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Comparison of slam‐freezing and high‐pressure freezing effects on the DNA cholesteric liquid crystalline structure
Author(s) -
Leforestier A.,
Richter K.,
Livolant F.,
Dubochet J.
Publication year - 1996
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.1996.1090666.x
Subject(s) - vitrification , materials science , congelation , ice crystals , chemical physics , crystallography , chemical engineering , chemistry , thermodynamics , optics , medicine , physics , andrology , engineering
Using in parallel electron microscopy of ultrathin frozen‐hydrated sections and freeze‐fracture replicas, we compare the ultrastructural consequences of two freezing techniques: slam‐freezing at liquid helium temperature and high‐pressure freezing, on a model system, the DNA cholesteric liquid crystalline phase. Both freezing techniques are able to vitrify DNA liquid crystalline solutions containing up to 85% water, but induce structural rearrangements of the molecular organization. The cholesteric structure is preserved by the slam‐freezing method despite the formation of periodic distortions induced by the mechanical compressive stress. In contrast, high‐pressure freezing does not preserve the structure of the liquid crystal: the long‐range cholesteric stratification disappears, and the local continuous twist between molecules is modified. These results show that vitrification, though necessary, may not be a sufficient token of preservation of the native state of hydrated materials. We discuss the possible origins of the molecular rearrangements that have time to occur in the specimens as a result of the low freezing rate permitted by the high‐pressure freezing process.