Adsorption of surface functionalized silica nanoparticles onto mineral surfaces and decane/water interface

The adsorption of silica nanoparticles onto representative mineral surfaces and at the decane/water interface was studied. The effects of particle size (the mean diameters from 5 to 75?nm), concentration and surface type on the adsorption were studied in detail. Silica nanoparticles with four different surfaces [unmodified, surface modified with anionic (sulfonate), cationic (quaternary ammonium (quat)) or nonionic (polyethylene glycol (PEG)) surfactant] were used. The zeta potential of these silica nanoparticles ranges from ?79.8 to 15.3?mV. The shape of silica particles examined by a Hitachi-S5500 scanning transmission electron microscope (STEM) is quite spherical. The adsorption of all the nanoparticles (unmodified or surface modified) on quartz and calcite surfaces was found to be insignificant. We used interfacial tension (IFT) measurements to investigate the adsorption of silica nanoparticles at the decane/water interface. Unmodified nanoparticles or surface modified ones with sulfonate or quat do not significantly affect the IFT of the decane/water interface. It also does not appear that the particle size or concentration influences the IFT. However, the presence of PEG as a surface modifying material significantly reduces the IFT. The PEG surface modifier alone in an aqueous solution, without the nanoparticles, yields the same IFT reduction for an equivalent PEG concentration as that used for modifying the surface of nanoparticles. Contact angle measurements of a decane droplet on quartz or calcite plate immersed in water (or aqueous nanoparticle dispersion) showed a slight change in the contact angle in the presence of the studied nanoparticles. The results of contact angle measurements are in good agreement with experiments of adsorption of nanoparticles on mineral surfaces or decane/water interface. This study brings new insights into the understanding and modeling of the adsorption of surface-modified silica nanoparticles onto mineral surfaces and water/decane interface.     

Design, synthesis, and biological activities of some branched carbasugars: construction of a substituted 6-oxabicyclo[3.2.1]nonane skeleton

Transformation of cyclohexa-2,4-diene-1,2-diylbis(methylene) diacetate to various carbasugars is described. Photooxygenation of a cyclohexadiene derivative gave a bicyclicendoperoxide, which was reduced with thiourea to [2-[(acetyloxy)methyl]cyclohexa-2,4-dien-1-yl]methyl acetate. Epoxidation of the remaining double bond followed by epoxide ring-opening and hydrolysis of the acetate groups gave one of the target hexols. The bicyclic endoperoxide was rearranged to a diepoxide with CoTPP. The diepoxide was reacted with sulfamic acid in acetic anhydride, resulting in the formation of a new branched carbasugar as well as in the formation of cyclitols with a 6-oxabicyclo[3.2.1]nonane skeleton. The mechanism of the formation of the products is discussed. The inhibition activity of six cyclitol derivatives was tested against α-glycosidase.     

Synthesis,characterization, and antimicrobial activities of Cu(I), Ag(I), Au(I), and Co(II) complexes with [CH3N(CH2PPh2)2]

Transition metal complexes of ditertiary aminomethylphosphine ligand, (Ph₂PCH₂)NCH₃ [N,N‐bis(diphenylphospinomethyl)aminomethane], dppam, with metal ions which are Ag(I), Au(I), Cu(I), and Co(II) have been synthesized under nitrogen atmosphere by the Schlenk method. [Ag(dppam)₂]NO₃ ( 1 ), [Au(dppam)₂]Cl ( 2 ), and [Cu(dppam)₂]Cl ( 3 ) complexes have been isolated as colorless solids, whereas [CoCl₂(dppam)] ( 4 ) complex as a blue solid. All complexes have been characterized by atomic absorption, FT‐IR, NMR (¹H, ¹³C, ³¹P) spectroscopic, thermogravimetric/differantial thermal analysis (TG/DTA), and elemental analysis techniques. Antimicrobial activity of 1 , 2 , 3 , and 4 were studied in vitro on 13 bacteria and 4 yeasts. The cobalt(II) phosphine complex has shown the best antimicrobial activity in comparison with the other metal complexes. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:484–491, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20145     

Furo- and thieno-fused 1,3-diazepine-4,6-diones

We report the first preparation of furo- and thieno-fused 1,3-diazepine-4,6-dione derivatives starting from ethyl 2-(2-methoxy-2-oxoethyl)-3-furancarboxylate and -thiophencarboxylate. The ester functionalities connected to the hetero-ring were converted regiospecifically into the desired amides. The ester groups attached to the methylene unit were converted into isocyanates via Curtius rearrangement. The ring-closure reaction was performed in the presence of lithium bis(trimethylsilyl)amide at room temperature to give furo- and thieno-fused diazepinone derivatives.     

Thermal decomposition kinetics of polypyrrole and its star shaped copolymer

Thermal behavior of 2,4,6-tris(4-(1H-pyrrol-1-yl)phenoxy)-1,3,5-triazine monomer, polypyrrole, and their star shaped copolymer, were investigated using TG and DTA methods. It was found that Tria melts at 517 K and after than it starts to decompose. Decomposition proceeded in two stages which were corresponding to removal of branched groups and remaining core structure degradation, respectively. Polypyrrole and copolymer showed similar thermal behaviors. These compounds decomposed in three stages which are removal of solvent, removal of dopant anion and rest of structure decomposition. The calculation of activation energies of all reactions were realized using model-free (KAS and FWO) methods. The graphs were prepared which show the alteration of activation energy with decomposition ratio. Thermal analysis results showed that dopant anion and solvent removal activation energy values for copolymer are lower than polypyrrole. Star shaped loose-packed novel structure greatly facilitates solvent and dopant anion removal from copolymer. It can be concluded also that thermal analysis can be used as predict package structure of conducting polymers.     

Singular manifold analysis of the Einstein vacuum field equations

The Painlevé property of the vacuum Einstein field equations is investigated. It is observed that the field equations possess this property when spacetime admits commuting, nonnull two Killing vector fields.     

Response to "Comment on ‘Electric Multipole Moments for Some First-Row Diatomic Hydride Molecules' [Commun. Theor. Phys. 38 (2002) 256]"

The comment of Guseinov is irrelevant and also unjust. In contrast to his comment, we show that theobtained electric multipole moment values for some first-row diatomic molecules are original and better than his values(I.I. Guseinov, E. Akin, and A.M. Rzaeva, J. Mol. Struct. (Theochem) 453 (1998) 163) with respect to Hartree-Fockvalues. Moreover, it must be noted that all the formulas are cited in our paper (M. Orbay and T. Ozdogan, Commun.Theor. Phys. (Beijing, China) 35 (2001) 585) and corrigendum (M. Orbay and T. Ozdogan, Commun. Theor. Phys.(Beijing, China) 37 (2002) 768).     

Photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene

The photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydro-benzo[b]thiopene1 was carried out in the presence of thiourea in order to reductively trap the intermediate; however, the rearranged compound 3-cyano-7-hydroxy-2-thio-2,4,5,6,7,7a-hexahydroindole2 was isolated. The structure, determined by X-ray crystallography, is described, and the mechanism for the formation of2 is discussed.     

Photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydrobenzo[b]thiophene

The photooxygenation of 2-amino-3-cyano-4,5,6,7-tetrahydro-benzo[b]thiopene1 was carried out in the presence of thiourea in order to reductively trap the intermediate; however, the rearranged compound 3-cyano-7-hydroxy-2-thio-2,4,5,6,7,7a-hexahydroindole2 was isolated. The structure, determined by X-ray crystallography, is described, and the mechanism for the formation of2 is discussed.