Spectroscopic Studies of R(+)-α-Lipoic Acid—Cyclodextrin Complexes

Abstract

α-Lipoic acid (ALA) has a chiral center at the C6 position, and exists as two enantiomers, R(+)-ALA (RALA) and S(−)-ALA (SALA). RALA is naturally occurring, and is a cofactor for mitochondrial enzymes, therefore playing a major role in energy metabolism. However, RALA cannot be used for pharmaceuticals or nutraceuticals because it readily polymerizes via a 1,2-dithiolane ring-opening when exposed to light or heat. So, it is highly desired to find out the method to stabilize RALA. The purpose of this study is to provide the spectroscopic information of stabilized RALA and SALA through complexation with cyclodextrins (CDs), α-CD, β-CD and γ-CD and to examine the physical characteristics of the resultant complexes in the solid state. The RALA-CD structures were elucidated based on the micro fourier transform infrared (FT-IR) and Raman analyses. The FT-IR results showed that the C=O stretching vibration of RALA appeared at 1717 cm−1 and then shifted on formation of the RALA-CD complexes. The Raman spectra showed that the S–S and C–S stretching vibrations for RALA at 511 cm−1 (S–S), 631 cm−1 (C–S) and 675 cm−1 (C–S) drastically weakened and almost disappeared upon complexation with CDs. Several peaks indicative of O–H vibrations also shifted or changed in intensity. These results indicate that RALA and CDs form host-guest complexes by interacting with one another.

Structural Analysis of Crystalline R(+)-α-Lipoic Acid-α-cyclodextrin Complex Based on Microscopic and Spectroscopic Studies

“…The ATR/FT-IR spectra of RALA and α-CD are also shown in Figure 4 for comparison. The ATR/FT-IR spectra of crystalline RALA showed a peak at 1693 cm −1 due to the stretching of the carbonyl group in the carboxylic acid, which was in agreement with the results of our previous study [ 10 ]. Following the complexation of the RALA with α-CD, the ν as (C=O, carbonyl group of carboxylic acid) of RALA shifted from 1693 to 1707 cm −1 .…”

“…ATR/FT-IR spectroscopy can be used to analyze spectral signals and determine the existence of intermolecular interactions between the RALA and CD molecules. Microscopic FT-IR was used in our previous study to obtain a spectrum of the raw RALA-αCD complex [ 10 ]. In this study, ATR/FT-IR was applied to analyze the purified crystalline RALA-αCD complex, and the resulting spectrum is shown in Figure 4 for wavelengths in the range of 1300–2000 cm −1 .…”

“…Nevertheless, it was not possible in this instance to clarify the nature of the interactions between the host and guest molecules of these complexes in the solid state [ 9 ]. Notably, spectroscopic analysis of the RALA-CD complexes using a combination of Raman and FT-IR analysis provided structural information that showed that the 1,2-dithiolane and carbonyl moieties of RALA were interacting with the CDs [ 10 ]. The purpose of the current study was to estimate the specific sites of the intermolecular interactions between the individual molecules in the RALA-CD complexes.…”

Efficient Synthesis of a Maghemite/Gold Hybrid Nanoparticle System as a Magnetic Carrier for the Transport of Platinum-Based Metallotherapeutics

“…920 and 629 cm −1 could be connected with the deformation O–H vibrations and stretching C–S vibrations, respectively. These results can support the presence of HLA in the discussed mag/Au–HLA nanoparticles, since their positions correlate well with the positions of the peaks in the spectrum of free lipoic acid [ 39 , 40 ].…”

Inclusion Complex of alpha-Lipoic Acid Containing Alkalizer for Improving the Solubility and Stability Prepared by Co-grinding

“…In Germany, LA has been used for the treatment of diabetes induction of neuropathy more than 30 y. LA is the only antioxidant, which can be dissolved by the water-soluble and fat-soluble solutions simultaneously [5,6] . Therefore, LA is also used as food additive or antiaging agent in cosmetic applications.…”