Michael Wleklinski

Peptides have become an important modality in the pharmaceutical industry, as they demonstrate heightened potency and target specificity, a property influenced by their conformational structures in solutions. In early drug discovery, structure-based optimization of peptide solution conformation in iterative make-test-design cycles to access peptide drug leads involves large-scale screening. To date, workflows for studying peptide solution conformation reported in the literature are throughput- and resource-limited and do not meet the analytical needs in early discovery space. In this view,context, it is imperative to develop a methodology that exhibits a high analytical throughput, does not involve additional sample preparation steps, and can handle screening of large numbers of samples for solution conformation study. These important analytical requirements in an early discovery pipeline were addressed in this newly developed workflow, where hydrogen-deuterium exchange mass spectrometry (HDX-MS) was employed to gain insights into the relative solution structural conformation of peptides with ultra-high throughput (uHT) acoustic ejection mass spectrometry (AEMS). The described method exhibits a sampling rate of ∼3 s/sample with very low sample and solvent consumption. The format of this workflow provides the ease and convenience of investigating peptide HDX kinetic profiles, with negligible unwanted back-exchange. The capability of the workflow to discriminate conformational changes was established using myoglobin and apo-myoglobin as protein model systems. Using model peptides, we have further demonstrated the capability of the workflow to differentiate solution structural conformation based on their HDX profiles. This work is an example of a HT HDX-based solution structural conformation workflow that does not require additional sample preparation steps, using uHT AEMS with analytical characteristics suitable for a large sample size screening as part of the down-selection process in the early discovery stage.

Chemical reaction data in journal articles, patents, and even electronic laboratory notebooks are currently stored in various formats, often unstructured, which presents a significant barrier to downstream applications, including the training of machine-learning models. We present the Open Reaction Database (ORD), an open-access schema and infrastructure for structuring and sharing organic reaction data, including a centralized data repository. The ORD schema supports conventional and emerging technologies, from benchtop reactions to automated high-throughput experiments and flow chemistry. The data, schema, supporting code, and web-based user interfaces are all publicly available on GitHub. Our vision is that a consistent data representation and infrastructure to support data sharing will enable downstream applications that will greatly improve the state of the art with respect to computer-aided synthesis planning, reaction prediction, and other predictive chemistry tasks.

An integrated system utilizing mass spectrometry for reaction screening, continuous-flow optimization, and continuous crystallization of diphenhydramine has been developed.

Mass spectrometry (MS) is used to monitor chemical reactions in droplets. In almost all cases, such reactions are accelerated relative to the corresponding reactions in bulk, even after correction for concentration effects, and they serve to predict the likely success of scaled‐up reactions performed in microfluidic systems. The particular chemical targets used in these test studies are diazepam, atropine and diphenhydramine. In addition to a yes/no prediction of whether scaled‐up reaction is possible, in some cases valuable information was obtained that helped in optimization of reaction conditions, minimization of by‐products, and choice of catalyst. In a variant on the spray‐based charged droplet experiment, the Leidenfrost effect was used to generate larger, uncharged droplets and the same reactions were studied in this medium. These reactions were also accelerated but to smaller extents than in microdroplets, and they gave results that correspond even more closely to microfluidics data. The fact that MS was also used for online reaction monitoring in the microfluidic systems further enhances the potential role of MS in exploratory organic synthesis.

An ambient solution‐state method for making uniform nanobrushes composed of oriented 1D silver nanowires (NWs) with aspect ratios of 10²–10⁴ is reported. These structures are grown over cm² areas on conducting surfaces. Assemblies of NWs form uniform nanobrush structures, which can capture micrometer‐sized objects, such as bacteria and particulate matter. Variation in composition produces unique structures with catalytic properties.

Ionization of molecular species from one-dimensional (1D) tellurium nanowires (Te NWs) has been achieved at 1 V. Molecules with a range of chemical functional groups gave quality mass spectra with high signal/noise ratios and no fragment ions. Experiments suggest the possibility of emission of microdroplets of solution due to the intense fields at the ends or interfaces of nanostructures. It appears that electrolytic conduction of the solution wetting of the nanostructures and not the electronic conduction of the nanostructures themselves is involved in the ionization event. Anisotropy was seen when two-dimensionally aligned Te NWs were used for ionization. The orientation effect of aligned Te NWs on molecular ion intensity is demonstrated for many analytes including organic molecules and amino acids with experiments done using a silicon substrate having aligned Te NWs. These measurements suggest the possibility of creating a MS source that extends the applicability of mass spectrometry. Analysis of a variety of analytes, including amino acids, pesticides, and drugs, in pure form and in complex mixtures, is reported. These experiments suggest that 1D nanostructures in general could be excellent ionization sources.

Electrospray ionization of metal salt solutions followed by ambient heating transforms the resulting salt clusters into new species, primarily naked ionic metal clusters. The experiment is done by passing the clusters through a heated coiled loop outside the mass spectrometer which releases the counter-anion while generating the anionic or cationic naked metal cluster. The nature of the anion in the starting salt determines the type of metal cluster observed. For example, silver acetate upon heating generates only positive silver clusters, Ag_n ⁺, but silver fluoride generates both positive and negative silver clusters, Ag_n ^+/− (3 < n < 20). Both unheated and heated metal salt sprays yield ions with characteristic geometric and electronic magic numbers. There is also a strong odd/even effect in the cationic and anionic silver clusters. Thermochemical control is suggested as the basis for favored formation of the observed clusters, with anhydride elimination occurring from the acetates and fluorine elimination from the fluorides to give cationic and anionic clusters, respectively. Data on the intermediates observed as the temperature is ramped support this. The naked metal clusters react with gaseous reagents in the open air, including methyl substituted pyridines, hydrocarbons, common organic solvents, ozone, ethylene, and propylene. Argentation of hydrocarbons, including saturated hydrocarbons, is shown to occur and serves as a useful analytical ionization method. The new cluster formation methodology allows investigation of ligand–metal binding including in reactions of industrial importance, such as olefin epoxidation. These reactions provide insight into the physicochemical properties of silver cluster anions and cations. The potential use of the ion source in ion soft landing is demonstrated by reproducing the mass spectra of salts heated in air using a custom surface science instrument.

The analytical performance and a suggested mechanism for zero volt paper spray using chromatography paper are presented. A spray is generated by the action of the pneumatic force of the mass spectrometer (MS) vacuum at the inlet. Positive and negative ion signals are observed, and comparisons are made with standard kV paper spray (PS) ionization and nanoelectrospray ionization (nESI). While the range of analytes to which zero volt PS is applicable is very similar to kV PS and nESI, differences in the mass spectra of mixtures are interpreted in terms of the more significant effects of analyte surface activity in the gentler zero volt experiment than in the other methods due to the significantly lower charge. The signal intensity of zero volt PS is also lower than in the other methods. A Monte Carlo simulation based on statistical fluctuation of positive and negative ions in solution has been implemented to explain the production of ions from initially uncharged droplets. Uncharged droplets first break up due to aerodynamics forces until they are in the 2–4 μm size range and then undergo Coulombic fission. A model involving statistical charge fluctuations in both phases predicts detection limits similar to those observed experimentally and explains the effects of binary mixture components on relative ionization efficiencies. The proposed mechanism may also play a role in ionization by other voltage-free methods.