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1.
Kuz’mina L. G. Navasardyan M. A. Kalle P. Bezzubov S. I. 《Crystallography Reports》2021,66(3):420-423
Crystallography Reports - The crystal and molecular structures of Cl–C6H4–O–C16H33 (I) have been studied, and its differential scanning calorimetry (DSC) study is performed.... 相似文献
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T. K. Kwei Kalle Levon Giuliana Tesoro Frank Liu Abraham Mey-Marom Surya Munukutla 《先进技术聚合物》1993,4(9):537-547
The synthesis of molecular composites where rigid polymer molecules are reinforcing elements in a thermoset bisimide matrix has been investigated. The approach has been designed to avoid phase separation by selecting systems where reaction of amine-terminated rigid and semiflexible oligomers with maleimide unsaturation occurs prior to crosslinking of the thermoset. This objective has been met for some compositions. The concentration and molecular weight of the rigid oligomers have been varied. The structure of the reinforcing polymer, the reactivity of the maleimide and the conditions for composite synthesis are variables of critical importance, and further work must determine the promise and limitations of this approach. 相似文献
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Denisov AY Hannoush RN Gehring K Damha MJ 《Journal of the American Chemical Society》2003,125(38):11525-11531
We have recently shown that hairpins containing 2',5'-linked RNA loops exhibit superior thermodynamic stability compared to native hairpins comprised of 3',5'-RNA loops [Hannoush, R. N.; Damha, M. J. J. Am. Chem. Soc. 2001, 123, 12368-12374]. A remarkable feature of the 2',5'-r(UUCG) tetraloop is that, unlike the corresponding 3',5'-linked tetraloop, its stability is virtually independent of the hairpin stem composition. Here, we determine the solution structure of unusually stable hairpins of the sequence 5'-G(1)G(2)A(3)C(4)-(U(5)U(6)C(7)G(8))-G(9)(U/T(10))C(11)C(12)-3' containing a 2',5'-linked RNA (UUCG) loop and either an RNA or a DNA stem. The 2',5'-linked RNA loop adopts a new fold that is completely different from that previously observed for the native 3',5'-linked RNA loop. The 2',5'-RNA loop is stabilized by (a). U5.G8 wobble base pairing, with both nucleotide residues in the anti-conformation, (b). extensive base stacking, and (c). sugar-base and sugar-sugar contacts, all of which contribute to the extra stability of this hairpin structure. The U5:G8 base pair stacks on top of the C4:G9 loop-closing base pair and thus appears as a continuation of the stem. The loop uracil U6 base stacks above U5 base, while the cytosine C7 base protrudes out into the solvent and does not participate in any of the stabilizing interactions. The different sugar pucker and intrinsic bonding interactions within the 2',5'-linked ribonucleotides help explain the unusual stability and conformational properties displayed by 2',5'-RNA tetraloops. These findings are relevant for the design of more effective RNA-based aptamers, ribozymes, and antisense agents and identify the 2',5'-RNA loop as a novel structural motif. 相似文献
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Uppadine LH Gisselbrecht JP Kyritsakas N Nättinen K Rissanen K Lehn JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2549-2565
An extended family of heterometallic [(M1)2(M2)2(L-)4](n+) [2x2] grid-type arrays 1-9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A-C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R') substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the Fe(II) ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R'. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover Fe(II) centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1-9 and their respective mononuclear precursor complexes 10-13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the Co(III)/Co(II) redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the Co(III) or Fe(II) ions can be targeted in grids 2 and 5). The Fe(II) oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of Fe(II) centre in 7 or in 8. Such multistable heterometallic [2x2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity. 相似文献
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A method for the aerobic oxidation of cyclopentane-1,2-diols to the corresponding diketones over a commercial heterogeneous Pt/C catalyst is described. Unsubstituted and 3- or 4-substituted cyclopentane-1,2-diols are oxidized to 1,2-dicarbonyl compounds in good yields under the reported optimized reaction conditions (atmospheric air, 1 mol % of catalyst, 1 equiv of LiOH, aqueous solvents and 60 °C temperature). The method is applicable for producing cyclopentane-1,2-diketones in a scalable manner. 相似文献
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Dan Abramovich Kalle Karu Kenji Matsuki Jaroslaw Wlodarczyk 《Journal of the American Mathematical Society》2002,15(3):531-572
Building on work of the fourth author and Morelli's work, we prove the weak factorization conjecture for birational maps in characteristic zero: a birational map between complete nonsingular varieties over an algebraically closed field of characteristic zero is a composite of blowings up and blowings down with nonsingular centers.