Rosa Erra-Balsells

β‐Carboline alkaloids as matrices for UV‐matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry in positive and negative ion modes. Analysis of proteins of high molecular mass, and of cyclic and acyclic oligosaccharides

We report that commercially available beta-carbolines (nor-harmane (9H-pyrido[3,4-b]indole), harmane (1-methyl-9H-pyrido[3,4-b]indole), harmine (7-methoxy-1-methyl-9H-pyrido[3,4-b]indole), harmol (1-methyl-9H-pyrido[3,4-b]indol-7-ol), harmaline (3,4-dihydro-7-methoxy-1-methyl-9H-pyrido[3,4-b]indole) and harmalol (3,4-dihydro-1-methyl-9H-pyrido[3,4-b]indol-7-ol)), are useful MALDI matrices at 337 nm, for cyclic oligosaccharides (cyclodextrins, range 972-1290 Da), acyclic oligosaccharides (range 342-828 Da) and high molecular mass proteins (range 23,290-66,525 Da) in both positive and negative modes. This was investigated by using time-of-flight (TOF) mass spectrometers of different sensitivities, equipped with and without pulse extraction facilities. A comparison with conventional matrices for carbohydrates (DHB and DHB/HIC) indicates that beta-carbolines provide the same level of sensitivity and resolution in the positive mode, but offer the advantage of high levels of sensitivity and resolution in the negative mode. Harmaline has been found to be specially effective for the analysis of high-mass proteins in both modes, and also exhibits excellent experimental reproducibility of the results owing to the homogeneous crystallization of the analyte-matrix mixture over the entire sample surface area. Harmane and nor-harmane are both excellent matrices for high-mass proteins also. As MALDI matrices, beta-carbolines permit measurement of sulfated sugars in the negative ion mode as ([M-H]), and of neutral sugars and proteins as both [M + H]+ and [M-H]- in appropriate modes.

Diamond, titanium dioxide, titanium silicon oxide, and barium strontium titanium oxide nanoparticles as matrixes for direct matrix-assisted laser desorption/ionization mass spectrometry analysis of carbohydrates in plant tissues.

Nanoparticles (NPs) of diamond, titanium dioxide, titanium silicon oxide, barium strontium titanium oxide, and silver (Ag) were examined for their potential as MALDI matrixes for direct laser desorption/ionization of carbohydrates, especially fructans, from plant tissue. Two sample preparation methods including solvent-assisted and solvent-free (dry) NPs deposition were performed and compared. All examined NPs except for Ag could desorb/ionize standard sucrose and fructans in positive and in negative ion mode. Ag NPs yielded good signals only for nonsalt-doped samples that were measured in the negative ion mode. In the case of in vivo studies, except for Ag, all NPs studied could desorb/ionize carbohydrates from tissue in both the positive and negative ion modes. Furthermore, compared to the results obtained with soluble sugars extracted from plant tissues, fructans with higher molecular weight intact molecular ions could be detected when the plant tissues were directly profiled. The limit of detection (LOD) of fructans and the ratios between signal intensities and fructan concentrations were analyzed. NPs had similar LODs for standard fructan triose (1-kestose) in the positive ion mode and better LODs in the negative ion mode when compared with the common crystalline organic MALDI matrixes used for carbohydrates (2,5-dihydroxybenzoic acid and nor-harmane) or carbon nanotubes. Solvent-free NP deposition on tissues partially improves the signal acquisition. Although lower signal-to-noise ratio sugar signals were acquired from the tissues when compared to the solvent-assisted method, the reproducibility averaged over all sample was more uniform.

Photochemical reaction of full-aromatic β-carbolines in halomethanes 2. CHCl3: Electronic spectra and kinetics

Abstract The photochemical behaviour of full-aromatic β-carbolines (nor-harmane, harmane and harmine) in chloroform medium and the corresponding UV absorption and fluorescence emission spectra are discussed. Irreversible electron transfer from the singlet excited β-carboline molecule to the chloroform molecule in the transient excited charge transfer complex has been proposed as the primary photochemical process initiating the mechanism of secondary reactions in this system. The results obtained are interpreted in terms of diffusional quenching mechanism and are compared with those obtained using different halomethanes.

Direct Profiling of Phytochemicals in Tulip Tissues and In Vivo Monitoring of the Change of Carbohydrate Content in Tulip Bulbs by Probe Electrospray Ionization Mass Spectrometry

Probe electrospray ionization (PESI) is a recently developed ESI-based ionization technique which generates electrospray from the tip of a solid needle. In this study, we have applied PESI interfaced with a time of flight mass spectrometer (TOF-MS) for direct profiling of phytochemicals in a section of a tulip bulb in different regions, including basal plate, outer and inner rims of scale, flower bud and foliage leaves. Different parts of tulip petals and leaves have also been investigated. Carbohydrates, amino acids and other phytochemicals were detected. A series of in vivo PESI-MS experiments were carried out on the second outermost scales of four living tulip bulbs to monitoring the change of carbohydrate content during the first week of initial growth. The breakdown of carbohydrates was observed which was in accordance with previous reports achieved by other techniques. This study has indicated that PESI-MS can be used for rapid and direct analysis of phytochemicals in living biological systems with advantages of low sample consumption and little sample preparation. Therefore, PESI-MS can be a new choice for direct analysis/profiling of bioactive compounds or monitoring metabolic changes in living biological systems.

One- and Two-Photon Excitation of β-Carbolines in Aqueous Solution: pH-Dependent Spectroscopy, Photochemistry, and Photophysics

Beta-carboline (betaC) alkaloids are present in a wide range of biological systems and play a variety of significant photodependent roles. In this work, a study of the aqueous solution-phase photochemistry, photophysics, and spectroscopy of three important betaCs [norharmane (nHo), harmane (Ho), and harmine (Ha)] and two betaC derivatives [N-methylnorharmane (N-Me-nHo) and N-methylharmane (N-Me-Ho)] upon one- and two-photon excitation is presented. The results obtained depend significantly on pH, the ambient oxygen concentration, and the betaC substituent and provide unique insight into a variety of fundamental photophysical phenomena. The data reported herein should not only help to understand the roles played by betaC alkaloids in biological systems but should also help in the development of methods by which the photoinduced behavior of these important compounds can be controlled.

Photochemical behaviour of β-carbolines. Part4.1 Acid–base equilibria in the ground andexcited states in organic media

The protonation equilibrium of six β-carbolines has been studied in organic media. The pKa values in acetonitrile were determined by spectrophotometric methods. The pKa values in the first excited singlet state (pKa*) were calculated from the Forster cycle and the values compared with those obtained by fluorimetric titration. It is concluded that the acid–base equilibrium is not established during the lifetime of the excited state. The differences between the pKa of the ground and the electronic excited singlet states in different organic media (MeOH, EtOH, PriOH, ButOH, MeCN and CH2Cl2) were also calculated.

Photoisomerization of ionic liquid ammonium cinnamates: one-pot synthesis-isolation of Z-cinnamic acids.

Photoisomerization presents the only direct method for contra-thermodynamic E-Z isomerization of olefins. Synthetic applications of this method have been limited by its reversible nature, which leads to a photostationary-state mixture of both isomers. For the first time, a highly efficient one-pot preparation-isolation of solid ionic liquid Z-cinnamic acids by photoisomerization in acetonitrile solution of ionic liquid E-cinnamic acids is described.

Structural analysis of the N-glycans of the major cysteine proteinase of Trypanosoma cruzi Identification of sulfated high-mannose type oligosaccharides

Trypanosoma cruzi, the parasitic protozoan that causes Chagas disease, contains a major cysteine proteinase, cruzipain. This lysosomal enzyme bears an unusual C‐terminal extension that contains a number of post‐translational modifications, and most antibodies in natural and experimental infections are directed against it. In this report we took advantage of UV‐MALDI‐TOF mass spectrometry in conjunction with peptide N‐glycosidase F deglycosylation and high performance anion exchange chromatography analysis to address the structure of the N‐linked oligosaccharides present in this domain. The UV‐MALDI‐TOF MS analysis in the negative‐ion mode, using nor‐harmane as matrix, allowed us to determine a new striking feature in cruzipain: sulfated high‐mannose type oligosaccharides. Sulfated GlcNAc2Man3 to GlcNAc2Man9 species were identified. In accordance, after chemical or enzymatic desulfation, the corresponding signals disappeared. In addition, by UV‐MALDI‐TOF MS analysis (a) a main population of high‐mannose type oligosaccharides was shown in the positive‐ion mode, (b) lactosaminic glycans were also identified, among them, structures corresponding to monosialylated species were detected, and (c) as an interesting fact a fucosylated oligosaccharide was also detected. The presence of the deoxy sugar was further confirmed by high performance anion exchange chromatography. In conclusion, the total number of oligosaccharides occurring in cruzipain was shown to be much higher than previous estimates. This constitutes the first report on the presence of sulfated glycoproteins in Trypanosomatids.

Real‐time reaction monitoring by probe electrospray ionization mass spectrometry

Probe electrospray ionization (PESI) is a modified version of the electrospray ionization (ESI), where the capillary for sampling and spraying is replaced by a solid needle. High tolerance to salts and direct ambient sampling are major advantages of PESI compared with conventional ESI. In this study, PESI-MS was used to monitor some biological and chemical reactions in real-time, such as acid-induced protein denaturation, hydrogen/deuterium exchange (HDX) of peptides, and Schiff base formation. By using PESI-MS, time-resolved mass spectra and ion chromatograms can be obtained reproducibly. Real-time PESI-MS monitoring can give direct and detailed information on each chemical species taking part in reactions, and this is valuable for a better understanding of the whole reaction process and for the optimization of reaction parameters. PESI-MS can be considered as a potential tool for real-time reaction monitoring due to its simplicity in instrumental setup, direct sampling with minimum sample preparation and low sample consumption.

Photochemical reaction of β-carbolines in carbon tetrachloride—ethanol mixtures

Abstract The photochemical behavior of β-carbolines in carbon tetrachloride—ethanol mixtures in addition to the corresponding UV absorption spectra and fluorescence emission spectra are discussed. The irreversible electron transfer from the singlet excited β-carboline molecule to the carbon tetrachloride molecule in the transient excited charge transfer complex have been proposed as the primary photochemical processes initiating the mechanism of secondary reactions in the system studied. The results obtained can be interpreted in terms of a diffusional quenching mechanism.