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Influence of weak and strong donor groups on the fluorescence parameters and the intersystem crossing rate constant

Nijegorodov, N.; Mabbs, R.; Winkoun, D.P. (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2003)

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Abstract: Please refer to the attached article for an ABSTRACT. The abstract was not uploaded here due to formula appearance problem in UBRISA.

URI: http://hdl.handle.net/10311/402

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Nijegorodov_SAa59-2003.pdf (1.367Mb)

Intermediate and ion-pair formation in the outer-sphere reactions between azido-pentacyanocobaltate(III) and iron(II) polypyridyl complexes in aqueous medium

Ogunlusi, G.O.; Ige, J.; Oyetunji, O.A.; Ojo, J.F. (Springer Science+Business Media B.V., http://www.springer.com/chemistry/journal/11243, NaN, 2009)

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Abstract:	The kinetics of the reactions between azidopentacyanocobaltate(III), Co(CN)5N3 3-, and iron(II) polypyridyl complexes, Fe(LL)3 2? (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm-3 NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL)32+ was kept constant, and the second-order rate constants obtained for the reactions at 35 C were within the range of 0.156–0.219 dm3 mol-1 s-1 for LL = bipy and 0.090–0.118 dm3 mol-1 s-1 for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied in the range [H+] = 0.001–0.008 mol dm-3. The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed outerand inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k5) is slower than through the outer-sphere path (k4).
Description:	Symbols may not appear as they are in the original abstracts.
URI:	http://hdl.handle.net/10311/1035

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Ogunlusi_TMC_2009.pdf (948.9Kb)

Investigation of sustainability of rain-fed agriculture through soil moisture modeling in the Pandamatenga Plains of Botswana

Alemaw, B.F.; Chaoka, T.R.; Totolo, O. (Elsevier Ltd. http://www.elsevier.com/wps/find/journaldescription.cws_home/413/description#description, NaN, 2006)

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Abstract:

The agricultural economic sector of Botswana is limited mainly to range resources-based livestock and pockets of arable farming based on rainfall and limited irrigated agriculture at several places. In this study agricultural sustainability of rain-fed agriculture is investigated in Botswana by considering the Pandamatenga plains as a case study. Daily soil moisture regimes with respect to crop growth cycle were modelled using a water balance model based on 42 years of daily hydroclimatic inputs and corresponding simulated components of soil moisture, evaporation, surface runoff, and deep percolation. Using a sustainability criterion on crop water requirement and soil moisture availability during the cropping periods, it was found that rain-fed agriculture of maize, sunflower, and sorghum crops is sustainable. The relative sensitivity to drought of these crops was also found to conform to the Agromisa recommendations. In the pursuit to explore more IWRM opportunities, through the simulation of the corresponding direct runoff, we have also explored that more water harvesting opportunities exist in order to manage rainfall excesses effectively.

URI:

http://hdl.handle.net/10311/155

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alemaw_chaoka_totolo_06.pdf (2.112Mb)

license.txt (1.998Kb)

Isoflavonoids from Seeds of Millettia griffoniana (Bail), 15

Ngamga, D.; Yankep, E.; Tane, P.; Bezabih, M.; Ngadjui, B.T.; Fomum, Z.T.; Abegaz, B.M. (Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com, NaN, 2005)

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Abstract:	Three new isoflavonoids, griffonianone F, G and H were isolated from the seeds of Millettia griffoniana, along with the known prebarbigerone, pseudobaptigenin, pseudobaptigenin methyl ether, tephrosin, dipterixine, odorantine, 7,4’,5’-tetramethoxyisoflavone and isojamaicin. Their structures were assigned on the basis of spectroscopic data and chemical transformations.
URI:	http://hdl.handle.net/10311/274

Files in this item: 1

Isoflavonoids from Seeds.pdf (1.353Mb)

Kinetic studies on the reactions of some tetrakis(arylisocyanide)cobalt(II) complexes with pyridine in 2,2,2-trifluoroethanol

Oyetunji, O.A.; Paphane, B.D.; Becker, C.A.L. (Springer, http://www.springer.com/chemistry/journal/11243, NaN, 2006)

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Abstract:

The interaction of pyridine with four tetraki(arylisocyanide)cobalt(II) complexes, [Co(CNR)4(ClO4)2] R = 2,6- Me2C6H3 (A), 2,4,6-Me3C6H2 (B), 2,6-Et2C6H3 (C) and 2,6-iPr2C6H3 (D), have been studied in 2,2,2-trifluoroethanol medium. The kinetics of the reactions were investigated over the 293–318 K temperature range. The reaction profile exhibited two distinct processes, proposed to be an initial fast substitution followed by a slow reduction, for each of the reactions. The pseudo first-order rate constants for both processes increased with increasing concentration of pyridine with the reduction processes exhibiting saturation kinetics at high pyridine concentrations. Steric hindrance plays a significant role in the rates of the reactions, as the rates decrease in the order k(A) > k(B) > k(C) > k(D). The activation enthalpies, DH , increase from A to D while the activation entropies, DS , are relatively similar for the four reactions, indicating similar transition states and hence similar mechanisms. Complex B was first synthesized and characterized in this study.

URI:

http://hdl.handle.net/10311/1033

Files in this item: 1

Oyetunji_TMC_2006.pdf (911.4Kb)

Lanneanol: A new cytotoxic dihydroalkylcyclohexenol and phenolic compounds from Lannea nigritana (Sc. Ell.) Keay

Kapche, G.; Laatsch, H.; Fotso, S.; Kouam, S.; Wafo, P.; Ngadjui, B.; Abegaz, B. (Elsevier Ltd. www.elsevier.com/locate/biochemsyseco, NaN, 2007)

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Abstract:

The genus Lannea belongs to the family Anacardiaceae and consists of 40 species. Lannea nigritana (Sc. Elliot) Keay is a small tree of 3e6 m of height found in the tropical rain forest (Berhaut, 1971; Letouzey, 1972). It is used in the traditional medicine for the treatment of various infectious diseases (Berhaut, 1971; Burkill, 1985). The stem bark of this plant was collected in Makenene, Centre Province of Cameroon in December 2003. The identification was done by Mr. Nana from the National Herbarium of Yaounde where a voucher specimen (N 40408/HNC) documenting the collection is deposited.

URI:

http://hdl.handle.net/10311/252

Files in this item: 2

Lanneanol.pdf (2.606Mb)

license.txt (1.998Kb)

Novel natural products from marketed plants of eastern and southern Africa

Abegaz, B.M.; Ngadjui, B.T.; Bezabih, M.; Mdee, L.K. (International Union of Pure and Applied Chemistry. http://www.iupac.org/publications/pac/, NaN, 1999)

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Abstract:

Marketed plants are an important but a vulnerable group of plants whose investigations as well as conservation should be considered with priority. The chemistry, and in some cases biological activities of novel iso¯avonoids, nor-lignans, anthracene and naphthalene derivatives and poly prenylated ¯avonoids isolated and characterized from Hagenia abyssinica, Salsola somalensis, Hypoxis spp., Taverniera abyssinica, Aloe spp., Bulbine capitata, Rhamnus prinoides and Dorstenia spp. are discussed.

URI:

http://hdl.handle.net/10311/289

Files in this item: 1

Novel natural products.pdf (4.533Mb)

The phase separation behaviour and the viscoelastic properties of particles with non-adsorbing polymers: Part I - Experimental study

Goodwin, J.W.; Hughes, R.W.; Kwaambwa, H.M.; Reynolds, P.A. (Elseview Science B.V. www.elsevier.nl/locate/colsurfa, NaN, 2000)

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Abstract:

A series of well characterised cis-polyisoprene polymers have been added to dispersions of PHS coated PMMA particles in dodecane. At a molecular weight of 8000 g mol−1 and above, these systems showed phase separation at low particle volume fractions and above a critical polymer concentration. The rate of separation has been shown to be influenced by the viscosity of the polymer. At high polymer and particle volume fractions long lived metastable phases occurred. Above a critical concentration these were viscoelastic indicating an appreciable change in diffusion dynamics with two relaxation processes present. A significant Bingham yield stress was also observed. The Asakura Oosawa potential was not able to describe the observed rheological properties. At a molecular weight of 1000 g mol−1 no phase separation was observed. At high particle concentrations the yield stress was found to reduce with the addition of polymer. This was due to the polymer acting as a ‘solvent’ and penetrating the stabilising layer on the particles.

URI:

http://hdl.handle.net/10311/329

Files in this item: 1

Phase separation behaviour.pdf (2.723Mb)

Phenylpropanoid glycosides of Gnidia polycephala

Munkombwe N.M. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2003)

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Abstract:	Two phenylpropanoid glucosides, 2-O-b-d-glucosyloxy-4-methoxybenzenepropanoic acid and its methyl ester, together with syringin and adicardin were isolated from the stem of Gnidia polycephala and characterized by physical and spectroscopic data.
URI:	http://hdl.handle.net/10311/275

Files in this item: 2

Phenylpropanoid glycosides.pdf (2.288Mb)

Phenylpropanoid glycosides of Gnidia.pdf (155.6Kb)

Photochromism, anomalous multi-banded fluorescence and laser properties of some amino- and tosyl-amino derivative of oxadiazole

Nijegorodov, N.; Zvolinski, V.; Luhanga, P.V.C.; Mabbs, R.; Ahmad, J. (Elsevier Ltd. www.elsevier.com/locate/saa, NaN, 2006)

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Abstract:

The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293 K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6-5.2 kcal mol-1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha-Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed.

URI:

http://hdl.handle.net/10311/176

Files in this item: 2

license.txt (1.998Kb)

Photochromism, ... ivatives of oxadiazole.pdf (2.530Mb)

Photochromism, anomalous multi-banded fluorescence and laser properties of some amino- and tosyl-amino derivatives of oxadiazole

Nijegorodov, N; Zvolinski, V; Luhanga, P V C; Mabbs, R; Ahmad, J (Elsevier Science Ltd. www.elsevier.com/locate/saa, NaN, 2006)

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Abstract:

The multi-banded fluorescence and laser properties of 11 new amino- and tosylamino derivatives of 2,5-di(phenyl)-1,3,4-oxadiazole and oxadiazole in various solvents at 293K are reported. All the compounds investigated possess intra-molecular hydrogen quasi-bond (IHB) of 4.6–5.2 kcal mol−1 in the ground state. In the excited state they can undergo protolytic dissociation or intra-molecular photon-initiated transfer of proton and reveal anomalous fluorescence which cannot be explained within the framework of the Kasha and Kasha–Vavilov rules. Depending upon the excitation wavelength, solvent, concentration and pH of the medium, the compounds studied show a single, double, triple or even a four-banded fluorescence, which has not been reported earlier. The nature of multi-banded fluorescence is explained in terms of the possible photochromic processes in excited states. Quantum yields and decay times of the different fluorescence bands are reported. Anomalous dependence of quantum yield upon concentration of the solution is observed. Laser properties of the compounds studied are carefully tested. Laser action based on the fluorescence of the so-called bi-radical molecules is reported. Various possible arrangements of singlet and triplet levels of compounds investigated are discussed.

URI:

http://hdl.handle.net/10311/247

Files in this item: 2

license.txt (1.998Kb)

Nijegorodov_SAa65_2006.pdf (2.225Mb)

Prenylated arylbenzofuran derivatives from Morus mesozygia with antioxidant activity

Kapche, G.D.W.F.; Fozing, C.D.; Donfack, J.H.; Fotso, G.W.; Amadou, D.; Tchana, A.N.; Bezabih, M.; Moundipa, P F; Ngadjui, B.N.; Abegaz, B.M. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2008)

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Abstract:

Five prenylated arylbenzofurans, moracins Q–U, were isolated from Morus mesozygia (Moraceae). Their structures were elucidated on the basis of spectroscopic evidence. Along with these compounds, 3b-acetoxyurs- 12-en-11-one, marsformoxide, moracin C, moracin M, moracin K, artocarpesin, cycloartocarpesin, morachalcone A were also isolated. Four of the five compounds, (moracins R–U) displayed potent antioxidant activity.

URI:

http://hdl.handle.net/10311/315

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Prenylated arylbenzofuran.pdf (3.853Mb)

Prenylated chalcones, flavone and other constituents of the twigs of Dorstenia angusticornis and Dorstenia barteri var. subtriangularis

Ngadjui, B.; Watchueng, J.; Keumedjio, F.; Ngameni, B.; Simo, I.; Abegaz, B. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2004)

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Abstract:

The twigs of Dorstenia angusticornis and Dorstenia barteri var. subtriangularis yielded 16 compounds. Two novel diprenylated chalcones: 3,50-di-(2-hydroxy-3-methylbut-3-enyl)-4,20,40-trihydroxychalcone, 3, 4-(2,2-dimethylpyrano)-30-(2-hydroxy-3-methylbut- 3-enyl)-20,40-dihydroxychalcone and the known stipulin were isolated from both species. 3-(2-Hydroxy-3-methylbut-3-enyl)- 50-(3,3-dimethylallyl)-4,20,40-trihydroxychalcone and the known compounds: 4-hydroxylonchocarpin, kanzonol B, bartericins A, B, C and 30-(2-hydroxy -3-methylbut-3-enyl)-4,20,40-trihydroxychalcone were isolated from D. barteri while the known compounds: gancaonin Q, paratocarpins C, F, and lupeol were obtained from Dorstenia angusticornis. b-Sitosterol and its b-D-glucopyranoside were isolated from both species. Structures of these secondary metabolites were established using spectroscopic analysis, especially, NMR spectra in conjunction with 2D experiments, COSY, HMQC and HMBC.

URI:

http://hdl.handle.net/10311/253

Files in this item: 2

license.txt (1.998Kb)

Prenylated chalcones, flavone.pdf (3.563Mb)

Prenylated flavonoids and other constituents from the twigs of Dorstenia angusticornis (Moraceae)*

Simo, I.K.; Ngadjui, B.T.; Abegaz, B.M. (Elsevier Ltd. www.elsevier.com/locate/biochemsyseco, June 18, 2005)

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Abstract:

Dorstenia (Moraceae) is a mainly tropical genus of some 170 species (Mabberley, 1987). There are 23 species in Cameroon where a decoction of the leaves is administered for the treatment of cough, headache and stomach pain (Bouquet, 1969). The genus is made up largely of herbaceous perennials with succulent and non-succulent scrambling rhizomes (Berg et al., 1989). The twigs of Dorstenia angusticornis were collected in February 2002 from Kumba South West Province of Cameroon. Voucher specimen (No 28165/sfcam) is deposited at the National Herbarium Yaounde, Cameroon.

URI:

http://hdl.handle.net/10311/255

Files in this item: 1

Prenylated flavonoids and other constituents.pdf (1.986Mb)

Prenylated flavonoids, monoterpenoid furanocoumarins and other constituents from the twigs of Dorstenia elliptica (Moraceae)

Abegaz, B.M.; Ngadjui, B.T.; Folefoc, G.N.; Fotso, S.; Ambassa, P.; Bezabih, M.; Dongo, E.; Rise, F.; Petersen, D. (Elsevier Ltd. www.elsevier.com/locate/phytochem, NaN, 2003)

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Abstract:

A monoprenylated flavan and two monoterpenoid substituted furanocoumarins were isolated from the twigs of Dorstenia elliptica along with 3-(3,3-dimethylallyl)-4,20,40-trihydroxylchalcone, psoralen, bergapten, O-[3-(2,2-dimethyl-3-oxo-2H-furan-5-yl)butyl] bergaptol, b-sitosterol and its b-d-glucopyranoside. The structure of the flavan was determined as 6(1,1-dimethylallyl)-7,40- dihydroxylflavan and the monoterpenoid substituted furanocoumarins were assigned as O-[3-(2,2-dimethyl-3-oxo-2H-furan-5-yl)-3- hydroxybutyl]-bergaptol and O-[2-(5-hydroxy-2,6,6-trimethyl-3-oxo-2H-pyran-2-yl)ethyl]bergaptol, respectively, using spectroscopic analysis, especially, 2D NMR spectra.

URI:

http://hdl.handle.net/10311/286

Files in this item: 1

Prenylated flavonoids,.pdf (3.692Mb)

Progress in the chemistry of marketed traditionally used plants of Ethiopia

Abegaz, B.M. (Chemical Society of Ethiopia. http://www.aau.edu.et/faculties/sc/CSE/home.html, NaN, 1996)

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URI: http://hdl.handle.net/10311/345

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progress in the chemistry of.pdf (922.3Kb)

Quality and Compositional Studies of Some Edible Leguminosae Seed Oils in Botswana

Ketshajwang, K.K.; Holmback, J.; Yeboah, S.O. (AOCS Press. http://www.springerlink.com/content/120382/, NaN, 1998)

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Abstract:

Seed oils were extracted with n-hexane from three edible Leguminosae seeds: Tylosema esculentum, Xanthocercis zambesiaca, and Bauhinia petersiana, giving yields of 48.2, 17.6, and 20.8% (w/w), respectively. Some physical and chemical parameters were determined to ascertain the general characteristics of the oils. The saponification and iodine values indicated that all three oil samples could be classified among the olive group of oils. This inference was supported by the results of the detailed fatty acid composition of the oils as determined by capillary gas chromatography. The ratio of total unsaturated to total saturated fatty acids in all three oil samples was approximately 70:30, with either oleic or linoleic acid being the dominant fatty acid. These results were in agreement with a proton nuclear magnetic resonance analysis of the fatty acid classes in the seed oils. Thus, the analysis served to justify the use of the three Leguminosae seed oils in food preparations. The work has further indicated that, with their attractive properties, the seed oils from T. esculentum, X. zambesiaca, and B. petersiana are good candidates for further studies to evaluate their future commercial prospects in the Southern African region.

URI:

http://hdl.handle.net/10311/304

Files in this item: 1

quality and compositional.pdf (1.683Mb)

Reaction of a bulky phosphite with [Ru3(CO)12]: the molecular structure of one of the decomposition products

Magwaza, A.O.; Meijboom, R.; Muller, A.; Mavunkal, I.J. (Elsevier B.V. www.elsevier.com/locate/ica, NaN, 2008)

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Abstract:

Mono- and bis-substituted phosphite complexes [Ru3(CO)12 x Lx] (L = tris(2,4-di-tert-butylphenyl) phosphite; x = 1, 2) were synthesized by simple substitution reactions, and were characterized by spectroscopic methods. The monosubstituted ruthenium complex disproportionates in acetone producing a mononuclear ruthenium complex as one of the decomposition products. Single crystal X-ray diffraction analysis established the molecular structure of this new compound.

URI:

http://hdl.handle.net/10311/259

Files in this item: 2

license.txt (1.998Kb)

Reaction of a bulky phosphite with [Ru3(CO)12].pdf (1.989Mb)

Recent results from natural product research at the University of Botswana

Majinda, R.R.T; Abegaz, B.M.; Bezabih, M.; Ngadjui, B.T; Wanjala, C.C.W.; Mdee, L.K.; Bojase, G.; Silayo, A.; Masesane, I.; Yeboah, S.O. (IUPAC. http://www.iupac.org/publications/pac/, NaN, 2001)

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Abstract:

Marketed plants are very important items of trade in many parts of the world. The community uses these for a variety of purposes such as foods, cosmetics, flavors, spices, and medicines. It seems that plants that are used for medicinal purposes form the most common category. Four plants used for treatment of microbial infections, viz., Bolusanthus speciosus, Erythrina latissima, Crotalaria podocarpa, and Elephantorrhiza goetzei, were investigated, and these yielded several known and novel structures, some with appreciable antibiotic activity against the test organisms. The activity of some of the isolated plants and the parts of the plant from which these were obtained lend support to their traditional use. Bulbine abyssinica and B. capitata yielded phenylanthraquinones, some of which were shown to possess strong antiplasmodial activity. In addition, these yielded isofuranonaphthoquinones, which were also found to be weakly antiplasmodial and antioxidant. Scilla nervosa yielded several known and novel homoisoflavoinds of the 3-benzylchroman-4-ones and 3-benzylidinechroman- 4-one type, as well as some stilbenoids. The homoisoflavonoids showed strong antitumor activity against various cancer cell lines. Rhus pyroides gave a novel bichalcone, which showed weak antifeedant activity, consistent with the observation by farmers that the plant was avoided by corn cricket. Results from investigated Dorstenia species originating from Cameroon, Ethiopia, and Tanzania yielded styrenes, coumarins, chalcones, and flavonoids. The chalcones and flavonoids showed various levels of prenylation or geranylation, and an observation made so far is that prenylated flavonoids are only found in Dorstenia species of African origin. The only example of a bis-geranylated chalcone is found in Dorstenia.

URI:

http://hdl.handle.net/10311/308

Files in this item: 1

Files in this item: 2

license.txt (1.998Kb)

Rotenoid deriva ... nstituents of the twig.pdf (3.786Mb)

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Abstract:	Please refer to the attached article for an ABSTRACT. The abstract was not uploaded here due to formula appearance problem in UBRISA.
URI:	http://hdl.handle.net/10311/402