Features of laser desorption/ionization mass spectrometry fragmentation of vitamin B<Subscript>12</Subscript>

A comparative analysis of the laser desorption/ionization of vitamin B₁₂ by matrix-assisted laser desorption/ionization (MALDI) and desorption/ionization on porous silicon (DIOS) was carried out. The mass spectra obtained were interpreted and the pathways for ion formation and decomposition were established. The MALDI fragmentation of the positive vitamin B₁₂ ions is more extensive than the DIOS fragmentation. The most extensive fragmentation was found using the MALDI method for negative vitamin B₁₂ ions, which are lacking when using the DIOS method. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 251–256, July–August, 2007.     

Scanning microprobe matrix-assisted laser desorption ionization (SMALDI) mass spectrometry: instrumentation for sub-micrometer resolved LDI and MALDI surface analysis

A new instrument and method is described for laterally resolved mass spectrometric surface analysis. Fields of application are in both the life sciences and the material sciences. The instrument provides for imaging of the distribution of selected sample components from natural and artificial surfaces. Samples are either analyzed by laser desorption ionization (LDI) time-of-flight mass spectrometry or, after preparation with a suitable matrix, by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. Areas of 100 x 100 microm are scanned with minimal increments of 0.25 microm, and between 10,000 and 160,000 mass spectra are acquired per image within 3 to 50 min (scan rate up to 50 pixels per s). The effective lateral resolution is in the range of 0.6 to 1.5 microm depending on sample properties, preparation methods and laser wavelength. Optical investigation of the same sample area by UV confocal scanning laser microscopy was found to be very attractive in combination with scanning MALDI mass analysis because pixel-identical images can be created with both techniques providing for a strong increase in analytical information. This article describes the method and instrumentation, including first applicational examples in elemental analysis, imaging of pine tree roots, and investigation of MALDI sample morphology in biomolecular analysis.     

Analysis of biopolymers by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry is an analytical technique enabling the mass analysis of biopolymers with masses up to at least 300,000 Da. Incorporation of analyte in a matrix consisting of small highly absorbing organic molecules and excitation with short pulses of intense laser light enables the production of intact molecule ions to be analyzed in a time-of-flight mass spectrometer. Mass accuracies of up to 0.01% can be achieved from sample amounts of 1 pmol or less. Proteins, glycoproteins, oligonucleotides and oligosaccharides have been analyzed. The short analysis time of several minutes makes the method well suited for combination with other biochemical methods.     

The role of esterification on detection of protonated and deprotonated peptide ions in matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS)

Esterification was used to investigate how introduction of aliphatic chains within the peptide structure affects the MALDI response of ions analyzed in both polarity regimes. In binary mixtures containing equimolar amounts of a peptide with its correspondent alkyl ester, derivatization of the carboxylic groups has the tendency to increase MALDI detection of the modified protonated peptide ions. This positive effect on ion yield is more pronounced when longer alcohols are employed. In negative mode, the situation is antithetic and esterification produces a deleterious effect on the ion yield of the corresponding deprotonated species. From the data reported here we postulate that modifications of the acidic character of peptides prevent formation of anionic species under MALDI analysis. Furthermore, suppression of the formation pathway for anions alters the overall number of molecules which can undergo protonation. This results in an increased ion yield for the protonated esters.     

Structure determination of beta-glucans from Ganoderma lucidum with matrix-assisted laser desorption/ionization (MALDI) mass spectrometry

A novel method that uses matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to analyze molecular weight and sequencing of glucan in Ganoderma lucidum is presented. Thus, beta-glucan, which was isolated from fruiting bodies of G. lucidum, was measured in a direct and fast way using MALDI mass spectrometry. In addition, tandem mass spectrometry of permethylated glucans of G. lucidum, dextran, curdlan and maltohexaose were also pursued and different fragment patterns were obtained. The G. lucidum glucan structure was determined and this method for linkage analysis of permethylated glucan has been proven feasible.     

基质辅助激光解析电离-飞行时间质谱分析寡核苷酸G-四链体

我们发展了一种利用基质辅助激光解析电离飞行时间质谱技术(MALDI-TOF MS)分析对金属离子具有较高亲和力的寡核苷酸G-四链体的方法.考察了不同基质:3-羟基吡啶甲酸(3-HPA)与柠檬酸氢二铵(DHC)混合基质、3,4-二胺基苯基苯甲酮(DABP)及DABP/DHC混合基质,应用于G-四链体分析的效果.实验结果表...     

Tandem mass spectrometry of poly(ethylene imine)s by electrospray ionization (ESI) and matrix‐assisted laser desorption/ionization (MALDI)

In this contribution, linear poly(ethylene imine) (PEI) polymers, which are of importance in gene delivery, are investigated in detail by using electrospray ionization‐quadrupole‐time of flight (ESI‐Q‐TOF) and matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF) mass spectrometry (MS). The analyzed PEIs with different end groups were synthesized using the polymerization of substituted 2‐oxazoline via a living cationic ring‐opening polymerization (CROP) and a subsequent hydrolysis under acidic conditions. The main goal of this study was to identify linear PEI polymers in a detailed way to gain information about their fragmentation pathways. For this purpose, a detailed characterization of three different linear PEIs was performed by using ESI‐Q‐TOF and MALDI‐TOF MS in combination with collision‐induced dissociation (CID) experiments. In ESI‐MS as well as MALDI‐MS analysis, the obtained spectra of PEIs resulted in fitting mass distributions for the investigated PEIs. In the tandem MS analysis, a 1,2‐hydride shift with a charge‐remote rearrangement via a four‐membered cyclic transition state, as well as charge‐induced fragmentation reactions, was proposed as the main fragmentation mechanisms according to the obtained fragmentation products from the protonated parent peaks. In addition, heterolytic and homolytic cleavages were proposed as alternative fragmentation pathways. Moreover, a 1,4‐hydrogen elimination was proposed to explain different fragmentation products obtained from the sodiated parent peaks. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of quaternary protein ensembles by matrix assisted laser desorption/ionization mass spectrometry

The intact noncovalent structure of the homo-oligomeric complexes of streptavidin (52 kDa), alcohol dehydrogenase (150 kDa), and beef liver catalase (240 kDa) have been observed using the matrix 2,6-dihydroxyacetophenone in an organic solvent. Intact streptavidin tetramers could also be observed with ferulic acid and other hydroxyacetophenone derivatives. Intact complexes are observed only for the first shot at a given position, which may be due to physical segregation or precipitation of the noncovalent complexes at the crystal surface. This effect is independent of the macroscopic crystal structure or the type of substrate (hydrophobic versus hydrophilic). Observation of intact complexes is not affected by addition of less than 10 mM salts or buffers, and appears to be independent of the pH stability range of the protein samples investigated.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

Capillary isoelectric focusing coupled offline to matrix assisted laser desorption/ionization mass spectrometry

This work presents several critical details for making cIEF-MALDI-MS a robust technique which will allow for more routine application and aid in automation. This includes emphasis on the hardware necessary for syringe pump mobilization and proper protocol for preventing disruption from gas bubbles. Following these guidelines, excellent elution time reproducibility is demonstrated for six pI markers (RSD <5%). Additionally, the pI markers are used to calibrate the pH gradient and determine experimental pIs of proteins detected offline by mass spectrometry. This was demonstrated using a standard protein mixture of myoglobin and two forms of β-lactoglobulin. Experimental determination of protein pIs and molecular weights were found to be in agreement with literature values. The technical details discussed provide a sound foundation for applying the offline coupling of MALDI-MS with cIEF.     

Mass spectrometric determination of the electron affinity of C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>10</Subscript> and C<Subscript>60</Subscript>(CF<Subscript>3</Subscript>)<Subscript>12</Subscript> molecules

Knudsen cell mass spectrometry was used to study ion-molecular electron exchange reactions between some trifluoromethyl derivatives of C₆₀ fullerene. Electron affinity values were experimentally determined for C₆₀(CF₃)₁₀ and the S ₆ isomer of C₆₀(CF₃)₁₂ and compared with the results of calculations and the data in the literature.     

Ionic matrix for matrix-enhanced surface-assisted laser desorption ionization mass spectrometry imaging (ME-SALDI-MSI)

Matrix-enhanced surface-assisted laser desorption ionization mass spectrometry imaging (ME-SALDI MSI) has been previously demonstrated as a viable approach to improving MS imaging sensitivity. We describe here the employment of ionic matrices to replace conventional MALDI matrices as the coating layer with the aims of reducing analyte redistribution during sample preparation and improving matrix vacuum stability during imaging. In this study, CHCA/ANI (α-cyano-4-hydroxycinnamic acid/aniline) was deposited atop tissue samples through sublimation to eliminate redistribution of analytes of interest on the tissue surface. The resulting film was visually homogeneous under an optical microscope. Excellent vacuum stability of the ionic matrix was quantitatively compared with the conventional matrix. The subsequently improved ionization efficiency of the analytes over traditional MALDI was demonstrated. The benefits of using the ionic matrix in MS imaging were apparent in the analysis of garlic tissue sections in the ME-SALDI MSI mode.     

Study of synthetic aliphatic copolyamides by time-of-flight matrix assisted laser desorption/ionization mass spectrometry

Synthetic copolyamides based on aliphatic diamines (1,3-propanediamine and 1,4-butanediamine) and dichlorides of aliphatic carboxylic acids (adipic and sebacic acid dichlorides) were investigated using time-of-flight matrix assisted laser desorption/ionization mass spectrometry. Their mass spectra showed peaks for cationized (Na⁺ and K⁺) and protonated (less intense peaks) oligomers with NH₂-NH₂, NH₂-COOH, or COOH-COOH end groups. No cyclic oligomers were detected in the samples. The compositions of oligomers were determined, and the relative reactivities of homologous comonomers in polycondensation were estimated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1320–1324, July, 2007.     

Molecular histology analysis by matrix‐assisted laser desorption/ionization imaging mass spectrometry using gold nanoparticles as matrix

Gold nanoparticles (AuNPs) were applied and optimized as matrix for matrix‐assisted laser desorption/ionization mass spectrometry analysis of animal tissues, and enabled histological analysis of animal tissues at molecular level by imaging mass spectrometry (IMS). AuNPs were coated on animal tissue in a solvent‐free manner via argon ion sputtering. Metabolites, including neurotransmitters, fatty acids and nucleobases, were directly detected from mouse brain tissue. Based on region‐specific chemical profiles, fine histological features of mouse brain tissue and heterogeneous regions of tumor tissue were both revealed. Copyright © 2011 John Wiley & Sons, Ltd.     

Continuous flow infrared matrix‐assisted laser desorption electrospray ionization mass spectrometry

Continuous flow infrared matrix‐assisted laser desorption electrospray ionization (CF IR MALDESI) mass spectrometry was demonstrated for the on‐line analysis of liquid samples. Samples in aqueous solution were flowed through a 50 µm i.d. fused‐silica capillary at a flow rate of 1–6 µL/min. As analyte aqueous solution flowed through the capillary, a liquid sample bead formed at the capillary tip. A pulsed infrared optical parametric oscillator (OPO) laser with wavelength of 2.94 µm and a 20 Hz repetition rate was focused onto the capillary tip for sample desorption and ablation. The plume of ejected sample was entrained in an electrospray to form ions by MALDESI. The resulting ions were sampled into an ion trap mass spectrometer for analysis. Using CF IR MALDESI, several chemical and biochemical reactions were monitored on‐line: the chelation of 1,10‐phenanthroline with iron(II), insulin denaturation with 1,4‐dithiothreitol, and tryptic digestion of cytochrome c. Copyright © 2010 John Wiley & Sons, Ltd.     

Silver cluster interferences in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of nonpolar polymers

Potential difficulties associated with background silver salt clusters during matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of nonpolar polymers are reported. Silver salt cluster ions were observed from m/z 1500 to 7000 when acidic, polar matrices, such as 2,5-dihydroxybenzoic acid (DHB), all-trans-retinoic acid (RTA) or 2-(4-hydroxyphenylazo)benzoic acid (HABA), were used for the analysis of nonpolar polymers. These background signals could be greatly reduced or eliminated by the use of nonpolar matrices such as anthracene or pyrene. Representative examples of these background interferences are demonstrated during the analysis of low molecular weight nonpolar polymers including polybutadiene and polystyrene. Nonpolar polymers analyzed with acidic, polar matrices (e.g., RTA) and silver cationization reagents can yield lower quality mass spectral results when interferences due to silver clusters are present. Replacing the polar matrices with nonpolar matrices or the silver salts with copper salts substantially improved the quality of the analytical results. In addition, it was found that silver contamination cannot be completely removed from standard stainless steel sample plates, although the presence of silver contamination was greatly reduced after thorough cleaning of the sample plate with aluminum oxide grit. Carry-over silver may cationize polymer samples and complicate the interpretation of data obtained using nonpolar matrices in the absence of added cationization reagents.     

Bis(Allyloxycarbonyl)methano derivatives of fullerene C<Subscript>60</Subscript>

Mono-, bis-, tris-, tetrakis-, and hexakis-substituted cyclopropanation products of fullerene C₆₀ with diallyl malonate were synthesized according to Bingel-Hirsch. Except for the monocyclopropanation product, all other adducts were isolated as mixtures of regioisomers.     

Electrochemical properties of transition metal complexes with C<Subscript>60</Subscript> and C<Subscript>70</Subscript> fullerne ligands (review)

t-The electrochemical properties of exohedral complexes of transition metals with metallofragments coordinated to C₆₀ and C₇₀ fullerene ligands in different coordination modes are surveyed. The effect of the nature, composition, and structure of metal-containing fragments on the electrochemical properties of these complexes and stability of products formed in the oxidation and reduction of complexes is discussed.