A new route for the preparation of enriched iso-polylactide from rac-lactide via a Lewis acid catalyzed ring-opening of an epoxide.

Tetraphenylporphyrin aluminum(iii) salts, TPPAlX, where X = Me, OEt, OiPr, OCHMeCH2Cl, and Cl, and bis(triphenylphosphine)imminium chloride, PPN+Cl- (1 : 1) react with rac-lactide, rac-LA, in neat propylene oxide, PO, to yield chains of enriched isotactic polylactide, PLA, with end groups of PO-Cl and with time these yield cyclic polymers (PO)n(PLA) where n = 2 or 3 and even higher. There is no reaction between TPPAlOR (R = Et or iPr), PPN+Cl-, and rac-LA in neat THF at 25 °C even though TPPAlOR (R = Et or iPr) and PPN+Cl- in neat PO yields polypropylene oxide with a terminal OR group, H(PO)nOR. Taken together, Al(iii) acts as a Lewis acid in the ring-opening of PO, in which PPN+Cl- is present and the incipient ClCH2CHMeO- initiates the ROP of LA to yield anion chains of [(PLA)-OCHMeCH2Cl]-, and then the ring-opening of PO yields cycles, (PO)n(PLA), with the liberation of Cl-. The polymer was isolated by the addition of MeOH/HCl and end group analysis by mass spectrometry.

Fourier Transform Mass Spectrometry and Nuclear Magnetic Resonance Analysis for the Rapid and Accurate Characterization of Hexacosanoylceramide.

Ceramides are a central unit of all sphingolipids which have been identified as sites of biological recognition on cellular membranes mediating cell growth and differentiation. Several glycosphingolipids have been isolated, displaying immunomodulatory and anti-tumor activities. These molecules have generated considerable interest as potential vaccine adjuvants in humans. Accurate analyses of these and related sphingosine analogues are important for the characterization of structure, biological function, and metabolism. We report the complementary use of direct laser desorption ionization (DLDI), sheath flow electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) and high-field nuclear magnetic resonance (NMR) analysis for the rapid, accurate identification of hexacosanoylceramide and starting materials. DLDI does not require stringent sample preparation and yields representative ions. Sheath-flow ESI yields ions of the product and byproducts and was significantly better than monospray ESI due to improved compound solubility. Negative ion sheath flow ESI provided data of starting materials and products all in one acquisition as hexacosanoic acid does not ionize efficiently when ceramides are present. NMR provided characterization of these lipid molecules complementing the results obtained from MS analyses. NMR data was able to differentiate straight chain versus branched chain alkyl groups not easily obtained from mass spectrometry.

Detailed structural elucidation of polyesters and acrylates using Fourier transform mass spectrometry.

The detailed structural characterization of complex polymer architectures, like copolymers and polymer mixtures, by mass spectrometry presents a challenge. Even though soft ionization analyses revolutionized the characterization of large molecules and provided a means for determining the polymer's molecular weight distribution, polydispersity, and end groups, full microstructure elucidation and monomer sequencing by soft ionization alone is not possible. The combination of high-resolution Fourier transform mass spectrometry (FTMS) and tandem mass spectrometry (MS(n)) provides a powerful analytical tool for addressing these challenges. This tool was used in our work to separate and identify the products of polymerization between 12-hydroxystearic acid (HSA) and stearic acid (SA), to provide precise information about the exact location of caprolactones on the Tris(2-hydroxyethyl)isocyanurate (THEIC) molecule, and to sequence a glycidyl methacrylate/methyl methacrylate (GMA/MMA) copolymer. The results highlight the value of ultrahigh resolution and tandem mass spectrometry for fine structural characterization and sequencing of polymers.

Characterization of polyesters by matrix-assisted laser desorption/ionization and Fourier transform mass spectrometry.

Two homopolyesters, poly(neopentyl glycol-alt-isophthalic acid) and poly(hexanediol-alt-azelaic acid), and two copolyesters, poly(dipropoxylated bisphenol-A-alt-(isophthalic acid-co-adipic acid)) and poly(neopentyl glycol-alt-(adipic acid-co-isophthalic acid)) were analyzed by internal source matrix assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS). The high resolution and high mass accuracy provided by FTMS greatly facilitate the characterization of the polyester and copolyester samples. Isobaric resolution allows the ion abundances of overlapping isotopic envelopes to be assessed. Repeat units were confirmed and end functionality assigned. Single shot mass spectra of the entire polymeric distribution demonstrate that the dynamic range of this internal MALDI source instrument and the analyzer cell exceeds performance of those previously reported for higher field instruments. Corrections of space charge mass shift effects are demonstrated for the analytes using an external calibrant and (subsequent to confirmation of structure) via internal calibration which removes ambiguity due to space charge differences in calibrant and analyte spectra. Capillary gel permeation chromatography was used to prepare low polydispersity samples from a high polydispersity polyester, improving the measurement of molecular weight distribution two-fold while retaining the benefits of high resolution mass spectrometry for elucidation of oligomer identity.

Application of stored waveform ion modulation 2D-FTICR MS/MS to the analysis of complex mixtures.

Component identification of complex mixtures, whether they are from polymeric formulations or combinatorial synthesis, by conventional MS/MS techniques generally requires component separation by chromatography or mass spectrometry. An automated means of acquiring simultaneous MS/MS data from a complex mixture without prior separation is obtained from stored waveform ion modulation (SWIM) two-dimensional FTICR MS/MS. The technique applies a series of SWIFT excitation waveforms whose frequency domain magnitude spectrum is a sinusoid increasing in frequency from one waveform to the next. The controlled dissociation of the precursor ions produces an associated modulation of the product ion abundances. Fourier transformation of these abundances reveals the encoded modulation frequency from which connectivities of precursor and product ions are observed. The final result is total assignment of product ions for each precursor ion in a mixture from one automated experiment. We demonstrated the applicability of SWIM 2D-FTICR MS/MS to two diverse samples of industrial importance. We characterized structured polyester oligomers and products derived from combinatorial synthesis. Fragmentation pathways identified in standard serial ion isolation MS/MS experiments were observed for trimethylolpropane/methyl hexahydrophthalic anhydride. A 20-component sample derived from combinatorial synthesis was fragmented, and the template ion along with another key fragment ion was identified for each of the 20 components.