Poly(L‐lactide)/C60 nanocomposites: Effects of C60 on crystallization of poly(L‐lactide)

The effects of solvent type and concentration of C₆₀ on the crystallization of poly(L ‐lactide) (PLLA) during solvent evaporation, heating from room temperature, and cooling from the melt were investigated by polarized optical microscopy and differential scanning calorimetry. The addition of C₆₀ enhanced the PLLA crystallization during solvent evaporation, during heating of the melt‐quenched films, and during cooling from the melt of As‐cast films, except for heating and cooling of the PLLA film with 1 wt % of C₆₀ prepared with dichloromethane. In the case of solvent evaporation, the difference in crystallinity between the PLLA films with and without C₆₀ became higher for the solvent with a lower boiling point. In the case of heating of melt‐quenched films, the addition of C₆₀ had a small effect on the crystallinity of PLLA, whereas significantly lowered the peak top and ending temperatures of cold crystallization, except for melt‐quenched PLLA film with 1 wt % of C₆₀ prepared with dichloromethane. The crystallinity of PLLA was determined by the solvent type, rather than by the C₆₀ concentration. In the case of cooling from the melt of As‐cast films, the addition of C₆₀ elevated the crystallinity and cold crystallization temperature values of PLLA films, except for PLLA films prepared with dichloromethane. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2167–2176, 2007     

Alignment behaviour of symmetrical and asymmetrical triphenylenes possessing fluoroalkylated side chains on modified substrates

The alignment behaviour of triphenylene-based compounds possessing fluoroalkylated and alkyl side chains was investigated for the hexagonal columnar (Col_h) mesophase on polyimide-, cetyltrimethylammonium bromide (CTAB)-, and indium tin oxide-coated glass substrates by polarizing optical microscopy. It was found that 2,6,10-trinonyloxy-3,7,11-tris(1H,1H,2H,2H,3H,3H-perfluorononyloxy)triphenylene and 2,6,11-trinonyloxy-3,7,10-tris(1H,1H,2H,2H,3H,3H-perfluorononyloxy)triphenylene exhibit spontaneous homeotropic alignment on these substrates. On the other hand, it was found that 2,6,10-triheptyloxy-3,7,11-tris(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)triphenylene, 2,6,11-triheptyloxy-3,7,10-tris(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)triphenylene, 2,6,10-trihexyloxy-3,7,11-tris(1H,1H,2H,2H,3H,3H-perfluorohexyloxy)triphenylene, 2,6,11-trihexyloxy-3,7,10-tris(1H,1H,2H,2H,3H,3H-perfluorohexyloxy)triphenylene, 2,6,10-tributyloxy-3,7,11-tris(1H,1H,2H,2H,3H,3H-perfluorobutyloxy)triphenylene and 2,6,11-tributyloxy-3,7,10-tris(1H,1H,2H,2H,3H,3H-perfluorobutyloxy)triphenylene do not show such spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Col_h phase could be easily attained by the introduction of an appropriate length of the fluoromethylene chains in the peripheral parts of discogens. Therefore, it is suggested that the balance between the hydrocarbon part including the triphenylene core and the fluoroalkyl part determines the alignment control behaviour. Furthermore, it was found that alignment behaviour is independent of the rotation symmetry of the chemical structure but is dependent on the number of fluoromethylene chains in the chemical structure.     

Dual‐Function Probe to Detect Protease Activity for Fluorescence Measurement and 19F MRI

Dynamic duo : Magnetic resonance imaging (MRI) can visualize deep regions of living bodies, whereas fluorescence measurement offers excellent sensitivity. These methods thus offer signal enhancement potential for detecting enzyme activities. A dual‐mode off/on probe to detect caspase‐3 activity by fluorescence and ¹⁹F MRI is presented.

     

Thermochromic discotic 6-oxoverdazyls

6-Oxoverdazyls 1b[n], substituted with three 3,4,5-trialkoxyphenyl groups (n = 8 and 10), exhibit a columnar hexagonal phase (Col(h)) below 130 °C. They display reversible color change from red to green at the transition to the isotropic phase. XRD and magnetization data do not support dimerization of the radicals in the mesophase.     

First synthesis of decaturin C,an antiinsectant diterpenoid isolated from Penicillium thiersii

The first synthesis of (+)-decaturin C, an antiinsectant diterpenoid isolated from Penicillium thiersii, was accomplished by starting from (R)-(?)-Wieland–Miescher ketone, in which our original spiro-cyclization reaction was featured as a key step.     

Novel generation of selenoaldehydes through stannic chloride-induced unsymmetrical C-Se bond cleavage of bis(N,N-dimethylcarbamoylseleno)methanes

Treatment of a benzene or a CH₂Cl₂ solution of bis(N,N-dimethylcarbamoylseleno)methanes with SnCl₄ afforded β-1,3,5-triselenanes, and the key intermediates, acylselonium ions and selenoaldehydes, were successfully trapped by using allyltrimethylsilane or 2,3-dimethyl-1,3-butadiene to obtain the allylation products or the cycloadducts, respectively.     

Novel generation and ring closure of 1,3-thiaza-1,3-butadiene S-oxides through thermal cycloreversion of 6H-1,3,5-oxathiazine S-oxides

Heating of 6H-1,3,5-oxathiazine S-oxides efficiently afforded 1,2,4-oxathiazoles through the mechanism involving thermal cycloreversion of the substrates and the subsequent ring closure of the intermediary 1,3-thiaza-1,3-butadiene S-oxides.     

Synthesis of δ-thiolactams by the aza-Diels-Alder reaction of in situ generated allenyltrimethylsilylthioketenes with imines

Allenyltrimethylsilylthioketenes, generated in situ through [3,3] sigmatropic rearrangement of trimethylsilylethynyl propargyl sulfides, underwent facile [4+2] cycloaddition with imines to afford the corresponding δ-thiolactams. The resulting 2-trimethylsilyl-4-methylenetetrahydroquinolidine-2-thione, obtained by the [4+2] cycloaddition using piperideine as a dienophile, was transformed into (±)-lupinine in six steps.     

Mesomorphic properties of symmetrical and asymmetrical triphenylene homologues possessing fluoroalkylated side chains

Two types of homologues (symmetrical and asymmetrical in rotational symmetry) of novel triphenylene compounds possessing fluoroalkyl and alkyl side chains were synthesized via an alternative method. X-ray diffraction and DSC measurements showed that these homologues are thermotropic liquid crystals with a hexagonal columnar (Col_h) mesophase. The phase transition temperatures (Col_h-Iso) for both symmetrical and asymmetrical fluoroalkyloxytriphenylenes increase to about 180°C, and are independent of fluoromethylene chain and the rotational symmetry of chemical structure. The Col_h phase of symmetrical and asymmetrical fluoroalkyloxytriphenylenes possessing three fluoroalkyl side chains are more stable than fluoroalkyloxytriphenylenes possessing six fluoroalkyl side chains and alkyloxytriphenylenes. The X-ray diffraction patterns for symmetrical and asymmetrical fluoroalkyloxytriphenylenes, fluoroalkyloxytriphenylenes and alkyloxytriphenylenes in the wide-angle region are compared.     

Synthetic disproof of the structure proposed for solanacol, the germination stimulant for seeds of root parasitic weeds

The structure proposed for solanacol, the germination stimulant for seeds of root parasitic weeds isolated from tobacco (Nicotiana tabacum L.), was synthesized. Comparison of the ¹H NMR data of the synthetic compounds with those reported for solanacol showed the previously proposed structure to be incorrect.