Higuinaldo J. Chaves das Neves

Photochemical and thermal degradation of anthocyanidins

Abstract Photochemical and thermal degradation of four anthocyanidins (pelargonidin, delphinidin, malvidin and cyanidin) in aqueous acidic media was studied. The kinetics of the degradation were followed by absorption spectroscopy and high performance liquid chromatography. All anthocyanidins studied have shown a similar thermal degradation pattern. Chalcone was detected as an intermediary product, which undergoes cleavage yielding the final decomposition products, identified as (i) 2,4,6-trihydroxybenzaldehyde originated from ring A for all four anthocyanidins and (ii) 3,4,5-trihydroxybenzoic acid for delphinidin, 4-hydroxy-3,5-dimethoxybenzoic acid for malvidin, 3,4-dihydroxybenzoic acid for cyanidin, and 4-hydroxybenzoic acid for pelargonidin (all these originated from ring B). During the photochemical degradation, the formation of the same final products as for thermal reaction was observed, but through a different kinetic pathway involving the excitation of the flavylium cation. The substitution of the hydroxyl in position 3 by a glucoside gives rise to a large increase in the thermal stability, and a decrease in the quantum yield of the photochemical reaction.

Steroidal constituents from mature wheat straw

Abstract From the neutral fraction of the acetone extract of mature wheat straw ( Triticum aestivum ) two new steroid ketones: (24 R )-14α-methyl-5α-ergostan-3-one and 14α-methyl-5α-cholestan-3-one and two new tetracyclic triterpenoids: cycloart-5-ene-3β,25-diol and cycloart-3β,25-diol together with the known compounds: cholesterol, ergosterol, campesterol, stigmasterol, sitosterol, spinasterol and stigmastanol were identified.

Bioequivalence assessment of diltiazem preparations by means of discriminant analysis of data from solid-phase extraction and liquid chromatography

A solid-phase extraction technique for sample clean-up coupled with a new LC procedure is reported for the assay of diltiazem in plasma. The use of disposable cartridges provides selective extraction and easy automation. A new LC system based on LiChrospher RP 60 Select B columns is described. For routine analysis, the procedure provides a rapid simultaneous clean-up of several samples prior to chromatography and reproducible recoveries over a concentration range of 10-800 ng. The procedure was used to analyse the plasma samples from a bioequivalence study of three commercial diltiazem preparations. The pharmacokinetic parameters in 12 healthy male volunteers were determined and the assessment of bioequivalence was conducted by discriminant analysis.