Comparison of UPLC and HPLC for Determination of trans-10-Hydroxy-2-Decenoic Acid Content in Royal Jelly by Ultrasound-Assisted Extraction with Internal Standard

Two well-known derivatization procedures, H₂SO₄–butanol and H₂SO₄–methanol esterification, were compared for application to GC–MS identification of organic acids in Bayer process liquors. H₂SO₄–butanol and H₂SO₄–methanol derivatization must be combined for analysis of carboxylic acids. Twenty organic acids were identified by gas chromatography–mass spectrometry. Heptanedioic, 3-methylhexanedioic, octanedioic, 1,3-benzenedicarboxylic, nonanedioic, decanedioic, hexadecanoic, 9,12-octadecadienoic, octadecanoic, and phthalic acids were identified for the first time in Bayer liquors. The retention times (y) and carbon numbers (x) of these seven n-dicarboxylic acids (C₄–C₁₀) were fit to a linear relationship by use of Microsoft Excel. These dicarboxylic acids and two benzenedicarboxylic acids were quantified by use of the internal standard method.     

Surface Activity of Fatty Acid Salts in Aqueous Solutions

The surface activity of sodium, potassium and, ammonium salts of fatty acids [stearic, oleic, synthetic fatty acids (C_{1 3}-C_{1 5} fractions), higher fatty acids contained in bottoms after separation of volatile fatty acids from cotton oil] in aqueous solutions was studied and analyzed.     

Separation of C1-C5 aliphatic carboxylic acids on a highly sulfonated styrene-divinylbenzene copolymer resin column with a C6 aliphatic carboxylic acid solution as the mobile phase

Simultaneous separation of C₁-C₅ aliphatic carboxylic acids (formic, acetic, propionic, iso-butyric, butyric, iso-valeric and valeric acids) on a highly sulfonated styrene-divinylbenzene copolymer resin column (TSKgel SCX,  mm i.d.) was performed with C₆ aliphatic carboxylic acids (3-methyl-n-valeric, iso-caproic and caproic acids) solutions as the mobile phases. Using 0.05 mM sulfuric acid at pH 4.0 as the mobile phase, although good separation of these C₁-C₅ acids was achieved, peaks of the C₅ acids (iso-valeric and valeric acids) with large hydrophobicity tailed strongly. In contrast, using 1 mM C₆ acids at pH ca. 4.0 as the mobile phases, although vacant peaks corresponding to the C₆ acids in the mobile phase appeared, the peak shapes of the C₅ acids were improved greatly. Excellent simultaneous separation, symmetrical peaks and relatively high-sensitivity conductimetric detection for these C₁-C₅ acids were achieved on the TSKgel SCX column in 15 min with 1 mM iso-caproic acid at pH 4.0 as the mobile phase.     

5H-3-oxa-Octafluoropentanesulfonyl fluoride: a novel and efficient condensing agent for esterification, amidation and anhydridization

The use of 5H-3-oxa-octafluoropentanesulfonyl fluoride (HCF₂CF₂OCF₂CF₂SO₂F) as a novel and efficient condensing reagent for esterification of carboxylic acids with alcohols and amidation of carboxylic acids with amines in the presence of 1,3-diazabicyclo[5.4.0]-undec-7-ene (DBU) is reported. HCF₂CF₂OCF₂CF₂SO₂F cannot serve as a condensing agent for anhydridization of carboxylic acids, however, HCF₂CF₂OCF₂CF₂SO₂F/(CH₃)₃SiCN system can mediate anhydridization of some aromatic carboxylic acids.     

Carbon-13 spin–lattice relaxation in strongly associated molecules: Carboxylic acids

¹³C spin–lattice relaxation times determined for the protonated carbons of carboxylic acids and methyl esters give indications of solution dimerization with the free acids. Since isopthalic and fumaric acids have two carboxyl functions they are able to polymerize in solution. Unlike the case for molecular aggregation due to weak hydrogen bonding in solution (e.g. alcohols, phenols), the ¹³C T₁ values of mono carboxylic acids are not significantly affected by dilution to c. 10^?2 M. Variable temperature T₁ measurements of both the mono and dibasic acids gave activation energies for molecular reorientation of the order of 2 kcal mol^?1, considerably lower than E_a for hydrogen bonded alcohols and comparable with E_a for the unassociated methyl esters of propionic and benzoic acids.     

The synthesis of biscitraconimides and polybiscitraconimides

A series of N-alkylene biscitraconimides was synthesized from the corresponding N-alkylene-biscitraconamic acids or directly from itaconic anhydride and a homologous series of aliphatic diamines, H₂N(CH₂)_nNH₂, where n = 2 through 12. The biscitraconamic acids were synthesized from the α,ω-diamino-alkanes and itaconic anhydride. Isomerization of itaconic anhydride to citraconic anhydride occurs in the presence of the diamines to yield biscitraconamic acids instead of bisitaconamic acids expected and observed in similar studies. The intermediate biscitraconamic acids or the biscitraconimides were polymerized thermally between 175 and 225°C to tough ambered-colored films of polybiscitraconimides that exhibit good thermal stability.     

Thermal stability of amino acids

Thermal decomposition of L-α-amino acids RCH₂(NH₂)COOH where R = Me₂CH, Me₂CHCH₂, MeEtCH, and C₆H₅CH₂ was studied at temperatures below the melting points of their crystals. From the effective rate constants of the first order reactions energy parameters in the Arrhenius equation were calculated. Correlations between the reaction rate constants k _R and the inductive constants σ* of substituents R and also between the rate constants of the reactions and the dipole moments of amino acids was established. Value of ρ* parameter +8.8 in the Taft equation indicates the heterolytic mechanism of transformation of the amino acids. Chromato-mass spectrometric analysis of decomposition products shows that condensation, decarboxylation, and deamination of the amino acids take place.     

Substituent effects in π-(tricarbonylchromium)arenes: V. Thermodynamic dissociation constants of some substituted π-(tricarbonylchromium)benzoic acids

The thermodynamic dissociation constants of a series of 38 substituted π-(tricarbonylchromium)benzoic acids in 50% aqueous ethanol at 25°C have been determined. The results require revision of some literature values.The pK_a^*-values of the π-(tricarbonylchromium)benzoic acids were correlated with the electronic substituent parameters in terms of the Yukawa-Tsuno equation. The reaction constant (ρ) decreases from 1.4 for the benzoic acids to 0.8 for the π-(tricarbonylchromium)benzoic acids, reflecting the decreased ability of the complexed aromatic system to transmit electronic substituent effects. For the alkylsubstituted π-(tricarbonylchromium)benzoic acids, conformational effects of the Cr(CO)₃ group can account for some of the anomalies observed. The substituent parameters, σ_meta and σ_para, of the π-(Cr(CO)₃)phenyl group as a substituent were derived from the dissociation constants of the complexed phenylbenzoic acids.     

Stereocontrol during the radical polymerization of methyl methacrylates with combined Lewis acids: Aluminium trichloride (AlCl3) and iron dichloride tetrahydrate

The radical polymerization of methyl methacrylate (MMA) was carried out in the presence of combined Lewis acids of the AlCl₃-FeCl₂ system. Compared with the polymerization produced in the presence of single Lewis acids, AlCl₃ or FeCl₂, the MMA polymerization in the presence of AlCl₃-FeCl₂ composite in CHCl₃ or 1-butanol produced a polymer with a higher isotacticity and in toluene produced a polymer with a much higher isotacticity (mm = 50%). The molecular weight and polydispersity of PMMA in the presence of Lewis acids were similar with those in the absence of Lewis acids, although Lewis acids decelerate the polymerization of MMA. The effects of the Lewis acids were greater in a solvent with a lower polarity. A possible stereocontrol mechanism of the polymerization was proposed. The Lewis acid composite of AlCl₃-FeCl₂ readily formed a complex with growing species. These complexes possessed apparent bulkiness that changes the direction of monomer addition to the growing radical center.     

Liquid chromatography coupled with ultraviolet absorbance detection,electrospray ionization,collision‐induced dissociation and tandem mass spectrometry on a triple quadrupole for the on‐line characterization of polyphenols and methylxanthines in green coffee beans

Liquid chromatography coupled with a photodiode array detector, electrospray ionization, collision‐induced dissociation and tandem mass spectrometry (LC‐DAD/ESI‐CID‐MS/MS) on a triple quadrupole (QqQ) has been used to detect and characterize polyphenols and methylxanthines in green coffee beans: three phenolic acids (caffeic acid, ferulic acid and dimethoxycinnamic acid), three isomeric caffeoylquinic acids (M_r 354), three feruloylquinic acids (M_r 368), one p‐coumaroylquinic acid (M_r 338), three dicaffeoylquinic acids (M_r 516), three feruloyl‐caffeoylquinic acids (M_r 530), four p‐coumaroyl‐caffeoylquinic acids (M_r 500), three diferuloylquinic acids (M_r 544), six dimethoxycinnamoyl‐caffeoylquinic acids (M_r 544), three dimethoxycinnamoyl‐feruloylquinic acids (M_r 558), six cinnamoyl‐amino acid conjugates, three cinnamoyl glycosides, and three methylxanthines (caffeine, theobromine and theophylline). Dimethoxycinnamic acid, three isomers of dimethoxycinnamoyl‐caffeoylquinic acids and another three of dimethoxycinnamoyl‐feruloylquinic acids, as well as the three cinnamoyl glycosides, had not previously been reported in coffee beans. Structures have been assigned on the basis of the complementary information obtained from UV‐visible spectra, relative hydrophobicity, scan mode MS spectra, and fragmentation patterns in MS² spectra (both in the positive and negative ion modes) obtained using a QqQ at different collision energies. A structure diagnosis scheme is provided for the identification of different isomers of polyphenols and methylxanthines. Copyright © 2009 John Wiley & Sons, Ltd.     

An improved derivatization method for sensitive determination of fatty acids by high-performance liquid chromatography using 9-(2-hydroxylethyl)-carbazole as derivatization reagent with fluorescence detection

Summary Tagging techniques with reagents used for fluorescent detection for short and long-chain fatty acids using high-performance liquid chromatography are evaluated in terms of the tagging reactions, handing, flexibility, stability of the reagents. Emphasis is given to the applications of the tagging techniques to relatively high molecular mass fatty acids. The fatty acids or carboxylic compounds were derivatized to their corresponding esters with 9-(2-hydroxy ethyl)-carbazole (HEC) in acetonitrile at 60°C with N, N′-carbonyldiimidazole (CDI) as a coupling agent in the presence of 4-dimethylaminopyridine (DMAP). A mixture of esters of C₁−C₂₀ fatty acids was completely separated with 45 min using gradient elution on a reversed-phase C₁₈ column. The maximum fluorescence emission for the derivatized fatty acids is at 365 nm (λ_ex 293 nm). Studies on derivatization conditions indicated that fatty acids react rapidly and smoothly with HEC in the presence of CDI and DMAP in acetonitrile to give the corresponding sensitively fluorescent derivatives. The application of this method to the analysis of long chain fatty acids in plasma is also investigated. The LC separation shows good selectivity and reproducibility for fatty acids derivatives. The relative standard deviations (n=6) for each fatty acid derivative are <5.0%. The detection limits are at 38–57 fmol levels for C₁₄−C₂₀ fatty acids and lower levels for <C₁₄ fatty acids.     

Effective synthesis of novel O-acetylated compounds over ZrO2-Al2O3 solid acid

The solid acids such as ZrO₂, Al₂O₃ and ZrO₂-Al₂O₃ containing different ZrO₂ loadings (10–80 mol%) were prepared by solution combustion method (SCM) and characterized for their total surface acidity by NH₃-TPD/n-butylamine back titration method and crystallinity by powder X-ray diffraction (PXRD) technique. These solid acids were evaluated for their catalytic activity in the synthesis of novel O-acetylated products from substituted phenols, pyridine alcohols and aryl alcohols with acetic anhydride (AA) as an acetylating agent. The reaction conditions were optimized by varying the catalyst, molar ratio of the reactants, reaction temperature and amount of the catalyst. All the solid acids used in this study exhibited good catalytic activity in the reaction. In particular, ZrO₂-Al₂O₃ containing 80 mol% of ZrO₂ was found to be highly active in the acetylation reaction with high yield of acetylated products. Triangular correlation between the surface acidity, crystallinity and catalytic activity of solid acids was observed. These solid acids were found to be reactivable and reusable.     

Thermal Stability of Heteropoly Acids and Characterization of the Water Content in the Keggin Structure

The thermal stability of heteropoly acids of the Keggin type (H₄[SiMo₁₂O₄₀], H₃[PMo₁₂O₄₀], H₄[SiW₁₂O₄₀] and H₃[PW₁₂O₄₀]), being important new catalytic materials, was studied by DSC. Two groups of signals were observed: the low temperature endothermic peak group belongs to the water content, while the high temperature one is exothermic and indicates the thermal decomposition of the acids. The effect of microwave irradiation on the target compounds was also studied. The emphasis, however, was placed on the characterization of the water content of the acids. Several types of water can be classified and DSC curves provide additional information to explain the differences in the catalytic behavior. The study of the effect of heat treatment and the subsequent water absorption of the acids provided additional unique information concerning the pseudoliquid phase in the secondary structure of heteropoly acids. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of N‐methylated amino acids by GC‐MS after ethyl chloroformate derivatization

Methylation is an essential metabolic process in the biological systems, and it is significant for several biological reactions in living organisms. Methylated compounds are known to be involved in most of the bodily functions, and some of them serve as biomarkers. Theoretically, all α‐amino acids can be methylated, and it is possible to encounter them in most animal/plant samples. But the analytical data, especially the mass spectral data, are available only for a few of the methylated amino acids. Thus, it is essential to generate mass spectral data and to develop mass spectrometry methods for the identification of all possible methylated amino acids for future metabolomic studies. In this study, all N‐methyl and N,N‐dimethyl amino acids were synthesized by the methylation of α‐amino acids and characterized by a GC‐MS method. The methylated amino acids were derivatized with ethyl chloroformate and analyzed by GC‐MS under EI and methane/CI conditions. The EI mass spectra of ethyl chloroformate derivatives of N‐methyl ( 1–18 ) and N,N‐dimethyl amino acids ( 19–35 ) showed abundant [M‐COOC₂H₅]⁺ ions. The fragment ions due to loss of C₂H₄, CO₂, (CO₂ + C₂H₄) from [M‐COOC₂H₅]⁺ were of structure indicative for 1–18 . The EI spectra of 19–35 showed less number of fragment ions when compared with those of 1–18 . The side chain group (R) caused specific fragment ions characteristic to its structure. The methane/CI spectra of the studied compounds showed [M + H]⁺ ions to substantiate their molecular weights. The detected EI fragment ions were characteristic of the structure that made easy identification of the studied compounds, including isomeric/isobaric compounds. Fragmentation patterns of the studied compounds ( 1–35 ) were confirmed by high‐resolution mass spectra data and further substantiated by the data obtained from ¹³C₂‐labeled glycines and N‐ethoxycarbonyl methoxy esters. The method was applied to human plasma samples for the identification of amino acids and methylated amino acids. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of bicyclic diesters of malonic and succinic acids

Monoesters of malonic and succinic acids have been prepared in high yields by the BF₃·OEt₂-catalyzed addition of the acids to bicyclo[2.2.1]hept-2-ene. The synthesized monoesters were introduced in the reaction of esterification with saturated monoatomic alcohols С₂–С₇ in the presence of the KU-2-8 catalyst in the H-form, and the corresponding mixed diesters of dicarboxylic acids were obtained in high yields.     

Regularities in the Distribution of Substituted,Branched, and Unsaturated Carboxylic Acids Between Organic and Aqueous Phases

There is no linear correlation between the physicochemical characteristics of carboxylic acids, their pK _a in particular, and their distribution constants K _d in the diethyl ether-water system; a certain correlation with molar volume V _m was revealed. Better results were obtained with use of multiparameter equations including V _m, polarity, polarizability, and pK _a of the acids. For 14 branched and substituted carboxylic acids it was found that their distribution constants between organic and aqueous phases are described by linear multiparameter equations, polarity and basicity of the extractants being the determining factors. The coefficients of the polarity and basicity terms vary in parallel with the corresponding characteristics of the acids.     

Analysis of long-chain fatty acids in grey wastewater with in-vial derivatisation

The presence and levels of long-chain fatty acids (C₆–C₂₀) in grey wastewater from bathrooms have been investigated. The acids were purified and concentrated by solid-phase extraction on strong anion exchange discs, in-vial derivatised to their corresponding methyl ester and subsequently analysed by GC-MS. The method was able to quantify the acids at concentration <1?µg/L with a recovery of 31–97%. The levels of fatty acids were found in the range of <0.5 to 27?100?µg/L and the highest levels were found for the saturated lauric (C₁₂), palmitic (C₁₆) and stearic (C₁₈) acids. The treatment efficiency of a local treatment plant was evaluated by comparing concentrations of fatty acids at the inlet and the outlet. It was found that the treatability decreases with increasing chain length for the saturated acids (19–100% degradation) whereas the corresponding mono unsaturated acids were more easily degraded.     

Thermal stability of perfluoroalkanesulfonic acids and their anhydrides. New and easy approach to RFSO2ORF esters.

Perfluoroalkanesulfonic anhydrides (R_FSO₂)₂O when mixed with acids decompose into perfluoroalkanesulfonic esters R_FSO₂OR_F, thereby providing a new facile synthesis of these esters from perfluoroalkanesulfonic acids and phosphorus pentoxide.     

Isocratic Reverse-Phase HPLC for Determination of Organic Acids in Kargı Tulum Cheese

Reverse-phase HPLC was assessed for the determination of most important organic acids in Kargı Tulum cheese. The method with a simple treatment of the sample succeeded in eluting nine organic acids in a single chromatographic run with the aid of buffer–acetonitrile gradient. A gradient programme using a mobile phase of aqueous 0.5% (w/v) (NH₄)₂HPO₄–0.4% (v/v) acetonitrile at pH 2.24 was used to separate organic acids on a C₁₈ column. The best flow rate–time program was applied to take the chromatogram in 35 min with a high linearity and excellent repeatability. The main organic acids of Kargı Tulum cheese were lactic, acetic, citric, propionic and formic acids. Pyruvic, uric and orotic acids were found to be lower in content while butyric acid was not detected in the samples.

     

Direct polycondensation of aromatic dicarboxylic acids and bisphenols with tosyl chloride and N,N-dimethylformamide in pyridine

A Vilsmeier adduct derived from arylsulfonyl chlorides and DMF in pyridine was successfully used as a new condensating agent for the synthesis of aromatic polyesters by the direct polycondensation of aromatic dicarboxylic acids and bisphenols and also of hydroxybenzoic acids. Polymers of high molecular weights (M?_w = 78,000) with relatively narrow molecular weight distribution (M?_w/M?_n ≈ 3.0) were prepared by reacting aromatic dicarboxylic acids with the adduct in pyridine, followed by addition of bisphenols. The polycondensation was significantly affected by the amount of DMF, the nature of the arylsulfonyl chlorides, the conditions of initial reaction of the acids with the adduct, and the rate of reaction with bisphenols. The process was adaptable to the direct polycondensation of hydroxybenzoic acids, affording polymers of high molecular weight (η_inh = 1.73).