A new synthesis of islandicin and cynodontin

2-Methylanthraquinones with the 1∶4-dihydroxy system are conveniently prepared by the persulphate oxidation of the intermediate benzoylbenzoic acids and subsequent ring closure. 2-Methylquinizarin, islandicin and cynodontin have been prepared by this method as typical examples.     

Synthesis of amphiphilic triblock copolymers as multidentate ligands for biocompatible coating of quantum dots

One barrier to apply current tri-octylphosphine oxide (TOPO) based quantum dots (QDs) to biomedical imaging is that the TOPO on TOPO-QDs can be replaced by the proteins in living system, which may cause the degradation of QDs and/or deactivation of protein. In order to develop biocompatible optical imaging agents, a novel triblock copolymer, designed as a multidentate ligand, was synthesized to coat quantum dot nanocrystals (QDs). The copolymer consists of a polycarboxylic acid block at one end and a polythiol block at the other end with an intervening cross-linked poly(styrene-co-divinylbenzene) block bridging the ends. The multiple mercapto groups from the polythiol block act as multidentate ligands to stabilize QDs, while the polycarboxylic acid block improves the water solubility of QDs and offers reaction sites for surface modification or conjugation with bimolecules. The cross-linked poly(styrene-co-divinylbenzene) block provides a densely compacted hydrophobic shell. This shell will act as a barrier to inhibit the degradation of QDs by preventing the diffusion of ions and small molecules into the core of QDs. This new multidentate polymer coating facilitates the transfer of QDs from organic solvent into aqueous phase. The QDs directly bound to multidentate mercapto groups instead of TOPO are less likely to be affected by the mercapto or disulfide groups within proteins or other biomolecules. Therefore, this research will provide an alternative coating material instead of TOPO to produce QDs which could be more suitable for in vivo use under complex physiological conditions.     

Templating nanostructures by mesoporous materials with an emphasis on room temperature and cryogenic TEM studies

Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore shape and nanometric sizes, provide new gateways for the preparation of nanostructured materials having controlled shape and size with a very narrow distribution. The focus of the current review is on the synthesis of nanostructures templated by OMS either in bulk or in thin film form. The importance of electron microscopy as an indispensable technique in the structural characterization of OMS templated nanostructures, including cryo-TEM, electron tomography and HR-SEM, is highlighted in this review.     

Determination of isotopic ratio of boron in boric acid using laser mass spectrometry.

A reflectron time-of-flight mass spectrometer (RTOFMS) with a laser ablation ion source was used to determine the isotopic ratio of 10B/11B present in boric acid solutions, using graphite as the matrix. The atom % 10B values obtained were within +/-1% of the actual ones. The determination of the boron isotopic ratio using this method is, in comparison to other methods, faster, less expensive and easier to perform. The results are compared with the values determined using thermal ionization mass spectrometry.     

Electrical and optical properties of a novel nonconjugated conductive polymer,poly(β‐pinene)

Electrical conductivity in a novel nonconjugated conductive polymer, poly(β‐pinene), has been measured as a function of molar concentration of iodine. The conductivity increases about 10 orders of magnitude to a maximum value ?8 × 10^?3 S/cm. The molar concentration of iodine, corresponding to saturation, is ?0.85. The optical absorption measurements after light doping have shown two peaks: one at 4.0 eV and the other at 3.1 eV. The first peak is due to the radical cation, and the second due to the charge‐transfer between the double bond and the dopant. As observed in other nonconjugated conductive polymers, the second peak becomes broader and undergoes a red shift, upon higher doping. The FTIR spectroscopic studies have shown that the C?C stretching vibration at 1610 cm^?1 and the ?C? H bending vibration band at 728 cm^?1 decrease upon doping, because of decrease of double bonds. Photoluminescence studies of poly(β‐pinene) show a maximum value at 360 nm for excitation at 280 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3695–3698, 2005     

Evolution from quasielastic to deep-inelastic transfer in the system132Xe+natFe§

The pronounced isotope shift of⁸⁷Sr versus⁸⁷Sr observed recently in 5sns¹S₀ Rydberg states reflects the singlet-triplet mixing solely caused by magnetic hyperfine interaction. Using semiempirical estimates for the hyperfine coupling constant a_{5 s} and the singlet-triplet splitting ΔE_ST (n) excellent agreement between experimental and calculated values is obtained.     

Electronic and thermal properties of B2-type AlRE intermetallic compounds: A first principles study

The ground state electronic structure and thermal properties of B₂-type intermetallic compounds AlRE (RE: Pm, Sm, Eu, Tb, Gd and Dy) have been studied using a self-consistent tight-binding linear muffin-tin orbital (TB-LMTO) method at ambient as well as at high pressure. These compounds show metallic behavior under ambient condition. The band structure, total energy, density of states and ground state properties like lattice parameter, bulk modulus are calculated in the present work. The Debye-Grüneisen model is used to calculate the Debye temperature and the Grüneisen constant. The calculated results are in good agreement with the reported experimental and other theoretical results. The variation in the Debye temperature with pressure has also been reported. We present a detailed analysis of the role of f electrons of RE in the AlRE system.     

Crowding alters the folding kinetics of a β-hairpin by modulating the stability of intermediates

Crowded environments inside cells exert significant effects on protein structure, stability, and function, but their effects on (pre)folding dynamics and kinetics, especially at molecular levels, remain ill-understood. Here, we examine the latter for, as an initial candidate, a small de novo β-hairpin using extensive all-atom molecular dynamics simulations for crowder volume fractions φ up to 40%. We find that crowding does not introduce new folding intermediates or misfolded structures, although, as expected, it promotes compact structures and reduces the accessible conformational space. Furthermore, while hydrophobic-collapse-mediated folding is slightly enhanced, the turn-directed zipper mechanism (dominant in crowder-free situations) increases many-fold, becoming even more dominant. Interestingly, φ influences the stability of the folding intermediates (FI(1) and FI(2)) in an apparently counterintuitive manner, which can be understood only by considering specific intrachain interactions and intermediate (and hierarchical) structural transitions. For φ values <20%, native-turn formation is enhanced, and FI(1), characterized by a hairpin structure but slightly mismatched hydrophobic contacts, increases in frequency, thus enhancing eventual folding. However, higher φ values impede native-turn formation, and FI(2), which lacks native turns, re-emerges and increasingly acts as a kinetic trap. The change in the stability of these intermediates with φ strongly correlates with the hierarchical folding stages and their kinetics. The results show that crowding assists intermediate structural changes more by impeding backward transitions than by promoting forward transitions and that a delicate competition between reduction in configuration space and introduction of kinetic traps along the folding route is key to understanding folding kinetics under crowded conditions.