In Situ IRRAS Studies of NH Stretching Bands and Molecular Structures of the Monolayers of Amphiphiles Containing Amide and Amine Units at the Air−Water Interface

Abstract

The monolayers of the amphiphiles containing amide and amine units at the air-water interface on water surface have been studied using infrared reflection absorption spectroscopy (IRRAS). Sharp NH stretching bands are observed in the monolayers of N-octadecanoyl-l-alanine (ALA) (at pH 3.0) and N-octadecyloxalamide (OXA), while no NH stretching band is clearly detected in the monolayers of octadecan-1-amine (OA) and N-hexadecylethane-1,2-diamine (EDA) (at pH 9.3). It is considered that the presence and absence of the NH stretching bands are related to properties of amides and amines, roles of N-H bonds in hydrogen bond donor/acceptor, and orientation of transition moment directions of NH stretching vibrations. The intermolecular hydrogen-bonding interactions between the adjacent amides of ALA and OXA induce the parallel packing of the CCC planes of corresponding alkyl chains, while the chains are uniaxially oriented in the monolayers of OA and EDA. In the presence of CuCl2 in the subphase, Cu2+ ions coordinate to the headgroups of OA and EDA in the monolayers; moreover a new peak at 1220 cm(-1) is observed for the EDA monolayer and assigned to the CH2 twisting and wagging modes relevant to the ethylenediamine headgroups. The presence of the peak is related to the dehydration of the headgroups induced by the twisted tetrahedral coordination, and the coordinated headgroups undergo an orientation change with surface pressure.

In situ observation of peptide bond formation at the water–air interface

“…S2) under the same experimental conditions presented here. It has been proposed in the literature that metal complexes with amines at the air-water interface induced through surface compression can result in an orientational change of the molecules residing at the surface (36). The orienting effect of the complex at the surface promotes subsequent condensation to form peptide products as observed in our studies.…”

In Situ IRRAS Studies of Molecular Recognition of Barbituric Acid Lipids to Melamine at the Air–Water Interface

“…The assignments of the bands for the monolayers are listed in Table . We first reported in situ IRRAS detection of NH stretching vibrational bands from the monolayers at the air–water interface, and those NH stretching bands resulted from amide groups of the host monolayers. − Herein, the detected NH 2 stretching bands were attributed to the vibrational transitions of amino groups of recognized melamine molecules. NH stretching bands from amino groups at the air–water interface have not been observed using the IRRAS technique before.…”

Unraveling Tryptophan Modulated 2D DPPC Lattices: An Approach toward Stimuli Responsiveness of the Pulmonary Surfactant

“…Membrane lipid perturbation by tryptophan in the subphase could have arisen either from the acyl chain interfacial region or from the polar headgroup. However, most studies on the physical state of the membrane have been carried out using the C–H asymmetric and symmetric stretching bands …”

“…Thus, the two δ(N + (CH 3 ) 3 ) absorption bands belonging to E and A 1 symmetries are centered at 1475 and 1496 cm À1 for water and at 1480 and 1495 cm À1 for tryptophan subphase, corresponding to out of phase degenerative bending and in-phase symmetric bending modes, respectively. Since the choline portion of the headgroup will not form a hydrogen bond 37 with H 2 O, a difference of ∼5 cm À1 for E symmetry (cf. Table 1) indicates the environment of choline moiety to have been affected by tryptophan through cationÀπ and electrostatic interactions.…”

“…However, most studies on the physical state of the membrane have been carried out using the CÀH asymmetric and symmetric stretching bands. 37 The temperature dependent intensity ratios (cf. Figure S3, SI) for DPPC monolayers gave clear explanation where tryptophan induced a broad LE -LC phase transition.…”