Solvent and Temperature Dependencies of the Rates of Thermal -to- Isomerization of Tetra-()substituted 4-Aminoazobenzenes Containing 2,6-Dimethoxy Groups.

The kinetics of thermal -to- isomerization of two tetra-()substituted 4-aminoazobenzene derivatives containing 2,6-dimethoxy groups in the 4-aminobenzene ring and either 2',6'-dimethyl () or 2',6'-dichloro groups in another ring was studied in 16 and 9 solvents, respectively, at room temperature. In addition, the kinetics of isomerization of was studied at variable temperatures in 6 solvents. The solvent effects were analyzed in terms of multiparameter correlations using the Kamlet-Taft, Catalan, and Laurence scales.

Zwitterion-neutral form equilibria and binding selectivity of pyridineboronic acids.

A B NMR study of 3-pyridineboronic acid at variable pH in water and 50 vol% aqueous dioxane confirms that the tautomeric equilibrium of the acid is shifted to the zwitterionic form in water, but to the molecular form in the mixed organic solvent. Interactions of 3- and 4-pyridineboronic acids with sialic acid, fructose and several other diols were studied by potentiometric titrations in a wide range of pH in water and water-organic mixtures. In all reaction media the stability of boronate complexes increases upon an increase in pH for neutral low acidic diols such as fructose and glucose but has the opposite trend for highly acidic sialic and lactic acids occurring as anionic species.

Probing the Role of the Bridging Nitrogen in the Signaling Mechanism of an Anthracene-Boronic Acid Sugar Sensor and a Different Version of the PET-Based Mechanism.

The N-quaternized derivative of the James-Shinkai anthracene-boronic acid fluorescence sugar sensor was prepared to probe the role of the bridging nitrogen in the signaling mechanism of . Both and contain positively charged bridging groups NMe or NH, respectively, but lacks the ability to form the intramolecular ammonium-boronate doubly ionic hydrogen bond present in . Receptors and display opposite fluorescence vs pH profiles with a small turn-on effect of the sugar binding to the zwitterion of in contrast to a large effect observed with .

Anion Recognition by Benzoxaborole.

The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole () were determined by H and B NMR titrations in DMSO or MeCN. Compared to phenylboronic acid (PBA), is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F, HPO, and PhPO anions, which are coordinately bonded to , and partially with SO, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with .