A short and efficient synthesis of 1,5-anhydro-d-glucitol 6-phosphate

The important d-glucose and d-glucose 6-phosphate analogues 1,5-anhydro-d-glucitol and 1,5-anhydro-d-glucitol 6-phosphate were prepared from methyl-d-glucoside in high yield and purity. Protecting of the hydroxyl groups as their allyl ether followed by reductive cleavage of the glycosidic linkage with triethylsilane formed the protected anhydroglucitol. No ring rearrangement or ring contraction was observed during the reduction step. Using the PdCl₂-CuCl₂-activated charcoal system, the allyl ether bond was cleaved with a low loading of the catalyst (0.0025 equiv per allyl group). 1,5-Anhydro-d-glucitol 6-phosphate was prepared by the phosphylation of 1,5-anhydro-d-glucitol.     

STRUCTURAL STUDIES ON PYRAZOLYLPYRIDINE LIGANDS AND COMPLEXES. 2. COMPARISONS BETWEEN BISPYRAZOLYLPYRIDINE LINKAGE ISOMERS AND WITH 2,2′,6′,2″-TERPYRIDINE JERZY ZADYKOWICZ

Abstract

Crystal structures were obtained for the 3(C),2′;6′,3″(C)-linked bispyrazolylpyridines 2,6-di(2H-4,5,6,7-tetrahydroindazol-3-yl)pyridine (1), 2,6-di(l-methyl-4,5,6,7-tetrahydroindazol-3-yl)pyridine (2), 2,6-di(1 -(4-ethoxycarbonylphenyl)-4,5,6,7-tetrahydroindazol-3-yl)pyridine (3) and for the homoleptic Ru^II complex of 2, [Ru(2)₂]Cl₂, which crystallized with 7 molecules of CHCl₃. Ligand 1 adopts the inter-and intramolecularly hydrogen-bonded syn,syn rotameric conformation, while 2 and 3 were in the anti,anti forms. Relative to the latter, iigand distortions were assessed in 1 (considered as a H⁺ complex) and [Ru(2)₂]Cl₂. Comparisons were drawn with other tridentate ligands containing a pyridine nucleus, specifically the 1(N),2′;6′,1″(N″) linkage isomers and 2,2′;6′,2″-terpyridine, in both free and Ru^II complexed forms, as well as with their bidentate analogues. Unlike with bidentate ligands, the bonds to the pyridine moiety are shortest, the outer heterocyclic rings are drawn inward and, overall, the ligands remain fairly planar. Flanking substituents remain well splayed out in the 1,2′;6′,1″-linked bispyrazolylpyridines, are more parallel in the 3,2′;6′,3″ linkage isomers and are unfavorably compressed in terpyridines.     

Facile synthesis of multimeric micelles

Bringing it all together: Synthesis of a dimeric micelle (see scheme) is shown to produce specifically linked Janus-like micelles. The reaction conditions for dimeric micelle formation were optimized and the resulting micelles characterized. Trimeric, tetrameric, and multimeric micelles were also synthesized using the same technique.     

Regression Modeling and File Matching Using Possibly Erroneous Matching Variables

Many analyses require linking records from two databases comprising overlapping sets of individuals. In the absence of unique identifiers, the linkage procedure often involves matching on a set of categorical variables, such as demographics, common to both files. Typically, however, the resulting matches are inexact: some cross-classifications of the matching variables do not generate unique links across files. Further, the variables used for matching can be subject to reporting errors, which introduce additional uncertainty in analyses. We present a Bayesian file matching methodology designed to estimate regression models and match records simultaneously when categorical variables used for matching are subject to errors. The method relies on a hierarchical model that includes (1) the regression of interest involving variables from the two files given a vector indicating the links, (2) a model for the linking vector given the true values of the variables used for matching, (3) a model for reported values of the variables used for matching given their true values, and (4) a model for the true values of the variables used for matching. We describe algorithms for sampling from the posterior distribution of the model. We illustrate the methodology using artificial data and data from education records in the state of North Carolina.     

A Generalized Single Linkage Method for Estimating the Cluster Tree of a Density

The goal of clustering is to detect the presence of distinct groups in a dataset and assign group labels to the observations. Nonparametric clustering is based on the premise that the observations may be regarded as a sample from some underlying density in feature space and that groups correspond to modes of this density. The goal then is to find the modes and assign each observation to the domain of attraction of a mode. The modal structure of a density is summarized by its cluster tree; modes of the density correspond to leaves of the cluster tree. Estimating the cluster tree is the primary goal of nonparametric cluster analysis. We adopt a plug-in approach to cluster tree estimation: estimate the cluster tree of the feature density by the cluster tree of a density estimate. For some density estimates the cluster tree can be computed exactly; for others we have to be content with an approximation. We present a graph-based method that can approximate the cluster tree of any density estimate. Density estimates tend to have spurious modes caused by sampling variability, leading to spurious branches in the graph cluster tree. We propose excess mass as a measure for the size of a branch, reflecting the height of the corresponding peak of the density above the surrounding valley floor as well as its spatial extent. Excess mass can be used as a guide for pruning the graph cluster tree. We point out mathematical and algorithmic connections to single linkage clustering and illustrate our approach on several examples. Supplemental materials for the article, including an R package implementing generalized single linkage clustering, all datasets used in the examples, and R code producing the figures and numerical results, are available online.     

Hierarchical structures of correlations networks among Turkey’s exports and imports by currencies

We have examined the hierarchical structures of correlations networks among Turkey’s exports and imports by currencies for the 1996–2010 periods, using the concept of a minimal spanning tree (MST) and hierarchical tree (HT) which depend on the concept of ultrametricity. These trees are useful tools for understanding and detecting the global structure, taxonomy and hierarchy in financial markets. We derived a hierarchical organization and build the MSTs and HTs during the 1996–2001 and 2002–2010 periods. The reason for studying two different sub-periods, namely 1996–2001 and 2002–2010, is that the Euro (EUR) came into use in 2001, and some countries have made their exports and imports with Turkey via the EUR since 2002, and in order to test various time-windows and observe temporal evolution. We have carried out bootstrap analysis to associate a value of the statistical reliability to the links of the MSTs and HTs. We have also used the average linkage cluster analysis (ALCA) to observe the cluster structure more clearly. Moreover, we have obtained the bidimensional minimal spanning tree (BMST) due to economic trade being a bidimensional problem. From the structural topologies of these trees, we have identified different clusters of currencies according to their proximity and economic ties. Our results show that some currencies are more important within the network, due to a tighter connection with other currencies. We have also found that the obtained currencies play a key role for Turkey’s exports and imports and have important implications for the design of portfolio and investment strategies.     

聚乙烯醇的制备及其分子链键合方式的测定

对物理化学综合性实验“聚乙烯醇的制备及其分子链键合方式的测定”进行了研究,得出了最优制备聚乙酸乙烯酯（PVAc）的实验方案。对PVAc醇解得到聚乙烯醇（PVA）,采用黏度法测定了聚乙烯醇被高碘酸盐降解前后的相对分子质量,从而计算出PVA分子链中“头尾相接”和“头碰头”2种键合方式的比例。     

基于复杂网络的时间序列双变量联动波动

选择伦敦金与Au9999下午收盘价格作为样本数据研究时间序列双变量之间的联动波动规律.依据粗粒化方法,将伦敦金与Au9999价格的联动波动状态转化为由5个{P,N,M}字符组成的字符串,每个字符串代表5天的价格联动波动模态.将模态作为节点,模态之间的转化为边,构建价格联动波动复杂网络.运用复杂网络理论对时间序列双变量联动波动模态的统计、变化规律和演化机制进行分析.结果表明:时间序列双变量联动波动模态分布具有幂律性、群簇性和周期性,其联动波动模态主要通过少数几种模态进行转换与演化.本方法不仅可以研究不同类型时间序列双变量联动波动,同时可为多变量联动波动研究提供思路.     

Total synthesis of marinostatin, a serine protease inhibitor isolated from the marine bacterium Pseudoallteromonas sagamiensis

Marinostatin (MST) (1) isolated from a marine organism is a serine protease inhibitor consisting of 12 amino acids with two internal ester linkages that are formed between the β-hydroxyl and β-carboxyl groups, Thr³-Asp⁹ and Ser⁸-Asp¹¹. We synthesized MST by a regioselective esterification procedure employing two sets of orthogonally removable protecting groups at the side-chains of Asp and Ser/Thr. We optimized the esterification conditions to preferentially form the intramolecular ester linkages without any significant aspartimide (Asi) formation at Asp⁹ and Asp¹¹. The inhibitory potency of the synthetic MST against subtilisin (Ki, 0.6 nM) was comparable with a reported value for native MST (1.5 nM).     

Preparation of a new crown ether-based chiral stationary phase containing thioester linkage for the liquid chromatographic separation of enantiomers

A new chiral stationary phase (CSP) containing thioester linkages was prepared by bonding (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid to mercaptopropylsilica gel. The chiral recognition ability of the new CSP was found to be greater than that of the previously reported CSP containing amide linkages in the resolution of the various α-amino acids that were tested, except for that of Met, Ser and Thr. In the resolution of racemic amines and amino alcohols, the new CSP was always better than the one containing amide linkages in terms of the separation factors (α) and the resolutions (R_S). Given the identical elution orders on the two CSPs, it was concluded that the chiral recognition mechanism is not affected by the change of the linkage type. In addition, the new CSP was found to be quite stable under the acidic mobile phase conditions that were utilized, indicating that the thioester linkage is useful as a tethering group.