Characterization of Functional Groups in Estuarine Dissolved Organic Matter by DNP-enhanced 15N and 13C Solid-State NMR

Estuaries are key ecosystems with unique biodiversity and are of high economic importance. Along the estuaries, variations in environmental parameters, such as salinity and light penetration, can modify the characteristics of dissolved organic matter (DOM). Nevertheless, there is still limited information about the atomic-level transformations of DOM in this ecosystem. Solid-state NMR spectroscopy provides unique insights into the nature of functional groups in DOM. A major limitation of this technique is its lack of sensivity, which results in experimental time of tens of hours for the acquisition of ¹³C NMR spectra and generally precludes the observation of ¹⁵N nuclei for DOM. We show here how the sensitivity of solid-state NMR experiments on DOM of Seine estuary can be enhanced using dynamic nuclear polarization (DNP) under magic-angle spinning. This technique allows the acquisition of ¹³C NMR spectra of these samples in few minutes, instead of hours for conventional solid-state NMR. Both conventional and DNP-enhanced ¹³C NMR spectra indicate that the ¹³C local environments in DOM are not strongly modified along the Seine estuary. Furthermore, the sensitivity gain provided by the DNP allows the detection of ¹⁵N NMR signal of DOM, in spite of the low nitrogen content. These spectra reveal that the majority of nitrogen is in the amide form in these DOM samples and show an increased disorder around these amide groups near the mouth of the Seine.     

Quantification of Intracellular Thiols by HPLC-Fluorescence Detection

Biothiols, such as cysteine and glutathione, play important roles in various intracellular reactions represented by the redox equilibrium against oxidative stress. In this study, a method for intracellular thiol quantification using HPLC-fluorescence detection was developed. Thiols were derivatized with a thiol-specific fluorescence derivatization reagent, viz. ammonium 7-fluoro-2,1,3-benzoxadiazole-4-sulfonate (SBD-F), followed by reversed-phase separation on an InertSustain AQ-C18 column. Six different SBD-thiols (homocysteine, cysteine, cysteinylglycine, γ-glutamylcysteine, glutathione, and N-acetylcysteine as an internal standard) were separated within 30 min using a citric buffer (pH 3.0)/MeOH mobile phase. The calibration curves of all the SBD-thiols had strong linearity (R² > 0.999). Using this developed method, the thiol concentrations of human chronic myelogenous leukemia K562 cell samples were found to be 5.5–153 pmol/1 × 10⁶ cells. The time-dependent effect of a thiol scavenger, viz. N-ethyl maleimide, on intracellular thiol concentrations was also quantified. This method is useful for elucidating the role of intracellular sulfur metabolism.     

Photochemical Behavior of Single‐Walled Carbon Nanotubes in the Presence of Propylamine

This report describes the photochemical behavior of single‐walled carbon nanotubes (SWNTs) in the presence of propylamine. The SWNTs are characterized by absorption and Raman spectroscopy. The spectral changes due to photoirradiation indicate that reactions occur predominantly with the metallic SWNTs and small‐diameter SWNTs. The detection of amine radicalcation species by ESR spectroscopy reveals photoinduced electron transfer from the amine to the excited SWNTs. After exposure of the photoirradiated SWNTs to air, the characteristic spectra were recovered, except for that of the small‐diameter SWNTs. The results suggest that, after photoreduction of the SWNTs, subsequent selective sidewall functionalization of the small‐diameter SWNTs occurs.     

Electrochemical Synthesis of Thienoacene Derivatives: Transition-Metal-Free Dehydrogenative C−S Coupling Promoted by a Halogen Mediator

The first electrochemical dehydrogenative C−S bond formation leading to thienoacene derivatives is described. Several thienoacene derivatives were synthesized by dehydrogenative C−H/S−H coupling. The addition of ⁿBu₄NBr, which catalytically promoted the reaction as a halogen mediator, was essential.     

Encapsulations of La@C82 and La2@C80 inside single-walled boron nitride nanotubes

Possibility of encapsulations of metallofullerenes inside single-walled boron nitride nanotubes (BNNTs) is studied by using first-principles calculations. We find that both La@C₈₂ and La₂@C₈₀ can be exothermically encapsulated inside the (17, 0) and (14, 7) BNNTs. The minimum diameters of exothermically encapsulating both La@C₈₂ and La₂@C₈₀ inside BNNTs are predicated to be about 13.4 Å.     

Two-dimensional hydrophilic interaction chromatography coupling anion-exchange and hydrophilic interaction columns for separation of 2-pyridylamino derivatives of neutral and sialylated N-glycans

A novel chromatographic approach coupling anion-exchange (diethylaminoethylene) and hydrophilic-interaction (amide or zwitterionic type) columns was developed for the separating of 2-pyridylamino derivatives of N-glycans (PA-N-glycans). This is a kind of on-line, two-dimensional (2D) separation approach in hydrophilic-interaction chromatography (called the 2D-HILIC method), analogous to that of coupling cation- (or anion-, or mixed ion-) exchange and reversed-phase columns in hydrophobic interaction (reversed-phase) chromatography. The efficiency of the 2D-HILIC method was tested with biantennary neutral and sialylated PA-N-glycan standards by properly combining linear gradient elutions of water-acetonitrile and spiked-salt (ammonium acetate) elutions. The retention time RSDs of all the peaks in three sequential runs of a 100 min cycle are less than 0.52%, which indicates a reasonably good repeatability of the 2D-HILIC method. Then, the method was applied to a complex mixture of PA-N-glycans from human serum proteins. It was demonstrated that the neutral PA-N-glycans and mono-, di-, tri-, and tetrasialylated PA-N-glycans are able to be eluted in turn according to the number of sialic acids in an automated (programmed) single run.     

Computed Relative Populations of D2(22)‐C84 Endohedrals with Encapsulated Monomeric and Dimeric Water

Water monomer and dimer encapsulations into D₂(22)‐C₈₄ fullerene are evaluated. The encapsulation energy is computed at the M06‐2X/6‐31++G** level, and it is found that the monomer and dimer storage in C₈₄ yields an energy gain of 10.7 and 17.4 kcal mol^?1, respectively. Encapsulation equilibrium constants are computed by using partition functions based on the M06‐2X/6‐31G** and M06‐2X/6‐31++G** molecular data. Under high‐temperature/high‐pressure conditions, similar to that for the encapsulation of rare gases in fullerenes, the computed (H₂O)₂@C₈₄‐to‐H₂O@C₈₄ ratio is close to 1:2.     

Analysis of Individual High-Frequency Traders’ Buy–Sell Order Strategy Based on Multivariate Hawkes Process

Traders who instantly react to changes in the financial market and place orders in milliseconds are called high-frequency traders (HFTs). HFTs have recently become more prevalent and attracting attention in the study of market microstructures. In this study, we used data to track the order history of individual HFTs in the USD/JPY forex market to reveal how individual HFTs interact with the order book and what strategies they use to place their limit orders. Specifically, we introduced an 8-dimensional multivariate Hawkes process that included the excitations due to the occurrence of limit orders, cancel orders, and executions in the order book change, and performed maximum likelihood estimations of the limit order processes for 134 HFTs. As a result, we found that the limit order generation processes of 104 of the 134 HFTs were modeled by a multivariate Hawkes process. In this analysis of the EBS market, the HFTs whose strategies were modeled by the Hawkes process were categorized into three groups according to their excitation mechanisms: (1) those excited by executions; (2) those that were excited by the occurrences or cancellations of limit orders; and (3) those that were excited by their own orders.     

New fabrication approach to develop a high birefringence photo-crosslinked film based on a sulfur-containing liquid crystalline molecule with large temperature dependence of birefringence

ABSTRACT

We present a new fabrication approach to achieve a high birefringence film by means of photopolymerization based on an alkylthio-containing rod-like liquid crystalline molecule exhibiting large temperature dependence of birefringence. We designed a new reactive mesogen having alkylthio linkages (BPM–S). It was found that BPM–S had a larger increment of birefringence with decreasing temperature, relative to commercially available alkoxy analog LC242. This result could be thought to be due to enhanced intermolecular attractive interaction for an alkylthio mesogen implied by the proximity of laterally neighboring molecules and cybotactic nematic tendency based on wide-angle X-ray measurement. The uniaxially-aligned photo-polymerized film for BPM–S showed higher birefringence than that for LC 242.