Investigation of lipoic acid - 4-methoxybenzyl alcohol reaction and evaluation of its analytical usefulness

Estimation of Lipoyllysine Content in Meat and Its Antioxidative Capacity

During this research a simple, accurate, and environmentally friendly method to determine lipoyllysine and lipoic acid in meat was developed and validated. The presented approach was based on the hydrolysis of the proteins containing lipoic acid, reduction of disulfide bonds with tris(hydroxymethyl)phosphine, and precolumn derivatization of free thiol groups with 1-benzyl-2-chloropyridinium bromide long-term followed by HPLC separation with a diode-array detector. The method has been validated in accordance with the U.S. FDA guidelines and was linear in the range of 0.1-10 μmol/L in concentration with R2 values ≥0.9997 for both analytes. For lipoyllysine and lipoic acid, intra- and interday precision values were lower than 10%. The intraday accuracy values ranged from 91.0% to 99.4% for lipoyllysine and from 99.1% to 107.3% for lipoic acid, whereas the interday accuracy values for lipoyllysine and lipoic acid were 92.0-95.6% and 93.5-98.8%, respectively. Additionally, in this research the antioxidant activity of lipoyllysine and reduced lipoyllysine compound using spectrophotometric method with 1,1-diphenyl-2-picrylhydrazyl was examined for the first time. The data showed that dihydrolipoyllysine exhibits stronger antioxidant capacity than lipoyllysine based on a lower value of concentration required to achieve a 50% antioxidant effect in 1,1-diphenyl-2-picrylhydrazyl radical scavenging test.

The Equilibria in Lipid-Lipoic Acid Systems: Monolayers, Microelectrophoretic and Interfacial Tension Studies

In this examination, we investigated the effect of lipoic acid (LA) on the properties of biological membrane models (monolayers, bilayers, and liposomes) formed from phosphatidylcholine (PC) or phosphatidylserine (PS) using the Langmuir, microelectrophoresis, and interfacial tension methods. The Langmuir technique allowed us to calculate the π–A isotherms and determine the molecular surface areas of pure and mixed monolayers. Using mathematical equations, we established that LA and the lipids formed complexes at a 1:1 ratio. The interfacial tension method was based on Young and Laplace’s equation. We assumed the formation of a 1:1 complex in the PC–LA system. Using the mathematical relationships, we derived the parameters characterizing the resulting complex, i.e., the surface occupied by the complex and the interfacial tension and stability constant of the formed complex. The microelectrophoretic method was used to determine the dependence of the zeta potential of the lipid membranes as a function of the pH (pH 2 to 10) of the electrolyte solution. The results indicate that modification of PC or PS membranes with LA affects changes in the zeta potential and the isoelectric point values.