Phosphatidylcholines are the major phospholipid component of most eukaryotic cell membranes. Phosphatidylcholines have been shown to actively participate in regulatory and metabolic processes. Dysfunctional metabolic processes have been linked to human disease and can result in altered phosphatidylcholine structural features, such as permutation of fatty acid connectivity. Assignment and relative quantitation of structural isomers that arise from fatty acid permutation on the phosphatidylcholine backbone, so-called sn-isomers, is difficult with routine tandem mass spectrometry or with liquid chromatography without authentic standards. In this work, we report on the observation that phosphatidylcholines form abundant doubly charged metal ion complexes during electrospray ionization (ESI) and show that these complexes can be used to assign fatty acid moieties, relatively quantify sn-isomers in MS experiments, and mass spectrometrically separate phosphatidylcholines from other phospholipid classes in positive ion mode. Addition of Fe salts (20 mol %) to ESI spray solutions affords highly abundant doubly charged metal ion phosphatidylcholine complexes (∼110% of protonated compounds) and allows sensitive fragment ion detection (limit of detection = 100 pM). Higher energy collisional dissociation, collision-induced dissociation, and ultraviolet photodissociation of doubly charged complexes yield two fragment ions for every fatty acid moiety. The latter two tandem MS methods preferentially yield sn-2 associated product ions enabling relative sn-isomer quantification. The analytical utility of doubly charged phosphatidylcholine-metal ion complexes is demonstrated for polar lipid extracts, including extracts from diabetes type 1 and type 2 mouse models, and sn-isomer abundances are derived.

The effect of double bond functionalisation for selective double bond localisation by ultraviolet photodissociation of phosphatidylcholines is investigated. Paternò-Büchi reactions in nanoESI emitter tips enable attachment of acetophenone to double bonds of unsaturated phosphatidylcholines after 100 s of 254 nm light irradiation with about 50-80% reaction yield. Functionalized phosphatidylcholines dissociate upon 266 nm irradiation yielding double bond selective fragment ions in contrast to results for ultraviolet photodissociation of unmodified lipids. Ultraviolet photodissociation of Paternò-Büchi modified lipids results in a selectivity increase of up to 2.2 towards double bond localisation compared collision-induced dissociation experiments. Double bond localisation is also possible with ultraviolet photodissociation when alkali metal ion attachment to Paternò-Büchi modified phosphatidylcholines occurs in contrast to classic collision-induced dissociation experiments. The developed methodology is used to differentiate lipid double bond isomers and applied to phosphatidylcholines from egg yolk to identify 15 phosphatidylcholines. Results from this study demonstrate that locally depositing energy in close vicinity to cleavable bonds via ultraviolet photodissociation can result in increased dissociation selectivity. This method can help to disentangle contributions from different structural elements in complex tandem mass spectra of lipids and aid to the structural characterization of phospholipids in a "top-down" approach.

Ultraviolet photodissociation (UVPD) is a powerful and rapidly developing method in top-down proteomics. Sequence coverages can exceed those obtained with collision- and electron-induced fragmentation methods. Because of the recent interest...

Glycerophospholipids (GPs) are highly abundant in eukaryotic cells and take part in numerous fundamental physiological processes such as molecular signaling. The GP composition of samples is often analyzed using mass spectrometry (MS), but identification of some structural features, for example, differentiation of stereospecific numbering (sn) isomers by wellestablished tandem MS (MS 2 ) methods, is challenging. In particular, the formation of 1,3-dioxolane over 1,3-dioxane intermediates proposed to be responsible for the sn-selectivity of these tandem MS strategies has not been validated by spectroscopic methods. In this work, we present infrared multiple photon dissociation (IRMPD) spectra of phosphatidylcholine (PC) ions [PC 4:0/4:0 + H/Na/K] + and [PC 4:0/4:0 + Na/K − 183] + fragments generated by electrospray ionization (ESI)-MS and collision-induced dissociation (CID), respectively. IRMPD spectra of protonated, sodiated, and potassiated PC 4:0/4:0 differ in the phosphate-and ester-related bands, which are increasingly shifted to lower wavenumbers with higher adduct masses. Comparison of calculated and experimental IR spectra indicates the presence of multiple, two and one isomer(s) for [PC 4:0/4:0 + H] + , [PC 4:0/4:0 + Na] + , and [PC 4:0/4:0 + K] + , respectively. Isomers exhibiting pronounced sn-1 ester−ion interactions are computationally predicted to be energetically preferred for all species and are in line with experimental results. IRMPD spectra of [PC 4:0/4:0 + Na/K − 183] + are presented and shed the first light on the fragment ion structures, rationalizing MS-based lipidomics strategies that aim to characterize the sn-isomerism of GPs.

Ultraviolet photodissociation tandem mass spectrometry is a powerful tool to investigate the structure of biomolecules, due to its ability to generate rich fragmentation patterns or bond selective cleavage, as a function of used laser wavelength, laser fluence, dose (number of accumulated laser pulses), and available chromophores. Herein, we report first results obtained with a newly developed two-wavelength (266 nm and 213 nm) ultraviolet photodissociation setup coupled to a Fourier-transform ion cyclotron resonance mass spectrometer. Photoproduct yields for protonated 3-iodo-l-tyrosine were up to ∼75%. Dose and fluence dependent measurements for protonated 3-iodo-l-tyrosine, doubly charged protonated bradykinin and Fe(II) attached to 1,2-dioleoyl-sn-glycero-3-phosphocholine reveal that the ultraviolet photodissociation mechanism for photoproduct formation qualitatively differs between these model systems. Three derived photodissociation models were used to interpret the experimental results and show that while protonated 3-iodo-l-tyrosine and Fe(II) attached to 1,2-dioleoyl-sn-glycero-3-phosphocholine most likely dissociates via a single-photon process, fragmentation of doubly charged bradykinin ions was found to be most consistent with sequential two-photon dissociation (213 nm). The introduced dissociation models present an easy means to study the mechanism of ultraviolet photodissociation processes for a variety of analytes without prior knowledge of their photochemistry or to optimize experimental conditions by adjusting laser fluence or number of laser pulses.

of Thin In, -,Ga,As,P, -, Layers Lattice-Matched to InPGrowth studies enabled the deposition of In, ,lGao,29Aso,68P,,32 single quantum well structures with InP or In,,,,Ga,, ,2A~0.26P0.74 confinement layers lattice-matched to (001) InP by liquid phase epitaxy (LPE). Well widths in the order of 50-100 8, have been achieved using a conventional step cooling technique. The physical characterization has demonstrated the capability of the employed method to produce multilayered heterostructures which display confined particle states; quantum mechanically induced blue-shifts of the low temperature PL-emission up to 125 meV were measured. A remarkable reduction of the FWHM values of the shifted P L peaks was attained by optimization of the growth conditions.Ausgehend von Zuchtungsversuchen im Materialsystem (In, Ga)(As, P)/InP wurden gitterangepaRte Ino., ~Ga,,29Aso,6,Po,38 Single-Quantum-Well Strukturen mit InP-beziehungsweise In,,,,Ga,, , 2As,,2, . Po ,,-Barrieren mitteis Flussigphasenepitaxie (LPE) auf (001) InP hergestellt. Die physikalische Charakterisierung der Proben zeigte, daR die beschriebene Technik eingesetzt werden kann, urn Dunnschichtanordnungen zu zuchten, an denen quantenmechanisch induzierte Verschiebungen der Quantengrabenlumineszenz menbar sind. Diese hoherenergetischen Verschiebungen betrugen bei binaren Barrierenmaterial b k zu I25 meV. Durch Optimierung der Zuchtungsbedingungen wurde eine betrichtliche Reduzierung der Halbwertsbreiten der Tieftemperaturphotolumineszenz erreicht.

In this letter the liquid phase.epitaxial growth of Ino.,, Gao.aAso.sePo.a2 (Ag = 1.32 pn) single quantum well structures lattice matched to (001) InP substrates is repotted. The electrical and optical confinement was formed either by InP or Ino.saG~.,2Aso.26P0,74 (Ag = 1.05 pm). Low-temperature photoluminescence was employed to prove the samples capable of displaying quantum size effects. Energy upshifts up to 125 meV were measured for InP-clad quantum wells of about 50 b, thickness. All multilayered stacks originate from step-cooling growth