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排序方式: 共有159条查询结果,搜索用时 15 毫秒
1.
This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications. 相似文献
2.
A mild and efficient protocol for the coupling of indoles and pyrroles with allyl halides such as allyl bromide, crotyl bromide and propargyl bromide in the presence of gallium metal in a Bu4NBr-DMF-H2O system has been developed. The reaction is equally effective when cadmium is used in lieu of gallium and the corresponding 3-allyl indoles and 3-allyl pyrroles were obtained in almost comparable yields. 相似文献
3.
Pranjal Pathak Kriti Shrivastava Takayuki Ichikawa Ankur Jain Rini Singh 《Molecules (Basel, Switzerland)》2022,27(13)
The hunt for a cleaner energy carrier leads us to consider a source that produces no toxic byproducts. One of the targeted alternatives in this approach is hydrogen energy, which, unfortunately, suffers from a lack of efficient storage media. Solid-state hydrogen absorption systems, such as lithium amide (LiNH2) systems, may store up to 6.5 weight percent hydrogen. However, the temperature of hydrogenation and dehydrogenation is too high for practical use. Various molar ratios of LiNH2 with sodium hydride (NaH) and potassium hydride (KH) have been explored in this paper. The temperature of hydrogenation for LiNH2 combined with KH and NaH was found to be substantially lower than the temperature of individual LiNH2. This lower temperature operation of both LiNH2-NaH and LiNH2-KH systems was investigated in depth, and the eutectic melting phenomenon was observed. Systematic thermal studies of this amide-hydride system in different compositions were carried out, which enabled the plotting of a pseudo-binary phase diagram. The occurrence of eutectic interaction increased atomic mobility, which resulted in the kinetic modification followed by an increase in the reactivity of two materials. For these eutectic compositions, i.e., 0.15LiNH2-0.85NaH and 0.25LiNH2-0.75KH, the lowest melting temperature was found to be 307 °C and 235 °C, respectively. Morphological studies were used to investigate and present the detailed mechanism linked with this phenomenon. 相似文献
4.
5.
A mild, efficient, and solvent‐free protocol for tetrahydropyranylation of alcohols in the presence of a catalytic amount of SnCl2 · 2H2O is reported. Simple filtration of the reaction mixture through a short silica‐gel pad gives the pure products in excellent yields. Depyranylation can also be achieved by adding methanol under similar reaction conditions. 相似文献
6.
Saurabh K. Yadav Pranjal Chandra Rajendra N. Goyal Yoon-Bo Shim 《Chromatographia》2013,76(21-22):1439-1448
Anabolic steroids form one of the important classes of doping agents and their consumption has been found to give benefits to the athletes. Inspite of the fact that they also produce adverse effects and damage several organs and systems, their consumption is continuously increasing in competitive games. The World Anti-Doping Agency and International Olympic Committee have banned the use of anabolic steroids and several other compounds. This article focuses an over view of various chromatographic techniques commonly used for detecting anabolic steroids and their metabolites during last 3 years in human biological fluids to establish the cases of doping. The possibility of electrochemistry- and microchip-based techniques have been considered as possible techniques for future to achieve simple and fast analysis at the site of competitive games as the first tool to detect the cases of doping. 相似文献
7.
Relaxation dynamics of plasmons in Au−SiO2 core-shell nanoparticles have been followed by femtosecond pump-probe technique. The effect of excitation pump energy and surrounding medium on the time constants associated with the hot electron relaxation has been elucidated. A gradual increase in the electron-phonon relaxation time with pump energy is observed and can be attributed to the higher perturbation of the electron distribution in AuNPs at higher pump energy. Variation in time constants for the electron-phonon relaxation in different solvents is rationalized on the basis of their thermal conductivities, which govern the rate of dissipation of heat of photoexcited electrons in the nanoparticles. On the other hand, phonon-phonon relaxation is found to be much less effective than electron-phonon relaxation for the dissipation of energy of the excited electron and the time constants associated with it remain unaffected by thermal conductivity of the solvent. 相似文献
8.
Srinivasa Rao Karumuri Joydeep Choudhury Nirmal Kumar Sarkar Bandana Gogoi Ramendu Bhattacharjee 《Indian Journal of Physics》2010,84(6):647-652
Porphyrins have received numerous considerable attentions during recent years because of their great biological importance.
The most interesting areas of current research in molecular spectroscopy are the study of the vibrational ground and excited
states of polyatomic molecules especially for the Metalloporphyrins. In this paper, we have calculated the fundamental and
extrapolated vibrational energy levels of Magnesium, Nickel, Copper, Zinc, Metalloporphyrin molecules using U (2) algebraic
model Hamiltonian. The results obtained by this method are in good agreement with the experimental data. This study gives
a general approach for solving the vibrational spectra of Metalloporphyrin molecules. 相似文献
9.
Mixed valent Pd(0)/Pd(II) nano‐sized aggregates supported onto a chemically robust layered zirconium carboxyphosphonate framework is prepared and its catalytic activity in Suzuki‐Miyaura cross coupling reaction is explored. The exceptionally high catalytic efficacy of the heterogeneous catalyst in Suzuki‐Miyaura cross coupling reaction is signified by remarkably short reaction time 2 minutes and high turnover frequency of 1.3 x 104 hr?1. The catalyst can be recycled several times without significant loss of catalytic efficacy, while spectroscopic, structural and microscopic investigations suggest the integrity of the catalyst even after fifth catalytic cycle. The unique ability of the zirconium carboxyphosphonate framework to interact strongly with palladium in dual Pd(0)/Pd(II) oxidation states has been attributed to this remarkable augmentation of catalytic efficacy. 相似文献
10.
Gogoi Deepshikha Hussain Amreen A. Pal Arup R. 《Plasma Chemistry and Plasma Processing》2019,39(1):277-292
Plasma Chemistry and Plasma Processing - We report plasma based fabrication of an optoelectronic device with plasmon enhanced infrared sensitivity realized by integrating plasmonic gold... 相似文献