Linear Chain Structure Research Articles

Spectroscopic Identification of the Dinitrogen Fixation and Activation by Metal Carbide Cluster Anions PtCn- (n = 4-6).

Nitrogen fixation is confronted with great challenges in the field of chemistry. Herein, we report that single metal carbides PtCn- and PtCnN2- (n = 4-6) are indispensable intermediates in the process of nitrogen fixation by mass spectrometry coupled with anionic photoelectron spectroscopy, quantum chemical calculations, and simulated density-of-state spectra. The most stable isomers of these cluster anions are characterized to have linear chain structures. The fixation and activation of dinitrogen are facilitated by the charge transfer from Pt and Cn to N2. The significance of π back-donation of the 5d orbital of the Pt atom to the antibonding π orbits of N2 for dinitrogen fixation and activation is discussed in detail. This study not only provides a theoretical basis at the molecular level for the activation of dinitrogen by mononuclear metal carbide clusters but also provides a new paradigm for dinitrogen fixation.

Characterization of Chemical Properties of Inulin Isolated from Yacón Tuber

Inulin is a polysaccharide with linear fructan chain structure. Food industries widely use inulin as a low calorie sugar substitutions. Yacón (Smallanthus sonchifolius) tuber that are easily grown and contain higher inulin can be explored as local inulin sources. This research aimed to characterize the chemical properties of inulin isolated from yacón tuber. The methods of this study include proximate analysis of yacón tuber, inulin isolation, and characterization of purified inulin using FTIR. The results showed that yacón consisted of 91.23 water (analyzed as moisture), 0.12 proteins, 0.58 fats, 0.52 crude fibers, and 7.34% carbohydrates. The yield of inulin extracted from yacón tuber was 4.86% whereas its purity and actual content of inulin were 44.23 and 2.15%, respectively. The Osazon test revealed that the isolated inulin has similar crystalline with that from chicory. Based on characterization using the FTIR spectrophotometer, the isolated inulin had functional groups of C-O, C-H, CH2, O-H, and C=O. The spectrum of the isolated inulin has similarities with chicory inulin. Therefore, yacón tuber could be considered as a potential local inulin source in Indonesia.

Tuning the Single-Molecule Magnet and Photoluminescence Properties of Binuclear Dysprosium Complexes by Light

Lanthanide-based single-molecule magnets (Ln-SMMs) showing a synergistic magnetic and photoluminescence change in response to external stimuli are very attractive due to their potential applications in information storage, spintronics, and devices. In this paper, we report two dysprosium complexes containing Dy2O2 motifs and anthracene units, namely [Dy2(SCN)4(L)2(dmpma)2(H2O)2] (1) and [Dy2(SCN)4(L)2(depma)2(H2O)2] (2), where HL stands for 2,6-dimethoxyphenol, dmpma is 9-dimethylphosphonomethylanthracene, and depma is 9-diethylphosphonomethylanthracene. Both exhibit slow magnetization relaxation at zero dc field, characteristic of SMM behavior. Interestingly, complex 2 shows two thermally activated relaxation processes, attributed to the presence of disordered anthracene groups. The effective energy barriers are 117.7 K for 1 and 48.4 and 110.8 K for 2. Under 395 nm UV light irradiation, compounds 1 and 2 undergo a [4 + 4] photocycloaddition reaction to form [Dy2(SCN)4(L)2(dmpma2)(H2O)2]n (1UV) and [Dy2(SCN)4(L)2(depma2)(H2O)2]n·nH2O (2UV) with linear chain structures, where the structural transformation of complex 2 occurs in a single-crystal-to-single-crystal (SC-SC) fashion. Synergistic changes in photoluminescence and SMM behavior were observed for both compounds before and after light irradiation. The results show that the photodimerization of anthracene groups not only inhibits the magnetic relaxation in 1 and 2 and increases the magnetization reversal barrier (172.0 K for 1UV, 120.5 K for 2UV) but also eliminates the anthracene group disorder in compound 2, leading to a significant change in the magnetic dynamics from a dual-relaxation to a single-relaxation process.

Food-Energy Integration in Primary Production and Food Processing Results in a More Equal Distribution of Economic Value Across Regional Food Systems: Nordic Case Study from Circular Perspective

Circular food systems have been proposed as an alternative to the current dominant linear food chain structures. Biomass production for food and energy and nutrient recycling have been defined as the most important elements of circular food systems. Thus far, the potential role of food processing as a large biomass and energy user has gained little attention in studies of the circular bioeconomy. In this study, we explore how compatible bioenergy production is with the energy consumption of regional food processing and how such integrated systems may impact on the economic value created in regional food systems. We applied the nested circularity framework to three contrasting regions to study from an economic perspective the economic value created in primary production, food processing, and bioenergy production. In addition to this, we also calculated the value of external nutrient and energy inputs used in food production. Our results showed how energy production from agricultural biomasses can provide enough energy for food processing on a regional scale, but that this would require integrating food processing with primary production. As a result of this integration, the economic value created in food processing decreased substantially in two of the case study regions, but in contrast, the value increased in the third case study region. We suggest that regionalized food processing is an integral element of circular food systems, as it plays an important role in closing local and regional cycles of nutrients, food, and energy.

Luminescent Zn(II) and Cd(II) coordination polymers based on naphthalene tetracarboxylic acid and 4,4'-bipyridine for sensing of nitrobenzene, Fe3+ and Cr2O7 2− ions

Two luminescent Zn(II) and Cd(II) metal-organic frameworks (MOFs) containing 1,4,5,8-naphthalene tetracarboxylic acid (H4L’) and 4,4'-bipyridine (4bpy), [ZnL(4bpy)0.5(DMA)]n (1) and [CdL(4bpy)0.5]n (2) (L = 1,8-monoanhydride-1,4,5,8-naphthalenetetracarboxylate, DMA = N,N-dimethyl acetamide), were synthesized and characterized through X-ray diffraction, IR, and UV-Vis spectroscopy. 1 shows a 1D linear chain structure, while 2 shows a 2D baluster structure. Both show multiple H bonding and π-stacking interactions. Both compounds show ligand-based luminescence in the range 400-500 nm with contributions from both ligands. The luminescence is strongly dependent on the presence of potentially coordinating molecules. Luminescence quenching experiments show good sensitivities in detecting nitrobenzene (NB), Fe3+ and Cr2O7 2−.

Effects of molecular shape and flexibility on fast sound of organic liquids.

Inelastic x-ray scattering spectra of four organic liquids, n-hexane, cyclohexane, ethylene glycol dimethyl ether, and 1,4-dioxane, were measured, and the sound velocity in the nm-1 wavenumber and meV energy regimes was determined. Compared with the corresponding values in the hydrodynamic limit, the sound velocity in the nm-1 regime was faster, and the positive dispersion of the longitudinal modulus was stronger in liquids composed of ring structures (cyclohexane and 1,4-dioxane) than in those of linear chain structures (n-hexane and ethylene glycol dimethyl ether). Molecular dynamics simulation of n-hexane and cyclohexane was also performed. The difference in the positive dispersion of the longitudinal modulus was reproduced by simulation, and it was elucidated by the difference in the longitudinal modulus in the q = 0 limit and the THz frequency regime. The excess part of the longitudinal modulus from the hydrodynamic limit was further divided into various contributions, and the smaller excess modulus of n-hexane was mainly ascribed to two reasons. The first one is that the shear modulus of n-hexane is smaller in the THz regime, and the second one is that the positive dispersion of the bulk modulus due to the vibrational energy relaxation is weaker. The second mechanism was further interpreted in terms of the fast vibrational energy relaxation of intramolecular modes associated with the chain deformation of n-hexane.

Linear Chain Conditional Random Field for Operating Mode Identification and Multimode Process Monitoring.

As a supervised machine learning algorithm, conditional random fields are mainly used for fault classification, which cannot detect new unknown faults. In addition, faulty variable location based on them has not been studied. In this paper, conditional random fields with a linear chain structure are utilized for modeling multimode processes with transitions. A linear chain conditional random field model is trained by normal data with mode label. This model is able to distinguish transitions from stable modes well. After mode identification, the expectation of state feature function is developed for fault detection and faulty variable location. Case studies on the Tennessee Eastman process and continuous stirred tank reactor (CSTR) testify the effectiveness of the proposed approach.

Comprehensive Search of Stable Isomers of Alanine and Alanine Precursors in Prebiotic Syntheses.

Enantiomeric excesses of l-amino acids have been detected in meteorites; however, their molecular mechanism and prebiotic syntheses are still a matter of debate. To elucidate the origin of homochirality, alanine and the chiral precursors formed in prebiotic processes were investigated with regard to their stabilities among their isomers by employing the minimum energy principle, namely, the abundancy of a molecule in the interstellar medium is directly correlated to the stability among isomers. To facilitate the search for possible isomers, we developed a new isomer search algorithm, the random connection method, and performed a thorough search for all the stable isomers within a given chemical formula. We found that alanine and most of its precursors are located at higher energy by more than 5.7 kcal mol-1, with respect to the most stable isomer that consists of a linear-chain structure, whereas only the 2-aminopropanenitrile is the most stable isomer among all others possible. The inherent stability of the α-amino nitrile suggests that the 2-aminopropanenitrile is the dominant contribution in the formation of the common enantiomeric excess over α-amino acids.

Supramolecular porous frameworks of two Ni(II) coordination polymers with varying structures, porosities, and magnetic properties

Based on a simple benzimidazole derivative and nickel nitrate, two nickel(II) based supramolecular three-dimensional (3D) porous solids, namely {[Ni(Hbic)2(OH2)2]·H2O}n (1) and {[Ni(Hbic)2(OH2)]·2CH3OH}n (2) (H2bic = 1H-benzimidazole-5-carboxylic acid), were synthesized and characterized. Single crystal X-ray diffraction experiments revealed that compound 1 is a 1D coordination polymer with a linear chain structure while 2 is a 2D metal–organic framework (MOF) with a honeycomb network structure. Interestingly, the coordination chains in 1 and layers in 2 can form stable supramolecular 3D porous frameworks sustained by hydrogen bonding interactions and intermolecular π–π interactions. The distinct permanent porosity of the frameworks was established by N2 adsorption experiments. The Ni2+ centers in the two frameworks locate in two different distorted octahedral coordination environments, which lead to the varying crystal color with the effect of diverse supramolecular packing of the crystal structures. Magnetic investigation revealed that the frameworks exhibit significant easy-axis magnetic anisotropy with the zero-field splitting parameter D = -27.8 and −16.5 cm−1 for 1 and 2, respectively. However, no field-induced slow magnetic relaxation behaviors can be detected for 1 and 2. The foregoing results highlight that simple organic molecule can be used for the preparation of supramolecular magnetic frameworks with permanent porosity and coordination polymers-based supramolecular porous frameworks can act as a platform for tunable porosity and magnetic properties.

4α linear-chain state produced by Be9+Be9 collisions

The linear-chain (LC) structure provides significant insights into quantum many-body systems with geometric configurations. In this study, $4\ensuremath{\alpha}+2n$ LC was assessed in $^{18}\mathrm{O}$. The excitation energies, moment of inertia, and $\ensuremath{\alpha}$- and $^{9}\mathrm{Be}$-decay widths of the LC states were predicted using antisymmetrized molecular dynamics. We predict that there are two $4\ensuremath{\alpha}$ LC bands, ${K}^{\ensuremath{\pi}}={0}^{+}$ and ${K}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$, which exhibit different decay properties. We demonstrate that the ${K}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ LC states can be verified by the head-on $^{9}\mathrm{Be}+^{9}\mathrm{Be}$ collision experiments because their states exhibited large decay widths in the $^{9}\mathrm{Be}+^{9}\mathrm{Be}$ channel.

Syntheses, Structures, and Properties of Coordination Polymers with 2,5-Dihydroxy-1,4-Benzoquinone and 4,4'-Bipyridyl Synthesized by In Situ Hydrolysis Method.

The coordination polymers (CPs) with binary ligands, including 2,5-dihydroxy-1,4-benzoquinone (H2DHBQ) and 4,4′-bipyridyl (bpy), were synthesized using in situ hydrolysis of 2,5-dimethoxy-1,4-benzoquinone (DMBQ). Three kinds of CPs were obtained depending on the metal ions. For M = Mn and Zn, a 1D zigzag chain structure with cis conformation (cis-1D-M) was obtained, whereas Co, Ni, and Cu compounds afforded a 2D net structure with trans conformation (trans-2D-M) with a 1D pore. A linear chain structure was also obtained for M = Cu. Magnetic susceptibility (χMT) at 300 K in cis-1D-Mn and trans-2D-Co was evaluated to be 4.421 and 2.950 cm3 K mol–1, respectively, indicating that both compounds are in the high-spin state. According to the N2 adsorption isotherms at 77 K, trans-2D-Ni showed microporosity with the BET surface area of 177 m2 g–1, whereas the isomorphic trans-2D-Co rarely adsorbed N2 at 77 K. This phenomenon was explained by the difference of diffusion kinetics of the adsorbent molecules, which was supported by the CO2 adsorption isotherms at 195 K. The optical band gaps of cis-1D-Mn, cis-1D-Zn, trans-2D-Co, and trans-2D-Ni were estimated to be 1.6, 1.8, 1.0, and 1.1 eV, respectively, by using UV–vis–NIR spectroscopy.

Transformation behaviour of salts composed of calcium ions and phosphate esters with different linear alkyl chain structures in a simulated body fluid modified with alkaline phosphatase

ABSTRACT Ceramic biomaterials have been used for the treatment of bone defects and have stimulated intense research on such materials. We have previously reported that a salt composed of calcium ions and a phosphate ester (SCPE) transformed into hydroxyapatite (HAp) in a simulated body fluid (SBF) modified with alkaline phosphatase (ALP), and proposed SCPEs as a new category of ceramic biomaterials, namely bioresponsive ceramics. However, the factors that affect the transformation of SCPEs to HAp in the SBF remained unclear. Therefore, in this study, we investigated the behaviour of calcium salts of methyl phosphate (CaMeP), ethyl phosphate (CaEtP), butyl phosphate (CaBuP), and dodecyl phosphate (CaDoP) in SBF with and without ALP modification. For the standard SBF, an X-ray diffraction (XRD) analysis indicated that these SCPEs did not readily transform into calcium phosphate. However, CaMeP, CaEtP, and CaBuP were transformed into HAp and octacalcium phosphate in the SBF modified with ALP; therefore, these SCPEs can be categorised as bioresponsive ceramics. Although CaDoP did not exhibit a sufficient response to ALP to be detected by XRD, it is likely to be a bioresponsive ceramic based on the results of morphological observations. The transformation rate for the SCPEs decreased with increasing size of the linear alkyl group of the phosphate esters. The rate-determining steps for the transformation reaction of the SCPEs were changed from the dissolution of the SCPEs to the hydrolysis of the phosphate esters with increasing size of the phosphate ester alkyl groups. These findings contribute to designing novel bioresponsive ceramic biomaterials.

True-atomic-resolution insights into the structure and functional role of linear chains and low-barrier hydrogen bonds in proteins.

Hydrogen bonds are fundamental to the structure and function of biological macromolecules and have been explored in detail. The chains of hydrogen bonds (CHBs) and low-barrier hydrogen bonds (LBHBs) were proposed to play essential roles in enzyme catalysis and proton transport. However, high-resolution structural data from CHBs and LBHBs is limited. The challenge is that their 'visualization' requires ultrahigh-resolution structures of the ground and functionally important intermediate states to identify proton translocation events and perform their structural assignment. Our true-atomic-resolution structures of the light-driven proton pump bacteriorhodopsin, a model in studies of proton transport, show that CHBs and LBHBs not only serve as proton pathways, but also are indispensable for long-range communications, signaling and proton storage in proteins. The complete picture of CHBs and LBHBs discloses their multifunctional roles in providing protein functions and presents a consistent picture of proton transport and storage resolving long-standing debates and controversies.

Diversity of Metal-Fullerene Framework Structures Regulated by Metal Salts.

Taking into account the diversity of fullerene ligands and metal salts, metal–fullerene frameworks (MFFs) present a variety of structures. Currently, the structural control of MFFs mainly relies on the design and synthesis of fullerene ligands, while the influence of metal building units on the structures has been rarely studied. The present work represents a systematical investigation of fullerene-linked supramolecular architectures incorporating different metal salts. Treatment of a bidentate N,N-donors fullerene ligand (L1) with six metal salts ([Zn(NO3)2·6H2O, Cd(NO3)2·4H2O, Cu(NO3)2·3H2O, Cu(OAc)2·H2O, FeCl2·4H2O and FeCl3·6H2O]) produced six one-dimensional MFFs, i.e., ZnL1(NO3)2(H2O)2 (1), CdL1(NO3)2 (2), Cu(L1)(H2O)2(NO3)2 (3), CuL1(OAc)(CH3O) (4), FeL1Cl2 (5) and FeL1Cl2(FeCl4) (6). Compounds 1–3, built with nitrates with different metal centers (M(NO3)2, M = Zn, Cd, Cu), present a 1D stair-like, 1D zigzag, and 1D linear chain structure, respectively. Compound 4, synthesized with another Cu(II) salt, Cu(OAc)2, displays a dinuclear Cu-Cu connected 1D stair-like chain structure, rather than the single Cu linked 1D linear chain obtained from Cu(NO3)2. Compounds 5 and 6, assembled from iron chloride of different oxidation states (Fe(II)Cl2 and Fe(III)Cl3) reveal a 1D zigzag and a 1D stair-like chain structure, respectively. The results demonstrate the significant influences of metal salts on the structures of metal–fullerene frameworks.

Low-temperature solid-state synthesis of interlayer engineered VS4 for high-capacity and ultrafast sodium-ion storage

The quasi-layered VS4 is the stacked linear chain structure in which parallel chains are bonded by Van der Waals forces. Considering its wide interlayer and high sulfur content, VS4 is supposed to be a potential high-performance anode material for Na-ion storage. Herein, a novel and efficient low-temperature solid-state method is developed to synthesize interlayer engineered VS4 (IE-VS4). The intercalation of [NCN]2- anion expands the interlayer of VS4 to accelerate the Na-ion diffusion. Furthermore, The intercalated anion also reduces the band gap of VS4 and enhances the electronic conductivity. Thanks to these merits, the IE-VS4 enables standout Na-ion storage performance in terms of ultrafast rate capability (500 mAh g−1 at 20 A g−1), high capacity and superior cycle stability (550 mAh g−1 at 5 A g−1 after 2500 cycles). The developed large-scale synthesis method and the interlayer engineering strategy can synergistically promote the practical application of VS4 in electrochemical energy storage.

Synthesis, crystal structure, DFT studies and Hirshfeld surface analysis of Manganese(II) and Cadmium(II) coordination polymers of 2-aminopyridine and dicyanamide

Mn(II) and Cd(II) metal salts reacted with dicyanamide and 2-aminopyridine resulted in the formation of the ligand-rich linear polymeric chain structures [M(dca)2(2-Ampy)2]n (dca = dicyanamide, 2-Ampy = 2-Aminopyridine; M = Mn (1) or Cd (2)), of the same dimensionality, in which the metal centers are μ1,5-bridged by the dca anions. The complexes were characterized by elemental analysis, IR spectroscopy, UV–vis spectroscopy, thermal analysis and single crystal X-ray structure analysis. These coordination polymers crystallize in the Monoclinic space group Cc. The 3D crystal packing structure results from a combination of N—H/H—-N interactions followed by CH—π stacking interactions. Hirshfeld surface (HS) analysis of the polymers was undertaken to investigate further the intermolecular interactions. DFT calculations on 1 and 2 demonstrated a good correlation between the experimental and theoretical data. The in vitro antimicrobial activity of the manganese complex against selected micro-organisms is also reported.

Effects of rotation and valence nucleons in molecular α -chain nuclei

Effects of rotation and valence nucleons in molecular linear $\ensuremath{\alpha}$-chain nuclei are analyzed using a three-dimensional lattice cranking model based on covariant density functional theory. The structure of the mirror nuclei $^{16}\mathrm{C}$ and $^{16}\mathrm{Ne}$ is investigated as a function of rotational frequency. The valence nucleons, with respect to the $3\ensuremath{\alpha}$ linear chain core of $^{12}\mathrm{C}$, at low frequency occupy the $\ensuremath{\pi}$ molecular orbital. With increasing rotational frequency these nucleons transition from the $\ensuremath{\pi}$ orbital to the $\ensuremath{\sigma}$ molecular orbital, thus stabilizing the $3\ensuremath{\alpha}$ linear chain structure. It is predicted that the valence protons in $^{16}\mathrm{Ne}$ change occupation from the $\ensuremath{\pi}$ to the $\ensuremath{\sigma}$ molecular orbital at $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\approx}1.3$ MeV, a lower rotational frequency compared to $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\approx}1.7$ MeV for the valence neutrons in $^{16}\mathrm{C}$. The same effects of valence protons are found in $^{20}\mathrm{Mg}$, compared to the four valence neutrons in $^{20}\mathrm{O}$. The model is also used to examine the effect of alignment of valence nucleons on the relative positions and size of the three $\ensuremath{\alpha}$ clusters in the mirror nuclei $^{16}\mathrm{C}$ and $^{16}\mathrm{Ne}$.

Chain extension of thermoplastic polyamide elastomer and its foaming performance

AbstractThermoplastic polyamide elastomer (TPAE) foam material has various important applications, including in shoe materials, cushioning packaging, sports, and automobiles, owing to its excellent resilience and anti‐vibration performance. However, owing to its linear molecular chain structure, the melt viscoelasticity of TPAE is low, making it difficult to obtain lower‐density foamed materials. Therefore, it is crucial to improve the melt strength through chain extensions. Given its ability to react with carboxyl and amine groups, multifunctional epoxides were chosen as chain extenders to increase the melt viscoelasticity of TPAE. A rotational rheometer, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used to characterize the rheological properties and crystallization behavior of the modified TPAE. Adding epoxy‐type chain extender KL‐E4370 was conducive for forming the branch structure of TPAE and even a microgel structure, leading to increased melt viscoelasticity and reduced crystallinity of TPAE. Microcellular TPAE foams (cell sizes and densities of 30 μm and 1.5 × 108 cells cm−3, respectively) were successfully fabricated. With increasing concentrations of KL‐E4370, the foaming temperature zone of TPAE widened and the expansion ratio increased from 5.5 to 9 times, leading to a decrease and an increase in cell diameter and density, respectively, and improvement in the rupture and merging of cells.

Enhancing magnetorheology with precession magnetic fields

We demonstrate a new route to enhance magnetorheology using precession-like magnetic fields. This field configuration is generated by the superposition of a 2D rotational field applied orthogonal to a uniaxial DC field. Maintaining a columnar linear chain structure when applying a precession field was determined to be integral in increasing the average cluster size of the aggregates for low precession angles and a low Mason number. A yield stress increase was experimentally observed when reapplying a uniaxial DC field following the application of a controlled low-angle precession field indicating a favorable structural evolution had taken place under the unsteady field configuration. Experimental results of small-amplitude oscillatory shear tests and shear rheograms are supported by particle-level simulation 3D models and start-up tests.

Evolution mechanism of cyclized structure of PAN-based pre-oxidized fiber during low temperature carbonization process

The low temperature carbonization process is an important stage to realize the structural transition from the organic cyclized structure of PAN based pre-oxidized fiber to the inorganic pseudo-graphite structure of the ultimate carbon fiber. In the present paper, the evolution mechanism of cyclized structure and aggregation structure of PAN stabilized fiber during low temperature carbonization was studied by means of TGA, 13C-NMR, XRD, XPS and Raman. The results indicated that when the heat-treated temperature was lower than 450 °C, the mainly chemical reactions were the dehydrogenation and pyrolysis reactions in acyclic linear molecular chain or partial cyclized structure. At this stage, the growth of cyclized structure was not obvious. While the original ordered structure was destroyed gradually and the internal stress increased significantly. It induced the cyclized structure to be further oriented. When the temperature was higher than 450 °C, the polycondensation and reconstruction in aromatic heterocyclic structure was more important. The early aromatic heterocycles had many different structural scales, poor homogeneity and many defects in the heterocycles. At this stage, a new pseudo-graphite crystalline structure gradually formed and the d-spacing of graphite layer decreased slightly and crystallites size increased slowly with the increase of heat-treated temperature. When the temperature was higher than 550 °C, the pseudo-graphite base structure gradually formed. The d-spacing were further reduced slightly, and the crystallites size increased slowly. A new ordered basis structure was gradually developed into carbon fiber.