Blue upconversion emission from Tm<Superscript>3+</Superscript> sensitized by Nd<Superscript>3+</Superscript> in aluminum oxide crystalline ceramic powders

Upconversion (UC) emission in thulium (Tm³⁺) and neodymium (Nd³⁺) co-doped aluminum oxide ceramic powders prepared by combustion synthesis was investigated at room temperature using a continuous wave laser operating at 800 nm. Our sample containing Tm³⁺ (1 wt.%) did not show any UC emission but our sample co-doped with Tm³⁺ and Nd³⁺ in 1:2 wt.% proportion presented blue (∼480 nm) UC intensity more than one order of magnitude larger than our sample co-doped with Tm³⁺ and Nd³⁺ in 1:1 wt.% proportion. X-ray diffraction data showed the presence of α-Al₂O₃ and REAlO₃ (RE=Tm or Nd) crystalline phases in co-doped powders, while the singly doped powder has only α-Al₂O₃ phase. Our results show that the UC emission efficiency of Tm³⁺ and the host crystalline structure can be tailored by manipulating the Nd³⁺ doping concentration.     

Effect of molecular surface packing on the enzymatic activity modulation of an anchored protein on phospholipid Langmuir monolayers

The catalytic activity of a glycosylphosphatidylinositol (GPI)-anchored alkaline phosphatase has been studied in Langmuir phospholipid monolayers at different surface pressures. The enzyme substrate, p-nitrophenyl phosphate, was injected into the subphase of mixed enzyme/lipid Langmuir monolayers. Its hydrolysis product was followed by monitoring the absorbance at 410 nm in situ in the monolayer subphase of the Langmuir trough. Several surface pressures, corresponding to different molecular surface densities, were attained by lateral compression of the monolayers. The morphology of the monolayers, observed by fluorescence microscopy, showed three different types of domains owing to the heterogeneous partition of the enzyme within the mixed enzyme/lipid film. The catalytic activity was modulated by the enzyme surface density, and it increased until a pressure of 18 mN/m was reached, but it decreased significantly when the equilibrium in-plane elasticity (surface compressional modulus) increased more noticeably, resulting in alterations in the interface morphology. A model for the modulation of the enzyme orientation and catalytic activity by lipid/enzyme surface morphology and enzyme surface packing at the air/liquid interface is proposed. The results might have an important impact on the comprehension of the enzymatic activity regulation of GPI-anchored proteins in biomembranes.     

中国煤的磁共振研究

本文首次报道了用CPMAS,CRAMPS和DNP NMR研究中国煤的结果。证实了某些低变质程度的中国煤存在着异常的性质,预示着这些煤有特殊的化学结构。     

New Insights on Non-Enzymatic Oxidation of Ganglioside GM1 Using Mass Spectrometry

Gangliosides are acidic glycosphingolipids that are present in cell membranes and lipid raft domains, being particularly abundant in central nervous systems. They participate in modulating cell membrane properties, cell–cell recognition, cell regulation, and signaling. Disturbance in ganglioside metabolism has been correlated with the development of diseases, such as neurodegenerative diseases, and in inflammation. Both conditions are associated with an increased production of reactive oxidation species (ROS) that can induce changes in the structure of biomolecules, including lipids, leading to the loss or modification of their function. Oxidized phospholipids are usually involved in chronic diseases and inflammation. However, knowledge regarding oxidation of gangliosides is scarce. In order to evaluate the effect of ROS in gangliosides, an in vitro biomimetic model system was used to study the susceptibility of GM1 (Neu5Acα2-3(Galβ1-3GalNAcβ1-4)Galβ1-4Glcβ1Cer) to undergo oxidative modifications. Oxidation of GM1 under Fenton reaction conditions was monitored using high resolution electrospray ionization-mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS). Upon oxidation, GM1 underwent oxidative cleavages in the carbohydrate chain, leading to the formation of other gangliosides GM2 (GalNAcβ1-4Gal(Neu5Acα2-3)1-4Glcβ1Cer), GM3 (Neu5Acα2-3Galβ1-4Glcβ1Cer), asialo-GM1 (Galβ1-3GalNAcβ1-4Galβ1-4Glcβ1Cer), asialo-GM2 (GalNAcβ1-4Galβ1-4Glcβ1Cer), of the small glycolipids lactosylceramide (LacCer), glucosylceramide (GlcCer), and of ceramide (Cer). In addition, oxygenated GM1 and GM2 (as keto and hydroxy derivatives), glycans, oxidized glycans, and oxidized ceramides were also identified. Nonenzymatic oxidation of GM1 under oxidative stress contributes to the generation of other gangliosides that may participate in the imbalance of gangliosides metabolism in vivo, through uncontrolled enzymatic pathways and, consequently, play some role in neurodegenerative processes.

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Studies on the homogeneous acetylation of cellulose in the novel solvent dimethyl sulfoxide/tetrabutylammonium fluoride trihydrate

The novel solvent dimethyl sulfoxide (DMSO)/tetrabutylammonium fluoride trihydrate (TBAF . 3H(2)O) was studied for acetylation of linters cellulose. In order to control the degree of substitution (DS), acetylation of the macromolecule was carried out at different reaction time and temperature, molar ratio of reactants, as well as under variation of the concentration of TBAF . 3H(2)O in solution. Cellulose acetate (CA) was accessible with DS ranging from 0.43 to 2.77. The change in concentration of TBAF . 3H(2)O in DMSO showed a strong influence on DS. The most appropriate reaction conditions for acetylation of linters cellulose regarding maximal DS were evaluated. The structure of the CA was characterized by means of FTIR and NMR spectroscopy. The solubility of the CA depends not only on the DS but also on the reaction conditions applied, indicating a different distribution of acetate moieties both within and between polymer chains.     

Laser-induced fluorescence and UV detection of derivatized aldehydes in air samples using capillary electrophoresis

In this work, two capillary zone electrophoresis methodologies using UV absorption detection (214 nm) and laser-induced fluorescence detection (He/Cd laser, 325 nm excitation, 520 nm emission) of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde and acrolein) derivatized with dansylhydrazine (DNSH, 5-dimethylaminonaphthalene-1-sulfohydrazide) were proposed and validated. The aldehydes react with DNSH to form negatively charged molecules in methanolic medium. In both methodologies, nine DNSH-derivatives, including isomers of acetaldehyde, propionaldehyde and acrolein and two impurities were baseline separated in 20 mmol l(-1) phosphate buffer at pH 7.02, in less than 9 min. The limits of detection for the UV and LIF methodologies ranged from 1.1-9.5 microg l(-1) and 0.29-5.3 microg l(-1), respectively. The applicability of both methodologies to contemplate real samples was confirmed in the analysis of aldehyde-DNSH derivatives in indoor and outdoor air samples.     

Microwave-assisted synthesis of borneol esters and their antimicrobial activity

Seventeen borneol esters (1–17) were synthesised by conventional and microwave-assisted methodology using DIC/DMAP, and seven are described for the first time (8, 9, 10, 12, 13, 16 and 17). The microwave-assisted methodology was carried out without use of solvents, displayed short reaction times, and showed equal or higher yields for all the long-chain esters and three aromatic compounds (11, 12 and 14) when compared to the conventional approach. All the borneol esters were evaluated against the bacteria Streptococcus sanguinis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and the fungus Candida albicans. Compounds 12, 13 and 14 displayed promising antibacterial activity with a MIC equal to ampicilin (62.5 mg mL^?1) for some microorganisms. In fact, bornyl 3′,4′-dimethoxybenzoate (13) was active against all tested bacteria and fungus.     

Aqueous solution behavior of thermosensitive (N-isopropylacrylamide-acrylic acid-ethyl methacrylate) terpolymers

A series of N-isopropylacrylamide (NIPAM)-acrylic acid–ethyl methacrylate terpolymers with varied monomer compositions was prepared by radical polymerization. The solution behavior of these polymers was studied in dilute aqueous solution using spectrophotometry, fluorescence spectroscopy and high-sensitivity differential scanning calorimetry. The results obtained revealed that the lower critical solution temperatures depend strongly on the copolymer composition, solution pH and ionic strength. At a high pH, the ionization of acrylic acid (AA) units leads to an increase in solution cloud points (T_c). Solutions of polymers containing 10% or less of AA display a constant T_c for pH above 5.5, with 15% there is a continuous increase in T_c with pH and, for higher AA contents, no clouding was observed within the studied temperature range. Fluorescence probe studies were conducted by following the I ₁/I ₃ ratio of pyrene vibronic bands and the emission of anilinonaphtalene sulfonic acid, sodium salt (ANS), both approaches revealing the existence of hydrophobic domains for polymers with higher ethyl methacrylate content at temperatures lower than T_c, suggesting some extent of aggregation and/or a coil-to-globule transition. Scanning calorimetry measurements showed an endothermic transition at temperatures agreeing with the previously detected cloud points. Moreover, the transition curves became broader and with a smaller transition enthalpy, as both the AA content and the solution pH were increased. These broader transitions were interpreted to be the result of a wider molecular distribution upon polymer ionization, hence, displaying varied solution properties. The decrease in transition enthalpy was rationalized as a consequence of reminiscent hydration of NIPAM units, even after phase separation, owing to the presence of electric charges along the polymer chain.     

Electron ionization mass spectrometry: Quo vadis?

Mass spectrometry (MS) is a fundamental technique to identify compounds by their mass-to-charge ratio. It is known that MS can only detect target compounds when they are converted to ions in the gas phase. The ionization procedure is considered one of the most critical steps, and there are distinct techniques for it. One of them is electron ionization (EI), a widely used hard-ionization technique capable of generating several ions due to the excess energy employed. The existence of distinct ionization mechanisms turns EI capable of producing a fingerprint-like spectrum for each molecule. So, it is an essential technique for obtaining structural information. EI is often combined with chromatography to obtain a practical introduction of pretreated samples despite its excellent performance. EI–MS has been applied coupled with gas chromatography (GC) since the 1960s as both are very compatible. Currently, analytes of interest are more suitable for liquid chromatography (LC) analysis, so there are researchers dedicated to developing suitable interfaces for coupling LC and EI–MS. EI excels, as a reliable technique to fill the gap between GC and LC, possibly allowing them to coexist in a single instrument. In this work, the authors will present the fundamentals of EI–MS, emphasizing the development over the years, coupling with gas and LC, and future trends.     

Mixture-designed electrolytes for the MEKC separation of natural and synthetic steroids

In this work, the separation of 11 natural and synthetic steroids was studied using MEKC electrolytes modified by property-selected organic solvents: ethanol, ACN, and THF. The interplay between electrophoretic behavior and structural features was disclosed and the effects of organic modifiers to modulate retention and to alter selectivity were discussed in terms of system linear solvation energy relationships (LSER). The LSER indicated the total organic solvent percentage in the electrolyte as a major parameter to control retention and as a minor contribution, the hydrogen bond acidity. By evaluating the electropherograms obtained from mixture-designed electrolytes, a favorable separation condition for all solutes was achieved in ca. 25 min with an electrolyte composed of 20 mmol/L sodium tetraborate at pH 9.4, 20 mmol/L SDS and 20% EtOH (0.80% CV for migration time and 2.5% CV for peak area, n = five consecutive injections). The applicability of the proposed separation condition was demonstrated by the inspection of estrogens in urine sample (puberty stage).