The phosphate backbone-modified oligonucleotides described in this section are diastereoisomeric mixtures and form less stable hybrids than the normal phosphodiester oligonucleotiedes. However, the contribution of the P atom chirality to the overall destabilization of the hybrids may be less than expected and a distortion of the backbone due to stereoelectric factors has to be considered as well ( FROEHLER and MATTEUCCI 1988 ; IMBACH , personal communication ) .
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