Chemistry / Kimya
Permanent URI for this collectionhttps://hdl.handle.net/11147/4072
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Article Citation - WoS: 8Citation - Scopus: 8Genetic Multivariate Calibration for Near Infrared Spectroscopic Determination of Protein, Moisture, Dry Mass, Hardness and Other Residues of Wheat(John Wiley and Sons Inc., 2006) Özdemir, DurmuşDetermination of wheat flour quality parameters, such as protein, moisture, dry mass by wet chemistry analyses takes long time. Near infrared spectroscopy (NIR) coupled with multivariate calibration offers a fast and nondestructive alternative to obtain reliable results. However, due to the complexity of the spectra obtained from NIR, some wavelength selection is generally required to improve the predictive ability of multivariate calibration methods. In this study, two different wheat data sets are investigated with the aim of establishing successful calibration models using NIR spectra of wheat samples. The first data set (material 1) was obtained from the ftp address (ftp://ftp.clarkson.edu/pub/hopkepk/Chemdata/) and contained 100 NIR spectra of wheat of which wet chemical analysis of protein and moisture content were done with reference methods. The second data set (material 2) contained 176 spectra and was downloaded from http://www.spectroscopynow.com/Spy/basehtml/SpyH/1,1181, 2-1-2-0-0-newsdetail-0-74,00.html. This wheat data set was given with the quality parameters, such as protein content, moisture content, other residues, dry mass, protein content in dry mass and hardness that were determined previously. Multivariate calibration models generated with genetic inverse least squares method demonstrated very good prediction results for the parameter mentioned here. Overall, the average per cent recoveries (APR) ranged between 99.23% and 100.34% with a standard deviation (SD) ranging from 0.34 to 3.15 for all the parameters investigated, except hardness. The APR value of hardness was 103.32 with the SD of 14.97.Article Citation - WoS: 42Citation - Scopus: 43Investigation of Oxygen Permeation Through Composites of Pmma and Surface-Modified Zno Nanoparticles(John Wiley and Sons Inc., 2009) Hess, Sandra; Demir, Mustafa Muammer; Yakutkin, Vladimir; Baluschev, Stanislav; Wegner, GerhardOxygen permeabilities of nanocomposite films consisting of poly(methyl methacrylate) (PMMA) and different amounts of spherical zinc oxide (ZnO) nanoparticles were determined to investigate the barrier effect of this material with respect to particle content. A method was applied which is based on quenching of an excited phosphorescent dye by oxygen. Possible effects of the nanoparticles on the response of the dye molecules were investigated and were ruled out.Article Citation - WoS: 30Citation - Scopus: 30Glycidyl-Methacry Late-Based Electrospun Mats and Catalytic Silver Nanoparticles(John Wiley and Sons Inc., 2008) Demir, Mustafa Muammer; Uğur, Gökçe; Gülgün, Mehmet A.; Menceloğlu, Yusuf Z.P(AN-GMA) and PGMA fibers coated with monodisperse silver nanoparticles have been prepared by a combination of electrospinning and electroless plating. The morphology of the electrospun fibers remains unchanged after surface hydrazination. Oxidation of hydrazine in an ammoniacal solution of AgNO 3 reduces and deposits silver atoms along the fiber surface, which then coalesce to Ag particles. The size of the silver nanoparticles is varied between 20-60 nm. Since the density of the active sites for silver reduction is lower in P(AN-GMA), a smaller particle size could be obtained. The catalytic activity of the silver nanoparticles has been confirmed.Article Citation - WoS: 185Pmma/Zinc Oxide Nanocomposites Prepared by In-Situ Bulk Polymerization(John Wiley and Sons Inc., 2006) Demir, Mustafa Muammer; Memesa, Mine; Castignolles, Patrice; Wegner, GerhardDispersing surface-modified zinc oxide nano-particles (ZnO) in methyl methacrylate (MMA) improves the free radical bulk polymerization process as well as the thermal stability of the formed polymer. Hydroxy groups available on the ZnO surface may induce a degenerative transfer. This suppresses the gel effect, which leads to a better control of the heat evolution during the late stages of polymerization. The formation of chains having vinylidene end groups and head-to-head links is suppressed, which shifts the onset of thermal decomposition to the regime where decomposition occurs by random chain scission.Article Citation - WoS: 15Aggregation of Fillers Blended Into Random Elastomeric Networks: Theory and Comparison With Experiments(John Wiley and Sons Inc., 2006) Demir, Mustafa Muammer; Menceloğlu, Yusuf Ziya; Erman, BurakA theoretical model describing aggregation of filler particles in amorphous elastomers is proposed. The model is based on a counting technique originally used in genome analysis to characterize the size and distribution of overlapping segments randomly placed on a DNA molecule. In the present model, the particles are first assumed to aggregate randomly upon mixing into the elastomer and then-sizes are calculated. The sizes and distributions of aggregates are also studied in the presence of attractive interparticle forces. Results of the proposed model are compared with experimental data on silica-filled end-linked poly(dimethyl-siloxane) networks. Comparison of the theory and experiment shows that the random aggregation assumption where no attractive forces exist between the particles is not valid and a significant attraction between the silica particles is needed in the theory to justify the experimental data obtained using atomic force microscopy. For filler content below 1.45 vol.-%, the model agrees, qualitatively, with experiment and shows the increase in cluster size with increasing amount of filler. It also explains the increase in the dispersion of aggregate sizes with increasing amount of filler.Article Citation - WoS: 25Citation - Scopus: 23Structural Alteration of Cofactor Specificity in Corynebacterium 2,5-Diketo Acid Reductase(John Wiley and Sons Inc., 2004) Şanlı Mohamed, Gülşah; Banta, Scott; Anderson, Stephen; Blaber, MichaelCarynebacterium 2,5-Diketo-D-gluconic acid reductase (2,5-DKGR) catalyzes the reduction of 2,5-diketo-D-gluconic acid (2,5-DKG) to 2-Keto-L-gulonic acid (2-KLG). 2-KLG is an immediate precursor to L-ascorbic acid (vitamin C), and 2,5-DKGR is, therefore, an important enzyme in a novel industrial method for the production of vitamin C. 2,5-DKGR, as with most other members of the aldo-keto reductase (AKR) superfamily, exhibits a preference for NADPH compared to NADH as a cofactor in the stereo-specific reduction of substrate. The application of 2,5-DKGR in the industrial production of vitamin C would be greatly enhanced if NADH could be efficiently utilized as a cofactor. A mutant form of 2,5-DKGR has previously been identified that exhibits two orders of magnitude higher activity with NADH in comparison to the wild-type enzyme, while retaining a high level of activity with NADPH. We report here an X-ray crystal structure of the holo form of this mutant in complex with NADH cofactor, as well as thermodynamic stability data. By comparing the results to our previously reported X-ray structure of the holo form of wild-type 2,5-DKGR in complex with NADPH, the structural basis of the differential NAD(P)H selectivity of wild-type and mutant 2,5-DKGR enzymes has been identified.Article Citation - WoS: 14Citation - Scopus: 22Characterization of Airborne Particles and Droplets: Relation To Amount of Airborne Dust and Dust Collection Efficiency(John Wiley and Sons Inc., 2002) Polat, Mehmet; Polat, Hürriyet; Chander, Subhash; Hogg, RichardWater sprays have been commonly used to suppress airborne dust. Water is doped with surface-active agents to enhance the dust capture efficiency through a reduction of surface tension. Nevertheless, dust collection efficiencies have been less than satisfactory historically. A detailed characterization of freshly generated airborne dust particles and spray droplets was carried out in order to explain this observation. Such properties as the agglomeration state of the freshly generated airborne dust particles and the airborne dust production capacity of various materials were defined and quantified. Electrostatic charges on individual airborne particles and spray droplets were measured. It was demonstrated that freshly generated airborne dust particles were extensively agglomerated. The magnitude of agglomeration was a function of material type and decided the amount of dust becoming airborne from a given material. This explains why certain materials such as quartz and anthracite produce more dust than some others. It was demonstrated that surfactants could be employed to charge the spray droplets selectively. The sign and magnitude of the droplet charge was a function of surfactant type and concentration. A strong correlation between the droplet charge and dust collection efficiencies by spray droplets was observed for cationic surfactants, suggesting that surfactants affected collection efficiency in addition to enhancing wetting.Article Citation - WoS: 16Citation - Scopus: 19N,n-Dialkylaniline Tetraethynylethenes: a New Class of Chromophores Possessing an Emitting Charge-Transfer State. Experimental and Computational Studies(John Wiley and Sons Inc., 2001) Gobbi, Luca; Elmacı, Nuran; Lüthi, Hans Peter; Diederich, FrançoisThe photophysical properties of N,N-dimethylaniline- (DMA) substituted tetraethynylethene (TEE; 3,4-diethynylhex-3-ene-1,5-diyne) and related derivatives were investigated in a joint experimental and computational study. Measurements of the electronic emission spectra showed that these novel chromophores display a dual fluorescence which strongly depends on solvent polarity. Computational studies suggest that the twisted intramolecular charge-transfer state (TICT) model offers a possible explanation for the experimentally observed dual fluorescence. Time-dependent density functional calculations revealed that the initial excited state reached upon photoirradiation relaxes to a lower-energy TICT state in which either the dimethylamino group is twisted into an orthogonal position with respect to the remaining planar arylated TEE moiety or the entire DMA donor group takes an orthogonal orientation with respect to the rigid, planar TEE acceptor moiety. For the compounds investigated, the charge-transfer state responsible for the strongly solvent-dependent luminescence is directly connected with the initial excited state, namely, no crossing of states is involved.Article Citation - WoS: 21Citation - Scopus: 24Kinetics of Oil Dispersion in the Absence and Presence of Block Copolymers(John Wiley and Sons Inc., 1999) Polat, Hürriyet; Polat, Mehmet; Chander, SubhashA phenomenological model proposed describes droplet breakup in the turbitlently agitated lean oil-in-water dispersions and provides a correlation between the median droplet size in an agitated vessel of standard geometry and the time of dispersion. It was assumed that the droplet breakup takes place in the dispersion-only region and coalescence is negligible. Vie model described the data from this study and the literature quite satisfactorily under these conditions. The effect of adding triblock PEO/PPO/PEO copofymeric surfactants on the dispersion kinetics of oil was also investigated. Addition of surfactant reduced the median oil droplet size significanfty, and the extent of this reduction was a strong function of surfactant concentration. Application of the model on these data demonstrated that the change in the median droplet size could be divided into two distinct regions. The breakage rate was high initially, most probably due to continuous adsorption of surfactant molecules at the oil/water interface. A lower breakage rate was attained at longer tunes, as the surfactant molecules were depleted from the solution. The time of transition bet\veen the t\vo was affected strongly by the concentration of the surfactant added. Furthermore, the time of addition of the surfactant did not affect the final droplet-size distribution in the system.