Water dispersion of cellulose II nanocrystals prepared by TEMPO-mediated oxidation of mercerized cellulose at pH 4.8

Mercerized wood cellulose was oxidized by 4-acetamide-TEMPO/NaClO/NaClO₂ system at 60 °C and pH 4.8 for 1–5 days. Mostly individual nanocrystals 4–7 nm in width and 100–200 nm in length were obtained by ultrasonication of the oxidized product in water. The nanocrystals had the cellulose II structure, and carboxylate contents of 2.0–2.4 mmol/g, indicating that these carboxylate groups were selectively formed on the cellulose II crystallite surfaces in mercerized cellulose. Moreover, the original wood cellulose and mercerized cellulose were acid-hydrolyzed, and then subjected to the TEMPO-mediated oxidation under the same conditions at pH 4.8 to prepare reference samples. TEM images, light transmittance and rheological properties of water dispersions showed that the nanocrystals prepared from mercerized cellulose by the TEMPO oxidation and sonication in water had the highest dispersibility of individual nanocrystals with less amounts of bundles in water, resulting from the highest carboxylate contents.     

RAMA stain: A fast,sensitive and less protein‐modifying CBB R250 stain

SDS‐PAGE and CBB staining are two of the most popular methods used for protein analysis. Although many reports that describe such staining methods have been published, these conventional protocols require several hours or days for staining and de‐staining. In this study we describe a recently developed, fast and sensitive CBB staining method that utilizes the staining solution of RAMA that consists of the low‐cost reagents: CBB R250, acetic acid, methanol and ammonium sulfate, and the destaining solution of water. Our method dose dependently detects 12 nanograms protein within 60 min and with a wide protein spectrum. Although the features of the dose‐dependent relationship depend upon protein amounts and protein types, for most of the protein samples tested, a linear relationship was observed in the region from 12 to 330 ng. Moreover, through further washing, the detection sensitivity of protein is enhanced and reaches a maximum at 1.4 ng and then gradually decreases in the de‐staining process. It has been shown recently through MS analyses that the sensitive colloidal CBB staining methods frequently result in artifactual methylations due to the strong acid and long contact during staining and the destaining processes. Such artifacts were reported to be reduced by the replacement of strong inorganic acid with acetic acid and because RAMA utilizes acetic acid and is in contact with the proteins for a short time during staining and de‐staining, it is expected that in vitro artifacts will be reduced. Finally, MS analyses of RAMA‐stained protein bands were revealed not to have been methylated.     

Do benzodiazepines mimic reverse-turn structures?

The role of benzodiazepine derivatives (BZD) as a privileged scaffold that mimics beta-turn structures (Ripka et al. (1993) Tetrahedron 49:3593-3608) in peptide/protein recognition was reexamined in detail. Stable BZD ring conformers were determined with MM3, and experimental reverse-turn structures were extracted from the basis set of protein crystal structures previously defined by Ripka et al. Ideal beta-turns were also modeled and similarly compared with BZD conformers. Huge numbers of conformers were generated by systematically scanning the torsional degrees of freedom for BZDs, as well as those of ideal beta-turns for comparison. Using these structures, conformers of BZDs were fit to experimental structures as suggested by Ripka et al., or modeled classical beta-turn conformers, and the root-mean-square deviation (RMSD) values were calculated for each pairwise comparison. Pairs of conformers with the smallest RMSD values for overlap of the four alpha-beta side-chain orientations were selected. All overlaps of BZD conformers with experimental beta-turns yielded one or more comparisons where the least RMSD was significantly small, 0.48-0.86 angstroms, as previously suggested. Utilizing a different methodology, the overall conclusion that benzodiazepines could serve as reverse-turn mimetics of Ripka et al. is justified. The least RMSD values for the overlap of BZDs and modeled classical beta-turns were also less than 1 angstrom. When comparing BZDs with experimental or classical beta-turns, the set of experimental beta-turns selected by Ripka et al. fit the BZD scaffolds better than modeled classical beta-turns; however, all the experimental beta-turns did not fit a particular BZD scaffold better. A single BZD ring conformation, and/or chiral orientation, can mimic some, but not all, of the experimental beta-turn structures. BZD has two central ring conformations and one chiral center that explains why the four variations of the BZD scaffold can mimic all types of beta-turn structure examined. It was found, moreover, that the BZD scaffold also mimics each of the nine clusters of experimental orientations of side chains of reverse turns in the Protein Data Bank, when the new classification scheme for the four side-chain directions (the relative orientations of alpha-beta vectors of residues i through i+3) was considered (Tran et al. (2005) J Comput-Aided Mol Des 19:551-566).     

Anomalous enhancement of a single high-order harmonic by using a laser-ablation tin plume at 47 nm

We have successfully demonstrated intensity enhancement of a single high-order harmonic at a wavelength of 46.76 nm by using low-ionized tin ions in a laser-ablation plume as the nonlinear medium. The ablation plume was produced by irradiating a solid tin target with a 10 mJ energy picosecond laser pulse. Strong 17th-harmonic generation at a wavelength of 46.76 nm was observed with a conversion efficiency of about 10(-4). We attribute the strong enhancement of the single high-order harmonic to multiphoton resonance with a strong radiative transition of the Sn II ion.     

Single atomic contact adhesion and dissipation in dynamic force microscopy

By combining dynamic force microscopy experiments and first-principles calculations, we have studied the adhesion associated with a single atomic contact between a nanoasperity--the tip apex--and a semiconductor surface--the Ge(111)-c(2 x 8). The nanoasperity's termination has been atomically characterized by extensive comparisons of the measured short-range force at specific sites with the chemical forces calculated using many atomic models that vary in structure, composition, and relative orientation with respect to the surface. This thorough characterization has allowed us to explain the dissipation signal observed in atomic-resolution images and force spectroscopic measurements, as well as to identify a dissipation channel and the associated atomic processes.     

Ultrasonic speed microscopy for imaging of coronary artery

We have been developing a scanning acoustic microscope (SAM) system for medicine and biology featuring quantitative measurement of ultrasonic speed and attenuation of soft tissues. In the present study, we will propose a new concept ultrasonic speed microscopy that can measure the thickness and ultrasonic speed using fast Fourier transform of a single pulsed wave instead of continuous waves used in conventional SAM systems. Six coronary arteries were frozen and sectioned approximately 10 microm in thickness. They were mounted on glass slides without cover slips. The scanning time of a frame with 300 x 300 pixels was 121 s and two-dimensional distribution of ultrasonic speed was obtained. The ultrasonic speed was 1720 m/s in the thickened intima with collagen fiber, 1520 m/s in lipid deposition underlying fibrous cap and 1830 m/s in calcified lesion in the intima. These basic measurements will help understanding echogenecity in intravascular ultrasound (IVUS) images. Imaging of coronary artery with the ultrasonic speed microscopy provides important information for study of IVUS coronary imaging.     

Unique Substitution Effect at 5,5′‐Positions of Fused Azobenzene–Boron Complexes with a N=N π‐Conjugated System

A recent report illustrated superior optical properties, such as near‐infrared emission, of polymers connected at the 4,4′‐positions to a fused azobenzene–boron complex (BAz). In this study, it is initially demonstrated that further narrowing of the band gap can be realized through the substituent effect with bromine groups at the 5,5′‐positions of BAz compared with those at the 4,4′‐positions. From a series of mechanistic studies, perturbation of the energy levels was rationally explained by the difference in contributions of the inductive effect and the variable resonance effect, which was correlated with the degree of electron distribution of molecular orbitals at the substituent positions. Moreover, it was found that unique electronic states, such as delocalized HOMOs and LUMOs, should appear on the main chains of the BAz‐containing copolymers with fluorene and bithiophene units, according to the optical and electrochemical data and theoretical calculations. By taking advantage of property tunability and the dramatically low LUMO energy level (near ?4.0 eV) of the BAz unit, it can be said that BAz should be a conjugated building block favorable for building advanced optoelectronic devices.     

Total Synthesis of 1‐Hydroxytaxinine

1‐Hydroxytaxinine ( 1 ) is a cytotoxic taxane diterpenoid. Its central eight‐membered B‐ring possesses four oxygen‐functionalized centers (C1, C2, C9, and C10) and two quaternary carbon centers (C8 and C15), and is fused with six‐membered A‐ and C‐rings. The densely functionalized and intricately fused structure of 1 makes it a highly challenging synthetic target. Reported here is an efficient radical‐based strategy for assembling 1 from A‐ and C‐ring fragments. The A‐ring bearing an α‐alkoxyacyl telluride moiety underwent intermolecular coupling with the C‐ring fragment by a Et₃B/O₂‐promoted decarbonylative radical formation. After construction of the C8‐quaternary stereocenter, a pinacol coupling reaction using a low‐valent titanium reagent formed the B‐ring with stereoselective installation of the C1,C2‐diol. Subsequent manipulations at the A‐ and C‐rings furnished 1 in 26 total steps.     

Alexandrolide,a diatom growth inhibitor isolated from the dinoflagellate Alexandrium catenella

Alexandrolide (1), an allelopathic diatom growth inhibitor, was isolated from the cell free culture media of the dinoflagellate Alexandrium catenella, which is known as a paralytic shellfish toxin producer. The structure of 1 including partial absolute configuration was elucidated by detailed analyses of NMR spectra, protection of 1,3-diols with acetonide, and a modified Mosher method. The structure of 1 is characterized by a 19-membered ring structure comprising a dehydroalanine and a docosanoic acid derivative possessing a ketone, four hydroxy groups, an ester, and three branching methyls in the molecule. Alexandrolide showed selective growth inhibition against a diatom but not against dinoflagellates.