Physical Sciences and Mathematics Commons^™

Poly(Methacrylic) Acid And \Gamma-Methacryloxypropyltrimethoxy Silane/Clay Nanocomposites Prepared By In-Situ Polymerization, Ahmet Gültek, Turgay Seçki̇n, Yunus Önal, M. Gali̇p İçduygu

Turkish Journal of Chemistry

Poly(methacrylic acid) and poly(acrylic acid) nanocomposites were prepared by in-situ polymerization of \gamma-methacryloxypropyltrimethoxysilane (A174)/clay nanocomposites in which the macromonomer was generated by grafting A-174 onto activated clay samples via hydroxyl groups or via intercalation. In- situ polymerization was carried out in the presence of an initiator. It was found that the structural affinity between the methacrylic or acrylic acid monomers and the amount of clay played an important role in the hybrid structure. The nanocomposites were quantified by both X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), and differential thermal analysis (DTA).

Bromination Of Benzonorbornadiene Using A Mixture Of Sodium Bromide And Sodium Perborate At High Temperatures, Erdal Şenocak, Yavuz Taşkesenli̇gi̇l, Ferhan Tümer

Turkish Journal of Chemistry

Bromination of benzonorbornadiene (1) with sodium bromide in the presence of sodium perborate at room temperature gave only one product, the dibromide 2 produced via Wagner-Meerwein rearrangement. However, at high temperatures, bromination resulted predominantly in the formation of rearranged solvolytic products whose formation mechanisms are discussed.

New Triterpenic Saponins From Cephalaria Transsylvanica, Süheyla Kirmizigül, Hüseyi̇n Anil

Turkish Journal of Chemistry

Three new triterpenic saponins, 3-O-[\beta-D-xylopyranosyl (1 \to 4)-\beta-D-glucopyranosyl (1 \to 4)-\beta-D-glucopyranosyl (1 \to 3)-\alpha-L-rhamnopyranosyl (1 \to 4)-\beta-D-xylopyranosyl] hederagenin 28-O-[\beta-D-glucopy\-ranosyl (1 \to 4)-\beta-D-glucopyranosyl] ester (1), 3-O-[\beta-D-glucopyranosyl (1 \to 4)-\beta-D-glucopyranosyl (1 \to 3)-\alpha-L-rhamnopyranosyl (1 \to 4)-\beta-D-xylopyranosyl] hederagenin 28-O-[\beta -D-glucopyranosyl] ester (2) and 3-O-[\beta-D-glucopyranosyl (1 \to 3)-\alpha-L-rhamnopyranosyl (1 \to 4)-\beta-D-xylopyranosyl] hederagenin(3) were isolated from Cephalaria transsylvanica. After cleavage of the ester-glycosidic linkage of the bisdesmosidic compounds, two new prosapogenins, 3-O-[\beta-D-xylopyranosyl (1 \to 4)-\beta-D-glucpyranosyl (1 \to 4)-\beta-D-glucopyranosyl (1 \to 3)-\alpha-L-rhamnopyranosyl (1 \to 4)-\beta-D-xylopyranosyl] hederagenin (4) and 3-O-[\beta-D-glucopyranosyl (1 \to 4)- \beta-D-glucopyranosyl (1 \to 3)-\alpha-L-rhamnopyranosyl (1 \to 4)-\beta-D-xylopyranosyl] hederagenin (5) were also isolated. The structures …

Pyridine And Benzene Templated Potential Peptidomimetics, Kadi̇r Dabak

Turkish Journal of Chemistry

This study provides a new approach for the synthesis of pyridine and benzene templated potential peptidomimetics. By the attachment of various amino acid side chains in different combinations on the pyridine template at the 2- and 3- positions and on the benzene core at 1,2,4 positions, different peptidomimetics may be obtained. Arg-10, Leu-11 and Tyr-13 amino acid side chain mimics and their precursors were attached to the pyridine and benzene core with a special arrangement to produce potential peptidomimetics of omega-conotoxin MVIIA.

Metallation Of Mesitylene By Organolithium Compounds In The Presence Of Lithium Polyether Alkoxides, Tuba Kayhan, Ni̇han Nugay, Turgut Nugay

Turkish Journal of Chemistry

The catalytic effect of polyether alkoxides (PEAs) on the activity Of organolithium compounds as a metallating agent studied. The sites of metallation as mono, di, tri, and gem metallation at three different benzylic positions were investigated in terms of relative yield by using gas chromatography-mass spectroscopy (GC-MS couple) techniques. The yield of the trimetallated (1,3,5-metallated) mesitylene was optimized by improving the metallation conditions. Special attention was paid to the effect of metal type, alkoxide structure, solvent polarity, temperature and also relative mole ratios of was reactants such as alkoxide to mesitylene and n-butyllithium to mesitylene on metallation reactions. It was …

Hydrolysis Of Thionopeptides By The Aminopeptidase From Aeromonas Proteolytica:  Insight Into Substrate Binding, David L. Bienvenue, Danuta M. Gilner, Richard C. Holz

Chemistry Faculty Research and Publications

A series of l-leucine aniline analogues were synthesized that contained either a carbonyl or thiocarbonyl as a part of the amide bond. Additionally, the para-position on the phenyl ring of several substrates was altered with various electron-withdrawing or donating groups. The kinetic constants K_m and k_cat were determined for the hydrolysis of each of these compounds in the presence of the aminopeptidase from Aeromonas proteolytica (AAP) containing either Zn(II) or Cd(II). The dizinc(II) form of AAP ([ZnZn(AAP)]) was able to cleave both carbonyl and thiocarbonyl containing peptide substrates with similar efficiency. However, the dicadmium(II) form of AAP …

Polystyrene/Graphite Nanocomposites: Effect On Thermal Stability, Fawn Marie Uhl, Charles A. Wilkie

Chemistry Faculty Research and Publications

Nanocomposites consisting of polymer and clay have been shown to exhibit a significant reduction in flammability and an increase in mechanical properties. This work examines the effect of thermal stability and mechanical properties of nanocomposites prepared from potassium graphite and styrene. Synthesis of nanocomposites was accomplished by using potassium graphite (KC₈) as the initiator in the polymerization of styrene. A slight increase in thermal stability is observed but mechanical properties are decreased.

Silicon-Methoxide-Modified Clays And Their Polystyrene Nanocomposites, Jin Zhu, Paul Start, Kenneth A. Mauritz, Charles A. Wilkie

Chemistry Faculty Research and Publications

Silicon-methoxide-containing modified clays were obtained through cationic exchange between the sodium clay and the ammoniumcation of [3-(trimethoxysilyl) propyl]octadecyldimethylammoniumchloride (Si18). The nanocomposites were prepared through bulk polymerization of styrene in which the Si18 clay was dispersed. The silicon-methoxide offers the possibility of reaction between the methoxide and a clay hydroxyl group to link together the cation and the clay. The nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, and atomic force microscopy. Their thermal stability and flame retardancy were measured by thermogravimetric analysis (TGA) and cone calorimetry. Linkage between the silicon and the clay apparently occurs in the clay but …

Chemical Analysis By X-Ray Spectroscopy Near Phase Transitions In The Solid State, Juana Vivó Acrivos, L. Nguyen, T. Norman, C. T. Lin, W. Y. Liang, J. M. Honig, P Somasundaran

Juana Vivó Acrivos

The methods discussed in this work show that the types of changes which may be observed, by precise XAS measurements of Absorbance A versus temperature, across a phase transition are: the changes in the relaxation time of the final states  due to fluctuations near a phase transition; the detection of the anomalous Bragg condition coupled to phonon modes XAS enhancement that identifies the temperature interval where the phonon modes are active, the symmetry changes which introduce new allowed transitions to finite states below an element edge, near Tc indicate what symmetry changes occur, and the method of XTDAFST0 = …

Structure Of Xe+N Clusters (N=3–30): Simulation And Experiment, Jose A. Gascon, Randall W. Hall, Christoph Ludewigt, Helmut Haberland

Randall W. Hall

Bismuth Triflate Catalyzed Allylation Of Acetals: A Simple And Mild Method For Synthesis Of Homoallyl Ethers, Ram S. Mohan, Laura C. Wieland, Herbert M. Zerth

Ram S. Mohan

Applications Of Bismuth(Iii) Compounds In Organic Synthesis, Ram S. Mohan, Nicholas M. Leonard, Laura C. Wieland

Ram S. Mohan

No abstract provided.

Synthesis And Physico-Chemical Investigations On 16 And 18 Membered [N4] Macrocycles Modified With Appropriate Carbonyl Functions - A Closer Mimic To A Synthetic Cyclic Tetrapeptide; Isolation Of Stable Encapsulated Derivatives With Zn(Ii),Cd(Ii) And Hg(Ii) Ions, Z. A. Siddiqi, V. J. Mathew, Mohammad Mansoob Khan Dr

Dr. Mohammad Mansoob Khan

Reaction of 1, 2-diamine or 1,3-diamine with succinic/ phthalic anhydride in 1:1 molar ratio at RT in dioxane results in 16-membered or 18 membered macrocycle which posseses tetraamide/ tetrapeptide functions in the molecular unit which however, exhibit ample reactivity towards metallic substrates affording stable compounds with [MLX2 ] (M=Zn,Cd or Hg; X = CI, SCN or CI04 ) stoichiometry as evidenced from the physico-chemical investigations which confirm that the macrocyclic moieties (L| - L6 ) have the appropriate cavity sizes to encapsulate Zn(II), Cd (II) or Hg(II) ions via coordination through nitrogens of the amide/ peptide functions in tetradentate fashion …