Boronic acids diols

Shinkai (65) exploited the boronic acid-diol motif mentioned above to self-assemble a polymer based on pyridine-magnesium porphyrin interactions. In this case, the evidence for polymerization comes from lightscattering experiments in dilute solution which yielded an average molecular weight of 109 g mol-1 for this system. 

Zinc carboxylate interactions have been exploited as part of a fluorescent molecular sensor for uronic acids. The sensors feature two interactions coordination of the carboxylate to the zinc and a boronic acid diol interaction.389 Photoluminescent coordination polymers from hydrothermal syntheses containing Zn40 or Zn4(OH)2 cores with isophthalate or fumarate and 4,4 -bipyridine form two- and three-dimensional structures. Single X-ray diffraction of both dicarboxylates identified the network structure.373... 

Kamati VV, Gao X, Gao S, Yang W, Ni W, Sankar S, Wang B. A glucose-selective fluorescence sensor based on boronic acid-diol recognition. Bioorganic and Medicinal Chemistry Letters 2002, 12, 3373-3377. 

Swing mill, 1h at 70% of maximum capacity, boronic acid diol 1 1. 

G. Springsteen, B. H. Wang, A detailed examination of boronic acid-diol complexation, Tetrahedron 2002, 58, 5291. 

Scheme 5 Catecholamine sensors utilizing both amine-aldehyde and boronic acid-diol interactions.

Sarson et al. combined two kinds of reversible interactions, namely, boronic acid-diol and metal-pyridine interactions, to generate self-assembled polymers. A1 2 mixture of magnesium dicatechol porphyrin 41 and pyridine-3-boronic acid self-assembles into a polymer. The molecularweightwas estimated to be 10 by light scattering measurements. 

On the basis of the simple boronic acid-diol reaction at the moleeular level, this chapter focuses on polymer-polymer interaetions triggered by boronic acid-diol esterification. When boronie aeid-diol reaetions oeeur cooperatively along a polymer chain, the structural changes caused by the complexation can easily amplify over hierarchies of nanometer to mierome-ter scale. Even without any signal such as fluorescence emission, the boronic acid-diol reaction based on precise molecular recognition is detectable as phase transition at the micrometer scale. 

Figure 9.1 Polymer-polymer interactions assisted by boronic acid-diol reaction (a) boronic acid-appended polymer-hydroxylated polymer interaction, (b) boronic acid-appended polymer-saccharide interaction, and (c) boronic acid-functionalized molecule-hydroxylated polymer...

Boronic acids can be incorporated into polymers in order to improve polymer-polymer interactions and develop polymer based materials. The incorporation of specific boronic acid-diol interactions, dramatically improves the polymer properties. Such that, structural changes caused by the complex-ation are amplified and readily detected. Details of polymer-polymer interactions prompted by the boronic acid-diol interaction are reviewed in this chapter by Numata. 

Boronic Acid-Diol (Sugar) Equilibrium in Water... 

Freund has prepared polyaniline boronic acids by the electrochemical polymerization of 3-aminophenyl boronic acid [169, 170], The electrochemical potential of the polymer is sensitive to changes in the pK of the polymer as a result of boronic acid-diol complex formation. Fabre has also used polyaniline boronic acids as a con-ductiomeric sensor for dopamine [171]. 

Along this line, boronic acid-based polymer complexes are sensitive to glucose as a potential insulin delivery system, presumably due to the competitive binding of glucose to boronic acids, which disrupts the boronic acid-diol complex network within the polymer matrix (Scheme 13.5) [157]. In one study, the phenylboronic acid (PBA) moiety was attached to poly(M-vinyl-2-pyrrolidone) (NVP) to form poly(NVP-co-PBA)... 

Glucose-Responsive Systems Based on Boronic Acid-Diol Complexation... 

Rehybridisation of an sp boron complex to form the sp tetrahedral boronate species will therefore reduce the ring strain and lower the energy of the system. As a result it is thought that the dynamic equilibrium illustrated in Scheme 7 (and redrawn in Scheme 9 for clarity) between the neutral boronic acid diol complex 19 and the boronate anion diol complex 20 will shift to the right, causing the observed increase in the value of the acidity constant,... 

Over the period 2003-2004 the relationship between boronic acid diol complexation and acidity was studied computationally. Bock and co-workers... 

The observed stability constants (Afobs) for compounds 140( =3)-145( =g) and 146(pyrene) with saccharidcs, which have the ability to form a furanose ring with a jjn-periplanar anomeric hydroxyl pair (o-glucose, melibiose, o-fructose and lactulose) are large, consistent with our understanding of the boronic acid diol interaction. Equally, the low or zero values of the observed stability constants (Afobs) for saccharides unable to form a furanose ring with a. syw-periplanar anomeric hydroxyl pair (maltose and leucrose) are also consistent with current thinking. 

On complexation of a saccharide to a boronic acid there is a contraction of the O-B-0 bond angle with a concomitant increase in the addity of the boron species. Boronic acid diol complex formation is heavily pH dependent. Rate and stability constants increase by around four and five orders of magnitude, respectively, at pHs above the pA a of the boronic acid. 

Though the earliest references associated with boronate-linked materials date back to the 1950s, it has only been in the last 10-20 years that great strides have been made using these covalent-reversible boronic acid-diol interactions. 

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