Calcium chemical modification

Low methoxyl pectins have radically different properties, i.e. a small chemical modification has totally altered the way in which pectins behave. The low methoxyl pectins are set by calcium ions independently of the pH. Because hard water normally contains calcium ions care must be taken in selecting low methoxyl pectins when using hard water supplies or when moving recipes between factories. The gel produced in low methoxyl pectins has the egg box structure found in alginates (see Figure 6). 

Low methoxyl pectins have radically different properties to those of the high methoxyl forms - the small chemical modification has totally altered the way in which the pectins behave. The gelling conditions for low methoxyl pectin require a pH of 2.8-6.5 (outside of which range the product would be inedible) and between 10 and 80% soluble solids in the presence of calcium. 

Asp-49/35 is essential to optimal calcium binding and catalysis. Replacement of Asp-49 with other amino acids or chemical modification of the side-chain carboxylate reduces Acat to less than 5% of native rates (Fleer etai, 1981 Van den Berghe/a/., 1989). The close spatial coupling of Asp-49/35 with its respective catalytic histidine (His-48/34) ensures a fixed active site geometry. Stability of this bihelical substructure is critical because His-48/34 is supported by a side chain from an adjacent segment of the same helix (Tyr-52) and must hydrogen bond with a residue from the opposed helix (Asp-99/64) for function. 

Calcium carbonate does not have functional groups (its surface is inert), therefore interaction can only be improved by chemical modification. Some hydroxyl groups can be found from admixtures such as Ca(OH)2 but these admixtures may limit the ways in which calcium carbonate can be used because these admixtures increase the amount of absorbed moisture. Functional groups are frequently hydrophilic thus they attract water molecules. In many applications, moisture can either cause product instability, reduce cure rate, or reduce reinforcement. Caution is needed in selecting surface treatment to generate functional groups. 

Biomimetic coating of cholesterol with hydroxyapatite is characterised by an epitaxial relationship between cholesterol monohydrate recrystallised from polar solvents and hydroxyapatite, and thus enhances deposition rate. However, chemical modification of cholesterol, for example by phosphorylation destroys the epitaxy and hence this material fails to act as a viable template for calcium phosphate deposition (Laird, Mucalo and Yokogawa, 2006). This research may... 

Zinc and Calcium Stearate Synergism. With the Brabender plasti-corder, it is possible to follow the viscosity variations of a polymer because of physical or chemical modifications. The shape of the typical plasto-grams for PVC plasticized and stabilized with calcium stearate (Ca-(OCOR)2) (6.6 phr), zinc stearate (Zn(OCOR)2) (6.6 phr), and their mixture (3.3 phr both stearates), are shown in Figures 1, 2, and 3, respectively (-----). Because of degradation, the first peak corresponds to... 

Lyophilization (freeze-drying) is used as a means of preconcentration, although this process can involve some physical or chemical modification of the sample (Galanos and Kapoulas, 1965 Nanny and Minear, 1997). For example, Minear (1972) achieved preconcentration of between 100- and 240-fold for water samples that had previously been treated to remove calcium and magnesium ions. Lyophilization can also be used to remove solvent after a separation process, and has been used as part of a clean-up and concentration step preparatory to chromatographic separation of inositol phosphate esters. A sample containing... 

An example is the increase in lipid solubility achieved by chemical modification by tetracycline to give the derivative doxycycline. Doxycycline (Vibramycin) is more efficiently absorbed from the intestine than is tetracycline, partly because of better lipid solubility and partly because of a decreased tendency to form poorly soluble complexes with calcium. 

Khajeh, K. et al., Chemical modification of bacterial alpha-amylases Changes in tertiary structures and the effect of additional calcium, Biochim. Biophys. Acta Protein Struct. Mol. EnzymoL, 1548, 229, 2001. 

Chemical Modification of Halogenated Polystyrenes Using Rieke Calcium or Rieke Copper... 

Solid state studies for 2 1 complexes revealed that magnesium (see below)(6) and calcium (7) coordination spheres are different.Nevertheless,in both cases the benzoxazole moiety appears to play a key role in the specific complexation of the cationic guest.In a first set of experiments we carried out chemical modifications of this part of the molecule obtained by fermentation. 

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