau(w), of approximately 10 ps was attributed to the rotational motion of bulk water molecules. The slow mode with a relaxation time, tau, of 0.08-1 ns, depending on the n value, was attributed to the overall rotational motion of each carbobetaine in aqueous solution. The concentration normalized relaxation strength, Deltaepsilonc(-1), and tau value of the slow relaxation mode increased with increasing n. These findings were quantitatively explained on the basis of changes in the intercharge distance resulting in increased size and dipole moment of the carbobetaines. Above the contact concentration, collisions between solute molecules likely hindered their rotational motions, leading to an increase in tau. The middle relaxation mode found in longer Et(3)nCBs (n = 5 and 10) with a relaxation time, tau(Dh), of approximately 0.2 ns, more than 20 times as long as that of bulk water molecules, tau(w), was attributed to the dehydration of water molecules tightly bound to all Et(3)nCBs examined (including those with n < 5). This mode was not observed in the solutions of Et(3)nCBs with n < 5, since the tau values corresponding to overall rotation were close to or shorter than the tau(Dh) values.     

On the work of Basil Gordon

A review is given of several aspects of the work of Basil Gordon. These include: Rogers-Ramanujan identities, plane partitions, the method of weighted words, modular forms and partition congruences, and the asymptotics of partitions and related q-series.     

Hasse invariants for the Clausen elliptic curves

Gauss’s hypergeometric function gives periods of elliptic curves in Legendre normal form. Certain truncations of this hypergeometric function give the Hasse invariants for these curves. Here we study another form, which we call the Clausen form, and we prove that certain truncations of and in $\mathbb {F}_{p}[x]$ are related to the characteristic p Hasse invariants.