Browsing by Subject "Acetone"

Now showing 1 - 3 of 3

Open Access
Analysis of Fe nanoparticles using XPS measurements under d.c. or pulsed-voltage bias
(2010) Süzer, Şefik; Baer, D. R.; Engelhard, M. H.
The impact of solution exposure on the charging properties of oxide coatings on Fe metal-core oxide-shell nanoparticles has been examined by sample biasing during XPS measurements. The Fe nanoparticles were suspended in relatively unreactive acetone and analyzed after particles containing solutions were deposited on SiO2/Si or Au substrates. The particle and substrate combinations were subjected to ±10V d.c. or ±5V a.c., biasing in the form of square wave (SQW) pulses. The samples experienced variable degrees of charging for which low-energy electrons at ∼1eV, 20 μA and low-energy Ar+ ions were used to minimize it. Application of d.c. bias and/or SQW pulses significantly influences the extent of charging, which is utilized to gather additional analytical information about the sample under investigation. This approach allows separation of otherwise overlapping peaks. Accordingly, the O1s peaks of the silicon oxide substrate, the iron oxide nanoparticles, and that of the casting solvent can be separated from each other. Similarly, the C1s peak belonging to the solvent can be separated from that of the adventitious carbon. The charging shifts of the iron nanoparticles are strongly influenced by the solvent to which the particles were exposed. Hence, acetone exhibited the largest shift, water the smallest, and methanol in between. Dynamical measurements performed by application of the voltage stress in the form of SQW pulses provides information about the time constants of the processes involved, which leads us to postulate that these charging properties we probe in these systems stem mainly from ionic movement(s).
Open Access
Cu-catalyzed selective mono-N-pyridylation: Direct access to 2-aminoDMAP/sulfonamides as bifunctional organocatalysts
(2013) Isik, M.; Tanyeli, C.
Direct and selective mono-N-pyridylation of trans-(R,R)-cyclohexane-1,2- diamine is described here. Facile preparation of a novel chiral 2-aminoDMAP core catalaphore via Cu catalysis has led to the development of various sulfonamide/2-aminoDMAPs as bifunctional acid/base organocatalysts (most in two steps overall), which have been shown to very effectively promote asymmetric conjugate addition of acetylacetone to trans-β-nitroolefins with good to excellent yields (87-93%) and enantioselectivites (up to 99%). © 2013 American Chemical Society.
Open Access
Electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon
(Elsevier, 2017) Topuz, F.; Uyar, T.
The electrospinning of gelatin with tunable fiber morphology from round to flat/ribbon was shown, and the detailed studies were conducted to correlate the fiber morphology with electrospinning process parameters and gelatin concentration in electrospinning solution. Particularly, variations in the applied voltage and the concentration of gelatin led to the transition of fiber shape from round to flat/ribbon. The formation of flat-shaped fibers was attributed to rapid evaporation of the solvent (formic acid) from the fiber matrix with increasing the applied voltage and gelatin concentration. On the other hand, round fibers were due to the steady evaporation of formic acid throughout the cross-section of fibers. WAXS analysis revealed that the loss of triple-helical crystalline structure in gelatin after the electrospinning process. The gelatin fibers were cross-linked through treatment with toluene 2,4-diisocyanate (TDI) in a mixed solution of acetone and pyridine, and XPS confirmed the cross-linking of the fibers over an increased carbon content on the elemental composition of the fiber surface due to the incorporated TDI moieties. Overall, this study focuses on morphological tuning of gelatin electrospun fibers towards a flat/ribbon-like structure by variation of electrospinning parameters and polymer concentration, and thus, the proposed concept can be adapted towards flattened/ribbon-like fibers of other protein-based systems by electrospinning.