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251.
Rima J Aoun E Hanna K 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(7):1515-1521
The characteristics of host-guest complexation between beta-cyclodextrin (beta-CD) and phenanthrene derivatives (phenanthrene, n-propyl, n-butyl and n-hexyl-phenanthrene) were investigated by fluorescence spectrometry. Linear and non-linear regression methods were used to estimate the formation constants (K1). A 1:1 stoichiometric ratio and an effect of n-alkyl chain length on the formation constant were observed for the binary inclusion complex between guest and beta-CD. The formation constant dramatically increases with the length of n-alkyl, it starts from the value of 140 l mol(-1) for the phenanthrene to reach the value of 580 l mol(-1) for hexyl-phenanthrene. The effect of the temperature on the fluorescence intensity of each complex (guest-host) was also studied; and then the thermodynamic parameters were calculated. The main inclusion site seems to be aromatic moiety for short chain molecules, and it moves toward the alkyl chain part, as the chain becomes longer. 相似文献
252.
Although carbonylation of aryl halides is widely applied in synthesis, heterogeneous catalysts for this transformation are scarce. In order to heterogeneously catalyze the amidocarbonylation of bromoarenes, a polymer-supported catalytic system was assembled from Pd(dba)2 and a polymer-bound diphosphine chelate, prepared via solid-phase synthesis from serinol. The system efficiently converts aryl bromides into carboxamides in a reaction with CO and aliphatic or aromatic amines. Comparison with other supported phosphine ligands demonstrated the superiority of the chelate diphosphine structure. Remarkably, partial complexation of the polymer-tethered ligating sites with Pd forms notably better catalytic systems than the full complexation. The reactivity pattern of the catalytic system points to the oxidative addition as the rate-determining step of the catalytic cycle. 相似文献
253.
Shawky A. El-Shazly Abdalla A. S. Babaqi Mohamed T. Mohamed Amal A. Zaghlol Mohamed F. Amira 《Transition Metal Chemistry》1991,16(5):488-491
Summary The aquation kinetics of the chloropenta-aminecobalt(III) ion in H2O–EtOH mixtures have been determined. A new correlation is described for calculating the chemical potential from kinetic data and molar thermodynamic excess functions for binary mixtures. The rate constants correlate well with Grunwald-Winstein solvating power Y parameter and with the dielectric constant of the medium. The data supports the D mechanism. 相似文献
254.
Abdelrahman Maha M. Abdelwahab Nada S. Salama Fathy M. Ahmed Amal B. 《平面色谱法杂志一现代薄层色谱法》2016,29(5):372-379
JPC – Journal of Planar Chromatography – Modern TLC - Accurate, selective, and sensitive thin-layer chromatography (TLC)—densitometry and reversed-phase high-performance liquid... 相似文献
255.
V. S. Grinev O. A. Amal’chieva A. Yu. Egorova 《Russian Journal of Organic Chemistry》2016,52(5):655-660
Reactions of 5-alkyl- and 5-aryl-3H-furan-2-ones with 1,3- and 1,4-binucleophiles of aromatic series were carried out for the first time under various conditions. In the presence of a base the reaction resulted in 1-R-1,3-dihydro-2Н-pyrrol-2-ones, under milder conditions intermediates were isolated, 4-aryl-4-oxobutanamides. The structure of the latter was proved by spectral methods. By an example of 1-R-1,3-dihydro-2Н-pyrrol-2-ones the possibility was demonstrated of their functionalization via introducing an aryldiazenyl fragment. 相似文献
256.
Current algorithms for the calculation of peptide or protein pI, based on the charge associated with individual amino acids, can calculate pI values to within +/-0.2 pI units. Here, we present a new pI calculation algorithm that takes into account the effect of adjacent amino acids on the pI value. The algorithm accounts for the effect of adjacent amino acids+/-3 residues away from a charged aspartic or glutamic acid, as well as effects on the free C terminus, and applies a correction term to the corresponding pK values. The correction increments are derived from a 5000-peptide training set using a genetic optimization approach. The accuracy of the new pI values obtained with this method approaches the error associated with the manufacture of the IPG strip (<+/-0.03 pI units). The approach is demonstrated for cytosolic cell extracts derived from the breast-cancer cell line DU4475, and from membrane preparations from human lung-tissue samples. One potential application of a more highly accurate pI calculation is data filtering of MS/MS outputs that will allow for more complex database searches including gene finding, and validation, and detection of coding single-nucleotide polymorphisms in their expressed form. 相似文献
257.
Khadiga M. Kelani Maha A. Hegazy Amal M. Hassan Mahmoud A. Tantawy 《Electroanalysis》2023,35(1):e202100653
This work represents first attempt for potentiometric determination of the most recent antidiabetic; omarigliptin. Three sensors, employing potassium tetrakis (p-chlorophenyl) borate as a lipophilic cation exchanger, were developed and compared. One liquid contact ion-selective electrode and two carbon paste-based solid contact ones, plain one and another one modified with polyaniline nanoparticles, were employed. Performances of fabricated sensors were assessed as per IUPAC recommendations. Incorporation of hydrophobic polyaniline nanoparticles as ion-to-electron transducer layer at solid contact/ion-sensitive membrane interface enhanced sensitivity and stability of the third sensor showing LOD of 2.5×10−7 mol L−1 and slope of 58.57 mV decade−1. The three sensors were applied for omarigliptin determination in presence of its degradation products, in dosage form and spiked human plasma. 相似文献
258.
Ahmad Hussein Alomari Muneer Aziz Saleh Suhairul Hashim Amal Alsayaheen Ahmad Abukashabeh 《Isotopes in environmental and health studies》2019,55(2):211-226
An extensive study was conducted to determine the activity concentrations of natural and artificial radionuclides 226Ra, 232Th, 40K, and 137Cs in soil samples of each governate of Jordan. A total of 370 samples have been measured using a high-purity germanium detector. The activity concentration for 226Ra, 232Th, 40K, and 137Cs has mean values of 42?±?3, 23?±?3, 309?±?21, and 3.7?±?0.9 Bq kg–1, respectively. The highest mean activity concentration for 226Ra was found to be 138?±?4 Bq kg–1 in the Alkarak governate. In the Ajloun and Jarash governates, the highest mean activity concentration was 35?±?3 Bq kg–1 for 232Th, and 14.2?±?1.9 Bq kg–1 for 137Cs, respectively. Geological influence on the activity concentrations was investigated using the one-way analysis of variance (ANOVA) and independent samples. The ANOVA results indicate that there are strong significant differences between the activity concentrations of 232Th, 40K, and 137Cs based on geological formations the radionuclides occur. The main contribution to gamma dose rate was due to 226Ra activity concentration. Radium equivalent and external hazard index are associated with a mean value of 98 Bq kg–1, and 0.266, respectively. 相似文献
259.
Amal M. Abdel‐Karim A.H. Salama Fatma A. El‐Samahy Mervat El‐Sedik Fayez H. Osman 《Journal of Physical Organic Chemistry》2017,30(12)
The evaluation of the dielectric properties of s‐triazine and its mono‐, di‐, tri‐(trityloxy)triazine derivates as a function of temperature from room temperature to 200°C, and frequency varying from 50 Hz to 5 MHz was performed. The dielectric constant increases with the increase of both temperature and frequency. Moreover, from the measured dielectric loss ε″ we found that there are different types of electric energy losses in the presence of an alternating electric field from which we calculate the entropy ΔS and the enthalpy change ΔH of the dielectric relaxation for each sample. The dielectric relaxation was attributed to the phase transition of the s‐triazine derivatives. Additionally, ac‐electrical conductivity as a function of frequency at different temperatures were studied. Analysis of ac conductivity data indicates that the correlated barrier hopping model is the most suitable mechanism for the ac‐conductance behavior. X‐ray diffraction and scanning electron microscopy were performed on the compounds under consideration to determine the grain size of each sample, which was found in the range of 3 to 100 nm. 相似文献
260.
West Douglas X. Beraldo Heloisa Nassar Amal A. El-Saied Fathy A. Ayad Mohammed I. 《Transition Metal Chemistry》1999,24(4):421-424
Mononuclear and binuclear copper(II) complexes with four 4-acetamidobenzaldehyde N(4)-substituted thiosemicarbazones have been prepared in EtOH solution and characterized by physical and spectral methods. I.r., electronic, and e.s.r. spectra of the complexes, as well as i.r., electronic, and n.m.r. spectra of the thiosemicarbazones, have been obtained. These thiosemicarbazones coordinate as anionic or neutral ligands via the thiosemicarbazone moiety's imine nitrogen and thiolate/thione sulfur, the former on loss of the hydrazido hydrogen, N(2)H. 相似文献