Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

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Chapter 1. Introduction This chapter is an overview on the literature of self-association of small organic molecules. The chapter is presented in four parts. First, an introduction to aggregation of small molecules is given with the emphasis on micelles and gels(Parts 1 and 2) In part 3, a short overview is given on bile acid based aggregates and their applications. Lastly, the content of the thesis is outlined. Chapter 2. Solution properties of novel cationic bil salts: A structure-aggregation property study Scheme 1: Structures of Cationic bile salts(Refer PDF File) Bile Salts are biosurfactants and they are known to form micelles in aqueous medium. We studied the micellar properties of cationic bile salts(Scheme 1) and compared with their natural (anionic) counterparts. A serendipitous discovery of the gelation of a cationic bile salt(4) led us to investigate the aggregation properties of this new class of cationic hydrogelators. This chapter highlights the recent efforts on the study of side chain structure-aggregation property relationship of cationic bile salts. Bile acid analogues with a quaternary ammonium group(Scheme 1, compounds 2, 3, 4, 6, 8 and 12) on the side chain were found to efficiently gel aqueous salt solutions. Some of the cationic bile salts gelled water alone and many of them gelled aqueous salt solutions even in the presence of organic co-solvents(≤ 20%) such as ethanol, methanol, DMSO and DMF. A strong counter ion dependent gelation was observed. These gels showed interconnected fibrous networks. Unlike natural anionic bile salt gels(reported for NaDC, NaLC), the cationicgels reported here are pH independent. Cationic gels derived from DCA showed more solid-like rheological response compared to natural NaDC gels studied earlier by Tato et al. A strong structure(side-chain) andcounter-ion dependent flow of the cationic bile salt gels was seen. Chapter 3. Applications of cationic bile salts and their aggregates Cationic bile salts are useful in many ways. We have studied some of the applications of cationic bile salts(discussed in chapter 2) and their aggregates in this chapter. The chapter is presented in three parts. Part 1. Interaction of Cationic bile salts and DNA The bile acid amphiphilicity is believed to help the DNA binding process of polyamines. This has prompted us to study the DNA-bile salt binding interaction of bile salts. The binding of cationic bile salts has been expressed in terms of C50 values, which were determined from the plot of fluorescence of ethidium bromide bound DNA vs. bile salt concentration(Fig 1) The C50 values for cationic bile salts were estimated to be about 1.2 mM. Fig1: A plot of fluorescene of ethidium bromide bound DNA against bile salt concentration (Refer PDF File) Part 2. Cholesterol solubilization and crystallization studies in aqueous bile salt solutions. Dihydroxy bile salt micelles are well known for cholesterol dissolution(e.g. UDCA and CDCA). We studied the dissolution of cholesterol in the cationic bile salt micelles(of 21-25) and the results are discussed in this part. Scheme 2: Cationic bile salt chlorides studied for cholesterol dissolution (Refer PDF File) A powder dissolution method was used to study the solubility of anhydrous cholesterol in cationic bile salt solution. These cationic bile salt micelles can dissolve cholesterol to the same extent as the taurine conjugates of bile acids, but lesser than the natural anionic bile salts(Fig.2) Addition of PC(Phosphatidylcholine) to cationic bile salt micelles enhanced the micellar cholesterol solubilization. Fig 2:Cholesterol dissolution in cationic bile salt solutions(Refer PDF File) The crystal nucleation time of cholesterol did not change significantly by adding 5-30 mM of the cationic bile salts. The bile salt analogues did, however, attenuate cholesterol crystallization to a similar extent at all concentrations studied. All these effects wer comparable to those fo cholic acid. Part 3. Hydrogels as a reaction vessel for photodimerization Bile salt micelles have been shown to control the product selectivity in photochemical reactions. The dynamic nature of the bile salt micelles results in differential effects on reaction selectivity. The photodimerization of acenaphthylene(sheme 3) was studied in micellar and hydrogel medium(e.g. NaDC, 22, 28, etc.) The ratio of anti- to synphotodimer was found to be greater in gel bound state than in solution. Substitution on the CAN ring did not show larger variation on the product distribution from solution gel. Scheme 3: Photodimerization of acenaphthylene(Refer PDF File) Chapter 4. Bile acid derived sulfur analogues in designing novel materials. Part 1. A simple approach towards nanoparticle-gel hybrid material. Scheme 4: Scheme for the synthesis of thiols derived from bile acids (Refer PDF File) Our interest in bile acid based gelator molecules led us to explore the synthesis and properties of bile analogues with the side chain carboxylic acid replaced by a thiol(Scheme 4) to stabilize metal NPs. We reasoned that the specific self-aggregation modes of facially amphiphilic bile units would enable a metal NP capped by such a thiol to “lock” onto a gel fiber derived from a structurally related gelator molecule. AuNPs stabilized by 38-40 were obtained by the NaBH4 reduction of homogeneous methanolic solutions of the thiol and gold salt. These steroid capped nanoparticles were found to stay dispersed in a gel of 28, thus providing a simple approach to obtain gel-nanoparticle hybrid. A photograph of the hybrid material and their morphology are shown in Fig 3.(Refer PDF File) Chart 1: Structure of the gelator used for designing a hybrid material(Refer PDF File) Part 2. Gelation of aromatic solvents using sulfur analogues of bile acid A few of the sulfur derivatives were serendipitously fouond to gel organic solvents (Fig 4). Thiol 38 formed stable gels at room temperatures while the disulphide 36 formed stable gels below 5º C. The aggregation properties, morphology, and the melting profiles of gels of disulfides and thiols derived from bile acids have been highlighted in this part. Fig 4: A photograph of the gels derived from 38(Refer PDF File) (For Figures and Molecular Formula Pl refer the Original Thesis)

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The possibility of manipulating calcium (Ca2+) and potassium (K+) levels in seeds of Brassica rapa by altering parent plant nutrition and investigating the potential for increased salinity tolerance during germination, given that considerable amounts of literature imply that greater amounts of available exogenous Ca2+ and K+ can ameliorate the effects of salinity on both whole plant growth and germination, was evaluated. The investigation consisted of four growth trials. Two preliminary growth trials suggested that seed ion manipulation was possible without affecting the overall growth and vigour of the plant. After developing suitable high and low Ca2+ and K+ nutrient solutions for growth, a trial was carried out in a growth room and greenhouse, with various substrates and the seed of a certain size category was collected for subsequent ion and salinity tolerance analysis. Seed Ca2+ and K+ was significantly affected by growth substrate and nutrient solution and data showed that a significant negative regression relationship existed between seed Ca2+, K+ and Ca2+ + K+ levels and salinity tolerance. Further experimentation using hydroponic culture attempted to remove any possible effects of substrate and also to compare size categories of seed with a view to elucidating localisation of Ca2+ and K+. Seed Ca2+ was found to be significantly altered by nutrient solution in the two different sizes tested and higher Ca2+ nutrient solution was found to increase salinity tolerance in daughter seed. One significant negative regression correlation between salinity tolerance and seed K+ concentration existed in smaller seed, but disregarding seed size in a regression analysis of seed ion content and salinity tolerance, a significant negative relationship existed between seed Ca2+, K+ and Ca2++ K+. The results, especially in terms of Ca2+ nutrition, contradict much previous research that suggests increased salinity tolerance at germination can arise with the increased presence of Ca2+ and/or K+. Salinity tolerance was greater in seeds of larger size across all nutritional treatments and the smaller size range exhibited increased Ca2+ and K+ per μg seed. Ca2+ concentration in smaller seeds with greater surface area:volume ratios provided a clue to the potential localisation of Ca2+. Cross sectional staining showed that a greater proportion of seed Ca2+ may reside in the coat. This was confirmed by analysis which showed an approximate 50% split of total extractable seed Ca2+, regardless of size, between coat and embryo within a seed; the majority of which, per μg, resides in the coat. Further work looked at the relative solubility of the Ca2+ and K+ in these tissues and whole seed to look at the potential bioavailability of Ca2+ during germination from various parts of the seed. Most water soluble Ca2+ exists in the embryo and most insoluble Ca2+ exists in the coat, but coat Ca2+ was found to be ionically exchangeable and therefore bioavailable. K+ appeared mostly water soluble in embryo and coat. In line with previous whole plant research in this species, most Ca2+ is readily water soluble or ionically exchangeable in form and the possible negative effects of how increasing bioavailable Ca2+ may reduce salinity tolerance was discussed.

Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Soil salinity is a major limiting factor of plant and crop growth, because the absorption of water and nutrients is such a complex process while low and moderate salinity are omnipresent. Plant growth is affected negatively if a specific ion concentration exceeds its threshold and becomes toxic. The detrimental effect of soil affected by salt on crop production is increasing worldwide (Tanji, 1990). The level to which plants can tolerate high salinity levels is genetically controlled with several physiological and genetic mechanisms contributing to salt tolerance (Epstein & Rains, 1987). The most effective way of addressing the limitations of crop productivity in saline areas, is the development of salt tolerant varieties. Understanding the genetics of salt tolerance is, therefore, necessary for the development of an effective breeding strategy for salt tolerance. The department of Genetics (US) conducts a wide crosses research programme aiming to transfer genes for salt tolerance to wheat and triticale. The donor species, Thinopyrum disticum, an indigenous coastal wheat grass, adapted to high concentrations of salt, was crossed with cultivated rye (Secale cereale) in an attempt to study the genetics of salt tolerance (Marais et al., 1998). The primary goal of this study was to find molecular markers (RAPD and AFLP) which associate with chromosomes promoting salt tolerance for later attempts to transfer the genes to triticale. Seventy clones of secondary hybrids (Th disticum /4x-rye 1/2x-rye) were tested for salt tolerance and showed different levels of salt tolerance. RAPD-marker analyses were used to identify polymorphisms between salt tolerant and salt sensitive plants. Twelve RAPD primers produced clear, analyzable and repetitive polymorphic . fragments that can be used as useful markers. Different AFLP-primer combinations were tested against the genotypes of 15 clones (Marais & Marais 2001, unpublished data) and produced approximately 2000 clearly distinguishable AFLP fragments, of which 54 (3%) were polymorphic fragments. Two RAPD fragments and 4 AFLP fragments that can be used as possible markers for the presence of chromosomes that contribute to salt tolerance were identified. The interpretation of the markers was complicated by heterogeneity among plants with regard to the origin of their chromosomes and the genetic diversity of the rye genome. It is also possible that chromosome re-arrangement took place during backcrossing, which could have complicated the data. / AFRIKAANSE OPSOMMING: Versouting is een van die groot beperkende faktore op plant- en gewasgroei, omdat die opname van water en voedingstowwe so In ingewikkelde proses is en die effek van lae of matige versouting so alomteenwoordig is. Plantgroei word nadelig geaffekteer as 'n spesifieke ioonkonsentrasie sy drempelwaarde oorskry en toksies word. Die nadelige effek van soutgeaffekteerde grond op gewasproduksie, is wêreldwyd aan die toeneem (Tanji, 1990). Die vlak waartoe plante hoë konsentrasies sout kan hanteer is onder genetiese beheer met verskeie fisiologiese en genetiese meganismes wat 'n bydrae maak tot soutverdraagsaamheid (Epstein & Rains, 1987). Die mees effektiewe manier om die beperkinge op gewas produktiwiteit in versoute gebiede te oorkom, is die ontwikkeling van soutverdraagsame variëteite. Begrip van die genetika van soutverdraagsaamheid is dus noodsaaklik vir die ontwikkeling van In effektiewe telingsstrategie. Die departement Genetika (US) bedryf tans 'n wye-kruisings navorsingsprogram waarmee gepoog word om gene vir soutverdraagsaamheid na korog en koring oor te dra. Die skenkerspesie, Thinopyrum disticum, In inheemse strandkoringgras wat aangepas is by hoë konsentrasies sout, is gekruis met verboude rog (Secale cereale) in 'n poging om die oorerwing van soutverdraagsaamheid te bestudeer (Marais et al., 1998). Die hoofdoel van hierdie studie was om molekulêre merkers (RAPD en AFLP) te vind, wat assosieer met chromosome wat soutverdraagsaamheid bevorder en om nuttige merkers daar te stel vir latere pogings om die gene na korog en koring oor te dra. Ongeveer 70 klone van sekondêre hibriede (Th distichum I 4x-rog /I 2x-rog) is onderwerp aan souttoetse en het verskillende grade van soutverdraagsaamheid getoon. RAPDmerker analise is gebruik om polimorfismes te identifiseer tussen soutverdraagsame en soutsensitiewe plante. Twaalf RAPD inleiers het duidelike, ontleedbare en herhalende polimorfiese fragmente opgelewer en moontlike nuttige merkers uitgewys. Verskillende AFLP-inleier kombinasies, wat getoets is teen die genotipes van 15 klone (Marais & Marais, 2001 ongepubliseerde data) het ongeveer 2000 duidelik onderskeibare AFLP fragmente geproduseer, waarvan 54 (3%) polimorfiese fragmente was. Twee RAPD fragmente en 4 AFLP fragmente is geïdentifiseer wat as moontlike kandidaat merkers gebruik kan word vir die identifisering van chromosome wat bydra tot soutverdraagsaamheid . Die interpretasie van die merkers is bemoeilik deur heterogeniteit tussen die plante wat betref die agtergrond van chromosome wat hulle besit en die genetiese diversiteit van die rog genoom. Dit is ook moontlik dat chromosoom herrangskikking plaasgevind het tydens terugkruising, wat die data verder kon kompliseer.

This work sought to enforce aromatic interactions between compatible π-molecular orbital systems with ionic bonding. In this case the interacting partners are oppositely charged discotic triangulene derivatives. The observed properties of the heterodimeric ion-pairs likely arise due to a hypothetical synergy between electrostatics and π-interactions. The work presented here describes investigation of putative covalency arising from this hypothetical synergy in the electrostatics driven π-stacking. In order to probe this, various hypotheses were made and experiments were designed to test their validity. The results from the experiments show existence of contact ion-pairs and complex solvent-separated discotic ions in solution. The formation of complex ion-pairs arise due to the fact that the electrostatic interaction that brings the discotic ions together is strong, but does not neutralize when the contact is made. So, the dipole created by the monopoles in a dimeric contact ion-pair can attract ions at both termini forming oligomers. This process apparently continues towards highly aggregated states and then to nanometric species and at some point the material precipitates. The propensity to aggregate and form complex-ions limited our approach to the measurement of the energetics of the ion-pairing for two reasons: (1) the observables had a complex dependence on temperature, solvent, concentration and ionic strength; and (2) the mass in solution was undergoing kinetic evolution towards solid states. The turbidimetric effects arising due to aggregate formation further complicated the extraction of weak interactions between the ions and hence effects determination of ion-pairing constants.

4 pp. / Managing salts in Southwestern pecan orchards can be a major challenge for growers, due to limited soil permeability and/or low-quality irrigation water.