Greetings...
May be our observation is relevent to this and please go thourgh the article
Satheesh Kumar, P. and Gautham, N., "Unusual ring-shaped oligonucleotide crystals" (1999) Current Science 77, 1076-1078 http://www.iisc.ernet.in/~currsci/oct25/articles23.htm.
Best wishes,
Satheesh
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Dr. P.Satheesh Kumar Research Scholar Department of crystallography and Biophysics University of Madras Chennai - 600 025. India.