Batisai, E.Rambevha, Lesedi2026-06-172026-06-172026-05-19Rambevha, L. 2026. Separation of Isomers Using Host-Guest Methods. . .https://univendspace.univen.ac.za/handle/11602/3193M.Sc. in ChemistryDepartment of ChemistrySelective separation of positional isomers remains difficult due to their nearly identical physical and chemical properties. This study synthesized a new host molecule, 2-(1, 3- dioxo- 1 H- benzo [de] isoquinolin- 2 (3 H)-yl) acetic acid (H) and tested its ability to discriminate picoline isomers (2-, 3-, and 4-) and lutidine isomers (2,2-, 2,4-, 2,2-, 2,6-, and 3,5-). The approach involved crystallizing the host in the individual isomers and evaluating its potential as a supramolecular host for isomer separation. Single crystal X-ray diffraction (SCXRD) confirmed the formation of discrete 1:1 host–guest complexes with all isomers and revealed that the host-guest complexes primarily rely on a strong, directional hydrogen bond between the host's carboxylic acid group and the pyridyl nitrogen of the guest. The host and the guest further interact via C–H ··· O interactions. Hirshfeld surface analysis revealed that O ··· H/H ··· O and H ··· H contacts dominate intermolecular interactions, emphasizing the cooperative role of hydrogen bonds and van der Waals forces in stabilizing the complexes. Differential Scanning Calorimetry (DSC) analysis revealed unique thermal behaviors for each inclusion complex: H·2PIC releases the guest between 124 °C and 178 °C, H·3PIC at 129 °C and 186 °C, and H·4PIC between 170 °C and 198 °C. Thermogravimetric analysis (TGA) confirmed lutidine guest inclusion by showing distinct mass-loss steps: 3,5LUT is released from 137 to 191 °C, 2,6LUT from 117 to 146 °C, and 2,4LUT from 138 to 216 °C. The host framework remained stable up to around 351 °C, indicating structural stability after guest removal. Competition experiments were conducted by exposing the host to binary mixtures of picoline and lutidine isomers of varying ratios, and the results were analyzed using GC–MS and GC–FID. The selectivity coefficient (K) was calculated to determine the host's selectivity towards different mixtures of the guest. For picoline isomers, selectivity followed the order 4PIC > 3PIC > 2PIC, with the highest selectivity coefficient observed in the 3PIC: 2PIC mixture at an equimolar ratio of 1:1 (K = 14.43), surpassing the value of 10 typically associated with strong, practically useful selectivity. For lutidine isomers, the order was 3,5LUT > 2,4LUT > 2,6LUT. The most effective discrimination was observed in the 3,5LUT: 2,6LUT pair, with a K value of 39.82 at an equimolar ratio. This indicates a highly efficient molecular recognition process and potential for crystallization-based separation.1 online resource (xviii, 88 leaves): color illustrationsenUCTDDissertationRambevha L. Separation of Isomers Using Host-Guest Methods. []. , 2026 [cited yyyy month dd]. Available from:Rambevha, L. (2026). <i>Separation of Isomers Using Host-Guest Methods</i>. (). . Retrieved fromRambevha, Lesedi. <i>"Separation of Isomers Using Host-Guest Methods."</i> ., , 2026.TY - Dissertation AU - Rambevha, Lesedi AB - Selective separation of positional isomers remains difficult due to their nearly identical physical and chemical properties. This study synthesized a new host molecule, 2-(1, 3- dioxo- 1 H- benzo [de] isoquinolin- 2 (3 H)-yl) acetic acid (H) and tested its ability to discriminate picoline isomers (2-, 3-, and 4-) and lutidine isomers (2,2-, 2,4-, 2,2-, 2,6-, and 3,5-). The approach involved crystallizing the host in the individual isomers and evaluating its potential as a supramolecular host for isomer separation. Single crystal X-ray diffraction (SCXRD) confirmed the formation of discrete 1:1 host–guest complexes with all isomers and revealed that the host-guest complexes primarily rely on a strong, directional hydrogen bond between the host's carboxylic acid group and the pyridyl nitrogen of the guest. The host and the guest further interact via C–H ··· O interactions. Hirshfeld surface analysis revealed that O ··· H/H ··· O and H ··· H contacts dominate intermolecular interactions, emphasizing the cooperative role of hydrogen bonds and van der Waals forces in stabilizing the complexes. Differential Scanning Calorimetry (DSC) analysis revealed unique thermal behaviors for each inclusion complex: H·2PIC releases the guest between 124 °C and 178 °C, H·3PIC at 129 °C and 186 °C, and H·4PIC between 170 °C and 198 °C. Thermogravimetric analysis (TGA) confirmed lutidine guest inclusion by showing distinct mass-loss steps: 3,5LUT is released from 137 to 191 °C, 2,6LUT from 117 to 146 °C, and 2,4LUT from 138 to 216 °C. The host framework remained stable up to around 351 °C, indicating structural stability after guest removal. Competition experiments were conducted by exposing the host to binary mixtures of picoline and lutidine isomers of varying ratios, and the results were analyzed using GC–MS and GC–FID. The selectivity coefficient (K) was calculated to determine the host's selectivity towards different mixtures of the guest. For picoline isomers, selectivity followed the order 4PIC > 3PIC > 2PIC, with the highest selectivity coefficient observed in the 3PIC: 2PIC mixture at an equimolar ratio of 1:1 (K = 14.43), surpassing the value of 10 typically associated with strong, practically useful selectivity. For lutidine isomers, the order was 3,5LUT > 2,4LUT > 2,6LUT. The most effective discrimination was observed in the 3,5LUT: 2,6LUT pair, with a K value of 39.82 at an equimolar ratio. This indicates a highly efficient molecular recognition process and potential for crystallization-based separation. DA - 2026-05-19 DB - ResearchSpace DP - Univen LK - https://univendspace.univen.ac.za PY - 2026 T1 - Separation of Isomers Using Host-Guest Methods TI - Separation of Isomers Using Host-Guest Methods UR - ER -