Calix[4]arenes for the selective detection of Zn

1. A compound of Formula I:

or a salt thereof; wherein: each R 1 is a group of Formula:

R 2 is H, C 1 -C 8 alkyl, or C 3 -C 8 cycloalkyl;

R 3 is a 5-membered heteroaryl;

R 4 is H or C 1 -C 8 alkyl;

R 5 is C 1 -C 8 alkyl or C 1 -C 8 cycloalkyl; and

R 6 is H or C 1 -C 8 alkyl.

2. The compound of claim 1 , wherein R 1 is of Formula:

3. The compound of claim 1 , wherein R 2 is methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, amyl, octyl, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.

4. The compound of claim 1 , wherein R 2 is tert-butyl.

5. The compound of claim 1 , wherein R 4 is H, methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, amyl, octyl, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl.

6. The compound of claim 1 , wherein R 4 is tert-butyl.

7. The compound of claim 1 , wherein R 5 is methyl, ethyl, propyl, n-butyl, or tert-butyl.

8. The compound of claim 1 , wherein R 5 is butyl.

9. The compound of claim 1 , wherein R 6 is H.

10. The compound of claim 1 , wherein R 2 is tert-butyl and R 1 is a group of Formula:

11. A complex comprising the compound of claim 1 ; and a Zn 2+ ion.

12. The complex of claim 11 , wherein the Zn 2+ and the compound are present in a 1:1 molar ratio.

13. A method of determining the presence or absence of Zn 2+ in a solution, the method comprising: contacting the compound of claim 1 with a test sample to form a solution; and recording a fluorescence spectrum of the solution;

wherein:

in the presence of Zn 2+ , the solution exhibits fluorescence intensity at about 450 nm that is greater than a fluorescence intensity of a solution that contains the compound but does not contain Zn 2+ , thereby determining the presence or absence of Zn 2+ in the solution.

14. The method of claim 13 , wherein the test sample comprises serum.

15. The method of claim 13 , wherein the test sample comprises aqueous methanolic (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer.

16. The method of claim 13 , wherein a pH of the test sample is from about 6 to about 9.

17. The method of claim 13 that is selective for determining the presence of Zn 2+ in the presence of other metal ions in the sample.

18. The method of claim 17 that is selective for determining the presence of Zn 2+ in the presence of Hg 2+ , Cd 2+ , Li + , Na + , K + , Cs + , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ , Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , or Ag + .

19. A method of synthesis, comprising contacting a compound of Formula II:

with a compound of Formula III:

 and

Cu 2+ to provide a compound of Formula IV:

or a salt thereof;

wherein:

R 10 is

R 2 is H, C 1 -C 8 alkyl or C 3 -C 8 cycloalkyl; and

R 4 is H or C 1 -C 8 alkyl.

20. The method of claim 19 , further comprising contacting the compound of Formula IV with R 5 NH 2 , or a salt thereof, to provide a compound of Formula I

wherein: R 1 is

 and

R 5 is C 1 -C 8 alkyl or C 1 -C 8 cycloalkyl.