Simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its estimated degradation products using capillary zone electrophoresis

A commercial organoborane compound, pyridine-triphenylborane (PTPB), is often applied to ship hulls as an anti-fouling agent. We developed capillary zone electrophoresis (CZE) with direct UV detection for the simultaneous determination of PTPB and its estimated degradation products: diphenylborinic acid (DPB), phenylboronic acid (MPB), and phenol. The limits of detection (LODs) for PTPB, DPB, MPB, and phenol were, respectively, 25, 30, 50, and 29 μg/l at a signal-to-noise ratio of three. At concentrations of 0.5 mg/l, values of the relative standard deviation (RSD, n = 6, intra-day) of peak area were obtained, respectively, for PTPB, DPB, MPB, and phenol, as 4.1, 4.1, 4.7, and 3.4% for peak heights 3.6, 3.2, 1.7, and 1.4%, and for migration times 1.1, 1.1, 1.0, and 0.73%. The analytes were detected within 14 min. Simple photodegradation experiments were conducted to verify the usefulness of the proposed method for additional PTPB degradation investigations.     

High‐Yielding Synthesis of the Anti‐Influenza Neuraminidase Inhibitor (−)‐Oseltamivir by Two “One‐Pot” Sequences

The efficient asymmetric total synthesis of (?)‐oseltamivir, an antiviral reagent, has been accomplished by using two “one‐pot” reaction sequences, with excellent overall yield (60 %) and only one required purification by column chromatography. The first one‐pot reaction sequence consists of a diphenylprolinol silyl ether mediated asymmetric Michael reaction, a domino Michael reaction/Horner–Wadsworth–Emmons reaction combined with retro‐aldol/Horner–Wadsworth–Emmons reaction and retro Michael reactions, a thiol Michael reaction, and a base‐catalyzed isomerization. Six reactions can be successfully conducted in the second one‐pot reaction sequence; these are deprotection of a tert‐butyl ester and its conversion into an acyl chloride then an acyl azide, Curtius rearrangement, amide formation, reduction of a nitro group into an amine, and a retro Michael reaction of a thiol moiety. A column‐free synthesis of (?)‐oseltamivir has also been established.     

Electrochemical generation of silver acetylides from terminal alkynes with a Ag anode and integration into sequential Pd-catalysed coupling with arylboronic acids

An electro-oxidative method for generating silver acetylides from acetylenes with a Ag anode was developed. The reaction could be integrated into a Pd-catalysed electrochemical Sonogashira-type reaction. In the presence of the catalytic amount of Pd(OAc)(2) and 4-BzO-TEMPO, electro-generated silver acetylides reacted immediately with arylboronic acids to afford the corresponding coupling adducts in high yields.     

Complete chromatographic separation of steroids, including 17α and 17β-estradiols, using a carbazole-based polymeric organic phase in both reversed and normal-phase HPLC

Poly(2-N-carbazolylethyl acrylate) with terminal trimethoxysilyl groups was prepared as an organic phase and immobilized onto silica. The retention behavior of the column packed with this carbazole-based polymer-immobilized silica (Sil-CEA) was investigated by using various estrogenic steroids and corticoids in both reversed-phase and normal-phase liquid chromatography. As a result, complete separation was confirmed for eight kinds of steroids with Sil-CEA. The most specific separation with Sil-CEA can be emphasized by the high separation factor (e.g., α = 1.39 in methanol–water (7:3, v/v) at 35 °C) for 17α and 17β-estradiols, one of the most difficult pairs of isomers in chromatographic separation, whereas for two kinds of commercially available polymeric ODS columns as references α = 1.01, only, under the same conditions. Because the excellent separation and retention order with Sil-CEA was maintained even in a normal-phase mobile phase such as a hexane–2-propanol, it is estimated that the CEA phase has multiple interaction mechanisms through stronger interactions such as dipole–dipole, carbonyl–π, and hydrogen bonding interactions than the hydrophobic effect expected with ODS.     

Binary bubble languages and cool-lex order

A bubble language is a set of binary strings with a simple closure property: The first 01 of any string can be replaced by 10 to obtain another string in the set. Natural representations of many combinatorial objects are bubble languages. Examples include binary string representations of k-ary trees, unit interval graphs, linear-extensions of B-posets, binary necklaces and Lyndon words, and feasible solutions to knapsack problems. In co-lexicographic order, fixed-weight binary strings are ordered so that their suffixes of the form i¹⁰ occur (recursively) in the order i=max,max−1,…,min+1,min for some values of max and min. In cool-lex order the suffixes occur (recursively) in the order max−1,…,min+1,min,max. This small change has significant consequences. We prove that the strings in any bubble language appear in a Gray code order when listed in cool-lex order. This Gray code may be viewed from two different perspectives. On one hand, successive binary strings differ by one or two transpositions, and on the other hand, they differ by a shift of some substring one position to the right. This article also provides the theoretical foundation for many efficient generation algorithms, as well as the first construction of fixed-weight binary de Bruijn sequences; results that will appear in subsequent articles.     

Development of the Earth’s Field NMR Spectrometer for Liquid Screening

Earth??s field nuclear magnetic resonance (NMR) can be used for non-destructive in-bottle liquid screening by evaluating the spin?Clattice relaxation times of protons in various liquids. An Earth??s field NMR apparatus has been developed and optimized to measure the spin?Clattice relaxation times of various liquids contained in 500?ml PET bottles. Two methods to generate 90-degree readout pulses using transient oscillating signals generated in a resonator are reported. The lower detection limit of pure water was 1?ml. The minimum measurable spin?Clattice relaxation time was 50?ms.     

Experimental study of annular bright field (ABF) imaging using aberration-corrected scanning transmission electron microscopy (STEM)

Experimental parameters used in the annular bright field (ABF) imaging method were tested using images simulated with the multislice method. Images simulated under identical conditions were found to agree well with experimental images. The ABF technique was shown to be relatively insensitive to the sample thickness and the defocus. In experimental ABF images, atomic columns exhibited dark contrast over a wide range of specimen thickness and defocus values, from 10 to 70 nm and ?20 to +20 nm, respectively. A series of diffraction patterns at atomic columns, obtained using the diffraction imaging method, exhibited higher intensities in their central regions (0–11 mrad) for light elements and in their peripheral regions (11–22 mrad) for heavy elements. The results indicated that the contrast of light elements is enhanced by subtraction of the central region of the transmitted beam, since this is blocked by a circular mask in the ABF-STEM technique. Thus, the overall contrast of light elements is greatly improved, allowing them to be clearly visualized.     

Structure elucidation of a novel analog of sildenafil detected as an adulterant in a dietary supplement using LC-UV and LC/MS

A sildenafil-related compound was detected in a dietary supplement marketed as an aphrodisiac. The compound was detected during analysis of the dietary supplement using LC-UV and LC/electrospray ionization-MS. The structure of the compound was established using high resolution MS, NMR spectrometry, and X-ray crystal structure analysis. The compound was identified as 5-(5-((3,5-dimethylpiperazin-1-yl)sulfonyl)-2-ethoxyphenyl)-l-methyl-7-((1-methyl-4-nitro-1H-imidazol-5-yl)thio)-3-propyl-1H-pyrazolo[4,3-d] pyrimidine. Based on this structure, the compound was named nitroprodenafil. The dietary supplement was found to contain 90 mg nitroprodenafil/capsule. This article describes the structural characterization of a new sildenafil-related compound. The compound was detected during analysis of a dietary supplement using LC-UV and LC/electrospray ionization (ESI)-MS. The structure was established using high resolution MS (HRMS), NMR spectrometry, and X-ray crystal structure analysis. The structures of methisosildenafil, thiomethisosildenafil, and this new analog, named nitroprodenafil (21), are shown in Figure 1. In the Demizu et al. report, the compound is named mutaprodenafil instead ofnitroprodenafil. Considering the naming right, the authors of this paper think the use of mutaprodenafil is appropriate as the compound name, although nitroprodenafil is used.     

Effect of catalytic alkali metal bromide on Hofmann-type rearrangement of imides

The Hofmann-type rearrangement of aromatic and aliphatic imides using KBr as the catalyst proceeded to provide aromatic and aliphatic amino acid derivatives. We have also developed a new synthetic route to gabapentin with this method.     

A new method for accurately determining the modal equivalent stiffness ratio of bonded piezoelectric structures

This paper describes new methods for measuring the modal equivalent stiffness ratios and modal electromechanical coupling coefficients of piezoelectric elements attached to a host structure such as a beam. Modal equivalent stiffness ratios and modal electromechanical coupling coefficients are essential for estimating the performance and determining an optimum design of active vibration control and passive vibration suppression systems that use piezoelectric elements. Accurate determination of these modal parameters is also useful for other systems including piezoelectric sensors and energy generators. This paper not only describes the measurement methods but also presents the theoretical formulations derived by taking into account the effect of adhesive bonds. The formulations in this paper demonstrate the necessity of experimental measurements and the accuracy enhancements that the theoretical estimations can provide. Conventional methods for obtaining the modal equivalent stiffness ratios are sensitive to measurement errors, which result in the loss of accuracy, rendering these methods unreliable for many practical applications. The proposed methods use an inductor instead of an open circuit to address the abovementioned issue and, thereby, provide significant improvement in the accuracy. Because the loss factors of the experimental apparatus tend to compromise the accuracy of the proposed methods, a method using a negative resistor is proposed, theoretically analyzed, and confirmed to eliminate some of the errors introduced by loss factors. The advantages of the proposed methods and the effectiveness of theoretical analysis, considering the effect of adhesive bonds, are verified experimentally.