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Submitted

W, PROFNJENGALYDIAH.  Submitted.  e-learning module II contents for 'Coordination Chemistry'.. A 3rd year BED Science course material.. : UoN Abstract
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W, PROFNJENGALYDIAH.  Submitted.  Coordination chemistry ( Module II book for open distance learning). (Director, Centre for Open &Distance Learning, University of Nairobi). : UoN Abstract
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2013

Wawire*, MC, Jouvenot D, Loiseau F, Baudin P, Liatard S, Njenga L, Kamau GN, Casida ME.  2013.  Density-functional study of luminescence in polypyridineruthenium complexes. Journal of Photochemistry and Photobiology A: Chemistry. 276 :8–15. Abstract

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.

2012

and David M. Maina1, Lydia W. Njenga2, JO2 BK1MN.  2012.  Trace Element Concentrations in Some Traditional Diets Consumed in Selected Parts of Eastern Province of Kenya. Journal of Environmental Protection, 2012. 3:617-623. Abstract

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.

2007

W, PROFNJENGALYDIAH.  2007.  Njenga, L. W., Maina, D. M., Kariuki, D. N. and Mwangi, F. K., Aluminium exposure from Vegetables and Fresh raw vegetable Juices. Journal of Food Agriculture and Environment (JFAE). 5(1) (2007) 84-87. Journal of Food Agriculture and Environment (JFAE). 5(1) (2007) 84-87. : UoN Abstract

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.

2005

W, PROFNJENGALYDIAH, Kariuki DN, S.M.Ndegwa.  2005.  Water Labile fluoride from Fresh Raw Vegetable Juices from Markets in Nairobi, Kenya'.. Fluoride 38 (3) 205 - 208. : UoN Abstract

Analysis of water-labile fluoride in fresh vegetable juices from markets in Kenya was conducted by direct analysis with a fluoride ion selective electrode. Among 20 different vegetable juices, the fluoride content ranged from 1.2 mg FIL to 5.4 mg FIL. Some of the juices contained higher fluoride levels than the limits recommended by the World Health Organization for drinking water. Consumption of vegetable juices for healing therapy has become popular, and it is therefore important to consider the fluoride intake from this source. Calculation of the amount of fluoride that may be ingested from the juices based on the recommended formulations shows that the juices make a significant contribution to daily fluoride intake.

Keywords: Fluoride in juices; Fresh vegetables; Nairobi, Kenya; Vegetable juices; Water-labile fluoride.

W, PROFNJENGALYDIAH.  2005.  “Determination of labile fluoride in Kenyan soils”.. East African Journal of Physical Science 6 (2) (2005) 57-66.. : UoN AbstractWebsite

research theories for high school students

2004

N, PROFKARIUKIDAVID, W PROFNJENGALYDIAH.  2004.  Analysis of fluoride in locally available beverages: Comparison of direct, oven diffusion and hexamethyldisiloxane diffusion methods, August 2004 . International Journal of BioChemiPhysics, 13: 30 -35, 2004.. : UoN Abstract

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.

1997

W, PROFNJENGALYDIAH, Kaharna RW, Kariuki. HN, Kariuki DN.  1997.  Fluorosis in children and sources of fluoride around Lake Elementaita'.. Fluoride 30 19-25. : UoN Abstract

During a project to determine the fluoride levels of milk in Lake Elementaita region, the authors were astonished by the high levels of fluorosis in children living in the area. With special reference to children, a study was designed to establish and describe the levels of dental fluorosis and also to determine other sources of fluoride to the community. The levels of dental fluorosis were recorded using Thylstrup and Fejerskov classification method (TF) for children aged between 2-14 years. Biodata information, feeding habits and details of fluoride history were collected using a questionnaire form filled out with the help of teachers and/or parents.

Results pertain to both continuous and non-continuous residents for both primary and permanent dentition. The high fluorosis level of 95.8% was associated with the fluoride concentration in the community water supply and food.

Food samples analysed for fluoride include cow’s milk (the major source of nutrients for the children in the area), vegetables and water. Fluoride levels in drinking water from different boreholes were high, varying from 2.0-20.9 ug1mL. Milk fluoride levels in samples from seven localities ranged from 0.05-0.22 ug/mL (mean) and an individual animal range of 0.02-0.34 ug/g. Vegetables had fluoride levels between 7.9-59.3 ug/g with an exception of one with 296.6 ug/g. The soils in which the vegetables are grown had over 1000 ppm. This being a landscape formed by the process of faulting and volcanic activity, the dust from Lake Elementaita also had high fluoride concentration of 2300 ug/g.

Key words: Dental fluorosis; Fluoride sources; Kenya; Milk; Water

W, PROFNJENGALYDIAH.  1997.  Effects of interfering ions on hexamethyldisiloxane microdiffusion method'.. Talanta 44 1729-1733. : UoN Abstract

ABSTRACT

Acid diffusion in the presence of hexamethyldisiloxane (HMDS) enables complete recovery of ionic fluoride fromstandards containing varying concentrations of aluminium as one of the main interfering ions. Acid diffusion withoutHMDS shows a decrease in fluoride recovery as aluminium ion concentration increases. The fluoride concentrationin the trapping solution is determined directly on the diffusion cover with a combination fluoride electrode afterneutralising and buffering. The same procedure was used for the analysis of fluoride in soil and plant materialscontaining high concentrations of aluminium ions. For the same samples, the concentrations of aluminium, iron andsilicon were determined using atomic absorption spectrophotometer (AAS). © 1997 Elsevier Science B.V.

Keywords: HMDS microdiffusion; Interfering ions; GLC

1995

N, PROFKARIUKIDAVID, W PROFNJENGALYDIAH, Kimarua RW.  1995.  Comparison of two microdiffusion methods used to measure ionizable fluoride in cow's milk. Analyst, 120, 2245 (1995).. : UoN Abstract

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

1994

W, PROFNJENGALYDIAH, N PROFKARIUKIDAVID, W PROFNJENGALYDIAH.  1994.  Accumulation of fluoride in plants and vegetables'.. International Journal of BioChemiPhysics, 3, 23 - 25.. : UoN Abstract

Fluoride in plant and vegetable samples has beendetermined using the ion selective electrode.The analysis was carried out after ashingthe samples onan open flame, adding perchloric acid and allowing the hydrogen fluoride to diffuse into a sodium hydroxide layer. The results obtained show that kale and pumpkins can accumulate more than ten times their normal values of fluoridewhile plants were found to accumulate upto 100 ug/g fluoride when exposed to high levels of fluoride in water or soil.

W, PROFNJENGALYDIAH.  1994.  Fluoride content in some Kenyan tea leaves. International Journal of BioChemiPhysics, 3, 75 - 76. : UoN Abstract

Different grades and clones oftea from various parts ofKenya were analysed for total, acid and water labile fluoride using ion selectiveelectrode. It was found that, about 80-99% of total fluoride was acid labile while 40-90% of acid labile was water labile. The fluoridecontent was found to vary with the age of the leaves with the old leaves showing higher fluoride concentration indicate the values (orranges) of fluoride extracts and how they differed with age. High pH resistant clones were found to contain higher fluoride than lowpH resistant.

W, PROFNJENGALYDIAH.  1994.  Determination of labile fluoride in soils: An Intercomparison of Different Extracting Medias'.. International Journal of BioChemiPhysics, 3, 18 - 22.. : UoN Abstract

Labile fluoride in soil samples was extracted using sodium citrate - EDTA, sodium citrate - TISAB II, ammonium lactate, IMhydrochloric acid and water. Hydrochloric acid was found to give the highest fluoride level while water gave the lowest fluoride level.Shaking time andamount of sample showed that 1 1/2 hours shaking and lgm sample gave the best results with ammonium lactateextracting media Recovery of fluoride using ammonium lactate was found to be 90-100% efficient while medium clay samples gaveless than 90% fluoride.

1988

W, PROFNJENGALYDIAH, W PROFNJENGALYDIAH.  1988.  Determination of total fluoride in vegetables and plants by open-flame ashing and microdiffusion: comparison with furnace ashing and oxygen-flask combustion'.. Analytical Chemical Acta 212 (1988) 133-143. : UoN Abstract

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.

1983

W, PROFNJENGALYDIAH.  1983.  Dietary sources of fluoride in Kenya. Fluorosis Research Strategies', Proceedings of a workshop held in Nairobi, Kenya; S.Likimani, (Ed.) , 32-6 (1983).. : UoN Abstract

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.

1982

N, PROFKARIUKIDAVID, W PROFNJENGALYDIAH.  1982.  The distribution of fluoride in Kenya waters. Proceedings of the Environmental Chemistry Sub-region Workshop, National University of Lesotho, Roma, 32-6 (1982).. : UoN Abstract
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W, PROFNJENGALYDIAH.  1982.  Determination of Fluoride in Water and Tea Using Ion Selective Electrode and Calorimetric Methods'. M.Sc. Thesis, University of Nairobi. : UoN Abstract
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