Identification of individual acids in a commercial sample of naphthenic acids from petroleum by two-dimensional comprehensive gas chromatography/mass spectrometry

The identification of most individual members of the complex mixtures of carboxylic acids found in petroleum ('naphthenic acids') has eluded chemists for over a century; they remain unresolved by conventional gas chromatographic methods. Recently, however, we successfully used two-dimensional comprehensive gas chromatography/mass spectrometry to identify numerous individual diamondoid acids in the naphthenic acids of oil sands process water (OSPW). We have now applied the same methods to a study of a mixture of commercially available naphthenic acids originally refined from petroleum. The results confirm that OSPW and refined petroleum contain very different distributions of acids, as noted previously, although some of the diamondoid acids recently identified in OSPW were detectable in both. Rather, two-dimensional comprehensive gas chromatography/time-of-flight mass spectrometry (GCxGC/ToF-MS) of the methyl esters of the petroleum acids and of numerous acids synthesised for comparison showed that the former comprised mainly C(8-18) straight-chain, methyl-branched, acyclic isoprenoid, cyclohexyl and isomeric octahydropentalene, perhydroindane and perhydronaphthalene (decalin) acids. Some of the latter bicyclic acids occurred as both the non-alkyl-substituted isomers and the bicyclic ethanoic and propanoic acids. Also present in minor quantities was a range of phenyl carboxylic and substituted phenyl alkanoic acids, and traces of non-acids, including trimethylnaphthalenes, again identified by comparison with the synthesised compounds. These results represent some of the first identifications of multiple individual naphthenic acids in commercial mixtures originating from petroleum and provide a basis for future studies of the petroleum geochemistry, toxicities and environmental impacts of the acids. Furthermore, characterisation of the acids will be important for improving the understanding of the role of naphthenic acids in petroleum engineering, particularly for oil pipeline deposition problems.     

Sample preparation for organic acids in biological fluids

A review of sample preparation methods for organic acids in biological fluids, in particular serum and urine, is presented. It covers techniques on organic acid determination without sample preparation, release of organic acids from binding locations, removal of proteins by protein precipitation and ultrafiltration, isolation of the organic acids by liquid-liquid and liquid-solid extraction, purification of the extract, derivatization and pre-fractionation. The various alternative sample preparation steps are compared and critically discussed. Examples of applications including profile analysis of organic acids by gas chromatography (GC), determination of particular organic acids by GC or liquid chromatography and determination of fatty acids as a distinct chemical class of acids demonstrate that the kind of sample preparation chosen depends strongly on the analytical aims.     

Basic profiles of organic acids in urine

Altogether 143 of the organic acids regularly occurring in urine of healthy individuals are identified as methyl esters by gas chromatography-mass spectrometry with respect to their complete chemical structures. They are classified as dicarboxylic acids, oxocarboxylic acids, hydroxycarboxylic acids, aromatic acids, furancarboxylic acids, nitrogen-containing acids and acid conjugates. By pre-fractionating the complex mixture of the total organic acids, peak overlap is minimized, and substances in low concentrations can also be detected and identified. The qualitative patterns of the urinary organic acids in the fractions are constant and reproducible, and in many cases a reliable identification of organic acids is possible by gas chromatography alone, using methylene units and separation on OV-1701 capillary columns.     

Chiral separation and determination of the optical purity of thiamphenicol-related chiral compound by capillary zone electrophoresis with cyclodextrins as chiral selectors

Summary One classical method for quantitation of amino acids in proteins is hydrolysis of the proteins and determination of the free amino acids. Although the drastic experimental conditions necessary for complete hydrolysis always cause degradation of some of the amino acids, if mild hydrolysis conditions are used, a mixture of amino acids and oligopeptides is obtained. If these conditions are adequately tuned, the oligopeptides are almost exclusively dipeptides. For this reason we have initiated a study to find a derivatizing agent suitable for the analysis of amino acids and dipeptides by an absolute method of quantitation already tested for amino acids. FMOC-Cl was found to be a suitable derivatizing agent for this purpose.     

A novel derivatization reagent possessing a bromoquinolinium structure for biological carboxylic acids in HPLC‐ESI‐MS/MS

A novel bromoquinolinium reagent, i.e. 1‐(3‐aminopropyl)‐3‐bromoquinolinium bromide (APBQ), was synthesized for the analysis of carboxylic acids. A simple and practical precolumn derivatization procedure using the APBQ in RP chromatography and MS (HPLC‐MS) has been developed using bile acids and free fatty acids, as the representative carboxylic acids in biological samples. The APBQ efficiently reacted with carboxylic acids at 60°C for 60 min in the presence of N,N‐dicyclohexylcarbodiimide and pyridine as the activation reagents. Because the APBQ possesses a bromine atom in the structure, the identification of a series of carboxylic acids was easily achieved due to the characteristic bromine isotope pattern in the mass spectra. The APBQ also has a quaternary amine structure, thus the positively charged derivatives are predominate for the highly sensitive detection of carboxylic acids. The APBQ was successfully applied to the selective determination of biological carboxylic acids in human plasma. The bile acids (chenodeoxycholic acid and deoxycholic acid) and several saturated (stearic acid and palmitic acid) and unsaturated free fatty acids (oleic acid and linoleic acid) were reasonably determined by HPLC‐MS under the proposed procedure. Based on the results of analyses of human plasma and saliva, the proposed procedure using APBQ seems to be applicable for the qualitative and quantitative analyses of a series of carboxylic acids in biological samples.     

Analysis of deprotonated acids with silicon nanoparticle-assisted laser desorption/ ionization mass spectrometry

Chemically modified silicon nanoparticles were applied for the laser desorption/negative ionization of small acids. A series of substituted sulfonic acids and fatty acids was studied. Compared to desorption ionization on porous silicon (DIOS) and other matrix-less laser desorption/ionization techniques, silicon nanoparticle-assisted laser desorption/ionization (SPALDI) mass spectrometry allows for the analysis of acids in the negative ion mode without the observation of multimers or cation adducts. Using SPALDI, detection limits of many acids reached levels down to 50 pmol/μl. SPALDI of fatty acids with unmodified silicon nanoparticles was compared to SPALDI using the fluoroalkyl silylated silicon powder, with the unmodified particles showing better sensitivity for fatty acids, but with more low-mass background due to impurities and surfactants in the untreated silicon powder. The fatty acids exhibited a size-dependent response in both SPALDI and unmodified SPALDI, showing a signal intensity increase with the chain length of the fatty acids (C12-C18), leveling off at chain lengths of C18-C22. The size effect may be due to the crystallization of long chain fatty acids on the silicon. This hypothesis was further explored and supported by SPALDI of several, similar sized, unsaturated fatty acids with various crystallinities. Fatty acids in milk lipids and tick nymph samples were directly detected and their concentration ratios were determined by SPALDI mass spectrometry without complicated and time-consuming purification and esterification required in the traditional analysis of fatty acids by gas chromatography (GC). These results suggest that SPALDI mass spectrometry has the potential application in fast screening for small acids in crude samples with minimal sample preparation.     

Measurement of polyunsaturated fatty acids of myocardial lipids by high performance liquid chromatography

Summary This report describes a modified method for the separation and analysis of polyunsaturated fatty acids such as 20:4, 20:5, and 22:6, using HPLC. The results show that these fatty acids are well separated from the saturated acids. Since the unsaturated fatty acids elute earlier than saturated acids, and this method does not require the fractionation of free fatty acids using thin layer chromatography, a necessary step for the gas chromatographic analysis, the recoveries of polyunsaturated fatty acids were significantly higher as compared to those from gas chromatography. Furthermore, HPLC and gas chromatographic methods gave identical results for the acyl chain composition of phosphatidylserine. The advantages of using HPLC over gas chromatography in determining the acyl chain composition of free fatty acids and phospholipids are also discussed.     

黑蚂蚁的脂肪酸及抗氧化性能的分析

对黑蚂蚁中脂肪酸的组成和含量进行测定。采用索氏提取法提取其脂肪酸,再进行甲酯化处理,以气相色谱-质谱联用仪进行了分离和鉴定。由黑蚂蚁中分离鉴定出11种脂肪酸,占脂肪酸总量的99.78%,不饱和脂肪酸占脂肪酸总量的80.65%,饱和脂肪酸占脂肪酸总量的19.13。通过流动注射化学发光法分析了黑蚂蚁的抗氧化性能,结果表明,黑蚂蚁具有较强的抗氧化性能。     

Bile Acids: Physiological Activity and Perspectives of Using in Clinical and Laboratory Diagnostics

Bile acids play a significant role in the digestion of nutrients. In addition, bile acids perform a signaling function through their blood-circulating fraction. They regulate the activity of nuclear and membrane receptors, located in many tissues. The gut microbiota is an important factor influencing the effects of bile acids via enzymatic modification. Depending on the rate of healthy and pathogenic microbiota, a number of bile acids may support lipid and glucose homeostasis as well as shift to more toxic compounds participating in many pathological conditions. Thus, bile acids can be possible biomarkers of human pathology. However, the chemical structure of bile acids is similar and their analysis requires sensitive and specific methods of analysis. In this review, we provide information on the chemical structure and the biosynthesis of bile acids, their regulation, and their physiological role. In addition, the review describes the involvement of bile acids in various diseases of the digestive system, the approaches and challenges in the analysis of bile acids, and the prospects of their use in omics technologies.     

Profiling and characterisation by liquid chromatography/multi-stage mass spectrometry of the chlorogenic acids in Gardeniae Fructus

The chlorogenic acids of Gardeniae Fructus used traditionally as a Chinese herbal medicine (zhizi) have been investigated qualitatively by liquid chromatography/multi-stage mass spectrometry (LC/MS(4)). Twenty-nine chlorogenic acids were detected and twenty-five characterised to regioisomer level on the basis of their fragmentation, twenty-four for the first time from this source. Assignment to the level of individual regioisomers was possible for three caffeoylquinic acids, three dicaffeoylquinic acids, three sinapoylquinic acids, four caffeoyl-sinapoylquinic acids, two feruloyl-sinapoylquinic acids, one p-coumaroyl-sinapoylquinic acid, three (3-hydroxy, 3-methyl)glutaroylquinic acids, two (3-hydroxy, 3-methyl)glutaroyl-feruloylquinic acids, one (3-hydroxy, 3-methyl)glutaroyl-dicaffeoylquinic acid, and one (3-hydroxy, 3-methyl)glutaroyl-caffeoyl-feruloylquinic acid. Six (3-hydroxy, 3-methyl)glutaroyl-caffeoylquinic acids were detected and two were tentatively assigned as 3-caffeoyl-4-(3-hydroxy, 3-methyl)glutaroylquinic acid and 3-caffeoyl-5-(3-hydroxy, 3-methyl)glutaroylquinic acid. The (3-hydroxy, 3-methyl)glutaroyl residue modifies the mass spectral fragmentation behavior and elution sequence compared with the chlorogenic acids that contain only a cinnamic acid residue(s). Fourteen of these twenty-nine chlorogenic acids have not previously been reported from any source.     

Convenient Synthesis of a Library of Discrete Hydroxamic Acids Using the Hydroxythiophenol (Marshall) Resin

Several resins have reportedly been used to synthesize hydroxamic acids except for the hydroxythiophenol (Marshall) resin. Herein, we report the use of the Marshall resin to synthesize hydroxamic acids from carboxylic acids and its application to convert a library of 14 discrete aliphatic and aromatic carboxylic acids including N-protected amino acids to their corresponding hydroxamic acids in good yields.     

Scyllo-inositol as a convenient protecting group for aryl boronic acids in Suzuki–Miyaura cross-coupling reactions

Herein, we report air- and water-stable borate complexes between scyllo-inositol and aryl boronic acids. The complexes were less reactive than free aryl boronic acids under Suzuki–Miyaura cross-coupling reaction conditions; thus, the borate complexes were used as protected boronic acids. Although protecting groups for organoboronic acids are useful in coupling reactions, especially those used to produce π-conjugated molecules, only a few reports describing the use of protecting groups for boronic acids have been published. The proposed unique structural borate complex provides a novel protective method for aryl boronic acids.     

Methylthiohydantoin amino acids: chromatographic separation and comparison to phenylthiohydantoin amino acids

Most phenylthiohydantoin (PTH) amino acids and most methylthiohydantoin (MTH) amino acids may be separated from one another by thin-layer chromatography (TLC) using the same sequential development technique with the same two solvents. Similarly, a single solvent system may be used in high-performance liquid chromatography (HPLC) to separate most PTH-amino acids and most MTH-amino acids. When both TLC and HPLC separations are performed on a sample, all MTH-and PTH-amino acids can be uniquely identified. Since many solid-phase protein sequencing techniques generate both MTH-and PTH-amino acids, these analytical systems simplify identification of the amino acid derivatives. Although the chromatographic properties of MTH-and PTH-amino acids are similar, they are not identical (contrary to a previous report).     

临床化学上氨基酸、有机酸及核苷类的二维薄层色谱多相分离

在同一块薄层板上多相二维分离３０余种氨基酸、４０余种非挥发性有机酸和２０余种碱基。核苷类化合物。应用一对新的展开剂,用紫外灯－吖啶试剂－镉茚三酮试剂组合显色定位分析,改良了尿液非挥发性有机酸的溶剂萃取。尿液中此三类化合物提取物的多相二维色谱分离效果良好。     

Ligand-exchange chromatography of amino acids on copper-, cobalt- and zinc-chelex 100.

Procedures for the ligand-exchange chromatography of amino acids on copper-, cobalt-and zinc-Chelex 100 have been examined. Ligand exchange on the copper complex affords a simple and rapid method for the removal of amino acids (except for aspartic and glutamic acids) from dilute solutions. The influence of the pH on the binding of amino acids to the metal complex was also studied. The bound amino acids could be eluted with ammonium hydroxide which also causes a slight metal leakage. Chromatography on cobalt- and zinc-Chelex 100 showed that only the basic amino acids were quantitatively attached to these complexes at pH 8.3-9.5, whereas the others were predominantly EXCLUDED. This procedure can be used for the selective concentration and removal of basic amino acids in the presence of other amino acids.     

小鼠眼球中脂肪酸的组成分析

首次对小鼠眼球中的脂肪酸组成进行了气相色谱分析。小鼠眼球中的脂肪酸经氯仿－甲醇－盐酸混合液萃取,用甲醇－氢氧化钾法甲酯化,在２５ｍ×０．２５ｍｍＰＥＧ－２０Ｍ熔融石英毛细管柱内进行分离,眼球中１２种主要脂肪酸得到了定性和定量。测试结果提示：正常小鼠眼球中饱和脂肪酸含量较高,占全部脂肪酸含量的５２．８％;不饱和脂肪酸含量较少,但以多不饱和脂肪酸居多,占全部脂肪酸含量的１８．２％,不饱和脂肪酸与饱和脂肪酸的比值为０．６。可为有关眼疾病的治疗、预防及生化方面的深入研究提供有意义的信息。     

Ester‐Mediated Amide Bond Formation Driven by Wet–Dry Cycles: A Possible Path to Polypeptides on the Prebiotic Earth

Although it is generally accepted that amino acids were present on the prebiotic Earth, the mechanism by which α‐amino acids were condensed into polypeptides before the emergence of enzymes remains unsolved. Here, we demonstrate a prebiotically plausible mechanism for peptide (amide) bond formation that is enabled by α‐hydroxy acids, which were likely present along with amino acids on the early Earth. Together, α‐hydroxy acids and α‐amino acids form depsipeptides—oligomers with a combination of ester and amide linkages—in model prebiotic reactions that are driven by wet–cool/dry–hot cycles. Through a combination of ester–amide bond exchange and ester bond hydrolysis, depsipeptides are enriched with amino acids over time. These results support a long‐standing hypothesis that peptides might have arisen from ester‐based precursors.     

SKIN PERMEATION ENHANCEMENT BY FATTY ACIDS

The present study elucidates the skin permeation enhancement effects of a number of fatty acids, i.e. straight-chain saturated (SFA), monounsaturated (MUFA) and polyunsaturated acids (PUFA). The effects were studied using human stratum corneum (SC) and p-aminobenzoic acid (PABA) as a model permeant. The fatty acids in propylene glycol (FA/PG) were applied according to a pre-treatment/co-treatment protocol. SFA with 6 to 12 carbons exhibit a parabolic correlation between enhancement effect and chain-length, with a maximum at nonanoic-decanoic acids (with 9 and 10 carbons). All cis-6-, 9-, 11- or 13-octadecenoic acids (MUFA) enhance the permeation of PABA to the same extent. PUFA — linoleic (LA), α-linolenic (ALA) and arachidonic acids — enhance PABA permeation stronger than MUFA but additional double bonds do not further increase the degree of enhancement. The enhancement effects of fatty acids on the PABA penetration through SC are structure-dependent, associated with the existence of a balance between the permeability of pure fatty acids across SC and the interaction of the acids to skin lipids. Based on this and other studies, a set of mechanisms of action is proposed for fatty acids.     

O‐Arylation of Carboxylic Acids using (Phenyl)[2‐(trimethylsilyl)phenyl]iodonium Triflate as a Precursor of Arynes

Using (phenyl)[2‐(trimethylsilyl)phenyl]iodonium triflate as a precursor of arynes, Larock's method for O‐arylation of carboxylic acids and arynes was developed. A variety of acids including simple aliphatic carboxylic acids, aromatic carboxylic acids, allenoic acids, and p‐toluenesulfonic acid under mild reaction conditions could generate the aryl esters.     

Sequential ethoxycarbonylation, methoximation and tert-butyldimethylsilylation for simultaneous determination of amino acids and carboxylic acids by dual-column gas chromatography

Amino acids (AAs) in alkaline solution were first ethoxycarbonylated with subsequent methoximation of keto acids (KAs). After acidification and solid-phase extraction, tert-butyldimethylsilylation was performed for direct analysis by gas chromatography (GC) on dual-columns with different polarities, which provided simultaneous separation of multiple amino acids, carboxylic acids (CAs) and keto acids, facilitating accurate peak confirmation based on matching with retention index sets characteristic of each analyte. The present method was linear (r2 > or = 0.9955) with good precision (0.1-9.4%) and accuracy (-8.6 to 9.9%), allowing simultaneous screening for diagnostic amino acids along with carboxylic acids and keto acids in urine from a phenylketonuria patient.