Currently Leopold is involved in the courses Bioanalytical Chemistry and Modern Methods in Chemistry.

Please refer to externa website for info on Leopolds research.

https://ilaglab.wordpress.com/

 

A selection from Stockholm University publication database

• Solvent-Assisted Paper Spray Ionization Mass Spectrometry (SAPSI-MS) for the Analysis of Biomolecules and Biofluids

  2019. Nicoló Riboni (et al.). Scientific Reports 9

  Article

  Paper Spray Ionization (PSI) is commonly applied for the analysis of small molecules, including drugs, metabolites, and pesticides in biological fluids, due to its high versatility, simplicity, and low costs. In this study, a new setup called Solvent Assisted Paper Spray Ionization (SAPSI), able to increase data acquisition time, signal stability, and repeatability, is proposed to overcome common PSI drawbacks. The setup relies on an integrated solution to provide ionization potential and constant solvent flow to the paper tip. Specifically, the ion source was connected to the instrument fluidics along with the voltage supply systems, ensuring a close control over the ionization conditions. SAPSI was successfully applied for the analysis of different classes of biomolecules: amyloidogenic peptides, proteins, and N-glycans. The prolonged analysis time allowed real-time monitoring of processes taking places on the paper tip, such as amyloid peptides aggregation and disaggregation phenomena. The enhanced signal stability allowed to discriminate protein species characterized by different post translational modifications and adducts with electrophilic compounds, both in aqueous solutions and in biofluids, such as serum and cerebrospinal fluid, without any sample pretreatment. In the next future, application to clinical relevant modifications, could lead to the development of quick and cost-effective diagnostic tools.

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• Native Ion Mobility-Mass Spectrometry Reveals the Formation of beta-Barrel Shaped Amyloid-beta Hexamers in a Membrane-Mimicking Environment

  2019. Nicklas Österlund (et al.). Journal of the American Chemical Society 141 (26), 10440-10450

  Article

  The mechanisms behind the Amyloid-beta (A beta) peptide neurotoxicity in Alzheimer's disease are intensely studied and under debate. One suggested mechanism is that the peptides assemble in biological membranes to form beta-barrel shaped oligomeric pores that induce cell leakage. Direct detection of such putative assemblies and their exact oligomeric states is however complicated by a high level of heterogeneity. The theory consequently remains controversial, and the actual formation of pore structures is disputed. We herein overcome the heterogeneity problem by employing a native mass spectrometry approach and demonstrate that A beta(1-42) peptides form coclusters with membrane mimetic detergent micelles. The coclusters are gently ionized using nanoelectrospray and transferred into the mass spectrometer where the detergent molecules are stripped away using collisional activation. We show that A beta(1-42) indeed oligomerizes over time in the micellar environment, forming hexamers with collision cross sections in agreement with a general beta-barrel structure. We also show that such oligomers are maintained and even stabilized by addition of lipids. A beta(1-40) on the other hand form significantly lower amounts of oligomers, which are also of lower oligomeric state compared to A beta(1-42) oligomers. Our results thus support the oligomeric pore hypothesis as one important cell toxicity mechanism in Alzheimer's disease. The presented native mass spectrometry approach is a promising way to study such potentially very neurotoxic species and how they could be stabilized or destabilized by molecules of cellular or therapeutic relevance.

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• Chiral separation of beta-Methylamino-alanine (BMAA) enantiomers after (+)-1-(9-fluorenyl)-ethyl chloroformate (FLEC) derivatization and LC-MS/MS

  2019. Javier Zurita (et al.). Analytical Methods 11, 432-442

  Article

  β-Methylamino-L-alanine, a neurotoxin first isolated from the seeds of cycad tree Cycas circinalis, is widely spread in a variety of environments. New sensitive techniques and robust methodologies are needed to detect its presence in complex biological samples and to further understand its biochemical properties. In this context, the determination of the enantiomeric composition of natural BMAA is of great importance. In this study, a simple and easily implemented LC-ESI-MS/MS method was developed to determine the presence of both D- and L-BMAA enantiomers in samples of cycad seed (Cycas micronesica). The samples were subjected to enzymatic hydrolysis to avoid racemization that occurs during strong acid hydrolysis. Derivatization with (+)-1-(9-fluorenyl)-ethyl chloroformate (FLEC) was performed prior to LC-ESI-MS/MS to produce chromatographically separable derivatives of D- and L-BMAA. Together with the retention time, two MRM transitions and their peak area ratios were used to identify the compounds. The LOQ obtained was 0.3 μg BMAA per g wet weight for each enantiomer. Method repeatability was within 3 RSD% both intraday and interday and accuracy was 98–108%. An accurate enantiomeric composition was obtained from the samples of cycad seed, where L- and D-BMAA were detected at 50.13 ± 0.05 and 4.08 ± 0.04 μg BMAA per g wet weight respectively (n = 3).

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• Amyloid-beta Peptide Interactions with Amphiphilic Surfactants

  2018. Nicklas Österlund (et al.). ACS Chemical Neuroscience 9 (7), 1680-1692

  Article

  The amphiphilic nature of the amyloid-beta (A beta) peptide associated with Alzheimer's disease facilitates various interactions with biomolecules such as lipids and proteins, with effects on both structure and toxicity of the peptide. Here, we investigate these peptide-amphiphile interactions by experimental and computational studies of A beta(1-40) in the presence of surfactants with varying physicochemical properties. Our findings indicate that electrostatic peptide-surfactant interactions are required for coclustering and structure induction in the peptide and that the strength of the interaction depends on the surfactant net charge. Both aggregation-prone peptide-rich coclusters and stable surfactant-rich coclusters can form. Only A beta(1-40) monomers, but not oligomers, are inserted into surfactant micelles in this surfactant-rich state. Surfactant headgroup charge is suggested to be important as electrostatic peptide-surfactant interactions on the micellar surface seems to be an initiating step toward insertion. Thus, no peptide insertion or change in peptide secondary structure is observed using a nonionic surfactant. The hydrophobic peptide-surfactant interactions instead stabilize the A beta monomer, possibly by preventing self-interaction between the peptide core and C terminus, thereby effectively inhibiting the peptide aggregation process. These findings give increased understanding regarding the molecular driving forces for A beta aggregation and the peptide interaction with amphiphilic biomolecules.

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• Measurements of Atmospheric Proteinaceous Aerosol in the Arctic Using a Selective UHPLC/ESI-MS/MS Strategy

  2019. Farshid Mashayekhy Rad (et al.). Journal of the American Society for Mass Spectrometry 30 (1), 161-173

  Article

  In this article, an analytical methodology to investigate the proteinaceous content in atmospheric size-resolved aerosols collected at the Zeppelin observatory (79 °N, 12 °E) at Ny Ålesund, Svalbard, from September to December 2015, is proposed. Quantitative determination was performed after acidic hydrolysis using ultrahigh-performance liquid chromatography in reversed-phase mode coupled to electrospray ionization tandem mass spectrometry. Chromatographic separation, as well as specificity in the identification, was achieved by derivatization of the amino acids with N-butyl nicotinic acid N-hydroxysuccinimide ester prior to the analysis. The chromatographic run was performed within 11 min and instrumental levels of detection (LODs) were between 0.2 and 8.1 pg injected on the column, except for arginine which exhibited an LOD of 37 pg. Corresponding method LODs were between 0.01 and 1.9 fmol/m³, based on the average air sampling volume of 57 m³. The sum of free amino acids and hydrolyzed polyamino acids was shown to vary within 6–2914 and 0.02–1417 pmol/m³ for particles in sizes < 2 and 2–10 μm in equivalent aerodynamic diameter, respectively. Leucine, alanine, and valine were the most abundant among the amino acids in both aerosol size fractions. In an attempt to elucidate source areas of the collected aerosols, 5- to 10-day 3D backward trajectories reaching the sampling station were calculated. Overall, the method described here provides a first time estimate of the proteinaceous content, that is, the sum of free and polyamino acids, in size-resolved aerosols collected in the Arctic.

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Show all publications by Leopold Luna Ilag at Stockholm University