Thermodynamics of Complexes between Dibenzo‐24‐crown‐8 Derivatives and 1,2‐Bis(pyridinium)ethanes

Abstract

The binding behavior of para-substituted 1,2-bis(pyridinium)-ethane derivatives (X-PyCH 2 -CH 2 Py-X, X = H, Me, Ph, and Py) a-d with dibenzo-24-crown-8 (DB24C8, 1) and its derivatives, diformyldibenzo-24-crown-8 (2), dinitrodibenzo-24-crown-8 (3), dimethyldibenzo-24-crown-8 (4) and diaminodibenzo-24-crown-8 (5), has been comprehensively investigated by 1 H NMR and UV absorption spectroscopy and isothermal titration microcalorimetry in acetonitrile. The results obtained indicated that some of the complexes constructed from DB24C8 derivatives and 1,2-bis(pyridinium)ethane derivatives resulted in visible color changes. For example, upon

Templated versus non-templated synthesis of benzo-21-crown-7 and the influence of substituents on its complexing properties

“…They are 17090 (±500) M −1 , 8000 (±270) M −1 , 5640 (±190) M −1 , and 3050 (±60) M −1 , respectively. The lower binding ability of 4 relative to C7 is certainly due to the electron-withdrawing aldehyde group which decreases the electron-donating and hydrogen-bond accepting ability of the oxygen atoms on the catechol [32]. Consequently, electron-withdrawing substitution on C7 should be avoided when aiming at strong binding between the two building blocks.…”

Rigid Organization of Fluorescence-Active Ligands by Artificial Macrocyclic Receptor to Achieve the Thioflavin T-Amyloid Fibril Level Association

“…In addition, the peripheral hydrogen atoms around push–pull guest molecules are so acidic (electron-poor) that they can readily form hydrogen-bonding interconnection with the electron-rich oxygen atoms in DNC. , Therefore, we can reasonably infer that the π-stacking and hydrogen-bonding interactions are jointly contributed to the enthalpic gains in the present molecular binding system. Along with the dominant enthalpic gains, the moderate entropic changes further confirm that the mutual electrostatic desolvation effect is another primary determinant to govern the molecular recognition process in water, because lacking sulfonated groups, the complexation of organic cations with neutral crown ether derivatives always induces much more negative entropic loss in nonaqueous solvent …”

“…Along with the dominant enthalpic gains, the moderate entropic changes further confirm that the mutual electrostatic desolvation effect is another primary determinant to govern the molecular recognition process in water, because lacking sulfonated groups, the complexation of organic cations with neutral crown ether derivatives always induces much more negative entropic loss in nonaqueous solvent. 45 The calorimetric data in benzothiazolium salt systems clearly indicate that the extraordinarily strong binding of G1−G2 by DNC is driven not only by the highly negative enthalpic change but also by the positive entropic gain. The enthalpic gain may be attributed to the combined effect of the π-stacking, hydrophobic, and hydrogen-bonding interactions, while the favorable entropic gain, which is rarely observed for synthetic host−guest systems, may arise from the extensive dehydration from both the positively charged guests and negatively charged DNC upon charge-neutralizing sandwich complexation, as often observed for biological host−guest systems.…”

Solvent‐Free Synthesis of the Smallest Rotaxane Prepared to Date

“…We chose the dipropargylammonium ion (1-H + ) as the alkyne-terminated linear component in the small [2] in CD 3 CN suggested that the rates of exchange during the complexation and decomplexation processes were slow on the 1 H NMR spectroscopic timescale at 400 MHz under these conditions, but not sufficiently slow to provide the sharp signals required to obtain an accurate value for the association constant through the single-point method. [6] Instead, we used isothermal titration calorimetry (ITC) [7] to determine an association constant of (14 000 AE 1300) m À1 for the formation of the [2]pseudorotaxane from 21C7 and 1-H•BF 4 in CH 3 CN at 25 8C. [8] Concentration of an equimolar solution of the macrocycle 21C7 and the threadlike ion 1-H•BF 4 gave a sticky liquid, which we presumed to contain predominately the [2]pseudorotaxane [(21C7'1-H)•BF 4 ].…”