Chemistry

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Analyses of geophagic materials consumed by pregnant women in Embu, Meru and Chuka towns in eastern province, Kenya
(2011) Mwangi, Gichumbi J.; Ochieng, Ombaka; Mwangi, Gichumbi, J.; Ombaka, Ochieng
Geophagy is the deliberate consumption of soil and clay deposits by animals, including man. During pregnancy all the nourishment needed by the developing fetus comes from the mother, either the food she eats or the supplement she may take. The geochemical and mineralogical composition of the materials which are consumed by pregnant women from Meru, Embu and Chuka open air markets were studied. The geophagic materials were subjected to standard digestion procedures and analyzed for full assay and elemental analysis for Co, Zn, Mg, Cu, Pb and Cd using Atomic absorption spectrometry and Energy-dispersive x-ray fluorescence spectrometry in 30 geophagic samples. The mineralogical composition was investigated using X-ray diffractometry (XRD). The geochemical analysis revealed that the geophagic materials contain high levels of silica from 48.59 to 60.27%. Geophagic materials from Embu showed the highest concentration of Pb at 0.96 ppm. The levels of Pb in all samples exceeded the levels recommended by WHO/FAO limits of 0.01 ppm. The levels obtained for Cd in all the samples did not exceed the WHO/FAO limits of 0.003 ppm. The XRD data showed that the geophagic materials of the area consisted mainly of silica.
Antibacterial and Antifungal activities of Novel hydroxytriazenes.
(2012-04-02) Ombaka, A.O *; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from <12.5 to 50 μg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Antibacterial and antifungal activities of novel hydro
(2012) Ombaka, A. O.*; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from <12.5 to 50 μg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Antibacterial and antifungal activities of novel hydroxytriazenes
(2012-04-02) Ombaka, A. O.*; Muguna, A. T.; Gichumbi, J. M.
In a search for new leads potent antimicrobial agents, an array of novel hydroxytriazenes i-xi were synthesized and characterized through their melting point, crystal shape, colour and elemental analysis. In vitro microbiological evaluations were carried out for all the synthesized compounds against both bacterial and fungi using the turbidimetric method. The reagent number x and xi showed significant antibacterial activities against two gram positive [Streptococcus feacalis, Staphylococcus aureus, penicillin resistance (2500 units)]. All synthesized hydroxytriazenes except reagent number viii showed antifungal activities against five fungi [Candida albicans, Cryptococcus neoformans, Sporotrichum schenckii, Trichophyton mantagrophytes, Aspergillus fumigatus}. The minimum inhibitory concentration (mic) values against these bacteria and fungi ranged from < 12.5 to 50 µg/ml. Some hydroxytriazenes (x, xi) showed an unusual combined antibacterial and antifungal action, which suggest that hydroxytriazenes revealed a wide range of antimicrobial activity.
Application of arene ruthenium(II) complexes with pyridine-2-carboxaldimine ligands in the transfer hydrogenation of ketones
(Elsevier, 2016-05) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
The reaction of various pyridine-2-carboxaldimine ligands with the [(η6-arene)Ru(μ-Cl)Cl]2 dimer followed by a metathesis reaction with ammonium hexaflourophosphate, yielded the ruthenium(II) arene complex salts [(η6-arene)RuCl(C5H4N-2 CH N-Ar]PF6; where (arene = C6H6 (1), p-cymene (2), Ar = 3, 5-dimethyl phenyl (a), 2,3-dimethyl phenyl (b), 2,5-dimethyl phenyl (c), 3,4-dimethyl phenyl (d)). The compounds were characterized by elemental analysis, FT- IR, UV–vis and 1H and 13C NMR. Single crystal X-ray structures for compounds 1a, 1d and 2e were also determined and showed that the ruthenium(II) centre has a pseudo-octahedral geometry and the molecule adopted a three legged piano stool geometry in which the arene ring occupies the apex and the nitrogen atoms of the N,N′-bidentate ligand and the chloride atom the base of the stool. The Ru(II) complex salts were active for the catalytic transfer hydrogenation of ketones into alcohols in the presence of NaOH using 2-propanol as the hydrogen source at 82 °C. The complexes were suitable for a wide range of aliphatic, cyclic and aromatic ketones giving good turn over numbers.
Assessment of indegenious knowledge and practices on the use of clay among rural communities in Meru, Kenya
(2017) Mwiandi, Felicity Kaari *; Ombaka, Ochieng
A survey was conducted to ascertain the clay applications and its health effects on humans among the rural communities. Household survey, focus group discussion and direct observation were employed. A structured questionnaire with reliability coefficient of 0.82 was used to collect data. Majority of respondents were male (51.2%) aged 21 to 40 years, had primary education (32.2 %), monthly income below Ksh.5,000 (69.0 %) mainly from farming (47.1 %) and brickmaking (31.6 %); and less than 10 years (38.5 %) in clay production. Traditional applications of clay were pottery (81.0 %), brick making (55.7 %), cooking jikos (94.9 %) and plastering walls / floors (70.1 %). Food cooked from clay pots was perceived to taste different from those prepared using conventional utensils (91.3%). Most respondents (79.8%) ascertained that, they experienced skin irritation during clay production processes. The study findings give an insight of existing traditional clay applications. Furthermore it forms the basis on which the probable clay minerals in the study area can be explored for modern applications.
Assessment of Selected Physico-Chemical Parameters of Groundwater in Chuka Igambang’ombe Constituency, Kenya
(Chuka University, 2022) Maweu, Bonface K.; Chabari, Kithaka Samson; Nguku, James Kyalo; Chuka, University
Groundwater is an essential source of water for drinking and other domestic uses. Recently, there has been high dependence on groundwater due to water shortage as a result of changing climates, and higher costs of accessing piped water. An occurrence of the physico-chemical parameters of the groundwater in levels past the WHO highest permissible limits can cause serious health implications to the consumers of the groundwater. This study therefore, assessed the extent of the physico-chemical parameters concentration of the groundwater in Chuka, Igambang’ombe constituency. A total of five samples was collected from 5 boreholes in the Mucw’a and Ndagani regions surrounding the Chuka University main campus. Selected physical parameters were recorded onsite by use of portable apparatus. Samples for testing chemical parameters were collected and transported in cooler boxes to Chuka University laboratories for analysis. Physical parameters determined onsite were dissolved oxygen (DO), temperature, and the pH. Dissolved Oxygen meter, mercury thermometer, and pH meter were the equipment used to test the respective physical parameters. UV- spectrophotometry was used to analyze the chemical parameters: nitrates, and phosphates, where absorbance was recorded at a wavelength of 220-820 nm and 880nm respectively. The assessment was conducted during the relatively dry months of January to March. The temperature of the water ranged from 22.8-25.20C. The pH levels ranged from 4.50 – 9.50. The high altitude nitrate levels were 2.4mg/L, and 7.37mg/L at the low altitude. The phosphate concentrations were below detectable limits. The results were then compared with WHO standards for the highest permissible levels for the tested parameters to determine the suitability of the water for consumption. All the tested parameters lied within the WHO permissible limits for drinking water except for the pH levels.
). Characterization and classification of clay minerals for potential applications in Rugi ward, Kenya.
(African Journals Online, 2016-11-16) Ombaka, Ochieng
The applications of various clayey minerals are related to their structural, physical and chemical characteristics. The physical and chemical properties of the clayey minerals dictate their utilization in the process industries and beneficiation required before usage. The study aimed at establishing the potentiality of clayey minerals from the study area, and the possibility of exploring and exploiting them in order to spur industrial development and promote economic self reliance of Kenya as a nation. The plasticity, particle size, surface area, chemical and mineralogy composition, morphological, thermal analysis and other physical properties were studied using various techniques. The clay samples composed of albite (5-16.7%), kaolinite (11.4-36.2%), microcline (15.2-35.3%), quartz (24.3-68.1%), hornblende (7.6% in samples from Ngamwa only), and other mineral impurities in small amounts. Ngamwa clayey materials consist of high impurities of chemical oxides such as TiO2, MnO, MgO and Fe2O3. Generally, quartz and iron were the major impurities present in the samples from the concerned sites. The findings shows that clayey minerals from the study area can be exploited for commercial production of ceramic products after beneficiation using low cost and environmental friendly techniques in order to reduce the levels of iron, quartz, and other impurities to acceptable levels.
Characterization of clays from Tharaka-Nithi County in Kenya for Industrial and Agricultural Applications
(2015-03) Njoka, E. N. 1; Ombaka, O. 2*; Gichumbi, J. M. 2; Kibaara, D. I. 3; Nderi, O. M. 1
Clay samples from Tharaka-Nithi County in Kenya were characterized by hydrometer, X-ray fluorescence spectroscopy (XRF), atomic absorption spectroscopy (AAS), TGA, scanning electron microscopy (SEM) and powder diffraction (XRD) methods. The F-test and t-test were used to interpret the results. The major oxides present were Al 2 O 3 , SiO 2 and the minor ones were CaO, TiO 2 , MnO, Fe 2 O 3 , K 2 O, MgO and Na 2 O. The values of SiO 2 were greater than those of Al 2 O 3 , indicating that the samples were of clay minerals. The clay minerals with low cation exchange capacity (CEC) were present in the samples. The Atterberg limits showed that the inorganic clays of either low or intermediate plasticity having low contents of organic matter were present in the samples. The analysis further showed the availability of essential elements necessary for plant growth. The TGA analysis indicated that the decomposition of clay samples occurred in four steps. The scanning electron microscope photographs revealed that the samples contained a mixture of minerals of morphologies with crystallinity, high porosity and unstable under the electron beam. The major impurity in the clay is quartz, ranging from 22.6-31.9%. Albite is the most dominant component in the clay minerals contributing to 30.3 to 44.1%. The clay from the study area can be used as agro mineral additive to enhance soil fertility for crop production, a fluxing agent in ceramics and glass applications and also as functional fillers in the paint, plastic, rubber and adhesive industries after beneficiation.
Characterization of rice husk ash prepared by open air burning and furnace calcination
(Academic Journals, 2020) Kaleli, Mbinda Jonathan; Kamweru, Paul Kuria; Ndiritu, Francis Gichuki
Rice husk (RH) is an agricultural waste, and easily available in rice growing areas. The husk is mostly burnt as a way of getting rid of it. The ash obtained after burning or calcination may have economic application, mainly dependent on its properties. These properties in turn depend on the calcination method. However, for commercial viability, and for many applications, the calcination method should not only be as simple as possible but also cheap. This study characterized the elemental composition, crystallinity, functional bonds present and morphology of rice husk ash (RHA) obtained in two ways, that is, calcination of rice husks in a muffle furnace (FRHA) at a temperature of 700°C and open air burning (ORHA) at uncontrolled temperatures. The elemental composition done by Atomic Absorption Spectroscopy showed a high percentage of silicon that is 81.01 and 79.12% for ORHA and FRHA, respectively. X-ray fluorescence showed a high percentage of silica (SiO2), 95.45 and 94.85% for ORHA and FRHA, respectively. X-ray diffractograms indicate that the FRHA was crystalline with the highest peak at 21.8°; while ORHA was amorphous in nature. Fourier Transform Infra-Red spectra confirmed the presence of –OH groups and O-Si-O bonds in the two types of ash. Scanning electron microscopy analysis showed agglomerated ORHA, which may be due to the presence of hydrogen bonding between silanol groups on the surface of rice husk ash for FRHA, and presence of –OH groups in ORHA. The study shows that ORHA is as good as FRHA in applications where crystallinity is optional.
Characterization of rice husk ash prepared by open air burning and furnace calcination
(Academic Journals, 2020) Kaleli, Mbinda Jonathan; Kamweru, Paul Kuria; Gichumbi, Joel Mwangi; Ndiritu, Francis Gichuki
Rice husk (RH) is an agricultural waste, and easily available in rice growing areas. The husk is mostly burnt as a way of getting rid of it. The ash obtained after burning or calcination may have economic application, mainly dependent on its properties. These properties in turn depend on the calcination method. However, for commercial viability, and for many applications, the calcination method should not only be as simple as possible but also cheap. This study characterized the elemental composition, crystallinity, functional bonds present and morphology of rice husk ash (RHA) obtained in two ways, that is, calcination of rice husks in a muffle furnace (FRHA) at a temperature of 700°C and open air burning (ORHA) at uncontrolled temperatures. The elemental composition done by Atomic Absorption Spectroscopy showed a high percentage of silicon that is 81.01 and 79.12% for ORHA and FRHA, respectively. X-ray fluorescence showed a high percentage of silica (SiO2), 95.45 and 94.85% for ORHA and FRHA, respectively. X-ray diffractograms indicate that the FRHA was crystalline with the highest peak at 21.8°; while ORHA was amorphous in nature. Fourier Transform Infra-Red spectra confirmed the presence of –OH groups and O-Si-O bonds in the two types of ash. Scanning electron microscopy analysis showed agglomerated ORHA, which may be due to the presence of hydrogen bonding between silanol groups on the surface of rice husk ash for FRHA, and presence of –OH groups in ORHA. The study shows that ORHA is as good as FRHA in applications where crystallinity is optional.
Chemical And Mineralogical Analysis of Geophagic Materials Consumed By Pregnant Women In Eastern Nairobi And Nyanza Provinces In Kenya
(2011) Gichumbi, J.; Ombaka, O.
Geophagy is the purposeful or deliberate consumption of Earth and clay deposits by animals, including man. It is a special type of pica, which is defined as the craving and subsequent consumption of non-food substances. The geochemical and mineralogical composition of the geophagic materials consumed by pregnant women and sold in open air markets in Eastern, Nairobi and Nyanza provinces were studied. The mineralogical composition of selected soil samples was investigated using X-ray diffractometry (XRD).The XRD data showed that the soils in these areas consisted mainly quartz, and the clay mineral kaolinite. The preliminary elemental analysis was carried out using Energy dispersive x-ray fluorescence. The geophagic materials were subjected to standard digestion procedures and analyzed for Zn, Cu, Co, Pb and Cd by atomic absorption spectroscopy (AAS). Analysis results showed the geophagic materials contain elevated levels of Fe for a 2.5 g sample. The present study has shown that the geophagic materials from the three provinces open air markets consist mainly of silica and alumina. The levels of Pb exceeded the levels recommended by WHO/FAO limits of 0.01 ppm but the levels obtained for Cd in the samples from Nairobi exceed the WHO/FAO limits of 0.003 ppm
Chlorido-(η 6 -p-cymene)-(bis(pyrazol-1-yl)methaneκ 2N,N0 )Osmium(II) Tetrafluoroborate, C17H22BClF4N4Os
(MDPI, 2022) Mambanda, Allen; Kanyora, Amos K.; Ongoma, Peter; Gichumbi, Joel; Omondi, Reinner O.
The powder of the arene osmium(II) complex, [Os(II)(dpzm)(η 6 -p-cym)Cl]BF4 (dpzm = di(1H-pyrazol-1-yl)methane; η 6 -p-cym = para-cymene), with a formula of C17H22BClF4N4Os (referred to herein as 1) was isolated from the reaction of [(η 6 -p-cym)Os(µ-Cl)(Cl)]2 with dpzm dissolved in acetonitrile and under a flow of nitrogen gas. It was characterized by spectroscopic techniques (viz., FTIR, 1H NMR, UV-Visible absorption). Yellow crystal blocks of 1 were grown by the slow evaporation from the methanolic solution of its powder. The single-crystal X-ray structure of 1 was solved by diffraction analysis on a Bruker APEX Duo CCD area detector diffractometer using the Cu(Kα), λ = 1.54178 Å as the radiation source, and 1 crystallizes in the monoclinic crystal system and the C2/c (no. 15) space group.
Comparison of Chemical and Mineralogical Properties of Geophagic Materials from Taita and Mombasa, Kenya
(2012-10) Gichumbi, Joel M.; Maghanga, Justin Kambale; Ongulu, Roselyn; Cheshari, E.C; Gichuki, J.G.
Geophagy is the deliberate consumption of soil and clay deposits by animals including man. The practice is widespread particularly in pregnant women in Africa. This study of geophagic soil from coast province in Kenya had its primary objectives in analyzi
COMPLEXOMETRIC DETERMINATION OF ZINC USING HYDROXYTRIAZENE AS A METALLOCHROMIC INDICATOR
(2020) Ombaka, Ochieng
New metallochromic indicators belonging to the class of hydroxytriazenes has been evaluated for the direct complexometric determination of Zinc in the presence of diverse ions. Reagent no (i), (ii) and (iii) has been found to be excellent indicators in the titration with EDTA at pH 6.95-7.50, 6.90-7.60 and 7.00-7.50 respectively. The colour at the end point was from light green to colourless and the titration was carried out between temperature range of 20-600C. Cl- , Br- ,CH3COO- , CO3 2- , SO4 2- , NO2 - , SO3 2- , F- , NO3 - , I- , S 2- , WO4 2- , MO7O24 6- , NH4 + , Na+ , K+ , U(VI), Mn(II), Ba(II), Hg(II), Sn(II), Cd(II), Mg(II), Ca (II), Zr(IV) can be tolerated in the titration of zinc (II) when they are present in equivalent amount with that of zinc (II). However, PO4 3- , Co (II), Cu (II) and Ni (II) interferes and when present in the environmental samples, separation techniques such as masking and demasking agents must be employed. The utility of the technique was checked by using 3-Hydroxy-3-m-toly-1-0-Carboxyphenyltriazene for estimation of zinc in zinc-copper alloy and the results had a maximum relative error of +1.53 and standard deviation of ±0.0378 using Sodium thiosulphate to mask copper ions, hence the study clearly indicated that reagent no (i) and (ii) which have high sensitivity, high selectivity and fairly a wide pH range can be used as metallochromic indicators for estimation of zinc in environmental sample where zinc is the major element.
Complexometric determination on Nickel (ii) in its synthetic alloys using selected Hydroxytriazene as metallochromic indicator
(2019) Ombaka, Ochieng
A simple, rapid and reasonable selective Complexometric technique for nickel (II) determination using some selected hydroxytriazene as a metallochromic indicator is reported in the present study. The colour change at the end point was from greenish-yellow/yellow to colourless with sharp end point. The pH ranges were 9.3-9.7, 9.0-9.5, 8.5-9.0, 8.0-8.5 while temperature ranges were 25-60, 25-60, 25-60, 25-50 and 25-50 0C for reagent (i), (ii), (iii), (iv), and (v) respectively. Nickel(II) was determined accurately up to concentration as low as 3.0x10-3M for reagents (ii), (iv), and (v)) while for reagents (i) and (iii) the concentration range could be even lowered to 1.0x10-3M for the determination of nickel (II). The ions such as Cl-, Br-, CH3COO-, CO32-, PO43-, SO42-, C2O42-, S2O32-, NO2-, SO32-, S2-, HPO42-, F-, NO3, WO42-, MO7O246-, I-, NH4+, Na+, K+ did not show any interference in the determination of nickel (II) even when they were present in tenfold excess. Ba2+, Mg2+, Ca2+, were tolerated up to five-fold excess. However Mn2+, Pb2+, Hg2+, Sn2+, Th4+, Cd2+, Co2+, Cu2+,Zn2+, interfered even at equivalent amount. The method was used to determine nickel in its synthetic alloy with maximum relative error of 0.78 when using secondary masking agent.
Concentration of Inorganic Contaminants in Shallow Borehole Water in Chuka Sub-County, Kenya
(Journal of Chemical, Biological and Physical Sciences, 2020-11-24) Edith. M., Rugendo; Eric C., Njagi; Ochieng, Ombaka
Groundwater from shallow aquifers is an important source of portable water in Chuka Sub-County. However, most shallow boreholes in Chuka Sub-County are undocumented and susceptible to contamination by both geogenic and anthropogenic activities. This study was conducted to evaluate the quality of shallow boreholes water in Chuka Sub-County. Samples were collected from twenty boreholes in Chuka Sub County during the dry and wet seasons. The temperature, pH and conductivity were determined in situ using a meter. The concentration of cations was determined using ICP-MS. The concentrations of anions were determined using standard APHA analytical methods. The temperatures and conductivities of borehole waters were within the limits set by KEBS and WHO. The pH of water in most boreholes during the wet season was within the limits set by KEBS and WHO for portable water. However, borehole water at Karandini (T15) was highly acidic (pH of 3.95) during the wet season. During the dry season, borehole waters were slightly acidic (4.42 - 6.44) except for the borehole at Ndagani market (T11), whose water was alkaline (pH = 8.75). The concentrations of trace and toxic cations and anions (NO3 - , SO4 2- , Cl and PO4 3- ) were within the limits set by KEBS and WHO. However, the concentration of nitrate in several boreholes during the dry season was within the range that cause chronic health effects. Groundwater from most boreholes in Chuka Sub-County is generally safe for domestic uses but require regular monitoring for quality.
Crystal structure of chlorido-(η5-pentamethylcyclopenta dienyl)-((bis-pyrazol-1-yl) methane-κ2N, N′) rhodium (III) hexafluorophosphate
(2019-11-13) Gichumbi, Joel M.; Zamisa, Sizwe J.; Friedrich, Holger B.
C17H23ClN4RhF6P, monoclinic, P21/c (no. 14), a = 10.6954(2) Å, b = 15.3868(3) Å, c = 12.6130(2) Å, β = 90.5590(10)°, V = 2075.60(7) Å3, Z = 4, Rgt(F) = 0.0296, wRref(F2) = 0.0727, T = 100(2) K.
Crystal structure of chlorido-(η6 - toluene)(2,2′-bipyridine-κ2 N,N′)ruthenium(II) hexafluorophosphate, C17H16ClN2RuPF6
(De Gruyter, 2022) Gichumbi, Joel M.; Zamisa, Sizwe J.; Friedrich, Holger B.
C17H16ClN2RuPF6, monoclinic, P21/c (no. 14), a = 14.4426(9) Å, b = 8.3311(5) Å, c = 16.413(1) Å, β = 109.2690°, V = 1864.2(2) Å3 , Z = 4, Rgt(F) = 0.0309, wRref(F2 ) = 0.0697, T = 173 K.
Crystal structure of chlorido-(η6-p-cymene)-(N- (2-fluorophenyl)-1-(pyridin-2-yl) methanimine-κ2N, N′) ruthenium (II)–acetone (1/1), C22H23ClN2F7OPRu.
(2010-01) Gichumbi, Joel M.; Omondi, Bernard *; Friedrich, Holger B.
C 22 H 23 ClN 2 F 7 OPRu, monoclinic, P 2 1 / c (no. 14), a = 7.30480(10) Å, b = 12.9540(3) Å, c = 28.7076(6) Å, β = 96.6990(10)°, V = 2697.95(9) Å ³ , Z = 4, Rgt ( F ) = 0.0196, wRref ( F² ) = 0.0479, T = 100(2) K.

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