Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate-Mediated Biological Recognition

Useful strategies for the design of molecules to mimic carbohydrates have been developed over the past few years. Mimics of the target may contain new functional groups, a new scaffold, or both (in the schematic representation the natural ligand is shown on the left and the modified version on the right). Many examples of successful carbohydrate mimetics that interfere with sugar–protein and sugar–nucleic acid interactions are known.     

Design and Synthesis of Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate-Mediated Biological Recognition

Carbohydrates have been known as poor candidates for drug development. Recent studies have, however, shown that structurally simplified small molecules as mimics of complex carbohydrates recognized by receptors can be developed as inhibitors of carbohydrate-mediated biological recognition. In addition, small molecules with higher affinity and specificity than the parent ligands can be developed by incorporating additional hydrophobic or charged groups in the carbohydrate mimetic which contains essential functional groups for receptor binding. Representative examples are illustrated in the studies of sialyl Lewis x - selectin interactions, glycosidase and glycosyltransferase reactions and aminoglycoside antibiotic - RNA interactions.     

A New Group Theoretical Approach to the Nonorthogonal Problem in Valence Bond Theory

Introduction There has been a very significarnt resurgence of interest in ab initio valence bond calculations recently. This is because the VB calculation based on nonorthogonal basis can provide intuitive understanding about many very important phenomena in chemistry. However, practical calculation based on nonorthogonal basis is still a great challenge even to deal with a quite small system due to the well-known N! (or     

A Topological Approach to the Problem of Ring Structures

In the mechanized documentation of chemical literature, the definition of structural concept is very important. The usual for definitions for ring structures are inadequate. Essential ring structures are sometimes not recognized on the basis of these definitions and are therefore missed in a literature search. This is particularly true of bridged ring systems. The ring concept and ring condensation types are now redefined on a topological basis in the closest possible analogy to the intuitive approach of the chemist. In complicated molecular structures, these “fundamental rings” can be easily determined, either manually or by means of a programmed computer. The concept of the “ring complex” is defined and suggested as a preliminary screen in literature searches for ring structures. This will save machine time, and so reduce the cost of searches.     

Asphaltenes Flocculation in Light Crude Oils: A Chemical Approach to the Problem

This article describes the state‐of‐the‐art of the phenomena associated to the flocculation and precipitation of asphaltenes as well as the solutions used to prevent this kind of phase behavior problem in a Brazilian light (42⁰ API) crude oil. A discussion on how to diagnose this light crude tendency to flocculate its low concentration (0.3%) asphaltenes and on the approach to (chemically) mitigate the phenomena also are provided. To address the problem a comprehensive study was carried out as follows: 1) Scoping trials to assess the so‐called asphaltenes deposition envelope (ADE) of the crude, a key parameter to design the chemical injection system and to production management. To accomplish that a mono‐phase crude oil sample was collected and tests were performed on a PVT cell equipped with a solid detection system. These PVT results enabled us to evidence the reversibility of the asphaltenes flocculation process—above the bubble point pressure—which is in agreement with the Hildebrand theory for macromolecules in hydrotopic solutions and; 2) A suite of field experiments to address the following issues: asphaltenes flocculation inhibitor dosage optimization; how to collect inhibitor‐free oil samples for well site evaluation; adaptation of the existing analytical methods for well site analysis and: setting up guidelines against which measure the inhibitor performance in this low‐asphaltenes concentration crude oil.

The engineered solutions that ended up being developed from this comprehensive study are now incorporated to Petrobras flow assurance solutions portfolio.     

A New Approach to a-Bromochalcones

a-Bromo benzoylmethylene triphenylphosphorane 3 has been synthesized by the reaction of benzoylmethylene triphenylphosphorane 1 with N-bromosuccinimide in the yield of 87% and can react with aromatic aldehydes 4 to giveα-bromochalcones 5 in good yields.     

A New Approach to Glycopeptides

In only three or four steps glycosylated dipeptide and tripeptide fragments, respectively (see scheme), can be obtained from hydroxy amino acids by using a novel protecting group/activation concept. The method presented is even superior to the pentafluorophenyl ester method.     

A New Approach to the Synthesis of Bergapten

In this study, bergapten was synthesized in a yield of 55% from phloroglucinol as starting material, via a novel approach including monomethylation, Hoesch reaction, acetylation, deacetoxylation, Pechmann condensation and 2,3-dichloro-5,6- dicyano-1,4-benzoquinone(DDQ) dehydrogenation. With the adoption of the acetylation of enol tautomer, the deacetoxylation and the DDQ dehydrogenation, the novel approach differs greatly from the processes reported previously, though the starting material was the same or similar to those used on previous synthetic processes. The newly adopted reaction underwent easily, affording all reactions in high yields, especially acetylation and deacetoxylation and DDQ dehydrogenation in almost quantitative yields, ensuring a final yield higher than those previously reported.     

Hydrodynamic Model for Plasmonics: A Macroscopic Approach to a Microscopic Problem

In this concept, we present the basic assumptions and techniques underlying the hydrodynamic model of electron response in metals and demonstrate that the model can be easily incorporated into computational models. We discuss the role of the additional boundary conditions that arise due to nonlocal terms in the modified equation of motion and the ultimate impact on nanoplasmonic systems. The hydrodynamic model captures much of the microscopic dynamics relating to the fundamental quantum mechanical nature of the electrons and reveals intrinsic limitations to the confinement and enhancement of light around nanoscale features. The presence of such limits is investigated numerically for different configurations of plasmonic nanostructures.     

Filled Polysilsesquioxanes: A New Approach to Chemical Sensing

Summary : In an attempt to investigate new polymeric materials as constituents of an e-nose we focus our attention on a new emerging class of versatile three-dimensional polyhedral silicon polymers, called polysilsesquioxanes, containing nanosized inorganic cages. Such hybrid amphiphilic materials offer exceptional opportunities to create composites with singular properties. In particular we found that the polyhedral organosilsesquioxane (POSS) cages covalently attached to the polymer backbone as side-chain act as an “internal” filler with a nanometric homogeneous dispersion. We show how it is possible to fabricate sensing devices based on selected POSS matrix and, by a suitable choice of other “external” home-made fillers, (e.g. graphite, copper, silicon, zinc and their alloys) obtained by mechanical milling the response of the resulting composites towards different classes of compounds can be tuned. In particular we fabricated a new high sensitive relative humidity device, exhibiting a fivefold response change for relative humidity changing in the range 0% to 100%. This behaviour can not be modelled on the basis of the matrix swelling operating mechanism. Rather, the combined effect of the matrix and the filler has to be invoked in order to explain the formation of nanopores inside the material that are responsible of the porous behavior of our sensors.     

清洁工艺生产铅

一种新的湿法炼铅方法——碳酸化转化法，铅转化率达９０％以上，元素硫生成率为８０％以上。ＰｂＣＯ３可电解成金属铅或制成１０种铅化工产品。元素硫便于储存和运输。矿石中的ＦｅｘＳｙ对转化有催化作用。该方法彻底消除了火法炼铅过程中铅蒸气和二氧化硫对环境的污染，实现了清洁生产。     

A New Synthetic Approach to Salmeterol

In the present work a short and convenient route for the synthesis of salmeterol from salicylaldehyde has been developed.     

异黄酮类化合物的合成新方法

提出了一种新颖的合成异黄酮类化合物1, 2和3的方法. 以1,3-二甲氧基苯或1,3,5-三甲氧基苯为原料, 经Hoesch反应或Friedel-Crafts酰化反应、脱甲基反应、增碳关环一系列反应得到关键的甲氧基异黄酮化合物, 然后甲氧基异黄酮经过不同浓度氢溴酸的选择性水解反应制得含一个或多个羟基的异黄酮类化合物.     

A New Synthetic Approach to Elvucitabine

A new synthetic approach to elvucitabine started from L-xylose via the reactions of 10 steps in an overall yield of 20% was developed. The key steps included trimethylsilyl trifluoromethanesulfonate(TMSOTf)-mediated stereocontrolled β-glycosidation and exquisite choice of chloroacetyl group for the protection of hydroxyl groups as well as the corresponding deprotection under notably mild conditions. The structure of elvucitabine, in particular, the stereochemistry thereof, was unambiguously determined by comparison of the physical properties, such as ¹H NMR data and the specific rotation, of the synthesized sample with those reported.     

茶螺烷酮合成的新工艺

以α-紫罗兰酮为原料,经间氯过氧苯甲酸环氧化、甲醇钠开环、超声波辐射Pd/C催化甲酸铵选择性碳碳双键加H、硼氢化钠还原、脱水环化及乙酰丙酮亚钴催化烯丙位氧气氧化等6步反应,以总收率52.6％合成了食用香料2,6,10,10-四甲基-1-氧杂-螺[4.5]-6-癸烯-8-酮(茶螺烷酮)。 用IR、1H NMR、MS谱及元素分析等测试技术表征了产物的结构和组成。     

A New Approach to the Synthesis of Cortical Steroids

A new bondset for cortical steroid synthesis is developed from the dual concepts of convergent assembly and multiple construction. A short synthesis on this bondset is presented in which the final bond construction by electrocyclization took an unwanted course. Stereocontrol is discussed separately.     

Fluorescence Analysis: A New Approach

Abstract

The Video Fluorometer is a new instrument for fluorescence analysis which offers significant advantages for the study of complex systems. This instrument can acquire 241 fluorescence spectra, taken at 241 different exciting wavelengths in 16.7 milliseconds. These results are displayed in a three-dimensional graphical format in real time. Coupled with a laboratory computer, this instrument should provide new algorithms for the analysis of luminescence spectra of multi-component systems.     

一种制备镍纳米颗粒的新方法

通过超声照射使2-乙基己酸镍和金属钠在液体石蜡中发生置换反应, 成功地制备了具有六方晶型结构的表面修饰镍纳米颗粒, 并采用多种现代分析手段如TEM、ED、XRD、XPS和TG对所制备的产品进行结构、形貌和热稳定性能的表征. 结果表明, 所制得的镍纳米颗粒粒径较小, 分布范围在7～43 nm之间, 并有着良好的热稳定性能.