Surface Chemistry Studies on the Formation of Mixed Stearic Acid/Phenylalanine Dehydrogenase Langmuir and Langmuir–Blodgett Films

Abstract

This work investigates the physicochemical properties of mixed stearic acid (HSt)/phenylalanine dehydrogenase enzyme (PheDH) Langmuir films and their immobilization onto solid supports as Langmuir−Blodgett (LB) films. PheDH from the aqueous subphase enters the surfactant matrix up to an exclusion surface pressure of 25.3 mN/m, leading to the formation of stable and highly condensed mixed Langmuir monolayers. Hydrophobic interactions between the enzyme and HSt nonpolar groups tuned the secondary structure of PheDH, evidenced by the presence of βsheet structures as demonstrated by infrared and circular dichroism spectra. The floating monolayers were successfully transferred to solid quartz supports, yielding Y-type LB films, and then characterized employing fluorescence, circular dichroism, and microscopic techniques, which indicated that PheDH was co-immobilized with HSt proportionally to the number of transferred layers. The enzyme fluidized the HSt monolayers, reducing their maximum dipoles when condensed to their maximum, and disorganized the alkyl chains of the fatty acid, as detected with infrared spectroscopy. The stability of the mixed floating monolayers enabled their transfer to solid supports as LB films, which is important for producing optical and electrochemical sensors for phenylalanine whose molecular architecture can be controlled with precision.

The Past and the Future of Langmuir and Langmuir–Blodgett Films

“…Since enzymes are soluble in water, the formation of stable LB films requires optimization in Langmuir films . A stable quantity of enzymes at the air–water interface may be guaranteed either by using a high ionic strength in the aqueous subphase for the salting-out effect or by incorporating the enzyme in insoluble amphiphiles from the aqueous subphase. ,, In the latter case, the organized proteo-lipidic nanostructure provides a biomimetic environment for biocatalysis and bioelectronic devices. The LB films containing enzymes (pure or mixed with lipids) can be exposed to samples (usually liquid) with analytes that interact specifically with such enzymes.…”

Life at the interface: Engineering bio‐nanomaterials through interfacial molecular self‐assembly

“…Incorporation of graphene was found to productively alter the adsorbed enzyme's thermodynamic, structural, and metabolic properties, ultimately preserving functional protein on a supported air‐solid film (Scholl et al, 2022). This same group has demonstrated tunable catalytic activity of the enzymes asparaginase, urease, and phenylalanine dehydrogenase when co‐embedded within air‐solid assembled lipid films using carbon nanotube and algal polysaccharide additives (da Silva et al, 2021; Possarle et al, 2020; Rodrigues et al, 2018). These studies highlight the ability to exploit steric crowding at the surface of air‐solid interfaces to tune the bioactivity of physiosorbed proteins.…”