Top-down mass spectrometry of hybrid materials with hydrophobic peptide and hydrophilic or hydrophobic polymer blocks

Abstract

A multidimensional mass spectrometry (MS) methodology is introduced for the molecular level characterization of polymer-peptide (or polymer-protein) copolymers that cannot be crystallized or chromatographically purified. It encompasses electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) coupled with mass analysis, tandem mass spectrometry (MS(2)) and gas-phase separation by ion mobility mass spectrometry (IM-MS). The entire analysis is performed in the mass spectrometer ("top-down" approach) within milliseconds and with high sensitivity, as demonstrated for hybrid materials composed of hydrophobic poly(tert-butyl acrylate) (PtBA) or hydrophilic poly(acrylic acid) (PAA) blocks tethered to the hydrophobic decapeptide VPGVGVPGVG (VG2) via triazole linkages. The composition of the major products can be rapidly surveyed by MALDI-MS and MS(2). For a more comprehensive characterization, the ESI-IM-MS (and MS(2)) combination is more suitable, as it separates the hybrid materials based on their unique charges and shapes from unconjugated polymer and partially hydrolyzed products. Such separation is essential for reducing spectral congestion, deconvoluting overlapping compositions and enabling straightforward structural assignments, both for the hybrid copolymers as well as the polymer and peptide reactants. The IM dimension also permits the measurement of collision cross-sections (CCSs), which reveal molecular architecture. The MS and MS(2) spectra of the mobility separated ions conclusively showed that [PtBA-VG2]m and [PAA-VG2]m chains with the expected compositions and sequences were formed. Single and double copolymer blocks (m = 1-2) could be detected. Further, the CCSs of the hybrids, which were prepared via azide/alkyne cycloadditions, confirmed the formation of macrocyclic structures. The top-down methodology described would be particularly useful for the detection and identification of peptide/protein-polymer conjugates which are increasingly used in biomedical and pharmaceutical applications.

Multidimensional Mass Spectrometry of Synthetic Polymers and Advanced Materials

“…[P t BA‐VG2] 1 n ‐mers are most suitable for the simulations, as their intramolecular hydrogen‐bonding network is markedly simpler than that in [PAA‐VG2] 1 n ‐mers, thus facilitating geometry optimization. The calculated CSS of [P t BA n ‐VG2+2H] 2+ ions with ten acrylate repeat units ( n= 10) is 464 Å 2 for the cyclic and 499 Å 2 for the linear architecture . The measured CCS for this ion, 468 Å 2 , agrees excellently with the value predicted for the cyclic structure, providing strong evidence that all possible [3+2] cycloadditions take place (all‐triazole and no alkyne/azide functionalities).…”

“…Because of the 2D dispersion achieved by the combined MS and IM dimensions, the top‐down approach is applicable to mixtures and blends that are difficult to crystallize or purify for analysis by X‐ray diffraction or NMR spectroscopy. The top‐down procedure will be exemplified with an elastin‐mimetic hybrid material composed of hydrophilic poly(acrylic acid) (PAA) blocks attached covalently to blocks of the hydrophobic decapeptide VPGVGVPGVG (VG2) . This copolymer was prepared as shown in Scheme ; telechelic poly( tert ‐butyl acrylate) diazide and the dialkyne‐functionalized peptide X(VG2)X (X= N ‐acetylpropargylglycyl at the N‐terminus and propargylglycinamide at the C‐terminus) were first linked with a click‐chemistry reaction (Huisgen [3+2] cycloaddition) to form the hybrid multiblock copolymer [P t BA‐VG2] m .…”

“…The compositional assignments given in Figure a were deduced from the mass spectra extracted from the IM‐separated bands . A representative spectrum, obtained from the mobility region of triply charged PAA‐VG2, is depicted in Figure b; it contains one series with the PAA repeat unit, arising from triply protonated n ‐mers with one constituent block, namely [PAA‐VG2] 1 .…”

Coordination-Driven, Self-Assembly of a Polycyclic, Terpyridine-Based Nanobelt

“…The drift time scale of the TWIM-MS experiments was converted to a collision cross-section (CCS) scale by calibration with standards of known CCS, as has been reported [32][33][34]. Calibrant ions used were various charge states of insulin (bovine pancreas), ubiquitin (bovine red blood cells), lysozyme, and cytochrome C (horse heart) [35] against the corrected drift times (arrival times) of the corresponding ions measured in TWIM-MS experiments at the same traveling wave velocity, traveling wave height, and ion mobility gas flow settings used for the metallomacrocycles, viz.…”

Multidimensional mass spectrometry to characterize degradation products generated during MALDI of polystyrenes prepared by controlled radical polymerization techniques

“…Such an analytical set-up was previously reported to efficiently resolve isotope cluster overlaps of polymer ions in studies involving electrospray as the ionization source. [31][32][33][34] All MS/MS data were then analyzed based on the fragmentation rules reported for linear PS. 30 Briefly, dissociation reactions were described to occur according to radical mechanisms followed by various rearrangements, leading to product ions containing either one or the other end-group (as depicted in the Supporting Information Scheme S2) and detected in the low m/z range of MS/MS spectra.…”