Internal Rearrangement Research Articles

Silicate impedes arsenic release and oxidation from ferrihydrite

Silicate fertilization is a common farming practice and an effective method to mitigate arsenic (As) pollution in paddy. Investigating the interaction between silicate and ferrihydrite on As retention is key to comprehensively understand the mechanism of As sequestration by silicate fertilization. Our results indicated that the transformation of ferrihydrite into goethite and hematite was inversely proportional to Si/Fe ratios. The added silicate impeded the decrease of solution pH from neutral to acidity, and imposed strong inhibitory effect on goethite formation. The aqueous As in silicate-free system was 3.43 times higher than that with Si/Fe ratio at 0.33, but similar results were not observed in those with high-level As pollution due to the inhibitory effect of As on ferrihydrite transformation. Solid characterization showed that silicate was monomerically adsorbed to ferrihydrite through Si-O-Fe bond, which impeded the reductive dissolution, Fe atom exchange, internal atomic rearrangement and dehydration of ferrihydrite. As(III) oxidation weakened in silicate-coprecipitated ferrihydrite due to the lack of Fe(II) catalysis stem from ferrihydrite dissolution. This work demonstrated that As release could be effectively impeded through the inhibitory effect of silicate on ferrihydrite transformation, thereby providing new insights into the understanding of As accumulation reduction in rice by silicate fertilization.

Signatures of Structural Disorder in the Developing Drosophila Germband Epithelium

Epithelial cells generate functional tissues in developing embryos through collective movements and shape changes. In some morphogenetic events, a tissue dramatically reorganizes its internal structure—often generating high degrees of structural disorder—to accomplish changes in tissue shape. However, the origins of structural disorder in epithelia and what roles it might play in morphogenesis are poorly understood. We study this question in the germband epithelium, which undergoes dramatic changes in internal structure as cell rearrangements drive elongation of the embryo body axis. Using two order parameters that quantify volumetric and shear disorder, we show that structural disorder increases during body axis elongation and is strongly linked with specific developmental processes. Both disorder metrics begin to increase around the onset of axis elongation, but then plateau at values that are maintained throughout the process. Notably, the disorder plateau values for volumetric disorder are similar to those for random cell packings, suggesting this may reflect a limit on tissue behavior. In mutant embryos with disrupted external stresses from the ventral furrow, both disorder metrics reach wild-type maximum disorder values with a delay, correlating with delays in cell rearrangements. In contrast, in mutants with disrupted internal stresses and cell rearrangements, volumetric disorder is reduced compared to wild type, and shear disorder depends on specific external stress patterns. Together, these findings demonstrate that internal and external stresses both contribute to epithelial tissue disorder and suggest that the maximum values of disorder in a developing tissue reflect physical or biological limits on morphogenesis. Published by the American Physical Society 2024

Distribution Patterns of tfdI and tfdII Gene Clusters and New Insights into the Formation of the Architecture of pJP4, a Canonical 2,4-dichlorophenoxyacetic Acid (2,4-D) Degradation Plasmid

Currently, pJP4 is one of the best-known plasmids for the biodegradation of xenobiotics that mediate the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), which is associated with serious health and environmental risks. Although the sequencing and proposed theory of pJP4 formation occurred almost 20 years ago (2004), pJP4 is still the model object of many studies focused on the biodegradation of 2,4-D. The uniqueness of this plasmid is due to the presence of two evolutionarily distinct gene clusters, tfdI and tfdII, controlling the degradation of 2,4-D. Recent advances in plasmid biology, especially those concerning the characterization of new IncP-1 plasmids and the systematization of tfd gene cluster findings, serve as a basis for proposing new insights into the formation of the clusters’ architecture of the canonical plasmid, pJP4, and their distribution among other plasmids. In the present work, a comparative genomic and phylogenetic in silico study of plasmids with tfdI and tfdII clusters was carried out. The possible initial distribution patterns of tfdI clusters among plasmids of different incompatibility groups (non-IncP-1) and tfdII clusters among IncP-1 plasmids using the IS1071-based composite transposon were revealed. A new theory on the formation of the architecture of the tfdI and tfdII clusters of pJP4 through sequential internal rearrangements, recombination, and ISJP4 insertion, is proposed. In addition, small gene clusters resulting from internal rearrangements of pJP4 (tfdIISA and ORF31/32) served as fingerprints for exploring the distribution of tfdI and tfdII clusters. The revealed patterns and formulated theory extend the frontiers of plasmid biology and will be beneficial for understanding the role of plasmids in bacterial adaptation to xenobiotic-contaminated environments.

Crystallization and topology-induced dynamical heterogeneities in soft granular clusters

Soft-granular media, such as dense emulsions, foams or tissues, exhibit either fluid- or solidlike properties depending on the applied external stresses. Whereas bulk rheology of such materials has been thoroughly investigated, the internal structural mechanics of finite soft-granular structures with free interfaces is still poorly understood. Here, we report the spontaneous crystallization and melting inside a model soft granular cluster—a densely packed aggregate of N∼30−40 droplets engulfed by a fluid film—subject to a varying external flow. We develop machine learning tools to track the internal rearrangements in the quasi-two-dimensional cluster as it transits a sequence of constrictions. As the cluster relaxes from a state of strong mechanical deformations, we find differences in the dynamics of the grains within the interior of the cluster and those at its rim, with the latter experiencing larger deformations and less frequent rearrangements, effectively acting as an elastic membrane around a fluidlike core. We conclude that the observed structural-dynamical heterogeneity results from an interplay of the topological constrains, due to the presence of a closed interface, and the internal solid-fluid transitions. We discuss the universality of such behavior in various types of finite soft granular structures, including biological tissues. Published by the American Physical Society 2024

Circadian Rhythm of Distal Skin Temperature in Healthy Older and Young Women and Its Relationship with Sleep-Wake Rhythm and Environmental Factors under Natural Living Conditions.

Little is known about the healthy aging of the circadian timing system under natural living conditions. This study explores changes in the circadian rhythm of distal skin temperature (DST) with aging and relates these changes to sleep-wake timing and environmental influences. DST, sleep-wake timing, 24-h light exposure, and physical activity were measured and averaged over seven consecutive days using temperature sensors, actigraphy with a light meter, and sleep diaries in 35 healthy older women (60-79 years) and 30 young women (20-34 years). Circadian rhythm characteristics, describing strength (amplitude) and timing (acrophase) of the DST rhythm, were calculated using cosinor analysis. The older adults displayed an 18-19% smaller amplitude and a 66-73 min earlier acrophase (peak time) for DST rhythm than the young adults, indicating a weaker and phase-advanced DST rhythm. The phase advance for DST was not due to an earlier evening increase, but to a shorter nocturnal plateau period. Daytime light exposure inversely affected strength (amplitude) but not phasing of the DST rhythm in older adults. The DST rhythm was 3.5 times more advanced than the sleep-wake rhythm, showing an altered phase relationship (phase angle) between both rhythms with aging. The phase angle was more heterogeneous among older adults, showing differential aging. The phase advance for DST rhythm and the altered and heterogeneous phase relationship between DST and sleep-wake rhythms were not related to ambient light exposure and the physical activity of older adults. This suggests that healthy aging of the circadian system might be due to endogenous mechanisms such as an internal rearrangement rather than external influences.

X-ray structure and enzymatic study of a bacterial NADPH oxidase highlight the activation mechanism of eukaryotic NOX.

NADPH oxidases (NOX) are transmembrane proteins, widely spread in eukaryotes and prokaryotes, that produce reactive oxygen species (ROS). Eukaryotes use the ROS products for innate immune defense and signaling in critical (patho)physiological processes. Despite the recent structures of human NOX isoforms, the activation of electron transfer remains incompletely understood. SpNOX, a homolog from Streptococcus pneumoniae, can serves as a robust model for exploring electron transfers in the NOX family thanks to its constitutive activity. Crystal structures of SpNOX full-length and dehydrogenase (DH) domain constructs are revealed here. The isolated DH domain acts as a flavin reductase, and both constructs use either NADPH or NADH as substrate. Our findings suggest that hydride transfer from NAD(P)H to FAD is the rate-limiting step in electron transfer. We identify significance of F397 in nicotinamide access to flavin isoalloxazine and confirm flavin binding contributions from both DH and Transmembrane (TM) domains. Comparison with related enzymes suggests that distal access to heme may influence the final electron acceptor, while the relative position of DH and TM does not necessarily correlate with activity, contrary to previous suggestions. It rather suggests requirement of an internal rearrangement, within the DH domain, to switch from a resting to an active state. Thus, SpNOX appears to be a good model of active NOX2, which allows us to propose an explanation for NOX2's requirement for activation.

X-ray structure and enzymatic study of a bacterial NADPH oxidase highlight the activation mechanism of eukaryotic NOX

NADPH oxidases (NOX) are transmembrane proteins, widely spread in eukaryotes and prokaryotes, that produce reactive oxygen species (ROS). Eukaryotes use the ROS products for innate immune defense and signaling in critical (patho)physiological processes. Despite the recent structures of human NOX isoforms, the activation of electron transfer remains incompletely understood. SpNOX, a homolog from Streptococcus pneumoniae, can serves as a robust model for exploring electron transfers in the NOX family thanks to its constitutive activity. Crystal structures of SpNOX full-length and dehydrogenase (DH) domain constructs are revealed here. The isolated DH domain acts as a flavin reductase, and both constructs use either NADPH or NADH as substrate. Our findings suggest that hydride transfer from NAD(P)H to FAD is the rate-limiting step in electron transfer. We identify significance of F397 in nicotinamide access to flavin isoalloxazine and confirm flavin binding contributions from both DH and Transmembrane (TM) domains. Comparison with related enzymes suggests that distal access to heme may influence the final electron acceptor, while the relative position of DH and TM does not necessarily correlate with activity, contrary to previous suggestions. It rather suggests requirement of an internal rearrangement, within the DH domain, to switch from a resting to an active state. Thus, SpNOX appears to be a good model of active NOX2, which allows us to propose an explanation for NOX2’s requirement for activation.

An experimental framework to assess biomolecular condensates in bacteria

High-resolution imaging of biomolecular condensates in living cells is essential for correlating their properties to those observed through in vitro assays. However, such experiments are limited in bacteria due to resolution limitations. Here we present an experimental framework that probes the formation, reversibility, and dynamics of condensate-forming proteins in Escherichia coli as a means to determine the nature of biomolecular condensates in bacteria. We demonstrate that condensates form after passing a threshold concentration, maintain a soluble fraction, dissolve upon shifts in temperature and concentration, and exhibit dynamics consistent with internal rearrangement and exchange between condensed and soluble fractions. We also discover that an established marker for insoluble protein aggregates, IbpA, has different colocalization patterns with bacterial condensates and aggregates, demonstrating its potential applicability as a reporter to differentiate the two in vivo. Overall, this framework provides a generalizable, accessible, and rigorous set of experiments to probe the nature of biomolecular condensates on the sub-micron scale in bacterial cells.

A new chapter in the never ending story of cycloadditions: The puzzling case of SO2 and acetylene.

A comprehensive study of the different classes of cycloaddition reactions ([3+2], [2+2], and [2+1]) of SO2 to acetylene and ethylene has been performed using density functional theory (DFT) and composite wavefunction methods. The [3+2] cycloaddition reaction, that was previously explored in the context of the cycloaddition of thioformaldehyde S-methylide (TSM) to ethylene and acetylene, proceeds in a concerted way to the formation of stable heterocycles. In this paper, we extend our study to the [2+2] and [2+1] cycloadditions of SO2 to acetylene, which would produce 1,1-oxathiete-2-oxide and thiirene-1,1-dioxide, respectively. One of the main conclusions is that cyclic 1,1-oxathiete-2-oxide can open through a relatively easy breaking of the SO single bond and rearrange toward sulfinyl acetaldehyde (SA). The SA molecule can easily undergo several internal rearrangements, which eventually lead to sulfenic acid and sulfoxide derivatives of ethenone, 1,2,3-dioxathiole, and CO plus sulfinylmethane. The most probable path, however, produces 2-thioxoacetic acid, whose derivatives (or those of the corresponding acetate) are usually obtained by Willgerodt-Kindler-type sulfuration of acetates. This product can in turn decompose, leading to the final products CO2 and H2CS. Comparison of this decomposition path with that of 2-amino-2-thioxoacetic acid shows that the process occurs through different H-transfer processes.

Out with the old, in with the new: contrasts involving new features with acoustically salient cues are more likely to be acquired than those that redeploy L1 features

Feature-based approaches to second language (L2) phonology conceptualize the acquisition of new segments as operations that involve either the addition of new phonological features, or the rebundling of existent ones. While the deficit hypothesis assumes that only features that are fully specified in the L1 can be redeployed to the L2 in order to create new segments, it has been shown that features which are completely absent in the L1 can also be learned. This article investigates whether a learning scenario in which features are only partially available (that is, they are present in the L1, but are redundant with other features) is less challenging than learning an entirely new feature, even when the new feature has acoustically salient cues. Since Spanish has a much smaller vowel system /i e a o u/, L2 learners of German with Spanish as L1 need to learn a system with front rounded vowels as well as tense/lax contrasts. We tested L1 Spanish speakers' perception of the German contrasts /i/ ~ /I/ (e.g., Miete/mitte, where [+/– tense] is acquired) and /u/ ~ /y/ (e.g., Spulen/spülen, where L1 feature [+/–round] redeploys to a front vowel). The results showed that experienced L2 learners are more successful when discriminating between sounds in a feature acquisition scenario than in redeployment; however, neither of the non-native contrasts was easier to perceive than the other in the identification task. The differences in performance between tasks and in the acoustic saliency of the cues by contrast (F2 vs. duration and F1) suggests that L2 phonological acquisition is likely to take place at a surface level and favors learning through attunement to auditorily salient acoustic cues over internal rearrangement of abstract features, regardless of their presence in the L1.

Reinvestigation of the internal glycan rearrangement of Lewis a and blood group type H1 epitopes.

Protonated ions of fucose-containing oligosaccharides are prone to undergo internal glycan rearrangement which results in chimeric fragments that obfuscate mass-spectrometric analysis. Lack of accessible tools that would facilitate systematic analysis of glycans in the gas phase limits our understanding of this phenomenon. In this work, we use density functional theory modeling to interpret cryogenic IR spectra of Lewis a and blood group type H1 trisaccharides and to establish whether these trisaccharides undergo the rearrangement during gas-phase analysis. Structurally unconstrained search reveals that none of the parent ions constitute a thermodynamic global minimum. In contrast, predicted collision cross sections and anharmonic IR spectra provide a good match to available experimental data which allowed us to conclude that fucose migration does not occur in these antigens. By comparing the predicted structures with those obtained for Lewis x and blood group type H2 epitopes, we demonstrate that the availability of the mobile proton and a large difference in the relative stability of the parent ions and rearrangement products constitute the prerequisites for the rearrangement reaction.

Structural, dielectric, and electrochemical properties of pear-shaped CexLi2Zn0.5Mn0.5Ti3−xO8 supercapacitor: XRD and dielectric calculation

Complex nano-perovskite materials have recently gained attention as promising electrode materials for supercapacitors due to their high capacitances. The crystalline structure, dielectric properties, and electrochemical properties of LiZn0.5Mn0.5Ti3-xCexO8 (x = 0, 0.05, 0.1, & 0.15) pear-shaped nanoceramics, which were prepared through sol–gel reactions and sintered at 800 °C for 3 h, were explored. The XRD proves the well-crystalline structure for the prepared nanoceramic with the diffraction peaks corresponding to the cubic LiZnTi3O8 phase, the doped samples appearing with new peaks are matched to the cubic CeO2 phase. The impact of the Ce3+ ratio in the Li2Zn0.5Mn0.5Ti3O8 pear-shaped nanostructure on the dielectric properties of the nanoceramics is apparent, as the conductivity increases with increasing frequency and temperature. The electrochemical attitude can be ascribed to the LiZn0.5Mn0.5Ti3O8 pear-shaped nanostructure under the effect of Ce3+ ions producing continuous internal rearrangement. The capacitance values for Li2Zn0.5Mn0.5Ti3O8 doped with different ratios (3, 5, 10, 15%) Ce3+ are changed from 41.58 to 38.28 F.g-1, at scan rate (10) mVs-1. High electrocatalytic properties of the LiZn0.5Mn0.5Ti3-xCexO8 nanoceramics is approved using cyclic voltammetry, and electrochemical impedance spectroscopy. Furthermore, the Electrochemical analysis indicates that LiZn0.5Mn0.5Ti3-xCexO8 nanoceramics promising for supercapacitors applications.

The Biomimetic Synthesis of Polyarylated Fluorenes, Relevant to Selaginellaceae Polyphenols, Leading to the Spontaneous Formation of Stable Radicals.

This work reports a biomimetic synthesis of polyarylated fluorene derivatives. The molecules are formed via intramolecular electrophilic aromatic substitution, resembling a cyclization leading towards the natural selaginpulvilins from selaginellins. The scope of the reaction was investigated, and the products were obtained in 60-95 % yields. Some of the compounds decompose to a stable radical. We investigated the nature and the origin of the radical using experimental methods, including EPR or electrochemical measurements, as well as theoretical methods, such as DFT calculations. Based on our observations, we hypothesize, that phenoxy radicals are formed in the first instance, which however undergo internal rearrangement to thermodynamically more stable carbon-centered radicals. The preliminary data also show the cytotoxic properties of some of the molecules.

Symmetry breaking induced local electron rearrangement to enhance photocatalytic tetracycline hydrochloride oxidation and hydrogen evolution of carbon nitride

A symmetry breaking strategy was achieved by a sample doping approach and used to overcome the sluggish carrier transfer and insufficient light capture capacity of carbon nitride photocatalysts. The obtained local electronic structural reconstruction resulted in the generation of an intermediate energy level, which can regulate the band gap structure and boost the redox reaction progress. Furthermore, the DFT calculation results prove the electronic structure rearrangement brings adsorption characteristic changes for H2O and O2 molecules, leading to the variation of free radicals’ generation. Combing the advantages of band gap structure optimization and internal electron rearrangement, the phosphorus doped carbon nitride achieves a balance between light absorption properties and photocatalytic redox capacity, exhibiting stronger reduction capacity, high carrier separation efficiency, and optimized adsorption sites. Consequently, the phosphorus doped carbon nitride shows enhanced activities in photocatalytic tetracycline hydrochloride degradation (3.6-fold increase), peroxydisulfate activation (4.5-fold increase), and hydrogen generation (13.5-fold increase) compared to pristine carbon nitride. This research highlights the symmetry regulation strategy as a promising method for developing highly efficient multifunctional carbon nitride-based photocatalysts.

Light Scattering through a Drying Coating

Drying coatings undergo internal dynamic densification and rearrangement, which are challenging to discern with optical techniques due to their multiple scatterings of light. Experiments such as diffusing wave spectroscopy (DWS) and laser speckle imaging (LSI) leverage these multiple scatterings to reveal the in situ dynamics of the coating. In such experiments, the knowledge of the sample volume that can be accessed and therefore studied is fundamental, especially in cases of micrometer-scale coating thicknesses. In this paper, we present a robust and reliable method using transmission geometry to calculate the parameter l*, defined as the transport light mean-free path, which is strongly related to the volume of the sample that light explores in DWS and LSI experiments. We show how this dynamic parameter can be measured for liquid and solid film samples and, crucially, in the case of time-evolving samples, such as drying coatings of paint or ink, which has not been previously explored. We present a series of model ink samples and discuss the evolution of their densification during drying through quantification of dynamic l*.

The Magnetostriction of Amorphous Magnetic Microwires: The Role of the Local Atomic Environment and Internal Stresses Relaxation

We studied the magnetostriction coefficients, λs, Curie temperature, Tc, and their dependence on annealing conditions in Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 amorphous glass-coated microwires with rather different character of hysteresis loops. A positive λs ≈ 20 × 10−6 is observed in as-prepared Fe47Ni27Si11B13C2, while low and negative λs ≈ −0.3 × 10−6 is obtained for Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 microwire. Annealing affects the magnetostriction coefficients and Curie temperatures, Tc, of both Fe47Ni27Si11B13C2 and Co67Fe3.9Ni1.5B11.5Si14.5Mo1.6 glass-coated microwires in a similar way. Observed dependencies of hysteresis loops, λs and Tc on annealing conditions are discussed in terms of superposition of internal stresses relaxation and structural relaxation of studied microwires. We observed linear λs dependence on applied stress, σ, in both studied microwires. A decrease in the magnetostriction coefficient upon applied stress is observed for Co-rich microwires with low and negative magnetostriction coefficient. On the contrary, for Fe-Ni-rich microwires with a positive magnetostriction coefficient, an increase in the magnetostriction coefficient with applied stress is observed. The observed results are discussed considering the internal stresses relaxation and short range atomic rearrangements induced by annealing on hysteresis loops, magnetostriction coefficients and Curie temperatures of studied microwires.

Challenges in Imaging Analyses of Biomolecular Condensates in Cells Infected with Influenza A Virus.

Biomolecular condensates are crucial compartments within cells, relying on their material properties for function. They form and persist through weak, transient interactions, often undetectable by classical biochemical approaches. Hence, microscopy-based techniques have been the most reliable methods to detail the molecular mechanisms controlling their formation, material properties, and alterations, including dissolution or phase transitions due to cellular manipulation and disease, and to search for novel therapeutic strategies targeting biomolecular condensates. However, technical challenges in microscopy-based analysis persist. This paper discusses imaging, data acquisition, and analytical methodologies' advantages, challenges, and limitations in determining biophysical parameters explaining biomolecular condensate formation, dissolution, and phase transitions. In addition, we mention how machine learning is increasingly important for efficient image analysis, teaching programs what a condensate should resemble, aiding in the correlation and interpretation of information from diverse data sources. Influenza A virus forms liquid viral inclusions in the infected cell cytosol that serve as model biomolecular condensates for this study. Our previous work showcased the possibility of hardening these liquid inclusions, potentially leading to novel antiviral strategies. This was established using a framework involving live cell imaging to measure dynamics, internal rearrangement capacity, coalescence, and relaxation time. Additionally, we integrated thermodynamic characteristics by analysing fixed images through Z-projections. The aforementioned paper laid the foundation for this subsequent technical paper, which explores how different modalities in data acquisition and processing impact the robustness of results to detect bona fide phase transitions by measuring thermodynamic traits in fixed cells. Using solely this approach would greatly simplify screening pipelines. For this, we tested how single focal plane images, Z-projections, or volumetric analyses of images stained with antibodies or live tagged proteins altered the quantification of thermodynamic measurements. Customizing methodologies for different biomolecular condensates through advanced bioimaging significantly contributes to biological research and potential therapeutic advancements.

Plant-inspired rearrangement of liquid in a porous structure for controlled swelling

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10 μm membrane thickness) assessment of the dynamic variation of PFR in a 400 μm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%–75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s−1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.

Review of fragmentation of synthetic single-stranded oligonucleotides by tandem mass spectrometry from 2014 to 2022.

The fragmentation of oligonucleotides by mass spectrometry allows for the determination of their sequences. It is necessary to understand how oligonucleotides dissociate in the gas phase, which allows interpretation of data to obtain sequence information. Since 2014, a range of fragmentation mechanisms, including a novel internal rearrangement, have been proposed using different ion dissociation techniques. The recent publications have focused on the fragmentation of modified oligonucleotides such as locked nucleic acids, modified nucleobases (methylated, spacer, nebularine and aminopurine) and modification to the carbon 2'-position on the sugar ring; these modified oligonucleotides are of great interest as therapeutics. Comparisons of different dissociation techniques have been reported, including novel approaches such as plasma electron detachment dissociation and radical transfer dissociation. This review covers the period 2014-2022 and details the new knowledge gained with respect to oligonucleotide dissociation using tandem mass spectrometry (without priori sample digestion) during that time, with a specific focus on synthetic single-stranded oligonucleotides.

Improving the mechanical properties of 3D printed GelMA composite hydrogels by tannic acid

AbstractThe lack of advanced biomaterials is a major challenge in bio‐printing. Gelatin‐methacryloyl (GelMA) hydrogel, as one of the most commonly used biomaterials in 3D printing, has limited the applications of medicine because of its low mechanical properties. In this study, to enhance the mechanical strength of GelMA hydrogels, we prepared a composite hydrogel based on F127 diacrylate (F127DA) and GelMA, followed by lyophilization and tannic acid (TA) treatment. In this composite hydrogel, the F127DA could self‐assemble into nanomicelles as crosslinking centers for monomer polymerization, which provides additional energy dissipation in hydrogels due to the synergistic deformation of micelles and internal rearrangement of physical binding. After lyophilization of the composite hydrogel, the porous hydrogel was formed. The subsequent treatment of TA could diffuse into the inner of the hydrogel and react with the hydrogel via hydrogen bonds, resulting in the significant enhancement of mechanical properties. The maximum tensile deformation of the obtained hydrogel was about 11 times higher than that of GelMA. This work demonstrates a method to enhance the mechanical properties of 3D‐printed GelMA hydrogel with promising application in bioprinting.