Conformational studies of aliphatic secondary ozonides (propene, 1-butene and 1-heptene) by means of FTIR spectroscopy

Ozonization reaction of simple alkenes was studied by means of FT infrared absorption gas spectroscopy. The reaction was performed at 95 K in neat films of the reactants. IR absorption spectra of the gaseous products were recorded. The spectra were analyzed combining experimental results with theoretical calculations performed at B3LYP 6-311++G (3df, 3pd) level. We found that among all theoretically predicted conformers of propene secondary ozonide, only one which has the O-O half-chair configuration for the five membered ring and the radical attached in the equatorial position was present in the sample. Samples of 1-butene and 1-heptene secondary ozonides consist from two conformers of very similar energy (ΔH=0.3 kJ/mol). The most stable conformer for both ozonides is the one with O-O half-chair configuration of the five membered ring and the radical attached in equatorial position and the aliphatic chain in gauche position. The second stable conformer has the aliphatic chain in anti position.     

锂离子蓄电池正极材料LiFePO4研究进展

锂离子电池正极材料正在向着高比能量、长寿命、低成本、环境友好的方向发展,而具有橄榄石结构的LiFePO_4正极材料以其结构稳定、成本低、无污染等优点成为21世纪最理想的绿色电源,但自身也存在缺点。综述了锂离子电池正极材料LiFePO_4的研究进展。系统地阐述了LiFePO_4的晶体结构特征及性能、多种合成方法以及掺杂多种导电材料和控制晶体生长制备纳米粉体对材料性能的影响。对该材料的应用前景进行了展望,并提出了下一步可能的研究趋势。     

Dynamic Light Scattering and NMR Studies of Napin

We analyze the structure of napin (BngNAP1), a storage protein (m.w. 14.5 kDa) from Brassica napus. On the basis of the results of ¹H NMR spectroscopy and dynamic light scattering (DLS) studies, the overall shape and secondary structure of the molecule are estimated.     

Novel siloxane polymers as polymer electrolytes for high energy density lithium batteries

A variety of disubstituted (double-comb) polysiloxane polymers have been prepared containing linear, branched, and cyclic oligoethyleneoxide units, –(OCH₂CH₂)_n–, in the side chains and as part of the siloxane backbone. Copolymers, using mixtures of linear ethylene oxide side chains, were also synthesized. These polymers were doped with LiN(SO₂CF₃)₂ (LiTFSI, 1) and conductivities of the polymer-salt complexes were determined as a function of temperature and doping level. The maximum conductivity of these polymers at 25 ° C was 2.99 ×10^–4, for a copolymer containing equimolar amounts of side chains with n = 5 and 6.     

On the support of midconvex operators

Summary LetX be a real vector space,D a convex subset ofX and (Y, K) an order complete ordered vector space. The following sandwich theorem holds: Iff: D Y is midconvex,g: D Y {– } is midconcave andg f onD, then there exists a Jensen mappingh: D Y {– } such thatg h f onD. Using this theorem we show that a mappingf: D Y is midconvex if and only if it has Jensen support at every point ofD. Moreover, ifX is a Baire topological vector space and (Y, K) is an ordered topological vector space satisfying some additional conditions, then a mappingf: D Y is continuous whenever it has continuous Jensen support at every point ofD. As an application of these results we obtain the equality of some set-classes connected with additive and midconvex operators.Dedicated to the memory of Alexander M. Ostrowski on the occasion of the 100th anniversary of his birth     

Microwave assisted hydrothermal synthesis of tin niobates nanosheets with high cycle stability as lithium-ion battery anodes

SnNb₂O₆ and Sn₂Nb₂O₇ nanosheets were synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. Compared with Sn₂Nb₂O₇ and the previously reported pure Sn-based anode materials, the SnNb₂O₆ electrode exhibited outstanding cycling performance.     

π-facial interactions between Cl and [S4N3]. X-ray crystal structure of [S4N3]Cl

The X-ray structure of [S₄N₃]Cl reveals three independent molecules, which all display π-facial interactions between the Cl⁻ and the pseudo-aromatic [S₄N₃]⁺ rings to produce a structure containing “inverse sandwich” systems.     

Cross-Talk between Overlap Interactions in Biomolecules: A Case Study of the β-Turn Motif

Noncovalent interactions play a pivotal role in regulating protein conformation, stability and dynamics. Among the quantum mechanical (QM) overlap-based noncovalent interactions, n→π* is the best understood with studies ranging from small molecules to β-turns of model proteins such as GB1. However, these investigations do not explore the interplay between multiple overlap interactions in contributing to local structure and stability. In this work, we identify and characterize all noncovalent overlap interactions in the β-turn, an important secondary structural element that facilitates the folding of a polypeptide chain. Invoking a QM framework of natural bond orbitals, we demonstrate the role of several additional interactions such as n→σ* and π→π* that are energetically comparable to or larger than n→π*. We find that these interactions are sensitive to changes in the side chain of the residues in the β-turn of GB1, suggesting that the n→π* may not be the only component in dictating β-turn conformation and stability. Furthermore, a database search of n→σ* and π→π* in the PDB reveals that they are prevalent in most proteins and have significant interaction energies (∼1 kcal/mol). This indicates that all overlap interactions must be taken into account to obtain a comprehensive picture of their contributions to protein structure and energetics. Lastly, based on the extent of QM overlaps and interaction energies, we propose geometric criteria using which these additional interactions can be efficiently tracked in broad database searches.     

Effects of DNA secondary structure on oligonucleotide probe binding efficiency

Secondary structure motifs in nucleic acid probes generally impair intended hybridization reactions and so efforts to predict and avoid such structures are commonly employed in probe design schemes. Another key facet of probe design that has received much less attention, however, is that secondary structure at targeted probe binding site regions may also impair hybridization. Thus, evaluation of both probe and target site secondary structures together should improve hybridization prediction and design effectiveness. Several challenges confound this goal, including imperfect empirical rules and parameters underlying predictions and the fact that folding algorithms scale poorly with respect to sequence length. Here, we attempt to quantify the consequences of target site structure on predicted hybridization using sequences sampled from the human genome. We also provide a methodology for choosing a reasonable “window size” around target sites that is as small as possible without compromising folding algorithm prediction accuracy.     

Capillary gas chromatographic separation of C10–C12 secondary phenylalkanes on modified cyclodextrin stationary phases

The separation of isomers and enantiomers of branched C₁₀-C₁₂ phenylalkanes by gas chromatography on fused silica capillary columns coated with some modified β- and γ-cyclodextrins was studied. It was shown that the separation of positional isomers of C₁₀-C₁₂ phynylalkanes on modified cyclodextrin capillary columns is not better than that on a column coated with modified polyethylene glycol. Differences were found in the enantioselectivity of modified β- and γ-cyclodextrins for the separation of C₁₀-C₁₂ secondary phenylalkane enantiomers. While alkylderivatives of β-CDs resolve enantiomers of 3-phenylalkanes, alkyl derivatives of γ-CD resolve enantiomers of 2-phenylalkanes. Since shape selectivity factors of modified cyclodextrins have indicated no inclusion of the considered solutes in cyclodextrin cavities, enantioselective interactions most probably occur on the outer sphere of cyclodextrins.