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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.

SUBMITTER: Chen H

PROVIDER: S-EPMC3623541 | biostudies-literature | 2013 Apr

REPOSITORIES: biostudies-literature

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Heterogeneous ordered-disordered structure of the mesodomain in frozen sucrose-water solutions revealed by multiple electron paramagnetic resonance spectroscopies.

Chen Hanlin H Sun Li L Warncke Kurt K

Langmuir : the ACS journal of surfaces and colloids 20130319 13

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 i ...[more]

PMID: 23464733

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Project description:The fleeting ferric peroxo and hydroperoxo intermediates of dioxygen activation by hemoproteins can be readily trapped and characterized during cryoradiolytic reduction of ferrous hemoprotein-O2 complexes at 77 K. Previous cryoannealing studies suggested that the relaxation of cryogenerated hydroperoxoferric intermediates of myoglobin (Mb), hemoglobin, and horseradish peroxidase (HRP), either trapped directly at 77 K or generated by cryoannealing of a trapped peroxo-ferric state, proceeds through dissociation of bound H2O2 and formation of the ferric heme without formation of the ferryl porphyrin π-cation radical intermediate, compound I (Cpd I). Herein we have reinvestigated the mechanism of decays of the cryogenerated hydroperoxyferric intermediates of α- and β-chains of human hemoglobin, HRP, and chloroperoxidase (CPO). The latter two proteins are well-known to form spectroscopically detectable quasistable Cpds I. Peroxoferric intermediates are trapped during 77 K cryoreduction of oxy Mb, α-chains, and β-chains of human hemoglobin and CPO. They convert into hydroperoxoferric intermediates during annealing at temperatures above 160 K. The hydroperoxoferric intermediate of HRP is trapped directly at 77 K. All studied hydroperoxoferric intermediates decay with measurable rates at temperatures above 170 K with appreciable solvent kinetic isotope effects. The hydroperoxoferric intermediate of β-chains converts to the S = 3/2 Cpd I, which in turn decays to an electron paramagnetic resonance (EPR)-silent product at temperature above 220 K. For all the other hemoproteins studied, cryoannealing of the hydroperoxo intermediate directly yields an EPR-silent majority product. In each case, a second follow-up 77 K γ-irradiation of the annealed samples yields low-spin EPR signals characteristic of cryoreduced ferrylheme (compound II, Cpd II). This indicates that in general the hydroperoxoferric intermediates relax to Cpd I during cryoanealing at low temperatures, but when this state is not captured by reaction with a bound substrate, it is reduced to Cpd II by redox-active products of radiolysis.

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Heterogeneous ordered-disordered structure of the mesodomain in frozen sucrose-water solutions revealed by multiple electron paramagnetic resonance spectroscopies.

Publications

Heterogeneous ordered-disordered structure of the mesodomain in frozen sucrose-water solutions revealed by multiple electron paramagnetic resonance spectroscopies.

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