Resorcinarene bis-crown silver complexes and their application as antibacterial Langmuir–Blodgett films

Abstract

Silver complexes of a cation binding supramolecular host, resorcinarene bis-crown (CNBC5) with propyl, nonyl, decyl and undecyl alkyl chains were investigated by NMR titration, picrate extraction and single crystal X-ray diffraction. Binding studies showed that both 1 : 1 and 1 : 2 (host-Ag(+)) complexes are present in solution with only a slight effect of the lower rim alkyl chain length on the binding constants (log K 4.0-4.2 for 1 : 2 complexes). Solid state complexes of the resorcinarene bis-crowns bearing either C(3) or C(11) chains were obtained. Single crystal X-ray analyses showed that both derivatives bind silver ions by metal-arene and Ag···O coordination from the crown ether bridges and from the solvent, and pack in layered or bilayered fashion. Furthermore, the amphiphilic nature of C11BC5 was demonstrated using the Langmuir balance technique. Langmuir-Blodgett films of the amphiphilic C11BC5-Ag complex were transferred onto a substrate and shown to possess antibacterial activity against E. coli.

A perspective to resorcinarene crowns

“…The silver complex of resorcinarene bis-crown 5b packed into a similar kind layered structure as 5a·2Ag + complex crystallized from n-propanol and isopropyl alcohol (CCDC 833089) 40 and as with alkali metal complexes the 1:1 silver complex of the long alkyl chain biscrown 5h (CCDC 833090) formed bilayers as respective alkali metal complexes. However, instead of capsules, the upper rims of the complexes are shifted horizontally about half the length of the upper rim.…”

“…Knowing that resorcinarene biscrowns 5a-b, 5d and 5f-5h and their metal complexes can form different kinds of highly organized structures their ability to form SLNs, as well as the dependency of SLN properties on the alkyl chain lengths were investigated. 40 The particles were prepared by a solvent replacement method 43 where water was added to a THF solution of a bis-crown while vigorously stirring. The dynamic scattering experiment as well as SEM images showed that the obtained SLNs were 220-320 nm in diameter depending on their alkyl chain lengths.…”

Influence of lower rim C-methyl group on crystal forms and metal complexation of resorcinarene bis-crown-5

“…33,34 In addition, in C-ethyl bis-crown silver complexes the conformation of the host varied from a slightly twisted to significantly twisted boat depending on the size of the solvent coordinated to the included metal. In contrast, the boat conformation of host 1 is rather pinched with the horizontal aryl rings overbent in a 200° dihedral angle and the vertical aryl rings leaning slightly towards each other making the shape of 1 a compact block.…”

“…In 1:1 complex silver is coordinated by two Ag···O bonds (2.43-2.44 Å) to the crown ether bridge and by η 2 metal···arene coordination (2.50-2.61 Å) to the distal edge of the aromatic ring resembling the earlier examples of silver complexes ( Figure 10). 33,34 In addition, a water molecule forms a coordination bond (2.31 Å) to the cation on an open side of the binding pocket. The empty side of the cavity is filled by the inward leaning vertical aryl rings (dihedral angle -12.2˚) and a folded crown ether bridge in contrast to 1:1 silver complex of C-ethyl bis-crown capsule, in which the second binding pocket was filled with methanol and water molecules.…”

“…The comparison of the C 2 H 5 -C 11 H 23 derivatives of resorcinarene bis-crown-5 has indicated that lower rim alkyl chain affects the self-assembly and crystal packing of the bis-crown-5, but also the complexation properties of the host probably due to solubility differences. 30,34 These results prompted us to study how the conformational properties of the C-methyl resorcinarene manifest in the resorcinarene crown ether derivatives C-methyl bis-crown-5 and mono-crown-5, which turned out to show remarkably different solvate formation and crystal packing properties than their longer alkyl chain analogues.…”