Thin-Layer Chromatographic Determination of Alpha-Amyrin in the Bark of Mallotus philippensis Lamk

JPC – Journal of Planar Chromatography – Modern TLC - A simple, precise, and accurate high-performance thin-layer chro-matographic method has been established for determination of...     

Completions of commutative topological rings

Let R be a commutative ring and f a filter of ideals of R. We characterize when the Hausdorff completion of R with the f topology is a product of local Hausdorff completions. This generalizes a theorem of E. Matlis dealing with the completions of an integral domain relative to the topology of the classical torsion theory.     

Investigating out-of-specification test results of chemical composition based on metrological concepts

A metrological background for investigating out-of-specification (OOS) test results of chemical composition is discussed. When an OOS test result is identified, it is important to determine its root causes and to avoid reoccurrence of such results. An investigation of the root causes based on metrological concepts would be beneficial. It includes (1) assessment of validation data of the measurement process, (2) evaluation of the measurement uncertainty contributions, and (3) assessment of metrological traceability chains critical for measurement parameters and environmental conditions influencing the test results. The questions, how can the validation data be applied for this investigation, and how can measurement uncertainty contributions and/or metrological traceability chains change a probability of OOS test results, are analyzed.     

Noncovalent synthesis in aqueous solution and spectroscopic characterization of multi-porphyrin complexes

The interactions of the tetracationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (H(2)TMPyP) and its metallo derivatives (MTMPyP) (where M=copper(II), zinc(II), and gold(III) with the octa-anionic form (at neutral pH) of 5,11,17,23-tetrasulfonato-25,26,27,28-tetrakis(hydroxycarbonylmethoxy)calix[4]arene (C(4)TsTc) lead to a series of complex species whose stoichiometry and porphyrin sequence can be easily tuned. Crystallographic, spectroscopic, and diffusion NMR studies converge towards a common picture in which a central 1:4 porphyrin/calixarene unit serves as a template for the formation of more complex species. These species arise by successive, stepwise addition of single porphyrin molecules above and below the plane of the 1:4 central core to ultimately give a 7:4 complex. Noticeably, the stoichiometry of the various complex species corresponds to the actual concentration ratio of porphyrins and calixarenes in solution allowing the stoichiometry of these species to be easily tuned. This behavior and the remarkable stability of these species allow homo-porphyrin and hetero-(metallo)porphyrin species to be formed with control of not only the stoichiometry but also the sequence of the porphyrin array. The flexibility and ease of this approach permit, in principle, the design and synthesis of porphyrin arrays for predetermined purposes. For example, we have shown that it is very easy to design and obtain mixed porphyrin species in which a foreseen photoinduced electron-transfer is indeed observed.     

Tackling matrix effects during development of a liquid chromatographic-electrospray ionisation tandem mass spectrometric analysis of nine basic pharmaceuticals in aqueous environmental samples

When developing an LC-MS/MS-method matrix effects are a major issue. The effect of co-eluting compounds arising from the matrix can result in signal enhancement or suppression. During method development much attention should be paid to diminish matrix effects as much as possible. The present work evaluates matrix effects from aqueous environmental samples in the simultaneous analysis of a group of nine specific pharmaceuticals with LC-ESI/MS/MS: flubendazole, propiconazole, pipamperone, cinnarizine, ketoconazole, miconazole, rabeprazole, itraconazole and domperidone. Solutions to diminish signal suppression were examined: optimisation of the sample preparation, decrease of the flow rate, and the use of appropriate internal standards. Several SPE-stationary phases were tested in view of retention of the analytes: Oasis HLB, C8, Phenyl, Strata X-polymer RP sorbent and Strata X-polymeric SCX/RP sorbent. Oasis HLB showed the best retention for all analytes. The Oasis HLB SPE-method was optimised, but analyses showed high matrix suppression. Therefore, a second SPE-method, on a phenyl stationary phase (the second best option), was also optimised. A comparison of the matrix effect was made between the two procedures: the phenyl-method was less subject to matrix effects, however, the average matrix effect (ME%) of 46% indicated that matrix effects where still present. Several optimisation options for the phenyl-method were evaluated: addition of a ferric nitrate solution before extraction, application of an alkaline wash step, and use of a second SPE-cartridge, either a NH2-column or a florisil column. A more efficient sample clean-up was achieved by applying the extract after extraction on the phenyl column and after dilution with chloroform, onto a NH2-column (average ME%: 53%). In addition, applying a post-column split (1:5), further reduced matrix effects (average ME%: 65%). Labelled internal standards are the best way to tackle matrix effects, but no such internal standards were commercially available for the analytes of interest. The thorough search and application of four internal standards (structural analogues) was beneficial and compensates the matrix effect partially (average ME%: 83%). In an attempt to reduce the analysis time Speedisk phenyl columns were applied. Under these conditions matrix effects decreased even more while recoveries were between 91 and 109%. Different kinds of surface water samples were analyzed, and different matrix effects were observed. For this reason, standard addition will be used to perform quantitative analysis.     

Experimental parameters affecting sensitivity and specificity of a yeast assay for estrogenic compounds: results of an interlaboratory validation exercise

In vitro assays are considered as the first step in a tiered approach to compound screening for hormonal activity. Although many new assays have been developed in recent years, little attention has been paid towards assay validation. Our objective was to identify critical experimental parameters in a yeast estrogen screen (YES) that affect its sensitivity and specificity. We investigated the role of incubation time, solvent type, yeast inoculum growth stage and concentration on the outcome of the YES. Compounds tested included new and established agonists, antagonists and negative controls, and results were evaluated according to prefixed statistical criteria. In addition, we assessed the assay’s performance in a blind interlaboratory validation exercise (IVE). An incubation time of five days was necessary to positively identify the estrogenic properties of all agonists tested, when dissolved in DMSO. Longer incubation times were required when using an ethanol protocol. Similar estrogenic activity was reported for benzyl butyl phthalate, bisphenol-A, methoxychlor, permethrin and genistein in the IVE. One out of the three laboratories did not classify α,β-endosulfan, dissolved in DMSO, as an estrogen. The same was true for 4,4′-DDE and lindane, dissolved in ethanol, a result that might be attributable to an inappropriate yeast start concentration and/or growth stage. These validation experiments show that under appropriate experimental conditions the YES yields sensitive, specific and reliable results. Therefore it fulfills the requirements as a first step screening assay to evaluate the capacity of chemicals to interact with the estrogen receptor.     

A CCA-secure key-policy attribute-based proxy re-encryption in the adaptive corruption model for dropbox data sharing system

The notion of attribute-based proxy re-encryption extends the traditional proxy re-encryption to the attribute-based setting. In an attribute-based proxy re-encryption scheme, the proxy can convert a ciphertext under one access policy to another ciphertext under a new access policy without revealing the underlying plaintext. Attribute-based proxy re-encryption has been widely used in many applications, such as personal health record and cloud data sharing systems. In this work, we propose the notion of key-policy attribute-based proxy re-encryption, which supports any monotonic access structures on users’ keys. Furthermore, our scheme is proved against chosen-ciphertext attack secure in the adaptive model.