Probing Hydrogen Bond Energies by Mass Spectrometry Hai-Feng Su, - - PowerPoint PPT Presentation

Probing Hydrogen Bond Energies by Mass Spectrometry

Hai-Feng Su, Lan Xue,* Yun-Hua Li, Shui-Chao Lin, Yi-Mei Wen, Rong-Bin Huang, Su-Yuan Xie,* and Lan-Sun Zheng

• J. Am. Chem. Soc. 2013, 135, 6122–6129

State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, China Department of Chemistry, Ningde Normal University, China Amitava Srimany 24-08-2013

INTRODUCTION

• Hydrogen bond is a class of attractive interaction ubiquitous in materials and prevalent in

inorganic, organic, supramolecular, biological, medicinal, and pharmaceutical chemistry.

• Properties like catalyzed reactions, chelate cooperativity, mechanical properties, and glass

transition are highly sensitive to the strength of the hydrogen bond.

• Most of the available methods for determination of the hydrogen bond, such as NMR and IR

spectroscopy, are far from quantification regarding hydrogen bond energies.

• Historically, the shortening of distance between donor and acceptor determined by

crystallographic data corresponds with the strength of hydrogen bond.

• The crystal packing is driven possibly by a combination of various intermolecular forces, e.g.,

hydrogen bond, halogen bond, π−π interaction, or others. It is hard to distinguish the hydrogen bond from the other intermolecular forces by means of crystallography itself.

• In this paper, DESI-MS have been used to probe the hydrogen bonds in the complexes of

benzothiazoles and carboxylic acids.

RESULTS AND DISCUSSION

N S NH2

2-Aminobenzothiazole Hydrogen bond motifs in the cocrystals

Hydrogen bond lengths of compounds 1−5 from crystallographic data

DESI MS data ESI MS data

Pristine crystals of complex 1 and complex 3 Setting closely, no contact or overlap DESI-MS Pristine crystals of complex 1 and complex 3 Setting overlap DESI-MS Recrystallization of complex 1 and complex 3 DESI-MS

Position of protonation

2A6MBT ESI-MS CH3OH solvent 2A6MBT ESI-MS CH3OD solvent 2A6MBT.aze DESI-MS CH3OH solvent 2A6MBT.aze DESI-MS CH3OD solvent

Possible paths for the dissociation of 2A6MBT

Mass spectrum of 2A4MBT.octa acquired in a CID collision energy Fragmentation rate = Fragment intensity/Total (parent + fragment) intensity

Fragmentation efficiency curves for complexes 1−5

y = 2.754−0.007x Correlation between the length of O−H···N (Å) and the normalized collision energy (%) at 100% fragmentation rate

Correlation between the slope of the fragmentation efficiency curve and the average difference of the hydrogen bond between O−H···N and N−H···O (Å) y = 48.9−116.6x

Fragmentation efficiency curves for complexes 6−8

Complex O−H···N length (Å) from MS O−H···N length (Å) from crystallography N−H···O length (Å) from MS N−H···O length (Å) from crystallography 6: 2A6MOBT.mal 2.682 2.701(3) 2.963 2.833(3) 7: 2A6MOBT.pim 2.671

• 2.934
• 8: 2A6MOBT.seb

2.656 2.649(4) 2.965 3.057(5) H-bond length data from MS and crystallography

Hydrogen-bonded complex of 6 (top) and the corresponding hydrogen bond motifs in 1−5 and 8

SUMMARY AND CONCLUSIONS

• In this work, a mass spectrometric method, based on DESI-MS with CID fragmentation, for

probing the hydrogen bonds have been proposed.

• The strengths of the hydrogen bonds between the benzothiazoles and the carboxylic acids

determined by X-ray crystallography are well correlated with the slope of the fragmentation efficiency curves and the collision energy of CID at a 100% fragmentation rate in the fragmentation efficiency curves of the corresponding mass spectra.

• Mass spectrometry is a complement of X-ray crystallography for probing hydrogen bonds

because of some unavoidable additional forces in the crystal to influence the accurateness

• f crystallographic data.

FUTURE POSSIBILITIES

• This method can be just be extended towards other systems to probe H-bonds.
• MS can be used to probe metal complexes. For example, various metal-EDTA, metal-

porphyrin complexes can be probed to find relative binding strength of metals with the ligand.

• With different degree of dissociation of complexes in the gas phase, different gas phase

reactions can be initiated.

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