Hydrogen bonding induced order in supramolecular polymers

The self-assembly of small and relatively simple molecules has proven to be a powerful tool for the development of complex supramolecular nanostructures of defined size and shape. More recently, the understanding of supramolecular polymeric aggregates has become a research aim, with the aim to increase the knowledge of the non-covalent interactions in factors that govern self-assembly in these systems. This thesis addresses the development of supramolecular polymers, which are based benzene-1,3,5-tricarboxamides (BTAs) and traditional polymers. BTAs comprising alkyl side chains form helical supramolecular polymers in dilute solution and in the solid state as a result of the threefold helical arrangement of the intermolecular hydrogen bonds. The self-assembly properties of BTAs combined with traditional polymers has led to the development of novel supramolecular materials. Because the chirality of monomeric BTAs is expressed at the supramolecular level, these systems allow the use of a wide range of spectroscopic techniques to study the self-assembly. As a result, valuable insights into the formation of the supramolecular structure of the resulting polymers was obtained, which are crucial to further develop the field of supramolecular polymers. In Chapter 1, an overview is given of supramolecular systems that self-assemble by the formation of hydrogen bonds. Special attention is paid to hydrogen bond strength and to approaches to increase the binding strength. In addition, three classes of supramolecular assemblies, in which the formation is hydrogen bonding driven, are discussed based on literature examples. This short literature overview includes systems such as supramolecular polymeric networks, disc-shaped motifs with the ability to form long elongated supramolecular polymers and the final class describes supramolecular assemblies, which are limited in size and shape as a result of their design. In Chapter 2, the self-assembly of BTAs into helical aggregates when end-capped to or copolymerized with low molecular weight polyethylene butylene is investigated in solution and in the solid state. Self-assembly is evaluated with a variety of spectroscopic techniques such as CD, UV and IR. The introduction of BTAs results in the formation of phase segregated nanorods. In some cases, this leads to drastic improvements of the material properties, as revealed by tensile testing and oscillating shear rheology measurements. A systematic study on the role of polarity on the self-assembly of BTAs in solution and on their ability to phase segregate in the solid state is performed in Chapter 3. In dilute solution, the polarity is varied by mixing polar and apolar solvents. In the solid state, a wide range of backbone polarities is covered by end-capping of telechelics of varying polarity with the BTA motif. In both cases, an increase of polarity leads to a significant decrease of the stability of BTA aggregates, which in the solid state eventually results in the loss of nanorod formation This study gives a detailed understanding of the scope and limitations of BTA based polymers for various applications. In Chapter 4, the use of BTA functionalized polymers as hydrogelators is explored. BTAs equipped with aliphatic side chains are end-capped to polyethylene glycol via a short apolar spacer. In water, long entangled nanorods were formed as a result of intermolecular hydrogen bonding stabilized by hydrophobic interactions. At higher concentrations, strong and transparent gels were obtained. The supramolecular structure and the material properties of the gel are determined with CD spectroscopy and with oscillating shear measurements. A supramolecular polymer system that consists of a mixture of BTAs and UPys, end-capped to monofunctional polymers is introduced in Chapter 5. Both supramolecular motifs self-assemble in an orthogonal fashion in two separate types of phase segregated nanorods. After the addition of an a, ¿-telechelic polymer containing both the BTA and UPy motif (compatibilizer) to this system, a cross-linked network is formed. This is observed by the transformation of a viscous sticky liquid into a solid material with elastomeric properties as evidenced by oscillating shear rheology measurements. The preliminary results presented in this study show the potential of orthogonal self-assembly based on hydrogen bonding motifs. In the final Chapter, the ability of BTAs grafted to the side chain of polymethacrylate to form well-defined nanosized objects comprising an internal helical architecture is investigated. These polymeric structures form ordered chiral single-chain polymeric nanoparticles in a controlled fashion. Controlled folding is achieved by making use of photolabile deprotection chemistry and with the aid of heating and cooling steps. This process is quantitatively followed with CD spectroscopy. The high stability and chiral conformation of the folded particles make them excellent candidates for compartmentalized catalytic systems

Crystal Structure of Agaricus bisporus Mushroom Tyrosinase: Identity of the Tetramer Subunits and Interaction with Tropolone

Tyrosinase catalyzes the conversion of phenolic compounds into their quinone derivatives, which are precursors for the formation of melanin, a ubiquitous pigment in living organisms. Because of its importance for browning reactions in the food industry, the tyrosinase from the mushroom Agaricus bisporus has been investigated in depth. In previous studies the tyrosinase enzyme complex was shown to be a H2L2 tetramer, but no clues were obtained of the identities of the subunits, their mode of association, and the 3D structure of the complex. Here we unravel this tetramer at the molecular level. Its 2.3 Å resolution crystal structure is the first structure of the full fungal tyrosinase complex. The complex comprises two H subunits of ~392 residues and two L subunits of ~150 residues. The H subunit originates from the ppo3 gene and has a fold similar to other tyrosinases, but it is ~100 residues larger. The L subunit appeared to be the product of orf239342 and has a lectin-like fold. The H subunit contains a binuclear copper-binding site in the deoxy-state, in which three histidine residues coordinate each copper ion. The side chains of these histidines have their orientation fixed by hydrogen bonds or, in the case of His85, by a thioether bridge with the side chain of Cys83. The specific tyrosinase inhibitor tropolone forms a pre-Michaelis complex with the enzyme. It binds near the binuclear copper site without directly coordinating the copper ions. The function of the ORF239342 subunits is not known. Carbohydrate binding sites identified in other lectins are not conserved in ORF239342, and the subunits are over 25 Å away from the active site, making a role in activity unlikely. The structures explain how calcium ions stabilize the tetrameric state of the enzyme.

Оцінювання зволоженості гірських водозборів при математичному моделюванні дощових паводків

Розроблено процедуру оцінювання зволоженості водозбору, яка не потребує тривалого моделювання в оперативних умовах.Разработана процедура оценивания увлажненности водосбора, которая исключает необходимость продолжительного моделирования в оперативных условиях

Determination of sodium fatty acid in soap Formulation Using Fourier Transform Infrared (FTIR) spectroscopy and multivariate calibrations.

Fourier Transform Infrared (FTIR) spectroscopy using an attenuated total reflectance (ATR) accessory has been investigated as a method for the determination of sodium-fatty acid (sodium-FA) in soap formulations. Multivariate calibrations namely partial least squares regression (PLS) and principle component regression (PCR) were developed for the prediction of sodium-FA using spectral ranges on the basis of relevant IR absorption bands related to sodium-FA. The sodium-FA content in soap formulations was predicted accurately at wavenumbers of 1,570–1,550 cm−1, which is specific for RCOO− Na+ vibration. The PLS method was found to be a consistently better predictor when both PLS and principal component regression (PCR) analyses were used for quantification of sodium-FA. Furthermore, FTIR spectroscopy can be an alternative technique to American oil Chemist Society methods which use a titrimetric technique because FTIR offers rapid, easy sample preparation and is friendly to the environment

Colour reconnection in e+e- -> W+W- at sqrt(s) = 189 - 209 GeV

The effects of the final state interaction phenomenon known as colour reconnection are investigated at centre-of-mass energies in the range sqrt(s) ~ 189-209 GeV using the OPAL detector at LEP. Colour reconnection is expected to affect observables based on charged particles in hadronic decays of W+W-. Measurements of inclusive charged particle multiplicities, and of their angular distribution with respect to the four jet axes of the events, are used to test models of colour reconnection. The data are found to exclude extreme scenarios of the Sjostrand-Khoze Type I (SK-I) model and are compatible with other models, both with and without colour reconnection effects. In the context of the SK-I model, the best agreement with data is obtained for a reconnection probability of 37%. Assuming no colour reconnection, the charged particle multiplicity in hadronically decaying W bosons is measured to be (nqqch) = 19.38+-0.05(stat.)+-0.08 (syst.).Comment: 30 pages, 9 figures, Submitted to Euro. Phys. J.

Determination of alpha_s using Jet Rates at LEP with the OPAL detector

Hadronic events produced in e+e- collisions by the LEP collider and recorded by the OPAL detector were used to form distributions based on the number of reconstructed jets. The data were collected between 1995 and 2000 and correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates were determined using four different jet-finding algorithms (Cone, JADE, Durham and Cambridge). The differential two-jet rate and the average jet rate with the Durham and Cambridge algorithms were used to measure alpha(s) in the LEP energy range by fitting an expression in which order alpah_2s calculations were matched to a NLLA prediction and fitted to the data. Combining the measurements at different centre-of-mass energies, the value of alpha_s (Mz) was determined to be alpha(s)(Mz)=0.1177+-0.0006(stat.)+-0.0012$(expt.)+-0.0010(had.)+-0.0032(theo.) \.Comment: 40 pages, 17 figures, Submitted to Euro. Phys. J.

Scaling violations of quark and gluon jet fragmentation functions in e+e- annihilations at sqrt(s) = 91.2 and 183-209 GeV

Flavour inclusive, udsc and b fragmentation functions in unbiased jets, and flavour inclusive, udsc, b and gluon fragmentation functions in biased jets are measured in e+e- annihilations from data collected at centre-of-mass energies of 91.2, and 183-209 GeV with the OPAL detector at LEP. The unbiased jets are defined by hemispheres of inclusive hadronic events, while the biased jet measurements are based on three-jet events selected with jet algorithms. Several methods are employed to extract the fragmentation functions over a wide range of scales. Possible biases are studied in the results are obtained. The fragmentation functions are compared to results from lower energy e+e- experiments and with earlier LEP measurements and are found to be consistent. Scaling violations are observed and are found to be stronger for the fragmentation functions of gluon jets than for those of quarks. The measured fragmentation functions are compared to three recent theoretical next-to-leading order calculations and to the predictions of three Monte Carlo event generators. While the Monte Carlo models are in good agreement with the data, the theoretical predictions fail to describe the full set of results, in particular the b and gluon jet measurements.Comment: 46 pages, 17 figures, Submitted to Eur. Phys J.

Measurement of the rate of nu_e + d --> p + p + e^- interactions produced by 8B solar neutrinos at the Sudbury Neutrino Observatory

Solar neutrinos from the decay of $^8$B have been detected at the Sudbury Neutrino Observatory (SNO) via the charged current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to nu_e's, while the ES reaction also has a small sensitivity to nu_mu's and nu_tau's. The flux of nu_e's from ^8B decay measured by the CC reaction rate is \phi^CC(nu_e) = 1.75 +/- 0.07 (stat)+0.12/-0.11 (sys.) +/- 0.05(theor) x 10^6 /cm^2 s. Assuming no flavor transformation, the flux inferred from the ES reaction rate is \phi^ES(nu_x) = 2.39+/-0.34 (stat.)+0.16}/-0.14 (sys) x 10^6 /cm^2 s. Comparison of \phi^CC(nu_e) to the Super-Kamiokande Collaboration's precision value of \phi^ES(\nu_x) yields a 3.3 sigma difference, providing evidence that there is a non-electron flavor active neutrino component in the solar flux. The total flux of active ^8B neutrinos is thus determined to be 5.44 +/-0.99 x 10^6/cm^2 s, in close agreement with the predictions of solar models.Comment: 6 pages (LaTex), 3 figures, submitted to Phys. Rev. Letter