Unprecedented Structural Features Research Articles

Cage-like Cu5Cs4-Phenylsilsesquioxanes: Synthesis, Supramolecular Structures, and Catalytic Activity.

A small family of nonanuclear Cu5Cs4-based phenylsilsesquioxanes 1-2 were prepared by a convenient self-assembly approach and characterized by X-ray diffraction studies. The compounds 1 and 2 show some unprecedented structural features such as the presence of a [Ph14Si14O28]14- silsesquioxane ligand and a CuII5CsI4 nuclearity in which the metal cations occupy unusual positions within the cluster. Copper ions are "wrapped" into a silsesquioxane matrix, while cesium ions are located in external positions. This resulted in cesium-involved aggregation of coordination polymer structures. Both compounds 1 and 2 realize specific metallocene (cesium-phenyl) linkage between neighboring cages. Compound 2 is evaluated as a catalyst in the Baeyer-Villiger (B-V) oxidation of cyclohexanone and tandem cyclohexane oxidation/B-V oxidation of cyclohexanone with m-chloroperoxybenzoic acid (mCPBA) as an oxidant, in an aqueous acetonitrile medium, and HNO3 as the promoter. A quantitative yield of ε-caprolactone was achieved under conventional heating at 50 °C for 4 h or MW irradiation for 30 min (for cyclohexanone as substrate); 17 and 19% yields of lactone upon MW irradiation at 80 °C for 30 min and heating at 50 °C for 4 h, respectively (for cyclohexane as a substrate), were achieved. Complex 2 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with peroxides at 60 °C in acetonitrile. The maximum yield of cyclohexane oxidation products was 30%. Complex 2 exhibits high activity in the oxidation of alcohols.

Development of On-DNA Thiophene Synthesis for DEL Construction.

Thiophene and its substituted derivatives are a highly important class of heterocyclic compounds, with noteworthy applications in pharmaceutical ingredients. In this study, we leverage the unique reactivity of alkynes to generate thiophenes on-DNA, using a cascade iodination, Cadiot-Chodkiewicz coupling and heterocyclization. This approach, tackling on-DNA thiophene synthesis for the first time, generates diverse, and unprecedented structural and chemical features, which could be significant motifs in DEL screening as molecular recognition agents for drug discovery.

Bismuth-Based Metal Clusters─From Molecular Aesthetics to Contemporary Materials Science.

ConspectusBismuth-based research has become a highly topical field in recent years, yielding remarkable prospects for new fundamental insights and new materials applications, ranging from innovative catalysts to novel pharmaceuticals, due to this heavy metal's virtually nonradioactive and nontoxic properties. Given that the 6s2 electron pair can be stereochemically active under certain circumstances, bismuth atoms adopt a variety of coordination modes and bonding environments with oxidation states ranging from (formally) +V to -III. As a consequence, bismuth-based compounds cover the entire spectrum from simple coordination compounds to much more unusual cluster cations and cluster anions exhibiting metal-metal bonding in a homoatomic manner, or in concert with other s-, d-, p-, or f-block metal atoms. Such bismuth clusters show high potential for the development of new bismuth-based materials, but they are also interesting objects by themselves. Given the relatively recent development of bismuth-rich cluster molecules, a deep understanding of their properties─including unprecedented structural features, complex electronic structures, substantial heavy metal aromaticity, as well as their formation pathways─is still in its infancy. The topic thus spans a broad range from highly sophisticated synthetic chemistry through interdisciplinary experimental and theoretical analyses to materials science.Based on our recent work and several notable reports from other groups, this article will highlight the successful access to a number of novel bismuth-rich cluster ions emerging from both solution-based approaches and solid-state chemistry. It will shed light on the unique structural and electronic properties that cause chemical and physical peculiarities of such compounds. Selected examples include, but are not limited to, (1) the first encapsulation of actinide ions in intermetalloid clusters which additionally served to manifest substantial all-metal π-aromaticity with a (calculated) record ring current per electron; (2) a large metalloid {Zn12} unit stabilized in a porphine-related {Zn8Bi16} moiety in [K2Zn20Bi16]6-; (3) the largest assembly of bismuth atoms within one molecule, observed in [{Ru(cod)}4Bi18]4- that consists of two Bi-Bi-linked "[{Ru(cod)}2Bi9]2-" subunits.Notably, cluster growth has remained largely a black box, which is starting to be revealed, however. We discuss possible formation pathways of such (multi)metallic nanoarchitectures on the basis of smaller subunits that were detected by mass spectrometric analyses and could also be captured upon reaction with organometallic complexes. In addition to the intrinsic structural and electronic properties of the cluster anions and cluster cations reviewed herein, we will briefly introduce the emerging usage of bismuth-based compounds in material science and give an outlook to future developments.

On-DNA Alkyne Iodination and Acetylenic Coupling as a Useful Tool for DEL Synthesis.

1-Iodoalkynes and 1,3-diynes are versatile chemical intermediates and pharmaceutically valuable ingredients. In this study, copper mediated on-DNA alkyne iodination and Cadiot-Chodkiewicz coupling are developed for the first time. This generates diverse, systematic, and unprecedented topographic structural features, which could be invaluable as molecular recognition agents for drug discovery in DEL screening.

Penicillactonin and preaustinoid C, lactone-containing metabolites from a hot spring sediment Penicillium sp.

Phytochemical investigation of Penicillium sp. RO-11 strain, collected from the sediments of a hydrothermal spring located in the southwestern area of Saudi Arabia, afforded, along with previously isolated compounds, the undescribed polyketides penicillactonin (1), penipyranicin D (4) and isopyrenulin B (5) and the undescribed meroterpenoid preaustinoid C (7). The structures of these compounds were elucidated based on data from mass spectrometry, 1D and 2D NMR, and comparison between experimental and calculated ECD spectra. Penicillactonin and preaustinoid C bring unprecedented structural features, for which a biosynthetic rationale is proposed, further extending the chemodiversity associated to Penicillium fungi. Preaustinoid C showed significant activity against LPS-induced NO production and selective effect on IL-2 and IFN-γ gene regulation in activated Jurkat cells.

Euphocactoside, a New Megastigmane Glycoside from Euphorbia cactus Growing in Saudi Arabia.

A phytochemical investigation of the aerial parts of Euphorbia cactus Ehrenb. ex Boiss. revealed a new megastigmane, euphocactoside (5), along with eleven known metabolites. Euphocactoside (5) is the 3-O-glucoside derivative of a polyhydroxylated megastigmane showing unprecedented structural features. The structure of euphocactoside, including stereochemical details, was elucidated by extensive spectroscopic analysis based on 1D and 2D nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HR-ESIMS). The isolated compounds were evaluated for their cytotoxic activity against three different human cancer cell lines, namely, A549 (lung), LoVo (colon), and MCF-7 (breast), using MTT assay, and moderate to marginal activities were observed for compounds 1–3, 8 and 9 against all three cell lines.

PIN and CCCH Zn-finger domains coordinate RNA targeting in ZC3H12 family endoribonucleases.

The CCCH-type zinc finger (ZnF) containing ZC3H12 ribonucleases are crucial in post-transcriptional immune homoeostasis with ZC3H12A being the only structurally studied member of the family. In this study, we present a structural-biochemical characterization of ZC3H12C, which is linked with chronic immune disorders like psoriasis. We established that the RNA substrate is cooperatively recognized by the PIN and ZnF domains of ZC3H12C and analyzed the crystal structure of ZC3H12C bound to a single-stranded RNA substrate. The RNA engages in hydrogen-bonded contacts and stacking interactions with the PIN and ZnF domains simultaneously. The ZC3H12 ZnF shows unprecedented structural features not previously observed in any member of the CCCH-ZnF family and utilizes stacking interactions via a unique combination of spatially conserved aromatic residues to align the target transcript in a bent conformation onto the ZnF scaffold. Further comparative structural analysis of ZC3H12 CCCH-ZnF suggests that a trinucleotide sequence is recognized by ZC3H12 ZnF in target RNA. Our work not only describes the initial structure-biochemical study on ZC3H12C, but also provides the first molecular insight into RNA recognition by a ZC3H12 family member. Finally, our work points to an evolutionary code for RNA recognition adopted by CCCH-type ZnF proteins.

The Structural Difference of Isobaric N-Glycans of Two Microalgae Samples Reveals Taxonomic Distance.

Microalgae of the Chlorella clade are extensively investigated as an environmentally friendly source of renewable biofuels and high-value nutrients. In addition, essentially unprocessed Chlorella serves as wholesome food additive. A recent study on 80 commercial Chlorella preparations revealed an unexpected variety of protein-linked N-glycan patterns with unprecedented structural features, such as the occurrence of arabinose. Two groups of products exhibited a characteristic major N-glycan isobaric to the Man2GlcNAc2XylFuc N-glycan known from pineapple stem bromelain, but tandem mass spectrometry (MS/MS) analysis pointed at two types of N-glycan different from the bromelain structure, as well as from each other. Here we report the exact structures of these two novel N-glycan structures, elucidated by nuclear magnetic resonance spectroscopy and MS/MS, as well as on their phylogenetic context. Despite their humble size, these two N-glycans exhibited a very different design with structural features unrelated to those recently described for other Chlorella-clade strains. The major glycans of this study presented several novel structural features such as substitution by arabinose or xylose of the internal N-acetylglucosamine, as well as methylated sugars. ITS1-5.8S-ITS2 rDNA barcode analyses revealed that the xylose-containing structure derived from a product primarily comprising Scenedesmus species, and the arabinose-containing glycan type related to Chlorella species (SAG211-34 and FACHB-31) and to Auxenochlorella. This is another example where characteristic N-glycan structures distinguish phylogenetically different groups of microalgae.

Pb18 O8 Cl15 I5 : A Polar Lead Mixed Oxyhalide with Unprecedented Architecture and Excellent Infrared Nonlinear Optical Properties.

To develop high-performance nonlinear optical (NLO) materials for infrared (IR) applications, we have applied a rational element-composition design strategy and investigated the unexplored PbO-PbCl2 -PbI2 system. By doing so, we discovered a new polar lead mixed oxyhalide, Pb18 O8 Cl15 I5 , the first synthetic metal oxyhalide combining both Cl- and I- . Pb18 O8 Cl15 I5 reveals an unprecedented structural feature with two different dimensional types of oxocentered Pb-O units, namely, [O4 Pb8 ]8+ clusters and [OPb2 ]2+ chains. Centimeter-sized single crystals of Pb18 O8 Cl15 I5 have been successfully grown under ambient conditions. Remarkably, Pb18 O8 Cl15 I5 satisfies all fundamental yet rigorous criteria for high-performance IR NLO materials, exhibiting the widest IR transparency (up to 16.0 μm) among oxide-based crystals, strong second-harmonic generation response (1.05×AgGaS2 ), superior birefringence (0.086 at 636 nm), and a high laser-induced damage threshold (8.5×AgGaS2 ).

Pb18O8Cl15I5: A Polar Lead Mixed Oxyhalide with Unprecedented Architecture and Excellent Infrared Nonlinear Optical Properties

AbstractTo develop high‐performance nonlinear optical (NLO) materials for infrared (IR) applications, we have applied a rational element‐composition design strategy and investigated the unexplored PbO–PbCl2–PbI2 system. By doing so, we discovered a new polar lead mixed oxyhalide, Pb18O8Cl15I5, the first synthetic metal oxyhalide combining both Cl− and I−. Pb18O8Cl15I5 reveals an unprecedented structural feature with two different dimensional types of oxocentered Pb–O units, namely, [O4Pb8]8+ clusters and [OPb2]2+ chains. Centimeter‐sized single crystals of Pb18O8Cl15I5 have been successfully grown under ambient conditions. Remarkably, Pb18O8Cl15I5 satisfies all fundamental yet rigorous criteria for high‐performance IR NLO materials, exhibiting the widest IR transparency (up to 16.0 μm) among oxide‐based crystals, strong second‐harmonic generation response (1.05×AgGaS2), superior birefringence (0.086 at 636 nm), and a high laser‐induced damage threshold (8.5×AgGaS2).

Versatile {Cp2Ti} Grafted Hetero-Polyoxotungstate Clusters: Synthesis, Crystal Structure, and Photocurrent Properties.

Polyoxotungstate supported titanocene {Cp2Ti}2+ clusters H6{K8(Cp2Ti)2P4W24O88(PO4)2}·14H2O (1), H6[Na2P4W14O58(Cp2Ti)2]·12H2O (2), and H2[K6{Cp2Ti}{PW9O33(WO2)}2{NC5H3(COOK)2}(NC5H3(CH3)COOK)·22H2O] (3) have been synthesized, and their single crystal X-ray structures have revealed unprecedented and intriguing structural features. The synthesized compounds have been characterized by various spectroscopic techniques including UV-vis, cyclic voltammogram, NMR, ESI-MS, and inductive coupled plasma spectroscopy (ICP) in solution and also by IR, TGA, and diffuse reflectance in the solid state. Clusters 1 and 2 are rare examples of lacunary POM supported titanocene clusters obtained by incorporating various phosphorus heteroatoms to form elusive phosphotungstate assemblies, whereas 3 is an unprecedented organometallic as well as heteroleptic pyridyl functionalized POM. Clusters 1-3 show transient photocurrent ON/OFF behavior upon UV-light irradiation and also exhibit characteristic TiIV/III intravalence electron transfer. This behavior is also established by their cyclic voltammograms in mixed phosphate buffers (Na2HPO4/NaH2PO4) which show the evidence of POM supported {Cp2Ti}2+/+ species in their redox solution. Furthermore, ESR line broadening is also observed in these clusters at room temperature, a fact which also confirms the formation of partially reduced/oxidized {Cp2Ti}2+/+ species leading to TiIV/III intravalence electron transfers within all three clusters. The {Cp2Ti}2+ decorated polyoxometalate cluster 3 shows improved transient photocurrent behavior which may be due to the presence of pyridyl carboxyl ions which provide better surface contact for the cluster molecule through the carboxylate moiety to the ITO electrode.

Computational Tools for Discovering and Engineering Natural Product Biosynthetic Pathways.

Natural products (NPs), also known as secondary metabolites, are produced in bacteria, fungi, and plants. NPs represent a rich source of antibacterial, antifungal, and anticancer agents. Recent advances in DNA sequencing technologies and bioinformatics unveiled nature's great potential for synthesizing numerous NPs that may confer unprecedented structural and biological features. However, discovering novel bioactive NPs by genome mining remains a challenge. Moreover, even with interesting bioactivity, the low productivity of many NPs significantly limits their practical applications. Here we discuss the progress in developing bioinformatics tools for efficient discovery of bioactive NPs. In addition, we highlight computational methods for optimizing the productivity of NPs of pharmaceutical importance.

Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features

Natural hazard prediction and efficient crust exploration require dense seismic observations both in time and space. Seismological techniques provide ground-motion data, whose accuracy depends on sensor characteristics and spatial distribution. Here we demonstrate that dynamic strain determination is possible with conventional fibre-optic cables deployed for telecommunication. Extending recently distributed acoustic sensing (DAS) studies, we present high resolution spatially un-aliased broadband strain data. We recorded seismic signals from natural and man-made sources with 4-m spacing along a 15-km-long fibre-optic cable layout on Reykjanes Peninsula, SW-Iceland. We identify with unprecedented resolution structural features such as normal faults and volcanic dykes in the Reykjanes Oblique Rift, allowing us to infer new dynamic fault processes. Conventional seismometer recordings, acquired simultaneously, validate the spectral amplitude DAS response between 0.1 and 100 Hz bandwidth. We suggest that the networks of fibre-optic telecommunication lines worldwide could be used as seismometers opening a new window for Earth hazard assessment and exploration.

Double Salts and Mixed Crystals of Tellurium Clusters Te42+/Te82+ and TeCl3+ Ions with Anions based on Molybdenum and Zirconium (Oxy)chlorides

The reaction of elemental tellurium, tellurium tetrachloride, zirconium tetrachloride, and molybdenum oxytetrachloride yields black plate‐like crystals of Te4[MoZr2O2Cl11] (1) and yellow crystals of (TeCl3)2[Mo2O2Cl8]x[Zr2Cl10]1–x (2). Using molybdenum oxytrichloride instead of the oxytetrachloride, black crystals of (Te4)2[Mo2O2Cl8][ZrCl6] (3), Te8[ZrCl6] (4), and bronze‐colored crystals of Te4[ZrCl6] (5) are obtained. All obtained crystals are air‐sensitive and were characterized by single‐crystal X‐ray diffraction and energy‐dispersive X‐ray fluorescence spectroscopy. 1 contains a layered polymeric anion of unprecedented structural features with zirconium atoms coordinated in a pentagonal bipyramidal ZrO3Cl4 and ZrOCl6 environment. Magnetic susceptibility data of 1 and 2 show nearly ideal paramagnetic behavior according to the Curie law with magnetic moments of 1.55(7) μB for 1 and 1.66(6) μB for 2 indicating the presence of magnetically isolated d1 configured MoV. The double salt 3 adopts the structure type of the selenium containing congener (Se4)2[Mo2O2Cl8][ZrCl6], 4 and 5 are isotypic to the respective hafnium containing representatives Te4[HfCl6] and Te8[HfCl6].

The Rhazinilam-Leuconoxine-Mersicarpine Triad of Monoterpenoid Indole Alkaloids.

The rhazinilam-leuconoxine-mersicarpine triad of monoterpenoid indole alkaloids comprises a variety of diverse natural products with unprecedented structural features and intriguing biological activities. This subfamily of Aspidosperma alkaloids has drawn significant attention from the synthetic community which is reflected by over 20 syntheses within the last 5years. Numerous transformations and strategies have been developed to access the different key structural motifs such as the tetrahydroindolizine, α,β-unsaturated carbinolamide, diaza[5.5.6.6]fenestrane, and tetrahydro-2H-azepine frameworks. The present contribution comprehensively covers the abundant literature on this natural product class up to the end of May 2016, providing a detailed account of the formal and total syntheses which is complemented by an overview of their biosynthesis, spectroscopy, and pharmacology.

β‐Ag3RuO4, a Ruthenate(V) Featuring Spin Tetramers on a Two‐Dimensional Trigonal Lattice

AbstractOpen‐shell solids exhibit a plethora of intriguing physical phenomena that arise from a complex interplay of charge, spin, orbital, and spin‐state degrees of freedom. Comprehending these phenomena is an indispensable prerequisite for developing improved functional materials. This type of understanding can be achieved, on the one hand, by experimental and theoretical investigations into known systems, or by synthesizing new solids displaying unprecedented structural and/or electronic features. β‐Ag3RuO4 may serve as such a model system because it possesses a remarkable anionic structure, consisting of tetrameric polyoxoanions (Ru4O16)12−, and is an embedded fragment of a 2D trigonal MO2 lattice. The notorious frustration of antiferromagnetic (AF) exchange couplings on such lattices is thus lifted, and instead strong AF occurs within the oligomeric anion, where only one exchange path remains frustrated among the relevant six. The strong magnetic anisotropy of the [Ru4O16]12− ion, and the effectively orbital nature of its net magnetic moment, implies that this anion may reveal the properties of a single‐molecule magnet if well‐diluted in a diamagnetic matrix.

β-Ag3 RuO4, a Ruthenate(V) Featuring Spin Tetramers on a Two-Dimensional Trigonal Lattice.

Open-shell solids exhibit a plethora of intriguing physical phenomena that arise from a complex interplay of charge, spin, orbital, and spin-state degrees of freedom. Comprehending these phenomena is an indispensable prerequisite for developing improved functional materials. This type of understanding can be achieved, on the one hand, by experimental and theoretical investigations into known systems, or by synthesizing new solids displaying unprecedented structural and/or electronic features. β-Ag3 RuO4 may serve as such a model system because it possesses a remarkable anionic structure, consisting of tetrameric polyoxoanions (Ru4 O16 )(12-) , and is an embedded fragment of a 2D trigonal MO2 lattice. The notorious frustration of antiferromagnetic (AF) exchange couplings on such lattices is thus lifted, and instead strong AF occurs within the oligomeric anion, where only one exchange path remains frustrated among the relevant six. The strong magnetic anisotropy of the [Ru4 O16 ](12-) ion, and the effectively orbital nature of its net magnetic moment, implies that this anion may reveal the properties of a single-molecule magnet if well-diluted in a diamagnetic matrix.

ChemInform Abstract: Mesoporous Materials: Versatile Supports in Heterogeneous Catalysis for Liquid Phase Catalytic Transformations

AbstractReview: 158 refs.

Combined Experimental and Theoretical Investigation of Ligand and Anion Controlled Complex Formation with Unprecedented Structural Features and Photoluminescence Properties of Zinc(II) Complexes

By using two potential tridentate ligands, HL1 [4-chloro-2-[(2-morpholin-4-yl-ethylimino)-methyl]-phenol] and HL2 [4-chloro-2-[(3-morpholin-4-yl-propylimino)-methyl]-phenol], which differ by one methylene group in the alkyl chain, four new ZnII complexes, namely, [Zn(L2H)2](ClO4)2 (1), [Zn(L1)(H2O)2][Zn(L1)(SCN)2] (2), [Zn(L1)(dca)]n (3), and [Zn2(L1)2(N3)2(H2O)2] (4) [where dca = dicyanamide anion] were synthesized and structurally characterized. The results indicate that the slight structural difference between the ligands, HL1 and HL2, because of the one methylene group connecting the nitrogen atoms provokes a chemical behavior completely different from what was expected. Any attempt to isolate the Zn(L2) complexes with thiocyanato, dicyanamido, and azide was unsuccessful, and perchlorate complex 1 was always obtained. In contrast, with HL1 we obtained structural diversity on varying the anions, but we failed to isolate the analogous perchlorate complex of HL1. Single-crystal X-ray analyses revealed th...

ChemInform Abstract: Porous Materials in Catalysis: Challenges for Mesoporous Materials

AbstractReview: 134 refs.