Evaluation of headspace-gas chromatography/mass spectrometry for the analysis of benzene in vitamin C drinks; pitfalls of headspace in benzene detection

Recently, there have been reports regarding the presence of benzene in vitamin C drinks. This is caused by sodium benzoate and ascorbic acid (vitamin C), which can react together to induce benzene formation. While the headspace gas chromatography method is well known for the detection of benzene, there could be pitfalls in the process of benzene extraction. This study was performed to check if benzene could be generated under high-temperature incubation conditions. As a result, the amount of benzene detected by headspace-gas chromatography/mass spectrometry (HSGC/MS) was affected by temperature changes. As the temperature of the sample vial was increased, newly generated benzene from the headspace also increased, causing false-positive determination of benzene. Although 80 degrees C is generally accepted for the temperature of headspace sample vials, lower temperatures, such as 40 degrees C, minimize the false-positive identification of benzene. Considering that this minimization allows benzene to be quantified at around 5 ppb, this lower temperature should definitely be considered since benzene, which is formed in sodium benzoate, can appear in vitamin C drinks under certain circumstances. The proposed analysis method of benzene in vitamin C drinks by HSGC/MS at 40 degrees C is an accurate and universal method for the monitoring of benzene without false-positive identification.     

Atomic force microscopic studies of novel arborescent block and linear triblock polystyrene-polyisobutylene copolymers

This paper reports the investigation of the nanostructured surface morphology of novel arborescent polyisobutylene-block-polystyrene (PIB-PS) copolymers, in comparison with linear PS-PIB-PS triblock copolymers, using atomic force microscopy (AFM) in tapping mode. Arborescent PIB-PS samples displayed interesting new phase morphologies, which changed dramatically upon annealing but remained irregular. Linear PS-PIB-PS samples showed morphologies similar to those previously found by transmission electron microscopy (TEM) in cryomicrotomed bulk samples, ranging from spherical/cylindrical to lamellar nanometer-sized discreet PS phases dispersed in a continuous PIB matrix. Annealing the samples resulted in more ordered structures.Three-dimensional AFM image and section analysis indicated a height difference between PIB and PS in the block copolymers, which became more prominent during annealing. This feature was verified on compression moulded and protein coated samples. The arborescent PIB-PS materials displayed thermoplastic elastomeric behaviour with a tensile strength between 7 and 10 MPa and elongation ranging from 1000% to 1830%. In comparison, linear triblock samples had a tensile strength between 7 and 20 MPa and elongation ranging from 380% to 640%. Block copolymers with irregular elastomeric midsegments may emerge as a new class of TPEs.     

Hemoglobin as a Diagnosing Molecule for Biological Effects of Atmospheric-Pressure Plasma

The studies with proteins are necessary to understand the biological effects of atmospheric pressure plasma (APP). Among proteins, those with transient metal ions play key roles in many biological events and they are very sensitive to environmental redox states. Iron-containing hemoglobin (Hb) is investigated in this study, after APP treatments under two environmental gas conditions of pure N₂ and N₂?+?O₂ mixture. Monitoring the intensity change for absorption spectra could lead to a quantitative assessment of the effect of discharge plasma on Hb. Redox states of Hb are classified into five states including O₂-bound Hb (oxy-Hb), deoxy-Hb, met-Hb, NO-bound Hb (NO-Hb), and hemichrome. Chemically generated reactive species and some scavengers are applied to understand the chemical reactions. Our experimental results confirm the complex chemical reactions of APP and suggest the possible use of Hb as a model protein for the visualization of APP biological effects.     

Self-deprotonation and colorization of 1,3-bis(dicyanomethylidene)indan in polar media: a facile route to a minimal polymethine dye for NIR fluorescence imaging

Colorless 1,3-bis(dicyanomethylidene)indan is an organic acid (pK(a) ≈3.0) that turns blue in polar media owing to self-deprotonation. Moreover, its colored conjugate base shows potential as a minimal anionic polymethine dye for probing biomolecules in cells and in vivo through noncovalent complexation and near-infrared fluorescence signaling.     

Identification of oligosaccharides from histopathological sections by MALDI imaging mass spectrometry

Direct tissue analysis using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) provides the means for in situ molecular analysis of a wide variety of biomolecules. This technology—known as imaging mass spectrometry (IMS)—allows the measurement of biomolecules in their native biological environments without the need for target-specific reagents such as antibodies. In this study, we applied the IMS technique to formalin-fixed paraffin-embedded samples to identify a substance(s) responsible for the intestinal obstruction caused by an unidentified foreign body. In advance of IMS analysis, some pretreatments were applied. After the deparaffinization of sections, samples were subjected to enzyme digestion. The sections co-crystallized with matrix were desorbed and ionized by a laser pulse with scanning. A combination of α-amylase digestion and the 2,5-dihydroxybenzoic acid matrix gave the best mass spectrum. With the IMS Convolution software which we developed, we could automatically extract meaningful signals from the IMS datasets. The representative peak values were m/z 1,013, 1,175, 1,337, 1,499, 1,661, 1,823, and 1,985. Thus, it was revealed that the material was polymer with a 162-Da unit size, calculated from the even intervals. In comparison with the mass spectra of the histopathological specimen and authentic materials, the main component coincided with amylopectin rather than amylose. Tandem MS analysis proved that the main components were oligosaccharides. Finally, we confirmed the identification of amylopectin by staining with periodic acid-Schiff and iodine. These results for the first time show the advantages of MALDI-IMS in combination with enzyme digestion for the direct analysis of oligosaccharides as a major component of histopathological samples.     

Water-wire catalysis in photoinduced acid-base reactions

The pronounced ability of water to form a hyperdense hydrogen (H)-bond network among itself is at the heart of its exceptional properties. Due to the unique H-bonding capability and amphoteric nature, water is not only a passive medium, but also behaves as an active participant in many chemical and biological reactions. Here, we reveal the catalytic role of a short water wire, composed of two (or three) water molecules, in model aqueous acid-base reactions synthesizing 7-hydroxyquinoline derivatives. Utilizing femtosecond-resolved fluorescence spectroscopy, we tracked the trajectories of excited-state proton transfer and discovered that proton hopping along the water wire accomplishes the reaction more efficiently compared to the transfer occurring with bulk water clusters. Our finding suggests that the directionality of the proton movements along the charge-gradient H-bond network may be a key element for long-distance proton translocation in biological systems, as the H-bond networks wiring acidic and basic sites distal to each other can provide a shortcut for a proton in searching a global minimum on a complex energy landscape to its destination.     

Highly luminescent InP/GaP/ZnS nanocrystals and their application to white light-emitting diodes

Highly stable and luminescent InP/GaP/ZnS QDs with a maximum quantum yield of 85% were synthesized by in situ method. The GaP shell rendered passivation of the surface and removed the traps. TCSPC data showed an evidence for the GaP shell. InP/GaP/ZnS QDs show better stability than InP/ZnS. We studied the optical properties of white QD-LEDs corresponding to various QD concentrations. Among various concentrations, the white QD-LEDs with 0.5 mL of QDs exhibited a luminous efficiency of 54.71 lm/W, Ra of 80.56, and CCT of 7864 K.     

Phosphine-catalyzed intramolecular γ-umpolung addition of α-aminoalkylallenic esters: facile synthesis of 3-carbethoxy-2-alkyl-3-pyrrolines

An array of N-tosylated α-aminoalkylallenic esters was prepared and their cyclization under the influence of nucleophilic phosphine catalysts was explored. The α-aminoalkylallenic esters were prepared through aza-Baylis-Hillman reactions or novel DABCO-mediated decarboxylative rearrangements of allenylic carbamates. Conversion of these substrates to 3-carbethoxy-2-alkyl-3-pyrrolines was facilitated through Ph(3)P-catalyzed intramolecular γ-umpolung addition.     

Designed cyanide- and phenoxide-bridged Fe(III)Mn(III) single-molecule magnet constructed by highly blocked paramagnetic precursors

A tetranuclear Fe(III)(2)Mn(III)(2) compound was prepared using highly blocked precursors. The well-isolated molecular entity associated with appropriate magnetic anisotropy allows for single-molecule magnet behavior.