Analyte detection using near-infrared fluorophores
Embodiments of compounds for selectively detecting an analyte are disclosed, along with methods and kits for detecting analytes with the compounds. The compounds are bridged viologen conjugates including at least one fluorophore according to the general structure At least one of R 1 /R 2 , R 2 /R 3 , R 3 /R 4 , R 5 /R 6 , R 6 /R 7 , and/or R 7 /R 8 together form a substituted or unsubstituted cycloalkyl or aryl.
1. A compound according to Formula III
where X − is a halide or PF 6 − , and
each of R A and R B independently is a fluorophore having a structure according to formula (iii)
where each bond depicted as “ ” is a single or double bond as needed to satisfy valence requirements;
X 1 is O;
R 1 and R 2 independently are hydrogen, hydroxyl, oxygen, thiol, lower alkyl, carboxyalkyl, amino, alkoxy, halogen, or —NHR c where R c is
R 5 , R 7 , and R 8 independently are hydrogen, hydroxyl, thiol, lower alkyl, carboxyalkyl, amino, alkoxy, or halogen;
is hydrogen, hydroxyl, halogen, oxygen, sulfur, thiol, amino, alkyl amino, imino, iminium, alkyl imino, alkyl iminium, cycloalkyl imino or —NHR c ;
R 9 -R 12 independently are hydrogen, alkyl, carboxyl, nitro, amino, alkyl amino, or —SO 3 H;
R 13 is hydrogen, hydroxyl, lower alkyl, lower alkoxy, —SO 3 H or —COOR 14 where R 14 is hydrogen or lower alkyl and the bond depicted as “ ” in ring B is a double bond, or R 13 is one or more atoms forming a ring system with rings B and D and the bond depicted as “ ” in ring B is a single bond; and
at least one of R 1 , R 2 , or -R 5 -R 18 is a linker covalently binding the fluorophore to the viologen backbone,
wherein at least one of R 1 and R 8 is other than hydrogen, or R 13 is hydrogen, lower alkyl, lower alkoxy, or —SO 3 H, or R 13 is one or more atoms forming a ring system with rings B and D and the bond depicted as “ ” in ring B is a single bond, or R 5 is the linker.
2. The compound of claim 1 where R 13 is the linker.
3. The compound of claim 1 where R 13 is —COO— and forms a lactone ring, and at least one of R 1 , R 2 , or R 5 -R 12 or -R 15 -R 18 is the linker.
4. The compound of claim 1 where the fluorophore has a structure according to:
(a) formula (iii) R 18 is halogen, hydroxyl, thiol, amino, alkyl amino, or alkoxy; or
(b) formula (iii) where R 6 and R 16 are —NHR c .
5. A method for detecting an analyte, comprising:
forming a solution by combining a sample comprising an analyte with a compound according to claim 1 ;
allowing a reaction between the analyte and the compound in the solution to proceed for an effective period of time to a produce a detectable change in the solution's absorbance spectrum, emission spectrum, or both, where the change indicates that the analyte is present; and
detecting the change.
6. The method of claim 5 where detecting the change comprises:
exposing the solution to a light source; and
detecting the analyte by detecting fluorescence from the compound at a wavelength corresponding to an emission spectrum maximum of the compound after the reaction has proceeded for the effective period of time.
7. The method of claim 5 where the analyte comprises cysteine, homocysteine, glutathione, succinyl-5-amino-4-imidazolecarboxamide riboside, succinyladenosine, or a combination of succinyl-5-amino-4-imidazolecarboxamide riboside and succinyladenosine.
8. The method of claim 7 where the analyte is succinyl-5-amino-4-imidazolecarboxamide riboside, succinyladenosine, or a combination thereof, and the compound comprises at least one fluorophore according to:
(a) formula (iii):
where X 1 is oxygen and R 6 and R 16 are —NHR c .