Use of potassium-form cation-exchange resin as a conductimetric enhancer in ion-exclusion chromatography of aliphatic carboxylic acids

In this study, a cation-exchange resin (CEX) of the K⁺-form, i.e., an enhancer resin, is used as a postcolumn conductimetric enhancer in the ion-exclusion chromatography of aliphatic carboxylic acids. The enhancer resin is filled in the switching valve of an ion chromatograph; this valve is usually used as a suppressor valve in ion-exchange chromatography. An aliphatic carboxylic acid (e.g., CH₃COOH) separated by a weakly acidic CEX column of the H⁺-form converts into that of the K⁺-form (e.g., CH₃COOK) by passing through the enhancer resin. In contrast, the background conductivity decreases because a strong acid (e.g., HNO₃) with a higher conductimetric response in an eluent converts into a salt (e.g., KNO₃) with a lower conductimetric response. Since the pH of the eluent containing the resin enhancer increases from 3.27 to 5.85, the enhancer accelerates the dissociations of analyte acids. Consequently, peak heights and peak areas of aliphatic carboxylic acids (e.g., acetic acid, propionic acid, butyric acid, and valeric acid) with the enhancer resin are 6.3-8.0 times higher and 7.2-9.2 times larger, respectively, than those without the enhancer resin. Calibrations of peak areas for injected analytes are linear in the concentration range of 0.01-1.0 mM. The detection limits (signal-to-noise ratio = 3) range from 0.10 μM to 0.39 μM in this system, as opposed to those in the range of 0.24-7.1 μM in the separation column alone. The developed system is successfully applied to the determination of aliphatic carboxylic acids in a chicken droppings sample.     

Trifluoroacetaldehyde: A useful industrial bulk material for the synthesis of trifluoromethylated amino compounds

The synthesis of various trifluoromethylated amino compounds was studied using trifluoroacetaldehyde, an industrial bulk material, as a starting compound. One general application of trifluoroacetaldehyde is the preparation of trifluoroethylamino derivatives via reductive amination reaction. This synthesis includes the formation of the corresponding N,O-acetal intermediates followed by their reduction using NaBH₄ or 2-picoline borane complex, affording the target trifluoroethylamino compounds in moderate to good yields (47-87%).Another general application of trifluoroacetaldehyde is the synthesis of chiral α-substituted trifluoroethylamino compounds. In this synthesis, trifluoroacetaldehyde was first converted into the chiral trifluoromethyl tert-butyl sulfinimine, which was subjected to 1,2-nucleophilic addition reactions across its CN double bond. The addition of phenyllithium afforded α-(phenyl)trifluoroethylamino derivative in 83% yield and with 96% de. Allylation and Reformatsky reactions produced the corresponding α-substituted trifluoroethylamino derivatives in 82 and 58% yields and with 90 and 91% de, respectively.     

Theoretical study of the mechanism of valence tautomerism in cobalt complexes

Valence tautomerism is studied in the [Co(II-HS)(sq)(2)(bpy)]/[Co(III-LS)(sq)(cat)(bpy)] mononuclear cobalt complex by using DFT methods (HS, high spin; LS, low spin; cat, catecholate; sq, semiquinone; bpy, 2,2'-bipyridine). Calculations at the B3LYP* level of theory reproduce well the energy gap between the Co(II-HS) and Co(III-LS) forms giving an energy gap of 4.4 kcal/mol, which is comparable to the experimental value of 8.9 kcal/mol. Potential energy surfaces and crossing seams of the electronic states of the doublet, quartet, and sextet spin states are calculated along minimum energy paths connecting the energy minima corresponding to the different spin states. The calculated minimum energy crossing points (MECPs) are located at 8.8 kcal/mol in the doublet/sextet surfaces, at 10.2 kcal/mol in the doublet/quartet surfaces, and at 8.4 kcal/mol in the quartet/sextet surfaces relative to the doublet ground state. Considering the energy of the three spin states and the crossing points, the one-step relaxation mechanism between the Co(II-HS) and Co(III-LS) forms is the most probable. This research shows that mapping MECPs can be a useful strategy to analyze the potential energy surfaces of systems with complex deformation modes.     

Phase-shifting mask design for interference exposure of chirp blazed grating

An interference exposure system using a phase-shifting mask was proposed for generating periodic sawtooth optical intensity profile with chirp in period. Multiple space-harmonic waves are launched from the mask by diffraction, and the sawtooth optical intensity is formed by interference based on Fourier synthesis after propagation through an air gap. The design concept merely utilizing positive diffraction-order harmonics with tilt illumination of an exposure light and a design algorithm based on time-reversed configuration for calculating required phase shift amount were proposed and discussed. A phase-shifting mask for a blazed grating of very high chirp rate was designed to demonstrate its potential and feasibility. The grating period changes from 2.2 to 3.1 μm gradually within 0.3 mm length. Sawtooth-like optical intensity profile was confirmed by theoretical simulation as well as preliminary experimental results.     

Remark on the Helmholtz decomposition in domains with noncompact boundary

Let \(\varOmega \) be a domain in \(\mathbb {R}^{d+1}\) whose boundary is given as a uniform Lipschitz graph \(x_{d+1}=\eta (x)\) for \(x \in \mathbb {R}^d\) . For such a domain, it is known that the Helmholtz decomposition is not always valid in \(L^p(\varOmega )\) except for the energy space \(L^2 (\varOmega )\) . In this paper we show that the Helmholtz decomposition still holds in certain anisotropic spaces which include vector fields decaying slowly in the \(x_{d+1}\) variable. In particular, these classes include some infinite energy vector fields. For the purpose, we develop a new approach based on a factorization of divergence form elliptic operators whose coefficients are independent of one variable.     

High heat generation ability in AC magnetic field for nano-sized magnetic Y3Fe5O12 powder prepared by bead milling

Nano-sized magnetic Y₃Fe₅O₁₂ ferrite having a high heat generation ability in an AC magnetic field was prepared by bead milling. A commercial powder sample (non-milled sample) of ca. 2.9 μm in particle size did not show any temperature enhancement in the AC magnetic field. The heat generation ability in the AC magnetic field improved with a decrease in the average crystallite size for the bead-milled Y₃Fe₅O₁₂ ferrites. The highest heat ability in the AC magnetic field was for the fine Y₃Fe₅O₁₂ powder with a 15-nm crystallite size (the samples were milled for 4 h using 0.1 mm? beads). The heat generation ability of the excessively milled Y₃Fe₅O₁₂ samples decreased. The main reason for the high heat generation property of the milled samples was ascribed to an increase in the Néel relaxation of the superparamagnetic material. The heat generation ability was not influenced by the concentration of the ferrite powder. For the samples milled for 4 h using 0.1 mm? beads, the heat generation ability (W g⁻¹) was estimated using a 3.58×10⁻⁴ fH² frequency (f/kHz) and the magnetic field (H/kA m⁻¹), which is the highest reported value of superparamagnetic materials.