Boronic add sensor

Glucose chelating boronic add compounds used as sensors... 

Chemical sensors based on the competitive binding of sugars to the boronic add ligand have been reported. When 3-aminophenyl boronic acid was covalently linked to GSH-capped CdSe-ZnS QDs, the boronic acid ligand formed boronate esters with... 

The boronic add PET system has also been used in combination with other binding sites. James and co-workers have explored the D-glucosamine selective fluorescent systems 32a,b based on a boronic add and aza crown ether [87,88) (Figure 12.8). Sensors 32a,b consist of monoaza-18-crown-6 ether or monoaza-15binding site for the ammonium terminal of D-glucosamine hydrochloride, while a boronic add serves as a binding site for the diol part of D-glucosamine hydrochloride. 

The tertiary amine boronic add (N-B) interaction in a boronic acid-based PET sensor has strength in the range of 15-25 kJ mol ... 

An informed decision will therefore have to be taken in the future design of fluorescent sensors, such that the polarity of the chosen guest species complements the solvation within the binding pocket. While not a direct premise of complementarity between hydrophobicity of the appended fluorophore of the sensor and the pyranose form of the guest monosaccharide, it appears to be the case that boronic adds display enhanced selectivity for D-glucose over o-galactose when the hydrophobicity of the binding pocket is increased. 

So far, we have discussed the development of integrated molecular sensors using boronic adds. The systems contain a receptor and reporter (fluorophore or chromophore) as part of a discrete molecular unit. However, another approach towards boronic acid-based sensors is also possible where the receptor and a reporter unit are separate as in a competitive assay. A competitive assay requires that the receptor and reporter (typically a commerdal dye) associate under the measurement conditions. The receptor-reporter complex is then selectively dissociated by the addition of the appropriate guests. When the... 

Smith has prepared a grafted polymer containing a ribonucleoside 5 -tripho-sphate selective sensor. The polymers were prepared using poly(allylamine) (PAA) to which 10% of boronic add monomer unit 202 was grafted.Also, a library of potential sialic acid receptors was prepared. In this case, the polymers were prepared using PAA to which 2% of the boronic acid monomer unit 202 was grafted. The final polymers also contained various amounts of 4-hydroxybenzoic acid, 4-imidazolacetic acid, octanoic acid and/or succinic anhydride. 

Wang has synthesized boronic acids derived from nitrophenols such as 45 and 46 with possible use as a recognition and signalling unit for the construction of polyboronic add sensors [21]. Synthesis of boronic acid 45 involves crossboronate ester and deprotection of the methoxy group, whereas the dinitrophenyl boronic acid 46 is prepared by nitration of 2-methoxyboronic acid and subsequent cleavage of the methoxy ether with BBtj. The resulting functionalized boronic acids are both obtained in 90% yield (Scheme 3.15). 

Boronic acids have been used in the development of surface plasmon resonance (SPR) [174,175] quartz crystal microbalance (QCM) sensors [174,176,177], Faradaic impedance spectroscopy [177], ion-sensitive field effect transistors (ISFET) [178], and chemical exchange saturation transfer (CEST) contrast agents in magnetic resonance imaging (MRl) [179]. The swelling of phenylboronic add polymers has also been used to control the release of insulin (180,181]. 

The D-fructose selective monoboronic add-based sensor 78 was enhanced by James in 1995 with the introduction of a second boronic acid group to form the diboronic acid sensor This Receptor-Spacer-Fluorophore-Spacer-... 

James and co-workers have prepared a ferrocene monoboronic acid 187 and diboronic acid 188 as electrochemical saccharide sensors. The monoboronic acid system 187 has also been prepared and proposed as an electrochemical sensor for saccharides by Norrild. The electrochemical saccharide sensor 188 contains two boronic acid units (saccharide selectivity), one ferrocene unit (electrochemical read out) and a hexamethylene linker unit (for D-glucose selectivity). The electrochemical sensor 188 displays enhanced D-glucose (40 times) and D-galactose (17 times) selectivity when compared to the monoboronic add 187. 

---