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91.
92.
Mohamed S. El-Shahawi 《Transition Metal Chemistry》1993,18(4):385-390
Summary Amino acid complexes of CrCl3Py3 have been prepared and studied by elemental analysis, magnetic susceptibility, vibrational (i.r.), electronic and circular dichroism spectroscopy. Two peaks in the visible spectra are assigned to a d-d transition in pseudo octahedral symmetry. The spectrochemical parameters (Dq, B and
35) for the complexes were calculated which confirm that pyridine nitrogen and/or chlorine are not removed. Prolonged heating or bubbling of air through the solution of CrCl3-Py3 containing l-(-)-histidine or l-(-)-threonine for several hours enhanced formation of chromium (VI). 相似文献
93.
S. Abboudy A. E. Hamed M. E. Kassem L. I. Abou-El-Nasr 《Journal of Thermal Analysis and Calorimetry》1993,39(3):301-308
The influence of stoichiometric ratio on the phase transition of sodium potassium sulphate (NaxK1–x)2SO4 crystals is investigated in the temperature range 300–500 K. The stoichiometric ratiox is chosen to bex=0.2, 0.3, 0.4, 0.8 and 0.9. The study has been carried out by using differential scanning calorimetry, DSC technique. The value of the specific heat,C
p, at the transition temperature,T
c
, increases asx is increased up tox=0.4 and then decreases for higher values ofx. The change in the specific heat, C
p, is following a relation of the form C
p C
p (T–T
c
/T
c
)– with = 0.12 which is in a fair agreement with the 3d Ising model. Insertion of Cu2+ ions into the lattice of (NaxK1–x)2SO4 crystals leads to a multiple peak in the temperature dependence ofC
p. The results are discussed from thermodynamical point of view.We would like to thank Prof. E. F. El-Wahidy, Prof. of Solid State Physics and Head of Physics Department, Faculty of Science, Alexandria University, for his interest and support of this work. 相似文献
94.
95.
Mohamed E. Khalifa 《合成通讯》2020,50(17):2590-2616
Abstract Thiophenes are a highly important group of heterocycles and have been of great interest to researchers due to their various reactivities. Many synthetic strategies are used to generate functionalized thiophene derivatives. Several reactions are described, depending on the reactivity of the substituents attached to the thiophene nucleus toward different nucleophiles to yield the versatile thiophene products. Many diverse applications have been utilized for thiophenes from medicinal chemistry to material science. 相似文献
96.
Mohamed Brakta Denis Sinou Michel Becchi Joseph Banoub 《Journal of mass spectrometry : JMS》1992,27(5):621-624
A series of anomeric unsaturated C-glycosides were studied by negative ion mass spectrometry following keV ion bombardment The compounds bearing an acidic hydrogen show a prominent [M ? H]? peak; in the other cases, the [M ? H]? peak is of very low intensity. A retro-Diels–Alder fragmentation and the abstraction of a hydrogen atom from the aglycon residue are observed in all cases. 相似文献
97.
A polarographic procedure is described for the determination of paracetamol (acetaminophen) and salicylamide after treatment with nitrous acid. The different experimental parameters affecting the derivatization process and the polarographic analysis were studied. The derivatization products were found to be reduced at the dropping mercury electrode over the whole pH range in Britton-Robinson buffers. At pH 7.0, well defined diffusion-controlled cathodic waves were produced for both compounds. Plots of limiting current vs. concentration were linear over the ranges 0.05–0.75 and 0.25–1.5mM for paracetamol and salicylamide, respectively, in the d.c. mode, with minimum detectability of 2.5 × 10–6 and 1.25 × 10–5
M, respectively. The procedure was applied to the analysis of some pharmaceutical dosage forms and the results were in good agreement with those obtained by official and compendial methods. 相似文献
98.
N. A. Mohamed Farook 《Journal of solution chemistry》2007,36(3):345-356
The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each
of the 4-oxoacids, NCSA and H+. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition
state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA
with 4-oxoacids. 相似文献
99.
Pierre Netchitaïlo Mohamed Othman Bernard Decroix 《Journal of heterocyclic chemistry》1997,34(1):321-324
2-Thienylthiomethylphthalimides 3a,b were synthesized by action of Chloromethylphthalimide on 2-or 3-mercaptothiophene. Reduction of 3a,b and Wittig reaction using carbethoxycarbonyltriphenyl-phosphorane gave the corresponding acetic acids 5a,b which cyclized under Friedel and Crafts conditions to lead the thienothiazocinoisoindolediones 6a,b. Thienothiazinoisoindolones 7a,b were obtained from hydroxyisoindolones derivatives 4a,b in acid conditions via an acyliminium ion. 相似文献
100.
Nonribosomal peptide synthetases (NRPS) are multimodular biocatalysts that bacteria and fungi use to assemble many complex peptides with broad biological activities. The same modular enzymatic assembly line principles are found in fatty acid synthases (FAS), polyketide synthases (PKS), and most recently in hybrid NRPS/PKS multienzymes. FAS as well as PKS are known to function as homodimeric enzyme complexes, raising the question of whether NRPS may also act as homodimers. To test this hypothesis, biophysical methods (size exclusion chromatography, analytical equilibrium ultracentrifugation, and chemical crosslinking) and biochemical methods (two-affinity-tag-system and complementation studies with enzymes being inactivated in different catalytic domains) were applied to NRPS subunits from the gramicidin S (GrsA-ATE), tyrocidine (TycB(1)-CAT and TycB(2-3)-AT.CATE), and enterobactin (EntF-CATTe) biosynthetic systems. These methods had revealed the dimeric structure of FAS and PKS previously, but all three NRPS systems investigated are functionally active as monomers. 相似文献