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111.
Chlorosulfonyl substituted styrene–divinylbenzene copolymer is a highly reactive intermediate used in organic synthesis. It is obtained in three steps: (1) the polymeric support in the form of spherical beads is prepared by free radical polymerization of styrene; (2) the divinylbenzene mixture and the aromatic styrene groups of the obtained copolymer are sulfonated with chlorosulfonic acid in dichloroethane and (3) this is followed by chlorination of the sulfonyl groups with PCl5/POCl3 mixture. Chemical analysis shows that chlorosulfonation leads to both sulfonyl and chlorosulfonyl products in which content and ratio vary as a function of reaction parameters: maximum total group content of 5.1 meq/g is reached after 3 hr reaction, at 40°C with styrene to a chlorosulfonic acid molar ratio of 12.4:1. In the chlorination reaction, sulfonyl to chlorosulfonyl conversion is also observed to vary as a function of time and chlorinating mixture composition: 99.6 mol% conversion degree is attained after 2 hr reaction with styrene/PCl5/POCl3 in a molar ratio of 1:4:23. © 1997 John Wiley & Sons, Ltd. 相似文献
112.
Callystatin A, a polyketide marine natural product, has been known since 1997 after its isolation from the sponge Callyspongia truncata by Kobayashi et al. It belongs to the leptomcyin family of natural products with a highly conjugated and stereodefined skeleton. The challenging structural topographies and remarkable anti-proliferative properties of (?)-Callystatin A stimulated many researchers to pursue the total synthesis of this marine polyketide. This review is exclusively focused on the research undertaken towards the concise, asymmetric total synthesis of Callystatin A over the last two decades. The various target oriented synthetic pathways are discussed in a chronological order to give a comprehensive overview. 相似文献
113.
Advanced analytical techniques for the extraction and characterization of plant‐derived essential oils by gas chromatography with mass spectrometry
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In recent years, essential oils have received a growing interest because of the positive health effects of their novel characteristics such as antibacterial, antifungal, and antioxidant activities. For the extraction of plant‐derived essential oils, there is the need of advanced analytical techniques and innovative methodologies. An exhaustive study of hydrodistillation, supercritical fluid extraction, ultrasound‐ and microwave‐assisted extraction, solid‐phase microextraction, pressurized liquid extraction, pressurized hot water extraction, liquid–liquid extraction, liquid‐phase microextraction, matrix solid‐phase dispersion, and gas chromatography (one‐ and two‐dimensional) hyphenated with mass spectrometry for the extraction through various plant species and analysis of essential oils has been provided in this review. Essential oils are composed of mainly terpenes and terpenoids with low‐molecular‐weight aromatic and aliphatic constituents that are particularly important for public health. 相似文献
114.
A new mechanism bypass in a wall-bounded internal flow is proposed and the proposal is checked by direct numerical simulations
of high temporal and spatial resolution. The mechanism is based on the interactions of the localized perturbations, rather
than the effect of a single perturbation investigated so far in the classical bypass transition process. It is first shown
by theoretical considerations that two pairs of quasistreamwise vortices can interact near the wall in such a manner that
the compression (stretching) of the existing wall-normal vorticity induced by one of the pairs can enhance a new streamwise
vorticity zone that can lead to new coherent structures and enhance considerably the transition process. Direct numerical
simulations confirm this hypothesis. 相似文献
115.
Kamyar Yazdani Deondre Jordan Mo Yang Christopher R. Fullenkamp David R. Calabrese Robert Boer Thomas Hilimire Timothy E. H. Allen Rabia T. Khan John S. Schneekloth Jr. 《Angewandte Chemie (International ed. in English)》2023,62(11):e202211358
Small molecule targeting of RNA has emerged as a new frontier in medicinal chemistry, but compared to the protein targeting literature our understanding of chemical matter that binds to RNA is limited. In this study, we reported R epository O f BI nders to N ucleic acids (ROBIN), a new library of nucleic acid binders identified by small molecule microarray (SMM) screening. The complete results of 36 individual nucleic acid SMM screens against a library of 24 572 small molecules were reported (including a total of 1 627 072 interactions assayed). A set of 2 003 RNA-binding small molecules was identified, representing the largest fully public, experimentally derived library of its kind to date. Machine learning was used to develop highly predictive and interpretable models to characterize RNA-binding molecules. This work demonstrates that machine learning algorithms applied to experimentally derived sets of RNA binders are a powerful method to inform RNA-targeted chemical space. 相似文献
116.
Rabia Nazir Muhammad Mazhar Tehmina Wakeel Muhammad J. Akhtar Muhammad Siddique Muhammad Nadeem Nawazish A. Khan Muhammad R. Shah 《Journal of Thermal Analysis and Calorimetry》2012,110(2):707-713
Pyrolysis of trisbipyridineiron(II) chloride under controlled thermal conditions and inert atmosphere of argon gas yields a residue of iron nanoparticles. Evolved gas analysis by GC?CMS and 1H NMR revealed emission of bipyridine, 6-chlorobipyridine, 6,6??-dichlorbipyridine, bipyridine hydrochloride, and hydrochloric acid as decomposition products. CHN, XRPD, EDXRF, TEM, AFM, and 57Fe M?ssbauer spectroscopy of the residue indicated formation of pure iron nanoparticles in the size range of 50?C72?nm. Based on these results a mechanism for thermal degradation of trisbipyridineiron(II) chloride has been worked out. 相似文献
117.
Mostafa K. Rabia Ahmad Desoky M. Mohamad Nabawia M. Ismail Ali Abdo Mahmoud 《Russian Journal of General Chemistry》2013,83(12):2406-2412
New [(pyridine-2-carboxaldhyde)-3-isatin]-bishydrazone (cpish), [(2-acetylpyridine)-3-isatin]-bishydrazone (apish), and [(2-benzoyl pyridine)-3-isatin]-bishydrazone (bpish) have been synthesized and characterized by the elemental analysis, IR, NMR and electronic spectra. The bioefficiency of the [(2-pyridyl)-3-isatin]-bishydrazones have been examined for their in-vitro antibacterial and antifungal activity against many types of bacteria and fungal cultures which are common contaminants of the environment in Egypt and some of which are involved in human and animal diseases or in plant diseases or frequently reported from contaminated soil, water, and food substances. The results of these studies indicate that the [(2-pyridyl)-3-isatin]-bishydrazones possess notable antimicrobial properties. 相似文献
118.
Tariq Mahmud Rabia Rehman Aqsa Gulzar Amina Khalid Jamil Anwar Umer Shafique Muhammad Salman 《Arabian Journal of Chemistry》2010,3(4):219-224
Complexes of enaminones; 4-N,N-diethylamine-pent-3-ene-2-one [HL1], 4-N,N-di n-propylamine-pent-3-ene-2-one [HL2] and 4-N,N-dicyclohexylamine-pent-3-ene-2-one [HL3] with Fe(II) and Zn(II) ions were prepared by reacting the equimolar ethanolic solutions of the ligands (HL1, HL2 and HL3) with ethanolic metal solutions. The complexes formed, were characterized by infrared, ultraviolet and atomic absorption spectroscopy. Ligands and their metal complexes were tested against Escherichia coli and Staphylococcus aureus bacteria to assess their antibacterial action using disc diffusion method. Ligands were completely inactive against bacteria whereas the complex Zn (HL1) has significant action on both bacteria, indicating that it has a good potential as bactericide. Other complexes have normal antiseptic character. 相似文献
119.
This paper addresses an identical parallel machine scheduling problem with job release dates and unavailability periods to
minimize total weighted completion time. This problem is known to be NP-hard in the strong sense. We propose a new lower bound
that can be computed in polynomial time. The test on more than 8 400 randomly generated instances shows a very significant
improvement with respect to existing results for previously studied special cases: without unavailability constraints, unweighted
version, or identical job release dates. For instance, the average improvement for the unweighted problem is as much as 20.43%
for 2 machines, 53.03% for 7 machines and 66.70% for 15 machines. For some instances, the improvement can be even as much
as 93%. 相似文献
120.
Adrianna Gillman Rabia Djellouli Mohamed Amara 《Journal of Computational and Applied Mathematics》2007
A mixed-hybrid-type formulation is proposed for solving Helmholtz problems. This method is based on (a) a local approximation of the solution by oscillated finite element polynomials and (b) the use of Lagrange multipliers to “weakly” enforce the continuity across element boundaries. The computational complexity of the proposed discretization method is determined mainly by the total number of Lagrange multiplier degrees of freedom introduced at the interior edges of the finite element mesh, and the sparsity pattern of the corresponding system matrix. Preliminary numerical results are reported to illustrate the potential of the proposed solution methodology for solving efficiently Helmholtz problems in the mid- and high-frequency regimes. 相似文献