title: Heterogeneous ordered-disordered structure of the mesodomain in frozen sucrose-water solutions revealed by multiple electron paramagnetic resonance spectroscopies.
abstract: The microscopic structure of frozen aqueous sucrose solutions, over concentrations of 0-75% (w/v), is characterized by using multiple continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopic and relaxation techniques and the paramagnetic spin probe, TEMPOL. The temperature dependence of the TEMPOL EPR line-shape anisotropy reveals a mobility transition, specified at 205 K in pure water and 255 ± 5 K for >1% (w/v) added sucrose. The transition temperature is >>Tg, where Tg is the homogeneous water glass transition temperature, which shows that TEMPOL resides in the mesoscopic domain (mesodomain) at water-ice crystallite boundaries and that the mesodomain sucrose concentrations are comparable at >1% (w/v) added sucrose. Electron spin-echo envelope modulation (ESEEM) spectroscopy of TEMPOL-(2)H2-sucrose hyperfine interactions also indicates comparable sucrose concentrations in mesodomains at >1% (w/v) added sucrose. Electron spin-echo (ESE) detected longitudinal and phase memory relaxation times (T1 and TM, respectively) at 6 K indicate a general trend of increased mesodomain volume with added sucrose, in three stages: 1-15, 20-50, and >50% (w/v). The calibrated TEMPOL concentrations indicate that the mesodomain volume is less than the predicted maximally freeze-concentrated value [80 (w/w); 120% (w/v)], with transitions at 15-20% and 50% (w/v) starting sucrose. An ordered sucrose hydrate phase, which excludes TEMPOL, and a disordered, amorphous sucrose-water glass phase, in which TEMPOL resides, are proposed to compose a heterogeneous mesodomain. The results show that the ratio of ordered and disordered volume fractions in the mesodomain is exquisitely sensitive to the starting sucrose concentration.
authors: Department of Physics, N201 Mathematics and Science Center, Emory University, Atlanta, Georgia 30322-2430, United States.
authors: Hanlin
authors: H
authors: Chen
authors: Li
authors: L
authors: Sun
authors: Kurt
authors: K
authors: Warncke
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005615:Freezing; D015394:Molecular Structure; D012996:Solutions; D013395:Sucrose / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D012996:Solutions; D014867:Water; D013395:Sucrose