Publications (15)63.79 Total impact
-
Article: MALDI mass spectrometric determination of dendritic iron chelation stoichiometries and conditional affinity constants.
[show abstract] [hide abstract]
ABSTRACT: The iron chelation stoichiometries of a dendritic iron(III) chelator with N(1), N(3), N(5)-trimethylbenzene-1,3,5-tricarboxamide at its core, and containing 3 identical hexadentate tris-hydroxypyridinone branches D was studied by MALDI mass spectrometry. At pH 7.2, the speciation of the system included FeD, Fe(2)D and Fe(3)D species with the respective conditional stability constants of 26.74, 26.03 and 25.36. The differences in the stepwise affinity constants arise from the statistical distribution of iron(III), and there was no evidence for cooperativity between the iron-binding sites.Journal of Mass Spectrometry 06/2008; 43(5):617-22. · 3.27 Impact Factor -
Article: The fenton activity of iron(III) in the presence of deferiprone.
[show abstract] [hide abstract]
ABSTRACT: Hydroxyl radical production from a range of clinically relevant iron chelators in the presence of hydrogen peroxide was measured using the deoxyribose oxidation assay. Hydroxyl radical production from an iron complex is dependent on whether the ligand is able to completely surround the iron, thereby preventing access of reductants to the coordinated iron cation. The partially coordinated [(deferiprone)(2)Fe(III)](+) complex is able to generate hydroxyl radicals in the presence of oxidants, whereas the fully coordinated [(deferiprone)(3)Fe(III)](0) complex is not. Hydroxyl radical production from iron(III)deferiprone complexes is dependent on the molar ratio of iron to deferiprone, which, in turn, affects the speciation of the complex. Mass spectrometry data have confirmed the presence of the [(deferiprone)(2)Fe(III)](+) complex in aqueous solution. Hydroxyl radical production from the [(deferiprone)(2)Fe(III)](+) complex is maximal in the presence of equimolar ascorbate and hydrogen peroxide and is abolished in the absence of hydrogen peroxide. Under biological conditions, any [(deferiprone)(2)Fe(III)](+) complex formed intracellularly will be rapidly reduced by ascorbate. The resulting unstable iron(II) complex will dissociate to hexa-aquo iron(II), a major component of the endogenous intracellular labile iron pool.Journal of Pharmaceutical Sciences 05/2008; 97(4):1454-67. · 3.06 Impact Factor -
Article: Iron binding dendrimers: a novel approach for the treatment of haemochromatosis.
[show abstract] [hide abstract]
ABSTRACT: A range of iron binding dendrimers terminated with hexadentate ligands formed from hydroxypyridinone, hydroxypyranone, and catechol moieties have been synthesized in order to investigate their potential as clinically useful iron(III)-selective chelators capable of removing dietary iron from the gastrointestinal tract and preventing the development of iron overload typical of haemochromatosis and thalassaemia intermedia. The iron chelating abilities of these molecules have been characterized by MALDI-TOF mass spectrometry and UV spectrometry. Hydroxypyridinone-terminated dendrimers were found to possess a high affinity and selectivity for iron(III). A hydroxypyridinone-based dendrimer was demonstrated to be highly efficient at reducing the absorption of iron(III) in rat intestine. This family of dendrimers may find an application in the treatment of iron overload.Journal of Medicinal Chemistry 08/2006; 49(14):4171-82. · 5.25 Impact Factor -
Article: 3-Hydroxy-2-(5-hydroxypentyl)-4H-chromen-4-one: a bidentate or tridentate iron(III) ligand?
[show abstract] [hide abstract]
ABSTRACT: The pK(a) value and iron affinity constants for 3-hydroxy-2-(5-hydroxypentyl)-4H-chromen-4-one 1 have been determined by spectrophotometry using aqueous methanol solutions. The extrapolated affinity constants beta(1), beta(2), and beta(3)( )()for iron(III) in aqueous solution were 9.95, 18.69, and 26.02, respectively, with a corresponding pFe(3+) value of 14.64. Job plot and MS spectra data demonstrated that the 3:1 species is favored at pH 7.0. These results indicate that 1 acts as a bidentate ligand when coordinated to iron(III).Journal of Medicinal Chemistry 06/2006; 49(10):3028-31. · 5.25 Impact Factor -
Article: High affinity iron(III) scavenging by a novel hexadentate 3-hydroxypyridin-4-one-based dendrimer: synthesis and characterization.
[show abstract] [hide abstract]
ABSTRACT: The synthesis of a novel iron(III)-selective hydroxypyridinone hexadentate-terminated dendritic chelator based on a benzene tricarbonyl core polyamine dendrimer is described. The iron-chelating ability of the dendritic chelator was demonstrated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and UV-vis spectroscopy. The physicochemical properties of the isolated hexadentate unit were also investigated. The dendrimer was found to possess an extremely high affinity for iron(III), namely logK=34.8, pFe3+=30.6.Bioorganic & Medicinal Chemistry Letters 12/2005; 15(22):5007-11. · 2.55 Impact Factor -
Article: Structural characterization of chelator-terminated dendrimers and their synthetic intermediates by mass spectrometry.
[show abstract] [hide abstract]
ABSTRACT: Herein, we report the structural analysis of a novel family of iron-chelating dendrimers and their synthetic intermediates utilizing matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and electrospray ionization ion trap (ESI IT) MS. These dendrimers share a benzene tricarbonyl core moiety attached to three tripodal branching units, each linking to three terminal groups, ranging from carboxyl, catechol and 3-hydroxy-6-methyl-pyran-4-one moieties and their protected analogs. In order to monitor the progression of dendrimer synthesis, all intermediates and final products were mass analyzed by conventional MALDI-TOF MS with and without alkali metal spiking. For structural characterization, interpretable post-source decay (PSD) and electrospray ionization ion trap MS/MS spectra were obtained from proton, sodium and potassium adducts of the dendrimers. One major route of dendrimer fragmentation was at or adjacent to the amide bonds either of the terminal chelating groups or near the core moiety. Fragmentation in the latter case was primarily at the N-terminal side of the amide bond and was directed by the proximity of a tertiary carbon of the branching unit. Furthermore, it was found that terminal ester, ether and amide linkages to the protecting and chelating groups could be sequentially broken in a single MS/MS spectrum through multiple cleavages resulting in product ions of decreasing intensity. Moreover, such cleavages could also be induced in a stepwise manner in a multistage ion trap MS(n) experiment.Journal of Mass Spectrometry 10/2005; 40(9):1203-14. · 3.27 Impact Factor -
Article: Identification of placental transforming growth factor-beta and bikunin metabolites as contaminants of pharmaceutical human chorionic gonadotrophin preparations by proteomic techniques.
[show abstract] [hide abstract]
ABSTRACT: A contaminant protein complex found in pharmaceutical urinary human chorionic gonadotrophin preparations is reported to have anti-human immunodeficiency virus-associated Kaposi's sarcoma activity. The aim of this study was to isolate and characterize this protein complex by proteomic approaches. Size exclusion chromatography was used in the isolation of these human chorionic gonadotrophin-associated fragments. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the presence of a protein complex that dissociated into two protein bands under reducing conditions. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of this complex showed three polypeptides at approximately 6.2, 11.4, and 15.8 kDa. Peptide mass mapping and N-terminal amino acid sequencing identified two polypeptides as metabolites of placental transforming growth factor-beta (11.4 kDa) and bikunin (15.8 kDa). Subsequent matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of the anti-human immunodeficiency virus-associated Kaposi's sarcoma active preparations CG-10 (Sigma), Pregnyl (Organon), and Profasi (Serono) revealed the presence of metabolites of placental transforming growth factor-beta in all three; no other non-human chorionic gonadotrophin-related protein species were observed in these preparations. Our findings present evidence that urinary human chorionic gonadotrophin preparations are contaminated with metabolites of placental transforming growth factor-beta, which may have transforming growth factor-beta agonist actions, and metabolites of bikunin, which is a protease inhibitor. In combination these molecules may be responsible for the anti-human immunodeficiency virus-associated Kaposi's sarcoma activity demonstrated for these urinary human chorionic gonadotrophin preparations.Molecular & Cellular Proteomics 08/2005; 4(7):984-92. · 7.40 Impact Factor -
Article: C-terminal sequencing by mass spectrometry: application to gelatine-derived proline-rich peptides.
[show abstract] [hide abstract]
ABSTRACT: Protonated peptides derived from proline-rich proteins (PRP) are often difficult to sequence by standard collision-induced dissociation (CID) mass spectrometry (MS) due to preferential amide bond cleavage N-terminal to proline. In connection with bovine spongiform encephalopathy regulations, proteolytic products derived from the PRP collagen have been suggested as markers for contamination of animal feedstuffs with processed animal protein (Fernandez Ocaña, M. et al., Analyst 2004, 129, 111-115). Herein, we report the identification of these marker peptides using the strategy of C-terminal sequencing by CID MS from their sodium and lithium adducts. Upon fragmentation a new cationized peptide was produced that is one C-terminal amino acid shorter in length. This dissociation pathway allowed for the facile identification of the C-terminal residue by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry. Each newly formed cationized peptide was further fragmented by up to seven stages of electrospray ionization ion trap MS. Proline-rich C-terminal sequence tags were established which permitted successful database identification of collagen alpha type I proteins.PROTEOMICS 05/2005; 5(5):1209-16. · 4.51 Impact Factor -
Article: Widespread sulfenic acid formation in tissues in response to hydrogen peroxide.
[show abstract] [hide abstract]
ABSTRACT: A principal product of the reaction between a protein cysteinyl thiol and hydrogen peroxide is a protein sulfenic acid. Because protein sulfenic acid formation is reversible, it provides a mechanism whereby changes in cellular hydrogen peroxide concentration may directly control protein function. We have developed methods for the detection and purification of proteins oxidized in this way. The methodology is based on the arsenite-specific reduction of protein sulfenic acid under denaturing conditions and their subsequent labeling with biotin-maleimide. Arsenite-dependent signal generation was fully blocked by pretreatment with dimedone, consistent with its reactivity with sulfenic acids to form a covalent adduct that is nonreducible by thiols. The biotin tag facilitates the detection of protein sulfenic acids on Western blots probed with streptavidin-horseradish peroxidase and also their purification by streptavidin-agarose. We have characterized protein sulfenic acid formation in isolated hearts subjected to hydrogen peroxide treatment. We have also purified and identified a number of the proteins that are oxidized in this way by using a proteomic approach. Using Western immunoblotting we demonstrated that a highly significant proportion of some individual proteins (68% of total in one case) form the sulfenic derivative. We conclude that protein sulfenic acids are widespread physiologically relevant posttranslational oxidative modifications that can be detected at basal levels in healthy tissue, and are elevated in response to hydrogen peroxide. These approaches may find widespread utility in the study of oxidative stress, particularly because hydrogen peroxide is used extensively in models of disease or redox signaling.Proceedings of the National Academy of Sciences 01/2005; 101(52):17982-7. · 9.68 Impact Factor -
Article: MALDI post-source decay and LIFT-TOF/TOF investigation of alpha-cyano-4-hydroxycinnamic acid cluster interferences.
[show abstract] [hide abstract]
ABSTRACT: Large signals from alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix complexes with sodium and potassium ions were found to interfere with sensitive matrix-assisted laser desorption/ionization (MALDI) analysis of a hydrochloric acid digest of gelatine preparations. The nature of some selected matrix clusters was investigated by conventional post-source decay and LIFT-TOF/TOF experiments. The matrix clusters fragmented readily by neutral evaporation to give smaller sized matrix cluster species without matrix disintegration. Their characterization distinguished them from peptide signals, in particular from those that had the same nominal mass and differed only in the fractional part of the mass as encountered for gelatine-derived peptides. Knowledge of the molecular composition of these cluster species allowed using them for internal calibration of the MALDI mass spectra. The hydrolytic peptides could be analyzed with increased sensitivity when using 2,5-dihydroxy benzoic acid (DHB) as the MALDI matrix.Journal of the American Society for Mass Spectrometry 04/2004; 15(3):336-43. · 4.00 Impact Factor -
Article: BSE control: detection of gelatine-derived peptides in animal feed by mass spectrometry.
[show abstract] [hide abstract]
ABSTRACT: The epidemic of bovine spongiform encephalopathy (BSE) is thought to have resulted from feeding scrapie-infected sheep to cattle. This has led to a ban of feeding animals with "processed animal protein"(PAP). We report a novel approach for the mass spectrometric detection of PAP contamination in animal feedstuffs by detecting gelatine, a derivative of the major animal protein collagen. A method was developed to hydrolyse gelatine standards with hydrochloric acid, followed by detection of the derived hydrolytic peptides at m/z 828, 915, 957 and 1044 by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS-MS). The marker peptides can be detected at concentrations of 100 ng ml(-1) gelatine in water with MALDI. The procedure was adapted to obtain a suitable peptide map of gelatine extracted from spiked feed. The ratio of signal area of the gelatine-derived peptide at m/z 1044 to the internal standard at m/z 556 is shown to relate to the total amount of gelatine present in the sample.The Analyst 03/2004; 129(2):111-5. · 4.23 Impact Factor -
Article: MALDI TOF Post-Source Decay Investigation of Alkali Metal Adducts of Apolar Polypentylresorcinol Dendrimers
[show abstract] [hide abstract]
ABSTRACT: Polypentylresorcinol dendrimers of generation two and three with varying focal groups and terminal tetrahydropyranyl (THP) ethers could be efficiently ionized intact as their alkali metal ion adducts by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry using α-cyano-4-hydroxycinnamic acid matrix. Post-source decay (PSD) MALDI TOF experiments were carried out to confirm the dendrimer structures. Li and Na ion adducts consistently produced far more intense fragmentation, unlike K and Cs ion adducts which did not produce any noteworthy fragmentation. Fragment structures and pathways were proposed on the basis of these findings. A major route of decay is the sequential loss of terminal THP ethers which proved particularly useful in structure confirmation. Li was shown to be the cation of choice to aid the analysis of THP containing polypentylresorcinol dendrimers.10/2003; -
Article: Enhanced affinity capture MALDI-TOF MS: orientation of an immunoglobulin G using recombinant protein G.
[show abstract] [hide abstract]
ABSTRACT: Although immobilization of antigen-specific immunoglobulins onto matrix-assisted laser desorption/ionization (MALDI) targets allows the specific detection and enrichment of an antigen from complex biological fluids, the process of antibody immobilization is not optimal. The principal reason is that the antibody can bind to the template in various orientations, many of which block antigen recognition. An affinity capture MALDI mass spectrometry methodology was developed by covalently immobilizing an Fc receptor (recombinant protein G) onto MALDI gold targets for the purpose of orientating an immunoglobulin G, with the Fab domains pointing away from the target surface. The pregnancy and cancer marker, human chorionic gonadotropin beta core fragment (hCGbetacf), was our chosen test substance. To optimize the methodology, different surface densities of protein G and immunoglobulin were achieved by employing varying concentrations for immobilization. Captured amounts of hCGbetacf were compared using an external standard (cytochrome c). Orientation of immunoglobulin resulted in an approximately 3-fold increase in MALDI signal compared to using randomly immobilized antibody. Higher antibody concentrations resulted in diminished MALDI signals, which were explained by steric hindrance. Purification and enrichment of hCGbetacf was achieved from a test solution containing contaminant peptides and proteins using oriented immunoglobulins on-target.Analytical Chemistry 09/2002; 74(15):3677-83. · 5.86 Impact Factor -
Article: Speciation of Fe(III)–chelate complexes by electrospray ionization ion trap and laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry
[show abstract] [hide abstract]
ABSTRACT: Electrospray ionization mass spectrometry (ESI-MS) was employed as a relatively simple technique to investigate the speciation of complexes formed between Fe(III), the iron chelator 3-hydroxy-2-methyl-1-propyl-1H-pyridin-4-one (L) and citrate. The major species in aqueous solution at pH 6.0 of a 1:2:10 molar mixture Fe(III)/L/citrate is the Fe(III)L2 complex. No evidence for a mixed citrate complex was observed. Furthermore, evidence for the existence of a number of dimeric iron species is presented. All observed species in ESI were singly charged as evidenced by the isotopic envelopes. Laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry (LDI-FTICRMS) provided data that complemented and confirmed the ESI findings. We also demonstrate the possibility of chelated Fe(III) being converted to Fe(II) under ESI and LDI conditions. Copyright © 2002 John Wiley & Sons, Ltd.Rapid Communications in Mass Spectrometry 07/2002; 16(16):1556 - 1561. · 2.79 Impact Factor -
Article: Iron(III)-selective dendritic chelators
[show abstract] [hide abstract]
ABSTRACT: Two novel iron(III)-selective hexadentate chelator-terminated dendrimers have been synthesized in high yields. MALDI-TOF mass spectra demonstrate that both dendritic chelators bind iron(III) efficiently. Preliminary studies show that these molecules possess a high affinity for iron(III).Graphical abstractTetrahedron Letters 45(51):9393-9396. · 2.68 Impact Factor
Top co-authors
Top Journals
Institutions
-
2002–2008
-
King's College London
- • Institute of Pharmaceutical Science
- • Department of Pharmacy
- • Drug Control Centre
London, ENG, United Kingdom
-
-
2005
-
University of Vienna
- Department of Medicinal Chemistry
Vienna, Vienna, Austria -
Royal Holloway, University of London
Egham, ENG, United Kingdom
-
