| CPC A01M 1/026 (2013.01) [A01M 1/023 (2013.01); A01M 2200/011 (2013.01)] | 20 Claims | 
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               1. A composition comprising a gel medium and a cyclic thiol of the formula I 
              ![]() or a tautomer thereof, wherein 
                X is S or O; 
                Z1 and Z2 are each independently O or S; 
                R1 is selected from the group consisting of hydrogen, C4-C10 alkyl, C2-C12 alkenyl, C6-C10 aryl, 5- to 7-membered heteroaryl, —OR5, —SR5, —(OC1-C4 alkylene)xR5, —(SC1-C4 alkylene)yR5 —(OC1-C4 alkylene)x(SC1-C4 alkylene)yR5, —(SC1-C4 alkylene)y(OC1-C4 alkylene)xR5, C1-C3 alkylene(OC1-C4 alkylene)xR5, C1-C3 alkylene(SC1-C4 alkylene)yR5, C1-C3 alkylene(OC1-C4 alkylene)x(SC1-C4 alkylene)yR5, and C1-C3 alkylene(SC1-C4 alkylene)y(OC1-C4 alkylene)xR5; 
                R2 is selected from the group consisting of hydrogen, C4-C10 alkyl, C2-C12 alkenyl, C6-C10 aryl, 5- to 7-membered heteroaryl, —OR5, —SR5, —(OC1-C4 alkylene)xR5, —(SC1-C4 alkylene)yR5 —(OC1-C4 alkylene)x(SC1-C4 alkylene)yR5, —(SC1-C4 alkylene)y(OC1-C4 alkylene)xR5, C1-C3 alkylene(OC1-C4 alkylene)xR5, C1-C3 alkylene(SC1-C4 alkylene)yR5, C1-C3 alkylene(OC1-C4 alkylene)x(SC1-C4 alkylene)yR5, and C1-C3 alkylene(SC1-C4 alkylene)y(OC1-C4 alkylene)xR5; 
                R3, R3′, R4, and R4′ are each independently selected from the group consisting of hydrogen, C1-C8 alkyl, C2-C8 alkenyl, and C6-C10 aryl; 
                R5 is selected from the group consisting of hydrogen, C1-C8 alkyl, C2-C8 alkenyl, C6-C10 aryl, and a polymeric bulking group; 
                a is 0 or 1; and 
                x and y are each independently an integer from 1 to 10. 
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