Chemical modification, dissolution

Also, local changes in the structural and chemical variation of DNA may have important effects on the overall extent of chromatin folding. For instance, transitions from the B to the Z form of DNA will result in nucleosome dissolution (as discussed earlier) and this could affect the folding of the fiber. As well, chemical modifications of the bases such as methylation have been shown to increase the folding of the chromatin fiber when linker histones are present [250] although the mechanism involved in this later case remains to be elucidated. 

In the fourth chapter, Thomas Rosenau, Antje Potthast, and Paul Kosma describe current investigations on reactive intermediates and reaction mechanisms in cellulose chemistry. The chemical modification and regeneration of cellulose requires its activation and/or dissolution in media like sodium lye, N-mclhybnorpholine-N-oxide (NMMO), N, N-dimethylacetamide (DMAc), or in carbanilation mixtures containing dimethylsulfoxide (DMSO). In these media - very important for research and large-scale processes - the trapping and characterization of the intermediates has been carried out. 

Another approach to covalently attach carbon nanotubes is based on the chemical modification of a PEEK matrix which allows further covalent interaction with functionalized carbon nanotubes. In 2007 Babaa et al. (40) proposed a route to covalently graft commercial MWCNTs by using this approach. The process initiates by dissolution of PEEK in concentrated H2S04, leading to functionalization yields of 70%. MWCNTs covalently functionalized with... 

Not all ILs are good solvents for proteins, however. There is the interesting example of lipase. Lipase is soluble in both aqueous and organic solvents, so it can be easily solubilized in ILs. Certain lipases even become dispersed or dissolved in some ILs. Since lipase is a very stable enzyme, it catalyzes the hydrolysis of lipids. Enzymatic activity is reported to be maintained in ILs [1]. There is not much published on the solubilization of biomaterials in ILs. In the present chapter we introduce a procedure to use in solubilizing biomaterials in ILs. First we consider the preparation of the IL, and then the chemical modification of biomaterials suitable for dissolution. We have found this procedure helpful when we tried to use electrochemicaUy active biomaterials in ILs. 

The additives in polymers are analyzed using many different procedures, and many of these procedures require examination of extracts, dissolution of the polymer, chemical modifications of the sample using for example hydrolysis, etc. The analysis of additives especially when they are insoluble can be done successfully using pyrolytic techniques. A number of reports are dedicated to the analysis of additives using analytical pyrolysis [1-3]. However, a considerable volume of work on the analysis of additives using pyrolysis consists of routine procedures in industrial laboratories, and it is not reported in peer-reviewed journals. Also, since most additives are small molecules, a detailed description of pyrolysis studies on additives is not included in this book. 

Chemical modification By comonomers Enhanced dissolution and dyeing. Flame resistance. Antistatic, Improved hydrophilicity, Dyeing simultaneously with acid and basic colours. 

Dissolution of cellulose has three major purposes. The first is to prepare regenerated and man-made cellulose fibers or films from cellulose solutions at the industrial level. Environmentally friendly and cost-profitable systems to dissolve and regenerate cellulose are now required. The second purpose is to use cellulose solutions as homogeneous reaction media during chemical modifications, which have been investigated at the laboratory level. The last one is to analyze cellulose samples. Molecular mass and molecular mass distribution studies using cellulose solutions are included in this category. Numerous cellulose solvents have, therefore, been developed and studied for these purposes. 

When the pharmaceutical formulation of an active compound is ineffective, slight chemical modifications or formation of bioreversible derivatives (esters, amides, peptides) can improve its physico-chemical properties (lipophilicity, pK, polarity) and optimize the dissolution rates in the biological fluids and the passage through the very first biological membranes (cutaneous, intestinal, etc.). The global result is better penetration into the organism. Compared with the pharmaceutical formulation mentioned above, this process can be considered as a chemical formulation and will be considered in Chapter 39. 

Ideally, a drug molecule should have sufficient aqueous solubility for dissolution, an optimum partition coefficient, high diffusion through lipid layers and stable chemical groups. Such an ideal molecule usually does not exist. Hence, chemical modifications are generally directed toward that part of a molecule which is responsible for hindrance of the overall absorption process. 

Chemical modification of the water to increase the pH will enhance the dissolution of silica [63] and hence further increase corrosion of SiC. 

Henniges U, Schiehser S, Rosenau T, Potthast A (2009) Cellulose solubility dissolution and analysis of problematic cellulose pulps in the solvent system DMAc/LiCl. In Liebert TF, Heinze TJ, Edgar KJ (eds) Cellulose solvents for analysis, shaping and chemical modification. ACS symposium series, vol 1033. American Chemical Society, Washington, pp 165-177... 

Su L,Ji WK, Fan WZ, Dong XQ. Chemical modification of xanthan gum to increase dissolution rate. 

Chemical modifications are described below, however some chemical treatments that are carried out specifically to achieve physical changes, such as dissolution, are... 

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