Carboxylated macromolecules such as alginate and glycoproteins are abundant components of modern shallow marine sediments where they are secreted by bacteria and marine infauna. Both organic compounds are proton and metal reactive; hence, they have the potential to facilitate metal sorption and biomineralization reactions. In this study, lab experiments were coupled to field-based sampling to assess the role that these compounds play in microbial mats, with particular emphasis on the hypersaline lagoons of Los Roques, Venezuela. Here I applied a surface complexation approach to model proton and Cd adsorption behaviour of both uronic acid-rich alginate and mucin. Measured total site concentrations, available for metal adsorption, demonstrate that these compounds have the potential to induce metal partitioning in early diagenetic microenvironments. Field results from Venezuela are consistent with Mg- and trace metal- enrichment that follows a likely correlation with the degradation states of microbial biomass trapped during accretion of modern microbialites.

No description available.

In addition to AtCPL1-4, the genome of Arabidopsis thaliana encodes a large number of putative acid phosphatases. The predicted Arabidopsis SCP1-like small phosphatases (SSP) are highly homologous to the catalytic domain of eukaryotic RNA polymerase II carboxyl terminal domain (pol II CTD) phosphatases. Among the family members, SSP4, SSP4b and SSP5 form a unique group characterized by long N-terminal extensions. These three SSPs showed similar and ubiquitous gene expression. SSP4 and SSP4b were localized exclusively in the nuclei, while SSP5 accumulated both in the nucleus and cytoplasm. In vitro observation revealed that SSP4 and SSP4b dephosphorylated the pol II CTD-PO4 at both Ser2 and Ser5 in the conserved heptad repeats; however, SSP5 dephosphorylated only Ser5 of CTD-PO4. These results indicate that Arabidopsis SSP family encodes active CTD phosphatases similarly to animal SCP1 family proteins and plant CPLs family proteins, but with distinct substrate specificities. ssp mutants did not exhibit phenotypic abnormalities under normal growth conditions. However, ssp5 single mutants and ssp4 ssp4b ssp5 triple mutants showed enhanced sensitivity to ABA and glucose during seed germination. Yet, increased ABA-inducible gene expressions were not distinguishable in triple mutants compared to wild type plants upon ABA treatment. Unlike the ssp mutations, the cpl1 mutation strongly induced RD29A expression in response to cold, ABA and NaCl treatments. Thus, the cpl1 mutant is an ideal genetic background for an inducible gene expression system, in which the detrimental effect to host plants caused by a conventional constitutive expression could be avoided. Production of flavonoid such as anthocyanins in Arabidopsis is relatively easy to monitor and is regulated by transcription factors such as PAP1. PAP1 activates the expression of multiple enzymes in the anthocyanin biosynthesis pathway; however, high level of flavonoid production could cause vegetative growth retardation. To optimize flavonoid accumulation, a three-component system was designed consisting of a cold inducible RD29A-PAP1 expression cassette, a feedforward effector RD29A-CBF3, and a mutation in host repressor CPL1. Transgenic cpl1 plants containing both homozygous PAP1 and CBF3 transgenes produced 30-fold higher level of total anthocyanins than control plants upon cold treatment. LC/MS/MS analysis showed the flavonoid profile in cold-induced transgenic plants resembled that of previously reported pap1-D plants but were enriched for kaempferol derivatives. Furthermore, PAP1 and environmental signals synergistically regulate flavonoid pathway to produce a flavonoid blend that has not been produced by PAP1 overexpression or cold treatment alone. These results delineate the usability of the three-component inducible system in plant metabolic engineering.

No description available.

There is no available information in the literature on interaction between carboxyl hydrogen and ω-phenyl groups. Consequently, it was of interest to seek such interactions. Some form of interaction is evident from the study of the spectra of some phenylalkanoic acids and benzoyalkanoic acids.

<p> N-[(9-β-D-ribofuranosyl-9H-purin-6-yl)carbamoyl]- threonine, a hypermodified nucleoside found in transfer RNA represents the archetype structure of a group of synthetic ureidopurines which promote cell division in plants. L-threonine was shown to be incorporated into this nucleoside in Tobacco tissue and Rhizopogon roseolus transfer RNA. Also, this nucleoside was isolated as a free molecule in Rhizopogon roseolus growth medium.</p> <p> Chromatographic analysis of an enzymic hydrolysate of 3 g of yeast transfer RNA failed to indicate the presence of a lipophilic derivative of PCT riboside. It is concluded that PCT riboside occurs in transfer RNA with a free carboxyl group.</p> / Thesis / Master of Science (MSc)

Baxa is a pro-apoptotic member of the Bcl-2 protein family that regulates a key point in the control of apoptosis. The bax RNA undergoes a complex pattern of RNA splicing, with eight splice isoforms known to date. The next most abundant isoform to Baxa is Baxp, which has a unique carboxyl-terminal sequence and consequently lacks the transmembrane domain of Baxa. This study characterized Baxp as part of a larger project aimed at deducing the role of cellular localization in Bax protein function. A transient transfection assay was designed to determine the cell death activity of a protein in adherent cells. Baxp induced cell death to a greater extent than Baxa when transiently expressed in NIH 3T3 cells. The levels of Baxp expression were always low, regardless of the cell type or transfection method used. Additionally, Baxp adopted a conformation in which amino acids 13 to 19 are accessible to the monoclonal antibody 6A7. In Baxa this epitope is only exposed in the membrane-bound activated conformation that is associated with accessibility of the BH3 domain of Baxa that mediates protein-protein interactions among Bcl-2 family members. Although the mechanism remains elusive, Baxp was identified as a potent inducer of cell death. / Thesis / Master of Science (MSc)

Vaal University of Technology / ii Abstract The use of biosorption to complement conventional water treatment techniques has gained widespread appeal partly due to the abundance of waste materials that can be used as low cost biosorbents. However, some materials have not yet been exploited in this regard. This research was aimed at evaluating the biosorption potential of Mangifera indica (mango) seed shells that are readily available in several farming areas of the Limpopo and Mpumalanga Provinces of South Africa. In this work, powdered ethylenediaminetetraacetic acid (EDTA) functionalized biosorbent was prepared from alkali treated biomass of waste mango seed shells. The influence of alkali treatment and EDTA functionalization on the physicochemical properties of the biomass was characterized using Fourier transform infra-red spectroscopy, X-ray diffraction and thermogravimetric analysis. Results confirmed removal of hemicelluloses, conversion of crystalline to amorphous cellulose and the introduction of carboxyl, ester and tertiary amine groups from EDTA. Furthermore, the powdered biosorbent was immobilized using calcium alginate for adaptation to column sorption. The powdered biosorbents were tested for sorption of lead(II) ions using batch sorption experiment. Through EDTA functionalization, improvement in sorption capacity for lead(II) ions from 59.25 mg.g-1 to 306.33 mg.g-1 was realized. The Langmuir and Pseudo-nth order models most suitably simulated the equilibrium and kinetics of sorption by both functionalized and non-functionalized biomaterials. The calcium alginate immobilized biosorbent was evaluated for non-specific sorption of ionic species of copper, chromium, nickel and iron from electroplating wastewater through discontinuous column sorption experiments. Highest copper, chromium, nickel and iron removal was 12.3%, 14.8%, 4.4% and 13.8% from nonacidified samples at an initial pH of 3.4, and 15.5%, 18.7%, 13.7% and 17.3% from samples acidified to an initial pH of 1.8. Repeated sorption-desorption cycles involving acidified wastewater resulted in successive improvement in metal uptake against declining recovery indicating irreversible binding on –COOH groups formed from –CH2OH groups through a redox reaction involving reduction of chromium(VI) to chromium(III). Keywords: Mangifera indica; biosorption; alkali treatment; carboxyl functionalization; calcium alginate

This thesis is concerned with the use of Lewis base organocatalysts for carboxyl and acyl transfer reactions. Chapter 1 introduces the ability of organic Lewis bases other than DMAP-type to promote a range of asymmetric O-, N- and C-acyl transfer processes. This chapter summarizes the developments in catalyst architectures and approaches to these processes that have been disclosed to date in this dynamic area of asymmetric organocatalysis. Chapter 2 introduces studies into the synthesis of pyrrolyl carbonates via cyclization of gamma-amino esters and ring closing metathesis (RCM) of N-allylamides. The ability of a range of Lewis bases to promote the regioselective O- to C-carboxyl transfer of pyrrolyl carbonates is also presented. Chapter 3 introduces isothiourea DHPB as an efficient Lewis base catalyst for the diastereoselective C-acylation of silyl ketene acetals with anhydrides or benzoyl fluoride, giving 3-acyl-3-aryl or 3-acyl-3-alkylfuranones in excellent yields and stereoselectivities (up to 99:1 dr). Chapter 4 introduces C(2)-aryl substituted DHPB derived-isothioureas as efficient Lewis base catalysts for the enantioselective C-acylation of silyl ketene acetals with propionic anhydride, giving 3-acyl-3-aryl or 3-acyl-3-alkylfuranones in good isolated yields and enantioselectivities (up to 98% ee). This chapter also demonstrates that these chiral isothioureas are required for high reactivity and asymmetry in related acylation manifolds. Chapter 5 presents and overall conclusion for chapters 2,3 and 4. Chapter 6 contains full experimental procedures and characterization data for all compounds synthesized in Chapters 2, 3 and 4.

Natural gas is among the most dominant resources to provide energy supplies and Saudi Arabia ranks among the top 5 producers worldwide. However, prior to use of methane, natural gas has to be treated to remove other feed gas components, such as H2O, CO2, H2S, N2 and C2+ hydrocarbons. Most NG fields in KSA contain about 10 mol% carbon dioxide that has to be reduced to less than 2 mol% for pipeline delivery. The conventional unit operations for natural gas separations, that is, molecular sieves, amine absorption, cryogenic distillation, and turbo expansion exhibit some disadvantages in terms of economics, operational flexibility or system footprint. One of the most attractive alternative is membrane technology in either standalone- or hybrid system configuration. Currently, the only two membrane materials used in industrial natural gas applications are cellulose acetate and polyimide, which have moderate permeability and fairly low selectivity when tested under realistic industrial conditions. The goal for future research is to develop unique polymeric membranes, which can at least partially replace conventional gas processing in future natural gas projects. This will support global economics and specifically the economy of Saudi Arabia. Newly developed polymeric materials must meet certain criteria to be used on a commercial scale. These criteria include: (i) high permeability and selectivity, (ii) processability into thin films, (iii) mechanical and thermal stability, and (iv) chemical stability against feed gas components. This project focused on the removal of carbon dioxide from natural gas by developing and characterizing functionalized aromatic polyimide membrane materials that exhibit very high selectivity under aggressive mixed-gas conditions. 6FDA-DAR demonstrated a mixed-gas CO2/CH4 selectivity of 78 at a CO2 partial pressure of 10 bar with no pronounced indication of plasticization. Combining hydroxyl- and carboxyl groups in a miscible polyimide blend led to mixed-gas CO2/CH4 selectivity of 100 with no aging and no plasticization effects. This burgeoning membrane material has very high potential in large-scale natural gas separations with the best overall performance of any type developed to date.