The conformation space occupied by different classes of biomolecules measured by ion mobility-mass spectrometry (IM-MS) is described for utility in the characterization of complex biological samples. Although the qualitative separation of different classes of biomolecules on the basis of structure or collision cross section is known, there is relatively little quantitative cross-section information available for species apart from peptides. In this report, collision cross sections are measured for a large suite of biologically salient species, including oligonucleotides (n=96), carbohydrates (n=192), and lipids (n=53), which are compared to reported values for peptides (n= 610). In general, signals for each class are highly correlated, and at a given mass, these correlations result in predicted collision cross sections that increase in the order oligonucleotides
This report describes the rapid characterization of positional and structural carbohydrate isomers based on structural separations provided by ion mobility-mass spectrometry (IM-MS). Many of the diseases associated with glycoprotein variation can be more effectively treated with earlier detection substantiating the need for high-throughput methodologies for glycan characterization. This remains particularly difficult due to heterogeneity, branching, and large size of carbohydrate moieties which creates the potential for numerous isobaric positional and structural isomers that are difficult to characterize using conventional MS methods. IM-MS provides rapid (μs to ms) structural separations by IM and subsequent identification by MS which presents a means for characterization of positional and structural carbohydrate isomers. To chart the structural variation observed in IM-MS, the ion-neutral collision cross sections for over 300 carbohydrates are reported. This diversity can also be varied through the utility of using different alkali metals to tune separation selectivity via alkali metal-carbohydrate coordination. Furthermore, the advantages of combining either pre- and/or post-IM fragmentation prior to MS analysis is demonstrated for enhanced confidence in carbohydrate identification.
Matrix-assisted laser desorption/ionization-ion mobility-mass spectrometry (MALDI-IM-MS) was used to analyze low mass gold-thiolate fragments generated from thiolate-protected gold nanoparticles (AuNPs). This is the first report of using gas-phase structural separations by IM-MS for the characterization of AuNPs, revealing significant structural variation between organic and gold-thiolate ionic species. Through the separation of background chemical noise, gold-thiolate ion species corresponding to fragments from the AuNP surface can be isolated. In the negative ion mode, many of these fragments correlate to capping structural motifs observed in the literature. In the positive ion mode, the fragment ions do not correlate to predicted structural motifs, but are nearly identical to the positive ions generated from the gold-thiolate AuNP precursor complexes. This suggests that energetic processes during laser desorption/ionization induce a structural rearrangement in the capping gold-thiolate structure of the AuNP, resulting in the generation of positively charged gold-thiolate complexes similar to the precursors of AuNP formation by reduction and negatively charged complexes more representative of the AuNP surface.
Several complementary mass spectrometric imaging techniques allow mapping of various analytes within biological tissue sections. Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) quantitatively detects elements and isotopes with very high sensitivity and a particularly high dynamical range. Matrix-assisted laser desorption/ionization ion mobility mass spectrometry (MALDI-IM-MS) allows a pixel-by-pixel classification and identification of biomolecules.In order to dispose of the healthy hemisphere as an internal calibrant in addition to routinely used external standards, adjacent brain sections of mice with a unilateral 6-OHDA lesion of the medial forebrain bundle were chosen as exemplary samples. We demonstrate a comprehensive way of data acquisition and analysis by coregistering mass spectrometric data on photomicrographs as common reference space and thus providing trimodal spatial information. Registering subsequent planar element maps yielded continuous 3-dimensional data sets. Furthermore, we introduce a correction of MSI data for variable slice thickness applicable to all MSI techniques. In the present case, we observed increased concentrations of iron, manganese, and copper in the lesioned substantia nigra while monounsaturated lipid levels were decreased in the identical region of interest. Our techniques provide new insights into the intricate spatial relationship of morphology and chemistry within tissue.
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