Molecular Mobility in Amorphous Maltose and Maltitol from Phosphorescence of Erythrosin B

Abstract

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in amorphous thin films of maltose and maltitol at mole ratios of 0.8:10(4) dye:sugar to monitor the molecular mobility of these matrixes over the temperature range from -25 to over 110 degrees C. Analysis of the emission peak frequency and bandwidth (full width at half-maximum) and time-resolved intensity decay parameters provided information about thermally activated modes of matrix mobility that enhanced the rate of dipolar relaxation around the triplet state and the rate of intersystem crossing to the ground state (k(TS0)). Detectable dipolar relaxation began in the glassy state about 50 degrees C below T(g) in both maltose and maltitol; the relaxation rate, however, while 3-4 orders of magnitude slower than literature values for the beta relaxation determined from dielectric relaxation, had an activation energy only 2-fold smaller. Dipolar relaxation was further enhanced in the melt above T(g); the dipolar relaxation rates in the melt scaled nearly exactly with rates for the alpha relaxation determined from dielectric relaxation. Intensity decays were well fit using a stretched exponential decay function in which the lifetime (tau) and the stretching exponent (beta) were the physically significant parameters. In maltose, the magnitude of k(TS0) was essentially constant in the glass and increased dramatically at the T(g); in maltitol k(TS0) increased moderately at T(g) = -50 degrees C and more dramatically in the melt at T(g) = +20 degrees C. The value of k(TS0) in maltose:maltitol mixtures was significantly smaller than that seen in pure maltose and maltitol, suggesting that specific interactions decreased the mobility of the mixed sugar matrix; this phenomenon was comparable to the antiplasticization seen in mixtures of small molecule plasticizers with synthetic polymers and starch. The extent of inhomogeneous broadening and dynamic heterogeneity were essentially constant in the glass and increased dramatically in maltose and more gradually in maltitol at the glass transition.

Molecular Mobility and Oxygen Permeability in Amorphous Bovine Serum Albumin Films

“…The large increase in spectral bandwidth reflects a corresponding increase in the extent of inhomogeneous broadening of the emission spectrum 28 because of an increase in the width of the distribution of energetically distinct matrix environments in the BSA film. Similar trends have been seen in amorphous sucrose, 13 maltose, 25 and lactose 29 around their glass transition temperatures. Both the decrease in emission frequency and the increase in bandwidth thus provide indications that the protein matrix softened above õ50-60-C. …”

“…(1)]. This value, 32.88 T 0.5 kJ mol j1 , was significantly smaller than the values in water (36.9 T 0.6 kJ mol j1 ) or 66 wt.% aqueous sucrose (36.9 T 0.1 kJ mol j1 ) 13 and in polyvinyl alcohol (41.2 T 0.4 kJ mol j1 ), 23 similar to the values in amorphous sucrose (31.6 T 0.4 kJ mol j1 ) 13 and maltose (32.7 T 1.1 kJ mol j1 ), 25 and larger than the value in ethanol (28.5 T 2.5 kJ mol j1 ), 22 indicating that solvent or matrix properties modulate the singlet-triplet energy gap of Ery B.…”

Photophysical Probes of the Amorphous Solid State of Proteins

“…Data were fit to a stretched exponential, or Kohlrausch-Williams-Watts (KWW) decay model, 44 which has been used to fit the intensity decays of Ery B dispersed in a wide variety of amorphous solid sugars 21,26,32,33,[37][38][39][40] and proteins 23,34-36 :…”

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.…”

“…Glasses Phosphorescence emission energy and lifetime (intensity) from Ery B are sensitive to two distinct modes of molecular mobility in amorphous biomaterials 13,25,28 : matrix dipolar relaxation around the excited T 1 triplet state prior to emission that decreases the energy of the state and thus lowers the phosphorescence emission energy; and matrix collisions that promote intersystem crossing from the excited T 1 triplet state to the ground S 0 singlet state and thus increase k TS0 and lower the lifetime. This study of matrix mobility in amorphous sugars using Ery B phosphorescence indicates that both of these modes of molecular mobility are influenced by molecular size.…”