Crown ethers at the aqueous solution–air interface: 1. Assignments and surface spectroscopy

Abstract

The surface of aqueous solutions of 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5) has been studied using the surface sensitive technique vibrational sum frequency spectroscopy (VSFS). The NO, CN, COC and CH vibrational modes of these compounds at the air-water interface as well as OH vibrational modes of the surface water hydrating this compound have been targeted in order to obtain molecular information about arrangement and conformation of the adsorbed crown ether molecules at the air-water interface. The CH(2) vibrational modes of crown ethers have been identified and found to be split due to interaction with ether oxygen. The spectra provide evidence for the existence of a protonated crown complex moiety at the surface leading to the appearance of strongly ordered water species. The interfacial water species are influenced by the resulting charged interface and by the strong Zundel polarizability due to tunneling of the proton species between equivalent sites within the crown ring.

Mixtures of n-dodecyl-β-d-maltoside and hexaoxyethylene dodecyl ether — Surface properties, bulk properties, foam films, and foams

“…In an effort to more completely understand the hydration, spectroscopy and interfacial behaviour of ethyleneoxide head groups, experiments have been performed to attempt to constrain the EO and impose order upon it. This has been done by looking at crown ethers adsorbed at the air water interface [68]. These essentially consist of an ethyleneoxide chain (consisting of 5 EO units) which is pinned via ether linkages to adjoining carbons on a benzene ring.…”

Crown ethers at the aqueous solution–air interface. Part 2. Electrolyte effects, ethylene oxide hydration and temperature behaviour

“…All the spectral features analyzed in this study were fitted using a Lorentzian profile using the program Igor as described in our previous paper. 1…”

“…The peak assignments of the observed features present in this region for NB15C5 and B15C5 have been discussed in detail in the preceding paper. 1 Only NB15C5 was used to study the relationship between concentration and orientational response at the water-air interface. NB15C5 displays a good signal to noise ratio in both SSP and PPP polarization combinationsz in the region associated with the nitro moiety (n s (NO 2 ) and n(CN)).…”

“…This paper concerns the surface spectroscopy of crown ethers adsorbed at the aqueous solution interface and as such builds on a preceding paper. 1 In that paper the different vibrational modes belonging to two benzo-crown ethers and the ordered water of hydration in the slab interface y were identified and studied. Clear evidence was found that the crown-H 3 O + complex exists at the surface and leads to the appearance of highly ordered water species.…”

“…Theory A detailed explanation of the Vibrational Sum Frequency Spectroscopy (VSFS) theory can be found in other sources. 1,[10][11][12][13] Briefly, it is a nonlinear technique that provides information about the identity and orientation of species present at the interface with no contribution from the bulk solution, as well as their orientation. Under the electric dipole approximation, only molecules present in a noncentrosymmetric environment give a Sum Frequency (SF) response.…”