Construction of Cooperative and Responsive Supramolecular Systems for Molecular Functional Modulation

Abstract

The transfer and modulation of the molecular information are necessary processes for cooperative and responsive molecular functions. When functional molecules are responsive to external (intermolecular) as well as internal (intramolecular) stimuli, the molecules exhibit cooperative functions in principle. We have developed a variety of cooperative and responsive supramolecular systems created on the basis of new concepts for the molecular design of sophisticated functional systems. The first uses pseudomacrocycles including pseudocrown ether, pseudocryptands, and pseudocyclophanes as novel frameworks for response functions by utilizing a metal ion as an effector. The second utilizes a molecular gate responding to an external signal. The gate is opened and closed by a signal achieving perfect onoff switching for guest recognition. The next exploits metal-accumulated molecular systems bearing oligo C=N moieties as a binding site for metal ions. This strategy is remarkably useful for producing new binding sites by structural fixation of multi-metal complexes and to modulate properties of metal ions. Other cooperative molecular assembling systems for host generation are also demonstrated in this account. Metallo-frameworks and self-assembled metallo-systems recently developed in our laboratories, which have high potential for synergistic molecular functions, are discussed. Future cooperative functional systems will be widely applicable as multi-responsive multi-functional supramolecules, molecular functional cascades for successive molecular functions and function amplification. Study of cooperative and responsive molecular systems may lead to more general fields such as complex systems science, which is at the interface of chemistry, physics, biology, and mathematics.Responsive regulation of molecular functions requires information transfer at the molecular level (Figure 1).1 Receiving and releasing substances, such as molecules, metal ions, electrons, and photons, is regarded as an information transfer event. The properties of the substances, such as chirality, order, spatial arrangement, and the combination of atomic and molecular arrays can also provide information to control functions. These regulation systems are referred to as molecular systems responding to external stimuli and are also closely related to cooperative functional systems. Intramolecular and/ or intermolecular interactions play a very important role in cooperative functions. In other words, intramolecular and/or intermolecular communication between different parts of the molecules is necessary to generate the observed phenomena, which are very important and interesting with respect to molecular property memory and amplification of molecular functions. Cooperative systems generally consist of two parts, a receptor site for the stimulus and an active site for the function.

Pseudocryptand Hosts for Paraquats and Diquats

“…Encouraged by these exciting results, we explored other methods to drive pseudorotaxane formation by enforcing the folding of BMP32C10 necessary for formation of taco complexes, thus reducing the entropic penalty for complexation, through hydrogen bonding of suitable 5- and 5′-substitutents with di- and tritopic anions, i.e., formation of “pseudocryptands” in a noncovalent or truly supramolecular manner. The anions were introduced as tetraalkylammonium salts.…”

“…Because the synthesis of the pyridyl dibenzo-30-crown-10 cryptands and the recent introduction of pseudocryptands achieved association constants close to those of the corresponding cryptands with paraquat, effort has been put into exploring other pseudocryptands. Pseudocryptands are cyclic host compounds which contain one or two unconnected arms that noncovalently yield a cryptand-like structure upon guest binding; these compounds are an extension of the class of pseudomacrobicyclic compounds − that earlier were called lariat ethers , and now rigid U-shaped hosts called “tweezers”; − , however, the arms of the lariat ethers were designed to interact with the guests, while in the present work, some arms were designed to close the encapsulating host by interacting with each other or counter-anions of guests. Figure provides cartoon examples of pseudocryptands.…”

Bpytrisalen/Bpytrisaloph: A Triangular Platform That Spatially Arranges Different Multiple Labile Coordination Sites

“…32−48 The trisaloph has three saloph N 2 O 2 units at the vertex and a central cavity surrounded by six phenolic oxygen atoms. The diameter of the cavity is 5.6−5.8 Å (diagonal O−O), 32 which is suitable for the capture of one metal ion, such as a lanthanide 33,37,38,40 and an alkali metal, 43 by trinuclear trisaloph complexes. The O 6 cavity of the trisaloph complexes was also utilized to capture the M 3 or M 4 cluster (M = Zn or Cd) assisted by external bridging ligands such as acetates, and it was reported that subtle factors (metal, ligand, etc.)…”

“…The formation of an imine bond between a diamine derivative and a salicylaldehyde analogue to form the N 2 O 2 coordination units has been utilized to construct a rigid covalent scaffold and its multinuclear complexes. − In particular, trisaloph, a triangular macrocycle first reported in 2001, is formed by the condensation of the 1,4-diformyl-2,3-dihydroxybenzene linker and o -phenylenediamine. − The trisaloph has three saloph N 2 O 2 units at the vertex and a central cavity surrounded by six phenolic oxygen atoms. The diameter of the cavity is 5.6–5.8 Å (diagonal O–O), which is suitable for the capture of one metal ion, such as a lanthanide ,,, and an alkali metal, by trinuclear trisaloph complexes. The O 6 cavity of the trisaloph complexes was also utilized to capture the M 3 or M 4 cluster (M = Zn or Cd) assisted by external bridging ligands such as acetates, and it was reported that subtle factors (metal, ligand, etc.)…”

A metal–ion-responsive adhesive material via switching of molecular recognition properties

“…In this work, we focus on metal ions in surrounding environment as chemical stimuli. Metal ions are widely utilized as chemical stimuli to control living organisms 22 , supramolecular systems 23 24 25 or properties of soft materials like gels 26 27 28 29 30 31 32 , for their chemical selectivity, versatility and reversible nature of coordination bonds. Herein, we report a metal–ion-responsive functional material that can switch their chemically selective adhesion property by regulating inhibitory inclusion of metal ligands to host moieties.…”