Browsing by Author "Kinunda, Grace A."
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Item Hydrophobic π-π stacking interactions and hydrogen bonds drive self-aggregation of luteolin in water(Elsevier, 2022-06-23) Deogratias, Geradius; Shadrack, Daniel M; Munissi, Joan J.E.; Kinunda, Grace A.; Jacob, Fortunatus R.; Mtei, Regina P.; Masalu, Rose J.; Mwakyula, Issakwisa; Kiruri, Lucy W.; Nyandoro, Stephen S.Luteolin is a flavonoid obtained from different plant species. It is known for its versatile biological activities. However, the beneficial effects of luteolin have been limited to small concentrations as a result of poor water solubility. This study aimed at investigating the hydrophobic interaction and hydration of luteolin towards the improvement of its solubility when used as a drug. We report the aggregation properties of luteolin in water by varying the number of monomers using atomistic molecular dynamics simulation. Results show that the equilibrium structure of luteolin occurs in an aggregated state with different structural arrangements. As the monomers size increase, the antiparallel flipped conformation dominates over T-shaped antiparallel, T-shaped parallel, and antiparallel conformations. The formation of intramolecular hydrogen bonding of 0.19 nm between the keto-enol groups results in hydrophobic characteristics. A larger cluster exhibits slow hydrogen bond dynamics for luteolin-luteolin than luteolin-water interaction. Water structure at large cluster size exhibited slow dynamics and low self-diffusion of luteolin. The existence of hydrophobic π-π and hydrogen bonds between luteolin molecules drives strong self-aggregation resulting in poor water solubility. Breakage of these established interactions would result in increased solubility of luteolin in water.Item Hydrophobic π-π stacking interactions and hydrogen bonds drive self-aggregation of luteolin in water(Elsevier, 2022-06-28) Deogratias, Geradius; Shadrack, Daniel M.; Munissi, Joan J.E.; Kinunda, Grace A.; Jacob, Fortunatus R.; Mtei, Regina P.; Masalu, Rose J.; Mwakyula, Issakwisa; Kiruri, Lucy W.; Nyandoro, Stephen S.Luteolin is a flavonoid obtained from different plant species. It is known for its versatile biological activities. However, the beneficial effects of luteolin have been limited to small concentrations as a result of poor water solubility. This study aimed at investigating the hydrophobic interaction and hydration of luteolin towards the improvement of its solubility when used as a drug. We report the aggregation properties of luteolin in water by varying the number of monomers using atomistic molecular dynamics simulation. Results show that the equilibrium structure of luteolin occurs in an aggregated state with different structural arrangements. As the monomers size increase, the antiparallel flipped conformation dominates over T-shaped antiparallel, T-shaped parallel, and antiparallel conformations. The formation of intramolecular hydrogen bonding of 0.19 nm between the keto-enol groups results in hydrophobic characteristics. A larger cluster exhibits slow hydrogen bond dynamics for luteolin-luteolin than luteolin-water interaction. Water structure at large cluster size exhibited slow dynamics and low self-diffusion of luteolin. The existence of hydrophobic π-π and hydrogen bonds between luteolin molecules drives strong self-aggregation resulting in poor water solubility. Breakage of these established interactions would result in increased solubility of luteolin in water.Item Influence of heteroatoms on the optoelectronic properties of triphenylamine-based dyes for DSSCs application: A computational approach(Elsevier, 2022-02-23) Kirenga, Peter; Mkoma, Stelyus L.; Mlowe, Sixberth; Msambwa, Yohana; Kiruri, Lucy W.; Jacob, Fortunatus R.; Mgaya, James E.; Kinunda, Grace A.; Deogratias, GeradiusA series of sensitizers with D-π-π-A architectural framework have been fine-tuned through a variation of het eroatoms (NH, O, Se, and Te) in the π-spacers. Cyanoacrylic acid and hydantoin were used as the acceptor groups. The geometrical and electronic properties were investigated through density functional theory (DFT) and time-dependent DFT (TD-DFT) , respectively. To determine stable dye-TiO2 configuration, the binding energies are reported. The driving force of charge injection and dye regeneration range between 0.00 to − 0.77 eV and − 0.133 to − 1.60 eV, respectively, suggesting spontaneous processes. Chalcogen heteroatoms (S, Se, and Te) improved absorption within the visible and NIR regions. The binding energies of dye on (TiO2)6 cluster range between − 8.32 to − 9.62 eV and − 7.77 to − 8.98 eV for cyanoacrylic acid and hydantoin dyes, respectively. The findings suggest that the inclusion Se and Te heteroatoms may boost the performance of DSSCs when compared to parent materials containing S.Item Influence of heteroatoms on the optoelectronic properties of triphenylamine-based dyes for DSSCs application: A computational approach(Elsevier, 2022-02-27) Kirenga, Peter; Mkoma, Stelyus L.; Mlowe, Sixberth; Msambwa, Yohana; Kiruri, Lucy W.; Jacob, Fortunatus R.; Mgaya, James E.; Kinunda, Grace A.; Deogratias, GeradiusA series of sensitizers with D-π-π-A architectural framework have been fine-tuned through a variation of heteroatoms (NH, O, Se, and Te) in the π-spacers. Cyanoacrylic acid and hydantoin were used as the acceptor groups. The geometrical and electronic properties were investigated through density functional theory (DFT) and time-dependent DFT (TD-DFT) , respectively. To determine stable dye-TiO2 configuration, the binding energies are reported. The driving force of charge injection and dye regeneration range between 0.00 to −0.77 eV and −0.133 to −1.60 eV, respectively, suggesting spontaneous processes. Chalcogen heteroatoms (S, Se, and Te) improved absorption within the visible and NIR regions. The binding energies of dye on (TiO2)6 cluster range between −8.32 to −9.62 eV and −7.77 to −8.98 eV for cyanoacrylic acid and hydantoin dyes, respectively. The findings suggest that the inclusion Se and Te heteroatoms may boost the performance of DSSCs when compared to parent materials containing S.Item Optical and electronic properties of para-functionalized triphenylamine-based dyes: a theoretical study(Springer, 2021-11-09) Mkoma, Stelyus L.; Msambwa, Yohana; Jacob, Fortunatus R.; Kiruri, Lucy W.; Kinunda, Grace A.; Mlowe, Sixberth; Deogratias, GeradiusMolecular engineering of dyes has become a popular and most successful approach towards improvement of photovoltaic power conversion efficiency of dye-sensitized solar cells (DSSCs). We report the geometrical, optical, and electronic properties for para-substituted triphenylamine (TPA)-based dyes with D-π-π-A architecture. Results were realized through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. We used B3LYP/6–31 + G(d,p) and CAM-B3LYP/6–31 + G(d,p) level of theory for DFT and TD-DFT, respectively. Six electron-donating (ED) and electron-withdrawing (EW) groups were symmetrically grafted to the para-direction of the phenyl rings. Two anchoring groups namely: cyanoacrylic acid (CA) and hydantoin (HY) were used. Excellent relationships between electronic energies and the Hammett constants (σp) have been reported. The results show that variation of both anchoring groups and substituents significantly affect the absorption of the dyes; maximum absorption for CA dyes was found ranging between 514–571 nm and 470–503 nm for ED and EW groups, respectively, while for HY dyes demonstrated maximum absorption between 502–537 nm and 480–496 nm for ED and EW, respectively. A linear correlation between σp and λmax with R2 > 0.97 was obtained. In addition, the mapping of the HOMO and LUMO energies suggests the intramolecular charge transfer and a strong electronic coupling between dye and semiconductor. Our theoretical calculations show that electron-donating substituents enhance the optoelectronic properties of the dyes. Analysis of chemical descriptors suggests that dyes containing alternative anchoring group HY substituted with –NH2 and –N(CH3)2 may demonstrate improved performance of DSSCs.Item Optical and electronic properties of para‑functionalized triphenylamine‑based dyes: a theoretical study(Springer, 2021-11-09) Mkoma, Stelyus L.; Msambwa, Yohana; Jacob, Fortunatus R.; Kiruri, Lucy W.; Kinunda, Grace A.; Mlowe, Sixberth; Deogratias, GeradiusMolecular engineering of dyes has become a popular andmost successful approach towards improvement of photovoltaic power conversion efciency of dye-sensitized solar cells (DSSCs). We report the geometrical, optical, and electronic proper ties for para-substituted triphenylamine (TPA)-based dyes with D-π-π-A architecture. Results were realized through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. We used B3LYP/6–31+G(d,p) and CAM-B3LYP/6–31+G(d,p) level of theory for DFT and TD-DFT, respectively. Six electron-donating (ED) and electron withdrawing (EW) groups were symmetrically grafted to the para-direction of the phenyl rings. Two anchoring groups namely: cyanoacrylic acid (CA) and hydantoin (HY) were used. Excellent relationships between electronic energies and the Hammett constants (σp) have been reported. The results show that variation of both anchoring groups and substituents significantly affect the absorption of the dyes; maximum absorption for CA dyes was found ranging between 514–571 nm and 470–503 nm for ED and EW groups, respectively, while for HY dyes demonstrated maximum absorption between 502–537 nm and 480–496 nm for ED and EW, respectively. A linear correlation between σp and λmax with R2>0.97 was obtained. In addition, the mapping of the HOMO and LUMO energies suggests the intramolecular charge transfer and a strong electronic coupling between dye and semiconductor. Our theoretical calculations show that electron-donating substituents enhance the optoelectronic properties of the dyes. Analysis of chemical descriptors suggests that dyes containing alternative anchoring group HY substituted with –NH2 and –N(CH3)2 may demonstrate improved performance of DSSCs.