Nucleic acid base pairs

1. A composition comprising a pair of PNA oligomers which

i) hybridize to each other through base-pairing that comprises more than one of the following combinations:

wherein:

R 1 is chosen from hydrogen, halogen, substituted (C 1 -C 4 )-alkyl, unsubstituted (C 1 -C 4 )-alkyl, —NR 6 R 7 , substituted (C 1 -C 4 )-alkoxy, unsubstituted (C 1 -C 4 )-alkoxy, substituted (C 3 -C 6 )-cycloalkyl, unsubstituted (C 3 -C 6 )-cycloalkyl linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 2 is chosen from hydrogen, substituted (C 1 -C 4 )-alkyl, unsubstituted (C 1 -C 4 )-alkyl, —NR 6 R 7 , substituted (C 1 C 4 )-alkoxy, unsubstituted (C 1 C 4 )-alkoxy, substituted (C 3 -C 6 )-cycloalkyl, unsubstituted (C 3 -C 6 )-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 3 is group chosen from hydrogen, halogen, substituted (C 1 -C 20 )-alkyl, unsubstituted (C 1 -C 20 )-alkyl, —NR 6 R 7 , substituted (C 1 -C 20 )-alkoxy, unsubstituted (C 1 -C 20 )-alkoxy, substituted (C 3 -C 8 )-cycloalkyl, unsubstituted (C 3 -C 8 )-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 4 is chosen from hydrogen, halogen, substituted (C 1 -C 4 )-alkyl, unsubstituted (C 1 -C 4 )-alkyl, —NR 6 R 7 , substituted (C 1 -C 4 )-alkoxy, unsubstituted (C 1 -C 4 )-alkoxy, substituted (C 3 -C 6 )-cycloalkyl, unsubstituted (C 3 -C 6 )-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 4a is chosen from hydrogen, fluorine and chlorine;

R 4b is chosen from hydrogen, fluorine, and chlorine;

R 5 is chosen from hydrogen, substituted (C 1 -C 4 )-alkyl, unsubstituted (C 1 -C 4 )-alkyl, —NR 6 R 7 , substituted (C 1 -C 4 )-alkoxy, unsubstituted (C 1 -C 4 )-alkoxy, substituted (C 3 -C 6 )-cycloalkyl, unsubstituted (C 5 -C 6 )-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 6 and R 7 can be identical or different, and are chosen from hydrogen, substituted (C 1 -C 20 )-alkyl, and unsubstituted (C 1 -C 20 )-alkyl;

R 8 and R 12 can be identical or different, and are chosen from hydrogen, halogen,

 substituted (C 1 -C 20 )-alkoxy, unsubstituted (C 1 -C 20 )-alkoxy, substituted (C 3 -C 8 )-cycloalkyl, unsubstituted (C 3 -C 8 )-cycloalkyl, substituted (C 1 -C 20 )-alkyl, and unsubstituted (C 1 -C 20 )-alkyl; and

R 14 is chosen from hydrogen, substituted (C 1 -C 20 )-alkyl, unsubstituted (C 1 -C 20 )-alkyl, substituted (C 1 -C 20 )-alkoxy, unsubstituted (C 1 -C 20 )-alkoxy, substituted (C 3 -C 8 )-cycloalkyl, and unsubstituted (C 3 -C 8 )-cycloalkyl;

R 15 and R 16 are chosen from oxygen and sulfur;

R 17 and R 18 are chosen from hydrogen and —NH 2 ; and

(ii) do not interfere with RNA or DNA.

2. The composition according to claim 1 , wherein R 1 , R 3 , and R 4 each is hydrogen.

3. The composition according to claim 1 , wherein R 2 and R 5 can be identical or different and are chosen from linker, a polyamide backbone, and linker bound to a polyamide backbone.

4. The composition according to claim 1 , wherein:

R1, R3, and R4 each is hydrogen;

R2 and R5 can be identical or different and are chosen from a polyamide backbone and linker bound to polyamide backbone.

5. The composition according to claim 1 , wherein the base pairing comprises at least two hydrogen bonds.

6. The composition according to claim 5 , wherein the base pairing comprises three hydrogen bonds.

7. The composition according to claim 1 , wherein the base pairing comprises a Watson Crick-type hydrogen bonding geometry or a Hoogsteen-type hydrogen bonding geometry.

8. The composition of claim 1 wherein at least one of the PNA oligomers further comprises a polymer.

9. The composition of claim 8 wherein the polymer is dextran.

10. The composition of claim 1 , wherein at least one of the PNA oligomers comprises a linker.

11. The composition according to claim 10 , wherein the linker is chosen from a molecule comprising polyethylene glycol and a molecule comprising at least two units according to the Formula 1:

wherein R 1 and R 2 comprise NH or O, and R 3 comprises methyl, ethyl, propyl, CH 2 —O—CH 2 , and (CH 2 —O—CH 2 ) 2 .

12. A composition comprising a pair of PNA oligomers which (i) hybridize to each other through base-pairing and (ii) do not interfere with RNA or DNA,

wherein at least one of the PNA oligomers comprises at least one molecule chosen from:

wherein

R 1 is chosen from hydrogen, halogen, substituted (C 1 -C 4 )-alkyl, unsubstituted (C 1 -C 4 )-alkyl, —NR 6 R 7 , substituted (C 1 -C 4 )-alkoxy, unsubstituted (C 1 -C 4 )-alkoxy, substituted (C 3 -C 6 )-cycloalkyl, unsubstituted (C 3 -C 6 )-cycloalkyl linker, a polyamide backbone, and linker bound to a polyamide backbone; wherein:

R 2 is chosen from hydrogen, substituted (C1-C4)-alkyl, unsubstituted (C1-C4)-alkyl, —NR6R7, substituted (C1C4)-alkoxy, unsubstituted (C1C4)-alkoxy, substituted (C3-C6)-cycloalkyl, unsubstituted (C3-C6)-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R3 is group chosen from hydrogen, halogen, substituted (C1-C20)-alkyl, unsubstituted (C1-C20)-alkyl, —NR6R7, substituted (C1-C20)-alkoxy, unsubstituted (C1-C20)-alkoxy, substituted (C3-C8)-cycloalkyl, unsubstituted (C3-C8)-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R4 is chosen from hydrogen, halogen, substituted (C1-C4)-alkyl, unsubstituted (C1-C4)-alkyl, —NR6R7, substituted (C1-C4)-alkoxy, unsubstituted (C1-C4)-alkoxy, substituted (C3-C6)-cycloalkyl, unsubstituted (C3-C6)-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R 4a is chosen from hydrogen, fluorine and chlorine;

R 4b is chosen from hydrogen, fluorine, and chlorine;

R5 is chosen from hydrogen, substituted (C1-C4)-alkyl, unsubstituted (C1-C4)-alkyl, —NR6R7, substituted (C1-C4)-alkoxy, unsubstituted (C1-C4)-alkoxy, substituted (C3-C6)-cycloalkyl, unsubstituted (C5-C6)-cycloalkyl, linker, a polyamide backbone, and linker bound to a polyamide backbone;

R6 and R7 can be identical or different, and are chosen from hydrogen, substituted (C1-C20)-alkyl, and unsubstituted (C1-C20)-alkyl;

R8 and, R12 can be identical or different, and are chosen from hydrogen, halogen,

 substituted (C1-C20)-alkoxy, unsubstituted (C1-C20)-alkoxy, substituted (C3-C8)-cycloalkyl, unsubstituted (C3-C8)-cycloalkyl, substituted (C1-C20)-alkyl, and unsubstituted (C1-C20)-alkyl;

R14 is chosen from hydrogen, substituted (C1-C20)-alkyl, unsubstituted (C1-C20)-alkyl, substituted (C1-C20)-alkoxy, unsubstituted (C1-C20)-alkoxy, substituted (C3-C8)-cycloalkyl, and unsubstituted (C3-C8)-cycloalkyl;

R15 and R16 are chosen from oxygen and sulfur; and

R17 and R18 are chosen from hydrogen and —NH2.

13. The composition according to claim 12 , wherein R 1 , R 3 , and R 4 each is hydrogen.

14. The composition according to claim 12 , wherein R 2 and R 5 can be identical or different and are chosen from linker, backbone, and linker bound to backbone.

15. The composition according to claim 12 , wherein:

R 1 , R 3 , and R 4 each is hydrogen;

R 2 and R 5 can be identical or different and are chosen from a polyamide backbone and linker bound to polyamide backbone.

16. The composition of claim 12 , wherein at least one of the PNA oligomers further comprises a polymer.

17. The composition of claim 16 , wherein the polymer is dextran.

18. The composition of claim 10 , wherein at least one of the PNA oligomers comprises a linker.

19. The composition according to claim 18 , wherein the linker is chosen from a molecule comprising polyethylene glycol and a molecule comprising at least two units according to the Formula 1:

wherein R1 and R2 comprise NH or O, and R3 comprises methyl, ethyl, propyl, CH2-O—CH2, and (CH2-O—CH2)2.

20. The composition of claim 8 wherein the polymer is selected from polysaccharides, pullulans, chitins, chitosans, derivatized cellolosics, hydroxylated starch, carrageenans, alginates, agarose, synthetic polysaccharides, vinyl polymers, polyethylene glycols with polymer backbones, polypropylene glycols with polymer backbones, poly(ethylene oxide-co-propylene oxides) with polymer backbones, poly amino acids, proteins, and polynucleotides.

21. The composition of claim 16 wherein the polymer is selected from polysaccharides, pullulans, chitins, chitosans, derivatized cellolosics, hydroxylated starch, carrageenans, alginates, agarose, synthetic polysaccharides, vinyl polymers, polyethylene glycols with polymer backbones, polypropylene glycols with polymer backbones, poly(ethylene oxide-co-propylene oxides) with polymer backbones, poly amino acids, proteins, and polynucleotides.