No. 33 Physical properties of R(+) alpha Lipoic acid by Complexation with γ-Cyclodextrin
Continued from No.21_RALA-CD Alpha Lipoic acid γ-cyclodextrin complex
What is alpha Lipoic acid？
Alpha Lipoic acid exists in nature and is an essential cofactore of mitochondrial enzyme complexes. Glucose taken into cells is changed into pyruvic acid by glycolytic pathway. Pyruvic acid is changed into acetyl CoA by pyruvate dehydrogenase complex (PDC), then acetyl CoA is oxidized at TCA cycle and electron transfer system followed by generation of ATP. Lipoic acid is essential for PDC and glucose metabolism. Continuous high blood glucose level causes generation of advanced glycation end products (AGEs). It is explained that AGEs cause the complications of diabetes mellitus and aging. Alpha Lipoic acid which can works for conversion from glucose to energy is now very popular as anti glycation materials.
The carbon atom at C6 of Alpha Lipolic acid is chiral and the molecule exists an two enantiomers R-(+)-Lipoic acid (RALA) and S-(-)-lipoic acid (SALA). Only the RALA exists in nature and is an essential cofactor of four mitochondrial enzyme complexes. Since RALA (mp. 46-49℃) is unstable compound, it is easily decomposed and generates sticky insoluble polymer. Therefore, RALA has not been commercially available, but only racemic compound (mp. 60-62℃).
RALA-CD inclusion complexes were prepared, and their stability against heat and acid conditions were evaluated.
Analysis of RALA by HPLC
Unit : Integrated HPLC System LC-2010C (Shimadzu)
Column : CHIRALPAK AD-RH (Daicel) (4.6mm I.D. x 150mm)
Flow and temp. : 0.6mL/min, 25℃
Mobile phase : 25mM H3PO4：CH3CN=70：30
Detector : UV 215nm
Injection volume : 10μL
Retention time : 35min (SALA), 38min (RALA)
Efficiency of complexation process
RALA contents in RALA-CD complexes which were made by mixing RALA and CD (1:1 mol ratio) were analyzed by HPLC.
Stabilizing effect of CDs on RALA
Residual ratio of RALA under heated condition
(Light shielding, 70℃, saturated humidity, 2h)
Each samples were treated under the test conditions (light shielding, 70℃ and saturated humidity) for 2 hours, then residual RALA content was analyzed. The results were shown as residual ratio of RALA against initial value.
Evaluation of RALA-γ-CD complex
Stability of RALA in water condition
RALA contents in each samples were 0.5mg/mL.
Stability of RALA in Water (90℃)
Stability of RALA in heated water
RALA didn't dispersed in water. RALA was polymerized under heated condition.
Taste masking effect by γ-CD
Healthy adult aged 20's to 60's (Male 8, Female 7)
γ-CD, RALA-γ-CD , RALA-MCC*
(Both RALA-γ-CD and RALA-MCC contain 11% of RALA)
RALA-MCC：Physical mixture of RALA and crystalline cellulose.
Panelist didn't know the content of test sample.
Panelist rinses the mouth then lick the test sample followed by evaluation its pungency in the mouth.
No pungency = 0
1 (less pungency) to 10 (strong pungency)
【Screening and judge】
Two panelists who gave 1 score to γ-CD were eliminated.
Sum total of each sample were evaluated.
Pungent taste of RALA was decreased by γ-CD complexation.
Safety evaluation of RALA-γ-CD
Acute toxicity test
Body weight transition
mean ± S.D. (g)
LD50 > 2000mg/kgBW (Mice)
- RALA can make inclusion complex by α-CD, β-CD and γ-CD.
- The stability of RALA was improved by making inclusion complex with CD.
- RALA-γ-CD complex was stable even in solution.
- The pungency taste of RALA was decreased by γ-CD.
- LD50 of RALA-γ-CD complex was > 2000mg/kgBW (mice).
RALA-γ-CD complex is now available as functional food materials !