Bond Geometry Research Articles

A Multiresponsive Ferrocene-Based Chiral Overcrowded Alkene Twisting Liquid Crystals.

The reversible modulation of chirality has gained significant attention not only for fundamental stereochemical studies but also for numerous applications ranging from liquid crystals (LCs) to molecular motors and machines. This requires the construction of switchable molecules with (multiple) chiral elements in a highly enantioselective manner, which is often a significant synthetic challenge. Here, we show that the dimerization of an easily accessible enantiopure planar chiral ferrocene-indanone building block affords a multi-stimuli-responsive dimer (FcD) with pre-determined double bond geometry, helical chirality, and relative orientation of the two ferrocene motifs in high yield. This intrinsically planar chiral switch can not only undergo thermal or photochemical E/Z isomerization but can also be reversibly and quantitatively oxidized to both a monocationic and a dicationic state which is associated with significant changes in its (chir)optical properties. Specifically, FcD acts as a chiral dopant for cholesteric LCs with a helical twisting power (HTP) of 13 μm-1 which, upon oxidation, drops to near zero, resulting in an unprecedently large redox-tuning of the LC reflection color by up to 84 nm. Due to the straightforward stereoselective synthesis, FcD, and related chiral switches, are envisioned to be powerful building blocks for multi-stimuli-responsive molecular machines and in LC-based materials.

A Multiresponsive Ferrocene‐Based Chiral Overcrowded Alkene Twisting Liquid Crystals

AbstractThe reversible modulation of chirality has gained significant attention not only for fundamental stereochemical studies but also for numerous applications ranging from liquid crystals (LCs) to molecular motors and machines. This requires the construction of switchable molecules with (multiple) chiral elements in a highly enantioselective manner, which is often a significant synthetic challenge. Here, we show that the dimerization of an easily accessible enantiopure planar chiral ferrocene‐indanone building block affords a multi‐stimuli‐responsive dimer (FcD) with pre‐determined double bond geometry, helical chirality, and relative orientation of the two ferrocene motifs in high yield. This intrinsically planar chiral switch can not only undergo thermal or photochemical E/Z isomerization but can also be reversibly and quantitatively oxidized to both a monocationic and a dicationic state which is associated with significant changes in its (chir)optical properties. Specifically, FcD acts as a chiral dopant for cholesteric LCs with a helical twisting power (HTP) of 13 μm−1 which, upon oxidation, drops to near zero, resulting in an unprecedently large redox‐tuning of the LC reflection color by up to 84 nm. Due to the straightforward stereoselective synthesis, FcD, and related chiral switches, are envisioned to be powerful building blocks for multi‐stimuli‐responsive molecular machines and in LC‐based materials.

Superconducting transition of GdBa2Cu3O7-x/La0.7A0.3MnO3 (A=Sr and Ca) bilayers governed by tunable interlayer structural coupling

Bilayers composed of high-Tc cuprate superconductors (HTS) with manganites have garnered significant attention due to the complex interaction between two layers, leading to competition among various ordering phenomena. When HTS and manganties are interfaced, new functionalities can emerge that are absent in the individual components. Notably, epitaxial strain can alter crystal structures and electronic states, significantly impacting superconductivity in HTS/manganite heterostructures. In this study, we analyze the superconducting and ferromagnetic behaviors of GdBa2Cu3O7-x(GdBCO)/La0.7A0.3MnO3(LAMO, where A=Sr and Ca) bilayers, maintain a constant GdBCO thickness of 500 nm while varying the LAMO thickness from 25 to 100 nm. We focus on the local structural correlations between the two layers. Temperature-dependent EXAFS spectra were systematically measured at the Cu and Mn K-edges to investigate the local atomic structures of both layers across the superconducting transition temperature (Tc). Our spectroscopic measurements reveal distinct conformations of the MnO6 octahedra near Tc, which are absent in single-layer LSMO, indicating structural coupling between the layers. Additionally, our magnetization studies show a strong relationship between the structural coupling, magnetic anisotropy (MA), and the superconducting transition of the GdBCO/LAMO bilayers. The additional distortion of the MnO6 octahedra in the GdBCO/LAMO bilayer, likely stemming from structural coupling, may account for the changes in the superconducting transition associated with magnetic anisotropy. This modification of structural coupling can be controlled by adjusting the LAMO thickness, yet it remains highly dependent on the bond geometry of LAMO. The Mn-O bond in LCMO is stiffer than in LSMO, resulting in a smaller change in structural coupling with varying thickness in LCMO compared to LSMO. The disparity in structural coupling directly impacts the magnetic properties of the LAMO layer and subsequently influences the superconducting property ΔTc. Our findings highlight the significance of structural coupling as a critical factor affecting the superconductivity of GdBCO/LAMO bilayers. Furthermore, this study provide foundational insight for designing various applications, such as magnetic sensors and spintronic devices, by enhancing our understanding of local dynamics at the interface between ferromagnets and superconductors.

KOtBu Assisted Regio‐ and Stereo‐Selective Alkoxy‐Isomerization of Ortho‐Alkynyl Allylic Alcohols: Synthesis of Alkylidene Dihydroisobenzofurans and Indenones

AbstractA transition metal‐free synthesis of alkylidene dihydroisobenzofurans from the ortho‐alkynyl allylic alcohols is reported herein. Notably, a simple base tBuOK is utilized for the 5‐exo‐dig cyclization and double bond isomerization of ortho‐alkynyl allylic alcohols to furnish alkylidene dihydrobenzofurans with Z‐stereoselectivity under shorter reaction times. In addition, the geometry of the double bonds was confirmed by 1D Selective Gradient NOESY and 2D NMR (NOESY) analysis. Furthermore, the effectuality of the ortho‐alkynyl allylic alcohols has been shown by extending to the one‐pot synthesis of indanones via aqueous acid‐mediated hydrolysis (ring‐opening) of in‐situ formed dihydroisobenzofurans followed by intramolecular condensation reaction under acidic conditions

Strained single crystal high entropy oxide manganite thin films

The ability to accommodate multiple principal cations within a single crystallographic structure makes high entropy oxides (HEOs) ideal systems for exploring new composition–property relationships. In this work, the high-entropy design strategy is extended to strained single-crystal HEO-manganite (HEO-Mn) thin films. Phase-pure orthorhombic films of (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3 were deposited on three different single-crystal substrates: SrTiO3 (STO) (100), NdGaO3 (110), and LaAlO3 (LAO) (100), each inducing different degrees of epitaxial strain. Fully coherent growth of the thin films is observed in all cases, despite the high degree of lattice mismatch between HEO-Mn and LAO. Magnetometry measurements reveal distinct differences in the magnetic properties between epitaxially strained HEO-Mn thin films and their bulk crystalline HEO counterparts. In particular, the bulk polycrystalline HEO-Mn shows two magnetic transitions as opposed to a single one observed in epitaxial thin films. Moreover, the HEO-Mn film deposited on LAO exhibits a significant reduction in the Curie temperature, which is attributed to the strong variation of the in-plane lattice parameter along the thickness of the film and the resulting changes in the Mn–O–Mn bond geometry. Thus, this preliminary study demonstrates the potential of combining high entropy design with strain engineering to tailor the structure and functionality of perovskite manganites.

Recent Trends in Group 11 Hydrogen Bonding.

Conventional hydrogen bonding (H-bonding) has been extensively studied in organic and biological systems. However, its role in transition metal chemistry, particularly with Group 11 metals (i. e. Cu, Ag, Au) as hydrogen bond acceptors, remains relatively unexplored. Through a combination of experimental techniques, such as Nuclear Magnetic Resonance (NMR), Infrared spectroscopy (IR), X-Ray Diffraction (XRD), and computational calculations, several aspects of H-bonding interactions with Group 11 metals are examined, shedding light on its impact on structural motifs and reactivity. These include bond strengths, geometries, and effects on electronic structures. Understanding the intricacies of hydrogen bonding within transition metal chemistry holds promise for various applications, including catalytic transformations, the construction of molecular assemblies, synthesis of complexes displaying anticancer activities, or luminescence applications (e. g. Thermally Activated Delayed Fluorescence, TADF). This review encompasses the most significant recent advances, challenges, and future prospects in this emerging field.

Hydrogen incorporation mechanism in the lower-mantle bridgmanite

Abstract Bridgmanite, the most abundant mineral in the lower mantle, can play an essential role in deep-Earth hydrogen storage and circulation processes. To better evaluate the hydrogen storage capacity and its substitution mechanism in bridgmanite occurring in nature, we have synthesized high-quality single-crystal bridgmanite with a composition of (Mg0.88Fe0.052+Fe0.053+Al0.03)(Si0.88Al0.11H0.01)O3 at nearly water-saturated environments relevant to topmost lower mantle pressure and temperature conditions. The crystallographic site position of hydrogen in the synthetic (Fe,Al)-bearing bridgmanite is evaluated by a time-of-flight single-crystal neutron diffraction scheme, together with supporting evidence from polarized infrared spectroscopy. Analysis of the results shows that the primary hydrogen site has an OH bond direction nearly parallel to the crystallographic b axis of the orthorhombic bridgmanite lattice, where hydrogen is located along the line between two oxygen anions to form a straight geometry of covalent and hydrogen bonds. Our modeled results show that hydrogen is incorporated into the crystal structure via coupled substitution of Al3+ and H+ simultaneously exchanging for Si4+, which does not require any cation vacancy. The concentration of hydrogen evaluated by secondary-ion mass spectrometry and neutron diffraction is ~0.1 wt% H2O and consistent with each other, showing that neutron diffraction can be an alternative quantitative means for the characterization of trace amounts of hydrogen and its site occupancy in nominally anhydrous minerals.

Effect of arsenate and phosphate substitution on hydroxyl group in libethenite Cu2PO4OH - olivenite Cu2AsO4OH solid solution series

Libethenite and olivenite have been regarded as intriguing photocatalysts because of their singular structures. Copper hydroxy-phosphates and -arsenates exhibit distinctive properties: they incorporate bridging hydroxyl (OH) groups shared by neighboring copper atoms. In materials employed for photoelectrochemical applications, the significance of surface OH groups and OH-related defects frequently varies and is contingent upon the specific material system and the reaction under consideration. Hydroxyl groups can enhance photocatalytic performance by generating OH radicals or serving as crucial agents in catalytic reactions. Therefore, the presence of an OH group within the crystal structure of the material can give rise to potentially interesting behaviors. Seven compounds within the solid solution series of libethenite Cu2PO4OH and olivenite Cu2AsO4OH with stoichiometric ratio (Cu2(Px,As1- xO4)OH, x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1 were synthesized at 70 °C via aqueous solutions, and their properties were examined using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The effect of substituting (PO4)3– ions with (AsO4)3– ions on the alteration of the lattice parameters and spectral characteristics was elucidated by analyzing the correlation between the chemical composition and X-Ray diffraction peak positions. The substitution process leads to modifications in the unit cell parameters and volume. These isomorphic substitutions can be also discerned through alterations in the infrared and Raman spectra, which exhibit variations in the position and intensity of the bands corresponding to phosphates, arsenates, and hydroxyl ions. The incorporation of As into the solid solution resulted in altered bond lengths and geometries, which is consistent with the symmetry transition from orthorhombic libethenite to monoclinic olivenite. The variations in the unit cell parameters and the shifts in the peak position exhibited non-linear trends, and a discernible step was observed between the Cu2(P0·3As0.7)O4OH and Cu2(P0·5As0.5)O4OH intermediate phases. The findings of this study will prove beneficial in evaluating the feasibility of the libethenite-olivenite isometric series as a photocatalysts.

Elektrophile Aktivierung von S−Si‐Reagenzien mit Silyliumionen für deren regio‐ und diastereoselektive Addition an C−C‐Mehrfachbindungen

AbstractEs wird eine regioselektive silyliumionvermittelte Thiosilylierung von internen C−C‐Dreifachbindungen mit Kontrolle der Doppelbindungsgeometrie beschrieben. Im Zuge dieser Zweikomponentenreaktion eines Alkins und eines Thiosilans werden sowohl eine C(sp2)−S‐ als auch eine C(sp2)−Si‐Bindung mit einer trans‐Beziehung gebildet. Die hierdurch entstandene orthogonal funktionalisierte C−C‐Doppelbindung lässt sich chemoselektiv defunktionalisieren oder unter Erhalt der Alkenkonfiguration in Kreuzkupplungsreaktionen weiter umsetzen. Die Reaktionsvorschrift ist ebenfalls auf die regio‐ und diastereoselektive Thiosilylierung von terminalen Allenen anwendbar, was zu allylischen Thioethern, die eine Vinylsilaneinheit enthalten, führt. Diese Reaktionen beinhalten die elektrophile Aktivierung des S−Si‐Reagenzes, ein silyliertes Thiophenol und sogar Alkylthiolderivat, durch eine in situ erzeugte Carbokationzwischenstufe. Der Katalysecyclus wird durch ein bissilyliertes Aryl‐ oder Alkylsulfoniumion als ein Shuttle für das kationische Siliciumelektrophil aufrechterhalten. Dessen unabhängige Darstellung und strukturelle Charakterisierung durch Röntgenbeugung werden ebenfalls berichtet.

Electrophilic Activation of S-Si Reagents by Silylium Ions for Their Regio- and Diastereoselective Addition Across C-C Multiple Bonds.

A regioselective silylium-ion-promoted thiosilylation of internal C-C triple bonds with control over the double bond geometry is described. Both a C(sp2)-S and a C(sp2)-Si bond are formed with a trans relationship in this two-component reaction of an alkyne and a thiosilane. The resulting orthogonally functionalized C-C double bond can be chemoselectively defunctionalized or further processed by cross-coupling reactions with the alkene configuration retained. The procedure is also applicable to the regio- and diastereoselective thiosilylation of terminal allenes to arrive at allylic thioethers containing a vinylsilane unit. These reactions involve the electrophilic activation of the S-Si reagent, both a silylated thiophenol and even alkylthiol derivative, by an in situ-generated carbocation intermediate. The catalytic cycle is maintained by a bissilylated aryl- or alkylsulfonium ion as a shuttle for the cationic silicon electrophile. Its independent preparation and structural characterization by X-ray diffraction are also reported.

Hydrogen Bonding and Molecular Geometry in Isolated Hydrates of 2-Ethylthiazole Characterised by Microwave Spectroscopy.

Broadband microwave spectra of the isolated 2-ethylthiazole molecule, and complexes of 2-ethylthiazole⋅⋅⋅H2O and 2-ethylthiazole⋅⋅⋅(H2O)2 have been recorded by probing a gaseous sample containing low concentrations of 2-ethylthiazole and water within a carrier gas undergoing supersonic expansion. The identified conformer of the isolated 2-ethylthiazole molecule and the 2-ethylthiazole sub-unit within each of 2-ethylthiazole⋅⋅⋅H2O and 2-ethylthiazole⋅⋅⋅(H2O)2 have C1 symmetry. The angle that defines rotation of the ethyl group relative to the plane of the thiazole ring, ∠(S-C2-C6-C7), is -98.6(10)° within the isolated 2-ethylthiazole molecule. Analysis of molecular geometries and non-covalent interactions reveals each hydrate complex contains a non-linear primary, N⋅⋅⋅Hb-O, hydrogen bond between an O-H of H2O and the nitrogen atom while the O atom of the water molecule(s) interacts weakly with the ethyl group. The ∠(Hb⋅⋅⋅N-C2) parameter, which defines the position of the H2O molecule relative to the thiazole ring, is found to be significantly greater for 2-ethylthiazole⋅⋅⋅H2O than for thiazole⋅⋅⋅H2O. The distance between the O atoms is determined to be 2.894(21) Å within the dihydrate complex which is shorter than observed within the isolated water dimer. The primary hydrogen bond within 2-ethylthiazole⋅⋅⋅(H2O)2 is shorter and stronger than that in 2-ethylthiazole⋅⋅⋅H2O as a result of cooperative hydrogen bonding effects.

VCD spectra of chiral naphthalene-1-carboxamides in the solid-state

The VCD spectra of chiral 2,3-dihydro-1H-benzo[de]isoquinolin-1-one (8-substituted naphthalene-1-carboxamide, BIQ) were studied in KBr pellets. The X-ray diffractometry revealed that the Me, Ph, and pClPh BIQs crystalize in the monoclinic P21, while nBu, pMePh, and oMeOPh BIQs in the orthorhombic P212121 space group. Only the Me-BIQ crystal exhibits the presence of cyclic amide dimers, while the others contain chains of the amid group hydrogen bonds. For all BIQs, except pMePh, the most intense IR band in the 1750–1550 cm−1 region is located at ca. 1680 cm−1 and is accompanied by two weak ones at ca. 1618 and 1590 cm−1. For the pMePh derivative, four almost equally intense IR bands at 1662, 1639, 1614, and 1588 cm−1 are observed. This region of the IR spectra of BIQs, but pMePh, is well reproduced by calculations based on BIQ monomers. On the other hand, the complex IR pattern of pMePh is computationally reproduced when larger crystal fragments, like octamers, are considered. Registration of the VCD spectra enabled recognizing the complexity of IR contours at ca. 1680 cm−1 by the corresponding VCD motives. For (i) Me, Ph and pClPh (R)-enantiomers, two (+)(–) bands were distinguished and for (ii) nBu and pMePh ones, one VCD band with right-side asymmetry was found. For (iii) oMeOPh the VCD pattern cannot be unambiguously assigned. Thus, the VCD spectra in the ν(C=O) range diverse the studied compounds. Among the set of molecules, pMePh has exceptional crystal geometry. Therefore, its most intense ν(C=O) band position and shape can be connected with the geometry of the hydrogen bonds, interactions, and crystal packing. Interpretation of the VCD spectra is based on linear and packed BIQ octamers. This cluster model can reproduce the main features of the solid-state VCD of BIQs.

Monophasic coamorphous sulpiride: a leap in physicochemical attributes and dual inhibition of GlyT1 and P-glycoprotein, supported by experimental and computational insights

Study aimed to design and development of a supramolecular formulation of sulpiride (SUL) to enhance its solubility, dissolution and permeability by targeting a novel GlyT1 inhibition mechanism. SUL is commonly used to treat gastric and duodenal ulcers, migraine, anti-emetic, anti-depressive and anti-dyspeptic conditions. Additionally, Naringin (NARI) was incorporated as a co-former to enhance the drug’s intestinal permeability by targeting P-glycoprotein (P-gp) efflux inhibition. NARI, a flavonoid has diverse biological activities, including anti-apoptotic, anti-oxidant, and anti-inflammatory properties. This study aims to design and develop a supramolecular formulation of SUL with NARI to enhance its solubility, dissolution, and permeability by targeting a novel GlyT1 inhibition mechanism, extensive experimental characterization was performed using solid-state experimental techniques in conjunction with a computational approach. This approach included quantum mechanics-based molecular dynamics (MD) simulation and density functional theory (DFT) studies to investigate intermolecular interactions, phase transformation and various electronic structure-based properties. The findings of the miscibility study, radial distribution function (RDF) analysis, quantitative simulations of hydrogen/π–π bond interactions and geometry optimization aided in comprehending the coamorphization aspects of SUL-NARI Supramolecular systems. Molecular docking and MD simulation were performed for detailed binding affinity assessment and target validation. The solubility, dissolution and ex-vivo permeability studies demonstrated significant improvements with 31.88-fold, 9.13-fold and 1.83-fold increments, respectively. Furthermore, biological assessments revealed superior neuroprotective effects in the SUL-NARI coamorphous system compared to pure SUL. In conclusion, this study highlights the advantages of a drug-nutraceutical supramolecular formulation for improving the solubility and permeability of SUL, targeting novel schizophrenia treatment approaches through combined computational and experimental analyses. Communicated by Ramaswamy H. Sarma

Liquid Structure and Hydrogen Bonding in Aqueous Hydroxylammonium Nitrate.

Hydroxylammonium nitrate (HAN) has emerged as a promising component in ionic liquid-based spacecraft propellants. However, the physicochemical and structural properties of aqueous HAN have been largely overlooked. The purpose of this study is to investigate the hydrogen bonding in aqueous HAN and understand its implications on these properties and the proton transfer mechanism as a function of concentration. Classical polarizable molecular dynamics simulations have been employed with the APPLE&P force field to analyze the geometry of individual hydrogen bonds and the overall hydrogen-bonding network in various concentrations of aqueous HAN. Radial distribution functions (RDFs) and spatial distribution functions (SDFs) indicate the structural arrangement of the species and their hydrogen bonds. Projections of water density and the orientation of its electric dipole moment near the ions provide insight into the hydrogen-bonding network. The incorporation of water into the hydrogen-bonding network at high ion concentrations occurs via interstitial accommodation around the ions immediately outside the first solvation shell. While ion pairs are observed at all concentrations considered, the frequency of Ha···On hydrogen bonds increases substantially with the ion concentration. The findings contribute to a better fundamental understanding of HAN and the precursors of reactivity, crucial to the development of "green" spacecraft propellants.

Optimized adhesive application

In the manufacturing industry, the process of applying adhesive to join two substrates can be challenging. It requires precise placement of adhesive so that it is distributed in the desired pattern, ensuring a strong bond between the substrates. Overfilling is a common practice to ensure that the bond is not underfilled after the substrates are pressed together. However, this approach leads to unnecessary adhesive waste and can result in additional cleaning work. To address these issues, an optimization algorithm has been developed that can compute an initial adhesive pattern to flow into any desired geometry. The algorithm is based on a transient squeeze flow simulation, which iteratively removes fluid material as it flows out of the target bond domain. For example, to obtain a square bond geometry after a parallel squeezing process, the adhesive needs to be initially applied in a star shape. However, the algorithm is highly adaptable and can be used for many desired bond geometries as shown in this paper. The results are independent of the mesh resolution and fluid flow law, thus eliminating the need for complex rheological fluid characterization. The algorithm requires only two input parameters, namely the target bond geometry and the degree of compression. This highly simplifies the adaption of the proposed optimization method for manufacturers, and their design requirements can be considered with ease. The results are reliable and consistent despite the simulation’s complexity. Overall, this new optimization methodology represents a significant advance in adhesive application technology, eliminating the need of overfilling and thus making the manufacturing process more efficient, sustainable and cost-effective.

The diradicaloid electronic structure of dialumenes: a benchmark study at the Full-CI limit.

Multiply-bonded main group compounds of groups 13-15 are attracting significant interest not only because they provide fundamental insight into the nature of metal-metal bonding, but also for their potential in small molecule bond activation and catalysis. This includes dialumenes, neutral Al(I) compounds that contain AlAl double bonds, which display high reactivity owing to their intrinsic diradicaloid character. The electronic structure of the simplest dialumene, Al2H2, is here analyzed up to a practical Full-CI limit using DMRG and selected CI methods for the bond dissociation energy (BDE), geometry and properties of the electron density (difference density, ELF). Acquiring Full-CI reference values for the simplest dialumene (but possessing the highest diradical character) allows for a rigorous benchmarking of simpler correlated wavefunction theory (WFT) methods and density functional methods in treating the electronic structure of such systems. Single-reference coupled cluster theory using a RHF reference is found to reliably converge to the Full-CI limit and CCSD(T) is fully capable of capturing the diradical character, while multi-reference methods offer no clear advantages. Density functional methods struggle to fully describe the electronic structure complexity although non-hybrid functionals such as TPSS come close. Solving the inverse Kohn-Sham problem for a Full-CI-quality density revealed minimal density-driven errors in the TPSS-calculated BDE unlike high-percentage hybrids such as M06-2X. No density functional, however, predicts accurate relative energies. Fractional-occupation density plots at the TPSS level correlate well with WFT-based diradical character metrics, a useful result for determining diradical character in larger systems.

Fatty acid isomerism: analysis and selected biological functions.

The biological functions of fatty acids and the lipids in which they are esterified are determined by their chain length, double bond position and geometry and other structural motifs such as the presence of methyl branches. Unusual isomeric features in fatty acids of human foods such as conjugated double bonds or chain branching found in dairy products, some seeds and nuts, and marine foods potentially have important effects on human health. Recent advancements in identifying fatty acids with unusual double bond positions and pinpointing the position of methyl branches have empowered the study of their biological functions. We present recent advances in fatty acid structural elucidation by mass spectrometry in comparison with the more traditional methods. The double bond position can be determined by purely instrumental methods, specifically solvent-mediated covalent adduct chemical ionization (SM-CACI) and ozone induced dissociation (OzID), with charge inversion methods showing promise. Prior derivatization using the Paternò-Büchi (PB) reaction to yield stable structures that, upon collisional activation, yield the double bond position has emerged. The chemical ionization (CI) based three ion monitoring (MRM) method has been developed to simultaneously identify and quantify low-level branched chain fatty acids (BCFAs), unattainable by electron ionization (EI) based methods. Accurate identification and quantification of unusual fatty acid isomers has led to research progress in the discovery of biomarkers for cancer, diabetes, nonalcoholic fatty liver disease (NAFLD) and atherosclerosis. Modulation of eicosanoids, weight loss and the health significance of BCFAs are also presented. This review clearly shows that the improvement of analytical capacity is critical in the study of fatty acid biological functions, and stronger coupling of the methods discussed here with fatty acid mechanistic research is promising in generating more refined outcomes.

Conformational Studies of β-Azapeptoid Foldamers: A New Class of Peptidomimetics with Confined Dihedrals.

Controlling amide bond geometries and the secondary structures of β-peptoids is a challenging task as they contain several rotatable single bonds in their backbone. Herein, we describe the synthesis and conformational properties of novel "β-azapeptoids" with confined dihedrals. We discuss how the acylhydrazide sidechains in these molecules enforce trans amide geometries (ω ~180°) via steric and stereoelectronic effects. We also show that the Θ(Cα -Cβ ) and Ψ(OC-Cα ) backbone torsions of β-azapeptoids occupy a narrow range (170-180°) that can be rationalized by the staggered conformational preference of the backbone methylene carbons and a novel backbone nO →σ*Cβ-N interaction discovered in this study. However, the ϕ (Cβ -N) torsion remains freely rotatable and, depending on ϕ, the sidechains can be parallel, perpendicular, and anti-parallel relative to each other. In fact, we observed parallel and perpendicular relative orientations of sidechains in the crystal geometries of β-azapeptoid dimers. We show that ϕ of β-azapeptoids can be controlled by incorporating a bulky substituent at the backbone β-carbon, which could provide complete control over all the backbone dihedrals. Finally, we show that the ϕ and Ψ dihedrals of β-azapeptoids resemble that of a PPII helix and they retain PPII structure when incorporated in Host-guest proline peptides.

A novel approach to alloy-based bonding for piezoelectric sensor integrated in impedance-based structural health monitoring

ABSTRACT Structural health monitoring aided with the electromechanical impedance technique (EMI) is gaining popularity among researchers due to its dual sensing application and noise-free sensor results, and it is very sensitive to inceptive structural alternation. A thin coat of adhesive permanently bonds the piezoelectric transducers to the host structure. The bonding layers effect the mechanical interaction between the structure and the piezoelectric material as they act as a pure shear connector. Furthermore, the presence of shear alters the actuation and sensing capability of the PZT (Piezoelectric Transducer) patch, hence the efficiency of EMI technique. In this paper, a novel alloy (Sn-Ag) based bond is introduced for sensor integration and studied for bond behaviour in order to improve the bond’s quality in the EMI approach for structural health monitoring. The first part of experiment deals bond geometry degradation deals with the effect of disbond towards impedance-based coupled signature. The last part of experiment focuses on bond exposure to environmental degradation and it’s durability. From the experimental results, it is found that the Sn-Ag alloy-based bond formed between the structure and the piezoelectric transducer with the help of thermos-activated process is extremely strong and establishes a unique bond layer connection to the structure, which has a more resistive capacity towards moisture, chemical, and also temperature, compared with the epoxy-based bond.

Bandgap Pressure Coefficient of a CH3NH3PbI3 Thin Film Perovskite.

Recent scientific interest in examining the bandgap evolution of a MAPbI3 hybrid perovskite by applying hydrostatic pressure has mostly focused on a room-temperature tetragonal phase. In contrast, the pressure response of a low-temperature orthorhombic phase (OP) of MAPbI3 has not been explored and understood. In this research, we investigate for the first time how hydrostatic pressure alters the electronic landscape of the OP of MAPbI3. Pressure studies using photoluminescence combined with calculations within density functional theory at zero temperature allowed us to identify the main physical factors affecting the bandgap evolution of the OP of MAPbI3. The negative bandgap pressure coefficient was found to be strongly dependent on the temperature (α120K = -13.3 ± 0.1 meV/GPa, α80K = -29.8 ± 0.1 meV/GPa, and α40K = -36.3 ± 0.1 meV/GPa). Such dependence is related to the changes in the Pb-I bond length and geometry in the unit cell as the atomic configuration approaches the phase transition as well as the increasing phonon contribution to octahedral tilting as the temperature increases.