Akihiro Yoshino

Kinetics of interaction of 3-aminopropyltriethoxysilane on asilica gel surface using elemental analysis and diffuse reflectanceinfrared Fourier transform spectra

In order to study the kinetics of interaction of 3-aminopropyltriethoxysilane (APTS) on silica gel, silica gel samples reacted with APTS were prepared by sampling the reaction mixture from the reactor at various time intervals, and the concentrations of 3-aminopropylsilyl (APS) groups modified on the silica gel surface were determined by elemental analysis. From the reaction time dependence of the APS concentration, it has been found that, after an initial fast reaction of APTS and silica gel, a slower second reaction and a much slower third reaction subsequently occur. For the three processes, the reaction rate constants (k obs /s -1 ) have been estimated and found to be k obs i =1.00×10 -1 s -1 for the initial reaction, k obs s =6.91×10 -3 s -1 for the second reaction and k obs t =4.20×10 -4 s -1 for the third reaction. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were measured for the same samples. Bands at 3734–3739 cm -1 were observed in the OH stretch mode region, and were found to decrease in intensity with reaction time, reflecting the rate of reaction of APTS on the silica gel. Analysis of an OH stretching band has also furnished reaction rate constants that are very similar to those obtained from the time dependence of the APS concentration. A mechanism for the three reaction processes is postulated.

Polymerization process of the silane coupling agent 3-aminopropyltriethoxy silane – 1H NMR spectra and kinetics of ethanol release

Abstract In the 3-aminopropyltriethoxy silane–deuterated ethanol–H 2 O system, the rate of release of ethanol from the ethoxy groups, a reaction which occurs during the condensation process, has been followed by use of 1 H NMR spectroscopy at different temperatures. Two separate reaction processes have been identified, and values of the reaction rate constants and thermodynamic parameters ( E a , Δ H ‡ and Δ S ‡ ) have been calculated.

Raman scattering study of the interaction of 3-aminopropyltriethoxy silane on silica gel. Time-dependent conformational change of aminopropylsilyl segments

Abstract Silica gel samples, modified with 3-aminopropyltriethoxy silane (APTS), have been prepared by sequentially sampling the substrate from the reaction vessel at various time intervals, and the Raman spectra of these samples have been measured. The CH stretch Raman bands at 2938 and 2981 cm −1 became more intense as the reaction proceeded. Kinetic analyses were then carried out, after making the assumption that the time dependence of relative Raman peak heights ( I 2938 / I 800 and I 2981 / I 800 ) is a pseudo-first order. The rate constants obtained are k =8.05×10 −4 s −1 for the 2938 cm −1 band and k =9.45×10 −4 s −1 for the 2981 cm −1 band. We may assume that the dependence of the change in intensity of the CH stretch Raman bands on time is a reflection of the change in conformation of the APS moieties.

Chirality effects on 1H and 13C NMR chemical shifts for Aerosol OT in reverse micelles assisted by line shape simulations and two-dimensional pulse techniques

Abstract For the 1 H NMR spectrum of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in C 6 D 6 D 2 O, the very complex H3′ signals, which have not yet been elucidated, have now been successfully explained by superimposition of the four AB parts, and have been discussed in connection with the diastereoisomers arising from the three asymmetric carbon atoms. Discussion of the 13 C NMR signal assignment of AOT in organic solvents has previously been focused on the signals of the head group (CH(SO − 3 )CH 2 ) and on the CH 2 OCO and OCH 2 CH segments. In this study, the signals arising from the other segments of the two chains have been completely assigned to the individual carbon atoms of each 2-ethylhexyl chain, using pulse techniques. The secondary splitting of the 13 C chemical shifts was due to the chirality effect of an AOT molecule. In particular, the effect of the chiral centers was found to be concentrated on the α chain and to reach the C6′carbon.

Regioselective Cycloadditions of 1H-Azepine and 1H-1,2-Diazepine Derivatives with N,a-Diphenylnitrone and Nitrosobenzene

Reactions of 1-carbomethoxy-1H-azepine with N,α-diphenylnitrone afforded endo- and exo-[2+3]-type cycloadducts in almost the same ratio. Reactions of 1-carboethoxy-1H-azepine swith nitrosobenzene in chloroform afforded [4+2]- and [6+2]-types of cycloadducts. Analogous results were obtained in the reactions using 1-carboethoxy-1H-1,2-diazepine

Dextran-magnetite complex: temperature dependence of its NMR relaxivity.

The NMR relaxivity of proton by dextran-magnetite (DM) complex was examined at temperatures from 20 to 80 °C. The decrease in T1 relaxivity with increasing temperature is due to the thermal activation of motion of water molecules in and/or surrounding DM particle. The decrease in magnetization of magnetite core is the secondary effect. The temperature dependence of T1 relaxivity was found to depend on molecular weight of dextran. The motion of dextran chains binding to core may affect the thermal activation of “heavy water” interacted with dextran. The Arrhenius plots of T1 relaxivity showed different slopes at 20–40 °C and 50–80 °C, while, no change in slope was observed for Fe(NO3)3, CuSO4 and Gd-DTPA solutions.

Mechanical properties and microstructure of high toughness Fe-base filaments produced by glass-coated melt spinning

High toughness Fe57.5Co5Cr15Mn10Cu2B10Ti0.5 filaments having a high tensile strength of 1740 M Pa and high elongation of 11.0% were produced by the method of glass-coated melt spinning. A noticeable feature of the stress-strain curves of the filament was that rapid hardening to a high stress-level of more than 1500 M Pa was reached in the first few per cent of tensile elongation. The filament was 14.5μm diameter and micropolycrystalline with a grain size of 27 nm. The crystal structure of the filament was a mixture of bcc and fcc phases and the two phases were distributed homogeneously in the filament. The high toughness of the filament related to its micropolycrystalline structure and the uniformly mixed structure of bcc and fcc phases. After heat treatment at 573 K for 600 sec, the filament developed a higher toughness with a tensile strength of 2150 M Pa and an elongation of 12.0%.

1,3-DIPOLAR CYCLOADDITION OF N,ALPHA -DIPHENYLNITRONE TO THE 4,5-POSITIONSOF 1H-AZEPINE AND 1H-1,2-DIAZEPINE DERIVATIVES : FORMATION OF ENDO- AND EXO -TYPE CYCLOADDUCTS AND COMPUTER-ASSISTED LINE SHAPE SIMULATION OF THE NMR S PECTRA OF THE ADDUCTS

The reaction is considered to proceed through concerted [4 + 2]-type 1,3-dipolar cycloadditions of the nitrone to the 4,5-positions of the azepine or diazepine to give endo- and exo-type adducts because of the absence of stabilization effects by secondary orbital interactions in the transition states

Folded structures of L-leucylglycine oligopeptides and their aggregational behavior in aqueous solution: Raman scattering spectra and proton NMR spin-lattice relaxation studies.

The aggregational behavior of three L-leucylglycine oligopeptides (residue numbers of glycine are 3, 4, and 5) in aqueous solution was investigated by the use of Raman scattering and 1H NMR spin-lattice relaxation methods. The results indicate that their oligopeptides take up a folded structure to form dimeric aggregates above their critical aggregation concentration. The application of one-dimensional aggregate theory to these systems provides the following prediction. Elongation up to 6 glycine residues makes it possible to form dimeric aggregates, but further elongation (up to 7 glycine residues) makes the aggregates very unstable, and up to 8 or 9 glycine residues makes the formation of dimeric aggregates very difficult. The one-dimensional aggregate theory may be used to predict the existence of peptide aggregates through intermolecular hydrogen bonding.

Lateral conductance parallel to membrane surfaces: Effects of anesthetics and electrolytes at pre-transition

The effects of dilute salts and anesthetics were studied on the impedance dispersion in the dipalmitoylphosphatidylcholine (DPPC) liposomes. Below the pre-transition temperature, the apparent activation energy for conductance in DPPC-H2O without salts was equivalent to pure water, 18.2 kJ mol-1. This suggests that the mobile ions (H3O+ and OH-) interact negligibly with the lipid surface below the pre-transition temperature. At pre-transition temperature, the apparent activation energy of the conductance decreased by the increase in the DPPC concentrations. The effects of various salts (LiCl, NaCl, KCl, KBr, and KI) on the apparent activation energy of the conductance were studied. Changes in anions, but not in cations, affected the activation energy. The order of the effect was Cl- less than Br- less than I-. Cations appear to be highly immobilized by hydrogen bonding to the phosphate moiety of DPPC. The smaller the ionic radius, the more ions are fixed on the surface at the expense of the free-moving species. The apparent activation energy of the transfer of ions at the vesicle surface was estimated from the temperature-dependence of the dielectric constant, and was 61.0 kJ mol-1 in the absence of electrolytes. In the presence of electrolytes, the order of the activation energy was F- greater than Cl- greater than Br- greater than I-. When the ionic radius is smaller, these anions interact with the hydration layer at the vesicle surface and the ionic transfer may become sluggish. In the absence of electrolytes, the apparent activation energy of the dielectric constant decreased by the increase in halothane concentrations. In the presence of electrolytes, however, the addition of halothane increased the apparent activation energy. We propose that the adsorption of halothane on the vesicle surface produces two effects: (1) destruction of the hydration shell, and (2) increase in the binding of electrolytes to the vesicle surface. In the absence of electrolytes, the first effect predominates and the apparent activation energy is decreased. In the presence of electrolytes, the latter effect predominates and the apparent activation energy is increased.