NMR studies on thermal stability of α-helix conformation of melittin in pure ethanol and ethanol-water mixture solvents

AbstractRapid phthaloylation and succinylation of wheat straw hemicelluloses with phthaloyl dichloride (PdC) and succinyl chloride (SC) in N,Ndimethylformamide/ lithium chloride (DMF/LiCl) system using N-bromosuccinimide (NBS) as a catalyst was achieved for only 5 minutes at 50 °C by microwave irradiation. The degree of substitution (DS) ranged between 0.43 and 1.47. The effect of the molar ratios of xylose units in hemicelluloses to phthaloyl dichloride or succinyl chloride on the degree of substitution was investigated. It was found that the reactivity of succinyl chloride was higher as compared to Phthaloyl dichloride under similar experimental conditions. 13C NMR studies revealed that the esterification occurred at the C-3 and C-2 positions in the β-D-xylose units of hemicelluloses, but preferentially at C-3 position. However, it should be noted that microwave irradiation did result in more degradation of the macromolecular hemicelluloses than conventional heating technique as shown by a lower thermal stability of the hemicellulosic derivatives obtained by microwave irradiation than those obtained by conventional heating technique.

Download Full-text

Rectorite Pillared with Ce-Modified Aluminum Oxide

MRS Proceedings ◽

10.1557/proc-371-181 ◽

1994 ◽

Vol 371 ◽

Author(s):

Jianxin Wu ◽

Edward F. Rakiewicz ◽

Robert R. Gatte

Keyword(s):

Thermal Stability ◽

Aluminum Oxide ◽

Mas Nmr ◽

Cerium Nitrate ◽

Interlayer Distance ◽

Nmr Studies ◽

Adsorption Analysis ◽

Argon Adsorption ◽

Thermal Stability Of

AbstractRectorite clay was pillared with an Al/Ce-cluster pillaring agent made from aluminum chlorhydrol and cerium nitrate. The resulting product had an interlayer distance of 15.7 Å, which was significantly larger than the interlayer distance obtained using conventional aluminum chlorhydrol as the pillaring agent (8.4 Å). Argon adsorption analysis indicates that the pores of the AL/Ce-cluster pillared rectorite are non-uniform, with pore diameters ranging from 5 to 16Å. 29Si MAS NMR studies showed that calcining the natural rectorite changes the silicon environment, while the pillared rectorite clays are much more resistant to such changes upon calcination. It is suggested that pillaring reactions enhance the thermal stability of the rectorite by stabilizing the local silicon environment in the clay.

Download Full-text

The Ordered Phase Formation in Ti-Al-Ga Alloys

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069193 ◽

1970 ◽

Vol 28 ◽

pp. 440-441

Author(s):

Shiro Fujishiro ◽

Harold L. Gegel

Keyword(s):

Thermal Stability ◽

High Temperature ◽

Titanium Alloys ◽

Growth Kinetics ◽

Stoichiometric Composition ◽

Good Potential ◽

Alpha Titanium ◽

Cold Rolled ◽

Kinetics Of ◽

Thermal Stability Of

Ordered-alpha titanium alloys having a DO19 type structure have good potential for high temperature (600°C) applications, due to the thermal stability of the ordered phase and the inherent resistance to recrystallization of these alloys. Five different Ti-Al-Ga alloys consisting of equal atomic percents of aluminum and gallium solute additions up to the stoichiometric composition, Ti3(Al, Ga), were used to study the growth kinetics of the ordered phase and the nature of its interface.The alloys were homogenized in the beta region in a vacuum of about 5×10-7 torr, furnace cooled; reheated in air to 50°C below the alpha transus for hot working. The alloys were subsequently acid cleaned, annealed in vacuo, and cold rolled to about. 050 inch prior to additional homogenization

Download Full-text

Microstructure studies of tungsten silicide schottky contacts on Gaas

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100126445 ◽

1987 ◽

Vol 45 ◽

pp. 328-329

Author(s):

Yih-Cheng Shih ◽

E. L. Wilkie

Keyword(s):

Thermal Stability ◽

Field Effect Transistors ◽

Schottky Contact ◽

Schottky Contacts ◽

Excellent Thermal Stability ◽

Barrier Heights ◽

Gaas Substrates ◽

Film Adhesion ◽

Threshold Voltages ◽

Thermal Stability Of

Tungsten silicides (WSix) have been successfully used as the gate materials in self-aligned GaAs metal-semiconductor-field- effect transistors (MESFET). Thermal stability of the WSix/GaAs Schottky contact is of major concern since the n+ implanted source/drain regions must be annealed at high temperatures (∼ 800°C). WSi0.6 was considered the best composition to achieve good device performance due to its low stress and excellent thermal stability of the WSix/GaAs interface. The film adhesion and the uniformity in barrier heights and ideality factors of the WSi0.6 films have been improved by depositing a thin layer of pure W as the first layer on GaAs prior to WSi0.6 deposition. Recently WSi0.1 has been used successfully as the gate material in 1x10 μm GaAs FET's on the GaAs substrates which were sputter-cleaned prior to deposition. These GaAs FET's exhibited uniform threshold voltages across a 51 mm wafer with good film adhesion after annealing at 800°C for 10 min.

Download Full-text