Progress 09/01/01 to 08/31/05
Outputs
We have demonstrated that the phosphorescence of xanthene (erythrosin and eosin) and indole (tryptophan) probes are sensitive to both molecular mobility and dynamic site heterogeneity within amorphous sugars (glucose, sucrose, maltose, maltotriose, trehalose) and sugar alcohols (maltitol and lactitol). Phosphorescence was found to provide information on two modes of matrix mobility: dipolar relaxation of sugar hydroxyl groups and matrix vibrational relaxation due to larger-scale motions of the sugars. Dipolar relaxation was evaluated by analysis of the probe emission energy and collisional quenching was evaluated by analysis of the probe emission lifetime. Phosphorescence also provided insight into the extent of dynamic variability within the amorphous matrix due to differences in mobility at different sites. Dynamic site heterogeneity was evaluated by analysis of the variation in emission lifetime with differences in the excitation and emission wavelength. The
following physical model appears applicable to all amorphous sugars and sugar alcohols: In the glass and, to a lesser degree, the melt, there are a range of dynamic environments ranging from mobile ("red") sites to immobile ("blue") sites. Red sites exhibit fast dipolar relaxation and fast collisional quenching rates, and have lower apparent activation energy for the rate of collisional quenching, indicating that the matrix motions involve smaller cooperative units (perhaps reflecting regions with a weaker hydrogen bonding network). Blue sites, on the other hand, have slow dipolar relaxation and slow collisional quenching rates, and have higher apparent activation energy for the rate of collisional quenching, indicating that the motions involve larger cooperative units (perhaps reflecting regions with a stronger hydrogen bonded network). There are intriguing differences in molecular mobility between sugars and sugar alcohols. Mobility in maltitol, for example, was higher in the glass
and lower in the melt than in maltose, and the mobility in a 50:50 mixture was also higher in the glass than in maltitol, suggesting that strong interactions between the sugar and the sugar alcohol constrain mobility in the glass. Similar behavior was also seen in the lactose and lactitol mixtures. Sugars were found to vary in their intrinsic mobility: when plotted versus T-Tg lifetimes varied such that sucrose > maltose > trehalose, while the apparent activation energy for quenching (determined from Arrhenius plots of the non-radiative decay rates) also varied in the order sucrose > maltose > trehalose. These results suggest that mobility in the glassy state varies in the order trehalose > maltose > sucrose. Since the Tg values vary in the same order, this suggests that sugars with higher glass transition temperature also have higher molecular mobility within the glassy state. A similar trend was seen in the homologous series glucose, maltose, and maltotriose.
Impacts
This research provides insight into the molecular processes that control chemical and physical change within amorphous glassy sugars and sugar alcohols and in their melts close to the glass transition. These results indicate that amorphous carbohydrates are dynamically complex, exhibiting mobilites on time scales ranging from nanoseconds to seconds, and are dynamically heterogeneous, with sites exhibiting variations in molecular mobility that differ by up to 1000-fold. In addition, the mobility of sugars appears to vary inversely with the glass transition temperature such that sugars with higher Tg (trehalose, maltotriose) are more mobile in the glass than those with lower Tg (glucose, sucrose). These insights should assist in formulating novel foods and encapsulants with improved resistance to degradative reactions in sugars, proteins, lipids, vitamins, and bioactive natural compounds (nutraceuticals)and in formulating novel pharmaceutical carriers for drugs and
bioactive compounds with improved resistance to chemical and physical change.
Publications
- Shirke, S., Takhistov, P., & Ludescher, R. D. (2005) "Molecular Mobility in Amorphous Maltose and Maltitol from Phosphorescence of Erythrosin B." Journal of Physical Chemistry B 109, 16119-16126.
- Pravinata, L. C., You, Y., & Ludescher, R. D. (2005) "Erythrosin B Phosphorescence Monitors Molecular Mobility and Dynamic Site Heterogeneity in Amorphous Sucrose." Biophysical Journal 88, 3551-3561.
- Shirke, Sonali & Ludescher, R. D. (2005) "Dynamic Site Heterogeneity in Amorphous Maltose and Maltitol from Spectral Heterogeneity in Erythrosin B Phosphorescence." Carbohydrate Research 340, 2661-2669.
- Shirke, Sonali & Ludescher, R. D. (2005) "Molecular Mobility and the Glass Transition in Amorphous Glucose, Maltose, and Maltotriose." Carbohydrate Research 340, 2654-2660.
|
Progress 01/01/04 to 12/31/04
Outputs
Luminescence from erythrosin, eosin, and tryptophan was used to characterize molecular mobility in amorphous sugars. These probes sensed mobility and dynamic site heterogeneity on time scales from 1 ns to 1 s below and above Tg. Emission spectra monitored the extent of dipolar relaxation; phosphorescence lifetimes monitored the rate of collisional quenching. The phosphorescence intensity, spectra, and lifetimes of erythrosin and eosin sensed both molecular mobility and dynamic site heterogeneity in amorphous sucrose. Intensity and lifetimes decreased with increasing temperature and exhibited a break at the Tg. Emission spectra blue shifted with time. Emission lifetimes varied as a function of both excitation and emission wavelength; apparent activation energies for quenching also varied with wavelength. The following physical model explains these data: In the glass and, to a lesser degree, the melt, probes are distributed among dynamic environments ranging from mobile
sites with red-shifted emission (due to faster dipolar relaxation), shorter lifetimes (due to faster collisional quenching), and lower apparent activation energy, to more rigid sites with blue-shifted emission (due to slower dipolar relaxation), longer lifetime (due to slower collisional quenching), and higher apparent activation energy. These probes exhibited similar spectroscopic behavior in amorphous sucrose, maltose, lactose, maltitol and lactitol, suggesting that this heterogeneous dynamic model applies to all sugars. There are intriguing differences in the mobility between sugars and sugar alcohol, however. Mobility in maltitol was higher in the glass and lower in the melt than in maltose and the mobility in a 50:50 mixture was higher in the glass than in maltitol, suggesting that strong interactions between the sugar and the sugar alcohol constrain mobility in the glass. Luminescence of tryptophan was used to monitor mobility and dynamic site heterogeneity in amorphous sucrose,
maltose, and trehalose on the 1-10 ns and 0.001 to 1 s time scales. The amorphous sugars exhibit unexpectedly high rates of molecular mobility even in the glass state. The sugars also vary in terms of their intrinsic mobility: when plotted versus T-Tg lifetimes vary such that sucrose > maltose > trehalose while the apparent activation energy for quenching also varies in that order. Mobility in the glass thus appears to vary in the order trehalose > maltose > sucrose, the same ordering as Tg, suggesting that sugars with higher glass transition temperature also have higher molecular mobility within the glass. Measurements of the phosphorescence lifetime of tryptophan as a function of emission wavelength provide evidence of dynamic site heterogeneity within glassy sucrose, maltose, and trehalose at 20C. Lifetimes varied dramatically across the emission band, being highest near the emission maximum (at 440 nm) and decreasing somewhat at the blue and dramatically at the red edge. The
variation in non-radiative decay rate indicates that the tryptophan probes are distributed among sites with quenching rates that vary 1000-fold for sucrose, 150-fold for maltose, and 50-fold for trehalose.
Impacts
This research provides insight into the molecular processes that control chemical and physical change within amorphous glassy sugars. Such insight should assist in formulating novel foods and encapsulants with improved resistance to degradative reactions in sugars, proteins, lipids, vitamins, and bioactive natural compounds (nutraceuticals)and in formulating novel pharmaceutical carriers for drugs and bioactive compounds with improved resistance to chemical and physical change.
Publications
- Zunic, A. & Ludescher, R.D. (2004) Site heterogeneity and molecular mobility in glassy sugars. Biophysical Society, 48th Annual Meeting, Baltimore, MD (poster).
- Ludescher, R.D. & Zunic, A. (2004) Tryptophan luminescence detects molecular mobility in amorphous sugars. IFT Annual Meeting, Las Vegas, NV (poster).
- Zunic, A. (2004) Studies Of Molecular Mobility In Amorphous Sugars Using Fluorescence And Phosphorescence Of Tryptophan. MS Thesis, Rutgers University.
- Shirke, S., Nack, T.J., You, Y., & Ludescher, R.D. (2005) Phosphorescence probes molecular mobility and dynamic site heterogeneity in amorphous biomaterials. Biophysical Society, 49th Annual Meeting, Long Beach, CA (poster).
- Shirke, S. (2005) Molecular Mobility in Amorphous Sugars and Sugar Alcohols as Detected by Phosphorescence of Erythrosin B. MS Thesis, Rutgers University.
- Pravinata, L.C., You, Y., & Ludescher, R.D. (2004) Erythrosin B Phosphorescence Monitors Molecular Mobility and Dynamic Site Heterogeneity in Amorphous Sucrose. Biophysical Journal, in press.
- Zunic, A., Pravinata, L., & Ludescher, R.D. (2003) Tryptophan Phosphorescence is Sensitive to Molecular Mobility and Oxygen Diffusion in Glassy Sugars. Biophysical Society, 47th Annual Meeting, San Antonio, TX (poster).
- Pravinata, L.C. & Ludescher, R.D. (2003) Molecular Mobility Studies of Amorphous Sucrose and Cornstarch using a Novel Technique, Luminescence Spectroscopy. IFT Annual Meeting, Chicago, IL, (poster).
- Zunic, A. & Ludescher, R.D. (2003) Oxygen Diffusion and Molecular Mobility in Amorphous Sugars. IFT Annual Meeting, Chicago, IL, (poster).
- Pravinata, L. (2003) Molecular Mobility Of Amorphous Sucrose Detected By Phosphorescence Of Erythrosin B and Eosin Y. MS Thesis, Rutgers University.
- Ludescher, R.D. & Pravinata, L. (2004) Eosin phosphorescence detects site heterogeneity and molecular mobility in amorphous sucrose. Biophysical Society, 48th Annual Meeting, Baltimore, MD (poster).
- Pravinata, L. & Ludescher, R.D. (2002) Molecular Mobility Of Amorphous Sucrose Determined From Phosphorescence Of Erythrosin B. Biophysical Society, 46th Annual Meeting, San Francisco, CA (poster).
- Pravinata, L & Ludescher, R. D. (2002) Erythrosin B Phosphorescence As A Probe Of Molecular Mobility In Amorphous Sucrose. IFT Annual Meeting, Anaheim, CA (poster).
- Pravinata, L. & Ludescher, R. D. (2003) Evidence For Site-Heterogeneity In Amorphous Sucrose From Phosphorescence Of Erythrosin B. Biophysical Society, 47th Annual Meeting, San Antonio, TX (poster).
|
Progress 09/01/01 to 08/31/04
Outputs
Luminescence from erythrosin, eosin, and tryptophan was used to characterize molecular mobility in amorphous sugars. These probes sensed mobility and dynamic site heterogeneity on time scales from 1 ns to 1 s below and above Tg. Emission spectra monitored the extent of dipolar relaxation; phosphorescence lifetimes monitored the rate of collisional quenching. The phosphorescence intensity, spectra, and lifetimes of erythrosin and eosin sensed both molecular mobility and dynamic site heterogeneity in amorphous sucrose. Intensity and lifetimes decreased with increasing temperature and exhibited a break at the Tg. Emission spectra blue shifted with time. Emission lifetimes varied as a function of both excitation and emission wavelength; apparent activation energies for quenching also varied with wavelength. The following physical model explains these data: In the glass and, to a lesser degree, the melt, probes are distributed among dynamic environments ranging from mobile
sites with red-shifted emission (due to faster dipolar relaxation), shorter lifetimes (due to faster collisional quenching), and lower apparent activation energy, to more rigid sites with blue-shifted emission (due to slower dipolar relaxation), longer lifetime (due to slower collisional quenching), and higher apparent activation energy. These probes exhibited similar spectroscopic behavior in amorphous sucrose, maltose, lactose, maltitol and lactitol, suggesting that this heterogeneous dynamic model applies to all sugars. There are intriguing differences in the mobility between sugars and sugar alcohol, however. Mobility in maltitol was higher in the glass and lower in the melt than in maltose and the mobility in a 50:50 mixture was higher in the glass than in maltitol, suggesting that strong interactions between the sugar and the sugar alcohol constrain mobility in the glass. Luminescence of tryptophan was used to monitor mobility and dynamic site heterogeneity in amorphous sucrose,
maltose, and trehalose on the 1-10 ns and 0.001 to 1 s time scales. The amorphous sugars exhibit unexpectedly high rates of molecular mobility even in the glass state. The sugars also vary in terms of their intrinsic mobility: when plotted versus T-Tg lifetimes vary such that sucrose > maltose > trehalose while the apparent activation energy for quenching also varies in that order. Mobility in the glass thus appears to vary in the order trehalose > maltose > sucrose, the same ordering as Tg, suggesting that sugars with higher glass transition temperature also have higher molecular mobility within the glass. Measurements of the phosphorescence lifetime of tryptophan as a function of emission wavelength provide evidence of dynamic site heterogeneity within glassy sucrose, maltose, and trehalose at 20C. Lifetimes varied dramatically across the emission band, being highest near the emission maximum (at 440 nm) and decreasing somewhat at the blue and dramatically at the red edge. The
variation in non-radiative decay rate indicates that the tryptophan probes are distributed among sites with quenching rates that vary 1000-fold for sucrose, 150-fold for maltose, and 50-fold for trehalose.
Impacts
This research provides insight into the molecular processes that control chemical and physical change within amorphous glassy sugars. Such insight should assist in formulating novel foods and encapsulants with improved resistance to degradative reactions in sugars, proteins, lipids, vitamins, and bioactive natural compounds (nutraceuticals)and in formulating novel pharmaceutical carriers for drugs and bioactive compounds with improved resistance to chemical and physical change.
Publications
- Pravinata, L.C. & Ludescher, R.D. (2003) Molecular Mobility Studies of Amorphous Sucrose and Cornstarch using a Novel Technique, Luminescence Spectroscopy. IFT Annual Meeting, Chicago, IL, (poster).
- Zunic, A. & Ludescher, R.D. (2003) Oxygen Diffusion and Molecular Mobility in Amorphous Sugars. IFT Annual Meeting, Chicago, IL, (poster).
- Pravinata, L. (2003) Molecular Mobility Of Amorphous Sucrose Detected By Phosphorescence Of Erythrosin B and Eosin Y. MS Thesis, Rutgers University.
- Ludescher, R.D. & Pravinata, L. (2004) Eosin phosphorescence detects site heterogeneity and molecular mobility in amorphous sucrose. Biophysical Society, 48th Annual Meeting, Baltimore, MD (poster).
- Zunic, A. & Ludescher, R.D. (2004) Site heterogeneity and molecular mobility in glassy sugars. Biophysical Society, 48th Annual Meeting, Baltimore, MD (poster).
- Ludescher, R.D. & Zunic, A. (2004) Tryptophan luminescence detects molecular mobility in amorphous sugars. IFT Annual Meeting, Las Vegas, NV (poster).
- Zunic, A. (2004) Studies Of Molecular Mobility In Amorphous Sugars Using Fluorescence And Phosphorescence Of Tryptophan. MS Thesis, Rutgers University.
- Shirke, S., Nack, T.J., You, Y., & Ludescher, R.D. (2005) Phosphorescence probes molecular mobility and dynamic site heterogeneity in amorphous biomaterials. Biophysical Society, 49th Annual Meeting, Long Beach, CA (poster).
- Shirke, S. (2005) Molecular Mobility in Amorphous Sugars and Sugar Alcohols as Detected by Phosphorescence of Erythrosin B. MS Thesis, Rutgers University.
- Pravinata, L.C., You, Y., & Ludescher, R.D. (2004) Erythrosin B Phosphorescence Monitors Molecular Mobility and Dynamic Site Heterogeneity in Amorphous Sucrose. Biophysical Journal, in press.
- Zunic, A., Pravinata, L., & Ludescher, R.D. (2003) Tryptophan Phosphorescence is Sensitive to Molecular Mobility and Oxygen Diffusion in Glassy Sugars. Biophysical Society, 47th Annual Meeting, San Antonio, TX (poster).
- Pravinata, L. & Ludescher, R.D. (2002) Molecular Mobility Of Amorphous Sucrose Determined From Phosphorescence Of Erythrosin B. Biophysical Society, 46th Annual Meeting, San Francisco, CA (poster).
- Pravinata, L & Ludescher, R. D. (2002) Erythrosin B Phosphorescence As A Probe Of Molecular Mobility In Amorphous Sucrose. IFT Annual Meeting, Anaheim, CA (poster).
- Pravinata, L. & Ludescher, R. D. (2003) Evidence For Site-Heterogeneity In Amorphous Sucrose From Phosphorescence Of Erythrosin B. Biophysical Society, 47th Annual Meeting, San Antonio, TX (poster).
|
Progress 01/01/02 to 12/31/02
Outputs
In an effort to further develop molecular probes of mobility, we are investigating the steady-state and time resolved phosphorescence properties of erythrosin B (tetra-iodo-fluorescein, FD&C Red #3) in thin films of amorphous solid sucrose as a function of temperature. The phosphorescence intensity, emission energy, and red-edge excitation effect were all sensitive to localized molecular mobility on the one millisecond time scale in the glassy state and to more global modes of mobility activated at the glass transition. Phosphorescence emission in the amorphous sucrose was due to multiple erythrosin species ranging from a short-lived species with red-shifted emission spectrum to a long-lived species with blue-shifted emission spectrum. The erythrosin thus detects considerable site dynamic heterogeneity within both the glassy sucrose that persists above the glass transition within the sucrose melt. This study illustrates that phosphorescence from erythrosin B is
sensitive both to local dipolar relaxations in the glassy state as well as more global relaxations in the rubbery state of sucrose and provides further evidence of the value of phosphorescence as a probe of slow molecular mobility in amorphous bimaterials. Additional studies with the probe eosin Y (D&C Red #22), a structurally similar molecule with bromine instead of iodine and thus a longer phosphorescent lifetime, provide similar results on about the 10 millisecond time scale. This probe, however, is not sensitive to thermal hysteresis as the erythrosin probe, which exhibits longer lifetimes during cooling that during heating cycle. The origins of this discrepancy are being investigated. Studies of molecular mobility in amorphous sucrose, maltose, and trehalose using tryptophan phosphorescence indicate that Trp phosphorescence is essentially quenched by molecular collisions within the glassy sugars at temperatures significantly below Tg. Lower intensities and lifetimes in O2 (air)
than in pure N2 indicate appreciable rates of O2 diffusion even in the glassy sugars. O2 diffusion may be activated by sub-Tg transition(s) within the glassy sucrose. These studies demonstrate that glassy sugars exhibit extensive mobility that appears to modulate oxygen diffusion.
Impacts
This research provides insight into the molecular processes that control oxygen diffusion within amorphous glassy sugars. Such insight should assist in formulating novel foods and encapsulants with improved resistance to the oxidation of lipids, vitamins, and bioactive natural compounds (nutraceuticals)and in formulating novel pharmaceutical carriers for drugs and bioactive compounds with improved oxidation resistance.
Publications
- Pravinata, Linda & Ludescher, Richard D. (2002) "Erythrosin B Phosphorescence As A Probe Of Molecular Mobility In Amorphous Sucrose." IFT Annual Meeting, June 2002, Anaheim, CA.
- Pravinata, Linda & Ludescher, Richard D. (2002) "Molecular Mobility Of Amorphous Sucrose Determined From Phosphorescence Of Erythrosin B" 46th Annual Meeting, Biophysical Society, Biophysical Journal 82, 431a.
|
Progress 01/01/01 to 12/31/01
Outputs
No progress to report -- it is too early in the life of the project to report on research activities.
Impacts
(N/A)
Publications
- No publications reported this period
|
|