Species-specific isotope dilution analysis of mono-, di,and tri-butyltin compounds in sediment using gas chromatography-inductively coupled plasma mass spectrometry with synthesized 118Sn-enriched butyltins

A species-specific isotope dilution (ID) method is described for the determination of mono-, di, and tri-butyltin compounds in sediment by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS), where the mixture of 118Sn-enriched butyltin compounds synthesized in our laboratory was used as a spike. A correction method for the mass bias, a quantitative extraction of the butyltins from sediment, and an assay for the concentration of the standard solution for the reverse ID procedure were investigated to achieve a reliable ID analysis. The spike solution was added with tri-propyltin (TPrT), and the butyltins were extracted by mechanical shaking into acetic acid-tropolone-toluene. The extracted butyltins were ethylated with sodium tetraethylborate and measured by GC-ICP-MS. The mass bias correction factor for the butyltins was calculated with the measured area ratio of 120Sn/118Sn of TPrT in each chromatographic run, and the correction was carried out. The mass bias was well corrected with this in-run correction (the standard uncertainties of the corrected 120Sn/118Sn for the butyltins were in the range 0.03-0.45%, typically 0.25%, with triplicate measurement corresponding to 0.02-0.37% mass bias). The extraction efficiency of mono-butyltin (MBT) from sediment was improved by using tropolone-toluene as the solvent. Well-defined standard solutions for the reverse-ID procedure could be obtained by an assay for the purities of the natural abundance butyltin chloride reagents used for preparing the standard solutions. Overall uncertainties associated with the present method were estimated, where the sediment certified reference materials, PACS-2 and BCR 646, were analyzed. The uncertainty arising from the extraction was the main contributor to the overall uncertainties for MBT and di-butyltin (DBT) determinations, while with the case of tri-butyltin (TBT) determination the uncertainties arising from the purity of TBT chloride reagent used for preparing the standard solution was a large contributor to the overall uncertainties although the uncertainty arising from the extraction was also a main contributor. The analytical results of MBT, DBT, and TBT in both reference materials, except for MBT results in PACS-2, were in good agreement with the certified values in each. The result of MBT in PACS-2 (0.677 +/- 0.049 microg g(-1) as tin, mean +/- expanded uncertainty) was significantly higher than the certified value (0.45 +/- 0.05 microg g(-1)), but closely matched with the lately reported values (Rajendran, Tao, Nakazato and Miyazaki, Analyst, 2000, 125, 1757: 0.62 +/- 0.02 microg g(-1); Chiron, Roy, Cottier and Jeannot, J. Chromatogr. A, 2000, 879, 137: 0.634 +/- 0.082 microg g(-1); Alonso, Encinar, Gonzalez and Sanz-Medal, Anal. Bioanal. Chem., 2002, 373, 432: 0.64 +/- 0.04 microg g(-1). The present method is concluded to be reliable for the determination of MBT, DBT, and TBT in sediment.     

Daphnezomines P, Q, R and S, new alkaloids from Daphniphyllum humile

Four new alkaloids, daphnezomines P-S (1-4), have been isolated from the fruits of Daphniphyllum humile, and the structures and the stereochemistry were elucidated on the basis of spectroscopic data including 2D NMR and MS/MS spectra, and chemical correlations. Daphnezomines P (1) and Q (2) were the first Daphniphyllum alkaloids with an iridoid glycoside moiety.     

A new fluorescent metal sensor with two binding moieties

A new fluorescent chelator Oxa, having two metal-binding sites, was designed and synthesized in six steps. Oxa exhibited two distinctive dissociation constants for Zn²⁺ ( μM and  μM), with considerable fluorescence increase in aqueous buffer at pH 7.2. Affinities of Oxa for the other biologically important ions such as Ca²⁺ ( μM and  mM) and Mg²⁺ ( μM and could not be determined) in the same conditions were also obtained.     

Quantification of peptides using N‐terminal isotope coding and C‐terminal derivatization for sensitive analysis by micro liquid chromatography‐tandem mass spectrometry

Stable isotope‐coding coupled with mass spectrometry is a popular method for quantitative proteomics and peptide quantification. However, the efficiency of the derivatization reaction at a particular functional group, especially in complex structures, can affect accuracy. Here, we present a dual functional‐group derivatization of bioactive peptides followed by micro liquid chromatography‐tandem mass spectrometry (LC‐MS/MS). By separating the sensitivity‐enhancement and isotope‐coding derivatization reactions, suitable chemistries can be chosen. The peptide amino groups were reductively alkylated with acetaldehyde or acetaldehyde‐d₄ to afford N‐alkylated products with different masses. This process is simple, quick and high‐yield, and accurate comparative analysis can be achieved for the mass‐differentiated peptides. Then, the carboxyl groups were derivatized with 1‐(2‐pyrimidinyl)piperazine to increase MS/MS sensitivity. Angiotensins I–IV, bradykinin and neurotensin were analyzed after online solid phase extraction by micro LC‐MS/MS. In all instances, a greater than 17‐fold increase in sensitivity was achieved, compared with the analyses of the underivatized peptides. Furthermore, the values obtained from the present method were in agreement with the result from isotope dilution quantification using isotopically labeled angiotensin I [Asp‐Arg‐(Val‐d₈)‐Tyr‐Ile‐His‐Pro‐(Phe‐d₈)‐His‐Leu]. Copyright © 2016 John Wiley & Sons, Ltd.     

HfMnSb2: A Metal‐Ordered NiAs‐type Pnictide with a Conical Spin Order

The NiAs‐type structure is one of the most common structures in solids, but metal order has been almost exclusively limited to chalcogenides. The synthesis of HfMnSb₂ is reported with a novel metal‐ordered NiAs‐type structure. HfMnSb₂ undergoes a conical spin order below 270 K, in marked contrast to conventional magnetic order observed in NiAs‐type pnictides. We argue that the layered arrangement of Hf and Mn makes it a quasi 2D magnet, where the Mn layers with localized magnetic moments (Mn²⁺; S=5/2) can interact only through RKKY interactions, instead of metal–metal bonding that is otherwise dominant for typical NiAs‐type pnictides. This result suggests that controlling order–disorder in NiAs‐type pnictides enables a study of 2D‐to‐3D crossover behavior in itinerant magnetic system.     

Rhodium-catalyzed kinetic resolution of tertiary homoallyl alcohols via stereoselective carbon-carbon bond cleavage

A nonenzymatic kinetic resolution of tertiary homoallyl alcohols has been developed through a rhodium-catalyzed retro-allylation reaction under simple conditions. Selectivity factors of up to 12 have been achieved by employing (R)-H8-binap as the ligand, and the reaction can be conducted on a preparative scale.     

Size-selected infrared predissociation spectroscopy of neutral and cationic formamide-water clusters: stepwise growth of hydrated structures and intracluster hydrogen transfer induced by vacuum-ultraviolet photoionization

Vibrational spectroscopy of size-selected formamide-water clusters, FA-(H2O)n , n = 1-4, prepared in a supersonic jet is performed with vacuum-ultraviolet-ionization detected-infrared predissociation spectroscopy (VUV-ID-IRPDS). The cluster structures are determined through comparisons of the observed IR spectra with theoretical calculations at the MP2/6-31++G** level. The FA-(H2O)n , n = 1-3, clusters have ring-type structures, where water molecules act as both single donor and single acceptor in the hydrogen-bond network between the amino and carbonyl groups of FA. For FA-(H2O)4, on the other hand, the absence of the free NH stretching vibration indicates formation of a double ring type structure, where two NH bonds of the amino group and the carbonyl oxygen of FA form hydrogen bonds with water molecules. An infrared spectrum of the formamide-water cluster cation, [FA-H2O](+), is also observed with infrared predissociation spectroscopy of vacuum-ultraviolet-pumped ion (IRPDS-VUV-PI). No band is observed for the free OH stretches of neutral water. This shows [FA-H2O](+) has such a structure that one of the hydrogen atoms of the water moiety is transferred to the carbonyl oxygen of FA(+).     

Comprehensive analysis of the hydrogen bond network morphology and OH stretching vibrations in protonated methanol-water mixed clusters, H(+)(MeOH)1(H2O)n (n = 1-8)

Density functional theory (DFT) calculations of protonated methanol-water mixed clusters, H (+)(MeOH) 1(H 2O) n ( n = 1-8), were extensively carried out to analyze the hydrogen bond structures of the clusters. Various structural isomers were energy optimized, and their relative energies with zero point energy corrections and temperature dependence of the free energies were examined. Coexistence of different morphological isomers was suggested. Infrared spectra were simulated on the basis of the optimized structures. The infrared spectra were also experimentally measured for n = 3-9 in the OH stretching vibrational region. The observed broad bands in the hydrogen-bonded OH stretch region were assigned in comparison with the simulations. From the DFT calculations, the preferential proton location was also investigated. Clear correlations between the excess proton location and the cluster morphology were found.     

Enhanced Hydrogen Generation from Formic Acid by Half‐Sandwich Iridium(III) Complexes with Metal/NH Bifunctionality: A Pronounced Switch from Transfer Hydrogenation

By switching the catalytic function from transfer hydrogenation based on the metal/NH bifunctionality, facile dehydrogenation of formic acid was achieved by amido‐ and hydrido(amine)–Ir complexes derived from N‐triflyl‐1,2‐diphenylethylenediamine (TfDPEN) at ambient temperature even in the absence of base additives. Further acceleration was observed by the addition of water, leading to a maximum turnover frequency above 6000 h^?1. A proton‐relay mechanism guided by the protic amine ligand and water is postulated for effective protonation of metal hydrides.