Hydroxycinnamic Acid Antioxidants: An Electrochemical Overview

Table 4

Redox potentials and antioxidant activity of hydroxycinnamic acids, ester and amide derivatives.

Compound	MW (gmol^−1)	DPPH (TE)*	DPPH (IC50)^*†	𝐸𝑝 (mV)	Reference
p-Coumaric	164.16		>100	+736	[6]
Caffeic acid	180.16	1.29	16.6	+183	[7, 8]
Hydrocaffeic acid	182.18	2.05	15.4^#	+139	[8]
5-Bromocaffeic acid	259.05	1.01		+182	[7]
Methyl caffeate	194.18		14.0	+165	[9]
Ethyl caffeate	208.21		13.5	+170	[9]
Ethyl 5-bromocaffeate	287.11	0.938		+174	[7]
Propyl caffeate	222.24		14.5	+173	[9]
Butyl caffeate	236.26		14.1	+176	[9]
Hexylcaffeate	264.32	0.970		+175	[8]
Hexylhydrocaffeate	266.34	0.990		+125	[8]
Caffeoylhexylamide	263.34	1.11		+162	[8]
Hydrocaffeoylhexylamide	265.35	1.00		+125	[8]
Ferulic acid	194.19	0.781	44.6	+335; +447	[7]
Hydroferulic acid	196.20		84.0^#	+410	[8]
5-Bromoferulic acid	273.08	0.808		+335; +442	[7]
Methyl ferulate	208.21		74.7	+375	[9]
Ethyl ferulate	222.24		66.7	+370	[9]
Ethyl 5-bromoferulate	301.13	0.558		+365	[7]
Propyl ferulate	236.26		64.1	+364	[9]
Butyl ferulate	250.29		56.3	+343	[9]
Hexylferulate	278.35			+328	[8]
Hexylhydroferulate	280.36			+434	[8]
Feruloylhexylamide	277.36			+322	[8]
Hydroferuloylhexylamide	279.38			+388	[8]
Sinapic acid	224.21	0.862	32.2	+188; +295	[10]
Methyl sinapate	238.24		48.7	+219	[10]
Ethyl sinapate	252.26		51.9	+189	[10]
Propyl sinapate	266.29		50.6	+182	[10]
Butyl sinapate	280.32		50.1	+190	[10]
3,4,5-Trihydroxycinnamic acid	196.16		11.8	+11; +384	[11]
Ethyl 3,4,5-trihydroxycinnamate	224.21		15.1	+26; +133	[11]

 *The results of DPPH assays are usually expressed as TEAC (trolox equivalent antioxidant capacity) or IC₅₀ (concentration which is required to scavenge 50% of DPPH free radicals). These values are not convertible.
^†IC₅₀ is presented in μmol L⁻¹.
^#Unpublished results.