Investigation on thermoresponsive behavior of biodegradable poly(γ‐glutamic acid)‐graft‐L‐phenylalanine ethyl ester

The thermosensitivity of biodegradable and non‐toxic amphiphilic polymer derived from a naturally occurring polypeptide and a derivative of amino acid was first reported. The amphiphilic polymer consisted of poly(γ‐glutamic acid) (γ‐PGA) as a hydrophilic backbone, and L ‐phenylalanine ethyl ester (L ‐PAE) as a hydrophobic branch. Poly(γ‐glutamic acid)‐graft‐L ‐phenylalanine (γ‐PGA‐graft‐L ‐PAE) with grafting degrees of 7–49% were prepared by varying the content of a water‐soluble carbodiimide (WSC). γ‐PGA‐graft‐L ‐PAE with a grafting degree of 49% exhibited thermoresponsive phase transition behavior in an aqueous solution at around 80°C. The copolymers with grafting degrees in the range of 30–49% showed thermoresponsive properties in NaCl solution. A clouding temperature (T_cloud) could be adjusted by changing the polymer concentration and/or NaCl concentration. The thermoresponsive behavior was reversible. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

A chiral π-stacked vinyl polymer emitting white circularly polarized light

An optically active, π-stacked poly[2,7-bis(4-tert-butylphenyl)dibenzofulvene] having a preferred-handed helical conformation was synthesized by anionic polymerization. A thin film sample of the polymer exhibited broad-band white circularly polarized light (CPL) emission on photo excitation.     

Isolation and Structural Elucidation of Novel Mycosporine‐Like Amino Acids as Alarm Cues in the Defensive Ink Secretion of the Sea Hare Aplysia californica

Three new mycosporine‐like amino acids (MAAs), aplysiapalythines A, B, and C ( 1, 2 , and 3 , resp.) were isolated from opaline, a glandular component of the defensive ink secretion of sea hares (Aplysia californica) collected from waters off southern California. Here, we report the structure of these MAAs determined by mass spectrometry and NMR data. These new MAAs are structurally related to two known MAAs that are also present in sea hare opaline, i.e., asterina 330 ( 4 ) and palythine ( 5 ), and for which we also provide detailed data here for comparison. The fact that three of the five MAAs that we identified from sea hare opaline are novel molecules is interesting given that this represents a relatively large addition to the current list of known MAAs. This is likely because most researchers have identified MAAs through HPLC with UV detection, which is imprecise given similarities in UV spectra for different MAAs. Our findings suggest that there is much greater diversity of MAAs than is currently known. Results published elsewhere show that 1, 2 , and 4 are alarm cues for conspecific sea hares at natural concentrations, but 3 and 5 are not.     

Mechanism of high thermal stability of commercial polyesters and polyethers conjugated with bio‐based caffeic acid

In previous report, we discovered that a novel improvement technique to enhance the thermal properties of poly(L ‐lactide)s (PLLAs) by terminal conjugation with 3,4‐diacetoxycinnamic acid (DACA). In this study, we clarified the mechanism of the enhancement of thermal stability by using commercial polyesters and polyethers. The effect of thermal improvement by the terminal conjugation of DACA on poly(DL ‐lactide), poly(ε‐caprolactone), and poly(ethylene glycol) was almost the same as about 100 °C increase. The amount of residual tin catalyst, which enhances the thermal degradation of polyesters, was reduced at undetected level after the terminal conjugation of DACA probably due to the removal of tin during DACA conjugation process. Furthermore, the π‐π stacking interactions of DACA units and the chemical protection of terminal hydroxyl groups, which enhances intramolecular scission, were also important for the high thermal stability. We clarified that the extreme high thermal stability by DACA conjugation was induced by these above mechanisms. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Rational concept to recognize/extract single-walled carbon nanotubes with a specific chirality

Single-walled carbon nanotubes (SWNTs) have remarkable and unique electronic, mechanical, and thermal properties, which are closely related to their chiralities; thus, the chirality-selective recognition/extraction of the SWNTs is one of the central issues in nanotube science. However, any rational materials design enabling one to efficiently extract/solubilize pure SWNT with a desired chirality has yet not been demonstrated. Herein we report that certain chiral polyfluorene copolymers can well-recognize SWNTs with a certain chirality preferentially, leading to solubilization of specific chiral SWNTs. The chiral copolymers were prepared by the Ni(0)-catalyzed Yamamoto coupling reaction of 2,7-dibromo-9,9-di-n-decylfluorene and 2,7-dibromo-9,9-bis[(S)-(+)-2-methylbutyl]fluorene comonomers. The selectivity of the SWNT chirality was mainly determined by the relative fraction of the achiral and chiral side groups. By a molecular mechanics simulation, the cooperative interaction between the fluorene moiety, alkyl side chain, and graphene wall were responsible for the recognition/dissolution ability of SWNT chirality. This is a first example describing the rational design and synthesis of novel fluorene-based copolymers toward the recognition/extraction of targeted (n,?m) chirality of the SWNTs.     

Preparation and Unique pH‐Responsive Properties of Novel Biodegradable Nanocapsules Composed of Poly(γ‐glutamic acid) and Chitosan as Weak Polyelectrolytes

Novel biodegradable hollow nanocapsules composed of two kinds of weak polyelecrolytes, CT and γ‐PGA, were successfully prepared by the deposition of their LbL‐assembled films onto silica particles and the subsequent removal of the silica. These CT‐γ‐PGA hollow nanocapsules showed unique size increases at pH = 1.0, due to the swelling of capsule membranes induced by electrostatic repulsions between ammonium groups of CT components. On the other hand, no significant changes in the capsule size were observed at pH = 4.0, 7.0, and 10. By using the CT‐γ‐PGA nanocapsules, the release of encapsulated substances in response to acidic pH values was accomplished.

     

Graft Polymerization of Vinyl Monomers Onto Carbon Black by Use of the Redox System Consisting of Ceric Ions and Carbon Black Carrying Alcoholic Hydroxyl Groups

The radical graft polymerization of vinyl monomers onto carbon black initiated by a redox system consisting of ceric ion and carbon black having alcoholic hydroxyl groups was investigated. The introduction of alcoholic hydroxyl groups onto the carbon black surface was achieved by the reaction of carbon black with alcoholic hydroxyl radicals, formed by the reaction of alcohol with benzoyl peroxide. The rate of the polymerization of acrylamide (AAm) initiated by the redox system was found to increase in the following order of hydroxyl groups: 1-hydroxyoctyl < 1-hydroxypropyl < 1-hydroxyethyl < hydroxymethyl < 1-hydroxy-1-methylethyl. In the redox polymerization, poly-AAm was effectively grafted onto carbon black by propagation of the polymer from the radical formed by the reaction of ceric ions with the alcoholic hydroxy groups. The percentage of grafting increased with increasing conversion. By use of this redox system, poly(acrylic acid), polyacrylonitrile, and poly(N-vinyl-2-pyrrolidone) could be grafted onto carbon black, but poly(methyl methacrylate) and polystyrene could not be so grafted. The graft polymerization of AAm by use of a redox system consisting of ceric ion and PVA-grafted carbon black was also investigated.     

Syntheses,Crystal Structures and Ligand Field Properties of Iron(II) Complexes with PNP Ligands: Origin of Large Ligand Field by a Phosphorous Donor Atom

New iron(II) complexes were synthesized with two tridentate hybrid ligands having phosphorous and nitrogen donor sites, in order to quantitatively estimate the difference of the ligand-field strengths of phosphorous and nitrogen donor sites in cationic metal complexes. Iron(II) complexes with bis(dimethylphosphinoethyl)amine (PNP) and 2,6-bis(diphenylphosphinomethyl)pyridine (PpyP) ligands crystallized as un-symmetric facial-[Fe(PNP)₂](PF₆)₂·CH₃NO₂ and mer-[Fe(PpyP)₂](CF₃SO₃)₂, respectively, as expected from the steric congestion and from the tendency to avoid the mutual trans influence between two phosphorous donor sites. Both complexes are in the low-spin electronic state up to 400 K. The pseudo-D _4h coordination geometry of the PpyP complex made it possible to separate axial (2 × N) and equatorial (4 × P) contributions to the overall ligand-field by means of a spectrometric method: the difference in the ligand-field strengths by the equatorial Ph₂P-donor sites and by the axial 2,6-disubstituted pyridine donor sites is ca. 13,200 cm^?1. A significantly reduced inter-electronic repulsion parameter (425 cm^?1 for both PNP and PpyP complexes) from the value of the free ion (1,060 cm^?1) indicates covalent interaction between the Fe(II) and P atoms even in these cationic metal complexes. It is shown that the degree of covalency as well as the coordination bond strengths between various metal ions and phosphorous/nitrogen donor atoms is successfully explained by the relative energy levels of interacting atomic orbitals calculated on the basis of the Thomas–Fermi–Dirac potential.     

The Reduction of Sulfoxide by Iodide/Organic Acid System in the Solid State

A novel solid state reduction of sulfoxides including methionine sulfoxide to the corresponding sulfides by iodide/organic acid system is described.     

A facile preparation of 4-(1-Acetyl-4(1H)-pyridylidene)-2-oxazohn-5-ones

4-(1-Acetyl-4(1H)-pyridylidene)-2-oxazolin-5-ones were prepared by the reaction of acylglycines with pyridine and acetic anhydride under oxygen. Acidic and alkaline hydrolysis of 2-oxazolin-5-ones provided oxazole derivatives, pyridine derivatives, and carboxylic acids.