Two-dimensional (2D) correlation spectroscopy provides an important approach to the study of subtle spectral variations caused by intermolecular interactions. In our previous work, DAOSD (Double Asynchronous Orthogonal Sample Design) scheme was introduced to analyze subtle spectral variations of characteristic peaks of substance under intermolecular interactions. In this paper, we apply DAOSD scheme to probe weak coordination between lanthanide (III) ions and lactone group of organic ligands from natural pharmaceutical. Weak coordinative interaction between Nd3+ and carbonyl group in Nd(ClO4)3/artemisinin in acetonitrile solutions is characterized by using 2D UV/IR hetero-correlation spectroscopy. Experimental results demonstrate that subtle band-shift and variation on the absorptivity can be observed on both carbonyl band of artemisinin and f–f transition band of Nd3+ ions upon coordination.
Jin Zhang,Ran Guo,Anqi He,Shifu Weng,Xiuxiang Gao,Yizhuang Xu,Isao Noda,Jinguang Wu
In this work, we investigated the influence of polyvinylpyrrolidone (PVP) on the solubility of artemisinin in aqueous solution by using quantitative 1 H NMR. Experimental results demonstrate that about 4 times of incremental increase occurs on the solubility of artemisinin upon introducing PVP. In addition, dipole-dipole interaction between the ester group of artemisinin and the amide group of N -methylpyrrolidone (NMP), a model compound of PVP, is characterized by two-dimensional (2D) correlation FTIR spectroscopy with the DAOSD (Double Asynchronous Orthogonal Sample Design) approach developed in our previous work. The observation of cross peaks in a pair of 2D asynchronous spectra suggests that dipole-dipole interaction indeed occurs between the ester group of artemisinin and amide group of NMP. Moreover, the pattern of cross peaks indicates that the carbonyl band of artemisinin undergoes blue-shift while the bandwidth and absorptivity increases via interaction with NMP, and the amide band of NMP undergoes blue-shift while the absorptivity increases via interaction with artemisinin. Dipole-dipole interaction, as one of the strongest intermolecular interaction between artemisinin and excipient , may play an important role in the enhancement of the solubility of artemisinin in aqueous solution.
The interaction between theophylline and ethylenediamine , choline hydroxide and other alkaline compounds was investigated via UV–Vis spectroscopic method . Upon introduction of alkaline compounds, the π-π transition band of theophylline undergoes a red shift. This phenomenon is a result of removing a proton from the 7-position of a theophylline molecule. Moreover, cross peaks appear in 2D asynchronous spectra generated via the DAOSD approach on theophyllinate and various cation systems. These results suggest that cation-π interaction and cation-anion interactions occur between theophyllinate and various cations including ethylenediamine , choline , tetramethyl ammonium , K + and Cs + . The interaction between anionic theophyllinate and various cation may play a considerable role in the transmembrane transport of theophylline in medicinal process.
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