6 research outputs found
Energy-Resolved Ion Mobility Spectrometry: Composite Breakdown Curves for Distinguishing Isomeric Product Ions
Identification of lipopeptides (LpAA)
synthesized
from bacteria involves the study of structural characterization. Twenty LpAA have been characterized using commercial tandem high-resolution
mass spectrometers in negative electrospray, employing nonresonant
excitation in “RF only” collision cells and generally
behave identically. However, [LpAA-H]− (AA = Asp or Glu) shows surprising fragmentation pathways, yielding
a complementary fatty acid carboxylate and dehydrated amino acid fragment
anions. In this study, the dissociation mechanisms of [C12Glu-H]− were determinate using energy-resolved mass spectrometry
(ERMS). Product ion breakdown profiles are, generally, unimodal with
full width at half-maximum (fwhm) increasing as product ion m/z ratios decrease, except for the two
product ions of interest (fatty acid carboxylate and dehydrated glutamate)
characterized by broad and composite profiles. Such behavior was already
shown for other ions using a custom-built guided ion beam mass spectrometer.
In this study, we investigate the meaning of these particular profiles
from an ERMS breakdown, using fragmentation mechanisms depending on
the collision energy. ERMS on line with ion mobility spectrometry
(IMS), here called ER-IMS, provides a way to probe such questions.
Broad or composite profiles imply that the corresponding product ions
may be generated by two (or more) pathways, resulting in common or
isomeric product ion structures. ER-IMS analysis indicates that the
fatty acid carboxylate product ion is produced with a common structure
through different pathways, while dehydrated glutamate has two isomeric
forms depending on the mechanism involved. Drift time values correlate
with the calculated collision cross section that confirms the product
ion structures and fragmentation mechanisms
Asymmetric [2+2+1] cyclopentannulation of olefins. Ring expansion of 2-N-methyl-N-tosyl-cyclobutanone
alpha-N-Methyl-N-tosyl cyclobutanones 2 which had been previously prepared in good yields and high enantiomeric excesses from olefins and chiral keteniminium salts have been converted into the corresponding oxiranes 3 by reaction with dimethylsulfonium methylid. The stereochemistry of this reaction was found to be dependent on several factors which have been analyzed. Treatment of these oxiranes with a stoichiometric amount of lithium iodide in refluxing tetrahydrofuran gave excellent yields of monocyclic or fused cyclopentenones 4 resulting from a P-elimination of N-methyl-N-tosylamide from a primarily formed cyclopentanone. The ring-expansion was totally selective but for oxiranes attached to a bicyclo[4.2.0]octanone system. In all cases, the enantiomeric purities of the starting cyclobutanones were preserved throughout the sequence which thus represents a useful [2+2+1] strategy for the cyclopentannulation of olefins. (C) 2002 Elsevier Science Ltd. All rights reserved
Luminescent, Enantiopure, Phenylatopyridine Iridium-Based Coordination Capsules
The first molecular capsule based on an [Ir(ppy)<sub>2</sub>]<sup>+</sup> unit (ppy = 2-phenylatopyridine) has been prepared.
Following
the development of a method to resolve <i>rac</i>-[(Ir(ppy)<sub>2</sub>Cl)<sub>2</sub>] into its enantiopure forms, homochiral Ir<sub>6</sub>L<sub>4</sub> octahedra where obtained with the tritopic 1,3,5-tricyanobenzene.
Solution studies and X-ray diffraction show that these capsules encapsulate
four of the six associated counteranions and that these can be exchanged
for other anionic guests. Initial photophysical studies have shown
that an ensemble of weakly coordinating ligands can lead to luminescence
not present in comparable mononuclear systems
Luminescent, Enantiopure, Phenylatopyridine Iridium-Based Coordination Capsules
The first molecular capsule based on an [Ir(ppy)<sub>2</sub>]<sup>+</sup> unit (ppy = 2-phenylatopyridine) has been prepared.
Following
the development of a method to resolve <i>rac</i>-[(Ir(ppy)<sub>2</sub>Cl)<sub>2</sub>] into its enantiopure forms, homochiral Ir<sub>6</sub>L<sub>4</sub> octahedra where obtained with the tritopic 1,3,5-tricyanobenzene.
Solution studies and X-ray diffraction show that these capsules encapsulate
four of the six associated counteranions and that these can be exchanged
for other anionic guests. Initial photophysical studies have shown
that an ensemble of weakly coordinating ligands can lead to luminescence
not present in comparable mononuclear systems
Making hybrid [n]-rotaxanes as supramolecular arrays of molecular electron spin qubits
Quantum information processing (QIP) would require that the individual units involved--qubits--communicate to other qubits while retaining their identity. In many ways this resembles the way supramolecular chemistry brings together individual molecules into interlocked structures, where the assembly has one identity but where the individual components are still recognizable. Here a fully modular supramolecular strategy has been to link hybrid organic-inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and [7]-rotaxanes. The ring components are heterometallic octanuclear [Cr7NiF8(O2C(t)Bu)16](-) coordination cages and the thread components template the formation of the ring about the organic axle, and are further functionalized to act as a ligand, which leads to large supramolecular arrays of these heterometallic rings. As the rings have been proposed as qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin devices for QIP. Double electron-electron resonance experiments demonstrate inter-qubit interactions suitable for mediating two-qubit quantum logic gates
Luminescent, Enantiopure, Phenylatopyridine Iridium-Based Coordination Capsules
The first molecular capsule based on an [Ir(ppy)<sub>2</sub>]<sup>+</sup> unit (ppy = 2-phenylatopyridine) has been prepared.
Following
the development of a method to resolve <i>rac</i>-[(Ir(ppy)<sub>2</sub>Cl)<sub>2</sub>] into its enantiopure forms, homochiral Ir<sub>6</sub>L<sub>4</sub> octahedra where obtained with the tritopic 1,3,5-tricyanobenzene.
Solution studies and X-ray diffraction show that these capsules encapsulate
four of the six associated counteranions and that these can be exchanged
for other anionic guests. Initial photophysical studies have shown
that an ensemble of weakly coordinating ligands can lead to luminescence
not present in comparable mononuclear systems