Binding Properties of a Dinuclear Zinc(II) Salen-Type Molecular Tweezer with a Flexible Spacer in the Formation of Lewis Acid-Base Adducts with Diamines

Gabriella Munzi,Santo Di Bella,Giuseppe Consiglio,Salvatore Failla

doi:10.3390/inorganics9060049

Gabriella Munzi, Santo Di Bella + Show 2 more

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https://doi.org/10.3390/inorganics9060049

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Journal: Inorganics	Publication Date: Jun 16, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: University of Catania

Abstract

In this paper we report the binding properties, by combined 1H NMR, optical absorption, and fluorescence studies, of a molecular tweezer composed of two Zn(salen)-type Schiff-base units connected by a flexible spacer, towards a series of ditopic diamines having a strong Lewis basicity, with different chain length and rigidity. Except for the 1,2-diaminoethane, in all other cases the formation of stable 1:1 Lewis acid-base adducts with large binding constants is demonstrated. For α,ω-aliphatic diamines, binding constants progressively increase with the increasing length of the alkyl chain, thanks to the flexible nature of the spacer and the parallel decreased conformational strain upon binding. Stable adducts are also found even for short diamines with rigid molecular structures. Given their preorganized structure, these latter species are not subjected to loss of degrees of freedom. The binding characteristics of the tweezer have been exploited for the colorimetric and fluorometric selective and sensitive detection of piperazine.

Highlights

(c) Variation of the absorbance at 580 nm as a function of the concentration of 1,10-diaminodecane added and fit of the binding isotherm with Equation (1) (red line)
In view of the flexibility of the spacer in the tweezer 1, which in principle can accommodate almost any ditopic Lewis base, the different binding constants along the series could be attributed to a larger entropic cost of the loss of degrees of freedom for diamines with a shorter alkyl chain, while the involved longer α,ω-diamines are not subjected to conformational strain upon5boifn1d3 ing, resulting in larger intramolecular cyclic adducts, with gain of degrees of freedom of the flexible spacer of the tweezer
It turns out that the preorganized structure of PZ and DABCO favors the formation of stable adducts because, except for the entropic cost upon binding the diamine mtmoini1ne, etthoteo1s1e,tshtpheeescesieesspspeaecrieceiesnsoatarerseunbnojotetcstuseubdbjejtecotcetldeodstsotolfolodsssesgorofefdedesegogrfereefreseseoodf fofrmferee,decdooomnmt,r,acrocyonnttrotararayrlyiptothoaataliilc-ipdphiahamatitcincdedisaiamwmiintihneessshwowirtiththaslhkshoyorltrctahalaklikynyl. lchchaainin

Summary

Introduction

(c) Variation of the absorbance at 580 nm as a function of the concentration of 1,10-diaminodecane added and fit of the binding isotherm with Equation (1) (red line). (c) Variation of the absorbance at 580 nm as a function of the 4coonf -13 centration of 1,10-diaminodecane added and fit of the binding isotherm with Equation 1 (red line).

Results

Conclusion