Detection of 28 neurotransmitters and related compounds in biological fluids by liquid chromatography/tandem mass spectrometry

This work presents two liquid chromatography/tandem mass spectrometry (LC/MS/MS) acquisition modes: multiple reaction monitoring (MRM) and neutral loss scan (NL), for the analysis of 28 compounds in a mixture. This mixture includes 21 compounds related to the metabolism of three amino acids: tyrosine, tryptophan and glutamic acid, two pterins and five deuterated compounds used as internal standards. The identification of compounds is achieved using the retention times (RT) and the characteristic fragmentations of ionized compounds. The acquisition modes used for the detection of characteristic ions turned out to be complementary: the identification of expected compounds only is feasible by MRM while expected and unexpected compounds are detected by NL. In the first part of this work, the fragmentations characterizing each molecule of interest are described. These fragmentations are used in the second part for the detection by MRM and NL of selected compounds in mixture with and without biological fluids. Any preliminary extraction precedes the analysis of compounds in biological fluids.     

Statistics of the Popularity of Chemical Compounds in Relation to the Non-Target Analysis

The idea of popularity/abundance of chemical compounds is widely used in non-target chemical analysis involving environmental studies. To have a clear quantitative basis for this idea, frequency distributions of chemical compounds over indicators of their popularity/abundance are obtained and discussed. Popularity indicators are the number of information sources, the number of chemical vendors, counts of data records, and other variables assessed from two large databases, namely ChemSpider and PubChem. Distributions are approximated by power functions, special cases of Zipf distributions, which are characteristic of the results of human/social activity. Relatively small group of the most popular compounds has been denoted, conventionally accounting for a few percent (several million) of compounds. These compounds are most often explored in scientific research and are practically used. Accordingly, popular compounds have been taken into account as first analyte candidates for identification in non-target analysis.     

叠氮二异丁基铝的构造及其缔合-解离平衡研究

叠氮二异丁基铝（DBAA）是一个新合成的化合物。通过相对分子质量的测定、氢－核磁共振谱和铝－核磁共振谱的测定,确定了DBAA三聚体的分子构造;在溶液中研究了DBAA的三聚体和单晶体之间的缔合－解离平衡。这个平衡受溶剂性质、温度的影响。借助铝－核磁共振谱和相对分子质量的测定计算了DBAA三聚体的解离平衡常数、解离焓和解离熵等热力学数据。     

13C NMR specta of 4-quinolones and related compounds

Complete assignments are made for 23 4-quinolones and related compounds. Literature data are used to calculate chemical shifts for 17 of these compounds: calculated and experimental shifts are in excellent agreement—all within 5 ppm for nine of the compounds and a maximum discrepancy of 7.6 ppm.     

Prediction of the molar volume at the normal boiling point

A group contribution method for the prediction of the molar volume at the normal boiling point has been developed. The method can be used for organic and inorganic compounds. It cannot be used for elements and diatomic molecules. Group contributions are shown for a wide variety of hydrocarbons, organic halogen compounds, organic oxygen compounds, organic nitrogen compounds, organic sulfur compounds, organic boron compounds, organic silicon compounds, miscellaneous organics, and many inorganic compounds.Contrary to the corresponding states methods for the prediction of molar volumes, knowledge of critical properties, acentric factors, and reference volumes is not needed.     

TRIMETHYLAMMONIUM CHLOROCHROMATE ADSORBED ON ALUMINA AS A NEW REAGENT FOR THE CLEAVAGE OF OXIMES AND P-NITROPHENYLHYDRAZONES

Derivatives of carbonyl compounds such as oximes and p-nitrophenylhydrazones have played an important role in the protection of carbonyl compounds,as they are highly crystalline and stable compounds. They are also very extensively used for the characterization and purification of carbonyl compounds. Regeneration of carbonyl compounds from their derivatives under mild condition is an important process in synthetic organic chemistry.     

Thin-layer chromatographic separation and analysis of polynuclear aza heterocyclic compounds

Many thin-layer Chromatographic systems can be used for the general separation of aza heterocyclic compounds from polynuclear aromatic hydrocarbons. Several can be used for the separation of the aza compounds from each other. With alumina as the adsorbent the sterically hindered aza heterocyclic compounds can be readily separated from the non-hindered aza compounds.The use of the trifluoroacetic acid spot test on the thin-layer plate is discussed. Spectral data for the aza compounds are presented and discussed.     

Agostic bonds in cyclometalation

Cyclometalation reactions proceed very easily with one step reaction between metal compounds and substrates having a heteroatom such as O, S, N, P and As. However, under mild reaction conditions, many agostic compounds which are intermediates in these cyclometalation reactions, can be isolated. The metal compounds used for the formation of these agostic intermediates are both transition metal and main group metal compounds. The substrates are nitrogen-containing compounds, phosphorus-containing compounds, oxygen-containing compounds and sulfur-containing compounds. These agostic intermediates are mainly δ-C-H agostic compounds, some are γ-C-H agostic compounds and very few are ?-C-H-agostic compounds. The agostic intermediates are prepared, usually, under mild reaction conditions in the cyclometalation reaction. These agostic compounds are also prepared from cyclometalation reaction products, e.g., by the protonation, irradiation, and elimination of ligand molecules by vacuum, inert gas current, dehydration with a molecular sieves 4A, etc. Some agostic compounds are utilized for preparation of stable catalysts, e.g., hydrogenation catalysts.     

Analysis of alkaloids from different chemical groups by different liquid chromatography methods

Alkaloids are biologically active compounds widely used as pharmaceuticals and synthesised as secondary methabolites in plants. Many of these compounds are strongly toxic. Therefore, they are often subject of scientific interests and analysis. Since alkaloids — basic compounds appear in aqueous solutions as ionized and unionized forms, they are difficult for chromatographic separation for peak tailing, poor systems efficiency, poor separation and poor column-to-column reproducibility. For this reason it is necessity searching of more suitable chromatographic systems for analysis of the compounds.     

Influence of aromatic compounds in sugar chromatography on anion-exchange resins

In sugar separations by partition chromatography on anion-exchange resins in aqueous ethanol, phenolic compounds are eluted within the same range as sugars and interfere when non-specific detectors are used. The simultaneous application of the orcinol method for sugars and an ultraviolet-detector for the aromatic compounds makes it possible to determine both types of compounds in the same chromatographic run.     

Rapid determination of volatile compounds in grapes by HS-SPME coupled with GC-MS

Volatile compounds of grapes are responsible of varietal aroma. At the moment, methods used for analysis of these compounds are solvent-based, time-consuming and generally require large amounts of sample. In order to obtain an appropriate technique to study grape volatile compounds, HS-SPME method has been developed. The optimal sampling conditions were: 70 °C for 20 min with a 65-μm PDMS/DVB fibre. Sixteen volatile compounds have been quantified in pulp and skins of Muscat grapes. Terpenes, mainly linalool, geraniol and nerol, have been the volatiles present in the highest concentration, since these compounds contribute, to a larger extent, to the aroma of Muscat grapes and wines. So the proposed technique can be used for the characterisation of grape varieties or cultivars and for the determination of the aromatic maturity of grapes.     

Review: Separation and Pharmacology of Chiral Compounds in Traditional Chinese Medicine

More than 60% commonly used pharmaceutical active ingredients are chiral compounds. Developing more effective and safe chiral compounds has become a focus in the pharmaceutical industry. Chiral compounds widely exist in traditional Chinese medicine and include alkaloids, flavonoids, volatile oils, and amino acids. The characterization of chiral compounds used in traditional Chinese medicine remains limited. Here, the characterization of chiral compounds commonly used in traditional Chinese medicine is reviewed focusing upon their separation and pharmacology.     

Hidden active information in a random compound library: extraction using a pseudo-structure-activity relationship model

We propose a hypothesis that "a model of active compound can be provided by integrating information of compounds high-ranked by docking simulation of a random compound library". In our hypothesis, the inclusion of true active compounds in the high-ranked compound is not necessary. We regard the high-ranked compounds as being pseudo-active compounds. As a method to embody our hypothesis, we introduce a pseudo-structure-activity relationship (PSAR) model. Although the PSAR model is the same as a quantitative structure activity relationship (QSAR) model, in terms of statistical methodology, the implications of the training data are different. Known active compounds (ligands) are used as training data in the QSAR model, whereas the pseudo-active compounds are used in the PSAR model. In this study, Random Forest was used as a machine-learning algorithm. From tests for four functionally different targets, estrogen receptor antagonist (ER), thymidine kinase (TK), thrombin, and acetylcholine esterase (AChE), using five scoring functions, we obtained three conclusions: (1) the PSAR models significantly gave higher percentages of known ligands found than random sampling, and these results are sufficient to support our hypothesis; (2) the PSAR models gave higher percentages of known ligands found than normal scoring by scoring function, and these results demonstrate the practical usefulness of the PSAR model; and (3) the PSAR model can assess compounds failed in the docking simulation. Note that PSAR and QSAR models are used in different situations; the advantage of the PSAR model emerges when no ligand is available as training data or when one wants to find novel types of ligands, whereas the QSAR model is effective for finding compounds similar to known ligands when the ligands are already known.     

Solid-phase microextraction in the analysis of food taints and off-flavors

Selected food taints and off flavors, for which solid phase microextraction (SPME) has been used as a method for volatiles isolation, are the subject of review. Compounds responsible for musty and earthy odor off-flavors and taints in foods are discussed. This group contains haloanisoles, geosmin, and methylisoborneol. Chlorophenols are discussed as precursors of chloroanisoles and compounds impairing the flavor of food. Also described are volatile phenolic compounds responsible for medicinal off flavors, mainly ethyl phenols and vinyl phenols. Sulfur compounds that contribute to off-flavor are also discussed. Finally, a group of volatile compounds being the products of lipid oxidation are summarized. A short review of the formation, occurrence, and information on odor properties of all of these groups of compounds is given. Examples of SPME use for the analysis of compounds belonging to all described groups are shown. Elaboration of method parameters, fiber selection, experimental conditions, and quantitation of compounds are subjects of interest. Also, applications of SPME as a method for introduction of volatiles in mechanical olfaction technologies are shortly outlined.     

Ocular Delivery of Polyphenols: Meeting the Unmet Needs

Nature has become one of the main sources of exploration for researchers that search for new potential molecules to be used in therapy. Polyphenols are emerging as a class of compounds that have attracted the attention of pharmaceutical and biomedical scientists. Thanks to their structural peculiarities, polyphenolic compounds are characterized as good scavengers of free radical species. This, among other medicinal effects, permits them to interfere with different molecular pathways that are involved in the inflammatory process. Unfortunately, many compounds of this class possess low solubility in aqueous solvents and low stability. Ocular pathologies are spread worldwide. It is estimated that every individual at least once in their lifetime experiences some kind of eye disorder. Oxidative stress or inflammatory processes are the basic etiological mechanisms of many ocular pathologies. A variety of polyphenolic compounds have been proved to be efficient in suppressing some of the indicators of these pathologies in in vitro and in vivo models. Further application of polyphenolic compounds in ocular therapy lacks an adequate formulation approach. Therefore, more emphasis should be put in advanced delivery strategies that will overcome the limits of the delivery site as well as the ones related to the polyphenols in use. This review analyzes different drug delivery strategies that are employed for the formulation of polyphenolic compounds when used to treat ocular pathologies related to oxidative stress and inflammation.     

What is so special about the sorption behavior of highly fluorinated compounds?

Highly fluorinated organic compounds are often said to exhibit unique sorption and partition properties. Terms such as "fluorophilicity" have been used to describe these properties, and fudge factors depending on the degree of fluorination have been used in predictive partition models to make them work for fluorinated solutes. Here we demonstrate that highly fluorinated compounds differ from other molecules only in that they exhibit van der Waals interactions much smaller than those of other molecules of same size. A simple cavity model for partitioning is shown to give good results for fluorinated compounds if the nonspecific interactions are correctly parametrized.     

Development of a high-throughput method for the determination of organochlorinated compounds, nitromusks and pyrethroid insecticides in indoor dust

Investigation of chemical exposure inside the homes and offices where people spend the majority of their lives has only recently begun. These chemicals are degraded much more slowly than outdoor because they are more protected from sunlight, severe environmental conditions and microbial activity. Hence, indoor dust has been recognized as an important exposure pathway for organic contaminants. Pyrethroids are synthetic insecticides widely used in domestic environment for numerous applications and also in agriculture. Chlorobenzenes are a family of compounds used as intermediates in the production of a wide range of household consumer products. Nitromusks are a kind of synthetic musks used in the production of cleaning agents, detergents, and personal care products. A high-throughput method for the determination of these compounds in indoor dust samples has been developed. Microwave-assisted solvent extraction was used as the extraction technique whereas quantification of compounds was carried out by gas chromatography with micro-electron-capture detection. Several cleanup procedures were tested and finally a non-classical "on batch" procedure was selected, which allows increasing the throughput of the analysis while decreasing sample manipulation. Extraction conditions were optimized using a multifactorial experimental design approach. Quantitative recovery (84-103%) was achieved for all compounds and method precision was satisfactory. Limits of detection ranged from 0.22 ng g(-1) for lindane to 40 ng g(-1) for 1,4-dichlorobenzene. Standard reference material SRM 2585 was analyzed and the obtained values were in good agreement with the reported reference values for organochlorinated compounds and nitromusks. Pyrethroids and polychlorobenzenes have been analyzed for the first time in this reference material and some of them have been found. In addition, real samples collected in houses of north-western Spain have been analyzed by the proposed method and 17 of the 22 target compounds have been detected in the samples.     

Applicability Limits of Calculation Methods for Estimating the Enthalpy of Vaporization of Organophosphorus Compounds

Quantitative relationships used today for calculating the enthalpies of vaporization of organophosphorus compounds are analyzed. The parameters of equations used in these calculations largely depend on specific structural features and are common for closely related compounds only. With various P(III) derivatives as examples, narrow ranges are distinguished in which the enthalpies of vaporization can be estimated from the boiling points using common relationships. The group contributions of phosphorus-containing fragments for calculations by the additive scheme are determined.