Smart photoacoustics: A pulsed-laser system for analysis of rapid volume changes due to heat release, molecular conformational change, and charge solvation

摘要

The goal of "smart photoacoustics" is to rapidly analyze the rate and amplitude of photoinduced volume changes (ns to ps time window), as well as to diagnose the source of the measured volume change: heat release, molecular conformational change and/or electrostriction (solvation or desolvation of charged groups). In contrast, the older technique of "photoacoustic calorimetry" tacitly assumes that only heat release from photoexcited molecules contributes to signals. Smart photoacoustics uses hardware, software and chemical protocols to distinguish the different contributors to the observed signals. The method is demonstrated using two systems: the proton reactions of photoexcited pyranine (8-hydroxypyrene-1,3,6-trisulfonic acid) and the conformational changes in sperm whale carboxymyoglobin upon cleavage of the Fe-CO bond. Smart photoacoustics is the basis for the pulsed-laser photoacoustic instrument we are developing, which includes a sample chamber having thermoelectric control of temperature, magnetic stirring, control of transducer mounting tension, nitrogen flush of cuvette surfaces to eliminate condensation, argon degassing of samples, and two ports for monitoring optical properties of the sample. Central to the instrument is a Windows-based instrument-control program which uses a script language to completely automate the operation of the instrument, the collection of data and the analysis of the photoacoustic waveforms.