A molecular dynamics study of free energy of micelle formation for sodium dodecyl sulfate in water and its size distribution

Free energy of micelle formation has been evaluated for spherical sodium dodecyl sulfate (SDS) in water by a thermodynamic integration method combined with a series of large-scale molecular dynamics calculations following the chemical species model. In particular, free energy change delta mu(n+1)0 with respect to the addition of one surfactant molecule to the spherical micelle of size n was obtained as a function of n. The free energy profile showed a minimum followed by a maximum, which corresponds to a peak in the size distribution. The calculated peak size n = 57 near its critical micelle concentration is in good agreement with the experimental averaged aggregation number n = 55-75 of the SDS micelle. The distribution showed a rather sharp peak, indicating that the size is almost a monodisperse one. The size is likely to be insensitive to the total concentration of the surfactant.     

Intensely blue-fluorescent 2,5-bis(benzoimidazol-2-yl)pyrazine dyes with improved solubility: their synthesis, fluorescent properties, and application as microenvironment polarity probes

In order to improve the solubility of intensively fluorescent 2,5-bis(benzimidazol-2-yl)pyrazine (BBIP), we synthesized new BBIP derivatives (2, 3a,b, and 5a,b) possessing two alkyl chains at the N-1 and N-1′ positions of the two benzimidazole moieties. Characterization of these compounds demonstrated that they exhibit high fluorescence intensity even in protic solvents, as well as solvatochromic fluorescence, in which their fluorescence maxima in aqueous methanol exhibited bathochromic shift with increasing ?_r value of the medium. We utilized 5a as a microenvironment polarity probe to indicate the variation in polarity around the backbone of the temperature-sensitive poly(N-isopropylacrylamide) by measuring the spectral change caused by the thermal phase transition of the polymer.     

Phase diagram and oxygen annealing effect of FeTe1−xSex iron-based superconductor

Phase diagrams of as-grown and O₂-annealed FeTe_1?xSe_x determined from magnetic susceptibility measurement were obtained. For as-grown samples, the antiferromagnetic order was fully suppressed in the range region x≥0.15, and weak superconductivity appeared when x≥0.1. Beginning at x=0.5, weak superconductivity was found to evolve into bulk superconductivity. Interestingly, for O₂-annealed samples, complete suppression of magnetic order and the occurrence of bulk superconductivity were observed when x≥0.1. We found that O₂-annealing induces bulk superconductivity for FeTe_1?xSe_x. Oxygen probably plays a key role in the suppression of the magnetic order and the appearance of bulk superconductivity.     

Intermediate formation in the reduction of Ni-ferrite with irradiation of high-flux infrared beam up to 1823 K

Ni-ferrite (NiFe₂O₄) has a lower reaction temperature for the O₂-releasing reaction when irradiation by a high-flux solar beam than that predicted by the estimation based on the thermodynamic data. The reaction mechanism of Ni-ferrite in the O₂-releasing reaction of a two-step water-splitting process at high temperatures (1,273–1,823 K) was clarified by means of X-ray diffractometry (XRD), extended X-ray absorption fine structure (EXAFS) analysis, Mössbauer spectroscopy and Magnetization measurement. The analysis of the EXAFS and Mössbauer spectra for Ni-ferrite before and after the O₂-releasing reaction shows that a lattice defect (Fe³⁺ (B-site)?Fe³⁺ (interstitial A-site)) intermediate with a spinel-type structure was formed in the early stage of the O₂-releasing reaction (up to 1,723 K). It is suggested that irradiation by a high-flux infrared beam resulted in the formation of the lattice defect intermediate with a Frenkel defect. The formation of the lattice defect intermediate with a Frenkel defect was due to the high reactivity of Ni-ferrite in the O₂-releasing reaction, as compared with other ferrites.     

Thermolysis,photolysis, and oxidation of an overcrowded 1,3,2-dithiastannetane derivative

Reactions of a sterically crowded 1,3,2-dithiastannetane derivative bearing 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (=Tbt) and 2,4,6-triisopropylphenyl (=Tip) groups on the tin atom are described. Both thermolysis and photolysis of the 1,3,2-dithiastannetane [Tbt(Tip)SnS₂CPh₂] resulted in the formation of products derived from the corresponding stannanethione [Tbt(Tip)Sn=S], while the oxidation reaction by m -chloroperbenzoic acid gave a novel tincontaining heterocyclic system, an 1,2,4,5-oxadithiastannolane derivative.     

Cover Picture: Electrochemical Lossy Mode Resonance-based Fiber Optic Sensing for Electroactive Species (Electroanalysis 3/2023)

We present an electrochemical-lossy mode resonance (LMR) sensing method that detects refractive indices and electroactive species. The LMR peaks of indium-tin-oxide in the transmittance-wavelength spectra were significantly shifted as the applied potential between 1.0 and −0.5 V at 209 nm/V. The modulation was exploited for sensing the refractive index and electroactive species (ferrocyanide and methylene blue) in two ways: peak-wavelength tracking and potential scanning. The potential-scanning technique produced clear potential LMR peaks in the transmittance-potential spectra for the first time, which were corresponded to the external refractive index. Meanwhile, the limits of detection of ferrocyanide and methylene blue were 7.5 and 25.3 μM, respectively, in peak-wavelength tracking and 18.2 and 20.8 μM, respectively, in the potential scanning technique.