Anion-Responsive Fluorescent Supramolecular Gels.

Giacomo Picci,Jonathan W Steed,Matthew T Mulvee,Antonio Frontera,Claudia Caltagirone,Rosa M Gomila,Vito Lippolis

doi:10.3390/molecules27041257

Giacomo Picci, Jonathan W Steed + Show 5 more

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https://doi.org/10.3390/molecules27041257

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Abstract

Three novel bis-urea fluorescent low-molecular-weight gelators (LMWGs) based on the tetraethyl diphenylmethane spacer—namely, L1, L2, and L3, bearing indole, dansyl, and quinoline units as fluorogenic fragments, respectively, are able to form gel in different solvents. L2 and L3 gel in apolar solvents such as chlorobenzene and nitrobenzene. Gelator L1 is able to gel in the polar solvent mixture DMSO/H2O (H2O 15% v/v). This allowed the study of gel formation in the presence of anions as a third component. An interesting anion-dependent gel formation was observed with fluoride and benzoate inhibiting the gelation process and H2PO4−, thus causing a delay of 24 h in the gel formation. The interaction of L1 with the anions in solution was clarified by 1H-NMR titrations and the differences in the cooperativity of the two types of NH H-bond donor groups (one indole NH and two urea NHs) on L1 when binding BzO− or H2PO4− were taken into account to explain the inhibition of the gelation in the presence of BzO−. DFT calculations corroborate this hypothesis and, more importantly, demonstrate considering a trimeric model of the L1 gel that BzO− favours its disruption into monomers inhibiting the gel formation.

Highlights

Supramolecular chemistry is an area of chemistry of great interest that aims to investigate novel multimolecular systems in which the components are held together reversibly by noncovalent interactions
While classic gels are mostly based on polymer gelators, supramolecular gels are based on low-molecular-weight gelators (LMWGs), small molecules able to entrap solvent molecules into a nanostructured 3D network when selfassembling via noncovalent interactions such as hydrogen bonds, Van der Waals interactions, π-π stacking, and metal coordination [10,11,12]
We reported here three new fluorescent bis-urea LMWGs (L1–L3) bearing a diphenylmethane spacer and indole, dansyl, and quinoline substituents as fluorogenic fragments

Summary

Introduction

Supramolecular chemistry is an area of chemistry of great interest that aims to investigate novel multimolecular systems in which the components are held together reversibly by noncovalent interactions. Lehn [1], the interest in new supramolecular systems have found applications in many different fields, such as in cancer nanotheranostics [2], medicinal chemistry, sensing, extraction [3] and development of novel materials which are ready to move into the market or are already commercially available [4,5]. Supramolecular gels are an appealing and relatively new class of materials that have recently attracted the attention of the scientific community for their peculiar physical and chemical properties [6,7,8,9]. The possibility to form H bonds between anions and u has been exploited by supramolecular chemists for the design of2aonf 1i3on-sele or chemosensors [18]. Froorpthheosbe irceadsoinpsh, aennioynl-mreseptohnasinvee gdeelsrived c beafsfeidcioennutrefaosrartehceomfomromnlaytfioounndoifnrtohebluitsertagtuerles[1a1n,1d9].mDeestpailtleotgheeflasct[2th0a-t2th5i]s. class ocofnctormolIponof utthnhedipssriossptqueurdtiiteyes,powof ptehueldamre,asstceorrmiiabelsecihntahtlhleeenupgrseeessesonticfleltonhfeidesdifpfteolraebnteftoaarndmidorneissnasentddh,teshueccsohenlaessctttirhvueection o rfelsupoonrseesocfetnhet mgeatlesribaal tsoetdheopnreoseunrceporfeovnieosupescrifiecsaenairocnh. on the design of fluorescen

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