Hello! Please suggest what techniques can be used for detecting hydrogen-bonded systems in gas phase by mass spectrometry. MW of dimers = 332 Da. The essence of our problem is that we need to evaporate an organic solid (which is a hydrogen-bonded system, a cocrystal), and see whether any dimers or other complexes are formed in the gas phase. Is it possible that the ionizing voltage affects the stability of the dimers in the gas phase? Can one achieve "soft" sublimation conditions by reducing the heating rate and/or it is necessary to use isothermal mode at lower temperature? Are there are reports of such experiments that could allow us to study the dimers (n-mers) in gas phase?
Thanks in advance
we cannot detect Hydrogen bonded dimer, trimer.... species in gas phase in mass spectrometry, as molecules easily get separated as H- bonding is not very strong bond. during ionization molecules bind with H-bonding get separated.
Pankaj Yadav, you are right saying that "...molecules easily get separated as H- bonding is not very strong bond", but we are aware about the reports stydying dimers: Halogen‐Bonded Supramolecular Capsules in the Solid State, in Solution, and in the Gas Phase,10.1002/anie.201610884 and tetramers: Surprising solvent-induced structural rearrangements in large [N/I+/N] halogenbonded supramolecular capsules: an ion mobility-mass spectrometry study halogen-bonded, 10.1039/C8SC03040E in halogen-bonded systems. In both cases ESI-MS is used. If it is possible for a halogen-bonded system, then I think it is possible for a hydrogen-bonded system. But whether it is possible to obtain dimers using sublimation and detect them remains a big mystery to me.
Do you mean proton-bound dimers? Proton-bound dimers, trimers, etc. are very common with soft ionization such as electrospray, APCI, and DART. The relative abundance of species such [2M +H]+ increases with analyte concentration. You can also see anion-bound clusters in negative-ion mode. Very large clusters can be observed under the right conditions. Studies of gas-phase water clusters are a specific example.
Supramolecular complexes can be observed in the gas phase by ColdSpray, or electrospray ionization with cold, temperature-regulated solvent flow. The first papers on this were from Prof. Yamaguchi at Chiba University. JEOL sells a ColdSpray source for the AccuTOF-LP mass spectrometer. If you are introducing the sample by sublimation, it is uncertain that hydrogen-bonding will survive sample introduction. You can form complexes in the gas-phase at sufficiently high ion source pressures or by ion trapping, but to detect the complexes by mass spectrometry, there must be a charged site. So, you are most likely to observe ion-bound clusters.
Robert Cody, thanks for your reply. I meant the protons between the dimers, for example as shown in the picture. Is it possible to detected such dimers?
I'm not an expert on this subject, but here are some references:
Article Probing Hydrogen Bond Energies by Mass Spectrometry
Article Mass spectrometry of hydrogen bonded clusters of heterocycli...
Article Hydrogen bonding between water and methanol studied by tempe...
Article Characterization of Hydrogen Bonding Motifs in Proteins: Hyd...
You can adsorb the molecules of interest by introducing an adsorbent in a closed headspace vial during your evaporation process. You may find diverse papers related to gas-phase adsorption as GC-based applications (e.g. SPME, Stirbar sorptive ext., look at Gerstel and Markes portfolio for any ideas). Afterward, you can elute your clusters if they form as dimers, trimers, etc during the evaporation step with a convenient solvent. Thereafter you may inject your eluent into the SEC column to separate the compound by their MW differentiation. Couple your SEC with UV, FLD, conductivity, RID, or MALDI detectors since they work with a non-gas-phase forming principle and give responses in solution.
Emir
Robert Cody gave a few general examples, but all these studies correspond to protonated species. The case of water clusters was largely studied, i.e. (H2O)nH+.
If you ionize by an electron beam a neutral cluster, it will probably not survive with the excess energy added by the ionization process.
Infrared spectrometry is used to detect neutral dimers or higher adducts, in general in supersonic jets (i.e. cooling), to stabilize the weakly bonded species.
Microwave spectrometry is also a very specialized technique used for structure determination of H-bonded dimers.
I do not think that you can deduce the solid state structure from a gas-phase observation.
Jean-François Gal , thanks for your response. I'm afraid the dimer will probably not survive with the excess energy added by the ionization process. Is it possible to predict this process? Will it be correct to calculate the dimerization energy in gas phase and compare it with the ionization energy?
The dimerization energy will be in the range of hundredth of kJ/mol maximum probably less, and 1 eV is almost 100 kJ/mol. You cannot obtain information on the dimer this way.
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