Methanolic Potassium Hydroxide Research Articles

Analysis of carotenoids in ripe jackfruit (Artocarpus heterophyllus) kernel and study of their bioconversion in rats

AbstractVitamin A deficiency is of public health importance in Sri Lanka. Carotenoids are a significant source of provitamin A. The objective of this study was to analyse the carotenoid composition of jackfruit (Artocarpus heterophyllus sinhala: Waraka) kernel using MPLC and visible spectrophotometry and to determine the bioavailability and bioconversion of carotenoids present in jackfruit kernel by monitoring (i) the growth and (ii) levels of retinol and carotenoids in the liver and serum of Wistar rats provided with jackfruit incorporated into a standard daily diet. Carotenoid pigments were extracted using petroleum ether/methanol and saponified using 10% methanolic potassium hydroxide. Six carotenoids were detected in jackfruit kernel. The carotenes β‐carotene, α‐carotene, β‐zeacarotene, α‐zeacarotene and β‐carotene‐5,6‐epoxide and a dicarboxylic carotenoid, crocetin, were identified, corresponding theoretically to 141.6 retinol equivalents (RE) per 100 g. Our study indicated that jackfruit is a good source of provitamin A carotenoids, though not as good as papaya. Serum retinol concentrations in rats supplemented with jackfruit carotenoids were significantly higher (p = 0.008) compared with the control group. The same was true for liver retinol (p = 0.006). Quantification was carried out by RP‐HPLC. These results show that the biological conversion of provitamin A in jackfruit kernel appears satisfactory. Thus increased consumption of ripe jackfruit could be advocated as part of a strategy to prevent and control vitamin A deficiency in Sri Lanka. Copyright © 2004 Society of Chemical Industry

Facile Hydrolysis of Esters with KOH-Methanol at Ambient Temperature

A simple, rapid, and efficient method is reported for the hydrolysis of a variety of mono- and diesters of aromatic, aliphatic, fatty, and heterocyclic acids with potassium hydroxide in methanol at ambient temperature (∼35°C).

Spectrophotometric and fluorimetric determination of diazepam, bromazepam and clonazepam in pharmaceutical and urine samples

New spectrophotometric and fluorimetric methods have been developed to determine diazepam, bromazepam and clonazepam (1,4-benzodiazepines) in pure forms, pharmaceutical preparations and biological fluid. The new methods are based on measuring absorption or emission spectra in methanolic potassium hydroxide solution. Fluorimetric methods have proved selective with low detection limits, whereas photometric methods showed relatively high detection limits. Successive applications of developed methods for drugs determination in pharmaceutical preparations and urine samples were performed. Photometric methods gave linear calibration graphs in the ranges of 2.85–28.5, 0.316–3.16, and 0.316–3.16 μg ml −1 with detection limits of 1.27, 0.08 and 0.13 μg ml −1 for diazepam, bromazepam and clonazepam, respectively. Corresponding average errors of 2.60, 5.26 and 3.93 and relative standard deviations (R.S.D.s) of 2.79, 2.12 and 2.83, respectively, were obtained. Fluorimetric methods gave linear calibration graphs in the ranges of 0.03–0.34, 0.03–0.32 and 0.03–0.38 μg ml −1 with detection limits of 7.13, 5.67 and 16.47 ng ml −1 for diazepam, bromazepam and clonazepam, respectively. Corresponding average errors of 0.29, 4.33 and 5.42 and R.S.D.s of 1.27, 1.96 and 1.14 were obtained, respectively. Statistical Students t-test and F-test have been used and satisfactory results were obtained.

Microwave‐assisted saponification for the determination of 16 polycyclic aromatic hydrocarbons from pumpkin seed oils

AbstractThe production of pumpkin seed oil requires a roasting of the pumpkin seeds, at temperatures generally higher than 60°C. The roasting at elevated temperatures produces the typical taste of the pumpkin seed oil but may also be the source of a contamination with carcinogenic PAHs. Owing to their lipophilic character, their bioaccumulation, and their toxicity these compounds should be subject to mandatory monitoring. Since there is a lack of norms and legal limits for hot‐pressed oils, the limits set by the German Society of Fat Science of 25 μg/kg for the sum of 16 PAHs and 5 μg/kg for the heavy fraction for refined and cold‐pressed oils, such as olive oil and others, have to be applied. Sample preparation was performed by microwave‐assisted saponification with 1.5 M methanolic potassium hydroxide followed by a liquid‐liquid extraction and purification with sulfuric acid. A final clean up procedure was performed on activated silica gel combined with a preparative Bondesil‐cyano phase. For a selective measurement of the individual analytes, gas chromatography combined with mass spectroscopy was used in single ion monitoring mode. The overall analytical procedure was validated by systematic recovery experiments and by analyzing the certified reference material BCR CRM 458. Finally, this validated method was used for quality control of pumpkin seed oils from a producer co‐operative.

A Novel Laboratory Microcosm for Cocomposting Of Pentachlorophenol Contaminated Soil

A bench-scale composting system was constructed that relied on heat generation by microbial activity in the material rather than extraneous incubation. The system gave reproducible composting temperatures and eight microcosms could be operated simultaneously. These systems were used to investigate the feasibility of cocomposting pentachlorophenol (PCP) contaminated soil as a bioremediation strategy. Laboratory cocomposting of the contaminated soil successfully reduced PCP concentrations by 80%, from 68 mg/kg to 11 mg/kg in a six-week period. Losses of PCP from compost controls were minimal indicating that removal was due primarily to biotic processes. A comparison of residual PCP levels determined by dichloromethane (DCM) extraction and a methanolic potassium hydroxide (MeOH/KOH) digest prior to DCM extraction suggested that the residual PCP was bound to the compost matrix. Recovery of PCP at the end of a composting experiment using eight vessels simultaneously using the MeOH/KOH method indicated residual concentrations of 8-10 mg/kg.

Application of isotope dilution to the determination of methylmercury in fish tissue by solid-phase microextraction gas chromatography–mass spectrometry

Species-specific isotope dilution (ID) calibration using solid-phase microextraction (SPME) in combination with gas chromatography–mass spectrometry (GC–MS) for separation and detection of methylmercury (MeHg) in fish tissue is described. Samples were digested with methanolic potassium hydroxide. Analytes were propylated and headspace sampled with a polydimethylsiloxane-coated SPME fused-silica fiber. ID analysis was performed using a laboratory-synthesized 198Hg-enriched methylmercury (Me 198Hg) spike. Using selective ion monitoring (SIM) mode, the intensities of Me 202HgPr + at m/ z 260 and Me 198HgPr + at m/ z 256 were used to calculate the m/ z ratio at 260/256, which was used to quantify MeHg in NRCC CRM DORM-2 fish tissue. A MeHg concentration of 4.336±0.091 μg g −1 (one standard deviation, n=4) as Hg was obtained in DORM-2, in good agreement with the certified value of 4.47±0.32 μg g −1 (95% confidence interval). A concentration of 4.58±0.31 μg g −1 was determined by standard additions calibration using ethylmercury (EtHg) as an internal standard. The three-fold improvement in the precision of measured MeHg concentrations using ID highlights its superiority in providing more precise results compared to the method of standard additions. A method detection limit (3 S.D.) of 0.037 μg g −1 was estimated based on a 0.25 g subsample of DORM-2.

Determination of methylmercury in fish tissues by isotope dilution SPME-GC-ICP-MS

A method is described for the accurate and precise determination of monomethylmercury (MMHg) by species specific isotope dilution (ID) calibration using solid phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. Samples were digested with methanolic potassium hydroxide, derivatized in aqueous solution with sodium tetrapropylborate and headspace sampled with a polydimethylsiloxane coated SPME fused silica fiber. The analyte was then directly transferred from the fiber to the head of the GC column for desorption by insertion of the fiber through the heated injection port. Reverse spike ID analysis was performed to determine the accurate concentration of an in-house synthesized 198Hg-enriched monomethylmercury (MM198Hg) spike [candidate Certified Reference Material (CRM) EOM-1] using two natural abundance MMHg standards. Concentrations of 0.719 ± 0.015 and 4.484 ± 0.029 µg g−1 (one standard deviation, n = 4) as Hg were obtained for MMHg in NRCC CRMs DOLT-2 and DORM-2, respectively, using the present method. These are in good agreement with the certified values of 0.693 ± 0.053 and 4.47 ± 0.32 µg g−1 (as 95% confidence interval). A MMHg concentration of 4.69 ± 0.12 µg g−1 (one standard deviation, n = 4) as Hg in DORM-2 was subsequently determined by standard additions calibration using ethylmercury (EtHg) as an internal standard. A nearly 4-fold improvement in the precision of determination using ID was obtained, clearly demonstrating its superiority in providing more precise results compared to the method of standard additions. The method was applied to the determination of MMHg in a new biological CRM DOLT-3 and a concentration of 1.540 ± 0.025 µg g−1 (one standard deviation, n = 6) as Hg was obtained. A method detection limit (3σ) of 2.1 ng g−1 was estimated for a 0.25 g of subsample, sufficiently low for the routine determination of MMHg in most biological samples.

Solid phase microextraction capillary gas chromatography combined with furnace atomization plasma emission spectrometry for speciation of mercury in fish tissues

The use of solid phase microextraction in conjunction with tandem gas chromatography–furnace atomization plasma emission spectrometry (SPME–GC–FAPES) was evaluated for the determination of methylmercury and inorganic mercury in fish tissue. Samples were digested with methanolic potassium hydroxide, derivatized with sodium tetraethylborate and extracted by SPME. After the SPME extraction, species were separated by GC and detected by FAPES. All experimental parameters were optimized for best separation and analytical response. A repeatability precision of typically 2% can be achieved with long-term (3 months) reproducibility precision of 4.3%. Certified Reference Materials DORM-2, DOLT-2 and TORT-2 from the National Research Council of Canada were analyzed to verify the accuracy of this technique. Detection limits of 1.5 ng g −1 for methylmercury and 0.7 ng g −1 for inorganic mercury in biological tissues were obtained.

A comparison of alkyl derivatization methods for speciation of mercury based on solid phase microextraction gas chromatography with furnace atomization plasma emission spectrometry detection

Several derivatizing agents were evaluated for use in speciating mercury in biological samples using solid phase microextraction in conjunction with tandem gas chromatography-furnace atomization plasma emission spectrometry (SPME-GC-FAPES). Following digestion with methanolic potassium hydroxide, the pH of the samples was adjusted and NaCl added when necessary. The mercury species were then derivatized with sodium tetraphenylborate or sodium tetrapropylborate and extracted by SPME using a 100 µm PDMS coated fiber. The derivatized species were then separated by GC and detected by FAPES. All experimental parameters were optimized for best separation and analytical response. Propylation proved to be more sensitive, robust and faster than ethylation or phenylation, leading to procedural detection limits of 0.55 ng g−1 for methylmercury, 0.34 ng g−1 for ethylmercury and 0.23 ng g−1 for inorganic mercury. An intra-day and intra-fiber precision of typically 2.2% was achieved whereas long-term (4 months) and inter-fiber reproducibility precision was typically 4.4%. The accuracy of the method was validated by the analysis of Certified Reference Materials (DORM-2, DOLT-2 and TORT-2) from the National Research Council of Canada.

Chemical structure of the chlorination product of tribromoethylene

Reaction of tribromoethylene 1 with chlorine gave 1,1,2,2-tetrabromo-1-chloroethane 4 as the major product. Dehydrohalogenation of 4 with methanolic potassium hydroxide gave tribromochloroethylene 2. The structure of 4 was determined by X-ray crystallography. Molecular computations of 4 and its isomer 5 showed that 5 is slightly more stable.

Multiplicity control in the polygeminal diazeniumdiolation of active hydrogen bearing carbons: chemistry of a new type of trianionic molecular propeller.

Over a century ago, Traube reported the reaction of four nitric oxides with acetone and sodium ethoxide to yield sodium methanebis(diazene-N-oxide-N'-hydroxylate) and sodium acetate. However, when this reaction is carried out in the presence of nitric oxide at slightly elevated pressures (35-40 psi), a product corresponding to the addition of six nitric oxides, sodium methanetris(diazene-N-oxide-N'-hydroxylate), forms as the main product in addition to a trace of the previously observed sodium methanebis(diazene-N-oxide-N'-hydroxylate) and sodium acetate. The corresponding potassium salts form when potassium hydroxide is employed as the base, while lithium hydroxide results in the formation of lithium methanebis(diazene-N-oxide-N'-hydroxylate) exclusively. Nitric oxide reacts with 3,3-dimethylbutan-2-one in the presence of sodium and potassium hydroxide in methanol to yield sodium and potassium 3,3-dimethylbutan-2-one-1,1,1-tris(diazene-N-oxide-N'-hydroxylate), respectively. In contrast, the reaction in the presence of lithium hydroxide forms lithium methanebis(diazene-N-oxide-N'-hydroxylate) and lithium pivalate. The differential reactivity of nitric oxide with acetone and 3,3-dimethylbutan-2-one in the presence of the three bases is attributed to competing hydrolytic reactions of the acetyl and trimethylacetyl group-containing intermediates. A mechanism is proposed for the nitric oxide addition to active methyl groups in these reactions, where the product distribution between the di- and trisubstituted methanes is under kinetic control of the competing reactions. The products are characterized by NMR and IR spectroscopy, differential scanning calorimetry, and elemental analysis. Two differentially hydrated forms of potassium methanetris(diazene-N-oxide-N'-hydroxylate) are characterized by single-crystal X-ray diffraction. From the metathesis reaction of the silver salt of methanetris(diazene-N-oxide-N'-hydroxylate) with ammonium iodide, the corresponding ammonium salt is isolated in 59% yield, but only trace amounts of methylated products form in the reaction of the silver salt with methyl iodide. Density functional calculations (B3LYP/6-311++G) are used to evaluate the bonding, ground-state structures, and energy landscape for the different conformers of methanetris(diazene-N-oxide-N'-hydroxylate)(3-) trianion, a new type of a molecular propeller, and its corresponding triprotonated acid.

The Synthesis of Annulated Azepin-3-one Derivatives from 1,3,4-Pentatrienyl Nitrones by a Heterocyclization−Rearrangement Sequence

Treatment of various o-propargylaryl nitrones of type 6 with potassium hydroxide or sodium methoxide in methanol at room temperature provides 1,2-dihydro[c]benzazepin-3-ones 9. The high product yields and the ease of the reactions under surprisingly mild conditions are particularly intriguing in view of the complex mechanistic pathway involved in the overall transformation. A mechanism based on a multistep rearrangement is proposed, involving conjugated allene nitrones of type 13 as precursors of a 1,7-dipolar cyclization process that is followed by further bond reorganizations, with cyclopropanones 16 as key intermediates. In agreement with the allene formation is the fact that the same transformation can be achieved with the triple bond isomers 12 and 37, which contain terminal alkyl groups. The intermediacy of cyclopropanones 16 is supported by the competing formation of the isoindoles 20 as minor products. On treatment of dihydronaphtho-annulated nitrones 30 with base, formation of the azepinones 31 as the main products is also accompanied by that of the isomeric isoindoles 32. Some selective C=O and C=C hydrogenation reactions, together with conversions into the thioketone 42 and the vinyl bromide 9p, have been demonstrated with representative examples of 9.

Characterization of carotenoids in juice of red navel orange (Cara Cara).

High-performance liquid chromatography with photodiode array detection was applied for the separation and characterization of carotenoids from a red-fleshed navel orange (Cara Cara). Carotenoid pigments were extracted using hexane/acetone/ethanol and saponified using 10% methanolic potassium hydroxide. More than 29 carotenoid pigments were separated within 60 min using a ternary gradient (75% acetonitrile/25% methanol, methyl tert-butyl ether, and water) elution on a C(30) reversed-phase column. The presence of lycopene (3.9 +/- 1.1 ppm) and a relatively large percentage of beta-carotene were distinct differences in the pigment profile of this red navel orange juice as compared to the profile of standard navel orange juice. The juice color in the red navel was much deeper orange than that from navel orange; hue angle ranged from 84.1 to 89.4 for red navel compared to 98.2 to 100.5 for standard navel.

Evaluation of food antioxidant activity by photostorage chemiluminescence

A sensitive and simple method for measuring antioxidant activity was developed, based on antioxidant-dependant quenching of the chemiluminescence (CL) generated from photolyzed acridine and methanolic potassium hydroxide. This method was used to evaluate the antioxidant activity of food additives by measuring the inhibition of CL at a gradient of antioxidant concentrations. Adipic, tartaric, citric, ascorbic, malic, fumaric and 6-hydroxy-2,5,7,8-tetramethyl-2-carboxylic acid (Trolox) were employed as antioxidants. The method is more suitable for lipophilic compounds.

High-performance liquid chromatography for the characterization of carotenoids in the new sweet orange (Earlygold) grown in Florida, USA

High-performance liquid chromatography with photodiode array detection was developed for the separation and identification of carotenoids from a new sweet orange, Earlygold. Carotenoid pigments were extracted using hexane–acetone–ethanol and saponified using 10% methanolic potassium hydroxide. More than 25 carotenoid pigments were separated within 40 min using a ternary gradient (acetonitrile–methanol, methyl tert.-butyl ether and water) elution on a C 30 reversed-phase column. The carotenoid pattern of Earlygold was generally similar to the early season Hamlin but with some quantitative differences, especially with violaxanthin. Major carotenoids including violaxanthin, lutein, β-cryptoxanthin, antheraxanthin, luteoxanthin, zeaxanthin, β-carotene, and α-carotene were identified based on on-line spectral data obtained by a photodiode array detector, and comparison to the spectra of the standards and reported values. A numerical notation, the ratio of the peak heights between absorption bands, was also calculated to compare to the literature values.

Microwave-assisted extraction for methylmercury determination in sediments by high performance liquid chromatography-cold vapour-atomic fluorescence spectrometry

A simple and rapid procedure for methylmercury extraction from sediments based on microwave-assisted alkaline digestion with methanolic potassium hydroxide was optimized on parameters such as microwave power, extraction time and sample size. Organomercury species were extracted with dichloromethane in hydrochloric acid medium and back-extracted into ultra-pure water. The sediment extracts were injected into an analytical system composed of high-performance liquid chromatography-ultraviolet-post-column oxidation-cold vapour-atomic fluorescence spectrometry (HPLC-UV-PCO-CV-AFS) for methylmercury determination. Quantitative methylmercury recoveries were obtained when 0.15 g of sediment were suspended into 6 ml of 25% m/v methanolic potassium hydroxide and the slurry was exposed to microwave irradiation at 84 W for 2 min. The detection limit of proposed method was 12 ng g−1 while the relative standard deviation was less than 5%. The method was validated by the analysis of two sediment certified reference materials and the methylmercury concentrations found were in good agreement (95% confidence level) with the certified values.

Synthesis of Cyclic Sulfonamides via Intramolecular Copper-Catalyzed Reaction of Unsaturated Iminoiodinanes

Olefinic primary sulfonamides were treated with iodobenzene diacetate and potassium hydroxide in methanol to give intermediate iminoiodinanes. Catalytic copper(I) or (II) triflate then provided intramolecular nitrene delivery leading to aziridine formation except in one case where a rare copper-catalyzed C-H insertion was observed. The aziridines could be opened by various nucleophiles (methanol, thiophenol, allylmagnesium bromide, benzylamine) to give the corresponding substituted cyclic sulfonamides.

A convenient synthesis of novel pyrimidine analogues of o-hydroxy chalcones and pyrano [2,3-d]pyrimidines and their biological activities

A convenient method for the synthesis of new pyrimidine analogues of chalcones by condensation of 5-acetyl-1,3-diaryl-1,2,3,4-tetrahydro-6-hydroxy-4-oxo-2-thioxopyrimidines with aromatic aldehydes in aqueous methanolic potassium hydroxide (method A) and by condensation of 1,3-diaryl-2-thiobarbituric acids with cinnamoyl chlorides in presence of triethylamine (method B) is reported which on subsequent oxidative cyclization afforded 1,3,7-triaryl-1,2,3,4-tetrahydro-4,5-dioxo-2-thioxo-5 H-pyrano[2,3- d]pyrimidines which were evaluated for their antimicrobial activity.

Acid-Base Initiated Cyclization and Retrocyclization Reactions of Ethyl 2-(3-Acylselenoureido)benzoates, -thiophene-3-carboxylates and the Corresponding 2-(3-Acylisoselenoureido) Derivatives

Acid and base initiated cyclization and retrocyclization reactions of the selenoureas 1-6 and isoselenoureas 7-12 to fused 4H-1,3-selenazine and 1,2,3,4-tetrahydropyrimidine-4-one skeletons are reported. Fused 2-acylamino-4H-1,3-selenazine-4-ones 13-18 were formed by the action of concentrated sulfuric acid on acylselenoureas 1-6 or on 2,2-dimethylpropanoylisoselenoureas 10-12 at room temperature. On the other hand, benzoylisoselenoureas 7-9 were not obtained in this cyclocondensation under the same conditions. The reaction of potassium ethoxide on selenazines 13-18 in the ethanol solution evoked retrocyclization to the starting acylselenoureas 1-6. Both types of the title compounds, i.e. selenoureas 1-6 and isoselenoureas 7-12, were deprotonated in a methanol solution of potassium hydroxide used in an equimolar amount, giving rise to potassium salts 19-24, which were isolated only for the thiophene series. By heating the separated potassium salts 20, 21, 23 and 24 in the methanol solution provided, deacylation and isoselenoureas 26, 27 were formed. The in situ prepared salts 19, 22 cyclized under the same conditions with deacylation to 4-selanyl-3,4-dihydroquinazoline-4-one 28. The title compounds 1-6, 7-12 and products of their deacylation 26, 27 on boiling in methanolic potassium hydroxide cyclized to the corresponding fused 2-selenoxo-1,2,3,4-tetrahydropyrimidine-4-one potassium salts. These compounds provided pyrimidine-4-ones 28-30 on acidification. Acid initiated retrocyclization 28-30 to the corresponding 2-amino-4H-1,3-selenazine-4-ones was unsuccessful. C, H, N, Se elemental analyses, FTIR, 1H-NMR, and 13C-NMR spectroscopies supported the structure of synthesized compounds.A short review on cardiotonic steroids and their analogues is presented. The natural, semisynthetic and synthetic derivatives, as well as their mechanism of action and structure-activity relationships are shown, with a special reference to aminoguanidine derivatives.

Bi–KOH. An efficient reagent for the coupling of nitroarenes to azo and azoxy compounds

A simple and inexpensive procedure for the coupling of nitroarenes to azoxy compounds with bismuth and potassium hydroxide in methanol at ambient temperature is achieved. When carried out under microwave irradiation it gives exclusively azo compounds in excellent yields.