Differential ESI-MS behaviour of highly similar metallothioneins

ESI-MS can only be accepted as a quantification method when using standards with a high resemblance to the analyte(s). Unfortunately, this is usually not applicable to metallothioneins (MTs), a superfamily of singular metal-binding cysteine-rich proteins, present in all living organisms, since the absence of suitable reference material due to the high diversity among metal-MT species precludes their quantification by molecular mass spectrometry. Even thus, it is widely assumed that the intensities of the ESI-MS peaks of similar species are directly correlated with their relative concentration in the sample, and this has been extended to the determination of different MT proteins coexisting in a sample.Practically all organisms contain several MT isoforms, some of them exhibiting highly similar sequences, with conserved coordinating Cys residues. For the current analysis, we used as a model system the MT isoforms of two terrestrial snails (Helix pomatia and Cornu aspersum). Hence, distinct samples were prepared by mixing, at different molar ratios, the recombinant HpCuMT and HpCdMT isoforms from H. pomatia, or the recombinant CaCuMT, CaCdMT and CaCdCuMT isoforms from C. aspersum, and they were analyzed by ESI-MS both at neutral pH (for Zn-loaded MT forms) and at acidic pH (for the corresponding apo-forms). The results here presented reveal that the ESI-MS peak intensity of a single MT species strongly depends on its sensitivity to be ionized, and thus, on the presence or absence of metal ions bound. Furthermore, our data demonstrate that very similar MT isoforms of the same organism with similar pI (ranging from 7.9 to 8.3) can show a clear different sensitivity to ES ionization, something that cannot be readily predicted only by consideration of their amino acid content. In conclusion, even in this optimum case, deductions about quantity features of MT samples drawn from ESI-MS measurements should be carefully considered.     

Unimolecular rearrangements of ketene-O,O-acetals and fragmentations occurring in the gas phase

Gas phase skeletal rearrangements of regioisomeric 3‐cyano‐2‐methoxy‐3a‐alkylfuro[2,3‐b]‐ and [3,2‐b]indoles were evidenced by product ions [M ? 32]^+?, consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2‐indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M ? 32]^+? ion. Additional thermal gas‐phase reaction products were characterized by comparison with an authentic sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Neutral Hexacoordinate Tin(IV) Halide Complexes with 4,4'-Dimethy-2,2'-bipyridine

A series of three neutral, hexacoordinate tin(IV) complexes were synthesized by the reaction of 4,4'-dimethyl-2,2'-bipyridine (DMB) with SnX₄, X = Cl, Br, and I, as starting materials. The complexes (DMB)SnX₄ were characterized in solution by ¹H, ¹³C, and ¹¹⁹Sn NMR spectroscopy, and in the solid-state by ¹¹⁹Sn MAS NMR spectroscopy. In addition, single-crystal X-ray diffraction and elemental analysis were used to confirm the molecular structures. In these complexes, the tin atom adopts a distorted octahedral arrangement and the DMB acts as a bidentate N,N'-chelate ligand. Computational DFT methods were also employed to gain more insight into the nature of the bonding in these complexes, including the hypothetical complexes (DMB)SnX₄ (X = F, At). Additionally, the validity and reliability of the ¹¹⁹Sn NMR chemical shifts were examined. The calculated values were compared with the experimental signals and the effects of structure and solvent are discussed. Finally, all of the complexes (DMB)SnX₄ were successfully tested for the ring-opening polymerization (ROP) of bulk ε-caprolactone under non-dried and aerobic conditions as precatalyst.     

Synthesis and Unexpected Rearrangement of a Hydroxyphostone (1)

Abstract

During our investigations on the wide range of stereoselective alkylations of 6-membered ring phostones,¹ we uncovered a novel rearrangement of 3-(diphenylhydroxymethyl)-2-ethoxy-2-oxo-1,2-oxaphosphorinane (1). The cis/trans diastereomers of 1 were prepared by the reaction of benzophenone with the appropriate ylide of the parent phostone (3).² When trans- 1 was left unattended at rt in CH₂Cl₂ a new compound, 2, was isolated which showed a significant downfield ³¹P shift and a higher melting point. Upon heating to the melting point 2 decomposed to give 4, which suggests that 2 may be an intermediate in the conversion of 1 to the Wittig-like product 4. The IR, ¹H, ¹³C, ³¹P, and 2-D NMR spectral data along with independent synthesis confirmed the identity of 2. Subsequently, 2 was also produced in 70% yield when cis- 1 was treated with CH₂Cl₂/ether-HC1_aq at 50–60°C for 2 weeks, but this product was contaminated with 30% of the exocyclic alkene 5. No rearrangement was observed when 1 was treated with TsOH/EtOH or HPF₆; only 5 was produced. The stereochemistry and mechanisms of these transformations are presented.     

Extended WKB Method,Resonances and Supersymmetric Radial Barriers

Semiclassical approximations are implemented in the calculation of position and width of low-energy resonances for radial barriers. The numerical integrations are delimited by τ/τ _life≪8, with τ the period of a classical particle in the barrier trap and τ _life the resonance lifetime. These energies are used in the construction of ‘haired’ short-range potentials as the supersymmetric partners of a given radial barrier. The new potentials could be useful in the study of the transient phenomena which give rise to the Moshinsky’s diffraction in time.     

Stereospecific 5JHortho,OMe couplings in methoxyindoles,methoxycoumarins, and methoxyflavones

Long‐range coupling constants ⁵J_Hortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the –OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear ¹H–¹H couplings were confirmed by irradiation of the –OMe signal. Density functional theory calculations of ⁵J_Hortho,OMe using the modified aug‐cc‐pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software. Copyright © 2014 John Wiley & Sons, Ltd.     

A polyhedral approach to the stability of a family of coalitions

Using polyhedral combinatorics and graph theory results, we study unstable families of coalitions and analyze the effect of adding players or deleting coalitions in order to obtain a stable family. We also generalize the definitions and results to the case of fractional participation of players in coalitions.     

Efficient Palladium‐Catalyzed Aminocarbonylation of Aryl Iodides Using Palladium Nanoparticles Dispersed on Siliceous Mesocellular Foam

A highly dispersed nanopalladium catalyst supported on mesocellular foam (MCF), was successfully used in the heterogeneous catalysis of aminocarbonylation reactions. During the preliminary evaluation of this catalyst it was discovered that the supported palladium nanoparticles exhibited a “release and catch” effect, meaning that a minor amount of the heterogeneous palladium became soluble and catalyzed the reaction, after which it re‐deposited onto the support.     

New Saccharinato/Ammonia Complexes of Nickel(II) and Zinc(II). A Structural and Spectroscopic Study

Two new saccharinate/NH₃ complexes of composition [Ni(sac)₂(NH₃)₄] and [Zn(sac)₂(NH₃)₂] were obtained and their crystal structures determined by single crystal X‐ray diffractometry. The elongated octahedral Ni^II complex crystallizes in the monoclinic P2₁/c space group with Z = 2 whereas the tetrahedral Zn^II complex is triclinic (space group and Z = 2). For [Ni(sac)₂(NH₃)₄] the magnetic moment and electron absorption spectrum were obtained and discussed. The infrared spectra of both complexes were also recorded and briefly commented.