The application of diastereoselective free radical reactions in carbohydrate chemistry

This thesis focuses essentially on the application of diastereoselective radical reactions to the preparation of O- and C-glycosidic linkages. As such, the introduction surveys both the general area of glycoside synthesis and diastereoselective radical reactions and in particular, their use in carbohydrate chemistry. Methyl [Phenyl 4,5,7-tri-O-benzyl-3-deoxy-2-sulphonyl-β-D-arabino-2-heptulopyranoside]onate (sulphone ester) was prepared from tri-O-benzyl-D-glucal according to a method previously developed in the laboratory. The highly diastereoselective preparation of 6-C-glycosides was achieved by reductive desulphonylation of the sulphone ester with lithium naphthalenide followed by quenching with an alkyl halide and ultimately by Barton reductive decarboxylation. Diastereoselectivities in excess of 95:5 were routinely observed. Thermal elimination of phenylsulphinic acid from the sulphone ester gave the corresponding 1-carbomethoxy glycal. cw-Hydroxylation with osmium tetroxide gave exclusively the gluco-isomer. Acetonation, saponification and reductive decarboxylation gave l,2-O-isopropylidene-3,4,6-tri-O-benzyl-β-D-gluco-pyranose as a single anomer and the first example of a 1,2-trans-isopropylidene derivative of a pyranose sugar. Other β-O-gluco-pyranosides were prepared as single anomers by related process. The extension of the methodology to the preparation of β-O-manno-pyranosides was investigated. The extrapolation of the method to the preparation of furanosidic linkages was investigated. 2,3:4,6-Di-O-isopropylidene-2-keto-L-gulonic acid was chosen as starting material and methods were developed for its selective deprotection and protection. The stereoselectivity of the radical decarboxylation step was investigated. Finally, in the context of the C-glycoside synthesis, 6-trimethylsilylethoxymethyl chloride (SEM-Cl) was developed as a practical equivalent to formaldehyde in low temperature, non-aqueous aldol type reactions

Casuarina equisetifolia cone as sustainable adsorbent for removal of Malachite green dye from aqueous solution using batch experiment method

Various methods have been devised in order to treat the wastewaters before they are disposed into water bodies such as the rivers and the seas. One of the methods used is adsorption as it has the advantages of cheap, environmentally friendly and wide range of materials can be used. In this study Casuarina equisetifolia cone (CEC) was used to remove malachite green (MG) from aqueous solution and the adsorption process was investigated through contact time, pH, temperature, ionic strength and dye concentration. The experimental results indicated that CEC can operate well in high ionic strength solution and was not significantly affected by temperature. The adsorption process followed the pseudo-2nd order and can be described using the Langmuir model where the maximum adsorption capacity was determined as 58 mg g-1

Nutritional attributes of Hemiparasitic mistletoe Scurrula ferruginea in Brunei Darussalam

Three different associations of Scurrula ferruginea parasites on three different hosts, namely Tabebuia pallida, Acacia holosericea and Acacia auriculiformis were collected from the Brunei-Muara District, Brunei Darussalam. Moisture content and chemical analyses (ash content, total carbohydrate content, crude protein, proline and mineral content composition) were determined to explain the host-parasite physiological biochemistry. Scurrula ferruginea contained relatively higher moisture content (47 – 65%) and ash content (2.1-2.5%, dry basis) than the hosts (0.7-1.4%, dry basis). High nutrient and moisture contents in Scurrula ferruginea make it more preferred food source than its hosts for generalist herbivores in a given community. The mistletoe exhibited differential storage profile of total carbohydrate (1.9-6.4%, dry basis) and total nitrogen (1.2 – 3.0%, dry-basis) when compared to hosts (total carbohydrate 2.3 - 3.0 % dry basis; total nitrogen 1.6 - 2.1%). Meanwhile the proline content (24.9-56.0 mg/kg, dry basis) were found in Scurrula ferruginea. Among all the minerals analysed, potassium is the most abundant mineral present in all mistletoe-host associations. Data indicated that certain host desired solutes are preferentially absorbed and stored in mistletoe. </jats:p

Parkia speciosa (Petai) pod as a potential low-cost adsorbent for the removal of toxic crystal violet dye

This study focused on the use of Parkia speciosa (Petai) pod as a potential adsorbent for the removal of crystal violet (CV) dye. Batch adsorption isotherm experiments carried out under optimized conditions were fitted to six isotherm models, namely Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlich-Peterson and Sips. Of these, the Sips model best described the adsorption isotherm of Petai pod for the removal of CV dye, giving a desirable adsorption capacity (qmax) of 163.2 mg g-1. Adsorption kinetics was found to follow the pseudo-second order, and further, intra-particle diffusion played a significant role. This study also revealed that the adsorption of CV by Petai pod is influenced by the ionic strength of the medium. However, Petai pod showed resilience towards changes in medium pH.  </jats:p

Effective and Simple NaOH-Modification Method to Remove Methyl Violet Dye via Ipomoea aquatica Roots

In this study, a simple chemical modification was applied to a sustainable and abundantly available resource, kangkong root (KR), to remove methyl violet 2B (MV) dye. The chemically modified adsorbent (NaOH-KR) was obtained using NaOH solution treatment. Batch adsorption experiments were carried out to investigate the effects of pH, ionic strength, contact time, adsorbent dosage, and initial dye concentration. A regeneration experiment was also carried out to assess the potential of reusability. The adsorption process was modelled using various kinetics and isotherm models, whereby the best-fitting models were evaluated by using the coefficient of determination ( R 2 ) and error functions. The Sips ( R 2 = 0.9714 , χ2 =0.16) and pseudo-second-order ( R 2 = 0.9996 , χ 2 = 0.007 ) models were identified to best represent the adsorption process. The Sips model predicted a maximum adsorption capacity at 551.5 mg g-1 for NaOH-KR, which is 55% improvement in performance when compared to nonmodified KR. Lastly, the regeneration experiment showed that NaOH-KR was able to maintain reasonable dye removal even after five consecutive cycles of regenerating and reusing.</jats:p

Effective and Simple NaOH-Modification Method to Remove Methyl Violet Dye via Ipomoea aquatica Roots

In this study, a simple chemical modification was applied to a sustainable and abundantly available resource, kangkong root (KR), to remove methyl violet 2B (MV) dye. The chemically modified adsorbent (NaOH-KR) was obtained using NaOH solution treatment. Batch adsorption experiments were carried out to investigate the effects of pH, ionic strength, contact time, adsorbent dosage, and initial dye concentration. A regeneration experiment was also carried out to assess the potential of reusability. The adsorption process was modelled using various kinetics and isotherm models, whereby the best-fitting models were evaluated by using the coefficient of determination (R2) and error functions. The Sips (R2=0.9714, χ2 =0.16) and pseudo-second-order (R2=0.9996, χ2=0.007) models were identified to best represent the adsorption process. The Sips model predicted a maximum adsorption capacity at 551.5 mg g-1 for NaOH-KR, which is 55% improvement in performance when compared to nonmodified KR. Lastly, the regeneration experiment showed that NaOH-KR was able to maintain reasonable dye removal even after five consecutive cycles of regenerating and reusing