Abstract

The molecular structure and vibrational spectra of loganic acid (LA) were calculated using B3LYP density functional theory, the 6–311G(2d,2p) basis set, and the GAUSSIAN 03W program. The solid-phase FTIR and FT-Raman spectra of LA were recorded in the 100–4000 cm−1 range. The assignment of the observed bands to the respective normal modes was proposed on the basis of the PED approach. The stability of the LA molecule was considered using NBO analysis. The electron absorption and luminescence spectra were measured and discussed in terms of the calculated singlet, triplet, HOMO, and LUMO electron energies. The Stokes shift derived from the optical spectra was 20,915 cm−1.

Highlights

  • Loganic acid is an iridoid glucoside, an important biologically active component of several fruits such as cornelian cherry, cranberry, bilberry, and honeysuckle berries [1,2,3,4,5,6]

  • The conversion of loganic acid into loganin is catalyzed by loganic acid methyltransferase through the transfer of a methyl group from 5-adenosyl-methionine to the carboxylate of loganic acid [7,8,9]

  • The appearance and the number of these vibrations confirm that the whole cyclopentane[c]pyran (Φφ) system appears in a sofa conformation, similar to that proposed for loganin [35] and the molecular structure derived from DFT calculations carried out in this paper (Figure 1)

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Summary

Introduction

Loganic acid is an iridoid glucoside, an important biologically active component of several fruits such as cornelian cherry, cranberry, bilberry, and honeysuckle berries [1,2,3,4,5,6]. Iridoids comprise a large group of monoterpenoids with six-membered ring skeletons containing oxygen atoms fused to a cyclopentane ring They can be extracted from the plants both in the state of cyclopentanopyran monoterpenoid glucoside loganic acid and loganin [7]. Loganic acid exhibits activity for treating rheumatoid arthritis [19] and inflammation [20] This iridoid glucoside shows clear neuroprotective effects [21], defends against diet-induced hypertriglyceridemia and atherosclerosis [22], as well as exhibits antiadipogenic effects [23]. Its activity for treating rheumatoid arthritis [19] and inflammation [20] This iridoid glucoside shows clear neuroprotective effects [21], defends against diet-induced hypertriglyceridemia and atherosclerosis [22], as well as exhibits antiadipogenic effects o[2f 318].

Vibrational Spectra
Vibrations of the Pyran Ring
Carboxylic Group Vibrations
UV-Vis and Luminescence Spectra-Electron States and NBO Analysis
Materials and Methods
Conclusions
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