Dissolved oxygen amperometric sensor based on layer-by-layer assembly using host-guest supramolecular interactions

The development of a simple, efficient and sensitive sensor for dissolved oxygen is proposed using the host-guest binding of a supramolecular complex at a host surface by combining a self-assembled monolayer (SAM) of mono-(6-deoxy-6-mercapto)-β-cyclodextrin (βCDSH), iron (III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeTMPyP) and cyclodextrin-functionalized gold nanoparticles (CDAuNP). The supramolecular modified electrode showed excellent catalytic activity for oxygen reduction. The reduction potential of oxygen was shifted about 200 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare gold electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves probably 4-electrons with a rate constant (k_obs) of 7 × 10⁴ mol⁻¹ L s⁻¹. A linear response range from 0.2 up to 6.5 mg L⁻¹, with a sensitivity of 5.5 μA L mg⁻¹ (or 77.5 μA cm⁻² L mg⁻¹) and a detection limit of 0.02 mg L⁻¹ was obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 3.0% for 10 measurements of a solution of 6.5 mg L⁻¹ oxygen.     

Using Neural Networks or Linear Models to Predict the Characteristics of Microcapsules Containing Phase Change Materials

Summary: Microcapsules with large amount of PRS® paraffin wax encapsulated and narrow size distribution were prepared by shirasu porous glass (SPG) emulsification technique and a subsequent suspension like polymerization process and then examined by DSC, laser diffraction and SEM analyses. An experimental design approach, based on a central composite design, was used to determine quantitatively the effect of PRS® paraffin wax/styrene mass ratio (PRS/St), percentage of polyvinylpyrrolidone/styrene mass ratio (%PVP/St) and water/styrene mass ratio (H₂O/St) on the microparticles properties. The results were fitted using two black-box models. The empirical equations allow the prediction of the amount of the paraffin wax encapsulated and the mean particle size in number as a function of aforementioned synthesis variables. It was observed that both models allowed to drawn the same conclusions. %PVP/St mass ratio was the most important parameter affecting the particle size distribution decreasing the average particle size with the increase of %PVP/St. On the other hand, PRS/St mass ratio has a direct influence on the latent heat of fusion.     

Identification of archaeal proteins that affect the exosome function in vitro

Background  

The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors.     

Quantitative determination of formic acid in apple juices by H NMR spectrometry

A quantitative determination method of formic acid in apple juices is proposed by means of the proton nuclear magnetic resonance (¹H NMR) technique. Formic acid gives a singlet signal at the 8.2-8.4 ppm interval of the spectrum, and its area is used to determine the concentration of the acid. 1,3,5-Benzenetricarboxylic acid is added to the juice as an internal standard. Since the chemical shift of both species varies with the pH, ascorbic acid is also added to adjust it at 2.74 and to avoid the overlapping of the signals. Recoveries between 95 and 109% are obtained when the standard addition method is applied to the juices of five different cider apple varieties. The coefficient of variation obtained is 3.9% for intra-day repeatability (n = 5), and 4.6% for inter-day repeatability (n = 10). The limit of detection is 1.49 mg/l, calculated from “3S_y/x + intercept”. The described method is direct and no previous derivatization is needed.     

H-N HMBC as a valuable tool for the identification and characterization of nitrones

¹H-¹⁵N HMBC has been evaluated as an efficient and high-speed method to determine ¹⁵N chemical shifts for nitrones, which can be used to identify aromatic nitrones and to extract structural information by comparison with reference data. Substituent effects have been measured on C and N aryl groups separately, showing up the influence of electronic effects on C-aryl groups rather than N-aryl groups on the ¹⁵N chemical shifts. Steric effects are remarkable in the case of C-aryl-N-alkyl nitrones. Depending on N or C substitution, chemical shift changes in such an additive way that it is possible to predict chemical shifts for unknown nitrones.     

Hydrogen physisorption energies for bumpy,saturated, nitrogen-doped single-walled carbon nanotubes

Finite saturated regular carbon nanotubes (CNTs) are predicted to exhibit higher capacity as hydrogen storage media compared to unsaturated regular CNTs. In the present study, molecular hydrogen physisorption energies (MHPEs) for finite saturated and unsaturated bumpy defected CNTs were calculated by density functional theory (DFT-D3) methods at the B3LYP/6-31G(d) theory level, with rigorous inclusion of van der Waals interactions. The calculated MHPEs for both regular and bumpy defected armchair, chiral and zigzag CNTs with similar diameters and lengths, with and without nitrogen doping, were compared in terms of Eph/H₂, defined as the MHPE per hydrogen molecule adsorbed inside the nanotube. For all studied systems, Eph/H₂ increased with the number of physisorbed hydrogen molecules. Nitrogen doping of regular and bumpy CNTs resulted in an increase in the Eph/H₂ values, with the exception of bumpy chiral nanotubes. The results of this study demonstrate that bumpy defects are important nanotube structural features whose effects depend on nanotube chirality. For instance, bumpy defects were beneficial for undoped and doped zigzag nanotubes, resulting in a decrease in Eph/H₂ values for regular structures from 0.5 and 0.74 to 0.26 and 0.42 eV, respectively. By contrast, for doped armchair regular structures with an Eph/H₂ value of 0.38 eV, bumpy defects increased Eph/H₂ to 0.45 eV. These Eph/H₂ values for bumpy doped armchair and the zigzag nanotubes are all within the range of 0.1–0.5 eV/H₂ reported as ideal for reversible hydrogen storage under environmental conditions.     

High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA

The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)_n. Fluorescence measurements on (AT)_n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)_n structures with those reported previously for alternating (GC)_n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence.     

Montecrinanes A–C: Triterpenes with an Unprecedented Rearranged Tetracyclic Skeleton from Celastrus vulcanicola. Insights into Triterpenoid Biosynthesis Based on DFT Calculations

Three new triterpenoids with an unprecedented 6/6/6/6‐fused tetracyclic carbon skeleton, montecrinanes A–C ( 1 – 3 ), were isolated from the root bark of Celastrus vulcanicola, along with known D:B‐friedobaccharanes ( 4 – 6 ), and lupane‐type triterpenes ( 7 – 12 ). The stereostructures of the new metabolites were elucidated based on spectroscopic (1D and 2D NMR) and spectrometric (HR‐EIMS and HR‐ESIMS) techniques. Their absolute configurations were determined by both NMR spectroscopy, with (R)‐(?)‐α‐methoxyphenylacetic acid as a chiral derivatizing agent, and biogenetic considerations. Biogenetic pathways for montecrinane and D:B‐friedobaccharane skeletons were proposed and studied by DFT methods. The theoretical results support the energetic feasibility of the putative biogenetic pathways, in which the 1,2‐methyl shift from the secondary baccharenyl cation represents a novel and key reaction step for a new montecrinane skeleton.