Extending the possibility of an N-Troc-protected sialic acid donor toward variant sialo-glycoside synthesis

The potential of an N-Troc-protected sialic acid donor, equipped with phenylsulfenyl functionality as a leaving group, has been explored. As a result, the entitled donor was proven to be highly reactive and to have broad applicability toward the synthesis of variant sialo-glycans, which have N-glycolyl, de-N-acetyl, 1,5-lactam and 8-O-sulfo sialic acid analogs.     

集值Lebesgue—Stieltjes积分

本文首先刻划了B(R_ )上的集值测度,其次建立了(R_ B(R_ ))上的集值Lebesgue-Stieltjes积分.最后,进—步建立了集值随机Lebesgue-Stietjes积分的理论.     

A Modified SQP Method and Its Global Convergence

The sequential quadratic programming method developed by Wilson, Han andPowell may fail if the quadratic programming subproblems become infeasibleor if the associated sequence of search directions is unbounded. In [1], Hanand Burke give a modification to this method wherein the QP subproblem isaltered in a way which guarantees that the associated constraint region isnonempty and for which a robust convergence theory is established. In thispaper, we give a modification to the QP subproblem and provide a modifiedSQP method. Under some conditions, we prove that the algorithm eitherterminates at a Kuhn–Tucker point within finite steps or generates aninfinite sequence whose every cluster is a Kuhn–Tucker point.Finally, we give some numerical examples.     

Solid phase synthesis of azapeptides using an automatic synthesizer

Peptides containing azaglycine located terminally or within the backbone have been prepared in the solid phase by means of an automatic synthesizer.     

Rapid and reproducible capillary electrophoretic separation of double-stranded DNA fragments in a simple methyl cellulosic sieving system

Summary A rapid, robust and reproducible method providing excellent separation performance and simplicity using a 0.5% MC-4000 methyl cellulosic sieving medium in DB-1 coated capillaries has been developed. The method is suitable for qualitative comparison of DNA restriction profiles for fragments in the size range 100–1000 base pairs (bp). Efficiencies up to 8.5 million plates/m (1057 bp fragment) were recorded. Peak resolution of 6 bp (291/297 bp, 335/341 bp) and 4 bp (238/242 bp, 341/345 bp) was achieved. In addition, 1 bp partial resolution of 123/124 bp and 298/297 bp was obtained. Run-to-run (n=15), day-to-day (n=4), and capillary-to-capillary (n=3) variations of 0.1–0.2% RSD, 0.3–0.5% RSD, and 0.1–0.3% RSD, respectively, were observed. The MC-4000 sieving matrix was found to be better than hydroxypropyl methyl cellulose and hydroxypropyl cellulose, in terms of both performance and stability in the DB-1 coated capillaries. The efficiency and resolution in DB-WAX capillaries were inferior to those obtained in DB-1 capillaries. The commercially available DB-1 capillaries were stable for months in the sieving medium at pH 8.3 and could be regenerated to provide high efficiency after accidental current breaks.     

脂肪乳剂Intralipid代谢产物的高效液相色谱测定

本文介绍了利用ＨＰＬＣ色谱柱前衍生化技术简便，正确和灵敏地测定血清中游离脂肪酸的方法。在最佳条件下，一些脂肪酸的最低检知量为０．０４μｇ。方法已用于脂肪乳剂Ｉｎｔｒａｌｉｐｉｄ在诱发急性坏死性胰腺炎动物体内代谢产物测定。     

Substitution Reaction of Tetracyanoethylene with Acetone-Anils

The products from the condensation of acetone-anils ( 1 ) and TCNE reaction were characterized after separation. The main products, tricyanoethylene derivatives ( 7–9 ) were isolated with the malonodinitrile derivatives ( 10–12 ), respectively. The [2+2] cycloaddition product ( 13 ), namely 5-methoxy-3,4-(2′,2′,3′,3′-tetracyanocyclobutano)-l,2-dihydro-2,2,4-trimethylquinoline also has been isolated. The distribution of these three products is substituent dependent.     

Chemical reactivity of hypervalent silicon compounds: The local hard and soft acids and bases principle viewpoint

The silicon atom may increase its coordination number to values greater than four, to form pentacoordinated compounds. It has been observed experimentally that, in general, pentacoordinated compounds show greater reactivity than tetracoordinated compounds. In this work, density functional theory is used to calculate the global softness and the condensed softness of the silicon atom for SiH _n F_4−n and SiH _n F _5−n ¹⁻ . The values obtained show that the global and condensed softness are greater in the pentacoordinated compounds than in the tetracoordinated compounds, a result that explains the enhanced reactivity. If the results are analysed through a local version of the hard and soft acids and bases principle, it is possible to suggest that in nucleophilic substitution reactions, soft nucleophiles preferably react with SiH _n F _5−n ¹⁻ , and hard nucleophiles with SiH _n F_4−n .     

Quantitative Comparison of REAPDOR and TRAPDOR Experiments by Numerical Simulations and Determination of H–Al Distances in Zeolites

Quantitative H–Al distances in acid sites of two zeolites with MFI and IFR framework topology were obtained by numerical simulation of ¹H{²⁷Al} rotational echo adiabatic passage double resonance (REAPDOR) experiments. A ²⁷Al offset-dependent data set yields for each resolved ¹H NMR line a corresponding nuclear electric quadrupole coupling constant of the neighboring ²⁷Al site. This information is used for analyzing a second data set for on-resonance irradiation, where the dipolar evolution time (number of rotor cycles) was varied, to yield the ¹H–²⁷Al dipolar coupling constant. Numerical simulations indicate that the REAPDOR method does not depend significantly on the polar angles, defining the orientation of the electric field gradient tensor of ²⁷Al with respect to the Al–H dipolar vector. In contrast, the transfer of populations in double resonance sequence is sensitive to these angles, and it can be thus used to measure them.     

Facile preparation of new unsymmetrical curcumin derivatives by solid-phase synthesis strategy

Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy.