Insight into the Permeation Selectivity of Calix[n]arene-Based Langmuir−Blodgett Films:  Importance of Headgroup Association and the Solid Phase

Abstract

This paper reports the design and synthesis of 5,11,17,23,29,35-hexaacetyl-37,38,39,40,41,42-hexakis(1-hexadecyloxy)calix[6]arene (2) and 5,11,17,23-tetraamideoxime-25,26,27,28-tetrakis(1-hexadecyloxy)calix[4]arene(3), plus a detailed comparison of the membrane properties of corresponding Langmuir−Blodgett films with those assembled from 5,11,17,23,29,35-hexaamideoxime-37,38,39,40,41,42-hexakis(1-hexadecyloxy)calix[6]arene (1a). Surface pressure−area isotherms that were recorded for 1a and 2 over a pure water subphase at 25 °C showed significant hysteresis that was eliminated after two compression−expansion cycles; the limiting area in both cases was ca. 162 Å2/molecule. In sharp contrast, 3 showed no hysteresis at 25 °C and a limiting area of 107 Å2/molecule. Careful examination of the dependence of surface viscosity on temperature has provided compelling evidence for a solid-analogous to liquid-analogous phase transition occurring at 31 and 28 °C for monolayers of 1a and 2, respectively. Permeation measurements that were made across Langmuir−Blodgett (LB) films [four monolayers supported on poly[1-(trimethylsilyl)-1-propyne] with respect to helium and nitrogen] revealed high selectivity in the case of 1a and much lower selectivity with 2 and 3 at ambient (21−23 °C) temperatures. The implications of these findings, in terms of the further development of LB films as membranes for gas separations, are briefly discussed.

Pyrogallol[4]arenes Show Highly Variable Amphiphilic Behavior at the Air–Water Interface Dependent Upon Side Chain Length and Branching

“…The amphiphilic systems studied form stable monolayers when the straight chains are as short as n-propyl. Remarkably, n-propylpyrogallol [4]arene shows a behavior at the air-water interface that is indistinguishable from that of pyrogallolarenes bearing n-hexyl, n-nonyl, and n-dodecyl side chains. There is no report of amphiphilic side-chain-length dependence or Langmuir trough behavior for families of branched alkyl chain calixarenes or resorcinarenes.…”

“…Numerous attempts were made to stabilize both calix[-n]arene and calix[n]resocinarene monolayers. Throughout the remainder of the 1980s and the 1990s, the Langmuir trough was used to examine the stabilizing effects of varying the ionic composition, [4] ionic strength, [5] and pH [6] of the subphase on which the calix[n]arene derivatives were spread. Investigations into the effects of interior cavity size, [7] conformation, [8,9] and substitution [10][11][12][13][14][15][16] on monolayer formation and stability have been conducted by several groups during the past two decades.…”

“…Pyrogallol [4]arenes are relatives of both calixarenes [1] and resorcinarenes [2] but differ from their counterparts in that they derive from pyrogallol (1,2,3-trihydroxybenzene). The tetrameric macrocycles calix [4]arene, resorcin [4]arene, and pyrogallolarene possess 4, 8, or 12 hydroxyl groups, respectively.…”

“…The tetrameric macrocycles calix [4]arene, resorcin [4]arene, and pyrogallolarene possess 4, 8, or 12 hydroxyl groups, respectively. Pyrogallolarenes also differ from calixarenes by being alkylated at the methine carbon atoms of the macrocycle (see Scheme 1).…”

“…The behavior of pyrogallol [4]arenes (Pgs) substituted with normal and branched alkyl side chains at the air-water interface was examined on a Langmuir trough. The amphiphilic systems studied form stable monolayers when the straight chains are as short as n-propyl.…”