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91.
Othman Al-Flaijj Mohamed R. Shehata Mahmoud M. A. Mohamed Mohamed M. Shoukry 《Monatshefte für Chemie / Chemical Monthly》2001,39(1):349-366
The interaction of dimethyltin(IV) (DMT) with some selected DNA constituents was investigated potentiometrically. The stepwise formation constants of the complexes were determined, and
the concentration distribution of the various complex species was evaluated as a function of pH. The effect of dioxane on the protonation constants of the ligands and the formation constants of dimethyltin(IV) complexes
are discussed. The thermodynamic parameters Δ H° and ΔS° were calculated from the temperature dependence of the equilibrium
constants. 相似文献
92.
93.
Navzer D. Sachinvala David L. Winsor Othman Hamed Walter P. Niemczura Karol Maskos Tyrone L. Vigo Noelie R. Bertoniere 《先进技术聚合物》2002,13(6):413-427
Cellulose ( 1 ) was converted for the first time to 6‐phenyl‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 6 ) in 33% overall yield. Intermediates in the five‐step conversion of 1 to 6 were: 6‐O‐tritylcellulose ( 2 ), 6‐O‐trityl‐2,3‐di‐O‐methylcellulose ( 3 ), 2,3‐di‐O‐methylcellulose ( 4 ); and 6‐bromo‐6‐deoxy‐2,3‐di‐O‐methylcellulose ( 5 ). Elemental and quantitative carbon‐13 analyses were concurrently used to verify and confirm the degrees of substitution in each new polymer. Gel permeation chromotography (GPC) data were generated to monitor the changes in molecular weight (DPw) as the synthesis progressed, and the compound average decrease in cellulose DPw was ~ 27%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the decomposition of all polymers. The degradation temperatures ( °C) and percent char at 500 °C of cellulose derivatives 2 to 6 were 308.6 and 6.3%, 227.6 °C and 9.7%, 273.9 °C and 30.2%, 200.4 °C and 25.6%, and 207.2 °C and 27.0%, respectively. The glass transition temperature (Tg) of6‐O‐tritylcellulose by dynamic mechanical analysis (DMA) occurred at 126.7 °C and the modulus (E′, Pa) dropped 8.9 fold in the transition from ?150 °C to + 180 °C (6.6 × 109 to 7.4 × 108 Pa). Modulus at 20 °C was 3.26 × 109 Pa. Complete proton and carbon‐13 chemical shift assignments of the repeating unit of the title polymer were made by a combination of the HMQC and COSY NMR methods. Ultimate non‐destructive proof of carbon–carbon bond formation at C6 of the anhydroglucose moiety was established by generating correlations between resonances of CH26 (anhydroglucose) and C1′, H2′, and H6′ of the attached aryl ring using the heteronuclear multiple‐bond correlation (HMBC) method. In this study, we achieved three major objectives: (a) new methodologies for the chemical modification of cellulose were developed; (b) new cellulose derivatives were designed, prepared and characterized; (c) unequivocal structural proof for carbon–carbon bond formation with cellulose was derived non‐destructively by use of one‐ and two‐dimensional NMR methods. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
94.
Seik Weng Ng Abdul Hamid Othman Sri Nurestri Abdul Malek 《Journal of chemical crystallography》1994,24(5):331-335
1-(2-Hydroxyphenyl)-3-phenyl-1,3-propanedione crystallizes in the triclinic space group
(a=5.4233(5),b=13.910(1),c=17.036(1) Å, =68.311(6), =80.854(7), =78.760(8)°) as two independent enolic tautomers in which the hydroxyl and phenolic protons are hydrogen bonded to the ketonic oxygen atom. The structure was refined toR=0.039 for 2085I3(I) reflections. 1-(1,3-Benzodioxol-5-yl)-3-(2,4-dimethoxyphenyl)-1,3-propanedione, which belongs to the triclinic
space group (a=7.3990(7),b=8.1239(5),c=14.004(1) Å, =86.673(6). =88.574(7), =64.885(7)°) also exists in the enolic form. The structure was refined toR=0.040 for 1564I3(I) reflections. 相似文献
95.
Nur Hidayah Zulaikha Othman Zailani Normawati M. Yunus Asyraf Hanim Ab Rahim Mohamad Azmi Bustam 《Molecules (Basel, Switzerland)》2022,27(3)
Ionic liquids, which are extensively known as low-melting-point salts, have received significant attention as the promising solvent for CO2 capture. This work presents the synthesis, thermophysical properties and the CO2 absorption of a series of ammonium cations coupled with carboxylate anions producing ammonium-based protic ionic liquids (PILs), namely 2-ethylhexylammonium pentanoate ([EHA][C5]), 2-ethylhexylammonium hexanoate ([EHA][C6]), 2-ethylhexylammonium heptanoate ([EHA][C7]), bis-(2-ethylhexyl)ammonium pentanoate ([BEHA][C5]), bis-(2-ethylhexyl)ammonium hexanoate ([BEHA][C6]) and bis-(2-ethylhexyl)ammonium heptanoate ([BEHA][C7]). The chemical structures of the PILs were confirmed by using Nuclear Magnetic Resonance (NMR) spectroscopy while the density (ρ) and the dynamic viscosity (η) of the PILs were determined and analyzed in a range from 293.15K up to 363.15K. The refractive index (nD) was also measured at T = (293.15 to 333.15) K. Thermal analyses conducted via a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) indicated that all PILs have the thermal decomposition temperature, Td of greater than 416K and the presence of glass transition, Tg was detected in each PIL. The CO2 absorption of the PILs was studied up to 29 bar at 298.15 K and the experimental results showed that [BEHA][C7] had the highest CO2 absorption with 0.78 mol at 29 bar. The CO2 absorption values increase in the order of [C5] < [C6] < [C7] anion regardless of the nature of the cation. 相似文献
96.
The symmetric sinc-Galerkin method developed by Lund, when appliedto the second-order self-adjoint boundary value problem, givesrise to a symmetric coefficient matrix has a special structureso that it can be advantageously used in solving the discretesystem. In this paper, we employ the preconditioned conjugategradient method with banded matrices as preconditioners. Weprove that the condition number of the preconditioned matrixis uniformly bounded by a constant independent of the size ofthe matrix. In particular, we show that the solution of an n-by-ndiscrete symmetric sinc-Galerkin system can be obtained in O(nlog n) operations. We also extend our method to the self-adjointelliptic partial differential equation. Numerical results aregiven to illustrate the effectiveness of our fast iterativesolvers. 相似文献
97.
This paper reports photoelectrical properties of (As30Sb15Se55)100?xTex amorphous chalcogenide films (0 ? x ? 12.5 at.%) through measurements of ‘steady state’ and ‘transient’ photocurrents. The composition dependence of the steady state photocurrent at room temperature shows that the photoconductivity increases while the photosensitivity decreases with increasing Te content. A study of photoconductivity of (As30Sb15Se55)100?xTex at different levels of light intensity reveals that, the photoconductivity increases exponentially with increase in light intensity. The Photocurrent (Iph) when plotted against light intensity (G) follows a power law (Iph = Gγ) the exponent γ for (As30Sb15Se55)100?xTex films has been found nearly 0.5 suggesting bimolecular recombination. The transient photoconductivity shows that the lifetime of the carrier decreases with increasing the light intensity. This decrease suggests that the photoconductivity mechanism in our samples was controlled by the transition trapping processes. The increase of Te content results in a monotonic decrease in the band gap and the free carrier life time of (As30Sb15Se55)100?xTex thin films. These results were interpreted on the basis of the chemical-bond approach. 相似文献
98.
The angular distribution of the five-fold differential cross section for the electron impact double ionization of He (21
S) and He (23
S) has been studied. The kinematical conditions for maxima/minima in the angular distribution for the two cases have been compared.
The two-step process for the double ionization is found to contribute very little in the triplet case. 相似文献
99.
A one pot synthesis of thienoazepinoisoindolones from the reaction of hydroxylactam‐alcohols, under acidic treatment, is described via an N‐acyliminium olefin cyclization. 相似文献