“Stable Rh particles in hydrotalcite-derived catalysts coated on FeCrAlloy foams by electrosynthesis”. Benito P, Nuyts G, Monti M, de Nolf W, Fornasari G, Janssens K, Scavetta E, Vaccari A, Applied catalysis : B : environmental 179, 321 (2015). http://doi.org/10.1016/J.APCATB.2015.05.035
Abstract: Rh-based structured catalysts for the Catalytic Partial Oxidation of CH4 to syngas were prepared by electrosynthesis of Rh/Mg/Al hydrotalcite-type compounds on FeCrAlloy foams and calcination. The effects of Rh content, total metal concentration, and partial replacement of Mg2+ by Ni2+ in the electrolytic solution on coating thickness, Rh speciation, metallic particle size, and catalytic activity were investigated by SEM/EDS, mu-XRF/XANES and tests under diluted and concentrated reaction conditions. The amount of Rh species, present as Mg (RhxAl1-x)(2)O-4, depended on the thickness of the electrosynthesised layer as well as the Rh particle size and dispersion. Smaller and more dispersed particles were obtained by decreasing the Rh concentration in the electrolytic solution from Rh/Mg/Al=11/70/19 to 5/70/25 and 2/70/28 atomic ratio% (a.r.%) and in thinner rather than thicker layers. Despite the improvement in metallic particles features, the CH4 conversion was negatively affected by the low amount of active sites in the coating, the high metal support interaction and possibly the oxidation of metallic particles and carbon formation. A larger amount of solid containing well dispersed Rh particles was deposited by increasing the total metal concentration from 0.03 M to 0.06 M with the Rh/Mg/Al=5/70/25 a.r.%, and the catalytic performances were enhanced. The partial replacement of Mg2+ by Ni2+ gave rise to a very active bimetallic Rh/Ni catalyst, CH4 conversion and selectivity to syngas were above 90%, however, it slightly deactivated with time-on-stream. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 9.446
Times cited: 14
DOI: 10.1016/J.APCATB.2015.05.035
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“Plumbonacrite identified by X-ray powder diffraction tomography as a missing link during degradation of red lead in a Van Gogh painting”. Vanmeert F, van der Snickt G, Janssens K, Angewandte Chemie: international edition in English 54, 3607 (2015). http://doi.org/10.1002/ANIE.201411691
Abstract: Red lead, a semiconductor pigment used by artists since antiquity, is known to undergo several discoloration phenomena. These transformations are either described as darkening of the pigment caused by the formation of either plattnerite (β-PbO2) or galena (PbS) or as whitening by which red lead is converted into anglesite (PbSO4) or (hydro)cerussite (2 PbCO3⋅Pb(OH)2; PbCO3). X-ray powder diffraction tomography, a powerful analytical method that allows visualization of the internal distribution of different crystalline compounds in complex samples, was used to investigate a microscopic paint sample from a Van Gogh painting. A very rare lead mineral, plumbonacrite (3 PbCO3⋅ Pb(OH)2⋅PbO), was revealed to be present. This is the first reported occurrence of this compound in a painting dating from before the mid 20th century. It constitutes the missing link between on the one hand the photoinduced reduction of red lead and on the other hand (hydro)cerussite, and thus sheds new light on the whitening of red lead.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.994
Times cited: 24
DOI: 10.1002/ANIE.201411691
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“Formation of metallic mercury during photodegradation/photodarkening of \alpha-HgS : electrochemical evidence”. Anaf W, Janssens K, De Wael K, Angewandte Chemie: international edition in English 52, 12568 (2013). http://doi.org/10.1002/ANIE.201303977
Abstract: Das rote Pigment α-HgS neigt in Gegenwart von Licht und Chloridionen zur Schwärzung. Als Grund für die Zersetzung und Entfärbung werden die Bildung von (schwarzem) β-HgS oder Quecksilbermetall vermutet, doch diese Substanzen wurden noch nicht auf natürlich oder künstlich zersetzter HgS-Farbe nachgewiesen. Elektrochemische Experimente belegen nun die Bildung von Quecksilbermetall in Gegenwart von Licht und Chloridionen.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.994
Times cited: 19
DOI: 10.1002/ANIE.201303977
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“Integrated X-ray fluorescence and diffuse visible-to-near-infrared reflectance scanner for standoff elemental and molecular spectroscopic imaging of paints and works on paper”. Delaney JK, Conover DM, Dooley KA, Glinsman L, Janssens K, Loew M, Heritage science 6, 31 (2018). http://doi.org/10.1186/S40494-018-0197-Y
Abstract: Prior studies have shown the improved ability to identify artists' pigments by combining results from X-ray fluorescence (XRF), which provides elemental information, with reflectance spectroscopy in the visible to near infrared (400-1000 nm) that provides information on electronic transitions. Extending the spectral range of reflectance spectroscopy into the UV, 350-400 nm, allows identification of several white pigments since their electronic transitions occur in this region (e.g., zinc white and rutile and anatase forms of titanium white). Extending the range further into the infrared, out to 2500 nm, provides information on vibrational transitions of various functional groups, such as hydroxyl, carbonate, and methyl groups. This allows better identification of mineral-based pigments and some paint binders. The combination of elemental information with electronic and vibrational transitions provides a more robust method to identify artists' materials in situ. The collection of both sets of spectral information across works of art, such as paintings and works on paper, allows generating a more complete map of artists' materials. Here, we describe a 2-D scanner that simultaneously collects XRF spectra and reflectance spectra from 350 to 2500 nm across the surfaces of works of art. The scanner consists of a stationary, single pixel XRF spectrometer and fiber optic reflectance spectrometer along with a 2-D position-controlled easel that moves the artwork in front of the two detection systems. The dual-mode scanner has been tested on a variety of works of art from illuminated manuscripts (0.1 x 0.1 m(2)) to paintings as large as 1.7 x 1.9 m(2). The scanner is described and two sets of results are presented. The first is the XRF scanning of a large warped panel painting by Andrea del Sarto titled Charity. The second is a combined XRF and reflectance scan of Georges Seurat's painting titled Haymakers at Montfermeil. The XRF was collected at 1 mm spatial sampling and the reflectance spectral data at 3 mm. Combining the results from the data sets was found to enhance the identification of pigments as well as yield distribution maps, in spite of the relatively low reflectance spatial sampling. The elemental and reflectance maps allowed the identification and mapping of lead white, cobalt blue, viridian, ochres, and likely chrome yellow. The maps also provide information on the mixing of pigments. While the reflectance image cube has 10-20x larger spatial samples than desired, the elimination of having to use two hyperspectral cameras to cover the range from 400 to 2500 nm makes for a low cost dual modality scanner.
Keywords: A1 Journal article; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Times cited: 7
DOI: 10.1186/S40494-018-0197-Y
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“Combined Micro- and Macro scale X-ray powder diffraction mapping of degraded Orpiment paint in a 17th century still life painting by Martinus Nellius”. Simoen J, De Meyer S, Vanmeert F, De Keyser N, Avranovich E, van der Snickt G, Van Loon A, Keune K, Janssens K, Heritage science 7, 83 (2019). http://doi.org/10.1186/S40494-019-0324-4
Abstract: The spontaneous chemical alteration of artists' pigment materials may be caused by several degradation processes. Some of these are well known while others are still in need of more detailed investigation and documentation. These changes often become apparent as color modifications, either caused by a change in the oxidation state in the original material or the formation of degradation products or salts, via simple or more complex, multistep reactions. Arsenic-based pigments such as orpiment (As2S3) or realgar (alpha-As4S4) are prone to such alterations and are often described as easily oxidizing upon exposure to light. Macroscopic X-ray powder diffraction (MA-XRPD) imaging on a sub area of a still life painting by the 17th century Dutch painter Martinus Nellius was employed in combination with microscopic (mu-) XRPD imaging of a paint cross section taken in the area imaged by MA-XRPD. In this way, the in situ formation of secondary metal arsenate and sulfate species and their migration through the paint layer stack they originate from could be visualized. In the areas originally painted with orpiment, it could be shown that several secondary minerals such as schultenite (PbHAsO4), mimetite (Pb-5(AsO4)(3)Cl), palmierite (K2Pb(SO4)(2)) and syngenite (K2Ca(SO4)(2)center dot H2O) have formed. Closer inspection of the cross-sectioned paint layer stack with mu-XRPD illustrates that the arsenate minerals schultenite and mimetite have precipitated at the interface between the orpiment layer and the layer below that is rich in lead white, i.e. close to the depth of formation of the arsenate ions. The sulfate palmierite has mostly precipitated at the surface and upper layers of the painting.
Keywords: A1 Journal article; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Cultural Heritage Sciences (ARCHES)
Times cited: 2
DOI: 10.1186/S40494-019-0324-4
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“Cephalosporin antibiotics : electrochemical fingerprints and core structure reactions investigated by LC-MSMS”. Sleegers N, van Nuijs ALN, van den Berg M, De Wael K, Analytical chemistry 91, 2035 (2019). http://doi.org/10.1021/ACS.ANALCHEM.8B04487
Abstract: Electrochemistry and exploiting electrochemical fingerprints is a potent approach to address newly emerging surveillance needs, for instance for antibiotics. However, a comprehensive insight in the electrochemical oxidation behaviour and mechanism is re-quired for this sensing strategy. To address the lack in knowledge of the voltammetric behaviour of the cephalosporins antibiotics, a selection of cephalosporin antibiotics and two main intermediates were subjected to an electrochemical study of their redox behaviour by means of pulsed voltammetric techniques and small-scale electrolysis combined with HPLC-MS/MS analyses. Sur-prisingly, the detected oxidation products did not fit the earlier suggested oxidation of the sulfur group to the corresponding sul-foxide. The influence of different side chains, both at the three and the seven position of the β-lactam core structure on the elec-trochemical fingerprint were investigated. Additional oxidation signals at lower potentials were elucidated and linked to different side chains. These signals were further exploited to allow simultaneous detection of different cephalosporins in one voltammetric sweep. These fundamental insights can become the building blocks for an new on-site screening method.
Keywords: A1 Journal article; Pharmacology. Therapy; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Toxicological Centre
Impact Factor: 6.32
Times cited: 6
DOI: 10.1021/ACS.ANALCHEM.8B04487
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“Unraveling the mechanisms behind the complete suppression of cocaine electrochemical signals by chlorpromazine, promethazine, procaine, and dextromethorphan”. De Jong M, Sleegers N, Florea A, Van Loon J, van Nuijs ALN, Samyn N, De Wael K, Analytical chemistry 91, 15453 (2019). http://doi.org/10.1021/ACS.ANALCHEM.9B03128
Abstract: The present work investigates the challenges accompanied by the electrochemical cocaine detection in physiological conditions (pH 7) in the presence of chlorpromazine, promethazine, procaine, and dextromethorphan, frequently used cutting agents in cocaine street samples. The problem translates into the absence of the cocaine oxidation signal (signal suppression) when in a mixture with one of these compounds, leading to false negative results. Although a solution to this problem was provided through earlier experiments of our group, the mechanisms behind the suppression are now fundamentally investigated via electrochemical and liquid chromatography quadrupole-time-of-flight mass spectrometry (LC-QTOF-MS) strategies. The latter was used to confirm the passivation of the electrodes due to their interaction with promethazine and chlorpromazine. Electron transfer mechanisms were further identified via linear sweep voltammetry. Next, adsorption experiments were performed on the graphite screen printed electrodes both with and without potential assistance in order to confirm if the suppression of the cocaine signals is due to passivation induced by the cutting agents or their oxidized products. The proposed strategies allowed us to identify the mechanisms of cocaine suppression for each cutting agent mentioned. Suppression due to procaine and dextromethorphan is caused by fouling of the electrode surface by their oxidized forms, while for chlorpromazine and promethazine the suppression of the cocaine signal is related to the strong adsorption of these (nonoxidized) cutting agents onto the graphite electrode surface. These findings provide fundamental insights in possible suppression and other interfering mechanisms using electrochemistry in general not only in the drug detection sector.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Toxicological Centre; Product development
Impact Factor: 6.32
DOI: 10.1021/ACS.ANALCHEM.9B03128
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“Chemical Mapping by Macroscopic X-ray Powder Diffraction (MA-XRPD) of Van Gogh's Sunflowers : identification of areas with higher degradation risk”. Vanmeert F, Hendriks E, van der Snickt G, Monico L, Dik J, Janssens K, Angewandte Chemie: international edition in English 57, 7418 (2018). http://doi.org/10.1002/ANIE.201713293
Abstract: The discoloration rate of chrome yellow (CY), a class of synthetic inorganic pigments (PbCr1-xSxO4) frequently used by Van Gogh and his contemporaries, strongly depends on its sulfate content and on its crystalline structure (either monoclinic or orthorhombic). Macroscopic X-Ray powder diffraction imaging of selected areas on Van Gogh's Sunflowers (Van Gogh Museum, Amsterdam) revealed the presence of two subtypes of CY: the light-fast monoclinic PbCrO4 (LF-CY) and the light-sensitive monoclinic PbCr1-xSxO4 (x approximate to 0.5; LS-CY). The latter was encountered in large parts of the painting (e.g., in the pale-yellow background and the bright-yellow petals, but also in the green stems and flower hearts), thus indicating their higher risk for past or future darkening. Overall, it is present in more than 50% of the CY regions. Preferred orientation of LS-CY allows observation of a significant ordering of the elongated crystallites along the direction of Van Gogh's brush strokes.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.994
Times cited: 10
DOI: 10.1002/ANIE.201713293
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“Transmission and reflection mode macroscopic x-ray powder diffraction imaging for the noninvasive visualization of paint degradation in still life paintings by Jan Davidsz. de Heem”. Vanmeert F, De Keyser N, van Loon A, Klaassen L, Noble P, Janssens K, Analytical chemistry 91, 7153 (2019). http://doi.org/10.1021/ACS.ANALCHEM.9B00328
Abstract: The use of noninvasive chemical imaging techniques is becoming more widespread for the study of cultural heritage artifacts. Recently a mobile instrument for macroscopic X-ray powder diffraction (MA-XRPD) scanning was developed, which is capable of visualizing the distribution of crystalline (pigment) phases in quasi-flat-painted artifacts. In this study, MA-XRPD is used in both transmission and reflection mode for the analysis of three 17th century still life paintings, two paintings by Jan Davidsz. de Heem (1606-1684) and one copy painting after De Heem by an unknown artist. MA-XRPD allowed to reveal and map the presence of in situ-formed alteration products. In the works examined, two rare lead arsenate minerals, schultenite (PbHAsO4) and mimetite (Pb-5(AsO4)(3)Cl), were encountered, both at and below the paint surface; they are considered to be degradation products of the pigments realgar (alpha-As4S4) and orpiment (As2S3). In transmission mode, the depletion of lead white, present in the (second) ground layer, could be seen, illustrating the intrusive nature of this degradation process. In reflection mode, several sulfate salts, palmierite (K2Pb(SO4)(2)), syngenite (K2Ca(SO4)(2)center dot H2O), and gypsum (CaSO4 center dot 2H(2)O), could be detected, in particular, at the (top) surface of the copy painting. Estimates for the information depth and sensitivity of both transmission and reflection mode MA-XRPD for various pigments have been made. The possibility of MA-XRPD to allow for noninvasive identification and visualization of alteration products is considered a significant advantage and unique feature of this method. MA-XRPD can thus provide highly relevant information for assessing the conservation state of artworks and could guide possible future restoration treatments.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 5
DOI: 10.1021/ACS.ANALCHEM.9B00328
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“Electrochemical fingerprint of street samples for fast on-site screening of cocaine in seized drug powders”. De Jong M, Sleegers N, Kim J, Van Durme F, Samyn N, Wang J, De Wael K, Chemical science , 1 (2016). http://doi.org/10.1039/C5SC04309C
Abstract: We report on a wearable fingertip sensor for on-the-spot identification of cocaine and its cutting agents in street samples. Traditionally, on-site screening is performed by means of colour tests which are difficult to interpret and lack selectivity. By presenting the distinct voltammetric response of cocaine, cutting agents, binary mixtures of cocaine and street samples in solution and powder street samples, we were able to elucidate the electrochemical fingerprint of all these compounds. The new electrochemical concept holds considerable promise as an on-site screening method.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 8.668
Times cited: 37
DOI: 10.1039/C5SC04309C
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“Novel 2-naphthyl substituted zinc naphthalocyanine : synthesis, optical, electrochemical and spectroelectrochemical properties”. Dubinina TV, Moiseeva EO, Astvatsaturov DA, Borisova NE, Tarakanov PA, Trashin SA, De Wael K, Tomilova LG, New Journal Of Chemistry 44, 7849 (2020). http://doi.org/10.1039/D0NJ00987C
Abstract: New zinc naphthalocyanine with bulky 2-naphthyl groups was obtained. Aggregation drastically influences its optical and electrochemical behavior. Spectroelectrochemistry helps to establish the oxidation potential and reveals unusual color change.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.3
Times cited: 1
DOI: 10.1039/D0NJ00987C
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“Label-free impedance aptasensor for major peanut allergen Ara h 1”. Trashin S, De Jong M, Breugelmans T, Pilehvar S, De Wael K, Electroanalysis 27, 32 (2015). http://doi.org/10.1002/ELAN.201400365
Abstract: The peanut allergen Ara h 1 belonging to the vicilin family of seed storage proteins is known to be a suitable marker for peanut detection in foods. In the present work, we suggest an electrochemical detection of Ara h 1 using a recently selected 80-base DNA aptamer. The detection strategy relies on insulation effect of a bulky protein captured by an immobilized aptamer. The electrodes were modified by the aptamer and characterized using electrochemical impedance spectroscopy (EIS). The aptamer surface density and analytical parameters of the calibration curves for Ara h 1 were compared with the system prepared with thrombin binding aptamer (TBA) and operated in the same conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Applied Electrochemistry & Catalysis (ELCAT)
Times cited: 10
DOI: 10.1002/ELAN.201400365
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“An N-myristoylated globin with a redox-sensing function that regulates the defecation cycle in Caenorhabditis elegans”. Tilleman L, De Henau S, Pauwels M, Nagy N, Pintelon I, Braeckman BP, De Wael K, Van Doorslaer S, Adriaensen D, Timmermans J-P, Moens L, Dewilde S, PLoS ONE 7, e48768 (2012). http://doi.org/10.1371/JOURNAL.PONE.0048768
Abstract: Globins occur in all kingdoms of life where they fulfill a wide variety of functions. In the past they used to be primarily characterized as oxygen transport/storage proteins, but since the discovery of new members of the globin family like neuroglobin and cytoglobin, more diverse and complex functions have been assigned to this heterogeneous family. Here we propose a function for a membrane-bound globin of C. elegans, GLB-26. This globin was predicted to be myristoylated at its N-terminus, a post-translational modification only recently described in the globin family. In vivo, this globin is found in the membrane of the head mesodermal cell and in the tail stomato-intestinal and anal depressor muscle cells. Since GLB-26 is almost directly oxidized when exposed to oxygen, we postulate a possible function as electron transfer protein. Phenotypical studies show that GLB-26 takes part in regulating the length of the defecation cycle in C. elegans under oxidative stress conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 2.806
Times cited: 6
DOI: 10.1371/JOURNAL.PONE.0048768
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“Iron allocation in leaves of Fe-deficient cucumber plants fed with natural Fe complexes”. Zanin L, Tomasi N, Rizzardo C, Gottardi S, Terzano R, Alfeld M, Janssens K, De Nobili M, Mimmo T, Cesco S, Physiologia plantarum 154, 82 (2015). http://doi.org/10.1111/PPL.12296
Abstract: Iron (Fe) sources available for plants in the rhizospheric solution are mainly a mixture of complexes between Fe and organic ligands, including phytosiderophores (PS) and water-extractable humic substances (WEHS). In comparison with the other Fe sources, Fe-WEHS are more efficiently used by plants, and experimental evidences show that Fe translocation contributes to this better response. On the other hand, very little is known on the mechanisms involved in Fe allocation in leaves. In this work, physiological and molecular processes involved in Fe distribution in leaves of Fe-deficient Cucumis sativus supplied with Fe-PS or Fe-WEHS up to 5days were studied combining different techniques, such as radiochemical experiments, synchrotron micro X-ray fluorescence, real-time reverse transcription polymerase chain reaction and in situ hybridization. In Fe-WEHS-fed plants, Fe was rapidly (1day) allocated into the leaf veins, and after 5days, Fe was completely transferred into interveinal cells; moreover, the amount of accumulated Fe was much higher than with Fe-PS. This redistribution in Fe-WEHS plants was associated with an upregulation of genes encoding a ferric(III)-chelate reductase (FRO), a Fe2+ transporter (IRT1) and a natural resistance-associated macrophage protein (NRAMP). The localization of FRO and IRT1 transcripts next to the midveins, beside that of NRAMP in the interveinal area, may suggest a rapid and efficient response induced by the presence of Fe-WEHS in the extra-radical solution for the allocation in leaves of high amounts of Fe. In conclusion, Fe is more efficiently used when chelated to WEHS than PS and seems to involve Fe distribution and gene regulation of Fe acquisition mechanisms operating in leaves.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.33
Times cited: 14
DOI: 10.1111/PPL.12296
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“Nutrient accumulation in leaves of Fe-deficient cucumber plants treated with natural Fe complexes”. Tomasi N, Mimmo T, Terzano R, Alfeld M, Janssens K, Zanin L, Pinton R, Varanini Z, Cesco S, Biology and fertility of soils 50, 973 (2014). http://doi.org/10.1007/S00374-014-0919-6
Abstract: Plants mainly rely on a mixture of Fe complexes with different organic ligands, like carboxylates and soluble fractions of water-extractable humic substances (WEHSs), to sustain the supply of this micronutrient. It has been demonstrated that the Fe-WEHS complex is more efficiently acquired by plant roots as it enhances functionality of the mechanisms involved in Fe acquisition at the root and leaf levels, allowing a faster recovery of the Fe-deficiency symptoms. The aim of this work is to verify whether this recovery involves also the allocation and accumulation of nutrients other than Fe to and within the leaf tissues. Iron-deficient plants treated with Fe-WEHS recovered more quickly the functionality both to uptake nitrate at the root level and to fixate CO2 in the leaves than those supplied with Fe-citrate. Concomitantly, Fe-WEHS-treated plants also accumulated other cationic nutrients faster and at a higher extent. Synchrotron 2D-scanning μ-X-ray fluorescence analyses of the leaves revealed that the recovery promotes a change in the allocation of these nutrients from the vascular system (K, Cu, and Zn) or trichomes (Ca and Mn) to the entire leaf blade. Fe-WEHS treatment efficiently promotes the recovery from Fe-deficiency-induced chlorosis with an enhanced allocation of other nutrients into the leaves and promoting their distribution into the entire leaf blade.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.683
Times cited: 25
DOI: 10.1007/S00374-014-0919-6
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“Spatially resolved (semi)quantitative determination of iron (Fe) in plants by means of synchrotron micro X-ray fluorescence”. Terzano R, Alfeld M, Janssens K, Vekemans B, Schoonjans T, Vincze L, Tomasi N, Pinton R, Cesco S, Analytical and bioanalytical chemistry 405, 3341 (2013). http://doi.org/10.1007/S00216-013-6768-6
Abstract: Iron (Fe) is an essential element for plant growth and development; hence determining Fe distribution and concentration inside plant organs at the microscopic level is of great relevance to better understand its metabolism and bioavailability through the food chain. Among the available microanalytical techniques, synchrotron mu-XRF methods can provide a powerful and versatile array of analytical tools to study Fe distribution within plant samples. In the last years, the implementation of new algorithms and detection technologies has opened the way to more accurate (semi)quantitative analyses of complex matrices like plant materials. In this paper, for the first time the distribution of Fe within tomato roots has been imaged and quantified by means of confocal mu-XRF and exploiting a recently developed fundamental parameter-based algorithm. With this approach, Fe concentrations ranging from few hundreds of ppb to several hundreds of ppm can be determined at the microscopic level without cutting sections. Furthermore, Fe (semi)quantitative distribution maps were obtained for the first time by using two opposing detectors to collect simultaneously the XRF radiation emerging from both sides of an intact cucumber leaf.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.431
Times cited: 27
DOI: 10.1007/S00216-013-6768-6
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“The use of vitrum obsianum in the Roman Empire: some new insights and future prospects”. Cagno S, Cosyns P, Ceglia A, Nys K, Janssens K, Periodico di mineralogia 84, 465 (2015). http://doi.org/10.2451/2015PM0026
Abstract: The research on the use of obsidian in the Mediterranean is extensive but concerns almost exclusively volcanic glass from prehistoric and Bronze Age contexts. The consumption of obsidian during the Roman imperial period, however, has only occasionally received attention. Never a comprehensive account on what the Romans made in vitrum obsianum has been set up, nor have the sources exploited by them been examined. This paper provides a concise overview of the current knowledge on obsidian during the Roman imperial period and offers an introductory outline on potential research. The ancient writers inform us about the use of volcanic glass to create exclusive vessels, gemstones, mirrors and sculpture, but also about the creation of black appearing man-made glass initiated as a cheap and easier workable substitute of obsidian. The archaeological data on the other hand propose a more complex story with the occurrence of obsidian chunks in early Roman secondary glass workshops, and the bulky use of obsidian in late Antiquity to produce tesserae for the creation of wall and vault mosaics. Because it is extremely difficult to visually distinguish natural obsidian from man-made glass imitations we present in this paper data collected by means of non-destructive chemico-physical analyses SEM-EDX, portable X-ray fluorescence (p-XRF) and Raman spectroscopy to easily distinguish man-made glass from natural obsidian. In particular the use of portable instruments makes possible in situ analysis of objects in archaeological depots or museum collections to help defining distribution networks to better understand the shifting consumption patterns in Antiquity.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 0.883
Times cited: 2
DOI: 10.2451/2015PM0026
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“Rapid microwave synthesis of high aspect-ration ZnO nanotetrapods for swift bisphenol A detection”. Qurashi A, Rather JA, De Wael K, Merzougui B, Tabet N, Faiz M, The analyst 138, 4764 (2013). http://doi.org/10.1039/C3AN00336A
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.885
Times cited: 15
DOI: 10.1039/C3AN00336A
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“Digitally reconstructing Van Gogh's Field with Irises near Arles. Part 2: Pigment concentration maps”. Kirchner E, van der Lans I, Ligterink F, Geldof M, Gaibor ANP, Hendriks E, Janssens K, Delaney J, Color research and application 43, 158 (2018). http://doi.org/10.1002/COL.22164
Abstract: Colors in many paintings of great art historical value have changed over time, due to the combined effects of natural ageing, accumulated surface grime, and materials added during later conservation treatments. The physical restoration of the colors in such paintings is not possible. This article describes one part of work done to digitally restore the colors of Van Gogh's painting Field with Irises near Arles, dating from May 1888. We have used multispectral reflectance data to estimate absorption K and backscattering S parameters of Kubelka-Munk 2-constant theory. This was done for all 13 pigments known to have been used by Van Gogh in this painting, and based on this the concentration maps for each of these pigments were calculated. We validated the calculated concentration maps in several ways. For some pigments, we were able to predict spots on the painting where the pigment is expected to occur in unmixed form based on visual examination. For several other pigments, the concentration maps could be shown to agree with XRF data. Finally, for some other pigments the concentration maps were supported by additional evidence from microscopic examinations, remarks in Van Gogh's letters and from early color reproductions. For the 1.7 million pixels for which multispectral data is available, the average color difference between the calculated and measured spectral reflectance curves is CIEDE2000 = 1.05. This further confirms that the Kubelka-Munk calculations are well suited to describe the variety of spectral reflectance on the painting.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 0.798
Times cited: 4
DOI: 10.1002/COL.22164
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“Restoration of X-ray fluorescence images of hidden paintings”. Anitha A, Brasoveanu A, Duarte M, Hughes S, Daubechies I, Dik J, Janssens K, Alfeld M, Signal processing 93, 592 (2013). http://doi.org/10.1016/J.SIGPRO.2012.09.027
Abstract: This paper describes our methods for repairing and restoring images of hidden paintings (paintings that have been painted over and are now covered by a new surface painting) that have been obtained via noninvasive X-ray fluorescence imaging of their canvases. This recently developed imaging technique measures the concentrations of various chemical elements at each two-dimensional spatial location across the canvas. These concentrations in turn result from pigments present both in the surface painting and in the hidden painting beneath. These X-ray fluorescence images provide the best available data from which to noninvasively study a hidden painting. However, they are typically marred by artifacts of the imaging process, features of the surface painting, and areas of information loss. Repairing and restoring these images thus consists of three stages: (1) repairing acquisition artifacts in the dataset, (2) removal of features in the images that result from the surface painting rather than the hidden painting, and (3) identification and repair of areas of information loss. We describe methods we have developed to address each of these stages: a total-variation minimization approach to artifact correction, a novel method for underdetermined blind source separation with multimodal side information to address surface feature removal, and two application-specific new methods for automatically identifying particularly thick or X-ray absorbent surface features in the painting. Finally, we demonstrate the results of our methods on a hidden painting by the artist Vincent van Gogh. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.11
Times cited: 13
DOI: 10.1016/J.SIGPRO.2012.09.027
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“X-ray diffraction mapping for cultural heritage science : a review of experimental configurations and applications”. Gonzalez V, Cotte M, Vanmeert F, de Nolf W, Janssens K, Chemistry: a European journal 26, 1703 (2019). http://doi.org/10.1002/CHEM.201903284
Abstract: X-ray diffraction (XRD) mapping consists in the acquisition of XRD patterns at each pixel (or voxel) of an area (or volume). The spatial resolution ranges from the micrometer (mu XRD) to the millimeter (MA-XRD) scale, making the technique relevant for tiny samples up to large objects. Although XRD is primarily used for the identification of different materials in (complex) mixtures, additional information regarding the crystallite size, their orientation, and their in-depth distribution can also be obtained. Through mapping, these different types of information can be located on the studied sample/object. Cultural heritage objects are usually highly heterogeneous, and contain both original and later (degradation, conservation) materials. Their structural characterization is required both to determine ancient manufacturing processes and to evaluate their conservation state. Together with other mapping techniques, XRD mapping is increasingly used for these purposes. Here, the authors review applications as well as the various configurations for XRD mapping (synchrotron/laboratory X-ray source, poly-/monochromatic beam, micro/macro beam, 2D/3D, transmission/reflection mode). On-going hardware and software developments will further establish the technique as a key tool in heritage science.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 5.317
DOI: 10.1002/CHEM.201903284
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“Electrochemical determination of hydrogen peroxide with cytochrome c peroxidase and horse heart cytochrome c entrapped in a gelatin hydrogel”. De Wael K, Bashir Q, van Vlierberghe S, Dubruel P, Heering HA, Adriaens A, Bioelectrochemistry: an international journal devoted to electrochemical aspects of biology and biological aspects of electrochemistry 83, 15 (2012). http://doi.org/10.1016/J.BIOELECHEM.2011.07.001
Abstract: A novel and versatile method, based on a membrane-free enzyme electrode in which both the enzyme and a mediator protein are entrapped in a gelatine hydrogel was developed for the fabrication of biosensors. As a proof of principle, we prepared a hydrogen peroxide biosensor by successfully entrapping both horse heart cytochrome c (HHC) and Saccharomyces cerevisae cytochrome c peroxidase (CCP) in a gelatin matrix which is immobilized on a gold electrode. This electrode was first pretreated with 6-mercaptohexanol. The biosensor displayed a rapid response and an expanded linear response range from 0 to 0.3 mM (R = 0.987) with a detection limit of 1 × 10− 5 M in a HEPES buffer solution (pH 7.0). This method of encapsulation is now further investigated for industrial biosensor applications.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 3.346
Times cited: 31
DOI: 10.1016/J.BIOELECHEM.2011.07.001
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“Macroscopic x-ray powder diffraction imaging reveals Vermeer's discriminating use of lead white pigments in Girl with a Pearl Earring”. De Meyer S, Vanmeert F, Vertongen R, Van Loon A, Gonzalez V, Delaney J, Dooley K, Dik J, van der Snickt G, Vandivere A, Janssens K, Science Advances 5, eaax1975 (2019). http://doi.org/10.1126/SCIADV.AAX1975
Abstract: Until the 19th century, lead white was the most important white pigment used in oil paintings. Lead white is typically composed of two crystalline lead carbonates: hydrocerussite [2PbCO(3)center dot Pb(OH)(2)] and cerussite (PbCO3). Depending on the ratio between hydrocerussite and cerussite, lead white can be classified into different subtypes, each with different optical properties. Current methods to investigate and differentiate between lead white subtypes involve invasive sampling on a microscopic scale, introducing problems of paint damage and representativeness. In this study, a 17th century painting Girl with a Pearl Earring (by Johannes Vermeer, c. 1665, collection of the Mauritshuis, NL) was analyzed with a recently developed mobile and noninvasive macroscopic x-ray powder diffraction (MA-XRPD) scanner within the project Girl in the Spotlight. Four different subtypes of lead white were identified using XRPD imaging at the macroscopic and microscopic scale, implying that Vermeer was highly discriminatory in his use of lead white.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation); Antwerp Cultural Heritage Sciences (ARCHES)
Times cited: 3
DOI: 10.1126/SCIADV.AAX1975
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“Fullerene-\beta-cyclodextrin conjugate based electrochemical sensing device for ultrasensitive detection of p-nitrophenol”. Rather JA, Debnath P, De Wael K, Electroanalysis 25, 2145 (2013). http://doi.org/10.1002/ELAN.201300304
Abstract: The article describes the use of a fullerene (C60)-β-cyclodextrin conjugate, synthesized via 1,3-dipolar cycloaddition, for the ultrasensitive electrochemical detection of p-nitrophenol. This conjugate was successfully immobilized on the surface of a glassy carbon electrode and the developed device showed high activity towards p-nitrophenol due to the synergetic effect of C60, the latter becoming highly conductive upon reduction. The determination of p-nitrophenol was performed by using square wave voltammetry over a concentration range from 2.8×10−9 mol L−1 to 4.2×10−7 mol L−1 and the detection limit was calculated to be 1.2×10−9 mol L−1.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 2.851
Times cited: 13
DOI: 10.1002/ELAN.201300304
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“Exploring a hidden painting below the surface of Rene Magritte's Le Portrait”. van der Snickt G, Martins A, Delaney J, Janssens K, Zeibel J, Duffy M, McGlinchey C, Van Driel B, Dik J, Applied spectroscopy 70, 57 (2016). http://doi.org/10.1177/0003702815617123
Abstract: Two state-of-the-art methods for non-invasive visualization of subsurface (or overpainted) pictorial layers present in painted works of art are employed to study Le portrait, painted by Belgian artist Rene Magritte in 1935. X-ray radiography, a commonly used method for the nondestructive inspection of paintings, had revealed the presence of an underlying figurative composition, part of an earlier Magritte painting entitled La pose enchantee (1927) which originally depicted two full length nude female figures with exaggerated facial features. On the one hand, macroscopic X-ray fluorescence analysis (MA-XRF), a method capable of providing information on the distribution of the key chemical elements present in many artists' pigments, was employed. The ability of the X-rays to penetrate the upper layer of paint enabled the imaging of the facial features of the female figure and provided information on Magritte's palette for both surface and hidden composition. On the other hand, visible and near infrared hyperspectral imaging spectroscopies in transmission mode were also used, especially in the area of the table cloth in order to look through the upper representation and reveal the pictorial layer(s) below. MA-XRF provided elemental information on the pigment distributions in both the final painting and the prior whereas the transmission mode provided information related to preparatory sketches as well as revealing differences between the paints used in both compositions. These results illustrate very well the manner in which the two imaging methods complement each other, both in the sense of providing different types of information on the nature and presence of paint components/pigments and in the sense of being optimally suited to easily penetrate through different types of overpaint.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 1.529
Times cited: 13
DOI: 10.1177/0003702815617123
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“Optimized photoelectrochemical detection of essential drugs bearing phenolic groups”. Neven L, Thiruvottriyur Shanmugam S, Rahemi V, Trashin S, Sleegers N, Carrion EN, Gorun SM, De Wael K, Analytical chemistry 91, 9962 (2019). http://doi.org/10.1021/ACS.ANALCHEM.9B01706
Abstract: The World Health Organization (WHO) model “List of Essential Medicines” includes among indispensable medicines antibacterials and pain and migraine relievers. Monitoring their concentration in the environment, while challenging, is important in the context of antibiotic resistance as well as their production of highly toxic compounds via hydrolysis. Traditional detection methods such as high-performance liquid chromatography (HPLC) or LC combined with tandem mass spectrometry or UV-vis spectroscopy are time-consuming, have a high cost, require skilled operators and are difficult to adapt for field operations. In contrast, (electrochemical) sensors have elicited interest because of their rapid response, high selectivity, and sensitivity as well as potential for on-site detection. Previously, we reported a novel sensor system based on a type II photosensitizer, which combines the advantages of enzymatic sensors (high sensitivity) and photoelectrochemical sensors (easy baseline subtraction). Under red-light illumination, the photosensitizer produces singlet oxygen which oxidizes phenolic compounds present in the sample. The subsequent reduction of the oxidized phenolic compounds at the electrode surface gives rise to a quantifiable photocurrent and leads to the generation of a redox cycle. Herein we report the optimization in terms of pH and applied potential of the photoelectrochemical detection of the hydrolysis product of paracetamol, i.e., 4-aminophenol (4-AP), and two antibacterials, namely, cefadroxil (CFD, beta-lactam antibiotic) and doxycycline (DXC, tetracycline antibiotic). The optimized conditions resulted in a detection limit of 0.2 mu mol L-1 for DXC, but in a 10 times higher sensitivity, 20 nmol L-1, for CFD. An even higher sensitivity, 7 nmol L-1, was noted for 4-AP.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 2
DOI: 10.1021/ACS.ANALCHEM.9B01706
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“Microstructure characterization of oceanic polyethylene debris”. Rowenczyk L, Dazzi A, Deniset-Besseau A, Beltran V, Goudounèche D, Wong-Wah-Chung P, Boyron O, George M, Fabre P, Roux C, Mingotaud AF, ter Halle A, Environmental Science &, Technology 54, 4102 (2020). http://doi.org/10.1021/ACS.EST.9B07061
Abstract: Plastic pollution has become a worldwide concern. It was demonstrated that plastic breaks down to nanoscale particles in the environment, forming so-called nanoplastics. It is important to understand their ecological impact, but their structure is not elucidated. In this original work, we characterize the microstructure of oceanic polyethylene debris and compare it to the nonweathered objects. Cross sections are analyzed by several emergent mapping techniques. We highlight deep modifications of the debris within a layer a few hundred micrometers thick. The most intense modifications are macromolecule oxidation and a considerable decrease in the molecular weight. The adsorption of organic pollutants and trace metals is also confined to this outer layer. Fragmentation of the oxidized layer of the plastic debris is the most likely source of nanoplastics. Consequently the nanoplastic chemical nature differs greatly from plastics.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.4
Times cited: 3
DOI: 10.1021/ACS.EST.9B07061
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“Potentiometric sensors doped with biomolecules as a new approach to small molecule/biomolecule binding kinetics analysis”. Daems D, De Wael K, Vissenberg K, Van Camp G, Nagels L, Biosensors and bioelectronics 54, 515 (2014). http://doi.org/10.1016/J.BIOS.2013.11.045
Abstract: The most successful binding kinetics analysis systems at this moment include surface plasmon resonance (SPR), quartz microcrystal balance (QMB) and surface acoustic wave (SAW). Although these are powerful methods, they generally are complex, expensive and require the use of monolayers. Here, we report on potentiometric sensors as an inexpensive and simple alternative to do binding kinetics analysis between small molecules in solution and biomolecules (covalently) attached in a biopolymer sensor coating layer. As an example, dopamine and an anti-dopamine aptamer were used as the small molecule and the biomolecule respectively. Binding between both follows a Langmuir adsorption type model and creates a surface potential. The system operates in Flow Injection Analysis mode (FIA). Besides being an interesting new binding kinetics tool, the approach allows systematic design of potentiometric biosensors (in the present study a dopamine sensor), and gives new insights into the functioning of ion-selective electrodes (ISEs).
Keywords: A1 Journal article; Engineering sciences. Technology; Integrated Molecular Plant Physiology Research (IMPRES); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 7.78
Times cited: 10
DOI: 10.1016/J.BIOS.2013.11.045
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“Concentration related response potentiometric titrations to study the interaction of small molecules with large biomolecules”. Hamidi-Asl E, Daems D, De Wael K, Van Camp G, Nagels LJ, Analytical chemistry 86, 12243 (2014). http://doi.org/10.1021/AC503385X
Abstract: In the present article, the utility of a special potentiometric titration approach for recognition and calculation of biomolecule/small molecule interactions is reported. This approach is fast, sensitive, reproducible and inexpensive in comparison to the other methods for the determination of the association constant values (Ka) and the interaction energies (ΔG). The potentiometric titration measurement is based on the use of a classical polymeric membrane indicator electrode in a solution of the small molecule ligand. The biomolecule is used as a titrant. The potential is measured versus a reference electrode and transformed to a concentration related signal over the entire concentration interval, also at low concentrations, where the mV (y-axis) versus logcanalyte (x-axis) potentiometric calibration curve is not linear. In the procedure, the Ka is calculated for the interaction of cocaine with a cocaine binding aptamer and with an anti-cocaine antibody. To study the selectivity and cross-reactivity, other oligonucleotides and aptamers are tested, as well as other small ligand molecules such as tetrakis (4-chlorophenyl)borate, metergoline, lidocaine, and bromhexine. The calculated Ka compared favorably to the value reported in the literature using SPR. The potentiometric titration approach called Concentration related Response Potentiometry, is used to study molecular interaction for 7 macromolecular target molecules and 4 small molecule ligands.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 10
DOI: 10.1021/AC503385X
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“The use of potentiometric sensors to study (bio)molecular interactions”. De Wael K, Daems D, Van Camp G, Nagels LJ, Analytical chemistry 84, 4921 (2012). http://doi.org/10.1021/AC3005428
Abstract: Potentiometric sensors were used to study molecular interactions in liquid environments, with sensorgram methodology. This is demonstrated with a lipophilic rubber-, and with a collagen based hydrogel sensor coating. The investigated molecules were promazine and tartaric acid respectively. The sensors were placed in a hydrodynamic wall jet system for the recording of sensorgrams. mV sensor responses were first converted to a signal, expressing the concentration of adsorbed organic ions. Using a linearization method, a pseudo first order kinetic model of adsorption was shown to fit the experimental results perfectly. Kass, kon and koff values were calculated.. The technique can be used over 4 decades of concentration, and it is very sensitive to low MW compounds as well as to multiply charged large biomolecules. This study is the first to demonstrate the application of potentiometric sensors as an alternative and complement to SPR methods.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 10
DOI: 10.1021/AC3005428
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