Abstract:
The article presents influence of pH and glucose concentration on phenylboronic acid (PBA) fluorescence studied by steady-state and time-resolved measurements. Fluorescence of PBA decreases with growing pH. These changes reflected acid-base equilibrium of PBA and allowed to estimate value of pKd as 9.2, which is comparable with literature data. Fluorescence intensity of phenylboronic acid is quenched in presence of glucose. The effect of quenching is more pronounced with increasing pH. At pH 7 quenching can be described by Stern-Volmer equation, at pH 8 and 9 by modified one. The obtained quenching constants are growing with pH increase. The quenching of phenylboronic acid fluorescence by glucose is a static one, which is confirmed by time-resolved measurements. Two lifetimes were found for fluorescence decay of phenylboronic acid. The lifetimes are practically independent on pH and glucose concentration and also fraction of both lifetimes are nearly the same. The obtained Stern-Volmer constants can be interpreted as apparent equilibrium constants of ester formation between acid and glucose.
