Dynamic Light Scattering Studies on Crystallization of Isotactic Polystyrene from Dilute Solutions at High Supercoolings

Crystallization of isotactic polystyrene (it‐PS) from dilute solution at high supercooling has been investigated by dynamic light scattering (DLS). We successfully obtained simultaneously, in situ in solutions, the time developments of both random coils of it‐PS molecules and the growing crystals. The size of coils remains constant during growth, while the crystals pass through two stages, that is, an induction period at the early stage with very slow growth rates and a subsequent linear growth stage. It is confirmed that the temperature dependence of the linear growth rates, determined by DLS, agree well with that determined by electron microscopy. The temperature dependences of the growth rate and the inverse of induction time are dependent on the viscosity of solvent, which indicates that all dynamics are dominated by the segmental motion of polymer chains in solution at high supercoolings (low temperatures). Two possibilities are proposed for the induction period.     

A generalization of a theorem of Imai and its applications to Iwasawa theory

It is proved that, if $K$ is a complete discrete valuation field of mixed characteristic $(0,p)$ with residue field satisfying a mild condition, then any abelian variety over $K$ with potentially good reduction has finite $K(K^{1/p^\infty })$ -rational torsion subgroup. This can be used to remove certain conditions assumed in some theorems in Iwasawa theory.     

Concise Synthesis of Potassium Acyltrifluoroborates from Aldehydes through Copper(I)‐Catalyzed Borylation/Oxidation

Potassium acyltrifluoroborates (KATs) were prepared through copper(I)‐catalyzed borylation of aldehydes and subsequent oxidation. This synthetic route is characterized by the wide range of aldehydes accessible, favorable step economy, mild reaction conditions, and tolerance of various functional groups, and it enables the facile generation of a range of KATs, for example, bearing halide, sulfide, acetal, or ester moieties. Moreover, this method was applied to the three‐step synthesis of various α‐amino acid analogues that bear a KAT moiety on the C‐terminus by using naturally occurring amino acids as the starting material.     

Promotion of Cell Migration into a Hydrophobically modified Alaska Pollock Gelatin‐Based Hydrogel

In situ chemically cross‐linkable hydrogels composed of hexyl group–modified Alaska pollock–derived gelatin (C6‐ApGltn) and poly(ethylene glycol)‐based four‐armed cross‐linker is developed. Water droplets are quickly absorbed into the C6‐ApGltn hydrogel in the first 10 s compared with original ApGltn (Org‐ApGltn), and the final contact angle on C6‐ApGltn is significantly lower than that on Org‐ApGltn. Using a fluorescent probe, an increase in fluorescence intensity on C6‐ApGltn compared to that on Org‐ApGltn is found, indicating the formation of a hydrophobic pocket. Moreover, the promotion of cell migration into the C6‐ApGltn hydrogel is observed in vitro and in vivo compared with Org‐ApGltn hydrogel, despite no significant difference in elastic modulus. Therefore, the C6‐ApGltn hydrogel could potentially be used as a supporting material for cell transplantation and tissue/organ engineering.     

Topological aspects of excitons in artificial structure

The exciton properties of thin nanotube structures are investigated theoretically. Anisotropic size dependencies have been found in the exciton binding energy, the kinetic energy for the relative motions of an electron and a hole, and the wavefunction. These anisotropies arise from the different boundary conditions in the tube-length and circumferential directions, namely, the topological features of nanotubes. We also found that it is possible to change the topology of exciton wavefunctions by varying the tube-length and the tube-radius. These findings suggest that the optical properties of nanotubes such as oscillator strength or nonlinear susceptibilities can be controlled by tuning the structural parameters, thus yielding a novel guiding principle for designing optical functional materials.     

Two-dimensional structures of pyrimido[5,4-d]pyrimidine derivatives at solid/liquid interface

Two-dimensional structures of pyrimido[5,4-d]pyrimidine derivatives (PD) were studied by scanning tunneling microscopy (STM) at solid/liquid interface. In order to tune the intervals of functional unit (hydrogen bonding site) in the molecule, the PD with different numbers and length of alkyl chain were designed and synthesized. STM observation at highly oriented pyrolytic graphite (HOPG)/1-phenyloctane interface revealed that the PD with four alkyl chains formed a columnar structure, and the alkyl chains were not interdigitated. By contrast, the PD with two alkyl chains formed similar columnar structure, whereas the alkyl chains were interdigitated. These structural features of the PD indicates that the intervals of the functional unit, i.e., hydrogen bonding sites in the PD can be controlled by changing not only the length but also the number of alkyl chains.     

An Efficient Method for the Conjugation of Hydrophilic and Hydrophobic Components by Solid‐Phase‐Assisted Disulfide Ligation

Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid‐phase‐assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one‐pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid‐supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water‐insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution‐phase reactions were obtained in moderate yields (29–45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.     

Actinoperylone, a novel perylenequinone-type shunt product, from a deletion mutant of the actVA-ORF5 and ORF6 genes for actinorhodin biosynthesis in Streptomyces coelicolor A3(2)

A novel shunt product, actinoperylone, has been isolated from a deletion mutant of the actVA-ORF5 and ORF6 genes involved in the biosynthesis of a benzoisochromanequinone (BIQ) antibiotic actinorhodin (ACT) in Streptomyces coelicolor A3(2). Spectroscopic analysis revealed its perylenequinone-type skeleton with the four chiral centers, obviously derived from the dimerization of an ACT intermediate. The structure of actinoperylone indicates the essential role of ActVA-ORF5 in the oxygen introduction at C-6, which is common to the formation of BIQ chromophore. The present results also agree with the distribution of the actVA-ORF5 homologues in all known BIQ biosynthetic clusters in streptomycetes.     

Zinc underpotential deposition at Pt(111) and Pt(110) under the influence of boric acid and chloride anions

Zinc underpotential deposition (Zn UPD) was studied by cyclic voltammetry in solutions of various pH and composition, where the effects of the presence of boric acid or chloride in the solution were observed. We have found that the cyclic voltammograms of Zn UPD at Pt(111) were dependent on boric acid concentrations, zinc ion concentrations, and pH in acidic solutions. These suggest that the induced adsorption of borate by releasing of H⁺ is accompanied with Zn UPD. The preadsorbed chloride species on Pt(110) accelerate the UPD process by their removal just before the UPD, making the surface sites available for the process, and the UPD remains at identical electrode potentials, while the chloride ions do not take part in the induced adsorption on UPD Zn at Pt, as clearly found by the radiotracer method. These show that the anions play versatile roles in the process of adlayer formation by their different but essential chemical characteristics. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 745–751 The text was submitted by the authors in English.     

Matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-TOF)-based imaging mass spectrometry reveals a layered distribution of phospholipid molecular species in the mouse retina

We recently developed a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-TOF)-based imaging mass spectrometry (IMS) system. This system enables us to perform structural analyses using tandem mass spectrometry (MS/MS), as well as to visualize phospholipids and peptides in frozen sections. In the retina, phototransduction is regulated by the light-sensitive interaction between visual pigment-coupled receptor proteins, such as rhodopsin, and G proteins, such as transducin. There are some reports that the conformation of rhodopsin is influenced by the composition of phospholipids in the lipid bilayer membrane. However, these results were based on in vitro experiments and have not been analyzed in vivo. In this study, we visualized and identified phospholipids in mouse retinal sections with the MALDI-QIT-TOF-based IMS system. From a spectrum obtained by raster-scanned analysis of the sections, ions with high signal intensities were selected and analyzed by MS/MS. As a result, sixteen ions were identified as being from four diacyl-phosphatidylcholine (PC) species, i.e., PC (16:0/16:0), PC (16:0/18:1), PC (16:0/22:6), and PC (18:0/22:6), with different ion forms. The ion images revealed different distributions on the retinal sections: PC (16:0/18:1) was distributed in the inner nuclear layer and outer plexiform layer, PC (16:0/16:0) in the outer nuclear layer and inner segment, and both PC (16:0/22:6) and PC (18:0/22:6) in the outer segment and pigment epithelium. In conclusion, our in vivo IMS analyses demonstrated a three-zone distribution of PC species on the retinal sections. This approach may be useful for analyzing lipid changes and their contribution to phototransduction in the retina.