| 1. |
- Falk, Magnus, et al.
(författare)
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Mechanism of Bilirubin Oxidase : Fabrication and Characterization of Efficient Biocathode
- 2010
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Ingår i: Meeting abstracts (Electrochemical Society). - : ECS. - 1091-8213 .- 2151-2043. ; MA2010-02:1
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- To elucidate the mechanism of bilirubin oxidase (BOx)function in order to design efficient and stablebiocathodes working at different conditions, the enzymewas studied thoroughly. BOx is a copper-containing redoxenzyme that catalyzes the oxidation of a variety ofdifferent organic and inorganic compounds withconcomitant reduction of O2 directly to H2O.
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| 2. |
- Haberska, Karolina, et al.
(författare)
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Direct electron transfer reactions between human ceruloplasmin and electrodes.
- 2009
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Ingår i: Bioelectrochemistry. - : Elsevier BV. - 1878-562X .- 1567-5394. ; 76, s. 34-41
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Tidskriftsartikel (refereegranskat)abstract
- In an effort to find conditions favouring bioelectrocatalytic reduction of oxygen by surface-immobilised human ceruloplasmin (Cp), direct electron transfer (DET) reactions between Cp and an extended range of surfaces were considered. Exploiting advances in surface nanotechnology, bare and carbon-nanotube-modified spectrographic graphite electrodes as well as bare, thiol- and gold-nanoparticle-modified gold electrodes were considered, and ellipsometry provided clues as to the amount and form of adsorbed Cp. DET was studied under different conditions by cyclic voltammetry and chronoamperometry. Two Faradaic processes with midpoint potentials of about 400 mV and 700 mV vs. NHE, corresponding to the redox transformation of copper sites of Cp, were clearly observed. In spite of the significant amount of Cp adsorbed on the electrode surfaces, as well as the quite fast DET reactions between the redox enzyme and electrodes, bioelectrocatalytic reduction of oxygen by immobilised Cp was never registered. The bioelectrocatalytic inertness of this complex multi-functional redox enzyme interacting with a variety of surfaces might be associated with a very complex mechanism of intramolecular electron transfer involving a kinetic trapping behaviour.
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| 3. |
- Melander, Claes, et al.
(författare)
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Microchip immobilized enzyme reactors for hydrolysis of methyl cellulose
- 2005
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 77:10, s. 3284-3291
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Tidskriftsartikel (refereegranskat)abstract
- Microchip immobilized enzyme reactors (mu IMERs) with immobilized endoglucanases were applied for the hydrolysis of methyl cellulose (MC). MCs of various molecular weights were hydrolyzed using two mu IMERs containing immobilized celloendoglucanase Cel 5A from Bacillus agaradhaerens (BaCel 5A) connected in series. Hydrolysis by the mu IMER could be confirmed from the average molar masses and molar mass distributions measured by size exclusion chromatography (SEC) with online multiangle light scattering and refractive index detection. Methylated cellooligosaccharides with degrees of polymerization (DP) between 1 and 6 formed during hydrolysis were analyzed by direct infusion electrospray ionization ion-trap mass spectrometry (ESI-ITMS). Mass spectra of mu IMER- and batch-hydrolyzed samples were compared and no significant differences were found, indicating that mu IMER hydrolysis was as efficient as conventional batch hydrolysis. A fast and automated hydrolysis with online MS detection was achieved by connecting the mu IMER to high-performance liquid chromatography and ESI-ITMS. This online separation reduced the relative intensities of interfering signals and increased the signal-to-noise ratios in MS. The mu IMER hydrolysates were also subjected to SEC interfaced with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. With this technique, oligomers with DP 3-30 could be detected. The hydrolysis by they mu-IMER was performed within 60 min, i.e. significantly faster compared with batch hydrolysis usually performed for at least 24 h. The mu IMER also allowed hydrolysis after 10 days of continuous use. The method presented in this work offers new approaches for the analysis of derivatized cellulose and provides the possibility of convenient online, fast, and more versatile analysis compared with the traditional batch method.
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| 4. |
- Mie, Axel, et al.
(författare)
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Analysis of triazines and associated metabolites with electrospray ionization field-asymmetric ion mobility spectrometry/mass spectrometry.
- 2008
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Ingår i: Analytical Sciences. - 0910-6340. ; 24:8, s. 973-978
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Tidskriftsartikel (refereegranskat)abstract
- Triazines comprise an important pollutant class owing to continued use in certain countries, and owing to strong environmental persistence that leads to problems even in countries like Sweden where the use of triazines has been prohibited for some years. We investigated mass-selective detection for analysis of triazines. More specifically, we studied the background reduction and sensitivity enhancement that result from the use of a new interface technique, field-asymmetric ion mobility spectrometry (FAIMS), in conjunction with electrospray ionization ion-trap mass spectrometry. This technique allows for ion sorting and discrimination against the considerable "chemical noise", nonspecific cluster and fragment ions, which are typically generated in electrospray ionization. This paper presents results of a pilot study of triazines and some metabolites in ideal solvents. Our long-range goal is automated analysis with mass-selective detection coupled to membrane-based sample cleanup and enrichment for additional enhancement in sensitivity.
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| 5. |
- Mie, Axel, et al.
(författare)
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Enantiomer separation of amino acids by complexation with chiral reference compounds and high-field asymmetric waveform ion mobility spectrometry: Preliminary results and possible limitations
- 2007
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 79:7, s. 2850-2858
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Tidskriftsartikel (refereegranskat)abstract
- We present a new method for separation of enantiomers with high-field asymmetric waveform ion mobility spectrometry (FAIMS), coupled to mass spectrometric detection. Upon addition of an appropriate chiral reference compound to the analyte solution and subsequent ionization of the solution by electrospray ionization, analyte enantiomers formed diastereomeric complexes, which were potentially separable by FAIMS. The methodology being developed is intended to be general, but here amino acid analytes are specifically considered. In the examples presented herein, six pairs of amino acid enantiomers were successfully separated as metal-bound trimeric complexes of the form [M-II(L-Ref)(2)(D/L-A)-H](+), where M-II is a divalent metal ion, L-Ref is an amino acid in its L form acting as chiral reference compound, and A is the amino acid analyte. For example, D- and L-tryptophan were separated in FAIMS as [Ni-II(L-Asn)(2)(D-Trp)-H](+) and [Ni-II( L-Asn)(2)(L-Trp)-H](+). As FAIMS separation typically takes place over a time scale of only a few hundred milliseconds, the presented separation method opens new possibilities for rapid analysis of one analyte enantiomer in the presence of the other enantiomer. Preliminary quantification results are presented, which suggest that fast and sensitive quantitative chiral analyses can be performed with FAIMS. Method limitations are discussed in terms of diverse phenomena, which are not yet understood.
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| 6. |
- Mie, Axel, et al.
(författare)
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Terbutaline Enantiomer Separation and Quantification by Complexation and Field Asymmetric Ion Mobility Spectrometry-Tandem Mass Spectrometry.
- 2008
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 1520-6882 .- 0003-2700. ; 80:11, s. 4133-4140
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Tidskriftsartikel (refereegranskat)abstract
- Recently, we introduced a new approach to chiral separation and analysis of amino acids by chiral complexation and electrospray high-field asymmetric waveform ion mobility spectrometry coupled to mass spectrometry (ESI-FAIMS-MS). In the present work, we extended this approach to the separation of the drug compound terbutaline. Terbutaline enantiomers were complexed with metal ions and an amino acid to form diastereomeric complexes of the type [M (II)( l-Ref) 2((+)/(-)-A)-H] (+), where M (II) is a divalent metal ion, L-Ref is an amino acid in its L-form, and A is the terbutaline analyte. When metal and reference compound were suitably chosen, these complexes were separable by FAIMS. We also detected and characterized larger clusters that were transmitted at distinct FAIMS compensation voltages (CV), disturbing data analysis by disintegrating after the FAIMS separation and forming complexes of the same composition [M (II)( l-Ref) 2((+)/(-)-A)-H] (+), thus giving rise to additional peaks in the FAIMS CV spectra. This undesired phenomenon could be largely avoided by adjusting the mass spectrometer skimmer voltages in such a way that said larger clusters remained intact. In the quantitative part of the present work, we achieved a limit of detection of 0.10% (-)-terbutaline in a sample of (+)-terbutaline. The limit of detection and analysis time per sample compared favorably to literature values for chiral terbutaline separation by HPLC and CE.
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| 7. |
- Reimann, Curt, et al.
(författare)
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Introduction to biological mass spectrometry: Determining identity and species of origin of two proteins
- 2005
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Ingår i: Journal of Chemical Education. - 0021-9584. ; 82:8, s. 1215-1218
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Tidskriftsartikel (refereegranskat)abstract
- We describe a laboratory exercise that is designed to give advanced undergraduate students in analytical chemistry a meaningful introduction to biological mass spectrometry. We ask the students to solve a mystery: given two proteins, what are they, and from which animals do they originate? This exercise involves use of two mass spectrometers available in our institution: a fairly basic matrix-assisted laser desorption ionization time-of-flight (MALDI–TOF) unit and an electrospray ionization (ESI) ion-trap unit. Our exercise can be completed in two days (including analysis) and provides several interesting and educational surprises. The students, in small groups, are introduced to total mass measurement with ESI, proceed to peptide mass mapping with MALDI–TOF, and finally explore sequence information with ion-trap tandem (fragmentation) mass spectrometry. Even in the most advanced phase, we guide the students, but by this time they usually have their own ideas as to what avenues to pursue. We find that our students become excited after they solve the "mystery"of these proteins, and they receive enough education in the process to be able to join a research project involving biological mass spectrometry.
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| 8. |
- Reimann, Curt, et al.
(författare)
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Proteins in vacuo. A connection between mean overcrossing number and orientationally-averaged collision cross section
- 2002
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 4:16, s. 4058-4064
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the structure of protein ions in vacuo has received a lot of interest. Experimentally, such structures can only be characterized by global, low-resolution descriptors like the orientationally-averaged collision cross section (σ) over bar. An alternative descriptor of chain entanglement, the mean overcrossing number (N) over bar, is a very useful tool because it can distinguish sensitively between different conformations based on aspects of their geometry and topology. An overcrossing number distribution arises from an ensemble of different projections of the protein structure onto a viewing plane, where for each projection, the number of crossings by the set of line segments joining sequence-adjacent Calpha atoms is computed. (N) over bar is the mean of this distribution. Despite their usefulness, overcrossing numbers depend on the atomic coordinates and thus cannot be measured for protein ions in vacuo as can collision cross sections. In this work, we explore theoretically whether collision cross sections are correlated with overcrossing numbers. Using a group of diverse proteins with the same chain length as lysozyme and known X-ray structures, we find a weak correlation between (σ) over bar and (N) over bar. Thus, a nontrivial range of orientationally-averaged cross section values can be consistent with the same mean overcrossing number. Since (N) over bar comprises a very sensitive tool for the study of conformational rearrangements, we checked also for correlations between (σ) over bar and (N) over bar during molecular dynamics simulated unfolding and relaxation pathways of lysozyme in vacuo. For a given pathway, the two quantities are found to be highly correlated. Although neither (σ) over bar nor (N) over bar maps one-to-one onto a particular tertiary fold, they are both sensitive descriptors to monitor the conformational state of a protein along a pathway of dynamical change.
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| 9. |
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| 10. |
- Shipovskov, Stepan, et al.
(författare)
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Electrospray ionization mass spectrometry in enzymology: uncovering the mechanisms of two- substrate reactions
- 2007
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Ingår i: Analyst. - : Royal Society of Chemistry (RSC). - 1364-5528. ; 132:5, s. 397-402
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Forskningsöversikt (refereegranskat)abstract
- The purpose of this review is to draw attention to the use of electrospray ionization mass spectrometry ( ESI-MS) for monitoring the course of enzyme substrate interactions, in the particular case of complex systems in which two substrates participate. The determination and characterization of intra-molecular reactions, especially those that occur in the enzyme active site, is not a trivial task in chemical kinetics, typically requiring long measurement times and relatively expensive techniques such as nuclear magnetic resonance (NMR), X-ray crystallography or electron microscopy ( EM). However, nowadays almost all laboratories are equipped with or else have access to the ESI-MS technique. The aim of this review is to focus on the possibilities of employing even quite simple MS equipment to tackle different applications in studies of complex enzymatic systems.
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