A Comparison of DESI-MS and LC-MS for the Lipidomic Profiling of Human Cancer Tissue

In this study, we make a direct comparison between desorption electrospray ionization-mass spectrometry (DESI-MS) and ultraperformance liquid chromatography-electrospray ionization-mass spectrometry (UPLC-ESI-MS) platforms for the profiling of glycerophospholipid (GPL) species in esophageal cancer tissue. In particular, we studied the similarities and differences in the range of GPLs detected and the congruency of their relative abundances as detected by each analytical platform. The main differences between mass spectra of the two modalities were found to be associated with the variance in adduct formation of common GPLs, rather than the presence of different GPL species. Phosphatidylcholines as formate adducts in UPLC-ESI-MS accounted for the majority of differences in negative ion mode and alkali metal adducts of phosphatidylcholines in DESI-MS for positive ion mode. Comparison of the relative abundance of GPLs, normalized to a common peak, revealed a correlation coefficient of 0.70 (P < 0.001). The GPL profile detected by DESI-MS is congruent to UPLC-ESI-MS, which reaffirms the role of DESI-MS for lipidomic profiling and a potential premise for quantification.

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Fracture analysis of annealed PVDF films

The effect of annealing 50 μm thick, extruded poly(vinylidene fluoride) films in form (-PVDF) was investigated by differential scanning calorimetry and mechanical testing on unnotched and double-edge notched tensile specimens. As to the fracture behavior, micromechanisms of cavitation, spherulite breakdown, fiber bundle structure formation and - to β-phase transformation were detected. The progressive structural evolution taking place during annealing affected the deformation and fracture behavior significantly. While the annealing-induced subtle distinctions in microstructure are slightly reflected by the determined mechanical and essential work of fracture (EWF) properties, a distinct differentiation was possible by analysis of the process zone. A correlation between characteristic values of the process zone at necking and the endothermic transitions due to secondary crystallization determined by differential scanning calorimetry (DSC) was established. Annealing of PVDF films facilitates the micromechanism of cavitation, which is presumably related to perfection of morphological superstructures (spherulites) and, thus, interspherulitic stress concentration and failure.     

Structural, kinetic, and thermodynamic characterization of the interconverting isomers of MS-325, a gadolinium(III)-based magnetic resonance angiography contrast agent

The amphiphilic gadolinium complex MS-325 ((trisodium-{(2-(R)-[(4,4-diphenylcyclohexyl) phosphonooxymethyl] diethylenetriaminepentaacetato) (aquo)gadolinium(III)}) is a contrast agent for magnetic resonance angiography (MRA). MS-325 comprises a GdDTPA core with an appended phosphodiester moiety linked to a diphenylcyclohexyl group to facilitate noncovalent binding to serum albumin and extension of the plasma half-life in vivo. The chiral DTPA ligand (R) was derived from L-serine, and upon complexation with gadolinium, forms two interconvertible diastereomers, denoted herein as isomers A and B. X-ray crystallography of the tris(ethylenediamine)cobalt(III) salt derivative of isomer A revealed a structure in the polar acentric space group P32. The structure consisted of three independent molecules of the gadolinium complex in the asymmetric unit along with three Delta-[Co(en)3]3+ cations, and it represents an unusual example of spontaneous Pasteur resolution of the cobalt cation. The geometry of the coordination core was best described as a distorted trigonal prism, and the final R factor was 5.6%. The configuration of the chiral central nitrogen of the DTPA core was S. The Gd-water (2.47-2.48 A), the Gd-acetate oxygens (2.34-2.42 A), and the Gd-N bond distances (central N, 2.59-2.63 A; terminal N, 2.74-2.80 A) were similar to other reported GdDTPA structures. The structurally characterized single crystal was one of two interconvertable diastereomers (isomers A and B) that equilibrated to a ratio of 1.81 to 1 at pH 7.4 and were separable at elevated pH by ion-exchange chromatography. The rate of isomerization was highly pH dependent: k1 = (1.45 +/- 0.08) x 102[H+] + (4.16 +/- 0.30) x 105[H+]2; k-1 = (2.57 +/- 0.17) x 102[H+] + (7.54 +/- 0.60) x 105[H+]2.     

Coupling desorption electrospray ionization with ion mobility/mass spectrometry for analysis of protein structure: evidence for desorption of folded and denatured States

A desorption electrospray ionization (DESI) source has been coupled to an ion mobility time-of-flight mass spectrometer for the analysis of proteins. Analysis of solid-phase horse heart cytochrome c and chicken egg white lysozyme proteins with different DESI solvents and conditions shows similar mass spectra and charge state distributions to those formed when using electrospray to analyze these proteins in solution. The ion mobility data show evidence for compact ion structures [when the surface is exposed to a spray that favors retention of "nativelike" structures (50:50 water:methanol)] or elongated structures [when the surface is exposed to a spray that favors "denatured" structures (49:49:2 water:methanol:acetic acid)]. The results suggest that the DESI experiment is somewhat gentler than ESI and under appropriate conditions, it is possible to preserve structural information throughout the DESI process. Mechanisms that are consistent with these results are discussed.     

Characterization of DESI-FTICR mass spectrometry - from ECD to accurate mass tissue analysis

Implementation of desorption electrospray ionization (DESI) technique on a 9.4 T Fourier transform ion cyclotron resonance (FTICR) mass spectrometer is described. Desorption electrospray technique is capable of the direct investigation of natural samples without any need for sample preparation or chromatographic separation. Since the DESI mass spectra of natural samples are very complex owing to the lack of preseparation or cleanup, the ideal mass spectrometric analyzer for these applications is a high-resolution instrument such as FTICR mass spectrometer. DESI was implemented by constructing an electronically controlled source framework comprising six linear moving stages and one rotating stage. A three-dimensional linear stage was used to accommodate samples, while another 3D linear stage equipped with rotating stage was used as a spray mount. A modified electrosonic sprayer was used as a primary electrospray device. DESI-FTICR setup was characterized with regard to geometrical, electrical and flow conditions using deposited peptide samples in range of 1-100 pmol gross deposited amount on glass and polymer surfaces. Optimized conditions enabled the routine acquisition of DESI-MS spectra on the instrument at 130 000 resolution in the broadband mode and with comparable sensitivity to data reported in the literature. Since the main significance of DESI-FTICR MS is the combination of intact tissue analysis, the capabilities of the technique were demonstrated by analyzing murine liver samples. Presence of lysophospholipids in the liver tissue was tentatively associated with the lipid metabolism taking place in liver. DESI-FTICR is also a promising technique in the field of peptide analysis due to capability of top-down sequencing using electron capture dissociation. As a proof-of-principle experiment, a small synthetic polypeptide containing 36 amino acids was ionized using DESI and was sequenced in the FTICR by means of ECD (electron capture dissociation) fragmentation. Spectra gave almost full sequence information in agreement with the known amino acid sequence of the species.