Gas phase ion chemistry of an ion mobility spectrometry based explosive trace detector elucidated by tandem mass spectrometry.

The gas phase ion chemistry for an ion mobility spectrometer (IMS) based explosive detector has been elucidated using tandem mass spectrometry. The IMS system, which is operated with hexachloroethane and isobutyramide reagent gases and an ion shutter type gating scheme, is connected to the atmospheric pressure interface of a triple quadrupole mass spectrometer (MS/MS). Product ion masses, daughter ion masses, and reduced mobility values for a collection of nitro, nitrate, and peroxide explosives measured with the IMS/MS/MS instrument are reported. The mass and mobility data together with targeted isotopic labeling experiments and information about sample composition and reaction environment are leveraged to propose molecular formulas, structures, and ionization pathways for the various product ions. The major product ions are identified as [DNT-H](-) for DNT, [TNT-H](-) for TNT, [RDX+Cl](-) and [RDX+NO2](-) for RDX, [HMX+Cl](-) and [HMX+NO2](-) for HMX, [NO3](-) for EGDN, [NG+Cl](-) and [NG+NO3](-) for NG, [PETN+Cl](-) and [PETN+NO3](-) for PETN, [HNO3+NO3](-) for NH4NO3, [NO2](-) for DMNB, [HMTD-NC3H6O3+H+Cl](-) and [HMTD+H-CH2O-H2O2](+) for HMTD, and [(CH3)3CO2](+) for TATP. In general, the product ions identified for the IMS system studied here are consistent with the product ions reported previously for an ion trap mobility spectrometer (ITMS) based explosive trace detector, which is operated with dichloromethane and ammonia reagent gases and an ion trap type gating scheme. Differences between the explosive trace detectors include the [NG+Cl](-) and [PETN+Cl](-) product ions being major ions in the IMS system compared to minor ions in the ITMS system as well as the major product ion for TATP being [(CH3)3CO2](+) for the IMS system and [(CH3)2CNH2](+) for the ITMS system.

Cu(II) cross-linked antiparallel dipeptide duplexes using heterofunctional ligand-substituted aminoethylglycine.

Two artificial dipeptides containing both a pendant monodentate (pyridine (py)) and tridentate (terpyridine (tpy) or phenyl terpyridine (varphi-tpy)) ligand on an aminoethylglycine (aeg) backbone have been synthesized. These oligopeptides are fully characterized by one and two-dimensional NMR spectroscopy, mass spectrometry, and elemental analysis. The ligands were chosen because they coordinate Cu(2+) to form [Cu(py)(tpy)](2+) complexes; when bound to the dipeptide scaffold, Cu(2+) chelation cross-links the strands to form double-stranded duplex structures with an antiparallel arrangement. Using spectrophotometric titrations, we observe coordination of one Cu(2+) metal per dipeptide strand. Mass spectrometry, NMR spectroscopy, vapor pressure osmometry, and HPLC confirm that the resulting structures are the dipeptide duplex cross-linked by two metal centers.

Inorganic biomimetic nanostructures.

Supramolecular structures modeled after biological systems (DNA and enzymes) are being developed to simultaneously mimic natural biological functions including catalysis, information storage, and self-assembly and to engineer novel electronic and magnetic properties. Structural mimics of nucleic acids containing multiple metal-coordinating ligands, and comprising natural and artificial bases or completely synthetic systems, create stable double-stranded structures with new electronic, spectroscopic, and magnetic properties. Supramolecular inorganic mimics of enzymatic function, including metallonucleases and metalloproteases, have begun to be constructed. Alternatively, metal-organic-frameworks have potential as artificial catalysts with substrate-specificity and size-selectivity analogous to biological processes. This review describes some of the recent themes in inorganic supramolecular systems that aim to mimic and exploit nature's ability to self-assemble polyfunctional architectures for new materials and biological applications.

Tetraplatinated artificial oligopeptides afford high affinity intercalation into dsDNA.

This paper reports the binding of an artificial tetrapeptide to which are tethered four Pt(II) complexes (i.e., [Pt(tpy)(py)]48+) with a 12 base pair duplex DNA oligonucleotide. Isothermal Titration Calorimetry reveals that two tetrametallic peptides stoichiometrically bind to each DNA duplex with a binding constant, KB, of 1.7 x 106 M-1, with a change in free energy of -8.5 kcal/mol. This KB represents an affinity 2 orders of magnitude greater than that of the monometallic analogue [Pt(tpy)(pic)]2+ for the same dsDNA sequence. The metalated peptides bind by intercalation into the DNA, partially unwinding the helix while stabilizing the structure, causing an increase in the dsDNA melting temperature of 25 degrees C.