Analysis of phospholipids using an open‐tubular capillary column with a monolithic layer of molecularly imprinted polymer in capillary electrochromatography‐electrospray ionization‐tandem mass spectrometry

In this study, an open‐tubular capillary electrochromatography (OT‐CEC) column with a monolithic layer of molecularly imprinted polymer (MIP) based on methacrylic acid, ethylene glycol dimethacrylate, and 4‐styrenesulfonic acid was utilized for the simultaneous separation and characterization of phospholipid (PL) molecular structures by interfacing with electrospray ionization‐tandem mass spectrometry (ESI‐MS‐MS). Introducing an MIP‐based monolith along with charged species at the OT column made it possible to separate PL molecules based on differences in head groups and acyl chain lengths in CEC. For the interface of OT‐CEC with ESI‐MS‐MS, a simple nanospray interface utilizing a sheath flow was developed and the resulting OT‐CEC‐ESI‐MS‐MS was able to separate PL standards (phosphatidylserines, phosphatidylethanolamines, phosphatidylglycerols, phosphatidic acid, and lysophosphatidylglycerols). The developed method was applied to human urinary lipid extracts, and resulted in the separation and structural identification of 18 molecules by data‐dependent collision‐induced dissociation.     

Reductive Alkylation Causes the Formation of a Molten Globule-Like Intermediate Structure in <Emphasis Type="Italic">Geobacillus zalihae</Emphasis> Strain T1 Thermostable Lipase

A thermostable lipase from Geobacillus zalihae strain T1 was chemically modified using propionaldehyde via reductive alkylation. The targeted alkylation sites were lysines, in which T1 lipase possessed 11 residues. Far-UV circular dichroism (CD) spectra of both native and alkylated enzyme showed a similar broad minimum between 208 and 222 nm, thus suggesting a substantial amount of secondary structures in modified enzyme, as compared with the corresponding native enzyme. The hydrolytic activity of the modified enzymes dropped drastically by nearly 15-fold upon chemical modification, despite both the native and modified form showed distinctive α-helical bands at 208 and 222 nm in CD spectra, leading us to the hypothesis of formation of a molten globule (MG)-like structure. As cooperative unfolding transitions were observed, the modified lipase was distinguished from the native state, in which the former possessed a denaturation temperature (T _m) in lower temperature range at 61 °C while the latter at 68 °C. This was further supported by 8-anilino-1-naphthalenesulfonic acid (ANS) probed fluorescence which indicated higher exposure of hydrophobic residues, consequential of chemical modification. Based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, a small number of lysine residues were confirmed to be alkylated.     

Examination of Template Structural Effects on CEC Chiral Separation Performance of Molecule Imprinted Polymers Made by a Generalized Preparation Protocol

Some acidic chiral templates were used to prepare open tubular (OT) molecule imprinted polymer (MIP) capillary columns to explore the effects of molecular structures of templates on chiral recognition capabilities and to verify the feasibility of the general MIP preparation protocol introduced in the previous study. The templates are phenyl carboxylic acids and their derivatives. Optimization was carried out for chiral separation of template enantiomers for each MIP column through varying pH and composition of eluent. It was found that the preparation protocol can be successfully applied for the appropriate templates with functional groups fulfilling the three-points interaction rule. The chiral separation performances were quite satisfactory for MIPs of such templates although they are yet inferior to the separation performances of the MIP columns fabricated with the templates of profen drugs (2-arylpropionic acids with a large substituent on the phenyl ring). Subtle variations of the template molecular structures have been found to be critical to enhance chiral recognition ability of the resultant MIP column.     

Antioxidant and antityrosinase activities of various extracts from the fruiting bodies of Lentinus lepideus

Lentinus lepideus is an edible mushroom currently available in Korea. The acetone, methanol and hot water extracts were prepared and assayed for their antioxidant and antityrosinase inhibitory activities. The hot water extract showed the strongest β-carotene-linoleic acid inhibition compared to the other extracts. At 8 mg/mL, the methanolic extract showed a high reducing power of 1.21. The acetone and methanol extracts were more effective in scavenging DPPH radicals than the hot water extract. The strongest chelating effect was obtained from the methanolic extract. Xanthine oxidase and tyrosinase inhibitory activities of the acetonic, methanol and hot water extracts increased with increasing concentration. Gallic acid, chlorogenic acid, vanillin, naringin, naringenin, formononetin, and biochanin-A were detected in the acetonitrile and hydrochloric acid (5:1) solvent extract. This study suggests that fruiting bodies of L. lepideus can potentially be used as a readily accessible source of natural antioxidants.     

Ionic liquid-assisted carboxylation of amines by CO2: a mechanistic consideration

The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO(2) were experimentally and theoretically investigated. The carboxylation reaction of n-butylamine was greatly facilitated by the presence of an IL and the catalytic activity of the IL was strongly affected by the nucleophilicity of the anion. Computational study on the mechanistic aspects of the carboxylation with methylamine with or without the presence of an IL, 1-ethyl-3-methylimidazolium chloride, implies that the activation energies of the transition states and the intermediate ionic species could be lowered significantly through the multi-interactions of the carbonyl group of CO(2) with both cations and anions of the ILs.     

Exposure of defects in GaN by plasma etching

The effect of plasma exposure to n-type GaN surfaces has been examined. Etch pits are formed as a result of preferential sputtering at the sites of threading dislocations. Dark spots which are visible before plasma exposure can be attributed to screw dislocations, while those that emerge after plasma exposure are edge dislocations. The optimum condition for revealing defects clearly is derived, and has been adopted for the study of dislocations in a series of GaN epilayers grown under different conditions. A distinct trend in the dislocation density can be observed as the dopant concentration of the film varies. PACS 61.72.Ff; 68.37.Tj