Branching pattern and sequence analysis of underivatized oligosaccharides by combined MS/MS of singly and doubly charged molecular ions in negative-ion electrospray mass spectrometry

We previously reported that sequence and partial linkage information, including chain and blood-group types, of reducing oligosaccharides can be obtained from negative-ion electrospray CID MS/MS on a quadrupole-orthogonal time-of-flight instrument with high sensitivity and without derivatization (Chai, W.; Piskarev, V.; Lawson, A. M. Anal. Chem. 2001, 73, 651-657). In contrast to oligonucleotides and peptides, oligosaccharides can form branched structures that result in a greater degree of structural complexity. In the present work we apply negative-ion electrospray CID MS/MS to core-branching pattern analysis using nine 3,6-branched and variously fucosylated oligosaccharides based on hexasaccharide backbones LNH/LNnH as examples. The important features of the method are the combined use of CID MS/MS of singly and doubly charged molecular ions of underivatized oligosaccharides to deduce the branching pattern and to assign the structural details of each of the 3- and 6-branches. These spectra give complimentary structural information. In the spectra of [M - H]-, fragment ions from the 6-linked branch are dominant and those from the 3-linked branch are absent, while fragment ions from both branches occur in the spectra of [M - 2H]2-. This allows the distinction of fragment ions derived from either the 3- or 6-branches. In addition, a unique D2beta-3 ion, arising from double D-type cleavage at the 3-linked glycosidic bond of the branched Gal core residue, provides direct evidence of the branching pattern with sequence and partial linkage information being derived from C- and A-type fragmentations, respectively.     

Distribution of samarium and ytterbium in rats measured by enriched stable isotope tracer technique and INAA

In the present study a method using enriched stable isotope tracer and instrumental neutron activation analysis (INAA) was developed to study the dynamic distribution of rare earth elements (REEs) in a variety of organs and tissues of Wistar rats. Stable isotopes ¹⁵²Sm and ¹⁶⁸Yb were selected as tracers for the experiment. Intravenously injected ¹⁵²Sm and ¹⁶⁸Yb in chloride form could be quickly absorbed and distributed in almost all the organs and tissues of interest, including liver, skeleton, kidney, spleen, heart, lung, testicle, and blood serum. Liver and skeleton had high ability to take up ¹⁵²Sm and ¹⁶⁸Yb under the experimental conditions, whereas the contents of the elements in other organs were generally lower than 2% of the given dose during the whole experimental period. The difference in distribution of ¹⁵²Sm and ¹⁶⁸Yb in the body was also discussed.     

A new MnxOy/carbon nanorods derived from bimetallic Zn/Mn metal–organic framework as an efficient oxygen reduction reaction electrocatalyst for alkaline Zn-Air batteries

Journal of Solid State Electrochemistry - In this work, nanorods like bimetallic Zn/Mn metal–organic-frameworks (MOFs) are proposed as the precursor for preparing MnxOy/porous carbon...     

The Coordination Chemistry of f-Block Elements in Molten Salts

The coordination chemistry of f-block elements (lanthanide and actinide) in molten salts has become a resounding topic in view of its great importance to the research and development (R&D) of molten salt reactors and pyroprocessing. In this Review article, a general overview of the coordination chemistry of f-block elements in molten salts is provided including past achievements and recent advances. Particular emphases are placed on the oxidation state, speciation, and solution structure of f-block metal ions in molten salts, as well as their relationships with the salt composition. Furthermore, this review briefly discusses the spectroscopic and theoretical methods that complement each other in revealing the coordination properties.     

Simultaneous Determination of Seven Lipophilic and Hydrophilic Components in Salvia miltiorrhiza Bunge by LC-MS/MS Method and Its Application to a Transport Study in a Blood-Brain-Barrier Cell Model

Salvia miltiorrhiza Bunge (SM) has been extensively used in Alzheimer’s disease treatment, the permeability through the blood-brain barrier (BBB) determining its efficacy. However, the transport mechanism of SM components across the BBB remains to be clarified. A simple, precise, and sensitive method using LC-MS/MS was developed for simultaneous quantification of tanshinone I (TS I), dihydrotanshinone I (DTS I), tanshinone IIA (TS IIA), cryptotanshinone (CTS), protocatechuic aldehyde (PAL), protocatechuic acid (PCTA), and caffeic acid (CFA) in transport samples. The analytes were separated on a C18 column by gradient elution. Multiple reaction monitoring mode via electrospray ionization source was used to quantify the analytes in positive mode for TS I, DTS I, TS IIA, CTS, and negative mode for PAL, PCTA, and CFA. The linearity ranges were 0.1–8 ng/mL for TS I and DTS I, 0.2–8 ng/mL for TS IIA, 1–80 ng/mL for CTS, 20–800 ng/mL for PAL and CFA, and 10–4000 ng/mL for PCTA. The developed method was accurate and precise for the compounds. The relative matrix effect was less than 15%, and the analytes were stable for analysis. The established method was successfully applied for transport experiments on a BBB cell model to evaluate the apparent permeability of the seven components.     

Cu Doping-Induced Transformation from [Ag62S12(SBut)32]2+ to [Ag62−xCuxS12(SBut)32]4+ Nanocluster

The change in the valence state of nanocluster can induce remarkable changes in the properties and structure. However, achieving the valence state changes in nanoclusters is still a challenge. In this work, we use Cu²⁺ as dopant to “oxidize” [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ (4 free electrons) to obtain the new nanocluster: [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ with 2 free electrons. As revealed by its structure, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ (x=10∼21) has a similar structure to that of [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ precursor and all the Cu atoms occupy the surface site of nanocluster. It′s worth noting that with the Cu atoms doping, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ nanocluster is more stable than [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ at higher temperature and in electrochemical cycle. This result has laid a foundation for the subsequent application and exploration. Overall, this work reveals crystals structure of a new Ag−Cu nanocluster and offers a new insight into the electron reduction/oxidation of nanocluster.     

Construction of Hybrid Bimetallic Uranyl Compounds Based on a Preassembled Terpyridine Metalloligand

Six hybrid uranyl–transition metal compounds [UO₂Ni(cptpy)₂(HCOO)₂(DMF)(H₂O)] ( 1 ), [UO₂Ni(cptpy)₂(BTPA)₂] ( 2 ), [UO₂Fe(cptpy)₂(HCOO)₂(DMF)(H₂O)] ( 3 ), [UO₂Fe(cptpy)₂(BTPA)₂] ( 4 ), [UO₂Co(cptpy)₂(HCOO)₂(DMF)(H₂O)] ( 5 ), and [UO₂Co(cptpy)₂(BTPA)₂] ( 6 ), based on bifunctional ligand 4′-(4-carboxyphenyl)-2,2′:6′,2′′-terpyridine (Hcptpy) are reported (H₂BTPA = 4,4′-biphenyldicarboxylic acid). Single-crystal XRD revealed that all six compounds feature similar metalloligands, which consist of two cptpy⁻ anions and one transition metal cation. The metalloligand M(cptpy)₂ can be considered to be an extended linear dicarboxylic ligand with length of 22.12 Å. Compounds 1 , 3 , and 5 are isomers, and all of them feature 1D chain structures. The adjacent 1D chains are connected together by hydrogen bonds and π–π interactions to form a 3D porous structure, which is filled with solvent molecules and can be exchanged with I₂. Compounds 2 , 4 , and 6 are also isomers, and all of them feature 2D honeycomb (6,3) networks with hexagonal units of dimensions 41.91×26.89 Å, which are the largest among uranyl compounds with honeycomb networks. The large aperture allows two sets of equivalent networks to be entangled together to result in a 2D+2D→3D polycatenated framework. Remarkably, these uranyl compounds exhibit high catalytic activity for cycloaddition of carbon dioxide. Moreover, the geometric and electronic structures of compounds 1 and 2 are systematically discussed on the basis of DFT calculations.     

Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+) in Molten Salts

Molten salt electrolysis is a vital technique to produce high-purity lanthanide metals and alloys. However, the coordination environments of lanthanides in molten salts, which heavily affect the related redox potential and electrochemical properties, have not been well elucidated. Here, the competitive coordination of chloride and fluoride anions towards lanthanide cations (La³⁺ and Nd³⁺) is explored in molten LiCl-KCl-LiF-LnCl₃ salts using electrochemical, spectroscopic, and computational approaches. Electrochemical analyses show that significant negative shifts in the reduction potential of Ln³⁺ occur when F⁻ concentration increases, indicating that the F⁻ anions interact with Ln³⁺ via substituting the coordinated Cl⁻ anions, and confirm [LnCl_xF_y]^3−x−y (y_max=3) complexes are prevailing in molten salts. Spectroscopic and computational results on solution structures further reveal the competition between Cl⁻ and F⁻ anions, which leads to the formation of four distinct Ln(III) species: [LnCl₆]³⁻, [LnCl₅F]³⁻, [LnCl₄F₂]³⁻ and [LnCl₄F₃]⁴⁻. Among them, the seven-coordinated [LnCl₄F₃]⁴⁻ complex possesses a low-symmetry structure evidenced by the pattern change of Raman spectra. After comparing the polarizing power (Z/r) among different metal cations, it was concluded that Ln−F interaction is weaker than that between transition metal and F⁻ ions.