High Surface Pressure Research Articles

The effect of acyl chain length and saturation on the interactions of pirarubicin with phosphatidylethanolamines in 2D model urothelial cancer cell membranes

The interactions of an anticancer drug pirarubicin (THP) with a series of phosphatidylethanolamine (PE) lipids differing in the length and unsaturation degree of acyl chains were investigated using the Langmuir technique supplemented with Brewster angle microscopy (BAM) and thermodynamic analysis of compression-expansion cycles. The incorporation of the drug from the subphase into the lipid monolayer treated as a simple model of urothelial cancer cell membranes leads to the increase in the areas per molecule at lower surface pressures, while further compression of the monolayer at the air-water interface results in the expulsion of the drug. In the case of 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE) undergoing liquid expanded – liquid condensed (LE-LC) phase transition the isotherms in the presence and absence of THP are essentially indiscernible at higher surface pressures and the drug was found to locate in between the domains. For other lipids (1,2-distearoyl-sn-glycero-3-phosphoethanolamine, DSPE, 1-stearoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine, SOPE and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, DOPE) the isotherms recorded in the presence of THP were characterized by areas per molecule smaller than those for the isotherms obtained for lipids on a pure buffer. It shows that the drug, despite squeezing out from the lipid monolayer, is still interacting strongly with lipid molecules. The formation of THP/lipid aggregates takes place as shown by the results of the thermodynamic analysis for the compression-expansion cycles. It may explain a disruptive effect of THP on the lipid packing, which is supported by a decreased value of Cs−1max. The most significant interactions were observed for 1,2-dilinoleoyl-sn-glycero-3-phosphoethanolamine (DLOPE). Due to the tilt of the acyl chains caused by the presence of two double bonds in each chain, a pocket is formed allowing THP to effectively penetrate the hydrophobic part of the DLOPE monolayer even at higher surface pressures without squeezing-out effect. Interestingly, this penetration is not accompanied by any formation of lipid-drug aggregates as shown by thermodynamic analysis of hysteresis. Moreover, THP is also able to effectively incorporate into the preformed DLOPE layers. These results are important for the detailed explanation of the molecular mechanisms of the passive transport of THP through the urothelial cancer cell membranes, which are especially enriched in the longer chain, double unsaturated PE lipids such as DLOPE.

Langmuir layers of fullerene C60 and its mixtures with amphiphilic polymers

The application of dilational surface rheology and optical microscopy combined with the more conventional methods of surface tensiometry, ellipsometry and atomic force microscopy shows that the properties of mixed spread layers of fullerene C60 with poly(vinylpyrrolidone) (PVP) and poly(N-isopropylacrylamide) (PNIPAM) are determined by the polymer at low surface pressures (less than the maximum value for a pure polymer monolayer) and by the fullerene at higher surface pressures. In particular, the dependences of the dynamic surface elasticity on the surface pressure for the mixed layers have two local maxima corresponding to the polymer and fullerene. These results indicate that the layer consists of two separate phases at low surface pressures below the characteristic value of the polymer displacement from the interface. Although the collapse of the fullerene layers starts at surface pressures of far less than 70 mN/m, some patches of the layers sustain surface pressures up to this value. The high stability of the fullerene spread layer and its strong adhesion to water can be explained by the hydroxylation of the fullerene molecules where they contact the water. A similar explanation of the high stability of fullerene aggregates in bulk water has been proposed recently. The fullerene layer is heterogeneous and consists mainly of surface aggregates with dimensions of approximately 40–60 nm in the X-Y plane. The local folding of the layer of these aggregates at high surface pressures (>30 mN/m) leads to the striation patterns, which are typical for the collapse of nanoparticle monolayers.

Thermodynamic quantification of sodium dodecyl sulfate penetration in cholesterol and phospholipid monolayers

Sodium dodecyl sulfate (SDS) is one of the extensively used surfactants in bioprocesses. Present work analyzes the penetration of SDS in pure and mixed Langmuir monolayers consisting of 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol. A series of isotherms are obtained by compressing the monolayers over subphase containing varying concentrations of SDS. The extent of penetration of SDS is quantified in terms of its mole percentage in the monolayer by applying various thermodynamic equations derived from Gibbs adsorption equation. Analysis of pure monolayers shows that SDS penetration is directly correlated with the monolayer fluidity and the lipid packing density. We find that POPC monolayers, which do not pack closely on compression due to a kink in one of the acyl chains, exhibit higher SDS penetration than DPPC monolayers which are more rigid due to two saturated acyl chains that pack very efficiently. The SDS penetration is also analyzed in mixed lipid monolayers in which the lipids are present in molar proportions similar to that in the plasma membranes of mammalian cells. Thermodynamic quantification shows that mixed monolayers of DPPC with POPC (in 2:1 molar ratio) exhibit penetration similar to pure POPC monolayers indicating dominating effect of unsaturated phospholipids on membrane packing. We find lower SDS penetration in mixed cholesterol-POPC monolayers than pure POPC monolayers at all surface pressures and for all SDS subphase concentrations used. This confirms with the well-known condensation effect of cholesterol on POPC monolayers. Cholesterol is known to have a rigidifying effect on DPPC monolayers at low surface pressures and a fluidizing effect at high surface pressures. Consistent with these experimental observations, our thermodynamic quantification predicts lower SDS penetration at low pressures and higher penetration at high pressures when compared to pure DPPC monolayers. Thus, thermodynamic theories are able to accurately predict the experimentally observed trends for penetration in mixed monolayers of cholesterol with POPC and DPPC. Our work demonstrates that thermodynamic quantification is a reliable technique to estimate extent of penetration of various additives in pure and mixed lipid monolayers.

Cavity collapse near slot geometries

Abstract

Effect of polydispersity on the behaviour of the particle-laden interface

This paper studies the effect of polydispersity on the behaviour of micron size particles spread at the air–water interface using a modified Langmuir trough. Surface pressure isotherms of particles with different polydispersity prepared by mixing large and small particles in various ratios were studied. Upon lateral compression, the surface pressure of the monolayer consisting of the unimodal samples was found to increase faster than the surface pressure of the layer formed with the bimodal samples. Compared to the unimodal samples, the bimodal sample monolayers had higher compressibility at the highest surface pressure. The results showed an increasingly loose structure and smaller domains with an increasing ratio of large particles in the monolayer. A single bubble beneath the particle layer was grown and allowed to coalesce with the layer. The structure and motion of particles following the coalescence process was recorded by a high-speed camera. A mean square displacement was calculated from the trajectory of selected particles to evaluate the movement of these particles during the coalescence of the bubble with the particle layer. The peak of mean square displacement was higher for low packing density and lower at high packing density, indicating the particles have more movement at low packing density than at high packing density. It was also shown that the particles became more mobile with an increase in the proportion of large particles in the layer.

Enzyme activity preservation for galactose oxidase immobilized in stearic acid Langmuir-Blodgett films

The adsorption of the enzyme galactose oxidase onto stearic acid Langmuir monolayers was investigated with surface pressure-area isotherms, Brewster Angle Microscopy and polarization-modulated infrared reflection-absorption spectroscopy. The enzyme was incorporated in the monolayer at low surface pressures, expanding the lipid films, and further monolayer compression expelled it from the contact with the air phase and repositioned the enzyme below the lipid polar heads. The enzyme-lipid system was then stabilized by electrostatic interactions, leading the monolayer to condense at higher surface pressures, reducing the number of interfacial aggregates. The lipid-enzyme interactions at the interface made the monolayer less viscoelastic and more disordered as pointed by the reduced compressional modulus and decreased trans/gauche ratio for the lipid acyl chains. Also, the secondary structures of the adsorbed enzyme were kept as demonstrated with infrared spectroscopy. The condensed enzyme-lipid monolayer was transferred to solid supports as Langmuir-Blodgett films and the enzyme activity was detected, being preserved for one month. These results show how the molecular organization provided by the ultrathin films can help maintain the catalytic activity for immobilized enzymes, which is important, general speaking, for nanotechnology and biosensing manufacturing.

Development of adhesion preventing method during deep drawing of TP340 titanium sheets

ABSTRACT Generally, the adhesion of titanium alloys easily occurs between die and blank during press forming because the sliding and contact surface of die and blank with high surface pressure. In the case of titanium alloy sheets, it is especially difficult to prevent the adhesion. Thus, the various studies to prevent the occurrence of adhesion during press forming of titanium alloy sheets were carried out. For example, deep drawing with oil lubrication and with diamond-like carbon (DLC) coated die, it was difficult to prevent the adhesion, so the combination of DLC coated die and lubrication oil were utilised and the adhesion was prevented. Hence, it is necessary to develop the preventing method of the adhesion on die during deep drawing process. We have focused on the prevention of titanium surface oxide film peeling during deep drawing process to prevent the adhesion. We have developed the method to prevent the adhesion during dry deep drawing process. In this study, the compressed air was applied into die and the blank holding force with vibration technique was utilised during dry deep drawing of TP340 sheets. As a result, the occurrence of adhesion was prevented significantly by the application of developed methods.

Nanofibrous Membranes with High Air Permeability and Fluffy Structure based on Low Temperature Electrospinning Technology

Due to its small diameter and high density, electrospun nanofiber membranes have high resistance which obstacles their application. In this paper, we proposed a new electrospinning method based on low-temperature, which can affect the deposition process of electrospinning by utilizing the freezing process of steam in the receiving plate. The filling and supporting of ice could enlarge the pores of membranes and intervals among fibers, which caused the high porosity (92 %), rough surface, fluffy structure and low pressure drop (123 Pa) of polyvinylidene fluoride (PVDF) nanofibrous membranes. The results suggested that the electrospinning method is a promising way to prepare nanofibrous membranes with high air permeability and fluffy structure for air filtration.

Nanocellulose for Stabilization of Pickering Emulsions and Delivery of Nutraceuticals and Its Interfacial Adsorption Mechanism

Nanocellulose proved to be an efficient material for the preparation of Pickering emulsions with potential for replacing synthetic surfactants, which show toxic effects in the gastrointestinal (GI) tract. Its self-assembling capability, tensile strength, and stiffness make it an efficient material for stabilization of emulsions. Nanoemulsion systems stabilized with nanocellulose (NC) can be prepared for delivery of nutraceuticals with therapeutic utilities and achieving their controlled release in the GI tract. Stable emulsions can be produced even when the surface of droplets is covered by a low amount of NCs. Hydrophobic modification of NCs enhances their dispersibility in nonpolar solvents, and modification with cationic surfactants enables the production of emulsions with transitional phase inversion and production of water-in-oil emulsions. Grafting NCs with responsive polymers provides the opportunity of producing smart emulsifiers for delivery of nutraceuticals. The adsorption of NCs at the interfaces is influenced by their surface chemistry and charge and the emulsion conditions such as pH, temperature, and ionic strength. Their adsorption can be explained based on particle diffusion to the interface and charge-induced kinetic adsorption barrier. Modification of NCs allows achieving faster adsorption and higher surface pressure and surface coverage. Considering the economic and environmental benefits of NCs in replacing nonrenewable materials and their potential in producing stable Pickering emulsions, this review aims to highlight recent studies on the application of NCs for stabilization of Pickering emulsions and delivery of nutraceuticals, and discusses their interfacial adsorption mechanism, influenced by processing conditions, providing insights to food and drug manufacturers.

Probing Interfacial Structure and Dynamics of Model and Natural Asphaltenes at Fluid-Fluid Interfaces.

Asphaltenes are largely responsible for crude oil interfacial behavior. Due to their complex molecular nature, studying connections between interfacial properties and molecular structure is challenging, and these connections remain unclear. Several groups have reported on the interfacial behavior of asphaltenes, but a unified picture of both interfacial dynamics and thermodynamics is still missing. We seek to establish connections between asphaltene interfacial morphology and interfacial dynamics by combining interfacial dilatational deformation with microscopic structural imaging analysis. Understanding the behavior of natural asphaltene samples is made difficult by the inherent molecular variability. Therefore, we have also studied the behavior of an asphaltene model compound to draw fundamental structure-property relationships. This work contains simultaneous interfacial deformation and microscopy in systems of natural and model asphaltenes at air-water and decane-water interfaces. How the dynamics of natural asphaltenes influences the morphological and thermodynamic state of the air-water and decane-water interfaces is discussed based on the deviations observed between isotropic and anisotropic deformations. Areas where model asphaltenes can help us to understand the behavior of natural asphaltenes are identified such as its high surface pressure activity and aggregation character. An aggregation mechanism for model and natural asphaltenes is proposed based on an observed relationship between microscopic and millimetric aggregates.

Correlating mono- and bilayers of lipids to investigate the pronounced effects of steroid hormone 17α-ethynylestradiol on membrane models of DPPC/cholesterol

Risks to human health have been reported owing to prolonged exposure to hormones, whose action depends on their molecular-level interaction with cell membranes. In this study, we investigate the interaction of the synthetic hormone 17 α-ethynylestradiol (EE2) in two different membrane models, Langmuir monolayers and giant unilamellar vesicles (GUVs) made with a binary mixture of 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and cholesterol (Chol) in order to mimic the plasma membrane of mammalian cells. EE2 was found to expand the Langmuir monolayers, with shifts to larger areas per molecule in the surface pressure isotherm. In all of these observations, stronger effects were noted for the DPPC/Chol monolayers with XChol = 0.3, which mimics the proportion of phospholipid/sterol in the plasma membrane. At high surface pressures, EE2 is believed to weaken the attractive interactions between DPPC and Chol, in addition to affecting the ordering of the lipid chains as indicated in polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) measurements. In GUVs obtained with XChol = 0.3 mixtures, EE2 induced a phase contrast loss as a result of increased permeability of the lipid bilayer. The results with Langmuir monolayers and GUV combined point to EE2 action on representative cell membranes, which can be correlated with physiological effects caused by indirect intake of EE2.

Oceanographic Considerations for Exoplanet Life Detection

Abstract Liquid water oceans are at the center of our search for life on exoplanets because water is a strict requirement for life as we know it. However, oceans are dynamic habitats—and some oceans may be better hosts for life than others. In Earth’s ocean, circulation transports essential nutrients such as phosphate and is a first-order control on the distribution and productivity of life. Of particular importance is upward flow from the dark depths of the ocean in response to wind-driven divergence in surface layers. This “upwelling” returns essential nutrients that tend to accumulate at depth via sinking of organic particulates back to the sunlit regions where photosynthetic life thrives. Ocean dynamics are likely to impose constraints on the activity and atmospheric expression of photosynthetic life in exo-oceans as well, but we lack an understanding of how ocean dynamics may differ on other planets. We address this issue by exploring the sensitivity of ocean dynamics to a suite of planetary parameters using ROCKE-3D, a fully coupled ocean–atmosphere general circulation model. Our results suggest that planets that rotate slower and have higher surface pressure than Earth may be the most attractive targets for remote life detection because upwelling is enhanced under these conditions, resulting in greater nutrient supply to the surface biosphere. Seasonal deepening of the mixed layer on high-obliquity planets may also enhance nutrient replenishment from depth into the surface mixed layer. Efficient nutrient recycling favors greater biological activity, more biosignature production, and thus more detectable life. More generally, our results demonstrate the importance of considering oceanographic phenomena for exoplanet life detection and motivate future interdisciplinary contributions to the emerging field of exo-oceanography.

Relationships of ozone formation sensitivity with precursors emissions, meteorology and land use types, in Guangdong-Hong Kong-Macao Greater Bay Area, China

Due to the influences of precursors emissions, meteorology, geography and other factors, ozone formation sensitivity (OFS) is generally spatially and temporally heterogeneous. This study characterized detailed spatial and temporal variations of OFS in Guangdong-Hong Kong-Macao Greater Bay Area (GBA) from 2012 to 2016 based on OMI satellite data, and analyzed the relationships of OFS with precursors emissions, meteorology and land use types (LUTs). From 2012 to 2016, the OFS tended to be NOx-limited in GBA, with the value of FNR (HCHO/NO2) increasing from 2.04 to 2.22. According to the total annual emission statistics of precursors, NOx emissions decreased by 33.1% and VOCs emissions increased by 35.2% from 2012 to 2016, directly resulting in OFS tending to be NOx-limited. The Grey Relation Analysis results show that total column water (TCW), surface net solar radiation (SSR), air temperature at 2 m (T2) and surface pressure (SP) are the top four meteorological factors with the greatest influences on OFS. There are significant positive correlations between FNR and T2, SSR, TCW, and significant negative correlations between FNR and SP. In GBA, the OFS tends to be NOx-limited regime in wet season (higher T2, SSR, TCW and lower SP) and VOCs-limited regime in dry season (lower T2, SSR, TCW and higher SP). The FNR displays obvious gradient variations on different LUTs, with the highest in “Rural areas”, second in “Suburban areas” and lowest in “Urban areas”.

Warming early Mars with climate cycling: The effect of [formula omitted]-[formula omitted] collision-induced absorption

Explaining the evidence for surface liquid water on early Mars has been a challenge for climate modelers, as the sun was ∼30% less luminous during the late-Noachian. We propose that the additional greenhouse forcing of CO2-H2 collision-induced absorption is capable of bringing the surface temperature above freezing and can put early Mars into a limit-cycling regime. Limit cycles occur when insolation is low and CO2 outgassing rates are unable to balance with the rapid drawdown of CO2 during warm weathering periods. Planets in this regime will alternate between global glaciation and transient warm climate phases. This mechanism is capable of explaining the geomorphological evidence for transient warm periods in the martian record. Previous work has shown that collision-induced absorption of CO2-H2 was capable of deglaciating early Mars, but only with high H2 outgassing rates (greater than ∼600 Tmol/yr) and at high surface pressures (between 3 to 4 bars). We used new theoretically derived collision-induced absorption coefficients for CO2-H2 to reevaluate the climate limit cycling hypothesis for early Mars. Using the new and stronger absorption coefficients in our 1-dimensional radiative convective model as well as our energy balance model, we find that limit cycling can occur with an H2 outgassing rate as low as ∼300 Tmol/yr at surface pressures below 3 bars. Our results agree more closely with paleoparameters for early martian surface pressure and hydrogen abundance.

Real-time monitoring of the effect of carbon nanoparticles on the surface behavior of DPPC/DPPG Langmuir monolayer

Air pollution has become increasingly serious. Fine particulate matter (PM2.5) is the most well-known air pollutant, which leads to some common respiratory diseases when inhaled into the lungs to certain concentration. However, there is a lack of research on the process of dynamically monitoring the real-time effect of nanoparticles on the pulmonary surfactant monolayer. In this study, the DPPC/DPPG monolayer is prepared by the Langmuir method to simulate the lung surfactant monolayer during respiration and the carbon nanoparticles are introduced to the monolayer under different surface pressures to simulate the real dynamic process of inhaling nanoparticles during breathing. The effect of carbon nanoparticles on the surface behavior of DPPC/DPPG monolayer in real-time was examined in details by a combination of surface pressure (π)-area (A) isotherms, compressibility modulus (Cs-1)-surface pressure (π) isotherms and the Brewster angle microscopy (BAM). The results have shown that the introduction of carbon nanoparticles under different surface pressures affects the properties of lipid monolayers. The added carbon nanoparticles under lower surface pressure are easy to penetrate the lipid molecules to inhibit monolayer phase transition. When the carbon nanoparticles are introduced to the monolayer under higher surface pressure, they tend to self-aggregate to reduce the monolayer stability rather than interact with lipid tail chains. This work not only confirms the exotic hydrophobic carbon nanoparticles retain in the DPPC/DPPG monolayer irreversibly and affect the surface behavior of monolayer during respiration, but also opens a new idea for real-time monitoring of the effects of PM2.5 on lung health.

Scaling of cylinder-generated shock-wave/turbulent boundary-layer interactions

Scaling parameters of shock-wave/turbulent boundary-layer interactions generated by a semi-infinite standing cylinder were explored in a combined numerical and experimental effort, consisting of Reynolds-averaged Navier–Stokes simulations and high-speed schlieren imaging. The primary interaction variable, the cylinder diameter (d), and a secondary interaction variable, the boundary-layer thickness ($$\delta $$), were varied to study the effects of the parameter $$d/\delta $$. This was found to be an appropriate scaling parameter for mean features. The characteristic interaction variables (the maximum separation distance, S, and the triple-point height, $$h_\mathrm{tp}$$) followed a linear trend when normalized as $$S/\delta $$ and $$h_\mathrm{tp}/\delta $$; however, when the boundary layer became larger than the cylinder diameter, a power law trend became more representative. The parameter $$d/\delta $$ also determined the role that viscous effects have on the strength of the interaction, where a lower $$d/\delta $$ was characterized by a greater interaction scale and lower surface pressure peaks. Moreover, the high surface pressure on the cylinder leading edge due to the Edney interaction was found to be reduced for $$d/\delta \le 0.45$$, as the boundary layer encompassed the lambda-shock structure. Trends in the shapes or peaks of the auto-spectral density function were not observed based on $$d/\delta $$, but appeared to be dominated by broadband low-frequency ($$f < 1~\hbox {kHz}$$) content. While the position and structure of the interaction may change as a result of varying $$d/\delta $$, the effects on the unsteady dynamics were minimal.

A Composite Analysis of Snowfall Modes from Four Winter Seasons in Marquette, Michigan

AbstractPresented are four winter seasons of data from an enhanced precipitation instrument suite based at the National Weather Service (NWS) Office in Marquette (MQT), Michigan (250–500 cm of annual snow accumulation). In 2014 the site was augmented with a Micro Rain Radar (MRR) and a Precipitation Imaging Package (PIP). MRR observations are utilized to partition large-scale synoptically driven (deep) and surface-forced (shallow) snow events. Coincident PIP and NWS MQT meteorological surface observations illustrate different characteristics with respect to snow event category. Shallow snow events are often extremely shallow, with MRR-indicated precipitation heights of less than 1500 m above ground level. Large vertical reflectivity gradients indicate efficient particle growth, and increased boundary layer turbulence inferred from observations of spectral width implies increased aggregation in shallow snow events. Shallow snow events occur 2 times as often as deep events; however, both categories contribute approximately equally to estimated annual accumulation. PIP measurements reveal distinct regime-dependent snow microphysical differences, with shallow snow events having broader particle size distributions and comparatively fewer small particles and deep snow events having narrower particle size distributions and comparatively more small particles. In addition, coincident surface meteorological measurements indicate that most shallow snow events are associated with surface winds originating from the northwest (over Lake Superior), cold temperatures, and relatively high surface pressures, which are characteristics that are consistent with cold-air outbreaks. Deep snow events have meteorologically distinct conditions that are accordant with midlatitude cyclones and frontal structures, with mostly southwest surface winds, warmer temperatures approaching freezing, and lower surface pressures.

A detailed investigation on interactions between magnetite nanoparticles functionalized with aminated chitosan and a cell model membrane.

Magnetite nanoparticles are promising materials for application in magnetic resonance imaging, targeted drug delivery, enzyme immobilization and cancer therapies based on hyperthermia thanks to their biocompatibility, wide chemical affinity and superparamagnetic properties. However, there is still the lack of the knowledge of interactions between magnetite nanoparticles covered with the bioactive polymers and biological cells. In order to fulfil this gap, we have investigated interactions of newly synthetized magnetite nanoparticles functionalized with aminated chitosan (Fe3O4-aminated chitosan) and a model biological membrane made of dipalmitoylphosphatidylcholine (DPPC) using a Langmuir technique. Surface pressure-mean area per DPPC molecule isotherms and Brewster angle microscope images (BAM) recorded during compression of the two-component Fe3O4-aminated chitosan:DPPC films revealed the strong influence of the Fe3O4-aminated chitosan nanoparticles on the stability, phase state and structure of the phospholipid membrane. The studies on the adsorption/incorporation process of the Fe3O4-aminated chitosan nanoparticles showed that they can adsorb/incorporate into the DPPC model membrane at the surface pressure corresponding to this present in the cellular membrane under the biological conditions (35mN·m-1). The number of the adsorbed/incorporated Fe3O4-aminated chitosan nanoparticles can be regulated by the nanoparticles concentration in the neighbourhood of the DPPC model membrane even at high surface pressure of 35mN·m-1.

Tyrosinase enzyme Langmuir monolayer: Surface chemistry and spectroscopic study

This study investigates the surface chemistry properties of the tyrosinase enzyme Langmuir monolayer at air-aqueous interface using sodium chloride in the subphase to induce the surface activity of the enzyme. Investigation of surface packing and stability of the tyrosinase Langmuir monolayer were performed using surface chemistry experiments while spectroscopic analysis was done to study enzyme conformation. It was found that the tyrosinase enzyme forms a fluid film at air-aqueous interface with good stability as shown by compression-decompression cycles experiments and stability measurements at various surface pressures. UV-vis absorption and fluorescence measurements at different surface pressures revealed that the Langmuir monolayer has good homogeneity with no evidence of aggregates during compression. To gain insight on the conformation of tyrosinase Langmuir monolayer p-polarized infrared-reflection absorption spectroscopy was used. It was found that at high surface pressures the predominant secondary structures were β-sheets while at lower surface pressure both α -helices and β-sheets were present. The circular dichroism spectra were obtained by transferring the Langmuir monolayer at 10 mN.m−1 to a solid quartz support (Langmuir-Blodgett film, LB film), which showed that the major conformation present were α-helices. Images from the immobilized LB films were obtained using atomic force microscopy which showed homogenous and regular deposition with a mean thickness ranging from 3 to 4 nm.

-Identification of a novel intestinal phospholipase A2 from annular seabream: Insights into its catalytic mechanism and its role in biological processes

Phospholipase A2 (PLA2) is responsible for the lipid hydrolysis process. Fish PLA2 have warranted renewed interest due to their excellent properties in phospholipid digestion. We report for the first time the catalytic properties of a PLA2 secreted from the intestine of the annular seabream Diplodus annularis (IDaPLA2). The refolded IDaPLA2 was purified to homogeneity and showed a molecular mass of around 15 kDa attested by SDS-PAGE and MALDI-TOF analyses. Interestingly, IDaPLA2 revealed higher thermostability compared to mammal pancreatic sPLA2 as it was active and stable at 55 °C with specific activity of 290 U mg−1 on phosphatidylcholine (PC) as a substrate. Using the lipid monolayer technique, the activity of IDaPLA2 was found to be 21.68, 6.88 and 5.66 mol cm−2 min−1 mM−1 using phosphatidylglycerol (PG), PC and phosphatidylethanolamine (PE) monolayers, respectively, at surface pressures from 20−30 mN m−1. Interestingly, the interfacial activity of IDaPLA2 measured at higher surface pressures may highlight its ability to penetrate into phospholipid monolayers suggesting its involvement in cell lipid membrane degradation which can explain the cytotoxicity potential towards macrophage. The docking simulation data provided insights into the involvement of some key amino-acids in substrate binding and selectivity. The dynamic simulation proved the high stability of IDaPLA2. Overall, these results provide original evidence on the involvement of IDaPLA2 into the lipid hydrolysis suggesting it as a potential target in biotechnological applications.