Langmuir Films of p-tert-Butylcalix[8]arene. Conformations at the Water−Air Interface and Complexation of Fullerene C₆₀

Abstract

Langmuir monolayers of p-tert-butylcalix[8]arene (CAL8) at the water−air interface were studied as a function of temperature (between 288 and 308 K), of the spreading solvent (benzene, toluene, dichloromethane, chloroform, and carbon tetrachloride), and in a mixture with fullerene C60. Two different mixed systems were studied: (i) spreading isotherms (surface pressure versus molecular area) after separated spreading of CAL8 and C60 solutions (1/1 molar ratio) and (ii) spreading isotherms of the C60−CAL8 complex obtained from precipitation of freshly prepared and stabilized solutions of the two components in carbon tetrachloride. The results show that, at the water−air interface, CAL8 possesses a perpendicular “pleated-loop” conformation, regardless of the spreading solvent. However, the limiting areas do depend on the nature of the spreading solvent, indicating that the flexibility of the CAL8 backbone is significantly affected by the interactions with the spreading solvent, in analogy with the “memory effect” with the retention of the host conformation, even after the removal of the guest, found for bulk solutions. The complexation of C60 by CAL8 does not modify the calixarene's conformation. Films obtained by spreading equimolar solutions of CAL8 and C60 on the water surface show the same Π/A isotherms of the [C60−CAL8] complex, suggesting the formation of stable CAL8/C60 1/1 complexes at the air−water interface. Electronic spectra performed on Langmuir−Blodgett films and on collapsed material, both transferred on quartz plates, support the presence at the interface of the [C60−CAL8] host−guest system, indicating that the water interface acts as a complexation promoter.

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

“…This maximum head-group area is reflected in the transition observed for 3, 6, 8, and 9 at 130 2 ( Figure 1). The higher collapse pressures observed for pyrogallol [4]arenes bearing hexyl (6), nonyl (8), and dodecyl (9) side chains than for pyrogallol [4]arene 3 with a propyl side chain results from stronger van der Waals interactions of the longer alkyl chains. It is notable that the collapse pressures for 6, 8, and 9 are the same.…”

“…In a few cases, the side chains are functionalized, for example by a terminal halogen atoms. [8] A goal to prepare previously unstudied Pgs with branched side chains and to exploit interchain interactions that might augment or alter the organizational tendencies of the Pg head groups, was strongly encouraged by the results described above. Thus, compounds 4, 5, and 7, which have 2-propyl, 3-pentyl, and 4-heptyl side chains, respectively, were prepared, characterized, and studied.…”

“…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. Host-guest interactions involving these macrocycles have also been explored, especially the ability of calix[n]arene and calix [n]resorcinarenes to complex both alkali [17] and polyatomic cations [5] present in the subphase.…”

Studies on Mixed Monolayers and Langmuir–Blodgett Films of Schiff-Base Complex Cu(SBC18)2 and Calix[4]arene

“…7, the characterization absorptions are 279, 291 nm and 303, 345 nm for calix [4]arene and Cu(SBC 18 ) 2 , respectively. However, the bands of mixture with 1 : 1 Cu(SBC 18 ) 2 : calix [4]arene are not the simple adduct of the two components' absorptions and some degree of shift can be observed, indicating that interaction arising from headgroups truly exists in mixed LB films (25), which can be explained by the molecular arrangement shown in Fig. 6.…”

Structural Effects on the Langmuir Monolayers of Calix[4]arene Induced by Lower Rim Aromatic Substitution

“…Since calixarenes as the frequently used host compounds were introduced into the interface science at the end of 1980s, [1][2][3][4][5][6][7] Langmuir monolayers and Langmuir-Blodgett (LB) films of calixarenes have shown interesting properties and promising prospect. [8][9][10][11][12][13] Besides calixarene with long alkyl chains, [14][15][16] Shinkai has demonstrated that lower rim calix [4]arene esters without long alkyl chains can also form stable monolayers at the air/water interface, and the monolayers are able to recognize alkali cations.…”