Kimya

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Organik kimyada dipolar ve sterik etkileşimler
(Thesis (Assoc. Prof.) - Bogazici University. Institute of Sciences and Engineering, 1978., 1978.) Özbal, Hadi.
Katı fazda peptid sentezi
(Thesis (Assoc. Prof.) - Bogazici University. Institute of Science and Engineering, 1978., 1978.) Yakalı, Emel.
In this work, the syntheses of three new peptides (XXIV-Xxvr, Table 2.2) , each containing 39 amino acids, are reported. N-t-butyloxy-carbonyl-p-choloro-L-phenylalanine (XXVIIa) and N-t-htyloxycarbmyl-L-2- aminoheptanoic acid (XXVIIIa), necessary for the above syntheses, have also been prepared for the first the. These peptides are analogs of the "nonheme" peptide of cytochrame c which is a protein found in all cells having a nucleus.Cytochrame c from different species are known to show differences in their amino acid sequences. Horse heart cytochrame c (XXI) consists of one "heme c" group and 104 amino acid residues in a single polypeptide chain. The 66-104 fragment of this chain, ccmtaining 39 amino acids, is known as the nonheme peptide (XXIII) . The peptides synthesized differ from this nonheme peptide (XXIII) only in one position. In the first peptide (XXIV,) tyrosine-67 has been replaced by p-chloro-l-phenylalanine; in the second one, (XXIV) tyrosine-67 by p-chloro-L-phenylalanine; and in the third one (XXVI)', lyshe-79 by L-2-amhoheptanoic acid. Combination of these analogs with the native 1-65 heme peptide (XXIIb) of horse heart cytochrame c (XXI) wold yield semi-synthetic proteins. Studies on these semi-synthetic proteins would then give information about cytochrane c, which functions as an electron-transport, protein in the cells for the reduction of oxygen to water and the synthesis of adenosine triphosphate. Specifically, this information would be useful in detemining the mechanism of oxidation-reduction reactions , of cytochrame c and in understanding the structure-function relationships in the molecule. In the solid phase method applied in the synthesis of each peptide, the amino acid (104) which contains the free carboxyl group of the peptide has been attached to a polimer, known as the solid support, by forming a covalent bond between this carboxyl group and the polimer; and then all the other mino acids (103-66) have been added one at a time in a stepwise manner to this amino acid on the polimer. After the completion of addition, the free peptide has been released into solution by cleavage of the covalent bond between the peptide chain and the polimer. Finally, the peptide, obtahed in the solid form by lyophilization of the solution, has been purified by gel chromatography.
Poli-2-vinilfuran'ın organik reaksiyonları
(Thesis (Assoc. Prof.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1980., 1980.) Küsefoğlu, Selim.
The known and varied organic chemistry o f the furan ring has been used t o successfully transform poly-2-vinyl furan (PZVF) to a number of new polymeric systems. The Diels Alder adduct o f P2VF with maleicanhidride (3), the cross linking product of P2VF with asetone (7); the 2 - 4 dinitroph,enylhydrazine derivative of the acid hydrolysis product of P2VF (6) and the 5-aldehyde (8), 5-bromide (9) and 5-sulfonat (10) derivatives of P2VF have been synthesized and characterized using spectral and chemical techniques. The spectral and chemical properties o f the starting material P2VF which were not available in the literature have also been determined. Each o f the above syntheses involved the limitations and difficulties inherent in polymer reactions which had to be eliminated or minimized by judicial use of synthesis techniques. Although the physical propertiies o f the newly synthesized polymers lies outside the scope of this work, especially the P2VF maleican hidrite Diels-Alder adduct (3) and P2VF - asetone cross-linking product (7) deserve careful physical tests for further characterization.
Metil radikallerinin tetrametilsilan ile fotoliz reaksiyonunun incelenmesi
(Thesis (Assoc. Prof.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1982., 1982.) Arıcan, Haluk.
Bu çalışmada, metil radikalleri ile tetrametil silanda bulunan C-H bağlarının koparılma reaksiyonu incelenmiştir. Metil radikal kaynağı olarak aseton kullanılmıştır. Bugune kadar literatürde geçen metil radikallerinin tetrametilsilanla olan reaksiyonlarında radikal kaynağı olarak azometan kullanılmıştır. Aseton metil radikal kaynağı olarak ilk kez uygulanmış ve fotoliz reaksiyonunun sonunda elde edilen Arrhenius parametreleri benzeri reaksiyonlarınkilerle derinlenesine karşılaştırılmıştır. Ayrıca ürün analiz yöntemi olarak sisteme bir vanayla dogrudan baglı alev'iyon dedektörlü gaz kramatografisi kullanılmıştır. Bu yöntemle ürün analizi radikal sistemleri için ilk defa gerçekleştirilmiştir. Literatürde bulunan metilradikalleri ile tetra metilsilan (TMS) arasindaki Arrhecius parametreleri alınmiş ve en iyi deger hesap edilmiştir. Bu hesaplamayla elde edilen parametreler (log A = 11.41; E = 41.46 kjmnol -1) bu çalışma neticesinde doğan Arrhenius parametrelerinle (log A = 11.83; E = 44.65 kjmol-1) karşılaştırılmıştır. Bu karşılaştırma neticesinde de bulunan degerlerin digerleriyle iyi bir uyum içinde oldugu görülmüştür. Ayrıca bu kıyaslamayla yetinilmeyip, metil radikallerinden elde edilen degerler, CD3. CF3, CH2F, CHFJ, C H- ve C F 2 5 2F 5 radikallerinin tetra metil silanla olan reaksiyonlarının neticesi olan parametrelerle karşılaştırılmış ve radikal reaktivitelerine göre sıralandırılmıştır.
Euphorbia larica, euphorbia virgata, euphorbia chamaesyce ve euphorbia magalantha bitkilerinin flavonoidleri
(Thesis (Assoc. Prof.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1982., 1982.) Halfon, Belkıs.
Preparation and properties of white-pine-PMMA composites
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1983., 1983.) İnhan, Günseli Ayşe.; Küsefoğlu, Selim.
Wood-polymer composites fromTurkish White pine (pinea siber)-Polymethylmethacrylate (PMMA), are prepared by heat catalysis method. Monomer loss during polymerization i s prevented by impregnation of wood in PMMA + MMA solution and subsequent polymerization. Volatility of MMA is decreased in a significant degree. % conversion values greater than 85% are obtained. A.S.E. values are determined. It is observed that A.S.E. values for PMMA-MMA impregnated, polymerized samples are higher than pure MMA impregnated, polymerized ones, probably due to MMA shrinkage during polymerization which occurs less in the first case. A.S.E. values greater than 70% are observed for 70% polymer load for PMMA-MMA impregnated samples. Different results are obtained for hardness parallel to grain and for hardness perpendicular to grain. An increase of about 2 fold is observed in case of hardness perpendicular to grain whereas i n case of hardness parallel to grain a 3 fold increase is obtained. Staining wood samples with Rhodamine B dye and subsequent examination under U.V. showed that PMMA had penetrated inside the wood and polymer distribution was mainly along the grain.
An investigation of the carbon-carbon bond rupture in fluoroethanes by RRKM theory
(Thesis (Ph.D.)- Bogazici University. Institute for Graduate Studies in Social Sciences, 1983., 1983.) Aviyente, Viktorya.; İnel, Yüksel.
In this dissertation, the thermal decompositions of ethane, 1,1,2,2-tetrafl uoroethane, pentafl uoroethane and hexafl uoroethane have been subjected to a theoretical treatment i n terms of the quantum statistical RRKM theory. The RRKM theory assumes that the activated molecule has a certain amount of vibrational energy spread among the various vibrational degrees of freedom of the molecule. Then the probability of one particular mode of vibration acquiring so much of this energy that the vibration leads to dissociation into fragments is calculated. The experimental results have shown that the first order rate constant for unimolecular reactions is not a true constant but declines at low pressures. The decline or "fall-off" in the first order rate constant with pressure is an important criterion of unimolecular reactions. The rate constants in this fall-off region as well as the rate constants at the experimental pressures and temperatures for the carboncarbon bond rupture for the above molecules have been evaluated. As already known, the major difficulty in this field is the determination of the configuration of the transition state . This is done in two different ways where two different models are suggested in the first one, the complex is considered as a decomposing diatomic molecule in which the atoms have the masses of the actual fragments. From this assumption follows the derivation of the length of the critical bond (Gorin Model ). In the second one, the critical configuration has a value o f the reaction coordinate such that the number of accessible internal states o f the molecule is minimized. The R+ value given by the criterion of minimum state density is less than the value given by the Gorin Model at the rotational barrier. Choosing the critical configuration at the rotational barrier gives an overestimate of the animolecular rate. In fact, the kuni values calculated for the first model are higher than those obtained for the second one. I n the evaluation of the rate constants, the centrifugal effects which reduce the activation energy for the reaction and the anharmonicity, resulting in a decreasing spacing between successive vibrational levels , are considered. As a result , the pressure at which the rate constant reaches one half it slimiting high pressure value increases with the number of fluorine atoms. This behaviour is in harmony with activation energies for the carbon-carbon bond scission, increasing with the number of fluorine atoms in the hydrocarbon.
An investigation of the effect of CD, HG and ZN on the growth of two species of blue green algae
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1983., 1983.) Ağlarca, Zeynep.; Çalgan, Dilek.
In this research, effects of three metals, cadmium, mercury and zinc were investigated on two species of blue green algae, Anabaena flos aquae and Gloeocapsa. Cells were grown in sterile medium free of combined nitrogen and under continuous illumination. Metal ions were introduced as chloride salts and different concentrations of the metal ion solutions were used. Absorbance and cell counts were determined for each concentration of the metal ion solution and results were evaluated in terms of these two criteria. Zinc was found to be the most toxic metal for both Anabaena flos aquae and Gloeocapsa whereas the other metals showed inhibitory and stimulatory effects depending on the concentration of the metal ion solution. This showed that effect of the metal whether inhibitory or stimulatory is dependent on the species used and the metal ion itself.
Trace element analysis of metallic artifacts from Gedikli hoard by atomic absorption spectroscopy
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Benglian, Ani.; Özbal, Hadi.
The object of this study was to determine the trace and alloying elements of the metal artifacts recovered from Gedikli during excavation between 1964-1967. Most of the artifacts were from a cremation burial sight dated to Early Bronze Age, which includes pins, awls, ring , bracelets etc. About 20-25mg. samples, obtained from over 100 artifacts by drilling, are analysed using atomic absorption spectroscopy. The results showed that most of the samples were copper and copper alloys. Both tin and arsenic were present as an alloying element in some samples at about 7% and 5% respectively. Nearly half of the objects had both tin and arsenic together but at about 1% or less.Silver and iron were the other two elements that were present in almost all samples at trace levels. Zinc and lead concentrations were quite variable from trace levels to up to 27,4% and 15,5% respectively. Artifacts are classified according to type, shape and to presence or absence of certain elements. Histograms, correlations and cluster analysis were carried out on the trace element distribution of these groups to determine particular trends, manufacturing techniques and common are sources. The results showed that, there was no general trand in the trace element distribution in general for all artifacts. However, certain trends could be observed when artifacts are arrand-ged into subgroups. Umbrella headed pins were all tin bronzes with similar trace metal distribution. Two clusters were also observed between artifacts having tin, arsenic, lead and nikel elements which may indicade two different are sources. Even though the artifacts recovered, cover a relatively short time span, the heterogeneity of the trace element distribution could be an indication of different are sources, manufacturing techniques and trade routes. A complete examination of the sight will show if the objects are locally manufactured or not. Chronological arrangement of the artifacts would yield information on the technological development as well as on trade relations. This preliminary study shows that complete excavation of Gedikli could bring light to the metallurgy of the Bronze Age in the area.
Preparation of oleophilic perlite by polymer encapsulation
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1985., 1985.) Bayraktar, Durata.; Küsefoğlu, Selim.
A new oil adsorbing material was synthezised' using expanded perlite . To render perlite oleophilic and hydrophobic it was coated with a suitable hydrocarbon polymer. Perlite was first size classified to assure uniformity and purified from metallic oxide impurities by floatation in ether. After evaporation of adsorbed atmospheric water- it kiss coated using different polymers and different methods. Four subtances were chosen for coating: paraffin, polystyrene, high molecular weight polyethtylene and low molecular weight polyethylene. These substances were solvent deposited on perlite usingappropriatesolvents at suitable temperatures and the solvent was subsequently evaporated. Paraffin due to its volatility could be vapor deposited on perlite under vacuum without the use of solvent. Both paraffin and low molecular weight polyethylene were melt deposited on perlite because of their low melting temperatures. Using these techniques samples with various levels of coating of each material were obtained. These samples were then tested for their oil and water adsorption capability. Further they were conpared among themselves with respect to oil adsorption and cost to choose the best adsorbent. A coating method was also chosen to optimize cost and ease o f manufacture using t h e adsorbent with the highest oil adsorption capacity . Reproducility of the above experiments was tested to calculate accuracy and precision of the work performed. The best adsorbent was found t o be the 48 % low molecular weight polyethylene coated perlite obtained by the melt deposition method. The solid material thus prepared adsorbs 7.4 times its weight in liquid oil, no water, and costs about 108 TL/ Kg. Finally the capacity of the 48% low molecular weight polyethylene coated perlite for hydrocarbon vapor adsorption was tested by passing n-heptane saturated a i r through it. The material adsorbed about one to two its weight in gaseous hydrocarbon. The results were as expected : coating perlite with hydrocarbonlike polymers considerably decreased its water affinity and increased tremendously its oil adsorption capacity. This new material can be used as an efficient sorbent for adsorbing oil and other non-polar organic substances from water surfaces and city water, as well as hydrocarbon vapors from flue gases. It can probably be used in any field requiring oil or non-polar substance removal.
Conformational analysis of 2-substituted cyclohexanone ketal derivatives by molecular mechanics and nuclear magnetic resonance
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) Varnalı, Tereza.; Özbal, Hadi.
The present study is concerned with the application of the Molecular Mechanics Method to 2-substituted cyclohexanoneketals. The object is to find the conformational free energy difference between the equilibrating conformers and to compare the theoretical results to those found experimentally. For the application of molecular mechanics, models of the compounds underinvestigation were described, the inter-atomic distances and angles were computed, the most important interactions were determined and the parameters needed for calculations of the interactions and functions relating parameter to energy were chosen. First, molecular mechanics was applied to spiro- [5,4]-1-halo-6,9-dioxodecane (1 in Fig. 1.1.1) and spiro-[5,5]-1-halo-6, 10-dioxoundecane(2 in Fig.1.1.1) where the halogen was chlorine or bromine. The results obtained theoretically showed preference for the conformer bearing the axialhalogen in (2) system and the conformer bearing the equational halogenin (1) system, being in accordance to experimental results reported by Zefirovet et. al. Secondly, molecular mechanics was applied to spiro- [5,4]-1-halo-6,9-dioxodecane and spiro-[5,5]-1-nitro-6,10 undecane and the results obtained theoretically in contrast to halogens, showed preference for the conformation in which the nitro group is equatorial in both cases ( 1 ) and ( 2 ). Finally, the 4-t-butyl derivatives of the nitro-(1) and (2) systems, and the (1) and (2) systems were synthesized and the free energy difference between the equilibrating conformers were obtained experimentally using NMR parameters. Experimental results were in parallel to those found theoretically. In previous studies the nitro group has been shown to behave differently than halogens and similar groups due to its electronic distribution, size, structure and formal change. The unique behavior of the nitro group has been shown once more both theoretically and experimentally.
A parametric study of laboratory scale manifacture of sodiumallysulfonate
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Scieence and Engineering, 1986., 1986.) Börekcioğlu, Pınar.; Arıcan, Haluk.
The main aim of this work involyes the manufacture of sodium allylsulfonate from allylbromide and sodium sulfite by using laboratory scale testing of the commonly used industrial batch method(1). Yield of sodium allylsulfonate by processing conditions were examined. Sodium allylsulfonate (SAS), is mainly used in nickel electroplating bath as a brightening and levelling agent . It improves the throwing power of thebath, thus; yielding deposits of high brightness and good adherence. At the same time, it possesses the other properties of brightening agents by being a rapid adsorber on the cathode withit subsequent incorporation into the electrodeposit. It has strong inhibition action on the discharge of nickel ions without significantly affecting the discharge of hydronium ion . SAS also possesses the ability to considerably decrease the Nickel current efficiency within crease in SAS concentration in the electrolyte. Sodiumallylsulfonate, besides the other unsaturated sulfonates, is an important copolymerizable emulsifying agent in copolymerization with larger proportions of acrylonitrile for the preparation of dyeable acrylic fibers with improved whiteness. Because of the molecular structure; having a double bond; a sulfonate group and low molecular weight, Sodiumallylsulfonate is the preferred copolymer among the other unsaturated sulfonates. The compound was synthesized by using a new reagent other than recommended in literature. Allylbromide was used instead of allylchloride and methanol was used as the solvent in the reaction mixture. The analysis of the samples obtained from experiments, showed the identical properties with the commerciallyl used sample synthesized by allylchloride as the primary reagent. A number of experiments were carried out based on the same procedure but with different experimental reaction parameters . Physical and chemical tests were carried out on the products obtained . A process was then chosen to optimize the cost and ease of manufacture with the optimum results. The repetition of the experiments at the selected reaction conditions were examined, and it was found that at 44 and 180 minutes of reaction time the best yield and quality of SAS samples were obtained.
The predicted environmental distribution of substituted benzene derivatives
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) İşeri, Reyhan.; İnel, Yüksel.
The aim of this study is to calculate environmental equilibrium distributions of substituted benzenes and thus to indicate where each of them goes and what relative concentrations they adopt i n the environmental compartments. With the diversity of chemicals, reasons for predicting their environmental behaviour from their physicochemical properties such as vapor pressure, water solubility and n-octanol-water partition coefficient are obvious. In this study, Mackay's Level I Fugacity Model based on fugacity, a thermodynamic quantity related to chemical potential or activity that characterizes the escaping tendency from a phase, is used for calculations. The fugacity calculations are applied to an evaluative environment, " unit world" consisting of compartments of homogeneous air, soil, water, biota, suspended solids and sediment. Each compartment is assigned a reasonable volume and properties and I the equilibrium distributions of those chemicals are calculated using fugacity capacities that are calculated from physical and chemical data and partition coefficients. When the results are designed to yield priorities for each compartment, it is found that alkyl benzenes except butylbenzenexylenes, mono- and di -fluorobenzenes, mono- and di-bromobenzenes , mono-, di- tri-chlorobenzenes, iodobenzene for the air compartment, all phenols, all anilines , acetophenone, benzylcohol, butylbenzene, anisle, nitrobenzenes , diiodobenzenes , chlooiodobenzenes, bromoi odobenzenes, bromochl orobenzenes, iodobenzene, di bromobenzenes , tri bromobenzenes for the water compartment, diiodobenzenes, tribromobenzenes, hexachlorobenzene, bromoiodobenzenes, chloroiodobenzenes, tetrachlorobenzenes, pentachlorobenzene.for the biota, soil , sediment, and suspended solids compartments are priorities. During this work, good correlations between the mass partitioning of halobenzenes and total molecular surface area, molar volume and T hydrophobic substituent constant are obtained. The mass percentage values calculated by using the correlation equations obtained from this study are in agreement with those calculated through Mackay's Level I approach. Thus these correlations make it possible t o calculate the likely equilibrium distribution by using only one property.
The effect of selected pesticides on the growth and nitrogen fixation in cyanobacteria
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1992., 1992.) Güner (Sıvacı), Sima.; Çalgan, Dilek.
Algae, in general, are the primitive form of higher plants and they are found in water bodies and in moist locations such as tree trunks, walls, rocks and damp soil. Many species are found in all parts of the world, from the tropics to the polar regions. Water , light, temperature and the chemical composition of the medium are the factors that may stimulate or prevent the growth. The elements essential for the growth of algae are the same as those necessary for the growth of higher plants. Algae are used for the removal of pesticides from the aquatic environment, therefore their functions and responses to external effects resulting from the use of chemicals are of concern. The choice of algal species for bioassays is partly based on algae being the primary producers in aquatic ecosystems. Since pesticides are pollutants, it is better to analyze them on these living organisms, which can give an information about other higher plants. Contamination of aquatic and soil environments by pesticides results from agricultural origin. Pesticides enter the environment by direct or indirect routes. These agents can be sprayed on crops or dispersed in the field as a granular substance. Such pesticides are introduced directly into the aquatic environment. The cleaning of industrial mixing equipment, disposal of waste and accidents increase the amount of pesticides found in soil and water. Rain and other precipitation can carry pollutants to the fresh water systems, so causing harmful effects for the algae. The application of pesticides for plant protection and their persistent residues has direct effect on the fresh water algae and consequently the soil fertility. These pesticides applied directly or indirectly to soil may upset the ecological balance of the soil. This situation clearly explains the importance of studying the effects of pesticides on the different physiological and biological processes. Algal studies are recently well documented. Recent studies involve the use of some pesticides on algal cultures in order to examine their effects on growth and nitrogen fixation. Effects of chemical agents could quickly be investigated with blue-green algae before testing pesticides on higher plants. The aim of this study was to examine the toxicity effects of a herbicide 2,4- dichelorophenoxyacetic acid (2,4-D) and an insecticide methyl parathion on two algal species, one being a heterocystous filamentous cyanobacteria Anabaena cylindrica and the other, unicellular cyanobacteria Gloeocapsa. Toxicity determinations were based on the growth measurements of these species. Moreover, a specific property of blue-green algae, nitrogen fixing ability was determined by using acetylene reduction technique. During the experiments light intensity, temperature and pH were under the control.
Heterogeneous photocatalytic activity of transition-metal cation impregnated TiO2
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1993., 1993.) Rakshandeh (Bazargan), Parisa Deljouie.; İnel, Yüksel.
Irradiation of aqueous Ti02 dispersions containing metal ions with light of energy equal or greater than the bandgap of the catalyst. leads to a deposition on the semiconductor particle surface. This photodeposition process may be a phtotoreduction or an irreversible photosorption process depending on the redox potential of the couples in the solution. In this study, preparation of Ti02 impregnated by some selected cations of the first transition series: ( Cr(III), Mn(II), Fe(III), Fe(Il), Co(II) and Ni(II)] using dark and photocatalytic impregnation methods has been demonstrated. and the photocatalytic activity of these samples in photodegradation of 4-chlorophenol in aerated aqueous solutions has beeinvestigated by gas chromatography techniques. The effect of sulfate anion on the degree of 4-chlorophenol photooxidation to C02 has also been studied by the same method. The addition of alcohols, which scavenge the holes of the illuminated TiO2 renders the photodeposition process more efficient by preventing the recombination of holes with electrons on the catalyst's surface. This effect has been examined by using methanol as a model hole scavenger. Finally, BET surface areas for Co(II) and Ni(II) impregnated Ti02 samples were measured in a Micromeritics Flowsorb II 2300 instrument.
Photocatalytic degradation of phthalic anhydride and dicarboxylic acids
(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1994., 1994.) Ökte, Ayşe Neren.; İnel, Yüksel.
Exposure of Ti02 particles to light with an energy equal or greater than its bandgap leads to the creation of electrons and holes which are able to degrade toxic chemicals. In this study, in the presence of Degussa P25 TiO2, photocatalytic oxidation of phthalic anhydride, malonic acid, succinic acid, and adipic acid has been investigated by means of gas chromatography techniques following the CO2 formation. The alteration of pH of the aqueous suspension, TiO2 loading, anhydride or acids concentrations, irradiation time, flow rate, and light intensity changed the rate of formation sf C02 which has been investigated by the same method. It was also observed that the rate of CO2 formation increases linearly by increasing the temperature sf the suspension. The order of the reactions as well as the rate constants could be determined for the photocatalpic oxidation processes. As a consequence, by altering the concentration of malonic, succinic, and adipic acids we observed that their disappearance fits a Langmuir-Hinshelwood kinetic model. In other words, the photoocatalytic xidation reactions take place in the adsorbed phase, i.e., on the surface of Ti02. Rate constants was also calculated by including the correction term a(T) which stands in order to take into account the decrease in the solubility of CO2 with increasing temperature. These results led to the calculation of activation energy as: 3.19 kj/mole, 9.99 kj/mole, 15.59 kj/mole, and 14.38 kj/mole for phthalic anhydride, malonic acid, succinic acid, and adipic acid respectively. Finally, 0.43X10 -6 quantum yield for the CQ formation has been estimated from the proposed mechanisms.
Molecular dynamics study of macromolecular motions and polypeptide helical stabilities in solution
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1995., 1995.) Doruker, Pemra.; Bahar, Ivet.
Molecular dynamics simulations have been performed to investigate the relative importance of solvent effect and intramolecular conformational potentials on the properties of polymers in dilute solition. Bead-spring, free-rotating and polyethylene model chains, each composed of 30 beads, have been simulated in 738 solvent molecules. Results indicate that chain statistics are equally sensitive to solvent effect and intramolecular constraints, whereas local chain dynamics are predominantly described by intramolecular potentials. Translational diffusivities of all chains exhibit a linear decrease with increasing polymer-solvent interactions. A power law relation of the form t na is observed betveen the orientational correlation times t and the size n of chains segments for n = 8. a values increase with solvent quality. Stability of short helical polypeptides have been studied by molecular dynamics simulations. 13-residue polypeptides, composed of alanine, valine, serine or glycine, have been simulated in water and in vacuum. Water destabilizes the helical structure of alanine and valine, whereas glycine and serine exhibit intrinsic helix-breaking propensities in vacuum. Local solvation patterns around alanine Cb, valine Cg and serine Og atom are similar in helical state. Backbone hydrogen bonds are well protected by valine side chains, compared to alanine and serine.
A theoretical investigation of solvent effect on the conformational equilibria of 2-substituted cyclohexanone ketal derivatives
(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1995., 1995.) Sağ-Erdem, Safiye.; Varnalı, Tereza.; Aviyente, Viktorya.
The conformational equilibria of 6-substituted-1,4-dioxospiro-[4.5]decanes and 7substituted-1,5-dioxospiro [5.5]undecanes, relatively complex polar systems, with substituents X=-CH3, -F, -CI, -CN, -OH, -OCH3, -N02 have been studied. The complete geometry optimizations have been carried out sequentially in the gas phase and in solution to represent the effect of the solvent. The methodology consists of the semiempirical PM3 hamiltonian and the self consistent reaction field computations. The effect of the solvent is implemented by the "cavity model". Ab initio calculations have also been performed on 1 ,1 , 2-trihydroxy ethane as a model for the hydroxy derivatives of the ketals studied.The discussion of the results is focused on the solvent effects arising from structural aspects, steric and electrostatic interactions on the axial/equatorial relative stability. The role played by multipole moments is considered. Good agreement with available experimental data and with previous theoretical studies has been obtained in general. The semiempirical methods and the simple solvent models are useful to predict the main role of solute-solvent interactions in conformational equilibria of complex systems for which ab initio calculations cannot be performed.
Conformational analysis of 2-[(4-substituted-phenyl)seleno]-1,3-dithianes: |a theoretical approach
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Sciences and Engineering, 1997., 1997.) Şenyurt, Nurcan.; Aviyente, Viktorya.
In this study the conformational analysis of 2-(4-substituted-phenyl)seleno-1,3-dithiane with H, Cl, F, CH3, CF3, NO2, OCH3 and N(CH3)2 substituents have been studied computationally both in gas phase and in solvent with the semi-emprical PM3 method and ab initio HF/6-31G* basis sets. The optimized geometries have been discussed in terms of endo and exo anomeric effects and their presence in the axial conformers have been confirmed. The conformational free energies have been calculated in gaseous phase in solvent. Comparison between experimental and calculated values has shown that PM3 as well as HF/6-31G* can be used confidentially to treat conformational equilibrium for cyclohexane derivatives with S and Se.
Removal of impurities from copper and its alloys using ancient refining techniques
(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Sciences and Engineering, 1998., 1998.) Uluocak, Berivan Bilge Gedik. .; Özbal, Hadi.
There were two major objectives of this study both related to purification of impure copper metal using primitive refining techniques believed to have been used in antiquity. First part of the study was to remove iron impurity from bronze that is introduced when iron containing tin (hard-head) is used as source of tin. In the second part, simple refining methods are applied to highly impure copper metal obtained by smelting polymetallic copper ores. "Hard-head" which is a mixture of iron-tin compounds are biproduct of tin smelting process where cassiterite is contaminated with iron oreas. It was not possible to remove all of the tin held in hard-head and some tin is inevitably lost. Hard-head prills were prepared composed of 20 per cent iron ans 80 per cent tin under controller conditions, in clay crucibles. The hard-head prills were then added onto the molten copper metal in the furnace at 1200C. since all compositions of Sn-Fe compounds at 1200C and Cu and Fe does not make an alloy, tin is expected to be extracted by copper while rejecting the iron from the medium. The iron was then oxidized selectively either by the addition of natural fluxes (powdered marble and sand) or by fire-refining method. Experiments were carried out and it showed that, under addition of suitable fluxes, it was possible to remove over 85 per cent iron present in hard-head, leaving the concentration of iron in bronze under 0.5 per cent. The loss of tin, however was less than 20 per cent. It is concluded that unrefinable hard-head can be economically used in the production of bronze. Most primary copper ores are polymetallic in character and contains iron, lead, arsenic, nickel, antimony and zinc in varying amounts. There is ample evidence that such ores were smeltedtogether in antiquity yielding highly impure copper metal containing Pb, Zn, Sb, Ni, and Fe. To use such copper, it must be excessively refined. Fire refining methods were applied on the purification of impure copper that contains 20 per cent Pb, 5 per cent Zn, 5 per cent Sb, 2 per cent Ni, and 3 per cent Fe. Without any flux and using only air blast on the molten alloy, it was possible to remove about all of iron and zinc, and up to 50 per cent of the Pb, Sb, and Ni.

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