Binding pH

Binding pH is a critical factor for boronate affinity. Usually a lowest binding pH is provided to indicate the lowest pH condition of the sample environment in which a boronate affinity medium can work. The binding pH of boronate affinity is generally determined by the pkTa value of the boronic 

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Other proteins interact with the receptors indirectly through adapter molecules which have no catalytic activity. Two well-known adapter proteins are Grb2476 and She.477478 The 25-kDa protein Grb2 consists entirely of recognition domains, one SH2 and two SH3 domains (Fig. 11-14). The larger She, which is found in all mammalian tissues, contains a 200-residue phosphotyrosyl-binding PH domain (Chapter 7) at the N terminus, a... 

Barboiu M, Lehn JM (2002) Dynamic chemical devices modulation of contraction/extension molecular motion by coupled-ion binding/pH change-induced structural switching. Proc Natl Acad Sci USA 99 5201-5206... 

Effects of hgand binding, pH, temperature, denaturant, and so on, are readily studied. 

M. Barboiu, J.-M. Lehn, Dynamic Chemical Devices Modulation of Contrac-tion/Extension Molecular Motion by Coupled-Ion Binding/pH Change-Induced Structural Switching , Proc. Natl. Acad. Sci. USA, 99, 5201 (2002)... 

Although dinical microbiology laboratories report microbial susceptibility test results as sensitive or resistant to a particular antibiotic, this is not an absolute predictor of clinical response. In a given patient s infection, variables such as absorption of the drug, its penetration to the site of infection, and its activity once there (influenced, for example, by protein binding, pH, concentration of oxygen, metabolic state of the pathogen, intracellular location and concentration of microbes) profoundly alter the likelihood that effective therapy will result. 

Robertson, A.P., Goethite-humic acid interactions and their effects on copper(II) binding, Ph.D. Thesis. Stanford University, 1996, cited after [761]. 

As mentioned above, the binding pH of conventional boronate affinity in aqueous solution should be >8.5, which gives rise to not only the inconvenience of pH adjustment but also the risk of degradation of labile compounds since the pH of frequently used biosamples, such as blood, tear and saliva ranges from 4.5 to 8.0. To address this issue, novel boronic acids and innovative methods that allow for binding cis-diols in a real sample pH environment are in great demand. 

To reduce the binding pH, Scouten and co-workers first synthesized a novel boronate affinity ligand, catechol [2-(diethylamino)carbonyl-4-bromomethyljphenylboronate, which contains intramolecular B-O coordination. Then, this ligand was coupled to sulfhydryl cellulose. The novel boronate affinity gel bound the glycoprotein horseradish peroxidase (HRP) at neutral condition (pH 7.0), at which the immobilized enzyme retain 90.12% of its original activity. 

Although the above-mentioned binding pH has been reduced to 5.0, there is still an apparent gap for the direct application to urine because the pH of frequently used biosamples, particularly urine, ranges from 4.5 to 8.0. " Liu and co-workers further synthesized a pyridinylboronic acid-functionalized organic-silica hybrid monolithic capillary " to meet the broad pH range of urine samples. The preparation procedure is illustrated in Scheme 11.11. It included two steps (1) preparation of a chloropropyl-silica hybrid... 

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