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Earlier work on stream water and effluent from wastewater treatment plants in Blantyre, Malawi, has revealed high phosphate levels ranging from 0.63 to 5.50 mg/L. These phosphate levels would stimulate excessive growth of plants and toxic cyanobacteria in stagnant receiving water bodies hence posing a threat to aquatic life and water quality. Phosphate removal by kaolinite obtained from Linthipe, Malawi, was investigated as a function of pH, contact time, clay dosage, competing ions and initial phosphate concentration by means of jar tests. Phosphate uptake was pH dependent with adsorption mechanisms on kaolinite and iron oxide surfaces dominant generally below pH 7 and precipitation by calcium ions dominant above pH 7. Maximum phosphate removal occurred at high pH values of 11.22 (97.1%) and 10.96 (100%) for raw and treated kaolinite, respectively. Acid treated kaolinite indicated higher phosphate removal efficiency than the raw one at the normal working pH of 9.0 ± 0.2. This was attributed to release of extra calcium ions from CaCO 3 present in the kaolinite samples during acid treatment. At the maximum dosage of 80 g/L, percent phosphate removal was 69.7 ± 0.100% and 98.5 ± 0.0577% for raw and treated kaolinite, respectively. This indicates requirement for high dosages to effect phosphate removal from the aqueous solutions. Studies on the effects of competing ions indicate that phosphate uptake decreased in the presence of CO 3 2 - , was little affected by SO 4 2 - , and increased in the presence of Ca 2+ , and Mg 2+ ions. Furthermore, phosphate uptake approached equilibrium slowly at 20 °C and was faster at 40 °C.

This study assessed the ability of filamentous green algae; Spirogyra aequinoctialis to accumulate manganese, cadmium and lead from water. Water pH was also determined. Samples of S. aequinoctialis and their respective water environments were taken from designated sampling points in the city of Blantyre and Malawi during the rainy and dry season in order to capture seasonal variations. The concentration of metals in S. aequinoctialis were higher than in the corresponding water environment in both seasons, but lower in the rainy season than the dry season. In the rainy season the concentrations were (in S. aequinoctialis and (water)): Mn 0.432–5.641 mg/L (ND-0.530 mg/L), CdND- 0.016 mg/L (0.07–0.111 mg/L) andPbND- 0.965 mg/L (0.011–0.098 mg/L). In the dry season the concentrations were: Mn 0.281-16.132 mg/L (0.035–0.626 mg/L), Cd 0.22–0.912 mg/L (0.014–0.111 mg/L) and Pb ND- 0.972 mg/L (ND- 0.23 mg/L). This study has shown that S. aequinoctialis has the capability of accumulating manganese, cadmium and lead. Therefore it can be used as a biological indicator for long term heavy metal water pollution monitoring.

A study was carried out to determine fluoride concentration in groundwaters of Nathenje area situated in Lilongwe District in the central region of Malawi. Water samples were collected from 176 boreholes and shallow wells during different months in 2001 and 2002. Samples were then analysed for fluoride by using a fluoride electrode and an ion selective meter. The results showed that fluoride concentrations for the rainy season varied from

Iron is an essential metal for almost all living cells. In the interaction host-parasite, this metal is considered as a key element. The possession of highly efficient mechanisms to overcame the natural iron limitation imposed by the host, is critical for the parasite survival. Some parasite use siderophore to strip iron from the carrier proteins while others have evolved heme-mediated iron acquisition mechanisms. Although these mechanisms are complex and diverse, the presence of outer membrane receptors for iron compounds seems to be a general phenomenon. Despite the expanded understanding on the association rhizobia-legume, the knowledge of iron acquisition mechanism is one of the major interests of our group. We almost demonstrated that rhizobia were able to utilize hemin, hemoglobin, mioglobin leghemoglobin and siderophores (rhizobactin 242 and ferrichrome) as iron sources. Moreover, the uptake mechanism of these compounds share at least one component. According our previous work, it is conceivable that this component could be a protein from the Ton complex. These data support the idea that many of the processes found in the interaction rhizobialeguminous host, are variant of general processes implicated in other microand macroorganisms interactions. The present work aimed at the elucidation of the physiology and biochemistry of iron transport in rhizobia. In this study we examined the utilization of heme compounds and siderophores as iron sources in Sinorhizobium meliloti 242 grown on minimal medium.

Iron, an important element involved in many metabolic processes is virtually insoluble in aerobic conditions and biological pH. In most aerobic and facultative anaerobic microorganisms iron-limiting conditions induce the derepression of high-affinity transport systems involving: i) Fe+3-chelating agents (siderophores) and ii) transport membrane proteins including outer-membrane receptors for the ferric-siderophore complex. The ability to use heme-containing compounds as iron sources under iron-deficient conditions, has been also documented. In a previous paper we showed that rhizobia are able to use hemin, hemoglobin and leghemoglobin as iron sources and that siderophore-, heme-, hemoglobin- and leghemoglobin-mediated iron transport system expressed by R. meliloti 242 share at least one component (Noya et al., 1997).

The synthesis of multicolor fluorescent oligothiophene-N-succinimidyl esters (TSEs) is reported and their optical properties are discussed with the aid of ab initio calculations. The esters were coupled to proteins and to 3’-amino-modified oligonucleotides in mild conditions and with similar modalities. A comparative study of the bioconjugate of IgG1 anti-CD3 antibody labeled with a blue fluorescent TSE and with fluorescein isothiocyanate (FITC) is reported showing that the former achieves higher photoluminescence intensity and optical stability than the latter. Fluorescence resonance energy transfer experiments with TSE labeled oligonucleotides and examples of cellular imaging via TSE labeled proteins are reported.

Novel triphenylamine (TPA)-based organic dyes were synthesized and assessed for their performance in dye-sensitized solar cells (DSSCs). In the dyes considered the TPA group and the cyanoacetic acid have the role of electron-donor and -acceptor, respectively, whereas a thienyl-fluoro-phenyl-substituted was introduced as ?-linker to improve the dye performance in DSSCs. Experimental characterizations empasize that the presence of electron withdrawing substituents in the linker close to the electron-acceptor moiety leads to a more efficient intramolecular photoinduced charge transfer. In fact, photovoltaic experiments reveal that the DSSCs based on the thienyl-o-fluoro-phenyl substituted dyes yield a better solar-energy-to-electricity conversion efficiency.

This study reports oil the first monodispersed molecular materials embodying the dibenzothiophene-5,5-dioxide core for the achievement of blue electroluminescence. The core has been functionalised in its 2.8- or 3,7-positions with dimethyl-fluorene (2,8-DBTOF and 3,7-DBTOF) or methyl-carbazole (2,8-DBTOC and 3,7-DBTOC) groups. The obtained compounds were characterised by (1)H and (13)C NMR, APCI-MS, thermal analysis (TGA and DSQ and cyclic voltammetry. Their optical and photophysical properties were investigated by UV and PL measurements as well as by time-dependent density-functional theory calculations. The materials were successfully employed as active layers ill blue to purplish blue p-i-n OLED devices. that reached, in the case of 3,7-DBTOC, performances as high as 11 422 cd m(-2) and 3.25 cd A(-1).

We have analyzed singlet and triplet excitation energies in oligothiophenes (up to five rings) using time-dependent density-functional theory (TD-DFT) with different exchange-correlation functionals and compared them with results from the approximate coupled-cluster singles and doubles model (CC2) and experimental data. The excitation energies have been calculated in geometries obtained by TD-DFT optimization of the lowest excited singlet state and in the ground-state geometries of the neutral and anionic systems. TD-DFT methods underestimate photoluminescence energies but the energy difference between singlet and triplet states shows trends with the chain-length similar to CC2. We find that the second triplet excited state is below the first singlet excited state for long oligomers in contrast with the previous assignment of Rentsch et al. (Phys. Chem. Chem. Phys. 1999, 1, 1707). Their photodetachment photoelectron spectroscopy measurements are better described by considering higher triplet excited states.

Self-assembled monolayers (SAMs) of cobalt(II) 5,10,15,20-tetrakis(4-tert-butylphenyl)-porphyrin, a promising material for optical, photoelectrochemical, and chemical sensor applications, were prepared on Au(111) via axial ligation to 4-aminothiophenol, and studied by several surface science techniques. Scanning tunneling microscopy (STM) and spectroscopy (STS) measurements showed the apparent topology of the Au(111) herringbone structure reconstruction, but with bias-dependent contrast images and asymmetric I/V characteristics. Photoelectron spectroscopy confirmed the presence of metalloporphyrins on the surface, whereas near-edge X-ray absorption (NEXAFS) measurements revealed that the porphyrin ring was tilted by about 70 degrees with respect to the surface plane. The above effects are ascribed to the presence of oriented molecular dipole layers between the metal and the organic material as confirmed by a comparison with first-principles density-functional theory calculations. The measured bias-dependent STM profiles have been reproduced by a simple monodimensional tunneling model.