Browsing by Author "Gichumbi, J."

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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-(η6-p-cymene)-(bis(pyrazol-1-yl)methane- κ2N,Nl)Osmium(II) Tetrafluoroborate, C17H22BClF4N4Os
(MDPI, 2022) Mambanda, A.; Kanyora, A. K.; Ongoma, P.; Gichumbi, J.; Omondi, R. O.
The powder of the arene osmium(II) complex, [Os(II)(dpzm)(η6-p-cym)Cl]BF4 (dpzm = di(1H-pyrazol-1-yl)methane; η6-p-cym = para-cymene), with a formula of C17H22BClF4N4Os (referred to herein as 1) was isolated from the reaction of [(η6-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), 2 = 1.54178 Å as the radiation source, and 1 crystallizes in the monoclinic crystal system and the C2/c (no. 15) space group.
Crystal Structures of Half-Sandwich Ru(II) Complexes, [(η6-p- Cymene)(3-chloro-6-(1H-pyrazol-1-yl)pyridazine)Ru(X)]BF4, (X = Cl, Br, I)
(MDPI, 2022) Mambanda, A.; Ongoma, P.; Gichumbi, J.; Omondi, R. O.; Hunter, L. A.; Kanyora, A. K.
Herein, we report the synthesis and single-crystal X-ray structures of three (η6-p-cymene)Ru(II) tetrafluoroborate salts, viz., [(η6-p-cymene)(3-chloro-6-(1H-pyrazol-1-yl)pyridazine)Ru(X)]BF4, (X = Cl, Br, I), Ru1-3. They were prepared by the reactions of [(η6-p-cymene)Ru(µ-X)(X)]2, (X = Cl, Br, I) with two-mole equivalents of 3-chloro-6-(1H-pyrazol-1-yl)pyridazine, under inert conditions at ambient temperatures, and subsequently precipitated by the addition of excess BF4− ions. Orange crystalline precipitates were obtained in good yields, from which the respective single crystals for X-ray diffrac- tion analysis were recrystallized by slow evaporation from their methanolic/diethyl ether solutions. The Ru(II) complexes were characterized by various spectroscopic techniques and chemical meth- ods, which included FTIR, 1H/13C NMR, UV-visible absorption, mass spectrometry, and elemental analysis. The molecular structures were solved by single-crystal X-ray crystal diffraction analysis. The complexes crystallized in the monoclinic crystal system in the P21/c (Ru1-2) and P21/n (Ru3) space groups. Density Functionals Theoretical (DFT) calculations were performed in methanol to gain an understanding of the electronic and structural properties of the complexes. Trends in the data metrics were established, and selected data were compared with the diffraction data. The electrophilicity indices of Ru1-3 follow the order Ru3 > Ru2 > Ru1, and the trend is in line with their anticipated order of reactivity towards nucleophiles.