Depolymerization of Macromolecules

The depolymerization of sedimentary organic matter is generally the rate-limiting step in the 

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Mechanosensing is used to describe the process by which cells sense mechanical forces. Mechanochemical transduction is the phrase that is used to try to describe the biological processes by which external forces such as gravity influence the biochemical and genetic responses of cells and tissues. Specifically, these responses include stimulation of cell proliferation or apoptosis (death) and synthesis or catabolism of components of the extracellular matrix. These processes cause either increases in chemical energy (conversion of amino acids or other small molecules into macromolecules) or decreases in chemical energy (depolymerization of macromolecules). 

Hydrolysis of chemical bonds during microbial depolymerization of macromolecules weakens fibers, and this can be detected by measuring tensile properties, as illustrated in a study by Seves et al. [64], These researchers buried pieces of silk fabric (1 cm x 1 cm) in soil and these were incubated for up to 2 months. Yams were removed from fabric and subjected to a breaking load test. Prior to burial, the mean breaking load of the warp yams was 297 grams-force, whereas after 2 months incubation, this was drastically reduced to only 2 grams-force. 

Solid/liquid separation is important at all stages and depends on the extent of coal cleaning during pretreatment, depolymerization of coal macromolecules at the dissolution stage, and catalyst durability through the catalytic process. 

The mechanism proposed in Figure 3 can easily be applied to the oxidative depolymerization of the lignin macromolecule by nitrobenzene or copper(II) in aqueous alkali. A recent model of softwood lignin (24) contains 27% free benzylic hydroxyl groups and 12% aromatic ring-conjugated double bonds (stilbene... 

Sequence distribution and chemical structure of mass-selected macromolecules of macroinitiators derived from selected biopolyesters were accomplished recently with the aid of ESI-Mtechnique. The NMR and ESI-MS evaluation of the chemical structure of macroinitiators obtained by partial depolymerization of natural PHB, PHBV and PHO revealed that due to the elimination reaction they contain olefinic and carboxylic end groups. Based on the ESI-MS" studies of PHBV macroinitiator obtained by partial alkaline depolymerization of natural PHBV (containing 5 mole % of hydroxyvalerate units) the microstructure of this bacterial copolyester was assessed, starting from dimer up to the oligomer containing 22 repeat units. ... 

In principle, the chemical reactions of macromolecules should be similar to those of low-molecular-weight substances. Experimentally, however, either degradation is found to occur at very much lower temperatures or, occasionally, there is degradation into different products. The decomposition of poly(ethylene), for example, begins at 200°C lower than that of hexadecane. At 450°C, poly(methyl methacrylate) will be almost completely depolymerized into monomer, methyl methacrylate (Table 23-2). At this temperature, on the other hand, low-molecular-weight primary esters decompose into olefins and acids. The nature of the product also depends on whether the experiment is carried out at atmospheric pressure under nitrogen or under high vacuum (Table 23-3). 

It is assumed that the tumour cells use of hyaluronidase as a molecular sabotage for the depolymerization of extracellular matrix polysaccharide macromolecules for two reasons first, to facilitate the invasion between normal cells and form metastasis in the tissues and secondly, to use the ability of low molecular weight degradation HA products to stimulate angiogenesis by sprouting blood vessels in tumour tissue. In order to discuss the molecular mechanisms by which hyaluronan affects the cell proliferation and tumour growth, it is important to examine the differences between normal and tumour cells [72]. 

Melchiors, M., Keul, H., and Mocker, H. (1996]. Depolymerization of poly[(R]-3-hydroxybutyrate] to cyclic oligomers and polymerization of the q clic trimer An example of thermodynamic reqrcling. Macromolecules, 29,6442-6451. 

Liang Z A, Meng Y Z, Li L, Hay A S (2004), Novel synthesis of macrocyclic aromatic disulfide ohgomers by cyclo-depolymerization of aromatic disulfide pol3mers . Macromolecules, 37(16), 5837-5840. 

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