Research Articles (Chemistry and Polymer Science)
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- Item1-tert-Butyl 2-ethyl 5-bromo-3-(thiophen-2-ylcarbonyl)-1H-indole-1,2-dicarboxylate(International Union of Crystallography, 2013-01-16) Hassam, Mohammad; Smith, Vincent J.ENGLISH ABSTRACT: In the title compound, C21H20BrNO5S, the thiophene group is located above the mean plane of the indole ring and displays rotational disorder (i.e. rotation through 180). The site occupancy of the major component is 0.902 (2), while that of the minor component is 0.098 (2). In the crystal, pairs of weak C—HO interactions link the molecules into centrosymmetric dimers.
- Item4-Benzyloxylonchocarpin and muracatanes A-C from Ranunculus muricatus L. and their biological effects(MDPI, 2020-11-17) Hussain, Hidayat; Ali, Iftikhar; Wang, Daijie; Mamadalieva, Nilufar Z.; Hussain, Wahid; Csuk, Rene; Loesche, Anne; Fischer, Lucie; Staerk, Dan; Anam, Syariful; AlZain, Mashail N.; Mushtaq, Maria; Ul-Haq, Zaheer; Ullah, Riaz; Noman, Omar M.; Abbas, Ghulam; Green, Ivan R.ENGLISH ABSTRACT: Ranunculus muricatus L. is a spiny fruit buttercup that is used in various traditional medicinal systems. In the current investigation of R. muricatus, the new chalcone 4-benzyloxylonchocarpin (1), the new anthraquinone muracatanes A (2), the new-to-nature anthraquinone muracatanes B (3), and the new naphthalene analog muracatanes C (4) were isolated, in addition to the three previously reported compounds, 4-methoxylonchocarpin (5), β-sitosterol (6), and β-sitosterol β-D-glucopyranoside (7). Their structures were elucidated using 1D (1H and 13C) and 2D (COSY, HSQC, and HMBC) NMR spectroscopy and HR-ESI-MS. Chalcone 1 showed potent acetylcholinesterase inhibitory effects with Ki of 5.39 µM and Ki′ of 3.54 µM, but none of the isolated compounds showed inhibitory activity towards butyrylcholinesterase. Anthraquinone 3 illustrated α-glucosidase inhibitory effects with IC50-values of 164.46 ± 83.04 µM. Compound 5 displayed moderate cytotoxic activity towards ovarian carcinoma (A2780, IC50 = 25.4 µM), colorectal adenocarcinoma (HT29, IC50 = 20.2 µM), breast cancer (MCF7, IC50 = 23.7 µM), and thyroid carcinoma (SW1736, IC50 = 26.2 µM) while it was inactive towards pharynx carcinoma (FaDu: IC50 > 30 µM).
- ItemAcrolein dimer as a marker for direct detection of acrolein in wine(South African Society for Enology and Viticulture, 2012) Bauer, R.; Hiten, N. F.; Crouch, A. M.; Kossmann, J.; Burger, B. V.Acrolein is highly toxic and its presence in wine has been correlated with the development of bitterness. Analytical detection and quantification in aqueous solutions are challenging due to high reactivity and problems with chemical derivative analysis. Here we demonstrate the potential of a natural derivative, formed under conditions prevailing in wine, as a marker for acrolein detection. Solid-phase microextraction (SPME) coupled with gas chromatograph mass spectrometry (GC-MS) was validated as a technique for direct detection of the acrolein dimer. Conventional GC-MS analysis using a quadrupole mass spectrometer did not provide sufficient chromatographic resolution for the separation of the target analyte from interfering compounds. Accurate mass measurements with time-of-flight (TOF)-MS, on the other hand, allowed qualitative and quantitative measurements of the acrolein dimer. This work lays the analytical foundation for studies on the evolution of acrolein and its dimer in solution.
- ItemAdvancing membrane biology with poly(styrene-co-maleic acid)-based native nanodiscs(Elsevier, 2019) Overduin, Michael; Klumperman, BertENGLISH ABSTRACT: The elucidation of the structures and interactions of proteins and lipids in intact biological membranes remains largely uncharted territory. However, this information is crucial for understanding how organelles are assembled and how transmembrane machines transduce signals. The challenge of seeing how lipids and proteins engage each other in vivo remains difficult but is being aided by a group of amphipathic copolymers that spontaneously fragment native membranes into native nanodiscs. Poly(styrene-co-maleic acid) (SMA) copolymers have proven adept at converting membranes, cells and tissues directly into SMA lipid particles (SMALPs), allowing endogenous lipid: protein complexes to be prepared and analyzed. Unlike other amphipathic polymers such as amphipols, SMALP formation requires no conventional detergents, which typically strip lipid molecules from proteins and can destabilize multimers. A collaborative community of hundreds of investigators known as the SMALP network has emerged to develop and apply new technologies and identify new challenges and design potential solutions. In this contribution, we review recent practices and progress, focusing on novel SMA copolymers, modifications, alternatives and mechanisms. In addition, a brief overview will be provided, with reference to the further contributions to this special issue on the SMALP technology.
- ItemAdvantages of scanning probe microscopy in polymer science(Academy of Science for South Africa, 2004) Meincken, M.; Sanderson, R. D.We introduce the atomic force microscope (AFM) and its capabilities with special regard to its use in polymer science. It shows several advantages over other analytical techniques, such as scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Its main advantage is that the samples need not be prepared specially and can therefore be studied in their native environment. Further-more, the AFM can be used to detect physical properties locally on a molecular scale, which may be of interest for characterizing polymer blends or structured polymers.
- ItemAlkaloids with activity against the Zika virus vector Aedes aegypti (L.) - crinsarnine and sarniensinol, two new crinine and mesembrine type alkaloids isolated from the South African Plant Nerine sarniensis(MDPI, 2016-10-27) Masi, Marco; Cala, Antonio; Tabanca, Nurhayat; Cimmino, Alessio; Green, Ivan R.; Bloomquist, Jeffrey R.; Van Otterlo, Willem A. L.; Macias, Francisco A.; Evidente, AntonioTwo new Amaryllidaceae alkaloids, belonging to the mesembrine- and crinine-types, named crinsarnine (1) and sarniensinol (2), were isolated from the dried bulbs of Nerine sarniensis together with bowdensine (3), sarniensine (4), hippadine (5) and 1-O-acetyl-lycorine (6). Crinsarnine (1) and sarniensinol (2) were characterized using spectroscopic and chiroptical methods as (1S,2S,4aR,10bS)-2,7-dimethoxy-1,2,3,4,4a,6-hexahydro-5,11b-ethano[1,3]dioxolo-[4,5-j]phenanthridin- 1-yl acetate and (6-(3aR,4Z,6S,7aS)-6-methoxy-1-methyl-2,3,3a,6,7,7a-hexa-hydro-1H-indol-3a-yl)benzo [d][1,3]dioxol-5-yl)methanol, respectively. Furthermore, the complete spectroscopic characterization of bowdensine (3) is reported for the first time. Compounds 1–6 were evaluated against the Orlando reference strain of Aedes aegypti. None of compounds showed mortality against 1st instar Ae. aegypti larvae at the concentrations tested. In adult topical bioassays, only 1 displayed adulticidal activity with an LD50 = 2.29 ± 0.049 µg/mosquito. As regards the structure-activity relationship, the pretazettine and crinine scaffold in 2 and 4 and in 1 and 3 respectively, proved to be important for their activity, while the pyrrole[de]phenanthridine scaffold present in 5 and 6 was important for their reactivity. Among the pretazettine group compounds, opening of the B ring or the presence of a B ring lactone as well as the trans-stereochemistry of the A/B ring junction, appears to be important for activity, while in crinine-type alkaloids, the substituent at C-2 seems to play a role in their activity
- ItemAnalysis of gamma-ray and neutron-induced chromosome aberrations in CHO-K1 cells using the atomic force microscope(Academy of Science for South Africa, 2004) Meincken, M.; Smit, B. S.; Sanderson, R. D.; Slabbert J. P.THE ENUMERATION OF CHROMOSOME aberrations remains a popular method to relate DNA damage to radiation dose delivered, and is the basis of efforts to improve aberration assays. In the work reported here, atomic force microscopy was used to study the induction of chromosome aberrations in CHO-K1 cells, after irradiation with 1-3 Gy p(66)/Be neutrons and 2-7 Gy 60Co γ-rays. The investigation showed that small structures, not normally well defined using conventional microscopy, can be resolved and identified with the atomic force microscope. Furthermore, the height information gathered by atomic force microscopy is useful for eliminating counting mistakes, which might be caused by chromatid or chromosome overlaps. The superior resolution of atomic force microscopy over conventional optical microscopy renders the scoring of as few as 20 cells per dose point as sufficient to draw accurate dose curves that correctly express the biological damage induced by different radiation sources.
- ItemAntibacterial properties of tough and strong electrospun PMMA/PEO fiber mats filled with lanasol : a naturally occurring brominated substance(MDPI, 2014-09-09) Andersson, Richard L.; Martínez-Abad, Antonio; Lagaron, Jose M.; Gedde, Ulf W.; Mallon, Peter E.; Olsson, Richard T.; Hedenqvist, Mikael S.A new type of antimicrobial, biocompatible and toughness enhanced ultra-thin fiber mats for biomedical applications is presented. The tough and porous fiber mats were obtained by electrospinning solution-blended poly (methyl methacrylate) (PMMA) and polyethylene oxide (PEO), filled with up to 25 wt % of Lanasol—a naturally occurring brominated cyclic compound that can be extracted from red sea algae. Antibacterial effectiveness was tested following the industrial Standard JIS L 1902 and under agitated medium (ASTM E2149). Even at the lowest concentrations of Lanasol, 4 wt %, a significant bactericidal effect was seen with a 4-log (99.99%) reduction in bacterial viability against S. aureus, which is one of the leading causes of hospital-acquired (nosocomial) infections in the world. The mechanical fiber toughness was insignificantly altered up to the maximum Lanasol concentration tested, and was for all fiber mats orders of magnitudes higher than electrospun fibers based on solely PMMA. This antimicrobial fiber system, relying on a dissolved antimicrobial agent (demonstrated by X-ray diffraction and Infrared (IR)-spectroscopy) rather than a dispersed and “mixed-in” solid antibacterial particle phase, presents a new concept which opens the door to tougher, stronger and more ductile antimicrobial fibers.
- ItemAsikliese karbeenkomplekse maak eerste opslae in goudstormloop(LitNet Academic, 2012-12) Raubenheimer, Helgard G.OPSOMMING: Die eerste karbeenkomplekse van goud is reeds in 1971 deur Bonati en Minghetti gerapporteer. Verdere ontwikkelings na die 1980’s was stadig. Sedert 2007, toe die belangstelling in goudchemie reeds geweldig toegeneem het – en kort daarna amper dol geraak het – is die oorspronklike tipe asikliese diaminokarbeenkomplekse (ADK-komplekse) van goud weer te voorskyn gehaal, aangepas, beter gekarakteriseer en gebruik in teoretiese studies, luminessensie-ondersoeke, reaksies onder ongewone, hoë-energietoestande, stoïchiometriese omsettings, enkelkristalstudies en katalitiese reaksies waarin die goudatoom as reaktiewe sentrum optree. Die katalitiese ondersoeke konsentreer aanvanklik op chemo- en regioselektiewe transformasies, maar bereik uiteindelik ’n hoogtepunt met uiters suksesvolle enantioselektiewe sikliserings van geselekteerde alkynverbindings, waarin eers dikernige katalisatore en uiteindelik selfs monokernige ADK-goudkomplekse gebruik word. Sekere ADK-ligande beïnvloed die metaal elektronies en terselfdertyd stel dit die katalisator in staat om chirale inligting gedurende die aktiveringsproses optimaal aan die substraat oor te dra. In die lig van al hierdie inligting word nuwe voorstelle vir verdere ondersoek hier gemaak.
- ItemAttempted synthesis of a meta-metalated calix[4]arene(Beilstein-Institut, 2019) Jurisch, Christopher D.; Arnott, Gareth E.ENGLISH ABSTRACT: An evidence for the formation of a rare meta-metalated inherently chiral calix[4]arene is described. Our strategy involved using a mesoionic carbene to direct C–H activation, but proved to form an unexpectedly unstable intermediate that was identified through high-resolution mass spectrometry. On route to our target, a new optimized method to mononitrocalix[4]arenes was developed, including optimized and high yielding transformations to azide and 1,2,3-triazole derivatives which may have application in other areas of research.
- ItemAuII : skaars of afgeskeep? 'n Kritiese literatuuroorsig(LitNet, 2016-06-17) Raubenheimer, Helgard G.AFRIKAANSE OPSOMMING: Verbindings van AuII is reeds langer as 60 jaar bekend. ’n Literatuurstudie toon dat slegs ’n beperkte aantal struktuur- en bindingstipes tot dusver in suiwer vorm geïsoleer en gekarakteriseer kon word. Die grootste enkele groep bevat AuII as gekomplekseerde, kovalentgebonde [AuII–AuII]-eenhede en die twee goudatome is óf ligandgebrug (die grootste gros) óf óngebrug (’n handvol). Monokernige AuII-verbindings kom ook voor en word gekenmerk óf deur die teenwoordigheid van die eksotiese ligand Xe, óf weens chelaatvorming met bidentate of heksadentate S- of S- en O-donor-ligande, óf weens vierkantigvlak porfirien-kompleksvorming waarin imien-N en amied-N donorfunksies vervul. Die vorming van AuII gedurende nanogoudsintese, ’n rol daarvoor in homogene katalise, sowel as die stabilisering daarvan op verskillende vaste ondersteuningsplatforms, toon dat meer bruikbare toepassings in die toekoms verwag kan word. In die lig van resultate wat veral sedert 2000 verkry is, word die bestaande literatuur hier georden en bespreek en tekorte in die chemie van AuII uitgewys. Verskeie voorstelle vir verdere ondersoek word gemaak.
- ItemAvian exocrine secretions. I : chemical characterization of the volatile action of the uropygial secretion of the green woodhoopoe, Phoeniculus purpureus(Springer Verlag, 2004-08) Burger, B. V.; Reiter, B.; Borzyk, O.; Du Plessis, M. A.Using gas chromatography–mass spectrometry in conjunction with auxiliary techniques such as solid phase microextraction and determination of double bond positions by means of dimethyl disulfide derivatization, 45 constituents of the uropygial secretion of the green woodhoopoe, Phoeniculus purpureus, have been identified. The majority of these constituents are long-chain branched and unbranched alkanes, and (Z)-alkenes such as (Z)-9-tricosene, and a number of unidentified wax esters. The more volatile fraction of the secretion contained short-chain fatty acids, aldehydes, aliphatic and heterocyclic aromatic amines, ketones, and dimethyl sulfides. This group of volatile compounds is responsible for the obnoxious odor of the secretion and also for its defensive action against predators.
- ItemBreaking the trade-off between selectivity and adsorption capacity for gas separation(Elsevier Inc., 2021-11) Soumya, Naveen Kumar; Mukherjee, Nathan C.; Bezrukov, Andrey A.; Tan, Kui; Martins, Vinicius; Vandichel, Matthias; Pham, Tony; Van Wyk, Lisa M.; Oyekan, Kolade; Kumar, Amrit; Forrest, Katherine A.; Patil, Komal M.; Barbour, Leonard J.; Space, Brian; Huang, Yining; Kruger, Paul E.; Zaworotko, Michael J.The trade-off between selectivity and adsorption capacity with porous materials is a major roadblock to reducing the energy footprint of gas separation technologies. To address this matter, we report herein a systematic crystal engineering study of C2H2 removal from CO2 in a family of hybrid ultramicroporous materials (HUMs). The HUMs are composed of the same organic linker ligand, 4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, pypz, three inorganic pillar ligands, and two metal cations, thereby affording six isostructural pcu topology HUMs. All six HUMs exhibited strong binding sites for C2H2 and weaker affinity for CO2. The tuning of pore size and chemistry enabled by crystal engineering resulted in benchmark C2H2/CO2 separation performance. Fixed-bed dynamic column breakthrough experiments for an equimolar (v/v = 1:1) C2H2/CO2 binary gas mixture revealed that one sorbent, SIFSIX-21-Ni, was the first C2H2 selective sorbent that combines exceptional separation selectivity (27.7) with high adsorption capacity (4 mmol·g−1).
- ItemButenolides from plant-derived smoke : natural plant-growth regulators with antagonistic actions on seed germination(American Chemical Society and American Society of Pharmacognosy, 2010-01) Light, Marnie E.; Burger, B. V.; Staerk, Dan; Kohout, Ladislav; Van Staden, JohannesSmoke plays an intriguing role in promoting the germination of seeds of many species following a fire. Recently, a bicyclic compound containing a condensed butenolide moiety, 3-methyl-2H-furo[2,3-c]pyran-2-one (1), was reported as a potent germination promoter from plant-derived smoke. In this study, a related butenolide, 3,4,5-trimethylfuran- 2(5H)-one (2), which inhibits germination and significantly reduces the effect of 1 when applied simultaneously, was also isolated from plant-derived smoke. The interaction of these compounds with opposing actions on seed germination may have important ecological implications in a post-fire environment and could be useful molecules for understanding the events involved in breaking seed dormancy and promoting seed germination.
- ItemA calix[4]arene based boronic acid catalyst for amide bond formation : proof of principle study(ARKAT USA, 2018-06-25) Mafaune, Asslly Tafara; Arnott, Gareth E.ENGLISH ABSTRACT: A calix[4]arene boronic acid was synthesized and tested for catalysis in amide formation. The results were positive and paved the way for future designs, even though protodeboronation was observed under the conditions employed.
- ItemA calix[4]arene based boronic acid catalyst for amide bond formation: proof of principle study(ARKAT USA, Inc., 2019-06) Mafaune, Asslly Tafara; Arnott, Gareth E.ENGLISH ABSTRACT: A calix[4]arene boronic acid was synthesized and tested for catalysis in amide formation. The results were positive and paved the way for future designs, even though protodeboronation was observed under the conditions employed.
- ItemCation–π induced aggregation of water-soluble [PtII(diimine)(Ln-S,O)]+ complexes studied by ¹H DOSY NMR and TEM : from ‘dimer aggregates’ in acetonitrile to nano-aggregates (‘metallogels’) in water(Royal Society of Chemistry, 2013) Kotze, Izak A.; Gerber, Wilhelmus J.; Wu, Yu-Shan; Koch, Klaus R.See PDF file for an abstract.
- ItemCharacterization of volatiles and aroma-active compounds in honeybush (Cyclopia subternata) by GC-MS and GC-O analysis(American Chemical Society, 2012-03) Le Roux, Maritha.; Cronje, J. Christel; Burger, B. V.; Joubert, ElizabethVolatile organic compounds (VOCs) in fermented honeybush, Cyclopia subternata, were sampled by means of a high-capacity headspace sample enrichment probe (SEP) and analyzed by gas chromatography-mass spectrometry (GC-MS). Stereochemistry was determined by means of enantioselective GC-MS with derivatized β-cyclodextrin columns as chiral selectors. A total of 183 compounds, the majority of which are terpenoids (103; 56%), were identified by comparing their mass spectra and retention indices with those of reference compounds or tentatively identified by comparison with spectral library or literature data. Of these compounds, 37 were determined by gas chromatography-olfactometry (GC-O), using detection frequency (DF) and aroma extract dilution analysis (AEDA), to be odor-active (FD ≥ 2). (E)-β-Damascenone, (R/S)-linalool, (E)-β-damascone, geraniol, (E)-β-ionone, and (7E)-megastigma-5,7,9-trien-4-one were identified with the highest FD factors (≥512). The odors of certain compounds, that is, (6E,8Z)-megastigma-4,6,8-trien-3-one, (6E,8E)-megastigma-4,6,8-trien-3-one, (7E)-megastigma-5,7,9-trien-4-one, 10-epi-γ-eudesmol, epi-α- muurolol, and epi-α-cadinol, were perceived by GC-O assessors as typically honeybush-like. © 2012 American Chemical Society.
- ItemChemical characterization of territorial marking fluid of male Bengal tiger, Panthera tigris(Springer Verlag, 2008-05) Burger, B. V.; Viviers, M. Z.; Bekker, J. P. I.; Le Roux, M.; Fish, N.; Fourie, W. B.; Weibchen, G.The territorial marking fluid of the male Bengal tiger, Panthera tigris, consists of a mixture of urine and a small quantity of lipid material that may act as a controlled-release carrier for the volatile constituents of the fluid. Using gas chromatography and gas chromatography-mass spectrometry, 98 volatile compounds and elemental sulfur were identified in the marking fluid. Another 16 volatiles were tentatively identified. The majority of these compounds were alkanols, alkanals, 2-alkanones, branched and unbranched alkanoic acids, dimethyl esters of dicarboxylic acids, γ- and δ-lactones, and compounds containing nitrogen or sulfur. Several samples of the marking fluid contained pure (R)-3-methyl-2-octanone, (R)-3-methyl-2-nonanone, and (R)-3-methyl-2-decanone, but these ketones were partly or completely racemized in other samples. The γ-lactone (S)-(+)-(Z)-6-dodecen-4-olide and the C8 to C16 saturated (R)-γ-lactones and (S)-δ-lactones were present in high enantiomeric purities. The chiral carboxylic acids, 2-methylnonanoic acid, 2-methyldecanoic acid, 2-methylundecanoic acid, and 2-ethylhexanoic acid were racemates. Cadaverine, putrescine, and 2-acetylpyrroline, previously reported as constituents of tiger urine, were not detected. The dominant contribution of some ketones, fatty acids, and lactones to the composition of the headspace of the marking fluid suggests that these compounds may be important constituents of the pheromone. Although it constitutes only a small proportion, the lipid fraction of the fluid contained larger quantities of the volatile organic compounds than the aqueous fraction (urine). The lipid derives its role as controlled-release carrier of the chemical message left by the tiger, from its affinity for the volatiles of the marking fluid. Six proteins with masses ranging from 16 to 69 kDa, inter alia, the carboxylesterase-like urinary protein known as cauxin, previously identified in the urine of the domestic cat and other felid species, were identified in the urine fraction of the marking fluid. © 2008 Springer Science+Business Media, LLC.
- ItemChemical characterization of the constituents of the aroma of honeybush, Cyclopia genistoides(Elsevier, 2008-01) Le Roux, M.; Cronje, J. C.; Joubert, E.; Burger, B. V.A high-capacity headspace sample enrichment probe (SEP) was used in conjunction with gas chromatography-mass spectrometry (GC-MS) to analyse the volatile organic compounds present in the aroma of dry or infused, unfermented (green) and fermented C. genistoides, one of the South African Cyclopia species from which a herbal tea, known as honeybush tea, is made. Seventy-seven compounds were identified in the volatile fraction of the aroma of dry, green C. genistoides, comprising, inter alia, a large number of saturated and unsaturated alcohols, aldehydes and methyl ketones. In the aroma of dry, as well as infused, fermented C. genistoides, 79 compounds were identified, 46 of which were terpenoids that were mostly present in much lower relative concentrations in the unfermented material. The methodology developed and the results obtained in the analysis of the aroma of C. genistoides provide a basis for ongoing comparative studies on the chemical composition of a series of prominent Cyclopia species with the view to developing a rapid screening device and protocol for honeybush tea evaluation. © 2007 SAAB.