PH-responsive nature

Fiflure 14 Chemical structure of A(BC)2 star block copolymers with pH-responsive nature of the hydrophilic BC block, and TEM images showing different morphologies obtained as pH is varied. Reproduced with permission from Zhang, W. D. Zhang, W. Zhou, N. C. etal. J. Polym. ScL, Part A Polym. Chem. 2009, 47(22), 6304-631... 

The factors affecting the Maillard reaction include temperature, time, moisture content, concentration, pH, and nature of the reactants. - It has been shown that, out of 21 amino acids, glycine, lysine, tryptophan, and tyrosine provide the most intense browning when exposed to five saccharides, especially a-lactose. The Maillard reaction is also responsible for the decreased availability of lysine in proteinaceous foods. 

Chitosan (Fig. 16) is an amino-modified natural polysaccharide that canbe also used as a polymeric gel for the covalent binding of OND probes [61]. Chitosan offers several advantages for NA immobilization. Its pH responsive properties allow it to be easily immobilized onto glass slides for the construction of arrays. Specifically, chitosan is soluble at low pH, when its amine groups are protonated, but becomes insoluble when the pH is raised above its pKa 6.3). 

Carrier based pH membranes (4-7) have traditionally required the addition of trapped, hydrophobic negative sites, typically tetraphenylborate (TPB) and p-chlorotetraphenyl borate (p-CITPB). In comparative studies we have frequently noticed the improved pH response of the membranes containing additional sites compared with those with only naturally occurring fixed sites, found in all the PVCs we have tested. Specifically, there is a distinctive deterioration in accuracy in the latter sensors at low pH. In addition, membranes prepared from aminated PVC with TPB have previously shown a good pH response (8). However, our preliminary impedance studies have shown that undoped aminated PVC membranes have a relatively low conductivity when compared with the neutral carrier designs above. 

PEO-Br macroinitiators are often used to prepare ABC terpolymers through the macroinitiator approach. An interesting example wherein this approach has been utilized is the preparation of PEO-PDEAEMA-PHEMA (HEMA 2-hydroxyethyl methacrylate). The synthesis was performed in a one-pot reaction with sequential addition of monomers DEAEMA and HEMA. Accordingly the PHEMA block was converted by esterification, using excess succinic anhydride in pyridine, yielding the final product PEO-PDEAEMA-PSEMA. This triple-hydrophilic block terpolymer exhibits pH-responsive self-association. It forms three types of micelles, the corona of which changes its nature from cationic protonated PDEAEMA (low pH) to natural PEO (intermediate pH) and to anionic neutralized PSEMA (high pH), as a function of solution pH. ... 

Zhou and coworkers recently reported the synthesis of chitosan-based nanogels and their pH-responsive biomedical applications [123]. Nanogels have been prepared from chitosan and poly(methacrylic acid) (PMAA) polymers in two ways using covalent crosslinking or physical association between the polymers (Fig. 22). Naturally occurring chitin, chitosan, and their derivatives have found widespread applications in various biological settings [124]. 

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