Theoretical study of switching characteristics of molecular tweezers based on bis(Zn-salphen)
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ORIGINAL PAPER
Theoretical study of switching characteristics of molecular tweezers based on bis(Zn-salphen) Hui Li 1 & Qiuping Guan 1 & Zishang Jia 1 & Xueye Wang 1 Received: 21 May 2020 / Accepted: 31 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract A series of novel tweezers based on bis(Zn-salphen) complex is theoretically studied. Density functional theory (DFT) method is used to investigate the switchable properties of terpy/bis(Zn-salphen) complex (1, terpy=2,2′:6′,2″-terpyridine) and Br-phtpy/ bis(Zn-salphen) complex (2, Br-phtpy=4′-bromophenyl-2,2′:6′,2″-terpyridine). In this study, the free tweezers 1 and 2 can be converted from a “W” open form to a “U” closed form upon Ru(III) coordination. The switching performances were characterized by 1H NMR and absorption spectra. DFT calculations were carried out using a B3LYP-D3 functional and def2-SVP basis set for all atoms. 1H NMR spectra showed that terpyridine protons had an obvious upfield shift during complexation with RuCl3. The absorption spectrum was observed in the closed tweezers with a significant red shift and a decreased oscillator strength. In addition, the tweezers were reopened by introducing molecule pyrazine in the “U”-shaped conformation to form a host-guest system. The recognition ability of two Zn-salphen complexes was studied by geometrical optimization and absorption spectra. Keywords Density functional theory . Switchable tweezers . Terpyridine
Introduction Molecular tweezers are a kind of well-defined molecular receptors proposed by Whitlock in 1978 [1] due to its unique shape of two caffeine chromophores separated by a flexible or rigid spacer. Molecular tweezers are used widely as molecular receptors, because molecular tweezers have an open cavity of ca.7 Å and can form various host-guest systems with substrate molecules via non-covalent interactions (such as weak bond, aromatic stacking, metal coordination, or hydrophobic forces) [2]. In contrast to Whitlock’s tweezers, Klärner and coworkers [3] defined novel systems as molecular clips and tweezers based on their central spacer structure and the location of substrates within the receptor cavity, respectively. Due to its high selectivity to amino acid side chains, Klärner’s molecular tweezer CLR01 opens up new fields of pharmaceutical
* Xueye Wang [email protected] 1
Key Laboratory for Green Organic Synthesis and Application of Hunan Province, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan 411105, Hunan, People’s Republic of China
applications, involving enzyme inhibition and stabilization of disordered protein-protein interfaces (PPIs) [4, 5]. Currently, a large number of molecular tweezers have been rapidly developed and applied to chiral recognition [6], biosensor [7], and supramolecular polymers [8] since the seminal works of Whitlock [1], Zimmerman [9, 10], and Klärner [3]. To date, the use of rigid or semi-flexible spacers is the most commonl
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