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. 2014 May 1;2014(14):2972-2979.
doi: 10.1002/ejoc.201400025.

Calixarene-Mediated Liquid-Membrane Transport of Choline Conjugates

Birendra Babu Adhikari  1 , Ayu Fujii  1 , Michael P Schramm  1
Affiliations

Calixarene-Mediated Liquid-Membrane Transport of Choline Conjugates

Birendra Babu Adhikari et al. European J Org Chem. .

Abstract

A series of supramolecular calixarenes efficiently transport distinct molecular species through a liquid membrane when attached to a receptor-complementary choline handle. Calix-[6]arene hexacarboxylic acid was highly effective at transporting different target molecules against a pH gradient. Both carboxylic- and phosphonic-acid-functionalized calix[4]arenes effect transport without requiring a pH or ion gradient. NMR binding studies, two-phase solvent extraction, and three-phase transport experiments reveal the necessary and subtle parameters to effect the transport of molecules attached to a choline "handle". On the other hand, rescorin[4]arene cavitands, which have similar guest recognition profiles, did not transport guest molecules. These developments reveal new approaches towards attempting synthetic-receptor-mediated selective small-molecule transport in vesicular and cellular systems.

Keywords: Calixarenes; Cavitands; Choline conjugates; Host-guest systems; Liquid-membrane transport; Molecular recognition.

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Figures

Figure 1
Figure 1
Resorcinarene cavitands 1–3, calixarenes 4–6, and pillar[n]arene hosts 7 and 8, and fluorophore-conjugated guests 9–12 used in this work.
Figure 2
Figure 2
300 MHz 1H NMR spectra in 100% [D4]MeOH (δ = 3.32 ppm) of (a) FITC-choline 9, (b) host 6, (c) 1:0.5 host:guest, (d) 1:1 host:guest, (e) 1:2 host:guest.
Figure 3
Figure 3
300 MHz 1H NMR spectra in CDCl3 with 20% [D4]-MeOH (δ = 3.25 ppm) of (a) guest dansyl choline 12, (b) 1:1 host 8:guest 12, (c) host 8, (d) 1:1 host 7:guest 12, (e) host 7.
Figure 4
Figure 4
Transport of different substrates with calix[4]arene tetraphosphonic acid receptor 6 in a U-tube experiment. Source phase: MQ water (4mL), NBD-choline 11 (1 mm) and FITC-choline 9* (0.5 mm); organic phase: CH2Cl2 (10 mL), 6 (0.5 mm); receiving phase: MQ water; stirring speed = 400 rpm, room temperature, results are reported as the average of duplicate trials. For FITC-choline, the maximum deviation from the mean was ±0.3% (not shown), and for NBD-choline, it was ±0.8% (not shown). (* guest precipitation occurred at the interface when 1 mm solution was used.).
Figure 5
Figure 5
Charge balance for the extraction of guest 9 and transport by 6.
Figure 6
Figure 6
Acidification of the receiving phase with HCl accelerates transport of 11 by 5 over 84-fold.
Figure 7
Figure 7
U-shaped glass dimensions and experimental parameters.
See this image and copyright information in PMC

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