| Résumé : |
Like a Jules Vern novel, this lecture pretends to conduct a virtual journey around the collagen molecule, in order to focus on the most important features of this unique protein. The journey starts with modifications to the procollagen polypeptide in the endoplasmic reticulum including hydroxylation, glycosylation and disulfide-bond formation. Interchain disulfide links between the C-terminal propeptides of three procollagen molecules align the chains in register and initiate formation of the triple helix. The assembly process continues, zipperlike, towards the N-terminus. All modifications occur in a precise sequence and allow lateral alignment and formation of the triple helix. Further steps in constructing collagen are lateral alignment and formation of covalent cross-links that enable the helixes to pack into 50 nm diameter fibrils. How the staggered arrangement of collagen molecules gives rise to the striated appearance of the negatively stained fibril is presented. Covalent intramolecular and intermolecular cross-links form between modified lysine side chains within a collagen fibril. Interaction of fibrous and non-fibrous collagens, 67 nm periodicity, the so-called "mantra", types of collagen, hydroxyproline content, glycosaminoglycans, elastin, etc., are fully analyzed. A better knowledge of the hydroxyproline content and the type of collagen assembled in different animal tissues (cow, sheep, goat, fish, etc) are of utmost importance when processing leather wastes from tanneries. Special attention is given to chrome-tanned collagenic wastes due to the stability of chromium(III) cross-linked to collagenic fibers, thus reducing the yield of the biopolymers obtained. A search of the literature shows different treatments for this type of waste. The main ones are: i) strong chrome complexing agents; ii) calcium hydroxide hydrolysis at 100°C and iii) oxidation of chromium (III) to chromium (VI) by the action of hydrogen peroxide in alkaline medium. The latter is described in detail, on each one of the basic phases: dechroming process; chromium (VI) recovery through an ion-exchange resin (column - batch operation); isolation of new biopolymers; and defining options for different industrial uses. In addition, a set of different processes to treat raw collagenic wastes (non-tanned) from the leather industry (splits, fleshings, etc), including fish (salmon, cod, haddock, etc) are thoroughly described. Exclusion chromatography, ultrafiltration, and reverse osmosis have been used to determine the molecular weight of protein hydrolysates. Higher molecular weight expands the potential commercial applications to the veterinary, medical, and cosmetic fields (high-added value products). However, the biopolymer isolated from chrome-tanned collagenic wastes can be applied directly to the following industries: paper, wood, ink, textile and leather, as binders, biodegradable biopolymers, and protein based self-feeding biodegradable flower pots, fillers, retanning agents, casein substitute in photography, adhesives, etc. A second possibiity would be to produce low formaldehyde content eco-adhesives, collagen based "smart" fabric, etc. by chemical reaction with these biopolymers. Finally, use in this research of the Box-Hunter Rotatory, Orthogonal, and Composite Experimental Design will be discussed. |
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Ajouter le résultat dans votre panier Affiner la rechercheAlternative process for recovery of chrome(III)-effluents in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 92, N° 4 (07-08/2008)
