Quantum Chemical Studies on Tropospheric Nucleation Mechanisms Involving Sulfuric Acid

Nucleation is the first step of the process by which gas molecules in the atmosphere condense to form liquid or solid particles. Despite the importance of atmospheric new-particle formation for both climate and health-related issues, little information exists on its precise molecular-level mechanisms. In this thesis, potential nucleation mechanisms involving sulfuric acid together with either water and ammonia or reactive biogenic molecules are studied using quantum chemical methods. Quantum chemistry calculations are based on the numerical solution of Schrödinger's equation for a system of atoms and electrons subject to various sets of approximations, the precise details of which give rise to a large number of model chemistries. A comparison of several different model chemistries indicates that the computational method must be chosen with care if accurate results for sulfuric acid - water - ammonia clusters are desired. Specifically, binding energies are incorrectly predicted by some popular density functionals, and vibrational anharmonicity must be accounted for if quantitatively reliable formation free energies are desired. The calculations reported in this thesis show that a combination of different high-level energy corrections and advanced thermochemical analysis can quantitatively replicate experimental results concerning the hydration of sulfuric acid. The role of ammonia in sulfuric acid - water nucleation was revealed by a series of calculations on molecular clusters of increasing size with respect to all three co-ordinates; sulfuric acid, water and ammonia. As indicated by experimental measurements, ammonia significantly assists the growth of clusters in the sulfuric acid - co-ordinate. The calculations presented in this thesis predict that in atmospheric conditions, this effect becomes important as the number of acid molecules increases from two to three. On the other hand, small molecular clusters are unlikely to contain more than one ammonia molecule per sulfuric acid. This implies that the average NH3:H2SO4 mole ratio of small molecular clusters in atmospheric conditions is likely to be between 1:3 and 1:1. Calculations on charged clusters confirm the experimental result that the HSO4- ion is much more strongly hydrated than neutral sulfuric acid. Preliminary calculations on HSO4- NH3 clusters indicate that ammonia is likely to play at most a minor role in ion-induced nucleation in the sulfuric acid - water system. Calculations of thermodynamic and kinetic parameters for the reaction of stabilized Criegee Intermediates with sulfuric acid demonstrate that quantum chemistry is a powerful tool for investigating chemically complicated nucleation mechanisms. The calculations indicate that if the biogenic Criegee Intermediates have sufficiently long lifetimes in atmospheric conditions, the studied reaction may be an important source of nucleation precursors.

Impedance studies on high energy Li3+ irradiated PZT thin films

The ferroelectric Pb(Zr0.48Ti0.52)O-3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiatedfilms, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Synthetic and conformational studies on dehydroalanine-containing model peptides

Three model dipeptides containing a dehydroalanine residue (Ala) at the C-terminal, Boc-X-Ala-NHCH3 [X = Ala, Val, and Phe,] have been synthesized and their solution conformations investigated by 1H-NMR, IR, and CD spectroscopy. NMR studies on these peptides in CDCl3 clearly indicate that the NH group of dehydroalanine is involved in an intramolecular hydrogen bond. This conclusion is supported by IR studies also. Nuclear Overhauser effect (NOE) studies are also accommodative of an inverse -turn-type of conformation that is characterised by conformational angles of -70° and +70° around the X residue, and a C[stack i+1 ]H-Ni+2H interproton distance of 2.5 Å. It appears that unlike dehydrophenylalanine or dehydroleucine, which tend to stabilize -turn type of structures occupying the i + 2 position of the turn, dehydroalanine favors the formation of an inverse -turn, centered at the proceeding L-residue in such solvents as CDCl3 and (CD3)2SO. A comparison of solution conformation of Boc Val-Ala-NHCH3 with the corresponding saturated analogue, Boc-Val-Ala-NHCH3, is also presented and shows that dehydroalanine is responsible for inducing the turn structure. It may be possible to design peptides with different preferred conformations using the suitable dehydroamino acid.

Studies on the ionic transport and structural investigations of La0.5Li0.5TiO3 perovskite synthesized by wet chemical methods and the effect of Ce, Zr substitution at Ti site

La0.5Li0.5TiO3 perovskite was synthesized by various wet chemical methods. By adopting low temperature methods of preparation lithium loss from the material is prevented. La0.5Li0.5TiO3 (LLTO) was formed with cubic symmetry at 1473 K. LLTO was formed at relatively lower temperature by using hydrothermal preparation method. PVA gel-decomposition route yield tetragonal LLTO on annealing the dried gel at 1473 K. By using gel-carbonate route LiTi2O4 minor phase was found to remain even after heat-treatment at 1473 K. The hydroxylation of LLTO was done in deionized water as well as in dilute acetic acid medium. By hydroxylation process incorporation of hydroxyls and leaching out of Li+ was observed from the material. The Li+ concentration of these compositions was examined by AAS. The electrical conductivities of these compositions were measured by dc and ac impedance techniques at elevated temperatures. The activation energies of electrical conduction for these compositions were estimated from the experimental results. The measured activation energy of Li+ conduction is 0.34 eV. Unhydroxylated samples exhibit only Li+ conduction, whereas, the hydroxylated LLTO show proton conductivity at 298-550 K in addition to Li+ conductivity. The effect of Zr or Ce substitution in place of Ti were attempted. La0.5Li0.5ZrO3 Perovskite was not formed; instead pyrochlore phase (La2Zr2O7) along with monoclinic ZrO2 phases was observed above 1173 K; below 1173 K cubic ZrO2 is stable. (La0.5Li0.5)(2)CeO4 solid solution was formed in the case of Ce substitution at Ti sublattice on heat-treatment up to 1673 K. (c) 2005 Springer Science + Business Media, Inc.

Studies on structural and electrical properties of sprayed SnO2 : Sb films

Thin films of antimony-doped tin oxide (SnO2:Sb) were prepared by spray pyrolysis using stannous chloride (SnCl2) and antimony trichloride (SbCl3) as precursors. The antimony doping was varied from 0 to 4 wt%. Scanning electron microscopy (SEM) revealed the surface morphology to be very smooth, yet grainy in nature. X-ray diffraction (XRD) shows films to have preferred orientation, which varies with the extent of antimony doping: undoped films prefer the (2 1 1) orientation, while the (3 0 1) orientation is preferred for doping levels of 0.5 and 1.0 wt%. For higher doping levels, the (2 0 0) orientation is preferred. This difference in preferred orientations is reflected in the SEM of the films. Atomic force microscopy (AFM) reveals that film roughness is not affected by antimony doping. The minimum sheet resistance (2.17 ohm/square) achieved in the present study is lower than values reported to date in SnO2:Sb films prepared from SnCl2 precursor. The Hall mobility of undoped SnO2 films was found to be 109.52 cm(2)/V s, which reduces to 2.55 cm(2)/ Vs for the films doped with 4 wt% of Sb. On the other hand, the carrier concentration, which is 1.23 x 10(19) cm(-3) in undoped films, increases to 2.89 x 10(21) cm(-3) for the films doped with 4 wt% of Sb. (c) 2004 Elsevier B.V. All rights reserved.

Unfolding studies on soybean agglutinin and concanavalin a tetramers: A comparative account

The unfolding pathway of two very similar tetrameric legume lectins soybean agglutinin (SBA) and Concanavalin A ( ConA) were determined using GdnCl-induced denaturation. Both proteins displayed a reversible two-state unfolding mechanism. The analysis of isothermal denaturation data provided values for conformational stability of the two proteins. It was found that the DeltaG of unfolding of SBA was much higher than ConA at all the temperatures at which the experiments were done. ConA had a T-g 18 degreesC less than SBA. The higher conformational stability of SBA in comparison to ConA is largely due to substantial differences in their degrees of subunit interactions. Ionic interactions at the interface of the two proteins especially at the noncanonical interface seem to play a significant role in the observed stability differences between these two proteins. Furthermore, SBA is a glycoprotein with a GlcNac(2)Man(9) chain attached to Asn-75 of each subunit. The sugar chain in SBA lies at the noncanonical interface of the protein, and it is found to interact with the amino acid residues in the adjacent noncanonical interface. These interactions further stabilize SBA with respect to ConA, which is not glycosylated.

Studies on Binary Time Series Models with Applications to Empirical Macroeconomics and Finance

This thesis studies binary time series models and their applications in empirical macroeconomics and finance. In addition to previously suggested models, new dynamic extensions are proposed to the static probit model commonly used in the previous literature. In particular, we are interested in probit models with an autoregressive model structure. In Chapter 2, the main objective is to compare the predictive performance of the static and dynamic probit models in forecasting the U.S. and German business cycle recession periods. Financial variables, such as interest rates and stock market returns, are used as predictive variables. The empirical results suggest that the recession periods are predictable and dynamic probit models, especially models with the autoregressive structure, outperform the static model. Chapter 3 proposes a Lagrange Multiplier (LM) test for the usefulness of the autoregressive structure of the probit model. The finite sample properties of the LM test are considered with simulation experiments. Results indicate that the two alternative LM test statistics have reasonable size and power in large samples. In small samples, a parametric bootstrap method is suggested to obtain approximately correct size. In Chapter 4, the predictive power of dynamic probit models in predicting the direction of stock market returns are examined. The novel idea is to use recession forecast (see Chapter 2) as a predictor of the stock return sign. The evidence suggests that the signs of the U.S. excess stock returns over the risk-free return are predictable both in and out of sample. The new "error correction" probit model yields the best forecasts and it also outperforms other predictive models, such as ARMAX models, in terms of statistical and economic goodness-of-fit measures. Chapter 5 generalizes the analysis of univariate models considered in Chapters 2 4 to the case of a bivariate model. A new bivariate autoregressive probit model is applied to predict the current state of the U.S. business cycle and growth rate cycle periods. Evidence of predictability of both cycle indicators is obtained and the bivariate model is found to outperform the univariate models in terms of predictive power.

Structure determination and biochemical studies on Bacillus stearothermophilus E53Q serine hydroxymethyltransferase and its complexes provide insights on function and enzyme memory

Serine hydroxymethyltransferase (SHMT) belongs to the alpha-family of pyridoxal 5'-phosphate-dependent enzymes and catalyzes the reversible conversion of L-Ser and etrahydrofolate to Gly and 5,10-methylene tetrahydrofolate. 5,10-Methylene tetrahydrofolate serves as a source of one-carbon fragment in many biological processes. SHMT also catalyzes the tetrahydrofolate-independent conversion of L-allo-Thr to Gly and acetaldehyde. The crystal structure of Bacillus stearothermophilus SHMT (bsSHMT) suggested that E53 interacts with the substrate, L-Ser and etrahydrofolate. To elucidate the role of E53, it was mutated to Q and structural and biochemical studies were carried out with the mutant enzyme. The internal aldimine structure of E53QbsSHMT was similar to that of the except for significant changes at Q53, Y60 and Y61. The wild-type enzyme, carboxyl of Gly and side chain of L-Ser were in two conformations in the respective external aldimine structures. The mutant enzyme was completely inactive for tetrahydrofolate-depen dent cleavage of L-Ser, whereas there was a 1.5-fold increase in the rate of tetrahydrofolate-independent reaction with L-allo-Thr. The results obtained from these studies suggest that E53 plays an essential role in tetrahydrofolate/5-formyl tetrahydrofolate binding and in the proper positioning of C beta of L-Ser for direct attack by N5 of tetrahydrofolate. Most interestingly, the structure of the complex obtained by cocrystallization of E53QbsSHMT with Gly and 5-formyl tetrahydrofolate revealed the gem-diamine form of pyridoxal 5'-phosphate bound to Gly and active site Lys. However, density for 5-formyl tetrahydrofolate was not observed. Gly carboxylate was in a single conformation, whereas pyridoxal 5'-phosphate had two distinct conformations. The differences between the structures of this complex and Gly external aldimine suggest that the changes induced by initial binding of 5-formyl tetrahydrofolate are retained even though 5-formyl tetrahydrofolate is absent in the final structure. Spectral studies carried out with this mutant enzyme also suggest that 5-formyl tetrahydrofolate binds to the E53QbsSHMT-Gly complex forming a quinonoid intermediate and falls off within 4 h of dialysis, leaving behind the mutant enzyme in the gemdiamine form. This is the first report to provide direct evidence for enzyme memory based on the crystal structure of enzyme complexes.

The sources of moral motivation : studies on empathy, guilt, shame and values

The goals of this study were to analyze the forms of emotional tendencies that are likely to motivate moral behaviors, and to find correlates for these tendencies. In study 1, students narratives of their own guilt or shame experiences were analyzed. The results showed that pure shame was more likely to motivate avoidance than reparation, whereas guilt and combination of guilt and shame were likely to motivate reparation. However, all types of emotion could lead to chronic rumination if the person was not clearly responsible for the situation. In study 2, the relations of empathy with two measures of guilt were examined in a sample of 13- to 16-year-olds (N=113). Empathy was measured using Davis s IRI and guilt by Tangney s TOSCA and Hoffman s semi-projective story completion method that includes two different scenarios, guilt over cheating and guilt over inaction. Empathy correlated more strongly with both measures of guilt than the two measures correlated with each other. Hoffman s guilt over inaction was more strongly associated with empathy measures in girls than in boys, whereas for guilt over cheating the pattern was the opposite. Girls and boys who describe themselves as empathetic may emphasize different aspect of morality and feel guilty in different contexts. In study 3, cultural and gender differences in guilt and shame (TOSCA) and value priorities (the Schwartz Value Survey) were studied in samples of Finnish (N=156) and Peruvian (N=159) adolescents. Gender differences were found to be larger and more stereotypical among the Finns than among the Peruvians. Finnish girls were more prone to guilt and shame than boys were, whereas among the Peruvians there was no gender difference in guilt, and boys were more shame-prone than girls. The results support the view that psychological gender differences are largest individualistic societies. In study 4, the relations of value priorities to guilt, shame and empathy were examined in two samples, one of 15 19-year-old high school students (N = 207), and the other of military conscripts (N = 503). Guilt was, in both samples, positively related to valuing universalism, benevolence, tradition, and conformity, and negatively related to valuing power, hedonism, stimulation, and self-direction. The results for empathy were similar, but the relation to the openness conservation value dimension was weaker. Shame and personal distress were weakly related to values. In sum, shame without guilt and the TOSCA shame scale are tendencies that are unlikely to motivate moral behavior in Finnish cultural context. Guilt is likely to be connected to positive social behaviors, but excessive guilt can cause psychological problems. Moral emotional tendencies are related to culture, cultural conceptions of gender and to individual value priorities.

Studies on strontium titanate/barium zirconate superlattices

Artificial superlattices of SrTiO3 and BaZrO3 were grown epitaxially with different periodicities on SrRuO3 coated (00 1) SrTiO3 substrates by pulsed excimer laser ablation. Superlattices were structurally characterized by X-Ray theta-2 theta diffraction data. Electrical characterization was done in metal-insulation-metal configuration. Capacitance-voltage measurements showed limited amount of tunability. The DC field induced tunability has been observed to be sensitive to the periodicity of the superlattices, hence the effective strain present in the layers. Hysteretic behaviour in capacitance-voltage (C-V) and polarization versus electric field (P-E) results from the superlattices also indicate the sensitivity of the interfaces. Interfacial strain is supposed to be the most probable cause for such a behaviour which is also manifested in the variation of dielectric constant with individual layer thicknesses. (c) 2007 Elsevier Ltd. All rights reserved.

Studies on a chitooligosaccharide-specific lectin from Coccinia indica. Thermodynamics and kinetics of umbelliferyl glycoside binding.

Coccinia indica agglutinin (CIA) is a chitooligosaccharide-specific lectin with two binding sites/homodimer of M(r) 32,000. Quenching studies implied tryptophan involvement in binding activity, which was confirmed by chemical modification experiments (A. R. Sanadi and A. Surolia, submitted for publication). Binding of 4-methylumbelliferyl chitooligosaccharides has been carried out to study their binding by CIA. Reversal experiments confirm the validity of the data previously obtained (A. R. Sanadi and A. Surolia, submitted for publication) from intrinsic fluorescence studies. Surprisingly, unlike wheat germ agglutinin, there is no consistent thermodynamic effect of the chromophoric label on binding activities as compared with the native sugars. From the changes in the optical properties of the chromophoric group upon binding to CIA, it has been possible to confirm that the tryptophan located in the binding site is closest to the fourth subsite. Thermodynamic analysis shows that the binding of the labeled tetrasaccharide is very strongly entropically driven, with the terminal, nonreducing sugar residue protruding from the binding pocket. The results of stopped-flow kinetic studies on the binding of the chromophoric trisaccharide by CIA show that the mechanism of binding is a one-step process.

Thermodynamic and kinetic studies on the mechanism of binding of methylumbelliferyl galactosides to the basic agglutinin from winged bean (Psophocarpus tetragonolobus)

The binding of winged bean basic agglutinin (WBA I) to 4-methylumbelliferyl (MeUmb) galactosides was examined by extrinsic fluorescence titration and stopped-flow spectrofluorimetry. Upon binding to WBA I, MeUmb alpha-galactosides show quenching in fluorescence intensity, decrease in UV absorbance with a concomitant blue shift, and decrease in fluorescence excited-state lifetimes. However, their beta-analogues show enhancement in fluorescence intensity, increase in UV absorbance with a red shift, and an increase in fluorescence excited-state lifetimes. This implies that the umbelliferyl groups of alpha- and beta-galactosides experience non-polar and polar microenvironments, respectively, upon binding to WBA I. Replacement of the anomeric hydroxyl group of galactose by 4-methylumbelliferyl moiety increases the affinity of resulting saccharides. Substitution of C-2 hydroxyl of galactose by an acetamido group leads to increased affinity due to a favorable entropy change. This suggests that acetamido group of MeUmb-alpha/beta-GalNAc binds to a relatively non-polar subsite of WBA I. Most interestingly, this substitution also reduces the association rate constants dramatically. Inspection of the activation parameters reveals that the enthalpy of activation is the limiting factor for the differences in the forward rate constants for these saccharides and the entropic contribution to the activation energy is small

Thermodynamic and kinetic studies on the mechanism of binding of methylumbelliferyl glycosides to jacalin

The binding of Artocarpus integrifolia lectin (jacalin) to 4-methylumbelliferyl (Meumb)-glycosides, Gal alpha Meumb, Gal beta Meumb, GalNAc alpha Meumb, GalNAc beta-Meumb, and Gal beta 3GalNAc beta Meumb was examined by extrinsic fluorescence quenching titration and stopped flow spectrofluorimetry. The binding was characterized by 100% quenching of fluorescence of Meumb-glycosides. Their association constants range from 2.0 x 10(4) to 1.58 x 10(6) M-1 at 15 degrees C. Entropic contribution is the major stabilizing force for avid binding of Meumb-glycosides indicating the existence of a hydrophobic site that is complementary to their methylumbelliferyl group. The second order association rate constants for interaction of these sugars with lectin at 15 degrees C vary from 8.8 x 10(5) to 3.24 x 10(6) M-1 S-1, at pH 7.2. The first order dissociation rate constants range from 2.30 to 43.0 S-1 at 15 degrees C. Despite the differences in their association rate constants, the overall values of association constants for these saccharides are determined by their dissociation rate constants. The second order rate constant for the association of Meumb-glycosides follows a pattern consistent with the magnitude of the activation energies involved therin. Activation parameters for association of all ligands illustrate that the origin of the barrier between binding of jacalin to Meumb-glycosides is entropic, and the enthalpic contribution is small. A correlation between these parameters and the structure of the ligands on the association rates underscores the importance of steric factors in determining protein saccharide recognitions.

Group Beliefs : Studies on the Nature and Logic of Collective Doxastic Attitudes

This thesis studies the nature and logic of collective doxastic attitudes, or what is referred to in ordinary language as "group beliefs". Beliefs and other intentional attitudes are attributed to groups and collections of people, and such attributions are used to explain and predict the actions of groups. The thesis develops an understanding of group beliefs as voluntarily adopted views or acceptances rather than as ordinary beliefs. Such an understanding can provide new answers to questions concerning collective knowledge and justification of group beliefs, and it allows developing modal logics with collective doxastic and epistemic notions. The thesis consists of six articles. The first three articles are philosophical studies concerned with the nature of group beliefs. The last three articles are logical studies that aim at developing proof-theoretical calculi for reasoning about collective doxastic attitudes.

Studies on the tryptophan residues of soybean agglutinin. Involvement in saccharide binding

Modification of tryptophan side chains of soybean agglutinin (SBA) with N-bromosuccinimide results in a loss of the hemagglutinating and carbohydrate binding activities of the protein. One residue/subunit is probably essential for the binding activity. Modification leads to a large decrease in the fluorescene of the protein accompained by a blue shift. Iodide ion quenching of the protein fluorescence shows that saccharide binding results in a decreased accessibility of some of the tryptophan side chains. These results strongly point towards the involvement of tryptophan residues in the active site of SBA.