Chitin support

The solubility of chitin is remarkably poorer than that of cellulose, because of the high crystallinity of chitin, supported by hydrogen bonds mainly through the acetamido group. Dimethylacetamide containing 5-9% liCl (DMAc/IiCl), and N-methyl-2-pyrrohdinone/LiCl are systems where chitin can be dissolved up to 5%. The main chain of chitin is rigid at room temperature, so that mesomorphic properties may be expected at a sufficiently high concentration [67,68]. 

Periodate oxidation of di-iV-acetylchitobiose, tri-iV-acetylchitotriose, chitosan, and chitin supports the proposed glycosidic linkage at C-4 in the chitin molecule . Additional evidence for the structure deduced from the... 

Because 0-acyl chitins appear to be scarcely susceptible to lysozyme, the susceptibility of DBG to Upases has been studied to obtain insight into its biodegradability in vivo. The changes in infrared and X-ray diffraction spectra of the fibers support the slow degradation of DBG by Upases [125,126]. The chemical hydrolysis of DBG to chitin is the most recent way to produce regenerated chitin. 

Chitin (Fig. 27) was supported on silica by grinding the two solids together. The Pt complex was tested as a catalyst in the enantioselective hydrogenation of racemic 1-phenylethanol to obtain (i )-l-cyclohexylethanol [82]. Up to 65% yield with 100% ee was obtained and the catalyst was reused five times with almost the same results. 

There are several reports on the coating of bone-like hydroxyapatite onto natural polymer substrates. Kawashita et at. [57] reported that carboxymethylated chitin and gellan gum gels, which have carboxyl groups, can form hydroxyapatite on their surfaces in SBF if they are treated with a saturated Ca(OH)2 solution in advance, while curdlan gel, which has no carboxyl group, does not form hydroxyapatite in SBF, even if it is treated with Ca(OH)2 solution. These results support the hypothesis that carboxyl groups induce hydroxyapatite nucleation. Kokubo et at. [58,59] reported that non-woven fabrics of carboxymethylated chitin and alginate fibers also form hydroxyapatite on their surfaces in SBF if they are treated with Ca(OH)2 solution. 

The amount of chitin tetramer required to elicit the response, when administered as a single dose, was relatively high. One explanation for this phenomenon was that chitin oligomers are unstable in wheat leaf tissue, and that administration as a single dose did not properly mimic the low, but continual, levels that would be released from the polymer. This was supported by the observation that the tetramer, when administered... 

This paper is a review of x-ray diffraction work in the authors laboratory to refine the structures of cellulose I and II, and a- and B-chitin, concentrating on the methods used to select between alternate models. Cellulose I is shown to consist of an array of parallel chains, and this conclusion is supported by a separate refinement based on electron diffraction data. In the case of cellulose II, both parallel and antiparallel chain... 

Insects exposed to diflubenzuron and related compounds are unable to form normal cuticle (skin) because their ability to synthesize it is lost. Thus, the cuticle becomes thin and brittle, and is unable to support the insect or to withstand molting, a process requiring the shedding of the old cuticle, as in metamorphosis. Diflubenzuron and other chitin synthesis inhibitors have extremely low mammalian toxicity and are used against termites. 

In the introduction it was stated that the disturbances of the endocuticular matrix of Pieris brassicae larvae by the parent benzoylphenyl urea compound Du 19111 were caused by an influence on chitin formation, thus assigning to the benzoylphenyl ureas an insecticidal position equivalent to that of the fungicidal polyoxins. In the last part of this paper we shall try to adduce arguments supporting that statement. 

In this context the comparison of the insecticide diflubenzuron with the fungicide polyoxin D is interesting in more than one respect. It not only closes the circle in our paper, so to speak, but it can also furnish strong circumstantial evidence to support our hypothesis of the mode of action of diflubenzuron. Marks and Sowa were the first to compare diflubenzuron and polyoxin D in their effects on the A ecdyson-dependent in-vitro synthesis of chitin by the cockroach (Leucophaea maderae) leg regenerates (4, ) These authors found that both compounds almost completely inhibited the incorporation of C-labeled D-glucosamine into the chitin fraction. In a later study with 1 C-labeled N-acetyl-D-glucosamine similar results were obtained, and the I50 value of inhibition of chitin synthesis was found to be 6.1 1 x 10 -10m for diflubenzuron and 7.53 x 10"7 M for polyoxin D (4 8) The difference in intrinsic activity can partly be explained by the roughly hundredfold accumulation of dif lubenzuron in the insect tissue. 

Like cellulose, the primary biological function of chitin is for structural support. And like cellulose, it is quite insoluble. Strong acids hydrolyze the amide to give the protonated amine, which is soluble at low pH. Given its abundance in nature, there has always been interest in finding commercial application for chitin or its derivatives. So far these efforts have achieved only limited success. 

Takai, M. 1996. Forming squid chitin-salmon skin collagen complex suitable for human fibroblast adhesion and proliferation. Report of the cooperative study on Development of functional membrane using marine bioresources collagen. Supported by grant in aid of Ministry of International Trade and Industry of Japan for Industrial-Academe cooperation, 20. 

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