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Rationale: The mechanism underlying dopant‐assisted atmospheric pressure photoionization's (APPI) formation of ions is unclear and still under debate for many chemical classes. In this study, we reexamined the gas‐phase reaction mechanisms responsible for the generation of [M–H]+ precursor ions, resulting from the loss of a single hydrogen atom, in a series of N‐alkyl‐substituted thieno[3,4‐c]‐pyrrole‐4,6‐dione (TPD) derivatives. Methods: Atmospheric pressure photoionization combined with higher order MS/MSn using high‐resolution mass spectrometry (APPI‐HR‐CID‐MSn) and electronic structure calculations using density functional theory were used to determine the chemical structure of observed [M–H]+ ions. Results: As a result, the higher order MSn (n = 3) experiments revealed a reversed Diels–Alder fragmentation mechanism, leading to a common fragment ion at m/z 322 from the studied [M1–5–H]+ ion species. In addition, the calculation for two chemical structure models (N‐alkyl‐TPD1 and N‐alkyl‐TPD5) showed that the fragment structure, resulting from the removal of the hydrogen atom connected to the third carbon atom of the N‐alkyl side chain, has a more stable cyclic form compared with the linear one. Conclusions: The proposed chemical structure of the N‐alkyl TPD ion species, following the loss of a single hydrogen atom, was revealed during APPI‐HR‐CID‐MSn (n = 3) experiments on the [M–H]+ species. Hydrogen radical (H•) abstraction from the alkyl side chain (e.g., hexyl, heptyl, octyl, 2‐ethylhexyl, and nonyl) triggered a rearrangement in the radical cation structure of the N‐alkyl‐TPD derivatives, initiating cyclization and forming a six‐membered ring that connects the oxygen atom to the third carbon atom in the alkyl chain. In addition, theoretical calculations supported the APPI‐HR‐CID‐MSn (n = 3) experiments by demonstrating that the proposed chemical structure, resulting from the intramolecular cyclization of the N‐alkyl‐TPD ion species, was stable in the presence of chlorobenzene. These findings will aid the structural determination and elucidation of molecules with similar core structures. [ABSTRACT FROM AUTHOR]

We report the direct introduction of biological samples into a high-resolution mass spectrometer, the LTQ-Orbitrap, as a fast tool for metabolomic studies. A proof of concept study was performed on yeast cell extracts that were introduced into the mass spectrometer by using flow injection analysis, with an acquisition time of 3 min. Typical mass spectra contained a few thousand m/z signals, 400 of which were found to be analytically relevant (i.e., their intensity was 3-fold higher than that of the background noise and they occurred in at least 60% of the acquisition profiles under identical experimental conditions). The method was validated by studies of the matrix effect, linearity, and intra-assay precision. Accurate mass measurements in the Orbitrap discriminated between isobaric ions and also indicated the elemental composition of the ions of interest with mass errors below 5 ppm, for identification purposes. The proposed structures were then assessed by MS' experiments via the linear ion trap, together with accurate mass determination of the product ions in the Orbitrap analyzer. When applied to the study of cadmium toxicity, the method was as effective as that initially developed by using LC/ESI-MS/ MS for a targeted approach. The same metabolic finger-prints were also subjected to multivariate statistical analyses. The results highlighted a reorganization of amino acid metabolism under cadmium conditions in order to increase the biosynthesis of glutathione.

Pyrolysis coupled to metastable atom bombardment (MAB) and time-of-flight mass spectrometry (TOFMS) is used for generating mass spectra from bovine urine samples obtained from cattle treated with anabolic steroids. These spectra constitute fingerprints, which can be discriminated by multivariate statistical analysis. Four main conclusions can be drawn from this work: (i) The use of different metastable gases, such as Xe*, Kr*, or [N.sub.2]*, as an energy-tunable ionization beamline allows control of the internal energy and the dissociation processes of the produced odd electron molecular ions, thus giving rise to complementary mass spectra fingerprints. (ii) A variable transformation depending on the biofluid matrix suitably contracts the frequency distribution of the generated data for low m/z ratios holding information related to endogenous metabolites encountered in urine. (iii) Coupling variable selection to statistical pattern recognition methods results in low error rates (

Biotin synthase, enzyme which catalyzes the transformation of dethiobiotin (DTB) to biotin, has an absolute requirement for S-adenosylmethionine. It has been shown that AdoMet was not the sulfur donor and it could belong to the family of enzymes, namely, pyruvate formate-lyase, anaerobic ribonucleotide reductase and lysine 2,3-aminomutase, which employ AdoMet as a source of deoxyadenosyl radical. Investigations into this possibility showed the involvement of a deoxyadenosyl radical in the activation of the functionalized positions.

A library of eleven cationic gold(III) complexes of the general formula [(C C)Au(N N)]+ when C C is either biphenyl or 4,4'‐ditertbutyldiphenyl and N N is a bipyridine, phenanthroline or dipyridylamine derivative have been synthesized and characterized. Contrasting effects on the viability of the triple negative breast cancer cells MDA‐MB‐231 was observed from a preliminary screening. The antiproliferative activity of the seven most active complexes were further assayed on a larger panel of human cancer cells as well as on non‐cancerous cells for comparison. Two complexes stood out for being either highly active or highly selective. Eventually, reactivity studies with biologically meaningful amino acids, glutathione, higher order DNA structures and thioredoxin reductase (TrxR) revealed a markedly different behavior from that of the well‐known coordinatively isomeric [(C N C)Au(NHC)]+ structure. This makes the [(C C)Au(N N)]+ complexes a new class of organogold compounds with an original mode of action. [ABSTRACT FROM AUTHOR]

Abstract Background The transcription factor STAT3 (signal transducer and activator of transcription 3) is frequently activated in tumor cells. Activated STAT3 forms homodimers, or heterodimers with other TFs such as NF-κB, which becomes activated. Cytoplasmic STAT3 dimers are activated by tyrosine phosphorylation; they interact with importins via a nuclear localization signal (NLS) one of which is located within the DNA-binding domain formed by the dimer. In the nucleus, STAT3 regulates target gene expression by binding a consensus sequence within the promoter. STAT3-specific decoy oligonucleotides (STAT3-decoy ODN) that contain this consensus sequence inhibit the transcriptional activity of STAT3, leading to cell death; however, their mechanism of action is unclear. Results The mechanism of action of a STAT3-decoy ODN was analyzed in the colon carcinoma cell line SW 480. These cells' dependence on activated STAT3 was verified by showing that cell death is induced by STAT3-specific siRNAs or Stattic. STAT3-decoy ODN was shown to bind activated STAT3 within the cytoplasm, and to prevent its translocation to the nucleus, as well as that of STAT3-associated NF-κB, but it did not prevent the nuclear transfer of STAT3 with mutations in its DNA-binding domain. The complex formed by STAT3 and the STAT3-decoy ODN did not associate with importin, while STAT3 alone was found to co-immunoprecipitate with importin. Leptomycin B and vanadate both trap STAT3 in the nucleus. They were found here to oppose the cytoplasmic trapping of STAT3 by the STAT3-decoy ODN. Control decoys consisting of either a mutated STAT3-decoy ODN or a NF-κB-specific decoy ODN had no effect on STAT3 nuclear translocation. Finally, blockage of STAT3 nuclear transfer correlated with the induction of SW 480 cell death. Conclusions The inhibition of STAT3 by a STAT3-decoy ODN, leading to cell death, involves the entrapment of activated STAT3 dimers in the cytoplasm. A mechanism is suggested whereby this entrapment is due to STAT3-decoy ODN's inhibition of active STAT3/importin interaction. These observations point to the high potential of STAT3-decoy ODN as a reagent and to STAT3 nucleo-cytoplasmic shuttling in tumor cells as a potential target for effective anti-cancer compounds.

A low-energy collision induced dissociation (CID) (low-energy CID) approach that can determine both activation energy and activation entropy has been used to evaluate gas-phase binding energies of host-guest (H-G) complexes of a heteroditopic hemicryptophane cage host (Zn (II)@1) with a series of biologically relevant guests. In order to use this approach, preliminary calibration of the effective temperature of ions undergoing resonance excitation is required. This was accomplished by employing blackbody infrared radiative dissociation (BIRD) which allows direct measurement of activation parameters. Activation energies and pre-exponential factors were evaluated for more than 10 H-G complexes via the use of low-energy CID. The relatively long residence time of the ions inside the linear ion trap (maximum of 60 s) allowed the study of dissociations with rates below 1 s-1. This possibility, along with the large size of the investigated ions, ensures the fulfilment of rapid energy exchange (REX) conditions and, as a consequence, accurate application of the Arrhenius equation. Compared with the BIRD technique, low-energy CID allows access to higher effective temperatures, thereby permitting one to probe more endothermic decomposition pathways. Based on the measured activation parameters, guests bearing a phosphate (-OPO32-) functional group were found to bind more strongly with the encapsulating cage than those having a sulfonate (-SO³-) group; however, the latter ones make stronger bonds than those with a carboxylate (-CO2-) group. In addition, it was observed that the presence of trimethylammonium (-N(CH3)3+) or phenyl groups in the guest's structure improves the strength of H-G interactions. The use of this technique is very straightforward, and it does not require any instrumental modifications. Thus, it can be applied to other H-G chemistry studies where comparison of bond dissociation energies is of paramount importance. [ABSTRACT FROM AUTHOR]