Heavy element stable isotope ratios : analytical approaches and applications

Continuous developments in inorganic mass spectrometry techniques, including a combination of an inductively coupled plasma ion source and a magnetic sector-based mass spectrometer equipped with a multiple-collector array, have revolutionized the precision of isotope ratio measurements, and applications of inorganic mass spectrometry for biochemistry, geochemistry, and marine chemistry are beginning to appear on the horizon. Series of pioneering studies have revealed that natural stable isotope fractionations of many elements heavier than S (e.g., Fe, Cu, Zn, Sr, Ce, Nd, Mo, Cd, W, Tl, and U) are common on Earth, and it had been widely recognized that most physicochemical reactions or biochemical processes induce mass-dependent isotope fractionation. The variations in isotope ratios of the heavy elements can provide new insights into past and present biochemical and geochemical processes. To achieve this, the analytical community is actively solving problems such as spectral interference, mass discrimination drift, chemical separation and purification, and reduction of the contamination of analytes. This article describes data calibration and standardization protocols to allow interlaboratory comparisons or to maintain traceability of data, and basic principles of isotope fractionation in nature, together with high-selectivity and high-yield chemical separation and purification techniques for stable isotope studies.

Zwitterionic Corroles: Regioselective Nucleophilic Pyridination of a Doubly Linked Biscorrole

Pyridine attacks : Nucleophilic addition of pyridine derivatives to a doubly linked corrole, which is a stable singlet biradical species, occurs at the bay area with high regioselectivity to provide zwitterionic dimers (see picture; Ar=C₆F₅). Charge transfer between the anionic corrole and the pyridinium groups induces effective fluorescence quenching of the corrole dimer, which can be utilized for selective fluoride ion recognition.

     

Quantitative image reconstruction of GaN quantum dots from oversampled diffraction intensities alone

The missing data problem, i.e., the intensities at the center of diffraction patterns cannot be experimentally measured, is currently a major limitation for wider applications of coherent diffraction microscopy. We report here that, when the missing data are confined within the centrospeckle, the missing data problem can be reliably solved. With an improved instrument, we recorded 27 oversampled diffraction patterns at various orientations from a GaN quantum dot nanoparticle and performed quantitative image reconstruction from the diffraction intensities alone. This work in principle clears the way for single-shot imaging experiments using x-ray free electron lasers.     

Highly intense fluorescent diarylboron diketonate

Diarylboron diketonates were successfully prepared by the reaction of 1,3-diketone derivatives and arylboron compounds such as triphenylborane [BPh3] and fluorobis(pentafluorophenyl)borane diethyl etherate [(C6F5)2BF x OEt2]. The fluorescent emission of their complexes took place depending on the substituent of the arylboron moiety. In particular, a boron 1,3-bis(4-methoxyphenyl)-1,3-diketonate chelated by a strong electron-withdrawing C6F5 group exhibited the most intense fluorescence.     

The birch reduction of heterocyclic compounds V Birch reduction of 2‐ and 5‐acylfuran‐3‐carboxylic acids and reductive elimination of 2‐(arylmethoxymethyl)furan‐3‐carboxylic acids

The Birch reduction of 2‐ and 5‐acylfuran‐3‐carboxylic acid 1 and 4 gave 2‐acyl‐2,3‐dihydrofuran‐3‐carboxylic acid 2 and 5‐acyltetrahydrofuran‐3‐carboxylic acid 5 , respectively. Further examination of the reductive elimination was also studied on 2‐(arylmethoxymethyl)furan‐3‐carboxylic acids 7.     

Microstructure of the copolymers of methyl methacrylate with other methacrylates obtained by radical and anionic copolymerizations in tetrahydrofuran

Monomer reactivity ratios r₁ and r₂ were determined in the copolymerizations of methyl methacrylate (MMA, M₁) with 1, 1-diphenylethyl (DPEMA), α,α-dimethylbenzyl (DMBMA), tert-butyl (t-BuMA), diphenylmethyl (DPMMA), phenyl (PhMA), and 1-naphthyl (NpMA) methacrylates (M₂) in tetrahydrofuran (THF) by azobisisobutyronitrile (AIBN) at 60°C and butyllithium (n-BuLi) at ?78°C. The reactivities of the monomers were explained in terms of the polar effect of the ester groups in both copolymerizations. All the copolymers isolated in low yields were converted to PMMA either directly or by copoly(MMA—methacrylic acid) to determine the triad tacticities of the copolymers. Coisotactic parameters σ₁₂ and σ₂₁ were determined by assuming the terminal model statistics. The σ₂₁ values always accorded to the σ₂₁ values within experimental error, and in radical copolymerizations they were between isotactic parameters σ₁₁ and σ₂₂ of the homopolymerizations of MMA and M₂ monomers. In anionic copolymerizations, however, the σ₁₂ = σ₂₁ values varied, depending on the M₂ monomers. In copolymerization with DPEMA the values were less than both σ₁₁ and σ₂₂ with DMBMA they were between σ₁₁ and σ₂₂, with DPMMA, nearly equal to σ₁₁, and with PhMA and NpMA, greater than both σ₁₁ and σ₂₂. The application of these parameters to copolymerizations performed at high conversion was also investigated.     

Recent Progress in the Development of Solid‐State Luminescent o‐Carboranes with Stimuli Responsivity

o‐Carborane, a cluster compound containing boron and adjacent carbon atoms, displays intriguing luminescent properties. Recently, compounds containing o‐carborane units were found to show suppressed aggregation‐induced quenching and intense solid‐state emission; they also show potential for the development of stimuli‐responsive luminochromic materials. In this Minireview, we introduce three kinds of fundamental photochemical properties: aggregation‐induced emission, twisted intramolecular charge transfer in crystals, and environment‐sensitive excimer formation in solids. Based on these properties, several types of luminochromism, such as thermos‐, vapo‐, and mechanochromism, have been discovered. Based mainly on results from recent studies, we illustrate these mechanisms as well as unique luminescent behaviors of o‐carborane derivatives.     

Different shapes of spherical vaterite by photo-induced cis–trans isomerization of an azobenzene-containing polymer in a mixture of dimethyl sulfoxide and water

We studied the crystallization of CaCO₃ by the photoisomerization of azobenzene groups in poly[1-[4-[3-carboxy-4-hydroxyphenylazobenzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) in a mixture of dimethyl sulfoxide and water at 30 °C. The products were characterized by scanning electron microscopy (SEM), FT-IR, and powder X-ray diffraction (XRD) analysis. We observed that the different shapes of spherical vaterite particles were produced by the changes of configuration and polarity of the azobenzene groups in the polymer which resulted from photo-induced isomerization. The results indicate that the nucleation of primary particles of CaCO₃ was inhibited by in situ photo-induced cis–trans isomerization of PAZO. Therefore, we suggest that the shapes of the spherical vaterite can be effectively modified by photoisomerization of the azobenzene groups in the polymer at the initial stage of CaCO₃ crystallization.     

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10¹⁹ cm^–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10¹⁹ cm^–3) was more than 60 cm² V^–1 s^–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.     

Single InAs/InP quantum dot spectroscopy in 1.3–1.55 μm telecommunication band

We present an optical spectroscopy and photon correlation measurement at telecommunication wavelengths performed on single InAs/InP quantum dots. Two main approaches brought high optical quality: an application of a ‘double-cap’ growth method to metalorganic chemical vapor deposition, and fabrication of a small mesa structure using low-damage wet chemical etching. Sharp and discrete exciton transition lines have been observed on the single quantum dots, which widely cover the spectral range of 1.3–1.55 μm. Using a pulsed excitation source and gated single-photon detection modules, we observed a photon antibunching behavior for an isolated exciton emission line, indicating nonclassical light emission near the wavelength of 1.3 μm.