Coacervates molecules

In spite of the overwhelming evidence suggesting that recombinant resilin is amorphous, there are some results that suggest that a level of defined stmcmre cannot be completely ruled out. In particular, the fact that the protein solution coacervates when cooled (Figure 9.7) suggests that there is a degree of self-association between protein molecules. 

The coacervation of tropoelastin plays a crucial role in the assembly into elastic fibers. This coacervation is based on the LCST behavior of tropoelastin, which causes tropoelastins structure to become ordered upon raising the temperature. The loss of entropy of the biopolymer is compensated by the release of water from its chain [2, 18, 19]. This release of water results in dehydration of the hydrophobic side chains, and this is the onset of the self-assembly leading to the alignment of tropoelastin molecules. 

Other scientists took up Oparin s ideas, used them for their own concepts, and tried to form organic molecules from inorganic starting materials. The Mexican scientist A. L. Herrera reported in 1942 in an article entitled A New Theory of the Origin and Nature of Life on his investigations with sulphobes (Herrera, 1942). These are morphological units ( lifelike forms ) which he obtained from reactions between thiocyanates and formalin. Sulphobes are spherical in form, with a diameter between 1 and 100 pm, and can interact with their surroundings thus they can adsorb dyestuffs. In some ways, they resemble the coacervates studied by Oparin and his school (Sect. 10.2.2). 

There is evidence that random mixing of partially charge-neutralized hydrated polyelectrolyte complexes inside the coacervate phase imparts higher configurational entropy to these less stiff polyelectrolyte molecules as compared to those in the pre-coacervation phase (Kaibara et al.,... 

Interphasic - properties depending on the ability of the protein molecules to form separation and junction films between two inmiscible media, including emulsification, fat uptake, foaming, adsorption, and coacervation. 

Simple coacervation involves the use of either a second more-water soluble polymer or an aqueous non-solvent for the gelatin. This produces the partial dehydration/desolvation of the gelatin molecules at a temperature above the gelling point. This results in the separation of a liquid gelatin-rich phase in assocation with an equilibrium liquid (gelatin-poor) which under optimum separation conditions can be almost completely devoid of gelatin. 

Citrus oils readily form oxygenated products that are likely to congregate at oil/water interfaces and thereby cause a detectable change in IFT. The aldehydic components of citrus oil could react with the amine groups of the gelatin molecules present in the aqueous phases formed by complex coacervation and thereby affect IFT. In addition to chemical reactions, physical changes can occur at an interface and alter IFT. A visible interfacial film can form simply due to interfacial interactions that alter the interfacial solubility of one or more components. No chemical reactions need occur. An example is the formation of a visible interfacial film when 5 wt. per cent aqueous gum arabic solutions are placed in contact with benzene (3). Interfacial films or precipitates can also form when chemical reactions occur and yield products that congregate at interfaces. 

The process of coacervation is finely tuned to the physiological conditions of the extracellular matrix. Optimal coacervation of human tropo-elastin occurs at 37 °G, 150 mM NaCl, and pH 7-8 (Vrhovski et al, 1997). The arrangement of sequences in tropoelastin is critical to this process of coacervation, where association through hydrophobic domains depends on their contextual location in the molecule (Toonkool et al., 2001b). Tropoelastin association rapidly proceeds through a monomer to tuner transition, with little evidence of intermediate forms (Toonkool et al, 2001a). 

Polymers may be induced to encapsulate other molecules by a variety of means (Risch and Reineccius, 1995) as diverse as dipping, spray-drying, extrusion, evaporation, and coacervation each technique has its special applications, strengths, and weaknesses. Advantages in common are the protection and slow release of the encapsulate. In any of the mechanisms, a coagulable polymer precipitates around a core of labile material. Polysaccharides are regular encapsulating polymers (Risch and Reineccius, 1995) acacia gum is particularly efficacious because of its protein content. 

In favour of the metabolism paradigm there are, first of all, the results of the simulation experiments, and in particular the fact that the abiotic production of amino acids is so much easier than that of nucleic acids. Chemistry tells us that the primitive Earth could indeed generate enormous amounts of organic molecules that were potentially capable of having some type of metabolism, and of producing structures as complex as Oparin s coacervates, Fox s microspheres, or Wachtershauser s vesicles. 

Many therapeutic molecules can be encapsulated using other techniques, such as coac-ervation, micro- or nanospheres, microcapsules, or liposomes. Coacervation, often used for... 

Homogeneous, transparent solutions of proteins, carbohydrates, and other compounds can separate into two layers, one depleted and one enriched with these compounds. The process of separation of macromolecules into discrete entities is termed coacervation. The layer rich in molecules of the dissolved substance, referred to as the coacervate layer, actually consists of liquid "drops" or spherical microcapsules. The equilibrium liquid, which is the medium adjoining the coacervate layer, always contains less substance than the original solutions. The discrete liquid droplets resulting from macromolecular interactions might be made to serve as pseudocells from which pseudo tissues might be derived to constitute a restructured food. 

Classification and Nomenclature. Coacervates can be divided into simple ones and complex ones based on the complexity of their chemical composition. Simple coacervates form when a compound with a great affinity for water is added to a solution of a hydrophilic molecule, causing its dehydration and a decrease in its solubility. Molecules of the same chemical composition are thus involved in simple coacervation. Complex coacervates are obtained when solutions of positively charged molecules and negatively... 

Forces Affecting Coacervate Formation. The existence of coacervates also depends on the ratio of the forces of attraction and repulsion between the molecules involved in coacervation. 

Consequently, when coacervates are formed from precipitates, a dilution of the precipitates takes place, the precipitates swell and produce drops. If the drops are formed from solutions, a concentration of molecules in the drops is observed. 

Size, Concentration and Organization of the Molecules. Coacervate drops can range in size from several tenths of a micron to several hundred microns or even larger in diameter. The size of coacervate drops is affected by several factors. At the optimum temperature for the existence of a coacervate, the drops are largest. Coacervate drops are smaller when they consist of compounds whose isoelectric points are widely separated, and larger when the compounds have closer isoelectric points. The diameter of drops also increases with the concentration of the initial solutions from which the coacervates were obtained (11). 

Molecules of chemical compounds in the solutions collect in the coacervate drops. Coacervates are characterized by an increase in the concentration of the dry matter in the drops by a factor of several tens of times, as compared to the original solutions, and even more as compared to the equilibrium liquid. For example, under optimum conditions, gum arabic-gelatin coacervate drops contain 84% of the molecules, and 16% remains in the equilibrium liquid. In the coacervate from histone-DNA,... 

The wall of the coacervate drop can be made permeable, semi-permeable, or impermeable to diffusion of molecules through the microcapsule wall. The rate of release of the contents of the coacervate drop or intake of molecules from outside the drop depends on the nature of the polymer(s) which make up the wall material, the thickness of the microcapsule wall, the pore width of the wall, the molecular weight of permeating materials, and the degree to which the polymeric wall materials are cross-linked (2). 

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