A Tamed Reactive Intermediate

Lambert, Joseph B.

doi:10.1126/science.1167321

Cited by 6 publications

(7 citation statements)

References 9 publications

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“…Reaction is the “soul” of chemistry. In reaction schemes, “unobserved” intermediates were first hypothesized more than a century ago and only indirect evidence points to their existence because of their high reactivity [ 158 ]. The characterization of reactive intermediates is central to mechanistic and quantitative understanding of modern chemistry and a molecular view of biology.…”

Section: Discussionmentioning

confidence: 99%

The Expanding Role of Electrospray Ionization Mass Spectrometry for Probing Reactive Intermediates in Solution

et al. 2012

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Within the past decade, electrospray ionization mass spectrometry (ESI-MS) has rapidly occupied a prominent position for liquid-phase mechanistic studies due to its intrinsic advantages allowing for efficient “fishing” (rapid, sensitive, specific and simultaneous detection/identification) of multiple intermediates and products directly from a “real-world” solution. In this review we attempt to offer a comprehensive overview of the ESI-MS-based methodologies and strategies developed up to date to study reactive species in reaction solutions. A full description of general issues involved with probing reacting species from complex (bio)chemical reaction systems is briefly covered, including the potential sources of reactive intermediate (metabolite) generation, analytical aspects and challenges, basic rudiments of ESI-MS and the state-of-the-art technology. The main purpose of the present review is to highlight the utility of ESI-MS and its expanding role in probing reactive intermediates from various reactions in solution, with special focus on current progress in ESI-MS-based approaches for improving throughput, testing reality and real-time detection by using newly developed MS instruments and emerging ionization sources (such as ambient ESI techniques). In addition, the limitations of modern ESI-MS in detecting intermediates in organic reactions is also discussed.

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Section: Discussionmentioning

confidence: 99%

The Expanding Role of Electrospray Ionization Mass Spectrometry for Probing Reactive Intermediates in Solution

et al. 2012

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“…20 The iminium chemistry has been evaluated by diverse experimental 21−26 and theoretical 27−32 approaches and has become a basis for the numerous reports on diverse synthetic and catalytical pathways, including recent strategies based on these species, 33−35 despite the difficulties in characterizing the iminium intermediates in the reaction media. 20,36,37 The combination of ESI-MS/MS and infrared multiple photon dissociation (IRMPD) spectroscopy is one of the most powerful techniques to probe reaction systems and has been used to evaluate many reaction mechanisms. 38−43 The combination of high sensibility and dynamic range of mass spectrometry with the structural and conformational identification capabilities of infrared spectroscopy of gas phase ions allows structural identification of reaction intermediates not achieved by mass spectrometry alone or other spectroscopic techniques, especially when combined with theoretical calculations.…”

Section: ■ Introductionmentioning

confidence: 99%

Benzoxazine Formation Mechanism Evaluation by Direct Observation of Reaction Intermediates

2019

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Benzoxazine formation is a fundamental step in the preparation of polybenzoxazine resins, and a detailed description of the mechanism governing the formation of benzoxazine and side products is vital for improving the properties and performance of these resins. Determination of the nature and properties of reaction intermediates is not trivial. Therefore, a Mannich-type condensation of aniline, formaldehyde, and phenol was evaluated as a potential method to form benzoxazine. Coupling positive mode electrospray ionization mass spectrometry (ESI(+)-MS) with infrared multiple photon dissociation (IRMPD) spectroscopy allowed unambiguous determination of an iminium-based mechanism and the direct observation of iminium intermediates. The benzoxazine formation mechanism was indirectly confirmed by the observation of side products that are relevant to the polymerization step, and directly confirmed by the identification of four distinct reaction intermediates that were completely characterized by IRMPD spectroscopy. The benzoxazine monomer was also shown to undergo isomerization under standard ESI-MS analysis conditions, suggesting the presence of a mixture of three isomers during their usual ESI-MS analysis.

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“…This is also significant in a different sense. In a commentary on the results obtained by Baines and co-workers, Lambert and Müller had suggested that these unusual compounds could be employed as the starting point for new synthetic strategies: , as the Ge(II) dication lay uncoordinated and accessible at the center of the cage with plenty of space for substrates to enter, they could be approached by a range of substrates and new products could therefore be made from the subsequent interaction between the Ge(II) dication and the different substrates. However, no reports of such synthetic strategies have been reported to date.…”

Section: Results and Discussionmentioning

confidence: 99%

“…An even more interesting question pertains to the general expectation that had been observed about these systems when they were first reported nearly 12 years back: if they could be employed as the starting point for various synthetic routes because of the ready availability of a highly reactive naked germanium dication that could be subjected to remote bond activation reactions on a variety of substrates. 9 Such an expectation has not been realized. This is not because of steric constraints because the encapsulating cage provides ample space for the approach and departure of substrates.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, why does it stay isolated at the center of the cage, interacting only through electrostatic means with the atoms of the cage and forgoing almost any covalent interactions altogether? An even more interesting question pertains to the general expectation that had been observed about these systems when they were first reported nearly 12 years back: if they could be employed as the starting point for various synthetic routes because of the ready availability of a highly reactive naked germanium dication that could be subjected to remote bond activation reactions on a variety of substrates . Such an expectation has not been realized.…”

Section: Introductionmentioning

confidence: 99%

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Unraveling the Hidden Role of the Counteranion in “Cation in a Cage” Systems

et al. 2020

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The current work showcases general principles at play in systems consisting of cations present inside molecular cages. Such systems, relevant to chemistry and biology, have been carefully investigated by computational methods. The important Ge(II)-encapsulating cage systems have been studied first. The very fact that such compounds exist appears highly unlikely, given the highly reactive nature of the Ge(II) dication. Our studies reveal what really occurs in solution when such complexes are formed: the Ge(II) dications are actually present as [Ge−X] + (where X is the "non-coordinating" counterion employed in such systems) during entry and subsequent existence at the center of the cage. Hence, what is actually present is a "pseudomonocation". Interestingly, such pseudomonocationencapsulated cages are seen to be equally relevant in systems of biological importance, such as for dicationic s block-based ionophores. In explaining such cases, the concept of "isoionicity" is introduced, demonstrating that the counterion-coordinated dications are isoionic with a monocation, such as Li(I), isolated in the same ionophore.

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A Tamed Reactive Intermediate

Cited by 6 publications

References 9 publications

The Expanding Role of Electrospray Ionization Mass Spectrometry for Probing Reactive Intermediates in Solution

The Expanding Role of Electrospray Ionization Mass Spectrometry for Probing Reactive Intermediates in Solution

Benzoxazine Formation Mechanism Evaluation by Direct Observation of Reaction Intermediates

Unraveling the Hidden Role of the Counteranion in “Cation in a Cage” Systems

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