Department of Chemistry

Permanent URI for this community

https://hdl.handle.net/10566/386

Browse

Filter results by year or month

Now showing 1 - 20 of 657

Inhibition of HIV-1 enzymes, antioxidant and anti-inflammatory activities of Plectranthus barbatus
(Elsevier, 213) Kapewangolo, Petrina; Hussein, Ahmed A.; Meyer, Debra
Ethnopharmacological relevance: Plectranthus barbatus is widely used in African countries as an herbal remedy to manage HIV/AIDS and related conditions. Aim of the study: To investigate the HIV-1 inhibitory, anti-inflammatory and antioxidant properties of P. barbatus and thereby provide empirical evidence for the apparent anecdotal success of the extracts. Materials and methods: Ethanolic extract of P. barbatus's leaves was screened against two HIV-1 enzymes: protease (PR) and reverse transcriptase (RT). Cytotoxicity of the extract was determined through measuring tetrazolium dye uptake of peripheral blood mononuclear cells (PBMCs) and the TZM-bl cell line. Confirmatory assays for cytotoxicity were performed using flow cytometry and real-time cell electronic sensing (RT-CES). The free radical scavenging activity of the extract was investigated with 2,2- diphenyl-1-picrylhydrazyl while the anti-inflammatory properties of the plant extract were investigated using a Th1/Th2/Th17 cytometric bead array technique.
Analyzing chemical data in more than two dimensions: A tutorial on factor and cluster analysis
(Journal of chemical education, 1990) Auf der Heyde, Thomas P. E
This tutorial is intended to introduce factor and cluster analysis at a level that will afford a senior student-and the practicing chemist, for that matter-some insights into the workings of the computer packages employing these methods, without overwhelming him or her with mathematical detail in the process.
The synthesis, characterization and reactivity of some mononuclear hydrocarbyl compounds of iron
(University of the Western Cape, 1997) Joorst, Genevieve; Mapolie, S.F.
Mononuclear hydrocarbyl compounds of the type LnM(CH2)nCH:CH2 (L"M : Cp*Fe(CO)2 and CpFe(CO)2, n: 2-4,6), Cp(CO)zFe(CH2)nOH (n : 4-6,8) and Cp*(CO)2Fe(CH2)+OH have been synthesized. All these compounds have been l3 fully characterized using analytical techniques such as[R, H and C NMR spectroscopy, microanalysis and mass spectrometry The results of some activity studies on the above hydrocarbyl compounds are reported in this thesis. For example, the reactivity of the r'1l-alkenyl compounds Cp (CO)2Fe(CH2).CH=CHZ (n: 2 and 3) to hydrozirconation was studied. Although the expected binuclear hydrocarbyl compounds Cp(CO)2Fe(CH2)na2Zr(Cl)Cpz (n: 2 and 3) were not isolated, their presence in solution were detected by carrying out insitu reactions. The n1-alkenyl compounds were also subjected to a p-hydride abstraction reaction. This afforded a series of cationic n2-diene compounds with general formula {Cp(CO)zFe(CnH2n-2) } PF6. Some of the reactions of the w-hydroxyalkyls were also investigated. The bromination of these hydroxy species leads to the formation of w-bromoalkyls of the type Cp(CO)2Fe(CH2)'Br (n 4 and 8). The w-hydroxyalkyls cp(co)2Fe(CH2)nOH (n : 4-6,8) were reacted with trifluoroacetic acid which results in iron-carbon cleavage. Finally the reaction of some w-hydroxyalkyls with triflic anhydride gives different results depending on the type of solvent employed. In THF a metal containing polyether is isolated as the major product, while in diethyl ether the major species isolated is a o-chloroalkyl of the type Cp(Co)2Fe(CH2)nCl (n : 4 and 5)' In the case of the reaction in THF, a small amount of the binuclear hydrocarbyl compound [CpFe(Co)z]{p-(CHz)a}can be isolated if [CpFe(Co)z] is added to the reaction mixture
The synthesis of prodrugs and novel analogues of Beta-sympathomimetic bronchodilators
(University of the Western Cape, 1998) Adams, Mortimer Hilary; Ameer, Farouk; Green, Ivan R.
Prodrugs are reversible derivatives of active drugs destined to undergo chemical or enzymatic transformation to the active drug after administration in order that the active drug may subsequently elicit the desired pharmacological response . In synthesizing a prodrug, the physico chemical properties of a drug are altered by suitable functionalisation of an appropriate appendage of the drug molecule such that some barrier or problem may be circumvented or obviated in totality. Prodrugs of bronchodilators have been prod used with the aim of reducing enzymatic degradation, improving their bio-availability and, displaying a marked separation between their desirable bronchodilator and undesirable cardiovascular activities. Chlorphentermine (II), a lung accurnulating arnine, was used as a carrier molecule in novel prodrugs which potentially possess these attributes. Model prodrugs viz. CPE (20) and CPETA (t4), consisting of chlorpltentennine (ll) connected through a propionic ester link to ethanol and etafedrine (13), respectively, were synthesized by reacting the alcohols with acryloyl chloride and the resultant acrylates subsequently reacted with chlorphentennine (II). CPA (21), the prodmg hydrolysis product of CPE (20), was also synthesized. Closely related analoEres of CPETA (t4) narnely PETA (15) and CPAP' (16) were then synthesized. PETA (15) was synthesized by the condensation of methylamino- I -phenylpropane (phentenrtine) and etaf-edrine ( I 3).
Synthesis, characterisation and reactions of ferrocene anchored bis(phosphino) palladium (II) and platinum (II) aryldichalcogenide complexes
(University of the Western Cape, 2000) Maisela, Letladi lawrence; Darkwa, James; Crouch, Andrew M
Reactions of M(dppf)Cl2 (M : Pd, Pt) and Pd(dippf)Cl2 with equimolar amounts of the aryldichalcogen reagents, 1,2-benzenedithiol (1,2-(HS)C6H4(SH) (a)), 3,4-toluenedithiol ((HS)C6H3Me(SH)) (b), 3,6-dichloro 1,2-benzenedithiol ((HS)C6H2C12(SH)) (c), 2- mercaptophenol ((HS)C6H4(OH)) (d), thiosalicylic acid ((HS)C6H4(CO2H) (e) and thionicotinic acid (HS)C5H3N(CO2H)) (f) in the presence of triethylamine afforded complexes of the type M(dppf(SC6H4E-o) (where dppf : 1,1'- bis(diphenylphosphino)ferrocene and dippf : 1,1'-bis(diisopropylphosphino)ferrrocene). In addition to the above series, M(dpp0(SC6H5)2 (M : Pd, Pt) and Pd(dippf)(SC6H5)2 were prepared in an attempt to synthesise complexes of the general formula M(dppf)(SC6H4E-o) (M: Pd, Pt; E : Se, Te) via in situ generation of LiSC6H4ELi-o. All complexes isolated were characterised by a combination of IR, 1H, 31P {1H} NMR, mass spectrometry and elemental analysis. Further characterisation of Pd(dppf)(SC6H4S-o), Pd(dippf)(SC6H4S-o), Pd(dippf(SC6H3MeS-o), Pd(dippf)(SC6H5)2, Pt(dppf)(SC6H4S-o) and Pt(dppf)(SC6H4O -o) by single crystal X-ray diffraction studies confirmed the structures deduced from the spectroscopic data. Mass spectrometry data suggests that the Pt(II) complexes are more stable than the analogous Pd(II) complexes. Electrochemical data also show that the dippf complexes were easier to oxidise compared to the dppf, as were the Pd complexes compared to the Pt analogues. In complexes containing homoleptic sulfur ligands (1a-c, 2a-c and 3a-c) the ease of oxidation of the ligand was b > a > c which conforms to either the electron releasing group (b) or an electron withdrawing group (c) on the ligand. Aryldithiolato Pd(dppf) and Pd(dippf) complexes reacted with dimethylacetylene dicarboxylate (DMAD) to form hexamethylbenzene hexacarboxylate (HMBC) and tetramethylcyclobuta-1,3-diene tetracarboxylate (TMCTC) as the dominant products. The same series of aryldithiolato complexes that reacted with DMAD reacted reversibly with sulfur dioxide, a process that was monitored by UV-vis and 1H NMR spectroscopy.
The oxidation of the lower primary alcohols ln a catalytic membrane reactor
(University of the Western Cape, 2000) Masters, Gerard Jerome; Linkov, Vladimir M
Methanol and ethanol are important chemical feedstock used in industrial chemistry, since they are the starting materials for the synthesis of various products, including hydrocarbons and mild oxidation products. For instance, methanol can be oxidised to methyl format, which can be transformed into industrially important products such as N, N-dimethyl formamide or acetic acid. Both methanol and ethanol have also been used as probe reactions, in which they are used to characterise catalysts according to the type of active sites presents, namely redox, acidic or basic. The lower primary alcohols are also currently being used in fuel cell research, since the oxidation of alcohols has been proposed as an anode reaction for fuel cells. ln the latter case, the important reaction is the complete oxidation of the alcohol to carbon dioxide and water. lt is apparent from industrial examples that methanol oxidation can lead to various products by varying the nature of the catalyst and the reaction conditions.
An investigation into the elements influencing stock control and their relation to health care delivery in the public setting: Development of a stock control assessment tool
(University of the Western Cape, 2000) Kagee, Halima; Eagles, P F K
The aim of this study was to develop a Stock Control Assessment Tool for use in the public health care sector and then to apply it to identify problems in the stock control system. This would help authorities to optimize the system. The advantages experienced with such a dynamic Assessment Tool were many: The Tool was quick and easy to apply; it was user friendly; it provided an immediate SWOT analysis of a particular facility; it is in line with the SA NDP directives and it provides an indication of which structures are in place and whether they are functioning properly. Furthermore; it could determine the increase or decrease in performance of a facility (therefore identify trends within the functional status of a system) when data is collected over a period of time; and finally, it could also be used to prioritize drug policy directives. The following steps were established in the development of the Tool: A literature review of pharmaceutical stock control and Drug Supply Management was addressed to provide the background information for the motivation of this study and to identify the various elements that could influence stock control at a facility level. Observational studies were applied at selected private and public facilities to observe the impact of these identified stock control elements. An 'ideal' stock control system was then generated from the literature review and observational assessment. A structured questionnaire was developed and surveyed at these facilities to generate key areas of concern of a stock control system. A study and adaptation of the indicator methods used by the World Health Organization (WHO) to monitor drug use in health facilities resulted in the formulation of a practical Stock Control Assessment Tool based on 11 key indicators and a number of sub-indicators, all of which were objectively defined. The Tool was then applied at selected public facilities and the results were analyzed quantitatively, qualitatively and subjectively. Each of the indicators was then applied and results examined closely with a view to possible refinements of the indicator. The refinements were made and the Tool was re-applied at two selected facilities. These two facilities were randomly selected from the original six facilities included for the testing of the Tool. Final conclusions and specific recommendations were generated to improve the stock control systems at the selected public health care facilities.
Oxidative fixation of dinitrogen by photocatalysis
(University of Western Cape, 2000) Karriem, Fatiema; Key, David
The heterogeneous photocatalytic oxidation of dinitrogen to nitrate, NO3 and/or nitrite, no2 using peroxy species of titanium (IV) in aqueous suspensions has been investigated. The photocatalysts used were titanium peroxide and Degussa p25 TiO2 pretreated with H2O2. These photocatalysts were investigated by SEM and FTIR spectroscopy.
Titanium compounds and plant growth
(University of the Western Cape, 2001) Khoza, G; Raitt, L
The effect of titanium compounds on the growth of tomato plants, Lycopersicum esculentum (cultivar Floridade), was studied under greenhouse conditions. Aqueous suspensions (TiO2) and solutions (complexes of titanium (IV) with L(+)-ascorbic acid and oxalic acid) were applied as foliar sprays and soil treatments. A new compound of titanium (IV) with L(+)-ascorbic acid was prepared and characterised. Some titanium compounds appeared to enhance some growth parameters in some instances, but titanium did not consistently result in improved growth or increased nitrogen concentration within the plants. Titanium uptake was also monitored and established by means of PIXE measurements on plant tissue.
Electrochemical evaluation of chemically Modified microelectrodes
(2001) Moeletsi, JM; Crouch, AM
Aniline and N-alkylated substituted anilines have been polymerized by chemical and electrochemical methods. The chemically synthesized polymers indicated that N-alkylation improves solubility remarkably in common organic solvents. The compounds were characterized by FTIR, 1H NMR, TGA and also studied by cyclic voltammetry on glassy carbon macroelectrodes for comparison with electrochemical synthesized polymers.
ISOLATION AND CHARACTERIZATION OF ANTIMICROBIAL COMPOUNDS FROM GALENIA AFRICANA
(University of the Western Cape, 2001) Vries, Felicity; Green, I.R; Klaasen, J.A
Galenia africona, commonly known as "kraalbos" or "geelbos" belonging to the family Aizoaceae, is a dominant plant throughout the Namaqualand area. It is an active invader and is especially abundant in disturbed areas around kraals, along roads, and water points which shows that it grows well on trampled soil. "Kraalbos" is not very palatable to livestock, but is grazed under pressure. The plant can cause liver damage and severe ascites, a condition referred to as "waterpens" in sheep and occasionally in goats. The Hottentots chew the plant to relieve toothache and it is said to blister the mucous membrane of the mouth if used too much. The plant was also used in the treatment of veneral diseases. Dried samples of G. africana collected in Steinkopf and Concordia were sequentially extracted with various solvents starting with hexane, chloroform, ethanol and sterile distilled water. Each concentrated extract were tested for its inhibitory activity against fungi and bacteria by using the agar well diffusion method. The mycelial growth of Fusqrium graminearum and Fusarium verticillioides cultured on PDA was inhibited by the CHCI3 and EtOH extracts. The minimum inhibitory concentration (MIC) of these two extracts was calculated for both fungal and bacterial species. Overall results showed that the EtOH extract from G. africana has strong inhibitory activity in vitro against fungi and bacteria. The above findings advocate further investigation of the EtOH extract. It will be necessary to identiff the active components and to evaluate their potential for use as antimicrobials. The ethanol extract was purified using silica gel column chromatography and thin - layer chromatography. Four fractions showed significant antifungal activity as evidenced by a clear zone of inhibition. One fraction was tested against a range of fungi and a few bacterial isolates. This fraction inhibited the growth of most of the fungal isolates with Alternaria sp., Fusarium equiseti, F. gramineorum, F. verticillioides and Phaeomoniella clamydospora being the most sensitive ones. Both Bacillus sp. and Staphylococcus atffeus were inhibited in the presence of the fraction. The MIC's for fungi showed values ranging from 10 to 2.5% and bacteria from 2.5 to 1.25 %. The active fraction inoculated onto individual filter paper disks displayed potent antifungal activity on agar plates seeded with conidia of the various fungal isolates being tested. The filter paper disk method showed more sensitivity than the agar well diffusion method in the detection of the antifungal activity of the active fraction.
Polyphenolic, tannin and chemical compositional changes in leaves of sub-tropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations
(University of the Western Cape, 2002) Hattas, Dawood; Mabusela, Wilfred T
The effects of elevated atmospheric CO2 concentrations on plant polyphenolic concentration, tannin concentration and chemical composition were investigated in leaves of sub-tropical grass species and fynbos shrubs. The working hypothesis was based on predictions that carbon based secondary compounds (polyphenolics and tannins) would increase when carbon in excess of growth requirements accumulate in plant leaves under nutrient imbalanced conditions. This imbalance would arise due to an increase in atmospheric CO2 level. Furthermore, empirical evidence suggests that nutrient paucity would enhance carbon-based secondary compound production. This hypothesis was tested in two different systems involving plants with differential photosynthetic mechanisms and growth strategies. . Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in grass species from a natural, C+ dominated, sub-tropical grassland in KwaZulu/Natal. Three plots were subjected to different freeair CO2 enrichment treatments, i.e. elevated (550-800 ppm), intermediate (no more than 400 ppm) and ambient CO2 (currently at 365 ppm). One of the seven grass species, Alloteropsis semialafa, had Cs photosynthetic mechanism. o Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in three fynbos species grown in open-top chambers under controlled greenhouse conditions. The plants were grown under ambient (360 ppm) and ambient + 350 ppm CO2 in typical low nutrient acid sands of the fynbos biome. This study shows that despite some of the grasses having the capacity to produce tannin-like substances, polyphenolics and tannins do not increase in the grass species studied. Polyphenolic and tannin concentrations were increased only in Leucadendron laureolum amongst the fynbos species. Its sister species Leucadendron xanthoconus did not show any change in phenolic or tannin concentrations.
The synthesis of Ventiloquinones J and F
(University of Western Cape, 2002) van Eeden, Nestor; Green, lvan R
In chapter 2 the synthesis of ventiloquinone J is described, starting from vanillin, the key intermediate cis-3,4-dihydro-5,7-dimethoxy-10- methoxymethyleneoxy-1,3-dimethyl-1H-naphtho[2.3-c]pyran-6,9-dione was prepared in 19 steps by using inter alia Diels-Alder adduct formation, mild acetylation, oxymercuration and finally converted to ventiloquinone J in an overall yield of 0.5%. Protection of the C-10 position of the ventiloquinone J precursor was eventually effectively provided by the methoxymethyleneoxy (MOM) group which upon removal with acid treatment provided the hydroxy group in this position unambiguously in the final product. Attempts to effect this same protection using a benzyl group proved ineffective due to the extreme difficulty in separation of the cyclised stereoisomers; cis and trans 10- benzyloxy-3,4-dihydro -5,6,7,9-tetramethoxy-1,3-dimethyl-lH-naphthol2,3- c]pyrans In addition decomposition of the molecule occurred during the subsequent oxidation step affording low yields of the quinones and finally the unwanted isomer viz., the trans 1,3-dimethylpyran was the major product of the cyclisation. Protection of C-10 of the precursor to ventiloquinone J usingthe 2'-methoxyethoxymethyleneoxy (MEM) group proved problematic in that it was sensitive to the acidity of the silica gel stationary phase used for column chromatography, and that cyclisation of the intermediate alcohol, 2-(l'- hydroxyethyl)-4,5,6,8-tetramethoxy-l-(2'-methoxyethoxymethyleneoxy)-3- prop-2'-enylnaphthalene, Ied to a mixture of the corresponding cis and trans l,3-dimethyl pyrans in which the MEM protecting group had been lost in a combined crude yield of only 25%o. In addition all the MEM compounds showed considerable decomposition on standing. The synthesis of one of the initial target molecules, 6-hydroxy-7- methoxyeleutherin was not completed due to premature displacement of the required C-5 protecting groups employed in the naphthalene precursors upon acylations under Lewis acid Ventiloquinone F was successfully synthesised from 3,4,6- trimethoxybenzaldehyde in 12 steps making use of a Stobbe Condensation with methyl succinate to construct the desired oxygenated naphthalene nucleus. An overall yield of 9.5oh was obtained and its stereoisomer, isoventiloquinone F was also obtained in an overall yield of 10%.trans- 5-benzyloxy-3,4-dihydro-6,7,9'ttimethoxy-1,3-dimethyl-1I/- naphtho[2,3-c]pyran led to the formation of four pyranquinones which were successfully separated and purified. These were cis- and trans-5-benzyloxy- 3,4-dihydro-7-methoxy-1,3-dimethyl-lF/-naphthol2,3-clpytarr-6,9-diones as well as the corresponding cis and trans ortho quinone isomers.
The extraction, purification and evaluation of compounds from the leaves of Leonotis Leonorus for anticonvulsant activity
(University of the Western Cape, 2002) Muhizi, Theoneste; Green, Ivan R.; Amabeoku, George J.; Dept. of Chemistry; Faculty of Science
The aim of this study is to isolate and evaluate the anticonvulsant components from the leaves of Leonotis leonorus (L) R.aR. and to see if there is any change in activity with the origin of the plant material and I or the season in which plant material is collected. Therefore, in this study, two sites were chosen for collection of plant material and the collection was made in summer and in winter. Chemical, physical and pharmacological methods were used to isolate, identify and to evaluate compounds isolated from the leaves of Leonotis leonorus for anticonvulsant activity.
Polyphenolic, tannin and chemical compositional changes in leaves of sub-tropical grasses and fynbos shrubs at elevated atmospheric CO2 concentrations
(University of the Western Cape, 2002) Hattas, Dawood; Mabusela, Wilfred T; Stock, William D; Green, Ivan R
The effects of elevated atmospheric CO2 concentrations on plant polyphenolic concentration, tannin concentration and chemical composition were investigated in leaves of sub-tropical grass species and fynbos shrubs. The working hypothesis was based on predictions that carbon based secondary compounds (polyphenolics and tannins) would increase when carbon in excess of growth requirements accumulate in plant leaves under nutrient imbalanced conditions. This imbalance would arise due to an increase in atmospheric CO2 level. Furthermore, empirical evidence suggests that nutrient paucity would enhance carbon-based secondary compound production. This hypothesis was tested in two different systems involving plants with differential photosynthetic mechanisms and growth strategies. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in grass species from a natural, C4 dominated, sub-tropical grassland in KwaZulu/Natal. Three plots were subjected to different freeair CO2 enrichment treatments, i.e. elevated (550-800 ppm), intermediate no more than 400 ppm) and ambient CO2 (currently at 365 ppm). One of the seven grass species, Alloteropsis semialata, had C3 photosynthetic mechanism. Polyphenolics, tannins and chemical composition (N, P, C and TNC) were quantified in three fynbos species grown in open-top chambers under controlled greenhouse conditions. The plants were grown under ambient (360 ppm) and ambient+ 350 ppm CO2 in typical low nutrient acid sands of the fynbos biome. This study shows that despite some of the grasses having the capacity to produce tannin-like substances, polyphenolics and tannins do not increase in the grass species studied. Polyphenolic and tannin concentrations were increased only in Leucadendron laureolum amongst the fynbos species. Its sister species Leucadendron xanthoconus did not show any change in phenolic or tannin concentrations. Chemical composition in grasses were largely unaffected by elevated CO2, however, some species-specific responses were observed. The C3 A. semialata showed a decrease in P concentration and a consequent increase in C:P ratio at elevated CO2. Only L. laureolum showed a response in chemical composition at elevated CO2, whereas its sister species did not show any response except a decrease in N concentration. In conclusion, fast growing grass species invest extra carbon into growth rather than polyphenolics and tannins and show small species-specific chemical changes at elevated atmospheric CO2 concentrations. Increased investment into phenolics and tannins as well as changes in chemical composition in fynbos species were species-specific even within plants from the same genus. Thus generalizations about plant responses to elevated CO2 based on theoretical principles cannot be directly applied. This is especially true in complex natural environments where ecophysiological processes may dictate phytochemical responses.
Substituted nick el pyrazole and palladiumpyruzolyl complexes as catalyst precursors for ethylene polymeization
(University of the Western Cape, 2003) Nelana, S; Darkwa, J
This study concerns the synthesis of pyrazole and substituted pyrazole nickel complexes of the type [(3,5-R,R',pz)2NiB rz ( Pz : pyrazole; R = R' = cHr (1), tBu (a)l and of the type [(3,5-R,R'pz)aNiBrz R: H, R' : CHr (2)] R: R' :H (3)l' These complexes were synthesized by reacting (DME)NiBrz and the appropriate pyrazole or substituted pyrazole in dichloromethane. The products were obtained in moderate to good yields. All the complexes isolated were charac teizedby a combination of IR spectroscopy, tH NNm. spectroscopy and elemental analysis' Complexes I and 2 were further characteri zedby single crystal X-ray crystallography. Complex 1 was found to have a tetrahedral geometry and complex 2 has an octahedral geometry' In addition to the pyrazole nickel complexes, new pyr.volyl ligands with alkane-o'oldione linkers tRpzC(OXCHz),C(O)pzR); R: CHr' n: 0 (A1)' n:2 (A2)'n:3 (A3) and R: tBu, n = 3 (A4)] were synthesized. These new ligands were charactenzed by IR spectroscopy, ,H NNfi, "C NNffi. spectoscopy and elemental analysis' They were further reacted with (cHrCN)2PdCl2 in attempts to obtain a'obis(3'5- Rzpyrazolyl)alkane-cr,rodione palladium chloride complexes' These ligands tend to undergo hydrolysis when they are reacted wittr (CHTCN)zPdClz as confirmed by tH NMR spectral analysis. one complex, 1,5.bis(3,5.Mezpz)pentane-1,5-dione palladium chloride was successfully prepared under very dry solvent conditions' The 1,5-bis(3,5-Mezpz)pentane-1,Sdione palladium chloride complex was characteized by 'HNMR spectroscoPY.
Crystal structure of saposin B reveals a dimeric shell for lipid binding
(National Academy of Sciences, 2003) Ahn, Victoria E.; Faull, Kym F.; Whitelegge, Julian P.
Saposin B is a small, nonenzymatic glycosphingolipid activator protein required for the breakdown of cerebroside sulfates (sulfatides) within the lysosome. The protein can extract target lipids from membranes, forming soluble protein-lipid complexes that are recognized by arylsulfatase A. The crystal structure of human saposin B reveals an unusual shell-like dimer consisting of a monolayer of -helices enclosing a large hydrophobic cavity. Although the secondary structure of saposin B is similar to that of the known monomeric members of the saposin-like superfamily, the helices are repacked into a different tertiary arrangement to form the homodimer. A comparison of the two forms of the saposin B dimer suggests that extraction of target lipids from membranes involves a conformational change that facilitates access to the inner cavity.
The synthesis of methoxy-2-hydroxy-1,4- naphthoquinones and their reaction with aliphatic aldehydes under basic conditions.
(University of the Western Cape, 2003) Pearce, R.S; Ameer, F; Green, I.R
Although literature reports on the synthesis of variously substituted 2-hydroxy-1 ,4- naphthoquinones appeared to be reasonable; in our hands difficulty was experienced in duplicating much of the work. In order to address this problem, two protocols were used with the one involving conversion of substituted a-tetralones into hydroxyquinones using a solution of the tetralones in an oxygenated solution of tertiary butyl alcohol containing potassium tertiary butoxide, and the other involving Diels-Alder Condensation, oxidation, pyrolysis and basic hydrolysis of a 2-methoxy-1,4-naphthoquinone 79 into the corresponding 2-hydroxy analogue 80. Condensation reaction between 2-hydroxyy-8-methoxy-1,4-naphthoquinone 80 and caproaldehyde 111, produced the 3-alkenyl analogue 115 which was cyclised to the corresponding naphtho[2,3-b ]pyrenquinone 116 and eventually reduced to 8- methoxynaphtho[2,3-b ]pyran-5, 10-dione 1) 7. Condensation between 2-hydroxynaphthoquinone 80 and 4-dioxolanopentanal under basic conditions afforded the desired adduct which was cyclised with dichlorodicyanobenzoquinone, reduced and then hydrolysed with acid to produce 2- acetyl-3,4-dihydronaphtho[2,3-b ]pyran-5, 10-dione 125. By the employment of an alternative sequence of events, the corresponding 4-hydroxy analogue of the above 2- acetylnaphthopyrandione 125 was also prepared for evaluations. Finally condensation between 2-hydroxy-8-methoxy-1,4-naphthoquinone 80 and 5- dioxolanohexanal 128 under basic conditions afforded the 3-hexenyldioxolano 129 derivative, which was cyclised to the naphthopyrene 130 but the yields were disappointing in this instance.
An investigation into the synthesis, characterisation and some applications of novel metal-containing polymers and dendrimers of transition metals
(University of the Western Cape, 2003) Smith, Gregory Stuart; Mapolie, S.F.; Dept. of Chemistry; Faculty of Science
metal-containing complexes, that exhibit enhanced chemical and physical properties. This thesis describes the synthesis of new metal-containing linear polymers and dendritic molecules. Chapter 1 presents an overview of the field of metal-containing polymers, with particular attention to the synthesis of polymers via condensation polymerisation. This review includes the various types of metal-containing condensation polymers and the applications of these materials, where available. This discussion is followed by a brief summary of metal-containing dendrimers, which includes a concise description of their structure and applications in general. There are two routes to preparing metal-containing polymers. Chapter 2 describes the synthesis of three bifunctional organometallic monomers, of the general type [M]-O-{2,6-(CH2OH)2-4-CH3-C6H2}, where [M] represents the various metal-containing moieties, (η5-C5H5)(CO)2 Fe(CH2)3 (25), (η5-C5H4-CH2CH2CH2-)Re(CO)3 (26) and Fpdendr (27). These monomers were prepared using 2,6-bis(hydroxymethyl)-p-cresol as the key reagent. The monomers were used in classical polycondensation reactions with terephthaloyl chloride using ambient temperature solution techniques. This yielded new low molecular weight oligomeric polyesters, that were characterised using FTIR and 1HNMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and sizeexclusion chromatography. In Chapter 3, an alternate route to metal-containing polymers is described. In this case, bifunctional organic monomers were polymerised to give preformed organic polymers. Two types of organic polymers were prepared, viz. polyesters (with pendant vinyl moieties) and polyimines (with α-diimine units along the polymer backbone). Functionalisation of these preformed organic polymers with various metal sources was attempted. Hydrozirconation reactions of the vinyl polyesters with Schwartz’s reagent, Cp2Zr(H)Cl, were attempted and were largely unsuccessful. Competing reactions with the ester functionality prevailed, preventing the desired reaction. Reaction of the polyimines with PdCl2(COD) yielded insoluble, intractable metal-containing oligomers. Partial characterisation of the complexes is described. The synthesis of new poly(propylene imine) iminopyridyl metallodendrimers is described in Chapter 4. Schiff-base condensation reaction of the commercially available DAB dendrimers with 2-pyridinecarboxaldehyde, gave the dendrimers 51, 52, and 53, with four, eight and sixteen pyridylimine functionalities respectively on the periphery. Successful complexation reactions with PdCl2(COD), PtCl2(COD) and CuCl2 produced the corresponding metal-containing dendrimers, with either PdCl2 (54, 55, 56), PtCl2 (57) or CuCl2 (58) moieties bound on the periphery. The metallodendrimers were insoluble in the more common organic solvents, and were characterised by IR and 1H-NMR spectroscopy and microanalysis where possible. Dendrimers with salicylaldiminato ligands on the periphery were prepared by reacting the DAB dendrimers with salicylaldehyde. These ligands were reacted with various metal acetates in an attempt to prepare new metalcontaining salicylaldimine dendrimers. This work yielded either paramagnetic metal complexes or insoluble, intractable compounds. Chapter 5 describes the applications of the catalyst precursors (54, 55, 56, 57, 58), discussed in Chapter 4, in the polymerisation of ethylene and the use of complexes 54 and 55 as Heck cross-coupling catalyst precursors. The complexes all showed catalytic activity toward ethylene polymerisation. A discussion of their activity, the polyethylene molecular weight and microstructure is presented in this chapter. The precursors 54 and 55 are also effective catalysts in the Heck reactions, coupling iodobenzene with methyl acrylate, styrene and 1-octene in high conversions.
Thiolato schiff base complexes of nickel and palladium as mesogens and molecular wires
(University of the Western Cape, 2003) Moutloali, R.M; Darkwa, J
Thermal analysis data of compounds A, C, F and I established that they were nonmesogenic while E and G were found to be mesogenic. The lack of mesogenic behaviour of A could be attributed to hydrogen bonding. The non-mesogenic behaviour of C and F is due to reduced molecular anisotropy as a result of large lateral substituents. Complexes I decomposed at high temperatures and before melting and hence no liquid crystalline behaviour was found. It is likely that the high decomposition temperature is the result of increased molecular interactions. We found that removing the phosphine ligands and increasing molecular length induced liquid crystalline behaviour in complexes E. The more planar complexes G were also found to be liquid crystalline

Browse

Browsing by Issue Date

Results Per Page

Sort Options