Control of the fragility of a glass-forming liquid using the liquid-liquid phase transition

When a liquid approaches its glass-transition temperatures T(g), the structural relaxation time tau dramatically increases. This basic feature is ubiquitous, but this increase of tau can be classified between strong and fragile extremes using T(g) as a scaling parameter. Liquids, whose tau obeys the Arrhenius law, are called "strong," while "fragile" liquids have the super-Arrhenius behavior. Here we report the first continuous control of the fragility of liquid of the same material over a wide range of fragility, using a continuous liquid-liquid transition. Our study clearly demonstrates that the fragility is not a material-specific quantity, but is controlled by the order parameter governing the liquid-liquid transition, which may be the fraction of locally favored structures in the liquid.     

Viscoelastic phase separation of protein solutions

In addition to the known behavior of normal phase separation and gelation, we report novel phase-separation behavior of protein solutions as their intermediate case. A network structure of the protein-rich phase may be formed even if it is the minority phase, contrary to the conventional wisdom. This behavior is characteristic of viscoelastic phase separation found in polymer solutions. This kinetic pathway may play crucial roles in the complex phase ordering of protein solutions, in particular, protein network formation in biological systems and foods.     

Magnetic shielding effect of amine and ammonium groups obtained from proton chemical shifts of androstane derivatives

4-Aza-5α-androstanone(1α) and 4-aza-5β-androstanone(1β) were synthesized in order to obtain the NMR shielding parameters for the secondary amine group. A combination of the electric field effect and the anisotropy of the magnetic susceptibility of the CN bond can successfully reproduce the observed SIS values for these androstanes. Drastic chemical shift change of protons near-by nitrogen atom of ammonium salt was observed and shielding parameter for the secondary ammonium group was also obtained.     

Stereoselective synthesis of alkynyl C-2-deoxy-beta-d-ribofuranosides via intramolecular nicholas reaction: A versatile building block for nonnatural C-nucleosides

The reaction of 3,5-di-O-benzyl-2-deoxy-d-ribofuranose with various alkynyllithium reagents afforded diastereomeric mixtures of the corresponding ring-opened alkynyldiols. The resulting diastereomeric mixtures were successively treated with Co(2)(CO)(8), a catalytic amount of TfOH, Et(3)N, and iodine in one pot to give alkynyl C-3,5-di-O-benzyl-2-deoxy-beta-d-ribofuranosides with high beta-selectivities. The cobalt-mediated cyclization (intramolecular Nicholas reaction) is reversible; thus, thermodynamically more stable beta-anomers were obtained preferentially. The alkynyl C-deoxyribofuranosides were converted to a variety of C-deoxyribofuranoside derivatives.     

Relation between thermodynamics and kinetics of glass-forming liquids

Vitrification of a supercooled liquid is often characterized by the hypothetical kinetic instability point, the Vogel-Fulcher temperature T0, and the thermodynamic one, the Kauzmann temperature T(K). The widely believed relation T0 congruent with T(K) is regarded as the supporting evidence of a direct connection between the thermodynamics and kinetics of glass-forming liquids. Here we demonstrate that T(K)/T(0) systematically increases from unity with a decrease in the fragility, contrary to the common belief. This systematic deviation may be explained by a synergistic effect between the weaker cooperativity and the stronger tendency of short-range ordering in stronger glass formers.     

Absolute frequency measurement of an acetylene-stabilized laser at 1542 nm

The absolute frequency of an acetylene-stabilized laser at 1542 nm is measured at its second harmonic (771 nm) by use of a femtosecond optical comb based on a mode-locked Ti:sapphire laser. Frequency stability and reproducibility of the acetylene-stabilized laser are evaluated by the femtosecond comb with a H maser as a frequency reference. The absolute frequency of a laser diode stabilized on the P(16) transition of 13C2H2 is determined to be 194 369 569 383.6(1.3) kHz. The acetylene-stabilized laser serves as an important optical frequency standard for telecommunication applications.     

Positron annihilation studies of defects in 3CSiC hot-implanted with nitrogen and aluminum ions

2 ⁺ and Al⁺ at temperatures from room temperature (RT) to 1200 °C at doses of 10¹³ and 10¹⁵/cm². It is found from Doppler broadening spectra of annihilation gamma-rays obtained by varying the incident positron energy that hot-implantation gives rise to clustering of vacancies, whereas it suppresses amorphization and diminishes the thickness of damaged layers. The average size of such clusters increases with increasing implantation dose and temperature. Vacancy clustering by hot-implantation can be interpreted by the combination of vacancies during implantation. Vacancy type defects in the low-dose (10¹³/cm²) implanted samples are found to be removed by annealing at 1400 °C, whereas large vacancy clusters still remain after 1400 °C annealing in the high-dose (1 0¹⁵/cm²) implanted samples. It is also derived from the depth profile of positron diffusion length that positron scattering centers are produced after annealing at 1400 °C in all implanted samples. Received: 7 March 1997/Accepted: 6 May 1997     

Studies on thermal degradation of aliphatic polyamides by pyrolysis-glass capillary chromatography

A series of aliphatic polyamides samples (five kinds of α-aminocarboxyclic acid-type nylons and seven kinds of diamine-dicarboxyclic acid-type nylons) were pyrolysed in a vertical microfurnace-type pyrolyser at 550°C, and their high-resolution pyrograms were obtained by a glass capillary gas chromatograph directly attached to the pyrolyser. The characteristic peaks on the resulting pyrograms were identified using a mass spectrometer, which was also attached to the gas chromatograph. On the basis of the various characteristic degradation products identified, such as hydrocarbons, mononitriles, lactams, cyclopentanone hydrocarbons containing one amide group and mononitriles containing one amide group, general mechanisms for the degradation of the aliphatic polyamides were formulated.     

Microscopic approach to the antiproton-nucleus optical potential

By using the self-energy of an antiproton evaluated in nuclear matter, the antiproton effective interaction with a bound nucleon is derived and is found to have a drastic density dependence. The p?-nucleus optical potential constructed by folding the effective interaction well reproduces experimental data on the p?-nucleus absorption cross section as well as on the complex level shift of p?-atoms. In addition, it is pointed out that the strong spin-orbit interaction spreads each doublet and considerably affects the lower complex level shift.     

Oxygen atom transfer by an intermediate in the photosensitized oxygenation of diazo compounds

The photosensitized oxygenations of various diazo compounds in the presence of oxygen atom acceptors were carried out. An electrophilicity of the intermediate was investigated.