Enzymatic chemical degradation

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin and benzoic acid, but also other aromatics (Baciocchi et al. 1999, references therein). In principle, lignin could be a major nonfossil and renewable source of aromatic compounds, a feedstock for synthesis of useful products. The problem deserves finding new ion-radical routes to cleave lignin. At present, there is some shortage in oil, gas, and even coal, which had usually been well-available natural sources of aromatics. In the near future, biomass may (and must) replace fossil-originated materials in the manufacture of commercial carbon-based products. 

The chemical and enzymatic oxidative degradation of lignin (and coal) is used to obtain not only vanillin but also other aromatics (Baciocchi et al. 1999 and references therein). 

Enzymatic and chemical degradation of the benzoxazinoid acetal glucoside DIBOA-GIc. 

However, in many cases, dmg release takes place in parallel with polymer degradation. In such cases the mechanism of dmg release is complicated as dmg release occurs by dmg diffusion, polymer degradation and/or polymer dissolution. The permeability of the dmg through the polymer increases with time as the polymer matrix is gradually opened up by enzymatic/chemical cleavage. The references cited at the end of this chapter deal with the relevant mathematical treatments of this topic. 

Aminolevulinic acid (ALA), labelled with 13C at C(1). C(2), C(3), C(4) and C(5), has been synthesized64 from 13C-labelled KCN, glycine, Meldrum s acid or bromoacetate, prepared in turn from 13C-sodium acetate or 13C-acetic acid (equations 26 and 27). It was used for direct observation of the enzymatic transformation of ALA to porphobilinogen (PBG) by 13C-high-field FT-NMR spectroscopy without chemical degradation of the intermediate and the compounds. 

Low molecular weight components in unfiactionated heparins have been identified long before the development of clinically effective agents. However, because of technologic problems, they were not made available for clinical use. The very first LMWH was obtained by a fractionation method (3). However, this method only yielded a limited amount of the active product and was cost prohibitive. During the past decade, different chemical and enzymatic processes have been developed to obtain LMWH from the parent unfiactionated heparin (UFH). The depolymerization process for the production of LMWH is shown in Figure 5. Such methods as chemical degradation, enzymatic depolymerization... 

The stability of a drug in the gut is influenced by both chemical and enzymatic factors. Protection from chemical degradation may be accomplished via coating... 

It is the aim of this review to present a detailed overview on natural sources of benzoxazinones and their enzymatic and chemical degradation, on the synthetic access both to aglycones and acetal glucosides, on medical effects and on the molecular allelopathy of these bioactive natural products. 

As mentioned above, the assumption that e.g. the highly bioactive 4-acetylbenzoxazolin-2(3/ 0-one (4-ABOA), isolated from kernels of a fusarium resistant maize line [96-98] may have resulted from the enzymatic and chemical degradation of the precursor 5-acetyl-4-hydroxy-2- 3-D-glucopyranosyloxy-2//-l,4-benzoxazin-3(4/f)-one is possible, particularly since no means to inactivate 3-glucosidase have been undertaken during the isolation process (Fig. (13)). 

BIcomycinic acid is obtained by chemical degradation of Kcomycin A or enzymatic degradation of bleomycin Bj. It mn he trjitsformed readily into scmisynthelie bleomycins... 

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