Complex Coacervate Formation on a Heterogeneous Membrane

Complex coacervation between gelatin type B (GE) and chia mucilage (ChM) was studied. GE-ChM were mixed at mass ratios of 1:1, 2:1, 3:1, 4:1, and 1:2 in a pH range of 1.50 to 5.00, maintaining a total solid concentration of 0.2% (w/w), using turbidity and viscosity tests to obtain the highest yield of complex coacervates. To characterize the complex coacervates, morphology and Fourier-transform infrared spectroscopy (FTIR) were determined. The optimum yield for complex coacervation was achieved with a GE-ChM mass ratio of 2:1 and pH value of 3.6. The critical pH values associated with the formation of soluble (pHc ) and insoluble (pHɸ1 ) complexes, and complete dissociation (pHɸ2 ) at the optimum GE-ChM ratio were found to be 4.50, 4.10, and 2.00, respectively. It was observed that increasing the mass ratio of GE or ChM, the yield of complex coacervates decreased; the higher yields were obtained with the proportions of 2:1 and 1:1 with values of 68.25 ± 0.05% and 61.04 ± 0.05%, respectively. Capsules formed at mass ratios of 1:1, 2:1, and 3:1, had the characteristic grape agglomerate shape for complex coacervates. Further characterization with scanning electron microscopy (SEM) showed a spherical shape for capsules. FTIR spectrum of complex coacervates at optimum conditions had a combination of bands corresponding to GE and ChM, suggesting an interaction between GE-ChM during the formation of complex coacervates. Therefore, complex coacervates between GE-ChM can be formed, and could be used as an alternative as encapsulating agents to be applied in the food industry. PRACTICAL APPLICATION: Complex coacervation is a technique that is being studied in several applications in the food industry. However, studies are still being made to explore different possibilities of natural sources to be used in complex coacervation. This study showed that the combination of gelatin and chia mucilage may be an alternative as encapsulating agents for complex coacervation to be applied in the food industry.

Active compartmentalization is a fundamental property of life, as well as a key element in cell regulation. In order to build synthetic systems with emergent cell‐like properties, we need to develop active compartments that form, disappear, and change properties autonomously over time. Here, we report a new strategy to induce temporal changes in coacervates using the urea‐urease reaction. This reaction triggers the dissolution of complex coacervates after a controllable delay, as it increases ionic strength through the production of ammonium carbonate. This delayed dissolution can be directly used for a broad range of complex coacervates without any synthetic effort. Furthermore, ammonium carbonate can also decompose over time, evaporating from the solution. This combination of enzymatic synthesis and spontaneous decomposition of salt leads to transient coacervate dissolution, which can be used for the controlled release of cargo and for the modulation of a compartmentalized reaction. Cycles of dissolution/reformation can be repeated multiple times without any waste generation, although the number of cycles is limited by the denaturation of urease. Finally, by combining polyelectrolytes with a protected dipeptide, ureolysis can trigger the formation of multiphase coacervates, as well as the sequential formation, dissolution, and aggregation of simple and complex coacervates.

This work utilizes the fluorescence properties of the membrane probes 1-acyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]-sn-Glycero-3-phosphocholine (DANSYL), and ergosta-5,7,9(11),22-tetraen-3[beta]-ol (ERGO) to detect and characterize laterally phase-separated, cholesterol-rich domains in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/cholesterol, and egg lecithin(Egg-PC)/cholesterol model membrane systems. Specifically, the DANSYL membrane probe shows evidence of lateral phase separations in DMPC/Cholesterol and Egg-PC/Cholesterol membrane mixtures and can reveal liquid-ordered to liquid-disordered phase boundaries. Fluorescence resonance energy transfer from ERGO to DANSYL is used to characterize the size of the putative laterally phase separated cholesterol-rich domains in model membrane systems. The DANSYL red shifting data provides evidence for the presence of a lateral phase separation in the cholesterol regime that was thought to be only in the liquid ordered phase. Simulations were conducted using two vertically-coupled square two-dimensional lattices to simulate membrane bilayers containing a uniform size distribution of cholesterol immiscible domains of a predetermined size distribution. We substitute cholesterols and phospholipids with their fluorescent analogs and calculate the efficiency of energy transfer as a function of acceptor concentration for four membrane configurations. We show that the FRET model yields good size estimates for domains that range between 1 and 25 nm. We also find that the assumed fluorophore configuration in the FRET model leads to a constant under-prediction of these values. Finally, we demonstrate that when two parameters are open to the fit, the FRET model adequately predicts the donor partition coefficient in addition to the domain size. Finally, we present a steady-state and time-resolved fluorescence emission spectra analysis of the membrane probe 1-myristoyl-2-[12-[(5-dimethylamino-1-naphthalenesulfonyl)amino]dodecanoyl]-sn-Glycero-3-phosphocholine (DANSYL) in 1,2-dimyristoyl-sn-glycero-3-phosphocholine and cholesterol multi-lamellar vesicles prepared by modified rapid solvent exchange. We report that the dose-dependent cholesterol-induced blue shifts in the steady-state fluorescence emission spectra in 1,2-dimyristoyl-sn-glycero-3-phosphocholine multi-lamellar vesicles are due to complex solvent effects that include time-dependent dipolar relaxation, and the formation of internal charge transfer states. A key finding of this study is identification of two distinguishable DANSYL populations existing at both shallow and deep locations in membrane, these two DANSYL populations are evidence of the presence of laterally phase separated domains.

Complex coacervation refers to the liquid-liquid phase separation (LLPS) process occurring between charged macromolecules. The study of complex coacervation is of great interest due to its implications in the formation of membraneless organelles (MLOs) in living cells. However, the impacts of the crowded intracellular environment on the behavior and interactions of biomolecules involved in MLO formation are not fully understood. To address this knowledge gap, we investigated the effects of crowding on a model protein-polymer complex coacervate system. Specifically, we examined the influence of sucrose as a molecular crowder and polyethylene glycol (PEG) as a macromolecular crowder. Our results reveal that the presence of crowders led to the formation of larger coacervate droplets that remained stable over a 25-day period. While sucrose had a minimal effect on the physical properties of the coacervates, PEG led to the formation of coacervates with distinct characteristics, including higher density, increased protein and polymer content, and a more compact internal structure. These differences in coacervate properties can be attributed to the effects of crowders on individual macromolecules, such as the conformation of model polymers, and nonspecific interactions among model protein molecules. Moreover, our results show that sucrose and PEG have different partition behaviors: sucrose was present in both the coacervate and dilute phases, while PEG was observed to be excluded from the coacervate phase. Collectively, our findings provide insights into the understanding of crowding effects on complex coacervation, shedding light on the formation and properties of coacervates in the context of MLOs.

Sub-ten-nanometer heterogeneity of solid supported lipid membranes determined by solution atomic force microscopy

Complex coacervates obtained from peptide leucine and gum arabic: Formation and characterization

In this research, gum Arabic (GA) and whey protein nanofibrils (WPN) were employed for the encapsulation of curcumin as a bioactive compound with low water solubility through the complex coacervation method. The optimum conditions for the formation of complex coacervates were found at WPN/GA weight ratio of 1:1 and pH value of 3.0. The resulting complexes showed a high ability for loading of curcumin as a bioactive cargo. Fluorescence spectroscopy showed that the curcumin was loaded in the hydrophobic core of WPN/GA coacervates. The characteristics of curcumin-loaded coacervates were also evaluated by XRD and FT-IR analysis. The curcumin-loaded complex coacervates dispersions showed a shear thinning behavior. They also showed a good surface activity which makes them excellent candidates to fabricate new functional food emulsions and beverages. The results indicated that the antioxidant activity and photo-stability of curcumin were significantly improved by encapsulation into WPN/GA complexes. A sustained-release profile also was investigated for curcumin from WPN/GA complexes in the simulated gastrointestinal conditions. This study suggested that the WPN/GA electrostatic-driven complexes can be used as efficient carriers for curcumin delivery.

Adhesion Stabilizes Robust Lipid Heterogeneity in Supercritical Membranes at Physiological Temperature

Complex coacervation between β-lactoglobulin and Acacia gum: A nucleation and growth mechanism

Nanoencapsulation of zeaxanthin extracted from Lycium barbarum L. by complex coacervation with gelatin and CMC

The present work aimed to study the influence of the pH and protein ratio on the formation of complex coacervates of carboxymethylcellulose (CMC) and whey protein isolated nanoparticles (WPIN). These biopolymers and transglutaminase, as a cross-linking agent, were used to encapsulate sacha inchi oil (SIO) containing β-carotene (β-C). The stability of β-C from SIO microcapsules (β-SIO microcapsules) was evaluated under in vitro digestion using an INFOGEST 2.0 in vitro digestion protocol. The release of β-C in a simulated food model was studied, and mathematical models were used to determine the mechanism. A ratio of 1:6 (CMC/WPIN) at pH 3.5 was used for the formation of the complex. Chemical and morphological analyses suggested that SIO was microencapsulated and that a high encapsulation efficiency was obtained. The β-C from β-SIO microcapsules was preserved in vegetable oil (food model), and Fickian diffusion occurred. The β-C from β-SIO microcapsules was preserved under oral and gastric conditions, and higher release occurred during intestinal digestion when samples were subjected to in vitro digestion simulation. After in vitro digestion, the β-C from β-SIO microcapsules presented higher stability (83.37%) and acceptable bioaccessibility (31.16%). There are few studies in the literature of encapsulated SIO using the CMC/WPIN complex or studies of the release of β-carotene from SIO during in vitro digestion and in food simulants. The knowledge obtained in this study will facilitate the use and applications of β-C-loaded microcapsule delivery systems.

In this paper, for the first time, we have reported the formation of complex coacervate during interaction between hydrophobic protein, zein, and hydrophilic nanoclay, Laponite, in a 60% v/v ethanol solution at pH 4. Dynamic light scattering and viscosity measurements revealed the formation of zein–Laponite complexes during the interaction between zein at fixed concentration, CZ = 1 mg/mL, and varying concentrations of Laponite, CL (7.8 × 10–4 – 0.25% w/v). Further investigation of the zein–Laponite complexes using turbidity and zeta potential data showed that these complexes could be demarcated in three different regions: Region I, below the charge neutralization region (CZ = 1 mg/mL, CL ≤ 0.00625% w/v) where soluble complexes was formed during interaction between oppositely charged zein and Laponite; Region II, the charge neutralization region (CZ = 1 mg/mL, 0.00625 < CL ≤ 0.05% w/v) where zein–Laponite complexes form neutral coacervates; and Region III, the interesting overcharged coacervates region (CZ = 1 mg/mL, CL > 0.05% w/v). Investigation of coacervates using a fluorescence imaging technique showed that the size of neutral coacervates in region II was large (mean size = 1223.7 nm) owing to aggregation as compared to the small size of coacervates (mean size = 464.7 nm) in region III owing to repulsion between overcharged coacervates. Differential scanning calorimeter, DSC, revealed the presence of an ample amount of bound water in region III. The presence of bound water was evident from the presence of an additional peak at 107 °C in region III apart from normal enthalpy of evaporation of water from coacervates.

We use direct simulations of particle-polyelectrolyte mixtures using the single chain in mean field framework to extract the phase diagram for such systems. At high charges of the particles and low concentration of polymers, we observe the formation of a coacervate phase involving the particles and polyelectrolytes. At low particle charges and/or high concentration of polymers, the mixture undergoes a segregative phase separation into particle-rich and polymer-rich phases, respectively. We also present results for the influence of particle charge heterogeneity on the phase diagram.

Ethylcellulose microparticles containing chitosan and gelatin: pH-dependent release caused by complex coacervation

Enhanced nutraceutical potential of cannabidiol derived from industrial hemp using plant based complex coacervates