Structural tuning of Montmorillonite clays by pillaring: Designing of shape selective solid acid catalysts and PANI - Montmorillonite nanocomposites

Green chemistry boots eco-friendly,natural clays as catalysts in the chemical as well as in the pharmaceutical industry.Industry demands thermal stability,mechanical strength etc for the catalyst and there the modification methods becomes important.Pillaring tunes clays as efficient catalytic templates for shape selective organic synthesis.Here pillared clays are used as promising alternatives for the environmentally hazardous homogeneous catalysts in some industrially important Friedel-Crafts alkylation reactions of arenes with lower alchohols and higher olefins.The layer structure is enhanced upon pillaring and allows the nanocomposite formation with polyaniline to develop today’s nanoscale diameter devices.Present work gives an entry of pillared clays to the world of conducting composite nanofibers.

Ruthenium-Oxygen Coordination-Driven Self-Assembly of a Ru-8(II) Incomplete Prism: Synthesis, Structure, and Shape-Selective Molecular Recognition Study

Coordination-driven self-assembly of 1,3,5-benzenetricarboxylate (tma; 1) and oxalato-bridged p-cymeneruthenium(II) building block Ru-2(mu-eta(4)-C2O4)(MeOH)(2)(eta(6)-p-cymene)(2)](O3SCF3)(2) (2) affords an unusual octanuclear incomplete prism Ru-8(eta(6)-p-cymene)(8)(tma)(2)(mu-eta(4)-C2O4)(2)(OMe)(4)](O3SCF3)( 2) (3), which exhibits a remarkable shape-selective binding affinity for neutral phenolic compounds via hydrogen-bonding interactions (p-cymene = p-(PrC6H4Me)-Pr-i). Such a binding was confirmed by single-crystal X-ray diffraction analysis using 1,3,5-trihydroxybenzene as an analyte.

Coordination-driven self-assembly of 2D-metallamacrocycles using a shape-selective Pt(2)(II)-organometallic 90 degrees acceptor: design, synthesis and sensing study

Synthesis of a series of two-dimensional metallamacrocycles via coordination-driven self-assembly of a shape-selective Pt(2)(II)-molecular building unit incorporating carbazole-ethynyl functionality is described. An equimolar (1 : 1) combination of a Pt(2)(II)-organometallic 90 degrees acceptor, 1, with rigid linear ditopic donors (L(a) and L(b)) afforded [4 + 4] self-assembled octanuclear molecular squares, 2 and 3, in quantitative yields, respectively [L(a) = 4,4'-bipyridine; L(b) = trans-1,2-bis(4-pyridyl)ethylene]. Conversely, a similar treatment of 1 with an amide-based unsymmetrical flexible ditopic donor, L(c), resulted in the formation of a [2 + 2] self-sorted molecular rhomboid (4a) as a single product [L(c) = N-(4-pyridyl)isonicotinamide]. Despite the possibility of several linkage isomeric macrocycles (rhomboid, triangle and square) due to the different connectivity of L(c), the formation of a single and symmetrical molecular rhomboid (4a) as the only product is an interesting observation. All the self-assembled macrocycles (2, 3 and 4a) were fully characterized by multinuclear NMR ((1)H and (31)P) and ESI-MS analysis. Further structural insights about the size and shape of the macrocycles were obtained through energy minimization using density functional theory (DFT) calculations. Decoration of the starting carbazole building unit with Pt-ethynyl functionality enriches the assemblies to be more p-electron rich and luminescent in nature. Macrocycles 2 and 3 could sense the presence of electron deficient nitroaromatics in solution by quenching of the initial intensity upon gradual addition of picric acid (PA). They exhibited the largest quenching response with high selectivity for nitroaromatics compared to several other electron deficient aromatics tested.

Selective alkylation of aniline to N-methyl aniline using chromium manganese ferrospinels

Various compositions of chromium manganese ferrospinels were tested as catalysts for the vapour phase alkylation of aniline with methanol. The samples were prepared by room temperature co-precipitation technique and characterized by various physico-chemical methods. The acidity–basicity determination revealed that the samples possess greater amount of basic sites than acidic sites. All the ferrite samples proved to be selective and active for N-monoalkylation of aniline leading to N-methyl aniline; Cr0.6Mn0.4Fe2O4, Cr0.8Mn0.2Fe2O4 and CrFe2O4 exhibited cent percent selectivity for N-methyl aniline. Neither C-alkylated products nor any other side products were detected for all catalyst samples. The catalytic activity of the samples studied in this reaction is related to their acid–base properties and also on the cation distribution. Under the optimized reaction conditions all the systems showed constant activity for a long duration.

Surface-appropriate lipophobicity - Application in isobutene oligomerization over Teflon-modified silica-supported 12-silicotungstic acid

A series of silica-supported 12-silicotungstic acid catalysts (H4SiW12O40, abbreviated as HSiW), modified with various loadings of Teflon (HSiW/SiO2-Teflon), were prepared by an impregnation method. The surface properties of the catalysts were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), BET, infrared (IR) spectroscopy, NH3-TPD and the Drop Shape Analysis (DSA). SEM results combined with energy-dispersive X-ray (EDX) measurements of HSiW/SiO2-Teflon revealed that F-compound (Teflon) is effectively coated on the catalyst surface. The contact angles for water and oil of 50 wt% HSiW/SiO2 and HSiW/SiO2-Teflon indicate that HSiW/SiO2-Teflon catalyst enhances not only the surface hydrophobicity but also the surface lipophobicity by means of the addition of Teflon. Silica-supported 12-silicotungstic acid modified with Teflon exhibits higher C-8(=) selectivity and longer lifetime than that of silica-supported 12-silicotungstic acid in isobutene oligomerization. Thus, surface-appropriate lipophobicity of catalysts may be effective for decreasing the interaction between coke precursors and the catalyst surface and for removing deposited coke more easily.

Synthesis and properties of main chain discotic liquid crystalline polyethers based on rufigallol

Two series of thermotropic main chain discotic liquid crystalline polyethers, PR4m-n, based on rufigallol were prepared starting from the symmetric tetraethers of rufigallol, R4m; m and n represent the number of carbon atoms in the side chain and spacer segment, respectively. The symmetric tetraethers were in turn readily prepared by selective alkylation of rufigallol under controlled phase-transfer conditions. GPC analysis of the polymers suggested that they were all of moderate molecular weights, with M-n varying between 5400 and 17 000. The length of the spacer segment n in these polyethers was systematically varied, and its effect on the phase transition temperatures and the mesophase structure was examined using DSC, polarized light microscopy, and X-ray diffraction. It is noticed that when the spacer lengths are relatively long(n greater than or equal to 2m), the isotropization temperature (TD-i) decreases as the spacer length n increases, an observation that is in accordance with those previously made. However, when the spacer lengths are relatively small (n < 2m), the dependence of TD-i is quite the opposite; TD-i actually increases with an increase in spacer length. Furthermore, X-ray diffraction studies indicate that, in the discotic columnar mesophases that are formed, the columns pack in a hexagonal manner when n greater than or equal to 2m, while they do so in a rectangular lattice when n < 2m, leading to the formation of Dh and Dr mesophases, respectively. Finally, comparison of the discotic polyethers with their low molar mass analogues confirms the role of polymerization in stabilizing the mesophase; while all the polymers exhibit columnar mesophases, some of their low molar mass analogues are not liquid crystalline.

Phase-Transfer Catalysis in Segmented Flow in a Microchannel: Fluidic Control of Selectivity and Productivity

Precise control over the interfacial area of aqueous and organic slugs in segmented flow in a microchannel reactor provides an attractive means to optimize the yield and productivity of a phase-transfer-catalyzed reaction. Herein, we report the selective alkylation of phenylacetonitrile to the monoalkylated product in a microchannel of 250-mu m internal diameter operated in a continuous and solvent-free manner in the slug-flow regime. The conversion of phenylacetonitrile increased from 40% to 99% as a result of a 97% larger slug surface-to-volume ratio when the volumetric aqueous-to-organic phase flow ratio was raised from 1.0 to 6.1 at the same residence time. The larger surface-to-volume ratio significantly promoted catalyst phase transfer but decreased selectivity because of the simultaneous increase of the rate of the consecutive reaction to the dialkylated product. There exists all Optimum flow ratio with a maximum productivity. Conversion and selectivity in the microchannel reactor were both found to be significantly larger than in a stirred reactor.

Conception, synthèse et diversification de l'azaGly-Pro : un mime de tour beta, outil d'étude structure-activité : application au développement d'un nouvel agent tocolytique

Les accouchements prématurés constituent un problème médical majeur en constante augmentation et ce, malgré tous les efforts mis en œuvre afin de contrer le déclenchement des contractions avant terme. Cette thèse relate du ''design'' rationnel d'un nouvel agent thérapeutique (i.e., tocolytique) qui serait capable de 1) arrêter les contractions, et 2) prolonger la gestation. Pour ce faire, une nouvelle cible, la prostaglandine F2α et son récepteur ont été sélectionnés et le peptidomimétisme a été choisi afin de résoudre cette problématique. L'introduction contient un historique rapide de la conception à la synthèse (''drug design'') du peptide parent, le PDC113, premier peptide a avoir démontré des aptitudes tocolytiques suffisantes pour faire du peptidomimétisme. La deuxième partie de l'introduction présente les concepts du peptidomimétisme appliqués au PDC113 qui ont permis d'accéder au PDC113.824, inhibiteur allostérique du récepteur de la prostaglandine F2α, et explique comment ce mime nous a permis d'élucider les mécanismes de signalisation intracellulaire impliqués dans la contraction musculaire lisse. Cette thèse présente la conception, la synthèse et l'étude structure-activité de mimes de repliement de tour β au sein du mime peptidique original (PDC113.824) dans lequel nous avons remplacé l'azabicycloalkane central (l'indolizidin-2-one) par une série d'autres azabicycloalcanes connus et des acides aza-aminés dont nous avons élaboré la synthèse. Dans un premier temps, une nouvelle stratégie de synthèse en solution de l'aza-glycyl-proline à partir de la diphényle hydrazone et du chloroformate de p-nitrophényle a été réalisée. Cette stratégie a permis d'éliminer les réactions secondaires de cyclisation intramoléculaires communément obtenues lors de l'introduction d'acides aza-aminés avec les protections traditionnelles de type carbamate en présence de phosgène, mais aussi de faciliter l'accès en une étape à des dérivés peptidiques du type aza-glycyle. L'élongation de l'aza-glycyl-proline en solution nous a permis d'accéder à un nouveau mime tetrapeptidique du Smac, un activateur potentiel de l'apoptose au sein de cellules cancéreuses. Par la suite, nous avons développé une stratégie de diversification sélective de l'azote α du résidu azaglycine en utilisant différents types d'halogénures d'alkyle en présence de tert-butoxyde de potassium. Afin de valider le protocole d'alkylation de l'aza-dipeptide, différents halogénures d'alkyle ont été testés. Nous avons également démontré l'utilité des aza-dipeptides résultants en tant que ''building block'' afin d'accéder à une variété d'azapeptides. En effet, l'aza-dipeptide a été déprotégée sélectivement soit en N-terminal soit en C-terminal, respectivement. D'autre part, la libération de l'amine de l'ester méthylique de l'aza-alkylglycyl-proline a conduit à une catégorie de composés à potentiel thérapeutique, les azadicétopipérazines (aza-DKP) par cyclisation intramoléculaire. Enfin, notre intérêt quant au développement d'un nouvel agent tocolytique nous a amené à développer une nouvelle voie de synthèse en solution du PDC113.824 permettant ainsi d'élucider les voies de signalisation intracellulaires du récepteur de la prostaglandine F2α. Afin de valider l'importance de la stéréochimie et d'étudier la relation structure/ activité du mime, nous avons remplacé l'indolizidin-2-one (I2aa) centrale du PDC113.824 par une série d'autres azabicycloalcanes et azadipeptides. Les azabicycloalcanes D-I2aa, quinolizidinone, et indolizidin-9-one ont été synthétisés et incorporés au sein du dit peptide ne donnant aucune activité ni in vitro ni ex vivo, validant ainsi l'importance du tour β de type II' pour le maintien de l'activité biologique du PDC113.824. Finalement, l'insertion d'une série de dérivés aza(alkyl)glycyl-prolyles a mené à de nouveaux inhibiteurs allostériques du récepteur de la PGF2α, l'un contenant l'azaglycine et l'autre, l'azaphénylalanine. Cette thèse a ainsi contribué, grâce à la conception et l'application de nouvelles méthodes de synthèse d'aza-peptides, au développement de nouveaux composés à potentiel thérapeutique afin d'inhiber le travail prématuré.

Use of self-organizing maps and molecular descriptors to predict the cytotoxic activity of sesquiterpene lactones

Some sesquiterpene lactones (SLs) are the active compounds of a great number of traditionally medicinal plants from the Asteraceae family and possess considerable cytotoxic activity. Several studies in vitro have shown the inhibitory activity against cells derived from human carcinoma of the nasopharynx (KB). Chemical studies showed that the cytotoxic activity is due to the reaction of alpha,beta-unsaturated carbonyl structures of the SLs with thiols, such as cysteine. These studies support the view that SLs inhibit tumour growth by selective alkylation of growth-regulatory biological macromolecules, such as key enzymes, which control cell division, thereby inhibiting a variety of cellular functions, which directs the cells into apoptosis. In this study we investigated a set of 55 different sesquiterpene lactones, represented by 5 skeletons (22 germacranolides, 6 elemanolides, 2 eudesmanolides, 16 guaianolides and nor-derivatives and 9 pseudoguaianolides), in respect to their cytotoxic properties. The experimental results and 3D molecular descriptors were submitted to Kohonen self-organizing map (SOM) to classify (training set) and predict (test set) the cytotoxic activity. From the obtained results, it was concluded that only the geometrical descriptors showed satisfactory values. The Kohonen map obtained after training set using 25 geometrical descriptors shows a very significant match, mainly among the inactive compounds (similar to 84%). Analyzing both groups, the percentage seen is high (83%). The test set shows the highest match, where 89% of the substances had their cytotoxic activity correctly predicted. From these results, important properties for the inhibition potency are discussed for the whole dataset and for subsets of the different structural skeletons. (C) 2008 Elsevier Masson SAS. All rights reserved.