Nucleation and size distribution of nucleus during induction period of polyethylene crystallization

The crystallization process from supercooled melt results in the formation of nanosize nuclei in the earlier stage (induction period) through subsequent attachment or detachment of repeating unit to nuclei. The size distribution of nucleus f(N(j),t) in the induction period of nucleation process from the melts has not been experimentally confirmed yet by direct observation. The reason is that the number density of nuclei nu is too small to be detected experimentally. In our previous work, we showed the direct evidence of nucleation experimentally by means of small angle x-ray scattering (SAXS) technique. Further we have succeeded to observe the nucleation and f(N(j),t) of polymer crystallization from the melts by SAXS using synchrotron radiation. We increased nu by adding a nucleating agent to a polymer (polyethylene). The time evolution of f(N(j),t) was observed for the first time.     

Reaction of tertiary cyclopropyl silyl ethers with diethylaminosulfur trifluoride: the effects of substituents on the cleavage of the cyclopropane ring

The reaction of tertiary cyclopropanol silyl ethers with diethylaminosulfur trifluoride usually causes ring opening to produce allylic fluorides. However, cyclopropyl silyl ethers bearing a strong electron-donating substituent at C1 or an electron-withdrawing substituent at C2 do not afford allylic fluorides but fluorocyclopropanes. It has also been proved that an electron-donating substituent at C2 of the tertiary cyclopropanol silyl ethers promotes ring opening in the reaction with diethylaminosulfur trifluoride.     

Photoinduced conformational changes of azoaromatic polyaspartates containing octadecyl side chains

Copolymers of p-(phenylazo)benzyl-L-aspartate and n-octadecyl-L-aspartate exist as right- and left-handed α-helices in solution at 25°C depending on the copolymer composition: the reversal of helix sense from a right- to left-handed one occurs with increasing the azobenzene content. The α-helices of the copolymers are very sensitive to trifluoroacetic acid (TFA), and are converted into random coil below 2.0% of TFA. Among the copolymers, the copolymer containing 47% azobenzene groups is unique since it exhibits a TFA-induced conformational change from right-handed α-helix to random coil via left-handed α-helix. Upon UV light irradiation at 25°C, the copolymers containing 68 and 89% azobenzene groups caused the reversal in helix sense from a left- to right-handed one. The conformations of the copolymers were dependent on temperature, mostly right-handed and left-handed α-helices at lower and higher temperatures, respectively. On this basis, the copolymer containing 47% azobenzene groups could be made to undergo a photoinduced helix reversal at high temperatures.     

Nanometer-scale ordering in cast films of columnar metallomesogen as revealed by STM observations

STM observations were performed on a cast film of a columnar metallomesogen ([Cr(5C8)3]; 5C8 = 1-(3,4,5-trioctyloxyphenyl)-3-(3,4-dioctyloxyphenyl)propane-1,3-dionate anion) on a graphite surface, revealing the nanometer-scale surface ordering into an oblique lattice (a = 10.5 nm, b = 11.5 nm, alpha = 55 degrees) possibly due to the DeltaLambda-chiral interactions.     

Phase transitions of a polymer threading a membrane coupled to coil-globule transitions

We theoretically study phase transitions of a polymer threading through a pore imbedded in a membrane. We focus on the coupling between a partition of the polymer segments through the membrane and a coil-globule transition of the single polymer chain. Based on the Flory model for collapse transitions of a polymer chain, we calculate the fraction of polymer segments and the expansion factor of a polymer coil on each side of the membrane. We predict a first-order phase transition of a polymer threading a membrane; polymer segments in one side are discontinuously translocated into the other side, depending on solvent conditions and molecular weight of the polymer. We also discuss the equilibrium conformation of the polymer chain on each side of the membrane.     

Giant meso-meso-linked porphyrin arrays of micrometer molecular length and their fabrication

On the basis of the Ag(I)-promoted coupling reaction of zinc(II)-5,15-bis(3,5-dioctyloxyphenyl)porphyrin Z1, chain elongation has been attempted by using a stepwise doubling approach, which provides Z2, Z4, Z8, Z16, Z32, Z64, Z128, Z256, Z384, and Z512. The porphyrin arrays up to Z128 are sufficiently soluble in CHCl3 and THF despite their very long molecular lengths and rodlike structures, while the arrays over Z128 show a significant drop in solubility and stability. The discrete porphyrin arrays thus isolated were characterized by means of (1)H NMR spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, UV/Vis spectroscopy, gel-permeation chromatography (GPC), cyclic voltammetry (CV), single-crystal X-ray crystallography, scanning tunneling microscopy (STM), and atomic force microscopy (AFM). Contrary to expected linear conformations of the arrays Z n (where n is the number of porphyrins), the single molecular images of Z128, Z256, and Z512 revealed largely bent structures; this finding indicates the substantial conformational flexibility of Z n. We also exploited an effective synthetic route by means of which Z n can be fabricated with a thiol-protected aryl group to provide Z n S(2) through Z n Br(2), by bromination with N-bromosuccinimide and subsequent Pd-catalyzed Suzuki-Miyaura arylation. Finally, the reaction of Z256 provided Z512, Z768, and Z1024. Collectively, this work provides an important milestone in the preparation of sub-microscale discrete organic molecules and the fabrication of molecular-based materials, hence significantly contributing to device applications.     

Drastic change in the rate of photochemical rearrangement of 1,6-(N-phenyl)aza-[60]fulleroids by switching the excited states through simple methyl substitution on the phenyl group

The reaction rate for the photochemical rearrangement of 1,6-N-(substituted-phenyl)aza-[60]fulleroid 1 to 1,2-N-(substituted-phenyl)aziridino-[60]fullerene 2 differed ca. 3000-fold depending on the position and number of methyl substituents on the N-phenyl group. The required time for the completion of the reaction decreased in the order 2,6-dimethylphenyl (1d) < 2-methylphenyl (1b) < phenyl (1a) < 4-methylphenyl (1c). The difference was mainly due to switching of the excited states between normal (fast reactions) and charge-separated (slow reactions) triplet states, which was induced by steric interactions between the N-phenyl group and the C₆₀ moiety.     

Occurrence of the cis-peptide in gaseous N-methylformamide as revealed by rotational structure in its infrared spectrum

In the 0.12 cm^?1 resolution infrared absorption spectrum of gaseous N-methylformamide, a progression of peaks with a spacing of about 2.6 cm^?1 has been found in the 610-540 cm^?1 region. This is assignable to a conformer with the CO and NH bonds cis to each other.     

Photochromic isomerization of a dinuclear molybdenum complex with ethylene-1,2-dithiolate and disulfur ligands: x-ray structures of the two isomers

A photochromic complex with disulfur and dimethyl-ethylene-1,2-dithiolate ligands, [Mo(2)(mu-S(2))(mu-S(2)C(2)Me(2))(2)(S(2)C(2)Me(2))(2)] (3), was synthesized and characterized. Photoirradiation of 3 with visible light resulted in the formation of the isomer (3'). The electronic spectrum of 3' has a new intense peak in the near infrared region, and in the dark, the spectrum returns to that of 3. X-ray structural analyses of 3.C(6)H(6) and 3' revealed a large conformational change of the bridging dithiolate ligands: the two ligands in 3' come very close to each other compared to those in 3.C(6)H(6). Crystal data: 3.C(6)H(6), monoclinic, space group C2/c, a = 15.193(4) A, b = 14.287(3) A, c = 14.685(4) A, beta = 105.30(1) degrees, V = 3074(1) A(3), Z = 4; 3', monoclinic, space group C2/c, a = 21.5400(8) A, b = 9.5232(5) A, c = 13.9828(2) A, beta = 118.924(1) degrees, V = 2510.5(2) A(3), Z = 4. (1)H NMR spectra of 3 (3.06, 3.05, 1.66, and 1.31 ppm) and 3' (2.90, 2.75, 2.14, and 1.97 ppm) are also reported: each spectrum has four signals due to methyl groups, which accords well with the fact that each of the molecules, 3.C(6)H(6) and 3', has a crystallographic 2-fold axis.