Nucleic acid molecules with novel chemical compositions capable of modulating gene expression

A nucleic acid molecule having the formula XIII:

• iB-rprprprprprprpDsDsDsDsDsDsDsDsDsrprprprprprpr-iB
• wherein each r is independently a 2′-O-alkyl nucleotide, each D is independently a deoxyribonucleotide or 2′-arabinofluoro nucleotide, each s is independently a phosphorothioate, phosphorodithioate, 5′-thiophosphate, 3′-thiophosphate, or methylphosphonate internucleotide linkage, each p is independently a phosphodiester internucleotide linkage, and each iB is independently an inverted abasic moiety.