Study of Complexes of Lanthanum with Amino Acids by Titration Calorimeter

The stability constants and thermodynamic functions for complexes of lanthanum with eight kind of amino acids according to 1∶1 and 1∶2 in proportion have been determined by titration calorimeter at 298.15 K. The enthalpy change makes a predominant contribution to the stability of these complexes. The ring in amino acid associated with lanthanum ion helps to enhance the stability of complexes. Steric effects between rings in complexes leads to that the equilibrium constants of reaction of the complexes (1∶2) is much less than that of the complexes (1∶1).

A new strategy based on acid-alkali complexation for rapidly and accurately fishing phytochemicals in Sennae Folium

Objective:There are some anthraquinones,anthraquinones and flavonones in Sennae Folium which exhibited significant acidity,such as sennoside A/B and sennoside C/D.The current strategies used in separating these components are mainly based on conventional column chromatography which is time consuming,laborious and costly.This study is aimed at exploring a method of precipitation extraction of acid components in Sennae Folium.Using alkaloid as a"hook",it is reasonable to use the principle of"acid-alkali complexation"to"fish"the acidic components in Sennae Folium.Methods:Isothermal titration calorimeter(ITC)was used to measure the extraction efficiency of different alkaloids.Then,alkaloid determined by ITC was mixed with extracting solution of Sennae Folium to form complex.High performance liquid chromatography coupled with mass spectrometry(HPLC-MS2)was used to investigate the ingredients"fished"by berberine(Ber).The mechanism of"fishing"process was explained by ITC,optical activity,fluorescence spectrometry and scanning electron microscope.Results:The ITC results proved that the choice of"hook"was particularly important in the process of"fishing".Among the hooks,the fishing efficiency of the isoquinoline alkaloids(Ber)was the highest,reaching 10.3%.Nine ingredients were detected and determined by HPLC-MS2,and the main components were sennoside A/B and sennoside C/D.Based on ITC test of Ber and sennoside A,the combination mechanism of the two ingredients was a chemical reaction with a nearly binding ratio(2:1).Fluorescence and optical properties of the active ingredients were changed after complexation.By scanning electron microscope,we found that two types of components had obviously self-assembled behavior during the formation process.Conclusion:Ber successfully"fished"the main acidic components,sennoside A/B and sennoside C/D,from Sennae Folium.Combined with different characterizations,the"fishing"process was determined as a chemical association reaction induced by electrostatic interaction orπ-πstacking.Therefore,with special identification ability,the"fishing"process had the potential of practical application.