Closed-shell Structures Research Articles

Contact-force-based closed-loop control of shell structure additive manufacturing with continuous-fiber-reinforced polymer composites

Additive manufacturing (AM) is an automated process for fabricating complex structures, especially for continuous fiber-reinforced polymer (CFRP) composites with exceptional mechanical performance and reduced weight. The extrusion-based CFRP-AM process has been widely adopted but faces challenges with insufficient impregnation/adhesion and lack of geometrical accuracy. Existing research efforts exploit various mechatronics approaches and printing parameter adjustment techniques to enhance CFRP quality. Nevertheless, most of them are static or slow-varying; thus, they cannot dynamically adjust to local geometrical features and faults, which are particularly representative of the CFRP-AM process in high-curvature regions. To enable dynamic and rapid adjustment, this study exploits contact forces as major real-time feedback signals to dynamically control the feed velocity, layer height, and fiber extrusion rate. To create a continuous feedback control environment for dynamic adjustment, the study also proposes a novel helical CFRP-AM printing trajectory generation method for closed shell structures, such that the helical angles indirectly adjust the layer height of the parts. A material extrusion CFRP-AM platform combining a co-extrusion nozzle, an industrial robot, a six-degree-of-freedom load cell, and a real-time closed-loop control system is built to verify the proposed control framework. Three representative case studies are introduced to show the enhancements of the closed-loop CFRP-AM process, particularly in layer height adjustment, high-speed printing, and large curvature regions.

Pathway to Polyradicals: A Planar and Fully π-Conjugated Organic Tetraradical(oid).

In this work, we provide a general strategy to stabilize the ground state of polyradical(oid)s and make higher spin states thermally accessible. As a proof of concept, we propose to merge two planar fully π-conjugated diradical(oid)s to obtain a planar and cross-conjugated tetraradical(oid). Using multireference quantum chemistry methods, we show that the designed tetraradical(oid) is stabilized by aromaticity and delozalization in the π-system and has six thermally accessible spin states within 1.72 kcal/mol. Analysis of the electronic structure of these six states of the tetraradical(oid) shows that its frontier π-system consists of two weakly interacting subsystems: aromatic cycles and four unpaired electrons. Conjugation between unpaired electrons, which favors closed-shell structures, is mitigated by delocalization and the aromaticity of the bridging groups, leading to the synergistic cross-coupling between two diradical(oid) subunits to stabilize the tetraradical(oid) electronic structure.

Quantum fundaments of catalysis: true electronic potential energy.

Catalysis is a quantum phenomenon enthalpically driven by electronic correlations with many-particle effects in all of its branches, including electro-photo-catalysis and electron transfer. This means that only probability amplitudes provide a complete relationship between the state of catalysis and observations. Thus, in any atomic system material), competing space-time electronic interactions coexist to define its (related) properties such as stability, (super)conductivity, magnetism (spin-orbital ordering), chemisorption and catalysis. Catalysts, reactants, and chemisorbed and transition states have the possibility of optimizing quantum correlations to improve reaction kinetics. Active sites with closed-shell orbital configurations share a maximum number of spin-paired electrons, mainly optimizing coulombic attractions and covalency and defining weakly correlated closed-shell (WCCS) structures. However, in compositions with open-shell orbital configurations, at least, quantum spin exchange interactions (QSEIopenshells) arise, stabilising unpaired electrons in less covalent bonds and differentiating non-weakly (or strongly) correlated open-shell (NWCOS) systems. In NWCOS catalysts, electronic ground states can have bonds with diverse and rival spin-orbital orderings as well as ferro-, ferri- and multiple antiferro-magnetic textures, which deeply define their activities. Particularly in inter-atomic ferromagnetic (FM) bonds, the increase in relevance of non-classical quantum potentials can significantly optimize chemisorption energies, transition states (TSs), activation energies (overpotential) and spin-dependent electron transfer (conductivity), overall implying the need for explaining the thermodynamic and kinetic origin of catalysis from its true quantum electronic energy. To do so, we use the connection between the Born-Oppenheimer approximation and Virial theorem in the treatment of electronic kinetic and potential energies. Thus, the exact fundamental interactions that decompose TSs appear. The possibility of increasing the stabilization of TSs, due to quantum correlations on NWCO catalysts, opens the possibility of simultaneously reducing chemisorption enthalpies and activation barriers of reaction mechanisms, which implies the anticipation and explanation of positive deviations from the Brønsted-Evans-Polanyi principle.

Breaking the size constraint for nano cages using annular patchy particles.

Engineering structures like nanocages, shells, and containers, by self-assembly of colloids is a challenging problem. One of the main challenges is to define the shape of the individual subunits to control the radius of the closed shell structures. In this work, we have proposed a simple model for the subunit, which comprises a spheroidal or spherical hardcore decorated with an annular patch. The self-assembly of these building blocks leads to the formation of monodispersed spherical cages (close shells) or containers (curved clusters). For a spheroid with a given bonding range, the curvature of the shell is analytically related to only the patch angle of the building blocks and independent of the shape of the subunits. This model with only one control parameter can be used to engineer cages with the desired radius, which also have been verified using thermodynamic calculations. In the phase diagram of the system, 4 phases are identified which includes gas, closed shell, partially closed (containers) shell and percolated structures. When the diameters of the spherical cages formed are small, we observe an icosahedral symmetry similar to virus capsids. We also observed that the kinetics of the cage formation is very similar to the nucleation and growth kinetics of viruses and is the key factor in determining the yield of closed shells.

Transferable Machine Learning Interatomic Potential for Bond Dissociation Energy Prediction of Drug-like Molecules.

We present a transferable MACE interatomic potential that is applicable to open- and closed-shell drug-like molecules containing hydrogen, carbon, and oxygen atoms. Including an accurate description of radical species extends the scope of possible applications to bond dissociation energy (BDE) prediction, for example, in the context of cytochrome P450 (CYP) metabolism. The transferability of the MACE potential was validated on the COMP6 data set, containing only closed-shell molecules, where it reaches better accuracy than the readily available general ANI-2x potential. MACE achieves similar accuracy on two CYP metabolism-specific data sets, which include open- and closed-shell structures. This model enables us to calculate the aliphatic C-H BDE, which allows us to compare reaction energies of hydrogen abstraction, which is the rate-limiting step of the aliphatic hydroxylation reaction catalyzed by CYPs. On the "CYP 3A4" data set, MACE achieves a BDE RMSE of 1.37 kcal/mol and better prediction of BDE ranks than alternatives: the semiempirical AM1 and GFN2-xTB methods and the ALFABET model that directly predicts bond dissociation enthalpies. Finally, we highlight the smoothness of the MACE potential over paths of sp3C-H bond elongation and show that a minimal extension is enough for the MACE model to start finding reasonable minimum energy paths of methoxy radical-mediated hydrogen abstraction. Altogether, this work lays the ground for further extensions of scope in terms of chemical elements, (CYP-mediated) reaction classes and modeling the full reaction paths, not only BDEs.

Structural evolution, stability, electronic and bonding properties of sodium-doped magnesium cluster cations

Bimetallic sodium-doped magnesium cluster cations, NaMg n + (n= 2–12), have been investigated through a synergetic combination of the CALYPSO code and DFT calculations. The results reveal that the lowest-energy structures of NaMg n + exhibit linear, planar, triangular pyramid, pentagonal pyramid, and triangular prism topologies. The structures can be described as a substituted geometry of pure Mg clusters at the small size. Starting from n = 9, the dominant structures transform into a triangular prism-based configuration. Like anionic and neutral NaMg n clusters, the Na atom prefers the peripheral regions of the Mg n framework. Stability studies indicate NaMg4 + and NaMg10 + to be the~most stable clusters, which may benefit from their closed-shell electron structures. Analysis of the bonding nature shows stronger Mg-Mg interaction than the Na-Mg interaction in the NaMg4 + and NaMg10 + clusters. The reason is that covalent bonds are formed in the Mg-Mg regions, while there is no aggregation of electron density in the Na-Mg regions.

Tunable electrical conductivity in covalent organic frameworks by intercalation of electron acceptor molecules

Covalent organic frameworks (COFs) are crystalline organic materials with high porosity. The COFs are typically electrical insulators because of their wide bandgaps and closed-shell structures despite their π–π layer stacking motif suitable for carrier conduction. Here, we report a strategy for realizing tunable electrical conductivity in COFs by intercalating redox-active guest molecules. The approach is demonstrated using COF-5 with a boronate-ester-linked two-dimensional structure and one-dimensional nanopore channels infiltrated by 7,7,8,8-tetracyanoquinododimethane (TCNQ). Successful incorporation of guest TCNQ molecules into the cavities of the COF-5 host is confirmed by vibrational and optical spectroscopies and results in the appearance of guest–host charge-transfer transitions for TCNQ-intercalated COF-5. Overall electrical conductivities are enhanced by the carrier generation induced by the charge transfer between TCNQ and COF-5 with the retained layer-stacked structures in COF-5 also contributing to the conduction pathways. The tunable electronic properties of COFs realized by the host–guest strategies established here will further promote refinement of design principles of conductive COFs and deeper understanding of the conduction mechanism while simultaneously providing opportunities for using COFs in diverse applications.

Phellandrenes and Some Species from Them - A DFT Treatment

Phellandrenes are naturally occurring cyclic dienes belonging to cyclic monoterpene class and have many medicinal applications. In the present study, some resonance stabilized radicals from α- and β-phellandrene and also some closed shell structures from those radicals have been investigated within the constraints of density functional theory and basis set employed. For structure optimizations of the closed-shell and open-shell structures, B3LYP/6-311++G(d,p) and UB3LYP/6-311++G(d,p) level of theories have been adopted, respectively. All the systems considered have been found to be thermo chemically favorable and electronically stable. Various structural, quantum chemical and spectral properties of them have been obtained and discussed.

Some stable and closed-shell structures of anticancer drugs by graph theoretical parameters

The eigenvalues are significant in mathematics, but they are also relevant in other domains like as chemistry, economics, and a variety of others. In terms of our research, eigenvalues are used in chemistry to represent not only the form of energy but also the various physicochemical aspects of a chemical substance. We must comprehend the connection between mathematics and chemistry. The antibonding level is related to positive eigenvalues, the bonding level is associated to negative eigenvalues, and the nonbonding level is linked to zero eigenvalues. In this work, we studied some anticancer drug structures in terms of nullity, matching number, eigenvalues of adjacency matrix, and characteristics polynomials. As a result, Carmustine, Caulibugulone-E, Aspidostomide-E anticancer drug structures are stable, closed-shell molecules since their nullity is equal to zero.

Closed-shell and open-shell dual nature of singlet diradical compounds

Abstract Unlike triplet diradicals, singlet diradicals can vary in diradical character from 0 % to 100 % depending on linker units that allow two formally unpaired electrons to couple covalently. In principle, the electronic structure of singlet diradicals can be described as a quantum superposition of closed-shell and open-shell structures. This means that, depending on the external environment, singlet diradicals can behave as either closed-shell or open-shell species. This paper summarizes our progress in understanding the electronic structure of π-conjugated singlet diradical molecules in terms of closed-shell and open-shell dual nature. We first discuss the coexistence of intra- and intermolecular covalent bonding interactions in the π-dimer of a singlet diradical molecule. The intra- and intermolecular coupling of two formally unpaired electrons are related to closed-shell and open-shell nature of singlet diradical, respectively. Then we demonstrate the coexistence of the covalent bonding interactions in the one-dimensional stack of singlet diradical molecules having different diradical character. The relative strength of the interactions is varied with the magnitude of singlet diradical index y 0. Finally, we show the dual reactivity of a singlet diradical molecule, which undergoes rapid [4 + 2] and [4 + 4] cycloaddition reactions in the dark at room temperature. Closed-shell and open-shell nature endow the singlet diradical molecule with the reaction manner as diene and diradical species, respectively.

In Situ Generation of Red-to-NIR Emissive Radical Cations in the Stomach for Gastrointestinal Imaging.

Red-to-near-infrared (NIR) fluorescent probes, with advantages such as high spatiotemporal resolution and in situ sensing abilities,are highly attractive for diagnosis of gastrointestinal diseases and targeted drug development. However, conventional red-to-NIR fluorophores with electron closed-shell structures require tedious synthetic procedures for preparation, and it is difficult to further decorate them with sensing groups. In this study, a series of easily prepared pyrroles with simple structures that can quickly be transformed into red-to-NIR emissive radical cations in acidic buffer solution and in vivo stomachs is developed. The in-situ-generated red-to-NIR emissive pyrrole radical cations in the stomach have excellent biocompatibility and stability and can be used not only for intravital gastrointestinal imaging with high spatiotemporal resolution, but also for dynamic monitoring of the gastric emptying process and assessment of anti-gastric-acid therapy. The acidity-induced generation of pyrrole radical cations is believed to provide a facile strategy for developing red-to-NIR fluorophores and studying gastrointestinal diseases.

Controlling Diradical Character of Photogenerated Colored Isomers of Phenoxyl-Imidazolyl Radical Complexes.

We propose a rational method for evaluating the diradical character of the photochromic phenoxyl-imidazolyl radical complex (PIC) derivatives based on their radical-radical coupling reaction rates. PIC consists of an imidazole ring, a phenoxyl ring, and a bridging unit that structurally connects them. The C-N bond formed between the imidazole and phenoxyl rings can be dissociated photochemically in a homolytic manner. The photochromism of PIC differs significantly from other photochromic molecules in that the transient colored open-ring isomer has a diradical character. The colored open-ring isomer returns promptly to the initial colorless closed-ring isomer by the intramolecular radical recombination reaction. By changing the aromaticity and substitution position of the bridging unit, it is possible to control the degree of contribution of the open-shell diradical and closed-shell quinoidal structures to the open-ring isomer. Systematic investigation of the photochromic reactions of several PIC derivatives revealed that the half-life of the open-ring isomers reflects the diradical character. Thus, the radical recombination reaction rate of the open-ring isomer of the PIC derivatives is an excellent parameter of the diradical character.

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Air Stable Chalcogen-Doped Rubicenes with Diradical Character

Electronic relaxation of photoexcited open and closed shell adsorbates on semiconductors: Ag and Ag2 on TiO2.

A theoretical treatment based on the equations of motion of an electronic reduced density matrix, and related computational modeling, is used to describe and calculate relaxation times for nanostructured TiO2(110) surfaces, here for Ag and Ag2 adsorbates. The theoretical treatment deals with the preparation of a photoexcited system under two different conditions, by steady light absorption with a cutoff and by a light pulse, and describes the following relaxation of electronic densities. On the computational modeling, results are presented for electronic density of states, light absorbance, and relaxation dynamics, comparing results for Ag and Ag2 adsorbates. The aim of this work is to provide insight on the dynamics and magnitude of relaxation rates for a surface with adsorbed open- and closed-shell Ag species to determine whether the advantages in using them to enhance light absorbance remain valid in the presence of charge density relaxation. Different behaviors can be expected depending on whether the adsorbate particles (Ag metal clusters in our present choice) have electronic open-shell or closed-shell structures. Calculated electron and hole lifetimes are given for pure TiO2(110), Ag/TiO2(110), and Ag2/TiO2(110). The present results, while limited to chosen structures and photon wavelengths, show that relaxation rates are noticeably different for electrons and holes, but comparable in magnitude for pure and adsorbate surfaces. Overall, the introduction of the adsorbates does not lead to rapid loss of charge carriers, while they give large increases in light absorption. This appears to be advantageous for applications to photocatalysis.

Buckling Behavior of Thick Porous Functionally Graded Material Toroidal Shell Segments Under External Pressure and Elevated Temperature Including Tangential Edge Restraint

AbstractOwing to mathematical and geometrical complexities, there is an evident lack of stability analyses of thick closed shell structures with porosity. Based on an effective analytical approach, for the first time, simultaneous effects of porosities, elasticity of edge constraint, and surrounding elastic media on the buckling resistance capacity of thick functionally graded material (FGM) toroidal shell segments (TSSs) subjected to external pressure, elevated temperature, and combined thermomechanical loads are investigated in this paper. The volume fractions of constituents are varied across the thickness according to power law functions, and effective properties of the FGM are determined using a modified rule of mixture. The porosities exist in the FGM through even and uneven distributions. Governing equations are based on a higher-order shear deformation theory (HSDT) taking into account interactive pressure from surrounding elastic media. These equations are analytically solved and closed-form expressions of buckling loads are derived adopting the two-term form of deflection along with Galerkin method. Parametric studies indicate that the porosities have beneficial and deteriorative influences on the buckling resistance capacity of thermally loaded and pressure-loaded porous FGM TSSs, respectively. Furthermore, tangential constraints of edges lower the buckling resistance capacity of the shells, especially at elevated temperatures.

Synthesis, crystal structure, tropicity and charge transport properties of diindenothienothiophene derivatives

Bond lengths analysis highlights their closed-shell structures and gives insight on the bond lengths of diindenoacene diradicaloids. They are low band gap molecules with high electron affinity and exhibit ambipolar behavior in OFETs.

(Invited) Isolation and Structure Determination of Trifluoromethylated Gadoliniummetallofullerenes

Endohedral metallofullerenes have been extensively studied since the first experimental observation of La@C60 in a laser-vaporized supersonic beam in 1985. However, most of these studies have focused on metallofullerenes larger than C60 such as Ln@C82 (Ln: lanthanide). There are few examples for isolation of small-cage (C60, C70, C72, and C74) lanthanide metallofullerenes because of their extremely high chemical reactivity. Recently, we developed an in situ trifluoromethylation method for the extraction and purification of these missing metallofullerenes [1−3]. Here we report the isolation and structure determination of trifluoromethylated gadolinium metallofullerenes (Gd@C60(CF3)3, Gd@C60(CF3)5, Gd@C70(CF3)3, Gd@C74(CF3), and Gd@C74(CF3)3). Gd-metallofullerenes are promising as magnetic resonance imaging (MRI) contrast agents. The fully enclosing carbon cage completely prevents leaching of the Gd atoms, resulting in lower toxicity than commercially available metal chelate reagents such as Gd-DTPA.Trifluoromethylated Gd-metallofullerenes were synthesized by the modified arc-discharge method. PTFE rods are placed near the discharge area as CF3 source. During arc discharge, PTFE was decomposed and evaporated to produce CF3 radicals. Gd-metallofullerenes and empty fullerenes were extracted from the raw soot with o-xylene. Rapid separation of Gd-metallofullerenes from empty fullerenes was carried out by the TiCl4 Lewis acid method. High-performance liquid chromatography (HPLC) purification was conducted for isolation of trifluoromethylated Gd-metallofullerenes. Single crystals of trifluoromethylated Gd-metallofullerenes were obtained from solution. The single-crystal X-ray diffraction data for structure determination were collected at SPring-8 large synchrotron radiation facility.Figures show the molecular structures of Gd@C74(CF3) (I), Gd@C74(CF3) (II), and Gd@C74(CF3)3 derived from the X-ray crystal structure analysis. The closed-shell molecular structures are theoretically stable and have wide HOMO-LUMO energy gaps.[1] Z. Wang et al. Angew. Chem. Int. Ed. 55, 199 (2016).[2] A. Nakagawa et al. Nature. Commun. 9, 3073 (2018).[3] A. Nakagawa et al. R. Soc. Open Sci. 5, 181015 (2018). Figure 1

Binary Nanoalloy Clusters: A Case Study for FeCr Clusters.

A study of FexCry binary nanoalloy clusters is carried out for sizes n=x+y=13 and 55, the first two closed shell structures. While for n=13, various compositions like x=12 and y=1; x=11 and y=2; x=10 and y=3 ; x=1 and y=12 are studied, for the larger size (n=55) the morphology of a Fe-rich cluster (Fe42Cr13) and a Cr-rich cluster (Fe13Cr42) are analysed. The potential energy surface of the nanoalloys are scanned thoroughly using an evolutionary genetic algorithm in conjunction with a density functional theory based first principles method and the most stable clusters are picked up for every size and composition. A definite hierarchy in Cr-Cr,Fe-Cr and Fe-Fe bonding strengths is seen to determine the stability of the clusters. Cr-Cr bonding is promoted over Fe-Cr bonding which in turn is preferred over Fe-Fe bonding in the nanoalloy systems.

Structure Optimisation of Large Transition‐Metal Complexes with Extended Tight‐Binding Methods

AbstractLarge transition‐metal complexes are used in numerous areas of chemistry. Computer‐aided theoretical investigations of such complexes are limited by the sheer size of real systems often consisting of hundreds to thousands of atoms. Accordingly, the development and thorough evaluation of fast semi‐empirical quantum chemistry methods that are universally applicable to a large part of the periodic table is indispensable. Herein, we report on the capability of the recently developed GFNn‐xTB method family for full quantum‐mechanical geometry optimisation of medium to very large transition‐metal complexes and organometallic supramolecular structures. The results for a specially compiled benchmark set of 145 diverse closed‐shell transition‐metal complex structures for all metals up to Hg are presented. Further the GFNn‐xTB methods are tested on three established benchmark sets regarding reaction energies and barrier heights of organometallic reactions.

Structure Optimisation of Large Transition-Metal Complexes with Extended Tight-Binding Methods.

Large transition-metal complexes are used in numerous areas of chemistry. Computer-aided theoretical investigations of such complexes are limited by the sheer size of real systems often consisting of hundreds to thousands of atoms. Accordingly, the development and thorough evaluation of fast semi-empirical quantum chemistry methods that are universally applicable to a large part of the periodic table is indispensable. Herein, we report on the capability of the recently developed GFNn-xTB method family for full quantum-mechanical geometry optimisation of medium to very large transition-metal complexes and organometallic supramolecular structures. The results for a specially compiled benchmark set of 145 diverse closed-shell transition-metal complex structures for all metals up to Hg are presented. Further the GFNn-xTB methods are tested on three established benchmark sets regarding reaction energies and barrier heights of organometallic reactions.