Determining molecular properties with differential mobility spectrometry and machine learning.

The fast and accurate determination of molecular properties is highly desirable for many facets of chemical research, particularly in drug discovery where pre-clinical assays play an important role in paring down large sets of drug candidates. Here, we present the use of supervised machine learning to treat differential mobility spectrometry - mass spectrometry data for ten topological classes of drug candidates. We demonstrate that the gas-phase clustering behavior probed in our experiments can be used to predict the candidates' condensed phase molecular properties, such as cell permeability, solubility, polar surface area, and water/octanol distribution coefficient. All of these measurements are performed in minutes and require mere nanograms of each drug examined. Moreover, by tuning gas temperature within the differential mobility spectrometer, one can fine tune the extent of ion-solvent clustering to separate subtly different molecular geometries and to discriminate molecules of very similar physicochemical properties.

Characterizing the Tautomers of Protonated Aniline Using Differential Mobility Spectrometry and Mass Spectrometry.

The site of protonation for gas-phase aniline has been debated for many years, with many research groups contributing experimental and computational evidence for either the amino-protonated or the para-carbon-protonated tautomer as the gas-phase global minimum structure. Here, we employ differential mobility spectrometry (DMS) and mass spectrometry (MS) to separate and characterize the amino-protonated (N-protonated) and para-carbon-protonated ( p-protonated) tautomers of aniline. We demonstrate that upon electrospray ionization (ESI), aniline is protonated predominantly at the amino position. Similar analyses are conducted on another three isotopically labeled forms of aniline to confirm our structural assignments. We observe a significant reduction of the relative population of the p-protonated tautomer when a protic ESI solvent is employed (methanol/water) compared to when an aprotic solvent (acetonitrile) is employed. We also observe conversion of the p-protonated species into the N-protonated species upon clustering with protic solvent vapor post-DMS selection-a finding supported by previous experimental data acquired using DMS-MS.

FTIR matrix-isolation study of the reaction products of vanadium atoms with propene: observation of allylvanadium hydride as a precursor to sacrificial hydrogenation of propene.

Vanadium atoms have been reacted with different partial pressures of propene in Ar under matrix-isolation conditions, and the products have been observed using Fourier transform infrared (FTIR) spectroscopy. Under dilute propene in Ar conditions, new features are observed in the IR spectra corresponding to a C-H insertion product, identified here as H-V-(η(3)-allyl). Use of d(3)-propene (CD(3)-CH═CH(2)) demonstrates that the initial V-atom insertion occurs at the methyl group of the propene molecule, and DFT calculations have been used to support the identity of the initial product. Upon increasing the partial pressure of propene, additional features corresponding to propane (C(3)H(8)) are observed, with the hydrogen-atom source for the observed hydrogenation demonstrated to be additional propene units. Analysis of a systematic increase in the partial pressure of propene in the system demonstrates that the yield of propane correlates with the decrease of the allyl product, demonstrating the H-V(allyl) species as a reactive intermediate in the overall hydrogenation process. An overall mechanism is proposed to rationalize the formation of the insertion product and ultimately the products of hydrogenation, which agrees with previous gas-phase and matrix-isolation work involving propene and the related system, ethene.