7 Vavilova Ulitsa, Moscow
Directly accessible 8-substituted tetrahydroquinolines undergo 1,5-hydride shift-triggered cyclization to provide hardly accessible julolidine derivatives in 20-98% yield under scandium (III) triflate catalysis. The scope of the reaction, several follow-up transformations and a remarkable side-process discovered during the conditions optimization are highlighted.
A series of mononuclear aryl-substituted cyclopentadienyl complexes [CpPh3LnCl2(Me3tach)] (Ln = Tb (4), Ln = Nd
(5)), [CpPh2ArTbCl2(Me3tach)] (6), and [CpPh3LnCl2(Me3tacn)] (Ln = Tb (7), Ln = Nd (8), CpPh3: 1,2,4-triphenylcyclopentadienyl, CpPh2Ar: 1,2-diphenyl-4-(o-methoxyphenyl)cyclopentadienyl, Me3tach: 1,3,5-trimethyl-1,3,5-triazacyclohexane, Me3tacn: 1,4,7-trimethyl-1,4,7-triazacyclononane) have been synthesized from polynuclear precursors, using cyclic tridentate nitrogen-based ligands to prevent formation of ate complexes. All the obtained complexes have been studied by X-ray crystallography. Photophysical properties of the complexes have been investigated by optical spectroscopy, and all complexes exhibit luminescence in the nearinfrared (Nd) and visible (Tb) regions. The total quantum yield of photoluminescence for complex 4 is 50%. Complexes 5 and 8 in combination with Bu2Mg have been used in the polymerization of ethylene.
Rapid development in the area of cellulose biomass conversion to furanic platform chemicals has led to expectations of their valuable practical use. Impressive research progress in this direction has resulted in several achievements but at the same time identified a key challenge—the necessity to produce aromatic compounds. In this perspective, we analyze the current stage of development of the furanics-to-benzene conversion process (F2B process) in connection with a bioderived route to aromatic compounds. Cycloaddition reactions between bioderived C6-furans as diene components and alkene/alkyne units are discussed in detail, followed by considering the subsequent aromatization reaction. Progress in the development of the F2B process and future challenges are outlined in this perspective. The key role of the F2B process in the overall biomass to aromatics transformation is discussed in view of the implementation of carbon neutral sustainable technologies in practice.
A new family of protic ammonium ionic liquids (ILs) with various inorganic anions was synthesized from bio-derived 5-HMF. Starting with cellulose biomass, a complete preservation of the C6 unit was achieved throughout the synthetic sequence (no carbon loss). Evaluation of green metrics showed a significant advantage of the developed bio-derived pathway to access ILs from a natural renewable source, depending on feasible routes to 5-HMF manufacturing. The reduced number of synthetic steps and availability of the starting materials were the key advantages. Experimental physicochemical and biological studies, as well as computational modeling revealed a unique multifunctional intrinsic organization of these bio-derived ILs. The nature of interactions between the cations and anions of the novel ILs was mapped at the molecular level. The substituents in the cationic core and the nature of the original building blocks had a prominent impact on cytotoxicity of the novel ILs. The obtained results suggest possible sustainable applications of the least toxic ILs, while the regulation of biological activity of the ILs via the corresponding structural adjustments can find biological and medicinal applications. The 5-HMF-derived IL with a sulfate anion demonstrated potentially useful properties in dissolution of microcrystalline cellulose.
We report the accomplishment of the first stage of the development of a novel manually curated database on glycosyltransferase (GT) activities, CSDB_GT. CSDB_GT (http://csdb.glycoscience.ru/gt.html) has been supplemented with GT activities from Saccharomyces cerevisiae. Now it provides the close-to-complete coverage on experimentally confirmed GTs from the three most studied model organisms from the three kingdoms: Plantae (Arabidopsis thaliana, ca. 930 activities), Bacteria (Escherichia coli, ca. 820 activities), and Fungi (S. cerevisiae, ca. 270 activities).
3-(Bromomethyl)dihydrooxazolo[3,2-a]pyridinium bromide under the action of base gives stable non-aromatic methylidene structure which can be converted into aromatic oxazolopyridinium cation only under the action of a superacid. On the contrary, 2-bromomethyl isomer under the same conditions affords only aromatic cation. The structure of the products was confirmed by X-ray diffraction.
The unusual framework of the middle C-ring, “broken” as a result of biotransformations and oxidations in vivo and bearing an sp3-C connection, is of interest for biosynthetic investigations. The reported 39 natural compounds (55 including stereoisomers) have been analyzed and arranged into three structural groups. The biosynthetic origin of all these compounds has been thoroughly reviewed and revised, based on the found connections with oxidized angucyclinone structures. The data on biological activities has been summarized. Careful consideration of the origin of the structure allowed us to outline a hypothesis on the biological function as well as prospective applications of such atypical angucyclinones.
The coalescence of two Fe8N as well as the structure of the Fe16N2 cluster were studied using density functional theory with the generalized gradient approximation and a basis set of triple-zeta quality. It was found that the coalescence may proceed without an energy barrier and that the geometrical structures of the resulting clusters depend strongly on the mutual orientations of the initial moieties. The dissociation of N2 is energetically favorable on Fe16, and the nitrogen atoms share the same Fe atom in the lowest energy state of the Fe16N2 species. The attachment of two nitrogen atoms leads to a decrease in the total spin magnetic moment of the ground-state Fe16 host by 6 μB due to the peculiarities of chemical bonding in the magnetic clusters. In order to gain insight into the dependence of properties on charge and to estimate the bonding energies of both N atoms, we performed optimizations of Fe16N and the singly charged ions of both Fe16N2 and Fe16N. It was found that the electronic properties of the Fe16N2 cluster, such as electron affinity and ionization energy, do not appreciably depend on the attachment of nitrogen atoms but that the average binding energy per atom changes significantly. The lowering in total energy due to the attachment of two N atoms was found to be nearly independent of charge. The IR and Raman spectra were simulated for Fe16N2 and its ions, and it was found that the positions of the most intense peaks in the IR spectra strongly depend on charge and therefore present fingerprints of the charged states. The chemical bonding in the ground-state Fe16N20,±1 species was described in terms of the localized molecular orbitals.
The dependence of monovalent-ion selectivity of surface-sulfonated anion exchange membranes (s-AEMs) on the electrodialysis (ED) desalination current density, the concentration of equimolar ternary electrolyte (XCl + X2SO4) in the total concentration range 0.04–0.2 M, and the type of cations (X = H, Cs, Na) has been studied. The membrane current-voltage characteristics and values of the diffusion permeability coefficients in electrolyte solutions and their mixtures were measured. It was shown that Cl/SO4-selectivity coefficients (PCl|SO4) increase along with current density, reaching maximum values at the limiting current density (Ilim). The PCl|SO4 maximum value of 5.5 was achieved for the s-AEM-18 membrane in the ED-desalination of equimolar ternary electrolytes NaCl/Na2SO4, and CsCl/Cs2SO4 (total salt concentration 0.04 M) at 1.4 and 2.4 mA cm−2 current densities, respectively. At the overlimiting currents, the splitting of water and the decrease of Cl/SO4-selectivity were observed. The obtained experimental results are interpreted using simplified mass transfer and numerical simulations in the framework of Nernst-Planck-Poisson equations implemented in the COMSOL® Multiphysics software. The model represents the modified membrane as an asymmetric bipolar membrane with two diffusion boundary layers (DBL) in electrolyte solutions on both sides of the membrane interface. The model includes the water splitting at the bipolar boundary and the chemical equilibrium between sulfate and hydrogen sulfate ions. The numerical simulations qualitatively predict the behaviour of s-AEMs membranes when the abovementioned conditions change.
A novel class of fluorescent electron-deficient 5-hydroxyisoquinolones is proposed. The new luminophores are obtained via the reaction of stable and easily available hepta(methoxycarbonyl)cycloheptatrienyl potassium with alkylamines, anilines and acylhydrazines. The new one-pot protocol is efficient with a large scope of primary amines. The solvolysis of N-acylamino substituted 5-hydroxyisoquinolones and subsequent reactions have provided a pathway to further functionalization. Nearly all compounds have demonstrated fluorescence with considerably large the Stokes shifts (up to 6169 cm−1) except for those containing a nitro group as well as O-substituted products. In most other cases neither quantum yield nor absorption and emission maxima nor the Stokes shifts substantially depended on the substituent at the isoquinolinone ring nitrogen atom.
The use of stabilized exocyclic cyclopentadienone enolate, containing three ester groups and a dicyanomethylene fragment, allowed the replacement of unstable cyclopentadienones in the synthesis of arylhydrazonopentadiene chromophores. The presence of reaction centers in the resulting chromophores allowed three additional series of compounds to be obtained. Two series of compounds lost coplanarity in conjugated systems and exhibited reduced extinction coefficients, however, the absorption maxima were red-shifted. In one of the series of chromophores the formation of an imide cycle led to the record red-shift of the absorption maxima by up to 160 nm with only slightly reduced extinction coefficients.
Saturated vapor pressure of the diluent (toluene, cyclohexane, hexane, heptane) in four binary diluent – di-(2-ethylhexyl)phosphoric (D2EHPA) acid systems was measured by the static method at T = (288.15, 298.15, and 308.15) K in a wide concentration range. Experimental data obtained were correlated with UNIQUAC thermodynamic model taking into account the existence of D2EHPA in the liquid phase in the form of a dimer. Excess molar volumes were determined for binary solutions of D2EHPA with toluene, cyclohexane, heptane in the temperature range of (288.15–308.15) K and hexane at (288.15 and 298.15) K using the vibrating tube densimeter. The Redlich–Kister type polynomial equation was applied to describe the volumetric properties of the solutions.
The synthesis and crystal structure of the first molecular yttrium lactate complex, Y(Lac)3(H2O)2, is reported, where the coordination sphere of yttrium is saturated with lactate ligands and water molecules, resulting in a neutral moiety. In Y(Lac)3(H2O)2, hydrogen bonding between a-hydroxy groups and water molecules allows for the formation of 2D layers. A subtle variation in synthetic conditions, i.e. a slight increase in pH (5.5 instead of 4.5) promoted the formation of a semi-amorphous fibrous material with a presumed chemical composition of Y4(OH)5(C3H5O3)7·6H2O. The flattened fibres in this material are responsible for its good flexibility and foldability.
Metallocenes of the group 4 metals have attracted great attention as precursors of single-site catalysts forthe production of advanced polyolefins. The annelation of a cyclopentadienyl ring with a heterocyclicfragment fundamentally changes the electronic and structural characteristics ofg5-coordinated ligandsand provides new dimensions for the design of novel and effective catalysts. Heterocycle-fused half-sandwich and sandwich metal complexes, called heterocenes, have been extensively studied since theearly 2000s. This review describes the different synthetic strategies employed in the preparation ofheterocycle-fusedg1-g5andg5-g5ansa-ligand precursors, and further, discusses the synthesis, molec-ular structure, and catalytic applications of heterocenes.
The crystal structure of the new iodobismuthate (PyPy)2(PyPyH)2Bi6I26 was found to consist of unusual hexanuclear [Bi6I26]6– anions containing the linear I4 2– unit, and the experimental Bi–I bond lengths in this anion were used to obtain the relationship between bond length and bond energy. A statistical analysis of 229 crystal structures of iodobismuthates, based on the quantum chemically estimated strength of Bi–I bonds, revealed that the total energy of the Bi3+ polyhedron remains virtually constant at 64 ± 2 kcal mol–1, regardless of its geometry within this family of materials. Thus, the polyhedron geometry flexibly adapts to the relatively weak interactions between iodobismuthate anions and embedded cations.
2-Dialkylamino-arylidene-imidazolones undergo intermolecular tandem [1,5]-hydride shift and cyclization to form spirocyclic tetrahydroquinoline derivatives under TiCl4 promotion. Different substitutions on each of the aryl, amino and imidazole fragments are tolerated, which results in 20+ examples and 25–95% yields.
Inorganic-organic composites based on the foil and standard RALEX (R) cation-exchange heterogeneous membranes (Mega a.s., Czech Republic) were prepared by in situ modification with sulfated zirconia (S-ZrO2). The composite membranes were characterized by SEM, TGA, X-ray diffraction, and FTIR spectroscopy. The effect of S-ZrO2 doping on membrane transport properties was studied using measurements of water uptake, ion-exchange capacity, conductivity, cation diffusion, hydrogen permeability, current-voltage characteristics, and membrane specific permselectivity (Ca2+/Na+). The S-ZrO2 incorporation leads to an increase in conductivity and permselectivity of the composite membranes. The proton conductivity of the S-ZrO2-doped foil membrane (0.0316 S/cm at 30 degrees C) is 4 times higher than that of the pristine membrane. The Ca2+/Na+ permselectivity of the standard RALEX (R) CM membrane doped by S-ZrO2 reaches 3.8 at low current densities. Moreover, the composite membranes retain their selectivity during the long-term tests (> 50 h continuous electrodialysis). The sulfated zirconia doping of heterogeneous membranes demonstrated an excellent separation efficiency that can be used in wastewater treatment, desalination, and related electromembrane separation processes as well as to reduce scaling of electrodialysis modules.
The interaction of a nitrosyl iron complex with molecular oxygen was studied with Density Functional Theory. On the basis our analysis of the geometric and electronic structure of the complex, three variants of coordination of the oxygen molecule on it were investigated: the attachment of molecular oxygen to the iron center, an insertion of oxygen in between the Fe and NO and the bridging of two nitrosyl ligands. All of the coordination complexes require approximately the same amount of energy input to form. In all of the oxygen-enriched nitrosyl complexes we calculated, the doublet state was energetically below the quartet state. Next, we considered decomposition pathways since the products of all of these oxygen-attaching pathways may then decompose further. The result of this decomposition is either the release of nitrogen monoxide or the release of nitrogen dioxide. For all the three processes, transition and intermediate states were found, as well as the final products. The potential energy surfaces of the most important reactions were plotted. Finally, UV spectra of all the possible products of the oxidation of complex by molecular oxygen were calculated.
The unique optical and magnetic properties of lanthanide ions (Ln), like a gem, need the right faceting and the right setting. Azole carboxylic acids provide a unique platform for driving the structure of complex compounds ranging in dimensions from 0-D (molecular complexes) to 1-D, 2-D polymers and 3-D MOF (Metal Organic Framework) structures. The peculiarity of azolecarboxylate ligands is that numerous possible coordination fashions, including both carboxyl groups and nitrogen atoms, on the one hand, open up almost unlimited possibilities for obtaining materials with desired properties, for example, luminescent sources and sensors, molecular magnets, catalysts and materials for gas sorption and separation. Several coordination modes, dependent on the reaction conditions, make the structural diversity of lanthanide carboxylates difficult to predict and require systematic analysis. Our analysis is critical to produce efficient and advanced materials. This review describes and systematizes data on both synthesis and structure and functional properties of pyrazole-, imidazole-, 1,2,3-triazole, 1,2,4-triazole- and tetrazole-carboxylates of lanthanide metals and evaluates the achievements in this area of coordination chemistry. The author's view on the future of the chemistry of lanthanides azole carboxylates and possible new applications in materials science is also presented.
Exchange reactions of LnCl3 and CymCO2K in aqueous-organic medium in the presence of diethylene glycol (DEG) bring about isostructural tetranuclear cluster complexes with linear core, [Ln4(CymCO2)12(O(CH2CH2OH)2)2(H2O)4] ⋅ 2THF (Ln=Nd (1), Gd (2), Tb (3), Dy (4), Ho (5); Cym=(η5-C5H4)Mn(CO)3). The complexes have centrosymmetric structure and contain two types of Ln3+ coordination centers. Thermal decomposition of the complexes under argon and air atmospheres was studied; in the latter case it brings about mixed oxides LnMn2O5 as one of the products. The complexes 1–5 were characterized by dc- and ac-magnetic measurements. Complexes of Nd, Gd, and Dy exhibit the properties of single-molecule magnets (SMMs) with remagnetization barriers Δeff/kB of 14 K for 1 under 2500 Oe dc-field, 13 K for 2 under 1500 Oe dc-field, and with two barriers, 18 and 19 K, for 4 in zero field. The presence of field-induced slow relaxation of the magnetization detected for the complex 2 is a rare case for Gd complexes.