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991.
Gordon PM Fong R Deb SK Li NS Schwans JP Ye JD Piccirilli JA 《Chemistry & biology》2004,11(2):237-246
The 2'-hydroxyl group contributes inextricably to the functional behavior of many RNA molecules, fulfilling numerous essential chemical roles. To assess how hydroxyl groups impart functional behavior to RNA, we developed a series of experimental strategies using an array of nucleoside analogs. These strategies provide the means to investigate whether a hydroxyl group influences function directly (via hydrogen bonding or metal ion coordination), indirectly (via space-filling capacity, inductive effects, and sugar conformation), or through interactions with solvent. The nucleoside analogs span a broad range of chemical diversity, such that quantitative structure activity relationships (QSAR) now become possible in the exploration of RNA biology. We employed these strategies to investigate the spliced exons reopening (SER) reaction of the group II intron. Our results suggest that the cleavage site 2'-hydroxyl may mediate an interaction with a water molecule. 相似文献
992.
Majeti BK Singh RS Yadav SK Bathula SR Ramakrishna S Diwan PV Madhavendra SS Chaudhuri A 《Chemistry & biology》2004,11(4):427-437
Herein, we report enhanced intravenous mouse lung transfection using novel cyclic-head-group analogs of usually open-head cationic transfection lipids. Design and synthesis of the new cyclic-head lipid N,N-di-n-tetradecyl-3,4-dihydroxy-pyrrolidinium chloride (lipid 1) and its higher alkyl-chain analogs (lipids 2-4) and relative in vitro and in vivo gene transfer efficacies of cyclic-head lipids 1-4 to their corresponding open-head analogs [lipid 5, namely N,N-di-n-tetradecyl-N,N-(2-hydroxyethyl)ammonium chloride and its higher alkyl-chain analogs, lipids 6-8] have been described. In stark contrast to comparable in vitro transfection efficacies of both the cyclic- and open-head lipids, lipids 1-4 with cyclic heads were found to be significantly more efficient (by 5- to 11-fold) in transfecting mouse lung than their corresponding open-head analogs (5-8) upon intravenous administration. The cyclic-head lipid 3 with di-stearyl hydrophobic tail was found to be the most promising for future applications. 相似文献
993.
Huang F Zhou L Jones JW Gibson HW Ashraf-Khorassani M 《Chemical communications (Cambridge, England)》2004,(23):2670-2671
Dimers of inclusion complexes were formed from a new cryptand and viologens (paraquats) driven by dipole-dipole and face-to-face pi-stacking interactions as shown by mass spectrometric characterization and X-ray analysis. 相似文献
994.
Hodgson DM Stefane B Miles TJ Witherington J 《Chemical communications (Cambridge, England)》2004,(19):2234-2235
Organolithium-induced ring-opening of aziridines of 2,5-dihydrofuran (5 and 8) and 1,4-dimethoxybut-2-ene (16, 17 and 23) gives 3-substituted 2-aminobut-3-en-1-ols 9-15 and amino ethers 18-20 and 24-26. 相似文献
995.
Fleischer JW Carmon T Segev M Efremidis NK Christodoulides DN 《Physical review letters》2003,90(2):023902
We report the first experimental observation of discrete solitons in an array of optically induced waveguides. The waveguide lattice is induced in real time by illuminating a photorefractive crystal with a pair of interfering plane waves. We demonstrate two types of bright discrete solitons: in-phase self-localized states and the staggered (pi out-of-phase) soliton family. This experiment is the first observation of bright staggered solitons in any physical system. Our scheme paves the way for reconfigurable focusing and defocusing photonic lattices where low-power (mW) discrete solitons can be thoroughly investigated. 相似文献
996.
997.
We have performed systematic studies of intensity-related dynamics of the pulse repetition and carrier-envelope offset frequencies in mode-locked Ti:sapphire lasers. We compared the results far two laser systems that have different intracavity dispersion-compensation schemes. We found that the carrier-envelope phase noise and its dynamic response depend critically on the mode-locking conditions. An intensity-related shift of the laser spectrum was found to be instrumental in interpretations. 相似文献
998.
Cluster expansion methods are developed for calculating the spectral weight contributions of multiparticle excitations--continuum and bound states--to high orders. A complete 13th order calculation is carried out for the alternating Heisenberg chain. For lambda=0.27, relevant to the material Cu(NO3)(2).2.5D(2)O, we present detailed spectral weights for the two-triplet continuum and all bound states. We also examine the variation of the relative weights of one- and two-particle states with bond alternation from the dimerized to the uniform chain limit. 相似文献
999.
This Letter describes dynamic self-assembly in a system of stainless steel spheres ( approximately 1 mm in diameter) rolling on a flat dielectric surface under the influence of an external magnetic field that rotates parallel to the plane of the surface. As the spheres move, they charge triboelectrically. Self-assembly is mediated by two types of electrostatic interactions among these charges: (i) attraction between negatively charged regions of the surface and positively charged spheres and (ii) repulsion between the like-charged spheres. The spheres organize into highly ordered rings as a result of these electrostatic interactions. 相似文献
1000.
E. V. Kuz’min S. G. Ovchinnikov D. J. Singh 《Journal of Experimental and Theoretical Physics》2003,96(6):1124-1130
The spins of Ru5+ ions in Sr2YRuO6 form a face-centered cubic lattice with antiferromagnetic nearest neighbor interaction J≈25 meV. The antiferromagnetic structure of the first type experimentally observed below the Néel temperature T N =26 K corresponds to four frustrated spins of 12 nearest neighbors. In the Heisenberg model in the spin-wave approximation, the frustrations already cause instability of the antiferromagnetic state at T=0 K. This state is stabilized by weak anisotropy D or exchange interaction I with the next-nearest neighbors. Low D/J~I/J~10?3 values correspond to the experimental T N and sublattice magnetic moment values. 相似文献