Erythrosin B Phosphorescence Monitors Molecular Mobility and Dynamic Site Heterogeneity in Amorphous Sucrose

Abstract

Molecular mobility modulates the chemical and physical stability of amorphous biomaterials. This study used steady-state and time-resolved phosphorescence of erythrosin B to monitor mobility in thin films of amorphous solid sucrose as a function of temperature. The phosphorescence intensity (lifetime), emission energy, and red-edge excitation effect were all sensitive to localized molecular mobility on the microsecond timescale in the glass and to more global modes of mobility activated at the glass transition. Blue shifts in the emission spectrum with time after excitation and systematic variations in the phosphorescence lifetime with wavelength indicated that emission originates from multiple sites ranging from short lifetime species with red-shifted emission spectrum to long lifetime species with blue-shifted emission spectrum; the activation energy for nonradiative decay of the triplet state was considerably larger for the blue-emitting species in both the glass and the melt. This study illustrates that phosphorescence from erythrosin B is sensitive both to local dipolar relaxations in the glass as well as more global relaxations in the sucrose melt and provides evidence of the value of phosphorescence as a probe of dynamic site heterogeneity as well as overall molecular mobility in amorphous biomaterials.

Local Mobility in Amorphous Pharmaceuticals—Characterization and Implications on Stability

“…The faster relaxations in glassy toluene and picoline were also characterized by light scattering. 122 Pravinata et al 123 used timeresolved erythrosine B phosphorescence to probe local mobility as well as dynamic heterogeneity in amorphous sucrose. Richert 124 reported the use of dielectric hole-burning technique to investigate the heterogeneous dynamics of JG relaxations in glassy sorbitol.…”

Molecular mobility and oxygen permeability in amorphous β-lactoglobulin films

“…Hydrated globular proteins undergo a dynamical transition (Td) at 200 K, a phenomenon well documented by X-ray diffraction analysis of thermal B-factors (Rasmussen, Stock, Ringe, & Petsko, 1992), neutron scattering (Cusack, 1989;Cusack, Smith, Finney, Tidor, & Karplus, 1988;Doster, Cusack, & Petry, 1990;Loncharich & Brooks, 1990;, and differential scanning calorimetry (Barkalov, Bol'shakov, Gol'danskii, & Krupyanskii, 1992). This transition involves a change in protein motions from small amplitude, harmonic vibrations of covalently bonded atoms to large scale, anharmonic, collective motions of non-bonded atoms.…”

The Effect of Molecular Size on Molecular Mobility in Amorphous Oligosaccharides

“…The principle is that phosphorescence spectroscopy of triplet probes can examine the slow mobility motions occurring on the milliseconds to seconds time scale in highly viscous glasses and melts. Ery B is a food grade phosphorescence probe which has been found to be very sensitive to the molecular mobility in amorphous sugars [13][14][15][16][17][18][19][20]22,25,26 and proteins 27,28 . By embedding Ery B within the amorphous matrix, we can collect signals from probe molecules that are surrounded by matrix molecules and respond to the slow modes of mobility in local environments.…”

“…We initially used steady-state and time-resolved phosphorescence of the triplet probe erythrosin B to measure molecular mobility in the amorphous sucrose matrix 13 . The emission energy and collisional quenching rate obtained from phosphorescence measurements was found to respond sensitively to thermally induced changes in the physical state of the amorphous sucrose solid; the temperature at which a discontinuity occurred in an Arrhenius plot of matrix mobility was close to the macroscopic glass transition temperature T g .…”