The NMR structure of [Xd(C2)]4 investigated by molecular dynamics simulations

The i‐motif tetrameric structure is built up from two parallel duplexes intercalated in a head‐to‐tail orientation, and held together by hemiprotonated cytosine pairs. Two topologies exist for the i‐motif structure, one with outermost 3′ extremities and the other with outermost 5′ extremities, called the 3′E and 5′E topology, respectively. Since the comparison of sugar and phosphate group interactions between the two topologies is independent of the length of the intercalation motif, the relative stability of the 3′E and 5′E topologies therefore should not depend on this length. Nevertheless, it has been shown that the 3′E topology of the [d(C2)]4 is much more stable than the 5′E topology, and that the former is the only species observed in solution. In order to understand the reason for this atypical behavior, the NMR structure of the [Xd(C2)]4 was determined and analyzed by molecular dynamics simulations. In the NMR structure, the width of the narrow groove is slightly smaller than in previously determined i‐motif structures, which supports the importance of phosphodiester backbone interactions in the structure stability. The simulations show that the stacking of cytosines, essential for the i‐motif stability, is produced by a similar and non‐negative twisting of the phosphodiester backbones. The twisting is induced by an interaction between the backbones; the [Xd(C2)]4 in 5′E topology, exhibiting very limited interaction between the phosphodiester backbones, is thus unstable. Copyright © 2002 John Wiley & Sons, Ltd.     

中国近代纺织品纹样的演进

晚清民国初是中国纺织服装史上的一个重要时期。中国近代纺织品纹样的演进具有如下特点:(1)中国近代中西文明撞击交融的特定背景,在很大程度上决定了纺织品纹样的演化进程;(2)传统纺织品纹样进一步风格化和程式化,广义的吉祥纹样成了唯一的主题;(3)纺织品纹样中的外来因素趋增,甚至出现了外来纹样的直接运用;(4)生活方式和审美观念的变化造成条格纹样的盛行且成为当时的基本纹样。近代纺织品纹样既有繁琐拼凑之弊又有融蓄中西之长。     

Detecting conserved secondary structures in RNA molecules using constrained structural alignment

Constrained sequence alignment has been studied extensively in the past. Different forms of constraints have been investigated, where a constraint can be a subsequence, a regular expression, or a probability matrix of symbols and positions. However, constrained structural alignment has been investigated to a much lesser extent. In this paper, we present an efficient method for constrained structural alignment and apply the method to detecting conserved secondary structures, or structural motifs, in a set of RNA molecules. The proposed method combines both sequence and structural information of RNAs to find an optimal local alignment between two RNA secondary structures, one of which is a query and the other is a subject structure in the given set. The method allows a biologist to annotate conserved regions, or constraints, in the query RNA structure and incorporates these regions into the alignment process to obtain biologically more meaningful alignment scores. A statistical measure is developed to assess the significance of the scores. Experimental results based on detecting internal ribosome entry sites in the RNA molecules of hepatitis C virus and Trypanosoma brucei demonstrate the effectiveness of the proposed method and its superiority over existing techniques.     

Hierarchically Clustered HMM for Protein Sequence Motif Extraction with Variable Length

Protein sequence motifs extraction is an important field of bioinformatics since its relevance to the structural analysis. Two major problems are related to this field：（1） searching the motifs within the same protein family; and（2） assuming a window size for the motifs search. This work proposes the Hierarchically Clustered Hidden Markov Model（HC-HMM） approach, which represents the behavior and structure of proteins in terms of a Hidden Markov Model chain and hierarchically clusters each chain by minimizing distance between two given chains＇ structure and behavior. It is well known that HMM can be utilized for clustering, however, methods for clustering on Hidden Markov Models themselves are rarely studied. In this paper, we developed a hierarchical clustering based algorithm for HMMs to discover protein sequence motifs that transcend family boundaries with no assumption on the length of the motif. This paper carefully examines the effectiveness of this approach for motif extraction on 2593 proteins that share no more than 25% sequence identity. Many interesting motifs are generated.Three example motifs generated by the HC-HMM approach are analyzed and visualized with their tertiary structure.We believe the proposed method provides a unique protein sequence motif extraction strategy. The related data mining fields using Hidden Markova Model may also benefit from this clustering on HMM themselves approach.     

Anthracene-based ureidopyridyl fluororeceptor for dicarboxylates

Anthracene-labelled ureidopyridyl sensor 1 was designed and synthesized. The emission of the sensor increased in presence of dicarboxylates. The binding properties were studied using ¹H NMR, fluorescence and UV-vis spectroscopic methods. The sensor 1 shows modest selectivity for 1,4-phenylenediacetate.     

Assembly of Tungsten‐Oxide‐Based Pentagonal Motifs in Solution Leads to Nanoscale {W48}, {W56}, and {W92} Polyoxometalate Clusters

We report an approach to synthesize molecular tungsten‐oxide‐based pentagonal building blocks, in a new {W₂₁O₇₂} unit, and show how this leads to a family of gigantic molecular architectures including [H₁₂W₄₈O₁₆₄]^28? {W₄₈}, [H₂₀W₅₆O₁₉₀]^24? {W₅₆}, and [H₁₂W₉₂O₃₁₁]^58? {W₉₂}. The {W₄₈} and {W₅₆} clusters are both dimeric species incorporating two {W₂₁} units and the {W₅₆} species is the first example of a molecular metal oxide cluster containing a chiral “double‐stranded” motif which is stable in solution as confirmed by mass spectrometry. The {W₉₂} anion having four {W₂₁} units is one of the largest transition metal substituted isopolyoxotungstates known.     

某铅锌矿区儿童发铅水平及对健康影响的调查

为了解某铅锌矿区铅对儿童的危害情况,探讨铅污染对儿童智商及生长发育的影响,选择某铅锌矿区某冶炼厂区居住5年以上,年龄在6～10岁的儿童186名作为观察组,同时选择居住在距矿区40 km以外、年龄在6～10岁的儿童156名作为对照组,进行了儿童一般状况的体格检查(包括:缺钙、脱发、贫血、易患感冒)、智商测定(包括:语言智...     

Strongly decussated π-stacking in a Ag(I)–Co(III) complex containing a Ag2Co2 44 square tile motif

A mixed Co–Ag complex with 2,6-dicarboxypyridine (H₂PDC), AgCo(PDC)₂, was synthesized under hydrothermal conditions. The complex adopts a 2D layer structure formed by intramolecular π-stacking. Each Co(III) ion is chelated by two 2,6-dicarboxypyridine anions to give the [Co(PDC)₂]^? anion that is further extended by Ag⁺ to form 4⁴ square grids.