PROF LYDIA WANJIRU NJENGA

A density-functional theory (DFT) study of five ruthenium complexes has been carried out with the goal of gaining deeper insight into factors governing luminescence lifetimes. The five compounds are [Ru(bpy)3]2+ (1), [Ru(L1)2]2+ (2), [Ru(tpy)2]2+ (3), [Ru(L1)(tpy)]2+ (4), and [Ru(L2)2]2+ (5), where bpy = 2,2’-bipyridine, tpy = 2,2’;6’,2”-terpyridine, L1 = 1,1’-[2,6-pyridinediylbis(methylene)]bis[3-methylimidazolium] hexafluorophosphate and L2 = 1,1’-[2,6-pyridinediylbis(methylene)]bis[3-methylbenziimidazolium]. Experimental work, including the synthesis and photo-physical properties of 5 is also reported in the context of this study. Gas phase geometries optimized using X-ray crystallography geometries as start geometries were found to be close to the start geome-tries. Gas phase absorption spectra calculated using time-dependent DFT were found to be in good agreement with spectra measured in solution. A partial density of states (PDOS) analysis of the molecular orbitals shows that it is possible to recover a ligand field theory (LFT)-like picture. On the basis of this PDOS-derived LFT-like picture we propose two orbital-based luminescence indices, both motivated by the idea that luminescence quenching results from a low 3MLCT →3MC barrier. The first luminescence index is ∆E, the difference between the e∗g and lowest energy π *PDOS bands. The second luminescence index is d ×π, the product of the amount of π character in the t2g band with the amount of ruthenium d character in the 1 π* band. These luminescence measures are intended as qualitative rather than quantitative predictors. Low values of ∆E and high values of d ×π are shown to correlate with lack of luminescence for the five compounds studied in this paper, while high values of ∆E and low values of d × π correlate well with luminescence.

Dietary quality is vital in maintaining sound nutritional status. The ecological conditions thus influence the type of diets and their nutritional quality. The purpose of this study was to determine the trace element/mineral content of some of the commonly consumed diets in Machakos, Kitui, Makueni and Mwingi districts. Decorticated maize, beans and finger millet flour samples were purchased from the local markets. For each category, a total of ten samples were collected from each district. The samples were put in plastic bags, sealed and transported to the laboratory in the Institute of Nuclear Science & Technology, University of Nairobi for preparation and analysis. The cooking of the samples was carried out according to local traditional methods. In the decorticated samples, mean copper concentrations were observed to be below 20 g g-1; mean zinc concentrations ranged from 34 to 63 g g-1 and mean manganese concentrations were in a similar range of 34 to 78 g g-1. The mean iron concentrations were significantly high with a range of 161 g g-1 to 287 g g-1. A similar trend was observed in the beans where the mean copper concentrations varied from 11 to 33 g g-1, mean zinc concentrations ranged from a low value of 24 g g-1 to a high value of 35 g g-1, mean manganese concentrations varied from 33 g g-1 to 98 g g-1 and the mean iron con-centrations ranged from 227 g g-1 to 647 g g-1. The cooked Muthokoi samples from Machakos district had relatively high mean trace element concentrations: manganese – 109 g g-1; iron – 280 g g-1; copper – 19 g g-1; and zinc – 41 g g-1. The only exception was mean iron concentrations which were extremely high in samples from Mwingi District where the concentrations varied from 73 g g-1 to 1597 g g-1. In finger millet flour, the mean manganese concentrations varied from 95 to 290g g-1, whereas the mean iron concentrations ranged from 127 g g-1 to 259 g g-1. In contrast, the mean copper and zinc concentrations were low in comparison to the manganese and iron concentrations. As a whole, the mean copper concentrations in the diets are significantly low compared to the other three trace elements. However, the total content is not necessarily a reflection of the amount assimilated in the body. Finger millet was found to be an excellent source of manganese and iron whereas beans were observed to be good sources of iron. All the food crops were observed to poor sources of copper.

Keywords: Trace Elements, diets, semi-arid, Kenya.

Drinking of fresh vegetable raw juices for both cleansing and cure therapy has become very common in Kenya. Fresh raw vegetable juices have been recommended because they can boost the required minerals and vitamins in the body. This work was carried out to evaluate the amount of labile aluminium content in fresh raw vegetable juices and compare it with the total aluminum in vegetables. In addition, another objective was to determine the amount of aluminum leached out from aluminium pots during cooking. Out of 18 different vegetables analyzed, total aluminium ranged from 0.096 mg g-1 to 1.06 mg kg-1; carrots contained the lowest values while parsley contained the highest values. Labile aluminium in fresh raw vegetable juice ranged from 0.003 mg ml-1 to 0.181mg ml-1 and this gave 1 to 30% of the total aluminium. The amount taken per day during juice therapy, either as a detoxifier or a cure, ranged from 0.95 mg day-1 to as high as 40.22 mg day-1. But levels as high as 321.78 mg can be consumed depending on the volume of the juice consumed per day. The total aluminium consumed during juice therapy was found to be higher than that recommended by WHO. Aluminium pots were found to leach out some aluminium and the amount leached out was found to depend on the storage time and the age of the pot.

Key Words: Aluminium in vegetables, Nairobi, Kenya, vegetable juices, total and labile aluminium.

Analysis of fluoride in a variety of beverages was carried out using three different methods inconjunction with a fluoride ion selective electrode. The three methods gave comparable results for 26samples of fruit juices. However, 68% of the juices were found to contain fluoride levels higher than theWHO recommended limits (0.6 - 1.0 mgl-1). Soft drinks (sodas) and beers were found to contain values lower than 0.6 mgl-1. The amount of fluoride in tea infusion was found to increase both with increase inboiling time and amount of tea leaves used. Chocolate and coffee infusions were found to contain 4.3 mgl-1and 4.0 mgl-1fluoride, respectively.

Two microdiffusion methods for measuring ionizable fluoride in cows’ milk have been compared. The comparison includes diffusion time, amount of fluoride in spiked and unspiked milk samples and the effect of aluminium as an interfering ion. This work uses an acid diffusion technique involving hexamethyldisiloxane at room temperature and acid diffusion at 60 °C in the oven for 20 h. A significant difference was found in diffusion time and in the effect of aluminium ions. There was no significant difference in the amount of fluoride found in the milk samples using the two microdiffusion methods.

Keywords: Fluoride; microdiffusion; milk; fluoride-selective electrode; aluminium

The sample is ashed in a nickel crucible over an open flame with calcium hydroxide as thefixative; fluoride is separated by micro-diffusion and measured with a fluoride-selective electrode.The calcium hydroxide fixative permits a temperature of 800—850°C during the final ashing, sothat insoluble silicates are decomposed and fluoride is converted to an acid-soluble form. Otheradvantages over furnace ashing at 600°C are less contamination and more rapid ashing (20 mincompared to 6 h). The interference of aluminium and silica on microdiffusion was studied: per-chloric acid was found to be preferable to sulphuric acid as medium. A new way for preparingcalcium hydroxide suspension, low in fluoride, is described. The values found by the proposedmethod generally compare well with those obtained by oxygen flask combustion. Direct diffusion(i.e. without ashing) gave much lower values than the ashing methods, except for tea leaves.

Analysis offluoride concentrations in Kenyan waters have been carried out using two methods: the fluoride ion selective electrode method and colorimetric method. Water samplesanalysed were taken from boreholes and rivers in Nairobi. Central and Rift Valley Provincesand from the Rift Valley lakes. The high levels of fluoride content present in the Rift Valley lakes and boreholes would pose a threat if the water is used for drinking or for irrigation purposes. However the fluoride concentrations for most potable waters (especially those derived from rivers) is less than the accepted limits of 0.7-1.8 ppm. In order to account for the high incidence of dental fluorosis in Kenya, it is necessary to determine the fluoride intakefrom the total diet. A method suitable for analyzing fluoride content in foods and plant materials is discussed. Preliminary survey of fluoride concentrations for various foods showed: bananas, 4.2ppm; potatoes, 5.6 ppm; cabbages, 0.3ppm; maize 0.7ppm. High levels of fluoride were found in tea leaves in the range 229-340 ppm per kg. which is quite equivalent to 4.4-7.3 ppm F per 125 c.c. cup of tea. Fluoride concentration in coffee beans is quite low – 6.6 ppm per kg. and sodas, beer, cow’s milk have less than 0.01 ppm.