Hexacyanometalate molecular chemistry: di-, tri-, tetra-, hexa- and heptanuclear heterobimetallic complexes; control of nuclearity and structural anisotropy

Following a bottom-up approach to nanomaterials, we present a rational synthetic route to high-spin and anisotropic molecules based on hexacyanometalate [M(CN)(6)](3-) cores. Part 1 of this series was devoted to isotropic heptanuclear clusters; herein, we discuss the nuclearity and the structural anisotropy of nickel(II) derivatives. By changing either the stoichiometry, the nature of the terminal ligand, or the counterion, it is possible to tune the nuclearity of the polynuclear compounds and therefore to control the structural anisotropy. We present the synthesis and the characterisation by mass spectrometry, X-ray crystallography and magnetic susceptibility of bi-, tri-, tetra-, hexa- and heptanuclear species [M(CN)(n)(CN-M'L)(6-n)](m+) (with n=0-5; M=Cr(III), Co(III), M'=Ni(II); L=pentadentate ligand). Thus, with M=Cr(III), d(3), S=3/2, a dinuclear complex [Cr(III)(CN)(5)(CN-NiL(n))](9+), (L(n)=polydentate ligand) was built and characterised, showing a spin ground state, S(G)=5/2, with a ferromagnetic interaction J(Cr,Cu)=+18.5 cm(-1). With M=Co(III) (d(6), S=0) were built di-, tri-, tetra-, hexa and hepanuclear CoNi species: CoNi, CoNi(2), CoNi(3), CoNi(5) and CoNi(6). By a first approximation, they behave as one, two, three, five and six isolated nickel(II) complexes, respectively, but more accurate studies allow us to evaluate the weak antiferromagnetic coupling constant between two next-nearest neighbours M'-Co-M'.     

Identification of the elastic properties of an artificial capsule membrane with the compression test: effect of thickness

The mechanical properties of a capsule membrane are evaluated by means of a compression experiment between two parallel plates. Since large deformations of the membrane are involved, the choice of the wall material constitutive law is essential. In this paper, we explore different classical laws to describe the behavior of the membrane and evaluate also the limit of application of the thin shell approximation. A numerical study of the compression process is performed using Abaqus software and an inverse method is used to identify the material constants of the constitutive laws. The comparison between the model predictions and experimental measurements on capsules with serum albumin-alginate membranes, indicates that the thin shell approximation is valid only for thickness to radius ratios up to 5% and that thick membranes obey non linear elastomer type constitutive laws. The Young modulus of the membrane material is found to increase non-linearly with membrane thickness, thus indicating that fabrication of thicker serum albumin-alginate walls results in capsules stiffer than expected.     

Carbamazepine on a carbamazepine monolayer forms unique 1D supramolecular assemblies

High-resolution STM imaging of the structures formed by carbamazepine molecules adsorbed onto a pseudo-ordered carbamazepine monolayer on Au(111) shows the formation of previously unreported 1-dimensional supramolecular assemblies.     

Purification and structure elucidation of three naturally bioactive molecules from the new terrestrial Streptomyces sp. TN17 strain

Thirty litres of fermentation broth was extracted from the newly isolated Streptomyces sp. strain TN17 and various separation and purification steps led to the isolation of three pure bioactive compounds (1-3). Compound 1: cyclo (L-Leu-L-Arg), a diketopiperazine 'DKP' derivative; 2: di-(2-ethylhexyl) phthalate, a phthalate derivative; and 3: cyclo 1-[2-(cyclopentanecarbonyl-3-phenyl-propionyl]-pyrrolidine-2-carboxylic acid (1-carbamoyl-propyl)-amide, a cyclic tetrapeptide derivative. The chemical structure of these three active compounds was established on the basis of spectroscopic studies (MS and NMR) and by comparison with data from the literature. According to our biological studies, the pure compounds (1-3) possess antibacterial and antifungal activities.     

Lateral Deprotometallation-Trapping Reactions on Methylated Pyridines,Quinolines and Quinoxalines Using Lithium Diethylamide

The functionalization of methylated azines and diazines has aroused the interest of chemists given the structural diversity that it affords. Hindered lithium dialkylamides have been used to deprotometallate these substrates chemoselectively. In contrast, it can be observed that, despite some promising work, lithium diethylamide has been used very little for this purpose. Our objective here is on the one hand to make an inventory of what reagents have been used to deprotometallate methylpyridines, -quinolines and -quinoxalines, and on the other hand to describe the results obtained by seeking to functionalize a series of substrates with lithium diethylamide (picolines, 2,4-lutidine, methylquinolines and 2-methylquinoxaline). Our efforts to take advantage of the use of an in-situ trap (a zinc chloride chelate) in these reactions are also described.     

Sol–gel encapsulation of cresol red in presence of surfactants

Cresol Red (CR) pH indicator was encapsulated into silica network using the sol–gel process. Transparent monolithic disks of entrapped CR were obtained in the presence of cetyl trimethyl ammonium bromide (CTAB) or dodecyl dimethyl amino oxide (Genaminox LA,GLA) alkyl hydroxyethyl dimethyl ammonium chloride (HY, R = 12–14) and TX-100 surfactants. UV/VIS spectra showed that the encapsulated CR retains its structure in terms of its response to pH. At the neutral conditions it is found that the HY surfactant is considered as proton donor as favor the cationic form of the indicator, while CTAB surfactant favor the neutral, however GLA surfactant, the anionic form of CR is more favored because GLA has a zwitterionic head. The surfactant GLA with TEOS has shifted the equilibrium to the ionized form of CR due to the electrostatic interaction between the surfactant and the CR anion. Therefore their pH range is dependent on the nature of a surfactant used. It is found that the HY surfactant is more efficient as far as loading of CR is concern and it widened the working pH range.     

Detailed experimental and kinetic modeling study of 3-carene pyrolysis

3-Carene is an important potential biofuel with properties similar to the jet-propellant JP-10. Its thermal decomposition and combustion behavior is to date unknown, which is essential to assess its quality as a fuel. A combined experimental and kinetic modeling study has been conducted to understand the initial decomposition of 3-carene. The pyrolysis of 3-carene was investigated in a jet-stirred quartz reactor at atmospheric pressure, at temperatures varying from 650 to 1050 K, covering the complete conversion range. The decomposition of 3-carene was observed to start around 800 K, and it is almost complete at 970 K. Online gas chromatography shows that primarily aromatics are generated which suggests that 3-carene is not a good fuel candidate. The potential energy surface for the initial decomposition pathways determined by KinBot shows that a hydrogen elimination reaction dominates, giving primarily cara-2,4-diene. Next to this molecular pathway, radical pathways lead to aromatics via ring opening. The kinetic model was automatically generated with Genesys and consists of 2565 species and 9331 reactions. New quantum chemical calculations at the CBS-QB3 level of theory were needed to calculate rate coefficients and thermodynamic properties relevant for the primary decomposition of 3-carene. Both the conversion of 3-carene and the yields of the primary products (ie, benzene and hydrogen gas) are well predicted with this kinetic model. Rate of production analyses shows that the dominant pathways to convert 3-carene are hydrogen elimination reaction and radical chemistry.     

QUANTIS: Data quality assessment tool by clustering analysis

Automatically generated kinetic networks are ideally validated against a large set of accurate, reproducible, and easy-to-model experimental data. However, although this might seem simple, it proves to be quite challenging. QUANTIS, a publicly available Python package, is specifically developed to evaluate both the precision and accuracy of experimental data and to ensure a uniform, quick processing, and storage strategy that enables automated comparison of developed kinetic models. The precision is investigated with two clustering techniques, PCA and t-SNE, whereas the accuracy is probed with checks for the conservation laws. First, the developed tool processes, evaluates, and stores experimental yield data automatically. All data belonging to a given experiment, both unprocessed and processed, are stored in the form of an HDF5 container. The demonstration of QUANTIS on three different pyrolysis cases showed that it can help in identifying and overcoming instabilities in experimental datasets, reduce mass and molar balance closure discrepancies, and, by evaluating the visualized correlation matrices, increase understanding in the underlying reaction pathways. Inclusion of all experimental data in the HDF5 file makes it possible to automate simulating the experiment with CHEMKIN. Because of the employed InChI string identifiers for molecules, it is possible to automate the comparison experiment/simulation. QUANTIS and the concepts demonstrated therein is a potentially useful tool for data quality assessment, kinetic model validation, and refinement.     

Fluoroalkyl Radical Generation by Homolytic Bond Dissociation in Pentacarbonylmanganese Derivatives

Thermal decarbonylation of the acyl compounds [Mn(CO)₅(COR_F)] (R_F=CF₃, CHF₂, CH₂CF₃, CF₂CH₃) yielded the corresponding alkyl derivatives [Mn(CO)₅(R_F)], some of which have not been previously reported. The compounds were fully characterized by analytical and spectroscopic methods and by several single-crystal X-ray diffraction studies. The solution-phase IR characterization in the CO stretching region, with the assistance of DFT calculations, has allowed the assignment of several weak bands to vibrations of the [Mn(¹²CO)₄(eq-¹³CO)(R_F)] and [Mn(¹²CO)₄(ax-¹³CO)(R_F)] isotopomers and a ranking of the R_F donor power in the order CF₃<CHF₂<CH₂CF₃≈CF₂CH₃. The homolytic Mn−R_F bond cleavage in [Mn(CO)₅(R_F)] at various temperatures under saturation conditions with trapping of the generated R_F radicals by excess tris(trimethylsilyl)silane yielded activation parameters ΔH^≠ and ΔS^≠ that are believed to represent close estimates of the homolytic bond dissociation thermodynamic parameters. These values are in close agreement with those calculated in a recent DFT study (J. Organomet. Chem. 2018 , 864, 12–18). The ability of these complexes to undergo homolytic Mn−R_F bond cleavage was further demonstrated by the observation that [Mn(CO)₅(CF₃)] (the compound with the strongest Mn−R_F bond) initiated the radical polymerization of vinylidene fluoride (CH₂=CF₂) to produce poly(vinylidene fluoride) in good yields by either thermal (100 °C) or photochemical (UV or visible light) activation.