Biotinylated-spiperone ligands for quantum dot labeling of the dopamine D2 receptor in live cell cultures.

We have synthesized 3 analogs of the dopamine D2 receptor (D2 DR) antagonist spiperone that can be conjugated to streptavidin-coated quantum dots via a pegylated biotin derivative. Using fluorescent imaging we demonstrate that substitution on the spiro position is tolerated, whilst the length and rigidity of a spacer arm attached to spiperone is important in controlling specific labeling as well as minimizing nonspecific labeling to cells and the surface of cell culture dishes. The ligand with the most rigid linker IDT772 (4) had the best binding profile and had high specific binding to D2 DR expressing HEK-293T cells with low nonspecific binding to plates and HEK-293T cells that lacked the D2 DR.

Mass Spectrometry of Polyurethanes.

This review covers the applications of mass spectrometry (MS) and its hyphenated techniques to characterize polyurethane (PU) synthetic polymers and their respective hard and soft segments. PUs are commonly composed of hard segments including methylene bisphenyl diisocyanate (MDI) and toluene diisocyanate (TDI), and soft segments including polyester and polyether polyols. This literature review highlights MS techniques such as electrospray ionization (ESI), matrix assisted laser/desorption ionization (MALDI), ion mobility-mass spectrometry (IM-MS), and computational methods that have been used for the characterization of this polymer system. Here we review specific case studies where MS techniques have elucidated unique features pertaining to the makeup and structural integrity of complex PU materials and PU precursors.

Alkali Metal Cation Adduct Effect on Polybutylene Adipate Oligomers: Ion Mobility-Mass Spectrometry.

Polyurethane (PU) di-block copolymers are one of the most versatile polymeric materials, comprised of hard and soft segments that contribute to PU's broad range of applications. Polybutylene adipate (PBA) is a commonly used soft segment in PU systems. Characterizing the structure of PBA polymers is essential to understanding complex heterogeneity within a PU sample. In this study, ion mobility-mass spectrometry (IM-MS) and tandem mass spectrometry (MS/MS) are used to structurally characterize a PBA standard (Mn = 2250) adducted with a combination of monovalent alkali cations (Li, Na, K, Rb, and Cs). IM-MS profiles show unique trends associated with each cation-adducted PBA sample. Charge state trends: +1, +2, and +3 were extracted for cation-adducted PBA oligomers, and investigated to study gas-phase transitional folding. To quantitatively assess the gas-phase structural similarities and differences, a statistical test (ANOVA) was used to compare PBA oligomer-cation collisional cross sections (CCS). Fragmentation studies (MS/MS) identified the unique behavior of Li and Na for promoting 1,5 H-shift and 1,3 H-shift fragmentation, whereas the PBA precursor preferentially loses the larger K, Rb, and Cs cations as the ion activation energy is increased. The combination of adducted alkali cations, IM-MS, and MS/MS allow for unique structural characterization of this important PBA system.

Structural Characterization of Methylenedianiline Regioisomers by Ion Mobility-Mass Spectrometry and Tandem Mass Spectrometry. 4. 3-Ring and 4-Ring Isomers.

Matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) is used to characterize methylenedianiline (MDA) 3-ring and 4-ring species. Building on our previous MALDI-MS 2-ring MDA isomer study, here we compare 3-ring and 4-ring electrospray ionization (ESI) and MALDI results. In ESI, 3-ring and 4-ring MDAs each form a single [M + H]+ parent ion. However, in MALDI, each MDA multimer forms three unique precursor ions: [M + H]+, [M•]+, and [M - H]+. In this study, 3-ring and 4-ring MDA precursors are characterized to identify the unique fragment ions formed and their respective fragmentation pathways. In addition to the three possible precursors, the 3-ring and 4-ring species are higher-order oligomer precursors in polyurethane (PUR) production and thus provide additional insight into the polymeric behavior of these PUR hard block precursors. The combination of ion mobility-mass spectrometry (IM - MS) and tandem mass spectrometry (MS/MS) allow the structural characterization of these larger MDA multimers.

Structural Characterization of Methylenedianiline Regioisomers by Ion Mobility-Mass Spectrometry, Tandem Mass Spectrometry, and Computational Strategies. 3. MALDI Spectra of 2-Ring Isomers.

Characterization of methylenedianiline (MDA) 2-ring isomers (2,2'-, 2,4'-, and 4,4'-MDA) is reported using matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS), a common technique used for characterizing synthetic polymers. MDA is a precursor to methylene diphenyl diisocyanate (MDI), a hard block component in polyurethane (PUR) synthesis. This work focuses on comparing MALDI results to those of our previous electrospray ionization-mass spectrometry (ESI-MS) studies. In ESI, 2-ring MDA isomers formed single unique [M + H]+ (199 Da) parent ions, whereas in MALDI each isomer shows significant formation of three precursor ions: [M - H]+ = 197 Da, [M•]+ = 198 Da, and [M + H]+ = 199 Da. Structures and schemes are proposed for the MALDI fragment ions associated with each precursor ion. Ion mobility-mass spectrometry (IM-MS), tandem mass spectrometry (MS/MS), and computational methods were all critical in determining the structures for both precursor and fragment ions as well as the fragmentation mechanisms. The present study indicates that the [M - H]+ and [M•]+ ions are formed by the MALDI process, explaining why they were not observed with ESI.