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Intramolecular reductive coupling of diimines in the presence of Zn/Ti(O(i)Pr)2Cl2 gives the corresponding (+/-)-2,3-diarylpiperazines in 73-83% yields with dl/meso ratio >99%:<1%. The (+/-)-2,3-diphenylpiperazine obtained in this way was readily resolved partially using L-(+)-tartaric acid, and the enantiomeric purity was enhanced to >99% ee via preparation of hydrogen-bonded salt aggregates using oxalic acid. 相似文献
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Enantiomerically pure (R,R)-(+)-2,3-diphenylpiperazine with 98% ee was obtained by resolution of the corresponding racemic mixture using (1S)-(+)-10-camphorsulfonic acid. The partially resolved enriched sample of (S,S)-(-)-2,3-diphenylpiperazine with 73% ee was purified to obtain samples of 97% ee using different achiral acids via the preparation of either homochiral or heterochiral hydrogen bonded aggregates. 相似文献
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Vairaprakash P Ueki H Tashiro K Yaghi OM 《Journal of the American Chemical Society》2011,133(4):759-761
The Merrifield solid-phase peptide synthesis technique has been adapted to the synthesis of homo- and heterometallic metal?organic complex arrays (MOCAs). A terpyridine-appended and Fmoc-protected L-tyrosine derivative was metalated with Pt(II), Rh(III), or Ru(II) ions in solution and sequentially coupled at the surface of functionalized polymeric resin to give a metal complex triad (Rh?Pt?Ru), tetrad (Ru?Rh?Pt?Pt), pentad (Rh?Pt?Ru?Pt?Rh), and hexad (Rh?Pt?Ru?Pt?Rh?Pt) with specific metal sequence arrangements. These were cleaved from the resin, and their character was confirmed by mass spectrometry. 相似文献
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Rajamani Rajmohan Geoffrey Vrla Hisanori Ueki Kappamveettil Sajna Toshiaki Takei Hiroyoshi Ohtsu Masaki Kawano Pothiappan Vairaprakash Kentaro Tashiro 《化学:亚洲杂志》2020,15(6):766-769
Self‐assembly of a series of dimetallic sequences constructed on a backbone with two successive tyrosine moieties ( Fmoc‐M 1 ‐M 2 ‐CO2H ) revealed that the resultant morphology is clearly dependent on the metal sequence, where Re‐containing sequences such as homometallic Fmoc‐Re‐Re‐CO2H specifically afforded amyloid‐like nanofibers. These findings further allowed to achieve the fibrillation of a longer metal sequence containing three different metals ( Fmoc‐Rh‐Pt‐Re‐Re‐CO2H ). Cyclic voltammetry of the fibrillated Fmoc‐Re‐Re‐CO2H demonstrated that the redox activity of the metal complexes in the sequence is preserved in the nanofibrous forms. 相似文献
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Pothiappan Vairaprakash 《Tetrahedron letters》2008,49(7):1233-1236
Enantioselective intramolecular reductive coupling of diimines by chiral titanium complexes, prepared using a titanium(IV) reagent and hemisalen ligands derived from chiral β-amino alcohols, gives trans-2,3-diarylpiperazines in up to 97% ee. 相似文献
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Michelle A. Harris Tuba Sahin Jianbing Jiang Pothiappan Vairaprakash Pamela S. Parkes‐Loach Dariusz M. Niedzwiedzki Christine Kirmaier Paul A. Loach David F. Bocian Dewey Holten Jonathan S. Lindsey 《Photochemistry and photobiology》2014,90(6):1264-1276
Biohybrid light‐harvesting antennas are an emerging platform technology with versatile tailorability for solar‐energy conversion. These systems combine the proven peptide scaffold unit utilized for light harvesting by purple photosynthetic bacteria with attached synthetic chromophores to extend solar coverage beyond that of the natural systems. Herein, synthetic unattached chromophores are employed that partition into the organized milieu (e.g. detergent micelles) that house the LH1‐like biohybrid architectures. The synthetic chromophores include a hydrophobic boron‐dipyrrin dye (A1) and an amphiphilic bacteriochlorin (A2), which transfer energy with reasonable efficiency to the bacteriochlorophyll acceptor array (B875) of the LH1‐like cyclic oligomers. The energy‐transfer efficiencies are markedly increased upon covalent attachment of a bacteriochlorin (B1 or B2) to the peptide scaffold, where the latter likely acts as an energy‐transfer relay site for the (potentially diffusing) free chromophores. The efficiencies are consistent with a Förster (through‐space) mechanism for energy transfer. The overall energy‐transfer efficiency from the free chromophores via the relay to the target site can approach those obtained previously by relay‐assisted energy transfer from chromophores attached at distant sites on the peptides. Thus, the use of free accessory chromophores affords a simple design to enhance the overall light‐harvesting capacity of biohybrid LH1‐like architectures. 相似文献
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