Abstract: The range of applications for aptamers, small oligonucleotide-based receptors binding to their targets with high specificity and affinity, has been steadily expanding. Our understanding of the mechanisms governing aptamer-ligand recognition and binding is however lagging, stymieing the progress in the rational design of new aptamers and optimization of the known ones. Here we demonstrate the capabilities and limitations of native ion mobility-mass spectrometry for the analysis of their higher-order structure and non-covalent interactions. A set of related cocaine-binding aptamers, displaying a range of folding properties and ligand binding affinities, was used as a case study in both positive and negative electrospray ionization modes. Using carefully controlled experimental conditions, we probed their conformational behavior and interactions with the high-affinity ligand quinine as a surrogate for cocaine. The ratios of bound and unbound aptamers in the mass spectra were used to rank them according to their apparent quinine-binding affinity, qualitatively matching the published ranking order. The arrival time differences between the free aptamer and aptamer-quinine complexes were consistent with a small ligand-induced conformational change, and found to inversely correlate with the affinity of binding. This mass spectrometry-based approach provides a fast and convenient way to study the molecular basis of aptamer-ligand recognition.

Abstract: Two common procedures for wet destruction of biological materials for subsequent determination of selenium have been investigated. Rat organs and biological fluids were endogenously labelled with 75Se to monitor losses during the procedures. Addition of nitric and perchloric acids with gradual heating up to 210° seemed to be the best method: at this temperature the labelled selenium was still recovered quantitatively, and the destruction was fast and efficient.

Abstract: For the isocratic ion chromatography (IC) separation of low-molecular-mass organic acids and inorganic anions three different anion-exchange columns were studied: IonPac AS14 (9 ìm particle size), Allsep A-2 (7 ìm particle size), and IC SI-50 4E (5 ìm particle size). A complete baseline separation for all analyzed anions (i.e., F−, acetate, formate, Cl−, NO2−, Br−, NO3−, HPO42− and SO42−) in one analytical cycle of shorter than 17 min was achieved on the IC SI-50 4E column, using an eluent mixture of 3.2 mM Na2CO3 and 1.0 mM NaHCO3 with a flow rate of 1.0 mL min−1. On the IonPac AS14 column, it was possible to separate acetate from inorganic anions in one run (i.e., less than 9 min), but not formate, under the following conditions: 3.5 mM Na2CO3 plus 1.0 mM NaHCO3 with a flow rate of 1.2 mL min−1. Therefore, it was necessary to adapt a second run with a 2.0 mM Na2B4O7 solution as an eluent under a flow rate of 0.8 mL min−1 for the separation of organic ions, which considerably enlarged the analysis time. For the Allsep A-2 column, using an eluent mixture of 1.2 mM Na2CO3 plus 1.5 mM NaHCO3 with a flow rate of 1.6 mL min−1, it was possible to separate almost all anions in one run within 25 min, except the fluoride-acetate critical pair. A Certified Multianion Standard Solution PRIMUS for IC was used for the validation of the analytical methods. The lowest RSDs (less than 1%) and the best LODs (0.02, 0.2, 0.16, 0.11, 0.06, 0.05, 0.04, 0.14 and 0.09 mg L−1 for F−, Ac−, For−, Cl−, NO2−, Br−, NO3−, HPO42− and SO42−, respectively) were achieved using the IC SI-50 4E column. This column was applied for the separation of concerned ions in environmental precipitation samples such as snow, hail and rainwater.

Abstract: Bridging the gap between complex signal data output and clear interpretation by non-expert end-users is a major challenge many scientists face when converting their scientific technology into a real-life application. Currently, pattern recognition algorithms are the most frequently encountered signal data interpretation algorithms to close this gap, not in the least because of their straight-forward implementation via convenient software packages. Paradoxically, just because their implementation is so straight-forward, it becomes cumbersome to integrate the expert's domain-specific knowledge. In this work, a novel signal data interpretation approach is presented that uses this domain-specific knowledge as its fundament, thereby fully exploiting the unique expertise of the scientist. The new approach applies data preprocessing in an innovative way that transcends its usual purpose and is easy to translate into a software application. Multiple case studies illustrate the straight-forward application of the novel approach. Ultimately, the approach is highly suited for integration in various (bio)analytical applications that require interpretation of signal data.

Abstract: Methamphetamine (MA) is a synthetic psychoactive drug which is consumed both licitly and illicitly. In some countries it is prescribed for attention-deficit and hyperactivity disorder, and short-term treatment of obesity. More often though, it is abused for its psychostimulant properties. Unfortunately, the spread and abuse of this synthetic drug have increased globally, being reported as the most widely consumed synthetic psychoactive drug in the world in 2019. Attempting to overcome the shortcomings of the currently used on-site methods for MA detection in suspected cargos, the present study explores the potential of electrochemical identification of MA by means of square wave voltammetry on disposable graphite screen-printed electrodes. Hence, the analytical characterization of the method was evaluated under optimal conditions exhibiting a linear range between 50 mu M and 2.5 mM MA, a LOD of 16.7 mu M, a LOQ of 50.0 mu M and a sensitivity of 5.3 mu A mM-1. Interestingly, two zones in the potential window were identified for the detection of MA, depending on its concentration in solution. Furthermore, the oxidative pathway of MA was elucidated employing liquid chromatography – mass spectrometry to understand the change in the electrochemical profile. Thereafter, the selectivity of the method towards MA in mixtures with other drugs of abuse as well as common adulterants/cutting agents was evaluated. Finally, the described method was employed for the analysis of MA in confiscated samples and compared with forensic methods, displaying its potential as a fast and easy-to-use method for on-site analysis.

Abstract: Museum staff usually relies on a proven combination of X-ray radiography (XRR) and infrared reflectography (IRR) to study paintings in a non-destructive manner. In the last decades, however, the research toolbox of heritage scientists has expanded considerably, with a prime example being macro X-ray fluorescence (MA-XRF), producing element-specific images. The goal of this article is to illustrate the added value of augmenting MA-XRF with pulse phase thermography (PPT), a variant of active infrared thermographic imaging (IRT), which is an innovative diagnostic method that is able to reveal variations between or in materials, based on a different response to minor fluctuations in temperature when irradiated with optical radiation. By examining three 16thand 17th-century panel paintings we assess the extent in which combined MA-XRF and PPT contributes to a better understanding of two commonly encountered interventions to panel paintings: (a) Anstuckungen (enlargement of the panel) or (b) substitutions (replacement of part of the panel). Yielding information from different depths of the painting, these two techniques proved highly complementary with IRR and XRR, expanding the understanding of the build-up, genesis, and material history of the paintings. While MA-XRF documented the interventions to the wooden substrate indirectly by revealing variations in painting materials, paint handling and/ or layer sequence between the original part and the extended or replaced planks, PPT proved beneficial for the study of the wooden support itself, by providing a clear image of the wood structure quasi-free of distortion by the superimposed paint or cradling. XRR, on the other hand, revealed other features from the wood structure, not visible with PPT, and allowed looking through the wooden panels, revealing e.g. the dowels used for joining the planks. Additionally, IRR visualised dissimilarities in the underdrawings. In this way, the results indicate that PPT has the potential to become an acknowledged add-on to the expanding set of imaging methods for paintings, especially when used in combination with MA-XRF, IRR and XRR.

Abstract: Gian Giacomo Inchiocchio (1604-1656), better known as Barbelli, was one of the main exponents of Lombard painting of the seventeenth century. A large body of work is attributed to him, encompassing a wide range of drawings, murals, and oil paintings. However, despite his broad production, there are still many open questions regarding his painting techniques and materials. In this paper, a multi-analytical study of the cycle Stories of the life of Saint George that originally decorated the presbytery of the parish church of Casaletto Vaprio (Cremona, Italy) was performed, combining non-invasive techniques with the characterisation of selected micro samples. Results show that Barbelli used a very limited number of inorganic pigments, often mixing them together to create different colours and shades. Remains of caseinate and degradation products (i.e. weddellite and whewellite) related to the strappo intervention were also highlighted. The study helped to decipher the materials and technique of this painting, providing data that can be used as a reference to study his extensive production.

Abstract: Certified reference materials (NIST 1645, BCR 143, IAEA 7, BCR 141, NIESCRM02, and IAEA 375) were used for determining the performance of a secondary target energy-dispersive X-ray fluorescence (EDXRF) spectrometer, Epsilon 5 (PANalytical, Almelo, the Netherlands). For the evaluation of the EDXRF spectra with polarized-beam high-energy excitation, the WinAxil software package has been applied. The results showed that Epsilon 5, EDXRF spectrometry is favorable for the determination of elemental concentrations in geological samples, but the sample preparation has the largest influence on the precision. However, they presented good agreement with certified values for most of the elements.

Abstract: We compare the image-force barrier lowering (IFBL) and calculate the resulting contact resistance for four different metal-dielectric-two-dimensional (2D) material configurations. We analyze edge contacts in three different geometries (a homogeneous dielectric throughout, including the 2D layer; a homogeneous dielectric surrounding the 2D layer, both ungated and back gated) and also a top-contact assuming a homogeneous dielectric. The image potential energy of each configuration is determined and added to the Schottky energy barrier which is calculated assuming a textbook Schottky potential. For each configuration, the contact resistivity is calculated using the WKB approximation and the effective mass approximation using either SiO2 or HfO2 as the surrounding dielectric. We obtain the lowest contact resistance of 1 k Omega mu m by n-type doping an edge contacted transition metal-dichalcogenide (TMD) monolayer, sandwiched between SiO2 dielectric, with similar to 1012 cm-2 donor atoms. When this optimal configuration is used, the contact resistance is lowered by a factor of 50 compared to the situation when the IFBL is not considered.

Abstract: A first-principles study of the electric field gradient (EFG) calculated for ideal and In-111(Cd-111) implanted ZnO samples is reported in the present work. The study was made for ZnO ideal hexagonal structures and supercells were introduced in order to consider the possible implantation environments. The calculation was done using the “WIEN2k” code within the density functional theory, the exchange and correlation effects were determined by the GGA approximation. Three possible In-111(Cd-111) implantation configurations were studied, one substitutional incorporation at cation site and two interstitials. The obtained EFG values for the ideal structure and the substitutional site are in good agreement with the experimental reports measured by perturbed angular correlation (PAC) and high precision nuclear magnetic resonance (NMR). Thus, the ascription of substitutional incorporation of In-111(Cd-111) probe atom at the ZnO cation site after annealing was confirmed. (C) 2011 Elsevier Ltd. All rights reserved.

Abstract: Climate change is increasing the duration of alternating wet and dry spells. These fluctuations affect soil water availability and other soil properties which are crucial drivers of soil microbial communities. While soil microbial communities have a moderate capacity to recover once a drought ceases, the expected alternation of strongly opposing regimes can challenge their capacity to adapt. Here, we set up experimental grassland mesocosms where precipitation frequency was adjusted along a gradient while holding total precipitation constant. The gradient varied the duration of wet and dry spells from 1 to 60 days during a total of 120 days, where we hy-pothesized that especially intermediate durations would increase the importance of stochastic community as-sembly due to frequent alternation of opposing environmental regimes. We examined bacterial and fungal community composition, diversity, co-occurrence patterns and assembly mechanisms across these different precipitation treatments. Our results show that 1) intermediate regimes of wet and dry spells increased the stochasticity of microbial community assembly whereas microbial communities at low and high regimes were subjected to more deterministic assembly, and 2) more persistent precipitation regimes (>6 days duration) reduced the fungal diversity and network connectivity but had little effect on bacterial communities. Collec-tively, these findings indicate that longer alternating wet and dry events lead to a less predictable and connected soil microbial community. This study provides new insight into the likely mechanisms through which precipi-tation persistence alters soil microbial communities and their predictability.