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Biomedical subjects

C B Lebrilla

Publications and source records attributed to C B Lebrilla.

31 records · Page 2Linked to original sources
PubMed1997

A modular lymphographic magnetic resonance imaging contrast agent: contrast enhancement with DNA transfection potential.

A gadolinium-chelated liposomal contrast agent has been prepared, and magnetic resonance imaging (MRI) efficacy has been examined by indirect magnetic resonance lymphography. A lipidic N,N'-dimethylethylenediamine derivative (4) containing a 10,12-diyne-diacyl domain was treated with DTPA anhydride followed by GdCl3 complexation. The complex was confirmed using MALDI spectrometry. An equimolar mixture of the Gd-chelate lipid and a commercially available diyne-PE was formulated as a liposome suspension and irradiated with UV light prior to imaging experiments. Subcutaneous injection of the liposomal gadolinium agent and subsequent MRI of rabbit axillary and popliteal lymph nodes revealed significant contrast enhancement up to 4 h postinjection. To explore the possibility of imaging a DNA transfection event, the gadolinium contrast mixture was formulated with the cationic transfection lipid DOTAP and complexed with the reporter gene encoding luciferase. DNA transfection studies on the NIH3T3 cell line confirmed the transfection activity of the dual-purpose contrast agent and exemplified the potential toward development of an imaging and DNA delivery vehicle.

3T3 Cells↗
PubMed1997

Characterization of neutral oligosaccharide-alditols from Xenopus laevis egg jelly coats by matrix-assisted laser desorption Fourier transform mass spectrometry.

Neutral oligosaccharides were released by alkaline sodium borohydride reduction of the jelly coating from the South African clawed toad, Xenopus laevis. The oligosaccharides were isolated by HPLC and analyzed by matrix-assisted laser desorption ionization (MALDI)-Fourier transform mass spectrometry (FTMS). The mass spectrometry analysis allowed confirmation of 12 structures first proposed by Strecker et al. using nuclear magnetic resonance. In addition, seven new oligosaccharides with weak abundances were found and characterized by mass spectrometry. A method for discriminating metastable fragments from quasimolecular ions is described. It involves doping the sample with cesium chloride. Cesium-coordinated oligosaccharides do not fragment as readily as those coordinated to sodium. Tandem MS experiments are performed on an unknown oligosaccharide illustrating the potential of MALDI-collision-induced dissociation-FTMS.

Animals↗
PubMed1997

Direct analysis of sugar alcohol borate complexes in plant extracts by matrix-assisted laser desorption/ionization fourier transform mass spectrometry.

Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI/FTMS), operating in the negative ion mode, is used to directly observe sugar alcohol borate complexes in a number of plant fractions. The method involves virtually no sample workup and, in the case of celery phloem sap, requires only 40 nL of sap to observe the borate complex. The isolation and characterization of such soluble borate complexes is important in understanding the distribution of boron in plants. The results show that the complexes are composed of two mannitol or sorbitol ligands (L) complexed to a single borate center (B). In some cases, the boron is complexed to non-alditol monosaccharides. Sustained off-resonance collision irradiation dissociation of the BL2- complex, where L is a mannitol, gives fragments that confirm the proposed structure. Complexes of larger oligosaccharides have also been successfully observed using MALDI/FTMS. Semiempirical molecular orbital calculations (AM1) of the mannitol BL2- complex show that the most favorable configuration is with carbons 3 and 4 of both mannitol residues complexed to the borate. This allows maximum interaction of the remaining hydroxyls with the borate center.

Borates↗
PubMed1997

Isolation and characterization of soluble boron complexes in higher plants. The mechanism of phloem mobility of boron.

Boron (B) polyol complexes have been isolated and characterized from the phloem sap of celery (Apium graveolens L.) and the extrafloral nectar of peach (Prunus persica L.). In celery the direct analysis of untreated phloem sap by matrix-assisted laser desorption-Fourier transform mass spectrometry, with verification by high-performance liquid chromagraphy and gas chromatography-mass spectrometry, revealed that B is present in the phloem as the mannitol-B-mannitol complex. Molecular modeling further predicted that this complex is present in the 3,4 3',4' bis-mannitol configuration. In the extrafloral nectar of peach, B was present as a mixture of sorbitol-B-sorbitol, fructose-B-fructose, or sorbitol-B-fructose. To our knowledge, these findings represent the first successful isolation and characterization of soluble B complexes from higher plants and provide a mechanistic explanation for the observed phloem B mobility in these species.

Biological Transport↗
PubMed1996

Collision-induced dissociation of branched oligosaccharide ions with analysis and calculation of relative dissociation thresholds.

Collision-induced dissociation (CID) is used in an external source Fourier transform mass spectrometer (FTMS) equipped with matrix-assisted laser desorption/ionization (MALDI) to study a number of complex, branched oligosaccharides. The relative dissociation thresholds for various oligosaccharide fragmentation pathways have been calculated in terms of kinetic and center-of-mass frame energy. For two isomers of difucosyllacto-N-hexaose, the loss of the fucose sugar is always the lowest energy fragment observed and occurs at the same energy for both isomers when the oligosaccharide is coordinated to a sodium ion. When the oligosaccharide is complexed to cesium, the threshold for the removal of the fucose moiety increases, indicating that the cesium is involved in a coordination complex that stabilizes the sugar. MS/ MS/MS is performed on a sugar, mannose core, which does not readily fragment during MALDI. In all the sugars examined, CID produces additional structural information relative to MALDI/FTMS.

Carbohydrate Sequence↗
PubMed1996

A dual vacuum chamber fourier transform mass spectrometer with rapidly interchangeable LSIMS, MALDI, and ESI sources: initial results with LSIMS and MALDI.

A design is presented involving two separate vacuum chambers to provide nearly simultaneous capabilities of liquid secondary ion mass spectrometry (LSIMS), matrix-assisted laser desorption/ionization (MALDI), and electrospray ionization (ESI) in an external source Fourier transform mass spectrometer. The instrument consists of two vacuum chambers, one with five stages of differential pumping for a combined LSIMS/MALDI source. The chamber dedicated to ESI was formerly a three-stage chamber with LSIMS and electron ionization. Two additional stages were added with the ESI source. LSIMS and MALDI have similar vacuum requirements and were moved to a newly built chamber with two stages of pumping. We present our first results obtained on the new vacuum chamber. Data presented for the MALDI source show that, with only two stages of pumping, and with shorter radio frequency-only quadrupole rods for ion injection, spectra comparable to those obtained on the formerly three-stage instrument can be obtained. Characterization of the MALDI source and data on linear, cyclic, and branched oligosaccharides are given. Finally, the design of the secon chamber is proposed as a low-cost prototype for an external source FTMS instrument.

Carbohydrate Sequence↗
PubMed1996

Mass spectrometric analyses of beta-ketolactone oligomers, macrocyclic or catenane structures?

Mass spectrometry is used to develop an analytical method for a new class of organic oligomeric material, beta-ketolactones. Three different series with varying oligomeric sizes are examined. The oligomers may form at least two different structures, a macrocyclic and a catenane ring. Fast atom bombardment coupled with Fourier transform mass spectrometry provides a rapid and convenient method that provides both molecular weight information and abundant fragment ions that are structurally relevant. All the compounds are found to work well with the mass spectrometric analysis. Electrospray ionization coupled with triple-quadrupole mass spectrometry was also evaluated and found to yield results that are similar to FAB. On the basis of the FAB and the low-energy collisionally activated dissociation spectra, we conclude that these compounds are macrocyclic rings and not catenanes.

Chromatography, Liquid↗
PubMed1996

Bastadin 20 and bastadin O-sulfate esters from Ianthella basta: novel modulators of the Ry1R FKBP12 receptor complex.

New compounds bastadin 20 (9), 15,34-O-disulfatobastadin 7 (10), and 10-O-sulfatobastadin 3 (11) were isolated from Ianthella basta collected in Exmouth Gulf, Western Australia. Compounds 10 and 11 exhibited moderate differential activity as SR Ca2+ channel agonists (EC50 13.6 and 100 microM, respectively) of the Ry1R FKBP12 complex, while the potency of 9 was almost half that of 10 (EC50 20.6 microM). The problem of dereplication of bastadins was addressed using 1H-NMR "fingerprinting" of MeO signals in the corresponding permethyl bastadin derivatives.

Animals↗
PubMed1995

Exact mass determination for elemental analysis of ions produced by matrix-assisted laser desorption.

The exact masses of bastadins, cyclic peptides from marine sponges Ianthella basta, are determined using matrix-assisted laser desorption ionization (MALDI) coupled to a Fourier transform mass spectrometer. Two known compounds were mixed with the unknown to serve as internal calibrants. The mass of the calibrants bracketed the mass of the unknown compound. With this method, exact masses were obtained to within 5 ppm for single determinations, and less than 3 ppm for multiple determinations, allowing the derivation of elemental composition. This method is viable for routinely obtaining the exact masses of new compounds with MALDI.

Animals↗
PubMed1994

Effects of cations and charge types on the metastable decay rates of oligosaccharides.

Metastable decay rates of alpha-cyclodextrin and maltohexaose coordinated to proton and alkali metal ions were determined from ions produced by liquid secondary ion mass spectrometry in an external source Fourier transform mass spectrometry instrument. For both oligosaccharide compounds the decay rates of the protonated species are faster than any alkali metal coordinated species. Decay rates of the metal cationized species decrease in the order Li+, Na+, K+, and Cs+. The anion of alpha-cyclodextrin has the slowest measurable decomposition rate. The relationships between cation affinities and rates are explored.

Carbohydrate Sequence↗
PubMed1993

Liquid secondary ion mass spectrometry/Fourier transform mass spectrometry of oligosaccharide anions.

The liquid secondary ionization mass spectrometry of oligosaccharide anions is investigated with an external source quadrupole Fourier transform mass spectrometer (FTMS). Selected linear and cyclic oligosaccharides are analyzed to determine the performance of the external source FTMS in the anion mode. Fragmentation behavior of disaccharides is characterized and related to the fragmentation behavior of larger oligomers. General correlation is found between the linkages and the fragment ions observed.

Anions↗
PubMedDate not supplied

Ion-molecule reactions as probes of gas-phase structures of peptides and proteins.

A review with over 100 references describes the recent applications of ion-molecule reactions to the study of gas-phase protonated peptides and proteins. The topic is focused specifically on the proton transfer and hydrogen-deuterium exchange reactions of amino acids, peptides, and proteins. A brief background is given of the various methods used for assigning proton affinities and gas-phase basicities. The methods used for measuring the kinetics of deuterium incorporation of charged ion in the presence of a background pressure of deuterating reagents are also described. Ion-molecule reactions are used to determine, among other things, the gas-phase basicities and proton affinities of amino acids, peptides, and proteins, the sites of protonation, intra- and intermolecular interactions, and conformational differences and changes in gas-phase ionic species. Singly charged and multiply charged ions are both covered.

Gases↗