Cellulose in vitro

There have been few studies of polymer interconnections within the primary wall of monocots. An arabinoxylan from the primary wall of cultured, barley-aleurone cells,61 and a glucuronoarabinoxylan from maize-coleoptile primary-wall,200 have been shown to bind reversibly to cellulose in vitro, Because xylans are, quantitatively, the major component of monocot primary cell-walls, this interconnection is an important finding it is very likely to occur through multiple hydrogen-bonds, analogous to the interconnection between xyloglucan and cellulose in dicot cell-walls.56,57,59 It is also possible that heteroxylans participate in binding other cell-wall polymers to cellulose. 

In contrast to these findings, a glucuronoarabinoxylan isolated from oat coleoptiles did not bind to cellulose in vitro under reaction conditions that allowed other heteroxylans to bind.53 This oat heteroxylan had, however, a high percentage of arabinosyl side chains that would be likely to hinder binding sterically. A similar inability to bind to cellulose is exhibited by an arabinose-rich arabinoxylan isolated from cultured, barley-aleurone cell-walls.61... 

From the preceding discussions, it is evident that, in all systems studied, and, in particular, in higher plants, attempts to synthesize cellulose in vitro have met with only limited success this therefore leads to the conclusion that, for poorly understood reasons, the cellulose synthetase complex is a highly labile system. As a conclusion to this article, it may prove useful for future research to discuss possible reasons for this apparent lability. 

Lavasanifar A, Ghalandari R, Ataei Z, et al. Microencapsulation of theophylline using ethyl cellulose In vitro drug release and kinetic modeling. / Microencapsul 1997 14(1) 91-100. 

Attempts to synthesize cellulose in vitro by using detergent solubilized enzymes frequently lead to the accumulation of callose, a linear (1 3)- 3-D-glucan (Delmer 1987 Okuda et al. 1993). Even in the few cases where successful in vitro cellulose synthesis has been demonstrated, i.e., in blackberry (Lai Kee Him et al. 2002), cotton and mung bean (Kudlicka et al. 1995 Kudlicka et al. 1996 Kudlicka and... 

Marx-Figini, M. Comparison of the Biosynthesis of Cellulose in vitro and in vivo in Cotton Bolls. Nature 210, 754 (1966). 

Chloropromazine (8—34 wt% loading) has been microencapsulated in PCL-cellulose propionate blends by the emulsion solvent evaporation method (61). Phase separation for some ratios of the two polymers was detectable by SEM. The release rate from microcapsules in the size range of 180-250 pm in vitro (Fig. 11) was directly proportional to the PCL content of the blend, the half-life (50% drug release)... 

Partially deacetylated chitin, a cellulose-like biopolymer consisting predominantly of N-acetyl-D-glucosamine chains, in the form of films or crosslinked hydrogels has been used for the delivery of drugs (28,29). The suitability of chitin as a vehicle for the sustained release of drugs was examined using indomethacin and papaverine hydrochloride as model drugs (30). In vitro studies showed that over 80% of the indomethacin was released within 7 hr, whereas papaverine hydrochloride dissolved almost immediately. 

Zentner and coworkers [24,26] utilized this information in their development of a system that releases this drug over a 24 hr period. The use of NaCl to modulate the release of diltiazem presents an interesting problem in that the concentration of the solubility modifier must be maintained within certain limits and below its saturation solubility within the device. To solve this problem, core formulations were developed that contained both free and encapsulated NaCl. The encapsulated NaCl was prepared by placing a microporous coating of cellulose acetate butyrate containing 20 wt% sorbitol onto sieved NaCl crystals. The coated granules released NaCl over 12-14 hr period via an osmotic mechanism into either water or the core tablet formulation. The in vitro release profile for tablets (core I devices) containing 360 mg of diltiazem HC1 and 100 mg of NaCl equally divided between the immediate release and controlled release fractions... 

Extensions of BCS beyond the oral IR area has also been suggested, for example to apply BCS in the extended-release area. However, this will provide a major challenge since the release from different formulations will interact in different ways with in vitro test conditions and the physiological milieu in the gastrointestinal tract. For example, the plasma concentration-time profile differed for two felodipine ER tablets for which very similar in vitro profiles had been obtained, despite the fact that both tablets were of the hydrophilic matrix type based on cellulose derivates [70], This misleading result in vitro was due to interactions between the gel strength of the matrix and components in the dissolution test medium of no in vivo relevance. The situation for ER formulations would be further complicated by the need to predict potential food effects on the drug release in vivo. 

The first sensor proposed for detecting gastric and oesophageal pH24, made use of two fluorophores, fluorescein and eosin, immobilised onto fibrous particles of amino-ethyl cellulose, fixed on polyester foils. Only tested in vitro, the sensor reveals a satisfactory response time of around 20 seconds. 

Luccia, B. H. D., and Kunkel, M. E. (2002a). In vitro availability of calcium from sources of cellulose, methylcellulose, and psyllium. Food Chem. 77,139-146. 

The release behavior of aquo-CDDP from the conjugates was investigated in PBS at 37°C in vitro. The conjugates (10 mg) were dialyzed in PBS (pH = 7.4,20 mL) containing IM NaCl using a cellulose tube (cut off =1.0... 

Plant cell walls are complex, heterogeneous structures composed mainly of polymers, such as cellulose, hemicelluloses, and lignins. In spite of several decades of research, cell wall assembly and the biosynthesis and ultimate biodegradative pathways of individual polymers are still far from being fully understood. One simple example will suffice Even today, no enzyme capable of catalyzing cellulose formation in vitro has been obtained. 

It now appears that cellulose I is not exclusively the native polymorph present in all organisms. The results reported originally by Sisson (61), which provided evidence that cellulose II was the native polymorph present in Halicystis (Ulvophyceae) cell walls, were recently reinvestigated and confirmed (62). Additionally, cellulose II producing mutants of Aceiobacier have been isolated and analyzed with x-ray and low-dose electron diffraction (63). When cellotetraose is induced to crystallize in solution it forms a structure which has been used as a model compound approximating the crystallographic nature of cellulose II based on x-ray diffraction, electron diffraction and CP-MAS 13C NMR evidence (64). Significantly, in all cases where Aceiobacier cellulose synthase in vitro activity has been reported,... 

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