Reply to the Comment on “Realization of Lewis Basic Sodium Anion in the NaBH3− Cluster”

We reply to the comment by S. Pan and G. Frenking who challenged our interpretation of the Na^?:→BH₃ dative bond in the recently synthesized NaBH₃^? cluster. Our conclusion remains the same as that in our original paper ( https://doi.org/10.1002/anie.201907089 and https://doi.org/10.1002/ange.201907089 ). This conclusion is additionally supported by the energetic pathways and NBO charges calculated at UCCSD and CASMP2(4,4) levels of theory. We also discussed the suitability of the Laplacian of electron density (QTAIM) and Adaptive Natural Density Partitioning (AdNDP) method for bond type assignment. It seems that AdNDP yields more sensible results. This discussion reveals that the complex realm of bonding is full of semantic inconsistencies, and we invite experimentalists and theoreticians to elaborate this topic and find solutions incorporating different views on the dative bond.     

Direct analysis in real time mass spectrometry (DART‐MS) of highly non‐polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end‐groups were studied using direct analysis in real time mass spectrometry (DART‐MS). To facilitate the adduct ion formation under DART conditions, NH₄Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^? up to m/z 1100, and the deprotonated polyisobutylene succinic acid [M? H]^? were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄]⁺, adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^?, product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^? into a Cl^? ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄]⁺ ions, allowing us to obtain valuable information on the arm‐length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART‐MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.     

Observation of the multiple halogenation of peptides in the electrospray ionization source

The chlorination of peptides and proteins is an important posttranslational modification, which is a physiological signature of an enzyme myeloperoxidase and can serve as a potential biomarker of some diseases (Parkinson's disease, Alzheimer's disease, etc.). The quantification of the chlorinated peptides has been very challenging in part due to their low levels and artifacts associated with sample preparation. One of the most convenient and promising methods to detect and investigate the chlorinated peptides in the biological samples is the electrospray ionization (ESI) mass spectrometry coupled to the fragmentation techniques (collision‐induced dissociation and electron capture dissociation/electron transfer dissociation). We have shown that if the chlorine anions are present in the solution, then the peptide can undergo the chlorination during the ESI ionization. The effect was found to depend on the values of electric potentials of metal parts of the ESI interface. It was found that the grounding of ESI syringe results in the formation of an additional electric loop leading to the electrolytic production of Cl₂ and as a consequence the hypochlorous acid inside the ESI needle. Hypochlorous acid reacts with amino groups of peptides and proteins producing chloramine or causing the protein cleavage. In the paper, it is shown on the example of the solution of the several peptides in the presence of HCl that by manipulating the ESI syringe potential, it is possible to create complexes with up to five Cl atoms for sample peptides when the ESI is operated in the positive mode. Copyright © 2015 John Wiley & Sons, Ltd.     

铜催化α-重氮酮对硼氢键的不对称插入反应

手性有机硼化合物在有机合成、医药、材料等诸多领域中有广泛的应用,发展该类化合物的高效合成方法一直广受关注.此前,我们发展了过渡金属催化卡宾对硼氢键(B—H)的插入反应,并实现了α-重氮酯对B—H键的不对称插入反应.本文以手性螺环双噁唑啉配体和铜的络合物作为催化剂,首次实现了α-重氮酮对膦-硼烷加合物的B—H键不对称插入反应,获得了较高的收率和高达83%ee的对映选择性.该研究成果是为数不多的以α-重氮酮作为卡宾前体的不对称杂原子氢键插入反应,为手性α-硼取代酮化合物这类新的有机硼化合物的合成提供了有效方法.     

High resolution mass spectrometry based profiling of diet-related deoxyribonucleic acid adducts

Exposure of DNA to endo- and exogenous DNA binding chemicals can result in the formation of DNA adducts and is believed to be the first step in chemically induced carcinogenesis. DNA adductomics is a relatively new field of research which studies the formation of known and unknown DNA adducts in DNA due to exposure to genotoxic chemicals. In this study, a new UHPLC-HRMS(/MS)-based DNA adduct detection method was developed and validated. Four targeted DNA adducts, which all have been linked to dietary genotoxicity, were included in the described method; O⁶-methylguanine (O⁶-MeG), O⁶-carboxymethylguanine (O⁶-CMG), pyrimidopurinone (M1G) and methylhydroxypropanoguanine (CroG). As a supplementary tool for DNA adductomics, a DNA adduct database, which currently contains 123 different diet-related DNA adducts, was constructed. By means of the newly developed method and database, all 4 targeted DNA adducts and 32 untargeted DNA adducts could be detected in different DNA samples. The obtained results clearly demonstrate the merit of the described method for both targeted and untargeted DNA adduct detection in vitro and in vivo, whilst the diet-related DNA adduct database can distinctly facilitate data interpretation.     

APCI as an innovative ionization mode compared with EI and CI for the analysis of a large range of organophosphate esters using GC‐MS/MS

Organophosphate esters (OPEs) are chemical compounds incorporated into materials as flame‐proof and/or plasticizing agents. In this work, 13 non‐halogenated and 5 halogenated OPEs were studied. Their mass spectra were interpreted and compared in terms of fragmentation patterns and dominant ions via various ionization techniques [electron ionization (EI) and chemical ionization (CI) under vacuum and corona discharge atmospheric pressure chemical ionization (APCI)] on gas chromatography coupled to mass spectrometry (GC‐MS). The novelty of this paper relies on the investigation of APCI technique for the analysis of OPEs via favored protonation mechanism, where the mass spectra were mostly dominated by the quasi‐molecular ion [M + H]⁺. The EI mass spectra were dominated by ions such as [H₄PO₄]⁺, [M–R]⁺, [M–Cl]⁺, and [M–Br]⁺, and for some non‐halogenated aryl OPEs, [M]^+● was also observed. The CI mass spectra in positive mode were dominated by [M + H]⁺ and sometimes by [M–R]⁺, while in negative mode, [M–R]⁻ and more particularly [X]^‐ and [X₂]^‐● were mainly observed for the halogenated OPEs. Both EI and APCI techniques showed promising results for further development of instrumental method operating in selective reaction monitoring mode. Instrumental detection limits by using APCI mode were 2.5 to 25 times lower than using EI mode for the non‐brominated OPEs, while they were determined at 50‐100 times lower by the APCI mode than by the EI mode, for the two brominated OPEs. The method was applied to fish samples, and monitored transitions by using APCI mode showed higher specificity but lower stability compared with EI mode. The sensitivity in terms of signal‐to‐noise ratio varying from one compound to another. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of Naphtho[2,1-b]pyrano Pyrrolothiazole Derivatives through 1,3-Cycloaddition Reaction

Facile synthesis of a series of naphtho[2,1,b]pyrano pyrrolo thiazoles was accomplished in good yields in a one-pot reaction through intramolecular 1,3-dipolar cycloaddition of cyclic azomethine ylides with Baylis–Hillman adducts as dipolarophiles. The protocol is applicable to a wide variety of photochromic and biologically active napthopyrano products. The regio- and stereochemical outcome of the cycloaddition reaction was ascertained by x-ray crystallographic study of one of the cycloadducts.     

Facile fabrication of fast recyclable and multiple self‐healing epoxy materials through diels‐alder adduct cross‐linker

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2094–2103     

Extended X‐ray absorption fine structure and multiple‐scattering simulation of nickel dithiolene complexes Ni[S2C2(CF3)2]2n (n = −2, −1, 0) and an olefin adduct Ni[S2C2(CF3)2]2(1‐hexene)

A series of Ni dithiolene complexes Ni[S₂C₂(CF₃)]₂ⁿ (n = ?2, ?1, 0) ( 1 , 2 , 3 ) and a 1‐hexene adduct Ni[S₂C₂(CF₃)₂]₂(C₆H₁₂) ( 4 ) have been examined by Ni K‐edge X‐ray absorption near‐edge structure (XANES) and extended X‐ray absorption fine‐structure (EXAFS) spectroscopies. Ni XANES for 1 – 3 reveals clear pre‐edge features and approximately +0.7 eV shift in the Ni K‐edge position for `one‐electron' oxidation. EXAFS simulation shows that the Ni—S bond distances for 1 , 2 and 3 (2.11–2.16 Å) are within the typical values for square planar complexes and decrease by ～0.022 Å for each `one‐electron' oxidation. The changes in Ni K‐edge energy positions and Ni—S distances are consistent with the `non‐innocent' character of the dithiolene ligand. The Ni—C interactions at ～3.0 Å are analyzed and the multiple‐scattering parameters are also determined, leading to a better simulation for the overall EXAFS spectra. The 1‐hexene adduct 4 presents no pre‐edge feature, and its Ni K‐edge position shifts by ?0.8 eV in comparison with its starting dithiolene complex 3 . Consistently, EXAFS also showed that the Ni—S distances in 4 elongate by ～0.046 Å in comparison with 3 . The evidence confirms that the neutral complex is `reduced' upon addition of olefin, presumably by olefin donating the π‐electron density to the LUMO of 3 as suggested by UV/visible spectroscopy in the literature.     

New Acyclic Neutral Phosphorus Sulfides and Sulfide Oxides

A great number of binary neutral phosphorus sulfides was discovered and investigated. However all stable representatives of this family of compounds adopt a polycyclic structure in contrast to their lighter homologues, the nitrogen oxides. Acyclic representatives can be stabilized by adduct formation with a nitrogen base. The bis(pyridine) adduct py₂P₂S₅ of the unstable acyclic phosphorus sulfide P₂S₅ is readily obtained stirring P₄S₁₀ in pyridine at ambient temperature. X‐ray diffraction studies on single crystals of py₂P₂S₅ · 0.5 py ( 1b ) show a N₂O₅ like structure for the P₂S₅ framework. The long P–N distances of 1.86 Å indicate only weak coordination of the pyridine molecules to phosphorus. Single crystal X‐ray diffraction studies on py₂P₂S_4.34O_0.66 ( 2 ) reveal the presence of py₂P₂S₄O ( 3 ) together with py₂P₂S₅ in the crystal. Compound 3 contains the mixed phosphorus oxide sulfide molecule P₂S₄O stabilized as bis(pyridine) adduct. It is readily obtained from pyP₂S₅ by oxidation with KMnO₄ in pyridine. The oxygen atom occupies the bridging position between the two phosphorus atoms. Quantum chemical calculations at the MPW1PW91 level of theory as well as DTA/TG thermal analyses confirm the weak coordination of the pyridine molecules in py₂P₂S₅, py₂P₂S₄O, and py₂P₂S₇ to phosphorus.