Isoleucine Residues Determine Chiral Discrimination of Odorant-Binding Protein

Enzymes, receptors, and carrier proteins discriminate between enantiomers of natural and synthetic chemicals. Whereas the structural details of this phenomenon have been investigated in enzymes and receptors, much less is known for carrier proteins of hydrophobic ligands, particularly concerning the contribution of asymmetric centers in the side chains of amino acids to chirally selective binding. Working with a pig odorant-binding protein, we have found that the replacement of either one or both isoleucine residues in the binding pocket by leucines abolishes discrimination of menthol and carvone enantiomers. The results indicate that isoleucines are crucial for chiral discrimination of hydrophobic ligands, and that asymmetry in the side chain may be as important as the overall asymmetry of the protein. The results provide suggestions and guidelines for improving chiral selectivity of binding proteins and enzymes, with consequent applications in the production of enantiomerically pure drugs.     

本舰机动左右舷分辨方法研究

针对传统单根线列阵的左右舷分辩问题，经过深入分析，给出了本舰机动左右舷分辨方法中的一些影响因素，并对机动角度和滞后时间得出了定量结论。文中研究的内容对传统拖曳线列阵声纳的左右舷分辨和战术使用具有参考价值。     

溴化顺式-溴·氨·二(乙二胺)合钴(III)绝对不对称合成与拆分机理

分别用绝对不对称合成和改进的拆分方法制备标题配合物!-( )D-cis-[CoBr(NH3)(en)2]Br2(1)和"-(-)D-cis-[CoBr(NH3)(en)2]Br2(2),以及制备了cis-[CoBr(NH3)(en)2]Br·22H2O(3)(en=1,2-乙二胺).用元素分析、差热-热重、旋光度、UV-Vis、CD光谱等对产物进行了表征.通过CD光谱法获得了绝对不对称合成Co(III)配合物的产物ee值分布图.当利用绝对不对称合成得到的手性Co(III)配合物去“逆向拆分”外消旋溴代樟脑磺酸铵[NH4(dl-BCS)]时只获得部分拆分,初步认为这与交互拆分过程中阴阳离子之间的有效手性识别有关,对于手性Co(III)配合物的绝对不对称合成还提出了一个新的反应机理,即“催化-结晶诱导”机理.     

一厂多商联盟的利润分享方案和整段返利方法的确定

供应链中厂家与商家是一种合作竞争关系.本文从一厂一商型联盟的最大利润化的销售问题入手,在追求厂商供应链利润最大化的前提下,建立了一厂多商型联盟的利润模型.基于该模型,确定了联盟及厂商均可增加利润的分享方案,提出了基于分享方案而实行非固定的整段返利的数学表达式,且对整段返利的机制进行了讨论.研究结论表明用这一方法建立的返利机制,可以保障厂商联盟利润分享方案的实施.     

Linear Discrimination with Adaptive Ridge Classification Rules

This article considers the use of adaptive ridge classification rules for classifying an observation as coming from one of two multivariate normal distributionsN(μ⁽¹⁾, Σ) andN(μ⁽²⁾, Σ). In particular, the asymptotic expected error rates for a general class of these rules are obtained and are compared with that of the usual linear discriminant rule.     

Chiral ligand exchange chromatography on polygalactomannan (Guaran)

Summary The Chiral discriminating properties of the legume seed (Cyamopsis tetragonalobus) polysaccharide, guaran, has been investigated by this laboratory. Due to the presence of cis-hydroxyl groups in its molecule, guaran a galactomannan, forms tetracoordinated polymeric complexes with boron, resulting in cross-linking and gelling. Ligand exchange between the polymeric boron complex and a low molecular weight chiral diol can take place with stereoselectivity. The principle has been applied for the resolution of (±) mandelic acid by using ligand exchange chromatography.     

MALDI coupled to modified traveling wave ion mobility mass spectrometry for fast enantiomeric determination

In this work, the use of MALDI traveling wave ion mobility spectrometry‐mass spectrometry (MALDI‐TWIMS‐MS) for stereoselective structural analysis of direct cleavage and identification of 2‐substituted piperidines obtained through solid‐phase asymmetric synthesis by using heterogeneous 8‐phenylmenthyl‐based chiral auxiliary resins. A strategy for gas‐phase chiral and structural characterization of small molecular weight molecules by using MALDI‐IMS‐MS technique is discussed. Because both MALDI and IMS do not directly offer chiral resolution, an easy methodology by adding a chiral phase is described to carry out in situ online ion/molecule complexation with different chiral analytes inside the mass spectrometer. Piperidine enantiomers were resolved, and separation obtained shows dependence of surface areas. To corroborate this assumption and elucidate the separation mechanism to accomplish an analytical technique by which fast determination of the chirality of molecules may be determined for a wide range organic compound applications, it was performed DFT calculations to determine the cross‐sectional areas of proton‐bound dimer complexes. Drift times are affected by cross‐sectional areas, correlating bigger times with bigger molecular volumes during the ion mobility experiments of proton‐bound dimer complexes.     

Geographical Authentication of Gentiana Rigescens by High-Performance Liquid Chromatography and Infrared Spectroscopy

The chemical characteristics of Gentiana rigescens are extremely variable due to their geographical origins which should be determined to evaluate the quality of this species. Different with other herbs with official tissue for classification materials, the geographical characterization of raw herbal materials on the basis of nonmedicinal parts is rarely discussed. Chromatographic active components were used as references to characterize the chemical profiles of samples from various geographical origins. Based on spectra data matrix of different botanical parts, the chemometric methods of partial least square discrimination analysis and support vector machine discrimination analysis were used to develop mathematical models to classify samples from different geographical origins. In terms of six active components, we found that significant differences were present in the tissue of G. rigescens based on geographical origins. In addition, the region with higher content of gentiopicroside was selected to be the optimal cultivated location. Chemometric results indicated that leaves were the optimal material for geographical characterization of G. rigescens with 100% accuracy by support vector machine while the accuracies of roots, stems, and flowers were 90.91, 96.10, and 97.01%, respectively. Partial least square discrimination analysis showed that accuracy values for roots, stems, leaves, and flowers were 35.65, 67.53, 76.62, and 50.75%, respectively, which also indicated that leaves are the optimal material. In conclusion, northwest Yunnan Province with higher content of gentiopicroside was selected to be the optimal cultivation location. Furthermore, leaves should be used for the most accurate geographical authentication.     

Low Temperature Synthesis of Zeolite Films on Glassy Carbon: Towards Designing Molecularly Selective Electrochemical Devices

Faujasite‐type zeolite films have been grown on glassy carbon electrode surfaces embedded in an epoxy resin matrix by a quasi ambient temperature hydrothermal synthesis. The resulting zeolite modified electrodes are mechanically stable and provide an advantageous combination of electrochemical detection with charge and size selectivities at the molecular level, as demonstrated with the aid of some model electroactive probes or analytes (Ru(NH₃)₆³⁺, Fe(CN)₆^3?, Ru(bpy)₃²⁺, dopamine, ascorbic acid). To act efficiently as a physical molecular sieve barrier between the electrode surface and the external solution, these films must have a thickness of about 0.7 μm. These results open the door for further development of molecular sieving electrochemistry.     

溴化顺式-溴•氨•二(乙二胺)合钴(III)绝对不对称合成与拆分机理*

分别用绝对不对称合成和改进的拆分方法制备标题配合物Λ-(+)D-cis-[CoBr(NH3)(en)2]Br2(1)和Δ-(-)D-cis-[CoBr(NH3)(en)2]Br2(2), 以及制备了cis-[CoBr(NH3)(en)2]Br2·2H2O(3)(en=1,2-乙二胺). 用元素分析、差热-热重、旋光度、UV-Vis、CD 光谱等对产物进行了表征.通过CD 光谱法获得了绝对不对称合成Co(III)配合物的产物ee 值分布图援当利用绝对不对称合成得到的手性Co(III)配合物去“逆向拆分”外消旋溴代樟脑磺酸铵[NH4(dl-BCS)]时只获得部分拆分, 初步认为这与交互拆分过程中阴阳离子之间的有效手性识别有关, 对于手性Co(III)配合物的绝对不对称合成还提出了一个新的反应机理,即“催化-结晶诱导”机理.