Microscopic Structural Changes Research Articles

Structural insight into the cooperativity of spin crossover compounds.

Spin-crossover (SCO) compounds are promising materials for a wide variety of industrial applications. However, the fundamental understanding of their nature of transition and its effect on the physical properties are still being fervently explored; the microscopic knowledge of their transition is essential for tailoring their properties. Here an attempt is made to correlate the changes in macroscopic physical properties with microscopic structural changes in the orthorhombic and monoclinic polymorphs of the SCO compound Fe(PM-Bia)2(NCS)2 (PM = N-2'-pyridylmethylene and Bia = 4-aminobiphenyl) by employing single-crystal X-ray diffraction, magnetization and DSC measurements. The dependence of macroscopic properties on cooperativity, highlighting the role of hydrogen bonding, π-π and van der Waals interactions is discussed. Values of entropy, enthalpy and cooperativity are calculated numerically based on the Slichter-Drickamer model. The particle size dependence of the magnetic properties is probed along with the thermal exchange and the kinetic behavior of the two polymorphs based on the dependence of magnetization on temperature scan rate and a theoretical model is proposed for the calculation of the non-equilibrium spin-phase fraction. Also a scan-rate-dependent two-step behavior observed for the orthorhombic polymorph, which is absent for the monoclinic polymorph, is reported. Moreover, it is found that the radiation dose from synchrotron radiation affects the spin-crossover process and shifts the transition region to lower temperatures, implying that the spin crossover can be tuned with radiation damage.

Investigation of the effect of different distilled water, rainwater and seawater mass ratios on coal spontaneous combustion characteristics

When water comes into contact with coal, the risk of coal spontaneous combustion should be reassessed. In order to analyze the effect of distilled water, rainwater and seawater on the coal self-heating, thermogravimetric analysis (TGA) was applied to investigate the differences between the macroscopic oxidation properties of raw coal and water-immersed coal. The risk of coal spontaneous combustion increases after water immersion, but different types of water have different degrees of influence on the spontaneous combustion of coal. The microscopic pore structure and elemental changes on the surface of coal samples before and after water immersion were studied by Scanning Electron Microscope (SEM), low-pressure nitrogen gas adsorption (LP-N2GA) and Energy Dispersive Spectroscopy (EDS) experiments. Fourier infrared spectroscopy (FTIR) was used to investigate the change of active groups. The results show that the pore structure of coal samples immersed in water is much more developed than that of raw coal. In the low-temperature oxidation stage, moisture evaporation consumes much oxidation heat and inhibits the coal self-heating. After the stage, it promotes the coal spontaneous combustion. The content of the hydroxyl group increases, and the content of carbonyl and carboxyl decreases. The alkali metal elements can act as catalysts and active carriers of oxygen, enhancing the oxidation activity of coal. The results are helpful to understand the mechanism of different distilled water, rainwater and seawater mass ratios on coal spontaneous combustion and avoid potential self-heating after immersion.

Structure and interaction of therapeutic proteins in solution: a combined simulation and experimental study

The aggregation of therapeutic proteins in solution has attracted significant interest, driving efforts to understand the relationship between microscopic structural changes and protein-protein interactions determining aggregation processes in solution. Additionally, there is substantial interest in being able to predict aggregation based on protein structure as part of molecular developability assessments. Molecular Dynamics provides theoretical tools to complement experimental studies and to interrogate and identify the microscopic mechanisms determining aggregation. Here we perform all-atom MD simulations to study the structure and inter-protein interaction of the Fab and Fc fragments of the monoclonal antibody (mAb) COE3. We unravel the role of ion-protein interactions in building the ionic double layer and determining effective inter-protein interaction. Further, we demonstrate, using various state-of-the-art force fields (charmm, gromos, amber, opls/aa), that the protein solvation, ionic structure and protein-protein interaction depend significantly on the force field parameters. We perform SANS and Static Light Scattering experiments to assess the accuracy of the different forcefields. Comparison of the simulated and experimental results reveal significant differences in the forcefields' performance, particularly in their ability to predict the protein size in solution and inter-protein interactions quantified through the second virial coefficients. In addition, the performance of the forcefields is correlated with the protein hydration structure.

Effect of Resistin on the Heart Structure of Mouse

Background: In recent years, relevant studies had shown that a large number of adipokines were involved in energy homeostasis in the body, regulating the balance of glucose and lipid metabolism. Resistin was a special type of adipose factor and its discovery and related studies had shown a close relationship between resistin and heart disease. However, there was relatively little research on the structure of heart tissue, so we conducted this present study. Methods: In order to study the effect of resistin on the heart structure of mice, 20 healthy C57BL/6 mice were randomly divided into experimental and control groups(n=10). The mice of the experimental group were injected with 20 ìl/d of resistin solution through the tail vein. The mice of the control group were injected with the same volume of double distilled water. HandE staining, Wheat Germ Agglutinin (WGA) staining, Masson’s trichrome staining and electron microscopy were used to observe the changes of microscopic structure and ultrastructure of mouse cardiomyocytes. Result: The results of HandE staining showed that the myocardial cells in the experimental group were disordered, the cytoplasm was loosely distributed and the gap between adjacent cells increased. WGA staining showed that the fluorescence green intensity of the mice in the experimental group was higherthan that of the control group. The myocardial cell membrane thickened, the average cross-sectional area of cardiomyocytes was larger than that of the control group. The results of the Masson staining showed that the staining of the cytoplasm of myocardial cells in the experimental group was significantly shallow and the blue structure was significantly increased. The electron microscopy showed that the number of mitochondria decreased and the mitochondria lightly dissolved or disappear. This study confirmed that resistin could change the content of collagen fibers and myofibrils in myocardial cells, induce cardiac hypertrophy and cause certain damage to mitochondria of cardiomyocytes. It was speculated that it could affect the physiological function of cardiomyocytes to some extent.

Investigation of microscopic properties of some industrial wood species as a result of laser cutting

In this study, the changes in microscopic structures of cellular anatomical structures of somewood species that are frequently used in industrial production as a result of CNC laser processing wereinvestigated. For this purpose, laser cutting was performed on solid wood materials, using a CNC lasermachine with a 130-watt carbon dioxide gas glass tube, using 70% watts, at a speed of 15mm/s parallel toand perpendicular to the fibers. The behavior of the cellular anatomical structures of different types of woodsolid materials against laser processing was compared.

Nonlinear multiscale model for interstitial structures of densely ordered multi-walled carbon nanotube bundles

The microscopic structural changes upon mechanical deformation of coiled multi-walled carbon nanotube (MWCNT) yarns were investigated through a multiscale constitutive model. All-atom molecular dynamics simulations reveal a strong dependence of the nonlinear mechanical behavior on the diameter of the nanotubes composing the MWCNT bundles. Accordingly, the multiscale modeling is configured to predict the stress and interstitial area change experienced by each nanotube according to the diameter and position distribution of the nanotubes constituting the microstructure. From the proposed multiscale method, representative volume elements (RVEs) of MWCNT bundles with micrometer scale lengths are developed. The RVEs are applied to characterize the deformation of each nanotube due to the longitudinal sway and the stress concentration in the cross-section due to local tightening. The results are in good agreement with those of the all-atom cross-sectional model corresponding to each longitudinal position, which proves the validity of the developed RVEs.

Microscopic Origins of the Nonlinear Behavior of Particle-Filled Rubber Probed with Dynamic Strain XPCS.

The underlying microscopic response of filler networks in reinforced rubber to dynamic strain is not well understood due to the experimental difficulty of directly measuring filler network behavior in samples undergoing dynamic strain. This difficulty can be overcome with in situ X-ray photon correlation spectroscopy (XPCS) measurements. The contrast between the silica filler and the rubber matrix for X-ray scattering allows us to isolate the filler network behavior from the overall response of the rubber. This in situ XPCS technique probes the microscopic breakdown and reforming of the filler network structure, which are responsible for the nonlinear dependence of modulus on strain, known in the rubber science community as the Payne effect. These microscopic changes in the filler network structure have consequences for the macroscopic material performance, especially for the fuel efficiency of tire tread compounds. Here, we elucidate the behavior with in situ dynamic strain XPCS experiments on industrially relevant, vulcanized rubbers filled (13 vol %) with novel air-milled silica of ultrahigh-surface area (UHSA) (250 m2/g). The addition of a silane coupling agent to rubber containing this silica causes an unexpected and counterintuitive increase in the Payne effect and decrease in energy dissipation. For this rubber, we observe a nearly two-fold enhancement of the storage modulus and virtually equivalent loss tangent compared to a rubber containing a coupling agent and conventional silica. Interpretation of our in situ XPCS results simultaneously with interpretation of traditional dynamic mechanical analysis (DMA) strain sweep experiments reveals that the debonding or yielding of bridged bound rubber layers is key to understanding the behavior of rubber formulations containing the silane coupling agent and high-surface area silica. These results demonstrate that the combination of XPCS and DMA is a powerful method for unraveling the microscale filler response to strain which dictates the dynamic mechanical properties of reinforced soft matter composites. With this combination of techniques, we have elucidated the great promise of UHSA silica when used in concert with a silane coupling agent in filled rubber. Such composites simultaneously exhibit large moduli and low hysteresis under dynamic strain.

Changes in Essential Fatty Acids and Ileal Genes Associated with Metabolizing Enzymes and Fatty Acid Transporters in Rodent Models of Cystic Fibrosis.

Cystic fibrosis (CF), the result of mutations in the CF transmembrane conductance regulator (CFTR), causes essential fatty acid deficiency. The aim of this study was to characterize fatty acid handling in two rodent models of CF; one strain which harbors the loss of phenylalanine at position 508 (Phe508del) in CFTR and the other lacks functional CFTR (510X). Fatty acid concentrations were determined using gas chromatography in serum from Phe508del and 510X rats. The relative expression of genes responsible for fatty acid transport and metabolism were quantified using real-time PCR. Ileal tissue morphology was assessed histologically. There was an age-dependent decrease in eicosapentaenoic acid and the linoleic acid:α-linolenic acid ratio, a genotype-dependent decrease in docosapentaenoic acid (n-3) and an increase in the arachidonic acid:docosahexaenoic acid ratio in Phe508del rat serum, which was not observed in 510X rats. In the ileum, Cftr mRNA was increased in Phe508del rats but decreased in 510X rats. Further, Elvol2, Slc27a1, Slc27a2 and Got2 mRNA were increased in Phe508del rats only. As assessed by Sirius Red staining, collagen was increased in Phe508del and 510X ileum. Thus, CF rat models exhibit alterations in the concentration of circulating fatty acids, which may be due to altered transport and metabolism, in addition to fibrosis and microscopic structural changes in the ileum.

Dual-fungi competition and its influence on wood degradation

There are different fungi colonized on wood in nature, and the competition among them varies with wood species. In order to understand the fungal competition on different substrates and its influence on degradation of both softwood and hardwood, four typical wood-decaying fungi (P. chrysosporium, T. versicolor, P. placenta, G. trabeum) were grouped in pairs to investigate the dual-fungi interactions on potato dextrose agar (PDA) and two wood species [Cathay poplar (Populus cathayana Rehd.) and Southern pine (Pinus spp.)], the colonization behavior was recorded, and the mass losses (MLs), microscopic structure and chemical composition change of decayed wood samples were investigated. Three different interaction outcomes were observed in dual culturing of fungi, namely, partial replacement, complete replacement, and deadlock. Deadlock and partial replacement are common outcomes on PDA, while complete replacement is dominant on wood substrate. Wood degradation is highly related with the dominant fungi, wood species, and the colonization order of fungi. Among all dual cultures, T. versicolor-G. trabeum combination showed the strongest degradation ability on poplar wood, while G. trabeum-T. versicolor showed the highest ML on pine wood. Compared with monocultures, the higher ML values of most dual cultures indicated that the interaction between dual fungi can accelerate wood degradation. The results can benefit the understanding of the decay behavior on wood and also provide some thoughts on improving the microbial pretreatment efficiency of biomass.

The Lifetime Prediction and Insulation Failure Mechanism of XLPE for High-Voltage Cable

The performance parameters and service life of the insulation layer of high-voltage cables are the key to ensure safe cable operation. Through extracting the mechanical parameters of high voltage cable insulation layer under different thermal aging temperatures, a normal linear regression model is established to predict the service life of high voltage cables. Meanwhile, the physicochemical characteristics such as microscopic morphology and molecular structure changes of the cable insulation layer are analyzed, the dielectric properties and breakdown field strength under ac condition are tested and the macroscopic electrical properties of the insulation layer are studied, and the insulation failure mechanism is further analyzed. The experimental results show that the elongation at break retention rate of cross-linked polyethylene (XLPE) increases slowly with the aging time, and then decreases rapidly when it reaches 50% of the initial elongation at break retention rate. The normal linear regression prediction model is established based on the Arrhenius formula, and it can be obtained the life endpoint of XLPE high voltage cable about 65 years at an operating temperature of 70 °C. Further analysis, under the action of heat and oxygen, the crystal zone structure of cable insulation is seriously damaged, and the carbonyl index is significantly increased. Accordingly, when the aging failure point is reached, the dielectric permittivity and dielectric loss of insulation are significantly increased, and the breakdown performance is significantly decreased. The work has an important guiding significance for insulation condition assessment and life prediction of high voltage cable.

Influences of the number of non-consecutive joints on the dynamic mechanical properties and failure characteristics of a rock-like material

The dynamic mechanical properties and failure characteristics of jointed rocks are the focus of research in rock engineering. In this study, cement mortar specimens with 0–4 parallel non-consecutive joints were prepared. The split Hopkinson pressure bar (SHPB) was used for dynamic impact testing of prepared specimens. Nuclear magnetic resonance (NMR) was used to detect the pore structure deterioration of the specimens after impact. Finally, the failure characteristics of the specimens were studied by extracting the surface cracks of the specimens. The results show that the number of non-consecutive joints have a significant effect on the dynamic mechanical properties of cement mortar specimens. The increased number of joints will change the stress–strain curve from a single-peak shape to a multi-peak shape and enhance the ductility. The dynamic peak strengths and the proportion of dissipated energy of the specimens decrease with the increase of number of joints, but the magnitude of change decreases gradually. NMR analysis reveals the pore structure alterations of the specimens. After being impacted, the internal pores of the specimens increase significantly, especially the macro-pores and micro-pores. Some micro-pores become meso-pores and macro-pores, and some pores are connected. These changes of microscopic pore structure lead to macroscopic failure of specimens. A quantitative analysis of the porosity of the specimens shows that the rate of change in porosity is in direct proportion to the number of joints, which means that the greater the number of joints, the larger the damage degree of the specimens. The failure characteristics of the specimens indicate that tensile stress mainly dominates the fracture behavior of the specimens, while shear stress has limited damage to the specimens. After the tensile wing cracks start from both tips of the joint, they extend along the rock bridge to the adjacent joint or the end of the specimen. After the wing cracks coalesce, they form a rectangular failure zone. In addition, axial tensile cracks will start near the middle of the first joint and the middle of the last joint, extending to the top and bottom of the specimen, respectively. Slight shear cracks only develop at the joint ends.

Formation of precipitates in off-stoichiometric Ni-Mn-Sn Heusler alloys probed through the induced Sn-moment.

The shell-ferromagnetic effect originates from the segregation process in off-stoichiometric Ni-Mn-based Heusler alloys. In this work, we investigate the precipitation process of L21-ordered Ni2MnSn and L10-ordered NiMn in off-stoichiometric Ni50Mn45Sn5 during temper annealing, by X-ray diffraction (XRD) and 119Sn Mössbauer spectroscopy. While XRD probes long-range ordering of the lattice structure, Mössbauer spectroscopy probes nearest-neighbour interactions, reflected in the induced Sn magnetic moment. As shown in this work, the induced magnetic Sn moment can be used as a detector for microscopic structural changes and is, therefore, a powerful tool for investigating the formation of nano-precipitates. Similar research can be performed in the future, for example, on different pinning type magnets like Sm-Co or Nd-Fe-B.

Исследование сжимаемости цианамидов металлов и влияния давления на их электронные свойства

Based on the density functional theory, the effect of pressure on the structure and electronic properties of crystalline metal cyanamides Zn(CN2) and NaSc(CN2)2 has been studied. The negative linear compressibility of Zn(CN2) was revealed and its correlation with microscopic changes in the atomic structure under pressure was established. It is shown that NaSc(CN2)2 has a low compressibility (0.2 TPa-1) in a direction close to that of cyanamide anions. Based on the quantum topological analysis of the electron density, interatomic interactions were studied and it was found that the Zn-N and Sc-N bonds have a partially covalent character. The band gaps of Zn(CN2) and NaSc(CN2)2 at pressures up to 1 GPa have been determined and found to correspond to the UV range of 224-271 nm.

The Microscopic Pore Structure Change and Its Correction with the Macroscopic Physicomechanical Properties of Sandstones after Freeze–Thaw Cycles

The Microscopic Pore Structure Change and Its Correction with the Macroscopic Physicomechanical Properties of Sandstones after Freeze–Thaw Cycles

Microscopic structural changes during the freeze cross-linking reaction in carboxymethyl cellulose nanofiber hydrogels

Freeze cross-linking increases the mechanical strength of carboxymethyl cellulose nanofiber (CMCF) hydrogels. The structural changes of CMCF hydrogels during the freeze cross-linking reaction were investigated. The SEM images of CMCF hydrogels prepared with different reaction times showed that the CMCF hydrogel in the initial state of the cross-lining reaction (t ≤ 1 h) has a fibrous structure due to the original CMCF. As the reaction progressed (t ≥ 12 h), the fibrous structure was no longer present and a sheet structure with the average thickness of 1.5 ± 0.2 µm was observed. The XRD profiles indicated that the sheet consisted of a stable crystalline structure of cellulose II, in which CMCF was aligned along the (110) plane. It was also confirmed that using acidic aqueous solutions such as citric acid, DL-malic acid, lactic acid, or hydrogen chloride, as cross-linking agents yields CMCF hydrogels with the sheet structure and high compressive strength. On the other hands, when alkaline aqueous solution such as trisodium citrate, tripolyphosphate, or urea were used as cross-linking agents, brittle CMCF hydrogels with inhomogeneous fibrous structures were formed.

Peering into the optical properties of tunable window technology

Microscopic structural changes in windows can modulate the amount of heat and light throughput, but optimal application requires an in-depth understanding of the material’s optical properties.

Evaluation of microscopic structural changes during strain hardening of polyethylene solids using In situ Raman, SAXS, and WAXD measurements under step-cycle test

We have examined the mechanism of strain hardening of polyethylene (PE) using a step-cycle test with in situ Raman spectroscopy, small-angle X-ray scattering, and wide-angle X-ray diffraction measurements. A stable fibrillar structure was formed at the onset of strain hardening. The fraction of the long-consecutive trans chains increased and decreased with increasing and decreasing strain during the stretching and unloading steps, respectively. The peak shift of the C–C stretching mode showed a red shift by applying the stretching stress to the specimen, accompanied by the broadening of the peak width. The broadening of the Raman band is interpreted as the strong stretching load becoming concentrated on the taut-tie chains. According to these results, we concluded that the strain hardening was caused by the increment of the modulus resulting from the increase in the number of taut-tie chains caused by chain pull-out from the crystalline structure. ・ Strain hardening of PE was investigated via various measurements. ・ The strain-hardening behavior was dominated by plastic deformation. ・ Increasing the amount of taut-tie chains dominates the strain-hardening modulus.

Connecting macroscopic diffusion metrics of cardiac diffusion tensor imaging and microscopic myocardial structures based on simulation.

To investigate the relationship between microscopic myocardial structures and macroscopic measurements of diffusion tensor imaging (DTI), we proposed a cardiac DTI simulation method using the Bloch equationand the Monte Carlo random walk in a realistic myocardium model reconstructed from polarized light imaging (PLI) data of the entire human heart. To obtain a realistic simulation, with the constraints of prior knowledge pertaining to the maturational change of the myocardium structure, appropriate microstructure modeling parameters were iteratively determined by matching DTI simulations and real acquisitions of the same hearts in terms of helix angle, fractional anisotropy (FA) and mean diffusivity (MD) maps. Once a realistic simulation was obtained, we varied the extra-cellular volume (ECV) ratio, myocyte orientation heterogeneity and myocyte size, and explored the effects of microscopic changes in tissue structure on macroscopic diffusion metrics. The experimental results demonstrated the feasibility of simulating the DTI of the whole heart using PLI measurements. When varying ECV from 15% to 55%, mean FA decreased from 0.55 to 0.26, axial diffusivity increased by 0.6 μm2/ms, and radial diffusivity increased by 0.7 μm2/ms. When orientation heterogeneity was varied from 0 to 20∘, mean FA decreased from 0.4 to 0.3, axial diffusivity decreased by 0.08 μm2/ms, and radial diffusivity increased by 0.03 μm2/ms. When mean diameter of myocytes was varied from 6 μm to 10 μm, FA decreased from 0.67 to 0.46, axial and radial diffusivities increased by 0.05 and 0.2 μm2/ms, respectively.

An energy-efficient glass using biomimetic structures with excellent energy saving features in both hot and cold weather

Solar irradiation is the main factor contributing to ultra-high energy demand in buildings, and windows are crucial elements with a significant effect on the energy demand in indoor spaces, affecting the cooling, heating, and artificial lighting requirements. Inspired by hercules beetle utilizing the refractive index difference of spongy multilayer structure for infrared reflection and moth-eye using the continuous refractive index change of microscopic convex structure for anti-reflection, this study proposes a visibly transparent and infrared-reflective energy-efficient glass using biomimetic structures to save energy in buildings, based on the idea of regulating the radiation to match the energy utilization on-demand. The selected materials for the proposed biomimetic energy-efficient (BE) glass are SiO2, Al2O3, and Ag based on the idea of using the difference in refractive index of multilayer media for radiation regulating. The transmissivity and reflectivity of BE glass are examined adopting the finite-difference time-domain (FDTD) method. The numerical analysis results demonstrate that BE glass covered with a cone-shaped biomimetic moth-eye structure and a biomimetic multilayer structure exhibits visible light transmissivity of 82.37%, in addition to an infrared light reflectivity of over 90%, which is higher than that of the currently employed low-E glasses. The proposed BE glass offers excellent energy-saving features in both hot and cold weather and the energy consumption analysis indicates that comparing with conventional common glass, it could save about 20% total electrical consumption (43.5 kWh/m2) per year

Probing the microscopic structure and flexibility of oxidized DNA by molecular simulations

The oxidative damage of DNA is a compelling issue in molecular biophysics as it plays a vital role in the epigenetic control of gene expression and is believed to be associated with mutagenesis, carcinogenesis, and ageing. To understand the microscopic structural changes in physical properties of DNA and the resulting influence on its function due to oxidative damage of its nucleotide bases, we have conducted all-atom molecular dynamic simulations of double-stranded DNA (dsDNA) with its guanine bases being oxidized. The guanine bases are more prone to oxidative damage due to the lowest value of redox potential among all nucleobases. We have analyzed the local as well as global mechanical properties of native and oxidized dsDNA and explained those results by microscopic structural parameters and thermodynamic calculations. Our results show that the oxidative damage of dsDNA does not deform the Watson-Crick geometry; instead, the oxidized DNA structures are found to be better stabilized through electrostatic interactions. Moreover, oxidative damage changes the mechanical, helical, and groove parameters of dsDNA. The persistence length, stretch modulus, and torsional stiffness are found to be 48.87 nm, 1239.26 pN, and 477.30 pN.nm^2, respectively, for native dsDNA, and these values are 61.31 nm, 659.91 pN, and 407.79 pN.nm^2, respectively, when all the guanine bases of the dsDNA are oxidized. Compared to the global mechanical properties, the changes in helical and groove properties are found to be more prominent, concentrated locally at the oxidation sites, and causing the transition of the backbone conformations from BI to BII at the regions of oxidative damage.