Coacervate Droplets Research Articles

Preparation of agglomerated crystals for direct tabletting and microencapsulation by the spherical crystallization technique with a continuous system.

Adhesive and cohesive properties of chlorpromazine hydrochloride (CP) crystals were modified to improve their powder processing, e.g., direct tabletting and microencapsulation, by agglomeration. Moreover, sustained-released gelling microcapsules of CP were devised to prolong the pharmacological effect. The spherical crystallization technique was applied to prepare agglomerates for direct tabletting and microencapsulation to use them as core materials. The ethanolic solution dissolving CP was poured into a stirred cyclohexane, yielding spherically agglomerated crystals. The resultant agglomerates were free-flowing and easily packable spheres with average diameters of 200 to 1000 microns. The agglomerates reserved the high compressibility of the original powder having a small particle size (14 microns). The compression behavior represented by Heckel's equation suggested that the agglomerates were disintegrated to individual primary crystals at low compression pressures, and then they were closely repacked and plastically deformed at higher pressures. After agglomeration, microencapsulation was continuously performed in the same batch by a phase separation method. Coacervate droplets produced by pouring cyclohexane into a dichloromethane solution, dissolving polyvinyl acetate as a coating polymer, were added to the crystallization system under stirring, to prepare the microcapsules. By filling the microcapsules in gelatin hard capsules or tabletting them, their drug release rates became retarded compared with the physical mixture treated in the same way, having the same formulation as the microcapsules. This phenomenon was due to the gelation of polyvinyl acetate of the microcapsules in the dissolution medium, whose glass transition temperature is very low. This novel sustained-release dosage form is termed "gelled microcapsules."

One continuous process of agglomeration and microencapsulation for enoxacin. Preparation method and mechanism of microencapsulation.

A novel microencapsulation method was developed by using the wet spherical agglomeration (WSA) technique. Spherical agglomerates containing enoxacin (ENX) or lactose were prepared in the acetone-n-hexane-ammonia water (or distilled water) solvent system, and were microencapsulated continuously with the aminoalkylmethacrylate copolymer (Eudragit RS). Microencapsulation was performed with a modified organic phase separation by the non-solvent addition method. By selecting proper composition ratio of acetone and n-hexane, the WSA solvent system turned to a non-solvent for a wall material, i.e. Eudragit RS. Dichloromethane was used as a good solvent because it did not affect the characteristics of spherical agglomerates prepared in the WSA system. With this technique the Eudragit RS coacervate droplets were firstly generated in the solvent composed of a higher acetone volume ratio in the acetone/n-hexane mixture, and continuously the coacervate droplets were deposited efficiently onto the agglomerates by adding additional n-hexane into the system. Spherical microcapsules with the size ranged between 100 and 1000 microns, were successfully produced owing to the spherical shape of agglomerates containing ENX or lactose.

Microencapsulation by coacervation of poly(lactide‐co‐glycolide)—II: Encapsulation of a dispersed aqueous phase

AbstractThis paper is related to the phase separation of different copolyesters of lactides and glycolide solutions induced by the addition of silicone oil in order to promote microencapsulation of proteins. This coating process can be divided in three successive steps: phase separation of the coating polymer; adsorption of the coacervate droplets around the drug phase, and microcapsule solidification. This paper focuses on the physico‐chemical analysis of the second step. The knowledge of the interfacial tensions between the three liquid phases allows understanding of the microscopic evolution of the phase separation medium.

Microencapsulation of peptide: a study of the phase separation of poly( d,l-lactic acid-co-glycolic acid) copolymers 50/50 by silicone oil

In this work, the phase separation of different poly( d,l-lactic acid-co-glycolic acid) batches induced by the addition of silicone oil was studied, for peptide microencapsulation purposes. The phase separation phenomena can be divided in 4 steps according to the amount of incompatible polymer added. But the stabilization of the coacervate droplets and, consequently, the formation of the microspheres, can only be obtained in the third step defined as the stability window. Two experimental parameters influencing the presence, the width and the displacement of the stability window inside ternary diagrams, have been studied: the physicochemical nature of the copolymers and the viscosity of the silicone oil. The results are discussed with respect to the presence of low molecular weight compounds in the studied polymer batches. It is concluded that this characteristic dramatically affects the phase separation of the copolymers by modifying their overall hydrophobicity.

Polyethylene glycol: Catalytic effect on the crystallization of phosphoglucomutase at high salt concentration

A cold, aqueous solution containing (NH 4) 2SO 4 at 53% of saturation and 5.9% w/v polyethylene glycol-400 (PEG) produces PEG-rich coacervate droplets (16%(NH 4) 2SO 4 and 37% PEG) when warmed to 25°C. In partition experiments conducted at low protein concentration, phosphoglucomutase and several other common proteins concentrate at least 20-fold in the PEG-rich phase. A temperature-induced phase separation similar to that above, but conducted in the presence of 5 mg/ml of phosphoglucomutase, can produce coacervate droplets in which the concentration of protein is about 500 mg/ml and thus approaches that in the crystal phase. The nucleation and subsequent conversion of such droplets into micrometer-size crystals of phosphoglucomutase were studied by light microscopy. Nucleation usually occurs in the periphery of these droplets, and neither phase nucleates efficiently by itself, although both support growth. Most droplets do not nucleate and subsequently dissolve as the protein concentration in the surrounding medium is depleted by incorporation into growing srystals. A major role of PEG in the nucleation/crystallization process is to repress the formation of salt-induced, disordered aggregates whose non-lattice protein-protein interactions presumably are less mobile than those in the droplet phase. In this sense, PEG acts as a nucleation catalyst. Such a mode of action is supported by studies on the effect of PEG in the conversion of salt-induced aggregates of phosphoglucomutase into protein crystals. An analogous role in the nucleation and slow growth of much larger crystals under somewhat different conditions is inferred. Such a PEG-induced effect may be general for proteins that crystallize from concentrated salt solutions.

The effect of surfactants on the microencapsulation and release of phenobarbitone from gelatin-acacia complex coacervate microcapsules.

The effects of sodium lauryl sulphate (SLS), cetrimide and polysorbate 20 surfactants at concentrations below, at and above their critical micelle concentration (CMC) on the microencapsulation and release of phenobarbitone have been described. Bimodal particle size distributions were produced both in the absence and presence of each of the three surfactants. The presence of surfactant had little or no effect on the particle size distribution at any given stirring speed. A large variation was noted in the amount of phenobarbitone microencapsulated dependent upon the type of surfactant and its concentration. The amount of phenobarbitone encapsulated decreased with increasing concentration of polysorbate 20 and with SLS. Cetrimide (0.025 per cent w/v) enhanced encapsulation with 2 per cent w/w colloids but higher concentrations at the CMC and above decreased encapsulation. The results are explained in terms of decreased interfacial tension by the surfactant and by steric and electrostatic effects caused by surfactant adsorption onto the coacervate droplets and phenobarbitone particles.

Microelectrophoretic studies of gelatin and acacia for the prediction of complex coacervation

Microelectrophoretic measurements of the polyions acacia, acid-processed gelatin, and alkali-processed gelatin have been used to predict the optimum pH and ionic strength requirements for their complex coacervation and thus to maximize the amount of coacervate formed. Experimental data on the effect of pH and added salt on the coacervate volumes of acid-processed gelatin and acacia and alkali-processed gelatin and acacia have been used to confirm predictions made from microelectrophoretic measurements. Microelectrophoresis has also been carried out on gelatin/acacia coacervate droplets and the electrophoretic mobility profiles are identical to those of gelatin and acacia mixtures, adsorbed onto colloidal silica particles.

Microelectrophoretic studies of gelatin and acacia for the prediction of complex coacervation

Microelectrophoretic measurements of the polyions acacia, acid-processed gelatin, and alkali-processed gelatin have been used to predict the optimum pH and ionic strength requirements for their complex coacervation and thus to maximize the amount of coacervate formed. Experimental data on the effect of pH and added salt on the coacervate volumes of acid-processed gelatin and acacia and alkali-processed gelatin and acacia have been used to confirm predictions made from microelectrophoretic measurements. Microelectrophoresis has also been carried out on gelatin/acacia coacervate droplets and the electrophoretic mobility profiles are identical to those of gelatin and acacia mixtures, adsorbed onto colloidal silica particles.

Functions of the coacervate droplets

Functions of coacervate droplets as protocells are studied by using synthetic polymers. The coacervate droplets were made from PVA-A and PVA-S. When glycine or diglycine were in the surrounding medium, the coacervate droplets concentrated them. The concentration of glycine in the coacervate droplets was higher than that of diglycine. When this mixture was irradiated by UV light, the coacervate droplets protected them from the photochemical decomposition.

A protective function of the coacervates against UV light on the primitive Earth

Results from simulation experiments in the laboratory support the Oparin–Haldane hypothesis of chemical evolution1–4. The organic compounds produced may have accumulated in the primitive sea, constituting the so-called ‘primordial soup’ of organic molecules. Beyond this primordial stage, however, many developments were required before the emergence of the first cellular organism. The first cell need not necessarily have been a modern cell, complete with a membrane, a chromosome, ribosomes, enzymes, a metabolism, and the property of self-replication; the primary requirement of the protocell would have been the ability to evolve into a complete cell. There are many models of the protocell: for example coacervate droplets5–9, proteinoid microspheres10,11, micelles (lipid vesicles)12, and marigranules13,14. Of these, the coacervate droplets are of interest as they are dynamic6,7 and because their mechanism of formation is perhaps better understood15–16. Coacervate droplets are essentially small bounded spaces in which the concentration of substances is higher than in the surrounding medium and in which the distribution of the substances differs from that in the solutions. Their essential functions in the protocell model are: (1) selection; (2) concentration; (3) production of hypohydrous effects; (4) interaction; and (5) organization5–9. Here we report another possible function of the coacervate. We added glycine or diglycine to the coacervate system, then irradiated the system with an argon lamp. We report that the coacervate droplets concentrated glycine or diglycine, thus protecting them from decomposition by irradiation. These results suggest a protective function of the coacervate against UV light on the primitive Earth.

Effect of Polyisobutylene on Ethylcellulose-Walled Microcapsules: Wall Structure and Thickness of Salicylamide and Theophylline Microcapsules

Microcapsules were prepared by the ethylcellulose coacer-vation process which is based on the differential thermal solubility in cyclohexane. When a protective colloid, polyisobutylene, was present in adequate concentration, individually film-coated core particles formed. However, they were accompanied by small empty coacervate droplets, detectable by microscopic observation. Below the critical colloid concentration, the product had the form of an aggregate, in contrast to individual film-coated microcapsules. Increase of colloid concentration yielded microcapsules of higher drug content, because the coating became progressively thinner; there was a corresponding increase in the release rate of drugs from the microcapsules. Since the initial wall polymer/drug ratio and the particle size are constant, the drug content varied with the thicknesses of the wall membrane. This is shown here by removal of empty coacervate droplets by repeated decantations, enabling determination of drug content by chemical analysis. In contrast to results reported in the literature, in the presence of a protective colloid, microcapsule drug content decreased with decreasing particle size of the drug. This was caused by more complete uptake of the wall polymer on the increased surface of core material. The effect of protective colloid concentration on the apparent loss of wall polymer as empty droplets closely paralleled its effect on the size of stabilized coacervate droplets when core material was absent. It is proposed that stabilized droplet formation is a side reaction when core material is present, causing changes in wall thickness. This reaction not only affects the efficiency of the coating process but may be utilized to control wall thickness. First-order constants for drug release from salicylamide and theophylline microcapsules followed the same pattern as wall thickness and confirmed the validity of the measurements.

Interactions of dextran sulfate polymers with aqueous chromium(III) species

Precipitation phenomena in aqueous Cr(III) salt-sodium dextran sulfate (SDexS) systems were studied at 25 and 75°C. At the lower temperature a Cr 3+-dextran sulfate complex of stoichiometric composition yielded coacervate droplets at the mole ratio of sulfate groups on the polymer to weighed-in Cr(NO 3) 3 less than 3. The coacervate dissolved in the presence of an excess amount of NaNO 3. At higher polymer-to-chromium(III) ratios, no phase separation took place. Similar phenomena were observed in chrom alum-SDexS systems. At 75°C, chromium hydroxide particles of submicron size formed in systems containing 4 × 10 −4 M chrom alum (or chromium nitrate) and less than 0.01 wt% SDexS. A gel-like phase appeared at SDexS concentrations between 0.01 and 0.024 wt%, but no precipitation took place at still higher polymer contents.

ゼラチン―アラビアゴムコアセルベーション法によるスルファメトキサゾールマイクロカプセルのζ電位

Sulfamethoxazole was microencapsulated by a gelatin-acacia coacervation method. The zeta potential of the microcapsules prepared at various coacervation pH and the amounts of formaldehyde used as a hardening agent were measured in the buffer solutions with pH, 2.5 to 9.5 and ionic strength, 0.1. The formalization affected the electrophoretic properties of the microcapsules, which depended upon the amounts of formaldehyde used. A pretty amount of formaldehyde (e.g. 30ml) raised the zeta potential as compared with that of the unformalized one. While a plenty amount of formaldehyde used (e. g. 50ml) tended to reduce this action. This characteristic phenomena were caused to the different two actions of fromaldehyde, i. e. denaturalization of gelatin and liberation of acacia from the microcapsule wall.The zeta potential of the original sulfamethoxazole and the coacervate droplets were also measured. By following the changes in the zeta potential in due course of the preparation of microcapsules, the preparation process of microcapsules was elucidated electrophoretically. The zeta potential of spraydried microcapsules indicated that the gelatin in the microcapsule wall was denaturalized by spray drying.

The evolutionary significance of phase-separated microsystems.

The source, preparation, and properties of phase-separated systems such as lipid layers, coacervate droplets, sulphobes, and proteinoid microspheres are reviewed. These microsystems are of interest as partial models for the cell and as partial or total models for the protocell. Conceptual benefits from study of such models are: clues to experiments on origins, insights into principles of action and, in some instances, presumable models of the origin of the protocell. The benefits to evolution of organized chemical units are many, and can in part be analyzed. Ease of formation suggests that such units would have arisen early in primondiae organic evolution. Integration of these various concepts and the results of consequent experiments have contributed to the developing theory of the origins of primordial and of contemporary life.

Peptides and amino acids in the primordial hydrosphere

In this paper Oparin’s original concept of the primordial ocean being a “primeval broth” in which “protobionts” have evolved is reviewed on the basis of recent and previous data on the formation and decomposition of peptides and amino acids. It will be shown that peptides and amino acids could never reach significant concentrations in the ocean. Locally, in pools of transient existence, however, amino acids, peptides, and other molecules of biological significance could have been concentrated by various geological processes to yield a “primeval broth” in which prebiotic systems such as proteinoid microspheres and coacervate droplets, could have evolved.

Coacervate-like microspheres from lysine-rich proteinoid

Microspheres form isothermally from lysine-rich proteinoid when the ionic strength of the solution is increased with NaCl or other salts. Studies with different monovalent anions and with polymers of different amino acid composition indicate that charge neutralization and hydrophobic bonding contribute to microsphere formation. The particles also form in sea water, especially if heated or made slightly alkaline. The microspheres differ from those made from acidic proteinoid but resemble coacervate droplets in some ways (isothermal formation, limited stability, stabilization by quinone, uptake of dyes). Because the constituent lysine-rich proteinoid is of simulated prebiotic origin, the study is interpreted to add emphasis to and suggest an evolutionary continuity for coacervation phenomena.

Complex coacervation in sulfated polyvinyl alcohol- aminoacetalyzed polyvinyl alcohol system

The complex coacervation, defined as a liquid-liquid phase separation in the system of polycation-polyanionsolvent with or without added microsalt, was investigated with polyelectrolytes prepared from polyvinyl alcohol by partial esterification. In particular, conditions for the formation of coacervate droplets were discussed as functions of charge density and polymer concentration.

The role of water in the origin of life and its function in the primitive gene

A brief outline is presented of the structure of clays and of modern views on the structure of water. The interactions between clays and water are discussed, together with the effect of hydration on the adsorption and catalytic properties of clays. From these considerations an attempt is made to show that the hydrated silica surfaces of clay-water systems could have provided the necessary environment for the abiogenesis of primitive macromolecules. The transfer of catalytic functions to abiopolymers is outlined, and a possible route to growing, dividing coacervate droplets is described. Finally, attention is drawn to analogies between the clay-water system and living matter, and the suggestion is made that the structural properties of water could be the basis for the cellular communication network on which life depends.

Factors Influencing Microencapsulation of a Waxy Solid by Complex Coacervation

Microencapsulation of stearyl alcohol particles by complex coacervation in a gelatin-acacia system was studied. Spherical particles of solid stearyl alcohol were prepared by vibrating reed and vibrating capillary methods. Encapsulation was attempted on several size fractions of these particles by conventional procedures, but only particles below 250 μ in diameter were encapsulated. A modified procedure was developed to encapsulate particles larger than 250 μ. Microscopic observations indicated that the coacervate droplets had little affinity for the stearyl alcohol particles and that encapsulation of smaller particles was apparently accomplished by aggregation and coalescence of several droplets around the particles. Encapsulation of particles larger than 250 μ by the modified procedure was possibly the result of the direct interaction of gelatin with acacia on the surface of the particles.

Oparin's Hypothesis and the Evolution of Nucleoproteins

Previous articleNext article No AccessOparin's Hypothesis and the Evolution of NucleoproteinsUrless N. LanhamUrless N. Lanham Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 86, Number 829Jul. - Aug., 1952 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/281726 Views: 13Total views on this site Citations: 4Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Tony Z Jia, Po-Hsiang Wang, Tatsuya Niwa, Irena Mamajanov Connecting primitive phase separation to biotechnology, synthetic biology, and engineering, Journal of Biosciences 46, no.33 (Aug 2021).https://doi.org/10.1007/s12038-021-00204-zAntonio Lazcano Alexandr I. Oparin and the Origin of Life: A Historical Reassessment of the Heterotrophic Theory, Journal of Molecular Evolution 83, no.5-65-6 (Nov 2016): 214–222.https://doi.org/10.1007/s00239-016-9773-5 BIBLIOGRAPHY, (Jan 1965): 359–420.https://doi.org/10.1016/B978-1-4832-0047-7.50017-4 Bibliography, (Jan 1964): 387–433.https://doi.org/10.1016/B978-0-08-010139-2.50015-9