Study On Interaction Systems Of Bipyridylium Herbicides With Cucurbiturils And Their Anti-microbial And Weeding Activity

Nowadays supramolecular chemistry based on the theory of non-covalent bondshas become one of the hot fields of chemical research. Cucurbit[n]uril, Q[n], is arelatively new family of macrocyclic host molecules. They are rigid macrocycles witha unique cavity, rimmed by carbonyl oxygens. Cucurbit[n]urils can form inclusioncomplexes with organic guests, with the strongest complexes formed with positivelycharged guests. Moreover, the application of cucurbit[n]uril to explore thestabilization, biological activity of pesticide and medicament is very importance. Thiswill develop a new field for cucurbit[n]uril chemistry and provide new thoughtfulnessfor new pesticide development.In this work, a type of new cage coumpound-cucurbit[n]urils (Q[n]s) is selectedas host, viologens derivatives herbicides (PCns, 4,4'-bypyridyl derivatives) areselected as guests, and the interaction of the Q[n]s and PCns have been studied indetail by using ¹H NMR technique, electronic absorption spectroscopy, theoreticcalculation, cyclic voltammetry, classical redox reaction and single crystal X-raydiffraction determination methods. The used Q[n]s include cucurbituril (Q[6]),cucurbit[7]uril (Q[7]) andα,β,δ-hexamethylcucurbituril (HMeQ[6]), and the PCnsinclude N,N'-diethyl,-4,4'bypyridyl (PC2), N,N'-dibutyl-4,4'bypyridyl (PC4),N,N'-dihexyl,- 4,4'bypyridyl (PC6), N,N'-dioctyl,-4,4'bypyridyl (PC8). ¹H NMRrevealed that Q[n]s included the alkyl moieties of PCns and formed dumbbell likeinclusion complexes. These results were further confirmed by the electronicabsorption spectroscopy, theoretic calculation, and single crystal X-ray diffractiondetermination methods. The redox properties of the 4,4'-bypyridyl derivatives were also investigated by using cyclic voltammetry, classical redox reaction methodsbecause the weeding process of the 4,4'-bypyridyl derivatives involved in a radicalreaction. Based on above the investigation of the Q[n]s with PCns, the growthinhibition effect of the selected PCns on funguses, bacteria and actinomyces in soilwas also studied. Considering the poor solubility of the normal Q[n] in aqueoussolution could limit the application of the Q[n]s, a series of methyl-substituted Q[n]swere designed and synthesized in this work. A water solubleα,β,δ-HmeQ[6] wasselected for the investigation of the biological activity of PCns on the weed (WhiteClover, Trifolium repens).The selected 4,4'-bypyridyl derivatives (PCn, n = 2, 4, 6, ...), were synthesizedand characterized as literature reference. The interaction and interaction model of theQ[n]s and PCns have been studied in detail by using ¹H NMR technique, electronicabsorption spectroscopy, theoretic calculation, and single crystal X-ray diffractiondetermination methods. Also the redox properties of these inclusion complexes areinvestigated by using cyclic voltammetry, classical redox reaction methods. ¹H NMRresults revealed that the proton resonances of the alkyl moieties of the bound PCnsexperienced up-field shift, while the proton resonances of the viologen coreexperienced down-field shift, it suggested that two alkyl chains of the 4,4'-bypyridylderivatives were included in the cavities of two Q[n]s respectively, and dumbbell likehost-guest inclusion complexes could be formed. The absorbance (A) vs ratio ofmoles of the host Q[6] and guests (N_Q[6]/N_PCn data can be fitted to a 2:1 bindingmodel for the Q[6]-PCn systems atλ_max respectively. This most stable interactionmodel of the PCn-Q[n] complexes was confirmed by the results from ab initiocalculation.With the increase of the concentration of the host Q[6] or Q[7], One can see thedecrease of the reduction and oxidation peak current, particularly the reduction state,of the Q[n]-PCn interaction systems. This suggested that the interaction of the Q[6]and PCn can change the redox properties of both reactants (PCns) and products(PCn^±). Generally, the biological activity of PCns are related with the stability of the corresponding radical cation. Using sodium dithionate as a reducing agent, thestability of the radical cation of PCn which interacted with Q[n]s was investigated aridthe experimental results showed that the amount of the PC4⁺ and PC6⁺ reduced in thepresence of Q[6]. It suggested that the length of the alkyl chain on the guests couldinfluence on the stability of their radical cations.The experimental results showed that PCns can inhibit the growth of funguses,bacteria and actinomyces in soil, while the growth inhibition effect of thecorresponding Q[6]-PCns systems presented even better. It suggests that Q[6] plays arole a synergistic agent in this process. However, the poor solubility of Q[6] inaqueous solution is greatly limited its application, and synthesis water soluble Q[n]sbecome the main work in the next chapter.Based on the previous synthesized works, some new synthesis routes wereestablished, a series methyl-substituted Q[n]s were synthesized and characterized by¹H NMR and single crystal X-ray diffraction determination. Amongst them, five arenew members in the cucurbit[n]uril family, they areα,γ-TMeQ[5],α,β,γ-HMeQ[5],NMeQ[5],α,β,δ-HMeQ[6] and DDMeQ[6]. Seven crystal structures of these fiveMethyl-Q[n]s and some host-guest of PCn-Q[6] complexes have the stoichiometry of(?) respectively.The interaction of a water soluble HMeQ[6] with PCn were investigated and theresults confirmed a similar interaction model and properties to that of Q[6]-PCnsystems. The experiments for the biological activity PCn and HMeQ[6]-PCn revealedthat PC2 and PC4 have stronger biological activity on weeding of White Clover(Trifolium repens. L), and the longer the alkyl chain, the weaker the weeding effect. Inthe presence of the HMeQ[6], the biological activity on weeding of White Clover(Trifolium repens. L) for all HMeQ[6]-PCn systems are increased. It suggested thatthe host HMeQ[6] also played a role of a synergistic agent in this process.The investigation reveals that two alkyl chains of the 4,4'-bypyridyl derivativeswere included in the cavities of two Q[n]s respectively, and dumbbell like host-guest inclusion complexes could be formed, and in the presence of the host Q[n]s, theoxidation property of PCn and reduction property of PCn⁺ have been changed, and itcould strength the biological activity of the viologens derivatives herbicides.Cucurbit[n]urils can improve not only the antimicrobial activity of the PCns (such asfunguses, bacteria and actinomyces in soil) and but also the weeding activity of thePCns (such as White Clover, Trifolium repens. L). Moreover, Synthesis of newalkyl-substituted cucurbit[n]urils can not only increase the members in the Q[n]sfamily, but also provide suitable host for study of the biological activity of such asPCns and so on.