A simple and reliable semipreparative high-performance liquid chromatography technique for the isolation of marker-grade hyperforin from Hypericum perforatum L extract

The present work describes isolation of bioactive lipophilic constituent [namely, hyperforin from St. John's wort (Hypericum perforatum L.)], of approximately 98% purity by semipreparative high-performance liquid chromatography (LC). The extraction, isolation, and analysis of the collected compound is performed without the use of antioxidants and inert gas atmospheres at all the stages. Hyperforin, separated isocratically on a 12microm semiprep column, is obtained in high purity, lyophilized after the removal of the organic phase, and preserved at a low temperature. The purity of the collected marker compound is estimated by the use of LC-mass spectrometry and spectroscopic techniques.     

Membrane oscillations involving electrokinetic phenomena

Semi theoretical models have been proposed to account for the mechanism of membrane oscillations involving, electrokinetic phenomena in systems where (i) concentration difference deltaC is finite and deltaP is varying but the current is fixed, and (ii) deltaC=0, pressure difference deltaP is fixed across the membrane and imposed current is fixed. The formalism leads to the van der Pol equation in both cases. Computer simulation has also been attempted, which indicates oscillations in the former case.     

o-Iodosobenzoate as an oxidimetric titrant

o-Iodosobenzoate has been used as a titrant at pH 7 with potassium iodide and starch as indicator, under Andrews' titration conditions with iodine monochloride as preoxidant, and in acid medium with potassium bromide and Methyl Red as indicator. Methods are described for the determination of tetrathionate (through disulphide cleavage by cysteine), hydrogen sulphite, thiosulphate, xanthates, cysteine and glutathione in certain combinations (involving masking of sulphite and thiols with acrylonitrile). Hexacyanoferrate(II) is determined in the presence of arsenic(III), antimony(III) and thallium(I). Sulphathiazole, sulphadiazine and sulphamerazine consume six equivalents of bromine per mole, but phthalation or diazotization of the aromatic amino group prevents disubstitution of bromine in the benzene ring. Chloramphenicol is determined by reduction of its aromatic nitro group to an amino group, followed by bromination. Rutin and vitamin C react with eight and two equivalents of bromine per mole respectively.     

Determination of bromine in organic compounds by high-performance liquid chromatography

A method is proposed for the determination of bromine in organic compounds (which may also contain chlorine and iodine) by oxygen-flask combustion of the compound followed by pre-column reaction of bromide with acetanilide and 2-iodosobenzoic acid to form 4-bromoacetanilide which is then chromatographed on an ODS column with a mobile phase of methanol: water, 65:35 v/v, detection at 240 nm, and 4-N-acetylaminotoluene as internal standard. The method is rapid and precise (RSD 相似文献   

Determination of thiourea and its organic derivatives with iodine trichloride

Thiourea and its organic derivatives and thiosemicarbazide are determined in water, methanol or glacial acetic acid medium by reaction with an excess of iodine trichloride in the presence of mercuric chloride. The reaction is complete in 15 min. The excess of iodine trichloride is evaluated by adding potassium iodide and titrating the liberated iodine with thiosulphate. A variety of organic thioureas can be determined with an average accuracy and precision of 0.2%.     

Reactions of fluorinated acid anhydrides, (CF3CO)2O, (CF3SO2)2O and (FSO2)2O, with organometallic substrates of group 15 (As, Sb and Bi)

(C₆H₅)₃MX₂ (M = As, Sb; X = OCOCF₃ and M = Sb, Bi; X = SO₃F, SO₃CF₃) compounds prepared by the interaction of triphenylmetal(V) substrates with (CF₃CO)₂O, (CF₃SO₂)₂O and (FSO₂)₂O have been characterized by molecular weight determination, elemental and spectroscopic (IR, ¹H and ¹⁹F NMR, mass) analyses.     

Spectrophotometric determination of ascorbic acid in pharmaceuticals by background correction and flow injection

Background correction has been shown to be an effective and indispensable modification in the spectrophotometric determination of ascorbic acid. The decomposition of ascorbic acid in pharmaceutical samples was carried out by incubation with sodium hydroxide to give products that were insensitive to ultraviolet light. The rapid oxidation in air of ascorbic acid, especially in dilute solutions, was avoided by the use of the flow injection principle for spectrophotometric determination and by employing a carrier stream of an anti-oxidizing nature consisting of 6 micrograms ml(-1) of 2-mercaptoethanol in 0.25% sulphuric acid. The optimized method with a single channel manifold made use of a carrier stream flow rate of 1.1 ml min(-1), an injection volume of 50 microl, a delay coil of 50 cm (0.5 mm i.d.) and detection at 245 nm. The throughput was at least 180 injections h(-1). The proposed flow injection method yielded results for the analysis of 0-20 micrograms ml(-1) of ascorbic acid that were 99-102% (relative standard deviation 0.6% or better) in agreement with those produced by comparable methods involving titration with iodine, chloranil or 2,6-dichlorophenolindophenol [4-(2,6-dichloro-4-hydroxyphenylimino)cyclohexa-2,5-dieno ne], and high-performance liquid chromatography. When the agreement was not good (as low as 14% with respect to the method being compared), this was traced to the presence of substances which are known to interfere in one or other of the methods of comparison.     

N-Alkylation of diethyl acetamidomalonate: synthesis of constrained amino acid derivatives by ring-closing metathesis

An efficient method for N-alkylation of diethyl acetamidomalonate (DEAM) is reported. C-Alkenylation was achieved by treating the N-alkenylated DEAM with various electrophiles in the presence of Cs₂CO₃. RCM reactions of C- and N-alkenylated products gave cyclic amino acid derivatives in good yields.