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941.
A sensitive, enantioselective, high-performance liquid chromatographic (HPLC) method was developed and validated to determine S-(-)- and R-(+)-bisoprolol in human plasma. Baseline resolution was achieved using the teicoplanin macrocyclic antibiotic chiral stationary phase (CSP) known as Chirobiotic T with a polar ionic mobile phase (PIM) consisting of methanol-glacial acetic acid-triethylamine (100 : 0.02 : 0.025, v/v/v) at a flow rate of 1.5 ml/min and fluorescence detection set at 275 nm for excitation and 305 nm for emission. All analyses with S-(-)-atenolol as the internal standard were conducted at ambient temperature. The assay involved the use of a solid-phase extraction procedure for human plasma samples prior to HPLC analysis. The C18 cartridge gave good recovery rates for both enantiomers without any interference. The method was validated over the range of 20-200 ng/ml for each enantiomer concentration. Recovery rates for S-(-)- and R-(+)-bisoprolol enantiomers were in the range of 95-102%. The method proved to be precise (within-run precision expressed as % RSD ranged from 1.0-6.2% and between-run precision ranged from 0.9-6.7%) and accurate (within-run accuracies expressed as percentage error ranged from 0.2-4.8% and between-run accuracies ranged from 0.3-1.7%). The limit of quantitation and limit of detection for each enantiomer in human plasma were 20 and 5 ng/ml, respectively. 相似文献
942.
Ammar S Mahjoub MA Charfi N Skandarani I Chekir-Ghedira L Mighri Z 《Chemical & pharmaceutical bulletin》2007,55(3):385-388
A new skeleton of an O-heteroside natural substance named zinolol, the first representative of a new class of aminated hydroxyhydroquinone, has been isolated from the whole plant Anagallis monelli. Its structure has been established by one and two dimensional NMR spectroscopic procedures. Antioxidant, mutagenic, antimutagenic activities were realised and positive results were recorded. 相似文献
943.
On-the-fly dynamics is used to analyze the remarkably anharmonic infrared spectroscopy of crystalline HCl monohydrate, an ionic solid composed of H3O+ and Cl-. The dominant intense infrared feature is shown to originate from specific sections of the hydronium trajectory, in which one of the H-atoms interacts strongly with a neighboring Cl-. 相似文献
944.
Microphase separation induced by interfacial segregation of isotropic, spherical nanoparticles 总被引:1,自引:0,他引:1
In a recent experiment by Chung et al. [Nano Lett. 5, 1878 (2005)] and simulation by Stratford et al. [Science 309, 2198 (2005)] on immiscible blends containing nanoscale particles, it was shown that the phase separation of the two polymers can be prevented as a result of the aggregation of the nanoparticles at the interfaces between the two polymers. Motivated by these studies, we performed large scale systematic simulations, based on the dissipative particle dynamics approach, on immiscible binary (A-B) fluids containing moderate volume fractions of isotropic nanoscale spherical particles N. The nanoparticles preferentially segregate at the interfaces between the two fluids if the pairwise interactions between the three components are such that chi(AB)>/chi(AN)-chi(BN)/. We find that at later times, the average domain size saturates to a value, L approximately R(N)/phi(N), where R(N) and phi(N) are the radius and volume fraction of the nanoparticles, respectively. For small nanoparticles, however, full phase separation is observed. 相似文献
945.
Mohamed R. Shaaban Ahmad M. Farag Tamer S. Saleh Fayez H. Osman 《Journal of heterocyclic chemistry》2007,44(1):177-181
946.
Khadijah M. Al‐Zaydi Rita M. Borik Mohamed H. Elnagdi 《Journal of heterocyclic chemistry》2007,44(5):1187-1189
947.
Carpino LA Abdel-Maksoud AA Ionescu D Mansour EM Zewail MA 《The Journal of organic chemistry》2007,72(5):1729-1736
Of the three theoretically possible, Bsmoc-related, naphthothiophene sulfone-based amino-protecting groups, the two most readily available derivatives, the alpha- and beta-Nsmoc analogues, have been examined as substitutes for the Bsmoc residue in cases where the latter lead to oily protected amino acids or amino acid fluorides. All of the naphtho systems gave easily handled solid amino acid derivatives. The intermediate sulfone alcohol 11 used as the key reagent for introduction of the alpha-Nsmoc protecting group was readily made from alpha-tetralone (Scheme 1). The corresponding beta-analogue 17 was made similarly on a small scale, but due to the high cost of beta-tetralone, an alternate route involving reaction of rhodanine with alpha-naphthaldehyde was used for large-scale work (Scheme 2). All proteinogenic amino acids were converted to their alpha- and beta-Nsmoc derivatives. Deblocking studies showed that the reactivity toward deblocking by piperidine followed the order alpha-Nsmoc > Bsmoc > beta-Nsmoc. 1H NMR experiments showed that deblocking of the two new systems was mechanistically similar to that previously established for the Bsmoc derivative in that the reaction is initiated by Michael addition to the beta-carbon atom of the alpha,beta-unsaturated sulfone system. Application of alpha- and beta-Nsmoc amino acids to the solid-phase synthesis of two model peptides was examined. An advantage of the alpha-Nsmoc system over the long-known Bsmoc system proved to be the milder conditions needed for the deblocking step relative to the Bsmoc case, which is itself more readily deblocked than the classic Fmoc analogue. 相似文献
948.
The mixture {yNH4Cl + (1 − y)MgCl2} (aq) has been studied using the hygrometric method at the temperature 298.15 K. The water activities are measured at total molalities from 0.30 mol kg−1 up to saturation for different ionic strength fractions y of NH4Cl with y = 0.20, 0.50 and 0.80. The obtained data allow the deduction of osmotic coefficients. Experimental results are compared with the calculations using the models of Zdanovskii–Stokes–Robinson, Kusik and Meissner, Robinson and Stokes, Lietzke and Stoughton, Reilly–Wood and Robinson and Pitzer. Thermodynamic properties have been modeled using the Pitzer ion-interaction model with inclusion of an ionic strength dependence of the third virial coefficient for the binary systems. From these measurements and the obtained binary parameters β(0), β(1), C(0) and C(1), the mixing ionic parameters θNH4Mg and ψNH4MgCl are determined by the standard Pitzer model. The results show that a good accuracy is obtained with the standard Pitzer model using extended binary parameters. The parameters θNH4Mg and ψNH4MgCl were used for evaluation of activity coefficients in the mixture. The excess Gibbs energy is also determined. 相似文献
949.
Studies of interactions between silane coupling agents and cellulose fibers with liquid and solid-state NMR 总被引:1,自引:0,他引:1
Salon MC Gerbaud G Abdelmouleh M Bruzzese C Boufi S Belgacem MN 《Magnetic resonance in chemistry : MRC》2007,45(6):473-483
The hydrolysis of three alkoxy-silane coupling agents, gamma-methacryloxypropyl trimethoxy silane (MPS), gamma-aminopropyl triethoxy silane (APS), and gamma-diethylenetriaminopropyl trimethoxy silane (TAS), was carried out in ethanol/water solutions (80/20 w/w) at different pH values and followed by 1H, 13C and 29Si NMR spectroscopy. Acidic media were found to stabilize the hydrolyzed forms. As expected, the formation of silanol groups was followed by their self-condensation to generate oligomeric structures, yielding, ultimately, solid homopolycondensated structures, as analyzed by 29Si and 13C high-resolution solid-state NMR. Hydrolyzed MPS in acidic media was then successfully adsorbed onto a cellulose surface and the ensuing substrates submitted to thermal treatment at 110-120 degrees C under reduced pressure, in order to create covalent bonds between cellulose and the coupling agent. 相似文献
950.
Muhammad Umar Aslam Khan Iqra Iqbal Mohamed Nainar Mohamed Ansari Saiful Izwan Abd Razak Mohsin Ali Raza Amna Sajjad Faiza Jabeen Mohd Riduan Mohamad Norhana Jusoh 《Molecules (Basel, Switzerland)》2021,26(19)
The present research is based on the fabrication preparation of CS/PVA/GG blended hydrogel with nontoxic tetra orthosilicate (TEOS) for sustained paracetamol release. Different TEOS percentages were used because of their nontoxic behavior to study newly designed hydrogels’ crosslinking and physicochemical properties. These hydrogels were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and wetting to determine the functional, surface morphology, hydrophilic, or hydrophobic properties. The swelling analysis in different media, degradation in PBS, and drug release kinetics were conducted to observe their response against corresponding media. The FTIR analysis confirmed the components added and crosslinking between them, and surface morphology confirmed different surface and wetting behavior due to different crosslinking. In various solvents, including water, buffer, and electrolyte solutions, the swelling behaviour of hydrogel was investigated and observed that TEOS amount caused less hydrogel swelling. In acidic pH, hydrogels swell the most, while they swell the least at pH 7 or higher. These hydrogels are pH-sensitive and appropriate for controlled drug release. These hydrogels demonstrated that, as the ionic concentration was increased, swelling decreased due to decreased osmotic pressure in various electrolyte solutions. The antimicrobial analysis revealed that these hydrogels are highly antibacterial against Gram-positive (Staphylococcus aureus and Bacillus cereus) and Gram negative (Pseudomonas aeruginosa and Escherichia coli) bacterial strains. The drug release mechanism was 98% in phosphate buffer saline (PBS) media at pH 7.4 in 140 min. To analyze drug release behaviour, the drug release kinetics was assessed against different mathematical models (such as zero and first order, Higuchi, Baker–Lonsdale, Hixson, and Peppas). It was found that hydrogel (CPG2) follows the Peppas model with the highest value of regression (R2 = 0.98509). Hence, from the results, these hydrogels could be a potential biomaterial for wound dressing in biomedical applications. 相似文献