Experimental and Theoretical Investigation into the Correlation between Mass and Ion Mobility for Choline and Other Ammonium Cations in N<sub>2</sub>

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Noncovalent interactions of cucurbit [6]uril (CB[6]) with haloacetate and halide anions are investigated in the gas phase using electrospray ionization ion mobility mass spectrometry. Strong noncovalent interactions of monoiodoacetate, monobromoacetate, monochloroacetate, dichloroacetate, and trichloroacetate on the exterior surface of CB [6] are observed in the negative mode electrospray ionization mass spectra. The strong binding energy of the complex allows intramolecular S N 2 reaction of haloacetate, which yields externally bound CB[6]-halide complex, by collisional activation. Utilizing ion mobility technique, structures of exteriorly bound CB[6] complexes of haloacetate and halide anions are confirmed. Theoretically determined low energy structures using density functional theory (DFT) further support results from ion mobility studies. The DFT calculation reveals that the binding energy and conformation of haloacetate on the CB[6] surface affect the efficiency of the intramolecular S N 2 reaction of haloacetate, which correlate well with the experimental observation.

Section: Ion Mobility Study Of Cb[6]-haloacetate and Cb[6]-halide Commentioning

confidence: 67%

Unusual Complex Formation and Chemical Reaction of Haloacetate Anion on the Exterior Surface of Cucurbit[6]uril in the Gas Phase

Choi

Heo

et al. 2012

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“…A useful early review is that of Castleman and Keesee, but there are a number of more recent studies, including those from the Leone group[51], and others. A quantitative analysis of comparative modifier effects appears possible based on thermochemical free energy values from computational chemistry, optimized conformations considering energetics and steric hindrance, combined with computations of mobility [22, 52, 53] from predicted structures, and further investigations are in progress. The schema and thermochemistry for ion-cluster / modifier equilibria is summarized in Appendix A.…”

Section: Resultsmentioning

confidence: 99%

Understanding Gas Phase Modifier Interactions in Rapid Analysis by Differential Mobility-Tandem Mass Spectrometry

Kafle

Coy

Wong

et al. 2014

A systematic study involving the use and optimization of gas phase modifiers in quantitative differential mobility- mass spectrometry (DMS-MS) analysis is presented using mucleoside-adduct biomarkers of DNA damage as an important reference point for analysis in complex matrices. Commonly used polar protic and polar aprotic modifiers have been screened for use against two deoxyguanosine adducts of DNA: N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-4-ABP) and N-(deoxyguanosin-8-y1)-2-amino-l-methyl-6-phenylimidazo[4,5-b]pyridine (dG-C8-PhIP). Particular attention was paid to compensation voltage (CoV) shifts, peak shapes and product ion signal intensities while optimizing the DMS-MS conditions. The optimized parameters were then applied to rapid quantitation of the DNA adducts in calf thymus DNA. After a protein precipitation step, adduct levels corresponding to less than one modification in 106 normal DNA bases were detected using the DMS-MS platform. Based on DMS fundamentals and ab-initio thermochemical results we interpret the complexity of DMS modifier responses in terms of thermal activation and the development of solvent shells. At very high bulk gas temperature, modifier dipole moment may be the most important factor in cluster formation and cluster geometry in mobility differences, but at lower temperatures multi-neutral clusters are important and less predictable. This work provides a useful protocol for targeted DNA adduct quantitation and a basis for future work on DMS modifier effects.

“…Although limited structural parameters were reported, these structures appear to correspond to ACh01, ACh02, ACh04, and ACh05. A recent B3-LYP/6-31G(d,p) study by Kim et al [27], carried out to complement their ion mobility studies of tertiary amines and quaternary ammonium cations, found a global minimum that closely resembles ACh01.…”

Section: Dft Calculations On the Conformations Of Acetylcholinementioning

confidence: 99%

How does acetylcholine lose trimethylamine? A density functional theory study of four competing mechanisms

Lioe

Barlow

O’Hair

2009

Low-energy collision-induced dissociation (CID) of acetylcholine (ACh) yields only two fragment ions: the dominant C 4 H 7 O 2 ϩ ion at m/z 87, arising from trimethylamine loss; and protonated trimethylamine at m/z 60. Since the literature is replete with conflicting mechanisms for the loss of trimethylamine from ACh, in this article density functional theory (DFT) calculations are used to assess four competing mechanisms: (1) Path A involves a neighboring group attack to form a five-membered ring product, 2-methyl-1,3-dioxolan-2-ylium cation; (2) Path B is a neighboring group attack to form a three-membered ring product, 1-methyloxiranium ion; (3) Path C involves an intramolecular elimination reaction to form C¢O protonated vinylacetate; and (4) Path D is a 1,2-hydride migration reaction forming CH 2 -protonated vinylacetate. At the MP2/6-311ϩϩG(2d,p)//B3-LYP/6-31ϩG(d,p) level of theory path A is the kinetically favored pathway, with a transition-state energy barrier of 37.7 kcal mol Ϫ1 relative to the most stable conformer of ACh. The lowest energy pathway for the formation of protonated trimethylamine was also calculated to proceed via path A, involving proton transfer within the ion-molecule complex intermediate, with the exocylic methyl group being the proton donor. To confirm the site of proton transfer, low-energy CID of acetyl-d 3 -choline (d 3 -ACh) was carried out, which revealed loss of trimethylamine and the formation of Me 3 ND ϩ . (J Am Soc Mass Spectrom 2009, 20, 238 -246)