Electrospray ionization of dilute solutions of phenylpyridines (phpy) in the presence of nickel(II) chloride leads to gaseous ions of the type [Ni(phpy)(m)](2+) with m = 3-5 and [NiCl(phpy)(n)](+) with n = 1-3, which are characterized by various gas-phase experiments in combination with calculations using density functional theory. Of the regioisomeric phpy's, 2-phpy behaves drastically different compared to 3- and 4-phpy. Ion mobility mass spectrometry allows a differentiation of the gaseous ions and an elucidation of characteristic properties of the metal complexes. For 2-phpy, C-H bond activation in the [NiCl(phpy)(2)](+) complex is significant, whereas this route is almost suppressed for the corresponding complexes of 3- and 4-phpy and only occurs at elevated energies.
- MeSH
- kationty chemie MeSH
- komplexní sloučeniny chemie MeSH
- kvantová teorie MeSH
- nikl chemie MeSH
- plyny chemie MeSH
- pyridiny chemie MeSH
- stereoizomerie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- 2-phenylpyridine MeSH Prohlížeč
- kationty MeSH
- komplexní sloučeniny MeSH
- nickel chloride MeSH Prohlížeč
- nikl MeSH
- plyny MeSH
- pyridiny MeSH
RATIONALE: Heavy metals are both a problem for the environment and an important resource for industry. Their selective extraction by means of organic ligands therefore is an attractive topic. The coordination of three thiacrown ethers to late 3d-metal ions was investigated by a combination of electrospray ionization mass spectrometry (ESI-MS) and electron paramagnetic resonance (EPR). METHODS: The mass spectrometric experiments were carried out in an ion trap mass spectrometer with an ESI source. Absolute binding constants were estimated by comparison with data for 18-crown-6/Na(+). EPR spectroscopy was used as a complementary method for investigating the Cu(I) /Cu(II) redox couple. RESULTS: The study found that thiacrown ethers preferentially bind traces of copper even at an excess of other metal ions (Co(II), Ni(II), and Zn(II)). The absolute association constants of the Cu(I) complexes were about 10(8) M(-1), and about two orders of magnitude lower for the other 3d-metal cations. The EPR spectra demonstrated that the reduction from Cu(II) to Cu(I) upon formation of the [(thiacrown)Cu](+) species takes place in solution. CONCLUSIONS: ESI-MS demonstrated that the three thiacrown ligands examined had high binding constants as well as good selectivities for copper(I) at low concentrations, and in the presence of other metal ions. By a combination of ESI-MS and EPR spectrometry it was shown that the reduction from Cu(II) to Cu(I) occurred in solution.
- Publikační typ
- časopisecké články MeSH
Despite the simplicity of the molecule, the site of single deprotonation of p-hydroxybenzoic acid upon electrospray ionization (ESI) has recently formed a subject of debate in this journal. By means of NMR experiments in solution and gas-phase studies employing ion-mobility mass spectrometry (IM-MS), the apparent controversy is resolved. It is shown that irrespective of the solvent the carboxylate tautomer is preferred in solution, while the opposite holds true for isolated ions in the gas phase. The tautomer distribution sampled in the gas phase very much depends on the actual solvent used in ESI, the pH value, as well as the total concentration. Moreover, the occurrence of gas-phase reactions in the course of the ESI process influences the tautomer ratio. Implications for correlations between ESI mass spectra and solution-phase chemistry are discussed.
- Publikační typ
- časopisecké články MeSH
Mechanistic studies form the basis for a better understanding of chemical processes, helping researchers develop more sustainable reactions by increasing the yields of the desired products, reducing waste production, and lowering the consumption of resources and energy overall. Conventional methods for the investigation of reaction mechanisms in solution include kinetic studies, isotope labeling, trapping of reactive intermediates, and advanced spectroscopic techniques. Within the past decade, electrospray ionization mass spectrometry (ESI-MS) has provided an additional tool for mechanistic studies because researchers can directly probe liquid samples by mass spectrometry under gentle conditions. Specifically, ESI-MS allows researchers to identify the molecular entities present in solution over the course of a chemical transformation. ESI-MS is particularly useful for investigations of organic reactions or metal catalysis that involve ionic intermediates. Accordingly, researchers are increasingly using ESI-MS in mechanistic studies and catalyst development. However, a further understanding of the ESI process and how it can facilitate mechanistic studies has not accompanied this increased use of the technique. Therefore, at least in part the ESI-MS method not only has offered great promise for the elucidation of reaction mechanisms but also became a black box with the occasional risk of misinterpretation. In this Account, we summarize applications of ESI-MS for synthetic and mechanistic research. Recently researchers have established direct linkages between gas-phase data obtained via ESI-MS and processes occurring in solution, and these results reveal qualitative and quantitative correlations between ESI-MS measurements and solution properties. In this context, time dependences, concentration series, and counterion effects can serve as criteria that allow researchers assess if the gas-phase measurements correlate with the situation in the solution. Furthermore, we report developments that bridge the gap between gas-phase and solution-phase studies. We also describe predictions derived from ESI-MS that have been verified with solution-phase chemistry experiments.
- Publikační typ
- časopisecké články MeSH
Electron-transfer reactions between hydrocarbon dications and neutral hydrocarbons lead to an unequal deposition of the excess energy from the reaction in the pair of monocations formed. The initial observation of this phenomenon was explained by the different states accessible upon single-electron capture by a dication compared to single-electron ejection from a neutral compound. Alternatively, however, isomeric structures of the dicationic species, pronounced Franck-Condon effects, as well as excess energy in the dicationic precursors could cause the asymmetric energy partitioning in such dication/neutral collisions. Here, the investigation of this phenomenon in an interdisciplinary cooperation is described, shedding light not only upon a possible solution of the problem at hand, but also providing an example for the synergistic benefits of international research networks applying complementary approaches.
- Publikační typ
- časopisecké články MeSH
Even in the highly diluted gas phase, rather than electron transfer the benzene dication C(6)H(6)(2+) undergoes association with dinitrogen to form a transient C(6)H(6)N(2)(2+) dication which is best described as a ring-protonated phenyl diazonium ion. Isotopic labeling studies, photoionization experiments using synchrotron radiation, and quantum chemical computations fully support the formation of protonated diazonium, which is in turn a prototype species of superacidic chemistry in solution. Additionally, reactions of C(6)H(6)(2+) with background water involve the transient formation of diprotonated phenol and, among other things, afford a long-lived C(6)H(6)OH(2)(2+) dication, which is attributed to the hydration product of Hogeveen's elusive pyramidal structure of C(6)H(6)(2+), as the global minimum of doubly ionized benzene. Nitrogen is essential for the formation of the C(6)H(6)OH(2)(2+) dication in that it mediates the formation of the water adduct, while the bimolecular encounter of the C(6)H(6)(2+) dication with water only leads to (dissociative) electron transfer.
- Publikační typ
- časopisecké články MeSH
Oligo-Tröger bases are auspicious scaffolds of molecular engineering, which motivates studies on the mechanism of their interconversion and on the facile determination of the relative configuration of their diastereoisomers. Protonated, sodiated, and argentated species of those compounds were therefore studied via ion-mobility mass spectrometry (IM-MS), allowing differentiation on the basis of the shapes of the ions. First, the isomerization was confirmed to be acid-catalyzed as it takes place readily in the case of protonated Tröger bases, whereas the metallated bases are configurationally stable. Second, the corrected arrival times of the various isomers of the cationized bases were found to show distinct differences in IM-MS, and their excellent correlation with the cross sections obtained from quantum chemical calculations paves the way toward the easy identification of diastereoisomers.
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Electrospray ionization is suggested as a complementary technique for the investigation of the solution chemistry of metal salts, which allows us to achieve direct insight into the molecular entities present in solution. While the transfer of the metal ions from solution to the gas phase in the course of the electrospray process is associated with significant changes in concentration, pH, and also composition in the case of mixed solvents, systematic studies of concentration series can provide criteria to assess the extent to which the gas-phase data correlate with the situation in solution. While there does not exist a 1 ∶ 1 correlation between mass spectrometric measurements and solution properties, very useful qualitative molecular insights can be achieved and quantitative analysis can be made once the specific circumstances of the ionization process are taken into account.
- Publikační typ
- časopisecké články MeSH
