Multidimensional Mass Spectrometry Coupled with Separation by Polarity or Shape for the Characterization of Sugar-Based Nonionic Surfactants

Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) were interfaced with ultra-performance liquid chromatography (UPLC) and ion mobility (IM) separation to characterize a complex nonionic surfactant, consisting of a methylated glucose core (glucam) conjugated with poly­(ethylene oxide) (PEO_<i>n</i>) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEO_<i>n</i>-glucam) stearates. Reverse-phase LC-MS afforded fast separation according to polarity into five major fractions. Accurate mass measurements of the ions in the mass spectra extracted from these fractions enabled conclusive identification of six components in the surfactant, including PEO_<i>n</i>-glucam mono-, di-, and tristearates as well as free and esterified PEO_<i>n</i> as byproducts. MS/MS experiments provided corroborating evidence for the fatty acid content in each fraction based on the number of stearic acid losses observed. With IM-MS, the total surfactant ions were separated according to charge and shape into four distinct bands. Extracted mass spectra confirmed the presence of two disaccharide stearates in the surfactant, which were undetectable by LC-MS. PEO_<i>n</i>-glucam tristearates were, however, not observed upon IM-MS. Hence, LC-MS and IM-MS unveiled complementary compositional insight. With each method, certain components were particularly well separated from other ingredients (by either polarity or shape), to be detected with confidence. Consequently, combined LC-MS and IM-MS offer a superior approach for the characterization of surfactants and other amphiphilic polymers and for the differentiation of similarly composed amphiphilic blends. It is finally noteworthy that NH₄⁺ charges minimized chemical noise in MS mode and Li⁺ charges maximized the fragmentation efficiency in MS/MS mode

Sequence Analysis of Styrenic Copolymers by Tandem Mass Spectrometry

Styrene and smaller molar amounts of either <i>m</i>-dimethylsilylstyrene (<i>m</i>-DMSS) or <i>p</i>-dimethylsilylstyrene (<i>p</i>-DMSS) were copolymerized under living anionic polymerization conditions, and the compositions, architectures, and sequences of the resulting copolymers were characterized by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and tandem mass spectrometry (MS²). MS analysis revealed that linear copolymer chains containing phenyl–Si­(CH₃)₂H pendants were the major product for both DMSS comonomers. In addition, two-armed architectures with phenyl–Si­(CH₃)₂–benzyl branches were detected as minor products. The comonomer sequence in the linear chains was established by MS² experiments on lithiated oligomers, based on the DMSS content of fragments generated by backbone C–C bond scissions and with the help of reference MS² spectra obtained from a polystyrene homopolymer and polystyrene end-capped with a <i>p</i>-DMSS block. The MS² data provided conclusive evidence that copolymerization of styrene/DMSS mixtures leads to chains with a rather random distribution of the silylated comonomer when <i>m</i>-DMSS is used, but to chains with tapered block structures, with the silylated units near the initiator, when <i>p</i>-DMSS is used. Hence, MS² fragmentation patterns permit not only differentiation of the sequences generated in the synthesis, but also the determination of specific comonomer locations along the polymer chain

Large Fluorescence Response by Alcohol from a Bis(benzoxazole)–Zinc(II) Complex: The Role of Excited State Intramolecular Proton Transfer

The formation of a bis­(HBO) anion is known to turn on the fluorescence to give red emission, via controlling the excited-state intramolecular proton transfer (ESIPT). The poor stability of the formed anion, however, hampered its application. The anion stability is found to be greatly improved by attaching the anion to Zn²⁺ cation (i.e., forming zinc complex), whose emission is at λ_em ≈ 550 and 760 nm. Interestingly, addition of methanol to the zinc complex induces a remarkable red fluorescence (λ_em ≈ 630 nm, ϕ_fl ≈ 0.8). With the aid of spectroscopic studies (¹H NMR, UV–vis, fluorescence, and mass spectra), the structures of the zinc complexes are characterized. The emission species is identified as a dimer-like structure. The study thus reveals an effective fluorescence switching mechanism that could further advance the application of ESIPT-based sensors

Mass Spectrometry and Ion Mobility Characterization of Bioactive Peptide–Synthetic Polymer Conjugates

The bioconjugate BMP2-(PEO-HA)₂, composed of a dendron with two monodisperse poly­(ethylene oxide) (PEO) branches terminated by a hydroxyapatite binding peptide (HA), and a focal point substituted with a bone growth stimulating peptide (BMP2), has been comprehensively characterized by mass spectrometry (MS) methods, encompassing matrix-assisted laser desorption ionization (MALDI), electrospray ionization (ESI), tandem mass spectrometry (MS²), and ion mobility mass spectrometry (IM-MS). MS² experiments using different ion activation techniques validated the sequences of the synthetic, bioactive peptides HA and BMP2, which contained highly basic amino acid residues either at the N-terminus (BMP2) or C-terminus (HA). Application of MALDI-MS, ESI-MS, and IM-MS to the polymer–peptide biomaterial confirmed its composition. Collision cross-section measurements and molecular modeling indicated that BMP2-(PEO-HA)₂ exists in several folded and extended conformations, depending on the degree of protonation. Protonation of all basic sites of the hybrid material nearly doubles its conformational space and accessible surface area

Synthesis and Isomeric Characterization of Well-Defined 8‑Shaped Polystyrene Using Anionic Polymerization, Silicon Chloride Linking Chemistry, and Metathesis Ring Closure

A methodology to efficiently synthesize well-defined, 8-shaped polystyrene using anionic polymerization, silicon chloride linking chemistry, and metathesis ring closure has been developed, and the 8-shaped architecture was ascertained using the fragmentation pattern of the corresponding Ag⁺ adduct, acquired with tandem mass spectrometry. The 4-arm star precursor, 4-<i>star</i>-α-4-pentenyl­polystyrene, was formed by linking α-4-pentenyl­poly­(styryl)­lithium (PSLi) with 1,2-bis­(methyl­dichlorosilyl)­ethane and reacting the excess PSLi with 1,2-epoxybutane to facilitate purification. Ring closure of 4-<i>star</i>-α-4-pentenyl­polystyrene was carried out in dichloromethane under mild conditions using a Grubbs metathesis catalyst, bis­(tricyclohexyl­phosphine)­benzylidine ruthenium­(IV) chloride. Both the 4-arm star precursor and resulting 8-shaped polystyrene were characterized using SEC, NMR, and MALDI-ToF mass spectrometry (MS). Tandem mass spectrometry (MS²) was used for the first time to study the fragmentation pattern of 8-shaped polystyrene. The results confirmed the formation of the intra-silicon-linked, 8-shaped polystyrene isomer, but the observed spectra left open the possibility that the inter-silicon-linked, 8-shaped polystyrene isomer was also produced

Sulfonation Distribution in Sulfonated Polystyrene Ionomers Measured by MALDI-ToF MS

Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-ToF MS) was used to quantify the sulfonation level and sulfonation distribution of sulfonated polystyrene ionomers prepared by homogeneous solution sulfonation. The sulfonation levels obtained by MALDI-ToF MS and acid–base titration were compared, and the sulfonate distributions determined by MALDI-ToF MS were compared with theoretical random distributions. The results indicate that the sulfonation reaction used produces a sample with a random sulfonate distribution

Biosourced Amphiphilic Degradable Elastomers of Poly(glycerol sebacate): Synthesis and Network and Oligomer Characterization

Glycerol (G, a triol) and sebacic acid (S, an α,ω-dicarboxylic acid) were condensed in the bulk to obtain poly­(glycerol sebacate) (PGS) cross-linked elastomers which were characterized in terms of their swelling, thermal, and mechanical properties. The soluble precursors to the elastomers were characterized in terms of their size, size distribution, and composition. In particular, G–S mixtures of five different compositions (molar G:S ratio = 2:1, 2:2, 2:3, 2:4, and 2:5) were copolymerized in the bulk at 120 °C in a three-step strategy (first step under inert gas atmosphere, followed by two steps <i>in vacuo</i>). When the G:S molar ratio was equal to (2:3) or close to (2:4), the stoichiometrically matched, network formation took place from the second condensation step, whereas three reaction steps were necessary for network formation far from stoichiometry, at G:S molar ratios equal to 2:2 and 2:5; at a G:S molar ratio of 2:1, no network formation was observed at all. Network composition also proved to be an important structural property, directly influencing the swelling and thermomechanical behavior of the elastomers. In particular, at the stoichiometrically matched G:S ratio of 2:3, corresponding to the cross-linking density maximum, the sol fraction extracted from the elastomers and the elastomer degree of swelling in aqueous media and in organic solvents presented a minimum, whereas the storage moduli of PGS elastomeric membranes in the dry state, measured within the temperature range between 35 and 140 °C, exhibited a maximum. The molecular weights of all soluble network precursors were found to be below 5000 g mol^–1 (gel permeation chromatography), containing but traces of ring oligomers (electron-spray ionization mass spectrometry). ¹H NMR spectroscopy indicated that the precursor composition was close to that expected on the basis of the G:S feed ratio and that monomer-to-polymer conversion increased from the first to the second condensation step

Stoichiometric Self-Assembly of Isomeric, Shape-Persistent, Supramacromolecular Bowtie and Butterfly Structures

Two novel macromolecular constitutional isomers have been self-assembled from previously unreported terpyridine ligands in a three-component system. The terpyridine ligands were synthesized in high yields via a key Suzuki coupling. Restrictions of the possible outcomes for self-assembly ultimately provided optimum conditions for isolation of either a molecular bowtie or its isomeric butterfly motif. These isomers have been characterized by ESI-MS, TWIM-MS, ¹H NMR, and ¹³C NMR. Notably, these structural isomers have remarkably different drift times in ion mobility separation, corresponding to different sizes and shapes at high charge states

Sequence and Conformational Analysis of Peptide–Polymer Bioconjugates by Multidimensional Mass Spectrometry

The sequence and helical content of two alanine-rich peptides (AQK18 and GpAQK18, Gp: l-propargylglycine) and their conjugates with poly­(ethylene glycol) (PEG) have been investigated by multidimensional mass spectrometry (MS), encompassing electrospray ionization (ESI) or matrix-assisted laser desorption ionization (MALDI) interfaced with tandem mass spectrometry (MS²) fragmentation and shape-sensitive separation via ion mobility mass spectrometry (IM-MS). The composition, sequence, and molecular weight distribution of the peptides and bioconjugates were identified by MS and MS² experiments, which also confirmed the attachment of PEG at the C-terminus of the peptides. ESI coupled with IM-MS revealed the existence of random coil and α-helical conformers for the peptides in the gas phase. More importantly, the proportion of the helical conformation increased substantially after PEG attachment, suggesting that conjugation adds stability to this conformer. The conformational assemblies detected in the gas phase were largely formed in solution, as corroborated by independent circular dichroism (CD) experiments. The collision cross sections (rotationally averaged forward moving areas) of the random coil and helical conformers of the peptides and their PEG conjugates were simulated for comparison with the experimental values deduced by IM-MS in order to confirm the identity of the observed architectures and understand the stabilizing effect of the polymer chain. C-terminal PEGylation is shown to increase the positive charge density and to solvate intramolecular positive charges at the conjugation site, thereby enhancing the stability of α-helices, preserving their conformation and increasing helical propensity

Sorbitol–POSS Interactions on Development of Isotactic Polypropylene Composites

This study investigates the nature of interactions between the molecules of polyhedral oligomeric silsesquioxane (POSS) containing silanol functionalities (silanol–POSS) and di(benzylidene)sorbitol (DBS) encountered in the development of nanocomposite fibers from the compounds of POSS, DBS, and isotactic polypropylene (iPP). The interactions were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry, and oscillatory shear rheology. Mass and NMR spectrometry revealed that the molecules of silanol–POSS and DBS formed several amorphous noncovalent molecular complexes promoted by hydrogen bonding. More abundant complex formation was observed with silanol–POSS molecules carrying four silanol groups and phenyl substitutions. Such complex formation deterred fibrillation of DBS when the compounds of iPP, DBS, and silanol–POSS were cooled from homogeneous melt states. It was also revealed that POSS–DBS complexes were of much lower viscosity than iPP