Molecular Bond Research Articles

Study on thermal degradation of poly (1,4 phenylene terephthalamide) and its volatile products by unadorned setup of Pyrolysis and subsequent UV–VIS spectroscopy

Pyrolysis involves the elimination of moisture and volatile components from fibrous materials by cleavage of molecular bonds to finally obtain carbon-rich residues. Over the years, there have been numerous studies on the pyrolysis of poly (1,4 phenylene terephthalamide) (Kevlar) and characterization of volatile products by using various analytical techniques. The main objectives of this work were to exhibit a simple and straightforward pyrolysis method using a smelting furnace, concurrently condensing the volatile products on a cold surface, followed by acquiring information on progressive changes in concentrations of decomposition products and their difference in volatility using UV-Vis spectroscopy, and to subsequently demonstrate an interesting algorithm for separation of mixture spectra. Variations in concentration of major elements (C, N, S, and O) were also monitored as a function of pyrolysis temperature. An increase in the concentration of volatile products was observed above 500 °C, reaching maximum at 700 °C and then progressively decreases towards the final temperature of 1100 °C. Separation of mixture spectra was attempted using the concept of spectral matrix decomposition to decompose measured spectra into possible spectra of individual components with the objective of proposing a fast and inexpensive method coupled with computational aid that contributes to kinetic studies of pyrolytic processes.

A thorough investigation of the adsorption of metal ions in seawater on d-glucose and its analogues: A theoretical study

d-glucose and its analogues have been studied as potential adsorbents for the removal of Na+, K+, Mg2+ and Ca2+ ions in adsorption desalination studies. Density Functional Theory calculations have been employed to examine the preferential adsorption of these ions at all the available sites of the three chosen substrates. Structure, energy, frontier molecular orbital and natural bond order analyses revealed the nature and strength of the non-bonded interactions between the adsorbate and the adsorbent. Divalent metal ions formed stronger interactions with the substrates than the monovalent metal ions. Molecular electrostatic surface potential analysis helped to understand the charge separation after the metal ion (Mn+) adsorption at the available sites on the substrate. The stability of the studied Mn+-substrate complexes is attributed to non-bonded interactions between the polar heteroatoms on the carbon backbone of the substrate with the positively charged Mn+ ions through electronic charge transfer. These findings can significantly impact the design of new adsorbents for adsorption desalination technology based on naturally available substrates that can be used effectively at ambient temperature.

Fragmentation Dynamics of CO2q+ (q = 2, 3) in Collisions with 1 MeV Proton

The fragmentation dynamics of the CO2q+ (q = 2, 3) molecular ions formed under the impact of 1 MeV protons is studied using a recoil ion momentum spectrometer equipped with a multi-hit time- and position-sensitive detector. Both two-body and three-body fragmentation channels arising from the doubly and triply ionized molecular ions of CO2 are identified and analyzed. Kinetic energy release (KER) distributions have been obtained for various channels. With the help of Dalitz plots and Newton diagrams concerted and sequential processes have been assigned to observed fragmentation channels. In addition, angular correlations are used to determine the molecular geometry of the precursor molecular ion. It is found that the symmetric breakup into C+ + O+ + O+ involves asymmetric stretching of the molecular bonds in CO23+ prior to dissociation via concerted decay implying the fact that collisions with 1 MeV proton induces an asynchronous decay in CO2.

Insights into non-covalent interactions, molecular and electronic structures of 3-monosubstituted and 3,5-disubstituted 1,2-dithiolylium salts: Crystallographic visualization, Hirshfeld surface analysis and DFT Calculations

Compounds based on 3-monosubstituted and 3,5-disubstituted-1,2-dithiolylium salts are subjects of conventional visualization and Hirshfield surface (HS) analyses to investigate the structure and stability-directing effects of functional groups of substituents and counterions in controlling their solid-state behaviour. Both tools show the qualitative and quantitative interplay respectively of the rich network of interactions and short intermolecular contacts that culminate in important packing and geometrically aligned patterns in these compounds and the hierarchies that exist within such interplay. The hierarchies are attributed to the induction of secondary interactions and conformational variations. In addition, quantum chemical calculations of the M06/def2-TZVP model comprising the Minnesota 06 (M06) functional and Ahlrichs/Karlsruhe valence triple-zeta (with) polarization (def2-TZVP) basis set are further used to explore the structure-property relationship in these compounds. The optimization of their molecular geometries showed reasonable correlation with their respective experimental structures. Frontier molecular orbital (FMO) and natural bond orbital (NBO) investigations on the 3-D structures are used to identify intra- and intermolecular charge transfer potentials via cation→anion (donor/acceptor) interactions and their significant roles in stabilizing molecular moieties.

Enhancing the Mechanical Properties of Corn Starch Films for Sustainable Food Packaging by Optimizing Enzymatic Hydrolysis.

The objective of this study was to investigate the effects of enzymatic hydrolysis using α-amylase from Bacillus amyloliquefaciens on the mechanical properties of starch-based films. The process parameters of enzymatic hydrolysis and the degree of hydrolysis (DH) were optimized using a Box-Behnken design (BBD) and response surface methodology (RSM). The mechanical properties of the resulting hydrolyzed corn starch films (tensile strain at break, tensile stress at break, and Young's modulus) were evaluated. The results showed that the optimum DH for hydrolyzed corn starch films to achieve improved mechanical properties of the film-forming solutions was achieved at a corn starch to water ratio of 1:2.8, an enzyme to substrate ratio of 357 U/g, and an incubation temperature of 48 °C. Under the optimized conditions, the hydrolyzed corn starch film had a higher water absorption index of 2.32 ± 0.112% compared to the native corn starch film (control) of 0.81 ± 0.352%. The hydrolyzed corn starch films were more transparent than the control sample, with a light transmission of 78.5 ± 0.121% per mm. Fourier-transformed infrared spectroscopy (FTIR) analysis showed that the enzymatically hydrolyzed corn starch films had a more compact and solid structure in terms of molecular bonds, and the contact angle was also higher, at 79.21 ± 0.171° for this sample. The control sample had a higher melting point than the hydrolyzed corn starch film, as indicated by the significant difference in the temperature of the first endothermic event between the two films. The atomic force microscopy (AFM) characterization of the hydrolyzed corn starch film showed intermediate surface roughness. A comparison of the data from the two samples showed that the hydrolyzed corn starch film had better mechanical properties than the control sample, with a greater change in the storage modulus over a wider temperature range and higher values for the loss modulus and tan delta, indicating that the hydrolyzed corn starch film had better energy dissipation properties, as shown by thermal analysis. The improved mechanical properties of the resulting film of hydrolyzed corn starch were attributed to the enzymatic hydrolysis process, which breaks the starch molecules into smaller units, resulting in increased chain flexibility, improved film-forming ability, and stronger intermolecular bonds.

Molecular Docking and Dynamics Simulation Studies Predict Potential Anti-ADAR2 Inhibitors: Implications for the Treatment of Cancer, Neurological, Immunological and Infectious Diseases.

Altered RNA editing has been linked to several neurodevelopmental disorders, including autism spectrum disorder (ASD) and intellectual disability, in addition to depression, schizophrenia, some cancers, viral infections and autoimmune disorders. The human ADAR2 is a potential therapeutic target for managing these various disorders due to its crucial role in adenosine to inosine editing. This study applied consensus scoring to rank potential ADAR2 inhibitors after performing molecular docking with AutoDock Vina and Glide (Maestro), using a library of 35,161 compounds obtained from traditional Chinese medicine. A total of 47 compounds were predicted to be good binders of the human ADAR2 and had insignificant toxicity concerns. Molecular dynamics (MD) simulations, including the molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) procedure, also emphasized the binding of the shortlisted compounds. The potential compounds had plausible binding free energies ranging from -81.304 to -1068.26 kJ/mol from the MM/PBSA calculations. ZINC000085511995, a naphthoquinone had more negative binding free energy (-1068.26 kJ/mol) than inositol hexakisphosphate (IHP) [-873.873 kJ/mol], an agonist and a strong binder of ADAR2. The potential displacement of IHP by ZINC000085511995 in the IHP binding site of ADAR2 could be explored for possible deactivation of ADAR2. Bayesian-based biological activity prediction corroborates the neuropharmacological, antineoplastic and antiviral activity of the potential lead compounds. All the potential lead compounds, except ZINC000014612330 and ZINC000013462928, were predicted to be inhibitors of various deaminases. The potential lead compounds also had probability of activity (Pa) > 0.442 and probability of inactivity (Pi) < 0.116 values for treating acute neurologic disorders, except for ZINC000085996580 and ZINC000013462928. Pursuing these compounds for their anti-ADAR2 activities holds a promising future, especially against neurological disorders, some cancers and viral infections caused by RNA viruses. Molecular interaction, hydrogen bond and per-residue decomposition analyses predicted Arg400, Arg401, Lys519, Trp687, Glu689, and Lys690 as hot-spot residues in the ADAR2 IHP binding site. Most of the top compounds were observed to have naphthoquinone, indole, furanocoumarin or benzofuran moieties. Serotonin and tryptophan, which are beneficial in digestive regulation, improving sleep cycle and mood, are indole derivatives. These chemical series may have the potential to treat neurological disorders, prion diseases, some cancers, specific viral infections, metabolic disorders and eating disorders through the disruption of ADAR2 pathways. A total of nine potential lead compounds were shortlisted as plausible modulators of ADAR2.

Hydrogen Dissociation Reaction on First-Row Transition Metal Doped Nanobelts.

Zigzag molecular nanobelts have recently captured the interest of scientists because of their appealing aesthetic structures, intriguing chemical reactivities, and tantalizing features. In the current study, first-row transition metals supported on an H6-N3-belt[6]arene nanobelt are investigated for the electrocatalytic properties of these complexes for the hydrogen dissociation reaction (HDR). The interaction of the doped transition metal atom with the nanobelt is evaluated through interaction energy analysis, which reveals the significant thermodynamic stability of TM-doped nanobelt complexes. Electronic properties such as frontier molecular orbitals and natural bond orbitals analyses are also computed, to estimate the electronic perturbation upon doping. The highest reduction in the HOMO-LUMO energy gap compared to the bare nanobelt is seen in the case of the Zn@NB catalyst (4.76 eV). Furthermore, for the HDR reaction, the Sc@NB catalyst displays the best catalytic activity among the studied catalysts, with a hydrogen dissociation barrier of 0.13 eV, whereas the second-best catalytic activity is observed for the Zn@NB catalyst (0.36 eV). It is further found that multiple active sites, i.e., the presence of the metal atom and nitrogen atom moiety, help to facilitate the dissociation of the hydrogen molecule. These key findings of this study enhance the understanding of the relative stability, electronic features, and catalytic bindings of various TM@NB catalysts.

Plant-derived Antiviral Compounds as Potential COVID-19 Drug Candidates: In-silico Investigation in Search of SARS-CoV-2 Inhibitors

Corona virus disease 2019 (COVID-19) is an infectious disease caused by SARS-CoV-2, a newly discovered pathogenic corona virus that causes respiratory illness in humans and has now become a major challenge for the entire world. Although several vaccines for COVID-19 have been approved to date, lead compounds are still in high demand for the development of more promising or effective drugs and vaccines. According to the literature, antiviral drugs are used to treat COVID-19; thus, the current study is an attempt to screen lead molecules from plant-derived antiviral compounds. In this study, 33 plant-derived compounds with antiviral properties against corona viruses were used as ligand molecules, with Favilavir, Remdesivir, Ivermectin, and Dexamethasone serving as reference drugs. Molecular docking was performed between the selected ligands and the four main drug targets of SARS-CoV-2, Nucleocapsid Protein, Spike Glycoprotein, Proteases 3CLpro, and Helicase, and ADMET properties of screened compounds were observed. Docking results revealed that Reserpine, Tetrandrine, and Xanthoangelol F had a high Moldock score with each target, just like the current COVID-19 medications, Ivermectin and Remdesivir. Docking and ADMET studies indicate that Reserpine, Tetrandrine, and Xanthoangelol F may be potent lead compounds for the treatment of COVID-19 and should be investigated further. HIGHLIGHTS Corona virus disease 2019 (COVID-19) is an infectious disease caused by the SARS-CoV-2 virus that poses a threat to humans Plant-derived drugs have showed significant antiviral activity against SARS-CoV, MERS-CoV29, HCoV-229E, and HCoV-OC43 The current study is an in-silico evaluation of plant-derived SARS-CoV-2 inhibitors. Molecular docking and hydrogen bond interaction studies were performed between the selected plant-derived compounds and vital targets of SARS-CoV-2 to evaluate antiviral efficacy against COVID-19, followed by an ADMET study of the screened ligands This in-silico study determined the antiviral potential of plant-derived compounds against SARS-CoV-2, of which Reserpine, Tetrandrine, and Xanthoangelol F may be potent lead compounds for the treatment of COVID-19 GRAPHICAL ABSTRACT

A multiscale phase field fracture approach based on the non-affine microsphere model for rubber-like materials

Rubber-like materials have a broad scope of applications due to their unique properties like high stretchability and increased toughness. Hence, computational models for simulating their fracture behavior are paramount for designing them against failures. In this study, the phase field fracture approach is integrated with a multiscale polymer model for predicting the fracture behavior in elastomers. At the microscale, damaged polymer chains are modeled to be made up of a number of elastic chain segments pinned together. Using the phase field approach, the damage in the chains is represented using a continuous variable. Both the bond stretch internal energy and the entropic free energy of the chain are assumed to drive the damage, and the advantages of this assumption are expounded. A framework for utilizing the non-affine microsphere model for damaged systems is proposed by considering the minimization of a hypothetical undamaged free energy, ultimately connecting the chain stretch to the macroscale deformation gradient. At the macroscale, a thermodynamically consistent formulation is derived in which the total dissipation is assumed to be mainly due to the rupture of molecular bonds. Using a monolithic scheme, the proposed model is numerically implemented and the resulting three-dimensional simulation predictions are compared with existing experimental data. The capability of the model to qualitatively predict the propagation of complex crack paths and quantitatively estimate the overall fracture behavior is verified. Additionally, the effect of the length scale parameter on the predicted fracture behavior is studied for an inhomogeneous system.

Orbital Nature of Carboionic Monoradicals Made from Diradicals.

The electronic, optical, and solid state properties of a series of monoradicals, anions and cations obtained from starting neutral diradicals have been studied. Diradicals based on s-indacene and indenoacenes, with benzothiophenes fused and in different orientations, feature a varying degree of diradical character in the neutral state, which is here related with the properties of the radical redox forms. The analysis of their optical features in the polymethine monoradicals has been carried out in the framework of the molecular orbital and valence bond theories. Electronic UV-Vis-NIR absorption, X-ray solid-state diffraction and quantum chemical calculations have been carried out. Studies of the different positive-/negative-charged species, both residing in the same skeletal π-conjugated backbone, are rare for organic molecules. The key factor for the dual stabilization is the presence of the starting diradical character that enables to indistinctively accommodate a pseudo-hole and a pseudo-electron defect with certainly small reorganization energies for ambipolar charge transport.

Molecular Vibrational Polariton Dynamics: What Can Polaritons Do?

ConspectusWhen molecular vibrational modes strongly couple to virtual states of photonic modes, new molecular vibrational polariton states are formed, along with a large population of dark reservoir modes. The polaritons are much like the bonding and antibonding molecular orbitals when atomic orbitals form molecular bonds, while the dark modes are like nonbonding orbitals. Because the polariton states are half-matter and half-light, whose energy is shifted from the parental states, polaritons are predicted to modify chemistry under thermally activated conditions, leading to an exciting and emerging field known as polariton chemistry that could potentially shift paradigms in chemistry. Despite several published results supporting this concept, the chemical physics and mechanism of polariton chemistry remain elusive. One reason for this challenge is that previous works cannot differentiate polaritons from dark modes. This limitation makes delineating the contributions to chemistry from polaritons and dark states difficult. However, this level of insight is critical for developing a solid mechanism for polariton chemistry to design and predict the outcome of strong coupling with any given reaction. My group addressed the challenge of differentiating the dynamics of polaritons and dark modes by ultrafast two-dimensional infrared (2D IR) spectroscopy. Specifically, (1) we found that polaritons can facilitate intra- and intermolecular vibrational energy transfer, opening a pathway to control vibrational energy flow in liquid-phase molecular systems, and (2) by studying a single-step isomerization event, we verified that indeed polaritons can modify chemical dynamics under strong coupling conditions, but in contrast, the dark modes behave like uncoupled molecules and do not change the dynamics. This finding confirmed the central concept of polariton chemistry: polaritons modify the potential energy landscape of reactions. The result also clarified the role of dark modes, which lays a critical foundation for designing cavities for future polariton chemistry. Aside from using 2D IR spectroscopy to study polariton chemistry, we also used the same technique to develop molecular polaritons into a potential quantum simulation platform. We demonstrated that polaritons have Rabi oscillations, and using a checkerboard cavity design, we showed that polaritons could have large nonlinearity across space. We further used the checkerboard polaritons to simulate coherence transfer and visualize it. A unidirectional coherence transfer was observed, indicating non-Hermitian dynamics. The highlighted efforts in this Account provide a solid understanding of the capability of polaritons for chemistry and quantum information science. I conclude this Account by discussing a few challenges for moving polariton chemistry toward being predictable and making the polariton quantum platform a complement to existing systems.

Solution combustion synthesis of FeCr2O4:Zn,Al pigment powders

AbstractFeCr2O4:Zn,Al pigment powders were prepared via a solution combustion synthesis method. Effects of Zn and Al dopants and less/extra Fe content on the structure, molecular bonds, and optical properties of powders were studied. Results showed that addition of dopants as well as extra/less content of Fe led to weaker combustion and consequently lower X‐ray diffraction peak intensities, lattice parameters, and differential thermal analysis peak intensities. Moreover, Fourier transform infrared analysis illustrated that the band position of Cr–O and Fe–O bonds were shifted to higher frequencies with moving away from stoichiometry. In addition, scanning electron micrographs showed that in all samples, porous spongy microstructures were formed with highly flake‐like agglomerated particles. Furthermore, there was a significant difference between the powder samples and the tiles colored with in glaze powders due to the partial dissolution of pigments in contact with the molten glaze of tiles. In comparison to the tile colored with the stoichiometric FeCr2O4 pigments without dopants, the color difference (ΔE) in the tiles colored by the iron chromite pigments doped with Zn and Al dopants and less/extra Fe content reached the high values as large as ΔE = 36.19. The solar reflectance values (Rs) in near‐infrared region were above 50% in all samples. Near 80% Rs in the tile colored by the iron chromite pigment doped with 3 mol% Zn and the yellowish brown appearance (L* = 43.44, a* = 6.77, b* = 18.38, c* = 19.59, h = 69.79) showed that the sample was a good candidate for cool building materials such as roof tiles.

Qualitative characterization of nitrogen-containing compounds in jet and diesel fuel extracts by using (+) electrospray ionization coupled to a linear quadrupole ion trap/orbitrap mass spectrometer

The development of analytical methods for the characterization of nitrogen-containing compounds (NCCs) in liquid transportation fuels are critical, as these compounds adversely affect fuel storage and thermal stability. In this work, (+) electrospray ionization coupled to a linear quadrupole ion trap/orbitrap mass spectrometer provided detailed chemical analysis of the NCCs in jet and diesel fuels. Upon methanol extractions of the individual fuels (three jet fuels and one diesel), the methanol layer was diluted and injected into the ESI source where protonation was the dominant ionization reaction for the NCCs, which exhibited little to no fragmentation. Kendrick mass defect plots were constructed to facilitate chemical characterization. Many chemical classes of NCCs (i.e., alkylamines, pyridines, indoles, quinolines, carbazoles) were identified in the jet and diesel fuel extracts. Compositional differences were observed when the jet fuel extracts were compared to each other and when compared to the diesel extract. For example, the most abundant NCCs in Jet fuel 1 had empirical formulas of CnH(2n)N (decahydroquinolines/decahydroisoquinolines) and CnH(2n-6)N (indolines/tetrahydroquinolines/tetrahydroisoquinolines). Conversely, the most abundant NCCs in Jet fuel 2 had empirical formulas of CnH(2n-6)N and CnH(2n-10)N (quinolines/isoquinolines/naphthylamines) while the most abundant NCCs in Jet fuel 3 had empirical formulas of CnH(2n+4)N (alkylamines). The ionized NCCs derived from the jet fuels had wider carbon number ranges than compared to those reported in previous studies. The average molecular weights, ring and double bond equivalent values and total carbon numbers for the ionized NCCs in the four extracts ranged from 192.8–215.3 Da, 1.7–5.0 and 13.5–14.8, respectively. Further, the average carbon number for each homologue ion series (ions with the same empirical formula but differ by 14 Da) were determined. Collision-activated dissociation was also investigated to evaluate its efficacy at providing structural elucidation and isomeric differentiation for ionized NCCs. Overall, the high-resolution mass spectrometry measurements provided thorough chemical characterization that may aid in linking NCC compositions to storage and thermal stability failures and advance the current understanding of issues concerning fuel incompatibility upon the mixing of different fuels.

Multi-scale analysis of mechanical properties of KH-560 coupling agent modified PVA fiber-rubber concrete

ABSTRACT Amphiphilic Silane coupling agent (SCA) improves the weak bond between the two phases of rubber and hydration products, fills the interfacial gaps and effectively repairs the interfacial defects between rubber and hydration products. The addition of PVA fibers mainly improves the cracking performance and durability of concrete. However, most of the studies addressing this issue have been limited to phenomenology, ignoring the mechanism of action at the atomic structure level. Therefore, this study investigates the strengthening mechanism of the interfacial properties of KH-560 coupling agent-reinforced PVA fiber-rubber concrete from the multi-scale analysis of macro-mechanical properties, micro and fine structure, chemical composition and nano-optical level. Based on the results of macro-mechanical tests, it was found that the KH-560 coupling agent could improve the compressive, flexural and shear strength of PVA-rubber concrete, so that the damage morphology also changed from brittle damage to plastic damage, and the compressive strength of concrete was slightly reduced due to the addition of PVA, but the durability and cracking resistance were enhanced. XRD (X-ray diffraction), FT-IR (Fourier transform infrared spectroscopy) and SEM (scanning electron microscopy) tests observed the presence of some gels and polymers that filled the interfacial slits and effectively repaired the interfacial defects. The two-phase interface was simulated by molecular dynamics at the nano level, and it was found that KH560 molecules could be closely connected with C-S-H gel collectively through Si-O-Si chemical bonding, and KH560 molecular bonds were unevenly distributed between the C-S-H and rubber interfaces, while the addition of modifier KH560 and PVA fibers caused more hydrogen and ionic bonds at the interface, which enhanced the interfacial interaction energy. Systematic experiments were conducted on PVA fiber-rubber soil materials before and after SCA modification under macroscopic, microscopic, fine and nano-level multi-scale analyses, which ultimately lead to the design and performance improvement of SCA modification of PVA-rubber cement-based materials in a multi-scale framework. The graphic summary is shown in Figure 1.

Chemical Structure and Microscopic Morphology Changes of Dyed Wood Holocellulose Exposed to UV Irradiation.

Dyed wood is prone to photoaging when exposed to UV irradiation which decreases its decorative effect and service life. Holocellulose, as the main component of dyed wood, has a photodegradation behavior which is still unclear. To investigate the effect of UV irradiation on chemical structure and microscopic morphology changes of dyed wood holocellulose, Maple birch (Betulacostata Trautv) dyed wood and holocellulose were exposed to UV accelerated aging treatment; the photoresponsivity includes crystallization, chemical structure, thermal stability, and microstructure were studied. Results showed that UV radiation has no significant effect on the lattice structure of dyed wood fibers. The wood crystal zone diffraction 2θ and layer spacing was basically unchanged. With the UV radiation time extension, the relative crystallinity of dyed wood and holocellulose showed a trend of increasing first and then decreasing, but the overall change was not significant. The relative crystallinity change range of the dyed wood was not more than 3%, and the dyed holocellulose was not more than 5%. UV radiation caused the molecular chain chemical bond in the non-crystalline region of dyed holocellulose to break, the fiber underwent photooxidation degradation, and the surface photoetching feature was prominent. Wood fiber morphology was damaged and destroyed, finally leading to the degradation and corrosion of the dyed wood. Studying the photodegradation of holocellulose is helpful to understand the photochromic mechanism of dyed wood, and, further, to improve its weather resistance.

Selectivity Rule of Cryptands for Anions: Molecular Rigidity and Bonding Site.

Cryptands utilize inside CH or NH groups as hydrogen bond (H-bond) donors to capture anions such as halides. In this work, the nature and selectivity of confined hydrogen bonds inside cryptands were computationally analyzed with the energy decomposition scheme based on the block-localized wavefunction method (BLW-ED), aiming at an elucidation of governing factors in the binding between cryptands and anions. It was revealed that the intrinsic strengths of inward hydrogen bonds are dominated by the electrostatic attraction, while the anion preferences (selectivity) of inner CH and NH hydrogen bonds are governed by the Pauli exchange repulsion and electrostatic interaction, respectively. Typical conformers of cages are classified into two groups, including the C3(h) -symmetrical conformers, in which all halide anions are located near the centroids of cages, and the "semi-open" conformers, which exhibit shifted bonding sites for different halide anions. Accordingly, the difference in governing factors of selectivity is attributed to either the rigidity of cages or the binding site of anions for these two groups. In details, the C3 conformers of NH cryptands can be enlarged more remarkably than the C3(h) -symmetrical conformers of CH cryptands as the size of anion (ionic radius) increases, resulting in the relaxation of the Pauli repulsion and a dramatic reduction in electrostatic attraction, which eventually rules the selectivity of NH cryptands for halide anions. By contrary, the CH cryptands are more rigid and cannot effectively reduce the Pauli repulsion, which subsequently governs the anion preference. Unlike C3 conformers whose rigidity determines the selectivity, semi-open conformers exhibit different binding sites for different anions. From F- to I- , the bonding site shifts toward the outside end of the pocket inside the semi-open NH cryptand, leading to the significant reduction of the electrostatic interaction that dominates the anion preference. Differently, binding sites are much less affected by the size of anion inside the semi-open CH cryptand, in which the Pauli exchange repulsion remains the key factor for the selectivity of inner hydrogen bonds.

Quasi-static crack propagation in soft materials using the material-sink theory

In the present study, a finite element formulation for the material-sink approach aimed at modeling quasi-static crack propagation in hyperelastic solids is developed. Breakage of molecular bonds leads to material separation and appearance of two new surfaces of a crack. However, the bond breakage is diffusive, and the loss of local bonds leads to the localized material (molecular) loss. The latter notion triggers consideration of mass density as a variable that numerically decreases in the area where damage localizes into a crack. This physical notion requires mathematical consideration of mass balance as an additional and active law, which regularizes the computational model. From the numerical point of view, the developed finite element formulation has displacement and density degrees of freedom. Also, a monolithic approach was applied that ensures stable incrimination of the nonlinear problem. Numerical examples of the fracture of aneurysm material demonstrate the high robustness of the proposed approach.

Surface Roughening of Poly (methyl-methacrylate) Membranes by SF6-Glow-Discharge Plasma Etching

The (100 μm) thick of high density Polymethylmethacrylate PMMA membranes were prepared by solution cast method and treated by (42 W), low pressure, DC-discharge, SF6-Plasma for different exposure time: 10,30,60 and 80 min. The observed changes in membranes surface properties have been characterized by Scanning Electron Microscopy(SEM).The optical properties for plasma treated membranes has been characterized by UV-Visible Spectroscopy. The chemical structure changes have been characterized by Fourier Transformation Infrared Spectroscopy (FTIR).The (SEM) results indicates to significant changes in surface morphology of the polymer membranes after plasma treatment. The UV-Visible spectroscopy results shows clearly reduction of light transmission due to plasma treatment, also the (FTIR) results shows the changes in molecular bonds for polymer chains in surface structure of polymer membranes.

Characterizing molecular transformation of dissolved organic matter during high-solid anaerobic digestion of dewatered sludge using ESI FT-ICR MS

In this study, the effects of anaerobic digestion (AD) on molecular characteristics of dissolved organic matter (DOM) in the dewatered sludge has been described by advanced electrospray ionization combined with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) technology. With the progress of AD, molecular amounts in DOM samples increased with the lowering in the carbon atom number of average molecular formula and average double bond equivalent (DBE). CHON and CHONS groups are the two main organic substances in sludge with their relative DOM proportions of 29.64% and 32.56%, respectively. The resistants (i.e., refractory organic matter) mainly consist of the proteins regions of CHO groups as well as the proteins/lignin regions of CHON groups. The contrasting temporal trends in protein contents (e.g., decrease (CHO and CHON) vs. increase (CHONS)) may imply differences in their degradation characteristics. Likewise, the multi-N (N3, N4) and S2 organic groups in the sludge are converted to N2 and S1 molecules, while the relative abundance of O atoms (in Ox molecules) tends to increase. In addition, the resistants in sludge DOM contain high oxidizing C and low unsaturation. The overall results of this research are expected to provide the theoretical basis for further optimization of the sludge AD process.

The effect of acidification temperature and pH on intermolecular protein bonds and water mobility in heat and acid-induced milk gels

Pre-heated milk was gelled by acidification at 60, 70, 80, and 90 °C, to pH 5.2 or 4.6. The resultant milk gels were characterised in terms of composition, molecular protein bonds, and water mobility. The protein network structure of the gels was mainly governed by calcium bonds (30–63%), independent of the acidification temperature and pH. However, acidification temperature affected the aggregation kinetics and buffer capacity of the milk. Increased temperature led to an increase in total calcium in the gels (187% and 71% for pH 5.2 and 4.6 respectively) since colloidal calcium phosphate dissociated to a lesser degree, increasing the calcium bonds in the protein structure network. The largest water population in the gels was assigned to protons entrapped within the protein network, and the transverse relaxation time decreased with both increase in acidification temperature and decrease of pH, due to the increasing density of the gel aggregates.