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Self-assembled tin-based bridged hybrid materials

Hybrid materials where layers of tin oxide alternate with layers of hydrophobic organic chains were prepared by the hydrolysis of distannylated compounds containing an organic chain alpha,omega-disubstituted by tripropynylstannyl groups. In the case of an aliphatic chain, hydrolysis under microemulsion conditions led to the organization of the corresponding hybrid. These hydrolysis conditions also induced a high surface area and a defined mesoporosity in the hybrid. When a mixed aromatic-aliphatic spacer was used, weak hydrophobic interactions between the spacers were sufficient to generate the same type of organization in the corresponding material.     

Existence and stability of new nanoreactors: highly swollen hexagonal liquid crystals

We report the preparation of direct hexagonal liquid crystals, constituted of oil-swollen cylinders arranged on a triangular lattice in water. The volume ratio of oil over water, rho can be as large as 3.8. From the lattice parameter measured by small-angle X-ray scattering, we show that all the oil is indeed incorporated into the cylinders, thus allowing the diameter of the cylinders to be controlled over one decade range, provided that the ionic strength of the aqueous medium and rho are varied concomitantly. These hexagonal swollen liquid crystals (SLCs) have been first reported with sodium dodecyl sulfate as anionic surfactant, cyclohexane as solvent, 1-pentanol as co-surfactant, and sodium chloride as salt (Ramos, L.; Fabre, P. Langmuir 1997, 13, 13). The stability of these liquid crystals is investigated when the pH of the aqueous medium or the chemical nature of the components (salt and surfactant) is changed. We demonstrate that the range of stability is quite extended, rendering swollen hexagonal phases potentially useful for the fabrication of nanomaterials. As illustrations, we finally show that gelation of inorganic particles in the continuous aqueous medium of a SLC and polymerization within the oil-swollen cylinders of a SLC can be conducted without disrupting the hexagonal order of the system.     

Real estate price estimation in French cities using geocoding and machine learning

This paper reviews real estate price estimation in France, a market that has received little attention. We compare seven popular machine learning techniques by proposing a different approach that quantifies the relevance of location features in real estate price estimation with high and fine levels of granularity. We take advantage of a newly available open dataset provided by the French government that contains 5 years of historical data of real estate transactions. At a high level of granularity, we obtain important differences regarding the models’ prediction powers between cities with medium and high standards of living (precision differences beyond 70% in some cases). At a low level of granularity, we use geocoding to add precise geographical location features to the machine learning algorithm inputs. We obtain important improvements regarding the models’ forecasting powers relative to models trained without these features (improvements beyond 50% for some forecasting error measures). Our results also reveal that neural networks and random forest techniques particularly outperform other methods when geocoding features are not accounted for, while random forest, adaboost and gradient boosting perform well when geocoding features are considered. For identifying opportunities in the real estate market through real estate price prediction, our results can be of particular interest. They can also serve as a basis for price assessment in revenue management for durable and non-replenishable products such as real estate.

     

Structural determination of two new acacic acid-type saponins from the stem barks of Albizia zygia (DC.) J. F. Macbr

As a continuation of our interest in the study of triterpenoid saponins from Albizia zygia, phytochemical investigation of its stem barks led to the isolation of two new oleanane-type saponins, named zygiaosides C–D (1–2). Their structures were established on the basis of extensive analysis of 1D and 2D NMR (1H-, 13C NMR, DEPT, COSY, TOCSY, ROESY, HSQC and HMBC) experiments, HRESIMS studies, and by chemical evidence as, 3-O-[ β-d-glucopyranosyl-(1→2)-[α-l-arabinopyranosyl-(1→6)]-β-d-glucopyranosyl]-21-O-[(2E,6S)-2,6-dimethyl-6-O-(β-d-quinovopyranosyl) octa-2,7-dienoyl]acacic acid 28-O-α-l-arabinofuranosyl-(1→4)-[β-d-glucopyranosyl-(1→3)]-α-l-rhamnopyranosyl-(1→2)-β-d-glucopyranosyl ester (1) and 3- O-[β-d-glucopyranosyl-(1→2) -[ β-d-fucopyranosyl-(1→6)]-β-d-glucopyranosyl]-21-O-[(2E,6S)-2,6-dimethyl-6-O-(β-D-quinovopyranosyl) octa-2,7-dienoyl]acacic acid 28-O-α-l-arabinofuranosyl-(1→4)-[β-d-glucopyranosyl-(1→3)]-α-l-rhamnopyranosyl-(1→2)-β-d-glucopyranosyl ester (2).     

Ionic liquid crystals based on mesitylene-containing bis- and trisimidazolium salts

The synthesis of novel ionic liquid crystals (ILCs) based on bis- and trisimidazolium salts (I-, BF4-, and [N(SO2CF3)2]-) bearing hydrophobic hexadecyl chains and a bridging mesitylene moiety is reported. The study of their mesomorphic properties is presented, including the characterization of the Smectic A phase by differential scanning calorimetry and polarized optical microscopy. A detailed powder X-ray diffraction (p-XRD) study as a function of temperature confirmed that cooling gives rise to a glass transition from the liquid-crystalline smectic A phase to a metastable lamellar phase. In addition, in the case of bisimidazolium iodide, the ability of these molecules to form self-aggregates in solution has been demonstrated by diffusion nuclear magnetic resonance (NMR) experiments.     

Cytotoxic flavonoids and other constituents from the stem bark of Ochna schweinfurthiana

Seven flavonoids, hemerocallone (1), 6,7-dimethoxy-3′,4′-dimethoxyisoflavone (2), amentoflavone (4), agathisflavone (6), cupressuflavone (8), robustaflavone (9) and epicatechin (10), together with three other compounds, lithospermoside (3), β-D-fructofuranosyl-α-D-glucopyranoside (5) and 3β-O-D-glucopyranosyl-β-stigmasterol (7), were isolated from the ethyl acetate extract of the stem bark of Ochna schweinfurthiana F. Hoffm. All the compounds were characterised by spectroscopic and mass spectrometric methods, and by comparison with literature data. Cytotoxicity of the extracts and compounds against cervical adenocarcinoma (HeLa) cells was evaluated by MTT assay. Compounds 4 and 6 exhibited good cytotoxic activity, with IC₅₀ values of 20.7 and 10.0 μM, respectively.     

Nanostructuring of Ionic Bridged Silsesquioxanes

The transformation by hydrolysis/condensation of four new mesityl‐(bis or tris)imidazolium‐based alkoxysilane precursors into their corresponding bridged silsesquioxanes has been investigated. These precursors feature urea groups and either short or long alkylene chains, which are known to favor self‐assembly. The most regular nanostructures were obtained by a combination of the tripodal precursors with C₁₀H₂₀ alkylene chains, as shown by powder X‐ray diffraction (PXRD) analysis, independent of the reaction conditions.