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(n)) branches that were partially esterified with stearic acid to form ethoxylated glucam (PEO(n)-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(n)-glucam mono-, di-, and tristearates as well as free and esterified PEO(n) 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(n)-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.

Structure and conformation of the medium-sized chlorophosphazene rings.

Medium-sized cyclic oligomeric phosphazenes [PCl2N]m (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N]3 and [PCl2N]4. The medium-sized rings [PCl2N]m have been characterized by electrospray ionization-mass spectroscopy (ESI-MS), their (31)P chemical shifts have been reassigned, and their T1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N]5, and the crystal structures of [PCl2N]6, and [PCl2N]8 are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N]m (m = 3-5, 6, 8). The crystal structures of [P(OPh)2N]7 and [P(OPh)2N]8, which are derivatives of the respective [PCl2N]m, are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N]8 and [P(OPh)2N]8 with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.

Valency-dependent affinity of bioactive hydroxyapatite-binding dendrons.

Hydroxyapatite (HA)-coated surfaces are used widely as stationary phase for protein and enzyme purification, coatings for dental and orthopedic implants, and composite materials for tissue engineering substrates. More advanced applications are envisioned, but progress has been slowed by the limited ability to controllably functionalize the surface of HA with biomolecules in a translationally relevant manner. Herein we report the synthesis and characterization of a series of multivalent, HA-binding peptide bioconjugates with variable valency and tether length which afford the ability to precisely tune the desired binding behavior. The respective binding affinities of the multivalent constructs to HA surface were characterized by quartz crystal microbalance with dissipation monitoring (QCM-D) techniques, and the relationship between dendron structure and binding affinity was revealed. Tetravalent constructs of HA-binding peptides show a 100-fold enhancement in binding affinity compared to HA-binding peptide sequences reported previously. Both biotin and bone morphogenic protein-2 (BMP-2) derivative peptide were successfully linked to the focal point as initial demonstrations.

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.

Interfacing multistage mass spectrometry with liquid chromatography or ion mobility separation for synthetic polymer analysis.

Synthetic polymers are naturally mixtures of homologs, even in pure form. More complexity is introduced by the presence of different comonomers, end groups and/or macromolecular architectures. The analysis of such systems is substantially facilitated by interfacing mass spectrometry (MS), which disperses based on mass, with an additional level of separation involving either interactive liquid chromatography (LC) or ion mobility (IM) spectrometry, both of which are readily coupled online with electrospray ionization and MS detection. IM-MS separates in the gas phase, post-ionization and, therefore, is ideally suitable for labile and reactive polymers. Its usefulness is illustrated with the characterization of non-covalent siloxane-saccharide complexes, metallosupramolecular assemblies and an air- and moisture-sensitive inorganic polymer, poly(dichlorophosphazene). Conversely, LC-MS which separates in solution phase, before ionization, is most effective for the analysis of polymeric mixtures whose components differ in polarity. Interactive LC conditions can be optimized to disperse by the content of hydrophobic units, as is demonstrated for amphiphilic polyether copolymers and sugar-based nonionic surfactant blends. Both LC-MS and IM-MS can be extended into a third dimension by tandem mass spectrometry (MS(2)) studies on select oligomers, in order to obtain insight into individual end groups and isomeric architectures, comonomer sequences and degree of substitution, for example, by hydrophobic functionalities.

Fragmentation pathways of polymer ions.

Tandem mass spectrometry (MS/MS) is increasingly applied to synthetic polymers to characterize chain-end or in-chain substituents, distinguish isobaric and isomeric species, and determine macromolecular connectivities and architectures. For confident structural assignments, the fragmentation mechanisms of polymer ions must be understood, as they provide guidelines on how to deduce the desired information from the fragments observed in MS/MS spectra. This article reviews the fragmentation pathways of synthetic polymer ions that have been energized to decompose via collisionally activated dissociation (CAD), the most widely used activation method in polymer analysis. The compounds discussed encompass polystyrenes, poly(2-vinyl pyridine), polyacrylates, poly(vinyl acetate), aliphatic polyester copolymers, polyethers, and poly(dimethylsiloxane). For a number of these polymers, several substitution patterns and architectures are considered, and questions regarding the ionization agent and internal energy of the dissociating precursor ions are also addressed. Competing and consecutive dissociations are evaluated in terms of the structural insight they provide about the macromolecular structure. The fragmentation pathways of the diverse array of polymer ions examined fall into three categories, viz. (1) charge-directed fragmentations, (2) charge-remote rearrangements, and (3) charge-remote fragmentations via radical intermediates. Charge-remote processes predominate. Depending on the ionizing agent and the functional groups in the polymer, the incipient fragments arising by pathways (1)-(3) may form ion-molecule complexes that survive long enough to permit inter-fragment hydrogen atom, proton, or hydride transfers.