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421.
Kaanumalle LS Sivaguru J Sunoj RB Lakshminarasimhan PH Chandrasekhar J Ramamurthy V 《The Journal of organic chemistry》2002,67(25):8711-8720
Through a systematic study of several diphenylcyclopropane derivatives, we have inferred that the cations present within a zeolite control the excited-state chemistry of these systems. In the parent 1,2-diphenylcylopropane, the cation binds to the two phenyl rings in a sandwich-type arrangement, and such a mode of binding prevents cis-to-trans isomerization. Once an ester or amide group is introduced into the system (derivatives of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid), the cation binds to the carbonyl group present in these chromophores and such a binding has no influence on the cis-trans isomerization process. Cation-reactant structures computed at density functional theory level have been very valuable in rationalizing the observed photochemical behavior of diphenylcyclopropane derivatives included in zeolites. While the parent system, 1,2-diphenylcylopropane, has been extensively investigated in the context of chiral induction in solution, owing to its failure to isomerize from cis to trans, the same could not be investigated in zeolites. However, esters of 2beta,3beta-diphenylcyclopropane-1alpha-carboxylic acid could be studied within zeolites in the context of chiral induction. Chiral induction as high 20% ee and 55% de has been obtained with selected systems. These numbers, although low, are much higher than what has been obtained in solution with the same system or with the parent system by other investigators (maximum approximately 10% ee). 相似文献
422.
423.
Chandrasekhar V Azhakar R Senapati T Thilagar P Ghosh S Verma S Boomishankar R Steiner A Kögerler P 《Dalton transactions (Cambridge, England : 2003)》2008,(9):1150-1160
The reaction of cyclohexylphosphonic acid (C(6)H(11)PO(3)H(2)), anhydrous CuCl(2) and 2,2'-bipyridine (bpy) in the presence of triethylamine followed by a metathesis reaction with KNO(3) afforded [Cu(4)(mu-Cl)(2)(mu(3)-C(6)H(11)PO(3))(2)(bpy)(4)](NO(3))(2) (1). In an analogous reaction involving Cu(OAc)(2).H(2)O, the complex [Cu(4)(mu-CH(3)COO)(2)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4)](CH(3)COO)(2) (2) has been isolated. The three-component reaction involving Cu(NO(3))(2).3H(2)O, cyclohexylphosphonic acid and 2,2'-bipyridine in the presence of triethylamine afforded the tetranuclear assembly [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4) (H(2)O)(2)](NO(3))(3) (3). Replacing 2,2'-bipyridine with 1,10-phenanthroline (phen) in the above reaction resulted in [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(phen)(4)(H(2)O)(2)](NO(3))(3) (4). In all the copper(II) phosphonates (1-4) the two phosphonate ions bridge the four copper(II) ions in a capping coordination action. Each phosphonate ion bridges four copper(II) ions in a mu(4), eta(3) coordination mode or 4.211 of the Harris notation. Variable-temperature magnetic studies on reveal that all four complexes exhibit moderately strong intramolecular antiferromagnetic coupling. The DNA cleavage activity of complexes 1-4 is also described. Compounds 1 and 3 were able to completely convert the supercoiled pBR322 DNA form I to nick form II without any co-oxidant. In contrast, 50% conversion occurred with and 40% with 4. In the presence of magnesium monoperoxyphthalate all four compounds achieved rapid conversion of form I to form II. 相似文献
424.
A combination of "chiron" and "asymmetric" approaches is utilized to construct the southern (C 9-C 25) region of marine natural product spirastrellolide B. The key functionalities are derived from d-glucose and Sharpless asymmetric epoxidation and dihydroxylation. 相似文献
425.
Sarvjeet Kaur Bhanu Sharma E. S. Lin M. M. Lee Gulshan Kumar V. Chandrasekhar Shih-Sheng Sun Ashutosh S. Singh 《中国化学会会志》2023,70(11):2016-2021
Mutual induced-fit is well known process in biological system and playing crucial role in enzymatic catalysis, peptide-bond synthesis, protein synthesis, etc…, proceeds by mutual interactions of two or more than two components. However, in an artificial system, to mimic such process is challenging, especially by purely organic components. In this report, we have shown importance of mutual induced-fit in signal amplification of hydrogen-bonded capsule formation. Two different types of highly flexible ligands (one N-bridged and another triazine-bridged) are used. N-bridged tripodal ligand acting as clip over the adduct obtained from triazine-bridged ligand, bringing the resultant adduct in the cone-shape conformation. The resulting cone-shape conformation undergo solvent polarity dependent hydrogen-bonded capsule formation as a sole product. In absence of N-bridged tripodal ligand, only 50% capsule formation is observed through 1H NMR at 100 mM concentration. However, in the presence of N-bridged tripodal ligand, organic components undergo mutual interactions to opt the cone-shape conformation and 100% capsule is formed (independent of concentration). The complete process is characterized by IR-spectra, 1H and 13C NMR spectra, concentration dependent 1H NMR titration spectra, 1H-1H COSY, 1H-1H NOESY, DOSY NMR, high resolution ESI mass spectra, and also by energy-minimized structure. 相似文献
426.
Sureshan Muthusamy Rajamanikandan Sundarraj Srimari Srikanth Prabhu Dhamodharan Jeyakanthan Jeyaraman Saraboji Kadhirvel 《Structural chemistry》2022,33(3):935-947
Structural Chemistry - Lymphatic filariasis (LF) is one among the leading neglected diseases caused by mosquitoe-borne parasite Wuchereria bancrofti to humans. Though drugs are available for the... 相似文献
427.
Zheng Y Qi D Chandrasekhar N Gao X Troadec C Wee AT 《Langmuir : the ACS journal of surfaces and colloids》2007,23(16):8336-8342
Evaporated pentacene thin films with thicknesses from several nm to 150 nm on gold and silver substrates have been studied by ultraviolet photoelectron spectroscopy (UPS), near-edge X-ray absorption fine structure (NEXAFS), scanning tunneling microscopy (STM), and atomic force microscopy (AFM). It was found that pentacene thin-film structures, particularly their molecular orientations, are strongly influenced by the metal substrates. UPS measurements revealed a distinct change in the valence band structures of pentacene on Au compared to those on Ag, which is attributed to the different packing between adjacent molecules. Using NEXAFS, we observed 74+/-5 degrees and 46+/-5 degrees molecular tilt angles on Ag and Au, respectively, for all measured thicknesses. We propose that pentacene molecules stand up on the surface and form the "thin-film phase" structure on Ag. On Au, pentacene films grow in domains with molecules either lying flat or standing up on the substrate. Such a mixture of two crystalline phases leads to an average tilt angle of 46 degrees for the whole film and the change in valence band structures. STM and distance-voltage (z-V) spectroscopy studies confirm the existence of two crystalline phases on Au with different conducting properties. z-V spectra on the low conducting phase clearly indicate its nature as "thin-film phase". 相似文献
428.
Temperature-dependent investigations of excess electrons in molten solutions of cesium-doped cesium iodide (Cs-CsI) (mole fraction of Cs approximately 0.003) were performed applying femtosecond pump-probe absorption spectroscopy. The pulse-limited induced bleach observed at probe wavelengths from 600 to 1240 nm was attributed to the excitation of equilibrated excess electrons which were initially formed by melting a Cs-CsI mixture. The interpretation of the relaxation process is based on strongly localized polarons that constitute the majority of defect states in this melt. As expected, the bipolaron contribution was insignificant. The time constants (tau1) were found to be temperature dependent confirming our earlier findings in Na-NaI melts that ionic diffusion almost exclusively controls the dynamics of excess electrons in high temperature ionic liquids. Apart from this temperature dependence, the relaxation dynamics of excess electrons do not differ irrespective of the excitation regime (blue or red part of the respective stationary spectra). 相似文献
429.
The reaction of Cu2(O2CMe)(4).2H2O with tert-butylphosphonic acid and 3,5-di-tert-butylpyrazole in the presence of triethylamine leads to a high-yield synthesis of the tetranuclear compound [Cu2(3,5-t-Bu2PzH)2(t-BuPO3)2]2 (1). The latter has a distorted cubic cage structure and its core resembles the D4R (double-four-ring) motif found in zeolites. The phosphonate, [t-BuPO3]2-, functions as a dianionic tridentate ligand, while the pyrazole ligands are neutral and are monodentate. The coordination geometry at each copper atom is distorted square planar with a 3O,1N coordination environment. Magnetic measurements on 1 reveal that the chiT product continuously decreases to reach a value very close to zero at 1.8 K, indicating dominant antiferromagnetic interactions between Cu(II) ions that leads to an S=0 ground state. The tetranuclear cage 1 functions as a very effective artificial nuclease in the presence of an external oxidant, magnesium monoperoxyphthalate. 相似文献
430.
Stereoselective total syntheses of the antiprotozoal natural product (+)-passifloricin A and its C-6 epimer have been achieved in ~5% overall yield. The strategy is based on Jacobsen epoxidation, Grubbs’ metathesis and an Evans’ intramolecular oxa-Michael reaction. 相似文献