Carrageenan gels

Chibata, I., Immobilized Microbial Cells with Polyacrylamide Gel, Carrageenan and their Indushial Application, In Immobilized Microbial Cells , chap. 3. American Chemical Society, Washington, D.C., 1979. 

Locust Bean Gum. Locust bean gum [9000-40-2], also known as catob seed gum, is a galactomannan extracted from the endosperm of the catob tree seed which is cultivated in the Mediterranean area. The primary use of locust bean gum is in dairy appHcations such as ice cream. It is often used in conjunction with carrageenan because the chemical stmctures of the two enable them to cross-link and form a gel (85). 

Concentrations above 0.3% form a gel with borate which is reversible upon the subsequent addition of mannitol (a sequestrant for borate) or of acid. Usefiil combinations are formed with carrageenan (63) and xanthan gum (64) and agar. In many appHcations, it is used in combination with these gums at considerable cost savings. 

A useful property of the red seaweed extracts is their abiUty to form gels with water and milk. Kappa-carrageenan reacts with milk protein micelles, particularly kappa-casein micelles. The thickening effect of kappa-carrageenan in milk is 5—10 times greater than it is in water at a concentration of 0.025% in milk, a weak thixotropic gel is formed. 

ProStep, developed by Elan and marketed by Ledede, dehvers nicotine over 24 hours (107) and is available ia a 22 mg dose (108). The system consists of a nicotine-containing carrageenan gel embedded and heat-sealed iato a foil—polyethylene laminate to isolate the nicotine from a peripheral acryhc adhesive duriag storage. 

The GBR resin works well for nonionic and certain ionic polymers such as various native and derivatized starches, including sodium carboxymethylcel-lulose, methylcellulose, dextrans, carrageenans, hydroxypropyl methylcellu-lose, cellulose sulfate, and pullulans. GBR columns can be used in virtually any solvent or mixture of solvents from hexane to 1 M NaOH as long as they are miscible. Using sulfonated PDVB gels, mixtures of methanol and 0.1 M Na acetate will run many polar ionic-type polymers such as poly-2-acrylamido-2-methyl-l-propanesulfonic acid, polystyrene sulfonic acids, and poly aniline/ polystyrene sulfonic acid. Sulfonated columns can also be used with water glacial acetic acid mixtures, typically 90/10 (v/v). Polyacrylic acids run well on sulfonated gels in 0.2 M NaAc, pH 7.75. 

Subsequent work by Johansson and Lofroth [183] compared this result with those obtained from Brownian dynamics simulation of hard-sphere diffusion in polymer networks of wormlike chains. They concluded that their theory gave excellent agreement for small particles. For larger particles, the theory predicted a faster diffusion than was observed. They have also compared the diffusion coefficients from Eq. (73) to the experimental values [182] for diffusion of poly(ethylene glycol) in k-carrageenan gels and solutions. It was found that their theory can successfully predict the diffusion of solutes in both flexible and stiff polymer systems. Equation (73) is an example of the so-called stretched exponential function discussed further later. 

Pedersen, J.K.. Carrageenan, pectin and xanthan/locust bean gum gels. Trends in their food uses.Food Chem. 6 (1980) 77-88. 

Applications of sol-gel-processed interphase catalysts. Chemical Reviews, 102, 3543-3578. Pierre, A.C. (2004) The sol-gel encapsulation of enzymes. Biocatalysis and Biotransformation, 22, 145-170. Shchipunov, Yu.A. (2003) Sol-gel derived biomaterials of silica and carrageenans. Journal of Colloid and Interface Science, 268, 68-76. Shchipunov Yu.A. and Karpenko T.Yu. (2004) Hybrid polysaccharide-silica nanocomposites prepared by the sol-gel technique. Langmuir, 20, 3882-3887. 

Carrageenans and alginates present different conformations egg-box structure (alginates) and double helices (carrageenan) but both natural biopolymers are able to form gels and consequently, to control nanoparticle growth. 

Fig. 5.10 TEM micrographs of gel and nanoparticle formation of iron-loaded K-carrageenan at (A) pH 2 and (B) pH 13. In both casestheiron loadingwas 100%. ([57], CopyrightSpringer-Verlag 2000. With kind permission of Springer Science and Business Media).

Morris, E.R., Rees, D.A. and Robinson, G. (1980) Cation-specific aggregation of carrageenan helices Domain model of polymer gel structure. Journal of Molecular Biology, 138, 349-362. 

---