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91.
Janjua NK Shaheen A Yaqub A Perveen F Sabahat S Mumtaz M Jacob C Ba LA Mohammed HA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):1600-1604
Interactional studies of new flavonoid derivatives (Fl) with chicken blood ds.DNA were investigated spectrophotometrically in DMSO-H2O (9:1 v/v) at various temperatures. Spectral parameters suggest considerable binding between the flavonoid derivatives studied and ds.DNA. The binding constant values lie in the enhanced-binding range. Thermodynamic parameters obtained from UV studies also point to strong spontaneous binding of Fl with ds.DNA. Viscometric studies complimented the UV results where a small linear increase in relative viscosity of the DNA solution was observed with added optimal flavonoid concentration. An overall mixed mode of interaction (intercalative plus groove binding) is proposed between DNA and flavonoids. Conclusively, investigated flavonoid derivatives are found to be strong DNA binders and seem to be promising drug candidates like their natural analogues. 相似文献
92.
Chao CS Lin CY Mulani S Hung WC Mong KK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(43):12193-12202
Ether-protecting functions at C-2 hydroxy groups have been found to play participating roles in glycosylations when the reactions are conducted in nitrile solvent mixtures. The participation mechanism is based on intramolecular interaction between the lone electron pair of the oxygen atom of the C-2 ether function and the nitrile molecule when they are positioned in a cis configuration. A 1,2-cis glycosyl oxazolinium intermediate is formed. This participation, in conjunction with the anomeric effect of the glycosyl donor, confers high 1,2-trans selectivities on glycosylations. Further application of this concept has led to efficient preparations of α-(1→5)-arabinan oligomers. 相似文献
93.
Mohamed E. Shaheen Brian J. Fryer 《Spectrochimica Acta Part B: Atomic Spectroscopy》2011,66(8):627-636
Analytical data on sediments are of great importance in understanding and documenting environmental issues. For laboratories interested in in-situ chemical analysis of sediments by LA-ICP-MS, a major issue is the lack of appropriate matrix matched sediment reference materials. Those available were largely designed for partial extractions which generally do not reflect the total elemental compositions. In this work we provide a comprehensive study on chemical compositions of seven currently available sediment reference materials (Lake sediments: LKSD-1, LKSD-2, LKSD-3, Stream sediments: STSD-2, STSD-3, and Marine sediments: PACS-2, MESS-3) as determined by Solution Nebulization Inductively Coupled Plasma Mass Spectrometry (SN-ICP-MS) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) after digestion in a mixture of concentrated HNO3 and HF acids. We also report a simple method to prepare these sediment reference materials and more generally appropriate sediment cores for LA-ICP-MS analysis using epoxy resin. This sample preparation method maintains sediment integrity for high spatial resolution analysis which is required for tracing changes in environmental conditions over short time periods. This work also demonstrates the application of fs-LA-ICP-MS as a tool for direct, rapid and high spatial resolution analysis of sediments. 相似文献
94.
Bakhat Ali Rashad Mehmood Uzma Rasheed Mughal Abdul Malik Muhammad Safder Riaz Hussain Muhammad Imran Rasool Bakhsh Tareen 《Helvetica chimica acta》2012,95(4):586-593
Eremosides A–C ( 1 – 3 ), three new iridoid glucosides, were isolated from the AcOEt‐soluble fraction of the EtOH extract of the whole plant of Eremostachys loasifolia, along with buddlejoside B ( 4 ), 10‐O‐benzoylcatalpol ( 5 ), and pakiside A ( 6 ) reported for the first time from this species. The structures of these compounds were elucidated by spectroscopic data including 2D‐NMR, FAB‐MS, ESI‐MS, as well as by acid and basic hydrolyses. 相似文献
95.
Metalloenzymes are essential proteins with vital activity that promote high-efficiency enzymatic reactions. To ensure catalytic activity, stability, and reusability for safe, nontoxic, sustainable chemistry, and green organic synthesis, it is important to develop metalloenzyme-inspired polymer-supported metal catalysts. Here, we present a highly active, reusable, self-assembled catalyst of poly(imidazole-acrylamide) and palladium species inspired by metalloenzymes and apply our convolution methodology to the preparation of polymeric metal catalysts. Thus, a metalloenzyme-inspired polymeric imidazole Pd catalyst (MEPI-Pd) was readily prepared by the coordinative convolution of (NH(4))(2)PdCl(4) and poly[(N-vinylimidazole)-co-(N-isopropylacrylamide)(5)] in a methanol-water solution at 80 °C for 30 min. SEM observation revealed that MEPI-Pd has a globular-aggregated, self-assembled structure. TEM observation and XPS and EDX analyses indicated that PdCl(2) and Pd(0) nanoparticles were uniformly dispersed in MEPI-Pd. MEPI-Pd was utilized for the allylic arylation/alkenylation/vinylation of allylic esters and carbonates with aryl/alkenylboronic acids, vinylboronic acid esters, and tetraaryl borates. Even 0.8-40 mol ppm Pd of MEPI-Pd efficiently promoted allylic arylation/alkenylation/vinylation in alcohol and/or water with a catalytic turnover number (TON) of 20,000-1,250,000. Furthermore, MEPI-Pd efficiently promoted the Suzuki-Miyaura reaction of a variety of inactivated aryl chlorides as well as aryl bromides and iodides in water with a TON of up to 3,570,000. MEPI-Pd was reused for the allylic arylation and Suzuki-Miyaura reaction of an aryl chloride without loss of catalytic activity. 相似文献
96.
Self-assembly of copper sulfate and a poly(imidazole-acrylamide) amphiphile provided a highly active, reusable, globular, solid-phase catalyst for click chemistry. The self-assembled polymeric Cu catalyst was readily prepared from poly(N-isopropylacrylamide-co-N-vinylimidazole) and CuSO(4) via coordinative convolution. The surface of the catalyst was covered with globular particles tens of nanometers in diameter, and those sheetlike composites were layered to build an aggregated structure. Moreover, the imidazole units in the polymeric ligand coordinate to CuSO(4) to give a self-assembled, layered, polymeric copper complex. The insoluble amphiphilic polymeric imidazole Cu catalyst with even 4.5-45 mol ppm drove the Huisgen 1,3-dipolar cycloaddition of a variety of alkynes and organic azides, including the three-component cyclization of a variety of alkynes, organic halides, and sodium azide. The catalytic turnover number and frequency were up to 209000 and 6740 h(-1), respectively. The catalyst was readily reused without loss of catalytic activity to give the corresponding triazoles quantitatively. 相似文献
97.
Our light and electron microscopy observations have revealed that the chromatic unit for the caudal fin in the blue variant of the Siamese fighting fish consists exclusively of dermal chromatophores comprised of compact and overlapping light-reflecting motile iridophores underlined by a layer of light absorbing melanophores. The 2 subtypes that make up about 70% of the skin tissue are located just below the basal layer of the considerably thin epidermis. The administration of K-rich saline or norepinephrine induced prompt, but gradual and reversible, changes in the color of the skin from blue to a brown-yellowish color. The induced color change is attributable either to the neurotransmitter releasing effects of the K-rich saline or to the direct effects of norepinephrine on the postsynaptic alpha adrenergic receptors. Both of these agents induced aggregation of the melanosomes within the melanophores and apparently shifted the wavelength of the light reflected by the iridophores towards the shorter (blue) end of the spectrum. Based on the distribution and architectural arrangement of the iridophores and melanophores as well as their physiological responses, we conclude that the generation of the blue coloration in this fish predominantly occurs through motile iridophores via a multilayered thin-film interference phenomenon of the non-ideal type. The presence of the underlying melanophores provides a black sheet of melanin that enhances the chroma and purity of the color. 相似文献
98.
A new natural terpenoid, ixoroid (1), was isolated from the flower of Ixora coccinea, along with the known constituents stigmast-5-en-3-O-beta-D-glucoside (2), 5-O-caffeoylquinic acid (3) and D-mannitol (4). The structure of ixoroid was elucidated on the basis of extensive 1D- and 2D-NMR studies and mass spectrometry as 21,23-epoxy-tirucall-7-en-3beta-ol (1). 相似文献
99.
Nekrasov-Okounkov identity gives a product representation of the sum over partitions of a certain function of partition hook length. In this paper, we give several generalizations of the Nekrasov-Okounkov identity using the cyclic symmetry of the topological vertex. 相似文献
100.