BMD-TLC — the Useful Technique for Quantitative Analysis of Chelidonine,Chelerithrine and Berberine in Herbal Drugs

JPC – Journal of Planar Chromatography – Modern TLC - Three step bivariant multiple development thin-layer chromatography (BMD-TLC) technique was used in the quantitative analysis of...     

Atomic-scale pathway of the pyramid-to-dome transition during ge growth on Si(001)

By high resolution scanning tunneling microscopy, we investigate the morphological transition from pyramid to dome islands during the growth of Ge on Si(001). We show that pyramids grow from top to bottom and that, from a critical size on, incomplete facets are formed. We demonstrate that the bunching of the steps delimiting these facets evolves into the steeper dome facets. Based on first principles and Tersoff-potential calculations, we develop a microscopic model for the onset of the morphological transition, able to reproduce closely the experimentally observed behavior.     

Morphological and compositional evolution of the ge/si(001) surface during exposure to a si flux

By using scanning tunneling microscopy we found that the surface reconstruction of Ge/Si(001) epilayers evolves from (M x N) to (2 x N), and eventually to (2 x 1), during exposure to a Si flux. This sequence appears to be just the inverse of that observed during the growth of Ge or SiGe alloys on Si(001). However, molecular dynamics simulations supported by ab initio calculations allow us to interpret this morphological evolution in terms of Si migration through the epilayer and complex Si-Ge intermixing below the top Ge layer.     

Ion Mobility Mass Spectrometry Measures the Conformational Landscape of p27 and its Domains and how this is Modulated upon Interaction with Cdk2/cyclin A

Intrinsically disordered proteins have been reported to undergo disorder‐to‐order transitions upon binding to their partners in the cell. The extent of the ordering upon binding and the lack of order prior to binding is difficult to visualize with classical structure determination methods. Binding of p27 to the Cdk2/cyclin A complex is accompanied by partial folding of p27 in the KID domain, with the retention of dynamic behavior for function, particularly in the C‐terminal half of the protein. Herein, native ion mobility mass spectrometry (IM‐MS) is employed to measure the intrinsic dynamic properties of p27, both in isolation and within the trimeric complex with Cdk2/cyclin A. The trimeric Cdk2/cyclin A/p27‐KID complex possesses significant structural heterogeneity compared to Cdk2/cyclin A. These findings support the formation of a fuzzy complex in which both the N‐ and C‐termini of p27 interact with Cdk2/cyclin A in multiple, closely associated states.     

Thermal parameters determination of Co–Al–W as-cast alloy homogenization by DTA analysis

The γ–γ′ Co-based superalloys are newly developed class of refractory alloys which may replace commercial Ni-based superalloys owing to their favorable properties at high temperature. In case of new Co-based superalloys, the heat treatment aims to obtain microstructure composed of appropriate volume fraction of small cuboidal γ′-Co₃(Al,W) precipitates within the γ-Co matrix. However, due to a high tendency to interdendritic segregations of alloying elements, the alloys based on Co–Al–W system should be normally homogenized before further steps of heat treatment (solutionizing and aging). In this study, thermal analysis was applied for determination of temperature range for primary heat treatment of the Co–9Al–9W (at.%). The differential thermal analysis (DTA) measurements were carried out on the thermal analyzer NETZSCH STA 449 F3 Jupiter. On the base of obtained results, respectively, solvus of γ′ phase and solidus temperatures were determined, as well as the thermal range of Co₃W (DO₁₉) phase precipitation. As a consequence, the heat treatment without homogenizing (only solution and aging) was proposed as a most suitable way to obtain beneficial microstructure.     

The use of thin-layer chromatography in the assessment of the quality of lutein-containing dietary supplements

Bivariant multiple development thin-layer chromatography technique (BMD–TLC) along with high-performance liquid chromatography–diode array detection–electrospray ionization–mass spectrometry (HPLC–DAD–ESI–MS) analysis was used in determination of lutein or lutein mixed with zeaxanthin in eight dietary supplements. The developed two-step TLC separation procedure combined purification, compaction of samples and separation of the analyzed compounds what significantly shortened and simplified samples preparation. Qualitative analysis was based on co-chromatography with reference substances and HPLC–DAD–ESI–MS analysis. It was revealed that three of eight dietary supplements did not contain lutein. In turn, quantitative analysis with the use of developed TLC conditions along with densitometry showed that the amount of lutein or its mixture with zeaxanthin in the others differed from that claimed by producers.

     

Thermogravimetric investigations of new γ-γ′ cobalt-based superalloys

The aim of the study is characterization of high-temperature oxidation behavior of new Co-based superalloys by thermogravimetry (TG). The following alloys have been taken into account: Co–9Al–9W, Co–20–Ni–7Al–7W, Co–10Al–5Mo–2Nb and Co–20Ni–10Al–5Mo–2Nb (at.%). The thermogravimetric analysis was carried out in the temperature range 40–1200 °C of heating rate 5° min^?1. The investigation was performed using the thermal analyzer NETZSCH STA 449 F3 Jupiter. TG–DTG plots showed oxidation behavior up to 1200 °C and indicated the temperatures of further isothermal oxidation examinations. The oxidation behavior of basic Co–9Al–9W (at.%) alloy was compared to W-free Co–10Al–5Mo–2Nb and Co–20Ni–10Al–5Mo–2Nb (at.%) alloys. The obtained data showed different oxidation behavior dependably on the type of alloying elements. Moreover, the effect of Ni addition on oxidation performance was determined. The scales grown on Co-base superalloys after thermogravimetry were evaluated by means of scanning electron microscopy and energy dispersive spectroscopy.     

Simple synthesis of some pentafluoropropenyl derivatives of pyrimidine and purine based on addition-elimination reaction

Various pentafluoropropenyl derivatives of pyrimidine and purine bases have been obtained in good to high yield. The procedure involves the reaction of appropriate lithium derivatives prepared from both electron-rich and electron-poor pyrimidines, with the hexafluoropropene at a low temperature, via an addition-elimination process. Organolithiums of pyrimidine and purine bases give addition-elimination products as E/Z mixtures, whereas the products of the reaction of lithium amide of protected inosine with hexafluoropropene contain traces of an addition product as well as the stable perfluoroenamine. The methodology proposed allows a series of perfluorovinyl nucleobases to be obtained quickly and conveniently.     

Electron and hole focusing in CoSi2/Si(111) observed by ballistic electron emission microscopy

In ballistic electron emission microscopy (BEEM) the propagation of hot carriers in thin metal films has long been treated using a free electron model. While the model explains many experimental findings, it cannot account for the lateral resolution observed for both electrons and holes on epitaxial CoSi(2)/Si(111), where interfacial point defects of atomic size appear as small as 1.3 nm, even below a 5.6 nm thick film. We present ab initio calculations explaining this high resolution in terms of conduction (valence) band structure focusing of electrons (holes), according to a recent Green's function approach to the BEEM process.     

Thermal analysis of W-free Co–(Ni)–Al–Mo–Nb superalloys

CuAl layered double hydroxide (CuAl-LDH) was synthesized by co-precipitation. Sodium phenyl phosphate (SPP) and sodium dodecyl sulfate (SDS) are used to modify CuAl-LDH for preparing CuAl-(SPP)LDH and CuAl-(SDS)LDH, which were incorporated into epoxy resin (EP) to obtain EP/CuAl-(SPP)LDH and EP/CuAl-(SPP)LDH nanocomposites. The results indicate that SPP and SDS are intercalated into the interlayers of CuAl-LDH, and CuAl-(SPP)LDH has larger layer spacing than CuAl-(SDS)LDH. The thermal stability and flame-retardant performances of EP/CuAl-(SPP)LDH nanocomposites were better than those of EP/CuAl-(SDS)LDH composites. Compared with those of EP/4CuAl-(SDS)LDH nanocomposites, the peak heat release rate (PHRR) of EP/4CuAl-(SPP)LDH nanocomposites is reduced 25.8% and 55.6%, and peak smoke production rate (PSPR) value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, value of EP/4CuAl-(SPP)LDH nanocomposites is reduced 27.6% and 46.2%, respectively. The improved flame retardancy and smoke suppression performances of EP/CuAl-(SPP)LDH nanocomposites were attributed to the combination of copper compounds and SPP, promoting the formation of swollen, continuous and compact char layers on the surface of EP nanocomposites during combustion, eventually restraining the decomposition of EP nanocomposites.