Study On The Host-Guest Interactions Of Cucurbit[7] Uril On The Gold Nanospheres

Cucurbit[7]uril（CB[7]）is capable of forming inclusion complexes with various types of guests through host-guest interactions.Howerer,studies on the interaction between host and guest on the gold nanospheres are still rare.In this paper,the binding constants were determined and compared in three states（including free state,CB[7]was attached to the the gold nanospheres,guests attached to the the gold nanospheres）.The effect of last two states on the interaction strength between CB[7]and guests were studied.Guest 1 with phenyl,guest 2 with adamantyl and guest 3 with ferrocene group were designed and synthesized.They had a large difference in binding constant with CB[7].The inclusion behavior of CB[7]and three guests in aqueous phase was studied.The results indicated that their binding ratio to CB[7]was 1:1,guest 1 exhibited fast exchange kinetic between free and bound guest on the ¹H NMR chemical shift time scale,while 2 and 3exhibited slow exchange kinetics.The binding constants between 1,2,3 and CB[7]determined by ¹H NMR competition experiments were（1.9±0.4）×10⁹ M^-1,（1.6±0.8）×10¹⁵ M^-1 and（2.6±0.7）×10¹³ M^-1 respectively.The binding constants between CB[7]and guest 1 and 3 determined by competition ITC experiment were（1.9±0.6）×10⁹ M^-11 and（2.7±0.8）×10¹³ M^-1 respectively.The binding constants of the CB[7]and the guests（1and 3）measured by the two methods were basically the same,and the accuracy of the measurement results was mutually verified.CB[7]-stabilized gold nanospheres with a diameter of（5.84±0.77）nm were synthesized by one-pot method,and the coverage of CB[7]was 75%.Direct and competition ITC experiment were used to determine the binding constants between CB[7]on the gold nanospheres and benzylamine hydrochloride,guest 1 and 3.The results were（9.0±0.1）×10⁴ M^-1,（3.3±0.8）×10⁸ M^-1 and（4.7±2.2）×10¹11 M^-1 respectively.1-stabilized gold nanospheres with a diameter of（2.37±0.35）nm were synthesized,the binding constant between CB[7]with 1 on the gold nanospheres was（4.6±1.3）×10⁸M^-1 determined by competition ITC experiment.Finally,we compared the binding constants between CB[7]and guests in the above three states.The binding constant in free state is the largest;when guests were attached to gold nanospheres,the binding constant became smaller,which is 0.24 times that of the free state;when CB[7]was attached to gold nanospheres,the binding constants were the smallest,which is 0.18 times that of the free state.Therefore,when the guests were attached to the the gold nanospheres,the strength of interaction between CB[7]and guests will be weakened,but slightly stronger than when the CB[7]was attached to the gold nanospheres.