Evaluating cost impacts on reverse logistics using an Economic Order Quantity (EOQ) model with environmental and social considerations

Central European Journal of Operations Research - Societal awareness and legislation changes concerning sustainability have affected how organizations generate value for stakeholders, as well as...     

Highly sensitive and rapid determination of tacrolimus in peripheral blood mononuclear cells by liquid chromatography–tandem mass spectrometry

After solid organ transplantation, tacrolimus is given to prevent rejection. Therapeutic drug monitoring is used to reach target concentrations of tacrolimus in whole blood. Because the site of action of tacrolimus is the lymphocyte, and tacrolimus binds ~80% to erythrocytes, the intracellular tacrolimus concentration in lymphocytes is possibly more relevant. For this purpose, we aimed to develop, improve and validate a UPLC–MS/MS method to measure tacrolimus concentrations in isolated peripheral blood mononuclear cells (PBMCs). PBMCs were isolated using a Ficoll separation technique, followed by a washing step using red blood cell lysis. A cell suspension of 50 μL containing 1 million PBMCs was used in combination with MagSiMUS‐TDM^PREP. To each sample we added 30 μL lysis buffer, 20 μL reconstitution buffer containing ¹³C²H₄‐tacrolimus as internal standard, 40 μL MagSiMUS‐TDM^PREP Type I Particle Mix and 175 μL Organic Precipitation Reagent VI for methanol‐based protein precipitation. A 10 μL aliquot of the supernatant was injected into the UPLC–MS/MS system. The method was validated, resulting in high sensitivity and specificity. The method was linear (r² = 0.997) over the range 5.0–1250 pg/1 × 10⁶ PBMCs. The inaccuracy was <5% and the imprecision was <15%. The washing steps following Ficoll isolation could be performed at either room temperature or on ice, with no effect of the temperature on the results. A method for the analysis of tacrolimus concentrations in PBMCs was developed and successfully validated. Further research will be performed to investigate the correlation between concentrations in PBMCs and clinical outcome.     

New method for sintering silica frits for capillary microcolumns

One of the main steps in the manufacture of robust and efficient packed capillary microcolumns for electro- and capillary chromatography is the generation of porous devices to retain the packed beds. Frits based on sintered silica particles have been found to give the best results in terms of mechanical resistance and efficiency. The conventional procedure to produce these kinds of frits consists in a radial heating of the packed material with either a flame or an electrical resistance, but the frits thus obtained have many drawbacks as a result of the procedure rather than the silica per se as the base material. In the present work we investigated a new approach to produce silica-based retaining devices involving the frontal exposure of a short silica-particle bed packed at the end of a capillary tube. The capillary is radially insulated and frontally exposed to the heat of a muffle oven, generating a transfer of heat that is not radial but rather throughout the capillary axis. This procedure resulted in substantial advantages: an improved radial homogeneity, a protection of the external polyimide, and a generation of extremely short (400–600 μm) frits that were highly permeable and avoided bubble formation.     

Isolation and Immobilization of Influenza Virus-Specific N-SA-α-2,3-Gal Receptors Using Magnetic Nanoparticles Coated with Chitosan and Maackia amurensis Lectin

Avian influenza viruses preferentially bind to sialic acid alpha-2,3-galactose (N-SA-α-2,3-Gal) receptors on epithelial cells. Herein, we describe a procedure we have developed for isolation of N-SA-α-2,3-Gal receptors from porcine trachea using magnetic nanoparticles (NPs) coated with chitosan (NP-Ch) and functionalized with Maackia amurensis lectin (NP-lectin). Magnetic nanoparticles were coated with chitosan in a one-step co-precipitation, and then M. amurensis lectin was immobilized covalently using glutaraldehyde. Lectin coated nanoparticles were incubated with sialic acid enriched fraction of tracheal homogenate, and N-SA-α-2,3-Gal receptor was extracted under magnetic field in two cycles. The presence of 66.4 kDa protein was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The interaction of immobilized receptor (NP-Ch-R) with M. amurensis lectin (NP-Ch-R-L) was demonstrated by Fourier transform infrared spectrometry (FTIR) and thermogravimetric analysis (TGA).     

极化中子衍射及在电子自旋密度研究中的应用

极化中子衍射方法常用于研究含未配对电子化合物中电子自旋密度的分布．分子中电子自旋密度分布从一个独特的角度反映化合物的磁性质．本文介绍极化中子衍射方法的背景知识和基本原理．包括中子源、中子和X射线衍射、极化中子衍射,以及一些常用的实验数据处理方法．选用几个实例总结了用极化中子衍射方法得到的电子自旋密度分布在无机和有机化学中的应用．通过单分子磁体[Fe8O2（OH）12（tacn）6]^8＋和氰基桥联化合物K2[Mn（H2O）2]3[Mo（CN）7]2·6H2O,说明如何用该方法研究金属原子间的磁相互作用;并通过Ru（acac）3这个只含一个未配对电子的化合物来说明如何获得化合物中金属和配体上小的自旋密度;最后介绍了该方法在nitronylnitroxide自由基研究中的应用．     

A unified interpretation of several combinatorial dualities

Several combinatorial structures exhibit a duality relation that yields interesting theorems, and, sometimes, useful explanations or interpretations of results that do not concern duality explicitly. We present a common characterization of the duality relations associated with matroids, clutters (Sperner families), oriented matroids, and weakly oriented matroids. The same conditions characterize the orthogonality relation on certain families of vector spaces. This leads to a notion of abstract duality.     

Sociocultural Factors Influencing Students' Learning in Science and Mathematics: An Analysis of the Perspectives of African American Students

The voices of African American students reveal sociocultural factors that influence their achievement in science and mathematics classes. Using a sociocultural theoretical framework ( Mercer & Covey, 1980 ), this ethnographic study interpreted the perspectives of five African American students as they discussed their learning experiences in science and mathematics classrooms. This framework acknowledges the vulnerability of the educational system to societal influences that inevitably assert cultural values and norms. The students' discussions provided insight into their beliefs about the varied ways in which sociocultural factors impact their learning in science and mathematics classrooms.     

Asymmetric enolate alkylation via templation with chiral synthetic receptors

C₃-Symmetric chiral receptors have been developed for enantioselective alkylation of sodium enolates of active methylene compounds. It has been demonstrated that a 1:1 binding complex forms between these receptors and sodium enolates in THF-d₈/CD₃CN by ¹H NMR titration experiments. Moderate enantiomeric enrichment of the benzylation product of 2-acetylcyclohexanone has been demonstrated using this strategy. Templation of enolate alkylation by synthetic receptors represents a new approach to asymmetric induction.     

Using nitrile-derivatized amino acids as infrared probes of local environment

It is well-known that the C=N stretching vibration in acetonitrile is sensitive to solvent. Therefore, we proposed in this contribution to use this vibrational mode to report local environment of a particular amino acid in proteins or local environmental changes upon binding or folding. We have studied the solvent-induced frequency shift of two nitrile-derivatized amino acids, which are, AlaCN and PheCN, in H(2)O and tetrahydrofuran (THF), respectively. Here, THF was used to approximate a protein's hydrophobic interior because of its low dielectric constant. As expected, the C=N stretching vibrations of both AlaCN and PheCN shift as much as approximately 10 cm(-1) toward higher frequency when THF was replaced with H2O, indicative of the sensitivity of this vibration to solvation. To further test the utility of nitrile-derivatized amino acids as probes of the environment within a peptide, we have studied the binding between calmodulin (CaM) and a peptide from the CaM binding domain of skeletal muscle myosin light chain kinase (MLCK(579-595)), which contains a single PheCN. MLCK(579-595) binds to CaM in a helical conformation. When the PheCN was substituted on the polar side of the helix, which was partially exposed to water, the C=N stretching vibration is similar to that of PheCN in water. In constrast, when PheCN is introduced at a site that becomes buried in the interior of the protein, the C=N stretch is similar to that of PheCN in THF. Together, these results suggest that the C=N stretching vibration of nitrile-derivatized amino acids can indeed be used as local internal environmental markers, especially for protein conformational studies.