1,1-bis(trimethylsilyl)-1-alkanols as silylcarbene equivalent

Silylcarbenes are generated by the pyrolysis of 1,1-bis(trimethylsilyl)-1-alkanols with elimination of trimethylsilanol.     

Processing and characterization of Pb(Mg,Nb)O3-PbTiO3 thin films from metal alkoxide-derived gels

The sol-gel processing is one of promising methods to fabricate well-derived integrated thin films at relatively low temperature. Ferroelectric niobates films do afford the possibilities for adding the values by the hybridization with semiconductor and/or electro-optic systems. The molecular level designing of the precursor solution was stressed as well as the control of key processing factors. The advantages of this sol-gel have been extended to prepare the ferroelectric Pb(Mg, Nb)O₃-PbTiO₃ solid solution films integrated on Si wafers. The crystallization of the films with desired crystal structure could be promoted by the controlled partial hydrolysis of designed alkoxide solution in the intermediate state and the pre-heated treatment of alkoxide-derived films in flow of water vapor and oxygen gas mixture.     

Synthesis and properties of new polyesters having tetrahydrofuran rings in their main chains

New polyesters 6a–6c consisting of 2,4-linked tetrahydrofuran rings were synthesized by bulk polycondensation of methyl trans- and cis-4-hydroxytetrahydrofuran-2-carboxylates ( 5a and 5b ) and a stereoisomeric mixture of methyl 4-hydroxy-5-methyltetrahydrofuran-2-carboxylate ( 5c ) at high temperature. These monomers were prepared from methyl glycolate or methyl lactate and diethyl maleate through a four-step reaction sequence. The polycondensation was carried out without solvent at different temperatures ranging from 150 to 220°C. Titanium isopropoxide was most effective among the catalysts examined, giving polyesters with number-average molecular weights up to 2 × 10⁴. Polyester 6a consisting of trans-2,4-linked tetrahydrofuran rings was soluble in trifluoroacetic acid and a mixed solvent of chloroform and methanol (10/1, v/v). Polyester 6b composed of cis-2,4-linked tetrahydrofuran rings was soluble in dimethyl sulfoxide and dimethylformamide in addition to the two solvents for 6a . Polyester 6c with 5-methyl-substituted tetrahydrofuran rings was composed of a mixture of stereoisomeric units and thus was soluble in a variety of solvents including chloroform, tetrahydrofuran, acetonitrile, dimethyl sulfoxide, and dimethylformamide. The glass transition temperatures of 6a, 6b , and 6c determined by DSC were 109, 88, and 66°C. These polyesters were found to be very slowly hydrolyzed in a neutral phosphate buffer solution at ambient temperature. © 1993 John Wiley & Sons, Inc.     

Molecular dynamics study of the methanol effect on the membrane morphology of perfluorosulfonic ionomers

The membranes of a perfluorosulfonic acid polymer swollen in 10-80 wt % methanol solution were investigated to elucidate the methanol effect on their morphologies, such as size of the solvent cluster, solvent location, and polymer structure, by using isothermal-isobaric molecular dynamics simulations. In higher methanol concentrations, we found less-spherical solvent aggregation and a more spread polymer structure because of the ampholytic nature of methanol. The partial radial distribution functions between solvent oxygen and fluorocarbons, which are composed of the main chain, clearly show that methanol is located closer to the polymer matrix than water. On the other hand, water is preferentially located in the vicinity of an acidic headgroup, SO(3)(-), compared with methanol, although both have similar attractive interaction energies to the acidic group. Furthermore, we discussed solvent dynamics and hydrogen bonding between sulfonic oxygen and solvent O-H groups.     

Temperature and Oxygen Partial Pressure Dependences of the Surface Tension of Liquid Sn–Ag and Sn–Cu Lead-free Solder Alloys

Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and the oxygen partial pressure is less than about 10⁻¹³ atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less than 0.9.     

Rigid-body dynamics in the isothermal-isobaric ensemble: a test on the accuracy and computational efficiency

We have developed a time-reversible rigid-body (rRB) molecular dynamics algorithm in the isothermal-isobaric (NPT) ensemble. The algorithm is an extension of rigid-body dynamics [Matubayasi and Nakahara, J Chem Phys 1999, 110, 3291] to the NPT ensemble on the basis of non-Hamiltonian statistical mechanics [Martyna, G. J. et al., J Chem Phys 1994, 101, 4177]. A series of MD simulations of water as well as fully hydrated lipid bilayer systems have been undertaken to investigate the accuracy and efficiency of the algorithm. The rRB algorithm was shown to be superior to the state-of-the-art constraint-dynamics algorithm SHAKE/RATTLE/ROLL, with respect to computational efficiency. However, it was revealed that both algorithms produced accurate trajectories of molecules in the NPT as well as NVT ensembles, as long as a reasonably short time step was used. A couple of multiple time-step (MTS) integration schemes were also examined. The advantage of the rRB algorithm for computational efficiency increased when the MD simulation was carried out using MTS on parallel processing computer systems; total computer time for MTS-MD of a lipid bilayer using 64 processors was reduced by about 40% using rRB instead of SHAKE/RATTLE/ROLL.     

Electrical and magnetic properties of ion-exchangeable layered ruthenates

An ion-exchangeable ruthenate with a layered structure, K_0.2RuO_2.1, was prepared by solid-state reactions. The interlayer cation was exchanged with H⁺, C₂H₅NH₃⁺, and ((C₄H₉)₄N⁺) through proton-exchange, ion-exchange, and guest-exchange reactions. The electrical and magnetic properties of the products were characterized by DC resistivity and susceptibility measurements. Layered K_0.2RuO_2.1 exhibited metallic conduction between 300 and 13 K. The products exhibited similar magnetic behavior despite the differences in the type of interlayer cation, suggesting that the ruthenate sheet in the protonated form and the intercalation compounds possesses metallic nature.     

Ionic liquid crystal as a hole transport layer of dye-sensitized solar cells

Use of a new ionic liquid crystal, 1-dodecyl-3-methylimidazolium iodide, and iodine as an electrolyte of dye-sensitized solar cells leads to a high short circuit photocurrent density and a high light-to-electricity conversion efficiency, due to a self-assembled structure of the imidazolium cations, resulting in high conductivity of the electrolyte.     

An economical approach for peptide synthesis via regioselective C–N bond cleavage of lactams

An economical, solvent-free, and metal-free method for peptide synthesis via C–N bond cleavage using lactams has been developed. The method not only eliminates the need for condensation agents and their auxiliaries, which are essential for conventional peptide synthesis, but also exhibits high atom economy. The reaction is versatile because it can tolerate side chains bearing a range of functional groups, affording up to >99% yields of the corresponding peptides without racemisation or polymerisation. Moreover, the developed strategy enables peptide segment coupling, providing access to a hexapeptide that occurs as a repeat sequence in spider silk proteins.

An economical, solvent-free, and metal-free method for peptide synthesis via C–N bond cleavage using lactams has been developed.