Nature of the Interaction between a Peptidolipid Langmuir Monolayer and Paraoxon in the Subphase

Abstract

Surface potential and Infrared Reflection−absorption spectroscopy (IRRAS) measurements have been used to investigate the interaction between a peptidolipid (stearoyl−Phe−Trp−Ser−His−Glu) Langmuir monolayer and paraoxon aqueous solution as subphase. The molecular recognition in this system involved π−π interactions between the nitrobenzene group of paraoxon and aromatic groups in the peptidolipid. Of particular importance was the dependence of the surface potential on the concentration of paraoxon. Effects were practically negligible for 1.0 × 10-5 and 1.0 × 10-6 M paraoxon concentrations, but the Langmuir monolayer surface potential dropped due to the interaction with paraoxon at a concentration equal or higher than 1.0 × 10-4 M. At 1.5 × 10-3 M, the surface potential−area (ΔV−A) isotherm for the peptidolipid displayed an unusual shape, with an almost constant, near-zero surface potential during the monolayer compression. This was interpreted on the basis of IRRAS results as being due to reorientation of the benzene ring of paraoxon, which changed from parallel to the air−water interface in the absence of a monolayer to a tilted orientation upon interacting with the peptidolipid monolayer.

Nanomaterials for Diagnosis: Challenges and Applications in Smart Devices Based on Molecular Recognition

“…175 Such biosensors could be made from cholesterol oxidase 176,177 to detect cholesterol, from uricase 178,179 to detect uric acid, from urease to detect urea, 39,180−182 and from organophosphorous hydrolase (OPH) bonded to a fluorescein probe to detect paraoxon. OPH was also used for sensing paraoxon interacting with LbL films of chitosan 183 and for antibodies interacting with LB films of viologen and protein-A. 184 In biosensors produced with LbL films, the number of enzyme layers can increase the sensitivity owing to an increased amount deposited.…”

Surface FTIR Techniques to Analyze the Conformation of Proteins/ Peptides in H2O Environment

“…The technique of IRRAS for the Langmuir monolayer was developed in 1985 [33]. Subsequently, some proteins were shown to be also able to form a Lanmguir monolayer and IRRAS has been consequently used to analyze protein samples in the Langmuir monolayer [14,[34][35][36][37][38], which covers the surface of H 2 O. IRRAS can not only detect the FTIR signal of proteins, but also valuate the orientation of the proteins sample in the Langmuir monolayer due to the selection rules as discussed below [14,[34][35][36]38].…”

“…One variable is the polarization of the incident IR beam and the other is the incident angle, which is the angle between the incident IR beam and the normal of the air-water interface [38,39]. As shown in Figure 2, the incident IR beam and the normal of the air-water interface compose the incident plane.…”

“…As shown in Figure 2, the incident IR beam and the normal of the air-water interface compose the incident plane. If the electric field of the incident IR beam is polarized in the incident plane, the IR is p-polarized [38,39]. The IR is s-polarized when the electrical field is perpendicular to the incident plane [38,39].…”

“…If the electric field of the incident IR beam is polarized in the incident plane, the IR is p-polarized [38,39]. The IR is s-polarized when the electrical field is perpendicular to the incident plane [38,39]. The peak intensity of a certain vibration depends on the orientation of the vibration, the polarization, and the incident angle.…”