Chemical constituents of Isodon melissoides.
Four new diterpenoids, melissoidesin E (1), F (2), G (4) and H (5), together with one known diterpenoid and two lignan glycosides, were isolated from aerial parts of Isodon melissoides. Their structures were established by spectral analysis and comparison with related compounds. The lignan glycosides (compounds 7 and 8) were the first examples to be isolated from the genus Isodon plants.
Four new diterpenoids from Isodon melissoides.
Three new 11beta,16beta-epoxy-ent-kauranoids melissoidesins I-K (1-3) and one new ent-abietanoid melissoidesin L (4) were obtained from the aerial parts of Isodon melissoides (BENTHAM) H. HARA, their structures were established on the basis of the spectral methods, especially two dimensional (2D) NMR spectroscopy.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.