| β-Cyclodextrin (CD) and polyethylene glycol (PEG) are a kind of cyclic oligosaccharides and polymers, respectively. Their special structures make them to be able to form inclusion complexes and aggregates with a variety of guests, such as organic molecules, inorganic ions, polymers, as well as rare gases and so on. The present work first reveals the differences of noncovalent interaction in cyclodextrin chemistry and the coordination interaction in coordination chemistry. Further,β-CD and PEG as representative organic and polymer molecule are selected as hosts for the formation of inclusion complexes and aggregates, respectively, to investigate the effect of noncovalent interaction on coordination interaction of ethylenediaminetetraacetic acid disodium salt and its analogs with metal ions. Dealing with data analysis for a multicomponent system it is important and necessary to consider the mutual influence of each type of the interactions on the other, which permits us to discuss the importance of the mutual influence and further understand factors related to different interactions in multicomponent systems. The main contents are as follows:1. The significant differences in spectral character, thermal decomposition and chemical reactivity of ethylenediaminetetraacetic acid and its sodium salts (NanH4-nEDTA, n = 0, 24, ligands) between before and after adduct withβ-CD were discussed first. The results from this study demonstrate that there is a close relation between the spectral performances (e.g. microstructures and molecular arrangements) of the series of the adducts, NanH4-nEDTA–β-CD, dominated by noncovalent interactions, and the nature of the ligands. Interesting changes in thermal decomposition behaviors ofβ-CD and the ligands upon adduct in air and under nitrogen atmosphere are observed. For instance, the presence ofβ-CD significantly accelerates the decomposition of the ligands at a lower temperature such as 653 K in air. Also, those results from thermogravimetry measurement provide direct evidence that under nitrogen atmosphere NanH4-nEDTA play different roles in altering the maximum decomposition temperature, rate and residual mass ofβ-CD. Further, different change patterns in coordination reactivities of the four ligands towards copper chloride in the absence and presence ofβ-CD reveal that the variability of the effect induced by noncovalent interaction between the ligands andβ-CD plays an important role in the coordination environment around Cu (II) ions. We are of the opinion that the results would provide a significant bridge between physical chemistry and supramolecular chemistry, and help us further understand factors related to noncovalent interactions.2. The presence of the noncovalent interaction between Na2H2EDTA andβ-CD were observed based on the changes in crystal patterns and thermal behaviors before and after interaction. Results from electric conductivity measurements confirmed this presence and showed that the extent of the noncovalent interaction was associated with the concentration ofβ-CD. More importantly, the noncovalent interaction led to a decreased coordination interaction of Na2H2EDTA and copper chloride. And this decrease exhibited a concentration dependence ofβ-CD. Similar phenomena were also observed in the case of several analogs of Na2H2EDTA by UV-Vis spectroscopy. A possible explanation was proposed based on the hypothesis that there was a competitive relationship between the noncovalent interaction and the coordination interaction. Further, nuclear magnetic resonance measurements provided important information on the difference in interaction modes ofβ-CD with H2EDTA2– and [Cu(EDTA)]2–.3. Based on the above results, we try to answer a fundamental question: what is the consequence of the noncovalent interaction between a polymer and a coordination compound Here, PEG-4000 and copper complex of H4EDTA were employed to solve this problem. Our results indicated several interesting findings. First, the introduction of H2[Cu(EDTA)] had no effect on the stacking structure of PEG-4000 (PEG-b) but led to a large change in surface structure of the polymer. Second, there was a significant difference (117 K) in the maximum degradation temperature between the PEG and its adduct H2[Cu(EDTA)]-PEG-b, suggesting that the noncovalent interaction can drastically improve the thermal stability of the PEG. Third, sintering experiments showed that H2[Cu(EDTA)] and H2[Cu(EDTA)]-PEG-b produced completely different decomposition products. The former formed Cu crystals in nitrogen and CuO in air, but the latter generated two types of Cu and CuCl crystals with a good crystalline under the two atmospheres. Finally, three independent measurements: viscosity, conductivity and nuclear magnetic resonance in solution, provided useful information and insights from both sides of the noncovalent interaction. Probable interaction mechanisms and interaction sites were proposed. The current research could create the foundation for a new understanding of how the noncovalent adduct interaction between a metallic complex and a polymer relates to the change in physical and chemical properties of the adducted components. |
