Analysis of neem oils by LC–MS and degradation kinetics of azadirachtin-A in a controlled environment

Since it was first isolated, the oil extracted from seeds of neem (Azadirachtin indica A juss) has been extensively studied in terms of its efficacy as an insecticide. Several industrial formulations are produced as emulsifiable solutions containing a stated titer of the active ingredient azadirachtin-A (AZ-A). The work reported here is the characterization of a formulation of this insecticide marketed under the name of Neem-azal T/S and kinetic studies of the major active ingredient of this formulation. We initially performed liquid–liquid extraction to isolate the neem oil from other ingredients in the commercial mixture. This was followed by a purification using flash chromatography and semi-preparative chromatography, leading to ¹³C NMR identification of structures such as azadirachtin-A, azadirachtin-B, and azadirachtin-H. The neem extract was also characterized by HPLC–MS using two ionization sources, APCI (atmospheric pressure chemical ionization) and ESI (electrospray ionization) in positive and negative ion modes of detection. This led to the identification of other compounds present in the extract—azadirachtin-D, azadirachtin-I, deacetylnimbin, deacetylsalannin, nimbin, and salannin. The comparative study of data gathered by use of the two ionization sources is discussed and shows that the ESI source enables the largest number of structures to be identified. In a second part, kinetic changes in the main product (AZ-A) were studied under precise conditions of pH (2, 4, 6, and 8), temperature (40 to 70 °C), and light (UV, dark room and in daylight). This enabled us to determine the degradation kinetics of the product (AZ-A) over time. The activation energy of the molecule (75±9 kJ mol^–1) was determined by examining thermal stability in the range 40 to 70 °C. The degradation products of this compound were identified by use of HPLC–MS and HPLC–MS–MS. The results enabled proposal of a chemical degradation reaction route for AZ-A under different conditions of pH and temperature. The data show that at room temperature and pH between 4 and 5 the product degrades into two preferential forms that are hydrolyzed to a single product over time and as a function of pH change.     

Mechanisms and kinetics of polymerization of thermoplastic polyimides. II. Study of “bridged” dianhydride/aromatic amine systems

The aim of the present work was to identify and follow the main and side reactions involved in the ring dehydration of amic acid prepared from “bridged” dianhydrides whose central substituent is an electron acceptor or donor, and an aromatic diamine. Several isomeric structures may appear as a result of the opening reactivity and selectivity of anhydride groups towards the aromatic amine. Reaction mechanisms and kinetics were thus studied in solvent phase with HPLC and ¹³C-NMR and in solid molten phase by FTIR and solid ¹³C-NMR. The experimental conditions (liquid and solid) and the structure of the products (type of central substituent) affecting the mechanisms and kinetics of the reactions were noted. © 1993 John Wiley & Sons, Inc.     

Structure de modèles de polyesters—3[1] transférabilité de structure état solide (RX,RMN 13C solide) état dissous (RMN 13C, 1H) du bistriméthyl-3,3,5 cyclohexyl phtalate

The structure of bis-3,3,5-trimethyl cyclohexyl phthlate is described for the solid state (X-rays, ¹³C NMR) and in solution (¹³C and ¹H NMR). The results show similarity of structure in the two states.     

Sur la Similitude des Déformations du Noyau Cyclohexanonique Induites par les Groupes Tertiobutyle et gem-Diméthyle

X-ray and NMR (250 MHz) data for chlorinated 4,4-dimethylcyclohexanones lead to the following conclusions: carbonyl and chlorine substituent effects on ²J and ³J coupling constants are similar to those observed for 4-tert-butylcyclohexanones. In other respects, the gem dimethyl and the tert-butyl groups induce on the ring similar large ⁴J coupling constants (H-3′? C-3? C-4? C-5? H-5′); the results can be interpreted in terms of local gemoetric deformations and additivity of these deformations. The determination of dihedral angles by Lambert's method and from X-ray data shows the identity of the structures in the solid state and the dissolved state and confirms the great structural similarity between 4-tert-butyl- and 4,4-dimethylcyclohexanone derivatives.     

Authenticity control of essential oils containing citronellal and citral by chiral and stable-isotope gas-chromatographic analysis

Enantioselective capillary GC on a Supelco β-DEX 225 column (heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin SPB 20poly—20% diphenyl, 80% dimethylsiloxane) and isotope-ratio mass spectrometry, coupled online with capillary GC on an HP5 column have been used for origin-specific analysis and authenticity control of essential oils, for example lemon (Citrus limon), lemongrass (Cymbopogon citratus and Cymbopogon flexuosus), citronella (Cymbopogon nardus L.—Ceylon type and Cymbopogon winterianus—Java type), Litsea cubeba, Lippia citriodora, lemon myrtle (Backhousia citriodora), lemon gum (Eucalyptus citriodora), and, especially, precious lemon balm oil (Melissa officinalis L.). Isotope data (δ¹³C_PDB and δ²H_V-SMOW) for citral (neral + geranial) and citronellal from on-line GC–C/Py–IRMS and chiral data for citronellal in these essential oils are reported. The possibility of using these data to determine the origin of these essential oils and to detect adulteration is discussed. Principal-components analysis (PCA) of specific compounds in two essential oils of lemongrass and Litsea cubeba was performed as a practical statistical method for distinguishing between these two types of oil.     

Analyse structurale des méthyl et diméthyl cyclohexanols par chromatographie gaz liquid et résonance magnétique nucléaire du C

Structural analysis of methyl and dimethyl cyclohexanols using gas-lquid chromatography and C¹³ nuclear magnetic resonance

Kováts' retention indices and C¹³ chemical shifts of all twenty dimethyl cyclohexanols have been measured and assigned. It has been found that there are good linear relationships between carbon chemical shifts and the Kováts' indices.     

Ring dehydration mechanisms and kinetics of polyamic acid models in solution and in the solid state

We have synthesized and studied the ring dehydration mechanisms and kinetics of polyamic acid models in solution and in the solid state using ¹³C-NMR (solid and liquid), HPLC, FTIR, and x-ray diffraction. Results obtained in solution show the role of temperature, catalysts, and the basicity of the amine in ring dehydration mechanisms and kinetics, as well as conformation and intramolecular bonds in the amic acid bond in the solid state. © 1993 John Wiley & Sons, Inc.