DEUSS: a perdeuterated poly(oxyethylene)-based resin for improving HRMAS NMR studies of solid-supported molecules

A novel resin called DEUSS (perdeuterated poly(oxyethylene)-based solid support) has been prepared by anionic polymerization of deuterated [D4]ethylene oxide, followed by cross-linking with deuterated epichlorohydrin. DEUSS can be suspended in a wide range of solvents including organic and aqueous solutions, in which it displays a high swelling capacity. As measured by proton HRMAS of the swollen polymer, the signal intensity of the oxyethylene protons is reduced by a factor of 110 relative to the corresponding nondeuterated poly(oxyethylene)poly(oxypropylene) (POEPOP) resin, thus facilitating detailed HRMAS NMR studies of covalently linked molecules. This 1H NMR invisible matrix was used for the solid-phase synthesis of peptides, oligoureas, and a series of amides as well as their characterization by HRMAS NMR spectroscopy. On-bead NMR spectra of high quality and with resolution comparable to that of liquid samples were obtained and readily interpreted. The complete absence of the parasite resin signals will be of great advantage, for example, for the optimization of multistep solid-phase stereoselective reactions, and for the conformational study of resin-bound molecules in a large variety of solvents.     

蝎型钒氧配合物的合成、结构及量子化学研究

设计合成了两种新型的以聚类吡唑硼酸盐为配体的钒氧配合物VO(acac)[HB(pz)3](1)和VO(acac)[HB(3,5-Me2pz)3]·CH3CN(2). 运用元素分析、 红外光谱和紫外光谱对所合成的配合物进行了表征, 并用X射线衍射测定了它们的晶体结构. 同时, 采用量子化学的Hartree Fock方法和自然轨道分析方法(NBO), 使用3-21G*(6d, 7f)基组计算得到了两个分子体系的分子轨道、原子电荷以及键级, 并对其结构进行了分析.     

Siloxane-Based Nanobuilding Blocks by Reaction Between Silanediol and Trifunctional Silicon Alkoxides

The preparation of nanostructured organic-inorganic materials by assembling of nanobuilding blocks allows controlling the extent of phase interaction, which in its turn governs structure-properties relationships. We present here the synthesis of siloxane-based nanobuilding blocks prepared by reacting diphenylsilanediol with vinyltriethoxysilane and triethoxysilane. The reaction products were obtained by non-hydrolytic condensation between silanediol and ethoxide groups in inert atmosphere, in the presence of pyridine, triethylamine or butyl lithium. Different synthetic conditions were examined by means of ATR-FTIR and NMR spectroscopies, showing the formation of siloxane bonds. In the case of triethoxysilane the reaction carried out in the presence of pyridine leads to Si–H bond preservation in the final product. Air stable products with improved Si–O–Si hydrolytic stability can be obtained by removal of the base after the reaction completion. The condensation products can be described as a mixture of siloxane rings involving difunctional and trifunctional silicon units.     

Linking Chiral Clusters with Molybdate Building Blocks: From Homochiral Helical Supramolecular Arrays to Coordination Helices

The synthesis of four new oxo‐centered Fe clusters ( 1 a – c , 2 ) of the form [Fe^III₃(μ₃‐O)(CH₂=CHCOO)₆] with acrylate as the bridging ligand gives rise to potentially intrinsically chiral oxo‐centered {M₃} trimers that show a tendency to spontaneously resolve upon crystallization. For instance, 1 a , [Fe^III₃(μ₃‐O)(CH₂=CHCOO)₆‐(H₂O)₃]⁺, crystallizes in the chiral space group P3₁ as a chloride salt. Crystallization of 1 b , [Fe₃(μ₃‐O)(C₂H₃CO₂)₆(H₂O)₃]NO₃?4.5H₂O, from aqueous solution followed by recrystallization from acetonitrile also gives rise to spontaneous resolution to yield the homochiral salt [Fe₃(μ₃‐O)(C₂H₃CO₂)₆‐(H₂O)₃]NO₃?CH₃CN of 1 c (space group P2₁2₁2₁). Furthermore, the reaction of 1 a with hexamolybdate in acetonitrile gives the helical coordination polymer {[(Fe₃(μ₃‐O)L₆(H₂O))(MoO₄)‐(Fe₃(μ₃‐O)L₆(H₂O)₂)]?2CH₃CN?H₂O}_∞ 2 (L: H₂C?CHCOO), which crystallizes in the space group P2₁. The nature of the ligand geometry allows the formation of atropisomers in both the discrete ( 1 a – c ) and linked {Fe₃} clusters ( 2 ), which is described along with a magnetic analysis of 1 a and 2 .     

Kinetic versus thermodynamic control during the formation of [2]rotaxanes by a dynamic template-directed clipping process

A template-directed dynamic clipping procedure has generated a library of nine [2]rotaxanes that have been formed from three dialkylammonium salts-acting as the dumbbell-shaped components-and three dynamic, imino bond-containing, [24]crown-8-like macrocycles-acting as the ring-shaped components-which are themselves assembled from three dialdehydes and one diamine. The rates of formation of these [2]rotaxanes differ dramatically, from minutes to days depending on the choice of dialkylammonium ion and dialdehyde, as do their thermodynamic stabilities. Generally, [2]rotaxanes formed by using 2,6-diformylpyridine as the dialdehyde component, or bis(3,5-bis(trifluoromethyl)benzyl)ammonium hexafluorophosphate as the dumbbell-shaped component, assembled the most rapidly. Those rotaxanes containing this particular electron-deficient dumbbell-shaped unit, or 2,5-diformylfuran units in the macroring, were the most stable thermodynamically. The relative thermodynamic stabilities of all nine of the [2]rotaxanes were determined by competition experiments that were monitored by (1)H NMR spectroscopy.     

Solvating,manipulating, damaging,and repairing DNA in a computer

This work highlights four different topics in modeling of DNA: (i) the importance of water and ions together with the structure and function of DNA; the hydration structure around the ions appears to be the determining factor in the ion coordination to DNA, as demonstrated in the results of our MD simulations; (ii) how MD simulations can be used to simulate single molecule manipulation experiments as a complement to reveal the structural dynamics of the studied biomolecules; (iii) how damaged DNA can be studied in computer simulations; and (iv) how repair of damaged DNA can be studied theoretically. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007