Bent Chain Research Articles

Electronic Structures of Small Stoichiometric ZnxOx Clusters.

Stoichiometric ZnxOx clusters in the subnanometer size regime have been the topic of several computational and mass spectrometry studies that showed the particular stability of the stoichiometric species relative to nonstoichiometric species (ZnxOy, x ≠ y). In the current study, we present the angle-resolved anion photoelectron (PE) spectra of stoichiometric ZnxOx-clusters (2 ≤ x ≤ 5), which are interpreted with supporting computational studies that include natural orbital ionization calculations on detachment transition cross sections. All spectra show evidence of Dxh ring structures, which had been predicted to be the most stable structures in previous computational studies. However, a new lowest energy isomer is reported for the Zn2O2 anion and neutral, a bent chain, which is readily reconciled with the most intense feature in the Zn2O2- PE spectrum. The computed PE angular distributions (PADs) associated with the lowest energy cluster structures identified computationally agree with the experimental results, with the exception of Zn5O5-, the experimental PAD of which suggests that strong vibronic coupling may be introducing anomalies. While the lowest lying electronic state of the Zn2O2 chain structure is a triplet state, all neutral ring structures (including Zn2O2, the anion of which also populates the ion beam), favor a singlet electronic state. The computed singlet-triplet splitting of the Dxh structures increases monotonically with x. Overall, we find that the properties of the ring structures evolve smoothly, rather than in the punctuated manner typically seen in the small cluster size regime.

Chain-length dependence in adsorption of perfluoroalkylcarboxylic acid on vesicles composed of amphiphiles with two bent hydrophobic chains

Abstract Per- and polyfluoroalkyl substances (PFAS) are widely used but can have harmful effects on the human body. Activated carbon has been used to remove PFAS from water; however, vesicles consisting of amphiphiles are adsorbent candidates. Optimization of PFAS adsorption using vesicles has not yet been achieved. We analyzed the chain-length dependence of perfluorocarboxylic acid (PFCA) adsorption on vesicles composed of amphiphiles with two bent hydrophobic chains containing cis-double bonds to reveal the interaction between vesicles and PFCA.

The relevance of curvature-induced quadrupolar interactions in dipolar chain aggregation.

The aggregation of dipolar chains driven by thermal fluctuations in an external strong (electric or magnetic) field is investigated theoretically. We discover a new simple electrostatic mechanism that rationalizes the counter-intuitive lateral coalescence of dipolar chains. There, we first demonstrate that two bent dipolar chains can either attract or repel each other depending if they possess similar or opposite curvatures, respectively. Upon bending, dipolar chains become the siege of polarization-induced local charges that in turn lead to quadrupolar couplings. This striking feature is then exploited to understand our conducted Monte Carlo simulations at finite temperature where thermal fluctuations cause local curvatures in the formed dipolar chains. The related quadrupolar attractive mode with correlated chain-curvatures is clearly identified in the simulation snapshots. Our findings shed new light on a longstanding problem in soft matter and related areas.

Structure of racemic duloxetine hydro-chloride.

Duloxetine hydro-chloride (trade name Cymbalta) is marketed as a single enanti-omer (S)-N-methyl-3-(naphthalen-1-yl-oxy)-3-(thio-phen-2-yl)propyl-am-in-ium chloride, C18H20NOS+·Cl-, which is twice as effective as the (R)-enanti-omer in serotonin uptake. Here, we report the crystal structure of duloxetine hydro-chloride in its racemic form (space group Pna21), where it shows significant differences in the mol-ecular conformation and packing in its extended structure compared to the previously reported (S)-enanti-omer crystal structure. Mol-ecules of this type, comprising aromatic groups with a single side chain terminated in a protonated secondary amine, are commonly found in active anti-depressants. A Cambridge Structural Database survey of mol-ecules with these features reveals a strong correlation between side-chain conformation and the crystal packing: an extended side chain leads to mol-ecules packed into separated layers of hydro-phobic and ionic hydro-philic phases. By comparison, mol-ecules with bent side chains, such as racemic duloxetine hydro-chloride, lead to crystal-packing motifs where an ionic hydro-philic phase is encapsulated within a hydro-phobic shell.

Light Guidance Aided by the Toroidal Dipole and the Magnetic Quadrupole in Silicon Slotted-Disk Chains.

Far-field scattering of high-index nanoparticles can be hugely reduced via interference of multipolar moments giving rise to the so-called anapole states. It has been suggested that this reduced scattering can contribute to efficient transmission along periodic chains of such nanoparticles. In this work, we analyze via numerical simulation and experiments the transmission of light along chains of regular and slotted silicon disks in the frequency region over the light cone. We do not observe transmission at wavelengths corresponding to the excitation of the first electric anapole for regular disks. However, large transmission along straight and curved chains is observed for slotted disks due to the simultaneous excitation of the toroidal dipole and magnetic quadrupole modes in the disks. Photonic band calculations unveil that such large transmission can be ascribed to leaky resonances, though bound states in the continuum do not appear in the structures under analysis. Experiments at telecom wavelengths using silicon disk chains confirm the numerical results for straight and bent chains. Our results provide new insights into the role of radiationless states in light guidance along nanoparticle chains and offer new avenues to utilize Mie resonances of simple nanophotonic structures for on-chip dielectric photonics.

Synergistic co-reaction of Zn2+ and H+ with carbonyl groups towards stable aqueous zinc–organic batteries

Aqueous Zn–organic batteries are attracting extensive attention because of the green and sustainable nature. However, most of organic cathodes suffer from limited stability (<3000 cycles) and low potential (∼0.8 V vs. Zn/Zn2+). Herein, we propose a novel polymer, poly (2-chloro-3,5,6-trisulfide-1,4-benzoquinone) (PCTB), as cathode for zinc battery, and demonstrate that the bent molecular chain and the electron-withdrawing group of PCTB facilitate Zn2+-storage. This polymer shows robust cycle stability (9000 cycles) with an increased potential of 1.02 V (vs. Zn/Zn2+). Such performance can be retained even with a high mass loading cathode (8 mgPCTB cm–2). Interestingly, the charge storage of PCTB depends on the synergistic Zn2+/H+ co-coordination reaction with carbonyl groups. Both DFT calculations and experiments demonstrate that the Zn2+ coordination dominates the capacity contribution, but which must be energized by a trace of H+ coordination. This might guide the design of the organic electrode materials.

The nature of supermolecular bonds: Investigating hydrocarbon linked beryllium solvated electron precursors.

Beryllium ammonia complexes Be(NH3)4 are known to bear two diffuse electrons in the periphery of a Be(NH3)4 2+ skeleton. The replacement of one ammonia with a methyl group forms CH3Be(NH3)3 with one peripheral electron, which is shown to maintain the hydrogenic-type shell model observed for Li(NH3)4. Two CH3Be(NH3)3 monomers are together linked by aliphatic chains to form strongly bound beryllium ammonia complexes, (NH3)3Be(CH2)nBe(NH3)3, n = 1-6, with one electron around each beryllium ammonia center. In the case of a linear carbon chain, this system can be seen as the analog of two hydrogen atoms approaching each other at specific distances (determined by n). We show that the two electrons occupy diffuse s-type orbitals and can couple exactly as in H2 in either a triplet or singlet state. For long hydrocarbon chains, the singlet is an open-shell singlet nearly degenerate with the triplet spin state, which transforms to a closed-shell singlet for n = 1 imitating the σ-covalent bond of H2. The biradical character of the system is analyzed, and the singlet-triplet splitting is estimated as a function of n based on multi-reference calculations. Finally, we consider the case of bent hydrocarbon chains, which allows the closer proximity of the two diffuse electrons for larger chains and the formation of a direct covalent bond between the two diffuse electrons, which happens for two Li(NH3)4 complexes converting the open-shell to closed-shell singlets. The energy cost for bending the hydrocarbon chain is nearly compensated by the formation of the weak covalent bond rendering bent and linear structures nearly isoenergetic.

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1-xO3 Solid Solutions.

A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li2MoO3, which has generally been considered as a phase with a well-defined chemical composition. Li2+xMo1-xO3 (-0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li2MoO4 in the temperature range of 650-1100 °C, with x decreasing with the increase of the reduction temperature. The solid solutions adopt a monoclinically distorted O3-type layered average structure and demonstrate a robust local ordering of the Li cations and Mo3 triangular clusters within the mixed Li/Mo cationic layers. The local structure was scrutinized in detail by electron diffraction and aberration-corrected scanning transmission electron microcopy (STEM), resulting in an ordering model comprising a uniform distribution of the Mo3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo3O13 groups) has been directly visualized using differential phase contrast STEM imaging. The established local structure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangement and provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li+ extraction from Li2+xMo1-xO3 in Li cells. According to DFT, all electrochemical capacity in Li2+xMo1-xO3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo3 triangular clusters into bent Mo3 chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltage plateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo3 chains into Mo2 dimers and further into individual Mo6+ cations.

The fate of three common plastic nanoparticles in water: A molecular dynamics study

The widespread contamination of aqueous environments with micro and nanoplastics (MNPs) is an emergent environmental problem that has been gathering increasing public concern. In addition to the known harmful effects on the ecosystems and living organisms, there have been raising worries that MNPs may adsorb trace pollutants such as heavy metals and organics, accumulate them and substantially concentrate them relative to their concentrations in the original aqueous medium. The tendency of MNPs to adsorb compounds may be linked to the particle sizes as well as to their final shapes. In order to assess MNPs behavior in the water environment, namely in terms of particle shapes, structures, interactions and aggregation, differently sized nanoparticles of three common plastics, polyethylene, polyethylene terephthalate and the polyamide nylon 6, were analyzed by molecular dynamics simulations. In all cases, a fast and spontaneous aggregation of the initially dispersed nanoparticles was observed yielding one single larger nanoparticle. In spite of the differences in the type of interactions between each plastic and water, no dispersal and solubilization of any plastic chains was observed during the simulations. The form of aggregation of the various nanoclusters was however very different: compact and ordered for polyethylene, globular and stringy for nylon6, while the PET bent chains form entangled piled-up structures with the aromatic rings preferentially oriented in a parallel-wise ordered way. In addition to the observed aggregation of all the smaller nanoparticles, a rearrangement and a spontaneous self-assembling ordering of the chains was observed as well, particularly in the polyethylene case. The results reinforce the observed tendency of the plastic chains to remain stably associated in clusters with a significant size, in the form of nanoparticles that resist further fragmentation and degradation for all the types of plastic, although the shapes of the particles differ among plastic types.

Density Functional Study of Metal-to-Ligand Charge Transfer and Hole-Hopping in Ruthenium(II) Complexes with Alkyl-Substituted Bipyridine Ligands.

In this study, we present a density functional study of four ruthenium complexes by means of UV–visible spectroscopy and Marcus theory. These molecules, [RuII(bipyP)(bipy)2] (P1), [RuII(bipyP)(dmb)2] (P2), [RuII(bipyP)(dtbb)2] (P3), and [RuII(bipyP)(dnb)2] (P4), where bipyP = 2,2′-bipyridine-4,4′-diphosphonic acid, bipy = 2,2′-bipyridine, dmb = 4,4′-dimethyl-2,2′-bipyridine, dtbb = 4,4′-di-tert-butyl-2,2′-bipyridine, and dnb = 4,4′-dinonyl-2,2′-bipyridine, are photosensitizers for applications in dye-sensitized photo-electrochemical cells (DSPECs). Because of the undetermined P4 conformation in the experiment, we modeled three P4 conformers with straight (P4-straight) and bent nonyl chains (P4-bend1 and bend2). UV–vis absorption spectra by time-dependent density functional theory showed intense metal-to-ligand charge transfer to anchor bipyridine ligands (MLCT-anchoring) at 445–460 nm, which accurately reproduce experimental data. The largest light-harvesting efficiency of the MLCT-anchoring state was observed in the P4-bend1 conformer, which has the lowest P4 energy. This may relate to greater electron injection in the P4 and supports experimental results of dye-only systems (do-DSPEC). The calculated charge transfer rates agree well with the experimental trend. The largest rate was obtained for P2, which was attributed to the expansion of the highest-occupied molecular orbital toward the ancillary bipy ligands and also to the short distances between dyes on the TiO2 surface. These results also support experimental results for P2, which was the best compound for lateral hole-hopping in a sacrificial agent-containing system (sa-DSPEC).

Closing rings with porous templates

Organic Synthesis The closure of large rings from linear substrates (macrocyclization) must avoid the competing coupling between molecules and the entropic penalty for folding long chains. Hydrophobic nanoscale cavities can assist in both folding of chains and avoiding intermolecular reactions. Liu et al. used a self-assembling molecule bearing bent chains of aromatic groups to create two-dimensional sheets with ∼2-nanometer pores. A palladium(0) catalyst performed Suzuki couplings on linear substrates bound in the pores to create >30-mer macrocycles. On formation, the macrocycles released spontaneously to enable subsequent rounds of reaction. J. Am. Chem. Soc. 142 , 1904 (2020).

Orientation Dependent Interaction and Self‐Assembly of Cubic Magnetic Colloids in a Nematic Liquid Crystal

AbstractSpherical microparticles dispersed in nematic liquid crystals have been extensively investigated in the past years. Here, experimental studies are reported on the elastic deformation, colloidal interaction, and self‐assembly of hematite microcubes with homeotropic surface anchoring in a nematic liquid crystal. It is demonstrated that the colloidal interaction and self‐assembly of cubic colloids are orientation dependent. In a notable departure from the conventional microspheres, the microcubes stabilize diverse structures, such as bent chains, branches, kinks, and closed‐loops. The microcubes reorient under external rotating magnetic field, thereby experiencing an elastic torque in the medium, which allows us to measure the magnetic moment through competition between elastic and magnetic torques. The findings envisage that the faceted magnetic colloids in liquid crystals are potential for developing new functional magnetic materials with specific morphologies.

Linear and bent triatomic molecules are not qualitatively different!

I, and other authors, have discussed in several recent publications that “linear” triatomic molecules (defined as having linear equilibrium structures) are necessarily observed as being bent on ro-vibrational average. We have demonstrated this theoretically by calculations of the rotation–vibration expectation values, [Formula: see text], where [Formula: see text] is the bond angle supplement, [Formula: see text] being the instantaneous value of the bond angle of the triatomic molecule A–B–C. Direct experimental evidence of bent average structures has been obtained by other authors in Coulomb explosion imaging experiments, and indirect evidence from re-interpretation of experimentally derived rotational constant values. In spite of a rather significant amount of evidence in support of the bent average structures, the idea has been heavily criticized. In the present work I discuss in more detail some of the arguments for the bent average structures put forward in previous papers, and I hope to correct and clarify some of the misunderstandings leading to the criticisms. Part of the criticism originates in a widespread, but fallacious, belief among spectroscopists that linear and bent chain molecules have qualitatively different energy-level and spectral intensity patterns. This is not true. One can view the linear-molecule energy level and spectral patterns as limiting cases of the bent-molecule ones.

Does Introduction of a Bent Tail Stabilize Biaxiality and Lateral Switching Behavior of Smectic A Liquid Crystal Phases of Rodlike Molecules?

By introducing an oleyl group at the end of the straight rodlike molecule, the effect of the tail shape on the liquid crystallinity, biaxiality, and lateral switching behavior of the smectic A phase was investigated. Three types of molecules possessing a fluorinated phenyl (pentafluorophenyl, 2,3,4-trifluorophenyl, or 2,3-difluorophenyl) group and a cis-octadec-9-enyl group were synthesized, and their liquid crystallinities were compared with the corresponding molecules with a straight alkyl ( trans-octadec-9-enyl or n-octadecanyl) group. In switching experiments, the molecules with a bent terminal chain showed higher spontaneous polarization ( Ps) values than those with a straight terminal chain. Further, the directional changes of the long molecular axes were suppressed for the molecules possessing a bent terminal chain. These results show that the introduction of a bent terminal chain is highly effective for stabilizing ferroelectric switching behaviors.

Let Digons be Bygones: The Fate of Excitons in Curved π-Systems.

We explore the diverse origins of unpolarized absorption and emission of molecular polygons consisting of π-conjugated oligomer chains held in a bent geometry by strain controlled at the vertex units. For this purpose, we make use of atomistic nonadiabatic excited-state molecular dynamics simulations of a bichromophore molecular polygon (digon) with bent chromophore chains. Both structural and photoexcited dynamics were found to affect polarization features. Bending strain induces exciton localization on individual chromophore units of the conjugated chains. The latter display different transition dipole moment orientations, a feature not present in the linear oligomer counterparts. In addition, bending makes exciton localization very sensitive to molecular distortions induced by thermal fluctuations. The excited-state dynamics reveals an ultrafast intramolecular energy redistribution that spreads the exciton equally among spatially separated chromophore fragments within the molecular system. As a result, digons become virtually unpolarized absorbers and emitters, in agreement with recent experimental studies on the single-molecule level.

The Multiple Hydrogen-Bonding Networks of Polyol Ribitol.

Conformational flexibility and non-covalent interactions determine the structure and activity of molecules in biological processes. In this work, the hydrogen bonding networks of the polyol ribitol have been determined for the first time using a combination of laser ablation and broadband rotational spectroscopy. Five conformations of ribitol have been identified, two with extended carbon chains and three with bent chains. All conformations are stabilized by sequential hydrogen bonding networks of either four or five intramolecular O-H⋅⋅⋅O bonds in a clockwise or counter-clockwise arrangement. The hydrogen bonding patterns are related to the extended or bent-chain conformations of ribitol, and involve 2OH-4OH or 2OH-5OH linkages, respectively. Interestingly, all hydrogen bonds wrap round the carbon backbone of ribitol rather than being located above or below it as it happens for other polyols and cyclic sugars.

High Proton Conduction of Organized Sulfonated Polyimide Thin Films with Planar and Bent Backbones

Fast proton conduction was achieved in organized lamellar structures with in-plane oriented structure parallel to the substrate surface using a lyotropic liquid-crystalline (LC) property. Alkyl sulfonated polyimides (ASPIs) with bent main chain structure were newly synthesized to investigate relations between the higher order structure and proton transport properties. Proton conductivity of all polyimide thin films was greater than 10–2 S/cm. Grazing-incidence small-angle X-ray scattering (GI-SAXS) revealed that both planar and bent ASPI thin films exhibited humidity-induced lyotropic lamellar structure. Infrared p-polarized multiple-angle incidence resolution (pMAIR) studies revealed that main chain backbones of both planar and bent ASPI thin films show an in-plane orientation parallel to the substrate surface. Results demonstrate that sulfonated alkyl side chains contribute strongly to the lyotropic LC property, which enhances molecular orderings and proton conductivity by water uptake. This study exten...

Super tough bentonite/SiO 2 -based dual nanocomposite hydrogels using silane as both an intercalator and a crosslinker

Abstract A new dual nanocomposite hydrogel with excellent mechanical properties have been developed by sol-gel reaction of vinyl triethoxysilane (VTES) and in situ radical polymerization of acrylamide (AM) and VTES in the dispersion of Bentonite (Bent). Unlike conventional cationic surfactant intercalators, VTES was used as both an intercalator and a crosslinker. Good intercalation and exfoliation were confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) results. The covalent interaction between Bent and silica by condensation of VTES was confirmed by Fourier transform infrared spectroscopy (FTIR) and 29Si solid-state NMR. The compressive stress of the gel reached up to 4.65 MPa with ha huge fracture energy of 6285.59 J m− 2 (water content of 85 wt%). The gel showed a high cross-linking density of 77.17 mol m− 3 by dynamic viscoelastic measurement. The compressive stress increased to above 25 MPa when the water content decreased to 50 wt%. In the tough nanocomposite hydrogel, the nano-scaled SiO2 was covalently bonded to intercalated or exfoliated Bent and polymer chains, and thus greatly improved the mechanical properties of the gel

Smith-Purcell radiation from concave dotted gratings

We present the first-principles theory of Smith-Purcell effect from the concave dotted grating consisting of bent chains of separated micro- or nanoparticles. The numerical analysis demonstrates that the obtained spectral-angular distributions change significantly depending on the structure of the grating.

Structural insights into the substrate specificity of a glycoside hydrolase family 5 lichenase from Caldicellulosiruptor sp. F32.

Glycoside hydrolase (GH) family 5 is one of the largest GH families with various GH activities including lichenase, but the structural basis of the GH5 lichenase activity is still unknown. A novel thermostable lichenase F32EG5 belonging to GH5 was identified from an extremely thermophilic bacterium Caldicellulosiruptor sp. F32. F32EG5 is a bi-functional cellulose and a lichenan-degrading enzyme, and exhibited a high activity on β-1,3-1,4-glucan but side activity on cellulose. Thin-layer chromatography and NMR analyses indicated that F32EG5 cleaved the β-1,4 linkage or the β-1,3 linkage while a 4-O-substitued glucose residue linked to a glucose residue through a β-1,3 linkage, which is completely different from extensively studied GH16 lichenase that catalyses strict endo-hydrolysis of the β-1,4-glycosidic linkage adjacent to a 3-O-substitued glucose residue in the mixed-linked β-glucans. The crystal structure of F32EG5 was determined to 2.8 Å resolution, and the crystal structure of the complex of F32EG5 E193Q mutant and cellotetraose was determined to 1.7 Å resolution, which revealed that the exit subsites of substrate-binding sites contribute to both thermostability and substrate specificity of F32EG5. The sugar chain showed a sharp bend in the complex structure, suggesting that a substrate cleft fitting to the bent sugar chains in lichenan is a common feature of GH5 lichenases. The mechanism of thermostability and substrate selectivity of F32EG5 was further demonstrated by molecular dynamics simulation and site-directed mutagenesis. These results provide biochemical and structural insights into thermostability and substrate selectivity of GH5 lichenases, which have potential in industrial processes.